Study The Electrochemical Characteristics Of Conducting Polymers Modified Electrodes

Electrochemical supercapacitor is a new energy storage equipment betweenbatteries and electrostatic capacitors, which has higher energy density than that ofelectrostatic capacitor, higher power density than that of batteries, long-cycle life andwide-temperature range. It can be applied into many fields such as hybrid electricvehicle, mobile telephone and microcomputer. According to the principle ofenergy-storage there are two types of capacitors: electric double-layer capacitor andfaradaic pseudo-capacitor. Generally, the electrode materials of the super-capacitormainly include carbon materials, metal oxides and conducting polymers and so on. Itis considered that the electrode materials are the key part of the electrochemicalsuper-capacitor.In this dissertation, we have reviewed the development in research of electrodematerials of electrochemical capacitor devices, and prepared composite electrodematerials. The structures and morphologies of those materials were characterized byscanning electron microscopy (SEM). Their electrochemical performances have beenevaluated by cyclic voltammerty (CV), galvanostatic charge-discharge andelectrochemocal impedance spectre (EIS). The main contents of this dissertation areas the following:(1) The conducting PPy/PANI composite material was first successfully preparedon the GC surface using an electrochemical method combined with an in situchemical polymerization method. The surface morphology of the deposited PPy/PANIcomposite material was examined by SEM. The SEM presented the PANI fibril withdiameters of 100²00 nm, and the PPy particles with average diameters of ²50 nm.From all the SEM morphologies, it can be seen that the PPy/PANI compositeelectrode had a highly porous microstructure. In addition, all the CV curves were almost symmetric in anodic and cathodic directions and exhibited mirror imagecharacteristics to the i=0 axis in 0.5M PTS+0.5M H2SO4 electrolyte. The idealreversibility showed that the PPy/PANI composite electrode was a very promisingmaterial for redox supercapacitors applications. The EIS results proved that compositeelectrode had smaller internal resistances ( 8Ω) but it had bigger charge-transferresistance. The galvanostatic charge-discharge results indicated that the compositeelectrode had a high specific capacitance of ⁵91.7F·g·1 at 0.5 mA·cm^-2.(2) PANI was deposited potentiodynamically on GC substrate in the presence ofsulfuric acid. The PANI presented a large amount of fibrils with diameters of400⁵00 nm and the fibrils interveined together to form a three-dimensionalreticulation by SEM and there were many granules on the fibril substrate. The CVtests were focused on the PANI electrode in different electrolytes. We found that thePANI presented better electrochemistry performance in 0.5 M PTS than in 0.5MH2SO4 electrolyte under faster scan rates. The specific capacitance was ⁴31.8 F·g·1of PANI in 0.5 M PTS. The coulombic efficiency was achieved ⁹5.6%. The EIScurves show that the PANI electrode resistance Rs was about 2.2Ω. And its chargetransferresistance was about 7.877Ω. In addition, Low time constants (of the order ofms) was preferred for electrochemical supercapacitors in order to ensure fastcharge-discharge characteristics. All the results shown that the PANI in 0.5M PTSacid was a promising electrode material for redox supercapacitors applications.(3) PANI was deposited potentiostatically on activated carbons substrate. Fromthe SEM, the activated carbon was ¹2μm with the acetylene black with diameter of⁸0nm between them. The morphology of PANI deposited on carbon substrate wasporous with fibril structure. The PANI fibrils on the AC electrodes with diameters of¹00 nm interveined together to form a three-dimensional reticulation. There weremany granules on the PANI fibrils. The CV curves were presented that the ACelectrode exhibited rectangle but the PANI/AC composite electrode exhibited obviousredox peak. Furthermore, the circle stability of AC electrode was better than that ofPANI/AC electrode. The galvanostatic charge-discharge results shown that thePANI/AC electrode exhibited high specific capacitance of ⁹50 F·g^-1. In comparison with a value of ⁵38 F·g^-1 for the AC electrode, an increase in specific capacitancemore than 76% had been achieved. In addition, two kind electrodes also exhibitedhigh coulombic efficiency of ⁹4%. The EIS shown that the PANI electroderesistance Rs was about 4Ωand its charge-transfer resistance was about 3.7⁷.8Ω.All the results shown that the PANI/AC electrode was a promising material for redoxsupercapacitors applications.