Regulating the Spin State of Fe‐N ₄ Sites via Electronic Metal‐Support Interactions Enables Chloride‐Tolerant Bifunctional Oxygen Catalysis

As a next‐generation energy storage technology, seawater‐based zinc‐air batteries (SZABs) hold great promise for efficiently utilizing marine energy. However, oxygen electrocatalysis at the air cathode remains severely impeded by inherent sluggish kinetics and detrimental Cl − interference in chloride‐rich electrolytes. To address this bottleneck, we report an electronic metal‐support interactions (EMSIs)‐driven spin‐state engineering strategy, wherein Fe–NC support is integrated with low‐loading PtFeCu alloy nanoparticles. Experimental and theoretical studies reveal that the EMSIs trigger a critical spin‐state transition of Fe–N 4 centers from a low‐spin (t 2g 6 e g 0 ) to an intermediate‐spin (t 2g 5 e g 1 ) configuration, which effectively adjusts Fe–O d ‐ p orbital interactions and mitigates Cl − binding. The resulting catalyst delivers remarkable bifunctional activity and long‐term stability in alkaline seawater, delivering a high oxygen reduction reaction (ORR) half‐wave potential of 0.909 V, a low oxygen evolution reaction (OER) overpotential of 346 mV at 10 mA cm − 2 , and a narrow voltage gap of only 0.67 V. The assembled SZABs exhibit excellent power density and durability, demonstrating practical potential for maritime emergency and wearable energy devices. This work establishes spin‐state engineering as a potent paradigm for developing efficient and chloride‐tolerant seawater electrocatalysts, and offers mechanistic insights into spin‐state‐dependent catalysis.