Kinetics of Oxidation Processes on Lead Electrode in H2SO4 I. The Growth of the Lead Sulfate Layer

A mechan ism has been established by further studying the growth of the lead sulfate layer. At very small overpoten-12 rials, lead sulfate crystals are fo rmed through solution-precipitation mechan ism.- However, as the anodic overpotential 2 2+ increases, the migration and diffusion of the SO4- and Pb ions through the micropores of the anodic film become the controlling step. A t short times, the f low of the SO~- ion is dominant and its concentration increases linearly with the distance f rom the metal surface. But at long times, the f low of the Pb = § ion is dominant and its concentration drops almost linearly wi th the distance f rom the metal surface. Wherever the concentration of the dominant ion is small, the gradient of the diffusion potential is large. It is also shown that the grown current of the lead sulfate layer drops linearly with t-~ and there are two slopes to this curve wh ich corresponds to the processes above