The initial stages of lead oxidation in pH 9 to 14 aqueous solutions

Abstract

The initial stages of lead oxidation in a range of alkaline solutions of varying pH and ion content have been investigated with the use of cyclic voltammetry and potential step techniques. In both carbonate and borate buffered solutions (pH > 9), and in more alkaline solutions, Pb oxidation commences at a potential of ca. 140 mV vs. RHE. The initial product is considered to be Pb(OH)2, due to the proximity of this potential with the theoretically predicted one, and due to its invariance (vs. RHE) with pH. In pH 14 solutions, Pb(OH)2 is soluble, producing Pb(OH)3− and only a small amount of a stable surface film. At lower pH's, Pb(OH)2 is not predicted to be soluble, and in borate-buffered solutions, a stable, reducible film appears to form. In carbonate-buffered solutions, the surface film is very difficult to remove electrochemically. Although XPS analyses show the film to be essentially free of carbonate, it is clear that carbonate must be involved in some way in inhibiting film reduction. Keywords: lead, lead hydroxide, lead oxide, surface films, carbonate solutions, borate solutions, alkaline solutions, cyclic voltammetry.