Study On Electrodeposition Characterise Of Lead On Copper Electrode

Lead electrodeposition has been a subject of interest in the past due to its extensive application in the relevant fields. For example, purity lead was widely used in lead-acid battery. High purity active lead was applied in the production of semiconductors and the fabrication of electro-chromic devices. On the other hand, lead long-term toxicity is considered a very relevant environmental problem and thus other works have been dedicated to the study of lead electrochemical deposition either for the direct detection of the metal or for its recycling.Many research on lead electrodeposition have been reported, yet, the characteristic and morphological real-time evolution of the Pb UPD layer had not been reported. Cyclic voltammetry (CV), chronoamperometry (CA), scanning electronic microscope (SEM), X-ray energy dispersive spectroscopy (EDS), in situ spectroscopic ellipsometry (SE) and quantum chemical caculations were performed to explore lead electrodeposition on polycrystalline Cu surface and its mechanism under different scan rate, Pb²⁺ concentration, kinds of anion additive agent, scan potential and deposition time conditions. The main results obtained are as follows:Pb underpotential-deposition (UPD) on polycrystalline Cu proved to be an irreversible two-dimensional nucleation and growth process. The coverage of Pb UPD gradually increased and the increasing rate goes up during cathodic voltammetry scan. Thin Pb deposition layer has already acquired during Pb UPD process, so the Cu substrate is not optically ignored during Pb UPD process.Pb UPD peak potential turn positive with the increasing Pb²⁺ concentration. This is because as Pb²⁺ concentration increases equilibrium electrode potential become increasingly positive. Along with that, Pb UPD peak potential positively shift.Cl- could enhance the kinetics of Pb UPD, which might be associated with chloride ions could occur specific adsorption on copper electrode surface. Specific adsorption of Cl- on Cu substrate madeψ1 potential become negative, which promoted Pb²⁺ with positive charge reduction on the electrode surface. CH₃COO^- enhance the kinetics of Pb UPD on Cu(100), but at the same time it inhabit the kinetics of Pb UPD on Cu (111), this is because CH₃COO^- had preferential adsorption properties on Cu(100), and enhance Pb²⁺ reduction reaction occurred on Cu (100) crystal face.The analyses of SEM support the view of a 3D growth of Pb over-potential deposition (OPD) on Cu substrate. Progressive nucleation is observed for Pb OPD from KNO3 solution. But in the presence of Cl- or CH₃COO^-, a tendency towards instantaneous nucleation is revealed, signifying that Cl- or CH₃COO^- speed nucleation rate of Pb OPD on Cu substrate. The order of the anion enhance strength is Cl- > CH₃COO^-.Experimental results obtained by combined in situ SE and chronoamperometry studies of Pb OPD on Cu substrate reveal that Pb film thickness greater than 40nm can be considered as optically bulk.