Efficient Electro-Oxidation of Water near Its Reversible Potential by a Mesoporous IrOx Nanoparticle Film

We describe the formation of stable, adherent, mesoporous films of 2 nm diameter (IrOx)-O-IV nanoparticles on glassy carbon electrodes, by a previously unreported method of controlled potential electro-flocculation from pH 13 nanoparticle solutions. These films initiate O-2 evolution from water oxidation and then achieve 100% current efficiency, at overpotentials only similar to 0.15 and similar to 0.25 V higher, respectively, than the reversible H2O/O-2 potential. The overpotentials, measured at similar to 0.5 mA/cm(2), 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 O-2 evolution currents increase proportionately to multilayer nanoparticle film coverage but without a concurrent increase in overpotential.