Oxygen Reduction on Supported Iridium Oxide Films in Neutral Phosphate Buffer: Implications for Neural Stimulation

Abstract

Certain aspects of oxygen reduction on (hydrous) iridium oxide (IrO x ) films deposited galvanostatically on smooth Au and glassy carbon (GC) electrodes have been examined in aqueous O 2 -saturated neutral phosphate buffer (pH 7) solutions. Regardless of the nature of the substrate, the onset potential for O 2 reduction, E O2 onset , as determined by cyclic voltammetry, was ca. ―0.1 V vs saturated calomel electrode, which is very close to the corresponding E O2 onset found for both bare Au and GC electrodes. On this basis, the potential range in which the charge stored in the film is available for functional neural stimulation without generation of potentially harmful oxygen-derived species is on the order of 0.9 V. Studies involving a rotating Pt ring GC disk revealed that the reduction of dioxygen on IrO x |GC yields predominantly hydrogen peroxide. Further measurements performed with a rotating GC disk showed that IrO x | GC can oxidize hydrogen peroxide in the potential region associated with the more positive IrO x redox peak, a factor that might mitigate, at least in part, problems associated with the charge imbalance during the bipolar neural stimulation.