Two-dimensional electrocrystallisation oif PbCO 3 and Pb 3(CO 3) 2(OH) 2 on lead amalgam electrodes in sodium carbonate and bicarbonate solutions

Abstract

The formation of anodic monlayers on lead amalgam electrodes in aqueous carbonate or bi-carbonate solutions was investigated by potentiostatic step and linear sweep voltammetric methods. Powder X-ray diffraction and the electrochemical measurements show that in bicarboante solutions (pH = 8.3) the layer formed was PbCO 3 and in carbonate containing solutions (pH ⩾ 10.0) the layer was Pb 3(CO 3) 2(OH) 2. At low current densities, monolayer formation via a 2D nucleation and growth mechanism was rate controlling with a potential dependence of about 4 mV/decade. The potential step transients at all higher overpotentials possessed truncated peaks. It was shown that this could be explained by preferential nucleation occurring around the inner lip of the electrode capillary. Large dissolution currents were observed and are attributed to the dissolution of lead as a complex ion, possibly as Pb(CO 3) 2− 2.