Hydroxyl Spillover in Out-of-Plane Coordinated Fe-Co Dual-Atom Catalysts to Expedite Oxygen Electroreduction

Metal-nitrogen-carbon (M-N-C) materials have emerged as promising non-precious electrocatalysts for the oxygen reduction reaction (ORR). However, the origin of kinetic activity and the precise regulation of atomically active sites are not fully understood. Herein, we synthesized a Fe-Co dual-site catalyst with an out-of-plane coordination structure. Experimental and theoretical results show that, such out-of-plane configuration could adjust the local coordination environment of c-FeCoDAC, enhancing the d-p orbital hybridization between metals and the oxygen-containing intermediates, which improves the adsorption of the OOH* intermediate, and shifts the rate-limiting step from OO* + H₂O + e^-→OOH* + OH^- step to OH* desorption step, triggering the following OH* spillover process. The adsorbed OH* spontaneously migrates from Fe sites to adjacent Co sites on the curved surface structure due to thermodynamic favorability, where it undergoes further reduction and desorption, significantly reducing the energy barrier of the rate-determining step. Accordingly, the half-wave potential (E_1/2) of c-FeCoDAC was found to be 0.85 V, outperforming the benchmark Pt/C, while exhibiting superior durability and low peroxide yield, enabling its application in Zn-air batteries. This study provides new mechanistic insights for the rational design of curved M-N-C catalysts for efficient oxygen electroreduction.