On the alloy formation in the course of upd of Cd on gold

The alloy formation in the course of underpotential deposition (upd) of Cd on gold from HClO4 supporting electrolyte was studied by coupled voltammetric and electrochemical microbalance techniques. The experimental results were discussed in the light of data obtained from a radiotracer study of induced adsorption of anions. It has been demonstrated that the alloy formation is well reflected in the results of EQCM measurements and the changes in the induced adsorption of anions. The alloy formation and/or its dissolution is a slow process in comparison with the time scale of the usual voltammetric measurements (sweep rates from 5 to 100 mV s−1). The results of the long-time polarization experiments (lasting e.g. 30–60 min) have provided evidence for the continuous increase of the amount of underpotentially deposited Cd atoms during reduction and the slow dissolution of the embedded Cd accompanied by surface roughening during oxidation. These observations can be explained by a turnover process between the adsorbed Cd and the underlying Au atoms, as well as by a solid-state diffusion of these atoms through the alloyed phase.