Preparation Of Mesoporous Tungsten Trioxide Based Electrodes And Design Of Electrochromic Energy Storage Bi-functional Devices

Electrochromic energy storage smart window is a novel intelligent device that combines the functions of optical modulation and electric energy storage/release.It can be used to replace traditional architectural glass to further enhance the comfort and energy efficiency of modern buildings.Firstly,this device can modulate the illumination and heat radiation from outside by changing its transparency.Furthermore,its structure and working principle are similar to those of pseudocapacitor.Reversible optical transmittance change of the device is always accompanied by energy storage and release.Combining this novel smart window with power supply devices such as solar cell can achieve more efficient energy saving.The performance of electrode materials is a key factor in the commercialization of this smart window.Thus,we choose WO3 anode material as the research object and attempted to improve its performance by nanostructure design,metal element doping and crystallinity regulation.Nb-doped WO3 mesoporous films with different doping concentration were synthesized by sol-gel soft template method.Phase characterization shows that Nb doping dramatically affects the chemical state and crystallinity of the WO3 based electrodes,causing great changes in the electrochemical and electrochromic properties.The optimal Nb-doped(10%)WO3 electrode delivers superior comprehensive performance with a high specific capacity of 74.4 mAh g-at 2A g-,a large optical modulation range of 61.7%at 633 nm,and a fast response speed of 3.6 and 2.1 s for coloring and bleaching process.The enhanced properties can be attributed to the low crystallinity and increased oxygen vacancies caused by Nb doping,which improve the electronic conductivity of the electrode and provide numerous active sites for the redox reaction on the mesoporous wall surface.In view of the high price of the Nb element and the decreased cyclic stability of WO3 based electrode caused by Nb doping,we synthesized a new kind of mesoporous WO3 film with nanocrystalline nature by the same method,which has a combination of the good high rate properties of amorphous WO3 and long-term stability of crystalline WO3.This film possesses more prominent electrochromic properties with a large optical modulation range of 75.6%at 633 nm,and a response time of only 2.4 and 1.2 s for coloring and bleaching process,respectively.At last,an electrochromic energy storage device was constructed by assembling the WO3 anode with a PANI nanoparticle film cathode.The device shows large optical modulation range,ultrafast switching speed,and excellent long-term stability.Moreover,a red LED can be lighted up for nearly half a minute by two assembled devices placed in series.The WO3 based electrode and electrochromic energy storage bifunctional device in this thesis provide new ideas and important references for the development of novel smart window in the future.