CYCLIC VOLTAMMETRIC BEHAVIOR AND SOME SURFACE CHARACTERISTICS OF THE LEAD ELECTRODE IN AQUEOUS NABR SOLUTIONS

The anodic behaviour of the lead electrode in aqueous 0.05-3.00 M NaBr solutions was investigated by means of linear sweep voltammetry. The voltammograms showed one anodic peak current density (j(ap)) corresponding to the formation of a thin passivating layer of PbBr2. The obtained data depicted a gradual increase of j(ap) and shifting of the corresponding potential (E(ap)) to more negative values with increase of C(NaBr). A detailed study of the formation/reduction of PbBr2 on the surface of lead electrodes in aqueous 0.10-1.00 M NaBr solution was carried out by cyclic voltammetry. The results indicated that the formation of PbBr2 is controlled by diffusion of Br- ions to the anode surface. Irrespective the voltammetric conditions, the study proved that the formation/reduction of the PbBr2 surface layer is a reversible process. The role played by the operating voltammetric conditions in the building up of a relatively thick PbBr2 surface layer that could resist rupture and/or breakdown is discussed. The as-formed PbBr2 layers were examined by scanning electron microscopy and X-ray diffractometry. The microstructure showed some morphological modifications which could be correlated to the operating conditions. On the other hand, X-ray diffraction analysis proved that, under all conditions, the anodic surface products consist solely of PbBr, in the orthorhombic crystalline structure.