Synergistic effect of mechanical stimuli and defects on the catalytic activity of Janus transition metal dichalcogenides for hydrogen evolution reaction: an explicit first-principles study

Developing catalysts based on transition metal dichalcogenides (TMDs) represents a promising aspect for the application of TMD materials. Our extensive first-principles calculations and ab initio molecular dynamics simulations, which incorporate an explicit solvation model, reveal that the introduction of vacancy defects into Janus TMD (MXY, where M = Mo or W; X/Y = S, Se, or Te, and X ≠ Y) monolayers can activate their catalytic capability for the hydrogen evolution reaction (HER). The application of biaxial tensile strain further enhances the catalytic activity of vacancy-defected WSeS, WSSe and WTeS monolayers, but weakens that of other Janus TMD monolayers. When the electronegativity of the top surface X atoms of a vacancy-defected MXY monolayer is relatively weaker, applying a biaxial tensile strain leads to lower elastic energy and higher hydrogen adsorption energy at the vacancy site for the MXY monolayer, along with a larger deviation in its hydrogen adsorption Gibbs free energy. The unveiled relationship between mechanical energy, hydrogen adsorption energy, and surface electronegativity deepens our understanding of the role of mechanical stimuli in modulating and improving the catalytic activity of Janus TMDs for the HER.