Transforming Single-Atom Site to Dual-Atom Site in Fe-N-C Catalysts: A Universal Strategy for Enhancing Durability in...

Fe-N-C catalyst is the most promising non-noble metal oxygen reduction catalyst for proton-exchange membrane fuel cells (PEMFCs); however, their practical applications are still limited by unsatisfactory long-term stability. This is because the N atoms of the active FeN₄ moiety are easy to protonate, leading to the leaching of Fe atoms, and the H₂O₂ generated during oxygen reduction reaction (ORR) process triggers the Fenton reaction, further accelerating the dissolution of Fe. To address these critical stability challenge, we developed a general strategy to transform FeN₄ single-atom sites to Fe₂N₆ dual-atom sites in Fe-N-C catalysts with various carbon substrates. This is achieved by treating the presynthesized Fe-N-C catalysts in a H₂/Ar atmosphere to break the C─N bonds near the FeN₄ sites while introducing Fe and N precursors to form the Fe₂N₆ sites. Our theoretical calculations and experimental results demonstrate that the newly formed Fe₂N₆ sites are structurally more stable in acidic ORR and produce negligible H₂O₂ (<1%). Therefore, the transformed Fe-N-C catalyst exhibits an extremely low Fe demetalation ratio (0.61 at%) in 0.1 M HClO₄ after 80k cycling. More surprisingly, the transformed Fe-N-C catalyst can effectively decompose H₂O₂ with a high decomposition rate of 15.7 mmol min^-1, approaching that of the state-of-the art Pt/C catalyst (17 mmol min^-1). As a result, the transformed Fe-N-C catalyst assembled PEMFC operates stably for 300 h with only 7% current density attenuation, whereas that of the pristine Fe-N-C catalyst-based device declines by 84% within 100 h.