Novel Two-Dimensional Janus MoSiGeN₄ and WSiGeN₄ as Highly Efficient Photocatalysts for Spontaneous Overall Water...

Searching for highly efficient and eco-friendly photocatalysts for water splitting is essential for renewable conversion and storage of inexhaustible solar energy but remains a great challenge. Herein, based on the new emerging two-dimensional (2D) material of MoSi₂N₄, we report novel Janus MoSiGeN₄ and WSiGeN₄ structures with excellent stabilities and great potentials in photocatalytic applications through first-principles calculations. Comprehensive studies show that MoSi₂N₄, MoSiGeN₄, and WSiGeN₄ exhibit semiconductor characteristics with an indirect gap, appropriate band gaps, and strong optical absorbance in the visible spectrum. Excitingly, by constructing Janus structures, an intrinsic electric field is realized that enhances the spatial separation and anisotropic migration of photoexcited electrons and holes. Further, this strategy can also alter the band alignment to provide an adequate photoexcited carrier driving force for water redox reactions. Moreover, the surface N vacancy can effectively lower the energy demand of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) so that the catalytic process can be self-sustained under the potential provided by the photocatalyst alone. Particularly, the overall water splitting can proceed simultaneously and spontaneously on the surface of MoSiGeN₄ and WSiGeN₄ when pH is 3 or ≥8, respectively. These explorations offer new prospects for the design of highly efficient photocatalysts.