Regulating the Spin State of Fe-N4 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-N4 centers from a low-spin (t2g 6 eg 0) to an intermediate-spin (t2g 5 eg 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.