Water management strategies for PGM-free catalyst layers for polymer electrolyte fuel cells

Abstract Platinum group metal–free (PGM-free) catalysts are promising candidates to catalyze the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs). Because of their low activity, larger loadings are used resulting in thicker catalyst layers. Transport, particularly water management, thereby becomes a more prominent performance factor. Currently, very few works attempted to understand water management in PGM-free catalyst layers, mainly because of other challenges that had to be overcome first, such as enhancing their activity and durability. The field has also been active in a hypothesis discussion of micropores flooding that led to the belief that poor stability of the PEFC performance is linked to active sites flooding within the micropores. We present here an overview of recent advances in understanding water management in the PGM-free catalyst layer for oxygen reduction reaction in PEFCs and provide an opinion on design guidance in optimizing catalyst layers to avoid flooding.