Cationic Vacancy Modulates Co Spin State in CoP for pH-Universal and Seawater Hydrogen Evolution

Abstract Precisely controlling cationic vacancy concentration to tune the spin configuration of metal sites remains a challenge for designing high-performance hydrogen evolution reaction (HER) electrocatalysts. Here, we demonstrated a density functional theory-guided strategy to programmatically engineer cationic vacancies in cobalt phosphide (CoP), enabling targeted modulation of the Co spin state. Theoretical screening identified 8.33% cation vacancies as optimal, which rearranged the unpaired 3d electrons of adjacent Co atoms, lowered the Co magnetic moment to 0.944 μB, and achieved near-thermoneutral hydrogen adsorption free energy (ΔGH* = 0.027 eV). Guided by this prediction, we synthesized CoP-V-0.5 with experimentally determined vacancy concentrations of 10.1% (bulk, ICP-OES) and 7.07% (surface, XPS), which closely approximated the theoretical optimum (8.33%) and validated the DFT-guided design. The optimized catalysts exhibited outstanding HER activity, requiring only 94, 116, and 106 mV to achieve 100 mA cm–2 in 1.0 M KOH, 0.5 M H2SO4, and 1.0 M PBS, respectively, and operated stably for 50 h in alkaline seawater. This work established a theory-guided, spin-mediated paradigm for defect engineering in electrocatalysis.