Electronic and Lattice Modulation of Co _x P Nanosheets by In‐Situ Doped Boron to Enhance Activity and *Cl Anti‐Poisoning in Alkaline Seawater Electrolysis

ABSTRACT The high chloride (Cl) concentration in seawater presents a critical challenge for hydrogen production via seawater electrolysis by deactivating catalysts through active site passivation, highlighting the need for catalyst innovation. Herein, in situ boron‐doped Co ₂ P/CoP (B‐Co _x P) ultrathin nanosheet arrays are prepared as high‐performance bifunctional electrocatalysts for seawater decomposition. Density functional theory (DFT) simulations, comprehensive characterizations, and in‐situ analyses reveal that boron doping enhances electron density around Co centers, induces lattice distortions, and significantly elevates catalytic activity and durability. Moreover, boron doping reduces *Cl retention time at active sites—defined as the DFT‐derived residence time of adsorbed Cl intermediates based on their adsorption energies—effectively mitigating Cl‐induced poisoning. In a three‐electrode system, B‐Co _x P achieves exceptional bifunctional performance with overpotentials of 11 mV for hydrogen evolution reaction and 196 mV for oxygen evolution reaction to deliver 10 and 50 mA·cm ^–2 , respectively—a result that showcases its superior bifunctional properties surpassing noble metal‐based counterparts. In an alkaline electrolyzer, it delivers 1.56 A·cm ^–2 at 2.87 V for seawater electrolysis with outstanding stability over 500 h, preserving active site integrity via boron's robust protective role. This study defines a paradigm for designing advanced seawater electrolysis catalysts through a strategic in‐situ doping approach.