Preparation And Electrochemical Properties Of Transition Metal Oxide Nanomaterials

Transition metal oxides have been attracting more and more attention because their potential applications in many fields.When their size and dimensionality is down to the nanometer scale, they will exhibit novel physical and chemical properties of different from their bulk counterparts.Recently, researches have been focused on controlling the morphologies of transition metal oxide nanostructures and organizing them into hierarchical or complicated structures. In recent years,Cobalt oxide and Manganese oxide nanomaterials have attracted much attention because their interesting optical, magnetic, transport, electrochemical and field-emission properties,which will find potential applications in catalysis, sensors, energy storage and conversion in secondary batteries and flat panel display devices.In this thesis,hydrothermal methods and further heat treatment are used to fabricate diverse nanostructures of manganese oxide (Mn2O3), cobalt oxide (Co3O4) and lead oxide (PbO). The electrochemical properties of the products have been studied. The detailed contents are listed as follows:(1) Different structures of MnCO3 were synthesized at room temperature or by a hydrothermal method. The MnCO3 phase obtained at room temperature could be transferred to Mn2O3 plates by heat treatment at 600℃. In contrast, porous Mn2O3 nanostructures can be obtained after the heat treatment of MnCO3 precursors prepared by hydrothermal method. Interestingly, Mn2O3 phase can be also formed by heat treatment of the MnC03 phase obtained at room temperature (Mn-RT) at 120℃. Experimental results clearly demonstrate a structure evolution from MnCO3 precursors to Mn2O3 structures on the completion of the reaction. The formation mechanism of the above materials were further investigated by TEM and FTIR. The capacitive properties of the Mn2O3 materials were characterized by cyclic voltammetry. The results show that the morphologies and structures of Mn2O3 samples play important roles on their capacitances.(2) The cobaltic oxide (Co3O4) of different structures were synthesized by hydrothermal method from Co(NO3)2·6H2O and glycerol at 200℃. The morphology and phase of the Co3O4 can be controlled by adjusting the experimental parameters that include reaction time and the molar ratio of Co(NO3)2·6H2O to glycerol. The possible formation mechanism of Co3O4 is discussed on the basis of experimental results. Pure Co3O4 nanofibers were fabricated by calcined the product at 500C for 2h. The as-synthesized products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infra-red spectra (FTIR). The capacitive properties of the Co3O4 materials were characterized by cyclic voltammetry, indicated that the shape and size of Co3O4 had remarkable influence on its capacitive performance.(3) Single crystal colloidal structures of basic lead (Pb3(CO3)2(OH)2) were controllable synthesized by a simple precipitating method through changing the molar of Pb(NO3)2 to Na2CO3 at room temperature. However, micro-scale polygonal plate structures for Pb3(CO3)2(OH)2 can be obtained due to the effect of the Ostwald ripening if the synthesis were underwent hydrothermal treatments at 200℃. The products are characterized by a series of techniques, such as XRD, SEM, TEM and FTIR. The formation mechanisms of the nanostructures are proposed based on the experimental results. These products synthesized at room temperature were further calcined in a tube furnace at 600℃in air for 3h, and the different morphological lead oxide are obtained. The electrochemical properties have been studied for the samples using three electrodes systems.