Preparation And Polymerization Mechanism Research Of Electrodeposited Polyaniline In Organic System

Among the conductive polymer, due to polyaniline has the properties of structure diversification, higher conductivity, cheap monomer, easy polymerization good chemical stability, unique doped phenomenon, excellent electrochromic property, reversible oxidation reducible, photoelectric property, nonlinear optical, volume potential responsiveness, it become the hotspot research in conductive polymer field. In this thesis, we have prepared pure PANI by CV in organic system, a series of experiments were conducted to research on preparation techniques of electrodes, optimization of the best polymerization parameters and the polymerization mechanism. The morphologies, structures of those materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared Spectroscopy (FTIR). And the electrochemical characterisations of these materials were carried out by means of cyclic voltammetry (CV); electrochemical impedance spectroscopy (EIS).The main contents of this thesis are as follows:(1) Preparation of pure PANI film electrode and electrochemical performance Under an organic system (acetonitrile, acetic acid and LiClO₄), we prepared the thin film of PANI deposited on GC substrate using the CV method. The aniline begin to oxide when the potential increasingly scans to 0.7V, there exist a critical potential 1.8V during the polymerization, and the polymerization succeed even at the potential as high as 2.5V which is higher than that in inorganic system and could highly enhance the ED of PANI as a supercapacitor. The potential range between 0.2⁰.8V in organic system where PANI shows good electroconductivity is wider than that reported in inorganic electrolyte (0.2⁰.6V). The SEM of the PANI film present a large amount of fibers with diameters of tens to hundreds nanometer in the mass and the fibers inter-twine together to form a three-dimensional reticulation.(2) The influence of the amount of electrolytes to the polymerization of PANI in organic system.The PANI film were obtained on the GC and gold electrode while changing the amount of the supporting electrolyte (LiClO₄) and protonic acid (acetic acid) of the organic system respectively. The results show that when the system only contains acetic acid and no LiClO₄, the polymerization failed and there is nothing on the electrode except the color of the electrolyte turns into brown; when the system only contains LiClO₄ and no acetic acid, the polymerization succeeded but the combining of PANI film with electrode is not good and the PANI film is easy to fall off; when the amount of acetic acid is constant and changing the amount of LiClO₄, the effect of polymerization gets better, which obviously reflects the function of LiClO₄ as the supporting electrolyte; when the amount of LiClO₄ is constant and changing the amount of acetic acid, the effect of polymerization gets worse, which demonstrates the influence of acetic acid as weak electrolyte to the low diffusion coefficient of the active groups in the system. According to the above experiments, we ascertain the best parameters of polymerization: 0.2M aniline + 0.5M lithium perchlorate + 1M acetic acid in acetonitrile, polymerization potential range: -0.2².2V.(3) Electrochemical deposition mechanism of PANI in organic system.According to the above experiments, we found the electrochemical deposition mechanism of PANI in organic electrolyte is different from that in inorganic system due to the low diffusion coefficient of the active groups in the organic system. The electrochemical deposition of PANI is a free radical-induced autocatalytic process, the specific process is as follows: (a) The ammonium cations of aniline salt which are formed by the reaction of aniline monomer with proton acid are oxidated into cation radicals in the solution; (b) The cation radicals react with the ammonium cations of aniline salt to form aniline dimmer; (c) The aniline dimmer can be oxidated and immediately combined with aniline salt to form trimer, then, the polymer chains are growing as the polymerization repeats, so a certain length of polymer chains are generated and deposited on the electrode surface eventually. But the diffusion coefficient of the active groups in the organic system is low, so the diffusion of the active groups has become the controlling step of the polymerization. The success of the polymerization of PANI in organic system provides scientific basis for the further development and utilization of PANI.