Investigation of Stacking Effects of Bilayer MoSSe on Photocatalytic Water Splitting

Abstract

Stacking two-dimensional materials into a heterostructure, which is also known as van der Waals epitaxy, is an effective method to tune the properties of pristine monolayer structures. Recently, Janus monolayer MoSSe has been successfully fabricated in an experiment, which might be beneficial for photocatalytic water splitting due to the inner electric field caused by the breaking of the inversion symmetry. Considering that the bilayer structure has natural advantages over the monolayer structure in photocatalytic water splitting, we systematically investigate the six stacking configurations of the bilayer MoSSe. All these stacking configurations are stable according to their calculated formation energies. The stacking effect of the properties such as the band gap and charge distribution in the vertical direction are much stronger than those in the in-plane direction. Only the AB_SSe case has a direct band gap when spin–orbit coupling is considered. Moreover, AB_SSe is excellent material for photocatalytic water splitting also because of its high adsorption spectrum, suitable band edge position, and type II heterojunction. The direct band gap and type II heterojunction may be attributed to the broken strong inversion symmetry. Our work is helpful in understanding the mechanism of the stacking effect in the bilayer MoSSe and can promote the application of bilayer transition-metal dichalcogenides in photocatalytic water splitting.

Rolling the WSSe Bilayer into Double-Walled Nanotube for the Enhanced Photocatalytic Water-Splitting Performance

“…For the recently emerged Janus MoSSe layered materials, it has been theoretically predicted that, stacking the monolayers to form bilayers could effectively narrow the band gap [ 11 , 12 ], causing a reinforced optical absorption, which is similar to the cases of C 3 N 4 and PtSSe [ 13 , 14 ]. In the meantime, the dipole moment of Janus MoSSe layered materials, which is represented by the plane electrostatic potential difference between the two surfaces, has been found to almost linearly increase with the growing thickness [ 11 , 12 , 15 ]. Furthermore, the observed type-II band alignment in the Janus MoSSe bilayers could suppress the recombination of photo-excited carriers for the thorough-going spatial separation [ 16 ].…”

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).…”

2D van der Waals Heterojunction Nanophotonic Devices: From Fabrication to Performance

“…[92] In fact, it has been widely proven that heterojunction photocatalysts can promote the spatial separation of photogenerated electron hole pairs, to achieve higher overall photocatalytic activity. [93][94][95] Qin et al designed a 2D ZnInS 4 /g-C 3 N 4 vdWh with S vacancy photocatalyst for hydrogen evolution (see Figure 9a). [96] The optimized S vacancy ZnInS 4 /g-C 3 N 4 vdWh has a hydrogen production efficiency of 6095.1 µmol h −1 g −1 .…”