A Molecular Engineering Strategy to Stabilize N-Bridged Bilayer Atomic Fe–N ₄ Sites on N-Doped Porous Carbon for Oxygen Reduction

Challenges in rationally fabricating high-performance Fe–N/C catalysts for oxygen reduction reaction (ORR)-related energy devices give strong motivation to modulate the electronic structure of surface Fe active centers. Herein, a molecular engineering strategy is developed to prepare an Fe–N/C catalyst with surface enrichment of N-bridged bilayer FeN4 (N4Fe–N–FeN4) active sites. A dual-Fe-atom nanocluster, constructed of [Fe(CN)6]3– coupled with Fe3+–N4 in hemin by molecular interaction, is used to transform into the bilayer N4Fe–N–FeN4 site on N-doped porous carbon by confined pyrolysis. Theoretical calculations reveal that N-bridged sublayer FeN4 modulates the electronic structure of the surface-layer FeN4 site and therefore decreases the ORR energy barrier at the surface Fe active center. Thus, the resulting catalyst shows ORR performance with half-wave potentials of 0.815 V under acidic conditions and 0.890 V in alkaline media. More importantly, ORR-related energy devices are assembled, exhibiting performance such as high peak power densities of 760 mW cm–2 for a H2–O2 fuel cell and 354 mW cm–2 for a Zn–O2 battery. This study not only provides a strategy for developing high-performance next-generation catalysts but also elucidates insights into the electrocatalytic mechanisms, contributing to advances in energy devices.