ELECTROCHEMISTRY OF YB3+ AND EU3+ AT NAFION MODIFIED ELECTRODES

The influence of the electrodeposition of a thin mercury film on the voltammetric behaviour of Yb3+ and Eu3+ incorporated by ion-exchange in Nation® coated glassy carbon electrodes is examined. A significant role of the nature of the electrode material is observed only in the case of Yb3+ and the improvement in the reversibility and reproducibility of the voltammograms observed after mercury deposition is attributed to the higher overpotential required for hydrogen evolution on mercury. No such effect is observed in fact in the case of Eu3+, which is reduced at far less negative potential values than Yb3+ and, in this case, reversible and reproducible voltammetric patterns are obtained at both modified electrodes. The detailed analysis of the ion-exchange process demonstrates that mercury deposition does not cause deterioration of the ion-exchange properties of the Nation coating, while the nature of the supporting electrolyte cations examined (Li+, Na+, K+, Rb+, NH+4, tetraethylammonium) proves to influence significantly both the extent and rate of incorporation. The ion-exchange distribution and selectivity coefficients of Nation for the two rare earth cations studied are also reported together with the relevant apparent diffusion coefficients. © 1990.