Anode Defects’ Propagation to the Electrolyte and Catalyst Layers in Polymer Electrolyte Membrane Fuel Cells

Abstract

Defects known to shorten the lifetime of polymer electrolyte membrane fuel cells (PEMFC) can appear on different membrane electrode assembly (MEA) components and under different forms due to manufacturing processes or operational aging of the fuel cell [1, 2]. Defects-propagation in polymer electrolyte membrane fuel cells membrane electrode assemblies (MEA) is investigated via Accelerated Stress Tests (AST) combining load (hence potential) cycling, 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 and instrumented 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 terms of membrane thinning and anode ECSA loss: significant membrane thinning is observed for the defective segments, while anode ECSA loss is measured downstream in the direction of the hydrogen flow. The cathode degradation is poorly affected by the presence of the anode defects. In addition, membrane degradation also appears to propagate downstream the channels when the AST is prolonged for a long period of time. 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. However, oxygen crossover -toward the hydrogen compartment- is probably detected through slight variations in the anode local potential: this lead to the conclusion that the membrane and anode accelerated degradations are seemingly governed by chemical mechanisms like gas crossover rather than electrochemical mechanisms induced by high-potential excursions. Guilminot, E. et al. Membrane and Active Layer Degradation upon PEMFC Steady-State Operation. J. Electrochem. Soc. 154, B1106 (2007).Dubau, L. et al. A review of PEM fuel cell durability: Materials degradation, local heterogeneities of aging and possible mitigation strategies. Wiley Interdiscip. Rev. Energy Environ. 3, 540–560 (2014). Figure 1