Lattice Chloride Shielding and Reconstructed Phosphate Armor for Stable Seawater Electrolysis

ABSTRACT Achieving selective oxygen evolution while suppressing competing chlorine evolution and chloride‐induced corrosion remains a key challenge for practical seawater electrolysis. Herein, a series of halogen‐modified heterostructures, X‐Co(OH) 2 @CoP 4 (X = F, Cl, Br, I), are constructed via an electrochemical synthesis strategy, in which Cl‐Co(OH) 2 @CoP 4 exhibits the optimal catalytic performance following a volcano‐type activity trend. In situ and ex situ analyses reveal that lattice Cl incorporation coupled with reconstructed phosphate species establishes a dual‐protection mechanism that promotes selective OH − adsorption while suppressing competing chlorine evolution reactions during seawater electrolysis. Specifically, lattice Cl regulates the electronic structure of Co centers and suppresses chloride‐induced corrosion, while the surface CoP 4 layer undergoes in situ transformation into phosphate species under anodic polarization, generating a protective outer layer. Density functional theory calculations further confirm that halogen incorporation enhances OH − selectivity and lowers the reaction free‐energy change. Benefiting from this cooperative regulation strategy, a symmetric Cl‐Co(OH) 2 @CoP 4 electrolyzer delivers a current density of 500 mA cm −2 at only 1.67 V in alkaline seawater and operates stably for over 2700 h. This work provides an effective strategy for constructing corrosion‐resistant electrocatalysts that integrate intrinsic electronic regulation with dynamic surface protection for practical seawater electrolysis.