Axial-polarized curvature-type single-site catalysts for efficient oxygen Electroreduction

FeN based molecular complexes with clear structure-activity relationships are promising low-cost alternatives to precious-metal catalysts toward the oxygen reduction reaction (ORR). Nevertheless, how heterogenized molecular configurations affect catalytic performance remains poorly understood. Herein, single-site iron phthalocyanine (FePc) is selected as a model to clarify the correlation between out-of-plane structural modulation and ORR enhancement. Density functional theory calculations reveal that out-of-plane FePc (op-FePc) switches oxygen adsorption from end-on to side-on configuration via optimized orbital hybridization, facilitating the ORR via a kinetically favorable dissociative pathway. Finite element simulations combined with in situ spectroelectrochemical measurements confirm that op-FePc optimizes intermediate adsorption energies and induces strong local electrostatic fields, which jointly accelerate proton and electron transfer. The resultant op-FePc exhibits a prominent ORR half-wave potential of 0.916 V versus the reversible hydrogen electrode and a Tafel slope of 36 mV dec^-1, which are competitive with those of the state-of-the-art Fe-N-C catalysts. When applied to rechargeable zinc-air batteries, it delivers a peak power density of 247 mW cm^-2 and a specific capacity of 811.2 mAh g^-1_Zn. This work demonstrates that molecular out-of-plane engineering is an effective strategy to regulate the catalytic behavior of molecular electrocatalysts for high-efficiency energy conversion.