Preparation Of Nanostructured Vanadium Pentoxide Film And Its Electrochromic And Capacitive Properties

During the electrochemical redox reaction processes, many transition metal oxides can change their optical parameters(such as transmissivity, reflectivity and absorptivity) persistently and reversibly(named Electrochromism), as well as show energy fast storage/release properties(named Faradic capacitance or Pseudocapacitance). Based on their unique electrochromic and pseudocapacitive performance, these materials have exhibited enormous applications in many fields, such as smart windows, energy-efficient displays, antiglare mirrors, back-up power sources for transportation fields and substitute power sources for microelectronic devices. Taking into account that vanadium oxide has been studied extensively as a high-pseudocapacitane electrode material and it is the only one oxide which is both anodic and cathodic coloration, this dissertation is mainly carried out the study of the preparation and optical-electrochemical performance of the nanostructured vanadium oxide films on ITO substrates.Colloidal crystal templates on ITO substrates were prepared with monodispersed polystyrene(PS) sphere suspension by vertical deposition method on ITO substrates. The templates have a large area FCC manner ordering. By anodic deposition with colloidal crystal templates, three-dimensionally ordered macroporous(3DOM) vanadium oxide films were obtained. The as-deposited vanadium oxide was amorphous within small number of V2O5?1.6H2 O nuclei. Because of the larger surface area and shorter Li-ion diffusion distance, the 3DOM vanadium oxide films exhibited improved electrochromic and pseudocapacitive performance than the dense vanadium oxide films prepared without templates. And the 3DOM films with smaller pore size showed larger transmittance contrast, faster switching response and larger specific capacitanceThe Li-ion chemical diffusion coefficients in 3DOM vanadium oxide films were investigated by cyclic voltammetry and potential step chronoamperometry methods. Compared with the dense film, 3DOM film exhibited improved Li-ion chemical diffusion coefficient, and the coefficient increased with the decrease of pore size in 3DOM structure. The effective diffusion coefficients of 3DOM film with pore size of 210 nm was improved up to ～5 times of that in the dense film.After annealing treatment, the morphology of amorphous 3DOM vanadium oxide film can be transformed. After being annealed at 350 ℃ for 4h, the morphology of 3DOM film(pore size of 250nm) was changed into 3D nanorod architecture stacked by crystalline/amorphous core/shell V2O5 nanorods. Futher increasing the annealing time to 7h lead the nanorods fully crystalized. PS sphere-assisted heterogeneous nucleation during electrodeposition and the anisotropic bonding of the V2O5 layered structure are the two most important factors for the morphology transformation during annealing process. Because of the large surface area, short Li-ion diffusion distance, and good electrolyte penetration, both of these two 3D nanorod architectures showed improved mutilcolor electrochromic performance. Electrochemical measurements exhibited the 3D nanorod architecture annealed for 4h exhited highest pseudocapacitance. After being annealed at 450℃ for 4h, the amorphous 3DOM vanadium oxide film was changed into 3D nanofiber architecture stacked by crystalline V2O5 nanofibers. SEM and HRTEM examinations exhibited Ostwald Ripening, Oriented Attachment, and Atom Rearrangement were the main mechanisms for the crystal coarsening process which lead the elongation of nanofibers during annealing treatment. Electrochemical measurements indicated that the 3D nanofiber architecture didnot show pseudocapacitive property, but it can exhibit good elelctrochromic performance in the voltage range of ?1V.By applying constant anodic current-density electropolymerization method, the surface of V2O5 nanofibers can be uniformly coated by polyaniline, polypyrrole, and poly(3,4-ethylenedioxythiophene) films, leading to V2O5/conducting polymer core/shell nanofibers. With different electropolymerization times, the thickness of conduting polymer films can be controlled. And with the increase of electropolymerization time, the morphology of the composite nanofiber was changed from cylinder shape to trepang-like shape. Electrochemical measurements showed that the conduting polymer coating film can significantly prevent the fragmentation and dissolve of V2O5 fibers during the cycling testing process.