Dual-Function Electrochromic Supercapacitors Displaying Real-Time Capacity in Color

Dual-function electrochromic supercapacitors (ECSs) that indicate their real-time charge capacity in color are fabricated using tungsten trioxide (WO 3 ) and Li-doped ion gels containing hydroquinone (HQ). The ECSs can simultaneously serve as either electrochromic devices or supercapacitors. The coloration/bleaching and charging/discharging characteristics are investigated between 0 and −1.5 V. At the optimal HQ concentration, large transmittance contrast (∼91%), high coloration efficiency (∼61.9 cm 2 /C), high areal capacitance (∼13.6 mF/cm 2 ), and good charging/discharging cyclic stability are achieved. Flexible ECSs are fabricated on plastic substrates by exploiting the elastic characteristics of the gel electrolytes, and they exhibit good bending durability. Moreover, practical feasibility is evaluated by demonstrating the use of the ECSs as an energy storage device and a power source.