Flexoelectricity enhanced water splitting and hydrogen evolution reaction on grain boundaries of monolayer transition metal dichalcogenides

Our extensive first-principles calculations reveal that the chemical activities of monolayer transition metal dichalcogenides (TMDs) MX₂ (M = Mo or W, and X = Te, Se, or S) for water splitting and hydrogen evolution are modified and promoted on their grain boundaries (GBs) when in-plane tensile loadings are applied. Compared with monolayer TMDs without GBs, the flexoelectricity induced by nonuniform deformation and strain gradient significantly enhances the charge polarizations of X and M atoms at the GB sites of monolayer TMDs, which facilitates the dissociation of water molecules on the GB sites and reduces the reaction barrier of hydrogen evolution reaction. The energy barriers of splitting water molecules and hydrogen adsorption free energies on the GB sites decrease with increasing the flexoelectric effect. These results highlight an attractive way of utilizing the flexoelectric effect of GB-containing TMDs to improve their surface catalytic capability for hydrogen generation.