Electrochemical behaviour of a lead electrode in phosphoric acid

A lead electrode was studied in 6 and 12 iM H3PO4 Oxidation of a freshly polished electrode occurred in the -0.5 to -0.3 V vs. SCE range, and led to PbHPO4 growth on the electrode surface. The dissolution of this layer by electrochemical reduction occurred between -0.5 and -0.7 V. The influence of temperature (20 degreesC and 65 degreesC) was investigated and showed that the anodic and the cathodic peaks were increasing, and more markedly for the 12 M H3PO4 The ratio Q(cathodic)/ Q(anodic) (Q = electrical charge flowing through the electrode) was equal or close to the unity at 20 OC and decreased as the temperature was increased. The influence of Cl-, Br- and I- ions was also evaluated. The addition of Cl- and Br- predominantly led to Pb-5(PO4)(3)Cl and Pb-5(PO4)(3)Br, respectively, while I- led to a mixture of PbI2 and PbHPO4.