The electrochemical behaviour of UO22+ solutions at Nafion®-coated glassy carbon electrodes has been examined and compared with the behaviour observed at uncoated electrodes. At pH 2.4, two reduction processes are always observed at both electrodes; however, the mechanism involved in the first process is affected strongly by the presence of the polymeric coating. While in homogeneous solution the first reduction product UO2+ is quite stable and reacts only with electrogenerated UIII, in the presence of Nafion the local high concentration of H+ inside the coating causes it to disproportionate. The relevance of the ion exchange competition between H+ and Na+ to this reaction is proved.
The influence of the applied potential on the rate and extent of incorporation was also studied. The ion exchange characteristics of Nafion for the different oxidation states generated by reducing UO22+ have been compared qualitatively and the selectivity coefficients for UIV and UVI determined. The values obtained indicate a selectivity of Nafion for UIV about 20 times higher than that for UVI, so that preconcentration from UO22+ dilute solutions can be achieved by applying a suitable reducing potential at the modified electrode.