MnO₂/Graphene/Carbon Paper Composites Prepared By Electrochemical Deposition Method And Their Capacitance Properties For Capacitor

Electrochemical capacitors, as a new type of energy storage deVices have been widely applied in many fields because of their high power density, high energy density and long life characteristics. In order to meet the needs of the modern portable electronic de Vices, the development of a set of capacitors with ultra-thin, high energy storage, high-power, lightweight, and environmental protection properties has arose great interest in the synthesis of high energy, low cost, environmentally friendly materials as electrode materials for electrochemical capacitors. In this thesis, the carbon papers (CP) with a relatively high specific surface area, high electrical conductivity are used as the substrate material, and the manganese dioxide (MnO2) and the MnO2/graphene composites have been deposited on the Cps by using the electrochemical deposition method, and the capacitor performance of the materials has also been investigated in detail.(1) Using the CPs treated by different thermal treatment as work electrode, the structure of the CPs was charaterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy analysis (XPS) and X-ray diffraction spectroscopy (XRD), and the capacitor properties of the CPs have been measured by using cyclic voltammetry (CV) methods, it was found that the surface structure and the electrochemical properties of the CPs were strongly influnced by the method of the treatment.(2) The CPs treated by thermal annealing with some defects were used as working electrodes, potassium permanganate-phosphate buffer solution was used as the electrolyte, then the MnO2had been deposited on the surface of the fibers in the CPs by using CV method. The obtained samples were characterized by SEM, XRD, and the performance of the capacitor of the materials has been measured by CV, galvanostatic charge-discharge (CD) and EIS. The results show that the morphologies and capacitive properties of the electrodes are influenced by the defects of the carbon fibers, the thickness of the MnO2layer on the fibers. The optimum CPs coated with230nm thickness of MnO2exhibits the best charge-discharge performance, and the specific capacitance of MnO2deposited on the CPs reaches to about745F g-1when 1A g-1current density was used.(3) The CPs treated by thermal annealing with some defects are used as work electrodes, potassium permanganate-graphene oxide-phosphate buffer solution is used as the electrolyte, then the MnO2/Graphene (MnO2/G) has been deposited on the surface of the fibers in the CPs by using CV method. The obtained samples were characterized by SEM, XRD, and the performance of the capacitor of the materials had been measured by CV, CD and EIS. The results showed that the capacitive properties and the morphologies of the materials were influenced by the ratio of graphene oxide to potassium permanganate. When the concentration ratio of the graphene oxide to potassium permanganate isl:3, the specific capacitance of MnO2in the composites was larger84F g-1than that of pure MnO2and reaches to829F g-1.