Surface oxidation protection strategy of CoS₂ by V₂O₅ for electrocatalytic hydrogen evolution reaction

Transition metal sulfides (TMSs) are promising electrocatalysts for hydrogen evolution reaction (HER), while TMSs usually suffer from inevitable surface oxidation in air, and the impact of the surface oxidation on their HER catalytic activity remains unclear. Herein, we demonstrate an effective strategy for reducing the surface oxidation degree of easily oxidized CoS₂ by introducing glued vanadium pentoxide (V₂O₅) nanoclusters, taking advantage of the preferential adsorption and strong interaction between high-valence V and O₂. Combining oxidation protection and elaborate oxidation control experiments reveal that reduced surface oxidation degree of CoS₂ is conducive to affording promising HER catalytic performance, as the oxidized surface of CoS₂ can hinder the dissociation of water and thus is harmful to the HER process. Direct evidence is provided that surface oxidation should be carefully considered for TMS-based HER catalysts. The present work not only develops a new strategy for protecting CoS₂ from surface oxidation, but also provides deep insight into the impact of surface oxidation on the HER performance of transition metal compounds.