An Ab Initio Study of Two Dimensional SnX₂ and Janus SnXY (X = S, Se) Nanosheets as Potential Photocatalysts for Water Splitting

Discriminating appropriate two-dimensional (2D) photocatalysts for hydrogen generation is among the most prospective schemes to tackle with environmental contaminations. Unfortunately, the inferior capability to harvest solar light together with fast recombination of photoexcited carriers can severely reduce the catalytic ability with consequent limited commercial applications. In this work, a series of single-layer MXY (M = Ge, Sn; X, Y = S, Se, and Te) containing T- and H-phases about photocatalytic capabilities are systematically explored by first-principles calculations. First, the T- and H-MXY monolayers possess transformable band gaps of 0–2.37 and 0–1.49 eV, respectively. Astonishingly, the values of T-GeS 2, T-SnS 2, T-SnSe 2, T-SnSSe, and H-SnS 2 monolayers are higher than the threshold of redox potential difference (1.23 eV). Also, importantly, the carrier mobilities of anisotropic T-MXY monolayers can reach ∼1 × 10 4 cm 2 V –1 s –1, which can rapidly transfer and accelerate the separation of the photoexcited carriers during photocatalytic reactions. Inspired by these significant benefits, the T-MXY monolayers have been built for photocatalytic water-splitting. Significantly, the driving force of photoexcited carriers in T-SnX 2 and Janus T-SnSSe monolayers can greatly promote during the redox reactions. Furthermore, the hydrogen reduction and water oxidation reactions of T-SnX 2 and T-SnXY monolayers can proceed spontaneously under irradiation. In addition, the few-layer and even monolayer T-SnS 2 and T-SnSe 2 have been experimentally synthesized in the literature. The potential photocatalysts of single-layer T-MXY have the 0.25–0.29 J m –2 cleavage energies, and ab initio molecular dynamics simulations further validate their stability. Our results provide support for 2D group-IV–VI chalcogenides for photocatalytic water splitting.