Study On Polyaniline/Active Carbon Composite For Supercapacitor

The supercapacitor is a new type electrochemical energy storage device between the traditional dielectric capacitor and the battery. The supercapacitor can provide high energy density, high power density and have long cycle life and less pollution. According to the principle of energy-storage there are two types of supercapacitors: electric double-layer capacitor and faradaic pseudocapacitor. Electrode material mainly includes carbon material, metal oxide and conducting polymer.In this paper, Polyaniline(PANI)/active carbon(AC) composite materials were synthesized by in-situ polymerization of aniline on activated carbon with ammonium persulfate(APS) as oxidant. We discussed the effect of process conditions of polymerization (such as the molar ratio of aniline to APS and the ratio of aniline to AC, H⁺ concentration, lithium salt) on the capacitance of PANI/AC composites. The surface morphology and crystallitic structure of composites were examined by scanning electron microscope (SEM) and X-ray Diffraction. The structure of composites was analyzed by FT-IR. The electrochemical performances of the composite are tested with cyclic voltammetry, charge-discharge and electrochemical impedance spectrometry in 6mol/L KOH solution using Hg/HgO as reference electrode.The experiment results show that when the molar ratio (AC/aniline) is relatively low, with the increase of oxidant, the conversion of aniline was also increased, but the capacitance of composite materials dropped prominently. With ratio of AC to aniline increased, the conversion of aniline and the capacitance value of composite also increased in keeping the ratio of AC to aniline constant. When AC: aniline : APS=7:1:1, the conversion of aniline up to more than 95% and the capacitance value of electrode materials increased from 239 F·g^-1 (pure AC) to 409 F·g^-1 ,which is 71．1% higher than pure AC. The special surface area of AC is not the predominant factor in capacitance of PANI/AC composites. Perhaps the mesopore volume and macropore volume play a more important role.The capacitance of PANI/AC composite with lithium (Li) salt added during polymerization was highly increased, from 372 F·g^-1 to 466 F·g^-1 , which is 25．3% higher than without Li-added PANI/AC. The retention rate of capacitance after many cycles was highly improved. With the increase of HCL concentration, the special capacitance of composite increases first and then decreases. When the concentration of [H⁺] is between 2．0mol·L^-1 and 2．5mol·L^-1 , the composites have better capacitance. The capacitance of composite increases first and then falls as the increase of the addition of Li salt.