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

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.