Versatile two-dimensional silicon diphosphide (SiP2) for photocatalytic water splitting

Abstract

The development of two-dimensional (2D) photocatalysts with excellent visible light absorption and favorable band alignment is critical for highly-efficient water splitting. Here we systematically study the structural, electronic and optical properties of an experimentally unexplored 2D Silicon Diphosphide (SiP₂) based on density functional theory (DFT). We found that the single-layer SiP₂ is highly feasible to obtain experimentally by mechanical cleavage and it is dynamically stable by analyzing its vibrational normal mode. Two dimensional SiP₂ possesses a direct band gap of 2.25 eV, which is much smaller than those of more widely studied photocatalysts including titania (3.2 eV) and graphitic carbon nitride (2.7 eV), thus displaying excellent ability for sunlight harvesting. Most interestingly, the positions of the conduction band minimum (CBM) and valence band maximum (VBM) in 2D SiP₂ fit perfectly the water oxidation and reduction potentials, making it a potential new 2D material that is suitable as a nanoscale photocatalyst for photo-electrochemical water splitting.