Engineering the d-Orbital Electronic Delocalization of Atomic Fe–Co Dual-Metal Sites through Fe₃C Nanoparticle Integration to Enhance Oxygen Reduction

Bimetallic single-atom catalysts have garnered considerable interest in the field of the oxygen reduction reaction due to their unique electronic configurations and synergistic catalytic effects. However, precise modulation of d-orbital electron distribution at single-atom sites and comprehensive elucidation of the underlying catalytic mechanisms continue to present significant challenges. Herein, the FeCo(mlm)–N–C catalyst, integrating atomically dispersed Fe–Co dual-metal sites and Fe3C nanoparticles, was synthesized by using an encapsulation and ligand exchange strategy. Comprehensive analyses and theoretical simulations reveal that the incorporation of Fe3C nanoparticles induces significant d-orbital electron delocalization at the Fe active sites. This tailored electronic configuration effectively modulates Fe d–O p hybridization between the Fe active sites and adsorbed OH*. Consequently, it optimizes the occupancies of bonding and antibonding orbitals, thereby accelerating OH* desorption. This mechanism enables FeCo(mlm)–N–C to exhibit excellent catalytic performance and remarkable stability in both acidic and alkaline environments, while demonstrating superior activity in zinc-air batteries and proton exchange membrane fuel cells. This work not only presents a highly efficient non-noble metal electrocatalyst but also provides valuable insights into the rational development of advanced transition metal–nitrogen–carbon catalysts for energy-related applications.