Strain engineering of type-II C2N/WS2 van der Waals heterojunction for highly enhanced photocatalytic hydrogen evolution

The first-principles calculations demonstrate that the photocatalytic performance of type-II C2N/WS2 van der Waals heterobilayer can be improved to a new and high level by applying weak biaxial strain, with desired band structure, tunable interface charge transfer, superior visible-light absorption, and ideal hydrogen evolution reaction (HER) activity. Tensile strains can largely reduce the energy gap, strengthen the interfacial interactions, and promote the visible-light absorption of C2N/WS2 heterostructure, and even induce a direct band gap of 1.70 eV for overall water splitting at 2% strain. Compressive strains like −2% can upshift the valence band and conduction band positions of the C2N/WS2 bilayer to acquire outstanding redox abilities, and enhance the interface charge transfer and separation by increasing the electrostatic potential drop. More importantly, the cycle between spontaneous H∗ adsorption and energetically favorable H2 release may be realized by dynamic strains between ±2%, maximizing the HER activities of C2N/WS2 heterostructure.