Electrodeposition Of Silver And Silver Alloy In Choline-based Deep Eutectic Solvents

In recent years,deep eutectic solvents（DESs）have attracted extensive attention from researchers due to their unique advantages such as non-toxicity,low cost,and high purity.DESs are easy to prepare,harmless to nature,and exhibit similar physical properties to ionic liquids（ILs）.In this paper,Choline Chloride（（ChCl）-Urea）was used as the base solution to study the electrochemical behavior mechanism of silver and silver tin electrodeposition,and the influence of the additive NH₄Cl on the electrodeposition of silver was analyzed.Use infrared（Fourier transform-infrared spectroscopy,FT-IR）to study the functional groups and spatial configuration of the base fluid;use a conductivity meter to conduct conductivity test research on eutectic ionic liquids;use cyclic voltammetry（Voltammetry,CV）Conduct electrochemical testing and research on basic liquid and metal ions;use Chronoamperometry（CA）to study the growth and nucleation methods of silver and silver tin;use Scanning electron microscopy（SEM）and energy dispersive spectrdmeter,EDS)to study the microscopic morphology of the coating obtained by electrodeposition and its constituent elements;use X-ray diffraction（XRD）to study the phase composition of the coating;use Tafel test to study the corrosion resistance of the coating;Use X-ray Photoelectron Spectroscopy（XPS）to study coating elements.The research results are as follows:Silver ion is a one-step reduction process in the eutectic solvent of choline chloride-urea（ChCl-Urea）.The equilibrium potential Eeq of the Ag（I）/Ag（0）electrode system in the choline chloride-urea（ChCl-Urea）eutectic solvent is-0.112V（relative to the silver reference electrode）,and the exchange current density J⁰=2.92±0.2μcm^-2,transmission coefficientα=0.16±0.2.The results of transient analysis of potentiostatic current density show that the individual contribution to the total current is j（t）:the three-dimensional nucleation of silver with controlled diffusion j_3D-dc（t）and the proton reduction reaction j _PR（t）.The integral data results of the j-t diagrams of these contributions indicate that the amount of charge in each process can be controlled by changing the potential.SEM,EDS and cross-section results show that silver grows in dendrites under-0.97V potential,and its thickness is 22.98μm.Moreover,XPS analysis results show that the silver coating is composed of Ag₂O and Ag.Silver ion is also a one-step reduction process in choline chloride-ethylene glycol （ChCl-EG）eutectic solvent.At a temperature of 25°C,the nucleation and growth of silver deviates from the theoretical curve,which does not conform to three-dimensional instantaneous nucleation or three-dimensional continuous nucleation;at 50°C,the nucleation and growth mode of silver appears as three-dimensional instantaneous nucleation;at 80°C,The growth mode tends to three-dimensional continuous nucleation.The silver coating obtained by electrodeposition on the nickel substrate grows in the shape of a leaf,and the fine granular coating is obtained by electrodepositing on the brass.The combination of silver and the brass substrate is closer and the particles are more dense.Using ChCl-Urea-0.1mol/L Sn Cl₂·2H₂O-0.1mol/L Ag NO₃ system to electrodeposit silver and tin,when silver and tin coexist in the ionic liquid,only one cathodic deposition peak appears,and its peak current is-11.1μA·cm^-2,the micro morphology of the coating obtained by electrodeposition under different potential conditions are loose pine branches.In the ChCl-Urea-0.1mol/LAg NO₃ system,0.1mol/L、0.2mol/L、0.5mol/L NH₄Cl was added respectively,and the reduction process of silver ions was an irreversible process controlled by diffusion.Adding different NH₄Cl concentrations does not change the preferred orientation of silver crystal growth.