Two-step synthesis of tungsten disulfide and its evaluation as electrocatalyst for hydrogen evolution reaction (HER)

Abstract

The development of affordable alternative energies has gained great interest in recent years. Among them, hydrogen evolution reaction (HER) from water splitting has become of great interest as a source of clean energy. This work aims to develop WS2 synthesized from WO3 prepared by a hydrothermal method assisted by ionic liquid (IL) 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO4]), and followed by a heat treatment under nitrogen (N2) atmosphere. Different proportions of IL were used to assess the effect in the WS2 morphology to improve the performance towards the HER in an acidic medium. The resulting compounds were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with energy dispersive spectroscopy, and electrochemical techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometric measurements. WS2 synthesized from WO3 employing IL depicted superior electrocatalytic performance for the HER compared to WS2 prepared without IL. The WS2 sample that involved 2 mL of IL (WS2-2) presented the smaller particle size and the largest crystallite size, two key parameters to perform adequate redox processes: in addition, this sample showed the lowest overpotential value (120 mV), a Tafel slope of 85 mV/dec, and the lowest charge transfer resistance value. These results showed that using the appropriate proportion of ionic liquid as an additive helps to generate smaller WS2 particles, thus generating higher current density, and reducing the overpotential value enhancing the electrocatalytic performance to carry out the HER.