Stabilizing High-Activity FeN₅ Sites via an Adaptive N-linked Carbon Bilayer for Stable Fuel Cells

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 FeN₄ moieties into stabilized FeN₅ 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 H₂-O₂ and showing negligible decay over 45 h at 0.6 V in H₂-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.