Semiconducting Scandium/Yttrium Chalcohalides: Promising Visible-Light-Driven Photocatalysts for Overall Water Splitting

Two-dimensional (2D) photocatalysts have attracted significant attention in photocatalytic water splitting due to their high surface-area-to-volume ratio and tunable electronic properties. However, enhancing the absorption capacity of 2D photocatalysts remains a fundamental challenge. Through first-principles calculations, we have identified eight scandium/yttrium chalcohalide monolayers (ScSI, ScTeI, ScSeZ, and YTeZ; Z = Cl, Br, I) in the α phase as promising candidates for visible-light-driven overall water splitting, exhibiting appropriate band gaps and band-edge positions. Our analysis of optical absorption spectra demonstrated that the visible-light response increases with the number of layers. Particularly, the absorption intensity of α-ScTeI increases from 15% for the monolayer to 45% for the seven-layer structure. In addition, both monolayer and bulk α-ScTeI show a low exciton binding energy, comparable to that of MoS₂, while demonstrating a superior carrier mobility and a longer hot carrier cooling time. These characteristics make them promising candidates for photocatalysis. Our discovery of van der Waals scandium/yttrium chalcohalides as efficient photocatalysts introduces potential candidates for overall water splitting and scalable hydrogen production.