Study On Electrochemical Preparation And Supercapacitive Properties Of Co, Mn Oxides

The supercapacitor is a new type of energy storage devices with excellent performance of high power density, quick charging and discharging, long cycle life and maintenance-free. Metal oxide materials used in supercapacitors have received much attention in the recent years because of their high capacitive and high energy characteristics. Hydrous RuO₂ is an ideal metal oxide material for supercapacitors because it possesses capacitance as high as 768 F/g. However, the high cost of RuO2 inhibits its commercial use. So cheaper alternatives with acceptable pseudocapacitive properties have been widely studied and developed. In this thesis, micro- and nanostructured Mn and Co oxides were prepared by electrochemical methods and the capacitive properties of the oxides were studied in detail. The main results obtained in this thesis are presented as follows:1. CoO_x.yH₂O porous films were electrodeposited successfully on graphite electrode through H₂ gas template. The CoO_x.yH₂O porous film/graphite electrode exhibites high electrochemical reversibility and high power characteristics. The active material possesses a specific capacitance of 64.8 F/g and has an excellent long-term cycle stability. The effect of deposition current on morphology and capacitive behaviour of the film was also evaluated. With cathodic deposition current increased, pores diameter of the film becomes large and better specific capacitance can be obtained.2. Co-doped manganese oxide nanowires were prepared by potentiodynamic deposition method at a very high scan rate of 500 mV/s. The effect of Co content on the morphology and electrochemial properties of manganese oxide was studied in detail. The results indicate that: when the content of Co increases gradually, the diameter of nanowires becomes smaller; the conductivity of manganese oxide improves obviouly, which is attributed to the improvement of power characteristics and charge-discharge properties of manganese oxides.3. The 3D nanoporous structured MnO_x was deposited on graphite electrode with DBS as the soft template using galvanostatic technique. The electrochemical properties of the MnO_x/G electrode were investigated in 0.1 M Na₂SO₄ by cyclic voltammetry and galvanostatic charge-discharge method. The results show that the MnO_x/G electrode has good power characteristics and charge-discharge properties. The specific energy is as high as 86.8 Wh/kg and specific surface capacitance of 0.125 F/cm² can be obtained.