The materials and chemicals used in this study are listed in section 1 in the Supplementary Information (SI). In order to synthesize a highly competitive nanosized oxide-electrode, h-WO3 was synthesized via hydrothermal precipitation as powder or directly deposited under identical conditions on titanium or nickel substrates (synthesis procedure can be found in section 2 in SI; The survey spectra (Figure ) of prepared h-WO3 show distinct peaks corresponding to W 4F, O 1s, N 1s, and Ti 2p respectively. The W 4f spectra show two sets of binaries deconvoluted peaks with varying intensities (Figure ). The first set of peaks at binding energies of 35.87 and 38.00 eV reveal the high intensity and predominant peak area under a curve of 95% corresponding to W 6+ . In contrast, the other set of two peaks revealed very low intensity and area under the curve at a binding energy of 34.62 and 36.87 eV which corresponds to W 5+ . The W +5 represents the defects of the h-WO3 surface indicating the presence of oxygen vacancies .