Growth Processes of the Anodic Crystalline Layer on Potentiostatic Oxidation of Lead in Sulfuric Acid

The dependence of the composition of the anodic layer, the electric capacity, and the current on the quantity of electricity passed on potentiostatic oxidation of lead in sulfuric acid are investigated. Oxidation runs were performed in the lead sulfate, the lead oxide, and the lead dioxide potential regions. It was established that at all oxidation potentials the electrode is passivated by the formation of a dense crystalline layer after passing a given quantity of electricity. Subsequently this layer grows. If the oxidation takes place in the lead oxide region, tetragonal and basic lead sulfate form during the growth of the anodic layer. On oxidation in the lead dioxide region, tetragonal and form in the deposit (at −950 mV with respect to the electrode). At +1000 and +1100 mV after the formation of , is oxidized to . The change in the composition on oxidation is due to change in ionic conductivity between the crystals. When the current through the anodic layer begins to be transported by O 2− at the lead/anodic layer interface, tetragonal is formed. If the oxidation potential exceeds +950 mV, forms in addition to the tetragonal monoxide. At potentials more positive than +1000 mV, the solute Pb 2+ ions are oxidized to at the .