Photo-catalyzed surface hydrolysis of iridium(iii) ions on semiconductors: a facile method for the preparation of semiconductor/IrO_x composite photoanodes toward oxygen evolution reaction

We previously reported that the hydrolysis of Ir³⁺ in homogeneous solution could be triggered by irradiation with light whose energy was larger than a threshold value. In this work, we demonstrated that, by introducing Fe₂O₃ particles into solution, the incident light energy-restriction for the photo-catalyzed hydrolysis could be broken and the hydrolysis occurred at the Fe₂O₃/solution interface. The photo-generated holes on the Fe₂O₃ surface played a key role in oxidizing Ir(iii) to Ir(iv) species and triggered the deposition of IrO_x. We showed that this photo-catalyzed surface hydrolysis is a universal phenomenon that takes place on the surface of many n-type semiconductors such as Fe₂O₃, TiO₂, and Ag₃PO₄. As IrO_x is an efficient catalyst for oxygen evolution reaction, surface hydrolysis is a general, facile and efficient strategy to prepare semiconductor/IrO_x composites, which can be used as anodic materials for photoelectrochemical water splitting.