Radiotracer study of the specific adsorption of HCO3- ions on a platinum electrode

The adsorption of HCO3- ions was studied by a radiotracer method using C-14 labelled Na2CO3 (c less than or equal to 10(-2) mol dm(-3)) in the presence of a great excess of ClO4- ions (0.5 mol dm(-3) NaClO4 supporting electrolyte). A reversible adsorption of labelled species was found at pH values above 9. The voltammetric and differential voltradiometric behaviour of a Pt electrode in labelled carbonate solution shows a parallelism indicating the adsorption competition between hydrogen and carbonate species. Increasing the pH of the solution leads to a significant decrease in the extent of the adsorption of the labelled species. This phenomenon can be explained either by the transformation of adsorbing HCO3- into non-adsorbing CO32- molecules or by the increasing role of the competitive adsorption of OH- ions at higher OH- concentrations. At pH values lower than 9 the slow strong chemisorption reported in the literature can be easily followed by the radiotracer technique. (C) 1998 Elsevier Science S.A. All rights reserved.