Fabrication And Properties Of Self-powered Electrochromic Devices Based On Polypyrrole

Due to its fast and reversible color change,electrochromic materials have broad application prospects in the fields of building energy conservation,display and so on.The application of electrochromic material in the building can decrease the consumption of energy.However,electrochromic material requires an external power source to operate,which not only generates energy consumption but also increases the complexity of the device.Therefore,the self-powered electrochromic device has become a research hotspot.The material used in the electrochromic device exhibits good redox property,which is similar to that of the cathode materials of the battery.Therefore,the active metal anode can be used to reduce the electrochromic material to cause discoloration.Interestingly,the reduced state of material is unstable in the air so that the color of the device can be recovered after being oxidized by oxygen in air.Currently,self-powered electrochromic devices based on Prussian blue?PB?,tungsten oxide and polyaniline have already been reported.However,self-powered electrochromic device based on polypyrrole?PPy?has not been reported.Herein,we focus on the preparation and properties of PPy electrochromic device,PPy/Al and PPy/PB/Al self-powered electrochromic devices.?1?PPy film was prepared by electrochemical polymerization method and was assembled into electrochromic devices.The deposition time of PPy film and the effect of dopant species on its electrochromic properties were studied.The results indicate that the longer deposition time lead to the larger optical modulation,the longer bleaching time,and the shorter coloration time when p-toluenesulfonic acid is used as the dopant.In comparison with the PPy film doped by oxalic acid and DL-tartaric acid with the same deposition time,the maximum optical modulation of 55.3%and best stability are achieved with dopant of p-toluenesulfonic acid.While the response of the PPy film with dopant of oxalic acid is the fastest.The coloration and bleaching time are 2.3 s and 0.6 s,respectively.The minimum optical modulation of 31.5%is obtained for the PPy film with dopant of DL-tartaric acid.?2?Uniform PPy film was prepared by electrochemical polymerization method,which consists of nanospheres and the thickness is about 13?m.A pair of redox peaks is observed in the cyclic voltammetry curves.The peaks of current densities can decrease linearly with the decrease of the scan rates.The self-powered device consisting of the PPy film,Al and KCl electrolyte can function as both an electrochromic device and a battery.As an electrochromic device,the maximum optical modulation of the PPy/Al device is 59.0%at wavelength of698.5 nm.The response time of the device is 6.5 s.As a battery,the open circuit voltage of the device is about 0.94 V,and the initial specific capacity is 75.25 mAh g^-1.As the PPy/Al device is discharged,the color is changed from black to yellow.The color of the device can recover to black after it is charged.Therefore the capacity can be indicated by its color.The capacity of the self-rechargeable PPy/Al device can be recovered to 89.0%after 24 h in air.?3?PPy/PB composite film was prepared by electrodepositon method.Two pairs of redox peaks are observed in the CV curves,which corresponds to Prussian blue/Prussian white and reduced/oxidized sate of PPy,respectively.The self-powered device consisting of the PPy/PB film,Al and KCl electrolyte can function as both an electrochromic device and a battery.As an electrochromic device,the maximum optical modulation of the PPy/PB/Al device is about63.3%at wavelength of 800 nm.The response time of the device is 5.6 s.As a battery,the open circuit voltage of the device is about 1.20 V,and the initial specific capacity is 87.80mAh g^-1.As the PPy/PB/Al device is discharged,the color is changed from black/blue to yellow.The color of the device can recover to black/blue after it is charged.Therefore the capacity can be indicated by its color.The capacity of the self-rechargeable PPy/PB/Al device can be recovered to 62.9%after 15 h in air.