Thermally prepared Ti/RhOx electrodes IV: O2 evolution in acid solution

Ti/RhOx layers were prepared by thermal decomposition of Rh chloride hydrate at 400–600 °C. Oxide electrodes were characterized electrochemically by cyclic voltammetry and steady-state current–potential curves in aqueous H2SO4. Integration of voltammetric curves gave the surface charge which is proportional to the surface concentration of active sites. A maximum was observed for a calcination temperature around 430 °C. A hump is visible close to 500 °C, indicating a second transition. O2 evolution was found to take place on Ti/RhOx electrodes with a Tafel slope close to 80 mV and a reaction order with respect to H+ slightly <|−1|. The mechanism did not depend appreciably on the calcination temperature. The layer of RhOx was found to resist to O2 evolution, as indicated by the stability of the voltammetric charge in the course of the experiments. The activity is dominated by surface area effects, true electrocatalytic factors being marginal.