Fabrication And Performance Of Flexible Electrochromic Devices Based On Electrospinning Process

With the continuous development of flexible device research in recent years,the research on combining flexible electronics with electrochromic devices has received extensive attention.Electrochromic devices（ECDs）have the advantages of rich colors,low energy consumption,and open-circuit memory.By combining wearable,self-powered,and sensing technologies,flexible ECDs endow devices with features such as light weight,visual storage,and adaptive stealth.However,there are many problems in the current preparation methods of flexible ECDs,which are not only limited by the substrate area,production scale,and production efficiency but also difficult to maintain mechanical stability during the deformation process,which cannot meet the application requirements.The key to realizing the stable performance of flexible ECD lies in the stability of the active material and the electrode and in maintaining good interfacial contact between the flexible electrode and the active layer during the deformation process.In response to these problems,in this paper,by preparing electrochromic active materials,selecting conductive electrodes with excellent mechanical properties,and using electrospinning technology to construct flexible electrochromic fibers with both mechanical stability and good electrochemical activity.The morphology,structure,and electrochemical activity of electrochromic active materials,electrochromic films,and fibers were investigated respectively.The main research contents are as follows:（1）Preparation of sheet-like structure polyaniline（PANI）The type of acidic dopant and the polymerization time have significant effects on the properties of PANI.To prepare PANI with stable structure and high solubility,three different protic acids—p-toluenesulfonic acid（p-TSA）,sulfuric acid（H₂SO₄）,and camphor sulfonic acid（CSA）were selected to prepare PANI by chemical oxidative polymerization.The doped PANI has fibrous,short rod-like,and two-dimensional lamellar morphologies,respectively,while the more two-dimensional lamellar structures in PANI-CSA indicate the directional growth of specific crystal planes,and the structural arrangement is more ordered.When the reaction time was prolonged from 2 h to 6 h,the morphology of PANI transitioned from plate-like to directional growth sheets and finally grew into nanofibers.Therefore,the optimal polymerization conditions were determined:CSA as a dopant was chemically oxidized for 4 h to obtain PANI with higher crystallinity.Hybrid ions provide an effective transport channel,and the doping of CSA can improve the solubility of PANI,which is beneficial to the preparation of a uniformly dispersed spinning solution.（2）Preparation and electrochemical properties of PANI/PEO fiber membranesElectrochromic fibrous films were prepared on three conductive fiber substrates based on highly soluble polyaniline using electrospinning technology.The effects of polymer substrates（polyvinylpyrrolidone（PVP）,polyvinyl alcohol（PVA）,and polyethylene oxide（PEO））and their compositions on fiber morphology were compared and analyzed.PEO was selected as the polymer substrate,and the solvent system was CHCI₃:DMF=6:1,PANI/PEO fiber film with uniform loading of PANI was successfully prepared.Stainless steel yarn,silver wire,and carbon fiber are used as fiber electrodes respectively,and a fiber film is uniformly deposited on its surface.The film is not only in close contact with the substrate but also has high porosity,a large specific surface,and stable chemical properties,which is conducive to the penetration of electrolyte.Ions provide storage and diffusion channels.The electrochemical test results show that the three kinds of color-changing fibers have redox activity.After 50 cycles of testing,the fiber film on the stainless-steel yarn does not fall off and the performance is stable.10wt%PANI-PEO exhibited the highest redox peak current and the smallest charge transfer resistance in the range of 0.25～0.7 V,showing the best capacitance characteristics and improved charge storage capacity and transfer efficiency.（3）Preparation and electrochemical properties of WO₃/PVDF fiber membraneAmorphous tungsten oxide（WO₃）was prepared by the hydrothermal method as electrochromic material,and WO₃ was uniformly loaded on polyvinylidene fluoride（PVDF）fibers by electrospinning process to prepare electrochromic materials with controllable morphology and structure.film.The results showed that amorphous WO₃ nanoparticles with a size of about 30 nm-50 nm were obtained after a reaction time of 1 h.The loose structure provided abundant ion transport channels and was more prone to redox reactions.By optimizing the composition of the spinning solution,adjusting the electrospinning parameters,and improving the conductivity of the film,the WO₃/PVDF composite film was prepared.When the liquid composition is WO₃:PVDF=3:4,the internal resistance is 11Ω,the charge transfer resistance is the lowest,the charge transfer efficiency and electrochemical active area are the largest,and the peak current is the most obvious.After adding 0.05 wt%Ag nanowires,the conductivity of the film was improved,the charge transfer resistance was reduced,and the ion transport efficiency in the film was improved,which was beneficial to shortening the color changing response time and improving the coloring efficiency.