Transforming Single‐atom Site to Dual‐atom Site in Fe‐N‐C Catalysts: A Universal Strategy for Enhancing Durability in Proton‐Exchange Membrane Fuel Cells

Abstract

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. Here, 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 pre‐synthesized 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 produces negligible H2O2 (< 1%). Therefore, the transformed Fe‐N‐C catalyst exhibits an extremely low Fe de‐metalation ratio (0.61 at%) in 0.1 M HClO4 after 80,000 potential cycles. 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, while that of the pristine Fe‐N‐C catalyst‐based device declines by 84% within 100 h.