MECHANISM AND KINETICS OF THE REDUCTION OF IN(III) IONS AT A POLYCRYSTALLINE GOLD ELECTRODE FROM HIGHLY CONCENTRATED ZNCL2 SOLUTIONS

The mechanism of the cathodic reduction of In(III) at gold has been st udied by rotating disc and ring-disc voltammetry in highly concentrate d aqueous ZnCl2 solutions. At concentration of the base electrolyte hi gher than 7 mol dm-3, the voltammetric curves recorded at the disc ele ctrode split into two well-separated waves which correspond to the suc cessive charge transfer reactions: In(III) + 2e- --> In(I) and In(I) e- --> In. By the use of coulometric and potentiometric techniques, t he formal potentials of the In(III)/In(I), In(III)/In and In(I)/In red ox couples as well as the equilibrium constants of the reproportionati on reaction In(III) + 2 In half arrow left over half arrow right 3 In( I) has been determined and discussed. The kinetic parameters of the ln (III)/In(I) electrode reaction have been also evaluated and discussed.