Photocatalyst-Mediator Interface Modification by Surface-Metal Cations of a Dye-Sensitized H2 Evolution Photocatalyst

To develop highly active H-2 evolving dye-sensitized photocatalysts (DSPs) applicable for Z-scheme water splitting, we synthesized a series of Ru(II)-dye-double-layered DSPs, X '- RuCP6-Zr-RuP6@Pt-TiO2 (X '-DSP) with different surface bound metal cations (X ' = Fe2+, Y3+, Zr4+, Hf4+, and Bi3+). In 0.5 M KI aqueous solution, the photocatalytic H2 evolution activity under blue light irradiation (lambda = 460 +/- 15 nm) increased in the following order: nonmetal-modified DSP, H+-DSP (turn over number for 6 h irradiation = 35.2) < Fe2+-DSP (54.9) asymptotic to Bi3+-DSP (55.2) < Hf4+-DSP (65.5)asymptotic to Zr4+-DSP (68.3)asymptotic to Y3+-DSP (71.5), suggesting that the redox-inactive and highly charged metal cations tend to improve the electron donation from the iodide electron mediator. On the other hand, DSPs having heavy metal cations, Hf4+-DSP (18.4) and Bi3+-DSP (16.6), exhibited better activity under green light irradiation (lambda = 530 +/- 15 nm) than Zr4+-DSP (15.7) and H+-DSP (7.80), implying the contribution of a heavy atom effect of the surface-bound metal cation to partially allow the spin-forbidden metal-to-ligand charge-transfer excitation.

Automated summary

In this study, a series of Ru(II)-dye-double-layered DSPs with different surface bound metal cations were synthesized and their photocatalytic H2 evolution activity was investigated. The results showed that redox-inactive and highly charged metal cations improve the electron donation, while heavy metal cations contribute to the metal-to-ligand charge-transfer excitation.