First-Principles Study of Two-Dimensional Layered MoSi 2 N 4 and WSi 2 N 4 for Photocatalytic Water Splitting

Two-dimensional (2D) materials have attracted increasing interest due to their excellent properties and various applications such as energy storage, sensors, composites and catalysis. Recently, 2D van der Waals (vdW) layered materials, MoSi 2 N 4 and WSi 2 N 4 , have been synthesized successfully by CVD methods. Here, we have investigated the structure, optoelectronic properties and electron–hole excitation characteristics of two-dimensional MoSi 2 N 4 , MoSi 2 P 4 , and WSi 2 N 4 using first-principles calculations to determine whether they can be applied for photocatalytic hydrolysis. The results showed that replacing N atoms in 2D MoSi 2 N 4 with P atoms could not only reduce the bandgap, but also make the band position more negative, while replacing Mo atoms with W atoms could expand and move the bands towards more positive direction. H + ions can obtain electrons to generate H 2 from the conduction band of WSi 2 N 4 where the conduction band minimum (CBM) and valence band maximum (VBM) is –0.43 and –2.49 eV, respectively. Time-dependent density functional theory is used to explain that the experimentally measured UV–Vis spectra in which visible light absorption is broader and more intense in WSi 2 N 4 than in MoSi 2 N 4 and WSi 2 N 4 is a promising photocatalyst for H 2 generation from water.