Solar-light-driven production of hydrogen (H-2) from water using semiconductor photocatalysts is one of the breakthrough technologies of the sustainable and economical solar energy conversion process. However, the conventional oxidation product in water splitting reactions is mainly oxygen gas with low economic benefit. In this paper, photocatalytic simultaneous production of hypochlorous acid (HClO) as a high-value oxidant along with H-2 in saline water under simulated solar light was successfully achieved for the first time using SrTiO3:Al photocatalyst systems. Loading of a co-catalyst was found to be essential to proceed the photocatalytic H-2/HClO production reaction, in particular the RhCrOx(0.1 wt%)-loaded SrTiO3:Al photocatalyst (RhCrOx/SrTiO3:Al) showed the highest activity. In the RhCrOx, the Rh species acts as a co-catalyst to promote proton reduction, and CrOx suppresses the decomposition of the produced HClO. The HClO production rates on the RhCrOx/SrTiO3:Al photocatalyst increased with increasing the Cl- substrate concentration, whereas HClO was produced even in the diluted NaCl aqueous solution of ca. 0.001 M. Moreover, RhCrOx/SrTiO3:Al photocatalyst films, in which the photocatalyst particles are fixed onto a glass substrate, were prepared by simple screen printing followed by a drying and calcination process. The RhCrOx/SrTiO3:Al photocatalyst film produced H-2/HClO from saline water under simulated solar light. The evolution rate of H-2/HClO on the RhCrOx/SrTiO3:Al photocatalyst film was found to be almost the same as that on the corresponding suspended particles thanks to the porous structure enabling an efficient mass transfer.
