Research On Application Of Conducting Polyaniline In Supercapacitor

Supercapacitors have been recognized as new electrochemical energy storage devices which performance between the rechargeable batteries and the typical dielectric capacitors. The performances of supercapacitors are mainly determined by electrode materials which include carbon materials, metal oxides and conducting polymers and so on. In the family of conducting polymer, however, the conducting polyaniline (PANI) has attracted considerable attention due to its unique performances. In this thesis, we have prepared pure PANI and its composite electrode materials, mainly researched the capacitive behaviours of PANI in different electrolytes. The morphologies, structures and elements of those materials were characterized by scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and X-Ray energy dispersive spectrum (EDS). And the electrochemical characterisations of these materials were carried out by means of cyclic voltammetry (CV); galvanostatic charge-discharge experiments; Potential step method; electrochemical impedance spectroscopy (EIS); and simulation with equivalent circuit. The main contents of this thesis are as the following:(1) Preparation of pure PANI film electrode and electrochemical performanceUnder an aqueous solutions system, we prepared the thin film of PANI deposited on GC substrate using the CV method. The SEM results indicated the obtained PANI films form uniform rods with average diameter of 100 nm and interveined together to be a three-dimensional reticulation. Based on the CV analysises, it was found that the pseudocapacitive performance of PANI/GC electrode in p-TSA was inferior to that in H2SO4 at a low scan rate (1-5 mV/s), while its superiority was shown gradually with the increase of scan rate, especially at a high scan rate of 100 mV/s. Cyclic voltammetric (CV) experiments, electrochemical impedance spectroscopy (EIS) and single potential step studies were carried out to investigate the effects of the counterions. The results revealed that there were different dynamic behaviors in nature in these two electrolytes. Based on the results, we could predicte that the PANI material had a more suitable heavy load charge-discharge performance in p-TSA electrolyte.(2) Preparation of composite electrodes of PANI/MnO2 and performanceUnder an aqueous solutions system, the PANI/MnO2 films were obtained on the stainless steel nets by electrochemical codeposition from aniline and MnS04 solutions, which realized the combination of organic polymer and inorganic metal oxides.The supercapacitive performance of this composites electrode was respectively investigated in inorganic aqueous solutions and organic nonaqueous electrolytes. The XRD patterns reveal the amorphous nature of MnO2 in the composites. A large amount of fibers of PANI/MnO2 thin films with diameters of 100-150 nm can be found from the.SEM picture. Based on the CV and galvanostatic charge-discharge analysises, the PANI/MnO2 electrodes present not good cycle performances in 1.0 M Na2SO4 at pH 2.5, but it has a high specific capacitance (SC) of 715 F/g. While in an orgnic electrolyte (1 M LiClO4/AN), the films showed a better supercapacitive performances which display a SC of 512 F/g and a capacity fade of just 28% after 600 charge/discharge cycles at a current density of 2.0 mA/cm2 and a window of 1.2 V, Which indicated that the organic electrolyte is suitable for PANI/MnO2 hybrid material to apply in supercapacitors. To the best of our knowledge, this is the first report about supercapacitive behaviours of PANI/MnO2 in an organic electrolyte.(3) Preparation of composite electrodes of PANI/MnO2/AC and performancesWe firstly prepared the AC electrodes which use the high surface area actived carbon as the main electrode materials and the stainless steel nets as the substrate, and then the electrodepositions of PANI/MnO2 hybrid films were produced simultaneously on the AC substrate electrodes through CV. The results of SEM and EDS suggest the codeposition of MnO2 with the growth of PANI on the AC substrate. In addition, the PANI/MnO2 films present a large amount of fibers with diameters of 100-150 nm in the mass and the fibers inter-twine together to form a three-dimensional reticulation. The XRD patterns reveal the amorphous nature of MnO2 in the composites. Results show that the capacitance and stability of this thin film were excellent under a high potential window in 1.0 M LiC104 in acetonitrile, The capacitance of PANI/MnO2/AC can reach 408 F/g at a current density of 4.0 mA/cm2 and maintains about 82% of the initial capacitance after 1500 cycles in the potential range of [0,1.2 V] vs. Ag/AgCl. The coulombic efficiency is higher than 95%. In addition, the coated PANI/MnO2 phase produces SC as high as 1292 F/g. In this work, an asymmetric capacitor has been developed with the PANI/MnO2/AC positive and pure AC negative electrodes, which is able to deliver a specific energy as high as 61 Wh/kg at a specific power of 172 W/kg in the range of [0,2.0 V]. These results indicate that the organic electrolyte is a promising candidate for PANI/MnO2 material application in supercapacitors.