Fabrication And Electrochromic Performance Of Quantum Dots And Polyoxometalates

Electrochromic means that the optical properties of a material,such as its absorbance,transmittance or reflectance,change reversibly and continuously during the insertion or extraction of electric charge.Electrochromic materials in military camouflage,satellite thermal control,high-contrast displays and intelligent windows have also been reported.Polyoxometalates（POMs）can realize a rapid and reversible oxidation-reduction process with the same structure.Most POMs can exhibit dark blue color when reduction after accepting electrons,and then revert to colorless when oxidized.This reversible electrochromic property of POMs makes them attractive candidates for inorganic electrochromic materials.Due to the synergistic effect of quantum dots（QDs）and POMs,the electrochromic performance of materials can be enhanced by incorporating QDs into POMs-based materials.In this paper,we focus on the preparation of POMs/QDs materials by layer-by-layer method（LbL）and investigation of the electrochromic performances.The composition and growth of the composite films were monitored by UV-vis spectra,the morphology of the composite films were characterized by electron scanning microscope,and the electrochromic properties of composite materials were studied by electrochemical test.The specific work is as follows:1.The composite membrane materials consisting of tri-vanadium substituted Dawson-type tungstateα-K_6+n[P₂W_18-nV_nO₆₂]·18H₂O（n=1,3）(abbreviation:P₂W₁₇V and P₂W₁₅V₃),CdS QDs and PEI which can realize multi-color adjustment were fabricated.The electrochromic performance test shows that:the electrochromic performances of single component POMs-based films are enhanced by the CdS QDs has been successfully incorporated.The performance of PEI/[P₂W₁₅V₃/PEI-CdS]₂₀ film is the best,it can be realized from colorless to blue then to purple blue,the optical contrast is 38.05%,response time for recolorstion and bleaching is 3.57 s and 6.94 s,respectively,the maximum coloring efficiency is 94.04 cm²·C^-1,whose compared with theα-P₂W₁₅V₃ film,the optical contrast increased by 46.07%and the color efficiency increased by 96.53%,the electrochromic performance is improved remarkably.The PEI/[P₂W₁₇V/PEI-CdS]_n composite film has the best electrochromic performance at 20 layers,which can realize the change from colorless to blue,the optical contrast and the coloring efficiency increased to32.55%and 78.31 cm²·C^-1,respectively.Which increased by 33.24%and 21.24%compared with the optical contrast and the coloring efficiency of PEI/[P₂W₁₇V/PEI]₂₀.2.The composite membrane materials consisting of Dawson-type tungstate K₆[P₂W₁₈O₆₂]·14H₂O(P₂W₁₈),CdS QDs and PEI with fast response and high coloring efficiency were fabricated.The electrochromic performance test shows that:when the CdS QDs were compounded for 4 min and the number of layers is 20,the composite film of PEI/[P₂W₁₈（7 min）/PEI-CdS（4 min）]₂₀ has the best performance,the coloring time and bleaching time are 1.93 s and 2.24 s,respectively,and the coloring efficiency is improved to 127.18 cm²·C^-1.The composite film displays adjustable colors and undergoes transitions from colorless,light blue and dark blue.3.ThecompositemembranematerialsconsistingofPreyssler-type K_12.5Na_1.5[NaP₅W₃₀O₁₁₀]·15H₂O(P₅W₃₀),CdS QDs and PEI with high optical contrast were fabricated.The electrochromic performance test shows that:the composite film PEI/[P₅W₃₀/PEI-CdS]₂₀ exhibits the best performance,resulting in an optical contrast is increased to 51.04%,the switching times are 2.58 s for coloration and 1.96 s for bleaching,and the coloring efficiency is up to 127.18 cm²·C^-1.In conclusion,in this paper,based on the synergistic effect of POMs and QDs,the three kinds of POMs/QDs electrochromic composite materials were preparation by LbL method,respectively,which can be realized from colorless to blue then to purple blue,with fast response time,high coloring efficiency and high light contrast.This work can provide reference for the development of POMs/QDs composite materials in electrochromic field.