Preparation And Electrochromic Properties Of Composite Materials Based On Tungstophosphate And Tungsten Oxide

WO₃ has the characteristics of low cost,extensive research and unique physical and chemical properties,and is widely used in the fields of electricity/photochromism,photocatalysis and gas sensing.Among them,WO₃has the advantages of low coloring voltage,non-toxicity,and good coloring memory performance.It is the only electrochromic material that has entered the industrialization.However,the prepared WO₃films and devices still have many problems in the improvement of electrochromic performance.Improving the shortcomings of long coloring/fading time and poor stability is of key significance for the further development of excellent performance and multifunctional electrochromic materials.At present,the method of nanometerization and composite of WO₃itself is an effective means to improve the performance.The construction of nanocomposite materials can shorten the ion diffusion path,increase the effective ion contact area,and achieve the purpose of improving the electrochromic performance.Polyoxometalates（POMs）have excellent redox properties and show great application potential in the field of electrochromism.Combining WO₃nanoparticles with polyoxometalates can improve the shortcomings of WO₃nanoparticles in terms of electrochromic properties.The work of this paper improves the electrochromic properties of WO₃nanoparticles by selecting different types of tungstophosphate to modify WO₃nanoparticles.The WO₃/tungstophosphate composite film is prepared by the layer-by-layer self assembly method（Lb L）,using UV-vis spectroscopy（UV-vis）,X-ray photoelectric spectrometer（XPS）,scanning electron microscopy（SEM）and cyclic voltammetry（CV）,and the electrochromic properties of composite films were studied by electrochemical test.The structure,morphology and electrochemical performance of the composite film were characterized.The research content is as follows:1.The classic Keggin-type tungstophosphate H₃[α-PW₁₂O₄₀](PW₁₂)and WO₃nanoparticles nanocomposite film is prepared by the sol-gel method and the layer-by-layer self assembly method.The preparation process is simple and easy to operate.WO₃nanoparticles modified with tungstophosphate showed a larger contact area and improved electrochromic performance.However,the stability is not satisfactory,which is related to the types of tungstophosphate and electrolytes selected.2.The electrochromic performance of tungstophosphate in the H⁺-based electrolyte is better than that in the Li⁺-based electrolyte,but the H⁺-based electrolyte will damage the metal oxide electrode,which is not conducive to the assembly of electrochromic devices and the actual application.Select three kinds of vanadium with good electrochemical activity to replace Dawson-type tungstophosphateα-K_6+n[P₂W_18-nV_nO₆₂]·18H₂O（n=1,2,3）(P₂W₁₇V,P₂W₁₆V₂,P₂W₁₅V₃)and WO₃nanoparticles,comparing the electrochromic performance of three kinds of vanadium substituted modified WO₃nanoparticles composite films in Li⁺-based electrolytes,the stability of the three composite films is significantly improved.Because of P₂W₁₅V₃contains three V⁵⁺,it is easier to attract electrons,so[P₂W₁₅V₃/PEI/WO₃/PEI]₂₀composite film has the best performance and is assembled into an electrochromic device.3.Select Preyssler-type tungstophosphate K_12.5Na_1.5[Na P₅W₃₀O₁₁₀]·15H₂O(P₅W₃₀)with a large amount of negative charge and WO₃nanoparticles to compare the electrochromic performance of the composite film in H⁺-based and Li⁺-based electrolytes.The composite film showed improved electrochromic performance in Li⁺-based electrolytes,due to the synergistic effect of tungstophosphate and WO₃nanoparticles,which increased the ion transmission rate,and finally successfully assembled into an electrochromic device,which was color change from blue to colorless.This work can provide references for the development of WO₃/polyoxometalates composite films in the field of electrochromism.