On the electrodeposition mechanism of Pb on copper substrate from a perchlorate solution studied by electrochemical quartz crystal microbalance

摘要

Electrodeposition mechanism of lead on polycrystalline copper from a perchlorate solution in the presence of chloride ions was investigated. Electrochemical quartz crystal microbalance data including frequency and resistance were simultaneously recorded with cyclic voltammograms and current transients. The change of frequency and resistance shows that a rigid bulk film forms at the potentials more negative than −0.52 V saturated calomel electrode (SCE), exhibiting the overpotential deposits of Pb (OPD). However, at the potentials ranging from −0.38 to −0.43 V SCE, a monolayer of lead as the underpotential deposit of Pb (UPD) is formed. The measured real mass of the OPD of Pb compared to the charge passed through the cell elucidates the formation of Pb (II). The magnitude of the applied overpotential has considerable effect on the growth of the OPD of lead. The Pb OPDs formed at the lower overpotentials (or applied potentials in a range of −0.54 to −0.58 V SCE) show slight positive deviation of the electrochemical equivalent (M) of Pb (II). We ascribe this evidence to the possible incorporation of adsorbed/alloyed elements like chlorine in the film composition. At the higher overpotentials (or applied potentials of negative than −0.58 V SCE), the ratio starts to decrease, mainly due to the hydrogen evolution associated with the possible morphology change of deposit. Our results also show that the nucleation and growth of Pb OPD can be described with the instantaneous mechanism based on Scharifker–Hills prediction with nondimensional plots.