WS2 Composites

To improve the electrical and catalytic properties of WS₂, the synthesis of WS₂ composites from other materials with good electrical conductivity is a promising approach. Composites are materials in which one material is the matrix and another material is used as the reinforcement. The various materials complement each other in terms of properties and create a synergistic effect, resulting in an overall performance superior to the original material.

In recent studies, the most attention has been paid to the incorporation of nano WS₂ into conductive carbon matrix by various synthetic methods, including graphene, carbon nanotubes, and amorphous carbon. In terms of synthesis, the hydrothermal method is the most commonly used method because of its simple steps.

Two-dimensional carbon materials are found to have high electrical conductivity and good flexibility. Therefore, the construction of homogeneous mixtures of highly conductive 2D carbonaceous nanosheets and WS₂ nanostructures is expected to promote electron transport and improve the electrical conductivity of the WS₂ composites.

For example, Yang et al. synthesized WS₂/reduced graphene oxide (RGO) hybrid nanosheets through a hydrothermal reaction process achieved at low temperatures, which demonstrated the connection with RGO support. Since graphene is a soft material with a low bending stiffness, it can be easily tuned into different morphologies.

In addition, studies have also reported the synthesis of WS₂ nanotube/graphene hybrids (Gs) from graphene oxide (GO) solutions. In the subsequent hydrothermal reaction, the conversion from GO to Gs was performed, and the Gs could curl and cross-link to form a three-dimensional (3D) network. Similarly, Chen et al. reported a convenient and green synthesis method of WS₂/RGO/WO₃ hybrids by aerosol treatment. The crinkled morphology of RGO provides abundant defects and folds, which is considered one of the potential factors to improve the electrocatalytic performance of WS₂.

In addition, CVD methods for the preparation of WS₂ composites as well as for thickness control are also a better approach. Besides, carbon nanotubes (CNTs) are valuable candidates for bonding with WS₂ because of their excellent mechanical strength, large specific surface area (50-450 m².g^-1), and good electrical conductivity compared to other conventional templates. Several approaches can be carried out to fabricate composite structures.

For example, Yue et al. synthesized multi-walled carbon nanotubes (MWCNTs-WS₂) by a low-temperature hydrothermal reduction strategy. Lin et al. demonstrated a unique method to synthesize WS₂ nanoparticles on vertically aligned CNTs by thermally annealing W-coated CNTs in sulfur vapor. Single-walled carbon nanotubes (SWCNTs) show mechanical flexibility and superior electrical conductivity, which are more favorable for charge transport than MWCNTs.

To date, several studies have been conducted on the construction of WS₂-SWCNT composite structures. For example, researchers have synthesized three-dimensional WS₂@SWCNT foams using a simple hydrothermal method and a subsequent freeze-drying process. Due to the elastic three-dimensional conductive network, it is possible to provide conductive pathways to facilitate the transfer of WS₂ charges.

In addition, an innovative ternary WS₂/CuO/SWCNT porous hybrid was fabricated by electrostatic-assisted self-assembly and vacuum filtration processes. In this hybrid, the positively charged CuO nanosheets are easily assembled with the negatively charged WS₂ nanosheets and SWCNTs to form a flocculent network.

In addition, amorphous carbon has attracted sufficient attention due to its low cost compared to graphene and carbon nanotubes. Among them, commercially available Super P is a typical binding material to improve the electrochemical performance of WS₂. As a conductive additive, the incorporation of Super P can help reduce the size and improve the dispersion of nanocomposites, which can accelerate the insertion/extraction reaction between WS₂-Super P nanocomposite electrodes and electrolytes.

For example, Huang et al. prepared WS₂-super P nanocomposite powders by a simple two-step process including hydrothermal and sulfide reduction reactions. In addition, Li et al. synthesized WS₂ nanosheet-carbon (WS₂/C) composites by a simple two-step process of ball milling and sulfide reaction.

Article Source: Sun, CB., Zhong, YW., Fu, WJ. et al. Tungsten disulfide nanomaterials for energy conversion and storage. Tungsten 2, 109–133 (2020).

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