Versatile Gold Telluride Iodide Monolayer as a Potential Photocatalyst for Water Splitting.

Two-dimensional materials promise great potential for photochemical water splitting due to the abundant active sites and large surface area, but few of the known materials meet the rigorous requirements. In this work, we systematically investigate structural, electronic, and optical properties of an experimentally unexplored 2D material, i.e., gold telluride iodide (AuTeI) monolayer using density functional theory and Bethe-Salpeter equation approaches. Bulk AuTeI is a layered material and was realized in experiments a few decades ago. However, its bandgap is relatively small for water splitting. We find the exfoliation of monolayer AuTeI from the bulk phase is highly favorable, and 2D AuTeI is dynamically stable. The bandgap of 2D AuTeI becomes larger due to the quantum confinement effect. Importantly, the edge positions of the conduction band minimum and valence band maximum of 2D AuTeI perfectly fit the water oxidation and reduction potentials, enabling it a promising photocatalyst for water splitting. Additionally, the exciton binding energy of 2D AuTeI is calculated to be 0.35 eV, suggesting efficient electron-hole separation. Our results highlight a new and experimentally accessible 2D material for potential application in photocatalytic water splitting.