Stabilizing Fe─N─C Fuel Cell Catalysts via Nitrogen‐Doped Twisted Bilayer‐Mediated Single Atom Spin Regulation

Iron–nitrogen co‐doped carbon catalysts have attracted considerable attention in proton exchange membrane fuel cells (PEMFCs) due to their comparable oxygen reduction reaction (ORR) activity to the widely used commercial Pt/C. However, their practical application is hindered by insufficient long‐term stability. Herein, we report an Fe─N─C catalyst with a nitrogen‐doped bilayer‐like graphitic carbon architecture, denoted as Fe SA ‐Fe AC /N‐tBLG. Through a melamine‐assisted interlayer‐selective assembly and nitrogen‐rich spatial confinement strategy, Fe single atoms (Fe SAs ) are primarily stabilized in the ZIF‐8‐derived inner carbon layer enriched with Fe─N coordination sites, whereas Fe atomic clusters (Fe ACs ) are preferentially formed within or near the melamine‐derived outer nitrogen‐doped carbon layer. This spatially coupled configuration enhances the resistance of Fe SAs against dissolution. Moreover, the outer‐layer Fe ACs modulate the local magnetic environment and induce a favorable spin‐state transition in the inner‐layer Fe SAs from low‐spin to medium‐spin. This spin‐state transition could optimize the electronic structure of the active sites for ORR catalysis. Benefiting from enhanced resistance to dissolution and the spin‐state modulation of the inner‐layer Fe SAs , the as‐prepared Fe SA ‐Fe AC /N‐tBLG cathode catalyst enables an H 2 ‐air single PEMFC to deliver a peak power density of 647 mW cm −2 . It also maintains approximately 90% of its initial peak power density after 30,000 cycles of accelerated stress testing. This work provides theoretical and experimental insights into the design of metal–nitrogen–carbon electrocatalysts with both high activity and durability.