Is platinum-loaded titania the best material for dye-sensitized hydrogen evolution under visible light?

A dye-sensitized photocatalyst combining Pt-loaded TiO2 and Ru(II) tris-diimine sensitizer (RuP) was constructed and its activity for photochemical hydrogen evolution was compared with that of Pt-intercalated HCa2Nb3O10 nanosheets. When the sacrificial donor ethylenediaminetetraacetic acid (EDTA) disodium salt dihydrate was used, RuP/Pt/TiO2 showed higher activity than RuP/Pt/HCa2Nb3O10. In contrast, when NaI (a reversible electron donor) was used, RuP/Pt/TiO2 showed little activity due to back electron transfer to the electron acceptor (I3-), which was generated as the oxidation product of I-. By modification with anionic polymers (sodium poly(styrenesulfonate) or sodium polymethacrylate) that could inhibit the scavenging of conduction band electrons by I3-, the H2 production activity from aqueous NaI was improved, but it did not exceed that of RuP/Pt/HCa2Nb3O10. Transient absorption measurements showed that the rate of semiconductor-to-dye back electron transfer was slower in the case of TiO2 than HCa2Nb3O10, but the electron transfer reaction to I3- was much faster. These results indicate that Pt/TiO2 is useful for reactions with sacrificial reductants (e.g., EDTA), where the back electron transfer reaction to the more reducible product can be neglected. However, more careful design of the catalyst will be necessary when a reversible electron donor is employed. (c) 2024, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.