Capacitive Polypyrrole And Its Composites By Dynamic Three Phase Electropolymerization

In face of resource shortages, energy crisis, climate change and many other global issues, conventional energy has been difficult to meet the requirements of the development of human society. Therefore, exploring environmental friendly, promising and sustainable new energy has become the great challenge of this century. In this case, the exploitation and utilization of new energy sources, such as solar energy, hydropower, biomass energy, and new technologies to improve energy utilization efficiency is an effective way to solve this problem. The new energy materials are the key to implement the transformation and application of new energy, which are also the core and basis of the development of new energy industry. Owing to its excellent electronic and environmental stability, facile synthesis, especially a unique and reversible doping/de-doping chemical property, conducting polymers have been exploited in many potential applications, such as the developing of supercapacitors, batteries, electronic and optical apparatuses, sensors, etc. In recent decades, in order to further improve the performance of conductive polymers, researchers have paid much attention to explore and study the new methods for preparing conductive polymers with special micro/nano structure. Recently, our gourp have demonstrated the interesting aspects of a dynamic three-phase electrode process and the validity of the D3PIE method for fabricating free-standing conductive polymer films. This thesis focuses on preparing free-standing conductive polypyrrole films with special micro/nano structure by this method and studying the capacitive performance of the polypyrrole films. The main contents and results were summarized as follows:(1) Free-standing polypyrrole film was electrosynthesized at the interface between an HClO4aqueous solution and a pyrrole chloroform solution through a dynamic three-phase interline electropolymerization (D3PIE) process. The cyclic voltammetary measurements showed that the onset potential for the oxidation of pyrrole mononers was～0.2V vs. Hg/Hg2SO4, and the radial expansion of conductive polymer film gradually increased the reaction currents. Under potentiostatic conditions, higher potentials, higher counterion (perchlorate) concentrations and higher monomer concentrations all caused a faster growth of polymer, and the aqueous perchlorate ions appeared the most sensitive factor for the reaction currents. The electropolymerization proceeded with a current efficiency of more than97%at different applied potentials. In the initial stage of electropolymerization, the reaction currents and the diameters of polymer films increased linearly with the operating times, and a simple model can be used to describe the growth behavior of the circular polymer film. However, several factors can cause the deviation from an ideal linear relation in the later stage of electropolymerization. Higher aqueous perchlorate concentration increased the penetration amount of perchlorate ions to organic solvent phase, resulting in the longitudinal growth of PPy polymers. In addition, the prepared PPy films exhibited significantly different microstructures between the side towards water and the side towards organic solvent, and the aqueous perchlorate concentration and monomer concentration both affect the morphologies of films greatly. In order to observe a well-defined expansion of three-phase interline, lower concentrations of aqueous perchlorate ions and monomers are preferable. Moreover, the PPy films exhibited a higher capacitive electrochemical response when characterised in higher electrolyte and monomer concentration. Without any additional shaping and conducting materials, the highest specific capacitance of352F g-1was obtained at0.5A g-1. The films prepared at three-phase interline are promising electrode materials for application in electrochemical supercapacitors.(2) PPy/PEDOT composite films at different Py/EDOT ratios (1:1、1:5、2:1、10:1) were synthesized through a dynamic three-phase interline electropolymerization (D3PIE) process. PPy and PEDOT were distributed evenly in the composite film, in which PPy was the main part. With the increase of EDOT concentration, the content of PEDOT in the composite film have also been increased. The proportion of Py/EDOT had a great effect on the growth of the PPy/PEDOT composite film. When the proportion of Py/EDOT≤1:1, the oxidation current and the growth rate of PPy film along the oil/water interface increased obviously. The higher concentration of EDOT (1.0mol L-1) caused a faster growth of PPy/PEDOT composite film, indicating better conductivity of PPy/PEDOT composite. In addition, the prepared PPy/PEDOT film exhibited different microstructures between the side towards water phase and oil phase, which was similar to the morphologies of pure PPy film. Moreover, PPy/PEDOT film showed better capacitive performance, faster charge and discharge performance and better stability, which combined the merits of pure PPy and PEDOT. Without any additional shaping and conducting materials, the highest specific capacitance of290F g-1was obtained at0.5A g-1.(3) Free-standing PPy/CNTs and PPy/C composite films were synthesized based on the carbon materials liquid/liquid interface assembly and the D3PI electrochemistry technologies. The pattern of the films prepared by this method looks like a lotus leaf and the thickness of film is only3μm. The results showed that the amounts of CNTs or C at oil/water interface had a great influence on the apparent area of PPy/CNTs (PPy/C) film and the polymerization current. When the amount of CNTs was0.182μg mm-2, the apparent area of PPy/CNTs film could reach1500mm2for600s. With the increase of the concentration of CNTs or C, the conductivity of the interface would be improved since more CNTs or C dispersed at oil/water interface, which could facilitated the growth of the PPy/CNTs (PPy/C) film along the interface. However, the thickness of the PPy/CNTs (PPy/C) film was confined due to the mass transfer hindering by the excessive CNTs or C at the interface. Therefore, the polymerization current firstly increased and then decreased with the increasing of CNTs or C amount. Similarly, the morphology of PPy/CNTs (PPy/C) film also showed great difference between the side towards water phase and oil phase. The structure towards water phase showed the similar structure of CNTs or C, while the structure towards oil phase seemed to be similar with the pure PPy film with micro-nano porous structure. Furthermore, the obtained PPy/CNTs and PPy/C composite films exhibited a higher capacitive electrochemical response at high scan rate, the specific capacitance can reach250F g-1at200mV s-1, which might be promising electrode materials for application in electrochemical supercapacitors.(4) For the first time, PPy/MnO2composite film was synthesized based on the hydrous MnO2nanoparticles liquid/liquid interface assembly and the D3PI electrochemistry technologies. Firstly, a flexible MnO2film formed at flat oilwater interface, and then the D3PI electropolymerization was followed. The amounts of MnO2at oil/water interface had great influence on the the polymerization current and the growth of PPy/MnO2composite film. With the increase of the concentration of MnO2, the apparent area of PPy/MnO2composite film had no significant change, but the thickness of the PPy/MnO2film was confined due to the mass transfer hindering by the excessive MnO2at the interface. Therefore, the polymerization current decreased with the increasing of the concentration of MnO2. Likewise, the morphology of PPy/MnO2film showed great difference between the side towards water phase and oil phase. With the increase of the concentration of MnO2, the side towards water phase showed much denser and more spheroidal particles, while the porous structure of other side disappeared gradually. Although the PPy/MnO2film showed good capacitive performance, the specific capacitance had no obvious increase compared with the pure PPy film.