Studies On Preparation And Properties Of Electrode Materials For Electrochemical Capacitors

As a member of chemical power source family, electrochemical capacitors, which combine the advantages of both dielectric capacitors that can deliver high power within a very small period and rechargeable batteries that store high energy, have found an increasing important role in power source applications such as hybrid electric vehicles, short-term power source for mobile electronic devices, etc. For forming supercapacitance, studies show that the electrode materials play the most important role. It must show not only redox characteristic that is not possessed by general bulk materials, but also the characteristic matching of the pore structure and the surface area.In this dissertation, the basic principle of electrochemical capacitors, the research developments of electrode materials were reviewed. Three kinds of nanostructured materials were prepared and an attempt was made to apply them as active electrode materials for electrochemical capacitors. we synthesized amorphous cobalt sulfide and study its electrochemical capacitive performance in neutral and alkaline solution. Exploring the electrochemical characteristics of this material will direct a new type of supercapacitor materials. The main studies are as follows:1, A novel composite of Co(OH)₂ and TiO₂ nanotubes was synthesized by a chemical precipitation method. Co(OH)₂/TiO₂ nanotubes composites and its microstructure were characterized by transmission electron microscopy(TEM), X-ray diffraction pattern(XRD). The electrochemical capacitance performance of this composite was investigated by cyclic voltammetry and charge-discharge tests with a three-electrode system in 6 M KOH solution, we propose that TiO₂ nanotubes provide the three-dimensional nanotube network structure for the composite and make the Co(OH)₂ dispersed. For these reasons, the TiO₂ nanotubes used as a framework for Co(OH)₂ improve the utilization of Co(OH)2 greatly.2, The CoS_x was prepared by a very simply chemical precipitation method. The electrochemical capacitance performance of this compound was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge tests with a three-electrode system. The results show that CoS_x has excellent electrochemical capacitive characteristic with potential range -0.3～0.35 V (vs SCE) in 6 M KOH solution. Charge-discharge behaviors have been observed with the highest specific capacitance values of 475 F/g at the current density of 5mA/cm², even at the high current density of 50mA/cm², CoS_x also shows the high specific capacitance values of 369 F/g. According to the cyclic voltammetry (CV) curves of electrodes in this two kinds of solution, we assume the mechanism of electrochemical oxidation of cobalt sulfide consulting the redox mechanism of Co(OH)₂ in alkaline electrolyte.3, Transition metal (Ni, Mn) sulfides as a new class of supercapacitors material was firstly studied. The electrochemical capacitance performance of these sulfides was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge tests with a three-electrode system in alkaline electrolyte and neutral electrolyte. The results show that NiS_x has electrochemical pseudocapacitive characteristic in alkaline electrolyte, MnS_x has electrochemical double-layer capacitive characteristic in neutral electrolyte.