High performance electrochromic poly(5-cyanoindole)/TiO2 nanocomposite material for intelligent supercapacitor

Abstract A new type of dual-functional poly(5-cyanoindole) (P5ICN)/TiO2 nanocomposites with porous network structure is prepared by combining the hydrothermal synthesis and electrodeposition. Due to the synergy effect of P5ICN and TiO2, the prepared P5ICN/TiO2 nanocomposites have excellent electrochromic and supercapacitive properties. The color of P5ICN/TiO2 nanocomposites can change between light yellow and dark-green under different voltage. The electron withdrawing -C≡N group decreases the band gap of polyindole, which enable a good band gap matching between P5ICN and TiO2, thus improving the electron transport capacity of the material. Benefiting from the highly ordered nanorod structure of TiO2, P5ICN/TiO2 nanocomposites shows enhanced pseudocapacitive behavior. When the current density is 0.3 mA cm−2, this material exhibits the highest specific capacitance (36.18 mF cm−2). An asymmetric electrochromic supercapacitor device (ESD) is also fabricated by using P5ICN/TiO2 nanocomposites and poly(3,4-ethylenedioxythiophene) (PEDOT) as anode materials and cathode materials, respectively. This ESD also has a high specific capacitance of 14.7 mF cm−2 and shows obvious color change from yellow–green to blue-black during the charging and discharging process. Therefore, the level of stored energy for the device can be intelligently monitored by its color change. It is believed that this new ESD will have potential application in the field of smart electronics.