Effect of thermal annealing on phase structure and hydrogen evolution reaction of molybdenum carbide thin films prepared by co-sputtering

Abstract

Molybdenum carbide (Mo_xC) has attracted extensive attention owing to its rich valence states and excellent catalytic activity. Herein, the influences of thermal annealing on phase structure and hydrogen evolution reaction (HER) of Mo_xC thin films have been systematically studied by X-ray diffractometer, scanning electron spectroscopy, transmittance electron spectroscopy, and X-ray photoelectron spectroscopy. It has been found that annealing temperature shows a high impact on the phase structure of the Mo_xC thin films. The as-sputtered Mo_xC film and the films annealed at the temperatures of 500–600 °C are nearly in the mono α-MoC phase; the films annealed at 700 °C are β-Mo₂C phase, while the film annealed at 650 °C is in mixed MoC/Mo₂C phases. The MoC/Mo₂C hybrid films exhibit promoted HER performance with overpotential as low as 119 mV at 10 mA cm⁻² and the corresponding Tafel slope of 73 mV dec⁻¹ in acid, where the structural transformation from MoC to MoC/Mo₂C hybrid gives rise to the optimized electronic structure and intensively regulates the H adsorption energy. Benefiting from the synergistic effect of the dual-phase MoC/Mo₂C characteristics, the MoC/Mo₂C@CP hybrids can be directly used as binder-free electrocatalysts. This work provides an archetype for modulating the phase of Mo_xC thin film by a co-sputtering strategy for an efficient hydrogen evolution reaction.