Janus monolayer SnPAs: a stable two-dimensional direct band gap semiconductor for overall photocatalytic water-splitting in a wide pH range

Abstract

Two-dimensional (2D) Janus materials, characterised by their intrinsic structural asymmetry, have emerged as a research frontier in photocatalysis due to their exceptional optoelectronic properties. In this work, we employed first-principles calculations to propose a novel 2D Janus material, the SnPAs monolayer, as a promising candidate for photocatalytic water-splitting. Structurally, the SnPAs monolayer exhibits excellent energetic, mechanical, dynamic, and thermal stability. Regarding electronic properties, the SnPAs monolayer possesses a direct band gap of 1.89 eV. Moreover, it exhibits high electron mobilities (10^3 -10^5 cm^2 V ^-1 s ^-1 ) with orientation-dependent transport characteristics. Its optical properties reveal strong anisotropy and high optical absorption in the visible-ultraviolet region (approximately 10^4 -10^5 cm^-1 ). In terms of the photocatalytic properties, the solar-to-hydrogen energy conversion efficiency can reach up to 10.57%. The band edge position and Gibbs free energy calculation show that the SnPAs monolayer can achieve overall water-splitting by sunlight across a broad pH range from 0 to 7. This work establishes a theoretical foundation for SnPAs as a high-performance photocatalyst and offers practical guidance for its experimental application.