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

To develop highly active H evolving dye-sensitized photocatalysts (DSPs) applicable for Z-scheme water splitting, we synthesized a series of Ru(II)-dye-double-layered DSPs, X'--Zr-@Pt-TiO () with different surface-bound metal cations (X' = Fe, Y, Zr, Hf, and Bi). In 0.5 M KI aqueous solution, the photocatalytic H evolution activity under blue light irradiation (λ = 460 ± 15 nm) increased in the following order: nonmetal-modified DSP, (turn over number for 6 h irradiation = 35.2) < (54.9) ≈ (55.2) < (65.5) ≈ (68.3) ≈ (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, (18.4) and (16.6), exhibited better activity under green light irradiation (λ = 530 ± 15 nm) than (15.7) and (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.