Rapid synthesis and characterizations of defect-enhanced WO3-δ thin film electrode for effective energy storage application in asymmetric supercapacitor devices

•Pseudocapacitive defect-enhanced WO3-δ thin film anode was developed with improved conductivity, charge carrier concentration, and areal capacitance by mild de-oxidation of electrodeposited WO3.•Microstructural analysis revealed the presence of lower valence W5+ in the WO3-δ film and confirmed monoclinic phase W18O49 of the doped thin film electrode.•Electrochemical characterizations confirmed the superior pseudocapacitive charge storage metrics via its improved capacitance and reduced equivalent series as well as charge transfer resistance over WO3 thin film.•the oxygen vacancy-doped WO3-δ electrode shows a strong charge storage capability in the far negative operating potential range, which indicates its suitability as an anode electrode for the fabrication of high-energy asymmetric supercapacitors.•This study demonstrated the synthesis of oxygen vacancy-doped WO3-δ thin film through a fast and binder-free room-temperature approach without the popular energy-consuming vacuum and controlled atmosphere processing. Oxygen vacancy-doped WO3-δ thin film electrode with improved conductivity and high areal capacitance was synthesized via mild electrochemical oxygen de-intercalation of electrodeposited WO3 thin film. The X-ray diffraction (XRD) analysis revealed the presence of monoclinic phase W18O49 of the doped thin film electrode. Raman spectroscopy analysis confirmed the presence of lower valence W5+ in the WO3-δ film. Electrical characterizations of doped WO3-δ and undoped WO3 films show that the doped electrode exhibits far lower sheet resistance and resistivity than the undoped WO3 sample. Mott-Schottky analysis of the samples shows that the vacancy-doped WO3-x possesses a higher donor concentration than the stoichiometric WO3. Electrochemical characterizations by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD,) and electrochemical impedance spectroscopy (EIS) confirmed the superior pseudocapacitive charge storage metrics via its improved volumetric capacitance of 366.12 F·cm−3 (16.0 mF·cm−2) and reduced equivalent series as well as charge transfer resistance over WO3 thin film. This study demonstrated the synthesis of oxygen vacancy-doped WO3-δ thin film using a homemade two-electrode cell facility instead of the popular energy-consuming vacuum-assisted film deposition under controlled-atmosphere conditions. Besides, the vacancy-doped WO3-δ electrode shows a strong charge storage capability in the far negative operating potential range, i