Stabilizing High‐Activity FeN 5 Sites via an Adaptive N‐linked Carbon Bilayer for Stable Fuel Cells

ABSTRACT The practical application of Fe‐N‐C catalysts in proton exchange membrane fuel cells is fundamentally constrained by the inherent activity‐stability trade‐off. Here, we propose a “repair‐and‐upgrade” engineering strategy that not only repairs pyrolysis‐induced defects through carbon and nitrogen supplementation but also evolves conventional FeN 4 moieties into stabilized FeN 5 configurations via an in situ constructed carbon bilayer. The axial nitrogen modulates the electronic structure of Fe center to enhance catalytic activity, while the adaptive interlayer spacing of the N‐linked carbon bilayer compensates for fluctuations in the axial Fe─N bond length during catalysis, therefore anchoring the Fe active sites. When integrated into membrane electrode assemblies, the catalyst delivers a high peak power density of 1221 mW cm −2 and exhibits exceptional durability, retaining over 85% of its initial power density after 10,000 cycles in H 2 ‐O 2 and showing negligible decay over 45 h at 0.6 V in H 2 ‐air tests. This work presents a novel design strategy for stable single‐atom catalysts, centered on creating an adaptive local environment that ensures exceptional electrocatalytic stability.