Controllable Synthesis And Improved Electrochromic Properties Of Tungsten Trioxide Films

Electrochromism has attracted extensive research interest due to the highly reversible and durable optical property. Developing cost-effective strategy to fabricate electrochromic materials with fast switching speed and long cycle life is significant for the next generation high performance electrochromic device. This thesis focuses on thin WO3 electrochromic film. We attempt to improve its performance by designing and fabricating core-shell nanoarray structure or doping. We have synthesized crystallize/amorphous WO3 core/shell and Mo-doped WO3 nanowire films, and systematically studied their electrochromic property and multifunctional optical-electrochemical properties.To fabricate array with high porosity and to control the degree of crystallinity, we have combined hydrothermal method and electro-deposition to controllably synthesized crystalline/amorphous WO3 core/shell nanowire film (c-WO3@a-WO3). The core is the crystallized WO3 nanowire formed during hydrothermal method. The shell is electro-deposited amorphous WO3 nanoshell. Compared with bare amorphous WO3 film and WO3 nanowire, the optimized c-WO3@a-WO3 core/shell nanowire film has wider optical modulation range (70.3% at 750 nm,42.0% at 2000 nm,51.4% at 10μm), faster electro-chromic switching speed (3.5/4.8 s), higher coloration efficiency (43.2 cm2 C-1) and more stable cyclability (68.5% retention after 3000 cycles). Experimental analysis indicates that the amorphous shell could improve the ion mobility and durability of the shell, as well as improving the switching speed, coloration efficiency and cyclability.Mo-doping has also been used to improve the electrochromic performance of WO3. We have used hydrothermal method to fabricated Mo-doped WO3 nanowire film. Small amount of uniform Mo doping can decrease the crystallinity of the WO3 film but won’t change its morphology. Compared with bare WO3 film, the Mo doped (2 at. Wt.%) WO3 nanowire film exhibits enhanced electrochromic performance including faster bleaching speed (3.2/2.6 s), higher coloration efficiency (123.5 cm2 C-1) and wider modulation range (56.7% at 750 nm,83.0% at 1600 nm and 48.5% at 10 μm). Mo-doping could increasethediffusion coefficient of ion (H+) and improve the electrochromic property. Besides, we have demonstrated the multifunctional property of using Mo-doped WO3 as both energy storage and electro-chromic materials. Such dual properties provide possibility to visualize its state of charge. This newly developed multifunctional optical-electrochemical electrode material would lay the foundation for developing new multifunctional optical-energy storage device.