The effect of antimony on the anodic behaviour of lead in H 2SO 4 solution : Part II. Dependence of the phase composition of the anodic layer on the oxidation potential

Abstract

The behaviour of a Pb+12% Sb electrode (eutectic composition) in the lead oxide and the lead dioxide potential regions has been investigated. For this purpose the electrode was first oxidized at a constant potential for 0.5 h and then subjected to negative potential sweeps at a scan rate of 10 mV/s. The electrode was illuminated and its photocurrent was measured. It was established that parallel to the formation of PbO, PbO n and PbO 2 in the different potential regions, other phases are also formed in which some of the lead ions (Pb 2+ and Pb 4+ in the above oxides) are replaced by Sb 3+ (and probably Sb 5+) ions. At potentials up to 0.80 V, substituted Pb (1−x)(Sb) xO oxide and PbO are formed; between 0.80 and 1.20 V, non-stoichiometric Pb (1−x)(Sb) xO n ; and in the highly positive range, Pb (1−x)(Sb) xO 2 is distinguished. Lead dioxide and Pb (1−x)(Sb) xO 2 may be formed simultaneously. The substituted lead oxides are amorphous or/and their X-ray diffraction patterns overlap those of the pure lead oxides. The first two substituted lead + antimony oxides are photoactive, while the last one exhibits high electron conductivity. It is reduced at potentials more negative than that of PbO 2 reduction, which may extend the discharge processes of the PbO 2 active mass and hence increase its capacity.