PGM‐Free Cathode Catalysts for PEM Fuel Cells: A Mini‐Review on Stability Challenges

Abstract In recent years, significant progress has been achieved in the development of platinum group metal‐free (PGM‐free) oxygen reduction reaction (ORR) catalysts for proton exchange membrane (PEM) fuel cells. At the same time the limited durability of these catalysts remains a great challenge that needs to be addressed. This mini‐review summarizes the recent progress in understanding the main causes of instability of PGM‐free ORR catalysts in acidic environments, focusing on transition metal/nitrogen codoped systems (M‐N‐C catalysts, M: Fe, Co, Mn), particularly MN x moiety active sites. Of several possible degradation mechanisms, demetalation and carbon oxidation are found to be the most likely reasons for M‐N‐C catalysts/cathodes degradation.