Copper And Nickel Electrodeposited Electrochromic Devices Based On Eutectic Solvents

Electrochromic means that the light absorption of materials which can be tuned reversibly and persistently by the occurrence of electrochemical reactions.The properties led to the development of many applications,which includes anti-glare rearview mirror,color change display,electrochromic clothing,smart windows,smart cards and electronic paper and so on.The materials which with electrochromic properties are called electrochromic materials.Electrochromic materials are mainly divided into two kinds:inorganic electrochromic materials and organic electrochromic materials.Transition metal oxides are the typical electrochromic materials,such as tungsten oxide,molybdenum oxide,nickel oxide.And organic electrochromic materials mainly include polythiophene and its derivatives,viologen,metal phthalocyanine compounds,etc.Among them,viologen has been widely studied.These materials have good discoloration properties,but they are difficult to prepare,toxic and expensive.Therefore,it is crucial to find the material which can be made briefly,cheap and green.Metal is the ideal dimming material for dynamic Windows.The high extinction coefficient of the metals causes them almost completely block visible and infrared light at thicknesses of 20–30 nm,which makes the windows have good optical contrast.At the same time,many metals are chemically inert,photostable,and color neutral.And it is also cheap and widely available in nature.Thus,metal is a promising electrochromic material.Compared with other methods,metal electrodeposition has a lot of advantages,includes low cost,fast deposition speed,simply and easily controllable reaction,and strong regulation for particle size and distribution.However,metal electrodeposition often prone to hydrogen evolution and have high toxicity in ordinary aqueous or organic solvents.Deep eutectic solvents?DES?are welcomed for their advantages of low vapor pressure,easy to obtain and prepare,high solubility,low toxicity and degradability,excellent electrochemical performance,and simple separation of reaction products.Accordingly,it is widely used in the fields of lubrication,functional material preparation,electrochemistry,organic synthesis and biomass catalytic conversion.In addition,deep eutectic solvent plays an important role in electrodeposition due to its wide electrochemical window and absence of hydrogen embrittlement.In this thesis,the electrochromic device was prepared by using the deep eutectic solvent which consists of choline chloride and ethylene glycol,copper or nickel as main electrochromic material,the transparent ITO electrode as the working electrode,and the copper tape or nickel foam as the counter electrode respectively.Results showed that the addition of ascorbic acid could make the solution of Cu???keeping colorless,thus,the copper device has a high optical contrast.In addition,the copper can deposit and strip from the Pt/ITO electrode reversibly which prepared by pulse deposition method.The copper device was successfully obtained by controlling the parameters of deposited platinum without affecting the optical transparency.Moreover,the maximum coloring efficiency is 83 cm²·C^-1 at the most sensitive wavelength of the human eye at 550 nm,and the working voltage of the device is-0.4V.The device has low power consumption,low cost and simple structure.The electrochromic devices based on reversible electrodeposition behavior of Nickel on bare ITO electrode in DES were also studied.The coloring efficiency of the liquid-type Nickel-based electrochromic devices at 550 nm is about 148 cm²·C^-1.By using SiO₂ to gelatinization of DES,the solid-type electrochromic devices with a higher coloring efficiency(175 cm²·C^-1)were obtained.