Study of underpotential deposition of metals using the quartz crystal microbalance

Abstract

Underpotential deposition (UPD) of the metals lead, cadmium and thallium, onto a polycrystalline silver substrate, has been studied. The amount of charge and mass transferred during the UPD process is examined, in situ, with voltammetry and with the quartz crystal microbalance (QCM), simultaneously. The measured charge and mass consumptions show good agreement with the expected values for Cd 2+/Ag up to 1.5 monolayers (ML) and for Pb 2+/Ag up to 0.7 ML. An anomaly occurs in the UPD of Tl +/Ag. While the measured mass change is consistent with the expected value, each Tl ion seems to contribute approximately two charges upon adsorption before the completion of the first UPD layer instead of one. In the second UPD layer the value of discharge returns to the valence number z = 1.