Preparation and Electrochromic Characterization of Nanocrystalline Nio-Base Thin Films

Abstract

A precursor solution was prepared by dissolving anhydrous nickel chloride, anhydrous cobalt chloride and citric acid in butanol and ethanol. The solution was refluxed under continuous stirring, and then through hydrolyzing to change to a stable sol. To aerate dry NH3into the solution after being refluxed can deposit the chloride ions completely .The thin films were deposited by dip-coating method. The thin films were Characterized by atomic force microscopy (AFM), X-ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochromic performance of films were Characterized by means of electrochemical (cyclic voltammetry) measurements, and optical (transmittance) method. Results show that the thin films can transform from amorphous into cubic-NiO nanocrystalline heated at 280°С for 30 min and the xerogel powder must be heated at 300°С for 30 min. The results of films heated at different temperature show that the film heated below crystal temperature has a loose, island amorphous structure, and that of the films heated at 300°С has a compact, regular square structure. The results of cyclic voltammogram and transmittance spectra of films suggest that the molar ratio of Ni/Co=5 cobalt doped can obviously decrease the potential of oxidation and reduction reaction, and make the films present the lowest transmittance in visible range in colored state. The films prepared showed electrochromic reversibility only in crystal state. The film heated at 300°С for 30 min occurred the highest intensity of the peak of current density of oxidation and reduction..