Inartificial Two-Dimensional Ge4Se9 Janus Structures with Appropriate Direct Band Gaps and Intrinsic Polarization Boosted Charge Separation for Photocatalytic Water Splitting.

Two-dimensional (2D) Janus structures, which are totally different from prevailing 2D structures, are more interesting for photocatalytic water splitting. Here we proposed some inartificial 2D Ge4Se9 Janus structures. Excellent photocatalytic properties are revealed: (a) Ge4Se9 structures exhibit layer-independent direct gap character with appropriate band gaps of 2.53, 2.22, 2.11, and 2.03 eV for monolayered, bilayered, triple-layered, and four-layered structures, respectively. (b) Band edge positions of these 2D structures are suitable for the driving of the evolution reaction of water splitting. (c) More importantly, owning to intrinsic electric polarization, the charge densities of the valence band maximum (VBM) and the conduction band minimum (CBM) of triple-layered and four-layered Ge4Se9 structures can be notably separated. (d) In addition, we also observed that these 2D structures can possess rather pronounced optical absorption in the visible light region. This work discloses some inartificial 2D Janus structures whose fascinating properties render them as promising photocatalysts for water splitting.