Theoretical prediction of two-dimensional WSi2N4 materials for photocatalytic water splitting

Abstract

Recently, novel two-dimensional (2D) crystals, MSi2N4 (M = Mo, W) materials, have been successfully synthesized experimentally and have comparable excellent catalytic properties as that of MoS2. The suitability of MA2Z4 family materials in photocatalytic water splitting can't be fully determined by whether the bandgap edge of the material cross the standard redox potential of water. Photoelectric properties and electron–hole separation are also critical factors to be considered. We investigated the bandgap edge positions and the photoelectric and the electron–hole excitation properties of 2D MoSi2N4 and its family of materials (CrSi2N4, WSi2N4) in water by first-principles calculations, and the results indicate that WSi2N4 may be a relatively high-performing photocatalyst. Relative to the MoSi2N4 bandgap (1.74 eV), the bandgap of WSi2N4 is 2.06 eV, and the conduction-band minimum edge band potential (−0.42 eV) is close to the hydrogen precipitation potential in water at pH = 7. The bandgaps of the MSi2N4 (M = Mo, W) materials cross the water redox potential (1.23 eV), and both have favorable adsorption for H2O molecules. However, compared with the absorption spectrum and excited states of MoSi2N4 in water, WSi2N4 exhibits a broader and more enhanced visible light absorption range and intensity as well as a higher electron–hole separation. 2D WSi2N4 could achieve the half-reaction of photocatalytic water splitting under visible light irradiation, and the photogenerated electrons in the conduction band can spontaneously reduce H+ ions to hydrogen, suggesting that WSi2N4 might be composed of a heterogeneous structure with other photocatalysts to accomplish the redox of water.