Ionic-liquid-mediated active-site control of MoS ₂ for the electrocatalytic hydrogen evolution reaction

The layered crystal MoS ₂ has been proposed as an alternative to noble metals as the electrocatalyst for the hydrogen evolution reaction (HER). However, the activity of this catalyst is limited by the number of available edge sites. It was previously shown that, by using an imidazolium ionic liquid as synthesis medium, nanometre-size crystal layers of MoS ₂ can be prepared which exhibit a very high number of active edge sites as well as a de-layered morphology, both of which contribute to HER electrocatalytic activity. Herein, it is examined how to control these features synthetically by using a range of ionic liquids as synthesis media. Non-coordinating ILs with a planar heterocyclic cation produced MoS ₂ with the de-layered morphology, which was subsequently shown to be highly advantageous for HER electrocatalytic activity. The results furthermore suggest that the crystallinity, and in turn the catalytic activity, of the MoS ₂ layers can be improved by employing an IL with specific solvation properties. These results provide the basis for a synthetic strategy for increasing the HER electrocatalytic activity of MoS ₂ by tuning its crystal properties, and thus improving its potential for use in hydrogen production technologies.