Photocatalytic water splitting under visible light utilizing I3/I and IO3/I redox mediators by Z-scheme system using surface treated PtOx/WO3 as O2 evolution photocatalyst

Water oxidation reactions over a surface treated PtO x /WO 3 photocatalyst in the presence of IO 3 or I 3 ions were investigated. When the IO 3 ion was used as an electron acceptor, PtO x /WO 3 treated by thermal treatment using Cs 2 CO 3 aqueous solution followed by H + -exchange-treatment (PtO x /H-Cs-WO 3 ) showed ca. 4 times higher activity compared with PtO x /WO 3 without surface treatment. The apparent quantum yield at 420 nm was 20%. Moreover, when the I 3 ion was used as the electron acceptor, the activity of PtO x /WO 3 was negligible, while PtO x /H-Cs-WO 3 showed a high activity for water oxidation. The cesium surface treatment also had an excellent effect for the improvement of photocatalytic performance of TiO 2 . The activity of a water splitting reaction under visible light by the Z-scheme system that combined Pt/SrTiO 3 :Cr/Ta with PtO x /H-Cs-WO 3 was 3 times higher than that using PtO x /WO 3 as an O 2 evolution photocatalyst. Moreover, owing to the contribution from both IO 3 and I 3 ions as redox mediators, the water splitting reaction stoichiometrically proceeded in a wider pH region (pH 29). Photocatalytic water splitting under visible light by the Z-scheme system was improved by surface treatment for PtO x /WO 3 due to the effective suppression of undesirable reactions.