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1
Koep, Erik Kenneth. "A Quantitative Determination of Electrode Kinetics using Micropatterned Electrodes". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10524.
Testo completoAbstract (sommario):
Interfacial polarization resistances limit the performance of many thin film solid-state devices, especially at low temperatures. To improve performance, a fundamental understanding of the electrode kinetics that govern interfacial reaction rates must be developed. The goal of this work is to determine site-specific reaction mechanisms and the relative significance of various reactions in order to quantify optimum structural parameters within the cathode microstructure. Key parameters include the length of triple phase boundary (TPB), the quantity of exposed electrolyte/electrode surface, and the ratio of electrolyte to electrode material. These parameters, when studied in a specific system, can be incorporated into broader models, which will encompass the specific conductivity of each component to develop an optimized three-dimensional network.
The emphasis of this work is the systematic control and manipulation of potential cathodic reaction sites in order to develop an understanding of the relative importance of specific reaction sites. Since the physical dimensions of reaction sites are relatively small, an approach has been developed that utilizes micro-fabrication (similar to that used in integrated-circuit fabrication) to produce small and highly controlled microstructures.
Investigations were made into the nature and reactivity of Triple Phase Boundaries (hereafter TPB) through the use of patterned platinum electrodes since only the TPBs are active in these electrodes. After the processing details of micro-fabrication were established for the platinum electrodes, patterned Mixed-Ionic/Electronic Conducting (MIEC) electrodes were fabricated and studied using impedance spectroscopy to determine the contributions from the MIEC surface versus the TPB. Systematically changing the geometry of the MIEC electrodes (thickness and line width) allowed for the determination of the effect of ambipolar transport within the MIEC on the activity of MIEC surfaces versus the TPB. This information is critical to rational design of functionally graded electrodes (with optimal particle size, shape, porosity and conductivity). In addition to experimental studies, representative patterned electrode samples were made available for collaborative studies with surface scientists at other institutions to provide additional techniques (such as Raman Spectroscopy) on the carefully designed and controlled cathode surfaces.
2
Nwosu, Nkem O. E. "Optimisation of electroless co-deposited solid oxide fuel cell electrodes". Thesis, Edinburgh Napier University, 2013. http://researchrepository.napier.ac.uk/Output/6448.
Testo completoAbstract (sommario):
Research already carried out on the use of the recently patented electroless nickel ceramic codeposition technique as a method of manufacturing solid oxide fuel cell (SOFC) electrodes has thus far indicated that, while functional electrodes can be manufactured by the technique, for optimum performance of the cell, amplification of the ceramic content of the coatings is still required. By mainly employing external agents such as surface active agents (surfactants) and magnetic fields (in a bid to aid ceramic particle stability), this research focused on the prospect of increasing the ceramic content of cermets co-deposited for use as SOFC electrodes. A total of 137 co-deposited samples were produced from different bath compositions. As a prelude to the study, the interactions between the ceramic powders used (yttria stabilised zirconia (YSZ) / lanthanum strontium manganate (LSM)) and the medium for the deposition process – the electroless nickel solution, were investigated by zeta potentiometry and ultraviolet-visible spectroscopy techniques. The results obtained from the studies led to a variation of a series of fundamental plating factors such as the ceramic bath loading and particle size of the powders. While the former was found to yield the highest ceramic content in the coating at a bath loading of 50 g/l, variation of latter notably produced mixed results. With the introduction of surfactants, it was noted that above the surfactant's (sodium dodecyl sulphate) critical micelle concentration, the incorporation of ceramic particles (YSZ) into the nickel matrix steadily increased to as much as 60 volume %. An inverse relationship was though found to exist between the coating thickness and the surfactant's bath concentration. Uniform coatings were found to be associated with low magnetic field strengths while although increased magnetic field strengths positively resulted in the amplification of particle incorporation into the coating, a lack of cohesion between the coating and the substrate – as indicated by coating flake-off, was observed at such strengths. It is suggested that because the magnetic flux was more dominant than the normally ionic plating mechanism, the particles co-deposited under the influence of a high magnetic field were relatively unstable after the coating process. Since LSM is alkaline in nature this work confirms that future research on the application of electroless nickel ceramic co-deposition as a method of manufacturing SOFC cathodes, be focused on the use of alkaline electroless nickel baths rather than the acidic solutions, which better suite YSZ particles.
3
Seon, Hongsun 1965. "Electrode erosion and arc stability in transferred arcs with graphite electrodes". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=108637.
Testo completoAbstract (sommario):
Arc stability and erosion behavior were studied on a hollow graphite DC cathode in an argon atmosphere at atmospheric pressure. It was found that the arc stability is associated with the electron emission mode transition of the cathode operation. Estimation of current densities, SEM pictures, Fast Fourier Transform (FFT) of total voltage, and measurement of cathode surface temperature supported this. Stable arcs are in the thermionic emission regime while unstable arcs in the thermofield emission regime. Higher argon gas flow rate is believed to cause the shift of the mode from the thermofield emission to the thermionic emission by increasing the arc root temperature through steepening the thermal gradient at the arc root and increasing ionization phenomena inside the arc. Sharp cathode tip geometry usually leads to the thermionic emission while a rounded tip geometry encourages the thermofield emission. For the unstable arcs, the high voltage fluctuation resulted from the jumping of the arc root between different cathode spots and changes in the arc length. In the stable arcs, however, the voltage was almost constant because of the absence of arc jumping. The standard deviation of the voltage was used as the arc stability indicator and was less than 3 V for the stable arc in this transferred arc system.The erosion rate of the cathode in this work ranged from 0.41 to 2.61 mug/C. At 150 A runs the arc stability strongly influenced the erosion rate; as the arc stability increased, the erosion rate decreased. Higher currents runs (300 and 400 A), however, showed the opposite trend because of the carbon vapor redeposition. The total erosion rates of 150 A runs were separated into the stable (Es) and the unstable (Eu) erosion rate. The Eu was more than 3 times higher in this work. It is believed that the thermofield emission of the unstable arcs produced more erosion because of the higher local heat flux to the cathode spots.
4
Sand, Sara Catherine. "TiO2/CNT Composite Electrodes in Dye-Sensitized Solar Cell Electrodes". Ohio University Honors Tutorial College / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1492721176795399.
Testo completo
5
Liu, Yong. "Novel nanostructured electrodes". Department of Chemistry - Faculty of Science, 2007. http://ro.uow.edu.au/theses/14.
Testo completoAbstract (sommario):
Nanotechnology provides an effective and direct way to create novel properties and phenomena through the reduction in material sizes without changing the materials’ chemical composition. A number of routes to the preparation of novel nanostructured electrodes were investigated in this thesis. These involve the formation of nanoporous opaline electrodes, three dimensional nanofibrous networks and the synthesis of flexible nanoelectrodes based on highly dense ordered aligned carbon nanotubes and conducting polymers. Excellent improvements with the use of nanostructures in a wide range of application areas such as methanol oxidation, photoelectrochemical cells, enzyme biosensors, cell culturing and energy storage are presented in this research work.Nanoporous opaline structures including inverse opals and opals were prepared by either electrodepositing Pt or sputter coating ITO onto self-assembled polystyrene (PS) synthetic opals, followed by the removal of the PS opal templates. A highly ordered dense nanoporous structure with the porous structure on the top (so-called Pt inverse opal) or with the porous structure on the bottom (so-called ITO opal) was consequently obtained after the removal of PS templates. The improvement in electrochemical area with the use of nanostructures was observed during electrochemical characterisation. The resultant nanostructured Pt inverse opal electrodes were employed in electro-oxidation of methanol. Compared with the Pt film electrode, the nanostructured Pt inverse opal electrode showed a higher catalytic performance and good stability with a 100 mV negative shift of the potential of methanol oxidation. The mesoporous ITO opal electrode was used as the substrate for the electrodeposition of polyterthiophene and the resultant structure was subsequently utilized in photoelectrochemical cells. An excellent power-conversion efficiency of 0.109% and an outstanding short circuit current density of 1470 μA•cm-2 for polyterthiophene deposited at room temperature were obtained; dramatically improved from the previous published work.Nanofibrous electrodes were fabricated from biomaterials (such as DNA and poly(styrene-β-isobutylene-β-styrene) (SIBS)) and single-walled carbon nanotubes (SWNTs) using the electrospinning technique. Initial studies quantitatively determined the influence of solution properties (such as the solution ionic conductivity, surface tension and viscosity) and process parameters (e.g. tip-to-collector distance, applied potential and the feed rate) on the electrospinning results. Results showed that good electrospun fibrous networks could be obtained from the solution with comparatively high conductivity and viscosity with low surface tension. It was also found that the average diameter of the electrospun fibers decreased with decreased feed rates, increased tip-to-collector distance and increase in the potential employed. With the addition of SWNT, both biomaterial nanofiber electrodes exhibited enhanced electrochemical properties. The resulting DNA based electrospun fiber electrode showed a broad linearity range and high sensitivity in enzyme biosensors. The SIBS/SWNT nanofibrous electrode demonstrated excellent biocompatibility and suitability for the growth of L-929 cells.Flexible, light and highly conductive nanostructured electrodes were prepared from aligned carbon nanotubes (ACNTs) and conducting polymers by coating with Pt coated poly(vinylidene fluoride) (PVDF) or poly(3,4-ethylenedioxythiophene) (PEDOT)/PVDF. Pt nanoparticles were subsequently electrodeposited on the ACNT/Pt/PVDF structure. The utilization of the nanostructured ACNT/conducting polymer electrodes in anodic methanol oxidation and as anodic materials in Lithium-ion batteries was demonstrated. Pt nanoparticles coated ACNT/Pt/PVDF electrode exhibited an outstanding electrochemical capacity (133 Fg-1) and amazing electrochemical surface area (143 m2g-1 for Pt nanoparticles). The Pt nanoparticles-ACNT/Pt/PVDF electrode also showed a 2.5 times higher steady current density for methanol oxidation when compared with the ACNT/Pt/PVDF electrode. A stable current density over a long period (more than 12 hours) was obtained. A 50% improvement in capacity during Lithium-ion battery tests when compared with a SWNT paper was obtained with the ACNT/PEDOT/PVDF electrode.Nanostructured flexible and conductive electrodes were also obtained from ACNTs and biomaterials (such as SIBS and poly(lactide-co-glycolide)). SWNTs or Pt were introduced to improve the conductivity. A significant improvement in electrochemical properties with the addition of Pt or SWNT was obtained. The biocompatibility of ACNTs, SWNTs and Pt was confirmed during cell culturing experiments.
6
Maxwell, Virginia Margaret. "Ion-selective electrodes". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329972.
Testo completo
7
Laing, M. E. "Polymer coated electrodes". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238164.
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8
Curran, Dominic. "Electrochemically modified electrodes". Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333807.
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9
Al-Lolage, Firas Ahmed Thanon. "Amperometric enzyme electrodes". Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/419053/.
Testo completoAbstract (sommario):
This thesis studies the conditions required to achieve direct electron transfer and the experimental tests needed to unequivocally demonstrate that it occurs. Many publications claim to observe direct electron transfer to redox enzymes (for example in the case of glucose oxidase) but the evidence presented is often incomplete and unconvincing. The first part of this thesis argues that the vast majority, if not all, of these claims of DET for GOx are incorrect. It presents results for glucose oxidase (GOx) adsorbed on multi‐walled carbon nanotubes (MWCNTs), a typical nanostructured GOx electrode, that clearly show that the surface redox peaks usually observed in these cases are due to free, adsorbed flavin and not due, as claimed, to DET to flavin within the enzyme. Also, the results can be explained by adsorption of enzymatically active GOx at the electrode surface and the detection of the decrease in the oxygen concentration at the electrode surface due to the enzyme catalysed oxidation of D‐glucose. The second part of this thesis establishes a flexible and structured method based on the use of site‐directed mutagenesis to introduce cysteine residues at specific locations on the enzyme surface followed by the reaction between the free thiol group and maleimide groups formed on the electrode surface to immobilise the mutated enzymes. It is preferable to immobilise redox proteins and enzymes in a specific orientation, but still with some flexibility to optimise reaction kinetics. Using cellobiose dehydrogenase (CDH) as a model system, multiwall carbon nanotube electrodes were first covalently modified with maleimide groups following a modular approach combining electrochemical surface attachment and solid phase synthesis methodology. Five CDH variants were used in this study, the CDH‐modified electrodes were tested for direct electron transfer (DET), showing high catalytic currents and excellent long‐term storage stability. A potential‐dependent Michaelis‐Menten model for the CDH modified GC/MWCNT has been constructed and a master equation employed to simulate the DET and MET experimental results. Several mechanisms were suggested to explain the DET and MET for CDH. The internal electron transfer (IET) has been shown to be the rate determining step in the proposed mechanism. This was confirmed by the simulated data along with the experimental results. The simulated data suggests the presence of two populations of immobilised enzymes, MET and DET enzyme. The validity of the aforementioned immobilisation method, was further examined. Three bilirubin oxidase (BOD) variants were used in this study, which were modified to bear a free cysteine residue in different positions at the surface of the enzyme, allowing fast and selective attachment to maleimide‐modified GC/MWCNT electrodes. The catalytic mechanism of O2 reduction by the Magnaporthe oryzae BOD covalently immobilized on multiwall carbon nanotube (MWCNT) electrodes, in the presence of Cl ̅ and at different pH, was electrochemically investigated. The results highlight for the first time the influence of chloride ions on the direct oxygen reduction by MoBOD as a function of pH.
10
Eloul, Shaltiel. "Diffusion to electrodes". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:88c5f1d0-9f2f-49d5-b46d-6eeb5b7d4bfe.
Testo completoAbstract (sommario):
This thesis develops diffusion models for modern electrochemical experiments involving the transport of particles to electrodes and adsorbing surfaces. In particular, the models are related to the 'impact' method where particles stochastically arrive at an electrode and detected electrochemically. The studies are carried out using numerical simulations and also analytical methods. Chapter 1 is introductory and outlines some fundamental concepts in mass transport and kinetics, and their relation to electrochemical measurements which are of importance for the reader. Chapter 2 describes the numerical methods which are used for electrochemical simulations. Chapter 3 focuses on a specific two dimensional simulation system and the development of a high performance voltammetry simulation. Chapters 4 and 5 study the stochastic impacts of particles at an electrode surface. In Chapter 4, a 'diffusion only' model is developed using a probabilistic study and random walk simulations in order to provide expressions that can be used in so-called `impact' experiments. In Chapter 5, the practical cases of microdisc and microwire electrodes are investigated. Expressions for the number of impacts are developed and the concept of the lower limit of detection in ultra-dilute solutions is introduced. Then, a comparison study between the microwire electrode and the microdisc electrode explores a geometrical effect and its implications for experimental setups. In Chapter 6, a numerical and analytical study is developed to examine the effect of hindered diffusion as a particle moves close to an adsorbing surface. The study identifies the conditions under which this hindered diffusion is signiffcant even in a non-confined space. The study shows that the domination of hindered diffusion is strongly dependant on the sizes of both the particle and the target. The study focuses on a variety of target shapes and allows the number of hits/impacts to be estimated in practical 'impact' experiments. Moreover, a drastic effect on the calculation of the mean first passage time is observed for a sub-micron sized target, showing the importance of this effect not only for electrochemistry but also in biological systems. Chapters 7 and 8 investigate the properties of an adsorbing insulating surface adjacent to an electrode. In Chapter 7, a numerical study of the effect of 'shielding' by the insulating sheath is carried out. The study examines the in uence of this effect on the magnitude of the current in chronoamperometry experiments. Chapter 8 explores the case of reversible adsorption on the insulating surface for voltammetric enhancement by pre-concentration on the sheath surface. The results identify the conditions under which enhancement of the voltammetric signal can be observed. Finally, Chapter 9 looks at geometrical effects on the current response of insulating particles modified with an electroactive surface layer. Numerical models are developed to model the diffusion of charge transfer between electro-active sites on a modified surface of insulating particles. The current-time responses are simulated for particles with the shape of a sphere, a cube/cuboid, and a cylinder on an electrode. The characteristic currenttime responses are calculated for the various shapes. The observations show that the model can be utilised in experiments to determine the coverage or the diffusion coeficient of charge dissipation on modified insulating particles and, in some situations to identify the particle shape.
11
Li, Jian-Wei. "Zeolite-modified electrodes /". [S.l.] : [s.n.], 1993. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
Testo completo
12
Aixill, W. Joanne. "Electrode processes". Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:9578fd22-42fe-41cc-9d92-96f8272956d8.
Testo completoAbstract (sommario):
The work presented in this thesis first characterises a high speed channel flow cell and then applies the system to the electro-reduction of nitromethane in aqueous solution. Potential step transient measurements are carried out with the current-time transients simulated using a model based on the absence of axial diffusion. The excellent agreement between theory and experiment confirms the proposed mass transport model and further demonstrates that the combination of current-time transients recorded using the high speed channel flow cell and numerical simulations provide a powerful tool to access homogeneous rate constants of the order 1 x 106s̄¹. The high speed channel flow cell is then used in combination with a range of complementary electrochemical techniques, numerical modelling, in-situ ESR, single crystal experiments and kinetic isotope measurements to infer a mechanistic scheme for the complex electro-reduction pathway of nitromethane in aqueous solution. Platinum, gold, mercury/copper and mercury/gold electrodes are investigated enabling the most conclusive description of the reduction mechanism to date. The reaction pathway is shown to follow an ECEEE type process with the chemical step proceeding at the electrode surface. The heterogeneous rate constant, khet, describing the chemical step is calculated for each electrode surface. For platinum in the pH range 7.0 - 9.0 this value is 0.3 ± 0.06 cm s̄¹. For mercury/copper it is 0.18 cm s̄¹, for gold/mercury it is 0.06 cm s̄¹ and for Au it is 0.095 cm s̄¹. Consideration of these values shows a surprising independence of the heterogeneous rate constant on the chemical identity of the surface with all of the values being similar to within less than an order of magnitude. The reason for the apparent paradox of the observed surface indifference of the chemical reaction step is explained by a homogeneous H transfer from the carbon to the oxygen of the nitromethane radical anion, formed form the initial electron transfer step, occurring in the layer of solution immediately adjacent to the electrode solution as shown in the scheme below. The resulting species, •CH2 N(OH))ˉ then undergoes a rapid irreversible adsorption to the electrode surface and subsequent transformation to the final product the hydroxylamine, CH3NHOH. It is proposed that if the energy barrier to the adsorption of •CH2 N(OH))ˉ is less than that required for the H atom transfer then the reaction rate will be insensitive to the adsorption step and hence the chemical identity of the electrode. This introduces the concept of a whole new electrochemical process: the surface indifferent electrocatalytic reaction.
13
Blum, Richard Alan. "An Electronic System for Extracellular Neural Stimulation and Recording". Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16192.
Testo completoAbstract (sommario):
A system for extracellular neural interfacing that had the capability for stimulation and recording at multiple electrodes was presented. As the core of this system was a custom integrated circuit (IC) that contained low-noise amplifiers, stimulation buffers, and artifact-elimination circuitry. The artifact-elimination circuitry was necessary to prevent the activity of the stimulation buffers from interfering with the normal functioning of the low-noise amplifiers.
The integrated circuits were fabricated in in a 0.35 micron CMOS process. We measured input-referred noise levels for the amplifiers as low as 3.50 microvolts (rms) in the in the bandwidth 30 Hz-3 kHz, corresponding to the frequency range of neural action potentials. The power consumption was 120 microwatts, corresponding to a noise-efficiency factor of 14.5. It was possible to resume recording signals within 2 ms of a stimulation, using the same electrode for both stimulation and recording.
A filtering algorithm to remove the post-discharge artifact was also presented. The filtering was implemented using a field-programmable gate array (FPGA). The filtering algorithm itself consisted of blanking for the duration of the stimulation and artifact-elimination, followed by a wavelet de-noising. The wavelet de-noising split the signal into frequency ranges, discarded those ranges that did not correspond to neural signals, applied a threshold to the retained signals, and recombined the different frequency ranges into a single signal. The combination of the filtering with the artifact-elimination IC resulted in the capability for artifact-free recordings.
14
Ferrara, Daro 1961. "DETECTION OF PHENOTHIAZINES USING COATED WIRE ION-SELECTIVE ELECTRODES". Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/276493.
Testo completo
15
Barron, Olivia. "Gas diffusion electrodes for high temperature polymer electrolyte membrane fuel cells membrane electrode assemblies". University of the Western Cape, 2014. http://hdl.handle.net/11394/4323.
Testo completoAbstract (sommario):
Philosophiae Doctor - PhDThe need for simplified polymer electrolyte membrane fuel cell (PEMFCs) systems, which do not require extensive fuel processing, has led to increased study in the field of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) applications. Although these HT-PEMFCs can operate with less complex systems, they are not without their own challenges; challenges which are introduced due to their higher operation temperature. This study aims to address two of the main challenges associated with HT-PEMFCs; the need for alternative catalyst layer (CL) ionomers and the prevention of excess phosphoric acid (PA) leaching into the CL. The first part of the study involves the evaluation of suitable proton conducting materials for use in the CL of high temperature membrane electrode assemblies (HT-MEAs), with the final part of the study focusing on development of a novel MEA architecture comprising an acid controlling region. The feasibility of the materials in HT-MEAs was evaluated by comparison to standard MEA configurations.
16
Maloy, Lucia. "Comparison of Single-Use and Multiple-Use Electrodes for Sensory, Motor Threshold Amplitudes and Force Production". BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1995.
Testo completoAbstract (sommario):
Context: Electrodes play an important role in interfacing tissue with electrical stimulation devices. Manufacturers recommend that adhesive metallic mesh cloth electrodes be used no more than 10 times before they are discarded, however, clinically the electrodes are often used up to 30 times. Another concern is sanitation. When electrodes are used on different patients, there is a chance for cross-contamination and bacterial growth on the electrode. Objective: To compare amplitudes of perceived sensation, motor twitch and force produced at specific amplitudes using single-use electrodes that run no risk of cross-contamination, and multiple-use electrodes. Design: Mixed model ANOVA with the subject blocked. Setting: Therapeutic modalities research laboratory. Patients or Other Participants: 20 subjects comprised of 7 males (age 24.7 yrs ± 2.3 yrs, skin fold thickness 5.9 mm ± 2.4 mm) and 13 females (age 21.5 yrs ± 2.3 yrs, skin fold thickness 10.7 mm ± 4.1 mm) recruited by volunteer sample mainly from athletic and athletic training populations. They drew random numbers to determine which group they were assigned to. Interventions: Each subject had electrodes placed on their wrist extensors muscles. Measures were recorded of what intensity it took to achieve perceived sensation, motor twitch, and force produced at a specific intensity. To determine decay, multiple use electrodes were tested initially and on the 10th use. After the multiple use electrodes were tested initially, they were leached out. After eight uses, pretest procedures were repeated (10th use electrode) as the final trial on the subjects. Single use electrodes were tested one time. Main Outcome Measures: The dependent variables were sensation, motor twitch and force production. The experiment was a repeated measures study, using mixed models ANOVA with subjects blocked. Alpha was set at p<0.05. Data was analyzed using a SAS proc mixed 9.1. Results: There was no statistical difference between the measures taken during the initial trial and final trial of the multiple use electrodes for muscle twitch (FMUI MUF muscle twitch= 107.3, p= 0.09) and force production (FMUI MUF force production=28.7, p= 0.11). There was a significant difference between the single use and the multiple use electrodes for the initial and final trial. Average values in mA for perceived sensory were: single use 9.73, multiple use initial 16.70 , multiple use final 21.03; observed muscle twitch: single use 15.87, multiple use initial 29.16, multiple use final 31.78; and force produced: single use 22.8 Newtons, multiple use initial 10.0 Newtons, multiple use final 5.0 Newtons. Conclusion: Single-use electrodes produce more conductive power with fewer milliamps compared to multiple-use electrodes. Single use electrodes are just as, or more efficient as the multiple use electrodes and have the added advantage of eliminating the possibility of cross-contamination of bacteria from patient to patient.
17
Ferrigno, Rosaria. "Electrodes interdigitées de puissance /". [S.l.] : [s.n.], 1998. http://library.epfl.ch/theses/?nr=1767.
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18
Khanfar, Mohammad F. "Molybdenum-modified platinum electrodes /". Internet access available to MUN users only, 2003. http://collections.mun.ca/u?/theses,160874.
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19
Davies, Trevor J. "Voltammetry at heterogeneous electrodes". Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427873.
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20
Perera, Kuruppuwattage Sarath Daya. "Electroactive-polymer modified electrodes". Thesis, Queen's University Belfast, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336004.
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21
Beh, Seng Kee. "Membranes for enzyme electrodes". Thesis, Cardiff University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305091.
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22
Tinlin, James Robert. "Photoelectrocatalysis by TIOâ‚‚ electrodes". Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270802.
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23
Hall, Geoffrey F. "Organic phase enzyme electrodes". Thesis, Cranfield University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278720.
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24
Saini, S. "Organic phase enzyme electrodes". Thesis, Cranfield University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332925.
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25
Kalia, Yogeshvar Nath. "Development of enzyme electrodes". Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46856.
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26
Moorcroft, Matthew James. "Electroanalysis at activated electrodes". Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:6089e63c-3db2-4627-90e7-13763efcbd07.
Testo completoAbstract (sommario):
This thesis details advances made within the field of electroanalytical chemistry through the use of working electrodes that have been activated through application of ultrasound, heat, geometry, chemical modification or composition. Initially the thesis reports the enhanced analytical utility of chemically and compositionally modified working electrodes when directed towards the detection and determination of NO3¯ and NO2¯ anions in environmental samples. This has been achieved through the use of electrodes that have been a) modified with a Cu deposit and b) fashioned from a Cu-Ni alloy. Nitrate and nitrite anions have been successfully determined in a variety of passivating matrices, at analytically relevant detection limits of the order of 10-6 M with a dynamic linear range extending from 10 to 200 μM. The methods presented have been shown to surpass existing electrochemical techniques in terms of nitrate/nitrite speciation through separation of the voltammetric signals, where existing analyses have reported the intereference of both species when present in the same solution. The use of ultrasound as a further enhancement to the sensitivity and versatility of the electrochemical detection of nitrate at a chemically modified electrode is then presented. The influence of ultrasound is shown to remove a portion of the deposited copper, but a significant catalytic layer remains, resulting in greater sensitivity during insonation. The effect of temperature on electrochemical systems involving one- and two-electron redox reactions of K4Fe(CN)6, Ru(NH3)6Cl3, Fe(C5H5)2, N,N,N',N'tetramethylphenylenediamine, N,N'dimethylphenylenediamine and tris(4- bromophenyl)amine have been studied under hydrothermal conditions using a novel hydrodynamic method based on a conventional channel flow cell where the working electrode is heated by radio frequency radiation. The diffusion activation parameters obtained with the radio frequency channel cell and computer simulation were compared with independent data from microelectrode high temperature experiments. The application of the heated flow cell as a tool for mechanistic studies is discussed with the investigation of the well characterised ECE reaction of m-iodo-nitrobenzene in acetonitrile, giving a value of 80 ± 5 kJ mol-1 for the activation energy of the rate constant for the decomposition of the m-iodo-nitrobenzene radical anion. This represents the first observation of an ECE or mechanistically complex reaction at a locally heated electrode. The work presented in the final two chapters of this thesis examines the enhanced activation achieved from modification of the electrode geometry, and in particular the application of microelectrodes to the development of electroanalytical techniques. The electrochemical reduction of the inhalation anaesthetic agent enflurane (2-chloro-1,1,2- trifluoroethyl difluoromethyl ether) is reported at a variety of microelectrode substrates (Au, Ag, Cu, Pt and glassy carbon) with electrode dimensions varying from 5 to 60 μm. The solvents water, dimethylsulfoxide and acetonitrile were investigated along with the supporting electrolytes potassium chloride, tetrabutylammonium hexafluorophosphate and various tetraalkylammonium perchlorates. The use of a gold microelectrode with dimethyl sulfoxide solvent and tetraethylammonium perchlorate as the supporting electrolyte was found to give well-defined voltammetry. Linear calibration curves were obtained between 0 and 2 % v/v (gaseous additions) or up to 135 mM (gravimetric additions), offering scope for the development of a rapid, inexpensive electrochemical gas sensor. The analytical utility of the system has been investigated in the presence of oxygen and nitrous oxide in DMSO solvent. The superoxide anion radical, formed from the electro-reduction of dissolved oxygen, is shown to react with enflurane complicating their simultaneous detection. The kinetics of the enflurane / superoxide reaction are found to be first order with respect to both superoxide and enflurane with a rate constant of 0.25 M-1 s-1 determined by three independent methods: steady-state voltammetry, digital simulation of cyclic voltammetric data and UV/Vis spectroscopic analysis.
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Jiang, Lixue. "Structure Engineering towards High-Performance Electrodes for Electrochemical Energy Conversion and Storage". Thesis, Griffith University, 2019. http://hdl.handle.net/10072/389748.
Testo completoAbstract (sommario):
Major concerns about the effects of increasing fossil fuel consumption on the environment and energy security have prompted the development of sustainable and environmentally-friendly energy conversion and storage technologies based on electrochemical processes (e.g. water electrolysers, batteries and supercapacitors). Electrode materials are a key component of these technologies, and high-performance electrode systems are essential for the realization of a clean-energy-based economy. Numerous efforts have been made to develop advanced electrode materials for energy conversion and storage applications. However, current electrode synthesis methods are usually energy-intensive, not environmentally friendly, difficult to scale, or costly to produce. This thesis aims to utilize electrode structure engineering to develop highperformance electrodes based on earth-abundant materials via low-cost, energy-efficient and green synthesis strategies. Further, the applications of these electrodes in various energy conversion and storage applications are explored.
Nickel-iron oxides or hydroxides are considered promising electrocatalysts for the oxygen evolution reaction, featuring a high activity and long cycling life in alkaline solution. A room temperature, electroless method has been developed here to grow nickel-iron hydroxides on a nickel foam current collector. The activity of nickel foam for the oxygen evolution reaction can be remarkably enhanced by simply immersing the nickel foam in a ferric nitrate solution at room temperature. During this process, the oxidation of the nickel foam surface by ferric nitrate ions increases the near-surface concentration of hydroxide ions, which results in the in situ deposition of a highly active, amorphous nickel-iron hydroxide layer. This phenomenon is described in Chapter 2 of this thesis.
Carbon cloth is a widely-adopted current collector for the fabrication of electrodes. A facile, two-step method has been investigated here to turn commercial carbon cloth into a high-performance electrode for zinc-air batteries. Mild acid oxidation followed by air calcination directly activate carbon cloth to generate uniform, nanoporous and superhydrophilic surface structures with optimized, oxygen-rich functional groups and dramatically increased surface area. This two-step-activated carbon cloth exhibits superior bifunctional oxygen electrocatalytic activity and durability. A rechargeable, flexible zinc-air battery using the activated carbon cloth as a binder-free, flexible air electrode yields a remarkably high peak power density, high flexibility, and good cycling performance, with a small charge-discharge voltage gap. This work is elaborated in Chapter 3.
Cost-effective synthesis of large-scale, uniform electrode materials with high activity and cycling stability is challenging. In Chapter 4, a reaction environment confinement strategy for scalable and reproducible production of nanostructured materials is proposed. Nickel foam is simply immersed in metal nitrate aqueous solution, with the volume of solution per unit area of nickel foam kept very low. A precisely designed reactor with a spiral tunnel ensures the same width of solution on each side of the nickel foam. The reaction environment is confined to ensure reproducible and uniform synthesis of nanostructured materials across the Ni foam. This approach has the largest REAVC (ratio of electrode area to precursor volume consumption) value reported so far, 2.0 cm2 mL-1. The synthesized nickel-iron hydroxides/nickel foam electrodes with uniformity in both microstructure and electrochemical properties exhibit remarkable activity for both the oxygen evolution reaction and hydrogen evolution reaction.
Manganese oxides are a class of promising electrode materials for high performance supercapacitors. However, not all types of manganese oxides with different phases are electrochemically active, and their crystal structures have a considerable effect on their capacitance. In Chapter 5, a facile strategy is developed for the transformation of manganese oxide from the orthorhombic to birnessite crystal structure. The product exhibits significantly enhanced electrochemical performance as a supercapacitor electrode. This work opens up new possibilities for changing the crystal structure of manganese oxides towards optimized properties in electrochemical applications.
This thesis makes significant contributions to our understanding of electrode structure engineering, materials science and electrochemical energy conversion and storage through: (i) designing novel nanostructured nickel-foam-based electrode systems with high electrocatalytic activity towards water oxidation via a simple immersion strategy at ambient temperature; (ii) developing facile activation procedures to endow commercially available, inactive carbon cloth with oxygen-rich functional groups and high oxygen electrocatalytic activity; (iii) controlling ion diffusion in a confined zone for uniform deposition of active materials over large-size electrodes, electrodes useful for various electrochemical applications; (iv) probing the phase transformation of manganese oxides from orthorhombic to birnessite, a material with enhanced electrochemical performance; (v) investigating the growth mechanisms of these advanced electrode materials to understand the origin of their exceptional activity.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text
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Myedi, Noluthando. "Electrochemical kinetics and sensing of conjugated dienes in acetonitrile". University of the Western Cape, 2011. http://hdl.handle.net/11394/5424.
Testo completoAbstract (sommario):
>Magister Scientiae - MScThis thesis focuses on the electroanalysis of some dienes (2-methyl-1.3-butadiene (MBD), tran-1.3-pentadiene (PD), 1.3-cyclohexadiene (CHD) and 3-cyclooctadiene (COD)) found in gasoline and the development of simple electrochemical diene sensors. The detection of dienes in fuels is important as they readily polymerise and form gum in fuel tanks. The electroctivity of the dienes was studied with glassy carbon electrode (GCE) and Pt electrode in tetrabutylammonium perchlorate (TBAP)/acetonitrile solution. Polyaniline-polystyrene sulfonic acid (PANi-PSSA) composite films were electro-deposited or drop-coated on GCE, with and without gold nanoparticles (AuNPs) and characterized by cyclic voltammetry (CV), high resolution transmission electron microscopy (HRTEM) and ultraviolet-visible (UV-vis) spectroscopy. Both composite polymers were found to be of nanofibral structure, and the spherical gold nanoparticles were dispersed uniformly within the polymer. The dienes exhibited no redox peaks on GCE/PANi-PSSA and GCE/PANi-PSSA/AuNPs electrode systems from -1.0 V to +1.5 V, beyond which PANi would overoxidize and lose its electroactivity. Therefore, cyclic voltammetry and steady state amperometry of the four dienes (MBD, PD, CHD and COD) were studied with unmodified Pt and GCE electrodes. Subtractively normalised interfacial-fourier transform infra-red (SNIFTIR) spectroscopic studies of the dienes were performed with Pt electrode. SNIFTIR data showed that there was a definite electro-oxidation of 1.3-cyclohexadiene as electrode potential was changed from E = 770 mV to E = 1638 mV. Severe electrode fouling was observed when steady state amperometric detection of CHD, as a representative diene, was performed on Pt electrode. Randel-Sevčik analysis of the CVs of the dienes on Pt electrode gave diffusion coefficient (Dox) values of 10.65 cm²/s, 9.55 cm²/s, 3.20 cm²/s and 3.96 cm²/s for CHD, COD, PD, and MBD, respectively. The corresponding detection limits (3σn-1) were 0.0106 M, 0.0111 M, 0.0109 M, and 0.0107 M.
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Nimley, Christopher. "Fabrication and Characterization of a Disk Ring Shaped Dual Nanometer-Sized Electrode and Its Application to Generation-Collection". Digital Commons @ East Tennessee State University, 2011. https://dc.etsu.edu/etd/1315.
Testo completoAbstract (sommario):
This research reports on the fabrication and characterization of integrated dual nanometer-sized electrodes. The electrodes are made of closely spaced nanometer-sized platinum and gold achieved by inserting and pulling platinum wire in cylindrical glass pipette plated with gold. Cyclic voltammetry has been used to characterize the electrodes. Our results show that both electrodes can work individually and can accomplish generation/collection experiments. Factors that may affect the performance of the electrodes as well as formation mechanism of the gold film by electroless plating are discussed.
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Mathebe, Ntlatseng Gretta Rhoda. "Fabrication and kinetic modeling of cytochrome P4502D6 amperometric biosensors for serotonin reuptake inhibitors". Thesis, University of the Western Cape, 2005. http://hdl.handle.net/11394/1589.
Testo completoAbstract (sommario):
Magister Scientiae - MScAn amperometric biosensor was prepared by in situ deposition of cytochrome P4502D6 (CYP2D6, P4502D6) enzyme on a polyaniline (PANI)-doped glassy carbon electrode. The PANI film was electrochemically deposited on the electrode at 100 mV s-1 against Ag/AgCl. Cyclic voltammetric characterisation of the PANI film in 1 M HCl solution showed two distinct redox peaks, which prove that the PANI film was electroactive and exhibited fast reversible electrochemistry. The surface concentration and film thickness of the adsorbed electroactive species was estimated to be 1.85 x 10 -7 mol cm -2 and approximately 16 nm, respectively. Cytochrome P4502D6 was electrostatically immobilised onto the surface of the PANI film and cyclic voltammetry was used to monitor the serotonin reuptake inhibitors (fluoxetine, fluvoxamine and citalopram) in phosphate buffer solution. Fluoxetine was found to be a substrate of CYP2D6 at low concentrations but inhibits enzyme activity at high concentrations; this was consistent with uncompetitive substrate inhibition kinetics. Thus PANI-mediated electrochemistry can be used to observe monooxygenation reaction of CYP2D6.
South Africa
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Singh, Kanwardeep. "A comparison of electrode recruitment characteristics and muscle fatigue using intramuscular and nerve trunk electrodes". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37980.pdf.
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Santana-Aguiar, Francisco Aurelio. "Characterisation of electrode microarrays produced photolithographically and with thiol self-assembled monolayers on gold electrodes". Thesis, Durham University, 2009. http://etheses.dur.ac.uk/45/.
Testo completoAbstract (sommario):
The macroscale electrochemical theory breaks down with microstructures smaller than the dimensions of the diffusion layer, showing that such electrodes have significant quantitative effects and qualitative advantages. The great advantage of microelectrodes over macroelectrodes is the minimisation of interference, which gives rise to much lower detection limits. Microelectrodes have much reduced ohmic drops and capacitive effects and can be used in the absence of supporting electrolyte. These features have opened a growing interest in the fabrication and application of microelectrodes in various areas. There are different microelectrode geometries, but disc type is the most used. Microelectrode arrays have been proposed as a way of increasing the magnitude of the current (produced for a single microelectrode), while maintaining the advantages of the single microelectrode. Although the inlaid microdisc microelectrode can be considered as one the most popular microelectrode geometry, there is also a need to consider conical recessed, recessed and protruding microdiscs as photolithographic microfabrication techniques often result in non-ideal geometries. It has been proved using surface imaging techniques such as scanning Kelvin nanoprobe (SKN), scanning electron microscopy (SEM) and white light interferometer microscopy that conical recessed electrodes with gradient potential along the recessed walls are formed during standard photolithographic methods for producing microelectrode arrays. Microarrays are ubiquitously used for high-throughput measurements using various signal transduction techniques. Ideally each sensor in a microarray platform should perform optimally to ensure an error free response. In this thesis, a simple method for designing a microelectrode array platform (MEA) is described, allowing a ‘defective’ cluster of sensing arrays to be easily identified. It is possible to extend this concept for multiple analyses on a single chip. Molecular electronic is a promising technology which would be an alternative. The concept of molecular electronics is the use of single molecules or arrays, or layers of molecules for the fabrication of electronic components such as wires, switches, and storage elements. Indeed, functionalised thiol monolayer-based microelectrode array may provide unique possibilities, facilitating electrochemical measurements involving electron transfer via electron tunnelling. The conjugated structure of rigid, linear molecule increases greatly the rate of electron transfer across the monolayer. Charge transfer and self-assembly characteristics of novel fully conjugated molecules molecular wires (synthesised at the Department of Chemistry and Centre for Molecular and Nanoscale Electronics, Durham University) assembled on flat gold electrodes are evaluated using Marcus model of electron-transfer and tunnelling theory. The behaviour of these wires is compared with heptanethiol and dodecanethiol SAMs. A preliminary study for application of self-assembled monolayer of molecular wires in microelectrode arrays for multiple analyses on a single chip has been successfully reached.
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Sahar, Abdallah. "Etude par analyse spectrale de processus aux electrodes fortement aleatoires". Paris 6, 1988. http://www.theses.fr/1988PA066522.
Testo completoAbstract (sommario):
Le but de ce travail a consiste a etudier deux processus electrochimiques a comportement fortement aleatoire, a savoir le degagement de bulles gazeuses sur une electrode et l'electrolyse en lit fluidise
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Hernández, Rodríguez Elba María. "Solid Oxide Electrolysis Cells electrodes based on mesoporous materials". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/665269.
Testo completoAbstract (sommario):
The need of substituting the current energetic model by a system based on clean Renewable Energy Sources (RES) have gained more importance in the last decades due to the environmental issues related to the use of fossil fuels. These energy sources are site-specific and intermittent, what makes essential the development of Energy Storage Systems (ESS) that allows the storage of the electricity generated by renewable energies.
Among the technologies under development for the storage of electrical energy, Solid Oxide Electrolysis Cells (SOECs) have been proposed in the last decades as a promising technology. Achieving efficiencies higher than 85%, SOEC technology is able to convert electrical energy into chemical energy through the reduction of H2O, CO2 or the combination of both; generating H2, CO or syngas (H2 +CO). The implementation of this technology based on renewable electrical energy, combined with fuel cells would allow closing the carbon cycle.
The work presented in this thesis has been devoted to enhance the performance of SOEC. The approach that is presented for that propose is based on the implementation of high surface area and thermally stable mesoporous metal oxide materials on the fabrication of SOEC electrodes. High performance and stability of the electrodes was expected during its characterization. Structural and electrochemical characterization techniques have been applied during the development of this thesis for this purpose.
The thesis is organized in eight chapters briefly described in the following:
Chapter 1 briefly analyses the current energy scenario presenting electrolysers as a promising technology for the storage of electrical energy. Besides, basic principles of SOECs operation and the state-of-the-art materials of SOECs are reviewed.
Chapter 2 describes all the experimental methods and techniques employed in this thesis for the synthesis and characterization of synthesised materials and fabricated cells.
Chapter 3 presents the results obtained from the structural characterization of the mesoporous materials and fabricated electrodes, revealing the successful implantation of the hard-template method for obtaining Sm0.2Ce0.8O1.9 (SDC), Ce0.8Gd0.2O1.9 (CGO) and NiO mesoporous powders, and the fabrication of SDC-SSC (Sm0.5Sr0.5CoO3-δ), CGO- LSCF (La0.6Sr0.4Co0.2Fe0.8O3) and NiO-SDC electrodes based on mesoporous materials. The attachment of the mesoporous scaffold for the fabrication of oxygen electrodes has been optimized at 900 °C.
Chapter 4 compares electrolyte- and fuel electrode-supported cell configurations based on the same oxygen electrode. The electrochemical performance and the microstructural characterization of these cells are considered for that purpose. Showing a maximum current density of -0.83 and -0.81 A/cm2 on electrolysis and co- electrolysis modes respectively, fuel electrode-supported cells are considered more suitable for SOEC fabrication.
Chapter 5 presents a study focused on analysing the influence of the oxygen electrode interface on the SOEC performance. The electrochemical and microstructural characterization of barrier layers and oxygen electrodes fabricated applying different methods are discussed in this chapter. The combination of a barrier layer fabricated by Pulsed Laser Deposition (PLD) with an oxygen electrode based on mesoporous materials resulted on the injection of up to -1 A/cm2, what allows concluding that this
interface microstructure is directed related with the best performing SOECs in this thesis.
Chapter 6 shows the performance of SOEC cells on co-electrolysis mode containing the optimized oxygen electrode, fabricated by infiltration of mesoporous scaffolds. The long-term stability of infiltrated mesoporous composites have been demonstrated during 1400 h, registering degradation rates of 2%/kh and <1%/kh when current densities of -0.5 A/cm2 and -0.75 A/cm2 are injected, respectively.
Chapter 7 shows results of the scale-up of the mesoporous-based electrodes for the fabrication of large area cells. Their electrochemical performance shows high fuel flexibility, injecting -0.82 A/cm2 on co-electrolysis mode; and long-term stability injecting -0.5 A/cm2 for 600 h.
The conclusions of this thesis are presented in Chapter 8.Una de las principales desventajas de las fuentes de energías renovables es que producen energía eléctrica de forma discontinua. Los electrolizadores de alta temperatura basados en óxidos sólidos (SOEC) se presentan como una tecnología prometedora para el almacenamiento de energía eléctrica. Alcanzando eficiencias mayores de un 85%, los electrolizadores SOEC permite convertir energía eléctrica en energía química mediante la reducción de las moléculas de agua (H2O), dióxido de carbono (CO2), o la combinación de ambas; generándose hidrógeno (H2), monóxido de carbono (CO) o gas de síntesis (H2 +CO) como producto. El trabajo que se presenta en esta tesis tiene como objetico mejorar el rendimiento de los electrolizadores SOEC mediante la utilización de óxidos metálicos mesoporosos, caracterizados por poseer alta área superficial y ser estables a altas temperaturas. Esta tesis está organizada en ocho capítulos. Los capítulos 3, 4, 5, 6 y 7 presentan los resultados alcanzados: El capítulo 3 presenta la caracterización estructural de los materiales mesoporosos y de los electrodos fabricados. Además, la temperatura de adhesión del material mesoporoso ha sido optimizada y se ha fijado a 900 °C. El capítulo 4 compara electrolizadores fabricados soportados por el electrodo de combustible y por el electrolito. Los resultados muestran que las densidades de corriente más altas fueron inyectadas en los electrolizadores soportados por el electrodo de combustible, considerándose esta configuración la más apropiada. El capítulo 5 presenta la influencia de la microstructura de la intercara del electrodo de oxígeno en el rendimiento de los electrolizadores SOEC. La caracterización electroquímica, apoyada por la caracterización microestructural, ha demostrado que la máxima densidad de corriente ha sido inyectada por el electrolizador cuya barrera de difusión ha sido depositado por láser pulsado (PLD) y la capa funcional del electrodo de oxígeno mediante infiltración de materiales mesoporosos. El capítulo 6 estudia el electrodo de oxígeno optimizado. Durante 1400 h de operación continua y caracterización microstructural, se ha demostrado la estabilidad de este electrodo. Por último, el capítulo 7 muestra los resultados obtenidos del escalado de los electrodos mesoporosos en celdas de mayor área (25 cm2). La caracterización electroquímica muestra alta flexibilidad ante las composiciones de gases utilizadas, y estabilidad de los electrodos mesoporosos propuestos.
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Hüsser, Oskar E. "Photoelectrochemistry at (semi) insulating electrodes /". Zürich, 1987. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8384.
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Sekretaryova, Alina. "Novel reagentless electrodes for biosensing". Licentiate thesis, Linköpings universitet, Kemiska och optiska sensorsystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-112345.
Testo completoAbstract (sommario):
Analytical chemical information is needed in all areas of human activity including health care, pharmacology, food control and environmental chemistry. Today one of the main challenges in analytical chemistry is the development of methods to perform accurate and sensitive rapid analysis and monitoring of analytes in ‘real’ samples. Electrochemical biosensors are ideally suited for these applications. Despite the wide application of electrochemical biosensors, they have some limitations. Thus, there is a demand on improvement of biosensor performance together with a necessity of simplification required for their mass production. In this thesis the work is focused on the development of electrochemical sensors with improved performance applicable for mass production, e.g. by screen printing. Biosensors using immobilized oxidases as the bio-recognition element are among the most widely used electrochemical devices. Electrical communication between redox enzymes and electrodes can be established by using natural or synthetic electron carriers as mediators. However, sensors based on soluble electronshuttling redox couples have low operational stability due to the leakage of water-soluble mediators to the solution. We have found a new hydrophobic mediator for oxidases – unsubstituted phenothiazine. Phenothiazine and glucose oxidase, lactate oxidase or cholesterol oxidase were successfully co-immobilized in a sol-gel membrane on a screen-printed electrode to construct glucose, lactate and cholesterol biosensors, respectively. All elaborated biosensors with phenothiazine as a mediator exhibited long-term operational stability. A kinetic study of the mediator has shown that phenothiazine is able to function as an efficient mediator in oxidase-based biosensors. To improve sensitivity of the biosensors and simplify their production we have developed a simple approach for production of graphite microelectrode arrays. Arrays of microband electrodes were produced by screen printing followed by scissor cutting, which enabled the realization of microband arrays at the cut edge. The analytical performance of the system is illustrated by the detection of ascorbic acid through direct oxidation and by detection of glucose using a phenothiazine mediated glucose biosensor. Both systems showed enhanced sensitivity due to improved mass transport. Moreover, the developed approach can be adapted to automated electrode recovery. Finally, two enzyme-based electrocatalytic systems with oxidation and reduction responses, respectively, have been combined into a fuel cell generating a current as an analytical output (a so-called self-powered biosensor). This was possible as a result of the development of the phenothiazine mediated enzyme electrodes, which enabled the construction of a cholesterol biosensor with self-powered configuration. The biosensor generates a current when analyte (cholesterol) is added to the cell. The biosensor has been applied for whole plasma analysis. All developed concepts in the thesis are compatible with a wide range of applications and some of them may even be possible to realize in a fully integrated biosensor unit based on printed electronics.
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Luscombe, Darryl L., e mikewood@deakin edu au. "Studies with voltammetric microdisk electrodes". Deakin University. School of Sciences, 1991. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20051201.153433.
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Marozzi, Paolo. "3D Electromagnetic characterization ofimplantable electrodes". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-117730.
Testo completoAbstract (sommario):
Bioimpedance is a common feature of every tissue and its analysis allows the understanding of the physiological state of the tissue under test as well as its changes. The increase of glucose concentration can be detected by monitoring the tissue bioimpedance. In high risk situations and subjects like athletes, several checks with high accuracy are required each day. The scientific community has focused its efforts to find an integrated solution for in-vivo implantable bioimpedance measurement devices. The implantable devices have better accuracy since they are placed closer to the tissues under test. The objective of this thesis is to characterize the different shapes and configurations of probes suitable for bioimpedance in-vivo measurement applications. The electrode modeling and simulation, and analysis of its interaction with the tissue are performed by using the electronic design automation software ADS, from Agilent. Two shapes and six configurations are considered and analysed. The chosen geometry is capable of developing the least amount of tissue reaction around the electrode, so as to ensure the best performance for a four-electrode measurement.
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Szente, Roberto Nunes. "Erosion of plasma torch electrodes". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74256.
Testo completoAbstract (sommario):
The erosion of copper electrodes in a concentric cylinder geometry with magnetically driven arcs was studied at steady state for currents up to 250 A in a variety of gases and gas mixtures, magnetic field strengths and gas flow rates. The effects of arc velocity, gas composition, current density and heat transfer to the cathode on erosion rates were examined.The arc velocity varied with the magnetic field strength and arc current accordingly to a newly developed equation, V $ alpha$ B$ sp{0.60}$ I$ sp{0.56}$, when the cathode surface was slightly contaminated with C, Cl, O or N. The composition of the surfaces was found using Auger and ESCA spectroscopy. A surface drag force, a new force opposing to the arc motion was proposed. In the case of clean and heavily contaminated surfaces (contaminant layers thicker than 10 microns), the surface drag becomes the major force opposing the arc movement. Work function measurements showed that surface drag increased as electron emission became more difficult.
A novel technique was developed to determine the current distribution of the arc foot on the electrodes. A correlation between the arc foot current density and erosion rate was proposed. The effects of the surface composition, magnetic field and arc velocity on the arc current distribution were also examined.
A conceptual model was developed for electrode erosion; the model was supported by experimental results and by the results of simulations using macroscopic and microscopic heat transfer models.
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Daly, Colette Lynn. "Binding studies using membrane electrodes". Thesis, University of Salford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252942.
Testo completoAbstract (sommario):
The research embodied within this thesis has contributed to the development and application of a novel electrode technique. The electrodes fabricated herein consist of a thin PVC/Poly (vinylchloride) membrane which is made sensitive to a particular organic cation, for example Acridine Orange. The only requirements necessary to make an electrode were that the substance to be incorporated into the membrane be cationic, water soluble and surface active. These membrane electrodes gave an emf directly proportional to the log of the ( concentration of organic cations present in solution.
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Pratt, Keith Francis Edwin. "Modelling of amperometric enzyme electrodes". Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260018.
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Cox, Philip. "Electrosynthesis on non-metal electrodes". Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252664.
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Cleghorn, Simon John Charles. "Electrocatalytic hydrogenation at palladium electrodes". Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332771.
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Mount, A. R. "The development of modified electrodes". Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47326.
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Murphy, Lindy Jane. "Conducting organic salt enzyme electrodes". Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46459.
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Parsons, Keith Paul. "Conducting polymers for modified electrodes". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38134.
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Wilson, Peter John. "Electrochemical ESR of modified electrodes". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47717.
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Craston, D. H. "The development of enzyme electrodes". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37981.
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Li, Fengbin. "Studies of polymer modified electrodes". Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46412.
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Tebbutt, Peter. "The development of modified electrodes". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38173.
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