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

Abstract

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.

The rapid electrochemical activation of MoTe2 for the hydrogen evolution reaction

“…Recently, we 6 and others 7 reported that the monoclinic metallic phase of molybdenum telluride, 1T′-MoTe 2 is a competent electrocatalyst for the hydrogen evolution reaction, albeit only capable of achieving a rather modest current density of −10 mA cm −2 at overpotentials of around 360 mV in sulfuric acid 6,7 . This contrasts with the electrocatalytic activity displayed by the semiconducting 2H-MoTe 2 polymorph, which was found to be largely catalytically inert.…”

Selective phase growth and precise-layer control in MoTe2

“…Based on the assumption that a monolayer of MoTe 2 should be ca. 0.7 nm thick (based on the length of the c-parameter in MoTe 2 according to synchrotron Xray diffraction studies) 30 we estimated that the resulting film contains six MoTe 2 layers. A typical AFM image for this sixlayered MoTe 2 across a scan area of 5 μm × 5 μm is shown in Fig.…”

TMDs beyond MoS2 for Electrochemical Energy Storage

“…(c‐i) Adapted with permission from Ref. ; Copyright 2017, Wiley‐VCH. (d‐i) Adapted with permission from Ref.…”