Molybdenum Ditelluride Rendered into an Efficient and Stable Electrocatalyst for the Hydrogen Evolution Reaction by Polymorphic Control

The electrocatalytic hydrogen evolution reaction (HER) is of central importance for the production of H2 from sustainable sources. Currently, Pt is the best electrocatalyst for this transformation, but other materials based on less-precious elements are now attracting increased attention. Of these alternatives, the molybdenum chalcogenides show particular promise. MoS2 has been explored extensively in this regard, which has highlighted the important role of polymorphism for catalytic activity. However, the conversion into an active polymorph is complex, and the stability of the catalyst under electrochemical conditions is poor. In contrast, MoTe2 has been barely studied as an electrocatalyst for the HER. Herein, we isolate the semiconducting and metallic polymorphs of MoTe2 using an easy solid-state route and show that interconversion between the two polymorphs of MoTe2 can be achieved without a change in morphology by a simple temperature-annealing protocol. Although the semiconducting form is a rather poor electrocatalyst for the HER, the metallic 1T′-MoTe2 polymorph is an efficient and stable electrocatalyst for the HER in 1 m H2SO4. Even in the bulk form, it achieved a low overpotential with a Tafel slope of (78±4) mV dec−1 and full Faradaic efficiency. These findings highlight the importance of polymorphic control in the development of HER catalysts and suggest an efficient route for the discovery of new and improved electrocatalysts.