Mg-ni Electrochromics Functional Films Fabricated By Electrodeposition And Their Properties

Owing to their low power consumption, high coloration efficiency (CE), and excellent memory effect under an open circuit condition, electrochromic (EC) materials, which are able to reversibly change their optical properties upon charge insertion/extraction, have received high attention in the past decades. Electrochromism can be defined as a persistent and reversible optical transformation induced by electrochemical processes. EC materials can be classified into two categories as anode colored and cathode colored materials by electrochemical reaction modes.As a kind of anode colored material, NiO is one of these attractive materials due to its high electrochromic efficiency, large dynamic range, good cyclic reversibility, and low cost. Several physical and chemical methods, such as sputter coating, vacuum evaporation, pulsed laser deposition, spray pyrolysis, sol-gel, chemical deposition and electrochemical deposition, have been used to fabricate nickel oxide films. However, the materials prepared by above methods must subject to an annealing process in order to show electrochromic properties.In this thesis, without further annealing treatment, NiO thin films with reversible electrochromic properties were fabricated using electrochemical technique in organic solution (N,N-dimethylformamide solution, DMF solution) controlled by potentiostatic electrolysis. Fluorine-doped tin oxide (SnO₂:F, FTO) glass plates were used as substrates as well as cathodes. Appropriate experimental conditions for the film deposition were chose based on our investigation on the effect of solvent dehydration methods and electrodeposition voltages. Cyclic voltammetry was used to study the electrochromic processes. Ultraviolet-visible transmission spectroscopy was applied to measure electrochromic properties of the deposited films. High resolution transmission electron microscopy (HRTEM) was employed to analyze the composition and structure of the films. Thickness of the films was revealed by scanning electron microscopy (SEM). Results show that, after ten potential cycles in 0.5 M NaOH solution, the thin films obtained present a large visible light transmittance variation (e.g. -73% at wavelength of 550 nm) between bleached and colored states, and their cycling durability between the two states is more than 6000 cycles. The films also show good stability in the air and rapid response to the state alteration.In addition, we modified the NiO film by doping Mg and compared the relevant properties of Mg-NiO with the undoped NiO films. Effects of temperature, type and amount of complexing agent, and electrodeposition voltage on the properties of the two kinds of films were investigated, and an optimum experimental condition for Mg doping was set up. The maximum molar concentration of magnesium in the film is about 24%. It is found that the Mg doping into NiO films did not approve the electrochromic properties of the films. Therefore, the detail role played by the Mg doping into NiO films need to be further studied in the future.