A COMPARATIVE-STUDY OF THE ELECTROCHEMISTRY OF TIN IONS IN THE ZNCL2-DEGREES-C(XNACL MIXTURES AT 450)

The electrochemistry of Sn(II) was studied with voltammetry, chronopot entiometry and chronoamperometry at tungsten (W) and glassy carbon (GC ) electrodes in the acidic and basic zinc chloride + sodium chloride ( ZnCl2 + 2NaCl, 2ZnCl(2) + 3NaCl, ZnCl2 + NaCl) molten salts at 450 deg rees C. The voltammograms showed peaks attributed to the presence of t hree 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 powe r when the amount of ZnCl2 increases in the melt, and this seem to ari se from differences in the solvation of the metal ions in basic and ac idic melts. The electrodeposition of tin was uncomplicated at W but on GC was complicated by nucleation. In addition the voltammograms corre sponding to the electrochemical Sn(IV)/Sn(II) exchange have a better d efinition on GC than on W, on which some waves were accompanied by cur rent oscillations due to the formation of volatile SnCl4. The two elec trochemical exchanges were found to be quasi-reversible, and the value s of the kinetic parameters, k(0) and alpha for both reactions were ob tained. Mass transport towards the electrode is a simple diffusion pro cess and the diffusion coefficient D-Sn(II) was calculated. (C) 1997 E lsevier Science S.A.