The Fabrication And Electrochromic Performance Regulation Of Composite Materials By Combination Of Polyoxotungstate With TiO₂ Nanowires

Polyoxometalates?POMs?have been investigated as electrochromic materials for a long time due to their excellent redox reversibility while giving rise to colored mixed-valence state species.However,similar to traditional inorganic electrochromic materials,low optical contrast,slow response time and single-color change of polyoxometalate-based materials still limit their further applications.Recently,a large number of researches demonstrate that regulate the morphology and microstructure of materials could accelerate the electron/ion reaction rate and promote the reaction kinetics.At the same time,changing the element composition and crystal structure of materials could effectively improve the material's performance and endow the material with the corresponding unique properties.In addition,with the development and utilization of new materials and nanotechnology,the construction of nanocomposites is considered as an effective way to improve the properties of materials.In view of the above problems,a series of substituted polyoxometalates with unique properties were obtained by adjusting the element composition and structure of the polyoxotungstate acid.And a series of composite films were obtained by combining the obtained POMs with a three-dimensional TiO₂ nanowire by electrodeposition method and layer-by-layer self-assembly method.The surface morphology,structure,composition and chemical properties of electrochromic films were studied by IR,UV-vis,SEM,TEM,AFM and XPS.The electrochromic properties of the films were tested by in-situ spectroscopy with electrochemical workstation and UV-vis.The testing methods mainly include cyclic voltammetry and chronoamperometry.The main contents are as follows:1.A nanocomposite thin film composed of a composite monocerium substituted sandwich-type polyoxotungstate cluster K₁₇[Ce(P₂W₁₇O₆₁)₂]·nH₂O and TiO₂nanowires is constructed via electrodeposition method and hydrothermal synthesis method.The electrochemical deposition method is short in time and easy to operate.The obtained composite film exhibited significantly enhanced electrochromic properties.Combining the characterization and electrochemical test results,the improved electrochromic properties could be attributed to the unique three-dimensional structure of the TiO₂ nanowire substrate,which can provide high specific surface area and rapid redox reaction kinetics characteristics,thereby significantly improving electrochromic properties.2.A nano-composite electrochromic multilayer film was prepared by combine tri-vanadium substituted polyoxometalate?-K₉[P₂W₁₅V₃O₆₂]·18H₂O and TiO₂nanowires through LbL method.Due to the unique structural advantages of TiO₂nanowires,the electrochromic properties of the composite film have been significantly improved.In addition,the prepared film has the characteristics of multi-color adjustment due to the substitution of V element for W,which could exhibit the change from colorless to blue-violet.3.Mono-transition metal substituted Dawson-type polyoxometalate?-K₈[P₂W₁₇O₆₁Ni^II?H₂O?]·18H₂O and TiO₂ nanowires were prepared as a nano-composite electrochromic multilayer by LbL method.And a composite film with excellent electrochromic performance and pH sensing characteristics were obtained.The electrochromic composite film confirms the great potential of polyoxometalates in the field of multifunctional electrochromic materials,and provides reference information for exploring suitable polyoxometalates structures as multifunctional materials.