Preparation Of Tungsten Oxide Nanoarray Films And Theirs Zinc Based Electrochromic Properties

Zinc-based electrochromic refers to the reversible change of optical properties of material caused by the intercalation/deintercalation of Zn²⁺ions.Because of its low cost,high safety and good compatibility with various electrolyte aqueous solutions,the zinc-based electrochromic has attracted much attention of researchers in universities and enterprises.Since the zinc-based electrochromism is a newly born technology,its electrochromic properties and related kinetic processes are still unclear.Further exploration and development of zinc-based electrochromic technology,understanding its working mechanism and improving the coloration efficiency have great research significance and application prospects for promoting the commercial application of zinc-based electrochromic devices.In this thesis,we selected the classic electrochromic material of tungsten oxide(WO₃)as the research target,and systematically studied the relationship between the morphology control of WO₃ nanoarrays films and their zinc-based electrochromic properties and related working mechanisms,including the morphology control of WO₃ nanoarray films,the zinc-based electrochromic and energy storage performance,and the zinc-based dual-band electrochromic performance.The main content includes the following aspects:(1)WO₃ films with different micro-morphologies were prepared by hydrothermal method.A series of WO₃ films with morphologies such as nanorods,nanosheets and nanoclusters were prepared by systematically exploring the type of guiding agent,reaction temperature and volume ratio of hydrothermal solvent in the hydrothermal reaction.The corresponding growth mechanism of WO₃ films was also discussed.This provides a material basis for the study of morphology dependent zinc-based electrochromic of WO₃ films.(2)The WO₃ films with shape of nanorods and WO₃ nanoflake prepared above were used as the research objects.The electrochromic characterization of these films was carried out in a three-electrode electrochemical cell with aqueous zinc ion electrolyte solution.The results showed that the optical modulation range of WO₃ nanorod and WO₃ nanoflake film at 550 nm were 72.4%and 61%,their coloration time were 3 s and 9 s,their bleaching time were 2.2 s and 7 s,the coloration efficiency were 67.6 cm² C^-1 and 53.8 cm² C^-1respectively.Through the analysis of electrochemical mechanism,WO₃ nanorod film has better electrochromic performance.The reason is that the surface area of WO₃ nanorod is larger than that of nanoflake,which leads to a larger surface driving capacitance contribution in electrochromic process.A zinc-based electrochromic device was fabricated using WO₃ nanorods as symmetric electrodes.The device exhibits a“blue-transparent”electrochromic phenomenon through the principle of“color superposition”between the symmetric electrodes.The optical modulation range is 76%at 550 nm.In addition,the device has an area capacitance of 64 m Ah m^-2 corresponding to a current density of 0.72 A m^-2,showing excellent energy storage performance.The work in this chapter shows that the zinc-based electrochromic and energy storage performance of WO₃ film can be improved by adjusting of its micro-morphology.(3)WO₃ nanosheet films with different thicknesses were prepared by changing the volume ratio of water and ethylene glycol as solvent.The dual-band zinc-based electrochromic properties of these films were studied in zinc perchlorate electrolyte.The results show that the nanosheets prepared by H₂O/EG=1/2 are in the“bright”mode(both visible(VIS)and near infrared(NIR)band are transparent)at 1.2 V.When the potential is 1.2-0.2 V,it switches to“cold”mode that shielding most of the NIR while maintaining good VIS light transmittance.When the applied potential drops to 0 V,it triggers a“dark”mode in which the film blocks most of VIS and almost all of NIR light.The optical modulation ranges of film at 633 nm(VIS)and 1200 nm(NIR)were 65.6%and71.9%,respectively,the coloration time were 9 s and 7.5 s,the bleaching time were 15 s and 9.8 s.The WO₃ film prepared by solvent of H₂O/EG=1/2 have more better dual-band electrochromic performance,because the array structure of the film has a larger active specific surface area and a smaller impedance.The cyclic stability test shows that the film still remained 93%of the initial capacity after 500 cycles,and 90%of the initial capacity after 1000 cycles,showing good cycle stability.The work in this chapter shows that the morphology control of the film provides a new avenue to improve the performance of the dual-band zinc-based electrochromic.