Complementary Oxides Based Electrochromic Supercapacitor: Multiwavelength Switchable Solid State Device

Abstract

Multifunctional electrochromic devices make use of materials that exhibit other properties, like supercapacitors, batteries, solar cells, etc., in addition to electrochromism. The steady electrochemical performance and strong energy storage capacity are two benefits of inorganic electrochromic devices that make them attractive for industrial applications. Here, an all-inorganic solid-state electrochromic supercapacitor has been fabricated using electrodeposited MnO₂ and a complementary WO₃ electrode which shows multiwavelength color modulation on application of a voltage of as small as ±2 V. The device shows an appreciable color change from pale yellow to dark blue with a high optical modulation of 70% and a change in transmittance of 40% at 680 and 1050 nm wavelength, respectively, capable of an additional application as a heat cutter. The device shows a fast response while changing color with a switching time of as low as a half-second and a high coloration efficiency of 520 cm²/C. The device, in a handy gadget form, demonstrates exceptional stability at both wavelengths. The device shows excellent charge storage properties with fast charging and slow discharging and a maximum specific capacitance of 22.6 mF/cm² at a 0.1 mA/cm² current density. The device shows excellent cyclic stability with 95% capacitance retention after 500 charging/discharging cycles. A large-area device was also fabricated at lab scale for on-site demonstration. It maintained its superior electrochromic properties, suggesting its huge potential for use as energy storage electrochromic smart windows. Additionally, as a proof of demonstration for practical application, the two ssEED connected in series lighten a red LED in its fully charged state suggesting its multifunctional application.