Construction Of Conducting Polymer-Based Nanostructures And Their Applications In Multifunctional Electrochromic Devices

Electrochromism refers to the reversible and stable color change of electroactive materials under external applied voltage.Electrochromic materials have been widely used in smart windows,anti-glare rear-view mirrors,displays,military camouflage and e-books.The main electrochromic materials can be divided into three categories:transition metal oxides,organic small molecules and conducting polymers.Among them,conductive polymers have attracted widely attention due to ease of synthesis,low cost,fast response speed,low driving voltage and multicolor possibilities.However,the pure conducting polymers prepared by traditional electrochemical or chemical oxidation polymerization exhibit poor film-forming properties,weak processability and poor electrochromic properties.In addition,the electrochromic films constructed by electrochemical polymerization are hard to process into large-area devices due to the limitation of equipment and technology.In order to solve these problems,anodic coloring polyaniline（PANI）and cathodic coloring poly（3,4-ethylenedioxythiophene）（PEDOT）were selected as the research targets.The micro-nano structures of these conductive polymers were controlled by hybrid with other functional materials,designed into nano-size and molecular structure modification.These methods were used for improving the optical contrast,response speed,coloration efficiency and ion diffusion rate of conducting polymer-based electrochromic films in this research.Then the complementary quasi-state electrochromic device with high stability and ultrafast response speed was successfully constructed.The pseudo-capacitor and electrochromic device possess the same device structure and share the same electrochemical redox process.Therefore,a multifunctional energy storage electrochromic device based on conductive polymer porous nanostructures can be fabricated.Finally,large-area and patterning of energy storage electrochromic devices are successfully realized by a simple,efficient and low-cost spray-coating method.It is of great significance for design of electrochromic materials and large-scale production of electrochromic devices.This research mainly includes the following six aspects:1.Preparation,electrochromic and capacitance properties of one-dimensional PANI nanotube film.The natural HNTs nanotubes were used as template.The HNTs/PANI core-shell nanotubes were synthesized by in-situ chemical oxidative polymerization.And the one-dimensional PANI nanotubes were prepared by template method.PANI-NTs film shows significantly improved electrochromic and capacitive properties.The improved electrochemical performance is mainly attributed to the multi-layer porous nanostructure of PANI-NTs films,including the holes of nanotubes and the three-dimensional pores formed by the overlapping of one-dimensional nanotubes,which can significantly shorten the ion diffusion length,make the ion diffusion easier and provide more active sites for charge-transfer reaction.2.Preparation,electrochromic and energy storage properties of honeycomb-like anodic coloring H-PANI porous nanostructured films.Monodisperse silica（Si O₂）nanoparticles prepared by a modified Stober method were used as templates,and Si O₂/PANI nanocomposites were synthesized by in-situ chemical oxidation polymerization.Then honeycomb-like porous H-PANI nanostructures were prepared by template method for the first time.The honeycomb-like porous nanostructure is favorable for ion transport and diffusion,reducing redox potential and providing larger specific surface area for electrochemical redox reaction.H-PANI nanostructured film exhibits significant color changes（colorless,light yellow,green to dark blue）and enhanced electrochromic and energy storage properties,including larger optical contrast,faster response speed,higher coloring efficiency and larger specific capacitance.3.Preparation of cathodic coloring H-PEDOT porous nanostructured films and its electrochromic and capacitive properties.Three-dimensional honeycomb-like H-PEDOT porous nanostructures were successfully prepared by using monodisperse Si O₂ nanoparticles as templates for the first time.The porous nanostructures can effectively reduce the ion diffusion length,improve the ion diffusion rate and provide larger reaction area for charge-transfer reaction.Compared with the dense PEDOT films prepared by the same method,the H-PEDOT nanostructured film shows more obvious color change（from dark purple to sky blue）and better electrochromic and energy storage properties.And the contrast is increased by 6 times,the response speed is increased by 3 times,the coloring efficiency is increased by 15 times and the specific capacitance is increased by 1.5 times.4.Research on complementary quasi-solid-state electrochromic devices with high stability and ultra-fast response speed.The complementary quasi-solid-state electrochromic device was assembled by employing H-PANI nanostructured film,H-PEDOT nanostructured film and Li Cl O₄-PMMA-PC gel as positive electrode,negative electrode and electrolyte.The influences of device structure,voltage range,pulse time and conductive substrate on the electrochromic performance of complementary device（ECD-HPND）were systematically studied.Owing to the porous nanostructures of electroactive materials,complementary colors and good charge balance,the ECD-HPND shows high optical contrast（46%at 600 nm）,ultra-fast response speed（800 ms in coloring process and 700 ms in bleaching process）and excellent cycle stability（only 2.5%reduction in contrast after 1000 cycles）.The complementary flexible quasi-solid-state electrochromic device ECD-FL assembled by using ITO/PET instead of ITO glass also shows fast response speed（500 ms for coloring process and 600 ms for fading process）and good bending resistance（the contrast value of bending 500 cycles decreases only 4%）.5.Preparation and electrochemical performance of symmetrical and complementary energy storage electrochromic devices.A symmetrical energy storage electrochromic integrated device（ESSW-HPN）was fabricated by using two H-PANI nanostructured thin films as electrodes and PMMA-based gel as electrolytes.Due to the good charge balance of symmetrical-type device,ESSW-HPN shows good energy storage performance and electrochemical charge-discharge stability.However,the electrochromic properties of the device are very poor because the film electrodes cannot realize the color complementary.A complementary energy storage electrochromic integrated device（ESSW-HPE）was further constructed by using H-PANI,H-PEDOT and PMMA-based gel as anode,cathode and electrolyte.Both electrodes of ESSW-HPE can color and bleach simultaneously during charging and discharging.Therefore,ESSW-HPE shows good electrochromic performance,energy storage performance and electrochemical charge-discharge stability.Moreover,the energy storage level of the complementary ESSW-HPE can be monitored by the reversible color change during the charge-discharge process.6.Construction and electrochemical performance of high-performance,large-area and patterned energy-storage electrochromic devices.Firstly,solution-processable poly（o-methoxyaniline）（POMA）nanoparticles were successfully prepared by in-situ chemical oxidative polymerization.The diameter of POMA nanoparticles was about 10 nm.Because the-OCH₃ side chain of POMA molecular chain reduces the conjugation length and increases the flexibility of the molecular chain.POMA possesses better film-forming property,solubility and processability.POMA nanostructured films were successfully prepared by spray-coating method.Compared with pure PANI films,POMA films exhibit significantly improved electrochromic properties,such as larger optical contrast（70.6%at 700 nm）,faster response time（850 ms for coloring process and 960 ms for bleaching process）,higher coloring efficiency（103 cm²/C）and larger capacitance（401 F/g）.The high-performance quasi-solid-state energy storage electrochromic device（ESSW-S）was assembled by using POMA nanoparticle and commercial PEDOT:PSS films as anode and cathode.ESSW-S exhibits large optical modulation（62.2%at 600 nm）,fast response（960 ms for coloring process and 470 ms for bleaching process）,high coloring efficiency（437 cm²/C）and excellent cycle stability（The optical modulation value decreases only 0.1%after subjecting 2000 cycles）.In addition,three ESSW-S in series are able to light a 3 V blue LED successfully,which proves that ESSW-S possessed good energy storage performance.Then,a large-area（10×10 cm²）energy storage electrochromic integrated device（ESSW-L）was successfully assembled by a simple,efficient and low-cost spray-coating method.It is demonstrated that the energy storage electrochromic device fabricated by spray-coating method can maintain excellent electrochromic and energy storage performance on large-area device（ESSW-L,10×10 cm²）.Finally,due to the advantage of solution processability,the patterned energy storage electrochromic integrated devices（ESSW-P）with different high-quality patterns were successfully fabricated by spray-coating method with mask assistance.The patterned ESSW-P also shows excellent electrochromic and energy storage properties.Patterned energy storage electrochromic integrated devices with low energy consumption have potential application prospects in some static displays such as e-books,electronic billboards,which provides a new idea to broaden the application fields of electrochromic materials.In this paper,we systematically studied the relationship between the electrochemical properties and the porous nanostructures of conducting polymer.A complementary quasi-solid-state electrochromic device based on conductive polymer porous nanostructures was assembled and exhibits high stability and ultra-fast response speed.And the integration of energy storage and electrochromic function was successfully realized.Moreover,the energy storage level during charging and discharging can be observed by visual color change.A simple,efficient and low-cost spray-coating method was used to realize the large-area and patterning of energy storage electrochromic integrated devices.The solution-processable conductive polymer nanostructured materials have potential applications in smart window,anti-glare rearview mirror,display,military camouflage and wearable electronic devices.