RADIOACTIVE LABELING STUDY OF BISULFATE ADSORPTION ON COPPER ADATOMS DEPOSITED ON THE GOLD ELECTRODE IN NEUTRAL MEDIA

The formation of (sub)monolayer coverages of electrodeposited copper on gold in neutral perchloric electrolytes and its effect on bisulfate adsorption has been studied. The anion surface concentrations obtained through radiochemistry have been correlated with current-potential curves for the copper electrodeposition process. The anion adsorption is reversible and accessible to thermodynamic treatment. The standard Gibbs energy of adsorption (DELTA-G0) and the energy of interaction between adsorbed species vary with the copper/gold ratio controlled via electrodeposition. The DELTA-G0 value ranges from -105 to -115 kJ mol-1. The lateral interactions, represented by the second virial coefficient in the virial adsorption isotherm, are relatively weak. The observed increase in bisulfate adsorption on gold covered with no more than 1.3 monolayers of copper is correlated with the change in the effective electronic work function (potential of zero charge) of the electrode. At theta-Cu exceeding 2, the bisulfate adsorption follows an adsorption pattern which is characteristic of solid polycrystalline copper.