The Study Of High-performance Electrochromic Energy Storage Devices In Dawson-type Polyoxometalates-MnO₂ System

During charge insertion and extraction or redox processes,some materials produce a reversible change in color,a phenomenon known as electrochromic（EC）.When such materials are combined with supercapacitors,electrochromic supercapacitors（EESD）with intelligent color change function are obtained.Among them,Polyoxometalates（POMs）stand out among many other electrochromic materials due to their excellent UV stability and outstanding color-changing performance.This makes POMs a high-performance color-changing material.However,their application and research in electrochromic devices are relatively limited,especially as high-performance electrochromic energy storage devices are in the initial stage,and there are problems of a single method of POMs film preparation and unbalanced voltage distribution in the devices.Therefore,in this thesis,Dawson-type polyacid P₂W₁₈O₆₂^6-(P₂W₁₈)with good electrochromic properties is used as electrochromic material to prepare EC films by spin-coating method and add HKUST-1 interfacial layer with pore structure to regulate the morphology of the films.Meanwhile,MnO₂was used as the charge balance layer with its constituent devices,and the performance improvement was achieved.Next,a high-performance electrochromic-capacitor device was constructed with P₂W₁₈using Co-doped MnO₂as the counter electrode,and the working mechanism of both devices was systematically investigated.In the first part,the introduction of HKUST-1 particles into the films of P₂W₁₈improved the ion diffusion resistance in the films,and the large pore size of HKUST-1 also reduced the damage to the material structure during the ion embedding and detachment,which greatly improved the cycling stability of the composite films.Meanwhile,the porous structure of HKUST-1 provides the composite membrane with large specific surface area and active sites,which shortens the response time(t_c,90%=5.5s,t_b,90%=3.5s)and improves the coloration efficiency（102.19 cm²/C）and ion diffusion constant(1.267×10^-9cm²/s).HKUST-1/P₂W₁₈also exhibits excellent EC and energy storage when composed with MnO₂.2 cm²of the device can light up LED bulbs for more than one minute after charging.In the second part,Co in situ doping of MnO₂films was performed by electrodeposition method to address the problem of dark color and poor electrical conductivity of MnO₂.The introduction of Co ions played a supporting role to the lattice of MnO₂and increased the lattice constant,which facilitated the diffusion of Li ions in the electrolyte inside the material.The device composition with P₂W₁₈greatly improves the transmission rate of the EESD faded state and also increases the EC performance and energy storage capacity of the P₂W₁₈/Co-MnO₂-EESD device.The device exhibits excellent coloring efficiency（157.84 cm²/C）and faster response time(t_c,90%=3.5 s,t_b,90%=2.7 s),as well as greater optical modulation capability with aΔT of 76.5%at±2 V.It also has a more excellent capacitance（12.45 m F/cm²）.In addition,the introduction of Co gives the device a relatively good memory time.After the device is colorized and powered off,the optical contrast only decays 14%after ten hours.And the color of the device can change in real time with the change of energy storage state,which promotes the practical and intelligent development of dual-function devices.In conclusion,to address the problems of poor cycling stability and weak energy storage capacity of POMs in the field of EC,strategies to change the film formation method and optimize the counter electrode were proposed,which successfully improved the EC performance and energy storage performance of POMs and promoted the development of POMs in the field of EC.