Electrodeposition Of Metals From Amide Based Room Temperature Molten Salts

Two kinds of room temperature molten salts were used in this paper:urea-acetamide(or butyramide)-LiBr and AlCl3-butyramide.The former is used as the medium for electrodeposition of silver and aluminum,and the later is used for aluminum electrodeposition.The electrochemical behavior of silver and aluminum in the molten salts were investigated by Cyclic Voltammetry,chronoamperometry and potentiostatic techniques.Also the structure of molten salts was determined by Raman spectroscopy.It was found that the reduction of Ag(I)to Ag on tungsten electrode is an irreversible process in the urea-acetamide-LiBr(36.6mole%-52.8mole%-10.6mole%)molten salt.Chronoamperometry experiments presented that the nucleation mechanism of silver on the tungsten electrode is controlled by combination of diffusion and charge transfer process,which will turn to instantaneous nucleation under diffusion control with increasing of overpotential and temperature.The as-prepared silver nano-particular films are SERS active,and the enhancement factors are approximately 105?106.The homogeneous,free flowing liquid can be formed within the molar ratio range of AlCl3/butyramide from 0.8 to 1,7 at room temperature,while the molar ratio range of AlCl3/(butyramide+urea)from 0.8 to 1.7 when adding urea and LiBr.Raman spectra showed that both AlCl4-and Al2Cl7;complexes can be found in above amide-based molten salts,and the contents of two chloroaluminates are related to the molar ratio of AlCl3/butyramide.Al2Cl7-complex can be found within a molar ratio greater than 1.0 in AlCl3-butyramide system,only Al2Cl7;is found with a molar ratio of 1.7.After the lithium halides(LiX,X=F,Cl,Br)were added,the content of AlCl4-increases and the content of Al2Cl7-will decreases.The reduction of Al(III)to A1 occurs in the form of Al2Cl7-;complex which is the electroactive ion in two kinds of AlCl3-butyramide systems,and it can be described as 4 Al2Cl7-+3e-?Al+7 AlCl4-.The content of Al2Cl7-increases with the molar ratio of AlCl3/butyramide increasing,and the reduction onset potentials of Al(III)shift toward more positive values,indicating that Al(III)are easier to be reduced.XRD and SEM-EDS analysis revealed that aluminum films have the properties of high purity.Lithium halides are conducive to the formation of the density aluminum with fine grains,and promote the transformation of the preferred orientation direction from(111)to(200),especially for LiCl.