Durability challenges and perspective in the development of PGM-free electrocatalysts for the oxygen reduction reaction

Significant advancement in the development of highly active platinum group metal-free (PGM-free) electrocatalysts is giving rise to the possibility of a low-cost replacement for Pt electrocatalysts in polymer electrolyte fuel cells. However, before the successful implementation of PGM-free electrocatalysts, the challenge of long-term stability under fuel cell operating conditions needs to be addressed. In this opinion, the current status of PGM-free electrocatalyst performance and durability is reviewed. A perspective on the route for the study of degradation mechanisms in PGM-free electrocatalysts in both half-cell and membrane electrode assembly environments is presented. The analysis of proposed degradation mechanisms suggests classification into two relevant length scales: atomic scale and macro/mesoscale. Lastly, an overview of different characterization techniques (both experimental and theoretical) for studying different possible degradation mechanisms is outlined. Directly addressing the underlying mechanisms leading to loss of activity in PGM-free electrocatalysts will provide valuable insight necessary for the development of next-generation materials with improved durability capable of competing with Pt-based counterparts.