Electrodeposition Of Chromium In Deep Eutectic Solvent

Deep eutectic liquid was prepared from choline chloride（ChCl）,ethylene glycol（EG）and urea（Urea）.The electrodeposition of trivalent chromium was carried out,the spatial configuration and functional groups of raw materials and ionic liquids were studied by IR,the conductivity of ionic liquids was tested by conductivity meter,the electrochemical window of ionic liquids,the electrochemical behavior of Cr（Ⅲ）,the reversibility of redox reaction of Cr（Ⅲ）and the reaction control method were tested by CV Formula and kinetic parameters are systematically studied and analyzed;the electrocrystallization mechanism of Cr（Ⅲ）electrodeposition is studied and analyzed by using chronoamperometric curve（CA）;the electrodeposition process,micro morphology and element composition of trivalent chromium coating are studied and analyzed by using scanning electron microscope（SEM）and EDS;the metal coating is studied and analyzed by using X-ray diffraction（XRD）The phase composition of the coating was studied and analyzed;the mechanism of the additives was studied and analyzed by UV vis;the surface composition of the coating was analyzed in detail by X-ray photoelectron spectroscopy（XPS）.The physical and chemical properties of ionic liquids and the electrodeposition of metals are studied and analyzed by the above test and characterization methods.According to the research results,the following conclusions are drawn:（1）The main coordination forms of Cr（Ⅲ）in ionic liquids are[Cr（H₂O）₃Cl₃],[Cr（H₂O）₂Cl₄]^-1,which can be used as the first ligand to destroy the stable octahedral structure of trivalent chromium.（2）The results of cyclic voltammetry show that the reduction of Cr（Ⅲ）in ChCl-EG and ChCl-urea is a diffusion controlled and irreversible process.The reduction of Cr³⁺→Cr²⁺,Cr²⁺→Cr⁰ is carried out in two steps.In addition,urea,as the second ligand in the ChCl-urea system,participates in the reduction of Cr（Ⅲ）,making the complex to[Cr（Urea）_m（H₂O）_nCl₃]^3-m.（3）The chronoamperometric curves show that the nucleation process of Cr（Ⅲ）in ChCl-EG and ChCl-urea system is three-dimensional（3D）instantaneous nucleation.It is found that the peak current density increases with the increase of temperature,and the nucleation process changes accordingly.（4）Gaussian 16W program was used to optimize the calculation of the corresponding metal complexes in the system,and the stable structure,vibrational spectrum,front-line orbit,NBO and other electronic structure information of the trivalent chromium complexes that may exist in the ChCl-EG system were analyzed,such as[Cr（H₂O）₆]³⁺,[Cr（H₂O）₃Cl₃],[Cr（H₂O）₂Cl₄]^-1and[Cr（H₂O）₂CHOOCl₃]^-.