Electrochemical deposition of the first Cd monolayer on polycrystalline Pt and Au electrodes. An Upd study

Abstract

The underpotential deposition of Cd on polycrystalline Pt and Au was studied by voltammetry at stationary and rotating ring-disc electrodes. On Pt, the Cdads dissolution peaks overlap those related to the oxidation of Hads, thus hindering the precise evaluation of desorption charges. A model proposed to calculate such charges from voltammetry at stationary electrodes revealed a value of 285 μC cm-2 for the monolayer dissolution, which corresponds to a coverage of 90% with Cdads presenting an electrosorption valence of 0.5. Rotating ring-disc experiments fully confirmed such values. The misfit between atomic radii of Cd and Pt justifies the less-than-100% coverage. On the other hand, on Au, the absence of Hads simplifies the procedure for determination of dissolution charges for the Cd monolayer. Here, a value of only 41 μC cm-2 was calculated, which corresponds to a maximum coverage of 15%, with the electrosorption valence of 0.5. The results obtained in the collecting experiments with the rotating electrode are in complete agreement with those values.