Hydrogen production from water splitting by Z-scheme photocatalysis

The Z-scheme is a two-photocatalyst system for photocatalytic water splitting to produce hydrogen. The two-photocatalyst system is comprised of H2-catalyst and O2-catalyst to produce hydrogen and oxygen, respectively. Conventionally in Z-scheme, two catalysts are mixed in one reactor to perform photocatalytic water splitting, thus hydrogen and oxygen are produced as a mixture. Thus, the reverse reaction occurs to reduce the efficiency of water splitting. The cost of H2 separation is another drawback. Furthermore, a safety issue of H2-O2 explosion must be considered in the commercial process. This research used Pt/SrTiO3:Rh (H2-catalyst) and WO3 (O2-catalyst) discretely in two compartments of a connected twin reactor filled with aqueous solution. Two compartments of the twin reactor was separated by Nafion ion-exchanged membrane. Fe3+ and Fe2+ were added and served as electron-transfer mediates for redox reaction. The Nafion membrane was pretreated under Fe ion solution. The light source was 500W Halogen lamp. Under the visible-light irradiation, hydrogen and oxygen can be separately produced in two compartments simultaneously by photocatalytic water splitting. Under the optimal condition, the H2 yield reached 2.22 mole/g-h, and the molar ratio of H2/O2 was matched the stoichiometry of water splitting.