A COMBINED ELECTROCHEMICAL AND INSITU X-RAY-DIFFRACTION STUDY OF THE CYCLING OF WELL-DEFINED LEAD DIOXIDE LAYERS ON PLATINUM

Both ex-situ and, for the first time, in-situ X-ray diffraction have been used to study the potential cycling of PbO2/PbSO4 layers. It is shown by ex-situ X-ray diffraction that it is possible to deposit pure alpha-PbO2 and pure beta-PbO2, as well as mixtures of the two phases, onto a platinum anode from acidic lead nitrate solutions; the alpha-PbO2 is best formed at pH 4.3 with a current density of 3.5 mA cm-2, while the beta phase is favoured by a low pH and a higher current density. The reduction of layers of PbO2 0.3-3-mu-m thick in sulphuric acid is reported and the results for the different phases are compared. The conditions for converting the deposit back to PbO2 are defined. It is confirmed that reduction-oxidation of a substantial fraction of the PbO2 layer occurs only in a limited range of conditions. When the films do cycle, however, it is shown using in-situ X-ray diffraction that alpha-PbO2 is converted to the beta form.