Efficient Electro-Oxidation of Water near Its Reversible Potential by a Mesoporous IrO_<i>x</i> Nanoparticle Film

Abstract

We describe the formation of stable, adherent, mesoporous films of 2 nm diameter IrIVOx nanoparticles on glassy carbon electrodes, by a previously unreported method of controlled potential electro-flocculation from pH 13 nanoparticle solutions. These films initiate O2 evolution from water oxidation and then achieve 100% current efficiency, at overpotentials only ∼0.15 and ∼0.25 V higher, respectively, than the reversible H2O/O2 potential. The overpotentials, measured at ∼0.5 mA/cm2, are independent of pH and are the smallest yet reported for electrochemical water oxidation, a property important in possible uses in electrochemical solar cells. The films appear to be mesoporous and microscopically accessible, since O2 evolution currents increase proportionately to multilayer nanoparticle film coverage but without a concurrent increase in overpotential.