Two-dimensional few-layer group-III metal monochalcogenides as effective photocatalysts for overall water splitting in the visible range

Abstract

Using first-principles calculations, the photocatalytic performances of two dimensional (2D) few-layer group-III metal monochalcogenides MXs (M = Ga, In; X= S, Se) towards overall water splitting reaction are systematically investigated. On the basis of two criteria, i.e., the band edge positions need to straddle the oxidation potential of H₂O and the reduction potential of H₂, and an optimal band gap of ∼2.0 eV is required to enhance absorption in the visible range, it was found that few-layer GaSe is the most appropriate photocatalyst for overall water splitting. Further calculations revealed that: (i) with the number of layers increasing, few-layer GaSe tends to evolve into a direct bandgap semiconductor, and meanwhile, energy conversion efficiency of sunlight increases; (ii) carrier mobilities of few-layer GaSe are estimated to be as high as 880–7000 cm² V⁻¹ s⁻¹, and photogenerated electrons and holes tend to spatially separate; and (iii) few-layer GaSe is predicted to be highly stable at room temperature. In brief, few-layer GaSe is demonstrated to have high stabilities, suitable band edge positions, optimal band gap value, high carrier mobility, and effective spatial separation of photogenerated electron–hole pairs as well as excellent solar absorption, leading to its high promise as a next-generation 2D photocatalyst for overall water splitting in the visible range. Our results would motivate more experimental and theoretical research to further explore the potential of 2D few-layer GaSe as photocatalysts.