Special Morphological Manganese And Tin Oxide/Graphite Nanosheet Array Electrodes And Their Application In Symmetrical Supercapacitor

The higher energy density and power density are important parameters about the performance of the supercapacitor. Furthermore, the performance of the supercapacitor is closely related to the electrode materials. Currently, Carbon material has become one of the most studied electrode materials due to its wider potential window, good chemical stability and large surface areas. Graphene as a novel emerging carbon materials, possess many unique features such as larger specific surface area（up to 2630 m2·g-1）, excellent electrochemical stability and outstanding electron conductivity. However, in practical processes, graphene sheets usually suffer from agglomeration or restacking due to the strong van der Waals interactions, which lead to exhibits a lower performance than as expected. Therefore, it is extremely significant to construct graphene-like nanosheets with ordered spacial arrangement and high surface area, at same time, in close connection with substrate.In the present thesis work, we fabricate a carbon-based substrate through the chemical exfoliation of graphite rod. It has open 2D layer arry structure consisting of the graphite nanosheets which are perpendicular to the surface of the graphite substrate and parallel to each other in the arrangement. On the one hand, the surface of the graphite nanosheets contain a number of oxygenic groups such as like hydroxy, carboxyl and epoxyl, which proceed easily the electrochemical deposition due to the electrostatic interaction between these groups and metallic ions. On the other hand, the contact resistance between electrochemical active species and current substrate（graphite rod） is effectively decreased due to the seamless connection of the nanosheet arry with substrate. Moreover, we deposite electrochemically metal oxide nano-structures with high specific capacitance on the as-prepared ordered graphite nanosheet arry to obtain the composite electrodes with excellent performance. The symmetric supercapacitors are also assembled to evaluate the practical performance of the materials. In addition, the electrochemical properties of the composite electrode are measured and discussed systematicly. The main contents of this thesis are listed as follows:1. Electrochemical exfoliation of graphite rods under the action of an electric field force led to the formation of two-dimensional（2D） graphite nanosheet arrays（GNSA） perpendicular to the surface of the graphite substrate and parallel to each other in arrangement. Subsequently, SnO₂/graphite nanosheet array（SnO₂/GNSA） composite electrodes were prepared by the cathodic reduction electrodeposition method. The morphology, composition, and microstructure of the samples were characterized using field emission scanning electron microscopy（FESEM）, powder Xray diffraction（XRD）, and Fourier transform infrared（FT-IR） spectroscopy, respectively. Electrochemical measurements showed that the composite electrodes achieved specific capacitance values as high as 4105 F·m-2 in the potential window up to 1.4 V with a scan rate of 5 mV·s-1 in 0.5 mol·L-1 LiNO3 solution. The symmetric supercapacitor assembled with the as-prepared SnO₂/GNSAs exhibited excellent capacitive performance with energy density of 0.41 Wh·m-2 in the potential window up to 1.8 V and retention of 81% after 5000 cycles.2. The substrate of a two-dimensional（2D） graphite nanosheet array（GNSA） was fabricated by the electrochemical exfoliation of graphite rod. Subsequently, the MnOOH/graphite（MnOOH/GS） and MnOOH/graphite nanosheet arry（MnOOH/GNSA） composite electrodes were synthesized via a cathodic reduction electro-deposition method, by using the graphite and GNSA as substrate, respectively. The SEM results indicated that the composite electrodes have the nanoflowers in morphology, which is in favor of the intercalation of the electrolyte ions and effectively increases the contact area between electrolyte and materials. Electrochemical measurements indicated that MnOOH/GNSA composite electrodes could achieve the specific capacitance as high as 5724 F·m-2 with a scan rate of 5 mV·s-1 in 0.5 mol·L-1 LiNO3 electrolyte solution. The symmetric supercapacitor assembled with the MnOOH/GNSAs composite achieved energy density as high as 0.54 Wh·m-2 at the power density of 5.4 W·m-2 in the cell voltage up to 1.8 V.3. MnO₂-SnO₂/graphite nanosheet arry composite electrodes（MnO₂-SnO₂/ GNSA） were fabricated by a cathodic reduction electrodeposition in 0.5 mol·L-1 MnCl2、0.5 mol·L-1 NaNO3 and 0.05 mol·L-1 SnCl4 mixed solution at the constant temperature of 50 oC. Structural characterization showed that the graphite nanosheets were coated by MnO₂-SnO₂ to form a heterogeneous array composite electrode. The symmetric supercapacitor assembled with SnO₂/GNSAs present a relatively good electrochemical performance.