Thermal synthesis of electron deficient oxygen species on crystalline IrO2

Abstract

Water splitting is a promising technology in the path towards complete renewable energy within the hydrogen economy but overcoming the sluggishness of the oxygen evolution reaction (OER) is a major challenge. Iridium-based oxides remain the most attractive materials for the OER under acidic conditions since they offer the combination of activity and stability. Gaining knowledge about how these materials have such an ability is of great interest to develop improved electrocatalysts for the OER. Among the different iridium-based oxides the materials with high concentrations of electron deficient oxygen (OI−) have been shown to have higher OER activity, however, they also have high dissolution rates, seemingly due to the presence or formation of IrIII species. In contrast, rutile-type IrO2, which does not contain IrIII species, has high dissolution resistance but the OER activity remains comparatively low as only low coverages of OI− species are formed under OER. The apparent link between OI− and IrIII species that comes from these observations has yet to be proven. In this work, using ab initio thermodynamics and in situ X-ray photoelectron and absorption spectroscopy we show that the same electrophilic OI− species that appear on Ir-based oxides under OER can be formed on IrIV+δ by mild thermal oxidation of rutile-type IrO2, without the presence IrIII species.