Preparation And Electrochemistry Performance Of Poly-2,5-dihydroxyaniline/activated Carbon Composite Materials

Polyaniline has the lowest production cost among the conductive polymer family.Rearch of improving the structure and performance of polyaniline is an eternal theme.The electrochemical behavior of polyaniline （PANI） had been extensively and indepthresearched, but there were few reports about the electrochemical performance of itsderivative poly-2,5-dihydroxyaniline （PDHA）. Poly-2,5-dimethoxyaniline （PDMA）coating had been fabricated on active carbon （AC） substrates by cyclic voltammetry（CV）. After the methoxy groups （-OCH3） hydrolyzed into hydroxyl groups （-OH） toproduced PDHA, the introduced hydroquinone units in the PDHA polymer enhancedthe conductivity of the electrode. The resulted coatings were hydrolyzed to producePDHA/AC composite electrode. We also prepared PDMA-PANI/AC compositeelectrode in a certain ratio of monomers by electrochemical copolymerization, andthen hydrolyzed the copolymer to produce PDHA-PANI/AC composite electrode toimprove the capacitance of the composite electrode. Scanning electron microscope（SEM）, Fourier transform infrared （FTIR） spectroscopy, cyclic voltammetry （CV）,electrochemical impedance spectroscopy （EIS）, and galvanostatic charge/dischargetest were used to investigate the properties of these electrodes. A series of experimentswere conducted to research on preparation techniques of electrodes, optimization ofelectrolytes, assembly technology of capacitor. The rusults are as follows:1. Perparation and electrochemistry performance of AC electrode（1） We prepared AC electrode and the electrochemistry property of AC electrodein aqueous electrolyte was investigated. The galvanostatic charge/discharge resultsdemonstrated that, under a potential window of0¹.0V, the specific capacitance was214.84F g^-1. At a current density of3mA/cm², after700charg/discharg cycles, thecapacitance about92.7%of early stage of cycling. The capacitor using AC as anode and cathode was prepared and its electrochemical behavior materials wasinvestigated.（2） We prepared AC electrode and the electrochemistry property of ACelectrode in organic electrolyte of acetonitrile solution containing LiClO4wasinvestigated. The galvanostatic charge/discharge results demonstrated that, under apotential window of0¹.5V, the specific capacitance was117.49F g^-1. At a currentdensity of3mA cm^-2, after700charg/discharg cycles, the capacitance about90.2%ofearly stage of cycling. The capacitor using AC as anode and cathode was prepared andits electrochemical behavior materials was investigated.2. Perparation and electrochemistry performance of PDHA/AC compositeelectrode（1） Poly-2,5-dimethoxyaniline （PDMA） coating had been fabricated on activecarbon （AC） substrates by cyclic voltammetry （CV） in aqueous electrolyte. Theresulted coatings were hydrolyzed to produce poly-2,5-dihydroxyaniline （PDHA） toenhance the capacitance of the composite electrode. The galvanostaticcharge/discharge results demonstrated that, under a potential window of0¹.0V, thespecific capacitance was960F g^-1. At a current density of3mA cm^-2, after700charg/discharg cycles, the capacitance about89.2%of early stage of cycling.（2） Poly-2,5-dihydroxyaniline （PDHA） film was successfully prepared byelectrochemical method on the surface of active carbon （AC） electrodes in organicelectrolyte of acetonitrile solution containing LiClO4. FTIR spectroscopymeasurements indicated the presence of hydroquinone units in PDHA. At a currentdensity of3.0mA cm^-2, under a potential window of0¹.5V, the specificcapacitance was940F g^-1, after500charg/discharg cycles, the capacitance about86.4%of early stage of cycling. The specific energy of asymmetric capacitor whichconsists of PDHA/AC positive and AC negative electrodes was178Wh kg^-1at aspecific power of474W kg^-1under a potential window of0².0V.3. Perparation and electrochemistry performance of PANI-PDHA/AC compositeelectrode The PDHA-PANI coatings were synthesized on activated carbon substrate by CVmethod in the organic solution containing0.2M monomer in the mass ratio of2,5-dihydroxyaniline: aniline=0.15:0.85, The potential for polymerize was cycledbetween-0.2and+1.5V. The resulted coatings were hydrolyzed to producePDHA-PANI to enhance the capacitance of the composite electrode. Thegalvanostatic charge/discharge results demonstrated that, under a potential window of0¹.5V, the specific capacitance was421F g^-1. A comparative pecific capacitance of290.7F g^-1was obtained by polyaniline/AC under the similar conditions under apotential window of0¹.2V. That indicated that the introduced PDHA enhanced thecapacitance of the composite electrode.The specific energy of asymmetric capacitor which consists of PDHA-PANI/ACpositive and AC negative electrodes was167Wh kg^-1at a specific power of534Wkg-1under a potential window of0².6V.