Electrochemical Hydrogen Evolution at the Interface of Monolayer VS₂ and Water from First-Principles Calculations

Density functional theory calculations are carried out to study the hydrogen evolution reaction (HER) at the electrochemical double-layer interface of monolayer 2H phase VS₂ and water. Under typical conditions of HER, the catalyst surface is predicted to have a low hydrogen coverage of about 12%, whereas the aqueous solution side features a high hydronium concentration of about 8.3%. As a result, the HER takes place through the Volmer-Heyrovsky route, with an overall reaction barrier of about 1.0 eV, much larger than that of 1T phase VS₂. This result demonstrates that 2H phase VS₂ is much less reactive than its 1T phase counterpart, and the 1T-to-2H phase transformation induced by thickness reduction may deteriorate the HER activity of VS₂.