Effects Of Additives On Electrodeposition Behavior Of Silver And Silver Alloys In ChCl-EG

In recent years,Deep eutectic solvents（DESs）have attracted a lot of attention due to their unique advantages such as low cost,high purity and non-toxicity.It is also widely used in the field of electrodeposition of metals due to its wide electrochemical window,high stability,high solubility and good electrical conductivity.In this paper,ChCl-EG Deep eutectic solvent is used as electroplating solution for silver and silver-nickel alloy plating.5-5 dimethylhydantoin（DMH）was selected as the complexing agent for silver,and four additives,polyvinylpyrrolidone（PVP）,benzotriazole（BTA）,potassium bromide（KBr）and thiourea（Thiourea）,were used to investigate the effect on the electrochemical behaviour of silver electrodeposition.The effect of different combinations of PVP and sodium saccharin on the electrochemical behaviour of silver-nickel alloys was investigated in depth and the mechanism of action of the additives was explored.The effect of base fluids and additives on the electrochemical behaviour of silver ions was studied using cyclic voltammetry（CV）.A study of growth nucleation using chronoamperometry（CA）.The effect of additives on the cathodic process of the plating solution was investigated using linear sweep voltammetry;differential capacitance curves were used to investigate the adsorption of additives on the electrode surface;polarization curves and electrochemical Impedance Spectroscopy（EIS）was used to study the corrosion resistance of silver-nickel plating in 3.5 wt.%Na Cl.The results of the study are as follows:（1）In this paper,DMH was selected as the coordination system for silver.And the formulation of ChCL-EG-DMH base solution was determined:Ag NO₃ 0.15 mol/L,DMH0.6 mol/L,p H=10,temperature 50°C,deposition potential-0.78 V.（2）The effects of four additives,PVP,BTA,KBr and Thiourea,on the silver electrodeposition behavior in ChCl-EG-DMH bodies were investigated.The results of cyclic voltammetric curves indicate that the reaction Ag⁺（?）Ag is reversible.By applying the Randles-Sevcik equation,the D₀ for Ag⁺（?）Ag is 6.291×10^-8cm²/s at room temperature and the D₀ value increases to 4.352×10^-6cm²/s at 70℃.The timing current results show that the addition of the additive did not change the nucleation pattern of the silver,which is consistent with instantaneous nucleation for t/t_m<1 and deviates from instantaneous nucleation for t/t_m>1.The addition of the additive shifts the deposition potential of the silver negatively,increasing the cathodic polarisation.The results of the differential capacitance curves show that KBr and PVP reduce the differential capacitance value by 1～10μF by adsorption on the electrode surface,thus changing the silver micromorphology.The adsorption behaviour of KBr on copper substrates was simulated using Material Studio software and the results showed that the cavity（fcc）was the most stable structure for the adsorption model.SEM results showed that KBr and BTA as additives significantly increased the thickness of the silver layer and that the thickness of70.96μm was well suited for decorative and functional use.XRD results showed that The addition of KBr additive resulted in a highly selective orientation of the crystalline surface of the silver deposited layer（111）,resulting in a highly selective orientation of the Ag（111）electrodeposited layer.（3）The effect of ChCl-EG-DMH on the electrodeposition behaviour of silver nickel in vivo was investigated using a combination of PVP 2 g/L and sodium saccharin 0.84 g/L additive.The combination of PVP 2 g/L and sodium saccharin 0.84 g/L additive showed the highest polarisation effect.The addition of the additive shifted the reduction peak negatively.The reduction process of silver-nickel ions is an irreversible process controlled by diffusion.When the additive was added the nucleation pattern was closer to the three-dimensional transient nucleation form.The corrosion resistance of the silver-nickel plating was investigated and it was found that the self-corrosion potential shifted right to-0.2473 V and the corrosion current density decreased to(8.6486×10^-6 A/cm²)an order of magnitude less with the addition of the additive,giving the silver-nickel alloy a higher corrosion resistance.