A comparative study of the electrochemistry of tin ions in the ZnCl2 + xNaCl mixtures at 450°C

Abstract

The electrochemistry of Sn(II) was studied with voltammetry, chronopotentiometry and chronoamperometry at tungsten (W) and glass carbon (GC) electrodes in the acidic and basic zinc chloride + sodium chloride (ZnCl 2 + 2NaCl, 2ZnCl 2 + 3NaCl 2 + NaCl) molten salts at 450°C. The voltammograms showed peaks attributed to the presence of three oxidation states of tin, i.e. 0, II and IV, in all the mixtures. Both Sn(IV)/Sn(II) and Sn(II)/Sn systems increase their oxidation power when the amount of ZnCl 2 increases in the melt, and this seem to arise from differences in the solvation of the metal ions in basic and acidic melts. The electrodeposition of tin was uncomplicated at W but on GC was complicated by nucleation. In addition the voltammograms corresponding to the electrochemical Sn(IV)/Sn(II) exchange have a better definition on GC than on W, on which some waves were accompanied by current oscillations due to the formation of volatile SnCl 4 . The two electrochemical exchanges were found to be quasi-reversible, and the values of the kinetic parameters, k 0 and α for both reactions were obtained. Mass transport towards the electrode is a simple diffusion process and the diffusion coefficient D Sn( II ) was calculated.