Oxygen Vacancies of WO _3‐x Enhance the Performance of Asymmetric Supercapacitors

Abstract The study about the relationship between micro‐nano structure and performance in supercapacitors is important. Oxygen vacancies are prevalent in tungsten oxide. The effect of oxygen vacancies in WO 3‐x on supercapacitors is currently unclear. In this study, we synthesized WO 3‐x , an electrode material with rich oxygen vacancies, using a solvothermal‐calcination method. The micro‐nano structures of WO 3‐x was characterized using SEM, EDS, XRD, FTIR, XPS, and UV–vis absorption spectrum, WO 3 serving as a comparative control. The above structural characterization demonstrated that there are more oxygen vacancies in WO 3‐x than WO 3 . The electrochemical performance of the WO 3‐x electrode was assessed through both three‐electrode and asymmetric supercapacitors (ASCs). The results of CV and EIS indicate that better capacitance performance comes from more electron transport (larger current in CV) and faster electron transport (smaller R ct in EIS). The GCD tests show that WO 3‐x has a greater specific capacitance (35.03 F g −1 ) than WO 3 (19.76 F g −1 ) at a current density of 0.1 A g −1 across a potential range of 0.0 to 3.5 V. Additionally, WO 3‐x ASC displays superior cycling stability, maintaining 69.07% of its initial specific capacitance over 10,000 cycles at 0.5 A g −1 . These results imply that oxygen vacancies in WO 3‐x make it a promising candidate for supercapacitor applications.