Abstract: The state-of-the-art Fe/N/C catalyst has presented comparable initial cathode performance to the benchmark Pt/C catalyst in proton exchange membrane fuel cells (PEMFCs). However, the major bottleneck is its significant activity decay in real-world PEMFC cells. The superposed “fast decay” and “slow decay” have been well documented to describe the degradation process of Fe/N/C catalysts during PEMFC operation. The fast decay has been well understood in close relation to the demetallation at the initial 15-h stability test. Nevertheless, it is still unclear how the remanent active sites evolve after demetallation. To this end, the catalyst performance and evolution of a typical Fe/N/C active site were herein investigated through postmortem characterizations of the membrane electrode assemblies (MEAs) after different operations. It is presented that 1 bar pressure and 80 °C temperature are the optimized conditions for Fe/N/C MEA. Particularly, the “fast decay” in the initial 15 h is immune to the various operating parameters, while the “slow decay” highly depends on the applied temperature and pressure. According to the X-ray absorption spectra (XAS) analysis and stability test of MEA, the gradual evolution of Fe-N coordination to Fe-O is found correlated with the “slow decay” and accounts for the catalyst decay after the demetallation process.

Key words: Fe/N/C, Stability, Decay mechanism, Metal oxidation, PEMFCs