Cyclic voltammetric behavior of the lead electrode in sodium sulfate solutions

Cyclic voltammograms (CVs) of the Pb electrode were obtained in Na2SO4 solutions as a function of starting potential, electrolyte concentration, voltage range and voltage scanning rate. The shape of the voltammograms was found to depend on the starting potential as well on the sweep number. This is probably due to changes in the activation state of the electrode surface. In the first sweep, the anodic portion of the voltammograms is characterized by a shoulder and three peaks as a result of the formation of PbSO4, PbO, PbO2 and transformation of PbSO4 to PbO2, respectively, on the electrode surface before the evolution of oxygen. On the other hand, in the second and later sweeps, an additional anodic peak appeared which may be due to the formation of intermediate oxides. The cathodic portion shows the occurrence of three peaks corresponding to the reduction of PbO2 to PbSO4, PbO2 to PbO and the latter with PbSO4 to spongy lead, respectively, followed by the formation of PbH2 before evolution of hydrogen. A correlation was made between the anodic peaks and their corresponding cathodic ones. Increasing the sulfate anion concentration increased the highest of the peak currents and shifted the anodic peak potentials towards more negative values. A linear relationship was obtained between the logarithm of the anodic peak current densities and the logarithm Of SO42- anion concentration. An increase in the scan rate enhanced the current density of both the anodic and cathodic branches. Also, the anodic potentials are shifted towards more positive values, whereas the cathodic peaks are shifted in the negative direction, indicating irreversible formation of the passive film on the electrode surface. (C) 2001 Elsevier Science B.V. All rights reserved.