Phase Engineering of Metastable Transition Metal Dichalcogenides via Ionic Liquid Assisted Synthesis

Abstract

Metallic group VIB transition metal dichalcogenides (1T-TMDs) have attracted great interest because of their outstanding performance in electrocatalysis, supercapacitors, batteries, and so on, whereas the strict fabrication conditions and thermodynamical metastability of 1T-TMDs greatly restrict their extensive applications. Therefore, it is significant to obtain stable and high-concentration 1T-TMDs in a simple and large-scale strategy. Herein, we report a facile and large-scale synthesis of high-concentration 1T-TMDs via an ionic liquid (IL) assisted hydrothermal strategy, including 1T-MoS2 (the obtained MoS2 sample was denoted as MoS2-IL), 1T-WS2, 1T-MoSe2, and 1T-WSe2. More importantly, we found that IL can adsorb on the surface of 1T-MoS2, where the steric hindrance, π–π stacking, and hydrogen bonds of ionic liquid collectively induce the formation of the 1T-MoS2. In addition, DFT calculation reveals that electrons are transferred from [BMIM]­SCN (1-butyl-3-methylimidazolium thiocyanate) to 1T-MoS2 layers by hydrogen bonds, which enhances the stability of 1T-MoS2, so the MoS2-IL performs with high stability for 180 days at room temperature without obvious change. Furthermore, the MoS2-IL exhibits excellent HER performance with an overpotential of 196 mV at 10 mA cm–2 in acid conditions.

Coexisting Phases in Transition Metal Dichalcogenides: Overview, Synthesis, Applications, and Prospects

“…62 To enhance stability, the introduction of extra electrons into the t 2g orbitals of metal atoms (Figure 2c), as observed in coexisting phases in MoS 2 , has proven to significantly extend the stability of 1T-MoS 2 for up to 180 days at room temperature. 138 Colloidal. In the realm of controlling precursor materials for TMDCs, colloidal synthesis offers a sophisticated approach.…”

Recent Strategies for the Synthesis of Phase-Pure Ultrathin 1T/1T′ Transition Metal Dichalcogenide Nanosheets

“…This method can also be used for synthesizing phase-pure 1T′ monolayer MoSe 2 , WS 2 , and WSe 2 nanocrystals, as shown in Figures (f), (g), and (h). Similarly, although the ionic liquid 1-butyl-3-methylimidazolium thiocyanate is an alternative to oleylamine and promotes both charge transfer and steric hindrance via molecular adsorption, the final products are 1T MoS 2 , MoSe 2 , WS 2 , and WSe 2 …”

“…Moreover, the metastable phase requires a mild temperature for growing Group VIB TMD nanosheets. Meanwhile, the phase purity achieved using wet chemical synthesis is hardly satisfactory, and impurity concentrations are sometimes severely high owing to complex reactions in the solution. , For mechanical exfoliation, the yield is the main concern; and although the size control is not always perfect for chemical exfoliation, the yield is high. Therefore, endeavors are needed to improve the synthesis recipes for cost-effectively preparing high-quality TMDs, or a more specific strategy is necessary for considering different TMD features; that is, the synthesis should be well designed according to the application of the as-prepared TMD nanosheets.…”

Engineering polymorphs in colloidal metal dichalcogenides: precursor-mediated phase control, molecular insights into crystallisation kinetics and promising electrochemical activity

“…26,27 Recent advancements in colloidal synthesis have led to synthetic colloidal protocols for TMDs forming specic phases, such as 2H, 1T/1T ′ , by selecting suitable precursors and ligands. 4,[28][29][30][31] The majority of research relating ligand-precursor coordination to nanocrystal crystal phase has primarily focused on non-layered covalently linked nanocrystallites, and a generic and simple approach for phase engineering in layered van der Waals structures has yet to be established. Further, in terms of catalytic activity, hierarchical heterostructures containing interfacing mixed phases resulted in enhancements in catalytic activity attributed to improved synergistic effects from electrical conductivity and active sites.…”