Spin-State Engineering of Iron Phthalocyanine D-Orbitals via Atomic Fe-N4 Coupling for Enhanced Oxygen Reduction Reaction.

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-N4 atomic sites anchored on nitrogen-doped carbon nanotubes (FePc-Fe-NCNT). The strong electronic coupling between FePc and the Fe-N4-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 dz2 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.