Pyridine‐Isomerism‐Driven Spin Engineering at a COP‐Fe ₃ O ₄ Interface for High‐Performance Oxygen Reduction Electrocatalysis

ABSTRACT The oxygen reduction reaction (ORR) activity of earth‐abundant transition‐metal (TMOs) oxides is limited by inefficient interfacial charge transfer and unfavorable surface adsorption. Here, we report pyridine‐isomerism‐driven interfacial spin‐engineering in covalent organic polymer (COP)‐Fe ₃ O ₄ hybrids, where molecularly defined pyridinic environments program the electronic/spin structure of Fe ₃ O ₄ nanocrystals. Using 2,3‐ and 3,4‐diaminopyridine as isomeric building blocks, we construct pyridinic‐rich COPs that anchor Fe ₃ O ₄ and selectively tune metal‐polymer interaction. The 2,3‐COP positions the pyridinic N adjacent to the ─C═C─N─ linkage, strengthening COP‐Fe ₃ O ₄ interactions, enhancing interfacial electron withdrawal, and inducing a low‐ to intermediate‐spin transition of Fe species. Spectroscopic analysis corroborates this reconfiguration, which upshifts the Fe d‐band center, enriches unpaired electrons, and optimizes Fe‐O covalency, thereby lowering the barrier for OOH* activation and promoting a selective four‐electron ORR pathway with improved stability. Consequently, the designed 2,3‐COP‐Fe ₃ O ₄ electrocatalyst exhibits a stable half‐wave potential of 0.890 V in alkaline electrolyte, outperforming the noble‐metal benchmark. Moreover, when implemented in aqueous Zn‐air batteries, it delivers a maximum power density of 315.4 mW cm ⁻² and maintains stable operation for over 800 h at 10 mA cm ⁻² , exceeding most reported systems. These findings establish pyridine‐isomerism‐directed spin‐engineering as a versatile and scalable platform for designing applicable high‐performance TMO‐based electrocatalysts.