Alloying of ReS ₂ and VS ₂ Nanosheets Enhances Electrocatalytic Hydrogen Evolution Reaction

Abstract Modulating the electronic structure of transition metal dichalcogenides (TMDs) via alloying is challenging despite the additional potential applications. In this study, a solvothermal reaction is used to synthesize composition‐tuned ReS ₂ –VS ₂ (Re _{1‐ x} V _x S ₂ ) alloy nanosheets featuring an expanded interlayer distance. Increasing x induces a phase transition from the semiconducting 1T″ phase ReS ₂ to the metallic 3R‐stacking 1T phase VS ₂ . Alloying via homogeneous atomic mixing renders the nanosheets more metallic and with less oxidation than VS ₂ . First‐principles calculations consistently predict the 1T″–1T phase transition of the atomically mixed alloy structures. The calculation also suggests that intercalation drives the 3R stacking of 1T phase VS ₂ . The Re _{1‐ x} V _x S ₂ nanosheets at x = 0.3–0.8 exhibit enhanced electrocatalytic activity toward water‐splitting hydrogen evolution reaction (HER) in an acid electrolyte. In situ X‐ray absorption fine structure measurements reveal that the metallicity of the alloys is fully retained during HER. The density of states and Gibbs free energy calculations show that alloying increases the metallicity and thus effectively activates the basal S atoms toward the HER, supporting the observed increased HER performance of the alloy nanosheets.