Electrochemical behavior of lead in sulfuric acid solutions

The electrochemical behavior of the lead electrode has been studied by cycl ic voltammetry (CV) in sulfuric acid solutions, with concentrations ranged from 0.05 to 5 M. Also, the effect of a sweep rate, the range of potential polarisation and temperature has been examined. Special attention has been paid to unusual anodic processes, i.e., "anodic excursion" peaks that accom pany the main reduction peak. The presence of a small, and previously unrec ognized cathodic peak, preceding "anodic excursion" peaks, has been documen ted. Since all these peaks appear on the CVs only when the electrode potent ial is cycled in a wide potential range, limited by hydrogen and oxygen evo lution, it has been proposed that they are related to the reduction of the lead dioxide to the bare metal, occurring at high negative potentials. The presence of a small reduction peak preceding "anodic excursion" peaks, as w ell as the presence of the main reduction peak of the lead dioxide has also been related to the exposure of the bare metal. When the lead dioxide, for med at high positive potentials, is reduced (PbOz(2) --> PbSO4), a large in crease of the molar volume is expected and, as a result, the surface cracks , exposing the bare metal. These parts of the surface are then oxidized in "anodic excursion" peaks. To repeat these redox processes, the electrode ha s to be reduced again at high negative potentials, i.e., at the conditions when reduction to the metal occurs. The CVs performed only in a positive po tential range confirmed that the reduction of PbO2 to PbSO4, which follows the formation of PbO2, is not related to the "anodic excursion" peaks and i t also means that no cracks of the surface occur, as long as the potential cycling of the electrode to high negative potentials, and the resulting red uction to the metal, are avoided. Therefore, when the lead electrode is use d as a positive electrode in a battery, no corrosion due to the exposure of the bare metal is expected. (C) 2000 Elsevier Science S.A. All rights rese rved.