f-p-d Gradient Orbital Coupling Induced Spin State Enhancement of Atomic Fe Sites for Efficient and Stable Oxygen Reduction Reaction

Advancing energy conversion technologies requires cost-efficient electrocatalysts for the oxygen reduction reaction (ORR). Iron phthalocyanine (FePc) emerges as a scalable and economical ORR electrocatalyst. However, the Fe–N₄ configuration in FePc still falls short of the satisfied ORR activity and stability under electrocatalytic conditions. Here, an effective f-p-d (Eu–O–Fe) gradient orbital coupling strategy is introduced by integrating FePc with Eu₂O₃ (FePc/Eu₂O₃) to enhance the spin state and ORR performance of the Fe center through a precisely designed, scalable synthetic approach. The Eu─O bond promotes electron delocalization and shifts the spin state of Fe center from low-spin to intermediate-spin, increasing the e_g​ orbital occupancy. This modification optimizes the adsorption of oxygen-containing intermediates and lowers the ORR energy barrier. Notably, the increased spin state of Fe accelerates charge transfer by releasing more unpaired electrons, improving reaction kinetics. Furthermore, the f-band serves as a buffer layer for electron compensation during ORR, further stabilizing the covalency and electronic configuration of atomic Fe and boosting durability. The one-batch synthesis produces exceeding 300 g of FePc/Eu₂O₃, achieving a half-wave potential of 0.931 V (vs RHE) at a cost less than 1/15 of commercial Pt/C. It demonstrates exceptional ORR performance in aluminum–air batteries, highlighting its significant application potential. © 2025 The Author(s). Advanced Functional Materials published by Wiley-VCH GmbH.