Regulatingthe Co-Spin State in a CoP/Co₂P Heterojunction by PhosphorusVacancies for Efficient Seawater HydrogenEvolution

Hydrogen energy production through seawater splitting is an essential route for a sustainable energy society; however, it is impeded by chlorine corrosion. Therefore, the rational design of highly efficient electrocatalysts for hydrogen evolution by repelling chlorine ion effects is key to unlocking its wide operation. Herein, we report the facile construction of a cobalt phosphide heterojunction with phosphorus vacancies for efficient hydrogen evolution, which needs overpotentials of 82/287 mV and 75/237 mV to achieve a current density of 10/100 mA cm^–2 in 1 M KOH and simulated seawater (1 M KOH + 0.5 M NaCl), respectively, outperforming numerous reported non-noble-metal-based electrocatalysts in water/seawater systems. Additionally, the catalyst demonstrates long-time stability over a 120 h period in simulated seawater. More profoundly, both experimental and computational results demonstrate that phosphorus vacancies induce a higher spin state in cobalt atoms within phosphides, which accelerates the desorption of hydrogen species and creates a significant repulsive effect on Cl^–, consequently contributing to significantly enhanced hydrogen evolution in simulated seawater.