2D Tungsten Chalcogenides: Synthesis, Properties and Applications

Abstract

Their fascinating properties are the result of the layered structure held together by weak van der Waals forces similarly to graphene, however, in TMDCs one layer is much more complex; consisting of a hexagonal plane of transition metals (typically metals of group IV-VII) sandwiched between two planes of chalcogens (S, Se, and Te) by strong covalent bonds (Figure 1). In 2004, the pioneering isolation of graphene sheets [1] gave a tremendous boost to the scientific community scrutinizing similar layered materials which can be separated relatively easily to single-layers or so-called monolayers. Based on their unique electronic transport properties and advantageous band structure these materials are suggested to have a great number of applications in transistors, [2][3][4] solar cells, [5][6][7] optoelectronic devices, [8,9] catalysts, [10] and sensors. [11] As might be anticipated their properties at atomic scale, greatly differ from their bulk counterpart. Recently, monolayers of MoS 2 and WS 2 have been found to exhibit direct semiconducting band gap in the visible spectrum rather than an indirect one that is well-known for their bulk phase. [12] In addition to material thickness, the band gap can be further fine-tuned, implying also beneficial changes in material properties, by doping TMDCs with different chalcogen atoms. As an example, when the thickness of MoS 2 is reduced from bulk to monolayer a significant increase in the band gap can be observed, from ≈1.2 to ≈1.8 eV, [12] accompanied with an indirectto-direct transition, and as expected, single layers also exhibit Layered transition metal chalcogenides possess properties that not only open up broad fundamental scientific enquiries but also indicate that a myriad of applications can be developed by using these materials. This is also true for tungsten-based chalcogenides which can provide an assortment of structural forms with different electronic flairs as well as chemical activity. Such emergence of tungsten based chalcogenides as advanced forms of materials lead several investigators to believe that a tremendous opportunity lies in understanding their fundamental properties, and by utilizing that knowledge the authors may create function specific materials through structural tailoring, defect engineering, chemical modifications as well as by combining them with other layered materials with complementary functionalities. Indeed several current scientific endeavors have indicated that an incredible potential for developing these materials for future applications development in key technology sectors such as energy, electronics, sensors, and catalysis are perhaps viable. This review article is an attempt to capture this essence by providing a summary of key scientific investigations related to various aspects of synthesis, characterization, modifications, and high value applications.Finally, some open questions and a discussion on imminent research needs and directions in developing tungsten based chalcogenide materials for future applications are present...

Novel WS2/Fe0.95S1.05 Hierarchical Nanosphere as a Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction

“…The E 1 2g and A 1g peaks of the hybrid catalyst are slightly blue‐shifted, indicating that there is a strong interaction between the different phases [12] . Therefore, the reduction of Raman shift spacing and the existence of Fe−S vibration peaks provided a supportive evidence for the synthesis of WS 2 /Fe 0.95 S 1.05 hybrid catalysts [33] . The scanning electron microscope (SEM) image of Figure 1c show the structural morphologies of the as‐synthesized WS 2 /Fe 0.95 S 1.05 ‐2 hybrid catalyst.…”

“…[12] Therefore, the reduction of Raman shift spacing and the existence of FeÀ S vibration peaks provided a supportive evidence for the synthesis of WS 2 / Fe 0.95 S 1.05 hybrid catalysts. [33] The scanning electron microscope (SEM) image of Figure 1c show the structural morphologies of the as-synthesized WS 2 /Fe 0.95 S 1.05 -2 hybrid catalyst. The average particle size of the nanospheres is 500-600 nm, and there are regular nanosheets on the surface, which is conducive to the exposure of active sites and provides the possibility of high catalytic activity.…”

Enhanced Electrical Performance of Van der Waals Heterostructure

“…[ 8–12 ] The direct bandgap also results in the photoluminescence (PL) of monolayer MoS 2 , which opens the possibility of many optoelectronic applications. [ 13 ]…”

Controlled Growth of Edge‐Enriched ReS2 Nanoflowers on Carbon Cloth Using Chemical Vapor Deposition for Hydrogen Evolution

“…Unlike the well‐studied Mo‐, W‐, or Hf‐based dichalcogenides, [ 13–17 ] ReS 2 naturally tends to crystallize in a distorted 1T structure. [ 18 ] Due to this distorted T phase structure, the interlayer coupling between ReS 2 layers becomes much weaker.…”