Preparation, Compound And Electrochemical Capacitance Performance Of Polyaniline

Supercapacitors (Electrochemical capacitors) has become an important energy storage devices due to irreplaceable advantages such as their high power density, strong energy storage ability, fast charing and discharging, no environmental pollution, long cycle life, wide work temperature range and so on. Based on the charge storage mechanism, supercapacitors are divided into two types:Electric double layer capacitors and pseudocapacitors. Carbon materials used in EDLC have long life (>105cycles) but their low specific capacitance. Conductive polymers and metal oxides used in supercapacitors have high specific capacitance due to fast redox reactions. Among various potential pseudocapacitor electrode materials, conductive polymer is one of the most promising materials. Of those, polyaniline (PANI) has become an important electrode material in energy storage devices because of the advantages of high theoretical capacitance, tunable redox state, simple and multiple synthesis methods, low cost, high environmental stability and so on.In this paper, the preparation and capacitive performance of conductive polyaniline and PANI/RGO composite are systematically studied, and some satisfactory results are harvested. The thesis is divided into four chapters, the main research contents and innovative points are summarized as follows:The first chapter summarizes the molecular structure, the doping mechanism and applications of PANI. Furthermore, the synthesis methods of nano-sized PANI are introduced in recent years. Finally, research ideas and new approaches for fabricating nano-structured PANI and its composite as electrode materials in supercapacitors are put forward.The second chapter is the synthesis and capacitive performance of PANI nanofibers by conventional hydrothermal polymerization using aniline as the monomer and camphorsulfonic acid as the dopant. The result indicates that PANI nanofibers of50～80nm in diameter were successfully obtained. With the increase of the current from0.5A g-1up to2A g-1, specific capacitance decreases from486F g-1to363F g-1with the capacitance retention of74%. In addition, the PANI electrode exhibits a lower inter resistance. Accordingly, the as-prepared PANI nanofibers had high specific capacitance and good rate performances, which had the potential applications in electrochemical capacitors.The third chapter is the inverse microemulsion synthesis and capacitive performance of PANI. Using aniline as the monomer, HC1aqueous solution as the dopant, different morphological PANI is prepared by low-temperature polymerization method and hydrothermal method under the hexadecyl trimethyl ammonium bromide (CTAB)/n-pentanol/cyclohexane/H2O quaternary system. This chapter is divided into two parts:1. By employing hydrothermal-assisted reverse microemulsion polymerization method for the first time, we successfully fabricate the cotton-like PANI with porous structure. Results indicate that PANI produced has a specific capacitance of429F g-1at a current density of0.5A g-1. Even at high current of2A g-1, its capacitance still retains322F g-1with75%capacitance retention. Accordingly, the as-prepared PANI has high specific capacitance and good rate performances, sugggesting the potential applications in electrochemical capacitors.2. By employing reverse microemulsion polymerization under low temperature, PANI networks assembled from highly crystalline, porous and superfine nanofibers. Morphological and structural characterization shows that PANI has a narrow diameter of15-25nm and a length of100～200nm. The electrochemical tests reveal that these superfine PANI fibers have high specific capacitance (493F g-1at a current density of0.5A g-1) and good rate capability (with the increase of the current from0.5up to2A g-1, PANI still retains more than80%).The forth chapter is synthesis and capacitive performance of PANI/RGO. Using aniline as the monomer, CSA as the dopant, cluster-like PANI and PANI/RGO composite are prepared by hydrothermal method under the hexadecyl trimethyl ammonium bromide (CTAB)/n-pentanol/cyclohexane/H2O quaternary system. This chapter is divided into two parts:1. By employing hydrothermally assisted reverse microemulsion polymerization for the first time in the presence of camphorsulfonic acid as a dopant, self-aggregated polyaniline (PANI) nanowires were synthesized and subsequently organized into three-dimensional cluster-connected networks. And discussed the influence of different molar ratio (CSA/AN) on polyaniline morphology. A probable assembly mechanism for such an interesting morphology was also proposed. Used as an electrode material, PANI achieved high specific capacitance of510F g-1at0.5Ag-1constant current. Even at high rate (2A g-1), a368F g-1capacitance was still retained, indicating relatively good power performance, which may be related to the morphology and structure of nanomaterials.2. By employing hydrothermal-assisted in-situ reverse microemulsion polymerization, a unique hierarchical porous PANI/RGO composite is synthesized for the first time. The result demonstrates that the PANI/RGO has high specific capacitances and good rate capability. Furthermore, its capacitance retention reaches as high as76%over1000cycles, indicating good cycling performance.