Anode defects' propagation in Polymer Electrolyte Membrane Fuel Cells
Résumé
Defects-propagation in polymer electrolyte membrane fuel cells membrane electrode assemblies (MEA) is investigated via Accelerated Stress Tests (AST) combining load (hence potential) and load-driven humidity cycling, and open-circuit voltage. Customized MEA with lack of anode catalyst layer at two different locations -near the hydrogen inlet or outlet- are fabricated and subjected to the AST. Periodical electrochemical characterizations are performed using a segmented cell, enabling to track the cell performance and anode/cathode electrochemical surface area (ECSA) over the test period with a spatial resolution along the gas channels. These observations are completed by post mortem analyses of the MEA.
The MEA accelerated degradation is obvious, with multiple impacts on the cell performance and materials. More specifically, the results brought first evidence of defects propagation, in term of anode ECSA loss, in the direction of the hydrogen flow. The cathode ECSA is also impacted, although seemingly homogeneously. Significant membrane thinning is observed for the defective segments, without propagation to the adjacent ones. Anode and cathode local potential monitoring during the AST reveals the absence of cathode high-potential excursion, in both the segments with/without initial defects: the membrane and anode accelerated degradation is governed by chemical mechanisms like gas crossover rather than electrochemical mechanisms induced by high-potential excursions.
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