One-step molten-salt synthesis of adjustable composition molybdenum carbide-based electrocatalysts for hydrogen evolution in both acidic and alkaline media

Molybdenum carbide is deemed a potential electrode material for the hydrogen evolution reaction (HER) under different pH condition electrolytes because of its unique metal-like electronic structure. Herein, we report a series of molybdenum carbide-based catalytic electrodes that were prepared by adjusting the proportion of glucose and ammonium molybdate in the molten salt. The prepared electrocatalysts mainly include Mo₂C, Mo₂C/C and Mo₂C/MoO₂. The composition influences electronic structure and microstructure of Mo₂C, impacting the HER performance. As for Mo₂C/C, because of the regulation of the carbon substrate, the charge transfer efficiency and electronic structure were improved. It exhibits satisfactory HER performance with low overpotentials at 10 mA cm⁻² in alkaline (280 mV) and acidic electrolytes (264 mV). Meanwhile, it presents good Tafel slopes of 102 mV dec⁻¹ (alkaline) and 88 mV dec⁻¹ (acidic). The outstanding HER performance can be ascribed to the full exposure of the active sites and a strong in situ coupling between the carbon matrix and the nanoscale Mo₂C. The carbon matrix not only offers abundant nucleation sites that prevent agglomeration of the Mo₂C nanosheets, but also exhibits charge transfer towards Mo₂C. This synthesis strategy may provide an idea for preparing transition metal carbide-based composite materials to apply in energy fields.