Designing Metallic MoO Nanostructures on Rigid Substrates for Electrochemical Water Activation.

In situ growth of metallic MoO films on fluorine-doped tin oxide (FTO) and MoO powder in solution was achieved simultaneously by a simple hydrothermal process employing citric acid as the surfactant. The growth mechanism of MoO nanostructures (NSs) at the heterogeneous interface and in homogeneous medium proceeds in a different manner in which seeds grow in a preferred orientation on FTO, whereas they propagate in all directions in solution. The high lattice matching of FTO and MoO favours the film growth which could not be obtained on other conventional substrates. The disc morphology of MoO nanostructures was changed to other diverse morphology by varying the synthesis conditions, particularly by the addition of nitric acid. A competitive effect of nitric acid and citric acid on the structure direction produced various shapes. The electrochemical water activation studies show that hydrogen-annealed MoO is an excellent hydrogen evolution reaction (HER) catalyst with good stability. H-MoO film/FTO displays a low onset overpotential of72 mV with a Tafel slope of 84.1 mV dec , whereas the powder form exhibits an onset overpotential of 46 mV with a Tafel slope of 71.6 mV dec . The large active surface area, exposure of fringe facets of (110) and the lesser electrochemical charge-transfer resistance offered by the hydrogen-annealed MoO NSs play a major role in the enhanced HER activity.