Adsorption and underpotential deposition of lead at electrodeposited platinum electrodes

Abstract

The underpotential deposition (UPD) of lead at electrodeposited platinum electrodes has been studied using the electrochemical quartz crystal microbalance (EQCM). At higher values of [Pb 2+] mass responses accompanying cyclic voltammetric experiments reveal large mass changes as the UPD deposit develops and is stripped but, when [Pb 2+] is low, subtraction of the response seen for platinum in the absence of UPD reveals that the UPD process is not at equilibrium under the conditions used and continues developing over the potential range between 0.45 V and −0.3 V. Mass responses to simple injection experiments reveal the presence of adsorbed Pb 2+ on oxidized electrodes. Coverage of Pb ads 2+ increases with potential between 0.9 V and 1.2 V and approaches 0.09 when [Pb 2+]= 2 mM and E = 1 V. UPD of lead at platinum thus involves a combination of discharge of adsorbed species and reduction of lead ions from solution. UPD coverages were determined over a wide range of potential from mass transients resulting from potential steps and the injection of Pb 2+ into the electrolyte. The isotherm obtained agrees well with previously published data and demonstrates that EQCM mass data can be used for the estimation of UPD coverages.