Electroanalytical investigations on electrodeposited lead dioxide
Résumé
Electrodeposition of compact layers of lead dioxide was performed in order to prepare anode materials. Depending on the mode of preparation, the relative amounts of the two crystallographic forms ? and ? were different. Cyclic voltammetry experiments were performed in concentrated sulphuric acid for the study of the PbO2/PbSO4 transformation. Whatever the composition of the deposit (pure ? form, pure ? form or ? + ? mixtures), only one passivation peak may be observed at low potential during the first reduction scan, corresponding to the transformation of bulky PbO2 crystallites into PbSO4. PbO2 is recovered during the reverse re-oxidation scan. In all the following voltammograms, two reduction peaks are observed. They are attributed to the transformation of (i) the remaining bulky PbO2 crystallites (low potential peak) and (ii) the small PbO2 crystallites resulting from the re-oxidation of PbSO4 (high potential peak). The bulky PbO2 crystallites are gradually transformed into smaller particles so that larger and larger amounts of active mass are involved in the reduction process. The results are discussed, taking into account those obtained from X-ray diffractograms. In addition, a method is proposed for the calculation of the current efficiency of the PbO2 electrodeposition. The lead dioxide layer was first completely reduced in hot acid medium, and the amount of resulting soluble Pb(II) was determined by square wave voltammetry, using a mercury electrode. The results obtained with acid or alkaline plating solutions differ considerably and indicate that PbO2 formed in alkaline plating solutions is highly non-stoichiometric.