Distance and Coordination Synergy in FeCoNC Dual-Atom Catalysts: Volcano-Type Structure-Activity-Stability Relationship for the ORR

Developing non-precious-metal catalysts with high activity and stability for the oxygen reduction reaction (ORR) remains a central challenge for polymer electrolyte membrane fuel cells. While Fe–Co dual-atom catalysts have attracted considerable interest, the interplay between Fe–Co distance and local coordination environment in governing activity and stability is not well understood. Here, we systematically investigate FeCoNC models with varying Fe–Co distances and N coordination numbers using density functional theory and ab initio molecular dynamics simulations. A clear structure–activity–stability relationship emerges: the Fe–N4/Co–N4 configuration at intermediate Fe–Co distance delivers optimal overall performance, exhibiting low ORR overpotential and high electrochemical stability. This balanced behavior stems from moderate Fe–Co d-orbital coupling, which tunes the spin density and charge distribution to yield favorable adsorption strength, while N4 coordination and Fe–Co interaction strengthen metal–support anchoring and suppress metal oxidation and dissolution. Excessively short Fe–Co distances with N2/N3 coordination increase spin density and unbalance charge distribution, reducing activity and stability, whereas large separations weaken dual-atom synergy, causing the sites to behave as isolated single atoms. This work establishes a design principle for dual-atom ORR catalysts: controlled Fe–Co spacing and N4 coordination enable balanced d-orbital coupling and charge transfer, achieving both high activity and long-term stability.