Improving Electrochemical Stability Of Conducting Polymer As Electrode Materials For Supercapacitor

Polypyrrole (PPy) and polyaniline (PANI) has been extensively investigated as the most promising conducting polymer. Especially, as electrode materials for supercapacitor, conducting PPy and PANI can effectively store energy by the characteristic doping-undoping mechanism and show both the electrical double layer (EDL) capacitance and faradaic pseudocapacitance. Unfortunately, the degradation of the electrochemical stability of PPy and PANI occurred during the long charge-discharge process severely restricts its applications in the area of supercapacitors. To overcome this potential problem, nanometer-sized conducting polymer composites with a variety of morphologies have been synthesized.In this paper, the working principle of electrochemical supercapacitor, the kind of electrode materials, and the development of conducting polymer composites as electrode materials were specifically summarized.We reported the synthesis of PPy/inorganic hybrid materials to overcome its poor cycling stability using carbon materials (such as graphene and sulfonated graphene) or rare-earth oxides (such as Pr6O11) as supporting materials. Sulfonated graphene (SG) nanosheets was used as the unique dopant for the in situ chemical oxidative polymerization of pyrrole. The structures of PPy/SG and PPy/GNS composites had been characterized by TEM, SEM, FTIR, Raman and XRD techniques. As electrode materials of supercapacitor, the electrochemical behavior of PPy/SG and PPy/GNS was comparatively studied. A series of praseodymium oxide/polypyrrole (Pr6O11/PPy) nanocomposites with core/shell structure were synthesized by the in situ surface-initiated polymerization technique. The specific capacitance and cyclic stability of nanocomposites electrode in 1.0 mol/L NaNO3 electrolyte solution were tested. These results demonstrated that the electrical conductivity and the specific capacitance of the PPy/inorganic hybrid materials increased. The cyclic stability of the polymer electrodes was improved significantly.PANI materials with crosslinked structure (CPANI) were prepared by two methods of the chemical oxidative copolymerization of aniline with p-phenylenediamine (PPDA) and triphenylamine (TPA), and the thermal treatment to conventional linear polyaniline (LPANI). Their morphology and structure were compared with LPANI via TEM, SEM, FTIR, XRD and TGA techniques. The electrochemical performance of the samples was studied by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests. The CPANI electrode exhibited specific capacitance of 455 F/g in 1 mol/L H2SO4 electrolyte. About 89% of its original specific capacitance could be remained after 1300 cycles. The electrochemical performance of CPANI electrode was much higher than the PANI electrode. CPANI composites were suggested as a promising electrode material for high performance supercapacitors.Finally, fluorescent brightener CBS-X dye with strong fluorescence has a long p-conjugated system and two anions for doping reaction. Fluorescent polypyrrole nanospheres (PPy/CBS-X) with uniform diameter were synthesized via a chemical oxidation polymerization with fluorescent brightener CBS-X as dopant. The effect of the feeding ratio of CBS-X on the morphology, fluorescent, electrical and electrochemical properties of the resultant PPy materials was investigated thoroughly. The sample exhibited the largest specific area of about 100 m2/g. When being used as electrode material for supercapacitors, it also possessed the high electrochemical specific capacitance (245.8 F/g). Its capacitance retention still remained 85.6% of the original capacitance after 1000 cycles. Most interestingly, the electrochemical activity of the fluorescent PPy/CBS-X could be easily monitored by photoluminescence. These features make the fluorescent polypyrrole nanospheres potential smart electrode material for high performance supercapacitors.