Decomposition of water into H2 and O2 by a two-step photoexcitation reaction over a Pt-TiO2 photocatalyst in NaNO2 and Na2CO3 aqueous solution

Both H-2 and O-2 were evolved when a suspension of Pt-TiO2 in aqueous NaNO2 was irradiated with UV light with wavelengths greater than 200 nm. The activity and stability were promoted by the addition of Na2CO3 to the NaNO2 solution, and stoichiometric decomposition of water into H-2 and O-2 (H-2/O-2 = 2) took place for a long time (>5 days). A new two-step photoexcitation mechanism (a Z-scheme system) is proposed, whereby the Pt-TiO2 serves as a photocatalyst for H, evolution, the NO3-/NO2- couple serves as a redox mediator, and O-2 evolution occurs via direct photoexcitation of NO3- ion. (C) 2005 Elsevier B.V. All rights reserved.