First-principles study on photocatalytic properties of janus monolayer MoSi2N2P2 and MoSi2P2As2

Two Janus two-dimensional monolayer MoSi2N2P2 and MoSi2P2As2 are constructed based on monolayer MoSi2N4. High structural stability of such materials are confirmed by the phonon dispersion spectrums. The MoSi2N2P2 and MoSi2P2As2 monolayers are indirect and direct semiconductors, respectively. For conventional water splitting photocatalysis, band gaps bigger than 1.23 eV are demanded for straddling the water redox potential, causing a waste of infrared part of solar energy. Fortunately, with band gaps smaller than 1.14 eV, the present Janus materials can provide sufficient driving force for water redox reactions on the separate sides due to the different electrostatic potential. More interestingly, these materials show strong absorption on visible light, ultraviolet light, and especially on infrared light. Finally, the redox ability can be furthermore modulated by pH value. These results indicate that the presently predicted Janus materials are expected as candidates of high-efficiency photocatalysis for water decomposition.