Photocatalytic decomposition of water into H2 and O2 by a two-step photoexcitation reaction using a WO3 suspension catalyst and an Fe3+/Fe2+ redox system

H2 and O2 gas evolution in a stoichiometric ratio (H2:O2 = 2:1) has been realized over a RuO2-WO3 photocatalyst suspended in an aqueous solution containing an Fe3+/Fe2+ redox system. O2 gas was evolved and Fe3+ ions were reduced to Fe2+ ions on a WO3 powder catalyst excited by visible light at less than 460 nm and UV light. Fe2+ ions excited by UV light at less than 280 nm were oxidized back to Fe3+ ions with the evolution of H2 gas. The reaction mechanism is similar to the Z-scheme in photosynthesis.