Synthesis Of 2D Oxygen Vacancy WO_3-x Nanosheets And Its Application In Electrochromic Devices

Tungsten oxide（WO₃）materials are attracting more attention in the application of electrochromic technology due to their good electrochromic properties.The shortcoming such as the limited electrochromic properties,complex process of device fabrication and assembly,and high cost seriously hinders the development of WO₃ electrochromic products.To address the above issues,the effective approach is to optimize the synthesis of tungsten oxide with high electrochromic performance and the structure of electrochromic devices.Therefore,this thesis is devoted to the synthesis of two-dimensional tungsten oxide nanoplates and their applications as cathode electrochromic materials in electrochromic devices.Three parts are included:1.Synthesis and electrochromic properties of oxygen vacancy WO_3-x nanosheets.In this part,the oxygen vacancies firstly were introduced into tungsten oxide by solvothermal method to synthesize WO_3-x nanosheets.Then WO_3-xwas filmed on the FTO glass through the dip-coating process.The electrochromic performance test showed that the optical modulation range of WO_3-x film on FTO glass is as high as 79.5%,the coloring efficiency is90.2 cm² C^-1,and the switching time of the coloring/bleaching state at 670nm is 6.2/8.1 s.Besides,the obtained WO_3-x films also possessed a discharge-specific capacitance of 58.8 m F cm^-2 under the discharge current density of 0.1 m A cm^-2.Subsequently,an electrochromic device that simulates an intelligent window was fabricated with WO_3-x film,and the test results showed that the optical modulation range of the device was82.1%,the coloring efficiency was 111.8 cm² C^-1 with good cyclic stability（maintains 71.6%of the maximum dynamic modulation range after 1000cycles）.This synthesis strategy provided a feasible path for the fabrication of high-performance electrochromic devices based on WO_3-x.The excellent electrochromic properties of WO_3-x films can be attributed to their good conductivity and ion diffusion efficiency of WO_3-x nanosheets due to their two-dimensional structure and abundant oxygen vacancies.2.Fabrication and performance study of chemically self-charged Zn//WO_3-x electrochromic smart devices.Zn//WO_3-x device with dual-function was assembled using Zn²⁺-Al³⁺mixed ion hydrogel as an electrolyte,zinc metal as the negative electrode,and WO_3-x film as the positive electrode（electrochromic layer）.Due to the spontaneous oxidation of colored WO_3-x by dissolved oxygen in the hydrogel electrolyte,the device can be bleached（colorless and transparent state）by simply disconnecting zinc and WO_3-x electrodes,which also indicated that an important role of the device as a self-rechargeable transparent battery.Therefore,the fabricated Zn//WO_3-x device is a self-powered electrochromic window without an external power supply.The test of electrochromic performance showed that the optical modulation range of the Zn//WO_3-x device is as high as 85.4%under the wavelength of670 nm,the self-coloring time is 8.7 s,the chemical self-charging bleaching time is about 0.55 h,and the open-circuit voltage recovery time is about 3 h.The energy storage capacity is up to 198 m Ah g^-1.Therefore,the electrochromic performance was effectively improved and chemical self-charging performance was achieved by the solid-state mixed ion hydrogel electrolyte strategy.Furthermore,this unique structural combination can further promote the development of intelligent energy storage devices suitable for user-device interaction.3.Preparation and performance study of electrochromic devices based on WO_3-x ink.As the electrochromic active material,the synthesized WO_3-xnanosheets were employed to prepare the printable electrochromic ink with the assistance of carboxymethyl cellulose as a tackifier,and a mixture of ethanol-water as solvent.Firstly,the printability of the WO_3-x ink on different printing substrates was analyzed.Then,the printed substrate was applied to constructed electrochromic devices,and the related electrochromic properties and the application scene were studied.The results demonstrated that the prepared ink showed good dispersion stability even after being stored for more than two months.The clear and complete text and smooth lines printed on the substrate illustrated an excellent printability of WO_3-x ink.Besides,apparent color changes with a uniform discoloration effect were observed in the process of coloring and fading.Furthermore,the printed QR code can be quickly identified by intelligent code scanning equipment,which showed the universal printing suitability of the ink on the mainstream transparent conductive substrate and potential market applications.