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) photocatalystsfor hydrogen generation is among the most prospective schemes to tacklewith environmental contaminations. Unfortunately, the inferior capabilityto harvest solar light together with fast recombination of photoexcitedcarriers can severely reduce the catalytic ability with consequentlimited commercial applications. In this work, a series of single-layerMXY (M = Ge, Sn; X, Y = S, Se, and Te) containing T- and H-phasesabout photocatalytic capabilities are systematically explored by first-principlescalculations. First, the T- and H-MXY monolayers possess transformableband gaps of 0-2.37 and 0-1.49 eV, respectively. Astonishingly,the values of T-GeS2, T-SnS2, T-SnSe2, T-SnSSe, and H-SnS2 monolayers are higher than the thresholdof redox potential difference (1.23 eV). Also, importantly, the carriermobilities of anisotropic T-MXY monolayers can reach similar to 1 x10(4) cm(2) V-1 s(-1), which can rapidly transfer and accelerate the separation of thephotoexcited carriers during photocatalytic reactions. Inspired bythese significant benefits, the T-MXY monolayers have been built forphotocatalytic water-splitting. Significantly, the driving force ofphotoexcited carriers in T-SnX2 and Janus T-SnSSe monolayerscan greatly promote during the redox reactions. Furthermore, the hydrogenreduction and water oxidation reactions of T-SnX2 and T-SnXYmonolayers can proceed spontaneously under irradiation. In addition,the few-layer and even monolayer T-SnS2 and T-SnSe2 have been experimentally synthesized in the literature. Thepotential photocatalysts of single-layer T-MXY have the 0.25-0.29J m(-2) cleavage energies, and ab initio moleculardynamics simulations further validate their stability. Our resultsprovide support for 2D group-IV-VI chalcogenides for photocatalyticwater splitting.