Installation of metal clusters adjacent to dual-Fe sites for enhanced oxygen reduction

Fe-based dual-metal center catalysts, featuring intermetallic <i>d-d</i> orbital coupling, have garnered significant interest for enhancing the oxygen reduction reaction (ORR). Modulation of the adjacent microenvironment to dual-metal sites is central to further enhancing the ORR performance, but remains an underexplored area. In this study, an atomic-scale electrocatalyst, consisting of dual-Fe sites and Fe-based atomic clusters (Fe_DS/MC-NC), is synthesized. Driven by these Fe-based atomic clusters, Fe_DS/MC-NC achieves a half-wave potential of up to 0.920 V vs reversible hydrogen electrode (RHE) during the ORR and exhibits a kinetic current density up to 7 times that of commercial Pt/C at 0.880 V vs RHE. Additionally, Fe_DS/MC-NC achieves a maximum power density of 214.6 mW cm^-2 and maintains a negligible expansion of the voltage window after >1000 cycles for Zn-air batteries. Theoretical calculations reveal that the Fe₃O₄ clusters contribute significantly to the dual-Fe sites in Fe_DS/MC-NC. These Fe₃O₄ clusters, positioned adjacent to the dual-Fe sites, induce spin polarization of the active centers through a weak interaction. This results in a positive shift of the spin-down orbitals toward the vicinity of the Fermi energy level, enhancing the adsorption of the key reaction intermediate OOH* and ultimately accelerating the reaction kinetics. This work may open up an avenue to construct dual-metal center catalysts with tunable atomic structures.