Kinetics and mechanism of the electroreduction of anodic layers formed on lead in 5 M H 2SO 4 at 25°C

Abstract

The potentiostatic electroreduction of anodic layers containing Pb(II)-species formed on lead has been investigated in 5 M H 2SO 4 at 25°C. By properly adjusting both the anodic layer formation and the electroreduction conditions three well-defined processes could be distinguished. (i) The electroreduction of the primary PbSO 4 layer which involves mainly an instantaneous nucleation and three-dimensional growth mechanism under diffusion control. (ii) The electroreduction of the PbO layer, which builds up progressively beneath the initially grown PbSO 4 porous layer, consists of two current contributions; one term can be associated with an instantaneous nucleation and 2D growth under diffusion control and the other one, which is the main current contribution, can be related to a progressive nucleation and 3D growth mechanism under charge transfer control. The latter includes a death correction term for either the growing or the disappearing right circular cones phase centres. (iii) The electroreduction of the composite PbSO 4-PbO layer which can be successfully described in accordance with a complex mechanism by taking into account the simultaneous influence of the two single surface layer constituents.