Derivative Ga2S3 monolayers as water-splitting photocatalysts: Enhanced solar to hydrogen conversion for reduced dipole

The intrinsic dipole inside two-dimensional (2D) materials is always expected to enhance solar water splitting, while atomic replacement is a widely applied approach to designing water-splitting photocatalysts. However, the relationship between solar conversion between atomic replacement is unclear. Herein, the water-splitting photocatalytic performance of derivative Ga2S3 (D-Ga2S3) monolayers including Ga2S2Se-b, Ga2S2Se-m, and Ga2S2Se-t are investigated using first-principles studies. Theoretical calculations demonstrate that D-Ga2S3 monolayers can be synthesized due to structural stability, and impressively their dipole moments can be regulated by atomic replacement. They hold separated conduction band minimums (CBMs) and valence band maximums (VBMs), thus supporting hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) in different atomic regions. They have abundant driving forces for water splitting due to large overpotentials. Because of moderate bandgaps, they absorb large amounts of visible and infrared light. Among them, Ga2S2Se-m and Ga2S2Se-t monolayers possess solar-to-hydrogen (STH) efficiency (∼18%), far exceeding the commercial standard (10%). More remarkably, we find that the intrinsic dipole is inversely related to the STH efficiency and can be purposefully regulated by atomic replacement. Thereby, this work directly correlates the STH efficiency with the atomic replacement. Finally, the HER and OER of single-layer Ga2S2Se-t can be accomplished under light irradiation.