Iodization engineering at vacancy defects re-balances charge distribution of FeN₄ active sites

Regulating the electronic structure of FeN₄ active sites in iron‑nitrogen‑carbon (Fe-N-C) catalysts represents a promising approach to enhance their intrinsic activity for the oxygen reduction reaction (ORR). However, developing effective strategies to achieve heteroatom-doping near FeN₄ sites and gaining mechanistic insights into their ORR electrocatalytic behavior remain significant challenges. In this work, we propose an iodization engineering approach to modulate the charge distribution of FeN₄ centers in a Fe and iodine (I) co-doped N-containing carbon framework (Fe-N-I/CF) catalyst, and investigate the regulatory mechanism of I-doping on the electronic structure of the Fe active sites through spectroscopic characterizations and theoretical calculations. Strategic I-doping at N-rich vacancy defects adjacent to atomic FeN₄ sites with an average FeI distance of ∼4.2 Å can effectively rebalance the local charge distribution of the Fe center. This rebalancing lowers the free energy barrier of the rate-determining step and induces a continuous downshift of the d-band center, thereby enhancing ORR electrocatalytic performance. The optimized Fe-N-I/CF catalyst exhibits a high half-wave potential of 0.937 V (vs. RHE) and enables zinc-air batteries to achieve a peak power density of 268.8 mW cm^-2 with excellent stability over 720 h.