| Electrochemical capacitor(EC) has been extensively studied by a large number of scholars for its unique energy storage advantage. Exploring the better performance and wider application of the electrode materials is the key to study EC. Conducting polymers with high capacitance, electrochemical reversibility and so on, have attracted superior attention. Among conducting polymers, the capacitance performance of polyaniline(PANI) is particularly outstanding. In spite of various advantages for PANI, its poor cycle stability and rate performance are the main obstacles that prevent its application in real devices. To overcome this problem, the research has focused on incorporating materials which with great chemical stability and excellent electrical conductivity into PANI. Carbon materials have been extensively investigated since they have above advantages.In this paper, PANI with various morphologies are fabricated by different polymerization methods and their capacitance performance are systematically studied. In order to enhance their capacitance and improve their cycle stability, we incorporate multi-walled carbon nanotube(MWCNT) or reduced grahpene oxide(RGO) into PANI system. This thesis is divided into four chapters, which discusses and manifests the advantages of PANI/carbon materials composites as electrode materials from theoretical and experimental points.The fist chapter: the composition and working principle of EC are summarized; the structure, conductive mechanism, doping mechanism and synthetic method of PANI are introduced; the study and application of electrochemical capacitor with PANI and its composites as electrode materials are elaborated.The second chapter: by employing microemulsion polymerization, cross-linked PANI(cPANI) are successfully prepared, where dioctyl sulfosuccinate sodium salt, camphorsulfonic acid and ammonium persulfate are used as the surfactant, the doping acid and the initiator, respectively. Morphology analysis shows that cPANI has network structure composed of cross-linked fibers. The capacitance performance of cPANI is estimated by means of cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Its specific capacitance(Csp) can reach 498.7 F/g at a current density of 0.5 A/g; as the current density increases to 2.0 A/g, its Csp falls to 362.4 F/g with 72.7 % capacitance retention. After 1000 charge-discharge cycles at a current density of 5.0 A/g, cPANI remains 65.1% in specific capacitance. We obtain cross-linked polyaniline@multi-walled carbon nanotube(cPANI@MWCNT) composite by in-situ polymerization route so as to improve the capacitance performance of cPANI. The morphology analysis shows that cross-linked PANI network aggregates are located on the MWCNT to form core-shell architectures. The capacitance performance of the composite is investigated by the above electrochemical means. The Csp of the composite is 639.7 F/g at a current density of 0.5 A/g, which is 28.4% higher than that of cPANI. The Csp of 521.8 F/g can be achieved at 2.0 A/g, and 81.6% of its initial capacitance is still retained at high current. Its specific capacitance retention retains 77.2 % after 1000 charge-discharge cycles. The composite has not only higher specific capacitance, but also greater rate performance and cycle stability, indicating that the addition of MWCNT can effectively improve capacitance performance of the composite.The third chapter: by employing simple chemical oxidation polymerization method, granular PANI are successfully prepared, and the granular PANI/MWCNT composite are also obtained by in-situ polymerization route, where camphorsulfonic acid and ammonium persulfate are used as the doping acid and the initiator, respectively. The Csp of granular PANI can reach 451.9 F/g at a current density of 0.5 A/g; as the current density increases to 2.0 A/g, its Csp falls to 274.6 F/g with 60.8% capacitance retention. After 1000 charge-discharge cycles at a current density of 5.0 A/g, granular PANI remains 57.9% in specific capacitance. Above results indicate granular PANI has a poor rate performance and cycle stability. In order to overcome the above drawbacks, we introduce MWCNT into PANI system to obtain granular PANI/MWCNT composite. The Csp of the composite is 629.0 F/g at a current density of 0.5 A/g, as the current density increases to 2.0 A/g, its Csp falls to 494.0 F/g with 78.5% capacitance retention. Its specific capacitance retention is 74.4% after 1000 charge-discharge cycles, which is 28.5% higher than that of pure PANI. The results exhibit that the capacitance performance of the composite is better than that of pure PANI.The forth chapter: by employing microemulsion polymerization, tubular PANI are successfully prepared, where sodium dodecyl sulfate, camphorsulfonic acid and ammonium persulfate are used as the surfactant, the doping acid and the initiator, respectively. PANI with special morphology composed of short fiber arrays are compactly located on the tubes. The Csp of tubular PANI is 457.3 F/g at a current density of 0.5 A/g; as the current density increases to 2.0 A/g, its Csp falls to 212.4 F/g with 46.5% capacitance retention, indicating a poor rate performance. After 1000 charge-discharge cycles at a current density of 5.0 A/g, tubular PANI remains 63.6% in specific capacitance. In order to improve the rate performance and cycle stability of pure PANI, a series of PANI/RGO composites are prepared by in-situ polymerization route, which are designated as PANI/RGO 1, PANI/ RGO 2 and PANI/ RGO 3. The RGO content in these composites is estimated to 10.7%, 22.7% and 52.6 %, respectively. Morphology analysis shows that PANI fibers distribute on the surface of RGO. The Csp of PANI/RGO 1, PANI/ RGO 2 and PANI/ RGO 3 are 655.5, 684.2 and 570.5 F/g respectively at a current density of 0.5 A/g. With the increase of the MWCNT amount, both the rate performance(66.1, 74.3 and 78.7%respectively) and cycle stability(75.8, 81.8 and 84.7%respectively) of various PANI/RGO composites are promoted. |
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