Gas phase photo-reactor for H2 production from dilute aqueous organic waste solutions

The treatment of aqueous organic waste streams by solar irradiation may be an interesting solution towards a sustainable production of H2, especially for wastes which are too dilute to be processed by conventional catalytic routes. In this context we have developed and realized a photo-reactor of new concept, working in gas phase, to generate H2 by water photoelectrolysis or photo-reforming of organic compounds (such as ethanol). The core of the reactor is a TiO2-based photo-active material, prepared as a thin film, which promotes light harvesting and charge separation when irradiated by sunlight. The organic gas phase is generated directly in situ from the bottom of the reactor by keeping an aqueous organic solution in evaporation. Results showed the many advantages of operating in gas phase with respect to the conventional slurry photo-reactors, in terms of H2 production rate. By using Pt nano-particles deposited on TiO2 substrates and an aqueous solution of 10 vol.% ethanol, about 380 !mol/h of H2 were detected in the outside stream from the photo-reactor. Although the actual implementation of the gas phase photo-reactor is still a long way off for water splitting, its applicability in photo-reforming of dilute aqueous organic solutions may economically be convenient in the near future.