Analysis of the oxidation process of anodic Pb(II) films on lead in sulfuric acid solution
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Electro-oxidation of the anodic Pb(II) film formed on lead at 0.6 V in H2SO4 solution for 20 min is analysed using non-linear regression, chrono-amperometry and linear sweep voltammetry. It is shown that the overall current transient of the oxidation at 1.4 V can be separated into the following contributions: (i) oxidation of the Pb(II)-containing phases into PbO2 which involves mainly an instantaneous nucleation and two-dimensional growth mechanism under charge-transfer control (2DIC); (ii) oxidation of the lead substrate into PbO under the diffusion control of oxygen ions, and (iii) evolution of oxygen on the electrode. The plumbous phases that participate in the oxidation process include an inner layer of (PbO+PbO . PbSO4) together with an adjacent part of an outer layer of PbSO4. Several electrochemical quantities of significance with respect to this oxidation process have been calculated, such as the thickness of the PbO2 formed, the degree of oxidation of the Pb(II)-containing phases, as well as the diffusion coefficient of O2- in the concurring oxidation process of Pb to PbO.