Abstract
The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo2C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo2+ species (Mo2C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo2C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo2C). The 2% Pt-Mo2C required a η10 of 79 mV, and outperformed that of pure β-Mo2C (η10 = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H2SO4. Also, the 2% Pt-Mo2C catalyst demonstrated a high stability for the HER in 0.5 M H2SO4. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure.
Highlights
To solve environmental and energy problems, development of alternatively clean energy technology is becoming more and more important over the past several decades
A series of transition metal doped nano-wire molybdenum carbide (M-Mo2 C) samples were fabricated via annealing of metal (M) doped MoOx /organic precursors under an Ar flow at 800 ◦ C
Compared with β-Mo2 C and 2% Fe-Mo2 C, low Tafel slopes were obtained for other metal doped molybdenum carbide catalysts. This indicates that for Co, Ni, Cu, Ag, and Pt doped molybdenum carbide catalysts, the rate-determining step is Hads desorption. These results suggest that the hydrogen evolution reaction (HER) kinetics on the molybdenum carbide-based catalyst surface could be influenced by doping of transition metal on its surface
Summary
To solve environmental and energy problems, development of alternatively clean energy technology is becoming more and more important over the past several decades. The Co-Mo2 C nanowire with an optimal Co/Mo ratio of 0.02 displayed a low overpotential (η10 = 140 and 118 mV for reaching a current density of −10 mA/cm[2 ]; η100 = 200 and 195 mV for reaching a current density of −100 mA/cm[2] in 0.5 M H2 SO4 and 1.0 M KOH, respectively) They considered that this high catalytic performance was resulted from the effective Co inserting into the molybdenum carbide crystal structure, which increased the Mo2 C surface electron density around the Fermi level, resulting in the reduced strength of Mo-H for facilitated HER kinetics [22]. Our previous works demonstrated that supported transition metal nanoparticles (with lower loading amount, e.g., 2% or 5%) could dramatically affect the molybdenum carbide surface properties such as electron density or surface nano-structure, and these catalysts showed different catalytic performances in gas-solid reactions such as methanol steam reforming, the water gas shift reaction, and the formic acid decomposition reaction [7,8,10,23,24].
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