Tunable Electronic and Optical Properties of Monolayer and Multilayer Janus MoSSe as a Photocatalyst for Solar Water Splitting: A First-Principles Study

Abstract

Recently, novel two-dimensional materials for solar water splitting have drawn enormous research attention for the interesting tunable electronic and optical properties. We investigate the geometry, electronic, and optical properties of the monolayer (ML) and multilayer Janus MoSSe with the first-principles calculations. We find that the ML Janus MoSSe is a semiconductor with a direct band gap of 2.14 eV, which is suitable for absorbing visual light efficiently. It also holds an appropriate band edge alignment with the water redox potentials. The biaxial strain could effectively modulate the electronic and optical properties of the ML MoSSe, from a direct semiconductor to the indirect one, even to be metal. As for the bilayer (BL) MoSSe, the stacking order could effectively affect the electronic, optical, and redox properties. The most stable stacking order is the A′B type, followed by the AA′, AA-SeSe, AA-SS, and AA-SSe stacking faults. For the BL MoSSe, they are all indirect semiconductors. The indirect band gap of the multilayer MoSSe decreases monotonously as the number of layers increases, maybe due to the quantum confinement effect and interaction between the layers. The appropriate optical and band alignment with the water redox potentials together with the rich modulation methods imply that MoSSe could be used as an efficient photocatalysist for the water splitting.

Recent Progress of Janus 2D Transition Metal Chalcogenides: From Theory to Experiments

“…Similar to the traditional MX 2 , the bandgap of MoSSe increases with a decrease in thickness due to the quantum confinement effect. [55] For the N 2 XY (NN′X 2 ) monolayers, the Ga 2 STe, Ga 2 SeTe, In 2 Ste, and In 2 SeTe are direct bandgap semiconductors, with the CBM and VBM located at the Γ point, while the Ga 2 SSe, In 2 SSe, GaInS 2 , GaInSe 2 , and GaInTe 2 are indirect bandgap semiconductors. The bandgap of Janus N 2 XY (NN′X 2 ) ranges from 0.89 to 2.03 eV, which is slightly smaller than the conventional NX monolayers.…”

Strain Engineering and Electric Field Tunable Electronic Properties of Janus MoSSe/WX2 (X = S, Se) van der Waals Heterostructures

“…[14] The Janus MoSSe monolayer is a direct semiconductor with a band gap of 1.35 eV. [16][17][18] Guan et al [19] demonstrated that Janus MoSSe is a potential candidate for photocatalytic water splitting with enhanced activity originating from the asymmetrical structure. Jin et al [20] found that Janus MoSSe is an ideal material for nanoscale sensors with high gas sensitivity and surface selectivity.…”

Janus transition metal dichalcogenides: a superior platform for photocatalytic water splitting

“…Moreover, since the electronic properties of nanomaterials can be well adjusted by external stimuli, it has been found that tensile strain and transition metal atom adsorption could strengthen optical absorption [9,29]. More interestingly, in 2D Janus MoSSe BL, the light absorption can be improved effectively by changing the stacking configurations [10,11,15].…”

“…This will substantially enhance the light utilization efficiency. Motivated by these beneficial properties, a large number of 2D Janus single layers (SLs) and bilayers (BLs) have been designed for the application of photocatalytic water splitting, such as III 2 XY (III = Ga and In; X, Y = S, Se, and Te, and X ̸ = Y) SLs [7,8], MXY (M = Mo, W) SL and BL [9][10][11][12][13], ScXY SLs [14], PtSSe SL and BL [15], and MXZ (M = Zr, and Hf; X = S and Se; Z = O and S; X ̸ = Z) SLs [16]. Based on the reaction mechanism, photocatalytic water splitting can be divided into four steps (see figure 1(b)): (1) adsorption of water molecules, (2) utilization of sunlight, (3) charge separation and transport, and (4) surface hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).…”