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

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. [ABSTRACT FROM AUTHOR]