Zinc cobaltite micro-stars with a zinc oxide nano-stubs overlayer based supercapacitor colors a polyaniline//tungsten oxide electrochromic device

•Binder/carbon free cathode is fabricated with ZnCo2O4 porous micro-stars with a ZnO coating.•Sub-stoichiometry of ZnO ameliorates the electrical conduction in the composite.•Ion/electron transfer and transport processes in ZCO are greatly enhanced by the addition of ZnO.•Green tea-carbon//ZnO@ZnCo2O4 supercapacitor gives a capacitance = 555 f g−1 and e = 173 Wh kg−1.•Polyaniline//WO3 electrochromic device is turned deep blue by the charged supercapacitor. Zinc cobaltite(ZnCo2O4) micro-star shaped porous superstructure, on coating with zinc oxide(ZnO) nano-stubs, and coupling with porous flaky activated carbon(AC) from green tea, yielded asymmetric supercapacitor(ASC) with greatly enhanced performance parameters: specific capacitance(SC) of 557 F g−1, energy and power density(E and P) maxima of 173 Wh kg−1 and ∼3 kW kg−1, compared to reported ASCs of carbon/ZnCo2O4 composites and pure ZnCo2O4 or ZnO. Sub-stoichiometry in ZnO overlayer endows it with good electrical conductivity (14.6 mS cm−1), enhancing overall electron circulation in composite and due to direct contact between two oxides, with different morphologies and sufficient porosity, electrolyte penetration is deep, and ample ion-accommodation sites prevail in ZnO@ZnCo2O4 composite, which translate into increased SC, E, P, rate-response and cycle life. Usefulness of high-performance AC//ZnO@ZnCo2O4 ASC is ratified by connecting it in its fully charged state to electrochromic device (ECD) of polyaniline and tungsten oxide, and large integrated transmission modulation of 45.8% was rendered in ECD over bulk of visible region (480–800 nm). This demonstration of self-powering ECD proved efficacy of these devices for futuristic applications, where, dual functions of energy storage and saving can be tapped, by using such low cost, highly efficient devices, that can not only work independently, but can also work in tandem. [Display omitted]