Preparation And Electrochemical Performance Study Of Polypyrrole-based Flexible Supercapacitors

The rapid development of wearable electronic devices has triggered the research on flexible supercapacitors.Flexibility of the supercapacitors is mainly determined by the flexible electrodes,thus,the research on flexible electrode materials has attracted extensive attention.Among numerous electrode materials,conducting polymer polypyrrole（PPy）has been widely employed as electrode material for flexible supercapacitors due to its high specific capacitance,high electrical conductivity,environmental friendliness,ease of synthesis,high flexibility,and structural diversity.However,the structure of PPy easily becomes unstable due to the doping and de-doping of counter ions associated with the charge-discharge process,resulting in the deterioration in the cycling stability of PPy-based supercapacitors.In this thesis,two kinds of PPy electrodes with good cycling stability are prepared by vapor phase polymerization（VPP）method:a fiber electrode based on porous PPy network,and a cloth electrode based on PPy nanotube.The polymerization processes of PPy on different substrates are studied,the morphologies and structures of PPy are characterized,and the properties of flexible PPy electrodes and the corresponding assembled supercapacitors are tested and analyzed.The main work contents are as follows:（1）Flexible wire electrodes are fabricated by depositing porous PPy networks on soft stainless steel wire through VPP.In the process of VPP,the concentration of oxidant（ferric p-toluenesulfonate）,soaking time,polymerization time,and the number of PPy layers are controlled to optimize the content of PPy on the stainless steel wires.The experimental results show that when the concentration of ferric p-toluenesulfonate solution is 30%,the soaking time is 30 min,the VPP time is 20 min,and the number of PPy layers is 3,the electrode shows the best electrochemical performance:the length specific capacitance reaches 6.75 m F cm^-1 at a scan rate of 5 m V s^-1,and the capacitance retention achieves 58.2%when the scan rate is100 m V s^-1.The supercapacitor assembled with this electrode has a capacitance retention of79.1%after 5000 charge-discharge cycles,and the energy of the supercapacitor is sufficient to drive a micro photodetector.In addition,it also shows good mechanical flexibility,and the cyclic voltammetry curves remain nearly unchanged under 90°and 180°bending.（2）Using complex of methyl orange and ferric chloride as oxidative template,a flexible cloth electrode is fabricated by depositing PPy nanotube on hydrophilic carbon cloth（CC）using VPP.During the VPP process,the content of PPy deposited on CC is controlled by varying the polymerization time.The experimental results show that when the polymerization time is 20 min,the prepared PPy nanotube electrode has excellent area specific capacitance(78.9 m F cm^-2 at a scan speed of 5 m V s^-1)and good flexibility.The supercapacitor assembled with this electrode exhibits cycling stability and good mechanical flexibility.The supercapacitor shows a capacitance retention of 76.7%after 10,000 charge-discharge cycles,and the capacitance does not change significantly after 500 cycles of bending.