Physico-chemical characterization of Co3O4 prepared by thermal decomposition. II. Response to solutions pH

Layers of Co3O4 were deposited onto a titanium support by thermal decomposition of aqueous or alcoholic solutions of cobalt nitrate. The opecircuit potential of electrodes prepared at temperatures between 200 and 700 °C was measured as a function of pH in chloride-containing and perchlorate-containing solutions. The potential E-pH relationship was found to depend on the direction of change in the pH. When the solution was changed from alkaline to acid the E-pH plots exhibited a break at about pH 5. A closely nernstein response over more than 10 pH units was observed when the solution was varied from acid to alkaline. The calcination temperature was found to have an effect at temperatures higher than about 500 °C. These observations have been interpreted in terms of specific surface chemical equilibria. The characteristics of the E-pH relationship follow closely the features of the surface acid-base properties as observed by means of potentiometric titration in previous work. © 1984.