Activation of Cascade Pathway for Oxygen Reduction via 4f-3d Orbital Ladder-Driven Dual-Site Synergy

The oxygen reduction reaction (ORR) remains a major obstacle in green electrochemical energy conversion, driving the pursuit of cost-effective noble-metal-free catalysts. Transition metal (TM) and rare-earth (RE) compounds have emerged as promising alternatives. However, their catalytic activity is hindered by sluggish electron transfer and restrictive scaling relationships. Herein, a TM/RE heterostructural catalyst that integrates the complementary features of Fe₃N's tunable 3d orbitals and spin polarization with CeO₂'s partially filled 4f orbitals and facile Ce⁴⁺/Ce³⁺ redox transitions, enabling dual-phase catalytic participation, is designed. The Fe₃N/CeO₂ heterostructure forms a dual-site catalytic heterointerface, which promotes charge redistribution and optimizes intermediate adsorption. This synergy originates from the 4f-3d orbital ladder via Ce─O─Fe coordination, enabling directed electron transfer, Fermi level equilibration, and increased carrier density. The interfacial coupling further modulates the Fe spin state, enhances Ce─O covalency, and enriches unpaired electrons, thereby co-activating both phases and establishing a cascade pathway at the heterointerface that circumvents conventional scaling constraints. The proposed mechanism is further verified by in situ Raman spectroscopy and theoretical calculations. The Fe₃N/CeO₂ achieves a half-wave potential of 0.874 V and delivers a maximum power density of 157.8 mW cm^-2 in aluminum-air batteries, outperforming commercial Pt/C and underscoring the application prospects of RE-based heterostructures for next-generation energy technologies.