Intrinsic Electric Field and Excellent Photocatalytic Solar-to-Hydrogen Efficiency in 2D Janus Transition Metal Dichalcogenide

By using systematic first-principles calculations, the stability and electronic properties of 2D Janus transition metal dichalcogenides with intrinsic electric field for photocatalytic applications are investigated. A total of 18 MXY (M = V, Nb, Ta, Cr, Mo, W; X/Y = S, Se, Te) have been considered, in which nine structures are found to be stable, as indicated by phonon spectra and molecular dynamics simulations. By comparing the type and size of bandgap, carrier mobility of electrons/holes, and vacuum level difference of X/Y surfaces, the following three candidates are successfully obtained: CrSSe, MoSSe, and WSSe, which show promising photocatalytic activity toward water splitting. In particular, the computed conduction band edge of one surface is much higher than the redox potential of H⁺/H₂, and valence band edge of the other surface is significantly lower than the oxidation potential of H₂O/O₂, which is beneficial for maximized performance. As a direct-bandgap semiconductor, 2D CrSSe exhibits excellent visible-infrared light absorption capability, and the predicted solar-to-hydrogen efficiency reaches an unprecedented level of 30%. These results not only provide physical insights into the design of novel 2D structures, but also shed light on their future implementation for photocatalytic water splitting and other important energy-related applications.