Preparation Of Ion-intercalated Tungsten Oxide Nanosheets Aqueous Ink And Its Electrochromic Device

With the depletion of fossil energy and the increasing environmental problems,Energy Conservation&Emission Reduction has attracted the world’s attention.Electrochromic smart glass has the advantages of low power consumption,active modulation of solar radiation and so on,which holds great potential in the field of building energy conservation.However,the commercialization of the large area electrochromic smart window is still not mature since the preparation of electrochromic films is mainly based on physical deposition methods（magnetron sputtering）which have the features of high cost,low optical modulation and slow response.Two-dimensional（2D）materials usually have high specific surface area due to the extremely thin feature which facilities the ion diffusion,and leading the improvement of the electrochromic performance.Meanwhile,2D materials have large horizontal size which make it have strong adhesion to the substrate and form uniform film on the substrate.Furthermore,the 2D electrochromic material is made into ink,and the thin films can be prepared at low cost and high efficiency by printing electronic technology based on liquid phase processing.Based on the above challenges,this thesis focus on the synthesis of tungsten oxide nanosheets and their highly dispersed aqueous ink.The main contents are listed as follow:（1）Na-ion intercalated tungsten oxide(Na₂W₄O₁₃)nanosheets were synthesized by molten salt method.In this method,molten sodium nitrate is used as reaction medium,and ammonium tungsten hydrate is added as precursor,which realizing massive synthesis of Na₂W₄O₁₃ nanosheets in a few minutes.The results of XRD、SEM and AFM characterization show that Na₂W₄O₁₃ nanosheets possess good two-dimensional morphology and high crystallinity with the thickness around 3.8 nm.（2）Li_xNa_2-xW₄O₁₃ nanosheets aqueous ink was prepared by modification of Na₂W₄O₁₃nanosheets via Li-ion exchange.The dispersity improvement of nanosheets in water result from the enhancement of the electric double layer effect.As prolonging the Li-ion exchange time,the atomic ratio of Na to W in the nanosheets decreased from 0.46 to 0.19,and its zeta-potential decreased from-42 m V to-55 m V.The results of density functional theory show that the process of Li-ion exchange is energetically favorable.The interface energies of four low-index facets of Li₂W₄O₁₃（including（100）,（001）,（011）and（01（?）））in water is less than those of pristine Na₂W₄O₁₃,which improved the dispersity of nanosheets in water.（3）Li_xNa_2-xW₄O₁₃ nanosheets film was prepared by spraying the Li_xNa_2-xW₄O₁₃nanosheets aqueous ink.Li_xNa_2-xW₄O₁₃ nanosheets film exhibits fast switching response with10.1 s/1.6 s for the coloration/bleaching process respectively at 550 nm,and its coloration efficiency is 25.2 cm²/C.The assembled Li_xNa_2-xW₄O₁₃-prussian white（PW）complementary electrochromic device（2×2.5 cm²）exhibits large optical modulation as well as fast coloration/bleaching response of 2 s/1.4 s at 550 nm.This device also has a coloration efficiency of 67.2 cm²/C and great cyclic stability even over 1000 cycles.Furthermore,we demonstrated the potential of Li_xNa_2-xW₄O₁₃ nanosheets aqueous ink in fabricating flexible and large area electrochromic devices.