ELECTROCHEMICAL DEPOSITION OF THE FIRST CD MONOLAYER ON POLYCRYSTALLINE PT AND AU ELECTRODES - AN UPD STUDY

The underpotential deposition of Cd on polycrystalline Pt and Au was s tudied by voltammetry at stationary and rotating ring-disc electrodes. On Pt, the Cd-ads dissolution peaks overlap those related to the oxid ation of H-ads thus hindering the precise evaluation of desorption cha rges. A model proposed to calculate such charges from voltammetry at s tationary electrodes revealed a value of 285 mu C cm(-2) for the monol ayer dissolution, which corresponds to a coverage of 90% with Cd-ads p resenting an electrosorption valence of 0.5. Rotating ring-disc experi ments 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 mu C cm(-2) was calculated, which corresponds to a maximum coverage of 1 5%, with the electrosorption valence of 0.5. The results obtained in t he collecting experiments with the rotating electrode are in complete agreement with those values.