Solar-driven simultaneous production of hypochlorous acid and hydrogen from saline water over RhCrOx-loaded SrTiO3 photocatalyst systems

Abstract

Solar-light-driven production of hydrogen (H₂) 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 H₂ 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 H₂/HClO production reaction, in particular the RhCrO_x(0.1 wt%)-loaded SrTiO₃:Al photocatalyst (RhCrO_x/SrTiO₃:Al) showed the highest activity. In the RhCrO_x, the Rh species acts as a co-catalyst to promote proton reduction, and CrO_x suppresses the decomposition of the produced HClO. The HClO production rates on the RhCrO_x/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, RhCrO_x/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 RhCrO_x/SrTiO₃:Al photocatalyst film produced H₂/HClO from saline water under simulated solar light. The evolution rate of H₂/HClO on the RhCrO_x/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.