γ‑Ray Defect-Driven Axial Fe─O─C Bridging Enables FeN₄ Coordination Field Modulation Toward High-Performance Seawater...

Conventional planar FeN₄-based single-atom catalysts are limited by their D₄h-symmetric electronic structure, causing poor matching of adsorption-desorption energy-barrier for multiple oxygen reduction reaction (ORR) intermediates and susceptibility to Cl^- corrosion and deactivation in chlorine-rich seawater environments. Hence, we constructed FeN_4-OH/single-walled carbon nanotube (FeN_4-OH/CNTs) single-atom catalysts featuring axial ·OH coordination through γ-ray-irradiation-based modification. Results revealed that γ-ray irradiation induced an axially coordinated FeN_4-OH structure, breaking the electronic symmetry of planar FeN₄. Reshaped the electric field gradient and spin electron distribution at the Fe center, achieving a controllable transition from low spin to high spin. This structure addressed insufficient O₂ adsorption and reactant activation in the original configuration while preventing active-site poisoning from excessive intermediate adsorption. It also markedly suppressed strong Fe-Cl^- interactions, endowing the catalyst with outstanding Cl^- corrosion resistance. FeN_4-OH/CNTs also exhibited higher intrinsic ORR activity surpassing that of commercial Pt/C in a simulated seawater electrolyte. An assembled seawater-based zinc-air battery achieved a peak power density (294 mW cm^-2) and long-term cycling stability (>300 h). This study provides reliable experimental evidence and theoretical guidance for rationally designing and constructing high-performance, corrosion-resistant single-atom catalysts for marine energy conversion applications.