Electrodeposition And Properties Of Co-doped Nicke Oxide Electrochromic Thin Film

Electrochromism (EC) is a phenomenon that materials can reversibly change their optical properties(colors and transparency in the outside) under an applied electric field. As a novel functional material, EC materials can be used in producing display devices, smart windows and glare-free mirrors etc. They have aroused a great interest in many fields like information, electron, energy sources, architecture, national defence, and become one of popular research fields.Among various EC materials, nickel oxide (NiO), as a representative of the anode colored materials(bleached in the reduced state and colored in the oxidized state), has attracted many researchers for its high coloration efficiency, strong reversibility, short response time and long cycle life. In order to further improve its EC properties, optimizing process parameters and doping method are considered two effective ways.In this paper, Co-doped NiO films were prepared on the surface of FTO conducting glasses using electrochemical method with NiCl₂ as main salt, CoCl₂ as dopant and LiClO₄ as supporting electrolyte in N, N-dimehtyl formamide (DMF) organic solution. Effects of Co doping on the structure and properties of NiO film were investigated. The surface morphology, chemical composition, structure and EC properties (including optical electrochemical and life properties) of the film were characterized.Optimal technical parameters of the film preparation were confirmed. as the Co concentration: 0.0029 mol/L; the deposition voltage: 2.5 V; the deposition time: 10 min; the deposition temperature: room temperature; the anode: Ni sheet(the top three factors were the main factors affected the result). The Co/Ni molar ratio in the Co-doped NiO film is 0.16/1, and Co substituted the site of Ni in the NiO lattice leading to the formation of Nix-yCoyO compound. Compared with the undoped NiO film, the addition of cobalt refined the particles of the NiO film, which increased the variation of transmittance up to 76.3%, improved the reversibility of the redox reaction, increased the coloration efficiency and reduced the response time of the colored/bleached state by 1 s respectively. However, the film exhibited poor color memory and storage ability in alkali solution though it was excellent in air. In addition, the cycle life of the film decreased compared with the undoped one.