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Preparation and capacitance performance of manganese dioxide and polyaniline complex

Author: XuXiaoCun
Tutor: LiuKaiYu
School: Central South University
Course: Applied Chemistry
Keywords: supercapacitor nano-MnO2 composite material interfacial synthesis soft-template
CLC: O631.3
Type: Master's thesis
Year: 2010
Downloads: 189
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Abstract

Electrochemical capacitors are new kinds of energy storage devices. Electrode material is one of important factors that affect the performance of Ecs.MnO2 is a good alternative material which possesses good performance, rich reserves, low price and environment friendly and so on. Originally, the MnO2 materials with irregular morphology and larger particle size were mainly prepared by electrolytic process which was costly. Therefore, in recent years, researchers paid close attention to the preparation methods of MnO2 materials and conducted so much research for the preparation. The studies showed that morphologies and properties of products were prepared by differnet methods.In this thesis, MnO2 was synthesized by interfacial method and soft-template method and the performance of MnO2 was optimized. The details of the work are as follows:Nano-mangannese dioxide was prepared by interfacial method through redox reaction with Mn2+ and MnO4- at the interface between organic phase and aqueous phase at room temperature. Interfacial synthesis at organic-aqueous is an alternative and useful approach compared to conventional homogeneous synthesis.The formation process and electrochemical capacititance properties of nano-MnO2 were discussed. XRD results showed that the sample was a mixture crystalline of a-MnO2 andγ-MnO2. SEM images demonstrated that the as-prepared MnO2 was formed by nanorods with the length of 300 nm together. The first discharge capacity of MnO2 electrode was 243 F/g, the capacity retention was 72.5% and 59.3% after 569 cycles at the current of 200 mA/g and 100 mA/g, respectively. All the electrochemical tests demonstrated that the as-prepared MnO2 not only possessed good electrochemical capacitance performance, but also suited to discharge at higher current.Nano-MnO2 was synthesized by co-precipitation method with the existence of Pluronicl23 as the soft template in aqueous solution. The influence of the concentration of Pluronicl23 on the structure and capacitive performance of MnO2 were studied. When the concentration of Pluronicl23 was lower than the concentration of critical micelle, the results showed that the MnO2 sample was badly-crystallized because the self-assembly could not happen, While when concentration of Pluronicl23 was so high that oxidation-reduction reaction was not fully reached due to manganese ions coated by Pluronicl23,and Mn3O4 was thus obtained. When the concentration of Pluronicl23 was 8 g/L, the spherical a-MnO2 was well-crystallizied formed by nanorods which exhibited the highest specific capacitance reaching to 103 F/g and remained at 48.1 F/g after 500 cycles.In order to improve electrochemical properties of MnO2 material,MnO2 /polyaniline composite was prepared by polymerization of aniline in acidic conditions using ultrasonic technology. Electrochemical properties of MnO2/PANI electrodes were investigated by cyclic voltammetry(CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy(EIS).Introduction of polymerization aniline not only was helpful to the structure and morphology of MnO2, but also improved the electrochemical performance of MnO2 material.The MnO2 composite displayed a discharge capacity of 190.8 F/g at a current density of 100 mA/g, there is only 4.7% of capacity decay and coulombic efficiency remianed above 97% after 500 cycles.

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