Deactivation of thermally formed Ru/Ti oxide electrodes : An AC impedance characterization study

A comparison of the data for the fresh and the deactivated anodes suggests that the deactivated anodes have similar electrochemical characteristics as freshly formed, low-Ru-content (about 5 at%) oxide films. The experimentally obtained ac impedance data were compared to the calculated impedance, based on a porous film model in which a one-electron surface redox reaction occurs. While the fit is good at medium-to-high frequencies, the inclusion of a diffusion-controlled process for the low at% Ru films is required to achieve a good fit also at low frequencies. These results support the hypothesis that the deactivation of originally high at% Ru anodes is due to the depletion of Ru from the oxide film, causing its electrochemical behaviour to become more similar to that of freshly formed low at% Ru oxide films. 45 refs.