Stoichiometrically Optimized Electrochromic Complex [V2O2+ξ(OH)3‐ξ] Based Electrode: Prototype Supercapacitor with Multicolor Indicator

Abstract The systematic structure modification of metal oxides is becoming more attractive, and effective strategies for structural tunning are highly desirable for improving their practical color‐modulating energy storage performances. Here, the ability of a stoichiometrically tuned oxide‐hydroxide complex of porous vanadium oxide, namely [V 2 O 2+ξ (OH) 3‐ξ ] ξ = 0:3 for multifunctional electrochromic supercapacitor application is demonstrated. Theoretically, the pre‐optimized oxide complex is synthesized using a simple wet chemical etching technique in its optimized stoichiometry [V 2 O 2+ξ (OH) 3‐ξ ] with ξ = 0, providing more electroactive surface sites. The multifunctional electrode shows a high charge storage property of 610 Fg −1 at 1A g −1 , as well as good electrochromic properties with high color contrast of 70% and 50% at 428 and 640 nm wavelengths, faster switching, and high coloration efficiency. When assembled in a solid‐state symmetric electrochromic supercapacitor device, it exhibits an ultrahigh power density of 1066 mWcm −2 , high energy density of 246 mWhcm −2 , and high specific capacitance of 290 mFcm −2 at 0.2 mAcm −2 . A prepared prototype device displays red when fully charged, green when half charged, and blue when fully discharged. A clear evidence of optimizing the multifunctional performance of electrochromic supercapacitor by stoichiometrical tuning is presented along with demonstrating a device prototype of a 25 cm 2 large device for real‐life applications.