Tailoring Metal Spin State and Axial Coordination Structure of FeN 4 via Orbital Coupling Strategy for Enhanced Oxygen Reduction

ABSTRACT The spin electronic structures of transition metals (TMs) can be theoretically modulated by coupling effect between rare‐earth 4f orbitals and 3d orbitals of TMs. However, systematic studies on the precise regulation of Fe spin states for enhanced ORR performance remain limited. Crucially, the mechanistic link between 4f‐3d hybridization, d‐band electron filling at Fe sites, and the spin‐dependent adsorption of key intermediates (*OOH, *O, OH) lacks atomic‐scale experimental and theoretical validation. Herein, we develop an Fe‐N 4 O/PrO 2 catalyst to investigate the influence of 4f‐3d hybridization on ORR activity and stability. Crystal field distortion in the Fe‐N 4 O/PrO 2 system induces an elevated Fe spin state, where electron redistribution preferentially occupies the 3d z 2 orbitals of Fe active sites. This electronic configuration promotes σ‐orbital occupation in the Fe‐*O 2 adduct, thereby optimizing O 2 adsorption and facilitating the ORR process. As a result, the Fe‐N 4 O/PrO 2 catalyst demonstrates exceptional alkaline ORR performance, achieving the high half‐wave potential ( E 1/2 = 0.93 V). Meanwhile, the transition of the Fe center spin configuration optimizes the adsorption/desorption energetics of oxygen intermediates, mitigating the corrosion of Fe active sites by the 2e − by‐product H 2 O 2 and thereby realizing exceptional ORR catalytic stability.