Active Sites and Stability Study of Fe/N/C Catalyst in PEMFCs: A Decade of Stunning Progress and the Remaining Challenges

Over the past few decades, Fe/N/C, as the most promising platinum group metal (PGM) alternative, has provided a unique roadmap for developing proton exchange membrane fuel cells (PEMFCs) due to the low-cost and earth-abundant elements. However, the high-performance Fe/N/C catalysts always demonstrate poor stability, especially during real-world fuel cell operation, which has attracted increased attention in recent years. Great efforts have been devoted in the past decade to understanding active sites and their degradation mechanisms. Herein, we review the progress in the past decade in terms of active site identification and degradation phenomena/mechanisms of Fe/N/C catalysts, particularly in PEMFCs (rather than the conventional three-electrode system). Meanwhile, we also highlight the latest advances in improving the stability of PGM-free catalysts. At the end of this critical review, perspectives are provided to determine the potential strategies to further improve the activity and stability of Fe/N/C catalysts for PEMFCs.