Design and first-principles study of Sc2SSeCl2 monolayer as a promising photocatalyst for water splitting

Currently, two-dimensional photocatalysts for water splitting commonly face challenges such as low solar-to-hydrogen (STH) conversion efficiency, high reaction barriers, and rapid recombination of photogenerated electron–hole pairs. These factors significantly limit their performance and practical applications. To address these issues, this study proposes a novel two-dimensional Sc₂SSeCl₂ monolayer based on first-principles calculations. This material achieves a high STH efficiency of 15.74 %, well exceeding the 10 % threshold required for commercial viability. Under the influence of the photogenerated electric field, the oxygen evolution reaction (OER) exhibits extremely low energy barriers, with two reaction steps proceeding nearly spontaneously, demonstrating excellent catalytic kinetics. Furthermore, using the deformation potential (DP) theory, the hole mobility is calculated to be 2.30 × 10⁴ cm² V⁻¹ s⁻¹, while the electron mobility is 6612.56 cm² V⁻¹ s⁻¹. In comparison, the electron-phonon coupling method yields a hole mobility of 875.34 cm² V⁻¹ s⁻¹ and an electron mobility of 181.47 cm² V⁻¹ s⁻¹. Both methods indicate that the material exhibits excellent charge carrier mobility, with the hole mobility significantly higher than that of electrons. Moreover, the DP method generally predicts higher mobilities than the electron-phonon coupling method, reflecting the influence of different theoretical models on mobility calculations. Additionally, the material possesses a moderate indirect bandgap of 2.56 eV and strong visible light absorption capability. In summary, Sc₂SSeCl₂ effectively overcomes the key bottlenecks of two-dimensional photocatalysts and shows broad application prospects in photocatalytic water splitting.