LAUSR

The electronic and catalytic properties of Janus bismuth oxyhalide (Bi2O2XY, where X/Y = Cl, Br, or I, and X ≠ Y) for the hydrogen evolution reaction (HER) are evaluated through first-principles calculations. Janus Bi2O2XY shows an enhanced separation efficiency of electron-hole pairs and an augmented utilization of solar energy due to Janus asymmetry. The asymmetric halogen surfaces on both sides of Janus Bi2O2XY induce an electrostatic potential difference, which leads to a staggered band alignment. The solar-to-hydrogen (STH) efficiencies of Janus Bi2O2BrI and Bi2O2ClI have greatly improved compared to those of pristine BiOBr and BiOCl. Additionally, Janus Bi2O2XY achieves stronger internal electric fields (IEFs) and a more suitable Gibbs free energy of hydrogen adsorption (ΔGH) than pristine BiOX. Moreover, the halogen layer with a smaller electronegativity in Janus Bi2O2XY forms a stronger IEF with the oxygen layer; consequently, the ΔGH of terminations value is closer to the ideal value for the HER. The localized edge states in the p-orbital density of states (DOS) projected onto O atoms are responsible for the HER activity of terminations. This work provides a comprehensive understanding of Janus Bi2O2XY for the HER and provides a strategy for improving photocatalysis.