Asymmetric Fe-N 4 -O sites enabled by axial oxygen coordination for high-efficiency Zn-air batteries

Abstract Iron-nitrogen-carbon (Fe-N-C) catalysts are a promising class of non-precious electrocatalysts for the oxygen reduction reaction (ORR), with strong potential for integration into emerging energy technologies. Here, an oxygen-bridged axial coordination strategy is employed to anchor iron phthalocyanine (FePc) onto manganese oxide decorated carbon nanotubes (Mn3O4-CNTs). The resulting synergy between asymmetric Fe-N4-O sites and heterojunction interfaces finely tailors the local coordination of Fe centers, which induces electron transfer from the Fe center to the axial O atom and downshifts the Fe d-band center, thereby weakening the adsorption strength of oxygen-containing intermediates and substantially boosting ORR activity. In alkaline media, the optimized FePc-Mn3O4-CNTs catalyst exhibits a high half-wave potential (E1/2) of 0.89 V vs. reversible hydrogen electrode (RHE), a low Tafel slope of 41.51 mV·dec–1, and follows an efficient four-electron pathway. This catalytic performance translates directly into a zinc-air battery that delivers a peak power density of 171.81 mW·cm–2, a specific capacity of 754.12 mAh·g–1, and stable operation for 160 h. This work demonstrates a coordinated strategy combining axial coordination engineering with heterojunction design to synergistically optimize the catalytic properties of Fe-N-C molecular catalysts.