Dissertations / Theses on the topic 'Electrochemical experiments'

Low-temperature waste heat recovery is an important component of generating a more efficient, cost-effective and environmentally-friendly energy source. To meet this goal, thermo-electrochemical cells (TECs) are cost-effective electrochemical devices that produce a steady electric current under an applied temperature difference between their electrodes. However, current TECs have low conversion efficiencies. On this project, I developed a comprehensive multiscale model that couples the governing equations in TECs. The model was used to understand the fundamental principles and limitations in TECs, and to find the optimum cell thickness, aspect ratio and number of cells in a series stack. Doped multiwall carbon nanotubes (MWCNTs) were then explored as alternative electrodes for TECs. One of the main objectives of this dissertation is to study multiwall carbon nanotube/ionic liquid (MWCNT/IL) mixtures as alternative electrolytes for TECs. Previous authors showed that the addition of carbon nanotubes (CNTs) to a solvent-free IL electrolyte improves the efficiency of dye solar cells by 300%. My research plan involved a spectroscopy analysis of imidazolium-based ionic liquids (IILs) mixed with MWCNTs using impedance spectroscopy and nuclear magnetic resonance. The results show that the combination of interfacial polarization and ion pair dissociation effects reduces mass transfer resistances and enhances the power of TECs at low wt% of MWCNTs. This happens in spite of reduced open circuit voltage due to percolated networks.

Hydrogen production is an interesting way to store solar energy and to diversify the range of applications for indirect solar power. A promising production method is to use electric power from solar photovoltaic cells to split water in an electrolysis setup. To efficiently run such a setup, one must however have an efficient catalytic material on the two electrodes. This work presents a study of a catalytic material for the oxygen evolution electrode; nickel hydroxide. The study is performed both experimentally and theoretically. In the experimental part, an electrode material was synthesized by growing nitrogen doped carbon nanotubes (NCNTs) on a carbon paper (CP) and then decorating the NCNTs with the catalytic material. Scanning electron microscopy (SEM) images of the electrode material showed that the NCNTs were individually coated with a spiky nickel hydroxide nanostructure, with a very large surface area. Electrodes with both as-prepared catalytic material and catalytic material first treated in an alkaline solution were then tested in a three-electrode electrolysis setup, in alkaline conditions. It was found that the overpotential for onset of the oxygen evolution reaction (OER) was roughly 0.27 V, which is in the range of previous reports. In contradiction to other reports, the data of this work however indicated that aging the catalytic material decreased its activity and hence that the phase often stated as the more active, was in fact the less active phase. The overall efficiency of the electrodes was found to be low, most likely due to overloading of active material in the electrode structure. The theoretical part of the work focused on using Density Functional Theory (DFT) simulations to analyze the OER pathway on three different surfaces of the catalytic material. To simulate the effect of an alkaline environment these surfaces were also passivated with hydroxyl groups in some of the simulations. The lowest overpotential for OER onset found in the calculations was 0.68 V. The calculations further showed that, for the pathways with the smallest overpotentials, the limiting reaction step was a step where an adsorbed hydroxyl group was deprotonated by a hydroxide ion from the solution and oxidized to an adsorbed oxygen atom. In addition, the calculations also indicated that passivation of the surfaces had the important effect of lowering the overpotentials for two of the three studied surfaces.
Vätgasproduktion är en mycket intressant metod för att lagra solenergi och för att diversifiera applikationsområdena för indirekt solenergi. En lovande metod är att använda elektrisk energi från solceller för att dela vattenmolekyler i en elektrolysuppställning. För att en sådan elektrolys ska bli effektiv, måste man dock ha effektiva katalysatorer på de två elektroderna. Denna rapport presenterar en studie av nickelhydroxid, ett katalytiskt material för elektroden vid vilken syrgas produceras. Studien har utförts både teoretiskt och experimentellt. I den experimentella delen syntetiserades ett elektrodmaterial genom att kolpapper kläddes i kvävedopade kolnanorör, som sedan dekorerades med katalytiskt material. Avbildningar av elektrodmaterialet med svepelektronmikroskopi visade att kolnanorören var individuellt klädda av en taggig nickelhydroxidstruktur, med mycket stor ytarea. Elektroder direkt från syntes och elektroder som först behandlas i basisk lösning testades sedan i en tre-elektrodupppställning, i basisk lösning. Överspänningen för att starta den syrgasproducerande reaktionen uppmättes till cirka 0.27 V, vilket ligger i ett intervall av tidigare rapporterade värden. I motsats till andra rapporter, indikerade denna studie att det åldrade materialet var mindre aktivt och därmed att den fas som ofta antas vara mer aktiv, här var den mindre aktiva fasen. Elektrodernas generella aktivitet var dock låg, förmodligen beroende på en för stor mängd katalytiskt material i elektroderna. I det teoretiska arbetet användes DFT (Density Functional Theory) för att analysera reaktionsvägen för den syrgasproducerande reaktionen. Reaktionsvägen studerades på tre av materialets ytor. För att simulera effekten av en basisk omgivning, passiverades dessa ytor också med hydroxylgrupper i vissa simuleringar. Den lägsta överspänningen för att starta reaktionen beräknades till 0.68 V. För reaktionsvägarna med de minsta överspänningarna, visade beräkningarna vidare att det begränsande reaktionssteget var ett steg där en adsorberad hydroxylgrupp deprotonerades av en hydroxidjon från elektrolyten och oxiderades till en adsorberad syreatom. Slutligen visade beräkningarna även att passivering av ytorna minskade den nödvändiga överspänningen för två av de tre studerade ytorna.

This thesis presents results of studies using the technique of surface-enhanced Raman scattering (SERS) spectroscopy to investigate surface processes occurring on gold during electrochemical experiments in thiosulfate solutions and during leaching in ammoniacal copper(II) thiosulfate systems. The gold SERS electrode was characterised using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). SEM investigations of the SERS activated gold surface showed the presence of electrodeposited dendrites with nanoscale features. XRD studies of the dendrites showed them to be polycrystalline with a large proportion of Au(111). Rotating disk electrode (RDE) studies of polished and SERS electrodes were undertaken in order to clarify the electrochemistry of various thiosulfate systems. The ex situ techniques of XPS and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to determine the presence of sulfur, copper and nitrogen on leached or electro-oxidised surfaces. Voltammetric methods were used to determine sulfur and copper surface coverages at various potentials in sulfide, thiosulfate and ammoniacal copper(II) thiosulfate media. The electro-oxidation of sulfide was examined as a model system in order to identify spectral features and coverage associated with various potential-dependent sulfur layers. In the hydrogen evolution region, a surface layer formed by underpotential deposition in acid and basic media was characterised by a gold-sulfur stretching band, Au-S, attributed in the literature to a monoatomic stretching mode of sulfur bonded to gold. The surface coverage in this potential region was limited to 0.35 ML, representing adsorption in a (3x3)R30 structure. Bands were found to be absent that would have indicated the adsorption of SH– species as has been reported in the literature. A facile change in the position of the Au-S band with potential, unaccompanied by Faradaic processes, was seen when the adsorbed (3x3)R30 sulfur layer was examined in a sulfide-free solution. This may indicate a change in sulfur adsorption sites with potential in the hydrogen evolution region. At potentials above the S II/S0 reversible value in sulfide solutions, the surface coverage increased and S-S bands were observed, indicating the formation of an adsorbed polysulfide species, Au-Sn. A change in the position of the Au-S band was seen to accompany the formation of the S-S bands. As coverage further increased, bands due to S-S-S bending, S-S-S, developed that were characteristic of cyclo octasulfur, S8. On removal from sulfide solution and rinsing, a characteristic SERS spectrum was observed ex situ. The spectrum showed a characteristic S-S at 460 cm-1 and Au-S at 325 cm-1 and was assigned to an adlayer of S8 adsorbed on gold in a crown configuration, Au S8. Gold was polarised in thiosulfate solutions at a potential at which gold dissolution is known to occur. In situ SERS spectra showed bands characteristic of S-S bonding and Au2S to occur after 1 hr for thiosulfate with sodium and ammonium counter-ions and for both systems in the presence of ammonia. XPS studies of polished gold held in sodium thiosulfate under these conditions showed S 2p binding energies corresponding to metal sulfide and pyritic sulfur, S22-. After 72 hrs at the mixed potential in air saturated sodium thiosulfate, SERS investigations showed a spectrum with Au-S8 characteristics. XPS studies on a polished electrode under these conditions showed a third type of S 2p binding with a binding energy between that of pyritic sulfur and S8. The sodium thiosulfate system showed an adsorbed tetrathionate-like surface species, Au-S4O6, to be present at the mixed potential and to disappear with increased potential prior to the formation of bulk S8 via an Au-S8 intermediate. In the presence of the ammonium cation at high potentials, Au-Sn bands appear in the presence of a more intense and broad Au-S characteristic of gold sulfide, Au2S. This was assigned to a mixed gold sulfide/polysulfide phase, Au2S/Sn. With addition of ammonia, the surface species Au S4O6, Au2S/Sn and, tentatively, adsorbed NH3 were observed above the mixed potential. For gold in air-saturated copper(II) ammoniacal thiosulfate media, bands due S-S at 382 cm-1 and symmetric S-O stretching, symS-O, at 1017 cm-1 developed during leaching at the mixed potential. These modes diminished and, when rinsed and examined in water, were replaced by a single band at 255 cm 1 assigned to a metal sulfide stretch. In typical leach solutions, sulfur and copper coverages showed a 2:1 atomic ratio after leaching for 16 h. Ex situ ATR and XPS studies showed that ammonia was adsorbed to a surface copper sulfide. Kinetic studies using atomic absorption spectroscopy (AAS) to measure gold in solution showed that the ammoniacal copper(II) thiosulfate leaching solution exhibited higher dissolution rates in the presence of the sodium counter ion than the ammonium. Thiourea as an additive to thiosulfate solutions was seen to disrupt S-S bonding in both Au-S8 and Au2S/Sn surface structures.

This thesis presents results of studies using the technique of surface-enhanced Raman scattering (SERS) spectroscopy to investigate surface processes occurring on gold during electrochemical experiments in thiosulfate solutions and during leaching in ammoniacal copper(II) thiosulfate systems. The gold SERS electrode was characterised using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). SEM investigations of the SERS activated gold surface showed the presence of electrodeposited dendrites with nanoscale features. XRD studies of the dendrites showed them to be polycrystalline with a large proportion of Au(111). Rotating disk electrode (RDE) studies of polished and SERS electrodes were undertaken in order to clarify the electrochemistry of various thiosulfate systems. The ex situ techniques of XPS and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to determine the presence of sulfur, copper and nitrogen on leached or electro-oxidised surfaces. Voltammetric methods were used to determine sulfur and copper surface coverages at various potentials in sulfide, thiosulfate and ammoniacal copper(II) thiosulfate media. The electro-oxidation of sulfide was examined as a model system in order to identify spectral features and coverage associated with various potential-dependent sulfur layers. In the hydrogen evolution region, a surface layer formed by underpotential deposition in acid and basic media was characterised by a gold-sulfur stretching band, ï ®Au-S, attributed in the literature to a monoatomic stretching mode of sulfur bonded to gold. The surface coverage in this potential region was limited to 0.35 ML, representing adsorption in a (3x3)R30ï‚° structure. Bands were found to be absent that would have indicated the adsorption of SH– species as has been reported in the literature. A facile change in the position of the ï ®Au-S band with potential, unaccompanied by Faradaic processes, was seen when the adsorbed (3x3)R30ï‚° sulfur layer was examined in a sulfide-free solution. This may indicate a change in sulfur adsorption sites with potential in the hydrogen evolution region. At potentials above the S II/S0 reversible value in sulfide solutions, the surface coverage increased and ï ®S-S bands were observed, indicating the formation of an adsorbed polysulfide species, Au-Sn. A change in the position of the ï ®Au-S band was seen to accompany the formation of the ï ®S-S bands. As coverage further increased, bands due to S-S-S bending, ï ¤S-S-S, developed that were characteristic of cyclo octasulfur, S8. On removal from sulfide solution and rinsing, a characteristic SERS spectrum was observed ex situ. The spectrum showed a characteristic ï ®S-S at 460 cm-1 and ï ®Au-S at 325 cm-1 and was assigned to an adlayer of S8 adsorbed on gold in a crown configuration, Au S8. Gold was polarised in thiosulfate solutions at a potential at which gold dissolution is known to occur. In situ SERS spectra showed bands characteristic of S-S bonding and Au2S to occur after 1 hr for thiosulfate with sodium and ammonium counter-ions and for both systems in the presence of ammonia. XPS studies of polished gold held in sodium thiosulfate under these conditions showed S 2p binding energies corresponding to metal sulfide and pyritic sulfur, S22-. After 72 hrs at the mixed potential in air saturated sodium thiosulfate, SERS investigations showed a spectrum with Au-S8 characteristics. XPS studies on a polished electrode under these conditions showed a third type of S 2p binding with a binding energy between that of pyritic sulfur and S8. The sodium thiosulfate system showed an adsorbed tetrathionate-like surface species, Au-S4O6, to be present at the mixed potential and to disappear with increased potential prior to the formation of bulk S8 via an Au-S8 intermediate. In the presence of the ammonium cation at high potentials, Au-Sn bands appear in the presence of a more intense and broad ï ®Au-S characteristic of gold sulfide, Au2S. This was assigned to a mixed gold sulfide/polysulfide phase, Au2S/Sn. With addition of ammonia, the surface species Au S4O6, Au2S/Sn and, tentatively, adsorbed NH3 were observed above the mixed potential. For gold in air-saturated copper(II) ammoniacal thiosulfate media, bands due ï ®S-S at 382 cm-1 and symmetric S-O stretching, ï ®symS-O, at 1017 cm-1 developed during leaching at the mixed potential. These modes diminished and, when rinsed and examined in water, were replaced by a single band at 255 cm 1 assigned to a metal sulfide stretch. In typical leach solutions, sulfur and copper coverages showed a 2:1 atomic ratio after leaching for 16 h. Ex situ ATR and XPS studies showed that ammonia was adsorbed to a surface copper sulfide. Kinetic studies using atomic absorption spectroscopy (AAS) to measure gold in solution showed that the ammoniacal copper(II) thiosulfate leaching solution exhibited higher dissolution rates in the presence of the sodium counter ion than the ammonium. Thiourea as an additive to thiosulfate solutions was seen to disrupt S-S bonding in both Au-S8 and Au2S/Sn surface structures.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical Sciences
Full Text

A study of the electrochemistry of the PbS-H₂O and PbS-KEX-H₂O systems has been made by carrying out thermodynamic calculations, electrochemical experiments and microflotation tests. Particular attention has been paid to how well this system can be described by equilibrium thermodynamics. The thermodynamic calculations are more comprehensive than previous ones of this type since they are based on a mass balance which includes both insoluble and soluble species. The data they provide include equilibrium concentrations of all dissolved species at any E_h and pH and an E_h-pH stability diagram for each collector addition. Also, two- and three-dimensional plots showing the effect of E_h and pH on xanthate uptake by the galena surface have been presented for the first time. These are particularly useful because they can be directly compared to observed flotation data. The results of voltammetry, IGP and potential-step experiments suggest that the oxidation of galena at pH 6.8 and 9.2 begins at a potential below the value predicted by bulk thermodynamics with the electrosorption of OH⁻ and the formation of a metal-deficient sulfide and a surface lead oxide. When oxidation becomes extensive enough, bulk products, Sº and PbO, begin to nucleate. Thiosulfate is detected at pH 9.2, but only becomes significant at high potentials. The electrochemical experiments indicate that xanthate adsorbs onto galena via a one-electron transfer chemisorption reaction in the first monolayer and via the formation of PbX₂ in subsequent layers. It also appears that galena oxidation and xanthate adsorption are competitive processes that tend to inhibit each other. Ground galena exhibits natural floatability at pH 9.2 as long as oxidation extends to the formation of a metal-deficient sulfide, but not to bulk PbO. When 10⁻⁵ M xanthate is added, the upper potential limit for flotation agrees well with the value predicted from thermodynamics for the decomposition of PbX₂. The lower limit, on the other hand, is at least 200 mv lower than any of the predicted values. PbS dissolves anodically at pH 1.1 and 4.6 to form Pb²⁺ and Sº first by a random surface process and then by a nucleation and growth mechanism once oxidation becomes extensive enough. At pH 0, the relation between the open-circuit potential and mineral solubility, as predicted by the thermodynamic calculations, agrees quantitatively with that determined experimentally. However, as the pH is increased to 1.1 and 4.6, the system becomes increasingly less reversible.
Ph. D.

O objetivo deste trabalho foi formular e otimizar uma mistura de quatro substâncias atóxicas como inibidores de corrosão para o aço carbono ABNT 1005 em meio de água de resfriamento industrial. As substâncias estudadas foram o molibdato de sódio, o tungstato de sódio, a ftalocianina de cobre e um tensoativo polimérico a base de silano de peso molecular 17.000 g.mol-1. As técnicas usadas neste estudo foram medidas de potencial de corrosão, espectroscopia de impedância eletroquímica e curva de polarização anódicas e catódicas. O tratamento dos resultados de espectroscopia de impedância eletroquímica foi feito por meio da modelagem com circuitos elétricos equivalentes, que permitiu quantificar parâmetros como resistência a transferência e carga (Rtc) e capacitância dupla camada elétrica, (Cdl). Para caracterizar a superfície do metal foram obtidas imagens por microscopia eletrônica de varredura, onde foi comprovada a alteração da superfície pela presença das substâncias estudadas. Pelas curvas de polarização foi verificado que todas as substâncias estudadas se comportam como inibidores de corrosão anódicos no meio estudado, isto é, diminuem a velocidade de dissolução do metal na presença de maiores concentrações. O uso de um projeto fatorial completo, do tipo 24 foi decisivo para identificar os principais efeitos e interações entre as substâncias; sendo que os mais importantes foram devidos à presença de molibdato e tungstato de sódio, ou seja, a presença destas duas substâncias aumentou a resistência à transferência de carga do aço carbono no meio estudado. Em seguida, a análise estatística do projeto fatorial composto permitiu estimar a concentração ótima para a mistura de molibdato e tungstato de sódio; como o ponto de máximo da função superfície de resposta obtida. A concentração ótima estimada de molibdato e de tungstato de sódio foi de 3,6 x10-3M e 3,5x10-3M respectivamente. Finalmente, foi feita a avaliação ao longo de um período de tempo de 88 horas que permitiu identificar que o melhor comportamento da Rtc e da Cdl foi entre 48 e 72 horas de imersão.
The aim of this investigation is to obtain the optimum formulation of four nontoxics substances tested as corrosion inhibitors for ABNT 1005 carbon steel in watercooling systems. The studied substances were: sodium molybdate, sodium tungstate, copper phthalocyanine and a modified copolymer of polyoxialkylene and polidimethysiloxane. Electrochemical techniques as corrosion potential, impedance spectroscopy (EIS) and potenciodynamic anodic and cathodic polarization curves were used. Electrochemical impedance spectroscopy results were fitted through equivalent electric circuit modeling that allowed quantifying parameters like: the charge transfer resistance (Rtc) and double layer capacitance (Cdl) among others. In order to characterize the metal surface, scanning electronic microscopy images were obtained. These images allowed to evidence the surface alteration resulted from the addition of the studied inhibitors. Using polarization curves were verified that all substances studied behave as anodic corrosion inhibitors, this is, metal dissolution rate decrease when higher inhibitors concentrations were added. By applying a 24 design of experiments (DOE) were possible to identify the main effects and interactions between the substances (entry variables) on the charge transfer resistance (response variable). The main effects and interactions were obtained due to the presence of sodium molybdate and sodium tungstate; the Rtc got higher values as result of the presence of sodium molybdate and sodium tungstate. As a next step, using a design of experiments with central point was allowed to estimate the optimum concentration of sodium molybdate and sodium tungstate as result of the maximum of response surface obtained from statistic analysis in a wider range of concentrations. The optimum concentration estimated was 3,6x10-3M and 3,5x10-3M from sodium molybdate and sodium tungstate respectively. Finally it was done an immersion time evaluation until 88 hours using the optimum inhibitors concentration; the best performance of de Rtc and Cdl were between 48 and 72 hours of immersion.

The research detailed herein has been conducted in two different areas. The first research goal was to develop and study a supramolecular system coupling two light absorber units to a central metal site capable of collecting two electrons; this has been accomplished. The complex {[(bpy)2Ru(dpp)]2RhCl2}(PF6)5 was synthesized and characterized using electrochemistry and electronic absorption spectroscopy. The electrochemical properties of {[(bpy)2Ru(dpp)]2RhCl₂}(PF6)5 were probed with cyclic voltammetry and bulk electrolysis studies to investigate the behavior of the system upon two-electron reduction of the rhodium metal center. Bulk electrolysis showed that the rhodium center underwent two-electron reduction. A water modulation of product distribution for the bulk electrolysis studies was found, and the nature of this process was studied. In the presence of water, two-electron reduction of the rhodium metal center afforded a RhI complex that had lost two chloride ligands: {[(bpy)2Ru(dpp)]2RhI}+5. In the absence of sufficient water, two-electron reduction yields a breakdown of the trimetallic resulting in [(bpy)2Ru(dpp)]+2 and {[(bpy)2Ru(dpp)]RhICl₂}+. The second research goal was to develop integrated molecular modeling, synthesis, and characterization laboratory experiments, to incorporate into the undergraduate inorganic laboratory curriculum, and to evaluate and modify this curricular approach. This was accomplished with organometallic [Mo(CO)4(N-N)] complexes, where N-N is a bidentate nitrogen donor ligand. [Mo(CO)4(N-N)] complexes were selected because they were amendable to molecular modeling and could be synthesized via two synthetic routes with reasonable yields, low reaction times, and were air stable. Many of these complexes are new, so a series of [Mo(CO)4(N-N)] complexes were synthesized by either thermal or photochemical substitution reactions. The systems were characterized using cyclic voltammetry, electronic absorption spectroscopy, and ¹H NMR spectroscopy. Molecular modeling was performed on the series of [Mo(CO)4(N-N)] complexes using the CAChe software from Oxford Molecular, Ltd. These calculations typically provided reasonable structures, orbital locations, and relative orbital energies for the [Mo(CO)4(N-N)] systems. Correlations between the computational and experimental data were established. The electronic absorption spectral MLCT frequency versus calculated HOMO-LUMO energy gap, Epa versus calculated HOMO energy, E1/2red versus calculated LUMO energy, and 1H NMR chemical shift for [Mo(CO)4(1,10-phen)] and the substituted [Mo(CO)4(1,10-phen)] complexes versus ZINDO calculated partial charge were compared, where 1,10-phen = 1,10-phenanthroline. From the analyses of physical versus computational data, it was concluded that molecular modeling results are useful in predicting physical data for these complexes. The integrated molecular modeling, synthesis, and characterization experiment was developed and incorporated into the undergraduate inorganic chemistry laboratory. In both 1998 and 1999, a qualitative evaluation of student response was completed. This was done using a recorded interview technique; interviews were subsequently transcribed and rendered to extract themes. This interview style was an effective evaluation technique for this project, providing the detailed comments and student feedback that were desired. These interviews showed that the majority of the students both enjoyed this experiment and felt that the exposure to molecular modeling was worthwhile within this type of integrated lab forum. The students felt this experiment aided in their understanding of the orbital properties of inorganic systems. Student comments and suggestions facilitated modifications for future offerings in 1999 and 2000. Continued evaluation and expansion of this curricular approach are in progress.
Ph. D.

This thesis reports the development of sonoelectrochemistry as a technique for sample analysis. Complementary modelling gives an insight into the mass transport and electrode reaction mechanisms. Separate studies were conducted as follows: - Initially an copper(II) acetate buffer system was used as its speciation can be determined. In order to establish under which conditions analysis could be conducted the effect of speciation was examined. These were applied to the Anodic Stripping Voltammetry (ASV) determination of copper in the acetate solution and to facilitate the use of a traditionally inhospitable electrochemical medium: real ale with minimal pre-treatment. Both gave detection limits of the range (1-100) μg L^-1 and in quantitative agreement with Atomic Absorption Spectroscopy. - The effect of acoustic streaming under mild insonation was studied by modelling Square Wave Voltammetry (SWV) of ASV and was found, when compared to experiment, to be the dominating factor. When the latter is strongly present two distinct mass.transport regimes were identified. Studies of chemical and electrochemical processes suggested that the acoustic streaming model fails under more extreme conditions. - SWV voltammetry was modelled for reversible electrochemical reactions leading to a refinement of existing analytical theory and the ASV modelling extended to account for surface morphology and finite electrode kinetics. Droplets on an electrode surface subjected to a potential sweep give rise to voltammetric traces attributed to charge insertion. Three mechanisms for this are proposed: (i) charge injection at the droplets surface, (ii) charge injection at the three phase boundary and (iii) the droplet is saturated with counter ions and electron transfer occurs at the electrode surface. These are solved numerically and incorporate Regular Solution Theory to account for non-ideal interactions. Comparing with experimental data an approximate model identified the processes occurring for small droplets. A Marangoni-type convection is suggested for larger droplets.

En els últims anys, a causa de la necessitat de diàgnostics ràpids i de millores en sensat, s’han utilitzat nous elements de reconeixement en biosensors. Un tipus d’aquests nous elements de reconeixement són els aptàmers. Els aptàmers són cadenes sintètiques de ADN o ARN les quals són seleccionades in vitro i tenen la capacitat d’unir-se a proteïnes, ions, cèl.lules, fàrmacs i lligands de baix pes molecular, reconeixent les seves molècules diana amb alta afinitat i especificitat. Diversos biosensors basats en aptàmers, també anomenats aptasensors, han sigut desenvolupats recentment. D’entre totes les tècniques de transducció utilitzades en biosensors, l’Espectrocòpia Electroquímica d’Impedància ha sigut àmpliament emprada como a eina per caracteritzar la superficies de sensors i estudiar esdeveniments en el biosensat en la superficie d’elèctrodes. La característica més important que presenta aquesta tècnica és que no requereix cap espècie marcada per a la transducció, per tant, aquesta tècnica de detecció pot utilitzar-se per dissenyar protocols de detecció directa sense marcatge, evitant assajos més cars i laboriosos. El principal objectiu d’aquesta tesi doctoral va ser el desenvolupament d’aptasensors utilitzant la tècnica electroquímica d’impedància esmentada anteriorment. Per a això, diferents tipus d’elèctrodes van ser utilitzats, tals com elèctrodes de compòsit grafit-epoxi, elèctrodes de biocompòsit grafit-epoxi modificats amb molècules d’avidina i elèctrodes comercials serigrafiats de nanotubs de carboni de paret múltiple. El treball es va dividir principalmente en dues parts d'acord amb la detecció de dues proteïnes diferents. La primera part es va focalitzar en la detecció de trombina. Primer de tot, es van comparar i avaluar diversos aptasensors de detecció directa sense marcatge basat en diferents tècniques d'immobilització dels aptàmers, tals com: adsorció física humida, afinitat avidina-biotina i enllaç covalent mitjançant activació electroquímica de la superfície de l'elèctrode i mitjançant inserció electroquímica. Posteriorment, els elèctrodes de biocompòsit van ser comparats com a plataformes en genosensat i aptasensat. Amb la finalitat d'amplificar el senyal impedimètric obtingut utilitzant elèctrodes de biocompòsit, un protocol sàndwich va ser emprat incloent nanopartícules d'or modificades amb estreptavidina i tractament amplificador de plata. La segona part de l'estudi es va basar en la detecció de citocrom c. Primerament, es va realitzar un simple aptasensor de detecció directa sense marcatge per a la detecció d'aquesta proteïna utilitzant la tècnica d'immobilització d'adsorció física humida. Finalment, i amb l'objectiu d'amplificar el señal impedimètric, es va desenvolupar un assaig tipus sándwich híbrid d’aptàmer i anticòs utilitzant elèctrodes serigrafiats de nanotubs de carboni de paret múltiple. D'aquesta manera, la tesi explora i compara una àmplia gamma de procediments d'immobilització, l'ús de detecció directa sense marcatge o nanomaterial modificat amb biomolècules en diferents protocols directes o d'amplificació, i l'ús de reconeixement directe i sándwich per amplificar la sensibilitat i/o la selectivitat de l'assaig.
In the recent years, due to the need for rapid diagnosis and improvements in sensing, new recognition elements are employed in biosensors. One kind of these new recognition elements are aptamers. Aptamers are synthetic strands of DNA or RNA which are selected in vitro and have the ability to bind to proteins, ions, whole cells, drugs and low molecular weight ligands recognizing their target with high affinity and specificity. Several aptamer-based biosensors, also called aptasensors, have been recently developed. Among all the transduction techniques employed in biosensors, Electrochemical Impedance Spectroscopy has widely used as a tool for characterizing sensor platforms and for studying biosensing events at the surface of the electrodes. The important feature presented by this technique is that it does not require any labelled species for the transduction; thus, this detection technique can be used for designing label-free protocols thus avoiding more expensive and time-consuming assays. The main aim of this PhD work was the development of aptasensors using the electrochemical impedance technique previously mentioned for protein detection. For that, different types of electrodes were used, such as Graphite Epoxy Composite electrodes (GECs), Avidin Graphite Epoxy Composite electrodes (AvGECs) and commercial Multi-Walled carbon nanotubes screen printed electrodes (MWCNT-SPE). The work was divided in two main parts according to the detection of the two different proteins. The first part was focused on thrombin detection. First of all, different impedimetric label-free aptasensors based on several aptamer immobilization techniques such as wet physical adsorption, avidin-biotin affinity and covalent bond via electrochemical activation of the electrode surface and via electrochemical grafting were developed and evaluated. Then, AvGECs electrodes were compared as a platform for genosensing and aptasensing. With the aim to amplying the obtained impedimetric signal using AvGECs, an aptamer sandwich protocol for thrombin detection was used including streptavidin gold-nanoparticles (Strep-AuNPs) and silver enhancement treatment. The second part of the study was based on cytochrome c detection. Firstly, a simple label-free aptasensor for the detection of this protein using a wet physical adsorption immobilization technique was performed. Finally, with the goal to amplify the impedimetric signal, a hybrid aptamer-antibody sandwich assay using MWCNT-SPE for the detection of the target protein was carried out. In this way, the thesis explores and compares a wide scope of immobilization procedures, the use of label-free or nanocomponent modified biomolecules in different direct or amplified protocols, and the use of direct recognition and sandwich alternatives to enhance sensitivity and/or selectivity of the assay

This thesis presents numerical and experimental investigations into Electrochemical Machining (ECM). The aim is to develop a computer program to predict the shape of a workpiece machined by the ECM process. The program is able to simulate various applications of EC machining which are drilling, milling, turning and shaped tube electrochemical drilling (STED). The program has been developed in a MATLAB environment. In this present work, EC-drilling, EC-milling and EC-turning are analysed as three-dimensional problems whereas STED is simulated in two-dimensions. Experiments have been carried out to verify the accuracy of the predicted results in the cases of EC-milling and EC-turning. The ECM modeller is based on the boundary element method (BEM) and uses Laplace's equation to determine the current distribution at nodes on the workpiece surface. In 3D, the surfaces of the tool and the workpiece are discretised into continuous linear triangular element types whereas in 2D, the boundaries of the tool and workpiece are discretised into linear elements. The ECM modeller is completely self-contained, i.e. it does not rely on any other commercial package. The program contains modules to automatically discretize the surfaces/boundaries of the tool and workpiece. Since the simulation of the ECM process is a temporal problem, several time steps are required to obtain the final workpiece shape. At the end of each time step, the shape of the workpiece is calculated using Faraday's laws. However, the workpiece's shape changes with progressing time steps causing the elements to become stretched and distorted. Mesh refinement techniques are built in the ECM modeller, and these subdivide the mesh automatically when necessary.The effect of time step on the predicted 3D shape of a hole in EC-drilling is investigated. The effect of discontinuity in the slope between neighbouring elements is also studied. Results obtained from the ECM modeller are compared with 2D analytical results to verify the accuracy that can be obtained from the ECM modeller. Milling features ranging from a simple slot to a pocket with a complex protrusion were machined in order to determine the feasibility of the EC milling process. These features were machined on a 3-axes CNC machine converted to permit EC milling. The effect of tool geometry, tool feed rate, applied voltage and step-over distances on the dimensions, shape and surface finish of the machined features were investigated. A pocket with a human shape protrusion was machined using two different types of tool paths, namely contour-parallel and zig-zag. Both types resulted in the base surface of the pocket being concave and the final dimensions of the pockets are compared with the design drawing to determine the effect of tool path type on the accuracy of machining. The ECM modeller was used to simulate the machining of a thin-walled turned component. The machining parameters, i.e. initial gap, rotational speed, and applied voltage, were specified by the collaborating company. Since only a small amount of material had to be removed from the thin-walled component, the tool was held stationary i.e. a feed in the radial or longitudinal direction was not required. By taking advantage of the axi-symmetric nature of a turned component, only a sector of the component was analysed thereby reducing the computing time considerably. The accuracy of the modeller was verified by comparing the predicted time to machine the thin-walled component with the actual machining time. The initial investigations in STED were both experimental and numerical in nature and they studied the effect of applied voltage, tool feed rate and electrolyte pressure on the dimensions of the holes. Later investigations were numerical and an iterative methodology has been developed to calculate a set of feed rates which could machine a specified turbulator shape.

El progreso de la nanociencia y la nanotecnología está haciendo posible generar nuevos materiales basados en estructuras de carbono con propiedades únicas y con numerosas aplicaciones tecnológicas. Entre estas aplicaciones se encuentra la mejora de los biosensores, dispositivos capaces de realizar análisis químicos con gran rapidez.
Las propiedades mecánicas y eléctricas extraordinarias de los nanotubos de carbono han estimulado extensamente su investigación a lo largo de todo el mundo desde su descubrimiento por Sumio Iijima en 1991. En esta tesis, el estudio del comportamiento electrocatalítico de nanotubos de carbono y al mismo tiempo el diseño de nuevos (bio)sensores electroquímicos han sido el principal objetivo, haciendo uso de diferentes alternativas de integración dentro de los sistemas de (bio)detección, basadas en modificaciones de las superficies del electrodo con nanotubos de carbono, o en el uso de nanotubos de carbono basados en (bio)compositos.
The extraordinary mechanical properties and unique electrical properties of carbon nanotubes (CNTs) have stimulated extensive research activities across the world since their discovery by Sumio Iijima in 1991. The range of applications for CNTs is indeed wide ranging from nanoelectronics, with quantum wire interconnects and field emission devices to composites, chemical sensors and biosensors. The application of CNTs to design novel and improved (bio)sensors is the principal objective of this thesis. Different alternatives for CNTs integration into (bio)sensing systems have been developed and the results obtained including some previous theoretical introduction, the state of the art in the field, conclusions and future prospects are presented through the 7 chapters of this PhD thesis.

La convergència de la nanotecnologia i la biotecnologia porta al desenvolupament de nous coneixements científics i tècnics que permeten millorar el benestar humà. Dins d'aquest nou camp de la nanobiotecnologia, el camp dels (bio)sensors és el més desenvolupat i el que té el major potencial per a aplicacions a curt termini. En aquest context, els (bio)sensors basats en principis electroquímics destaquen pels seus avantatges com la simplicitat, robustesa, baix cost, capacitat de miniaturització i d’integració de dispositius. Aquests sensors són cada vegada més atractius ja que permeten un diagnòstic ràpid i simple en camps com la biotecnologia, la investigació clínica i ambiental. Històricament, el carboni ha estat un material d'elèctrode molt utilitzat i pràctic per les seves propietats desitjables per a aplicacions electroquímiques. Disponible en una gran varietat d'estructures, els elèctrodes de carboni ofereixen, en general, una bona conductivitat elèctrica, alta estabilitat tèrmica i mecànica, una àmplia finestra operable de potencial amb cinètica d'oxidació lenta i, en molts casos, activitat electrocatalítica. A més d'això, se'ls reconeix com a materials de manipulació ràpida i fàcil. Cal també elogiar la seva química de superfície rica que ha estat explotada per a influir en la reactivitat superficial. Així doncs, les diferents estructures de carboni han tingut durant molt temps un paper important en el desenvolupament d'elèctrodes sòlids. Més recentment, amb l'aparició dels nanotubs de carboni (CNTs) s'han intensificat algunes d'aquestes propietats i s’ha impulsat d'una manera sense precedent les aplicacions electroquímiques i electroanalítiques. La mida nanomètrica i la alta relació d'aspecte dels nanotubs de carboni són els trets més distintius que han contribuït a les innovadores aplicacions electroquímiques i el que permet establir les diferències pel que fa als materials de carboni. En conseqüència, l'objectiu principal d'aquest treball ha estat explotar les propietats dels nanotubs de carboni per al disseny de nanodispositius. Les destacades propietats electroquímiques han impulsat el disseny de diverses configuracions d'elèctrodes. Això, combinat amb les seves propietats químiques i versatilitat de (bio)funcionalització, ha fet que aquests materials siguin molt adequats per al desenvolupament de biosensors electroquímics. La primera part de l'estudi s'ha centrat en l'ús de nanotubs de carboni com a transductors electroquímics i la relació entre la seva estructura i reactivitat electroquímica. Es va trobar que les vores dels nanotubs de carboni juguen un paper important en la resposta electroquímica; fet que es va utilitzar per al disseny i desenvolupament de noves plataformes d'elèctrodes basats en els nanotubs. A la segona part de l'estudi, hem aprofitat la capacitat dels nanotubs de carboni per a ser adaptats en diferents disposicions geomètriques, la seva biocompatibilitat, robustesa química i la seva possibilitat de funcionalització química covalent i no covalent, per al desenvolupament de (bio)sensors. En concret, s’ha avaluat el comportament del (bio)sensor d’elèctrodes de diferents configuracions de carboni funcionalitzats amb proteïnes redox (catalasa i mioglobina). Aquestes proteïnes presenten una alta sensibilitat a l'oxigen i peròxid d'hidrogen i són capaces de catalitzar la reducció d'aquestes espècies, convertint-se com a prometedors sensors d'oxigen i peròxid. Seguint el mateix enfocament, s'han utilitzat matrius de microelectrodes basades en CNTs covalentment funcionalitzats amb sondes d'ADN específiques o amb aptàmers. La detecció d'hibridació o de la interacció específica entre els aptàmers i les proteïnes han estat controlats amb diferents tècniques electroquímiques (voltametria cíclica, cronocoulometia o impedància) en presència de marcadors d'oxidació-reducció. La tercera i última part de l'estudi se centra en explotar el caràcter semiconductor dels nanotubs de carboni amb l'ús de la configuració en transistor d'efecte de camp (Field Effect Transistor FET). El dispositiu CNT-FET ha estat optimitzat per funcionar en medi líquid mitjançant la realització de protocols de passivació. Això, juntament amb l'ús de connectors pirè bifuncionals per a la immobilització dels aptàmers, ha permès la detecció sensible electrònica de les interaccions proteïna/aptamer. A més, també hem estat capaços de seguir l’absorció de proteïnes i canvis conformacionals de les parets dels CNTs. Els resultats d'aquest treball mostren que aquests dispositius electroquímics i electrònics basats en nanotubs de carboni poden arribar a ser molt prometedors per a la detecció de biomolècules i per al seguiment de processos biològics.
The convergence of nano and biotechnology is enabling scientific and technical knowledge for improving human well being. Within this new field of nanobiotechnology, the area of (bio)sensors is the most developed and the one which has the highest potential for short-term applications. In this context, (bio) sensors based on electrochemical principles stand out due to their marked advantages in terms of simplicity, robustness, low cost, miniaturization capability and integration to devices. These sensors are becoming very attractive for rapid and simple diagnostic, in fields such as biotechnology, clinical and environmental research. Historically, carbon has been a widely used and practical electrode material due to its desirable properties for electrochemical applications. Available in a variety of structures, carbon electrodes provide, in general, good electrical conductivity, high thermal and mechanical stability, a wide operable potential window with slow oxidation kinetics and, in many cases, electrocatalytical activity. On top of that, they are recognized as versatile and easy handling materials, and also praised by their rich surface chemistry which has been exploited to influence surface reactivity. Thus, different forms of carbon have played for a long time an important role in solid electrode development. More recently, the appearance of carbon nanotubes (CNTs) has intensified some of these properties and propelled in an unprecedented way their electrochemical and electroanalytical applications. The nanometre size and high aspect ratio of the carbon nanotubes are the distinct features which have contributed more to innovative electrochemical applications and to establish the differences with respect to other carbon materials. Accordingly, the principal aim of this work has been to exploit the properties of carbon nanotubes to design novel nanodevices. The prominent electrochemical properties of carbon nanotubes have impelled the design of diverse electrode configurations. That, combined with their chemical properties and (bio)functionalization versatility have made these materials very appropriate for the development of electrochemical biosensors. The first part of the study has been focused on the use of carbon nanotubes as electrochemical transducers and the relation between their structure and their electrochemical reactivity. It was found that the edges of carbon nanotubes play an important role in the electrochemical response, which was then used for the design and development of new carbon nanotubes-based electrode platforms. In the second part of the study, we have taken advantage of the capability of CNTs for being tailored in different geometrical arrangements, from their biocompatibility, their chemical robustness and their interesting covalent/non-covalent chemical functionalization possibilities, to develop biosensor platforms. Specifically, the (bio)sensor behaviour of different carbon configurations functionalized with redox proteins (catalase and myoglobin) has been evaluated. Such proteins exhibit high sensitivity to oxygen and peroxide and are capable to catalyze the reduction of such species, which hold promise as oxygen and peroxide sensors. Then, following the same approach, we have used CNT microelectrode arrays covalently functionalized with specific DNA probes or with aptamers. The detection of hybridization events or the specific interaction between aptamers and proteins were sensitively monitored by different electrochemical techniques (cyclic voltammetry, chronocoulometry or impedance spectroscopy) in presence of redox markers. The third and last part of the study is focused on exploiting the semiconductor character of carbon nanotubes for sensor technology by using a field effect transistor configuration (FET). The CNT-FET device has been optimized for operating in liquid environment by performing passivation protocols. This, together with the use of bifunctional pyrene linkers for the immobilization of the aptamers, has allowed sensitive electronic detection of protein/aptamer interaction. Additionally, we were also able to follow up protein adsorption and protein conformational changes on the CNT walls under liquid gating. The results of this thesis work show that these electrochemical and electronic CNT devices can become highly promising for biomolecule sensing and for the monitoring of biological processes.

En la actualidad existe una preocupación creciente en lo concerniente a los problemas medioambientales provocados por la actividad humana y en cómo estos problemas pueden afectar a nuestra salud. Uno de los problemas medioambientales más acuciantes es la creciente presencia de gases contaminantes en la atmósfera, y la investigación en este campo trata de determinar tanto las especies que son perjudiciales como las concentraciones a partir de las cuales son nocivas. Por lo que a este último punto se refiere, las legislaciones medioambientales son cada vez más restrictivas respecto a las concentraciones máximas permitidas, por lo que se necesitan materiales capaces de detectar concentraciones de gases contaminantes cada vez más pequeñas. Y no tan sólo eso sino que, además, sean de coste moderado para permitir un uso particular de ellos. Es en este contexto en el que se enmarca esta tesis, que trata del estudio de nuevos materiales que permitan la detección de gases nocivos como el monóxido de carbono o el metano a bajas concentraciones y a un coste menor que los actuales materiales, permitiendo la comercialización de estos detectores a escala masiva.

Uno de los materiales más estudiado por lo que a este tipo de materiales se refiere es el SnO2. Para optimizar la detección de este tipo de gases por parte de este material, uno de los procesos cruciales consiste en la adición de pequeñas cantidades de metales. Esta adición y, por tanto, las características de estos materiales como detectores de gases depende del método usado. En este trabajo se estudia un nuevo método de adición de metales sobre SnO2 basado en una reacción electroquímica espontánea que añade estos metales en forma de partículas nanométricas sobre este material, lo que constituye una característica fundamental para optimizar la detección de gases. El método constituye, por tanto, una interesante alternativa a otros métodos usados en la actualidad, con el importante añadido de ser un método de bajo coste y fácilmente implementable a escala industrial.

Por otro lado, en este trabajo también se ha empezado el estudio electroquímico de las reacciones de oxidación y reducción del estaño. El objetivo final de este estudio es la formación electroquímica de una capa de SnO2 de propiedades perfectamente controlables de manera que, al poner esta capa en contacto con un cierto gas, se pueda medir la influencia del gas en estas propiedades y, por tanto, desarrollar sensores electroquímicos de gases. Más aún, lo que se pretende es estudiar en condiciones realistas los mecanismos de intercambio electrónico implicados en la detección de gases para entender estos procesos. Es por ello que se ha empezado el estudio electroquímico del monocristal de Sn (100) y, como primer paso de este estudio, se ha desarrollado un proceso químico de preparación de la superficie de este monocristal que también se puede aplicar al policristal de estaño. Este proceso mejora sensiblemente los procesos usados hasta la fecha ya que disminuye considerablemente la contaminación en la superficie y, además, es capaz, en el caso del monocristal, de preparar superfies atómicamente planas siendo, por su sencillez y resultados, un método ideal para preparar estas superficies y efectuar estudios mecanísticos en este sistema.

In this thesis, pH and potassium all-solid-state ISE based on potentiometry and bioimpedance sensors were designed, fabricated and integrated in a miniaturized array for its application in endoscopic surgery for in vivo ischemia detection inside the stomach. To achieve this goal, the developed array withstood the low pH and corrosive condition in the gastric juice of the stomach, by modifying the surface with a conductive Ag/AgCl ink containing hydrophilic and hydrophobic groups. That creates a stable and robust candidate for low pH applications. However, these sensors have to demonstrate besides stability, high sensitivity, and selectivity. For this purpose, different ionophores specific to a single ion were tested. Octadecyl isonicotinate was the one that shown better results as pH ionophore and valinomycin, bis [(benzo-15-crown-4)-4-ylmethyl] pimelate for potassium detection. All these ionophores were embedded in PVC polymer membrane containing also plasticizers such as 2-nitrophenyl octyl ether, bis (1-butylpentyl) adipate (BBPA) and liphophilic anionic additives such as potassium tetrakis (4-chlorophenyl) borate (KTpClPB). The specific compositions of membranes to detect potassium or pH were optimized for the better performance of the sensors. pH ISE sensor shows a nernstian behavior (-54,38 mV/pH) at low pH and a nearly nernstian behavior at physiological pH (-34,899 mV/pH). Bioimpedance sensor was tested and optimized in vitro with different solutions of ions concentration to mimic ischemia detection and with different kinds of tissues from different nature. For this purpose, chicken fat and breast tissues were taken as a model for mimicking non-ischemic and ischemic states respectively. The effect of electrodes insulation as well as the pressure applied on the tissue was studied. The dependence of the impedance response with different pressure applied to the sensor was overcome by applying magnetic field attachment. The sensor array was modified with ring magnets which were attracted by an external magnet, giving stable and reliable signal discarding mechanical motion. The shape and size of the sensor array were designed for being adapted to the commercially available gastroendoscopes. Round shaped cylinder of 7 mm diameter was fabricated with 12 electrodes pin of 600 µm diameter, containing 3 RE, 3 pH and 2 potassium all-solid-state sensors and 4 electrodes in a row for impedance measurements. The sensor array was successfully integrated in commercial endoscope and inserted inside the pig stomach. The blood flow of certain area of the stomach was interrupted by ligating or crossclamping vessels and organ wall. Ischemia and reperfusion steps were sensed successfully with potassium and pH sensors. These results also indicate that information about hypoxic tissue damage can be collected with this array. Ischemia was also sensed on small intestine tissue by opening the abdominal part of the body and getting the sensor array in contact with the intestine. By crossclamping of mesenteric artery by tourniquets and scissors, ischemic and reperfusion states were controlled. Results proved that ischemia and reperfusion can be monitored by our integrated sensor array. As a conclusion, a novel all-solid-state potentiometric, miniaturized, low cost and mass producible pH, potassium all-solid-state ISE and impedance sensors integrated in an array was successfully fabricated for detecting ischemia inside the stomach by means of endoscopic techniques and also on small intestine. This array was tested in vitro and vivo giving reproducible and reliable results. The developed all-solid-state pH sensors permit low pH sensing from 0.7-2.5, which is the only example in the literature that allows so low pH detection, and so make this sensor a unique device for stomach detection.
El diagnóstico médico es uno de los campos que han obtenido más ventajas de la capacidad de los electrodos selectivos de iones (ESI) para la detección de iones, ya que los cambios en la concentración de estos elementos están directamente relacionados con diferentes enfermedades. La detección de isquemia es una de las favorecidas por estos sensores. La isquemia es una disminución del suministro de sangre a un órgano y se requiere una detección rápida y precisa. Los métodos de detección in situ en el tejido de los órganos conllevan una detección temprana de la isquemia y el estómago es uno de los órganos más importantes en la detección de Ischemia. Sin embargo, el bajo pH del jugo gástrico del estómago hace difícil la fabricación de sensores de estado sólido con ESI estables y funcionales, principalmente debido a la interferencia de aniones y al problema de la adhesión entre la membrana ESI y la superficie del electrodo. En esta tesis, se han diseñado y fabricado electrodos selección de iones de pH y potasio ESI de estado sólido basados en la potenciometría y sensores de bioimpedancia y se han integrado en una matriz en miniatura para su aplicación en la cirugía endoscópica para la detección de isquemia in vivo en el interior del estómago. El conjunto de sensores se integró con éxito en endoscopio comercial y se inserto en el interior del estómago de un cerdo. El flujo de sangre de cierta área del estómago se interrumpió mediante la ligación o pinzamiento de los vasos sanguineos y la pared del órgano. Los pasos de isquemia y reperfusión fueron detectados con éxito con los sensores de potasio y de pH. Estos resultados también indican que se puede obtener información sobre el daño en el tejido hipóxico recogido con esta matriz. Los sensores de pH de sólido desarrollados permiten la detección pH bajos de 0,7 a 2,5, que es el único ejemplo en la literatura de detección de pH tan bajos con este tipo de sensores y por lo tanto hacen que sea este sensor de un dispositivo único para la detección de isquemia en el estómago.

En esta Tesis de Doctorado se han desarrollado sistemas lab-on-a-chip (LOC) funcionalizados de bajo coste para su uso como herramientas analíticas en aplicaciones medio ambientales y biomédicas. Inicialmente se exploró el potencial de LOCs fotónicos (PhLOC) previamente definidos en nuestro grupo, como sistemas en análisis. Se aplicaron sistemas microfluídicos de Reflexión Interna Múltiple (MIR) fabricados en polímeros de bajo coste, como polydimetilsiloxano (PDMS), siguiendo un procedimiento rápido de fabricación, en la detección de diferentes analitos (células e iones de metales pesados) y su funcionamiento se comparó con el de otras técnicas analíticas más convencionales. Para dotar de selectividad a los PhLOCs se desarrollaron y compararon diferentes protocolos de modificación de superficies para la inmovilización de proteínas en los materiales poliméricos utilizados para la fabricación de estos sistemas. Estos métodos mantienen inalteradas las propiedades ópticas y estructurales del material. Se utilizó la peroxidasa de rábano (HRP) como proteína modelo para estos estudios, y las superficies biofuncionalizadas resultantes se testaron mediante la medición de la actividad enzimática en la reacción de reducción de peróxido de hidrógeno en presencia del mediador redox 2,2’azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), cuyo producto enzimático de color verde pudo ser detectado mediante medidas de absorbancia. Se midió la robustez del proceso de inmovilización mediante la medida de la actividad del HRP durante un periodo superior a un mes. Finalmente, se añadieron nuevos componentes fluídicos y funcionalidades a los PhLOCs previamente aplicados para mejorarsu desempeño. Estructuras microfluídicas tales como mezcladores biofuncionalizados (actuando en consecuencia como reactores) se integraron monolíticamente con el MIR, dando lugar a un PhLOC con mejores prestaciones analíticas. Estos nuevos elementos disminuyeron el tiempo de análisis y el volumen de muestra y reactivo. Con la integración de una celda electroquímica de oro en el substrato, se desarrolló un LOC con lectura de medida dual (DLOC), que permitió la transducción simultánea óptica y electroquímica e hizo el sistema desarrollado autoverificable, mejorando así su fiabilidad. Se mostró el potencial de este DLOC mediante el desarrollo de una herramienta analítica para la medida de glucosa. Se inmovilizaron glucosa oxidasa (GOx) y HRP siguiendo el protocolo desarrollado en esta Tesis y se aplicaron como receptores específicos para la detección de glucosa basada en una reacción enzimática en cascada utilizando el mediador redox ABTS. Como estudio adicional, se testó la aplicabilidad del protocolo de funcionalización en diferentes polímeros y también se llevó a cabo la inmovilización de componentes biológicos diferentes a enzimas.
In this PhD Thesis low-cost functionalized Lab-on-(bio)Chip systems (LOC) for their use as analytical tools for environmental and biomedical applications have been developed. Based on photonic LOC approaches (PhLOC) previously defined in our group, the potential of these devices in analysis was explored first. Multiple Internal Reflection (MIR) optofluidic systems made of cost-effective polymers, such as polydimethylsiloxane (PDMS), using rapid fabrication processes were applied for the detection of different analytes (cells and heavy metal ions) and their performance compared with other more conventional analytical techniques. In order to confer selectivity to the PhLOCs, different surface modification protocols for protein immobilization on the polymeric materials used in this work were developed and compared. These methods keep the optical and structural properties of the material unaltered. Horseradish peroxidase (HRP) was chosen as a model protein in these studies, and the resulting biofunctionalized surfaces tested by measuring the enzymatic activity to hydrogen peroxide in the presence of 2,2’azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) redox mediator, whose green colored enzymatic product could be detected by absorbance measurements. The stability of the immobilized HRP was also tested for periods longer than one month. Finally, other fluidic components and functionalities were added to the previously applied PhLOCs in order to enhance their performance. Microfluidic structures such as biofunctionalized mixers (therefore also playing the role of reactors) were monolithically integrated with a MIR, resulting in a PhLOC with enhanced analytical performance. These new elements decreased the analysis time and sample / reagent volumes. With the integration of a gold electrochemical cell in the substrate, a dual readout LOC (DLOC) was developed, which enabled simultaneous optical and electrochemical transduction and made the developed system self-verifying, thereby improving its reliability. The potential of this DLOC was shown by developing an analytical tool for measuring glucose. Glucose oxidase (GOx) and HRP were immobilized following the protocol developed in this Thesis and applied as the specific receptors for the detection of glucose based on an enzymatic cascade reaction also using ABTS redox mediator. As an additional study, the applicability of the developed functionalization protocol was tested on different polymers and the immobilization of biological components other than enzymes was also carried out.

La presente tesis describe el desarrollo de nuevos métodos de sensado basados en nuevas propiedades de nanomateriales aplicados en la detección de proteínas y ADN. El trabajo ha sido basado en dos plataformas de sensado: primero, electrodos serigrafiados de carbono (SPCEs). Estos electrodos fueron aplicados en un ensayo de detección por impedancia eléctrica de nanopartículas de oro (AuNPs). Del mismo modo, SPCE fueron adaptados mediante films de polythionina y nanopartículas de Iridio (IrOxNPs) para la detección de secuencias de ADN. La segunda plataforma utilizada fue basada en papel y tiene el formato de un inmunoensayo de flujo lateral (LFIA, del inglés lateral flow immunoassays). Esta plataforma se adaptó para la detección de una proteína específica Parathyroid like hormone (PTHLH) utilizando AuNPs como marcas, con el fin de obtener una nueva estrategia más simple, sin marcaje de isótopos radioactivos, menos costosa y más rápida. En el Capítulo 1 se da una visión general de las aplicaciones llevabas a cabo y mejoras aportadas por parte de nanomateriales en el campo de los biosensores, y las posibles aplicaciones en la detección de biomarcadores. En el Capítulo 2 se presentan los objetivos de la tesis. El uso de SPCE como plataforma para la detección de AuNPs mediante medidas de impedancia se presenta en el Capítulo 3 consiguiendo una mejor detección en comparación con métodos similares publicados para la detección de AuNPs. La técnica desarrollada es aplicada satisfactoriamente en la detección de AuNPs de diferente tamaño, y en un magnetoinmunoensayo utilizando AuNPs como marca para la detección de una proteína modelo. En el Capítulo 4, se presenta el trabajo relacionado con el desarrollo de nuevos sensores para la detección de DNA. El sistema está basado en la modificación de SPCEs mediante películas de un polímero y nanopartículas de óxido de iridio (IrOxNPs) sobre las cuales se inmovilizan secuencias de captura de DNA. La detección del ADN objetivo se consigue mediante medidas de impedancia eléctrica, basadas en el efecto de bloqueo del ADN hibridado para la difusión de un indicador redox a la superficie del electrodo. El biosensor resultante, que opera en modo libre de marcas, fue utilizado para la detección de secuencias de ADN específicas para el parásito de Leishmania. En el Capítulo 5 se presentan conclusiones generales y perspectivas futuras. En el Anexo A, se presenta el trabajo relacionado con las plataformas de papel para la detección de una proteína específica, PTHLH. El sistema de detección presentado es del tipo LFIA. La técnica desarrollada supone una alternativa menos costosa, más rápida y menos peligrosa a las técnicas disponibles actualmente. El límite de detección (LOD) conseguido está en el rango de ng mL-1 en muestras reales (medio de cultivo celular y lisado celulares). Además, se comprobó la compatibilidad del método desarrollado con suero humano utilizando suero humano con PTHLH añadido. En el Anexo B, se presenta el trabajo llevado a cabo en una estancia de investigación. En esta sección se presenta la fabricación de sensores electroquímicos de ADN (E-DNA) y basados en aptameros (E-Ab), y la aplicación de dicha tecnología en sensores serigrafiados de oro y en SPCE modificados con AuNPs. El Anexo C representa la investigación llevada a cabo como continuación de otra hecha anteriormente en nuestro grupo. Las condiciones y materiales encontrados previamente se aplicaron en la fabricación de una plataforma de nanocanales para la detección de una proteína secretada por células cultivadas directamente sobre la plataforma de sensado.
This thesis describes the study and development of new biosensing approaches based on novel properties of nanomaterials for the detection of proteins and DNA. The work has been performed in basis of two sensing platforms: first platform, the carbon screen-printed electrodes (SPCEs), were used in a more sensitive detection of gold nanoparticles (AuNPs) through electric impedance measurements. Furthemore, the same platform (SPCE) was adapted through polythinione films and iridium oxide nanoparticles (IrOxNPs) for the detection of specific DNA sequences in a label free assay. The second platform, paper-based platforms in format of Flow Immunoassay (LFIA), using gold nanoparticles as labels is adapted for the detection of a specific protein, Parathyroid like Hormone (PTHLH), with the aim to find a new strategy for simpler, non-hazardous, cheaper and faster detection of the protein. In Chapter 1 a general overview of the application of nanomaterials for the improvement of biosensors and its application in the field of diagnostics and biomarkers detection is presented. In Chapter 2 the objectives of the thesis are presented. Use of SPCE as platform for detection of gold nanoparticles (AuNPs) through electric impedance measurements is presented in Chapter 3. The developed technique is successfully applied in the detection of AuNPs of different sizes, and in a magnetoimmnuoassay for the detection of a model protein using AuNPs as electrochemical labels. In Chapter 4, a novel biosensor for the detection of DNA is presented. The system is based in SPCE modified with polymer films and Iridium Oxide nanoparticles, where capturing DNA sequences have been immobilized. Detection of target DNA sequences is performed through electric impedance measurements, based in the blocking effect of the DNA against the diffusion of a redox indicator to the surface of the electrode. A label free immunoassay for detection of specific sequences of Leishmania parasite’s DNA is shown. In Chapter 5 general conclusions and future perspectives of the presented work are discussed. In Annex A the work related to the paper-based platform for protein detection is presented. In this annex, detection of a specific protein (parathyroid like hormone, PTHLH) through LFIA strips is described. The developed LFIA strips represent a cheaper, faster and non-hazardous alternative to current available systems for PTHLH detection. Limits of detection (LOD) in the range of ng mL-1 for PTHLH in real samples (cell culture media, cell lysates) are reported. Furthermore, the developed system is challenged using human serum spiked with PTHLH, proving the potential of the system to detect PTHLH In human serum. In Annex B the work carried out in a research stay is presented. In this section fabrication of electrochemical DNA (E-DNA), and electrochemical aptamer (E-Ab) biosensors is described. The aim of the work was focused on adapting the E-DNA and E-Ab technology to SPCE, using AuNPs as connecting platform between the thiol modified DNA and the SPCE. Annex C represents a research done as a continuation of a previous one done in the group related mostly to the study of compatible materials with interest to be used as cells growth platforms with interest in sensing. As continuation of this work, in Annex C the conditions and materials previously selected to grow cells are applied in a nanochannel platform for the detection of a protein secreted by the cells grown directly on the sensing platform.

The thesis is focused on the development and enhancement of the electrochemical properties of the carbon based supercapacitors and pseudocapacitors. To overcome the capacitance loss at the condition of fast charging in the carbon-based supercapacitors, a metal-oxide embedded porous carbon nanofiber with a 3-D electrode architecture is designed. This electrode reduces the electrode resistance and at the same time increases the associated values of capacitance at high rates. The investigation also indicates an essential role in the concentration of the metal oxide precursor towards the electrochemical behavior of the electrodes. This correlation could be useful to design better electrodes for supercapacitor, functioning with better energy and power density capabilities. Whereas, in the case of the water-based pseudocapacitors, it is shown that they suffer from low voltages. Two strategies were used to overcome this issue. (i) Exploring and improving the electrode material based non-carbon materials. In this regard, new materials from the family of MXenes are introduced, to achieve higher cell voltages. Under this frame, a new 2-D MXene based on Molybdenum Vanadium Carbide is proposed and its electrochemical characteristics were investigated. According to its characteristics, its coupling with 2-D Titanium Carbide MXene exhibits a higher cell voltage. The investigation reveals that the charge storage in 2-D molybdenum vanadium carbide MXene has the dependence on the type of electrolyte cations. For the case in point, small size monovalent cations, such as lithium and sodium ions, demonstrate lower hindrance to the charge storage, while large size monovalent potassium ions and bivalent magnesium ions suffer from hindrance effect, causing them to have lower charge storage than lithium and sodium ions. Therefore, the selection of appropriate electrolyte ions especially in the case of MXene based materials appears to be important, which is here found to be with the protonic and sodium ion based electrolytes. (ii) the proposed approach is based on the use of water-based super-concentrated salt solutions which are promising electrolytes to contribute to widening the cell voltage of aqueous pseudocapacitors. Likewise, besides this, it is also proposed that the coupling of 2-D Titanium Carbide MXene with the tunnel structures of Manganese Oxide using this super-concentrated electrolyte water in salt can enable a high voltage aqueous pseudocapacitive energy storage device. The investigation using this approach reveals that the concentration of the salt electrolyte plays a significant role in the values of charge storage in 2-D titanium carbides. Although an extremely high concentration of salt electrolytes widens the potential window, the electrolyte ions in such high concentration face difficulty to insert within the 2-D layers of titanium carbide MXene. On the contrary, the use of low concentrated salt solutions is not recommended, as they provide narrow potential windows. Consequently, during the cell assembling using super-concentrated electrolytes, a moderate concentration of salt electrolyte needs to be taken into attention. On this way, both wider potential window and high charge storage, can be achieved with pseudocapacitive materials like 2-D titanium carbides MXenes. The crystallographic tunnel size of manganese oxide plays a vital role in the charge storage. For instance, tunnel structures, both smaller and larger than the size of the electrolyte ions store fewer charges. As both of these tunnel phases of manganese oxide face difficulty for the insertion of the electrolyte ions. Therefore, manganese oxide with adequate tunnel size needs to be taken into account. Besides this, it is also essential to consider the electronic conductivity of the manganese oxide phase, as high electronic conductivity allows it to store more charges during the condition of fast charging. In regards of the cell assembly, after considering the above-mentioned understanding the practice of applying the voltage-hold test to determine the realistic cell voltage is helpful, as the cell assembled with such realistic voltages permits the cell to have long cycle life. Besides these understanding, remarkable performances were witnesses with the technologies developed in this thesis. For example: (i) the carbon-based electric double layer supercapacitor shows faster responses than the existing carbon-based supercapacitors, (ii) the pseudocapacitors shows high volumetric capacitances (> 35 F cm-3) than carbon-based supercapacitors. Besides this, pseudocapacitors also exhibit higher cells voltages than the existing pseudocapacitors. The pseudocapacitor cells developed in this exhibits high electrochemical stability (> 95 %) over thousands of cycles. Furthermore, the pseudocapacitor is more favorable than EDLCs in applications as they provide slower self-discharges than EDLCs. The above understanding, such as the selection of the electrode, electrode processing and the cell assembly is a tool for designing better supercapacitors.
La tesis se centra en el desarrollo del conocimiento orientado y conducido a la mejora de las propiedades electroquímicas de los supercapacitores, ya que sufren bajos valores de densidad de energía. Este inconveniente limita a los supercapacitores en las aplicaciones donde son necesarios tanto alta potencia como densidad de energía. Entonces, en este escenario, se identificaron dos problemas principales importantes: (a) las limitaciones de rendimiento del supercapacitor debido a la condición de carga rápida, y (b) el bajo voltaje de celda de los pseudocapacitores en electrolitos acuosos en comparación con los electrolitos orgánicos. Para superar la limitación de rendimiento en el primer problema, se muestra una alternativa original a través del electrospinning para diseñar nanofibras de carbono porosas con incrustaciones de óxido metálico con una arquitectura de electrodo 3D que contribuyen a reducir la resistencia del electrodo y al mismo tiempo aumentan los valores asociados de capacidad. La investigación indica un papel esencial en la concentración del precursor de óxido metálico hacia el comportamiento electroquímico de los electrodos. Esta correlación podría ser útil para diseñar mejores electrodos para supercapacitadores, funcionando con mejores capacidades de densidad de energía y potencia. En lo que respecta al problema relacionado con los bajos voltajes celulares en el pseudocapacitor acuoso, en lugar de utilizar materiales basados en carbono más estándar, se toma una metodología en términos de exploración y mejora basada en las propiedades del material del electrodo. Así, se introducen nuevos materiales de la familia de MXenes, para lograr voltajes de celda más altos. Bajo este marco, se propone un nuevo MXene 2-D basado en carburo de vanadio y molibdeno y se han investigado sus características electroquímicas. De acuerdo con sus características, su acoplamiento con carburo de titanio 2-D MXene exhibe un voltaje más alto en una celda pseudocapacitiva todo en MXene. Además de esto, el problema del bajo voltaje de la celda también se resuelve aplicando otro enfoque basado en la modificación del electrólito. El enfoque propuesto se basa en el uso de soluciones salinas superconcentradas a base de agua que son electrolitos prometedores en la ampliación del voltaje celular de los pseudocapacitores acuosos. Del mismo modo, también se propone que el acoplamiento del carburo de titanio 2-D MXene con las estructuras del túnel de óxido de manganeso utilizando este electrolito súper concentrado o agua en sal permite lograr una celda de pseudocapacitador acuoso de alto voltaje. En conjunto, la estrategia presentada a través de esta tesis en términos de preparación de electrodos, selección de materiales, ensamblaje celular y su evaluación de las propiedades electroquímicas es una herramienta para diseñar supercapacitores con mejores capacidades de energía y potencia.

En una primera parte de esta tesis fue desarrollado un nuevo electrodo a base de pasta de grafito-epoxi composite (GECE) conteniendo nitrato de bismuto [Bi(NO3)3] como precursor de bismuto incorporado [Bi(NO3)3-GECE)], como una posible alternativa para el análisis electroquímico por redisolución de metales pesados en cantidades traza. Los resultados claramente muestran las ventajas del Bi(NO3)3-GECE en combinación con la técnica de voltamperometría de redisolución anódica de onda cuadrada (SWASV) para la detección de metales pesados. Se llevaron a cabo medidas individuales y simultáneas de Pb y Cd y los resultados mostraron claramente las ventajas del Bi(NO3)3-GECE en combinación con la técnica SWASV para la detección de metales pesados. Con el uso del Bi(NO3)3-GECE construido se pueden realizar análisis rápidos y eficaces de iones de metal en cantidades traza como Pb y Cd entre otros en muestras ambientales de suelo, aguas naturales y aguas residuales. La ventaja inherente de la no necesidad de mercurio elimina muchas de las objeciones para el uso de métodos electroquímicos en la detección de tales especies en estos medios.
Comparando el Bi(NO3)3-GECE con el electrodo de película de mercurio comúnmente usado y electrodo de película de bismuto desarrollado antes por nuestro grupo, el nuevo electrodo propuesto ofrece un notable funcionamiento en el análisis de metales pesados en cantidades traza, que puede ser de gran ventaja en electroquímica, contribuyendo a una aplicabilidad más amplia de técnicas electroquímicas por redisolución relacionadas con electrodos "sin mercurio". Además de aplicaciones ambientales el electrodo desarrollado basado en bismuto tendría interés especial para la aplicación en la detección de puntos cuánticos (QDs) basados en metales pesados. Tales aplicaciones están actualmente en proceso de estudio en nuestro grupo de investigación para la detección de ADN.
Las otras partes de la tesis se dedican al desarrollo de nuevos sensores de ADN y proteínas basados en la misma técnica electroquímica de redisolución y el uso de nanopartículas de oro como marcas.
Actualmente la detección electroquímica de secuencias de ADN específicas vía el evento de hibridación es una cuestión importante por lo cual diversas estrategias han sido propuestas.
Genosensores electroquímicos de afinidad basados en el marcaje con nanopartículas de oro (AuNPs) y el uso de partículas paramagnéticas (MB) como plataforma para la inmovilización de la sonda de ADN de captura también han sido desarrollados en esta tesis a fin de demostrar la inducción magnética eficaz de un nuevo electrodo de grafito-epoxi composite-magnético (M-GECE) el cual fue construido también con pasta de grafito-epoxi composite con un pequeño imán de neodimio integrado.Todos los ensayos para la detección electroquímica de la hibridación del ADN desarrollados en esta tesis fueron basados en la detección directa de las marcas de AuNPs por medio de la técnica de voltametría de pulso diferencial (DPV) usando el M-GECE donde la intensidad de la corriente de la señal generada es directamente proporcional a la cantidad de ADN en la muestra. Como también ha sido demostrado, con el sensor de ADN asistido magnéticamente, el ADN analito condujo a una muy bien definida señal mientras que esencialmente ninguna señal fue observada para el ADN no complementario.
Un nuevo inmunoensayo electroquímico sensible ha sido desarrollado, también basado en AuNPs como marca y MB como plataforma. El método fue evaluado para un inmunoensayo heterogéneo no competitivo de una IgG humana como proteína modelo. La detección electroquímica fue llevada a cabo en la misma forma que lo fue para ADN.
La detección electroquímica de marcas de AuNPs en biosensores de afinidad usando métodos de redisolución permite el estudio detallado de la hibridación de ADN así como también inmuno-reacciones con interés en aplicaciones relacionadas con genosensores o inmunosensores. Los métodos electroquímicos usados para la detección de AuNPs como marca pueden ser muy prometedores tomando en cuenta su sensibilidad alta, límite de detección bajo, selectividad, simplicidad, bajo coste, y disponibilidad de instrumentos portátiles.
Como conclusión final, las estrategias de análisis electroquímico de ADN y proteínas fueron demostradas con éxito y debido a los resultados prometedores su uso en muestras reales es viable. Tales biosensores de ADN e inmunosensores dan lugar a un enorme potencial de aplicación principalmente para diagnóstico clínico y monitoreo ambiental entre otros campos.
In the first part of this thesis a new graphite-epoxy composite electrode containing bismuth nitrate [Bi(NO3)3-GECE)], as built-in bismuth precursor as a possible alternative for electrochemical stripping analysis of trace heavy metals has been developed. Individual and simultaneous measurements of Pb and Cd were carried out and the results clearly showed the advantages of the Bi(NO3)3-GECE in combination with square wave anodic stripping voltammetry (SWASV) technique for heavy metals detection. Fast and effective analyses of trace metal ions such as Pb and Cd among others in environmental samples of soil, natural waters and effluents can be carried out by using the new Bi(NO3)3-GECE constructed. The inherent advantage of no necessity of mercury removes many of the objections for the use of the developed sensor.
When comparing the Bi(NO3)3-GECE with the commonly used mercury film electrode and previously developed bismuth film electrode, the newly proposed electrode offers a remarkable performance in analysis of trace heavy metals, which can be advantageous in electrochemical, hence contributing to the wider applicability of electrochemical stripping techniques in connection with "mercury-free" electrodes. Beside environmental applications the developed bismuth based electrode would have special interest for application to heavy metal based quantum dots. Such applications are currently in the studying process at our research group for DNA detection.
The other parts of the thesis are dedicated to the application of electrochemical stripping analysis in connection to gold nanoparticles for DNA and protein detection.
Currently the electrochemical detection of specific DNA sequences via hybridization event is an important issue by which diverse strategies have been proposed. Affinity electrochemical genosensors based on labelling with gold nanoparticles (AuNPs) and the use of paramagnetic beads (MB) as platform for the immobilization of capture DNA probe have been also developed in this thesis in order to demonstrate the effective magnetic triggering of a new magnetic-graphite epoxy composite electrode (M-GECE) which was constructed with graphite-epoxy composite paste, with a small neodymium magnet integrated.
All the assays for the DNA hybridization electrochemical detection developed in this thesis were based on the direct detection of AuNPs labels (anchored onto the M-GECE) by means of differential pulse voltammetry (DPV). The intensity of the generated current is directly proportional to the amount of DNA at the sample. As also has been demonstrated, with this magnetically assisted DNA sensor, target DNA leaded to very well defined signal whereas essentially no signal was observed for non-complementary DNA.
By the other side a novel, sensitive electrochemical immunoassay has been also developed based in AuNPs as label and MB as platform. The method was studied and evaluated for a noncompetitive heterogeneous immunoassay of a human IgG as a model protein. The electrochemical detection was carried out in the same way that as for DNA.
The electrochemical detection of AuNPs labels in affinity biosensors using stripping methods allows the detailed study of DNA hybridization as well as immunoreactions with interest in genosensor or immunosensor applications. The developed detection methodologies may be very promising taking into account their high sensitivity, low detection limit, selectivity, simplicity, low cost, and availability of portable instruments.
As final conclusion, the DNA and protein electrochemical analysis strategies were successfully demonstrated and according to the promising results obtained its use for real samples is viable. Such DNA biosensors and immunosensors hold an enormous application potential principally for clinical diagnostic and environmental monitoring among other fields.

The present doctoral thesis is framed in the research and development (R & D) project between a private biotechnology company of molecular diagnostics Genomica SAU, the Institute for Bioengineering of Catalonia (IBEC), the University of Barcelona, and the Microfluidics ChipShop Company. The main objective of the project is making, implementation and marketing of a diagnostic device for early detection of DNA sequences involved with cancer. The multi device, or lab-on-chip (LOC), consists of a central automation unit (CAU), a system in miniature of DNA amplification or chain reaction polymerase (mini-PCR), and a biosensing platform (DNA chip) that consisting of a matrix or electrochemical array. The three elements are integrated by a microfluidic system in sandwich format cartridge. For this purpose, the aim of this thesis was the creation, characterization and optimization of the biochemical recognition platform between two single strands of DNA of dissimilar lengths but with some complementary sequences for the subsequent electrochemical detection of a hybridization event between them. Then, the integration into the cartridge of above platform was done. For the creation of this platform, we chose to use a self-assembled monolayer (SAM) of thiols as biorecognition interface of the 14 DNA sequences that are part of the project. During optimization of the interface chips individual gold and various molecules were used being chosen the molecule with two arms disulfide of polyethylene glycol (PEG) and a malaimida group at the end of one of them. This linker (or MalPEG linker) reacts with the gold surface due to the dative interaction between the sulfur atoms of the disulfide and the gold atoms from the surface of the chips. At the same time, the malaimida group reacts with the thiol group of the capture probes, joining. The PEG groups function as anti-adhesion molecules. Surface plasmon resonance (SPR) and cyclic voltammetry (CV) were techniques used to characterize the substrate and the hybridization event. For the manufacture of the cartridge, this was divided into two main blocks, the biosensing or electrochemical block and PCR block. The electrochemical block is composed of 4 layers, one of 64 working electrodes and gold paths for contact with the potentiostat, another layer that defines the area of the sensors must be functionalized gold and isolating the gold surface of the tracks. The third layer is a double-sided adhesive that has a hexagonal hole working as hybridization chamber, and the last layer is a screen printing layer with the reference electrode (RE) and counter electrodes. The above layers form an electrochemical cell wherein the hybridization will occurs. Regarding the PCR block, this is a system of two layers with a type microfluidic channel kind loop and its function is to contain the solutions during the process of DNA amplification by the mini-PCR. During the integration of the optimized SAM into an electrochemical cartridge a manual and automated ways were used to immobilize the capture probes. Several tests were performed in order to obtain the best conditions and ratios between the molecules to maximize the hybridization signal during the electrochemical detection.
El presente trabajo de tesis está enmarcado en un proyecto de investigación y desarrollo (I+D) entre la empresa privada Genomica S.A.U., el Instituto de Bioingeniería de Cataluña (IBEC), la Universidad de Barcelona y la empresa alemana ChipShop Microfluidics. El objetivo principal es el desarrollo, puesta a punto y comercialización de un dispositivo electroquímico de diagnóstico médico para etapas tempranas de cáncer. El objetivo de la tesis es la creación, optimización y posterior integración de una interfaz de biosensado de ADN en el dispositivo de diagnóstico, siendo pieza fundamental en el desarrollo de éste. La interfaz escogida fue una monocapa autoensamblada (SAM) que hace las veces de biosensor y que es capaz de anclar secuencias de ADN como sondas de captura y así poder detectar, selectivamente, las secuencias objetivo complementarias. El dispositivo también cuenta con un sistema microfluídico y un sistema de amplificación de ADN de reacción en cadena de la polimerasa en miniatura. La SAM esta inmovilizada en un array electroquímico que consta de 64 electrodos de trabajo que funcionan como elemento transductor de la señal electroquímica redox de los eventos de hibridación que ocurren sobre ellos. La funcionalización y puesta a punto del dispositivo se llevó a cabo inmovilizando múltiples sondas de captura después de una optimización de las concentraciones entre las diferentes partes constituyentes de la monocapa. Técnicas ópticas y electroquímicas fueron utilizadas para la caracterización de cada etapa y técnicas de fotolitografiado y de impresión por pantalla fueron utilizadas para la fabricación de los componentes del dispositivo. Finalmente, y después de algunos cambios surgidos durante el desarrollo del dispositivo, se llega a un diseño final y a las pruebas con muestras reales, proceso que aún está en etapa experimental.

Due to unique advantages of Jet Electrochemical Machining (Jet‐ECM) such as the absence of mechanical and thermal effects, there is an increasing demand for the implementation of the technology in industrial sectors. However, meeting the stringent quality requirements of the current technological level is a challenge in Jet‐ECM especially for complicated microstructures. Hence, the implementation of an adequate metrology system is necessary to minimise deviations and to enhance the process towards zero‐defect‐manufacturing. The metrology system should be capable of measuring the workpiece before machining in order to enable the machine to adjust the process parameters and to reach the desired micro‐structure. Post‐machining measurements to compare the machined part with the desired shape should be possible as well. This will enhance the machine to make corrections on the workpiece before delivery to the next section in a process chain. However, in order to reach the desired microstructures, the characteristics of workpiece like material properties and previously machined structures on the size and shape of the machined microstructure should be taken into consideration. This is done through the implementation of results of the fingerprint study into the process control. In this study the effects of previously machined single grooves which intersect the secondly machined groove on the size, shape and surface roughness are investigated. The previously machined groove was generated by milling or Jet‐ECM. Since at the intersections the gap size changes and this lead to changes in current and current density, it is expected to observe changes in size and surface roughness. This investigation will show how grooves change at the intersections and whether the mentioned changes are significant. Besides, some suggestions will be provided in order to minimise the effects in Jet‐ECM of intersecting single grooves.

A numerical model has been developed, based on an implicit finite difference technique, for the solution of a set of coupled non-linear partial differential equations (based on the Nemst-Planck equation), and linear and non-linear algebraic equations. These equations govern the mass transport and homogeneous chemical reactions in a simplified membrane chlor-alkali cell anolyte compartment. Membrane chlor-alkali cells are used for the industrial production of chlorine and sodium hydroxide, by electrolysis of brine. The model has been developed in an attempt to gain insight into the very localised chemistry which occurs in the hydrodynamic boundary layers within the electrolyser; chemistry which is strongly suspected to have a significant influence on the bulk chemistry, particularly on the homogeneous reactions leading to loss of chlorine through the formation of thermodynamically stable unwanted by-products such as the chlorate ion. These effects are very difficult to measure experimentally, making modelling the most attractive option. A set of experiments have been performed on laboratory scale electrolysers, in an attempt to characterise the cell chemistry, and produce data for model validation. Results are presented from the model demonstrating that the numerical approach adopted produces stable and physically plausible results under a range of operating conditions. It also demonstrates that the chemistry in both the anode and membrane hydrodynamic boundary layers differs significantly from that in the bulk. The experimental work has provided valuable insight into the mechanism of the loss reactions. Results of the experimental work are also compared with the results of the modelling.

The electrodeposition is a technique that day by day is gaining positions among the mainly employed physical methods. This is due to the fact that electrodeposition shows some advantages over the physical techniques such as: versatility, selectivity, room temperature, high deposition rates, high thicknesses, among others. Therefore, the aim of this thesis is the use of the electrochemical technology to prepare Co-Ag nanostructured materials for magntoresistive applications.

The first step was the preparation of granular films. However, the big difference in the standard potentials of both metals discards their codeposition and therefore, the main problem to overcome was to reduce this difference. Different electrolytic baths containing different complexing agents (Bath 1: Thiourea, bath 2: Thiosulphate and bath 3: Chloride) were employed in order to favour the codeposition. After optimizing the composition of each solution, Co-Ag films with a distribution of nanometric cobalt particles into the silver matrix were obtained. However, the deposits prepared from baths 1 and 2 only showed giant magnetoresistnace (GMR) at low temperatures, fact that was attributed to the presence of sulphur in the magnetic/non-magnetic interfaces which hindered the magnetoresistance effect to take place. The use of a sulphur-free bath (bath 3) allowed obtaining films with GMR values up to 7% at room temperature, values higher than those published by others. The numerical analysis of the magnetoresistance curves, which allowed the decomposition of the magnetoresistance curves into its ferromagnetic (FM) and superparamagnetic (SPM) contribution, indicated the higher SPM contribution over the FM one in all the electrodeposition conditions.

On the other hand and taking profit of the versatility of the electrodeposition, Co-Ag multilayers were prepared. The magnetic (Co) and non-magnetic (Ag) layer deposition condition optimization was crucial to obtain the highest GMR values.

The electrochemical technology was also useful to prepara Co-Ag nanowires (both granular and multilayered nanowires) into the pores of polycarbonate membranes. Moreover, nanoparticles of the Co-Ag system were also prepared with a core-shell structure and by the microemulsion method. A voltammetric method was developed to univocally determine the correct core-shell structure formation. An strategy was also developed to measure the magnetoresistance of the last two kinds of nanomaterials (nanowires and nanoparticles) which corroborated their magnetoresistive behaviour.
L'electrodeposició és una tècnica que, dia rere dia, escala posicions entre les més habitualment emprades tècniques físiques de deposició. Aquest fet es deu principalment als avantatges que presenta la tècnica electroquímica front als mètodes físics, essent aquests: versatilitat, selectivitat, equipament senzill, temperatura ambient, elevades velocitats de deposició, gruixos importants,..Aquest projecte de tesi desenvolupa la preparació electroquímica de materials nanoestructurats cobalt-plata, material que potencialment és útil en aplicacions magnetorresistives.

El nostre objectiu inicial va ser la preparació de pel·lícules granulars. El primer problema que va haver de superar-se per aconseguir la codeposició d'ambdós metalls va ser reduir l'elevada diferència entre els seus potencials de deposició. Es van utilitzar diferents banys electrolítics contenint agents complexants (bany 1:Tiourea, bany 2: Tiosulfat i bany 3: Clorurs) per tal d'afavorir la codeposició, Les formulacions optimitzades d'aquests banys van permetre aconseguir dipòsits amb una dispersió de partícules nanomètriques de cobalt a la matriu de plata. No obstant això els dipòsits preparats a partir dels banys 1 i 2 únicament presentaren magnetorresistència gegant a temperatures criogèniques, fet que es va relacionar amb la presència de sofre a les interfases magnètiques/no magnètiques, proposta que es va confirmar posteriorment.

Afortunadament el bany base-clorurs (bany 3) va permetre obtenir dipòsits amb valors de GMR de fins a un 7% a temperatura ambient, valors sensiblement superiors als trobats a la literatura. Un tractament de les dades experimentals amb un model teòric va permetre establir la contribució a la magnetoresistència de les partícules de cobalt d'acord amb la seva mida.

D'altre banda aprofitant la versatilitat de l'electrodeposició, es va procedir a la preparació de multicapes Co-Ag. L'optimització de les condicions d'electrodeposició tant de la capa magnètica (Co) com de la capa no magnètica (Ag) va ser decisiva per tal d'obtenir estructures amb GMR.

El mètode electroquímic va ser útil per obtenir fils de mida nanomètrica de Co-Ag a partir de templates de membranes de policarbonat, tant granulars com en forma de multicapa. D'aquest material, Co-Ag, s'han preparat nanoparticules amb estructura nucli-corona pel mètode de la microemulsió, per les que s'ha desenvolupat un mètode electroquímic de caracterització que ha permès comprovar la correcta formació de les nanoparticles. Per la mesura de GMR d'aquests sistemes nanomètrics (nanofils i nanoparticles) s'ha dissenyat un procediment experimental de mesura que ha confirmat el caràcter magnetoresistiu de les nanoestructures.

El desarrollo de interfaces neuronales requiere el uso de nuevos materiales electroactivos y biocompatibles, que al aplicar campos eléctricos no causen efectos secundarios que pueden dañar los tejidos o degradar la funcionalidad del electrodo. A día de hoy, existen diferentes materiales electroactivos que se usan como electrodos en el sistema nervioso: oro, platino, carbón, Pt-Ir o IrOx entre otros, siendo este último el que ha mostrado superiores resultados. Una alta eficiencia electroquímica, estabilidad en condiciones biológicas y biocompatibilidad, han hecho del IrOx el material más prometedor como electrodo para estimulación y registro de señales neuronales. Sin embargo, los avances tecnológicos han generado una demanda de nuevos materiales con propiedades mejoradas y con menos inconvenientes que los actuales (bajos valores de capacidad de carga o la rigidez inherente de este tipo de óxidos, ya que presentan poca compatibilidad con los tejidos blandos). Estas mejoras se pueden conseguir con el uso de materiales híbridos, que unan las diferentes propiedades de los componentes. En este sentido, se han preparado electroquímicamente híbridos IrOx-CNTs, con propiedades mejoradas tras la adicción de nanotubos de carbono. La composición química de estos híbridos es muy parecida a la obtenida para IrOx, aunque la incorporación de nanotubos de carbono hace la superficie más rugosa, aumentando de esta manera el área superficial del material. Estas propiedades, junto con el aumento de la conductividad proporcionada por los nanotubos de carbono, tienen como consecuencia elevados valores de capacidad de carga electroquímica. También, la estabilidad de las capas resultantes mejora en comparación con las muestras de IrOx. Las pruebas de biocompatibilidad realizadas a las muestras IrOx-CNTs han mostrado una alta supervivencia y funcionalidad neural, parecida a la obtenida con IrOx o borosilicato (usado como referencia). Estos datos, validan este tipo de nuevos materiales como prometedores electrodos neurales. También se han preparado híbridos de IrOx con grafito y grafeno. En ambas capas, se ha observado la presencia de partículas de carbón, aunque la presencia de grafeno de única lámina no ha podido ser confirmada, y serán necesarios más experimentos. Las propiedades electroquímicas de estos híbridos, IrOx-grafito e IrOx-grafeno, son similares a las obtenidas para IrOx-CNTs, pero con mayores valores de capacidad de carga. Sin embargo, la estabilidad electroquímica es pobre para el híbrido de grafito, y finalmente la capa se despega, debido presuntamente, a la estructura heterogénea de los híbridos de grafito, en la cual, grandes partículas de carbón no están completamente introducidas en la matriz del IrOx. Híbridos de IrOx con grafeno dopado con nitrógeno se han preparado también, mostrando buenas propiedades y altos valores de capacidad de carga y estabilidad, incluso comparados con los resultados obtenidos para los híbridos con grafeno no dopado. El aumento de la conductividad en estos materiales se puede deber a la presencia de nitrógeno, que induce el aumento de defectos en las láminas de grafeno. La biocompatibilidad de estos materiales híbridos grafíticos está siendo estudiada. Tri-híbridos poliméricos también han sido sintetizados electroquímicamente, IrOx-PEDOT-CNTs. El uso de una matríz polimérica, ofrece más flexibilidad al futuro electrodo, lo que es deseable para aplicaciones en tejidos blandos. Sin embargo, los primeros resultados obtenidos muestran que el polímero encapsula los nanotubos de carbono y el IrOx, minimizando sus propiedades electroquímicas. Como consecuencia, la conducta electroquímica del material híbrido es muy similar a la obtenida en otros polímeros, como PEDOT-PSS. Las pruebas de biocompatibilidad para estos híbridos poliméricos muestran baja viabilidad neuronal, aunque un nuevo modelo de co-cultivos (astrocitos-neuronas) se ha propuesto para mejorar la biocompatibilidad en este tipo de materiales. Los materiales obtenidos en todos los casos, son capas bien adheridas, lo que permite su futuro uso como electrodos o substratos de crecimiento neuronal.
The development of neural interfaces requires new electroactive and biocompatible materials, capable to apply electric fields without secondary effects, as large impedances at the interface or radical formation, which can cause damage in the tissues and the degradation of the electrode functionality. Currently, different types of electroactive materials are available for application as electrodes in the neural system: gold, platinum, glassy carbon, Pt-Ir, TiN or IrOx, among others, being the last, the one with superior performance. Properties such as high electrochemical efficiencies, good bio-stability and significant biocompatibility, have turned out IrOx into one of the most promising material for neural recording and stimulation electrodes. However, new technological breakthroughs have generated a demand of novel materials, with enhanced properties and which also minimize the drawbacks found in the actual ones, as low stability under electrochemical conditions, small values for charge capacity or the inherent rigidity of these oxides, which involves low compatibility with soft tissues. These improvements required may be achieved by hybrid materials, which join different properties from both counterparts. In this sense, IrOx-CNTs have been electrochemically prepared with enhanced properties. The chemical composition at the surface is very similar to that for IrOx, but the incorporation of carbon nanotubes makes the surface rougher, increasing the available interface area of the material. These properties, joined with the conductivity provided by the CNTs, yield very high values for charge storage capacity in electrochemical measurements. Also, the stability of the resulting coatings is improved in comparison with bare IrOx. The biocompatibility tests have shown high cellular survival and neuron functionality, similar to those values obtained for bare IrOx or borosilicate (used for reference), which validates these new materials as promising neural electrodes. IrOx hybrids with graphite and graphene also have been prepared. In both coatings, the presence of carbon particles has been demonstrated, although the confirmation of graphene sheets instead of few-layered graphene needs more experimental studies. The electrochemical properties of these IrOx-graphene and IrOx-graphite hybrids are similar than those obtained for IrOx-CNTs electrodes, with high values of charge storage capacity. However, the stability during consecutive cycling for the graphite-hybrid is poor and the coating is finally delaminated. These results are presumably due to heterogeneous structure in graphite-hybrids, in which the big carbon particles are not completely embedded in the IrOx matrix. Also, IrOx hybrids with N-doped graphene have been prepared, showing promising properties and very high values for charge storage capacity and stability, even when compared with non-doped IrOx-graphene coatings. The enhanced conductivity of these materials can be related with the presence of nitrogen, which induces the increase of the defects in the graphene sheets. The biocompatibility of these graphitic materials is under study. Polymeric tri-hibrids, IrOx-PEDOT-CNTs, have been also electrochemically synthesized. The use of a polymeric matrix is an effort to confer more flexibility to the electrode, which is desirable for soft tissue applications. However, the first results show that the polymer may encapsulate the CNTs and the IrOx particles, minimizing the electrochemical properties of these species. As a consequence, the electrochemical performance of the hybrid material is similar to those obtained for other polymers, as PEDOT-PSS. The biocompatibility tests have shown low neuronal viability in these substrates; however, co-cultures have been proposed as a novel method to improve biocompatibility in these types of materials. The materials obtained in all cases, are well adehered coatings, which leads to an easy future perpespective for their use as electrodes or cells substrates.

Hydrogen production from reforming bio-fuels is considered as one of the major ways of utilizing renewable energy sources. Conventionally, most reforming catalysts are noble metal catalysts with high operation temperature above 1000 °C, which result in low thermal efficiency, long start-up time and use of high grade materials. These reasons hinder the development of hydrogen production technology. Novel self-sustained electrochemical promotion (SSEP) catalysts were developed and evaluated for heavy hydrocarbon reforming at relatively low temperatures, 450 to 650 °C. Typically, the SSEP catalysts contain NiO/Ni/CuO/Cu/CeO2 as a selective anodic phase, La0.9Sr0.1MnO3 (LSM) as a selective cathodic phase, yttria stabilized zirconia (YSZ) as an oxygen ion conduction phase, and Ni/Cu also as an electronic conduction phase. The reforming performance of the SSEP catalysts was evaluated using a fixed bed reforming reactor for n-pentadecane. A commercially available noble metal containing catalyst, 2.4 %Pt on CeO2 support, was evaluated using exactly the same method. The following conclusions can be drawn as a consequence of this study: 1) The fuel conversion for the SSEP catalyst was 10 folds of that for the noble metal catalyst and the yield of hydrogen and carbon monoxide for the SSEP catalysts was 100 folds of that for the noble metal catalyst at 450°C. 2) The mechanism of the SSEP catalysts was proved by the experimental results. 3) The study of the effect of each component and the effect of the concentration clearly reveals that the performance of the SSEP catalysts can be further improved to a higher level by many ways. In addition, all the catalysts were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscopy (TEM) and Accelerated Surface Area and Porosimetry Analyzer 2020 (ASAP 2020).

Electrochemical Ion Exchange (EIX) was studied to determine the viability of the process for treatment of metal bearing effluents containing Cu, Zn and Ni. Other metals used during the investigation were Na and Cs. The EIX process was examined at the laboratory scale and later in a pilot plant. Process performance and cell design were evaluated both in absorption and regeneration cycles. A mathematical representation of the system was developed based on the Nemst-Planck equation. Zirconium phosphate, Purolite S930 , Purolite S950 and Purolite PrAOH were the ion exchangers used during the study. The EIX cell was made of two perspex blocks, each 490 mm by 125 mm and 20 mm thick. Each block contained a half cell made up of an EIX electrode and a counter electrode on either side of a heterogeneous ion exchange membrane with dimensions of 280 mm by 63 mrn by 5 mm. The EIX electrode consisted of a platinised titanium mesh, acting as a current feeder, embedded in the membrane. The counter electrode was a platinised titanium mesh placed on the opposite side to the current feeder. The process was operated by applying a potential across the membrane.

Electrodeposition is one of the main techniques for fabricating conductive parts with one or two dimensions in the micron size range. This technique is utilized to coat surfaces with protective films of several micrometers thickness or fabricate standalone microstructures. In this process, an electrochemical reaction occurs on the electrode surface by applying an electric voltage, called overpotential. Different electrochemical practices were presented in the literature to obtain kinetic parameters of an electrochemical reaction but most of these practices are hard to implement for the reactions occur on a microelectrode. Toward addressing this issue, the first part of the dissertation work presents a combined experimental and analytical method which can more appropriately provides for the kinetic measurement on a microelectrode. Another issue which occurs for electrodeposition on microscale recessed areas is the deviation of the profile of the deposition front from the substrate shape. Non-uniform deposition front usually obtains for a deposit evolved from a flat substrate with microscale size. Consequently, a subsequent precision grinding process is required to level the surface of the electrodeposited microparts. In order to remove the need for this subsequent process, in the second and third parts of the dissertation work, multiphysics modeling was used to study the effects of the fabrication parameters on the uniformity of the deposit surface and suggest a design strategy. Surface texture of the deposit is another parameter which depends on the fabrication parameters. Several important characteristics of the electrodeposited coating including its wettability depend on the surface texture. The next part of the dissertation work presents an experimental investigation and a theoretical explanation for the effects of the overpotential and bath concentration on the surface texture of the copper deposit. As a result of this investigation, a novel two-step electrodeposition technique is developed to fabricate a superhydrophobic copper coating. In the last part of the dissertation work, similar investigation to the previous sections was presented for the effects of the fabrication parameters on the crystalline structure of the deposit. This investigation shows that nanocrystalline and superplastic materials can be fabricated by electrodeposition if appropriate fabrication parameters are applied.
Ph. D.

This thesis presents: 1) literature review on adhesive bonding technologies in aviation industry including surface pretreatments (pre-preparation), surface quality assurance, and surface chemistry analysis methods; and 2) development and study of a novel solid-state electrochemical sensor for surface chemistry analysis of composite surfaces. The performance of an adhesive bonding is greatly determined by the adherend?s surface pretreatments which could increase surface tension, surface roughness, and change surface chemistry thereby increasing bond strength and durability of polymer composite adhesive joints. The primary goal of the surface pretreatments is to increase the surface roughness, surface energy, chemical activity, and cleanliness of the composite adherend as much as possible. Methods of surface pretreatments are reviewed in this paper, including: (1) abrasion/solvent cleaning; (2) grit blasting; (3) peel-ply; (4) tear-ply; (5) acid etching/anodizing; (6) corona discharge treatment; (7) plasma treatment; (8) flame treatment; (9) laser treatment; (10) others. One of the critical issues in aviation industry for an adhesive bonding is to analyze the prepared composite surfaces using a nondestructive inspection (NDI) or nondestructive test (NDT) method to determine whether the quality of surfaces are ready for the following bonding processes. Existing NDI methods include: (1) Near-Infrared; (2) Electrical potential; (3) Transient thermal NDT; (4) Electrical Impedance Spectroscopy (EIS); (5) Neutron radiography; and (6) X-ray Photoelectron Spectroscopy (XPS). However, up till now, these methods cannot provide definitive analysis or online and in-field analysis. Because of the non-availability of an on-line, in-field NDI method for surface chemistry analysis, excess or inadequate surface treatment and quality control processes may exist in the current aircraft manufacture processes incurring either a high cost or potentially weak adhesive bonds. Electrochemical reactions usually occur in liquid electrolyte or on conducting electrode but not on non-conducting composite. Conventional electrochemical sensors involve liquid electrolytes which will cause contamination on composite surfaces when they are used for surface chemistry analysis. In this work, we explore an all solid-sate electrochemical sensor technology. Redox pairs or mediators are combined into a solid-state electrolyte, NafionTM. The mediators can pass electrons to or from the composite surfaces causing slight reduction or oxidation of the composite surfaces. The output current in response to cyclic polarization (cyclic potential scanning) is used as the indication of the surface contamination level. The sensors included a working or sensing electrode with mediated Nafion clusters, Nafion membrane, Pt catalyzed carbon counter electrode, and Ag|AgCl reference electrode. The working electrode and counter electrode were attached to the Nafion membrane from different sides. The sensors were tested on different kinds of surfaces: original, polished, and sulfuric acid treated acrylic samples and pristine peel ply prepared, polished, and sulfuric acid treated composite laminate surface samples. The sensors showed a high sensitivity to the surface contamination. The performances and possible mechanisms related to the electrochemical sensors are discussed.

Eine Reihe 3-(p-X-phenyl)-Thiophenmonomeren (X = -H, -CH3, -OCH3, -COCH3, -COOC2H5, -NO2) wurde elektrochemisch polymerisiert, um Filme zu erhalten, die umkehrbar reduziert und oxidiert werden konnten (n-und p-dotiert wurden). Die Oxidationspotentiale der Monomere und die formalen Potentiale der n und p-Dotierprozesse der Polymere wurden mit Resonanz- und induktiven Effekten der Substituenten (Hammett konstanten) am Phenylring sowie semiempirisch errechneten Bildungswärmen der Monomereradikalkationen korreliert. Außerdem wurden die Oxidationspotentiale mit den Ionisierungspotentialen der Monomere verglichen, die über die Dichtefunktionialtheorie (DFT) errechnet wurden, die der Energie für das Erzeugen der Radikalkationen entsprechen. Um theoretische Grundlagen für die Einstufen-Bildung regioregulär -konjungierter Oligo- und Polythiophene zu erhalten, wurden die elektronischen Zustände von 3-Phenylthiophen-Derivaten anhand von Molekülorbitalberechnungen auf Grundlage der Dichtefunktionaltheorie mit Becke’s Drei-Parameter-Funktion (B3LYP), sowie mit den Basissätzen 6-31G(d) und 3-21G(d) erklärt. Die Reaktivität der Verknüpfung von mono- und oligo-3-Phenylthiophenen wurde von den berechneten ungepaarten Elektronenspindichten der entsprechenden Radikal-Anionen abgeleitet. Die Ionisierungspotentiale, die den Energien zur Erzeugung der Radikal-Anionen während der Oxidation entsprechen, wurden abgeschätzt. Die aus den 3-Phenylthiophenen entstandenen regioselektiven Hauptprodukte können gut durch die Größe der Spindichten erklärt werden. Da die Verknüpfungsreaktion an der zwei-Position des Thiophnrings (C-2) sterisch durch die Phenylgruppe und den Thiophenring gehindert ist, startet die Initiierung der 3-Phenylthiophene über die Bildung eines Kopf-Schwanz-Dimers. Folglich spielt das Kopf-Schwanz-Dimer eine wichtige Rolle bei den Wachstumsreaktionen der 3-Phenylthiophene. Die Ursache dafür liegt darin, dass das Kopf-Schwanz-Dimer in 5-Position die höchste Spin-Dichte besitzt und die Wahrscheinlichkeit einer Kopf-Kopf-Verknüpfung aufgrund der sterischen Hinderung zwischen dem Thiophenring und der Phenylgruppe gering ist. Polymerfilme von 3-Phenylthiophenderivaten, die durch elektrochemische Polymerisation synthetisiert wurden, sind in situ und ex situ durch Resonanz-Raman-Spektroskopie bei verschiedenen Anregungswellenlängen, sowie durch in situ und ex situ UV-Vis Spektroskopie analysiert wurden. Die Entwicklung der in situ UV-Vis-Spektren der Polymer von 3-Phenylthiophene nach der Dotierung wird durch ähnliche Eigenschaften gekennzeichnet, wie für viele Polythiophene mit einem hohen Grad der Konjugation beobachtet. Während der schrittweisen Oxidation der Poly-3-phenylthiophen Filme verringert sich die Intensität der Absorption wegen des Überganges bei 450-566 nm und ein neues ausgedehntes Absorptionsband, das auf (bi)polaron Zustände bezogen wird erscheint bei ungefähr 730-890 nm. Andererseits wird während der Oxidation (p-Dotierung) des Poly3-phenylthiophen Filmes eine blau/hypsochrome Verschiebung für beide Absorptionsbänder beobachtet . Es wird durch die Tatsache erklärt, dass ein Polymer eine Verteilung der Kettenlängen enthält und die längste Polymer kette (dessen Absorption bei niedriger Energie auftritt), bei niedrigeren Potentialen zu oxidieren beginnt. Die elektrochemischen Bandlücken der Derivate von 3-Phenylthiophen sind durch zyklische Voltametrie gemessen worden. Der Effekt der Substituenten auf den Oxidations-/Reduktions- potentiale wird besprochen. Bei Bandlücken, die durch zyklische Voltammetrie erhalten wurden, hat sich herausgestellt, dass sie im Allgemeinen höher liegen als optische Bandlücken. Erste Resultate der in situ Resonanz-Raman-Spektroskopie, von dem elektrochemisch erzeugten Polymerderivate von 3-Phenylthiophen Filmen auf einer Platinelektrode, in einer organischen Elektrolytlösung, werden berichtet. Beobachtete Raman Banden werden zugewiesen; gegründet auf diesen Resultaten werden die zuvor angenommenen molekularen Strukturen diskutiert
A series of 3-(p-X-phenyl) thiophene monomers (X= –H, –CH3, –OCH3, –COCH3, –COOC2H5, –NO2) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects (Hammett constants) of the substituents on the phenyl ring as well as the semiempirically calculated heats of formation of the monomer radical cations. Moreover, the oxidation potentials of the monomers were correlated with the ionization potentials of the monomers calculated via density functional theory (DFT), which correspond to the energies for generating radical cations during oxidative processes. For obtaining a theoretical basis for the one-step formation of regioregular –conjugated oligo-and polythiophenes, the electronic states of 3-phenylthiophene derivatives were elucidated by molecular orbital calculations using density functional theory with the Becke-type three parameters functional (B3LYP), the 6-31G(d), and 3-21G(d) basis sets. The reactivity for coupling reaction of mono- and oligo-3-phenylthiophenes are inferred from the calculated unpaired electron spin densities of the respective radical cations, and the ionization potentials which correspond to the energies for generating radical cations during oxidative processes were estimated. The major regioselective products of the oligomerization of 3-phenylthiophene can be well understood in terms of the magnitude of spin densities. Since the steric hindrance between the phenyl group and thiophene ring interferes with the coupling reaction occurring between 2-postions (C–2) of thiophene rings, the initiating reaction of 3-phenylthiophene is generaton of a head-to-tail (HT) dimer. Thus, the head-to-tail (HT) dimer plays an important role in the propagation reactions of 3-phenylthiophene. This originates from the highest spin density at the 5- position of the HT dimer and low probability of the HH coupling due to the steric hindrance between thiophene ring and phenyl group. Polymer films of the 3-phenylthiophene derivatives prepared by electrochemical polymerization were analyzed, in situ and ex situ, with resonance Raman spectroscopy using several excitation wavelengths as well as in situ and ex situ UV-Vis-spectroscopy. The evolution of the in situ UV-Vis-spectra of poly 3-phenylthiophene derivatives upon doping is characterized by similar features as observed for many polythiophenes with high degree of conjugation. During stepwise oxidation of the poly-3-phenylthiophene films the intensity of the absorption due to the transition around 450–566 nm decreases and a new broad absorption band related to (bi)polaron states appears around 730-890 nm. On the other hand, during the oxidation (p-doping) of the poly-3-phenylthiophene films a blue/hypsochromic shift is observed for both absorption bands. It is explained by the fact that a polymer contains a distribution of chain lengths, and the longest polymer chains (the absorption of which occurs at lower energies) start to oxidize at lower potentials. The electrochemical bandgaps of 3-phenylthiophene derivatives have been measured by cyclic voltammetry. The effect of substituents on the oxidation / reduction potentials is discussed. Bandgaps obtained by cyclic voltammetry have been found to be in general higher than optical bandgaps. Preliminary results of in situ resonance Raman spectroscopy of electrochemically generated poly-3-phenylthiophene derivatives films on a platinum electrode exposed to an organic electrolyte solution are reported. Observed Raman bands are assigned; based on these results previously suggested molecular structures are discussed

The present Doctoral Thesis constitutes a comprehensive study of the removal of food azo dyes in aqueous matrices by single and coupled electrochemical separation and destruction technologies. First, the work was focused on the selection of the most appropriate technology and the progressive optimization of operation conditions for the effective and efficient removal of each dye. The degradation of Ponceau 4R, Carmoisine, Allura Red AC and their mixtures was studied by different electrochemical advanced oxidation processes (EAOPs) such as electro-oxidation (EO), electro-Fenton (EF) and photoelectro-Fenton (PEF) using BDD or Pt anode and stainless steel (SS) or air-diffusion cathode (ADE). Different aspects including decolorization and mineralization of solutions were studied in details. The results revealed that PEF is the most efficient and promising process to degrade food azo dyes at lab-scale. Complete decolorization and almost total mineralization with 96-98% TOC abatement was attained, with electrolysis time depending on the initial dye content and applied current. The kinetic decay of dye always obeyed a pseudo-first-order reaction. In view of the promising results obtained by PEF, the study of the degradation of dyes was scaled-up to a 2.5 L pre-pilot plant, which allowed demonstrating the viability of the solar photoelectro-Fenton to mineralize the dyes within a short time. Analyses of dyes and their mixtures treated by EAOPs allowed the identification of some intermediates and end products, and plausible reaction sequences were proposed to explain the transformation of each compound. The mineralization of dyes led to the conversion of the heteroatoms (N and S) present in the molecules to inorganic ions such as ammonium, nitrate and sulfate. The degradation of Tartazine solution was studied by electrocoagulation (EC), which is a process of high industrial interest, several EAOPs and the sequential combination of EC/EAOPs. The findings demonstrated that the sequential EC (Fe/SS) / PEF (BDD/ADE) treatment favors both, the fast color removal and the destruction of the remaining persistent organic matter in the pre-treated solution by PEF. The complete decolorization and mineralization of solutions were thus achieved within relatively short time periods thanks to coagulation by Fe(OH)n and oxidation by electrogenerated hydroxyl radical and active chlorine species.
La presente Tesis Doctoral se ha enfocado en el estudio exhaustivo de la eliminación de colorantes alimentarios azoicos en matrices acuosas mediante tecnologías electroquímicas de separación y de destrucción usadas individualmente o acopladas. En primer lugar se centró el trabajo en la elección de la tecnología más apropiada y la optimización progresiva de las condiciones de operación para una eliminación eficaz y eficiente de cada colorante. Se estudió la degradación de los colorantes Ponceau 4R, Carmoisina, Rojo Allura AC y de sus mezclas mediante diferentes procesos electroquímicos de oxidación avanzada (EAOPs) como la electrooxidación (EO), electro-Fenton (EF) y fotoelectro-Fenton (FEF), utilizando un ánodo de BDD o Pt y un cátodo de difusión de aire o acero inoxidable (SS), y evaluando diferentes aspectos relacionados con la decoloración y la mineralización. Los resultados revelaron que el proceso FEF es el más eficiente y prometedor para la degradación de los colorantes alimentarios a escala de laboratorio. Se alcanzó la decoloración total y una mineralización casi completa (96-98%), dependiendo el tiempo de electrolisis de la concentración inicial de colorante y de la corriente aplicada. En todos los casos, la cinética de degradación del colorante obedeció a una reacción de pseudo primer orden. En vista de los resultados prometedores obtenidos mediante FEF, el estudio de la degradación de los colorantes se amplió al uso de una planta pre-piloto de 2,5 L que permitió demostrar la viabilidad del proceso fotoelectro-Fenton solar (SFEF) para mineralizar los colorantes en tiempos cortos. Los análisis de las disoluciones de colorantes y de sus mezclas tratadas por EAOPs permitieron identificar los intermedios y productos finales, permitiendo así proponer esquemas de reacción para explicar la transformación de cada compuesto estudiado. La mineralización de los colorantes condujo a la conversión de los heteroátomos (N y S) presentes en las moléculas en iones inorgánicos, tales como nitrato, amonio y sulfato. Se estudió la degradación del colorante Tartrazina presente en una disolución de agua sintética mediante electrocoagulación (EC), que es un proceso de alto interés industrial, varios EAOPs, así como a través de la combinación secuencial EC/EAOPs. Los resultados demostraron que la combinación secuencial EC (Fe/SS) / FEF (BDD/ADE) favorece tanto la decoloración total como la destrucción completa de la materia orgánica persistente en la solución pre-tratada por FEF. Se consiguió una rápida decoloración y mineralización total de las disoluciones gracias a la coagulación por Fe(OH)n y la oxidación por radicales hidroxilo y/o especies de cloro activo electrogeneradas. El tratamiento combinado permitió superar los inconvenientes de la EC y el tiempo largo requerido por los EAOPs individuales, lo que condujo a una mayor rentabilidad de las tecnologías electroquímicas gracias a un menor consumo energético.

This thesis focuses on the synthesis of different types of NCs, their application to energy conversion and storage technologies, particularly LIBs, KIBs and DEFCs, and their structural transformation during electrochemical processes within these energy storage and conversion applications. The morphology and composition of target transition metal oxides, bimetallic NCs and phosphorous incorporated intermetallic NRs are characterized in detail to follow the alterations during application. An understanding of the correlation between structural, chemical and electrochemical properties will allow a more rational design of functional nanomaterials. The 1st chapter gives a general introduction to the rapid development and importance of renewable energy technologies in modern human society. Among which electrochemical energy storage and conversion technologies are particularly appealing in terms of cost, safety and environmental friendliness. The basic principles of Li-, Na- and K- ion battery technologies are discussed, including the battery structures, electrode materials and working mechanisms. Additionally, I describe the working principle of DEFCs and the electrocatalytic EOR. Strategies for synthesizing high performance NCs for electrochemical energy storage and conversion applications are also explained. Finally, in this chapter I discuss the phenomenon of NCs structural and chemical evolution during electrochemical operations and how their characterization in each system is needed for a thorough understanding of nanomaterials properties and applications. Chapter 1 also includes the objectives of the thesis. Chapter 2 describes a simple seed-mediated growth method at low temperature to grow heterstructered Mn3O4 on hollow Fe3O4 seeds. A moderate temperature (500 °C) annealing process is conducted to promote the solid-state reaction for hollow MnxFe3-xO4 NPs while conserving the original morphology. When serving as anode electrode materials, the polycrystalline shell, the internal void space and the high surface area of MnxFe3-xO4 NPs can effectively buffer the volume change of the NCs during lithiation and delithiation process to improve the stability and cycle life. The electrochemical activity of MnxFe3-xO4 NPs toward lithium reaction is evaluated and the relationship between the structure and electrochemical properties is explored. The excellent performance of hollow MnxFe3-xO4 NPs is associated with their crystal structure and composition, and with the presence of carbonized ligands, which further promote electrical conductivity and rapidly accommodate and release lithium ions while retaining a stable structure even after continuous charge/discharge cycles. This work was published in Nano Energy in 2019. Chapter 3 talks about the performance of bimetallic NPs as anodes in LIBs and KIBs. Monodisperse CoSn and NiSn NPs are synthesized through co-reduction and supported on commercial carbon materials. The obtained nanocomposites are tested as anode materials in half-cell LIBs, KIBs and full-cell LIBs. CoSn@C electrodes display excellent charge-discharge capacities with LIB half-cell and LIB full-cells. The capacities for KIB are stabilized at around 200 mAh g-1 with high coulombic efficiency over 400 cycles for CoSn@C and 100 mAh g-1 for NiSn@C over 300 cycles. The oxidation of NPs, the formation of SEI layer, the vast volume change during lithiation and delithiation processed caused the capacities decrease. This work was published in ACS Applied Materials & Interfaces in 2020. In chapter 4, a simple approach to produce intermetallic Pd3Pb nanocubes with well-defined cubic geometry and average size ranged from 6 nm to 10 nm is detailed. Pd3Pb/C catalysts present improved EOR electrocatalytic activities and stabilities. The EOR activity of Pd3Pb nanocubes is investigated through CV and CA techniques, which is size-dependent. All the catalysts exhibit a pronounced current decay during the first 500 s of continuous EOR operation, which is associated to the accumulation of strongly adsorbed reaction intermediates and the related blockage of reaction sites. The catalysts can be reactivated by simply cycling to effectively remove the poisoning species adsorbed on the surface and recover the electrocatalytic activity. A reorganization of Pd and Pb elements happens on Pd3Pb nanocubes during EOR, involving an outward/inward diffusion of Pd/Pb to equilibrate the stoichiometry of the NCs surface, which is driven by the different affinity of Pb and Pd towards oxygen and possibly ethanol, and the electrochemical oxidation/reduction of Pd. This work was published in Chemistry of Materials in 2020. Chapter 5 demonstrates the synthesis of colloidal Pd2Sn:P NRs through phosphorization of Pd2Sn NPs with a highly active reagent- hexamethylphosphorous triamide (HMPT) in a one-pot two-steps reaction. The Pd2Sn:P/C catalyst exhibits significantly enhanced activity toward EOR in alkaline media compared with Pd2Sn/C, PdP2/C and commercial Pd/C catalysts. The performance improvement is rationalized with the aid of DFT calculations considering the different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OH- adsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step. The Pd2Sn:P NRs is characterized with Sn- and P-rich surface, which correlates well with the higher percentages of oxidized tin and phosphorous, and the higher tendency to oxidation of Sn compared with Pd. DFT calculations prove that the presence of P can induce a higher chemical adsorption of OH- to facilitate the formation of CH3COOH, resulting in EOR activity increase. This work was accepted in Nano Energy in 2020.
Esta tesis se centra en la síntesis de diferentes tipos de nanocristales, su aplicación a las tecnologías de conversión y almacenamiento de energía, particularmente LIBs, KIBs y DEFCs, y su transformación estructural durante los procesos electroquímicos dentro de estas aplicaciones de almacenamiento y conversión de energía. La morfología y composición de nanocristales de óxidos de metales de transición, bimetálicos e intermetálicos que incroporan fósforo se caracterizan en detalle para seguir las alteraciones durante la aplicación. La comprensión de la correlación entre las propiedades estructurales, químicas y electroquímicas permitirá un diseño más racional de nanomateriales funcionales. El primer capítulo ofrece una introducción general al rápido desarrollo y la importancia de las tecnologías de energía renovable en la sociedad moderna. Entre ellas, las tecnologías de conversión y almacenamiento de energía electroquímica son particularmente atractivas en términos de costo, seguridad y respeto al medio ambiente. Se discuten los principios básicos de las tecnologías de baterías de iones de litio, sodio y potasio, incluidas las estructuras de las baterías, los materiales de los electrodos y los mecanismos de trabajo. Además, describo el principio de funcionamiento de las DEFCs y el EOR electrocatalítico. También se explican las estrategias para sintetizar nanocristales de alto rendimiento para aplicaciones de almacenamiento y conversión de energía electroquímica. Finalmente, en este capítulo discuto el fenómeno de la evolución estructural y química de los nanocristales durante las operaciones electroquímicas y cómo se necesita su caracterización en cada sistema para una comprensión profunda de las propiedades y aplicaciones de los nanomateriales. El capítulo 1 también incluye los objetivos de la tesis. El Capítulo 2 describe un método de crecimiento simple mediado por semillas a baja temperatura para crecer Mn3O4 en nanoparticulas huecas de Fe3O4. Se lleva a cabo un proceso de sinterizado a temperatura moderada (500 °C) para promover la reacción en estado sólido de las NPs y obtener partículas huecas de MnxFe3-xO4. Al ser usados como materiales de electrodo anódico, la cubierta policristalina, el espacio vacío interno y la gran área de superficie de las NPs de MnxFe3-xO4 pueden amortiguar de manera efectiva el cambio de volumen de los nanocristales durante el proceso de litiación y delitizacion para mejorar la estabilidad y la vida útil del ciclo. Se evalúa la actividad electroquímica de las NPs de MnxFe3- xO4 hacia la reacción de litio y se explora la relación entre la estructura y las propiedades electroquímicas. El excelente rendimiento de las NPs huecas de MnxFe3-xO4 está asociado con su estructura y composición cristalinas, y con la presencia de ligandos carbonizados, que promueven aún más la conductividad eléctrica y acomodan y liberan rápidamente iones de litio mientras retienen una estructura estable incluso después de ciclos continuos de carga/descarga . Este trabajo fue publicado en Nano Energy en 2019. El Capítulo 3 vesra sobre el rendimiento de los NPs bimetálicos como ánodos en LIBs y KIBs. NPs monodispersas de CoSn y NiSn se sintetizan mediante co-reducción y se soportan en materiales comerciales de carbono. Los nanocompuestos obtenidos se prueban como materiales anódicos en LIBs de media celda y KIBs y LIBs de celda completa. Los electrodos CoSn@C muestran excelentes capacidades de carga y descarga en media celda y celdas completas LIB. Las capacidades para KIB se estabilizan alrededor de 200 mAh g-1 con alta eficiencia culombiana durante 400 ciclos para CoSn@C y 100 mAh g-1 para NiSn@C durante 300 ciclos. La oxidación de las NPs, la formación de la capa SEI, el vasto cambio de volumen durante la litiación y la delitiación causaron la disminución de las capacidades. Este trabajo fue publicado en ACS Applied Materials & Interfaces en 2020. En el capítulo 4, se detalla un enfoque simple para producir nanocubos intermetálicas de Pd3Pb con geometría cúbica bien definida y un tamaño promedio de 6 nm a 10 nm. Los catalizadores de Pd3Pb/C presentan actividades y estabilidades electrocatalíticas EOR mejoradas. La actividad EOR de las NPs de Pd3Pb se investiga en función de su tamaño a través de técnicas CV y CA. Todos los catalizadores exhiben una disminución de corriente pronunciada durante los primeros 500 s de operación EOR continua, que está asociada con la acumulación de intermedios de reacción fuertemente adsorbidos y el bloqueo relacionado de los sitios de reacción. Los catalizadores pueden reactivarse simplemente ciclando para eliminar eficazmente las especies adsorbidas en la superficie y recuperar la actividad electrocatalítica. Una reorganización de los elementos Pd y Pb ocurre en las NPs de Pd3Pb durante EOR, lo que implica una difusión hacia afuera/hacia adentro de Pd/Pb para equilibrar la estequiometría de la superficie de los NCs, que es impulsada por la diferente afinidad de Pb y Pd hacia el oxígeno y posiblemente el etanol, y la oxidación/reducción electroquímica de Pd. Este trabajo fue publicado en Chemistry of Materials en 2020. El Capítulo 5 demuestra la síntesis de NRs coloidales de Pd2Sn que incorporan P a través de la fosforización de las NPs de Pd2Sn con un reactivo altamente activo. El catalizador Pd2Sn:P/C exhibe una actividad significativamente mejorada hacia EOR en medios alcalinos en comparación con Pd2Sn/C, PdP2/C y catalizadores comerciales de Pd/C. La mejora del rendimiento se racionaliza con la ayuda de los cálculos de DFT teniendo en cuenta los diferentes entornos químicos de fósforo. Dependiendo de su estado de oxidación, el fósforo superficial introduce sitios con adsorción de OH de baja energía y/o influye fuertemente en la estructura electrónica del paladio y el estaño para facilitar la oxidación del acetilo al ácido acético, que se considera el paso limitante de la tasa de EOR. El Pd2Sn:P se caracteriza por una superficie rica en Sn y P, que se correlaciona bien con los porcentajes más altos de estaño oxidado y fósforo, y la mayor tendencia a la oxidación de Sn en comparación con Pd. Los cálculos de DFT demuestran que la presencia de P puede inducir una mayor adsorción química de OH- para facilitar la formación de CH3COOH, lo que resulta en un aumento de la actividad EOR. Este trabajo fue aceptado en Nano Energy en 2020.

Lower back pain places an enormous economic burden on society and health authorities as it affects up to 80% of the population and has been attributed to intervertebral disc injury as well as the degenerative adaptations which occur with advancing age. Much of our understanding of disc mechanics comes from mathematical and finite element models; however, there is a lack of empirical data which is required for model validation. Additionally, the influence of mechano-electrochemical phenomena on fundamental mechanical properties such as permeability and Poisson's ratio is still not fully understood. Therefore, this thesis aimed to investigate the influence of such phenomena on disc mechanics whilst providing a comparison between multiphasic FE models and experimental data. Direct permeation experiments found that fluid velocity may be augmented through the nucleus pulposus via ionic osmotic pressure gradients which consist of fixed charge, mobile ion and electrical potential gradient s. A novel method to fully characterise, for the first time, the Poisson's ratio of the disc was developed. Poisson's ratio of the nucleus pulposus was found to be strain dependent and lower than previously thought, whilst solid matrix viscoelasticity may influence disc mechanics at high strain-rates. Confined compression experiments on the degenerate human nucleus pulposus found that the solid matrix bears the majority of load under axial compression due to the depletion of proteoglycans and the consequential reduction in mechano-electrochemical effects in this tissue. Poor agreement with biphasic theory may provide evidence of the degenerate nucleus pulposus exhibiting a heterogeneous structure and a dual permeability phase. Multiphasic models were developed and compared to experimental data. Differences were found between biphasic and triphasic models which resulted in varying agreement with experimental data thus the correct selection of numerical framework was found crucial when investigating disc mechanics. The data presented in this thesis are important for informing our overall understanding of disc mechanics, aiding the development future models as well as providing a benchmark for potential replacement materials to be critiqued against, particularly in terms of permeability and fluid pressurisation which are crucial to the load bearing capacity of the tissue.

The manufacturing of components with complex internal features, e.g. for automobile industry, aeronautics or medical applications, is a significant challenge. Such components are often machined in temporarily and locally separated stages of production. Due to these separated stages, the form deviations and positioning errors increase, which leads to additional efforts for the quality assurance. The technology that shall be developed within the project SwitchECM is supposed to enable machining of components with differing complex features in one single production stage and shall simultaneously allow for high precision. For this purpose, a multi-cathode system will be developed, in which every single cathode can be switched with specific parameters. The specific switching parameters shall be adjusted according to the requirements of the pre-defined features. For the manufacturing of different pre-defined features with one multi-cathode system the usage of pulsed direct current as well as continuous direct current shall be possible. Hence, removal experiments were carried out on 1.4301 stainless steel using a PEMCenter 8000 with varying feed rates and voltages at a pulsation frequency of 200 Hz. With this comparatively high frequency and a pulse duration of 4 ms pseudo direct current experiments are realized. The results are compared to experiments with a more common pulse frequency of 50 Hz. The mass removal analyses show, in which degree the transferability of experimental results from pulsed current to pseudo direct current or rather direct current is feasible.

OF THE PhD.


This PhD project has been fully developed at the department of physical-chemistry of the University of Barcelona. The work involves a fundamental study of passivity on iron electrodes by using advanced applications of Scanning Probe Microscopy techniques. The main concepts of the Semiconductor Electrochemistry have been introduced in a simple way to make them accessible for an electrochemist. The final conclusions deals with a quantitative diagram of the energy levels distribution at the oxide  electrolyte interface. The new methodologies developed in this PhD work are extensive to the quantitative study of the electron transfer through any electrode  liquid junction.
After an initial electrochemical characterization of the system, we succeed in coupling our three-electrode configuration into an STM microscope. Special efforts were put on the cell design which finally resulted in a robust ECSTM system that allowed the first in situ topographic and electric measurements of the Fe oxide  borate buffer interface under a strict electrochemical control. Additional ex situ microscopy and spectroscopy techniques were also used in combination to elaborate the first oxide growth mechanism and the quantitative electronic band diagram picture of the interface. Convinced that the different transitions of the electronic properties on the iron oxide surface governed its passivity and redox behavior, we went further in its electrical characterization and were embarked in the design of a new methodology to perform real electrochemical tunneling spectroscopy (ECTS). Although its experimental realization had been previously demonstrated on other ideal semiconducting electrodes, several technical difficulties had braked its wide fan of possibilities. Within the last two years of this Ph.D, we have invested efforts to solve the main technical problems and presented by the first time a novel procedure to record reproducible in situ electronic spectra of an electrode  electrolyte interface as a function of the oxidation state of the substrate. Their benefits go far beyond this study as it is shown in the Appendix A of this Ph.D. We found especially advantageous the combination of ECTS with the capacitance data of the same interface on determining its corresponding band diagram in a quantitative energy scale. Finally, the last block of the Ph.D. work have been devoted to the analysis and interpretation of the in situ tunneling spectroscopy data which have been employed firstly, to elaborate a complete mechanism of the formation and dissolution of the iron passive layer, and secondly, to revisit the concept of passivity from an electronic point of view. All these background was finally used on the quantitative electronic characterization of the passivity breakdown process of an iron electrode in the presence of chloride. The picture deduced in this last study is probably the highest impact feature of the present work since it directly addresses to the real capabilities that the technique shows on a dynamic process of remarkable technical impact.

Storing the fluctuating renewable energy into synthetic fuels or in batteries is meaningful due to the emerging energy crisis. In this thesis, four nanostructured catalysts based on two kinds of metal sulfides, namely Cu2S and SnS2, were produced and optimized to improve their performance towards three key electrochemical energy conversion processes, namely electrochemical oxygen evolution, photoelectrochemical water splitting and lithium-ion batteries. Chapter 1 presented a general introduction to explain the motivation of the thesis topic. In chapter 2, a metallic copper substrate was used as current collector and chemical template to produce Cu2S nanorod arrays for electrochemical oxygen evolution reaction (OER). Suitable characterization tools were applied to investigate the chemical, structural and morphological transformation in OER operation, during which the initial Cu2S nanorod arrays would perform as a “pre-catalyst” that in-situ changed to CuO nanowires. Notably, the Cu2S-derived CuO showed significant improved OER performance compared with that of CuO prepared by directly annealing a Cu(OH)2 precursor, in terms of both activity and stability. Thus obtained electrocatalyst can be ranked among the best Cu-based OER catalysts reported so far. To take advantage of the unlimited solar energy, an ultrathin SnS2 NPL with a suitable band gap around 2.2 eV was produced via a hot-injection solution-based process in chapter 3. The unsatisfied photoelectrochemical (PEC) performance of bare SnS2 motivated me to deposit Pt NPs on its surface as cocatalyst via in-situ reduction of a Pt salt. The resulting SnS2-Pt heterostructures with optimal Pt amount showed significant improvement (six fold) towards PEC water oxidation. Mott-Schottky analysis and PEC impedance spectroscopy (PEIS) were used to analyze in more detail the effect of Pt on the PEC performance. The optimal SnS2-Pt heterostructure presented acceptable performance towards PEC water splitting. However, it still suffered from a moderate stability due to the peel-off of the catalyst layer from the FTO surface. To solve this problem, in chapter 4 we detailed a simple, versatile and scalable amine/thiol- based molecular ink to grow nanostructured SnS2 layers directly on conductive substrates such as FTO, stainless steel and carbon cloth. Such layers on FTO were characterized by excellent photocurrent densities. The same strategy was used to produce SnS2-graphene composites, SnS2-xSex ternary coatings and even phase pure SnSe2 layers. Finally, the potential of this precursor ink to produce gram scale amounts of unsupported SnS2 was also investigated. Apart from the application as a photocatalyst, SnS2 can also be a promising anode material for Li-ion batteries (LIB). In chapter 5, nanostructured SnS2 with different morphologies produced in chapter 3 were tested as LIB anodes firstly to find that thin SnS2 NPLs provided the highest performance. Thereafter, a colloidal synthesis strategy to grow the same SnS2 NPLs within a matrix of porous g-C3N4 (CN) and graphite plates (GPs) was developed and the obtained materials were tested for LIB application. Such hierarchical SnS2/CN/GP composites using SnS2-NPL as active materials, porous CN to provide avenues for electrolyte diffusion and ease the volumetric expansion of SnS2, and GP as “highways” for charge transport displayed excellent rate capabilities (536.5 mAh g-1 at 2.0 A g-1) and an outstanding stability (~99.7 % retention after 400 cycles), which were partially associated with a high pseudocapacitance contribution (88.8 % at 1.0 mV s-1). The excellent electrochemical properties of these nanocomposites were ascribed to the synergy created between the three components. Overall, four nanostructured catalysts based on Cu2S and SnS2 were prepared, and proper optimizations/treatments were defined to improve their catalytic performance. The results shown in this thesis demonstrate the promising application of non-toxic, low cost metal sulfides in electrochemical energy conversion technologies.
En esta tesis, se produjeron y optimizaron cuatro catalizadores nanoestructurados basados en Cu2S y SnS2 para mejorar su rendimiento hacia la conversión de energía electroquímica. El Capítulo 1 presentó una introducción general para explicar la motivación del tema de tesis. En el capítulo 2, las matrices de las nanovarillas de Cu2S se sintetizaron in situ sobre un sustrato de cobre metálico para la reacción electroquímica de evolución de oxígeno (OER). Se aplicaron herramientas de caracterización adecuadas para investigar la transformación en la operación OER, durante la cual las matrices iniciales de las nanovarillas Cu2S in situ cambió a nanohilos de CuO. En particular, el CuO derivado de Cu2S mostró un rendimiento de OER significativamente mejor cuando comparado al de CuO preparado mediante el recocido. En el capítulo 3, se detalló un proceso basado en una solución de inyección en caliente para producir nanoplacas ultrafinas SnS2 (NPL). Posteriormente, se cultivóPt en su superficie mediante la reducción in situ de una sal de Pt. Posteriormente se probó el rendimiento fotoelectroquímico (PEC) de los fotoanodes hacia la oxidación del agua. Los fotoanodes de SnS2-Pt optimizados proporcionaron densidades de fotocorriente significativamente más altas que el SnS2 desnudo (seis veces). Se analizó el efecto de Pt. En el capítulo 4, se informó una tinta molecular simple para cultivar capas de SnS2 nanoestructuradas directamente sobre sustratos conductores. Tales capas nanoestructuradas en FTO se caracterizaron por excelentes densidades de fotocorriente. Se utilize la misma estrategia para producir compuestos de grafeno-SnS2, recubrimientos ternarios SnS2-xSex, capas de SnSe2 de fase pura e incluso polvo de SnS2 a gran escala. En el capítulo 5, el SnS2 nanoestructurado con diferentes morfologías se probaron como ánodos LIB en primer lugar para encontrar que los NPL de SnS2 delgados proporcionaban el mayor rendimiento. Posteriormente, se desarrolló una estrategia de síntesis coloidal para cultivar los mismos NPL de SnS2 dentro de una matriz de g-C3N4 (CN) poroso y placas de grafito (GP) y se probaron para la aplicación LIB. Tales compuestos jerárquicos SnS2/CN/GP mostraron excelentes propiedades electroquímicas, lo que se atribuye a la sinergia creada entre los tres componentes como se investigó.

En la presente Tesis se describe el estudio de fases en los sistemas Na- M-(O, F) con (M = Ti, V, Mn y Mo), incluyendo la preparación, en condiciones suaves, la caracterización cristaloquímica y el ensayo electroquímico en baterías de sodio. Los resultados más significativos obtenidos para M = Mn comprenden la síntesis en medio acuoso de los fluoruros Na2MnF5 y NaMnF3, y del nuevo oxifluoruro NaMnMoO3F3 · H2O, que presenta una estructura laminar con parámetros de celda a = 3.5947(1), b = 21.246(1) y c = 7.3893 (2) y grupo espacial Cmcm (No.63). En el caso de M = V, la síntesis por vía solvotermal en diferentes condiciones permitió la preparación de diversas fases tales como la ya conocida NaVF4 o la nueva criolita Na3-δVOF5 (a = 5,54034 (2) Å, b = 5,68041 (2) Å, c = 7,95229 (3) Å, β = 90.032 (7) y grupo espacial P21/n (nº14)). También se preparó a 100 ºC la quiolita Na5-δV3F14-δ (a= 10,5482 (2) Å, b= 10.4887 (1) Å y c= 10.3243 (1) Å, y grupo espacial Cmc21 (N° 36)) en un medio de reacción con concentraciones de más altas, la cual fue caracterizada mediante difracción de neutrones y radiación sincrotrón. En el caso de M= Ti, se preparó el oxifluoruro Na5Ti3O3F11 mediante síntesis asistida por microondas. Su estructura cristalina es también de tipo quiolita con grupo espacial Cmca (n° 64) y parámetros de celda a= 10,496(2) Å, b= 10,398(1) Å y c= 10,291(1) Å. El rendimiento electroquímico de dichos fluoruros y oxifluoruros resultó ser limitado, presumiblemente debido al carácter altamente aislante de los fluoruros y al hecho de que los potenciales redox, se encuentran fuera de la ventana de la estabilidad de los electrolitos convencionales, lo cual pudo confirmarse en algunos casos específicos mediante cálculos DFT. Finalmente, se llevó a cabo un estudio adicional dirigido a determinar los factores que afectan el comportamiento electroquímico y más concretamente la retención de la capacidad del Na2Ti3O7. Éste incluyó medidas in situ y ensayos de envejecimiento en contacto con el electrolito. Las conclusiones preliminares parecen indicar que la pérdida de la capacidad no está relaciona principalmente con la degradación estructural del compuesto sino con su reactividad con el electrolito.
This thesis reports on the preparation, using mostly mild synthetic routes, crystal chemical characterization and electrochemical testing in sodium based batteries of Na- M-(O,F) phases ( M= Ti, V, Mn and Mo). The most significant results achieved for M=Mn concern the synthesis in aqueous medium of Na2MnF5, NaMnF3 and the novel oxyfluoride NaMnMoO3F3·H2O which exhibits a layered structure with a = 3.5947(1), b = 21.246(1), and c = 7.3893(2) Å cell parameters and Cmcm (No.63) space group. In the case of M=V, solvothermal methods allowed to prepare different phases such as the already known NaVF4 or the new cryolite Na3-δVOF5 (a= 5.54034(2) Å, b= 5.68041(2) Å, c= 7.95229(3) Å cell parameters, β= 90.032(7)º and space group P21/n (nº14)) by modifying the synthesis conditions. The chiolite Na5-δV3F14-δ (a= 10.5482(2) Å, b= 10.4887(1) Å and c= 10.3243(1) Å and Cmc21 (nº 36) space group) was also prepared at 100 ºC but using higher HF concentration, and was characterized by means of neutron and SXRPD data. For M=Ti, an oxyfluoride with chiolite related structure with space group Cmca (nº 64) and cell parameters a= 10.496(2) Å, b= 10.398(1) Å and c= 10.291(1) Å. Na5Ti3O3F11 was prepared by a microwave assisted method. The electrochemical performance of all such fluoride and oxyfluoride phases was found to be poor if any, which is presumably related to the high insulating character of fluorides and to a redox operation potential outside the stability window of conventional electrolytes, as deduced in some specific cases from DFT calculations. Finally, additional research was carried out to get some insight on the factors affecting the capacity retention of Na2Ti3O7 upon electrochemical cycling, and which included both in situ experiments and ageing tests. Preliminar conclusions seem to indicate that capacity fading is mostly related to reactivity with the electrolyte and not related to structural degradation.

Electron Transfer (ET) plays essential roles in crucial biological processes such as cell respiration and photosynthesis. It takes place between redox proteins and in protein complexes that display an outstanding efficiency and environmental adaptability. Although the fundamental aspects of ET processes are well understood, more experimental methods are needed to determine electronic pathways. Understanding how ET works is important not only for fundamental reasons, but also for the potential technological applications of these redox‐active nanoscale systems. The general objective of this thesis is to investigate electron transfer in redox proteins at the single molecule level. To that end, we use Electrochemical Scanning Tunneling Microscopy (ECSTM) and conductive Atomic Force Microscopy (cAFM), excellent tools to study electronic materials and redox molecules including proteins. In this thesis, we focused on two redox protein systems: azurin, a small electron carrier protein and photosystem I, a light‐sensitive oxidoreductase protein complex. In azurin, we studied the protein conductance as a function of its redox state and location on the protein surface, and the effect of technical parameters such as the contact properties between azurin and the metal electrodes, and the mechanical force applied in such contact. For that we adapted our ECSTM setup for an alternating current method often used in ultrahigh vacuum (UHV) STMs. We also worked in the development of a methodology that combines AFM‐based single‐molecule force measurements with single‐molecule electrical measurements, while working in an electrochemically controlled environment. These techniques can lead to a more detailed description of the ET pathways, and to a deeper understanding of the complex relation between the structure of redox proteins and their electronic properties. In photosystem I, developed a method to immobilize complexes on a substrate suitable for ECSTM imaging and spectroscopy, atomically flat gold. In these conditions, we characterized photosystem I by imaging and spectroscopy, and evaluated its conductance and distance‐decay properties in a wide range of biologically relevant electrochemical potentials. The characterization of conduction pathways in redox proteins at the nanoscale would enable important advances in biochemistry and would cause a high impact in the field of nanotechnology.
La transferencia de electrones (ET) desempeña papeles esenciales en procesos biológicos cruciales como la respiración celular y la fotosíntesis. Tiene lugar inter‐ e intra‐ proteínas redox y en complejos de proteínas que muestran una eficiencia excepcional y gran capacidad de adaptación ambiental. Aunque los aspectos fundamentales de los procesos de ET se han estudiado en profundidad, se necesitan más métodos experimentales para determinar las vías electrónicas de ET. La comprensión de cómo funciona la ET es importante no sólo por razones fundamentales, sino también por las potenciales aplicaciones tecnológicas de estos sistemas redox nanoscópicos. El objetivo general de esta tesis es investigar la transferencia de electrones en las proteínas redox a nivel de molécula individual. Para ello utilizamos la Microscopía de Túnel Electroquímico (ECSTM) y la Microscopía de Fuerza Atómica Conductor (cAFM), que son excelentes herramientas para estudiar materiales electrónicos y moléculas redox, incluyendo proteínas. En esta tesis, nos centramos en dos sistemas de proteínas redox: azurina, una pequeña proteína portadora de electrones y el fotosistema I, un complejo de proteína oxidorreductasa sensible a la luz. En el estudio de la azurina, estudiamos la conductancia de las proteínas en función de su estado redox y el efecto de parámetros técnicos como las propiedades de contacto entre la azurina y los electrodos metálicos, y la fuerza mecánica aplicada en dicho contacto. Para ello hemos adaptado nuestra configuración de ECSTM para un método de corriente alterna a menudo utilizado en Microscopía de Túnel de ultra alto vacío (UHV‐STM). También trabajamos en el desarrollo de una metodología que combina medidas de fuerza de una sola molécula basadas en AFM con medidas eléctricas, mientras trabajamos en un ambiente controlado electroquímicamente. Estas técnicas pueden conducir a una comprensión más profunda de las vías de ET y de la compleja relación entre la estructura de las proteínas redox y sus propiedades electrónicas. En el estudio del fotosistema I, desarrollamos un método para inmovilizar complejos sobre un sustrato adecuado para la obtención de imágenes y espectroscopía con ECSTM, oro atómicamente plano. En estas condiciones, caracterizamos el fotosistema I mediante imágenes y espectroscopia, y evaluamos sus propiedades de conductancia y sus parámetros de decaimiento de la corriente con la distancia, en una amplia gama de potenciales electroquímicos biológicamente relevantes. La caracterización de las vías de conducción en las proteínas redox a escala nanométrica puede permitir importantes avances en bioquímica y causar un alto impacto en el campo de la nanotecnología.

Paracetamol, clofibric acid and chlorophene are paradigms of NSAIDs, blood lipid regulators and antimicrobials, respectively, which are three of the top sales PPCPs therapeutical groups all throughout the world. During the last decades, the impact of chemical pollution has focused almost exclusively on the conventional 'priority' pollutants, mainly pesticides and industrial intermediates exhibiting persistence in the environment. Another group that has received comparatively little attention includes both human and veterinary pharmaceutical compounds and personal care products (PPCPs). Nowadays, these compounds are also considered as persistent pollutants because they are continually introduced in the environment at ng-µg L-1 level through several routes due to their high worldwide consumption. Aquatic pollution is particularly troublesome considering that survival of living organisms, including human beings, is based on the water-cycle. PPCPs can pose a huge risk, under assessment at present, because long exposure to trace levels leads to unpredicted and unknown subtle effects. The enormous diversity of chemical composition of pollutants in waters excludes the possibility of using an universal treatment method and suggests the requirement of special treatment technologies for water decontamination. Therefore, more effective processes must be developed as a plausible alternative. In this sense, electrochemical processes such as EAOPs and AO using effective anodes appear to be an appealing environmentally friendly choice, since the main oxidant species is thought to be hydroxyl radical. EF and PEF processes using an O2-diffusion or a carbon-felt cathode are able to electrogenerate hydroxyl radicals in the bulk solution through Fenton's reaction, whereas in AO using a Pt or a BDD anode the same oxidizing agent is chemisorbed or physisorbed, respectively, at the electrode surface. Several experimental systems have been studied by combining different cathodes and anodes and by using several catalysts. For each pharmaceutical, optimum conditions for the mineralization process at laboratory scale have been established from the analysis of the TOC abatement and the corresponding MCE values. Subsequently, the degradation kinetics for the reaction between each drug and hydroxyl radicals has been reported. Finally, the possible reaction pathways for the electrochemical degradation of paracetamol, clofibric acid and chlorophene have been proposed. In addition, some particularities of the EF process have been clarified.
El paracetamol, l'àcid clofíbric i el clorofè són exemples representatius de tres dels grups terapèutics més comercialitzats de "PPCPs" ("Pharmaceuticals and Personal Care Products") arreu del món: fàrmacs antiinflamatoris no esteroídics, fàrmacs reguladors de lípids en sang i fàrmacs antimicrobials, respectivament. Els PPCPs, que inclouen fàrmacs i productes d'higiene personal, constitueixen un grup de substàncies al qual s'ha dedicat poca atenció fins fa relativament poc temps. Actualment aquests compostos també es cataloguen com a contaminants persistents, ja que són introduïts en el medi de manera continua a nivell de ng-µg L-1 a escala mundial. La contaminació del medi aquàtic és especialment preocupant si es té en compte la importància del cicle de l'aigua en la conservació del planeta i dels éssers que l'habiten. L'avaluació del risc i dels posibles efectes que se'n deriven es troba actualment en fase d'estudi, i pel moment no es desposa de prou dades que permetin afirmar amb contundència quin és el perill real. Avui dia l'estratègia seguida en l'àmbit del tractament d'aigües residuals que contenen diversos contaminants és la de combinar procediments successius, tot introduint tecnologies especials que siguin efectives contra compostos molts particulars. Per tant, és necessari desenvolupar mètodes més potents i efectius. Amb aquesta intenció, diversos processos electroquímics que inclouen l'Oxidació Anòdica i els Processos Electroquímics d'Oxidació Avançada es presenten com una atractiva alternativa compatible amb el medi ambient, ja que la principal espècie oxidant que intervé és el radical hidroxil. D'aquesta manera, s'han realitzat diferents experiments combinant varis ànodes i càtodes, i utilitzant diferents catalitzadors. A través de la reacció de Fenton, els processos electro-Fenton (EF) i fotoelectro-Fenton (PEF) amb càtodes de difusió d'oxigen o de feltre de carbó permeten produir radicals hidroxil en el si de la dissolució tractada.

En oxidació anòdica amb ànodes de platí (Pt) o diamant dopat amb bor (BDD) l'agent oxidant és el mateix, si bé es troba quimisorbit o fisisorbit, respectivament, en la superfície de l'elèctrode. Per al paracetamol s'ha fet un estudi dels processos EF i PEF amb un ànode de Pt i un càtode de difusió d'oxigen, i s'ha constatat el paper rellevant que tenen els diferents complexos formats entre els catalitzadors metàl·lics utilitzats i els àcids carboxílics generats al llarg de la degradació. També s'ha aplicat l'oxidació anòdica amb dos tipus d'ànodes, Pt i BDD, i un càtode de grafit. En el cas de l'àcid clofíbric s'ha introduït la combinació de l'ànode de BDD amb el càtode de difusió, fet que condueix a una millora significativa dels resultats. En aquest estudi s'ha posat de manifest la importància d'espècies oxidants diferents del radical hidroxil. Finalment, s'ha dut a terme un estudi profund de la degradació del clorofè mitjançant EF, utilitzant un càtode de difusió d'oxigen o un de feltre de carbó com a càtodes. Així, s'ha pogut explicar el sistema catalític Fe3+/Fe2+ sobre l'efectivitat de les cel·les amb ànodes de Pt i BDD. En definitiva, doncs, s'han proposat camins de reacció per a la degradació electroquímica del paracetamol i l'àcid clofíbric, i s'ha demostrat l'eliminació completa dels intermedis finals del clorofè.

Afin de relever le défi énergétique et climatique du 21ième siècle qui s’annonce, une solution consiste, pour valoriser la ressource solaire, à mettre au point des procédés de production de vecteurs énergétiques stockables par photosynthèse artificielle permettant la synthèse de carburants solaires, en particulier l’hydrogène. La compréhension de ses procédés et l’obtention de performances cinétiques et énergétiques élevées nécessitent le développement de modèles de connaissance génériques, robustes et prédictifs considérant le transfert de rayonnement comme processus physique contrôlant le procédé à plusieurs échelles mais aussi les différents autres phénomènes intervenant dans la structure ou la réification du modèle.Dans le cadre de ce travail de doctorat, le procédé photo-réactif au cœur de l’étude était la cellule photo-électrochimique. D’un fonctionnement plus complexe que le simple photoréacteur, avec une photo-anode et une (photo)cathode, la cellule photo-électrochimique dissocie spatialement les étapes d’oxydation et de réduction. En se basant à la fois sur la littérature existante (essentiellement dans le domaine de l’électrochimie) et en déployant les outils développés par l’équipe de recherche sur le transfert de rayonnement et la formulation du couplage thermocinétique, il a été possible d’établir des indicateurs de performance des cellules photo-électrochimiques.En parallèle de l’établissement de ce modèle, une démarche expérimentale a été entreprise en se basant tout d’abord sur une cellule commerciale de type Grätzel (DS-PEC) indiquant les tendances générales de tels convertisseurs de l’énergie des photons avec en particulier une chute de l’efficacité énergétique en fonction de la densité incidente de flux de photons. Un dispositif expérimental modulable (Minucell) a aussi été développé et validé afin de caractériser des photo-anodes de différentes compositions comme des électrodes de TiO2 imprégnées de chromophore pour un fonctionnement en cellule de Grätzel ou bien des électrodes d’hématite Fe2O3 (SC-PEC) où le semiconducteur joue à la fois les fonctions d’absorption des photons et de conduction des porteurs de charges. Surtout, le dispositif Minucell a permis de tester, caractériser et modéliser le comportement d’une cellule photo-électrochimique de type bio-inspiré pour la production d’H2 utilisant à la photo-anode un catalyseur moléculaire Ru-RuCat (développé par ICMMO Orsay/CEA Saclay) et à la cathode un catalyseur CoTAA (développé par LCEMCA Brest). Minucell a été utilisé pour caractériser chaque élément constitutif d’une cellule photo-électrochimique puis la cellule dans son ensemble, confirmant les tendances et observations obtenues sur les efficacités énergétiques.Ce travail préliminaire ouvre de très nombreuses perspectives de recherche, il pose des bases communes entre électrochimie et génie des systèmes photo-réactifs et donne des pistes quant à la conception et l’optimisation cinétique et énergétique des cellules photo-électrochimiques pour la production d’hydrogène et de carburants solaires
In order to meet the energy and climate challenge of the coming 21st century, one solution consists of developing processes for producing storable energy carriers by artificial photosynthesis to synthesize solar fuels, in particular hydrogen, in order to valorize the solar resource. The understanding of these processes and the achievement of high kinetic and energetic performances require the development of generic, robust and predictive knowledge models considering radiative transfer as a physical process controlling the process at several scales but also including the various other phenomena involved in the structure or reification of the model.In this PhD work, the photo-reactive process at the heart of the study was the photo-electrochemical cell. More complex than the simple photoreactor, with a photo-anode and a (photo)cathode, the photo-electrochemical cell spatially dissociates the oxidation and reduction steps. Based both on the existing literature (mainly in the field of electrochemistry) and by deploying the tools developed by the research team on radiative transfer and thermokinetic coupling formulation, it was possible to establish performance indicators of photo-electrochemical cells.In parallel to the establishment of this model, an experimental approach was undertaken based first on a commercial Grätzel-type cell (DS-PEC) indicating the general trends of such photon energy converters with in particular a drop in energy efficiency as a function of the incident photon flux density. A modular experimental device (Minucell) has also been developed and validated in order to characterize photo-anodes of different compositions such as chromophore impregnated TiO2 electrodes for operation in Grätzel cells or Fe2O3 hematite electrodes (SC-PEC) where the semiconductor plays both the functions of photon absorption and charge carrier conduction. Above all, the Minucell device allowed to test, characterize and model the behavior of a bio-inspired photo-electrochemical cell for H2 production using at the photo-anode a Ru-RuCat molecular catalyst (developed by ICMMO Orsay/CEA Saclay) and at the cathode a CoTAA catalyst (developed by LCEMCA Brest). Minucell was used to characterize each constituent element of a photo-electrochemical cell and then the cell as a whole confirming the trends and observations obtained on energy efficiencies.This preliminary work opens up a wide range of research prospects, lays common ground between electrochemistry and photo-reactive systems engineering, and provides insights into the design and kinetic and energy optimization of photo-electrochemical cells for the production of hydrogen and solar fuels

Nowadays, researchers have spent considerable effort on the development of new materials, with new properties and characteristics, and new methods of synthesis, in order to meet the demands of a market that is constantly evolving. In this sense, “New electrochemical strategies for synthesising micro- and nano-structures” proposes, generalizes and discusses the development of novel electrochemical methods, strategies or media to prepare different kinds of micro- and nanostructured materials. The leitmotiv could be focused on the possibility of preparing micro-patterned (Cu), nanoparticulated (Co, CoNi, CoPt), composited (CoPt-Ni), mesoporous (CoNi, CoPt, Pt, CoNi@Pt or CoNi@Au) or nanopowdered (CoPt) deposits with various shape (films, nanorods or nanowires) by using the proposed strategies (Electrochemical nano-Fabrication using Chemistry and Engineering (EnFACE) technology or classical/ionic liquid microemulsions as a soft electrodeposition templates) to obtain micro/nanomaterials for specific magnetic, catalytic or biomedical applications. The present thesis is organized in eight chapters, in which several published scientific papers in international journals with our original results have been included in order to discuss and analyze our work. The first one introduces the electrodeposition (Chapter 1) – history, theoretical fundaments, advantages and disadvantages and introduce the state-of-the-art of electrochemical micro- and nano-fabrication –, which is fundamental in order to understand our work. The aims and the experimental details of our research are presented and detailed in chapter 2 and chapter 3, respectively. It is important emphasize that “New electrochemical strategies for synthesising micro- and nano-structures” could be grouped into three main areas, according the aims introduced above: (a) The optimization of EnFACE technology as an alternative method to classical masked-electrodeposition to prepare metallic microstructures on large conductive substrates, with the final objective of proposing this technology as a scalable, economic and environmentally-friendly synthesis approach to microfabrication; this could be relevant in the electronics and sensors industries. This work is presented in chapter 4; (b) Proposing, discussing and analyzing the use of different types of classical microemulsions as new electrochemical media for synthesising nanostructures — that is, a new shape-controlled electrodeposition approach based on the use of soft-template systems. In this sense, the possibility of obtaining different types of Co-based structures with varied geometries and shapes as a function of the microemulsions conditions has been demonstrated. However, the low or moderate deposition rates and efficiencies leading us to explore and propose the use of alternative (water-in-ionic liquid) microemulsions as soft-template electrochemical media with improved conductivity and low environmental impact for shape-controlled electrodeposition. These electrodeposition media were tested to prepare magnetic nanostructured materials (nanoparticulated CoPt magnetic films or CoPt-Ni composites) with controlled size, composition and magnetism. Based on our results, the use of water –in-ionic liquid (W/IL) microemulsions have been revealed to be a versatile, green, simple and inexpensive approach to 1) synthesizing nanoparticles with controlled size and composition, and therefore magnetic behavior, by controlling the droplet size and aqueous solution concentration respectively, or 2) developing layers of composites using a one-step procedure, in which simultaneous electrodeposition from aqueous droplets and continuous ionic liquid components could take place. This work is presented in chapter 5; (c) Proposing, generalizing and discussing new electrochemical strategies (electrodeposition in water-in-ionic liquid, bicontinuous and ionic liquid-in-water microemulsions) for synthesising mesoporous nanomaterials ((Pt, CoPt, CoNi, CoNi @Au or CoNi@Pt) for catalysis (the electrooxidation of methanol or ethanol in order to propose competitive electrocatalysts with poor- Pt content for fuel cell reactions) or drug delivery with enhanced therapeutic effect as a consequence of their magnetic stimulation. This results are presented in chapter 6. Lastly, to complete the thesis, the main conclusions obtained are collected in chapter 7, while a summary of the thesis in Catalan language is given in chapter 8.
En aquesta tesi s’estudien i proposen noves estratègies de síntesi de micro- i nano-estructures metàl·liques amb potencials aplicacions en els camps de l’electrònica, catàlisi i alliberament de fàrmacs. El leitmotiv de la tesi serien (a) l’optimització de la preparació de micro-estructures de coure sobre grans àrees superficials, mitjançant la tecnologia EnFACE (Electrochemical nano-Fabrication using Chemistry and Engineering); demostrar, analitzar i generalitzar la viabilitat d’utilitzar (b) microemulsions clàssiques i (c) microemulsions base líquid iònic, com a plantilles toves, per a la síntesi diferents tipus de nano-estructures magnètiques (nanopartícules, compòsits, materials mesoporosos), permetent modular-ne les seves propietats, forma i característiques; i finalment (d) testar l’ús de les nano-estructures mesoporoses com a electro-catalitzadors per l’oxidació d’alcohols o vehicles intel·ligents per a l’alliberament de fàrmacs en medis cel·lulars. La tesi s’estructura en vuit capítols i inclou diverses publicacions en revistes científiques. En el primer capítol s’introdueix breument l’estat de l’art de l’electrodeposició de micro- i nano-materials, així com una breu ressenya històrica i els fonaments imprescindibles per a la comprensió del treball. El capítol 2 introdueix els objectius, mentre que en el capítol 3 es descriuen i detallen les condicions experimentals i equips emprats per a la síntesi, caracterització i aplicació dels materials fabricats. El capítol 4 es focalitza en la micro-fabricació fent una breu introducció a l’estat de l’art, així com discutir i optimitzar l’ús de la tecnologia EnFACE per a la micro-fabricació d’estructures de coure sobre substrats de grans dimensions. El capítol 5 es centra en la discussió i anàlisi de la viabilitat de l’ús de microemulsions clàssiques i base líquid-iònic per a l’electrodeposició amb forma controlada, basada en l’ús de plantilles toves. Finalment, el capítol 6 explora i estableix unes condicions de síntesi de nano-fils mesoporosos de diferents materials (base Co i Pt) per a la preparació d’electro-catalitzadors amb grans àrees superficials i alta activitat catalítica per a l’oxidació d’alcohols així com el seu ús com a vehicles dosificadors de fàrmacs. Finalment, el capítol 7 resumeix les conclusions de la tesi i el 8 presenta un resum en català.

El objetivo de esta tesis es el de la mejora del rendimiento de dispositivos electroquímcos miniaturizados, con énfasis en pilas de combustible microbianas y sensores electroquímicos. Para conseguir este objetivo, está tesis está centrada en el desarrollo de nuevos materiales para electrodos, nuevas geometrías para microelectrodos y mejor fabricación y procesos de encapsulado. Un inconveniente muy importante en la miniaturización de dispositivos electroquímicos está en la reducción de al superficie activa de los electrodos resultado en señales más pequeñas. Sin embargo, la introducción de técnicas de micromecanizado de silicio como pueden ser fotolitografía grabados seco y húmedo, deposición de metales o dieléctricos por métodos físicos o químicos o procesos térmicos rápidos se han convertido en una vía real para solventar todos los problemas relacionados la manufacturación de dispositivos electroquímicos miniaturizados. Además el uso de herramientas computacionales basadas en métodos de elementos finitos ha ayudado extraordinariamente al diseño de estos dispositivos porque la quinética del electrodo y el transporte de masa pueden ser simulados y estudiados antes de su fabricación. El primer capítulo es una introducción a los fundamentos de la electroquímica, al diseño, a la fabricación y a las aplicaciones desarrolladas en esta tesis. La primera sección se centra en explicar los aspectos fundamentales de la electroquímica. La segunda sección introduce las pilas de combustible, porque estos son los dispositivos electroquímicos desarrollados en el capítulo 4. Finalmente la última sección cubre los materiales y métodos utilizados, incluyendo la microfabricación de los electrodos y las técnicas de prototipaje utilizadas para fabricar las pilas de combustible microbianas. El segundo capítulo comienza con la teoría del transporte de masa en micropilares totalmente conductores. A continuación, el modelo computacional de un único dominio de un micropilar es desarrollado utilizando COMSOL. La fabricación de electrodos con arrays de micropilares totalmente conductores fue conseguida por electrodeposición de oro y también por la combinación de grabado seco y metalización por deposición de oro mediante sputtering. El capítulo cierra con la caracterización electroquímica de los dos arrays, lo que permitió comparar su respuesta y averiguar que ruta era la mejor. El capítulo tres se dirige a la síntesis y fabricación de discos de electrodos de carbón para detectar mercurio en muestras acuosas. Estos electrodos de carbón están basados en la pirólisis de fotoresina. Esta técnica combina fotolitografía y procesos térmicos rápidos. Además las ventanas activas de esos electrodos fueron definidas por deposición química de dieléctricos, también los electrodos fueron físicamente y electroquímicamente caracterizados. Una vez estos electrodos fueron completamente estudiados se utilizaron para detectar mercurio en soluciones. El último capítulo se centra en encontrar una aplicación a los electrodos de arrays de micropilares totalmente conductores. La aplicación escogida fue una pila de combustible microbiana miniaturizada fabricada mediante técnicas de prototipaje rápido, donde en cada caso una geometría diferente con el objeto de averiguar si los arrays de micropilares ayudan a mejorar el rendimiento eléctrico de las pilas de combustible microbianas.
The aim of this thesis is to improve the performance of miniaturized electrochemical devices, with emphasis in microbial fuel cells and electrochemical sensors. To achieve this goal, this thesis focuses on the development of new electrode materials, new microelectrode geometries, and better fabrication and packaging processes. An important drawback in the miniaturization of electrochemical devices lies in that the reduction of the active area of the electrodes results in smaller signals. However, the introduction of silicon micromachining techniques such as photolithography, wet and dry etching, metal or dielectric coating by physical and chemical deposition or rapid thermal processes has become a realistic way to solve all the problems regarding the manufacturing of miniaturized electrochemical devices. In addition the use of computational tools based on finite element methods has helped extraordinarily in the design of these devices because both electrode kinetics and mass transport can be simulated and studied prior to fabrication. The first chapter is an introduction of the fundamentals of electrochemistry, design, fabrication and applications to develop the work described in this thesis. The first section focuses on explaining the fundamental aspects of electrochemistry. The second section fuel cells are introduced because it is the electrochemical device developed in chapter 4. Finally the last section covers the materials and methods used, including the microfabrication of the electrodes and the prototyping techniques used to fabricate the miniaturized microbial fuel cells. The second chapter begins with the theory of mass transport at fully-conducting micropillars. Following this, the computational model of a single domain is developed using COMSOL. The fabrication of fully-conducting micropillar array electrodes was achieved by gold electrodeposition and also by a combination of dry etching and sputtered gold deposition. The chapter closes with the electrochemical characterization of both arrays, which allowed to compare their response and found out which route was better. Chapter three addresses the synthesis and fabrication of carbon disk electrodes to detect mercury in aqueous samples. These carbon electrodes are based on the pyrolysis of photoresist. This technique combines photolithograpy and a rapid thermal process. Besides the active window of these electrodes was defined by the chemical deposition of dielectric layers, also the electrodes were physically and electrochemically characterized. Once these electrodes were completely studied they were used to detect mercury in a stagnant solution. The last chapter focuses on finding an application for the fully-conducting micropillar array electrodes. The application chosen was a miniaturized microbial fuel cell fabricated by rapid-prototyping techniqueswhere in each case a different geometry with the aim of find out if the use of micropillar array helps to improve the electrical performance of microbial fuel cells.

Metal phosphides are an important class of functional materials that exhibit a wide range of applications for energy storage and conversion. However, the synthesis of metal phosphide nanoparticles and its scalability is often limited by the toxicity, air sensitivity and high cost of reagents used. In this thesis, a simple, scalable and cost-effective procedure was developed to produce metal phosphides using inexpensive, low-toxicity and air-stable triphenyl phosphite as phosphorus source. The use of chlorides or metal carbonyl as metal precursors and hexadecylamine as ligand allowed the synthesis of a variety of phosphide nanocrystals (NCs) including phosphides of Ni, Co, Cu, Fe, Mo. The use of NiCl2 and CoCl2 mixture as metal precursors, ternary metal phosphide Ni2-xCoxP (0≤x≤2) NCs could be obtained. The synthesis of Ni2-xCoxP involved the nucleation of amorphous Ni-P and its posterior crystallization and simultaneous incorporation of Co. Tuning the experimental parameters allows producing NCs with different composition, morphology and particle size. Ni2-xCoxP-based electrocatalysts exhibited enhanced electrocatalytic activity toward the hydrogen evolution reaction compared to binary phosphides. In particular, NiCoP electrocatalysts displayed very low overpotential of 97 mV at J = 10 mA cm-2 and an excellent long-term stability. Density functional theory (DFT) calculations of the Gibbs free energy for hydrogen adsorption at the surface of Ni2-xCoxP NCs showed NiCoP to have the most appropriate composition to optimize this parameter within the whole Ni2-xCoxP series. The use of chromium hexacarbonyl as metal precursor and high boiling point oleylamine as ligand, less-studied CrP NCs could also be produced. This method allows producing CrP with nanometric particle size and with a very high throughput and material yield. CrP NCs were mixed with carbon to prepare electrocatalysts, which exhibited remarkable activity and stability toward oxygen reduction reaction in an alkaline electrolyte and an absolute tolerance to methanol. DFT calculations demonstrated CrP to provide a very strong chemisorption of O2 which facilitates its reduction and explains the excellent performance. Besides, another phosphorus source hexamethylphosphorous triamide (HMPT) and new synthetic strategies were applied for the synthesis of SnP and PdP2 NCs. SnP NCs were produced from the reaction of HMPT and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in sodium-ion batteries, which displayed a high reversible capacity of 600 mA h g-1 at a current density of 100 mA g-1 and cycling stability for over 200 cycles. The excellent cycling performance was associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. The synthesis of PdP2 involves the reaction of palladium acetylacetonate and HMPT to nucleate defective Pd5P2 nanoparticles that subsequently, with further phosphorus incorporation, crystallize into PdP2. The produced PdP2 NCs showed high mass activity and long-term stability toward the ethanol oxidation reaction in alkaline media. The activity and stability of the PdP2-based catalyst were further improved by supporting PdP2 NCs onto reduced graphene oxide (rGO). PdP2/rGO catalysts showed high current densities up to 51.4 mA cm-2 and mass activities of 1.60 A mg-1Pd, that is 4.8 and 15 times higher than Pd NCs. Overall, in this thesis serval metal phosphide nanomaterials were produced by colloidal synthetic strategy, and showed highly performance for electrochemical energy conversion and storage applications.
Los fosfuros metálicos son materiales funcionales de gran interés e impacto en la sociedad debido a su gran rendimiento en almacenamiento y conversión de energía. Sin embargo, la síntesis de nanopartículas de fosfuros metálicos y su escalabilidad es limitada. En la presente tesis, se ha desarrollado un proceso de producción para nanopartículas de fosfuros metálicos simple, escalable y rentable. El éxito de los resultados radica en el uso de fosfito de trifenilo, considerado como una fuente de fósforo barata, estable al contacto con el aire y no tóxica, que además permite la síntesis de una gran variedad de nanocristales (NCs) (fosfuros de Ni, Co, Cu, Fe, Mo, así como fosfuros ternarios de Ni2-xCoxP). Optimizando los parámetros experimentales, es posible producir NCs de diferente composición, morfología y tamaño. Además, el uso de solventes de alto punto de ebullición, facilita la síntesis de materiales menos estudiados como el CrP. Los NCs de Ni2-xCoxP y CrP NCs pueden ser combinados con carbono dando lugar a electrocatalizadores útiles para reacciones tales como evolución de hidrógeno y reducción de oxígeno, respectivamente. El uso de otras fuentes de fósforo, como por ejemplo la triamida de hexametilfósforo, permite a su vez producir NCs de SnP y PdP2. En el caso particular de SnP, los NCs demostraton poseer una geometría esférica y una fase cristalográfica trigonal con una superestructura atribuida a los pares difósforos ordenados. Mezclados con carbón negro y utilizados como ánodos en baterías de ion sodio, estos NCs demostraron una alta capacidad reversible de 600 mA h g-1 a una densidad de corriente de 100 mA g-1 y estables durante más de 200 ciclos. Por otro lado, los NCs de PdP2 soportados sobre óxido de grafeno se utilizaron como electrocatalizadores para la oxidación de etanol, mostrando una alta densidad de corriente de hasta 51.4 mA cm-2 y una actividad de masa de 1.60 A mg-1Pd. En resumen, se han desarrollado métodos de síntesis basados en estrategias coloidales para poder producir una gran variedad de fosfuros metálicos a escala nanométrica, mostrando estos un gran rendimiento para su uso en conversión y almacenamiento de energía electroquímica.

In polymer electrolyte fuel cells (PEFC) chemical energy, in for example hydrogen, is converted by an electrochemical process into electrical energy. The PEFC has a working temperature generally below 100 °C. Under these conditions water management and transport of oxygen to the cathode are the parameters limiting the performance of the PEFC.

The purpose of this thesis was to better understand the complex processes in different parts of the PEFC. The rate-limiting processes in the cathode were studied using pure oxygen while varying oxygen pressure and humidity. Mass-transport limitations in the gas diffusion layer using oxygen diluted in nitrogen or helium was also studied. A large capacitive loop was seen at 1-10 Hz with 5-20 % oxygen. When nitrogen was changed to helium, which has a higher binary diffusion coefficient, the loop decreased and shifted to a higher frequency.

Steady-state and electrochemical impedance spectroscopy (EIS) models have been developed that accounts for water transport in the membrane and the influence of water on the anode. Due to water drag, the membrane resistance changes with current density. This gives rise to a low frequency loop in the complex plane plot. The loop appeared at a frequency of around 0.1 Hz and varied with D/L_m², where D is the water diffusion coefficient and L_m is the membrane thickness. The EIS model for the hydrogen electrode gave three to four semicircles in the complex plane plot when taking the influence of water concentration on the anode conductivity and kinetics into account. The high-frequency semicircle is attributed to the Volmer reaction, the medium-frequency semicircle to the pseudocapacitance resulting from the adsorbed hydrogen, and the low-frequency semicircles to variations in electrode performance with water concentration. These low-frequency semicircles appear in a frequency range overlapping with the low-frequency semicircles from the water transport in the membrane. The effects of current density and membrane thickness were studied experimentally. An expected shift in frequency, when varying the membrane thickness was seen. This shift confirms the theory that the low-frequency loop is connected to the water transport in the membrane.