Electrochemical behavior of lead in sulfuric acid solutions

The electrochemical behavior of the lead electrode has been studied by cyclic 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 accompany the main reduction peak. The presence of a small, and previously unrecognized cathodic peak, preceding “anodic excursion” peaks, has been documented. Since all these peaks appear on the CVs only when the electrode potential is cycled in a wide potential range, limited by hydrogen and oxygen evolution, 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 well 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, formed at high positive potentials, is reduced (PbO2→PbSO4), a large increase 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 has 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 potential range confirmed that the reduction of PbO2 to PbSO4, which follows the formation of PbO2, is not related to the “anodic excursion” peaks and it 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 reduction to the metal, are avoided. Therefore, when the lead electrode is used as a positive electrode in a battery, no corrosion due to the exposure of the bare metal is expected.