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

Fe-N-C catalysts containing atomic FeNx 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 FeNx 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 H2O2 and Fe sites via Fenton reactions.