Monolayer CdSnP₂S₆ with favorable band alignment and high solar-to-hydrogen efficiency

Developing two-dimensional photocatalysts with suitable band structures, efficient carrier transport, and favorable surface reaction activity is crucial for solar-driven water splitting. In this work, the photocatalytic performance of monolayer CdSnP₂S₆ was systematically investigated using first-principles calculations. The results show that CdSnP₂S₆ possesses good structural, thermal, dynamical, and mechanical stability. Electronic structure calculations reveal that monolayer CdSnP₂S₆ is an indirect semiconductor with suitable band-edge positions for overall water splitting. The pH-dependent band alignment further confirms that its conduction and valence band edges can straddle the water redox potentials over a broad pH range (0-14), indicating favorable thermodynamic feasibility under different reaction conditions. Optical absorption analysis shows that CdSnP₂S₆ exhibits strong light response in the visible-to-ultraviolet region, with a maximum absorption coefficient of about 5.20 × 10⁵ cm^-1. Surface reaction analysis suggests that S atoms serve as the main active sites for hydrogen evolution, and the hydrogen adsorption free energy can be significantly optimized under the photogenerated electric potential. Moreover, CdSnP₂S₆ exhibits a solar-to-hydrogen efficiency of 11.56%, exceeding the 10% benchmark for practical solar hydrogen production. These findings demonstrate that monolayer CdSnP₂S₆ is a promising two-dimensional photocatalyst for efficient overall water splitting.