HYDRATED STRUCTURES IN THE ANODIC LAYER FORMED ON LEAD ELECTRODES IN H2SO4 SOLUTION

SEM and TEM observations of the corrosion layer obtained during the po tentiostatic oxidation of lead electrodes in H2SO4 solution have shown that, at potentials above 1.00 V vs Hg/Hg2SO4, a lead dioxide layer i s formed with crystal and gel-like (hydrated) structures. The crystal zones of the corrosion layer contain alpha- and beta-PbO2 crystals. Ap plying controlled thermal degradation it has been established that hyd rated zones (denoted as PbO(OH)2) comprise about 10% of the corrosion layer. For comparison, the lead dioxide active mass of the lead-acid b attery is hydrated over 30%. On prolonged polarization of the lead dio xide electrode at 1.50 V, the basic electrochemical reaction that take s place is oxygen evolution. It has been suggested that this reaction occurs mainly at the interface crystal/gel-like zones. On opening the circuit, the electrode potential reaches the equilibrium potential for the PbO2/PbSO4 system within a rather long period. This potential dec ay is related to the diffusion of oxygen through the bulk of the corro sion layer (probably through its hydrated zones) to the solution and t o the metal. A suggestion is made that hydrated zones are also involve d in the oxygen reaction.