The Preparation And Capacitance Properties Of Graphene And Manganese Dioxide Composite Materials

Graphene and manganese dioxide composite materials were successfully prepared by chemical precipitation method, Fourier infrared (FT-IR), Thermo Gravimetric Analyzer (TGA), and X-ray powder diffraction technology (XRD) were used to determine the structure of the materials. Transmission electron microscope (TEM) was used to observe the surface morphology of materials. The capacitance performance was studied by cyclic voltammetry, charging-discharging curves and electrochemical impedance spectroscopy (EIS) in alkaline sodium solution. The results show that the characteristic absorption peaks of graphene and manganese dioxide were observed in FT-IR spectrum. XRD analysis results show that manganese oxide were amorphous. The TEM results show that the graphene has good dispersion, a small amount of folds and translucent sheet.In the progress of preparing graphene, investigating the effects of the reduction time of the graphene oxide and the mass ratio between NaBH4 and graphene oxide; In the progress of preparing graphene/graphene composite materials, investigating the effects to capacitor performance of the mass ration between graphene and hydrate manganese sulfate and the electrode quality of composites. The results showing that graphene has the good electrochemical performance when the reduction time is 10h and the mass ratio between sodium borohydride and graphene oxide is 8:1. Under the conditions of the relative optimization, when the mass ration between graphene and hydrate manganese sulfate is 1:3, the single electrode specific capacitance was up to 283 F·g-1, with the mass 2.20 mg, the single electrode specific capacitance reaches its maximum value.In electrochemical tests, investigating the effects of the sweep speed and current density to the capacitor performance between graphene, MnO2 and composites, results showing that at the relative optimized preparation conditions(the quality is 2.17 mg, voltage range between-1 V to 0.3 V, the current density is 2 mA·cm-2), in alkaline sodium solution, graphene/manganese dioxide composites showed better capacitance performance, and the special capacitance can reach 283 F·g-1, in the current density of 5 mA·cm-2, specific capacitance only decreased by 23%. Compared to graphene and manganese dioxide, graphene/manganese dioxide has good large current discharge capacity. In the current density of 2 mA·cm-2, after 1000 times of charging and discharging, the capacitance remained 85%, the cycle life improved 10% compared to the pure graphene and 20% to manganese dioxide. Electrochemical impedance spectroscopy experiment showed that graphene/manganese dioxide composite material has a small internal resistance, exhibit good pseudocapacitive performance.A symmetric capacitor, was assembled by using graphene/MnO2 as both of the electrodes and alkaline sodium solution as the electrolyte, the energy density is 35 Wh·kg-1, higher 63% than only assembling by manganese dioxide, the power density is 1926 W·kg-1, increased by 39% than only assembling by graphene, so the symmetrical type condenser composed by composite material has more outstanding performance.