The Investigation Of The Microstructure And Electrochemical Properties Of Low Dimensional Molybdenum Oxide Nanomaterials

Supercapacitors are new energy storage devices which own all excellent properties of both batteries and conventional capacitors. Compared with conventional capacitors, supercapacitors possess many advantages such as high power density, high energy density and long cycle life. In addition, supercapacitors are environmentally friendly and have the ability of balancing energy-storaging and environment-protecting. MoO3 is a kind of metal oxide electrode materials, which has rich processes of redox reaction. It is considered as a promising supercapacitor electrode material because of its high specific capacitance and good chemical stability. However, there are still some deficiencies of MoO3 electrode material, such as low voltage, low electronic conductivity, etc. Based on the above content, the investigations were carried out in this thesis as follows:The α-MoO3 nanobelts were producted by traditional hydrothermal method in which ammonium molybdate tetrahydrate was the precursor. The influence of the reaction temperature (120～200℃) and the reaction time (5-30h) on the structure, morphology, crystallinity and electrochemical performance was investigated. The results showed that with the increasing of reaction temperature and the reaction time, the morphology of α-MoO3 nanobelts tended to be uniform, and the degree of crystallinity gradually became good. The electrochemical performance of α-MoO3 nanobelts which were prepared in different reaction conditions was studied. The results indicated that the specific capacitance of α-MoO3 nanobelts in acidic electrolyte reached 932 F/g at the scanning rate of 10 mV/s. MoO3 nanbelts capacitors possessed the characteristics of pseudo-capacitance in acidic or alkaline electrolyte, while they possessed the characteristics of double-layer capacitance in neutral electrolyte. The specific capacitance of α-MoO3 nanobelts in acid or alkaline electrolyte is much higher than that in neutral solution. After 1000 cycles, MoO3 electrode capacitance retention rate was still 73.5%.Based on the above research on MoO3 nanobelts, polyaniline parcel layer was fabricated by means of in-situ polymerization on α-MoO3 nanobelts surface and then MoO3/PANI nanocomposite was obtained. The MoO3/PANI nanocomposite was characterized by many methods such as SEM, TEM, XRD, FTIR, Raman, TG. The influence of different parameters on morphology and structure of MoO3/PANI nanocomposite was studied. The results showed that with the increase of the amount of aniline, the thickness of PANI parcel layer increased and the surface gradually became rough. While, there was little influence of reaction time and pH values on the morphology of MoO3/PANI nanocomposite. In addition, the electrochemical performances of MoO3/PANI nanocomposites prepared with different parameters were investigated. It was found that the as-synthesized MoO3/PANI nanocomposites exhibited the improved electrochemical performance with high specific capacitance of 1268 F/g at a scan rate of 10 mV/s. The excellent supercapacitor performance of the MoO3/PANI nanocomposites was attributed to the synergic effect between the PANI conductive layer and the original α-MoO3 nanobelts.Molybdenum oxide nanocrystallines were fabricated in the reaction of anhydrous methanol and molybdenum acetylacetonate. The structure and morphology of the samples was characterized by TEM, XRD, Raman and XPS. The results indicated that the molybdenum oxide nanocrystallines with the size of about 10 nm was successfully prepared. With the increasing of reaction time and the concentration of reactants, the crystallinity of nanocrystallines was improved and the size of particles became large and uniform.