Alexey Ganin1 Jessica Mcglynn1

1, University of Glasgow, Glasgow, , United Kingdom

Sunlight is widely distributed geographically and provides enough energy in one hour to supply the world’s energy demands for a full year. However, this form of renewable energy is intermittent; thus current solar energy technologies must be fed into the grid or are otherwise wasted. Recent efforts have therefore been focused on the conversion of excess solar energy into a fuel in the form of hydrogen via water electrolysis. Subsequent oxidation of this hydrogen would allow for the release of energy (and water) without the need for fossil fuels. Due to the diffuse nature of solar power, a relatively modest current density of 10 mA cm-2 has been proposed as a benchmark for the comparison of hydrogen evolution reaction (HER) electrocatalysts, which roughly equates to a 10% efficient solar-to-fuels device. [1] Layered transition metal dichalcogenides (TMDs) can offer a viable solution for achieving appreciable conversion rates in low currents due to intrinsic and useful feature of any layered material, namely two-dimensionality. [2] The 2D nature of TMDs enables a maximum output from the entire surface of a catalyst and allows a simplistic and cheap design of future devices, for example, in form of atomically thin films. A semimetallic 1T′-MoTe2 with the monoclinic structure stands out among chalcogenides of molybdenum due to its remarkable ability to accommodate excess of electrons and thus, presenting an excellent prototype for studies of the role of electrochemical activation on catalytic properties of a 2D material. [3, 4] Herein, we report the synthesis, structure and properties of a new disordered MoTe2 material with self-enhanced catalytic activity for HER that reaches the overpotential value of –187 mV at j = 10 mA cm-2 after short potential cycling in 1 M H2SO4. The optimisation is coupled with a five-fold increase in turnover frequency and reduced charge transfer resistance as the HER progresses, all while preserving the electrochemically active surface area. By applying a solid state approach to the synthesis of the disordered MoTe2, we can exclude stoichiometry defects as the cause of the enhanced activity and conclude, in conjunction with electron microscopy, spectroscopy and X-ray diffraction experiments that the improved electrochemical performance is due to the intrinsic activation of the basal plane. The outcome of the studies on optimisation of MoTe2 thin films using the in operando cycling protocol is discussed as well in connection with how appreciable gains in future energy conversion and storage via HER may be achieved.

[1] Roger et al. Nat. Rev. Chem. 1, 0003 (2017).
[2] Pomerantseva et al. Advances in Physics: X, 2(2), 211 (2017)
[3] McGlynn et al. Energy Technol. 6, 345 (2018)
[4] Seok et al. 2D Mater. 4, 025061 (2017)