Janus Aluminum Oxysulfide Al2OS: A promising 2D direct semiconductor photocatalyst with strong visible light harvesting

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al 2 OS as an efficient photocatalyst material for hydrogen-production H 2 through the first-principles calculations. Janus Al 2 OS monolayer has been designed from the parental binary aluminum sulfide A l S by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine A l S and the derived Janus Al 2 OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, A l S monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al 2 OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al 2 OS, the absorption-coefficient of Janus Al 2 OS shows strong visible light harvesting compared to the parental A l S . Furthermore, the photocatalytic performance of Al 2 OS has been investigated. Our calculations demonstrate that the band edge position of Al 2 OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy Δ G H ∗ of Al 2 OS is 0.97 eV which is smaller than of the two-dimensional Janus G a 2 X Y (X, Y = S, Se, Te with X ≠ Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/Å of an external electrical field. Our results indicate that Janus Al 2 OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting. • Janus Aluminum Oxysulfide Al 2 OS designed from parental Aluminum Sulfide A l S . • 2D Al 2 OS monolayer exhibits a semiconductor behavior with a direct band gap. • 2D Al 2 OS shows strong optical absorption and suitable band edge position. • Calculated Gibbs free energies reveal the suitability of 2D Al 2 OS for overall water splitting. • Strain can tune the band structure while an external electric field enhanced photocatalytic performance.