Made available in DSpace on 2014-10-09T12:27:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:18Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

L'un des principaux freins au développement des piles à combustible de type PEMFC (Proton Exchange Membrane Fuel Cell) est lié aux phénomènes de dégradation des performances qui les pénalisent encore en termes de durée de vie. L'étude de ces phénomènes au niveau des composants de l’AME est un thème abordé aujourd'hui par de nombreuses équipes de recherche, mais une étude à une échelle d’un stack est nécessaire pour mieux comprendre les mécanismes en jeu. En effet, dans un stack les conditions de fonctionnement ne sont pas homogènes comme dans les cellules de laboratoire, notamment au niveau thermique. Ceci est particulièrement exacerbé dans les piles pour application automobile, dont la compacité contraint fortement la conception du circuit de refroidissement. De plus, les exigences en termes de démarrage à froid sont à prendre en compte, avec notamment la limitation de l'inertie thermique de l'empilement ou l'apparition d'hétérogénéités plus fortes pendant les phases transitoires.Ce travail de thèse se propose d'étudier l'effet d'hétérogénéités de température sur la performance d'une pile en application automobile et sa dégradation. L'étude est menée dans différentes conditions de fonctionnement: fonctionnement nominal, cyclage thermique et cyclage NEDC (New European Driving Cycles).Cette étude comporte une partie expérimentale, centrée sur des essais de vieillissement en pile et un travail sur le diagnostic électrochimique global et local. Elle est complétée par des expertises post-mortem des assemblages membrane-électrodes et des plaques testées. En parallèle, un travail de modélisation est mené pour relier les constatations expérimentales à une description des phénomènes en présence. L'influence du design des canaux de réactifs et de caloporteur sur le fonctionnement des piles est étudiée. Enfin, l’effet de la gestion thermique sur la dégradation des performances et sur la détérioration des composants de la pile est étudié. / One of the main challenges for Proton Exchange Membrane Fuel Cells development is the performance loss, which largely limits the durability. The study of the degradation phenomena of the different MEA components is a challenge addressed by many researchers, but a study at a stack scale is needed in order to better understand the ageing mechanisms. Indeed, in an industrial fuel cell the operating conditions are not homogeneous as for laboratory fuel cells, especially as regards thermal aspects. The heterogeneities are particularly emphasized for automotive fuel cells, because of the compactness constraint of the cooling circuit. Moreover, the requirements of cold start should be considered, as well as the inertial effects of the stacks and the increased heterogeneities during the driving cycles.In this work, the effects of the temperature heterogeneities and hot spots on the automotive fuel cell performances and degradations are investigated. The study is conducted in different conditions: nominal conditions, load/thermal cycling and New European Driving Cycles (NEDC).The work is composed of an experimental study, which consists of ageing tests on fuel cells and on-line diagnosis at both global and local scales. At the end of the tests, post-mortem analyses of the aged components are conducted. In parallel, a physic-based model is developed in order to predict the local temperature and humidity in the different components of the cell. Then, the impact of the reactive gases and cooling flow fields design on the thermal and water management of the cell is investigated. Finally, the experimental and modeling results are coupled in order to investigate the correlation between heat management, water management and degradations.

Les piles à combustible à membrane échangeuse de protons (PEMFC) sont sensibles aux polluantsde l’hydrogène et de l’air. Cette étude s’est focalisée sur l’impact du monoxyde de carbone (CO) et dusulfure d’hydrogène (H2S), deux polluants majeurs dans l’hydrogène (H2), suivant une approchecombinant expériences et modélisation.Le volet expérimental a consisté à étudier l’effet de la concentration des polluants individuels et enmélange et des chargements en catalyseurs, pour différents modes de fonctionnement. Cette étude amis en lumière un impact sur les deux électrodes (anode et cathode) dû à la distribution hétérogènedes polluants à la surface de l’anode et à la désactivation de la partie de la cathode en regard. Deplus, dans le cas d’un empoisonnement par H2S, cette étude a montré que la tension de cellule atteintun état quasi-stationnaire, en mode galvanostatique, ce qui n’avait jamais été mis en évidence dans lalittérature.Dans l’approche de modélisation multi-échelles, le couplage de l’électrochimie et de la fluidique ainsique le développement de différentes « briques » du modèle ont permis de perfectionner la descriptiondes phénomènes physico-chimiques. Le modèle permet maintenant de simuler le fonctionnementd’une cellule de pile à combustible dans les conditions opératoires réelles, en intégrant les cinétiquesd’empoisonnement du platine par CO et H2S.Enfin, la comparaison des données expérimentales et des simulations a montré des résultats trèssatisfaisants appuyant certains arguments pour l’interprétation de l’impact des impuretés de H2. / Protons exchange membrane fuel cells (PEMFC) are sensitive to hydrogen and air pollutants. Thisstudy is focused on the impact of carbon monoxide (CO) and hydrogen sulfide (H2S) which are twomajor impurities of hydrogen. A combined experimental and modeling approach has been followed.The experimental part consisted in studying the effect of the concentration of individual pollutants andmixtures, and the effect of catalyst loading, for different operating modes. This work has highlighted animpact on both electrodes (anode and cathode) due to a heterogeneous distribution of the pollutantson the anodic surface area and to a deactivation of the opposite cathodic surface area. Furthermore,in the case of H2S poisoning, this study has shown that the cell voltage can reach a quasi-steadystate, in galvanostatic mode, which had never been highlighted in the literature.In the multi-scales modeling approach, a coupling of the electrochemistry and fluidics as well as thedevelopment of new modules of the model have allowed improving the description of the physicochemicalphenomena. As a consequence, the model simulates a fuel cell in real operating conditions,including the kinetics of platinum poisoning by CO and H2S.Finally, experimental data and simulated data were compared and they showed satisfactory anduseful results for the understanding of the impact of H2 impurities.

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Made available in DSpace on 2014-10-09T12:34:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:29Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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O alto custo da produção de hidrogênio puro para ser usado como combustível para uma reação de oxidação de hidrogênio (ROH) em células a combustível faz com que seja atrativo o uso de hidrogênio gerado através da reforma de combustíveis fóssil. Entretanto, o hidrogênio gerado por reforma de outros combustíveis possui contaminantes como CO, que por se adsorver fortemente sobre a superfície do eletrodo de platina, prejudica em muito o processo de oxidação do hidrogênio. Assim o estudo de novos catalisadores mais resistentes a essa contaminação e de outros mecanismos que contribuam para um melhor desempenha de uma célula a combustível do tipo PEMFC, se faz necessário. Esse presente trabalho tem como objetivo o estudo dos catalisadores PtMo/C - 80:20, PtMoO2/C, PtMoO3/C, que foram sintetizados, e PtMoPtRu/C, PtMoPt3Fe/C e PtMoPt3FePtRu/C que foram obtidos através da mistura do PtMo/C - 80:20 sintetizado com os PtRu/C e PtFe/C que são comerciais, através da realização de curvas de polarização no estado estacionário, voltametrias cíclicas e degradação eletroquímica acelerada. Também foi avaliada a eficiência da membrana de Aquivion®, com relação ao cruzamento de subprodutos da degradação dos eletrodos, através de curvas de polarização no estado estacionário, voltametrias cíclicas e variação de temperatura de operação da célula PEMFC. O método usado para a síntese dos eletrocatalisadores se mostrou eficiente na obtenção dos catalisadores, obtendo-se os catalisadores com proporção bem próxima da desejada. Os resultados mostraram uma grande estabilidade química dos catalisadores mistos sendo o PtMoPt3FePtRu/C o mais estável e o PtMoPtRu/C o catalisador mais ativo para uma ROH. Os experimentos com a membrana de Aquivion® mostraram que essa é capaz de diminuir o cruzamento de subprodutos da degradação dos eletrodos. / The high cost of pure hydrogen production to be used as fuel for a hydrogen oxidation reaction (HOR) in fuel cells makes it attractive to use hydrogen generated by reforming of fossil fuels. However, the hydrogen generated by reforming other fuels has contaminants such as CO, which adsorb strongly on the surface of the platinum electrode, affect much the hydrogen oxidation process. Thus the study of new catalysts more resistant to such contamination and other mechanisms that contribute to a better performs of a fuel cell of the PEMFC type, it is necessary. This present study aims to study of catalysts PtMo/C - 80:20 PtMoO2/C, PtMoO3/C, which were synthesized and PtMoPtRu/C, PtMoPt3Fe/C and PtMoPt3FePtRu/C which were obtained by mixing the PtMo/C - 80:20 synthesized with PtRu/C and PtFe/C which are commercial, by performing polarization curves at steady state, cyclic voltammetry and electrochemical degradation accelerated. It also evaluated the efficiency of Aquivion® membrane with respect to the cross-products of degradation of the electrodes by means of polarization curves at steady state, cyclic voltammetry and operating temperature range of the cell PEMFC. The method used for the synthesis of electrocatalysts proved efficient in obtaining the catalysts, the catalysts obtaining very near to the desired proportion. The results showed a great chemical stability of the mixed catalyst being PtMoPt3FePtRu/C more stable and PtMoPtRu/C as catalyst more active for HOR. Experiments with Aquivion® membrane have shown that this can reduce the cross-products of degradation of the electrodes.