Photocatalyst-Mediator Interface Modification by Surface-Metal Cations of a Dye-Sensitized H 2 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'- RuCP 6 -Zr- RuP 6 @Pt-TiO 2 ( X'-DSP ) with different surface-bound metal cations (X' = Fe 2+ , Y 3+ , Zr 4+ , Hf 4+ , and Bi 3+ ). In 0.5 M KI aqueous solution, the photocatalytic H 2 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) < Fe 2+ -DSP (54.9) ≈ Bi 3+ -DSP (55.2) < Hf 4+ -DSP (65.5) ≈ Zr 4+ -DSP (68.3) ≈ Y 3+ -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, Hf 4+ -DSP (18.4) and Bi 3+ -DSP (16.6), exhibited better activity under green light irradiation (λ = 530 ± 15 nm) than Zr 4+ -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.