The effects of Pt cocatalyst particle size on charge transfer kinetics in dye-sensitized SrTiO3 photocatalysts for hydrogen evolution studied by time-resolved emission/absorption spectroscopy

Dye-sensitized H2 evolution systems were constructed from Pt-loaded SrTiO3 and Ru(II) complex photosensitizers as building blocks, and the impact of the Pt cocatalyst was investigated. In the presence of a stronger electron donor (sodium ascorbate), SrTiO3 loaded with larger Pt particles showed higher activity. On the other hand, the sample having smaller Pt particles gave higher activity in the presence of a weaker electron donor (ethylenediaminetetraacetic acid disodium salt dihydrate). Time-resolved emission/absorption measurements revealed that the larger Pt particles facilitated electron injection from the excited Ru sensitizer to Pt/SrTiO3, while the smaller one improved charge carrier separation by suppressing the back electron transfer reaction from Pt/SrTiO3 to the oxidized sensitizer. These results show that the cocatalyst particle size can affect the kinetics of the electron injection and carrier separation processes. Judicious choice of the Pt particle size can therefore improve the H2 evolution activity in accordance with the reaction system.