Study of surface effects in the formation of lead chloride on lead electrodes in aqueous HCl by electrochemical methods and scanning electron microscopy

• Published in: Electrochimica acta 1976-01, Vol.21 (5), p.357-365
• Main Authors: Barradas, R.G., Belinko, K., Shoesmith, W.
• Format: Article
• Language: English
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/0013-4686(76)85026-8

The formation of lead chloride on lead electrodes in aqueous HCl solutions was investigated using scanning electron microscopy (S.E.M.). Micrographs revealed the presence of two distinct surface layers of PbCl 2 on the electrode during anodic polarization; a basal layer of relatively small crystals and an upper layer of larger crystals. Passivation was found to result from blockage of the electrode by the larger crystals. A mechanistic scheme for the nucleation and growth of PbCl 2 on the electrode surface, involving precipitation of dissolved Pb 2+ complex species is proposed. This nucleation and growth process was found to be either “progressive” or “instantaneous” in nature depending upon the conditions under which the surface layer was formed. The reactivation phenomenon observed subsequent to passivation, under rotating disc electrode conditions, was found to involve a recrystallization process on the electrode surface. Steady-state currents in the reactivation region were found to be limited by the rate of diffusion of soluble Pb 2+ species away from the electrode surface. This provided a method of determining the concentration of soluble Pb 2+ species, c s Pb 2+ in equilibrium with the electrode surface. A plot of c s Pb 2+ vs Cl − concentration generated the solubility curve for PbCl 2 in HCl solutions.