Facile Spin-Coated MoS Thin Films from a Single-Source Precursor for HER Activity.

Hydrogen evolution reaction (HER) is one of the most promising ways to replace the consumption of fossil fuels with a clean and green energy source. HER requires a suitable material as a catalyst to lower overpotential and minimize energy consumption. MoS is an excellent candidate for the HER because of its suitable band structure. It is an economical and earth-abundant material compared to the standard electrode for HER, i.e., Pt. MoS thin films can be engineered to produce active sites for HER. We prepared large area thin films of MoS from a Mo single source precursor (MoCl) by means of spin coating, followed by post-annealing (sulfurization) with an additional sulfur source in an Ar/H environment. The obtained films have been characterized by Raman, X-ray diffraction (XRD), UV-vis, and X-ray photoelectron spectroscopy (XPS) before and after post-annealing. The obtained MoS films are found to be active for HER activity. The HER activity for a 10 nm thick MoS film is determined at an overvoltage of 290 mV, while for 50 nm films, HER activity is observed at 369 mV at a current density of 10 mA/cm. The HER performance of the thinner films of MoS is better than that of the thicker films of MoS. XPS results show that the obtained MoS films have sulfur deficiency (S-vacancies), which is beneficial for HER activity. The Tafel slope extracted from the polarization curve is 80 mV per decade, which is superior to those of single-crystal MoS and other 2D TMD materials.