Preparation And Characterization Of Conducting Polymer Modified Carbon Electrode

Supercapacitors attract growing attention to the use of electrical energy storge systems because of higher specific power than batteries and higher specific energy than conventional capacitor, owing to the high capacitance of the electrode materials. According to the mechanisms of energy storage, two types of supercapacitorare under development. One is an electric double-layer capacitor ,the other one is a redox pseudo-capacitor. Active carbon is the most frequently used as electrode material in EDLCs, due to the large surface area and porosity that ensure high specific capacitance. Conjugated conducting polymers have been investigated for use as electrode material in pseudo-capacitors. Accordingly, PAn/AC composite electrodes can provide higer capacitance by unite the double-layer capacitance of active carbon and the pseudo-capacitance of PAn.In this dissertation, the composite electrodes were prepared by chemical polymerization or electropolymerization PAn on the surface of caron powder or electrodes. The electrochemical properties of electrodes were systematically studied by cyclic voltammetry, electrochemical impedance spectrometry and constant current charge-discharge tests. Results came as follows:1. Preparation and optimization of active carbon electrodeThe conductivity increased with the increasing of specific surface of AC so that we used the AC with 2600m2/g specific surface as electrode material. The increase of carbon black and the ball milling time could improve the conductivity of electrode, but when the content of CB reached 30% or ball milling time reached 2 hours, the conductivity didn't change much. The capacitance declined with the increasing of carbon black or PTFE owing to their low capacitance. So it suggested that the best technologic conditions of preparing AC electrode were the ratio of AC, CB and PTFE being 8:1:1, ball milling time being 2 hours. The specific capacitance reached 306F/g, and the ESR was about 16Ω.2. Study of PAn/AC electrode prepared by chemical polymerizationIn-situ chemical polymerization method was used to prepare polyaniline-active carbon (PAn/AC) composite by depositing polyaniline on the surfce of AC powder. The specific capacitance of PAn/AC electrode was exhibited as high as 390F/g. In comparison with the AC electrode, an increase in capacitance more than 28% had been achieved, which identifies the significant contribution of pseudocapacitance from PAn on the overall capacitance. But the utilizing rate of PAn was only 49% and the ESR was about 80Ωwhich higher than AC electrode.3. Study of PAn/AC electrode prepared by electrochemical polymerizationCyclic voltammetry and potentiostatic methods were used to prepare PAn/AC composite electrode. The results shown that the properties of electrode prepared by cyclic voltammetry method were better than that by potentiostatic method. The polymerization potential was about 1.2V, on which higher than glass carbon electrode and Pt electrode. The polyaniline film could't be formed when the scan rate was higher than 10mV/s. The lower of the polymerization potential, the higher of the redox reversibility, the lower of ESR, the higher of PAn utilizing rate and specific capacitance. The best technologic conditions of polymerize PAn by cyclic voltammetry on AC electrode were the sweep range being -0.2~1.2V, the scan rate being 1mV/s. The specific capacitance of electrode reached 546F/g and an increase of 78% had been achieved. The utilizing rate of PAn was about 89%.