Preparation Of Tungsten Oxide Fibers With Nanosheet Structure And Their Electrochemical Properties

Tungsten oxide (WOx) is a kind of important semiconductor material withlow cost and structure diversity. It has many interesting characters such aselectrochromism, photocatalysis, gas sensing, information storage, and otherfunctions. In recent years, tungsten oxide nanomaterials have attracted everincreasing interest due to the much enhanced properties arising from the nanoeffects. In this thesis, tungsten oxide nanofibers with nanosheet structure wereprepared by electrospinning and electrochemical treatment. The preparationprocess, structure, and electrochemical property of the tungsten oxide fibers withnanosheet structural were investigated. The main research work is described asfollows:Composite nanofibers containing tungsten were prepared by electrospinning,using ammonium metatungstate (AMT) as a source of tungsten andpolyvinylpyrrolidone (PVP) as the thickener. The precursor nanofibers forgrowing the nanosheets were prepared by calcining the electrospun compositenanofibers at appropriate temperature in oxygen. The nanosheets were radiallyoriented from the precursor nanofibers by reaction in0.5M H2SO4solutionunder different applied potential. The experimental facilities used includeScanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectra (EDS),X-ray diffraction spectra (XRD), Raman spectra, and Infrared spectra(FTIR). Itwas well analyzed and investigated about the morphology, crystallinity, chemicalbond and composition of the fibers samples. The electrochemical properties ofthe fibers samples, especially the specific capacitance and the specific energywas researched.The diameter of the electrospun composite nanofibers is about100nm to150nm, and the fibers shows uniform appearance and smooth surface. Theprecursor nanofibers with different structure and diameter were prepared bycalcinating the electrospun composite nanofibers at300℃,400℃and500℃respectively in oxygen. When the temperature rises, the precursor nanofiberschanges into polycrystalline structure from amorphous, the diameter of the fibers becomes smaller and decreases from120nm to80nm respectively.The precursor nanofibers prepared at400℃grow into nanosheets fibersafter2h electrochemical treatment in sulfuric acid, respectively at9differentapplied potential parameters ranged in-0.6V to0.9V. The nanohseets with about10nm to30nm ultrathin thickness can be radially grown on the nanofibers.The electrochemical properties of the samples were tested in0.5M H2SO4electrolyte. The results show that the preparation temperature of the precursorfibers has a great impact on the electrochemical properties of th e nanosheetsfibers. The specific capacitance is higher, of which nanosheets fibers preparedfrom the precursor nanofibers that calcinated at400℃. The electrochemicalproperties of the nanosheets fibers also strongly dependent on applied potentialin the preparation process. The specific capacitance will decrease when theapplied potential is too high or too low. The nanosheets fibers prepared at-0.15V show specific capacitance of273.8F g-1and specific energy of24.3Wh kg-1,and the electrochemical properties are more excellent than nanosheets fibersprepared at other potentials.In this thesis, the nanosheets fibers prepared at appropriate conditionpossess outstanding electrochemical properties, the research of tungsten oxidefibers with nanosheet structure used in supercapacitors is a innovation, and thematerial will have a good prospect if used in supercapacitors.