Cyclic Voltammetric Behavior and Some Surface Characteristics of the Lead Electrode in Aqueous NaI Solutions

Abstract

Abstract Cyclic voltammograms of the quiescent lead electrode were examined in NaI solutions of various concentrations ranging between 0.03 and 1.30 M (1 M = 1 mol dm−3). Neither visual PbI2 surface layer nor a typical voltammogram could be obtained unless five complete cycles were preformed in advance. This behavior was not observed for the cyclic voltammetric behavior of the lead electrode in chloride and bromide solutions and consequently could be referred to the less aggressive nature of the I− ion in comparison to the former halide ions. The data proved that the formation of a passivating layer of PbI2 is a reversible process and depends primarily upon the concentration of NaI. By controlling the voltammetric conditions, particularly the number and mode of repeated cycles, thickening of the PbI2 surface layer could be feasible. Moreover, the microstructure of the PbI2 surface layer, as revealed by scanning electron microscopy, exhibited a simple correlation to the operating conditions. The obtained results pointed to the importance of the preceding complete cycles in building up of a relatively thick layer of spongy lead. Consequently, this layer is much more available for the formation of a thick, fine grained, and more compact PbI2 surface layer by a reasonable number of only anodic spans. Investigation of the anodic surface products by X-ray diffractometry proved that the layers are formed of PbI2 in the hexagonal crystalline structure and contamination by any other species could not be detected.