Driving Tetratomic Iron Clusters via a Ce ³⁺ /Ce ⁴⁺ Electron Pump for Enhanced Oxygen Electrocatalysis

The intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity can be effectively tailored by modifying the metal single-atom (SA) sites around atomic clusters (ACs). Here, strong interactions with single-atom Ce sites bind atomic Fe 4 clusters (Fe 4 ACs) containing Fe-O-Fe units onto Ce SA /N co-doped hollow carbon nanocage (Ce SA /HNC). The hollow nanocage-structured Ce SA /HNC with a large specific surface area, rich N-doped sites, and uniformly dispersed Ce single atoms can firmly anchor Fe 4 clusters to suppress aggregation. Owing to the strong synergism between Fe 4 AC active sites and a Ce SA electron regulator, Fe 4 -Ce SA /HNC delivers a high ORR half-wave potential of 0.931 V and a low OER overpotential of 326 mV at 10 mA cm −2, yielding an ultralow potential gap (Δ E ) of 0.619 V. Additionally, a liquid Zn-air battery based on this catalyst operates steadily for 1659 h. Experiment and theoretical calculations reveal that the Ce 4+ /Ce 3+ redox couple acts as an “electron pump” that stabilizes Fe against leaching via a cyclic electron transfer mechanism. Further mechanistic analysis demonstrates that the Fe 3d-O 2p orbital hybridization within the Fe-O-Fe units, together with the Fe 3d-Ce 4f orbital hybridization at the Fe 4 -Ce SA interface, jointly optimizes the adsorption strength of oxygen intermediates, thereby significantly boosting the ORR activity. This work advances highly effective energy-related electrocatalysis by providing a workable and feasible method for the accurate production of atomically distributed multi-metal core catalysts.