A performance de células a combustível de membrana de troca polimérica (PEMFC) alimentadas com hidrogênio contaminado com CO foi investigada para ânodos com eletrocatalisadores de PdPt/C e PdPtRu/C em diferentes proporções. Os materiais produzidos foram caracterizados por energia dispersiva de raios-X (EDX) e difração de raios-X (DRX). As propriedades eletrônicas da Pt foram analisadas por espectroscopia de absorção de raios-X (XAS) na região de XANES (X-ray absorption near edge structure). As avaliações do desempenho eletroquímico foram feitas através do levantamento sistemático de curvas de polarização de estado estacionário, voltametria cíclica e stripping de CO em células a combustível unitárias. Também foram feitas medidas de espectrometria eletroquímica diferencial de massas para avaliar o monitoramento de CO2 (massa/carga 44). Foi observada uma pequena diminuição da magnitude da linha branca nos espectros para as ligas PdPt/C e PdPtRu/C quando comparados com Pt/C, sendo que este fenômeno foi atribuído a um aumento de ocupação da banda Pt 5d. Melhores resultados com relação a tolerância ao CO da reação de oxidação de hidrogênio foram obtidos para os catalisadores PdPt/C e PdPtRu/C quando comparados com Pt e Pd puros. Nenhum efeito sinérgico favorável foi observado com a adição de Ru. O monitoramento de CO2 nos experimentos de espectrometria de massas (DEMS), enquanto as células eram alimentadas com H2 + 100 ppm CO, mostrou aumento na quantidade de formação deste produto somente para ânodos contendo PdPtRu/C e nenhuma formação de CO2 do início ao final das variações de potenciais nos casos dos eletrodos contendo PdPt/C. / The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PdPt/C and PdPtRu/C electrocatalysts at different ratios. The produced materials were characterized by energy dispersive (EDX) and X-ray diffraction (XRD). The electronics properties of Pt were analyzed by X-ray absorption spectroscopy (XAS) X-ray absorption near edge structure (XANES) in the region. Evaluations of the electrochemical performance were carried out by steady state single cell polarization measurements, cyclic voltammetry and the CO-stripping techniques. Measurements of differential electrochemical mass spectrometry (DEMS) were carried out to evaluate the CO2 (mass 44) formation. A small reduction of the white line magnitude was in the XANES spectro for the PdPt/C and PdPtRu/C alloys when compared with Pt/C. This phenomenon was assigned for the increase of occupation of the Pt 5d band. Higher CO-tolerances were obtained for the PdPt/C and PdPtRu/C catalysts when compared with those for pure Pd/C and Pt/C. No favorable synergistic effect occurred with Ru addition in the electrode performance for the PEMFC fed with H2+100 ppm CO. The CO2 (mass 44) monitoring with DEMS experiments with the cells fed with H2+100 ppm CO showed the formation of this product only to PdPtRu/C, while no CO2 formation could be detected from beginning to end potential in the cases of Pd/C and PdPt/C.

A performance de células a combustível de membrana de troca polimérica (PEMFC) alimentadas com hidrogênio contaminado com CO foi investigada para ânodos com eletrocatalisadores de PdPt/C e PdPtRu/C em diferentes proporções. Os materiais produzidos foram caracterizados por energia dispersiva de raios-X (EDX) e difração de raios-X (DRX). As propriedades eletrônicas da Pt foram analisadas por espectroscopia de absorção de raios-X (XAS) na região de XANES (X-ray absorption near edge structure). As avaliações do desempenho eletroquímico foram feitas através do levantamento sistemático de curvas de polarização de estado estacionário, voltametria cíclica e stripping de CO em células a combustível unitárias. Também foram feitas medidas de espectrometria eletroquímica diferencial de massas para avaliar o monitoramento de CO2 (massa/carga 44). Foi observada uma pequena diminuição da magnitude da linha branca nos espectros para as ligas PdPt/C e PdPtRu/C quando comparados com Pt/C, sendo que este fenômeno foi atribuído a um aumento de ocupação da banda Pt 5d. Melhores resultados com relação a tolerância ao CO da reação de oxidação de hidrogênio foram obtidos para os catalisadores PdPt/C e PdPtRu/C quando comparados com Pt e Pd puros. Nenhum efeito sinérgico favorável foi observado com a adição de Ru. O monitoramento de CO2 nos experimentos de espectrometria de massas (DEMS), enquanto as células eram alimentadas com H2 + 100 ppm CO, mostrou aumento na quantidade de formação deste produto somente para ânodos contendo PdPtRu/C e nenhuma formação de CO2 do início ao final das variações de potenciais nos casos dos eletrodos contendo PdPt/C. / The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PdPt/C and PdPtRu/C electrocatalysts at different ratios. The produced materials were characterized by energy dispersive (EDX) and X-ray diffraction (XRD). The electronics properties of Pt were analyzed by X-ray absorption spectroscopy (XAS) X-ray absorption near edge structure (XANES) in the region. Evaluations of the electrochemical performance were carried out by steady state single cell polarization measurements, cyclic voltammetry and the CO-stripping techniques. Measurements of differential electrochemical mass spectrometry (DEMS) were carried out to evaluate the CO2 (mass 44) formation. A small reduction of the white line magnitude was in the XANES spectro for the PdPt/C and PdPtRu/C alloys when compared with Pt/C. This phenomenon was assigned for the increase of occupation of the Pt 5d band. Higher CO-tolerances were obtained for the PdPt/C and PdPtRu/C catalysts when compared with those for pure Pd/C and Pt/C. No favorable synergistic effect occurred with Ru addition in the electrode performance for the PEMFC fed with H2+100 ppm CO. The CO2 (mass 44) monitoring with DEMS experiments with the cells fed with H2+100 ppm CO showed the formation of this product only to PdPtRu/C, while no CO2 formation could be detected from beginning to end potential in the cases of Pd/C and PdPt/C.

Le développement de technologies de l’énergie alternatives à la combustion des ressources fossiles est un enjeu majeur pour réduire l’émission des gaz à effet de serre et développer une économie durable. Dans cette optique, les piles à combustible à membrane échangeuses de protons (PEMFC) utilisent le platine en tant que catalyseur pour transformer l’énergie chimique en énergie électrique, en réduisant l’oxygène de l’air en eau et en oxydant l’hydrogène en protons. Dans la nature, les enzymes à cuivre et les hydrogénases catalysent respectivement ces réactions. Ces dernières, ainsi que des complexes bio-inspirés de leur site actif, ont été envisagés en tant qu’alternatives au platine, métal noble et coûteux. Ainsi, un complexe mononucléaire bisdiphosphine de nickel renfermant des acides aminés arginines en troisième sphère de coordination a été immobilisé sur une matrice de nanotubes de carbone (NTCs). Cette anode a démontré d’excellentes performances pour oxyder l’hydrogène avec des densités de courant élevées et sur une large gamme de pH. Son utilisation dans une PEMFC a permis d’obtenir une densité de puissance de 15 mW.cm-2, seulement cinq fois inférieure à celle d’une pile classique à base de platine préparée dans les mêmes conditions. Concernant la catalyse de réduction de l’oxygène, des méthodes covalentes ont été développéespour réaliser la connexion électronique directe de laccase de Trametes sp C30, ainsi qu’un mutant de cetten enzymesur matrice de NTCs L’’association du catalyseur de nickel avec une cathode à base de bilirubine oxydase immobilisée sur NTCs a permis de proposer un nouveau concept de pile hybride enzymatique/bio-inspirée. Une densité de puissance de l’ordre de 1,8 mW.cm-2 et une force électromotrice proche de 1V ont ainsi été mesurées pour cette pile sans métaux nobles. Le greffage de complexes de cuivre mono- et dinucléaires, bio-inspirés du site actif d’enzymes à cuivre et actifs vis-à-vis de la réduction de l’oxygène a enfin permis d’élaborer la première pile H2/air ne renfermant que des catalyseurs moléculaires et sans métaux nobles. Cette dernière délivre une densité de puissance de 160 µW.cm-2. / New energy technologies alternative to fossil fuels utilization is a key issue to mitigate greenhouse gases emission and develop a sustainable economy. In this context, platinum-based proton exchange membrane fuel cells use oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) to convert chemical energy into electrical energy. In nature multicopper oxidases and hydrogenases catalyze these two reactions, respectively. These enzymes and corresponding bioinspired catalysts have been used as alternatives to the rare and expensive platinum metal. First, a mononuclear bis-diphosphine nickel complex surrounded by arginine residues was immobilized onto carbon nanotubes (CNTs) and demonstrated excellent performances for HOR developing high current densities over a wide range of pH. This anode was integrated in a PEMFC, which achieved high power densities (15 mW cm-2), only five times lower as compared to classical PEMFC prepared under similar conditions. Regarding ORR catalysis, we covalently grafted LLaccases from Trametes sp C30 multicopper oxidases onto NTCs electrodes and achieved direct electron transfer. Using, bilirubin oxidase deposited on CNTs at the cathode side, we proposed a new concept of hybrid enzymatic/bio-inspired H2/air fuel cell. This hydrogen fuel cell delivered 1.8 mW.cm-2 and a high open circuit voltage of 1V. Finally, various copper complexes inspired from the active sites of copper enzymes were assessed for ORR and the first H2/air fuel cell containing noble metal-free molecular catalysts at both electrodes is reported, achieving 160 µW.cm-2 power density.

Le platine constitue le matériau de référence pour l’électroréduction de l’eau (HER) et l’électrooxydation du dihydrogène (HOR). Les propriétés physicochimiques de ce matériau d’électrode synthétisé sous forme Pt/C par la méthode BAE et les paramètres cinétiques des réactions électrochimiques HOR et HER à sa surface en milieu alcalin ont été déterminés. Le palladium et l’or ont aussi des activités intéressantes vis-à-vis de ces réactions. L’activité de ces métaux nobles supportés sur carbone et obtenus par la même méthode de synthèse a été étudiée dans les mêmes conditions pour établir une étude comparative.L’effet de Ni et Nb sur l’activité catalytique de Pt pour HOR et HER a aussi été étudié. Des catalyseurs de type PtxM1-x/C (M=Ni, Nb) ont été préparés et leurs propriétés physicochimiques ainsi que leurs activités électrocatalytiques étudiées. Bien que Ni et Nb ne catalysent pas ces réactions dans le domaine de potentiel scruté, leur présence induit des modifications du site catalytique et influence l’activité catalytique des différents matériaux d’électrode. Pour chaque catalyseur les paramètres cinétiques ont été déterminés et les résultats révèlent des catalyseurs bimétalliques très prometteurs. Les mesures de CO-stripping ont ensuite mis en évidence un effet électronique sur le platine favorable à l’oxydation du CO à bas potentiel sur les catalyseurs PtxNi1-x/C.Des résultats très encourageants ont montré que la modification du support de l’électrode (ajout de CeO2) a permis d’obtenir un catalyseur (Pt0,5Ni0,5/CeO2/C) possédant des activités catalytiques en HER et HOR similaires à celles de Pt/C tout en diminuant de 50% la quantité de Pt. / Platinum is the reference material for the electroreduction of water (HER) and the electrooxidation of hydrogen (HOR). The starting point of this work was the synthesis of Pt/C by the BAE method. The physicochemical properties of this material and the corresponding kinetic parameters for HOR and HER in alkaline medium were obtained. Palladium and gold also exhibit interesting activities towards these reactions. The activity of these metals supported on carbon and obtained by the same synthesis method was therefore studied in the same conditions so as to perform a comparative investigation.The effect of Ni and Nb on the catalytic activity of Pt for both reactions (HOR and HER) was also investigated. Thus, two sets of PtxM1-x/C (M = Ni, Nb) catalysts were prepared and their physicochemical properties and electrocatalytic activities studied in alkaline medium. Although Ni and Nb do not catalyze HOR nor HER in the scrutinized potential range, their presence can lead to changes in the catalytic site and consequently influence the electrocatalytic activity of the various materials towards the studied reactions. For each material, the kinetic parameters were determined for both HER and HOR and compared with those obtained for Pt/C. The results revealed very promising bimetallic catalysts. Moreover, the CO-stripping measurement highlighted an electronic effect on platinum favorable to the CO oxidation at low potential values for the PtxNi1-x/C materials.Finally, the modification of the electrode support by adding CeO2 resulted in a Pt0,5Ni0,5/CeO2/C catalyst exhibiting excellent catalytic activities towards HER and HOR while decreasing significantly (50%) the amount of Pt.

La thèse présentée traite principalement de l'influence de la composition et de l’état de surface d’électrodes à base de Ni sur la cinétique et le mécanisme des réactions d'oxydation/dégagement de l'hydrogène (HOR/HER) en milieu alcalin. En combinant les résultats de mesures électrochimiques avec une modélisation microcinétique, il a pu être montré que l'activité spécifique du Ni pour l’HOR/HER augmente jusqu'à 10 fois en présence à la fois d’oxydes de Ni et de Ni métallique à la surface de l'électrode. En outre, l'influence de l'addition d’un second métal aux électrocatalyseurs à base Ni sur leurs activités pour l’HOR/HER a été étudiée dans le cas des systèmes NiMo/C et NiCu/C. Dans les deux cas, une augmentation de l'activité spécifique a été observée par rapport à l'échantillon Ni/C de référence et a été attribuée à une diminution de l'énergie d'adsorption de l'hydrogène adsorbé sur Ni, espèce intermédiaire de l’HOR/HER. / The present thesis is mainly focused on the influence of the surface state of Ni electrodes on the kinetics and the mechanism of the hydrogen oxidation/evolution reactions (HOR/HER) in alkaline medium. By combining the results of electrochemical measurements with microkinetic modeling, it was shown that specific activity of Ni in the HOR/HER increases up to 10 times if along with metallic Ni, Ni oxide species are present on the electrode surface. In addition, the effect of the addition of a second metal to Ni electrocatalysts on their activity in the HOR/HER was investigated for NiMo/C and NiCu/C systems. In both cases an enhancement of specific activity was observed in comparison with the reference Ni/C sample, which was assigned to a decrease of the adsorption energy of the hydrogen intermediate on Ni participating in the HOR/HER.

A goal of the Swedish government is to increase the usage of renewable fuels and biomass-based fuels. Fuel cells, and especially the MCFC, are useful for these types of fuels. The Swedish market may benefit from the MCFC in two ways: increased efficiency of the biofuels and also utilisation of produced heat in district heating. Most of the commercial MCFC systems today are optimised for use with methane. The possibility to utilise biomass in Sweden makes it important to study how the MCFC may be adapted or optimised for good performance and low degradation with gas produced from biomass or other renewable fuels. This thesis is focused on methods that may be used to investigate and evaluate MCFC electrodes and electrolytes with renewable fuels i.e. CO2-containing gases. The methods and results are both experimental and mathematically modelled. The objectives of this thesis are to better understand how the performance of the anode is dependent on different fuels. Anode kinetics and the water-gas shift reaction have been investigated as well as the possibility to increase cell lifetime by increasing the initial electrolyte amount by having the anode as a reservoir. The effect of segregation of cations in the electrolyte during operation has also been studied. It was found that if the gas composition at the current collector inlet is in equilibrium according to the water gas-shift reaction the gas composition inside the electrode is almost uniform. However, if the gas is not in equilibrium then the concentration gradients inside the current collector have a large effect on the gas composition inside the electrode. The conversion of the gas in the gas flow channels according to the water-gas shift reaction depends on the gas flow rate. For an anode used in a gas mixture of humidified hydrogen and carbon dioxide that are not in equilibrium some solubility of Ni in a (Li/Na)2CO3 mixture was found. To have the anode act as an electrolyte reservoir to prolong cell lifetime the anode pore size should be carefully matched with that of the cathode and a bimodal pore-size distribution for the anode is preferable to have as good performance as possible for as large electrolyte filling degree interval as possible. Modelling results of segregation of cations in the electrolyte during operation indicate that the electrolyte composition changes during operation and that the lithium ions are enriched at the anode for both types of electrolyte used for the MCFC. The electrolyte composition changes are small but might have to be considered in long-time operation. The results from this thesis may be used to better understand how the MCFC may be used for operation with renewable fuels and how electrodes may be designed to prolong cell lifetime. / Ett av den svenska regeringens mål är att öka användandet av förnyelsebara bränslen och bränslen från biomassa. Bränsleceller och framförallt MCFC är användbara för dessa typer av bränslen. Den svenska marknaden kan dra fördelar av MCFC på två sätt; ökad bränsleutnyttjandegrad och utnyttjande av producerad värme för fjärrvärme. De flesta kommersiella MCFC-systemen idag är optimerade för användning av metan. Möjligheten att använda biomassa på den svenska marknaden gör det viktigt att studera hur MCFC kan anpassas eller optimeras för bra prestanda och låg degradering för användning med gas från biomassa eller andra förnyelsebara bränslen. Fokus i denna avhandling är på metoder som kan användas för att undersöka och utvärdera MCFC-elektroder och -elektrolyter med förnyelsebara bränslen, dvs. gaser innehållande CO2. Metoderna och resultaten är både experimentella och matematiskt modellerade. Målet med denna avhandling är att bättre förstå hur anodens prestanda beror på användningen av olika bränslen. Anodens kinetik och vattengasskiftreaktionen har studerats liksom möjligheten att förlänga cellens livstid genom att öka den initiala mängden elektrolyt medelst användning av anoden som reservoar. Effekten av segregation av katjoner i elektrolyten under last har också undersökts. Om gassammansättningen är i jämvikt enligt vattengasskiftreaktionen vid inloppet till strömtilledaren kommer gassammansättningen att vara nära uniform inuti elektroden. Om ingående gas inte är i jämvikt kommer stora koncentrationsgradienter uppkomma i strömtilledaren och påverka gassammansättningen i elektroden. Omsättningen med avseende på vattenskiftreaktionen av gasen i flödeskanalen verkar vara beroende av gasens flödeshastighet. För en anod som används i en uppfuktad blandning av vätgas och koldioxid som inte är i jämvikt befanns det att Ni har en viss löslighet i (Li/Na)2CO3. För att kunna använda anoden som reservoar för elektrolyt för att förlänga livstiden för MCFC skall anodens porstorleksfördelning överensstämma med katodens och ha en bimodal porstorleksfördelning för att ge en tillräckligt god prestanda i ett så stort elektrolytfyllnadsgradsintervall som möjligt. Modelleringsresultat för segregering av katjoner i elektrolyten under drift visar att litiumjoner anrikas i anoden för båda typerna av elektrolyt som används i MCFC. Elektrolytkoncentrationsförändringarna är små men kan behövas tas i beaktande vid långa driftstider. Denna avhandlings resultat kan användas för att bättre förstå hur MCFC skall anpassas för drift med förnyelsebara bränslen och hur elektroder kan utformas för att förlänga livstiden. / QC 20100630

This work reports on the cobalt pyridinoporphyrazinate (CoTmtppa) as a platinum-group metal-free catalyst for hydrogen evolution and oxidation reactions with the possibility of use in hydrogen energy and hydrogen potentiometric sensing. A different interaction of CoTmtppa with various electrode substrates, highly oriented pyrolytic graphite (HOPG) and annealed gold (Au(111)), affects its electrocatalytic behaviour in hydrogen reactions. The formation of a hydride-type complex with the bonding of hydrogen atoms to cobalt centre is supposed to be the rate-determining step. In the case of hydrogen evolution, the maximum catalytic activity of mediator was reached at pH = 11,0, when the HOPG/CoTmtppa showed overpotential decrease by 300 mV and an almost 60-fold increase of current densities compared to HOPG. The electrocatalytic activity of Au(111)/CoTmtppa resulted in a further decrease of overpotential by 175 mV in comparison with HOPG/Co(I)Tmtppa. The electrochemical oxidation of hydrogen was found to depend on hydrogen source which was electrochemically generated on-site or molecular hydrogen supplied from an external source. In the case of electrochemically generated hydrogen, the maximum activity of HOPG/CoTmtppa was reached at pH = 2.1 and an additional it was observed 50 % increase in current...

Au cours des dernières années, le développement des batteries Li-ion a révolutionné nos modes de vie. Compte tenu de la croissance exponentielle en batteries, le besoin se répercute sur les matériaux de base, qui sont entre autres, synthétisés à partir de sels de lithium de haute pureté. Nemaska Lithium, une entreprise partenaire du projet, est reconnue en tant que nouveau producteur d’hydroxyde de lithium, par l’entremise d’un procédé électromembranaire breveté. Comparativement au procédé conventionnel, la solution mise en place est l’une des méthodes la plus économique et écologique à l’échelle mondiale. Dans le but de diminuer encore plus les coûts énergétiques du procédé, l’usage d’une anode dépolarisée à l’hydrogène ((ADH); H2(g) ⇄ 2H+(aq) +2é; E=0,00 V) est considérée. Cette approche demande une certaine compréhension et optimisation de l’électrode à des fins d’adaptation pour l’électrolyse. Ainsi, ce travail tant fondamental qu’appliqué a été réalisé afin d’étudier les phénomènes se produisant à l’ADH. Dans un premier temps, une étude portée sur la cinétique de réaction de l’oxydation de l’hydrogène à l’aide d’une électrode à disque tournant est réalisée. L’influence d’ions lithium et d’une couche catalytique composite sur l’efficacité de la réaction a ainsi pu être démontrée. L’identification des limitations du système a ensuite permis l’optimisation de l’ADH à l’aide d’un plan d’expérience. L’ADH est composée d’un ionomère, d’un catalyseur et d’un support à catalyseur, qui ont des propriétés intrinsèques ayant un impact direct sur l’efficacité et la durabilité de celle-ci. Conséquemment, pour une étude de performance et d’optimisation, plusieurs configurations d’assemblage d’électrode à membrane (MEA) ont été considérées visant à faire varier les proportions des différentes composantes avec un plan d’expérience. Ce projet a ainsi permis l’étude menant à une meilleure compréhension d’une nouvelle technologie d’électrolyse membranaire. / In recent years, the development of Li-ion batteries has revolutionized our lifestyles. Given the exponential demand for batteries, the requirement is for base materials, which are synthesized from high-purity lithium salts. Nemaska Lithium, a partner in the project, is recognized as a new producer of lithium hydroxide, using a patented electromembrane process. Compared to the conventional process, this solution is one of the most economical and environmentally friendly methods worldwide. In order to further reduce the energy costs of the process, the use of a hydrogen depolarized anode ((HDA); H2(g) ⇄ 2H+(aq) +2é; E0=0,00 V) is considered. This approach requires some understanding and optimization of the electrode for electrolysis adaptations. Thus, this fundamental and applied work was conducted to study the phenomena occurring at the HDA. First, a study on the kinetics of the hydrogen oxidation reaction using a rotating disk electrode is performed. The influence of lithium ions and a composite catalytic layer on the efficiency of the reaction was demonstrated. The identification of system limitations allowed the optimization of the DHA using a design of experiment. The components of a HDA have intrinsic properties which have a direct impact on its efficiency and durability. They consist of an ionomer, a catalyst, and a catalyst support. Consequently, for a performance and optimization study, several membrane electrode assembly (MEA) configurations were considered in order to vary the proportions of the different components with a design of experiment. This study provided a better understanding and development of this new membrane electrolysis technology.