Fabrication Of Poly(3,4-ethylenedioxythiophene) On Carbon Materials And Their Electrochemical Properties

In twenty-first century, the problems of energy shortage and the increasingly serious environmental pollution challenge the technologies in our scientific and technical field. Various high energy storage devices will play an important role in the development of human society in the future. In recent years, the energy storage mechanisms of the supercapacitor and the research of the advanced nanostruc tured materials have been made a new breakthrough, so the electrochemical performance of the supercapacitor has been greatly improved. The design and fabrication of new composites by combining carbon substrates with high pseudocapacitance materials is an effective way to positively improve the properties of the composites. Manganese dioxide (MnO2) is one of the most attractive inorganic materials because of its high specific capacitance, large amount in resources, low cost, facile preparation and environmentally friendly properties. As one of widely used conducting polymers, poly(3,4-ethylenedioxythiophene)(PEDOT) not only offers all the above-mentioned advantages but also owns high conductivity, thus has been attracted lots of attention recently. In this work, carbon cloth wove by carbon fibers (CC) and carbon paper (paper) were selected as carbon substrates due to its good electrical conductivity, chemical stability, light weight and flexibility. PEDOT/CC, PEDOT/CP, PEDOT/MnO2/CC and MnO2/PEDOT/CC composites were prepared by evaporative vapor-phase polymerization (EVPP) methods and used as freestanding electrodes for supercapacitors. The morphologies and structures of composites were analyzed and the electrochemical performances were also measured and investigated.The carbon cloth (CC) substrate was firstly etched by H2SO4 for 4h. PEDOT/CC composites were fabricated by EVPP method by adjusting the experimental conditions such as ratio of monomer and oxidant (mole ratio), reaction time and temperature. The morphologies and structures of PEDOT deposited on CC were investigated by Field-emission scanning electron microscopy (FESEM), Raman, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were studied by cyclic voltammetry(CV), galvonostatic charging/discharging (CD) and impedance measurement techniques(EIS). The results show that PEDOT/CC composites displayed a better electrochemical performance with 7.1 for the ratio of monomer and oxidant (mole ratio), the reaction time of 185 min and 130 C as the temperature. The obtained composite PEDOT/CC-tl85 showed a uniform distribution of PEDOT needle-like structure with vertically directed high aspect ratio nanowires. The PEDOT/CC-t185 composites demonstrated a high specific capacitance of 211 mF/cm2 at a current density of 1 mA/cm2, and the specific capacitance still remained about 85.7% of its initial value after continuous 3000 charge/discharge cycles. When the current density increased by 10 times the specific capacitance of PEDOT/CC composites still kept 68.3% of the original value. The PEDOT/CC-t185 composites were assembled into a flexible super capacitor, the maximum instantaneous power density was 20.3 mW/cm, the maximum energy density was 18.56 μWh/cm2.Carbon paper (CP) has a greater electrical conductivity than CC. With the optimized reaction conditions, by controlling the content of EDOT monomers, a series of PEDOT/CP composite materials were prepared. The specific capacitance could reachto 138 mF/cm2 at 1 mA/cm2,when the current density 1 mA/cm2 from 10 mA/cm2, the specific capacitance kept 59.5% of the initial specific capacitance; cycle stability for 4000 cycles at the current density 2mA/cm2 maintained 72.6% of the initial specific capacitance. Although CP has a greater electrical conductivity, but the specfic capacity of PEDOT/CP compositeswas lower than that of PEDOT/CC composites.To achieve a higher specific capacitance, we made a ternary composite material such as PEDOT/MnO2/CC to research synergistic effects of simultaneous deposition of manganese dioxide and PEDOT on the surface of modificated carbon cloth, by constructing two different ternary composites:PEDOT/MnO2/CC, MnO2/PEDOT/CC. At the current density 1 mA/cm2, the specific capacitance of the two different ternary composites was 391.3 mF/cm2 and 295.7 mF/ cm2, maintained 46.3% and 70.8% when the current density increased from 1 mA/cm2 to 10 mA/cm2, respectively. At the current density of 1mA/cm2, the cycle life for 3000 cycles of the current charge and discharge of the two different ternary composites is 76%,86.4%, respectively. The PEDOT/MnO2/CC composites were also tested by two electrode system. The specific capacitance of the material was 495 mF/cm2 with the current density of 1 mA/cm2 and when the current density increased from 1 mA/cm2 to 10 mA/cm2, the specific capacitance kept 62.6% of the initial specific capacitance.