Fabrication Of Vanadium-based Oxides Nanostructures And Their Ele-ctrochemical And Field Emission Propertie S Investigation

In this dissertation, three kinds of V2O5nanostructures including nanowires, nanowaxberries and nanoflowers have been successfully fabricated through a one-step hydrothermal process. The microstructures and morphologies of the V2O5nanostructures were evaluated by X-ray diffraction, Raman spectrum, scanning electron microscopy and transmission electron microscopy. The influence of surfactant polymer polyvinyl pyrrolidone (PVP) in materials growth has been investigated. Meanwhile, electrochemical and field emission properties of the V2O5nanostructures were analyzed and discussed. Also, by using chemical vapor deposition (CVD) method, various kinds of low-dimensional V02(M) nanostructures with different morphologies have been synthesized, and their morphologies and structures were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The phase transition temperature of these materials has been analyzed by DSC. The detailed works are listed as below:1. Several V2O5nanostructures including nanowires, nanowaxberries and nanoflowers were successfully synthesized via a hydrothermal process with NH4VO3as precursor and polymer polyvinyl pyrrolidone (PVP) as surfactant. In the synthesis process, morphologies of the products are found to be sensitive to the concentration of the surfactant.2. Electrochemical properties measurements of three V2O5nanostructures were performed. The cyclic voltammograms tests for aqueous lithium ion battery were carried out with a scan rate of100mV/s for50cycles, and the results suggest that V2O5nanoflowers and nanowires have a better capacity retention on cycling than nanowaxberries. In addition, to evaluate how the morphology will affect the Li-ion diffusion coefficient in V2O5nanostructures, cyclic voltammetry (CV) measurement was carried out under different potential scanning rates. The scan rates are5,1050,150,200and300mVs-1, respectively. The results showing that V2O5nanoflowers have the best stability and highest Li ion diffusion coefficient compared to other two kinds of structures, which is most suitable for application in Li-ion battery electrodes.3. Field emission (FE) measurements of three different V2O5nanostructures were also performed. Results show that V2O5nanowaxberries have the lowest turn-on field, threshold field and the highest field-enhancement factor of2.9V/μm,5.7V/μm and2468, respectively, making them a promising material for field emitters.4. Five different kinds of VO2(M) low-dimensional nanostructures with different morphologies were synthesized using high-temperature furnace through chemical vapor deposition (CVD) method. The effect of reaction time, temperature and surfactant usage on the morphologies was studied. The phase-transition properties of the nanoneedles were measured by DSC. The growth mechanism of the nanorods was also studied.