CORROSION OF LEAD IN SULFURIC-ACID AT HIGH POTENTIALS

The corrosion of lead in sulfuric acid is studied in the potential region of 1. 35 v and above, which corresponds to conditions on the positive electrode of a lead-acid battery during overcharge. Under these conditions, a Pb/t-PbO/PbO//2 electrode is formed. The formation of t-PbO at high potentials in acid solution is possible because: (i) the outer PbO//2 layer inhibits ionic diffusion, leading to low concentrations of H** plus and SO//4** equals in the interior of the film, and (ii) the transport of oxygen to the Pb/t-PbO interface is hindered. The steady-state corrosion rate is probably controlled by the diffusion of oxygen through the oxide film. The processes that occur as the corrosion film discharges are also described.