Anion and water involvement in hydrous Ir oxide redox reactions in acidic solutions

The stoichiometry of the Ir oxide reaction in sulfuric acidic solutions was investigated by tracking the pH dependence of its principal Ir( + III) Ir( + IV) redox peaks. as well as monitoring the film mass change with in-situ quartz crystal microbalance measurements. A pH dependence of ca. - 68 mV v ersus a pH independent reference electrode was found for films grown by pot ential pulsing using a wire electrode. indicating the injection:expulsion o f protons and some solution anions during film reduction oxidation. The una ccounted mass change was interpreted as being due to water flux in/out of t he film. The pH dependence. and hence, the ion stoichiometry appears to be independent of the acidic solution used to grow the Ir oxide film, while th e acidic solution in which the oxide is cycled between its reduced and oxid ized states appears to influence the Ir( + III) Ir( + IV) reaction stoichio metry. Crown copyright (C) 1999 Published by Elsevier Science S.A. All righ ts reserved.