A self-rechargeable electrochromic battery based on electrodeposited polypyrrole film

Polypyrrole (PPy) film doped with p-toluenesulfonate has been grown on indium doped tin oxide (ITO) coated glass by electrochemical polymerization. The PPy film, aluminum (Al) sheet and KCl solution are assembled into a bi-functional electrochemical device exhibiting self-powered electrochromic device and self-rechargeable battery characteristics. As an electrochromic device, the maximum optical modulation of the PPy/Al device is 59.0% at the wavelength of 698.5 nm. The original black device will become yellow after connecting its two electrodes with a response time of 6.5 s. As a battery, the capacity of the PPy/Al device is 75.25 mAh g−1 when it was initially discharged at a constant current density of 1.0 A g−1. The open circuit voltage of the PPy/Al device is 0.94 V. The charging-discharging processes of the PPy/Al device accompany a clear color change. So the capacity of the PPy/Al device can be known from the color of the device. The PPy/Al device can recover its color and capacity after disconnecting its two electrodes, which is attributed to the spontaneous transformation of PPy film from its neutral state (yellow) to p-type doped state (black) by the oxidation of oxygen.