Prediction of direct Z-scheme H and H́-phase of MoSi₂N₄/MoSX (X = S, Se) van der Waals heterostructures: A promising candidate for photocatalysis

Photocatalysis has emerged as an appealing strategy for environmental remediation and sustainable energy production. The density functional theory (DFT) approximations were employed to investigate the heterostructures (HTS) of 2H and 2H́ polymorphs of MoSi₂N₄/ MoSX (X = S, Se) for photocatalytic applications. To ensure their applicability for water-splitting photocatalysis, we examined the heterostructures for desirable electronic properties. The structures (except 2H́-MoSi₂N₄/MoSSe) have a direct Z-scheme type-II alignment which further favors the carrier separation causing hydrogen and oxygen production at distant positions. The bandgaps of structures lie within the desirable range of 1.23 to 3 eV, favoring visible light absorption. The difference in the work function of monolayers (of about 0.5 to 1 eV) develops an electric field at the interface of HTS, causing the separation of carriers. The reduction potential lies between −3.8 to −4.6 eV, while the oxidation potential lies between −5.7 to −6.2 eV. It indicates that although oxidation potentials incorporate water redox levels, reduction potentials of some HTS do not. To ensure HER, Gibbs free energies were calculated. The vacancy defects at S/Se site gave ΔG_H^∗ less than the catalytic threshold of 0.2 eV. Due to ultrafast charge transfer, broad spectral response, and improved photocatalytic capability due to the formation of radicals at the surface, heterostructures can act as a competitive choice over monolayers for water-splitting photocatalysis.