Enhancement of the characteristics and HER activity of molybdenum carbide nanosheets for hydrogen evolution reaction

Abstract

The synthesis and characterization of metal carbides are necessary due to their intrinsic features that can improve the hydrogen evolution reaction. In this work, molybdenum carbide nanosheets were successfully synthesized via heat treatment at a temperature of 1200 °C under the flow of Ar gas. The as-prepared Mo₂C-1200 nanosheets exhibited a good specific surface area of 77.46 m² g⁻¹ and electrical conductivity of 104.50 μS cm⁻¹. The nanosheets showed an overpotential of 139 mV with a Tafel slope of 44 mV dec⁻¹ in 1 M KOH, while the overpotential and Tafel slope observed in 0.5 M H₂SO₄ were 166 mV and 88 mV dec⁻¹, respectively. Moreover, the Mo₂C-1200 nanosheets exhibited a turnover frequency of 210.75 m s⁻¹ in 1 M KOH and 304.10 ms⁻¹ in the 0.5 M H₂SO₄ electrolyte. Density functional theory was employed to evaluate the intrinsic features, and the Mo₂C-1200 nanosheets revealed an adsorption free energy of −0.68 eV, indicating facile adsorption of active hydrogen atoms at the active sites. The Mo₂C-1200 nanosheets exhibited a high current density for a long time during the stability test and maintained their shape and structure. Heat treatment and annealing process influenced the characteristics of the nanosheets: the specific surface area, electrical conductivity, Gibbs free energy and HER activity were significantly improved. Owing to these characteristics, the Mo₂C-1200 nanosheets can be considered an effective electrocatalyst for the HER.