| Electrochromic materials can proceed redox reaction under the action of electric field,meanwhile,are accompanied by reversible modulation of light transmittance,absorption and reflectance.Electrochromic materials have been used in many fields,smart window,no glare automobile rear-view mirrors,electrochromic display devices,for example.Tungsten trioxide?WO3?is the most widely studied electrochromic materials,which can achieve reversible color change between transparent and dark blue.Therefore,it is usually studied and applied in smart window and other fields.However,although the research of WO3 is relatively mature,there are still many problems need to be solved in practical application,such as insufficient coloring depth,long response time,poor color-changing cycle life and complicated preparation process.Based on above problems,a novel hydrothermal strategy of combining a capping agent with a polyhydroxy self-seeded agent was designed in this thesis for directly growing a high-performance WO3 electrochromic film on FTO-coated glass with a simple and fast process.Meanwhile,feasibility and superiority of this strategy was demonstrated by in-depth analysis and discussion of crystal growth process and electrochemical behaviors.In addition,in order to explore the application of electrochromic device,a nickel oxide/prussian blue?NiO/PB?composite nanosheet anodic electrochromic film was also designed to better match the prepared WO3 cathodic electrochromic film.Thus,by including these two different electrodes in one device,a bi-functional device with excellent electrochromic and energy storage properties was fabricated which exhibited promising application potential.And the main contents are as follow:?1?A novel glycerol-assisted hydrothermal method was designed to avoid the preparation of seed layer before film growth and make the adhesive force between WO3film and FTO strongger.Moreover,under the synergistic-effect mechanism of glycerol and appropriate amount?NH4?2SO4,a novel porous coral-like nanostructure and hexagonal crystal structure with more ion transport tunnels were obtained in prepared WO3 film.Meanwhile,a quantitative research method,which is an important experimental means,was used to discuss the influence mechanism of glycerol and?NH4?2SO4 to crystal growth and electrochemical properties.Finally,the WO3 film prepared at the optimal ratio could realize the reversible change between transparent and dark blue atą1 V.The excellent electrochromic properties included a fast switching time?6.0/5.0 s for bleaching/coloration?,a good coloration efficiency(56.5 cm2 C-1),and a large optical modulation?78.1%?at 630 nm.More importantly,the film obtained an outstanding cyclic stability?15 000 cycles without significant decay?.?2?In order to improve the performance of PB film,NiO nanosheets film was used as substrate to prepare a NiO/PB composite nanosheets electrochomic film by electrodeposition method.The composite film not only successfully combined two kinds of anodic electrochromic materials but also retained the hole structure between nanosheets,which was beneficial to the sufficient penetration of electrolyte in the film and the efficient transport of Li+.Finally,the prepared NiO/PB composite film exhibited a fast switching time?3.8/1.6 s for bleaching/coloration?and a lager optical modulation range.And compared with the prepared PB film,the electrochemical cyclic stability of NiO/PB composite film was significantly improved.The analysis indicated that the nanosheet structures was the key to improve electrochemical stability which could form a buffer effect on ion insertion and extraction.?3?For the one-step hydrothermal method,erythritol and NH4Cl were used to displace glycerol and?NH4?2SO4,thus,a WO3 film with hexagonal crystal structure and coral-like nanostructure was prepared under lower hydrothermal temperature.It was worth noting that the WO3 film exhibited larger optical modulation range?81.76%?,higher coloration efficiency(73.1 cm2 C-1)and faster switching speed?3.3/3.7 s for bleaching/coloration?.Then,an electrochromic energy storage device was successfully assembled with the prepared WO3 film used as negative electrode and NiO/PB film used as positive electrode.The device exhibited attractive electrochromic properties,which can realize reversible color change between transparent and dark blue,and the cyclic stability up to 4000 time.Meanwhile,the device also showed good energy storage property(a high areal capacitance of 11.50 mF cm-2 at current density of 0.05 mA cm-2)and the energy during process of bleaching can driver light emitting diode?LED?and liquid crystal display?LCD?. |
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