Study Of Mesoporous Carbon As Electrode Material For Supercapacitors

Supercapacitor is a new type of energy storage devices. The latest development in both theoretical and applicational research of the electrode materials for supercapacitor devices have been reviewed in this thesis. Furthermore, mesoporous carbon and manganese dioxide material was fabricated. Supercapacitor was mainly characterized by high charge-discharge efficiency and rates. Meanwhile, defect of low energy density can not be ignored. Therefore, it is urgent to study how to improve the energy density of supercapacitors. According to E=1/2CV², there are two methods—as we know--can improve the energy density effectively.One is to improve the specific capacitance of electrode materials. The main disadvantage of porous carbons used as supercapacitor electrode material lies on its low energy density. The specific capacitance of carbon supercapacitor depends highly on the specific surface area (SSA) of the carbon. Generally, it is an effective way to improve the SSA of the carbon in order to enhance the specific capacitance. But it was found that the specific capacitance of the carbon is not simply linear-dependent on the SSA. This is because there are so many factors that influence the specific capacitance of the carbon, such as SSA, pore size and pore size distribution, microporousity, pore shapes and functional groups on the surface of porous carbon. And these factors have complicated inter-relationship. Therefore, a serious and fundamental question rises that what is the guantitative relationship between the specific capacitance and these complicated factors. In this thesis, beginning with the elementary scene of electrode/electrolyte interface and the basic principle of BET, a novel theoretical model, on which reasonable approximation condition was employed, was propound to deduce the guantitative relationship between double layer capacitance and pore size and pore size distribution. Additionally, calculation method of effective pore size and effective specific surface area was pointed out. Furthermore, different boundary conditions were discussed in details according to the suggested theory. Finally, by using different SBA-15 molecular sieves served as hard template, nine mesoporous carbon were fabricated with sucrose or furfuryl alcohol served as carbon source and their specific capacitance was measured respectively to verify the theory we proposed from one aspect.The other one is to improve the cell potential of the capacitor. Firstly, powdery MnO₂ anode material which has a high Hydrogen Evolution Potential (HEP), was prepared successfully through a liquid phase redox strategy. The as-prepared MnO₂ was characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM). Electrochemical test suggested that the specific capacitance of as-prepared MnO₂ can reach as high as 209 F/g. Moreover, because of bearing the advantage of low Oxygen Evolution Potential (OEP), three mesoporous carbons with different SSA and microstructure, were chose as cathode material for MnO₂/OMC asymmetrical supercapacitor. The cell potential of asymmetrical capacitors is 2V in 2 mol/L NaNO3 electrolyte. And the specific capacitance of MnO₂/OMC hybrid capacitor can reach as high as 86.9 F/g at current density of 2.5mA/cm² when rod-like CMK-3 served as cathode material. In the end, we make a preliminary discussion on how the OMC cathode material acts on the electrochemical properties of MnO₂/OMC hybrid capacitor.