Electrochemical noise analysis of O₂ evolution on PbO ₂ 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, RuO ₂ and hydrous Co oxides); the composite oxide layers were generally obtained by anodic codeposition of fine particles (typically 0.1-1 μm 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 O₂ evolution on pure PbO₂, probably because of the much higher activation overpotential. Furthermore, on PbO₂ electrodes a plateau was obtained at intermediate frequencies (0.1-10 Hz), which was tentatively explained by bubble coalescence phenomena.