Preparations Of Poly(6-Carboxyl Indole) Nanowire Arrays And Its Properties Of Electrochromic Supercapacitors

Supercapacitor has become a hot spot in the field of electrochemical energy storage due to its advantages such as high power density,fast charge-discharge ability and long cycle life.At present,the development of supercapacitor with electrochromic function is one of the important research directions in the field of supercapacitor.Conducting polymers often have the characteristics of electrochromism and pseudocapacitance simultaneously,which plays a crucial role in the development of electrochromic supercapacitor.Indoles conducting polymers are widely studied and applied due to their good redox activity,thermal stability and conductivity.The nanoarray structure can effectively improve the electrochromic performance,capacitance and electrochemical stability of conducting polymer materials.In this thesis,poly（indole-6-carboxylic acid）（PICA）and PICA/TiO₂ composites with nanowire arrays structure were successfully prepared.The electrochemical properties,electrochromic properties and capacitance properties of the materials were studied.Two kinds of electrochromic supercapacitors were constructed based on the above-mentioned materials.The performance of the device was tested and the practical application of the device was also explored.1.PICA film with nanowire array structure was prepared by constant current method for the first time.The electrochemical properties of the film were characterized,and it was found that the polymer film had good redox activity and stability.Electrochromicpropertiesofpolymerfilmswereinvestigatedby spectroelectrochemistry.The results showed that the polymer film can be reversible transformed among yellow,green and brown,and the film showed high optical contrast and coloration efficiency at 490 nm,the maximum optical contrast was 33%and coloration efficiency was 142 cm² C^-1.The capacitance performance of the polymer film was characterized by charging and discharging test.The results showed that the areal specific capacitance of the polymer film was 16.20 mF cm^-2 when the charging current density was 0.1 mA cm^-2.Continuous charging and discharging stability test was also carried out to the polymer film.The polymer film showed good electrochemical stability.After 500 cycles of continuous charging and discharging,the electric capacity of the film can still maintain 93%.2.Electrochromic supercapacitor was constructed based on the prepared PICA nanowire array.The device can store energy along with color changes,and the device can transform from yellow to dark green,so we can monitor the energy storage state of the device through the color changes.The charge and discharge test of the electrochromic supercapacitor was carried out.The results showed that the areal specific capacitance of the device was 4.3 mF cm^-2 when the current density was 0.05mA cm^-2.After charging,the device can be used as a power source to light the LED lamp continuously for 90 s.The stability of device was also studied.The results showed that the device had good electrochemical stability.After 1000 cycles,the areal specific capacitance was 3.8 mF cm^-2,and it still holds 89%of the capacity.3.TiO₂ films with nanowire arrays structure were prepared by water thermal reaction on FTO transparent conductive glass,and the PICA/TiO₂ nanocomposites with nanowire array structure were also prepared by constant current method on TiO₂thin film electrode.Electrochemical research showed that the composite had good redox activity.The capacitive property of the composite was studied by charging and discharging test,and the areal specific capacitance of the composite electrode was23.45 mF cm^-2 when the current density was 0.05 mA cm^-2.Electrochemical impedance study showed that the electrode resistance of the composite material was 80Ω,which indicated that the material had good electrical conductivity and ion transport capacity.The spectroelectrochemical test showed that the composites could be reversible transformed among yellow,green and brown when the applied voltage ranged from-0.5 to 2.1 V.Kinetic studies showed that the optical contrast of the composite material at 720 nm reached 36%,and the response time from the oxidation state to the reduction state was 2.4 s,from the reduction state to the oxidation state was1.2 s.The results of electrochemical stability test showed that the stability of the composites was significantly improved compared with PICA.4.The electrochromic supercapacitor was constructed based on the prepared PICA/TiO₂ nanocomposite.When the device was charged,the electrochromic phenomenon was occurred and the device stored electrical energy simultaneously.The electrochemical properties of the device were characterized,and it was found that the device had a good reversible redox activity and stability.The capacitance performance of the device was tested by charging and discharging.The results showed that the areal specific capacitance of the device was 5.2 mF cm^-2 when the charge and discharge current density was 0.1 mA cm^-2.The internal equivalent resistance of the device was about 90Ω.This indicated that the device had good ion transmission capacity.The device can be reversible changed between yellow green and brown,and the energy storage state can be determined by the color change of the device.After charged,the device can be used as a capacitor to drive LED for 108 s.After 1000 cycles of cyclic voltammetry,91%of the electrical capacity can be remained,indicating good stability of the device.