Cl<sup>–</sup>‑Including Rh/IrO<sub><i>x</i></sub> Cocatalyst\nLoaded on a Rh,Sb-Codoped SrTiO<sub>3</sub> Photocatalyst for Water\nSplitting under Visible Light Irradiation

The chemical state of an IrO<sub><i>x</i></sub> cocatalyst\nand the effect of sequential loading of Rh species on the photocatalytic\nwater splitting activity of a SrTiO<sub>3</sub> photocatalyst codoped\nwith Rh and Sb (SrTiO<sub>3</sub>:Rh,Sb) were investigated. The highest\nactivity was obtained when the Ir species was loaded on SrTiO<sub>3</sub>:Rh,Sb at 673 K in air using (NH<sub>4</sub>)<sub>2</sub>IrCl<sub>6</sub>. X-ray fluorescence, X-ray absorption near-edge structure,\nand X-ray photoelectron spectroscopy measurements revealed that Cl<sup>–</sup> was included in the Ir species. By dispersing the\nphotocatalyst in water, a part of the Ir species was eluted, and some\nIr–Cl bonds were hydrolyzed, resulting in decreased amounts\nof Ir and Cl loaded on the photocatalyst. The elution hardly proceeded\nanymore during photocatalytic water splitting under visible light\nirradiation. In contrast, SrTiO<sub>3</sub>:Rh,Sb loaded with IrO<sub><i>x</i></sub>(OH)<sub><i>y</i></sub> without\nCl<sup>–</sup> using Ir(NO<sub>3</sub>)<sub>4</sub> did not\nshow water splitting activity. Therefore, it was necessary to include\nCl<sup>–</sup> in the Ir species prepared and during water\nsplitting. Moreover, the water splitting activity of SrTiO<sub>3</sub>:Rh,Sb loaded with Ir species was improved by sequential loading of Rh species by an adsorption\nmethod.