Preparation And Study Of Prussian Blue And Its Analogs Electrochromic Films

Electrochromic materials can change optical characteristics(transmittance,reflectance or absorptivity)with the change of applied voltage.Because the adjustable spectral range includes visible light and near-infrared band,electrochromic materials have application potential in smart window,display and camouflage.Prussian blue analogs(transition metal hexacyanoferrate,M_THCF)are open-framework compounds composed of Fe^?–C?N–M_T units,and Prussian blue(iron hexacyanoferrate,Fe HCF,M_T=Fe)is the most famous.Fe HCF film can realize a reversible change from blue to colorless under applied voltage.Also,Fe HCF film has been widely studied due to its harmless properties and easy preparation in large areas.Different M_THCFs can be obtained by replacing M_T with Cu,Ni,Zn and other transition metal elements.Starting from Fe HCF film,the electrochromic performances and electrochemical properties of molybdate hexacyanoferrate(molybdate hexacyanoferrate,Mo OHCF,M_T=Mo O₃)film and zinc hexacyanoferrate(zinc hexacyanoferrate,Zn HCF,M_T=Zn)film,as well as the relationships between crystal structure and components,were fully studied.On this basis,the RGBY film,which can realize reversible color change of red,blue,green and yellow under applied voltage,was prepared by coelectrodeposition of Fe HCF and Mo OHCF.Furthermore,in order to assemble electrochromic device without affecting the color characteristics of the RGBY film,white Zn HCF film was prepared by two-step electrodeposition method.Zn HCF film has good ion storage performance and cycling stability,and no color change occurs in the process of electrochemical redox.Using Zn HCF film as the counter electrode significantly improves the cycling life of RGBY electrochromic device.Finally,a concept of electrochromic spectral bionic leaf(electrochromic spectral bionic leaves,ECSBL)is proposed.Fe HCF powder is used as electrochromic material to realize the ECSBL that can change reversibility in green and yellow,and have spectral characteristics similar to those of plant leaves.The specific research contents of are as follows:(1)The electrochemical properties,electrochromic performances and the relationship between lattice structure and composition of Fe HCF thin film prepared by electrodeposition was studied to reveal the poor electrochromic performances and cycling stability caused by incomplete oxidation due to insufficient alkali cation ion content in Fe HCF film during electrochemical redox.Mo OHCF film which can change reverently in reddish brown and light yellow was prepared by electrodeposition method.It was confirmed that Mo OHCF film had complementary electrochromic performances with Fe HCF film and abundant alkali cation ion content.In order to obtain excellent Zn HCF film,a new two-step electrodeposition method was developed.Zn HCF film prepared by this method is white and the color does not change with applied voltage.In additon,it has excellent cycling stability(>10000 cycles),and is suitable for the ion storage layer in electrochromic device.(2)The RGBY film which can change reversibly between red,blue,green and yellow was prepared by coelectrodeposition method.The RGBY film is composed of Fe HCF and Mo OHCF at nanoscale,and therefore shows the electrochromic performances of both.In addition,Mo OHCF in RGBY film provides sufficient alkali cation ion for Fe HCF,which is conducive to the full progress of Fe HCF electrochemical redox process and improves the electrochromic performance of RGBY film.The absorptivity adjustment range of RGBY film at 730 and 440 nm are 0.81 and 0.43,respectively.The response time of RGBY films varies from 3 to 30 s between colors and maintains its optical properties without significant decay during 1000 cycles.Furthermore,a pixelated RGBY film was prepared to demonstrate the feasibility of electrochromic pixelation display.RGBY/Zn HCF electrochromic device is prepared and clearly shows four typical colors of red,blue,green and yellow.It can maintain 74.4%of its initial performance after 3600 s using.(3)Based on the principle of color mixing,a ECSBL with Fe HCF as electrochromic material and iron oxide yellow as color filler was developed.The effects of Fe HCF powder prepared by different methods on the spectral characteristics of the ECSBL were studied,and it was proved that the bionic leaf prepared by single crystal Fe HCF powder based on hydrothermal growth had the optimal spectral characteristics.The ECSBL can change reversibly between green(0.5 V)and yellow(-0.5 V).In green,the spectral similarity with green leaves reaches 0.51.In yellow,the spectral similarity with yellow leaves reaches 0.69.