Photoassisted Hydrothermal Synthesis of IrOx–TiO₂ for Enhanced Water Oxidation

Water oxidation is regarded as a bottleneck in water splitting, especially via the photocatalytic process, and thus there is still a need for a greatly improved catalyst system that not only has suitable carrier separation performance but also has low carrier migration resistance across the catalyst–solution interface. Herein, a photoassisted hydrothermal method is reported to synthesize samples of hydrophilic semiconductor nanoparticles, i.e., TiO₂ and IrOx–TiO₂, which show excellent hydrophilic behavior in comparison to reference samples. The O 1s line in X-ray photoelectron spectroscopy measurement proves that many surface OH groups and adsorbed water exist on the surface of the TiO₂. The loaded Ir species mainly exists in the metal state with a small amount of IrO₂. Through the synergistic effect of surface OH groups and the loaded IrOx, the IrOx–TiO₂-150-L sample gives the best photocatalytic water oxidation performance of 56.67 μmol/g·h under LED-365 illumination. Moreover, the sample exhibits a photocurrent response to visible light (LED-425). The electrochemical impedance spectroscopy and time-resolved photoluminescence results confirm that the samples of IrOx–TiO₂-L possess low carrier solid–liquid interface migration resistances and weak bulk carrier recombination ratios, and thus excellent photocatalytic water oxidation activity is obtained.