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The electrocatalytic behaviour of Ti-supported RuOz, prepared by thermal decomposition of RuC13, as substrate for oxygen evolution was investigated by a variety of techniques. B.E.T. adsorption experiments showed that the RuOz layers are highly porous with large surface area values which, however, decrease rapidly as the annealing temperature increases above -300°C. Both the charge involved in the cyclic voltammograms and the oxygen evolution rates are dependent on the true (rather than apparent) area of these electrode surfaces, and also on the pH of the solution. The results for oxygen evolution are discussed in terms of electrochemically generated unstable surface oxides whose decomposition is catalysed by protons in acid, and hydroxide ions in base.The lower reactivity of the oxide at intermediate pH value is attributed on the one hand to loss of protons by OH groups, resulting in oxygen bridging, and on the other to lack of enhanced coordination of surface ruthenium species by OH-ions, which in this pH region are present only at low activity. The charge associated with voltammetric sweeps is accounted for in terms of surface redox processes rather than bulk penetration of protons into the oxide. The need for surface area measurements as a guide to the interpretation of the electrochemical data in the case of these oxide systems is stressed.

An examination has been made of the mechanism of breakdown of passive films on iron in borate buffer solution false(normalpH=8.4false) caused by chloride ions. Various electrochemical kinetic criteria were measured. XPS, SIMS, and ISS studies were made of the systems used in the electrochemical work. The rate of breakdown was found to be proportional to cnormalCl− and cH+ and exponentially dependent on the electrode breakdown potential and field drop in the oxide film. XPS data showed that when chloride ions caused breakdown, the Onormaltotal/normalFe and H2O/normalFe ratios changed from 2 to 1.5 and 0.5 to 0.1, respectively. SIMS data revealed that heating passive films up to 200°C drove out water from the films and that chloride ions penetrated the whole film thickness on breakdown. ISS data indicated that on changing from a passive to a depassivated film, the O/normalFe ratio changed from 2.07 to 1.5. Discussion of the electrochemical kinetic data shows that it is inconsistent with adsorption‐displacement models, pore models, and chemico‐mechanical models, but is not inconsistent with ion‐exchange processes, point‐defect models, and hydrated polymeric oxide models. Confrontation of the spectroscopic data with the expectations of the latter three models shows some points of agreement with all these models, but the data taken together is most consistent with the hydrated polymeric oxide model.

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