Electrochemical noise analysis of O2 evolution on PbO2 and PbO2-matrix composites containing Co or Ru oxides

Electrochemical noise measurements have been performed on various electrode materials during oxygen evolution reaction. Fluctuations of both electrode potential and electrolyte resistance, recorded under galvanostatic polarization, have been analysed in order to separate ohmic and non-ohmic contributions. The anode materials compared in this study were PbO2 and composite oxides consisting of a PbO2 matrix and variable amounts of catalytic dispersed phases (CO3O4, RuO2 and hydrous Co oxides); the composite oxide layers were generally obtained by anodic codeposition of fine particles (typically 0.1-1 mum in size) with a PbO2 matrix electrochemically grown by Pb2+ oxidation. The power spectral density (PSD) of the electrolyte resistance fluctuations is very similar for PbO2 and composite electrodes, suggesting a similar gas evolution profile. On the contrary, the potential PSD is markedly different for PbO2 and composites containing catalytic particles. In the latter case, the potential fluctuations are entirely due to ohmic effects, while non-ohmic components are clearly dominant in the case of O-2 evolution on pure PbO2, probably because of the much higher activation overpotential. Furthermore, on PbO, electrodes a plateau was obtained at intermediate frequencies (0.1-10 Hz), which was tentatively explained by bubble coalescence phenomena. (C) 2003 Elsevier Ltd. All rights reserved.