Role of Water Oxidation Catalyst IrO₂ in Shuttling Photogenerated Holes Across TiO₂ Interface

Iridium oxide, a water oxidation cocatalyst, plays an important role in mediating the hole transfer process of a UV-irradiated TiO 2 system. Spectroscopic identification of trapped holes has enabled their characterization in colloidal TiO 2 suspension and monitoring of the transfer of trapped holes to IrO 2 . Titration of trapped holes with potassium iodide yields an estimate of three holes per particle during 7 min of UV irradiation of TiO 2 suspension in ethanol containing 5% acetic acid. The hole transfer to IrO 2 occurs with a rate constant of 6 × 10 5 s –1 . Interestingly, IrO 2 also catalyzes the recombination of trapped holes with reduced oxygen species. The results discussed here provide a mechanistic and kinetic insight into the catalytic role of IrO 2 in the photogenerated hole transfer process.