Rezumat
Dynamics of changes of no-current potential of the lead electrode in 2M sulfuric acid solution after cathodic treatment with released hydrogen is studied. It is shown that in the process of cathodic polarization simultaneously with the release of hydrogen a lead sulfate film is formed due to corrosion on the metal surface. The main component of the measured potential is voltage drop in the sulfate film. Two explanations of thermodynamically impossible coexistence of the processes of hydrogen release and lead corrosion are offered. The first is electrical inhomogeneity of the surface caused by localization of the current in the individual active points (microareas) and the lack of a protective cathodic potential at a distance from them. The second is voltage drop in the sulfate film, which is a component of the measured potential of the film-electrolyte interface. Thus, on the metal-film boundary there may be anodic polarization of the metal surface within the formal cathodic polarization. The challenging processes of growth and recrystallization of the sulfate film with hopping passivation lead are in progress after switching off the current. The anodic reaction of lead dissolution is a limiting process of the corrosion system.
Keywords: lead, lead sulfate, sulfuric acid, hydrogen processing, potential, corrosion.