Electrocatalytic hydrogen evolution reaction on sulfur-deficient MoS2 nanostructures

Molybdenum disulfide (MoS2) is a 2D layered structured material with a Mo:S of 1:2 and is a great attention seeker for hydrogen production through water-splitting. In the present work, we prepared nanostructured MoSx with different sulfur molar concentrations (x = 2, 1, 0.5) through a one-step hydrothermal method. The decrease in sulfur concentration resulted in a new phase that is MoO3 with a Mo:S of 1:0.5. The structural, morphological, and optical properties of all the samples were studied through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), and Ultraviolet–Visible (UV–Vis) spectroscopy, respectively. Moreover, the electrochemical behavior was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and Tafel slope. Optimum properties were observed for Mo:S (1:1) with an onset potential of 96 mV, an overpotential of 130 mV for hydrogen evolution reaction (HER) coupled with a specific capacitance of 889 F/g and low charge transfer resistance of 43 Ω. Further, it was noted that the electrocatalytic activity of MoS1 was better than that of the composite and bare MoO3. It is proposed that the excellent electrochemical activity arises from sulfur vacancies which provide active sites for HER and a free path for ions to flow through the material.