Preparation And Electrochemical Properties Of MnO₂/PPy Composites For Electrochemical Capacitors

In recent ten years, the new power technology instead of traditional petrochemical energy has been got more and more attention. Supercapacitors are new energy storage devices which have no pollution and longer cycle life, and can be charged within a short time. It is a practical answer to the world’s pressing need for clean and efficient power due to their advantages. Conductive polymer polypyrrole has a simple preparation and good electrochemical activities. Manganese dioxide also has a lot of advantages of cheap prices, sufficient and high specific capacity. As a result, the composites from polypyrrole and manganese dioxide have wide application.In this thesis, we use in-situ synthesis for the polypyrrole and PPy/MnO2composites preparation with different morphologies and electrical properties are discussed. Meanwhile, the structure and morphology of the obtained materials were characterized by XRD, FT-IR, SEM and TEM. The prepared composites with different morphologies have been characterized and a possible growth mechanism of PPy/MnO2composites is studied on the basis of the experimental results.This paper main study the conducting electric polymer polypyrrole and its composites used in the electrochemical performance of electrode materials for supercapacitor. The research contents involve as follows.(1) PPy nano particles were synthesized in aqueous solution and organic solution by low temperature hydrothermal method,using ferric chloride and pyrrole as raw material. We studyed the optimal synthesis process and found the method is simple, inexpensive and low pollution. Cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance measurements were also performed to evaluate the electrochemical properties of obtained PPy. It was showed that the specific capacitance of PPy nano particles was adjective.(2) MnO2/PPy composites were synthesized by chemical in-situ polymerization at room temperature, using KMnO4, FeCl3, MnSO4·H2O and pyrrole as the raw material.The morphology and structure of the products were characterized by X-ray diffraction(XRD), infrared spectroscopy (FTIR), Field Emission scanning electron microscopy(FE-SEM), transmission electron microscopy (TEM).It was showed that the obtained MnO2/PPy composites were amorphous and their particle size in the range of50～100nm. A specific capacitance of206.61F·g-1was obtained when the mass ratio of MnO2was30.86%. The attenuation was about20%after400charge-discharge cycles that indicates favorable capacitance retention ability. In addition, the CV curve of MnO2/PPy electrode showed good rectangular features,and the charge-discharge curve also showed typical capacitive behavior with a good linearity.(3) The impact of changing the electrolyte solution on the properties of composite materials had been investigated. MnO2/PPy composites were prepared by the same method with25%diethylene glycol butyl ether solvent as the electrolyte. The results showed that the particle size with organic electrolyte was less than that with the aqueous solution and the obtained MnO2/PPy composites were evenly distributed. The capacitance is about328.37F·g-1and almost no reduction after800charge-discharge cycles that shows the obtained MnO2/PPy composites with electrolyte solution had a good stability and the composites were an ideal supercapacitive material.