Plasma-induced vacancies in CoS₂ electrocatalysts to activate sulfur sites for hydrogen evolution reaction

Exploring efficient non-precious metal sulfides as electrocatalysts for the hydrogen evolution reaction (HER) is crucial. Cobalt disulfide (CoS2) has gained attention for its favorable intrinsic activity, impressive metal conductivity, and cost-effectiveness. However, the weak adsorption of H* at the sulfur (S) sites on the surface of CoS2 leaves room for enhancing its HER intrinsic activity. Vacancy engineering emerges as a valuable strategy to modulate the local charge density, optimizing hydrogen adsorption free energy and catalytic performance in HER. Taking advantage of plasma technology, known for its rapid and efficient defect creation, we synthesized porous CoS2 nanowire arrays enriched with S vacancies (Vs-CoS2/CC) through Ar plasma treatment. Notably, at a current density of 10 mA cm-2, Vs-CoS2/CC exhibits a lower overpotential (170 mV) compared to pure CoS2/CC (236 mV). Furthermore, Vs-CoS2/CC demonstrates exceptional electrochemical stability. Experimental data and density functional theory calculations jointly reveal that introducing S vacancies reduces local charge density around S atoms, activating inert sulfur sites and enhancing the intrinsic activity of CoS2 for HER. This study introduces a novel concept of defect-engineered activation in metal compound catalysts, employing a plasma approach to advance HER performance.