PEMFC performance decay during real-world automotive operation: Evincing degradation mechanisms and heterogeneity of ageing

Abstract

A long-term dynamic load cycle is performed on state-of-the-art membrane electrode assemblies, aiming to evaluate the degradation mechanisms of Polymer Electrolyte Membrane Fuel Cell under real-world automotive operations. The load cycle, adapted from the stack protocol defined in H2020 ID-FAST European project, includes load, pressure and temperatures cycling. Events that recover the temporary decay are included, specifically procedures classified in short-stops, cold-soaks, long-stops. Operando voltage and current distribution are measured through a segmented hardware, combined to local in-situ electrochemical characterization. Investigation is supported by scanning and transmission electron microscopy analysis, performed at different locations along-the-flow-field. Reversible degradation weights from few to 20 mV and changes local current distribution, mostly at air-inlet, since the dry-out of ionomer. Cycle efficiency decreases of 3%–9%: the largest irreversible performance losses are observed at air-inlet, while middle-region is the least impacted. Cathode catalyst layer and membrane are the most aged components: platinum active surface area drops in 200–400 h, because of electrochemical Ostwald ripening mechanism, and stabilizes around 62%–67% of initial value. Polymer membranes report ageing compatible with mechanical stress that causes localized thinning, increasing hydrogen crossover. Decay of ionomer in the catalyst layer is discussed, which would consistently explain alterations of mass transport resistance.