Dual-functional Electrochromic And Energy-storage Devices Based On Tungsten Oxide Nanostructures

Owing to the rapidly growing energy consumption and environment pollution,the research of high-performance energy converting and saving materials has become an urgent demand.Supercapacitors and electrochromic films,as energy-storing and energy-saving materials,have been widely investigated in the past few years.Electrochromism is the special functionality of materials whose optical properties can be reversibly and persistently changed by electrical signals.Supercapacitors are electrochemical energy storage devices equipped with high power density,rapid charge/discharge rate and long cycle life.Since supercapacitive and electrochromic behaviors of some particular materials are due to the same redox reactions in the same electrolyte,it would be highly attractive to integrate energy-storage and electrochromism functionality into one device,whose energy storage level could be distinguished by visual inspection.Tungsten oxide is supposed to be one of the most promising inorganic materials for electrochromic-supercapacitors.Visible color change takes place accompanied by the insertion/extraction of Li⁺ions into/out of tungsten oxide.Nanostructures can provide large active surface area and short ion transfer path due to the porous architectures.Prussian blue?PB?with stable three dimensional network,has been considered as a promising electrochromic and energy-storage material due to high redox reversibility.PB is an anodic electrochromic material reversing from bleached state to colored state at positive electrical signals.We choose tungsten oxide as well as PB for the negative and positive electrode materials,and assembled a complementary dual-functional device.Tungsten oxide and PB will simultaneously undergo electrochromic-supercapacitors processes,creating large optical modulation and areal capacitance.Tungsten oxide and PB could be formed on flexible substrates by magnetron sputtering and electrodeposition methods.The flexible electrochromic and energy-storage device demonstrates high potential for use in wearable devices and flexible displays,originating from the flexibility,lightness and low cost.In this work,we study dual-functional electrochromic and energy-storage divices based on tungsten oxide.The main work can be divided into three aspects as follow:?1?Dual-functional electrochromic and energy-storage electrodes based on WO₃nanostructures.As dual-functional electrode,the WO₃ nanosheets present superior electrochemical properties of wide optical modulation?64.5%?,fast switching time?6.6/3.8 s?and high area capacitance(14.9 mF cm^-2),benefit from the large surface area and distinct porous structures.Furthermore,bridging electrochromic behaviors with energy storage function is achieved for the WO₃ nanosheets electrode,in which the level of stored energy can be visually monitored by color variations during the capacitive process.?2?A symmetrical supercapacitor integrated with energy level indicating functionality.W₁₈O₄₉ nanowires were first synthesized on half of electrode by hydrothermal method,and then PB was synthetic on the other half through electrodeposition process.A W₁₈O₄₉-PB and PB-W₁₈O₄₉ electrodes were assembled into a symmetrical electrochromic-supercapacitor,presenting excellent charge storage properties along with fast color change.In addition,the supercapacitor can be charged by commercial solar cells and drive LED lights.?3?Flexible device based on tungsten oxide and PB for electrochromic and energy-storage applications.WO₃ and MoO₃-WO₃ film were formed on PET flexible substrates by magnetron sputtering,and then PB was synthetic on PET by electrodeposition process.WO₃ flexible electrode presents an optical modulation of64.5%and switching time of 6.6/3.8 s.PB flexible electrode demonstrates an optical modulation of 51.7%and switching time of 6.64.5/8.6 s.The flexible electrodes could be used in wearable electrochromic and energy-storage device.