Lattice Chloride Shielding and Reconstructed Phosphate Armor for Stable Seawater Electrolysis

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@CoP₄ (X = F, Cl, Br, I), are constructed via an electrochemical synthesis strategy, in which Cl-Co(OH)₂@CoP₄ 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 CoP₄ 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@CoP₄ 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.