Chronoamperometrische untersuchung von bleiniederschlägen auf goldelektroden

Abstract

The reduction of lead from aqueous solutions on the surface of gold electrodes is studied chronoamperometrically using a thin-layer technique employing a chamber type cell. The current balance of the deposition or dissolution of lead on the electrode is verified by coulometrical evaluation of the chronoamperograms. In the binary system Pb-Au there exist at room temperature two intermediate phases, namely Au 2Pb and AuPb 2. The lead deposited on gold forms at first a metallic monolayer, defined as a layer of electrically neutral lead atoms at the electrode-electrolyte interface, the deposit having the appropriate thickness of one atomic diameter of lead. The activity isotherm of lead, a Pb, depends upon the coverage of the electrode within the mono-layer region. The existence of the unsaturated (submonoatomic) coverage of the gold electrode leads to the splitting of the cathodic current transient into a so-called pre-wave region, within which the activity of the metal is less than unity, and a main peak with unit activity of the electrodeposited depolarizer. The formation of Au-Pb alloys only happens when the lead coverage reaches unit activity. The alloying of the lead deposited cathodically in the main peak gives rise during the anodic stripping to two new dissolution peaks of unsaturated lead layers, besides the current maxima of the main peak and the prewave region. As opposed to the prewave peaks, the shape and current-integral values of these intermediate peaks are found to be functions of various experimental parameters, for instance of the time interval between cathodic deposition and anodic stripping of the lead deposit.