Facile Spin-Coated MoS₂ 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. MoS₂ 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. MoS₂ thin films can be engineered to produce active sites for HER. We prepared large area thin films of MoS₂ from a Mo single source precursor (MoCl₅) by means of spin coating, followed by post-annealing (sulfurization) with an additional sulfur source in an Ar/H₂ 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 MoS₂ films are found to be active for HER activity. The HER activity for a 10 nm thick MoS₂ 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/cm². The HER performance of the thinner films of MoS₂ is better than that of the thicker films of MoS₂. XPS results show that the obtained MoS₂ 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 MoS₂ and other 2D TMD materials.