Fabrication And Broadband Modulation Properties Of Polyaniline Based Electrochromic Film

Electrochromic technology could reversibly adjust the optical properties of materials such as absorbance and transmittance by an applied electric field.Electrochromic devices with visible light modulation function have been commercially applied in the fields of anti-glare rearview mirrors and smart windows.Furthermore,the broadband electrochromic devices with visible light and infrared modulation function have attracted attention due to its urgent research needs and great research value in the fields of building energy saving,infrared self-adaptation and intelligent thermal control of spacecraft.Polyaniline（PANI）is an ideal broad-band electrochromic material because of its wide electrochromic spectral range and rich visible color variation.However,there are still many obstacles to development of high performance PANI based broadband electrochromic devices.In terms of device structure,the applicable wavelength range of existing conductive electrodes is too narrow to meet the demand of broad-band electrochromic devices.In terms of PANI film preparation,the thermal infrared modulation effect of PANI film is easily masked by infrared absorbing materials,resulting in a limited thermal infrared variation of the electrochromic devices.Regulating the microstructure of PANI film and avoiding the adverse effects of infrared absorbing materials is the key to enhancing the performance of broad-band electrochromic devices.In addition,the critical problems of fabrication large-area broad-band electrochromic devices and broad-band electrochromic devices combined with electromagnetic absorption function have not been effectively solved.Based on the above research background,a series of research have been conducted in this dissertation including the structural design of PANI based broadband electrochromic devices,the development and preparation of flexible conductive electrodes,the regulation of the micromorphology of PANI,the fabrication of large-area broadband electrochromic devices,and the design and fabrication of broadband electrochromic devices compatible with electromagnetic absorption function.The specific research conclusions are as follows:1.According to the requirement of broad-band electrochromic devices,a flexible conducting gold electrode with high reflectance in the range from visible light to thermal infrared was developed to fabricate PANI based visible-near-infrared electrochromic devices.The flexible conducting electrode achieved average reflectance of 97%and 94%in the near-infrared and thermal infrared ranges,respectively.The PANI based visible-near-infrared electrochromic devices achieved bright yellow,green and blackish green color variations and a tunable solar absorption ratio from 0.34 to 0.90.Under a standard sunlight irradiation,the device achieved a temperature adjustment of 9.2^oC.In addition,the device achieved maximum emissivity changes of 0.45 in the range of 3-5μm.By investigating the influence of materials in the electrochromic devices on the thermal infrared electrochromic property of the device,the adverse effects of infrared absorption of materials were clarified.This work provided a foundation for the development of PANI based broad-band electrochromic devices.2.In order to further enhance the broadband electrochromic property of electrochromic devices,flexible microporous conducting gold electrodes were developed by using microporous nylon membranes as substrates.The microporous conducting gold electrode provides the pathway for the electrolyte to reach the electrochromic layer to avoid the adverse effect of the infrared absorption of the electrolyte on the broadband electrochromic property of electrochromic devices.The coral-like PANI films were deposited on the surface of microporous conducting gold electrodes by a two-step electrodeposition method.The coral-like structure of PANI film facilitates the transport of electrolyte ions and increases its specific surface area.The coral-like PANI film based thermal infrared electrochromic-energy storage devices achieved reversible color changes of brownish yellow,green and dark green,and achieved maximum emissivity changes of0.42,0.49 and 0.47 in the ranges of 3-5μm,8-14μm and 2.5-15μm,respectively.In addition,the device obtained energy storage function,and a specific capacitance of 355F g^-1 was achieved at a current density of 1 A g^-1.The device had 98%capacitance retention after 1000 bending cycles.Meanwhile,the energy storage state of the device is observable,which can be inspected by the naked eye through the color change of the device.This work provided a new idea for the development of multifunctional broad-band electrochromic devices.3.In order to solve the problem of irregular morphology of PANI film,the morphology of PANI was regulated by introducing potassium polyvinyl sulfate（PVSK）as a template during the PANI electrochemical deposition process.The PVSK-PANI films have regular spherical particle morphology and higher electrochemical activity.The simple molecular structure of PVSK and its similar infrared absorption peak location with packaging materials（polyethylene）and doping acid（H₂SO₄）could avoid the adverse effects of the broadband electrochromic property of the device.The PVSK-PANI based large-area electrochromic devices with size of 20×20 cm² achieved maximum emissivity changes of 0.55,0.46 and 0.46 in ranges of 3-5μm,8-14μm,and 2.5-15μm respectively.At a background temperature of 70^oC,the large-area electrochromic device achieved a maximum adjustable infrared temperature of 10.4^oC.This work provided an effective strategy for the preparation of large-area electrochromic devices.4.To further expand the applicable wavelength range of electrochromic devices,a counter electrode with electromagnetic wave absorption function was developed based on the research of broad-band electrochromic devices.The Fe₃O₄@PANI composites with core-shell structure were prepared by in situ oxidative polymerization for preparing electromagnetic wave absorbing counter electrodes.The Fe₃O₄@PANI/PVDF based counter electrode achieved an electromagnetic wave absorption bandwidth of 3.5 GHz（14.5-18.0 GHz,RL<-10 d B）.The electromagnetic wave absorbing counter electrode could provide ion storage capability in broad-band electrochromic device to balance the charge of the electrochromic layer.On the side of electrochromic layer,the electromagnetic wave absorbing counter electrode based thermal infrared electrochromic device achieved yellow,green,and dark green color variations and achieved maximum emissivity changes of 0.44,0.45,and 0.43 in ranges of 3-5μm,8-14μm,and 2.5-15μm,respectively.This work solved the problem that electrochromic devices are challenging to combine with electromagnetic wave absorption function and expand the applicable wavelength range of electrochromic devices.