Spin‐State Engineering of Iron Phthalocyanine D‐Orbitals via Atomic Fe‐N 4 Coupling for Enhanced Oxygen Reduction Reaction

Abstract

Since the properties of electron transfer and orbital interactions in oxygen electrocatalysts are highly spin‐dependent, reaction kinetics and thermodynamics are very sensitive to the spin configuration. However, understanding the spin‐related origin of catalytic activity in heterogeneous molecular electrocatalysts still remains challenging. Herein, a molecular‐atomic coupled catalyst is constructed by integrating iron phthalocyanine (FePc) molecules with Fe‐N 4 atomic sites anchored on nitrogen‐doped carbon nanotubes (FePc‐Fe‐NCNT). The strong electronic coupling between FePc and the Fe‐N 4 ‐containing carbon substrate triggers a transition of the Fe sites from a low‐spin state to an intermediate‐spin state. Additionally, the formation of σ* bonds between the electron‐injected perpendicular d z2 orbitals of intermediate‐spin Fe and the 2p orbitals of adsorbed oxygen species suppresses site blocking and accelerates OH* desorption, thereby enhancing the reaction kinetics of the oxygen reduction reaction (ORR). The resulting catalyst exhibits exceptional ORR activity in alkaline media, reaching a half‐wave potential of 0.89 V and negligible degradation after 10,000 cycles. Remarkably, the quasi‐solid‐state Zinc‐air battery based on this prepared catalyst operates stably from −40 to 70 °C with minimal performance loss. This work reveals a spin‐state manipulation strategy for the development of advanced molecular catalysts and provides new insights into the regulation of electronic structure for energy conversion technologies.