A Study On The Preparation Of Electrochromic Conductive Polymers,Composites And Supercapacitor Performance

Supercapacitor(SC_S),as a kind of energy storage device,has the characteristics of fast charge and discharge rate,high power density,long cycle life and so on.Electrochromic materials are a kind of materials that can change color under different voltages.They are combined with SCs to prepare electrochromic supercapacitors(ESCs),which can directly reflect the energy storage state of the device through real-time color changes.It has important application significance in intelligent color-changing windows,intelligent wearable electronic devices and so on.Polyaniline(PANI)has been extensively studied due to its unique physical and chemical properties,that is,high ionic and electronic conductivity,good redox activity,low cost and simple preparation.However,the application of PANI in the field of electrochromic supercapacitors is greatly limited by its characteristics of insolubility,non-fusion,poor processability and poor stability due to its rigidity and strong hydrogen bonding between molecular chains.In order to realize its application,PANI should first form film on transparent conductive substrate to solve its solution processability.This thesis focuses on how to improve the electrochemical performance,solubility and cycle stability of PANI-based composite electrode materials,mainly in the following three aspects:(1)First,we prepare self-doped PANI(SPANI)-based electrode materials,and directly introduce doping groups on the polymer backbone to shorten the charge transfer time and improve the affinity between the interfaces.Subsequently,the electrochemical synthesis method was used to deposit externally doped PANI and SPANI on the conductive glass(ITO/FTO)substrate respectively,and the doping ratio was also explored.Furthermore,we also used modified aniline monomer containing methoxyalkyl(-OCH₃)on the aromatic ring to replace the original aniline for electrochemical deposition,and studied the effect of the number of electron-donating substituent-OCH₃ and its position on the aromatic ring on PANI.After a series of investigations,we found that the introduction of the concept of self-doping is feasible.Compared with externally doped PANI,self-doped PANI has a certain improvement in specific capacitance and electrochemical stability.The specific capacitances of SPANI-ITO and PANI-ITO electrodes were calculated from the CV curve to be 19.65 F g^-1 and4.35 F g^-1,respectively,and the capacitance retention rates after 500 cycles were 40.80%and 2.84%,respectively.Using WO₃/FTO as substrate,the mass ratio of 2,5-dimethoxyaniline(2,5-DMOAN)to o-aminobenzene sulfonic acid(SAN)was 1:2.When the electrode was charged and discharged at the current density of 0.1 A g^-1,the mass ratio capacitance of the composite thin film electrode could reach 32.41 F g^-1.(2)The solubility of PANI in most organic solvents is very poor,so to realize the large-scale and wide application of PANI materials,it is necessary to prepare soluble PANI.In order to further optimize the conductivity and stability of PANI-based electrode materials,we prepared soluble PANI by chemical oxidation,and added1,3,6,8-pyrenetetrasulfonic acid(1,3,6,8-Psas)as an anchoring dopant,its large steric hindrance can play a role in supporting the interchain in the polymer,and reduce the influence of the interaction between the chains,so that the polymer can obtain good solubility.In addition,1,3,6,8-Psas can also be used as a crosslinking agent,which can adjust the morphology of PANI and provide a rich pore structure for the composite electrode to increase the contact area with the electrolyte,thereby improving ion transport.This strategy of adding 1,3,6,8-Psas as a crosslinking agent and dopant during the in-situ polymerization of PANI can obtain solution-processable PANI and improve its electrochemical stability.After a series of investigations,WO₃/FTO composite electrode prepared by adding 1,3,6,8-Psas with a concentration of 0.015M in the process of PANI polymerization and then spraying the film has achieved the best electrochemical performance.According to the CV curve,the area specific capacitance of the composite electrode reached 72.11 m F cm^-2 at the scanning rate of 100 m V s^-1,and the capacitance retention of the composite electrode was 70.12%after 1000 CV cycles,which showed a large improvement compared with the PANI without doping.At the same time,in the electrochromic performance test,when the applied voltage is-0.2 V,the composite electrode fades and the color is light green;when the applied voltage is 0.8 V,it is colored and the color is dark blue.The coloring time of the composite electrode is 4.5 s,the fading time is 9.0 s,and the coloring efficiency at 800nm reaches 76.52 cm² C^-1.(3)In the above studies,the specific capacitance and electrochemical stability of the electrode have been improved to a certain extent,but the cyclic stability of the composite electrode still has some limitations.Therefore,we explored a novel preparation method to improve the electrochemical stability of PANI-based electrodes.Combining the interface reaction and the thioene click reaction,we propose a hanging solid-liquid surface reaction.First,the WO₃/FTO substrate is prepared by hydrothermal method,and then it is soaked in the ethanol solution of p-aminobenzoic acid to modify the surface of WO₃/FTO with a layer of amino groups,and then suspended and immersed in the PANI polymerization solution to achieve solid-liquid Surface polymerization.Through this interface-induced film forming method,WO₃ and PANI films can be covalently connected.This method has better electrochemical stability and more uniform conductivity than the composite electrode prepared by spraying.Moreover,this method is more conducive to the large-scale industrial production of PANI.After 8 hours of reaction,the capacitance retention rate of the composite electrode after 2000 cycles is still 97.79%,which has a huge improvement in electrochemical stability.The proposal of this method also provides a new idea for the preparation of other conductive polymer-based composite electrodes and large-scale industrial production.