On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

Abstract

Abstract Fe‐N‐C catalysts containing atomic FeN x sites are promising candidates as precious‐metal‐free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The durability of Fe‐N‐C catalysts in fuel cells has been extensively studied using accelerated stress tests (AST). Herein we reveal stronger degradation of the Fe‐N‐C structure and four‐times higher ORR activity loss when performing load cycling AST in O 2 ‐ vs. Ar‐saturated pH 1 electrolyte. Raman spectroscopy results show carbon corrosion after AST in O 2 , even when cycling at low potentials, while no corrosion occurred after any load cycling AST in Ar. The load‐cycling AST in O 2 leads to loss of a significant fraction of FeN x sites, as shown by energy dispersive X‐ray spectroscopy analyses, and to the formation of Fe oxides. The results support that the unexpected carbon corrosion occurring at such low potential in the presence of O 2 is due to reactive oxygen species produced between H 2 O 2 and Fe sites via Fenton reactions.