Study On The Performance Improvement Of Polyoxometalate Electrochromic Devices By Charge-balanced Species

Devices assembled with electrochromic materials are called electrochromic devices?ECDs?.Polyoxometalates?POMs?,also known as metal-oxygen cluster compounds,are an electrochromism?EC?material with excellent properties.However,there is not much research on ECD with polyacid as the complete structure of EC material.POMs are composed of three-dimensional tightly packed metal oxide skeletons.Generally,it has good redox reversible properties,can accept electrons and become a mixed valence complex,and the structure is basically unchanged.Due to its unique properties,polyacids have broad application prospects in the field of electrochromism,and thus attract more and more attention.Electrochromism is widely used in energy-saving smart windows,light modulation optics,military camouflage and transparent displays.The electrochromic device is mainly composed of a conductive substrate,an electrochromic material layer,an electrolyte layer,and a charge?ion?balance?storage?layer.Among them,the electrochromic layer is the most critical part for the device to obtain the color changing performance,and the other parts can maximize the color changing performance of the EC layer.Because ECD is a multi-layer structure device,each part can cooperate with each other to get the best performance ECD and build an efficient EC system.In electrochromic devices,the charge?ion?balance?storage?layer is an important part of the device.The charge?ion?balance?storage?layer can play a role in energy storage and balance charge,which will greatly improve the performance of electrochromic devices.Cooperating with the EC layer can also accelerate the insertion and extraction of ions and shorten the response time of electrochromism.This article mainly carried out two aspects of work.On the one hand,the study on the improvement of electrochromic performance by the redox couple in the electrolyte.A PW₁₂-TiO₂ film composite membrane was prepared,using LiI propylene carbonate?PC?solution containing I₂ as electrolyte,and the best choice and ratio of its electrochromic device electrolyte were studied.By optimizing the concentration of Li⁺,the ratio of I^-/I3^-in the electrolyte and the thickness of the EC film,based on the ECD of PW12,an optimized charge-balanced EC reaction can be achieved,achieving high?T of the device,fast response time and low operating voltage.At a wavelength of 680nm,with an applied voltage of+1.2 V?-1.8 V,?T can reach 60.0%.The I^-/I3^-redox pair in the electrolyte acts as an electron shuttle and charge storage substance in the process of electrochromism.The results show that the redox couple in the electrolyte is the key factor for the significantly improved electrochromic performance of PW12-based electrochromic devices.On the other hand,a fast-response Prussian blue-POMs electrochromic system was constructed.PW12,P2W18 and P2W17 were used as working electrodes,and Prussian blue was used as the counter electrode.The effects of polyacid types and working electrode film thickness on electrochromic properties were studied.The above polyacid is a cathode coloring material,and Prussian blue is an anode coloring material.The polyacid film and the Prussian blue film form a complementary electrochromic device with dual electrochromic film layers.Complementary devices have higher optical contrast,faster response time,and exhibit more excellent performance.Among the three kinds of polyacids,P2W17 has a unique structure,a larger specific surface area,and more vacancies,which facilitates the insertion and extraction of ions,and has good electrochromic performance,especially at a lower voltage Can achieve a higher?T,and the response time is rapid.