A novel membrane reactor for separating hydrogen and oxygen in photocatalytic water splitting

The Z-scheme of water splitting is comprised of H2-photocatalyst and O2-photocatalyst with aid of electron transfer mediator to produce hydrogen and oxygen, respectively. A twin reactor, which divided H2-photocatalyst and O2-photocatalyst in two compartments using a membrane, can separate H2 and O2 thus preventing backward reaction. Pt/SrTiO3:Rh and BiVO4 were used as the H2-photocatalyst and the O2-photocatalyst, respectively. The diffusion of electron mediator, Fe2+/Fe3+, through Nafion membrane was investigated. The transfer rate of mediator ions was remarkably larger than the photoreaction rate, indicating that membrane did not delay the water-splitting reaction in the twin reactor. Under the favorable condition, the hydrogen generation rate reached 0.65 μmol/g h and matched the H2/O2stoichiometric ratio of water splitting. We found that the generation of H2in the twin-reactor system was the rate-limiting step of the water-splitting reaction. By using the twin reactor, the deactivation of Pt/SrTiO3:Rh could be minimized due to the suppression of Fe(OH)3formation on the photocatalyst surface.