Study On Preparation Of Metals And Alloys By Electrodeposition In Deep Eutectic Solvent

Metal electrodeposition is a process in which metal ions are reduced and electrocrystallized on the surface of the cathode of the electrolytic cell by applying a voltage(current),and finally a metal layer is formed.Electrodeposition has the advantages of simple operation and low cost.Electrodeposition of metals and alloys is often carried out in aqueous systems or ionic liquids,but the aqueous system has hydrogen evolution reactions,and ionic liquids have problems such as toxicity and difficult biodegradation.As a new type of electrolyte system,deep eutectic solvent has the advantages of wide electrochemical window,low vapor pressure,easy preparation,biodegradability,etc.,and has broad application prospects in the field of metal electrodeposition.In this paper,two eutectic solvents,choline chloride-malonic acid and choline chloride-ethylene glycol are used as the basic electrolyte.Cyclic voltammetry and chronoamperometry were used to study the electrochemical reduction behaviors and nucleation methods of Bi,Sb,Sn,Te,and Cd in deep eutectic solvents.At the same time,single metal Bi,Sb,Sn,Te,Cd and CdTe,Sn-Sb alloys were prepared by constant potential electrodeposition method,and the electrodeposited products were characterized by SEM and XRD.Infrared spectroscopy and Raman spectroscopy were used to analyze the structure of the electrolyte and the existence of Bi3+,Sb3+,Sn2+,Te4+ and Cd2+ in the deep eutectic solvent.Studies have shown that through infrared spectroscopy,there are a large number of hydrogen bonds in these two deep eutectic solvents.Raman spectroscopy shows that Bi3+,Sb3+,Sn2+,Te4+,Cd2+Exist as complexes of[BiCl6]3-,[SbCl4]-,[SnCl3]-,[TeCl6]2-,[CdCl4]2-in deep eutectic solvents.The study of viscosity and conductivity shows that the viscosity and conductivity of the electrolyte are affected by the temperature of the system and the concentration of metal ions,which can be described by the Arrhenius formula.Cyclic voltammetry shows that the reductions of Bi3+,Sb3+,Sn2+,Te4+,and Cd2+in the corresponding system are all quasi-reversible processes controlled by diffusion,and the increase in temperature and increase the ion concentration to reduce the overpotential required for reduction.Chronoamperometry shows that at 343 K,the reduction of Bi,Sb,and Sn are all three-dimensional instantaneous nucleation controlled by diffusion.At 353 K,the reduction of Cd is a three-dimensional instantaneous nucleation controlled by diffusion.At 363 K,the reduction of Te at a low potential into a three-dimensional instantaneous nucleation controlled by diffusion,while at a high potential,it gradually develops in the direction of three-dimensional continuous nucleation.SEM shows that the deposition potential and deposition temperature have significant effects on the morphology of electrodeposited products.Increasing the Sb3+ concentration causes the morphology of the obtained Sn-Sb alloy deposition product to change from granular to dendritic crystals.Studies on the photoelectrochemical performance of CdTe thin films show that the CdTe thin films have good photoelectrochemical properties,respond to light signals sensitively,and have good periodicity and light response stability.Mott-Schottky analysis shows that increasing the concentration of Cd2+ changes the conductivity of the CdTe semiconductor film obtained by electrodeposition from p-type to n-type.