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AbstractAbstract
[en] This work investigates the local transient phenomena occurring in proton exchange membrane fuel cells (PEMFC) operated with a dead-ended anode. The dead-end mode consists in closing the anode outlet, which leads eventually to local hydrogen starvation due to the excessive accumulation of liquid water and nitrogen (because of membrane crossover) in the anode compartment. Such fuel-starvation events may remain undetected but can entail a significant rise of the anode (and thus cathode) potentials and accelerate carbon corrosion and catalyst degradation. To access local information, we developed an innovative segmented linear cell with reference electrodes along the gas channels. By simultaneously monitoring the local potentials and current densities during operation, we assessed the impact of fuel starvation and observed strong local cathode potential excursions close to the anode outlet. Aging protocols based on fuel cell operation with a dead-ended anode (longer than in real use condition) showed non-uniform cathode Electrochemical Surface Area (ECSA) losses and performance degradation along the cell area: the damage was more severe in the regions suffering the longest from fuel starvation. Parametric studies completed by numerical simulations showed that the fuel starvation is mainly governed by liquid water accumulation in the anode channels, as well as nitrogen crossover through the membrane. As a consequence, water management impacts significantly the cathode potential variations and thus the resulting electrode degradation. Starting from this founding, we propose strategies to improve fuel cell lifetime. (author)
[fr]
Cette these concerne les phenomenes locaux qui se produisent dans une pile a combustible a membrane (PEMFC) fonctionnant en mode bouche. Ce mode de fonctionnement consiste a alimenter l'anode en hydrogene sec tout en maintenant sa sortie fermee ce qui favorise l'accumulation d'eau et d'azote (issus du compartiment cathodique) pres de la sortie anodique. Certaines regions sont donc convenablement alimentees en gaz tandis que d'autres ne le sont plus. Ces desequilibres s'accompagnent de hausses localisees de potentiel (a l'anode et a la cathode) qui accelerent la degradation du catalyseur et de son support carbone a la cathode. Afin d'etudier ces degradations a une echelle locale, une cellule segmentee novatrice permettant la mesure simultanee des densites de courant et des potentiels locaux a ete developpee. Des protocoles de vieillissement acceleres reposant sur un fonctionnement prolonge en mode bouche montrent que les pics de potentiel ont pour consequence, apres quelques heures, une distribution non-uniforme de la surface active (ECSA) a la cathode et des courants le long de la cellule: les dommages sont plus prononces dans les zones les plus touchees par le deficit en hydrogene. Des etudes parametriques et un modele numerique permettent de comprendre que le deficit en hydrogene resulte principalement de l'accumulation d'eau liquide dans les canaux de l'anode, bien que l'azote joue egalement un role. Par consequent, la gestion de l'eau impacte fortement les variations de potentiel a la cathode et donc leurs consequences en termes de degradation; basees sur ces constatations, des solutions sont proposees pour ameliorer la duree de vie des piles. (auteur)Original Title
Phenomenes locaux instationnaires dans les piles a combustible a membrane (PEMFC) fonctionnant en mode bouche (dead-end)
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Source
2 Dec 2015; 263 p; 308 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; These Docteur de l'Universite de Lorraine, Specialite: Mecanique et Energetique
Record Type
Miscellaneous
Literature Type
Thesis/Dissertation
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AGING, CHEMICAL REACTION KINETICS, COMPUTERIZED SIMULATION, CORROSION, CURRENT DENSITY, ELECTRIC IMPEDANCE, ELECTRIC POTENTIAL, ELECTRODES, HEAT TRANSFER, HYDROGEN, LIFETIME, NITROGEN, OSMOSIS, PARAMETRIC ANALYSIS, PROTON EXCHANGE MEMBRANE FUEL CELLS, TEMPERATURE DISTRIBUTION, VOLTAMETRY, WATER SATURATION, WATER VAPOR
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