Rozprawy doktorskie na temat „Electro-Catalyst”

Gold supported titania nano-particle surfaces have been synthesised in order to understand supported electrochemical mechanisms through an inverse catalyst. The catalyst process investigated was the electro-oxidation of CO which is known to be promoted on Au nano-particles on a titania support. Synthesis proceeded via physical vapour deposition (PVD) of titanium onto a gold surface (both polycrystalline and 111 crystal), followed by alloying and oxidation to form discrete particles of titania on the surface, with variations in density of particles achieved by control of the initial titanium coverages. Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) measurements indicate these particles develop with consistent triangular and hexagonal shapes, with average diameters of 11.5 and 20 nm observed depending on alloying temperature. The procession of titanium deposition on the gold surface and subsequent alloy formation was followed by X-ray photoelectron spectroscopy (XPS) measurements, with the formation of pure TiO2 revealed once synthesis was complete, with minimal modification to the final electronic state of the underlying gold. Electrochemical testing in an acidic environment provides evidence for alteration of the electrooxidation of CO on these modified gold surfaces. A deactivation of the CO oxidation is observed with initial addition of titania, explained by the blocking of CO adsorption on the surface. This is followed by significant subsequent increases in activity with increasing densities of titania particles, with decreasing over-potential and increasing current density observed as the titania coverage increases. This observed effect on CO oxidation activity with titania coverage in the inverse system provides significant evidence for the action of either reactant spill-over or Ti-Au interface sites as being responsible for the changes in activity observed for titania modified gold systems, whether in the inverse or standard form.

Direct methanol fuel cells (DMFCs) are considered a clean source of electrical power for future energy demand, creating a potential to reduce our dependency on fossil fuels. Despite their advantages, including high energy density, efficiency and easy handling and distribution of fuel, the commercialization of DMFCs has suffered from some drawbacks, including methanol crossover and contamination of the system. Metal cation contaminants (such as Ni, Co, etc) introduced through the degradation of fuel cell components (bipolar plate and electro-catalyst layer) can significantly affect the Nafion-membrane properties and overall fuel cell performance. In the current study, a systematic approach is taken to characterize and identify the mechanism of the effect of metal solution contaminants on the activities of electro-catalysts of DMFCs. Cyclic voltammetry and rotating disk electrode (RDE) techniques were utilized in order to characterize the effect of various concentrations (i.e., 2x10-x M (x=1-7)) of six metal solution contaminants (i.e., Co, Ni and Zn with sulfate and nitrate as counter-anions) on the voltammetric properties and electro-catalytic activity of polycrystalline Pt during methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The results showed a decrease in the MOR and ORR activities of Pt as the concentration of metal solution increased. The effect of counter-anion on the Pt activity was further investigated. The results showed that a combined effect of counter-anions and metal cations may be responsible for the decrease in the electro-catalytic activity of Pt. The effect of metal solution contaminants on the Nafion-ionomer of anode electro-catalysts was investigated using Nafion-coated Pt electrode. Voltammetric properties and MOR activities of Nafion-coated and bare Pt electrodes in the presence of Ni solution contaminants were characterized using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The overall results showed a significant negative effect of Ni solution contaminants on the electro-catalytic activity of bare Pt electrode as compared to the Nafion-coated Pt electrode. Based on the results, it appears that Nafion-ionomer film may interact with metal cations (through its sulfonate groups) and repel them away from the Pt active sites, partially inhibiting the negative effect of metal cations on the Pt activity of Nafion-coated Pt electrode. The effect of metal solution contaminants on the carbon-supported platinum nanoparticle (Pt/C) with various Nafion-ionomer distributions and contents (i.e., Nafion-incorporated Pt/C and Nafion-coated Pt/C electrodes) was further investigated. Cyclic voltammetry and EIS techniques were employed to characterize the effect of Ni solution contaminants on the voltammetric properties and MOR activities of Nafion-incorporated and Nafion-coated Pt/C electrodes. The overall results showed a stronger negative effect of Ni solution contaminants on the electro-catalytic activity of Nafion-incorporated Pt/C electrodes as compared to the Nafion-coated Pt/C electrodes. This further confirms previous observations showing the sulfonate groups of Nafion-ionomer film may attract the Ni metal cations, localize them away from the Pt active sites, and subsequently suppress the negative effect of cations on the activity of Nafion-coated Pt/C electrodes.

This thesis concerns the development and the study of Iron-based water oxidation catalysts (WOCs) and how to immobilize them onto the hydrophobic surface of a carbon paste electrode. In the introductory chapter a general background of the field of water splitting and this thesis is given. In the second chapter, experimental performance is described from synthesis to measurements of a complete complex-doped electrode. The third chapter deals with the results and the discussion of the performed experiments. In chapter four, a descriptive conclusion of the obtained data is held.
Det här arbetet berör studien och utvecklingen utav järnbaserade katalysatorer, speciellt framtagna för för delning utav vatten. Utöver detta undersöks även om dessa katalysatorer (WOCs) kan immobiliseras på den hydrofoba ytan hos elektroder gjorda på kol-pasta. I det inledande kapitlet ges en generell bakgrund till området som berör delning utav vatten. I det andra kapitlet presenteras det experimentella utförandet utav synteser samt elektrokemiska mätningar som berörts under arbetets gång i jakten på en komplexdopad elektrod. I det tredje kapitlet diskuteras resultaten från mätningarna samt möjliga framtidsutsikter. I det fjärde kapitlet presenteras slutsatserna utav studien.

Doctor Scientiae - DSc
In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.
South Africa

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Electrocatalysts of type C/PtSnNiTi were prepared by thermal decomposition of polymeric precursors. The physico-chemical and electrochemical characterization of the electrocatalysts was performed by different techniques: X-ray diffraction, transmission electron microscopy, cyclic voltammetry and chronoamperometry. The X-ray diffraction results showed that the electrocatalysts comprise mainly Pt metal with face-centered cubic crystal structure and particle sizes ranging from 1.8 to 8.3 nm. In transmission electron microscopy analysis the average particle sizes observed were between 4 and 6 nm. The electrocatalysts were evaluated in the absence and presence of ethanol and glycerol in sulfuric acid medium. All showed activity towards alcohols oxidation. Furthermore, the Pt50Sn20Ni25Ti5 electrocatalyst showed the best results of cyclic voltammetry and chronoamperometry in presence of glycerol and ethanol respectively. The greater potency density obtained in cell tests was 20 mW/cm2 for the composition Pt50Sn20Ni25Ti5. Cyclic voltammetry data obtained in this study indicate that the addition of Ni and Ti in PtSn electrocatalysts increases its electrocatalytic activity toward alcohols oxidation
Eletrocatalisadores do tipo C/PtSnNiTi foram preparados por decomposição térmica dos precursores poliméricos. As caracterizações físico-química e eletroquímica foram feitas por diferentes técnicas: Difração de raios X, Microscopia eletrônica de transmissão, Voltametria cíclica, Cronoamperometria, Teste de célula e Teste de energia de ativação. Os resultados de difração de raios X mostraram que os catalisadores são principalmente compostos por Platina cúbica de face centrada e com tamanhos de partícula variando de 1,8 a 8,3 nm. Nas análises de microscopia eletrônica de transmissão foram observados tamanhos médios de partícula entre 4 e 6 nm. Os eletrocatalisadores foram avaliados na presença e ausência de etanol e glicerol em ácido sulfúrico. Todos mostraram atividade na oxidação dos álcoois. Além disso, a composição Pt50Sn20Ni25Ti5 apresentou os melhores resultados de voltametria cíclica e cronoamperometria na presença de glicerol e etanol. A maior densidade de potência obtida nos testes de célula foi de 20 mW/cm2 para a composição Pt50Sn20Ni25Ti5. De modo geral, os dados de voltametria cíclica obtidos nesse estudo indicam que a adição de Ni e Ti em catalisadores PtSn aumenta a atividade catalítica destes frente a oxidação de álcoois

Dans cette recherche, dans un premier temps, un nouveau catalyseur a été synthétisé par une nouvelle méthode de combustion et il a été également caractérisé et mis en oeuvre dans un réacteur photo catalytique afin de dégrader les composés organiques. Puis, ces photo-catalyseurs ont été immobilisés sur la surface de non-tissés de nano fibres polyamide obtenues par le procédé d'électro-filage (electro-spinning) en utilisant une machine semi-industrielle. Ensuite, les comportements mécaniques de non tissés de nano-fibre de polyamide (PA) ont été étudiés à court et à long terme par test de traction et de fluage. Ceci a permis d'une part d'évaluer finement les propriétés des non tissés et d'autre part de modéliser leur comportement au moyen de modèles analogiques. Le modèle de Kelvin-Voigt généralisé a montré sa robustesse. Ces non tissés de nanofibres ont été installés sur 1a paroi du réacteur afin d'avoir un réacteur en inox à lit fixe et d'éviter des inconvénients d'un système hétérogène. Les résultats d'analyse des solutions, nous ont montré une dégradation favorable des composés organiques et les produits intermédiaires dans un système de circulation fermée. La mise sous pression du réacteur a confirmé, comme montré dans les essais mécaniques, que les propriétés mécaniques des fibres dopées étaient suffisantes pour supporter les contraintes mécaniques liées au flux du liquide
In this research, at first, a new catalyst was synthesized by a new combustion method and it was also characterized and applied in a photo-catalytic reactor to degrade the organic compounds. Then, these photocatalysts were immobilized on the surface of nonwovens of polyamide nano fibers obtained by the electro-spinning process using a semi-industrial machine. Then, the mechanical behaviors of polyamide (PA) nano-fiber nonwovens were studied in the short and long term by tensile and creep test. This allowed on the one hand to evaluate finely the properties of nonwovens and on the other hand to model their behavior on average of analog models. The generalized Kelvin-Voigt model has shown its robustness. They were installed on the reactor wall in order to have a stainless steel fixed bed reactor and to avoid the disadvantages of a heterogencous system. The solution analysis results showed us a favorable degradation of organic compounds and intermediate products in a closed circulation system. Pressurizing the reactor confirmed, as shown in the mechanical tests, that the mechanical properties of the doped fibers were sufficient to withstand the mechanical stresses associated with the flow of the Jiquid

The aim of the present work was to screen the main methods for the synthesis of conjugated polymers for their suitability in the preparation of conductive polymer brushes. The main focus was put on the grafting of intrinsically soluble substituted regioregular polyalkylthiophenes because of their excellent optoelectronic properties. The resulting polymer films were characterized and their optoelectrical properties studied. For the first time, a synthesis of conductive polymer brushes on solid substrates using “grafting-from” method was performed. The most important, from my opinion, finding of this work is that regioregular head-to-tail poly-3-alkylthiophenes – benchmark materials for organic electronics - can be now selectively grafted from appropriately-terminated surfaces to produce polymer brushes of otherwise soluble polymers - the architecture earlier accessible only in the case of non-conductive polymers. In particular, we developed a new method to grow P3ATs via Kumada Catalyst Transfer Polymerization (KCTP) of 2-bromo-5-chloromagnesio-3-alkylthiophene. Exposure of the initiator layers to monomer solutions leads to selective chain-growth polycondensation of the monomers from the surface, resulting into P3AT brushes in a very economical way. The grafting process was investigated in detail and the structure of the resulting composite films was elucidated using several methods. The obtained data suggests that the grafting process occurs not only at the poly(4-bromstyrene) (PS-Br)/polymerization solution interface, but also deeply inside the swollen PS-Br films, penetrable for the catalyst and for the monomer The grafting process was investigated in detail and the structure of the resulting composite film was elucidated using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Conductive atomic force microscopy (C-AFM). The obtained data suggests that the grafting process occurs not only at the poly(4-bromostyrene), PS-Br/polymerization solution interface, but also deeply inside the swollen PS-Br film, which is penetrable for the catalyst and the monomer. The process results in an interpenetrated PS-Br/P3HT network, in which relatively short poly(3-hexylthiophene), P3HT grafts emanate from long, cross-linked PS-Br chains. A further method investigated during our work was to covalently graft regioirregular P3HT to substrates modified by macromolecular anchors using oxidative polymerization of 3HT with FeCl3. P3HT layers with variable thicknesses from 30 nm up to 200 nm were produced using two steps of polymerization reaction. The P3HT obtained by oxidative polymerization had always an irregular structure, which was a result of the starting monomer being asymmetric, which is undesired for electronic applications. The third method for the production of conductive polymer brushes was to graft regioregular poly(3,3''-dioctyl-[2,2';5',2'']terthiophene) (PDOTT) by electrochemical oxidative polycondensation of symmetrically substituted 3,3''-dioctyl-[2,2';5',2'']terthiophene (DOTT). A modification of the supporting ITO electrode by the self-assembled monolayers (SAMs) of compounds having polymerizable head-groups with properly adjusted oxidative potentials was found to be essential to achieve a covalent attachment of PDOTT chains. The polymer films produced show solvatochromism and electrochromism, as well as the previous two methods. After polymerization, the next step towards building organic electronic devices is applying the methods obtained in nano- and microscale production. Block copolymers constitute an attractive option for such surface-engineering, due to their ability to form a variety of nanoscale ordered phase-separated structures. However, block copolymers containing conjugated blocks are less abundant compared to their non-conjugated counterparts. Additionally, their phase behaviour at surfaces is not always predictable. We demonstrated in this work, how surface structures of non-conductive block copolymers, such as P4VP-b-PS-I, can be converted into (semi)conductive P4VP-b-PS-graft-P3HT chains via a surface-initiated polymerization of P3HT (Kumada Catalyst Transfer Polymerization (KCTP) from reactive surface-grafted block copolymers. This proves that our method is applicable to develop structured brushes of conductive polymers. We believe that it can be further exploited for novel, stimuli-responsive materials, for the construction of sensors, or for building various opto-electronic devices. The methods developed here can in principle be adapted for the preparation of any conductive block copolymers and conductive polymers, including other interesting architectures of conductive polymers, such as block copolymers, cylindrical brushes, star-like polymers, etc. To this end, one needs to synthesize properly-designed and multi-functional Ni-initiators before performing the polycondensation.

The aim of the present work was to screen the main methods for the synthesis of conjugated polymers for their suitability in the preparation of conductive polymer brushes. The main focus was put on the grafting of intrinsically soluble substituted regioregular polyalkylthiophenes because of their excellent optoelectronic properties. The resulting polymer films were characterized and their optoelectrical properties studied. For the first time, a synthesis of conductive polymer brushes on solid substrates using “grafting-from” method was performed. The most important, from my opinion, finding of this work is that regioregular head-to-tail poly-3-alkylthiophenes – benchmark materials for organic electronics - can be now selectively grafted from appropriately-terminated surfaces to produce polymer brushes of otherwise soluble polymers - the architecture earlier accessible only in the case of non-conductive polymers. In particular, we developed a new method to grow P3ATs via Kumada Catalyst Transfer Polymerization (KCTP) of 2-bromo-5-chloromagnesio-3-alkylthiophene. Exposure of the initiator layers to monomer solutions leads to selective chain-growth polycondensation of the monomers from the surface, resulting into P3AT brushes in a very economical way. The grafting process was investigated in detail and the structure of the resulting composite films was elucidated using several methods. The obtained data suggests that the grafting process occurs not only at the poly(4-bromstyrene) (PS-Br)/polymerization solution interface, but also deeply inside the swollen PS-Br films, penetrable for the catalyst and for the monomer The grafting process was investigated in detail and the structure of the resulting composite film was elucidated using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Conductive atomic force microscopy (C-AFM). The obtained data suggests that the grafting process occurs not only at the poly(4-bromostyrene), PS-Br/polymerization solution interface, but also deeply inside the swollen PS-Br film, which is penetrable for the catalyst and the monomer. The process results in an interpenetrated PS-Br/P3HT network, in which relatively short poly(3-hexylthiophene), P3HT grafts emanate from long, cross-linked PS-Br chains. A further method investigated during our work was to covalently graft regioirregular P3HT to substrates modified by macromolecular anchors using oxidative polymerization of 3HT with FeCl3. P3HT layers with variable thicknesses from 30 nm up to 200 nm were produced using two steps of polymerization reaction. The P3HT obtained by oxidative polymerization had always an irregular structure, which was a result of the starting monomer being asymmetric, which is undesired for electronic applications. The third method for the production of conductive polymer brushes was to graft regioregular poly(3,3''-dioctyl-[2,2';5',2'']terthiophene) (PDOTT) by electrochemical oxidative polycondensation of symmetrically substituted 3,3''-dioctyl-[2,2';5',2'']terthiophene (DOTT). A modification of the supporting ITO electrode by the self-assembled monolayers (SAMs) of compounds having polymerizable head-groups with properly adjusted oxidative potentials was found to be essential to achieve a covalent attachment of PDOTT chains. The polymer films produced show solvatochromism and electrochromism, as well as the previous two methods. After polymerization, the next step towards building organic electronic devices is applying the methods obtained in nano- and microscale production. Block copolymers constitute an attractive option for such surface-engineering, due to their ability to form a variety of nanoscale ordered phase-separated structures. However, block copolymers containing conjugated blocks are less abundant compared to their non-conjugated counterparts. Additionally, their phase behaviour at surfaces is not always predictable. We demonstrated in this work, how surface structures of non-conductive block copolymers, such as P4VP-b-PS-I, can be converted into (semi)conductive P4VP-b-PS-graft-P3HT chains via a surface-initiated polymerization of P3HT (Kumada Catalyst Transfer Polymerization (KCTP) from reactive surface-grafted block copolymers. This proves that our method is applicable to develop structured brushes of conductive polymers. We believe that it can be further exploited for novel, stimuli-responsive materials, for the construction of sensors, or for building various opto-electronic devices. The methods developed here can in principle be adapted for the preparation of any conductive block copolymers and conductive polymers, including other interesting architectures of conductive polymers, such as block copolymers, cylindrical brushes, star-like polymers, etc. To this end, one needs to synthesize properly-designed and multi-functional Ni-initiators before performing the polycondensation.

碩士
國立虎尾科技大學
機械與機電工程研究所
99
This study was to prepare the Pt-Ru-Ni alloy electrocatalyst for direct methanol fuel cells using Impregnation-reduction with three different reductants. The process of this work was divided into two steps. The first step was to use Enhylene glycol, Formic acid, NaBH4 ehthylene glycol as the reductants respectively to reduce hexachlorplatinic acid into Pt-Ru-Ni nanoparticles. Dispersion stability of the electrocatalyst nanoparticles on multi-walled carbon nanotube was examined respectively by changing the volumetric ratio of Pt-Ru-Ni and evaluated the catalytic activity of the catalysts by cyclic voltammetry (CV). 　　The second was to prepare Membrane and Electrode Assembly(MEA) with the best catalytic activity of the Pt:Ru:Ni(40:20:40) electrocatalyst under I-V characteristic curve for cyclic voltammetry. The catalysts used at the anode and cathode were applied on the membrane by a spraying method, sandwiched with carbon cloth, and hot pressed by changing temperature and pressure. The loading of the alloy electrocatalyst on electodes was 0.387mg/cm2. MEA performance was evaluated using a DMFC single cell with a 12.25 cm2 cross-section area and measured with a potentiometer which recorded the cell potential from the circuit voltage under constant current condition. The result indicated that the performance of MEA prepared by using Formic acid as the reductants was better than using the Enhylene glycol.

碩士
國立臺灣科技大學
化學工程系
107
Low-cost and high-efficient copper oxide, CuO, was used as an electrocatalyst for glycerol electro-oxidation reaction (GEOR). Copper oxide showed the onset potential of 1.25 V vs. RHE for GEOR in pH 13. High-performance liquid chromatography (HPLC), Raman spectroscopy and electrochemical method were used for analysis the products of GEOR. Considering that reactant adsorption, intermediate formation to product desorption are critical, HPLC was used for analyzing the product distribution in the bulk liquid while the in-situ Raman spectroscopy was employed to detect the surface reaction on the solid electrode. Accordingly, dihydroxyacetone (DHA), glycerate, glycolate, oxalate, and formate were detected quantitatively by HPLC. Interestingly, it was found that the product selectivity can be controlled by tuning the properties of the applied potential and solution pH. At the lower applied potential of 1.29 V vs. RHE in pH 13, three-carbon (C3) products have a higher selectivity, i.e. 26% for glycerate and 5% for DHA. However, C-C bond cleavage at higher potential was observed which lead to the formation of vast amount of formate and carbonate. From In-situ Raman spectroscopy, we found that the reaction pathway of GEOR in pH 13 by CuO catalyst started from the oxidation of secondary hydroxyl group, leading to the formation of DHA, and DHA spontaneously transferred to glyceraldehyde (GLAD). GLAD then oxidized to glycerate and continued the higher oxidation degree products. Lowering the pH to pH 9 can slow down the transformation of DHA to GLAD, thus, the ability of selective oxidation of glycerol to DHA (~60% selectivity) can be easily observed.

碩士
國立成功大學
化學工程學系碩博士班
99
A novel electro spinning process has been used to successfully fabricate Titanium dioxide (TiO2) nanofibers. The process not only retains the advantages of the traditional electro spinning process but also improves the yield of the nanofibers. In order to obtain the good quality the TiO2 nanofibers, the polymer binder PMMA was being selected. In the cause of obtaining the inorganic TiO2 nanofibers, the composite fibers must be sintered. However, the higher sinter temperature process will cause the TiO2 change phase from anatase to rutile. Furthermore, different size of the TiO2 nanofibers will be obtained by controlling the experiment parameters. In addition utilize this set of novel electro spinning equipment that can collect the large area nanofibers sheet. Finally, we will employ the TiO2 nanofibers for dye degradation test and appraise the efficiency of the photo catalyst.

碩士
國立屏東科技大學
環境工程與科學系所
99
How to use the photo-catalytic property of titanium dioxide (TiO2) in the air pollution control, for the removal of organic pollutants in environmental has caused much attentions internationally. The TiO2 photocatalyst can change its original absorption of excitation energy in the combination with other atoms into new elements; can make the TiO2 photocatalyst in visible light to be able to have a good efficiency. Until now any TiO2 catalyst must be photo excited by light has become a limitation in engineering applications. Researchers rarely reported that TiO2 can be excited electronically. If we can prepare a electro-conductive TiO2, then we can drive TiO2 photocatalyst by electricity. In this study we have used the sol-gel process to synthesis Bi/TiO2 powder, with the doping of the bismuth (Bi) 1 to 90% successfully. And experimental data result show the combination of Bi into TiO2 can increase conductivity to 98%. Use the Bi/TiO2 conductive catalyst powder to removal methyl bule dye from water solution, data shows that the best doping ratio is 1%, and other one better ratio is 90%, but Bi is very expensive so add less Bi would be more economic for future application.

In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.

碩士
明道大學
材料暨系統工程研究所
96
United Regenerative Fuel Cell (URFC) is a device which combines an electrolyzer and a fuel cell. It has the advantage of low cost, weight, and volume in comparison to Regenerative Fuel Cell (RFC). There are two main operation where the URFC is used. The first is a water electrolysis operation where hydrogen and oxygen are generated. The second is during a fuel cell operation, where hydrogen oxidation and oxygen reduction take place, as a result of this a current is produced. In this study, a new formula to improve the stardard Impregnation-reduction (IR) method is proposed to prepare an nanometer-sized Iridium catalyst and a Platinum/Iridium catalyst particle layer on the surface of a Nafion®membrane. A novel Platinum/Iridium catalyst structure on the surface of a Nafion®membrane is expected to improve oxidation activity for the oxygen electrode in the URFC. In addition, the IR process can produce a good binding for both the Nafion®membrane and the catalyst used, with the result of a more stable URFC is obtained. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Electron Probe X-ray Micro-Analysis (EPMA), X-ray Photoelectron Spectrometer (XPS), and Transmission Electron Microscope (TEM) were used to analyse the microstructure, phase, amount, particle size of the resulted catalyst, the deepness and thickness of catalyst on the PEM surface as well as the ratio of obtained alloy. Fourier-Transform Infrared Spectrometer (FTIR) was adopted to ensure the sample did not have any remaining alcohols. A potentialstat was used to test the water oxidation ability of the resulted catalyst. The results show that some alcohol was added during the impregnation process to let the IrCl62- become more positive to ion-exchange with the proton in PEM. Furthermore, the effective deposition of Ir particle on the surface of PEM required the reduction reaction temperature up to 80℃ and the pH of the solution from 2 to 3 during the reduction process. The resulting catalyst thickness is controlled by the amounts of precursor ion implants in the PEM, the amount of alcohol, the reduction time and the pH of solution. In order to get a higher oxidation performance for the oxygen electrode, we used a novel method to dope Ir in Pt layer. The atomic ratio of Pt over Ir is 9:1 with the resulting thickness of 1.5μm. The oxidation potentail of the obtained Pt/Ir is higher than that of Pt catalyst with 0.11V. Based on this criterion, the oxidation abilty of Pt/Ir catalyst is worse then that of pure Pt catalyst.

Ceria based materials have attracted a great deal of interest particularly in area of UV shielding, oxide ion conductivity, solid state electrolyte for fuel cells, automotive exhaust catalysis, water gas shift (WGS) reaction catalysis and also in thermo-chemical water splitting cycles to generate hydrogen. Therefore great deal of efforts was devoted to synthesize nanocrystalline ceria and related materials with different shape and sizes. For example, hierarchically mesostructured doped CeO2 showed potential photvoltic response for solar cell applications. Substitution of lower valent metal ions (Ca2+, Gd3+, Tb3+, Sm3+) in CeO2 enhances oxide ion conductivity for solid oxide fuel cell applications. Eventhough ZrO2 is a nonreducible oxide, CeO2-ZrO2 solid solution has attracted a lot of attention in exhaust catalysis because it exhibited high oxygen storage capacity (OSC). Noble metal ion (M = Pt4+/2+, Au3+, Rh3+, Pd2+ and Ag+) substituted CeO2 (Ce1-xMxO2-δ and Ti1-xMxO2-δ, x = 0.01-0.03) prepared by solution combustion method have shown much higher three-way catalytic property compared same amount of noble metal impregnated to CeO2. Ionically substituted Pt and Au in CeO2 also showed high WGS activity. CeO2-MOx (M= Mn, Fe, Cu, Ni) mixed oxides have shown high activity for hydrogen generation by thermal splitting of water. In chapter 1, we have discussed recent developments on various synthesis strategies of ceria based materials for specific catalytic application. In this thesis, we have explored new route to synthesize Ce1-xMxO2-δ and Ti1-xMxO2-δ (M = transition metal, noble metal) nanocrystallites. Specifically we have addressed the effect of reducible metal ion substitution on the OSC of CeO2 for auto exhaust treatment, hydrogen generation and electro-chemical applications. Controlled synthesis of CeO2 and Ce1-xMxO2-δ (M = Zr, Ti, Y, Pr and Fe) nanocrystallites by hydrothermal method is presented in Chapter 2. The method is based on complexation of metal ion by diethylenetriamine (DETA) or melamine and the simultaneous hydrolysis of metal ion complexes in hydrothermal condition. Size of the crystallites can be controlled by varying the time and temperature of the reaction. 15% Fe3+ ion substituted CeO2 (Ce0.85Fe0.15O2-δ) nanocrystallites have shown higher oxygen storage capacity than Ce0.5Zr0.5O2 at lower temperature. A brief description of material characterization techniques such as powder X-ray diffraction (XRD) and Rietveld refinement of structure, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) is presented. The home-built hydrogen uptake measurement system for OSC study and temperature programmed catalytic reaction system with a quadrupole mass spectrometer and an on-line gas-chromatograph for gas analysis is also described in this chapter. In chapter 3, hydrothermal synthesis of Ce1-xCrxO2+δ (0≤x≤1/3) nanocrystallites is presented. Up to 33% Cr ion substitution in CeO2 could be achieved only by the complexation of Ce(NH4)2(NO3)6 and CrO3 with DETA and simultaneous hydrolysis of the complexes in hydrothermal condition at 200 oC. Powder XRD, XPS and TEM studies confirm that the compound crystallizes in cubic fluorite structure where Ce exist in +4 oxidation state and Cr exist in 4+ and +6 (mixed valance) oxidation states in the ratio of 2: 1. Composition x = 0.33 (Ce2/3Cr1/3O2+δ) showed higher OSC (0.33 mol of [O]) than the maximum OSC observed for CeO2-ZrO2 solid solutions. Formation and higher OSC of Ce2/3Cr1/3O2+δ is attributed to interaction of Ce4+/3+ and Cr3+/4+/6+ redox couples in fluorite structure. The material shows oxygen evolution at ~400 oC in air and hence it is a true oxygen storage material. Oxygen evolution property of Ce0.67Cr0.33O2.11 and subsequent generation of hydrogen by thermal splitting of water is presented in chapter 4. Among the ceria based oxides, Ce0.67Cr0.33O2.11 being the only compound like UO2+δ to have excess oxygen possessing fluorite structure, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) by heating the material under N2 flow at relatively low temperature (465 oC) directly and almost stoichiometric amount of H2 (0.152 M/Mol of compound) is generated at much lower temperature (65 oC) by thermosplitting of water. The reversible nature of oxygen release and intake of this material is attributed to its fluorite structure and internal coupling between the Ce4+/Ce3+ and Cr4+/6+/Cr3+ redox couples. In chapter 5, we present the hydrothermal synthesis and three-way catalytic activity of Ce1-xRuxO2-δ (0≤x≤0.1) nanocrystallites. Powder XRD, Rietveld refinement, TEM and XPS reveals that the compounds crystallized in fluorite structure where Ru exist in +4 state and Ce in mixed valent (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen and Ce0.9Ru0.1O2-δ can reversibly releases 0.42[O]/mol of compound, which is higher than maximum OSC of 0.22 [O]/mol of compound observed for Ce0.50Zr0.50O2. Utilization of higher OSC of Ce1-xRuxO2-δ (x = 0.05 and 0.10) is also shown by low temperature CO oxidation with these catalysts, both in presence/absence of feed oxygen. Ru4+ ion act as active centre for reducing molecules (CO, hydrocarbon ‘HC’) and oxide ion vacancy acts as an active centre for O2 and NOx in this compound. Ce1-xRuxO2-δ not only act as a high oxygen storage material but it also shows high activity towards CO, hydrocarbon ‘HC’ oxidation and NO reduction by CO at low temperature with high N2 selectivity for 3-way catalysis. Study of water gas shift reaction over Ce0.95Ru0.05O2-δ catalyst is presented in chapter 6. The catalyst showed very high WGS activity in terms of high conversion rate (20.5 μmol.g-1.s-1 at 275 oC) and low activation energy (~50.6 kcal/mol). The reason for this seems to be high adsorption propensity of CO on Ru4+ ion and easy extraction of oxygen from lattice to form CO2. This step creates oxide ion vacancy in the catalyst lattice and H2O can adsorb on lattice sites oxygen vacancy and regenerate the lattice by releasing H2. Even in presence of externally fed CO2 and H2, complete conversion of CO to CO2 was observed with 100 % H2 selectivity with Ce0.95Ru0.05O2-δcatalyst in the temperature range of 305-385 oC and no trace of methane formation was observed in this temperature range. Catalyst does not deactivate in long duration on/off WGS reaction cycle because sintering of noble metal or active sites is avoided in this catalyst as Ru4+ ion is substituted in CeO2 lattice. Due to highly acidic nature of Ru4+ ion, surface carbonated formation is prohibited. In chapter 7, synthesis of Ce1-xFexO2-δ (0≤x≤0.45) and Ce0.65Fe0.33Pd0.02O2-δnanocrystallites is presented by sonochemical method. Powder XRD, XPS and TEM studies confirm that the compounds of ~4 nm sizes is crystallized in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and Ce0.67Fe0.33O1.835 reversibly releases 0.31[O] up to 600 oC which is higher or comparable to the maximum OSC observed for CeO2-ZrO2 based solid solutions. Due to internal interaction of Pd2+/0(0.89 V), Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V) redox couples, Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as highly active catalyst for CO oxidation and WGS reaction. Activation energy for CO oxidation with O2 over Ce0.65Fe0.33Pd0.02O1.815 is found as low as 38 kJ/mol. CO conversion to CO2 is 100% H2 specific in WGS reaction with these catalysts. Conversion rate was found as high 27.2 μmol.g-1.s-1 and activation energy was found 46.4 kJ/mol for Ce0.65Fe0.33Pd0.02O1.815. Only 1-3% Pt, Pd ion can be substituted in CeO2 is by the solution combustion method. We show that even up to 10% of Pt and Pd ion can be substituted in CeO2 by sonication method. In chapter 8, we present the sonochemical synthesis redox property and methanol electro-oxidation activity of hierarchical Ce1-xMxO2-δ (M = Pt and Pd, 0≤x≤0.1) nanocrystallites. Powder XRD, TEM, SEM and XPS study confirms that hierarchical structure compound crystallize in fluorite structure. Pt exists in +4 state and Ce in mixed valent (+3, +4) state in Ce1-xPtxO2-δ and Pd exist in +2 state and Ce in mixed valent (+3, +4) state in Ce1-xPdxO2-δ. Substitution of Pt and Pd ion in CeO2 activated the lattice oxygen. Hydrogen absorption study show higher H/Pt ratio ~8.1 and H/Pd ratio ~4.2 in respective oxides. Reversible nature of higher oxygen storage capacity or higher H/P, H/Pd ratio is due to interaction of redox couples of Pt4+/2+(0.91V), Pt2+/0(1.18V), Pd2+/0(0.92V) and Ce4+/3+(1.61V). Due to participation of lattice oxygen, Ce0.95Pt0.05O1.95 and Ce0.95Pd0.05O1.90 have shown higher electro-oxidation of methanol compared to same moles of Pt in 5%Pt/C. In chapter 9, we present sonochemical synthesis of Ti1-xPtxO2 (0≤x≤0.1) nanocrystallites: a new high capacity anode material for rechargeable Li ion battery. Continuing our interest in synthesis of nanomaterials, we thought if we can extend the same sonochemical method to synthesize metal ion doped TiO2. Doping of TiO2 with a suitable metal ion where dopant redox potential couples with that of titanium (Ti4+) and act as catalyst for additional reduction of Ti4+ to Ti2+ (Ti4+ →Ti3+→Ti2+) is envisaged here to enhance lithium storage even higher than one Li/TiO2. 10 atom % Pt ion substituted TiO2, Ti0.9Pt0.1O2 nanocrystallites of ~4 nm size was synthesized by sonochemical method using diethylenetriamine (DETA) as complexing agent. Powder XRD, Rietveld refinement, TEM and XPS studies reveal that Ti0.9Pt0.1O2 nanocrystallites crystallize in anatase structure and both Ti and Pt are in 4+ oxidation state. Due to Pt4+ ion substitution in TiO2, reducibility of TiO2 was enhanced and Ti4+ was reduced up to Ti2+ state via coupling of Pt states (Pt4+/Pt2+/Pt0) with Ti states (Ti4+/Ti3+/Ti2+). Galvanostatic cycling of Ti0.9Pt0.1O2 against lithium showed very high capacity of 430 mAhg-1 or exchange of ~1.5Li/Ti0.9Pt0.1O2 which is much higher than the highest capacity of 305 mAhg-1 or insertion of ~0.9Li/TiO2 achieved for TiO2(B) nanowires. In chapter 10, we present the conclusions and critical review on the study of transition metal and noble metal ion substituted CeO2 and TiO2.

Il processo di riduzione dell'anidride carbonica (CO2) ha suscitato negli ultimi anni grande attenzione nella comunità scientifica. Lo sviluppo di materiali e sistemi in grado di convertire H2O e CO2 in prodotti ad alto valore utilizzando energia rinnovabile e pulita, rappresenta una sfida particolarmente attraente per il prossimo futuro. In questo contesto, lo scopo del presente lavoro di Dottorato è stato quello di valutare diversi approcci, tra cui quelli foto- ed elettrocatalitici, per convertire la CO2 in sostanze chimiche e combustibili a più alto valore aggiunto. L'attività di ricerca ha riguardato sia la sintesi dei materiali catalitici utilizzati per la preparazione/ assemblaggio degli elettrodi sia la progettazione e ingegnerizzazione dei dispositivi elettrochimici. La maggior parte delle attività sono state svolte presso il laboratorio CASPE/INSTM (Laboratorio di Catalisi per la Produzione Sostenibile e l'Energia) dell'Università degli Studi di Messina. Durante il secondo anno, un mese è stato trascorso presso l'Institut Català d'Investigació Química (ICIQ Tarragona, Spagna) e due mesi presso l'Istituto di Chimica e Bioingegneria (ETH Zurigo, Svizzera) nell'ambito del Progetto H2020 A-LEAF e del Progetto di Ricerca e Mobilità ARCADIA. La tesi è organizzata in sei capitoli, più le conclusioni. Il capitolo 1 si concentra sulle questioni ambientali derivanti dall’accumulo della CO2, le implicazioni generali e le conseguenti opinioni e strategie adottate dalla comunità scientifica a lungo termine per affrontare queste problematiche, con riguardo alle principali strategie da attuare quali la cattura e stoccaggio del carbonio (CCS) e i vari metodi fotochimici, biochimici e foto ed elettrocatalitici. I capitoli 2 e 3 riguardano le basi teoriche dei metodi di riduzione foto ed elettrochimici della CO2, e comprendono lo stato dell'arte dei principali elettrodi foto- ed elettro-catalitici utilizzati fino ad ora e gli aspetti ingegneristici della progettazione del reattore. In particolare vengono discussi i dispositivi fotoelettrochimici e fotovoltaici più promettenti, con particolare attenzione alle strategie avanzate riguardanti l'accoppiamento di questi sistemi con diverse configurazioni e utilizzando diversi materiali avanzati, per ottenere prestazioni catalitiche più elevate. I capitoli 4 e 5 illustrano i risultati sperimentali ottenuti con gli approcci foto- ed elettrocatalitici di riduzione della CO2. Viene presentato lo stato dell’arte per questi due diversi approcci, insieme allo scopo specifico di ogni capitolo, evidenziandone in particolare le differenze ma anche i molti punti comuni in termini di meccanismo di reazione e cinetica. I catalizzatori utilizzati per l'indagine sperimentale sono materiali nanostrutturati a base di CuxO, preparati con diverse tecniche, come metodi di precipitazione, solvo-termali ed elettrodeposizione, che sono stati depositati su substrati metallici, ossidi metallici o a base di carbonio. In particolare, l'elettrodeposizione è un metodo molto versatile che permette una deposizione controllata diretta di Cu2O modulando alcuni parametri durante la sintesi, come il tempo di deposizione, il pH e il tipo di elettrolita. La maggior parte dello studio si è concentrata sul semiconduttore ossido rameoso (Cu2O), per le sue caratteristiche interessanti: si tratta di un materiale terrestre abbondante, non tossico, che possiede un band gap di circa 2.2 eV come materiale in bulk. Viene ampiamente utilizzato per sensibilizzatori di celle solari, sensori (vedi Capitolo 6) e nella fotocatalisi della CO2, in particolare per la formazione di CO e CH4. Il capitolo 4 di questo lavoro mostra che, grazie a un nuovo concetto di reattore foto (elettro) catalitico a flusso di gas, la selettività del processo può essere spostata verso prodotti a base di carbonio più interessanti, con la formazione di legami C-C. Questo nuovo dispositivo costruito nei nostri laboratori utilizza nanomembrane funzionalizzate con il rame, basate su una disposizione di nanotubi allineati di TiO2 (preparati mediante ossidazione anodica controllata) cresciuti su un substrato metallico microforato, che agiscono sia come collettore di elettroni sia come supporto meccanico per fornire la necessaria robustezza; questi poi sono stati funzionalizzati con CuxO mediante elettrodeposizione. Questo concetto è molto diverso dagli approcci fotocatalitici CO2 convenzionali. Per via delle caratteristiche e delle condizioni peculiari del nuovo fotoreattore (che lavora sotto un flusso di vapore saturato con CO2 gassosa che attraversa la nanomembrana fotocatalitica), è possibile evidenziare per la prima volta la conversione altamente selettiva della CO2 ad acidi carbossilici C1-C2 (formico, acetico e ossalico) senza formazione di H2, CO, CH4 o altri idrocarburi. L'ossido di rame introduce una via di reazione aggiuntiva alla formazione degli alcoli C1-C3 (metanolo, etanolo e isopropanolo) o ai prodotti derivati (formiato di metile). Le migliori prestazioni sono state ottenute quando le nanoparticelle di Cu2O (tipo p) sono depositate su nanotubi di TiO2 di tipo n, grazie alla creazione di una eterogiunzione di tipo p-n che migliora la raccolta della luce visibile, fornendo una resa quantica apparente (rapporto tra elettroni reagiti e fotoni assorbiti) con illuminazione solare del 21% circa. L'efficienza faradica su questo fotocatalizzatore è stata di circa il 42% a metanolo e il 44% ad acido acetico. Tra i campioni testati, in generale si osserva un'efficienza faradica fino al 47% a metanolo o fino al 73% ad acido acetico. La rilevanza di questi risultati sul meccanismo della fotoriduzione della CO2 è stata anche discussa nel Capitolo 4. Il capitolo 5 si concentra invece sulla riduzione elettrocatalitica della CO2. In questa parte del lavoro, CuxO è stato impiegato come ossido puro (a diversi stati di ossidazione, I e II) o drogato con altri elementi, come S e In (CuSx e Cu-In), per la progettazione di elettrodi compositi in grado di indirizzare la selettività del processo verso l'acido formico o il monossido di carbonio, rispettivamente, attraverso la modifica dell'energia di legame degli intermedi di reazione con i siti attivi catalitici. Nello specifico, le attività di ricerca hanno riguardato preliminarmente l'ottimizzazione delle condizioni operative in termini di configurazione del reattore, pH catodico, potenziale applicato all'elettrodo di lavoro (nel range indagato da -0.4 V a -1.0 V vs. RHE), flusso di ingresso della CO2 e tipo di membrana (cationica, anionica o bipolare). È stato definito un protocollo preciso per l'esecuzione di ogni test elettrochimico, che va dalla voltammetria ciclica e determinazione della capacità alle fasi di cronoamperometria, quest'ultima comprensiva della determinazione dei prodotti di riduzione della CO2. Il test con CuxO puro depositato su uno strato di gas-diffusion-layer (GDL) in presenza di un elettrolita liquido (soluzione acquosa KHCO3 0,1 M) ha mostrato che i) il carico ottimale del catalizzatore su GDL era 10 mg cm-2; ii) la migliore produttività ed efficienza faradica (FE) per acido formico e monossido di carbonio è stata ottenuta a -0,6 V vs. RHE (12.8 µmol h-1 e 5.5%, rispettivamente); il campione CuO/GDL si è comportato meglio di Cu2O/GDL, con un aumento delle prestazioni catalitiche (FE=12.6%). I comportamenti elettrochimici di entrambi gli elettrocatalizzatori sono stati studiati anche attraverso la spettroscopia di impedenza elettrochimica (EIS), evidenziando una resistenza al trasferimento di carica inferiore per CuO/GDL (6.5 Ω) rispetto a Cu2O/GDL (39.5 Ω). L'attività elettrocatalitica è aumentata notevolmente quando venivano usati elettrodi avanzati come CuSx e Cu-In, fornendo rispettivamente una FE ad acido formico del 58.5% e una FE% al monossido di carbonio del 55.6%. Diverse configurazioni delle celle sono state studiate utilizzando questi catalizzatori, a seconda dei percorsi del flusso di gas all'interno della cella nei tre diversi compartimenti (una camera gassosa, un compartimento liquido per il catolita ed un compartimento liquido per l'anolita). La migliore configurazione in termini di elevata FE e bassa formazione di H2 (mediante riduzione protonica come reazione collaterale) si è ottenuta separando l’evoluzione dei prodotti gassosi da quelli liquidi, ovvero raccogliendo i prodotti gassosi direttamente dall'uscita della camera gassosa, superando così le problematiche legate alla bassa solubilità della CO2 in acqua. Sono stati valutati anche i comportamenti di molte membrane selettive commerciali, cationiche (protoniche), anioniche e bipolari, anche rinforzate con teflon. I risultati hanno mostrato che la membrana protonica rinforzata con Teflon Nafion N324 e la membrana bipolare Fumasep FBM-PK hanno fornito la migliore attività; tuttavia, il Nafion rinforzato ha permesso di minimizzare meglio l'osmosi dell'elettrolita e il cross-over dei prodotti di riduzione, evitandone l'ossidazione sul lato anodico. Infine, il Capitolo 6 si concentra sulle strategie per la rilevazione del glucosio nei processi di biofermentazione e in particolare sui metodi amperometrici basati sull'utilizzo di sensori di glucosio non enzimatici. Il processo di biofermentazione più importante è la fermentazione alcolica, che consiste nella produzione di CO2 ed etanolo a partire da diversi substrati zuccherini come glucosio, saccarosio e fruttosio. Le applicazioni industriali oggi mirano a diminuire la dipendenza del petrolio greggio producendo bioetanolo, che viene miscelato con la benzina. In questo contesto, sono stati sviluppati dei sensori a base di Cu2O a forma di nanocubi, con particelle di dimensioni diverse, depositato su supporti commerciali di tipo “screen-printed carbon electrode” (SPCE). Le prestazioni di questi SPCE modificati con Cu sono state valutate in termini di selettività e sensibilità del glucosio mediante analisi di voltammetria ciclica e cronoamperometria e misure di impedenza. Gli elettrodi sviluppati hanno mostrato una buona sensibilità (1040µA/mM cm-2) e selettività nei confronti del rilevamento del glucosio con una risposta ad alto range lineare, senza interferenze da parte di altri substrati, suggerendo che i SPCE modificati con Cu2O potrebbe essere un modo semplice per fabbricare sensori economici e affidabili per monitorare il glucosio nei processi di biofermentazione.
The process of carbon dioxide (CO2) reduction has attracted a great attention in the scientific community in the last years. The development of materials and systems capable to convert H2O and CO2 into valuable products by using renewable and clean energy represents an attractive challenge for the next future. In this context, the aim of the present PhD work is to explore different routes by photo- and electrocatalytic approaches to convert CO2 into value-added chemicals and fuels. The research activity concerned both the synthesis of the catalytic materials used for the preparation/assembling of the electrodes and the design and engineering of the electrochemical devices. Most of the activities were carried out at the laboratory CASPE/INSTM (Laboratory of Catalysis for Sustainable Production and Energy) of the University of Messina. Moreover, during the second year, one month was spent at the Institut Català d'Investigació Química (ICIQ Tarragona, Spain) and two months at the Institute for Chemical and Bioengineering (ETH Zürich, Switzerland) in the framework of H2020 A-LEAF Project and Research and Mobility ARCADIA Project. The thesis is organized in six chapters, plus the conclusions. Chapter 1 focuses on CO2 environmental issues, general implications and consequent opinions and strategies adopted by the scientific community in a long-term period to address these problems, with regard to the main common carbon capture and storage (CCS) strategies and photochemical, biochemical, photo- and electrocatalytic routes. Chapters 2 and 3 concern the theoretical basis on photo- and electro-chemical CO2 reduction routes, including the state-of-the-art of the main photo- and electro-catalytic electrodes used so far and the engineering aspects of reactor design. In particular, the most promising photo-electro-chemical and photovoltaic devices are discussed, with emphasis on the advanced strategies concerning the coupling of these systems with different configurations and using different advanced materials, to achieve higher catalytic performances. Chapters 4 and 5 refer to the experimental results obtained by photo- and electro-catalytic approaches. The states of the art for these two different approaches are presented, together with the specific scope of each chapter, especially highlighting their differences but also the many common points in terms of reaction mechanism and kinetics. The catalysts used for the experimental investigation were nanostructured CuxO-based materials, prepared by different techniques, such as precipitation, solvothermal and electrodeposition methods, and then deposited on metallic, metal oxides or carbon-based substrates. Particularly, electrodeposition was a very versatile method allowing a direct controlled deposition of Cu2O by modulating some parameters during the synthesis, such as time deposition, pH and type of electrolyte. Most of the study was focused on cuprous oxide (Cu2O) semiconductor, for its interesting characteristics: it is an earth abundant material, non-toxic, showing a band gap of around 2.2 eV as bulk material. It has been widely used for solar cell sensitizers, sensors (see Chapter 6) and in CO2 photocatalysis, especially for the formation of CO and CH4. Chapter 4 of this work shows that, due to a novel concept of gas flow-through photo(electro)catalytic reactor, the process selectivity can be shifted to more interesting carbon products, involving the formation of C-C bonds. This novel homemade device uses copper-functionalized nanomembranes, based on aligned TiO2 nanotube arrays (prepared by controlled anodic oxidation) grown over a microperforated metallic substrate, acting as an electron collector and to provide the necessary robustness, which are then functionalized with CuxO by electrodeposition. This concept is quite different from the conventional CO2 photocatalytic approaches. Due to the peculiar characteristics and conditions in the novel photoreactor (working under a cross-flow of gaseous CO2 saturated with water crossing through the photocatalytic nanomembrane), it is possible to evidence for the first time the highly selective CO2 conversion to C1-C2 carboxylic acids (formic, acetic and oxalic acids) without formation of H2, CO, CH4 or other hydrocarbons. Copper-oxide introduces an additional reaction pathway to C1-C3 alcohols (methanol, ethanol and isopropanol) or derived products (methyl formate). The best performances were obtained when Cu2O nanoparticles (p-type) are deposited over n-type TiO2 nanotubes, due to the creation of a p-n type heterojunction that improves visible light harvesting, giving an apparent quantum yield (ratio between electrons reacted and photons absorbed) with solar illumination of about 21 %. The Faradaic Efficiency on this photocatalyst was about 42 % to methanol and 44 % to acetic acid. Among the tested samples, Faradaic Efficiency up to 47 % to methanol or up to 73 % to acetic acid are observed. The relevance of these results on the mechanism of CO2 photoreduction was also discussed along Chapter 4. Chapter 5 focuses instead on the electrocatalytic reduction of CO2. In this part of the work, Cu2O was employed as pure oxide (at different oxidation states, I and II) or doped with other elements, such as S and In (CuSx and Cu-In), for the design of composite electrodes able to address the process selectivity towards formic acid or carbon monoxide, respectively, through the modification of binding energy of the reaction intermediates with the catalytic active sites. Specifically, the research activities concerned preliminarily the optimization of the operating conditions in terms of reactor configuration, cathodic pH, applied potential at the working electrode (in the investigated range from -0.4 V to -1.0 V vs. RHE), CO2 inlet flow and type of membrane (i.e. cationic, anionic or bipolar). A precise protocol was defined for carrying out each electrochemical test, ranging from cyclic voltammetry and capacitance determination to chronoamperometry steps, the latter including the determination of CO2 reduction products. Testing with pure CuxO deposited on a carbon gas diffusion layer (GDL) in presence of a liquid electrolyte (0.1 M KHCO3 aqueous solution) showed that i) the optimal catalyst loading on GDL was 10 mg cm-2; ii) the best productivity and Faradaic efficiency (FE) to formic acid and carbon monoxide was obtained at -0.6 V vs. RHE (12.8 mol h-1 and 5.5%, respectively); CuO/GDL behaved better than Cu2O/GDL, with an increase of catalytic performance (i.e. FE = 12.6 %). The electrochemical behaviours of both the electrocatalysts were also investigated by Electrochemical Impedance Spectroscopy (EIS), evidencing a lower charge transfer resistance for CuO/GDL (6.5 Ω) with respect to Cu2O/GDL (39.5 Ω). The electrocatalytic activity strongly increased when advanced electrodes like CuSx and Cu-In were used, providing a FE to formic acid of 58.5% and a FE % to carbon monoxide of 55.6%, respectively. Different cell configurations were investigated by using these catalysts, depending on the pathways of gas flow within the cell in three different compartments (a gas chamber, a liquid catholyte compartment, a liquid anolyte compartment). The best configuration in terms of maximum FE and minimization of H2 formation (by proton reduction as side reaction) referred to the separation of gas and liquid products, collecting the gas products directly from the outlet of the gas chamber, thus overcoming issues related to the low solubility of CO2 in aqueous solution. The behaviours of many commercial selective membranes were also evaluated, i.e. cationic (protonic), anionic and bipolar, also reinforced with Teflon. Results showed that Teflon reinforced protonic (Nafion N324) and bipolar (Fumasep FBM-PK) membranes provided the best activity; however, the reinforced Nafion allowed better to minimize osmosis of electrolyte and cross-over of the reduction products, avoiding their oxidation at the anode side. Finally, Chapter 6 focuses on strategies for the glucose detection in biofermentation processes and particularly on the amperometric methods based on the use of non-enzymatic glucose sensors. The most important biofermentation process is the alcoholic fermentation, which consists in the production of CO2 and ethanol starting from several sugar substrates like glucose, sucrose and fructose. Industrial applications today are aimed to decrease the dependence of crude oil producing bioethanol, which is blended with the gasoline. In this context, Cu2O nanocubes deposited on commercial screen printed carbon electrodes (SPCEs) with different particles size were developed as sensors. The performances of these Cu-modified SPCEs were evaluated in terms of glucose selectivity and sensitivity by cyclic voltammetry and chronoamperometry analysis and impedance resistance measurements. The developed electrodes showed a good sensitivity (1040µA/mM cm-2) and selectivity towards the glucose detection with a high linear range response, without interference by other substrates, suggesting that the SPCE modification with Cu2O could be a simple way to fabricate inexpensive and reliable sensors to monitor glucose in bio-fermentation processes.