Preparation And Electrochemical Characterization Of Porous Novel Materials Composed By Manganese Oxides

Transition metal oxides have several phases due to their multi-form of oxidation states and their special crystal structures. Such materials have potential application in many areas such as data storage and energy storage. Manganese oxides with porous structure possess the characters of both nano materials and metal oxides. On one hand, they have various phases, such as MnO2, Mn3O4and Mn2O3. On the other hand, they exhibit some novel features attributed to their complex morphology and size. They attract considerable attentions as a potential candidate for RuO2used as electrode material for EC.In this thesis, a three-step method has been designed to synthesis MnO2hierarchical structure formed with nano-fibers. First, manganese oxalate precursors were prepared by a hydrothermal or precipitation method. Then, a following calcination process was carried out to obtain porous Mn2O3acted as an intermediate for the final product. In the third step, nano-fibrous MnO2was synthesized by an oxidation process through a solid phase transfer reaction in solution environment. During the whole synthesis process, morphology of the precursors was well retained from the precursors, to Mn2O3, to MnO2, which provide a3-D frame for the hierarchical structure.XRD, SEM, TG-DTA and EDS measurements were applied to characterize the phase, morphology and pore structure of the samples. The electrochemical properties of Mn2O3, Co-or Ni-doped MnO2were systematically investigated using cyclic voltammetry and galvanostatic charge/discharge.It shows that the frame structure and crystallinity of the precursors can be adjusted by both the solvent system and the doping ions. There is a solubility limit of Co and Ni in MnO2. Co-or Ni-doped MnO2not only contributes to the specific capacity but also improves the cycle performance of MnO2as electrode material for electrochemical capacitors.