Nanoscale Chevrel Phase Mo6S8 Prepared by a Molecular Precursor Approach for Highly Efficient Electrocatalysis of the Hydrogen Evolution Reaction in Acidic Media

Developing a simple, safe and efficient route for the preparation of nanoparticulate ternary Chevrel phases MxMo6S8 (CPs; where M = metal) is of great interest because of their applications in energy conversion and storage technologies. Currently, the wide use of these materials is restricted by the prolonged reaction time, the high energy demands required for their synthesis, the complexity of the preparation process and the ambiguity in the size of the resultant particles. Herein, we report a simple, efficient and controllable molecular precursor approach for the synthesis of nanoscale CP without the use of hydrogen gas as a reducing agent. A mixture of precursors based on molybdenum and copper dithiocarbamate complexes were subjected to thermolysis in the presence of finely divided molybdenum to furnish the copper CP, Cu2Mo6S8. The successful formation of the Cu2Mo6S8 CP is confirmed by X-ray diffraction analysis and Raman spectroscopy, while the surface chemistry of the material was examined by X-ray photoelectron spectroscopy photon depth profiling via tuneable synchrotron radiation. Microscopic characterisation results demonstrate that the synthesised material has a homogeneous structure at the nanoscale, in contrast to the microparticles obtained from conventional approaches previously reported. The prepared CP was assessed as an electrocatalyst for the hydrogen evolution reaction (HER) in acidic media. Due to its unique nanoscale texturing, the Cu-leached CP, Mo6S8, exhibits a highly promising electrocatalytic activity towards hydrogen evolution with an overpotential required to reach a current density of 10 mA cm-2 equal to 265 mV vs. RHE. The overpotential reduces to 232 mV upon mixing of the catalyst with 20% w/w of high conductivity carbon. It is expected that the proposed synthetic strategy, which represents a facile route to tailored CPs, can be extended to the preparation of versatile, easily tuneable CP Mo6S8-based electrode materials for applications in electrocatalysis.