Preparation And Properties Of TiO₂-based Electrochromic Films

Electrochromic materials with the unique optical control characteristics have shown broad application prospects in the fields of electronics,energy and defense,and have received widespread attention from all walks of life.However,the few color variables,long response time and poor cycle stability of the materials are still important factors restricting the development of electrochromic technology.Based on the above content,this paper takes inorganic material TiO₂ as the main research object,and uses a variety of methods such as doping,nanoporous,nanometerization,inorganic/organic composite to modify it to construct various types of TiO₂-based electrochromic materials.It mainly uses the electrochromic principle of ion double implantation or desorption to achieve the purpose of enhancing the material’s electrochromic color change magnitude,reversible stability,coloration efficiency,response time and optical modulation range,and further explores the TiO₂ electrochemical performance.Firstly,the research was carried out from the preparation method of TiO₂ materials.The metal Ti films were prepared on FTO glass by low-temperature molten salt electrodeposition method.The Ti films were oxidized by air heating to form TiO₂ films.These TiO₂ films have short electrochromic response time,high reversible stability and good coloration efficiency,but its optical modulation range is small and the preparation process is complicated.In order to solve the complex synthesis process and small optical modulation range of the above methods,the low-temperature molten salt electrolyte was improved to prepare TiO₂ thin films by direct electrodeposition.Compared with previous results,TiO₂thin film optical modulation range as high asΔT_600nm=49%,and simplify the procedure of thin film preparation.In addition,the cycling stability and environmental resistance stability of TiO₂ film can reach more than 80%.Secondly,the electrochromic and electrochemical properties of inorganic doped and composite TiO₂ nanometer films were studied by changing the electronic structure of TiO₂ material to improve charge migration,electron or ion transport in the electrochromic reaction system.Firstly,Co doped TiO₂films were synthesized by sol-gel method to achieve atomic-level doping.Compared with the undoped modified TiO₂ film,the low content of Co atom not only improves the optical modulation range of TiO₂films(ΔT_600nm=53.7%,ΔT_1500nm=71.4%,ΔT_14μm=65.2%),but also improves the coloration efficiency（CE=143 cm²/C）and response time（t_c=3.8 s and t_b=2.9 s）.Then,the Zn O-coated TiO₂ composite films were prepared by sol-gel method and chemical bath deposition method.Compared with the pure Zn O nanosheet film,the TiO₂@Zn O film nanosheet films have a core-shell nanosphere spherical structure.This structure provides more reactive attachment points for electron/ion transport,and increases the rate of migration and diffusion of electron/ion.Moreover,the TiO₂@Zn O core-shell nanosphere film has a wide optical modulation range(ΔT_600nm=71%)and great coloration efficiency（CE=84.24 cm²/C）and its cycle stability is improved.The above results indicate that the electrochromic material after doping/composite modification can improve electrochromic properties.Thirdly,the combination of organic polymer and TiO₂ can promote the integration of inorganic materials with high hardness support,good thermodynamic stability and organic materials with high electrical conductivity,good flexibility and color richness,so as to improve their cyclic stability and electrochemical performance.Therefore,TiO₂ electrochromic nano-film with organic type composite coated structure was prepared.TiO₂/poly-o-nitroaniline core-shell nanosphere film and TiO₂/poly-3-methylthiophene core-shell nanosphere film were prepared by the sol-gel method and electropolymerization method.TiO₂/poly-o-nitroaniline core-shell nanosphere film enriches the color change level and realizes the controllable conversion of yellow,blue and green colors.Moreover,the TiO₂/poly-o-nitroaniline core-shell nanosphere film has good cycle stability,high coloration efficiency（43.72 cm²/C）,and high transmittance modulation range(ΔT_600nm=55.7%).The TiO₂/poly-3-methylthiophene core-shell nanosphere film also has a controllable conversion effect of various colors（blue,green,orange and purple）due to the coloring superposition of TiO₂ and poly-3-methylthiophene.Moreover,the electrochemical cycle stability,coloration efficiency（121.9 cm²/C）,transmittance modulation range(ΔT_600nm=62%)and response time of TiO₂/poly-3-methylthiophene core-shell nanosphere film are better than that of TiO₂ and poly-3-methylthiophene.Finally,TiO₂ nanorods,TiO₂ nanoclusters and TiO₂ nanosheet structural thin films were prepared by various types of preparation methods（hydrothermal and solvothermal）and various types of structure directing agents.These films structures can provide more active sites for electrochemical reactions and ions diffusion,resulting in these films with good electrochemical and electrochromic properties.Especially the TiO₂ nanoclusters and nanosheet films in the visible and infrared bands,the optical modulations are 70.4%and 78.6%at 600 nm,61.1%and 75.1%at 1500 nm,37.5%and 52.3%at 14μm,respectively.The electrochromic bleaching and coloring times are 4.4/5.1 s and 3.9/4.3 s,respectively.The coloration efficiency is 98 cm²/C and 113 cm²/C,respectively.The optical modulations after 400 cycles are 94%and 95%of the starting values,respectively.