Nanocrystalline NiWO4-WO3-WO2.9 Composite Strings: Fabrication, Characterization and their Electrocatalytic Performance for Hydrogen Evolution Reaction

In this study, novel nano crystalline composite strings made from mixed nickel-tungsten oxides (NiWO4-WO3-WO2.9) have been fabricated. The NiWO4-WO3 fibers produced by the electrospinning method were post treated in an argon atmosphere at 800 degrees C which yielded NiWO4-WO3-WO2.9 nanocrystals attached together forming a string-like structure. The presence of WO2.9 phase was confirmed by both the XRD and TEM diffraction pattern analysis. String morphology and structure were found to change with different post treatment conditions such as by changing the calcination temperature from 550 degrees C under oxygen to 800 degrees C under pure argon atmosphere. This material was investigated for electrocatalytic hydrogen evolution reaction (HER) in 0.5 M H2SO4 and 0.1 M KOH electrolytes. These composite strings showed good electrocatalytic activity compared to the NiWO4-WO3 fibers reported previously (Anis et al. in J. Mater. Sci. 52:7269-7281, 2017). It was concluded that the presence of WO2.9 phase increases the electrocatalytic activity of the catalyst as compared to the NiWO4-WO3 fibers with overpotentials as low as 40 and 50 mV in 0.5 M H2SO4 and 0.1 M KOH, respectively.