MoxC/CNT Composites as Active Electrocatalysts for the Hydrogen Evolution Reaction under Alkaline Conditions

Low-cost electrocatalysts based on highly dispersed molybdenum carbide supported on carbon nanotubes (CNTs) were developed for the hydrogen evolution reaction (HER). The synthesis of MoxC/CNT was achieved by impregnation using ammonium heptamolybdate followed by a thermal treatment at 700 degrees C in CH4/H-2, H-2 or N-2. The composites were characterized by X-ray diffraction, N-2 physisorption, and X-ray photoelectron spectroscopy. beta-Mo2C was the main Mo carbide phase generated in N-2 or H-2, whereas alpha-MoC was the dominant phase formed in CH4/H-2. All the MoxC/CNT composites were catalytically active in the HER under alkaline conditions. The catalyst pretreated in pure H-2 exhibited the highest HER activity, which was found to correlate with a higher amount of Mo2C, a higher total Mo content and a higher Mo surface concentration compared with the other two less active samples. Amorphous carbon on the surface seems to play an important role in limiting the HER performance of the Mo carbide catalysts, and the treatment in H-2 removed it most effectively leading to high HER activity.