Study On Electrodeposition Behavior And Performance Of Chromium In ChCl-based Ionic Liquid

Choline chloride（ChCl）based ionic liquids（ILs）were used as a solvent system to analyze the electrochemical behavior and properties of trivalent chromium.The effects of H₂O and Li Cl as additives on electrochemical behavior and performance were studied.Ionic liquid conductivity is tested using a conductivity meter;Fourier transform-infrared spectroscopy（FT-IR）was used to determine the functional groups and spatial configurations in synthetic raw materials（ChCl,EG,CrCl₃·6H₂O）and ionic liquids.The surface tension of ionic liquids was determined using the capillary rise method;Ultraviolet-visible spectroscopy（UV-Vis）was used to determine the initial complex form of trivalent chromium in ionic liquids and the change of complexes after adding additives.Cycle Voltammetry（CV）was used to determine the electrochemical window,electroreduction step and electrochemical reduction behavior of chromium in ionic liquids.The nucleation mechanism of chromium in ionic liquids was determined by chronoamperometry（CA）.Scanning electron microscopy（SEM）and the supporting energy dispersive spectrdmeter（EDS）were used to observe the topography of the coating and determine the elemental composition;The Tafel curve was used to analyze the corrosion resistance of the coating.The conclusions from the above tests are as follows:In the ChCl-CrCl₃·6H₂O system:（1）With the increase of temperature,the conductivity of ionic liquids gradually increases.And with the increase of water content in the ChCl-CrCl₃·x H₂O system,the conductivity of ionic liquids also increases.（2）In the CrCl₃·6H₂O system,trivalent chromium ions belong to single-step irreversible reduction(Cr³⁺→Cr).（3）By comparing the infrared spectrum of ionic liquid raw materials（ChCl,CrCl₃·6H₂O）with the infrared spectrum of ionic liquid.It can be seen that a large number of hydrogen bonds are formed in the synthesis of ionic liquids,and no superfluous complexes are formed.（4）After using H₂O as an additive,the electrodeposited chromium coating is more refined than the coating obtained by pure ionic liquid,and the corrosion resistance is enhanced.In the ChCl-EG-CrCl₃·6H₂O system:（1）The UV-Vis spectrum analysis shows that in the ChCl-EG-CrCl₃·6H₂O system,the initial complex forms of the solution are[Cr（H₂O）₂Cl₄]^-,There are two kinds of Cr（H₂O）₃Cl₃],of which[Cr（H₂O）₃Cl₃]is the more dominant complex.After adding Li Cl,the complex species in the electrolyte are[Cr（H₂O）₃Cl₃]and[Cr（H₂O）₂Cl₄]^-,of which the content of[Cr（H₂O）₂Cl₄]^-is more.（2）It is known from the cyclic voltammetry curve that in the ChCl-EG-CrCl₃·6H₂O system,the trivalent chromium ion belongs to a two-step reduction(Cr³⁺→Cr²⁺→Cr),and the addition of Li Cl does not change its reduction step.（3）According to the chronoamperometry curve fitting,in the ChCl-EG-CrCl₃·6H₂O system,the nucleation mode of trivalent chromium belongs to three-dimensional instantaneous nucleation,and the addition of Li Cl does not change its nucleation mode.（4）After using Li Cl as an additive,the thickness of the coating obtained is increased compared with that of pure ionic liquid coating,and the content of elemental chromium is increased.