Perspective of Transition Metal Dichalcogenide Monolayers as Catalysts in Water Electrolysis

Two-dimensional (2D) transitional metal dichacogenides (TMDs) have recently attracted great attention due to their intriguing physical, chemical, electronic and magnetic properties, as well as diverse applications [1-4]. A TMD monolayer is one layer derived from the layered TMD structures, which is noted as a chemical formula of MX 2 , where M is a transition metal element, and X is a chalcogen (S, Se, or Te). Within the TMD monolayer, one metal-atom sub-layer is sandwiched between two X-atom sub-layers, where M-X bonds are mainly covalent by nature. The thickness of a TMD monolayer is about 2.5 ~ 4.0 Å. Generally, after applying proper external forces to layered TMDs, it's feasible to get few-layered TMDs, and even TMD monolayer. Generally, there are mainly three fabrication methods: liquid exfoliation, lithium intercalation and chemical vapor deposition (CVD)[1]. Liquid exfoliation method is suitable for large quantity fabrication, whereas lithium intercalation method serves high yield efficiency with inducing of phase transition in MX 2 monolayers. Furthermore, CVD method is dominantly used for the fabrication of large TMD monolayers with high quality.