Environmental pollution and health problems created by fossil fuels have led to the development of alternative energies such as solar and wind energies, hydroelectric power, and green hydrogen. The use of biohybrid materials in the development of this type of alternative energies is recent. Biohybrid materials are a unique type of advanced materials that have a biological component that can be a biomolecule or a whole cell and an abiotic or non-biological component that can be a ceramic, a synthetic polymer, or a metal, among others. They have applications in different fields that range from construction (such as bioconcrete) to catalysis (such as artificial enzymes). There are examples in the literature in which bacteria are hybridized with reduced graphene oxide or manganese oxide to catalyze the oxygen evolution of the electrochemical water splitting reaction that produces green hydrogen. The focus of this dissertation is to synthesize efficient biohybrid catalysts following a whole cell approach using electroactive bacteria as the biological component and metallic precursors that form particles ranging from single atoms, nanoclusters, and nanoparticles as the abiotic component. The Fe molecule that is part of the heme group of C-type cytochromes in the outer membrane of Geobacter sulfurreducens acted as the reduction center that allowed the synthesis and hybridization of the metals with the bacteria. Single atom metal catalyst of Ir, Pt, Ru, Cu, and Pd were synthesized and demonstrated a bifunctional catalytic activity towards the hydrogen evolution reaction and the oxygen evolution reaction. Ni single atoms were also synthesized with excellent activity in the water splitting reactions making this biohybrid catalyst very efficient but also green, as Ni is an abundant and cheap metal. Pd nanoclusters with size-control were synthesized by controlling the metal concentration, dosing, and incubation times and were tested in the electrochemical water splitting. Overall, the findings of these studies provide new knowledge on the field of biohybrid materials by contributing with novel methodologies for the synthesis of these materials and the application in the green hydrogen production with high efficiencies.

In the area of sustainable energy, a major focus has been to design robust electrocatalysts that can be used for the electrolysis of water to produce H2 with a sustainable energy source such as solar. Sustainable H2 generation would potentially be a prelude to the adoption of a hydrogen economy, allowing the phasing out of fossil fuels as a primary fuel source. Toward this end, there is a global research effort to develop electrocatalysts that would facilitate the kinetics of the two half-reactions that make up the water-splitting process: the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). A challenge is to develop active electrocatalysts that are largely composed of earth-abundant elements and show catalytic stability during water splitting at low pH, where the scientific community feels that commercial electrolysis will operate most efficiently. Currently, iridium oxide (IrO2) is being looked at for low pH water splitting because of its stability at low pH, but its relative scarcity (e.g., it is a precious metal) may well make it an unacceptable choice in the long run.In this dissertation, we focus on understanding the scientific issues that will allow the development of earth-abundant catalysts that contain a loading of Ir that is low as possible, while maintaining suitable activity and stability. We began by synthesizing a series of Ir-based OER electrocatalysts by incorporating varying amounts of Ir into 2D layered MnO2 (birnessite, nominally δ-MnO2) and 3D MnO2 (pyrolusite, β-MnO2) phases. The Ir-incorporated δ-MnO2 (Ir/δ-MnO2) electrocatalysts with 16-22 wt% Ir were synthesized by a wet chemical method using a ligating agent, such that Ir was present on the surface and partially intercalated into the interlayer of δ-MnO2. Ir-incorporated β-MnO2 (Ir/β-MnO2) was prepared for the first time via a thermally induced phase transition of Ir/δ-MnO2. This phase transition of δ-MnO2 to β-MnO2 was facilitated by the presence of Ir in the structure, as both Ir in IrO2 and Mn in β-MnO2 could adopt the more thermodynamically stable rutile structure. Extended X-ray absorption fine structure (EXAFS) of Ir/β-MnO2 showed that the catalyst consisted of Ir substituted into the crystalline β-MnO2 lattice, additionally, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM) imaging revealed micron-sized particles with non-uniform distribution of Ir in the MnO2. In 0.5 M H2SO4 electrolyte, 22 wt% Ir/β-MnO2 (60 〖μg〗_Ir cm_geo^(-2)) resulted in the most active catalyst with an η@10 (overpotential at 10 mA cm_geo^(-2)) of 337 mV and stability of 6 h. This electrocatalyst outperformed a commercial IrO2 on a per Ir mass basis. EXAFS, HAADF-STEM and X-ray absorption near edge structure (XANES) showed that 22 wt% Ir/β-MnO2 had a strained structure containing ~41% Mn3+, an OER active species, along with a modified Ir bonding due to the presence of Ir-O-Ir and Ir-O-Mn. Density functional theory (DFT) computation has demonstrated that this modified bonding environment in Ir/β-MnO2 has contributed to enhancing the thermodynamic stability of the structure. Furthermore, the literature suggests that the presence of Ir-O-Mn bond can favorably tune the d-orbital energy of Ir, enabling superior performance in the Ir/β-MnO2 compared to IrO2. The thesis research also included the investigation of the activity and stability of Ir/β-MnO2 that was synthesized via a novel strategy. The resulting material maintained a homogeneous distribution of Ir in the MnO2 lattice and exhibited excellent OER activity and stability. A surfactant-assisted (SA) synthesis method was carried out to achieve uniform doping of 22-28 wt.% Ir in 3D MnO2 (ramsdellite, R-MnO2). Upon annealing, Ir/R-MnO2 transformed to Ir/β-MnO2 (SA), composed of nano-sized particles. Electrochemical studies in 0.5 M H2SO4 showed that, Ir/β-MnO2 (SA) with 75.6 〖µg〗_Ir cm_geo^(-2) exhibited an η of 327 mV and exceptional stability (up to 50 h). At similar Ir mass loadings, the Ir/β-MnO2 (SA) outperformed Ir/R-MnO2 (SA) and commercial IrO2. This enhanced activity and stability was attributed to a thermodynamically stable structure composed of uniform distribution of Ir (Ir-O-Mn) in the MnO2 lattice. Overall, the research results presented in this dissertation contributed towards designing a novel class of Ir-MnO2 catalysts, which potentially will point the scientific community in the right direction for designing future noble metal-incorporated earth-abundant metal oxides for electrocatalytic energy conversion reactions. / Chemistry

No description available.

Cette thèse porte sur l’étude et le développement d’électrocatalyseurs à base d’iridium pour la réaction de dégagement de dioxygène (OER) dans les électrolyseurs à membrane échangeuse de protons. En raison de la dégradation marquée des électrocatalyseurs en conditions OER, nous nous sommes particulièrement intéressés à la recherche d’un compromis optimal entre activité catalytique et stabilité. Différents électrocatalyseurs (supportés sur noir de carbone, supportés sur oxydes métalliques dopés et non-supportés) ont été synthétisés et caractérisés par des méthodes électrochimiques et physico-chimiques, notamment par spectroscopie photoélectronique X, microscopie électronique en transmission à localisation identique et spectrométrie de masse à plasma à couplage inductif. Les électrocatalyseurs supportés sont les moins stables en conditions OER, notamment du fait de l’agglomération, la coalescence, la dissolution et le détachement des nanoparticules d’oxyde d’iridium. Ces deux derniers mécanismes de dégradation sont exacerbés par la corrosion des supports carbonés et la dissolution des éléments composant les supports oxydes métalliques dopés. Les électrocatalyseurs non-supportés offrent ainsi le meilleur compromis entre activité et stabilité. Les degrés d’oxydation Ir(III) et Ir(V) ont été identifiés comme les plus actifs pour l’OER en électrolyte acide tandis que l’oxyde Ir(IV) est le plus stable, l’espèce la moins stable étant l’iridium métallique Ir(0). La dégradation des couches catalytiques en cellule d’électrolyse PEM ne semble impacter que très peu les performances globales d’électrolyse par rapport à la dégradation des collecteurs de courant. / This thesis focuses on the study and the development of iridium-based electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers. This work investigates in particular electrocatalyst degradation phenomena and aims at reaching an optimal OER activity-stability ratio. Various electrocatalysts (supported on high-surface area carbon, supported on doped-metal oxides and unsupported) have been synthetized and characterized by electrochemical and physico-chemical methods such as X-ray photoelectron spectroscopy, identical-location transmission electron microscopy and inductively coupled plasma mass spectrometry. Supported electrocatalysts feature stability limitations in OER conditions as revealed by agglomeration, coalescence, dissolution, and detachment of iridium oxide nanoparticles, these last two degradation mechanisms being amplified by corrosion of the carbon supports and dissolution of the elements composing the doped metal oxide supports. Unsupported electrocatalysts currently represent the best compromise between OER activity and stability. Ir(III) and Ir(V) oxides were shown to be the most active towards the OER while Ir(IV) oxide is the most stable, the least stable species being metallic iridium Ir(0). In real PEM water electrolyzers, the global electrolysis performance seems to be less impacted by the degradation of catalytic layers than the degradation of current collectors.

We are facing an energy crisis because of the limitation of the fossil fuel and the pollution caused by burning it. Clean energy technologies, such as fuel cells and metal-air batteries, are studied extensively because of this high efficiency and less pollution. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential in the process of energy storage and conversion, and noble metals (e.g. Pt) are needed to catalyze the critical chemical reactions in these devices. Functionalized carbon nanomaterials such as heteroatom-doped and molecule-adsorbed graphene can be used as metal-free catalysts to replace the expensive and scarce platinum-based catalysts for the energy storage and conversion. Traditionally, experimental studies on the catalytic performance of carbon nanomaterials have been conducted extensively, however, there is a lack of computational studies to guide the experiments for rapid search for the best catalysts. In addition, theoretical mechanism and the rational design principle towards ORR and OER also need to be fully understood. In this dissertation, density functional theory calculations are performed to calculate the thermodynamic and electrochemical properties of heteroatom-doped graphene and molecule-adsorbed graphene for ORR and OER. Gibb's free energy, overpotential, charge transfer and edge effect are evaluated. The charge transfer analysis show the positive charges on the graphene surface caused by the heteroatom, hetero-edges and the adsorbed organic molecules play an essential role in improving the electrochemical properties of the carbon nanomaterials. Based on the calculations, design principles are introduced to rationally design and predict the electrochemical properties of doped graphene and molecule-adsorbed graphene as metal-free catalysts for ORR and OER. An intrinsic descriptor is discovered for the first time, which can be used as a materials parameter for rational design of the metal-free catalysts with carbon nanomaterials for energy storage and conversion. The success of the design principle provides a better understanding of the mechanism behind ORR and OER and a screening approach for the best catalyst for energy storage and conversion.

Nesta tese de doutorado foram desenvolvidos e caracterizados nanomateriais eletroativos, explorando estratégias de estabilização e os efeitos sinérgicos em nanomateriais multifuncionais baseados em alfa-hidróxido de níquel, com potencial aplicação nas mais essências e urgentes áreas de atuação científica e tecnológicas, como por exemplo na conversão e armazenamento de energia, e sensores amperométricos. Nesse sentido, foram desenvolvidos nanopartículas (NPs) de alfa-hidróxidos de níquel (α-Ni(OH)2) estabilizados pela formação de nanocompósitos com óxido de grafeno (GO), denominados de α-Ni(OH)2@GO. Analogamente, foram preparados NPs de sais de hidróxido duplo de níquel e cobalto (α- NiCo(OH)2), estabilizados pela incorporação cátions Co2+ na estrutura do α-Ni(OH)2, e o correspondente nanocompósito com óxido de grafeno reduzido (rGO) denominado de α- NiCo(OH)2@rGO. De modo geral, os nanocompósitos exibiram alta capacidade de carga em elevadas densidades de corrente, alta capacidade de retenção de carga e elevada estabilidade como consequência da interação sinergística de seus componentes, com potencial aplicação em dispositivos de armazenamento de energia de alto desempenho, como por exemplo em supercapacitores híbridos. Por outro lado, um dos principais desafios no campo da conversão de energia, concentra-se no desenvolvimento de eletrocatalisadores eficientes e robustos para impulsionar a cinética intrinsecamente lenta da reação de evolução de oxigênio (OER), que envolve etapas de transferência de elétrons acopladas a de prótons. Para isso, foram preparados nanocompósitos ternários baseados em NPs de αNi(OH)2 de diferentes tamanhos, octacarboxiftalocianina de ferro (FeOCPc) e rGO (α-NiFeOCPc@rGO). As NPs de α- Ni@rGO-K maiores e mais cristalinas e seus respectivos nanocompósitos mostraram propriedades eletrocatalíticas superiores para a OER quando comparados com os respectivos derivados de α-Ni(OH)2-Na, indicando a relevância do tamanho do nanocristal de α-Ni(OH)2 na estrutura do nanocompósito e consequente efeitos sinérgicos nas propriedades eletroquímicas e eletrocatalíticas dos nanocompósitos ternários. Além disso, foram desenvolvidos eletrodos modificados com NPs de hidróxido duplo lamelar de NiCe (α-NiCe) como sensores de alta sensibilidade, e de fundamental importância para detecção e quantificação de prednisona, uma droga proibida pelo Comitê Olímpico Internacional (COI). Em resumo, a incorporação de 20% em mols de íons Ce(III/IV) em nanopartículas de α- Ni(OH)2 aumentou a estabilidade deste material na fase alfa, conferindo melhores propriedades eletrocatalíticas responsáveis pela rápida oxidação da prednisona e de seus subprodutos de degradação, permitindo a preparação de sensores amperométricos com elevada sensibilidade e baixo limite de detecção (LOD) em comparação aos eletrodos modificados já reportando na literatura. Em suma, as estratégias no design de nanomateriais foram exploradas com sucesso para gerar novos nanomateriais e nanocompósitos com propriedades eletrocatalíticas e de armazenamento de carga aprimoradas, com potencial de aplicação em sensores e supercapacitores híbridos. / In this doctoral thesis, nanomaterials design strategies were explored in order to improve the stability of alpha-nickel hydroxide nanoparticles while developing synergistic effects, generating multifunctional electrochemically active nanomaterials and nanocomposites with potential application in amperometric sensors and energy conversion and storage devices. In this context, the α-Ni(OH)2 NPs were stabilized by generating double hydroxide salts, by interaction with octacarboxyphthalocyanine molecules and graphene oxide (GO) generating hybrid and nanocomposite materials, for example α-Ni(OH)2@GO. Nickel hydroxide NPs was stabilized by incorporation of Co2+ cation to produce α-NixCoy(OH)2 double hydroxide salts and the corresponding nanocomposite with reduced graphene oxide (rGO) designated - NiCo(OH)2@rGO. In this way, nanocomposites with potential application in high performance energy storage devices such as hybrid supercapacitors were produced, since exhibited large charge capacities at high current densities and great stability as a consequence of the synergistic interaction of their componentes. One of the main challenges in the field of energy conversion, the development of efficient and robust electrocatalysts to boost the intrinsically slow multielectronic multiprotonic transfer kinetics of the oxygen evolution reaction (OER) was also addressed using ternary nanocomposites based on α-Ni(OH)2 NPs, iron octacarboxyphthalocyanine (FeOCPc) and rGO (α-NiFeOCPc@rGO). The more crystalline - Ni@rGO-K NPs and their respective nanocomposites showed superior electrocatalytic properties when compared to the respective α-Ni(OH)2-Na derivatives, indicating the relevance of the α-Ni(OH)2 nanocrystal size and synergistic effects on their electrochemical and electrocatalytic properties. In addition, amperometric sensors based on NiCe layered doublehydroxide NPs (α-NiCe) were developed for determination of prednisone, a drug forbidden by the International Olympic Committee (IOC). The incorporation of 20 m% of Ce3+/4+ ions in α- Ni(OH)2 nanoparticles increased its stability in the alpha phase, conferring improved electrocatalytic properties responsible for the rapid oxidation of prednisone and its degradation byproducts, responsible for the higher sensitivity and lower detection limits (LOD) than similar devices reported in the literature. In short, nanomaterials design strategies were successfully explored to generated new nanomaterials and nanocomposites with enhanced electrocatalytic and charge storage properties with potential application in sensors and hybrid supercapacitors.

O dióxido de manganês (MnO2) é um catalisador eficiente de baixo custo utilizado no cátodo de baterias do tipo metal-ar e células a combustível alcalinas, sendo capaz de promover a redução completa de oxigênio pela rota 4e-. No entanto, o dióxido de manganês é um semicondutor e só pode ser utilizado como material eletródico nos dispositivos mencionados se combinado com algum suporte condutor. O suporte condutor mais utilizado para este fim é o carbono em pó. Entretanto, este material não possui estabilidade suficiente nas condições operacionais das células alcalinas, sendo convertido gradativamente em CO2. Uma das possíveis estratégias para tentar minimizar esta deficiência é incrementar a condutividade eletrônica do óxido puro pela dopagem com alguns cátions metálicos. Sendo assim, este trabalho tem como objetivo geral pesquisar de maneira sistemática o efeito da dopagem de dióxido de manganês com alguns cátions metálicos, como o Bi3+e Ce4+ nas propriedades físico-químicas e eletrocatalíticas deste óxido, visando o uso dos mesmos como em cátodos de baterias recarregáveis do tipo Zn-ar. As análises das características morfológicas dos catalisadores por meio de MEV e TEM mostram que os óxidos de manganês são gerados na forma de nano-bastões de 50 a 100 nm de comprimento. Os óxidos puros e dopados com bismuto e cério apresentam estruturas tetragonais típicas, ocorrendo expansão da célula unitária dos óxidos dopados pela troca de íons manganês pelos correspondentes dopantes na rede cristalina de MnO2. Os resultados eletroquímicos sugerem um aumento de condutividade do óxido dopado que possibilita seu uso sem mistura com carbono. Além disso, observa-se que a RRO é catalisada por um mecanismo que envolve a transferência de 4e- nestes materiais com participação de peróxido como intermediário. O óxido de manganês dopado com Bi apresentou promissor desempenho catalítico para a RDO, o que junto com os demais resultados apresentados para a RRO o qualificou a funcionar como o catalisador bifuncional mais promissor de todos os estudados em baterias do tipo metal-ar. Experimentos realizados em mini baterias do tipo Zn-ar demonstraram a total capacidade do catalisador dopado com bismuto operar como catalisador do eletrodo de ar, resultando num desempenho superior ao de um catalisador convencional de MnO2/C. / Manganese dioxide is at the same time an efficient and low-cost material used as cathode catalyst in the air electrode of metal-air and alkaline fuel cells, capable to promote the complete reduction of oxygen thru the 4e- mechanism. However, manganese dioxide is a semiconductor and can be used as electrodic material in the mentioned devices only combined with a conductor support. High surface area carbon powder is the most commonly used material for such purpose. The problem is that carbon suffers from severe instabilities in the experimental conditions that fuel cells and metal-air batteries operates, being gradually converted into CO2. A possible strategy to overcome or at least minimize the low oxide conductivity is by doping this material with some metallic cations. In this sense, the main purpose of this work was the systematic investigation of the physicochemical and electrocatalytic properties of Bi3+ and Ce4+ doped manganese dioxide materials used as cathode catalysts in the air electrode of alkaline type Zn-air batteries. The morphologic characterization performed SEM and TEM revealed that pure as well cation doped MnO2 are formed as poly dispersed nanorods with 50-100 nm length. Both pure and doped materials presented typical tetragonal structures, although a cell expansion was observed in the doped oxides caused by the exchange of some manganese cations by the doping counter parts. Electrochemical results suggest that a material with increased conductivity results from the doping process, allowing it to operate as air catalyst without the use of a carbon support. Besides, it is observed that the oxygen reduction reaction proceeds thru the 4e- mechanism on the doped oxides involving hydrogen peroxide as intermediate. The Bi doped oxide presented the best performance for the oxygen evolution reaction among all catalysts investigated. This result together with the superior performance for the oxygen reduction reaction presented by this material suggest that Bi doped MnO2 is a potential candidate to operate as an air catalyst of rechargeable alkaline metal-air batteries. Experiments conducted in a mini Zn-air battery using Bi doped MnO2 as air catalyst corroborated this observation.

O dióxido de manganês (MnO2) é um catalisador eficiente de baixo custo utilizado no cátodo de baterias do tipo metal-ar e células a combustível alcalinas, sendo capaz de promover a redução completa de oxigênio pela rota 4e-. No entanto, o dióxido de manganês é um semicondutor e só pode ser utilizado como material eletródico nos dispositivos mencionados se combinado com algum suporte condutor. O suporte condutor mais utilizado para este fim é o carbono em pó. Entretanto, este material não possui estabilidade suficiente nas condições operacionais das células alcalinas, sendo convertido gradativamente em CO2. Uma das possíveis estratégias para tentar minimizar esta deficiência é incrementar a condutividade eletrônica do óxido puro pela dopagem com alguns cátions metálicos. Sendo assim, este trabalho tem como objetivo geral pesquisar de maneira sistemática o efeito da dopagem de dióxido de manganês com alguns cátions metálicos, como o Bi3+e Ce4+ nas propriedades físico-químicas e eletrocatalíticas deste óxido, visando o uso dos mesmos como em cátodos de baterias recarregáveis do tipo Zn-ar. As análises das características morfológicas dos catalisadores por meio de MEV e TEM mostram que os óxidos de manganês são gerados na forma de nano-bastões de 50 a 100 nm de comprimento. Os óxidos puros e dopados com bismuto e cério apresentam estruturas tetragonais típicas, ocorrendo expansão da célula unitária dos óxidos dopados pela troca de íons manganês pelos correspondentes dopantes na rede cristalina de MnO2. Os resultados eletroquímicos sugerem um aumento de condutividade do óxido dopado que possibilita seu uso sem mistura com carbono. Além disso, observa-se que a RRO é catalisada por um mecanismo que envolve a transferência de 4e- nestes materiais com participação de peróxido como intermediário. O óxido de manganês dopado com Bi apresentou promissor desempenho catalítico para a RDO, o que junto com os demais resultados apresentados para a RRO o qualificou a funcionar como o catalisador bifuncional mais promissor de todos os estudados em baterias do tipo metal-ar. Experimentos realizados em mini baterias do tipo Zn-ar demonstraram a total capacidade do catalisador dopado com bismuto operar como catalisador do eletrodo de ar, resultando num desempenho superior ao de um catalisador convencional de MnO2/C. / Manganese dioxide is at the same time an efficient and low-cost material used as cathode catalyst in the air electrode of metal-air and alkaline fuel cells, capable to promote the complete reduction of oxygen thru the 4e- mechanism. However, manganese dioxide is a semiconductor and can be used as electrodic material in the mentioned devices only combined with a conductor support. High surface area carbon powder is the most commonly used material for such purpose. The problem is that carbon suffers from severe instabilities in the experimental conditions that fuel cells and metal-air batteries operates, being gradually converted into CO2. A possible strategy to overcome or at least minimize the low oxide conductivity is by doping this material with some metallic cations. In this sense, the main purpose of this work was the systematic investigation of the physicochemical and electrocatalytic properties of Bi3+ and Ce4+ doped manganese dioxide materials used as cathode catalysts in the air electrode of alkaline type Zn-air batteries. The morphologic characterization performed SEM and TEM revealed that pure as well cation doped MnO2 are formed as poly dispersed nanorods with 50-100 nm length. Both pure and doped materials presented typical tetragonal structures, although a cell expansion was observed in the doped oxides caused by the exchange of some manganese cations by the doping counter parts. Electrochemical results suggest that a material with increased conductivity results from the doping process, allowing it to operate as air catalyst without the use of a carbon support. Besides, it is observed that the oxygen reduction reaction proceeds thru the 4e- mechanism on the doped oxides involving hydrogen peroxide as intermediate. The Bi doped oxide presented the best performance for the oxygen evolution reaction among all catalysts investigated. This result together with the superior performance for the oxygen reduction reaction presented by this material suggest that Bi doped MnO2 is a potential candidate to operate as an air catalyst of rechargeable alkaline metal-air batteries. Experiments conducted in a mini Zn-air battery using Bi doped MnO2 as air catalyst corroborated this observation.

Les systèmes électrochimiques lithium-air sont des concepts naissants mais exhibent des performances théoriques intéressantes qui laissent espérer une rupture technologique dans le domaine des batteries pour véhicule électrique. La possibilité d'atteindre une densité d'énergie supérieure à 500 Wh kg-1 est effectivement en ligne de mire. A contrario de la technologie lithium-air anhydre, les systèmes lithium-air aqueux n'ont, jusqu'à présent, fait l'objet d'aucune étude approfondie. Ce travail concerne donc le développement d'un système lithium-air aqueux, à trois électrodes, et vise également à améliorer nos connaissances fondamentales dans le domaine. La présente étude se focalise sur le compartiment positif de la cellule, dans lequel les réactions de l'oxygène sont mises en jeu. Dans un premier temps, une électrode spécifiquement dédiée à la réaction de dégagement d'oxygène a été élaborée à partir d'un acier 316L. L'étude de son comportement a révélé une bonne propension à catalyser la réaction de dégagement d'oxygène ainsi qu'une bonne stabilité sur 3 000 heures de fonctionnement. Néanmoins, d'importants problèmes de catalyse ont pu être observés et attribués à la présence des ions lithium dans l'électrolyte de la batterie. Les ions Li+ bloquent les transitions électrochimiques des sites actifs à l'origine des propriétés d'électrocatalyse. Le comportement d'une électrode à air, composée de carbone et d'oxydes de manganèse, a par la suite été caractérisé dans ce milieu. L'étude révèle deux phénomènes importants réduisant la performance de l'électrode et dont l'origine a également été attribuée aux ions lithium : un blocage des transitions (MnIII/MnIV), et une stabilisation des groupements oxygénés à la surface du carbone. Pour finir, il a été proposé d'optimiser le système électrolytique en limitant l'activité des ions Li+ en solution et ainsi d'améliorer le rendement en potentiel de charge/décharge de la batterie. / The electrochemical lithium-air devices are emerging concepts and their very high theoretical performances have attracted a lot of attention, especially for an application in the electrical vehicle. A target of at least 500 Wh kg-1 is aimed for. The aqueous lithium-air devices have not yet been studied in detail which is not the case for the anhydrous lithium-air technology. This thesis firstly deals with the development of an aqueous lithium-air cell based on a three electrodes setup, and secondly attempts to improve our theoretical knowledge of these systems. This study particularly focuses on the positive compartment of the cell in which oxygen reactions occur. The first section is dedicated to the development of an oxygen evolution electrode made of 316L stainless steel. The study shows its ability to catalyze the oxygen evolution reaction as well its good stability over 3 000 hours of operation. Nevertheless, major problems of catalysis were observed and assigned to the presence of lithium ions in the electrolyte. Li+ ions inhibit the electrochemical oxidation of the active sites, which are needed for the electrocatalytic properties. The behavior of an air cathode was characterized in the same medium. The results show two important phenomena which reduces the electrode performance and which are also attributed to lithium ions : a deactivation of the (MnIII/MnIV) transition and a stabilization of the oxygenated groups at the carbon surface. Finally, an optimization of the electrolytic system was proposed by limiting the Li+ ions activity in solution, which improves the charge/discharge potential efficiency of the battery.

Le dihydrogène se présente comme un vecteur énergétique d'avenir pour la diversification des sources de production d'énergie. L'électrolyse de l'eau dans le système PEMWE (Proton Exchange Membrane Water Electrolyzer) permet l'obtention de dihydrogène de grande pureté. Les atouts de cette technologie induite par l'utilisation d'assemblage membrane électrode (AME) permettent son couplage aux énergies renouvelables. Toutefois, l'amélioration de l'activité catalytique des matériaux anodiques et leur stabilité pour baisser la tension de cellule et la diminution de la teneur en métaux nobles dans la composition des matériaux sont nécessaires.Lors de ces travaux de thèse, une voie de synthèse a été élaborée pour préparer des nanomatériaux à base de ruthénium. L'ajout d'iridium a permis dans un premier temps de prévenir l'oxyde de ruthénium de la dissolution tout en maintenant l'activité du catalyseur initial. Les meilleures performances catalytiques des AMEs en termes de densité de courant, de tension de cellule et de durabilité ont été délivrées avec les matériaux anodiques dont la composition molaire en Ru est supérieure à 70 %. La substitution partielle des métaux précieux (Ru et Ir) par du cérium et du niobium dans le but de proposer des catalyseurs à moindre coût a été aussi réalisée. Contrairement au niobium qui apporte une phase amorphe dans la structure du matériau, le cérium jusqu'à une teneur de 10 % permet de conserver les performances de l'anode telles que obtenues dans le matériau bimétallique. Le cérium se présente donc comme un métal prometteur à intégrer de manière appropriée dans la composition des matériaux anodiques. / Hydrogen seems to be the most promising energetic vector in order to diversify the sources of energy production. Water splitting in a Proton Exchange Membrane Water Electrolyzer (PEMWE) provides a sustainable way of producing clean hydrogen. One of the main advantages of this technology based on the utilization of Membrane Electrode Assembling (MEA) is its potential coupling with renewable energy sources. However, the improvement of the catalytic activity of anode materials, their stability and the reduction of the noble metal content in their composition are required.During this thesis work, a new synthesis approach that consists in hydrolysis of metallic precursors in ethanol medium has been undertaken to prepare non-supported ruthenium-based nanomaterials. The addition of iridium to the nanocatalysts composition prevents the ruthenium oxide from dissolution without decreasing the initial activity of the anode catalyst. The best catalytic performance of MEAs in terms of current density, cell voltage and durability were observed with anode materials whose ruthenium molar composition is higher than 70 %. The partial substitution of precious metals (Ru and Ir) either by cerium or niobium with the purpose of decreasing the catalysts cost was also attempted. While the substitution with niobium introduces an amorphous phase in the material structure, the trimetallic materials containing cerium were shown to be crystalline. Furthermore, cerium contents up to 10 % allows maintaining the catalytic activity of the trimetallic anode close to that obtained with the bimetallic oxide material. Thus cerium appears as a promising metal to include in a suitable way on the composition of anode materials.