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

ABSTRACT

To develop highly active H2 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 (λ = 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) ≈ Bi3+-DSP (55.2) < Hf4+-DSP (65.5) ≈ Zr4+-DSP (68.3) ≈ 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 (λ = 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.