Screening Multi-layered Two-dimensional Cd-chalcogenide Structures as Potential Candidates for Photocatalysis

In recent years, clean and sustainable energy generation by photocatalytic water splitting has gained enormous attention from researchers. Two-dimensional Cd-based structures play a central role in the research of semiconductor-based photocatalysis. Here, a few layers of cadmium monochalcogenides (CdX; X=S, Se, and Te) are theoretically investigated using density functional theory (DFT). For their potential applicability in photocatalysis, it is proposed that they are exfoliated from the wurtzite structure with an electronic gap that depends on the thickness of the proposed systems. Our calculations address a long-standing doubt about the stabilities of free-standing CdX monolayers (ML). Induced buckling removes the acoustic instabilities in 2D planar hexagonal CdX structures (due to interlayer interactions) that depend on the number of neighboring atomic layers present. All studied (and stable) systems have an electronic gap of >1.68 eV, calculated with hybrid functionals (HSE06). A band-edge alignment plot about the water's oxidation-reduction potential is constructed, and a potential energy surface is constructed for the hydrogen evolution reaction. Our calculations suggest that the chalcogenide site is most favorable for hydrogen adsorption, and the energy barrier falls within the experimentally achievable limits.