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Abstract:
Monometallic Mo and W carbides as well as highly mixed (Mo,W) carbides with various Mo/W ratios were synthesized directly on oxygen-functionalized carbon nanotubes (OCNTs), and used as noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. A purely orthorhombic structure was found in both monometallic and mixed carbide samples by X-ray diffraction. Transmission electron microscopy images showed that the carbide particles were highly dispersed on the OCNTs with well-controlled particle size. The homogeneous distribution of Mo and W in the carbides was confirmed by elemental mapping. (Mo,W)(2)C/OCNT with a Mo/W ratio of 3 : 1 showed the lowest overpotential to reach a current density of 10 mA/cm(2) (87 mV in 0.1 M KOH and 92 mV in 0.5 M H2SO4), and the smallest Tafel slope of 34 mV/dec. Long-term stability under both alkaline and acidic conditions was demonstrated for 24 h. Our results revealed that an optimal amount of W in the mixed carbide can significantly improve its performance in the HER following the Tafel reaction pathway, most likely due to the weakened Mo-H-ads bond.
