Hydrogen generation from direct Z-scheme for photocatalytic overall water splitting with the SiSe/SnSe2 and SiSe/SnSSe heterostructures

The direct Z-schemes of the photocatalytic overall water splitting with the SiSe/SnSe2, SiSe/SnSSe-I, and SiSe/SnSSe-II heterostructures are constructed based on the density functional theory calculations and nonadiabatic molecular dynamics (NAMD) simulations. The maximum solar-to-hydrogen efficiency (eta(STH)') reaches 19.18% and can be promoted to 28.71% under tensile biaxial strains. NAMD simulations indicate the transfer of the electron for hydrogen evolution reaction (HER) and hole for oxygen evolution reaction (OER) for SiSe/SnSe2 are apparently slower than those for the other two heterostructures, implicating the reduction and oxidation activities of this heterostructure are well-protected. Moreover, the shortest electron-hole recombination time is attributed to SiSe/SnSSe-I, indicating that it holds the best photocatalytic performance. Remarkably, the Gibbs free energies indicate that HER and OER with SiSe/SnSSe-I can spontaneously proceed, while OERs can but HERs cannot spontaneously proceed with the other two heterostructures. Therefore, the new found heterostructures, especially SiSe/SnSSe-I, are promising candidates in photocatalytic overall water splitting.