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

A dye-sensitized photocatalyst combining Pt-loaded TiO 2 and Ru(II) tris-diimine sensitizer ( RuP ) was constructed and its activity for photochemical hydrogen evolution was compared with that of Pt-intercalated HCa 2 Nb 3 O 10 nanosheets . When the sacrificial donor ethylenediaminetetraacetic acid (EDTA) disodium salt dihydrate was used, RuP /Pt/TiO 2 showed higher activity than RuP /Pt/HCa 2 Nb 3 O 10 . In contrast, when NaI (a reversible electron donor) was used, RuP /Pt/TiO 2 showed little activity due to back electron transfer to the electron acceptor (I 3 – ), 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 I 3 – , the H 2 production activity from aqueous NaI was improved, but it did not exceed that of RuP /Pt/HCa 2 Nb 3 O 10 . Transient absorption measurements showed that the rate of semiconductor-to-dye back electron transfer was slower in the case of TiO 2 than HCa 2 Nb 3 O 10 , but the electron transfer reaction to I 3 – was much faster. These results indicate that Pt/TiO 2 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. Pt/TiO 2 is a good building block for dye-sensitized H 2 evolution under visible light. However, the H 2 evolution activity is governed by the efficiency of back electron transfer reactions involving Pt/TiO 2 , dye and electron-accepting species.