Importance of Electron Mediator Transparency: Photocatalytic Hydrogen Production from Polyoxometalate using Dye‐double‐layered Photocatalysts

Abstract One‐directional electron transfer is crucial for two‐step photoexcitation (Z‐scheme) water‐splitting photocatalysis. We investigated the hydrogen evolution activity of PS‐double‐layered photocatalysts ( X‐DSP , X‐ RuCP 6 ‐Zr‐ RuP 6 @Pt/K x H 4‐x Nb 6 O 17 ; X=Zr 4+ , H + ) in the presence of highly charged polyoxometalates‐K 6 [SiV IV W 11 O 40 ] ⋅ nH 2 O ( V IV ‐POM ) and K 6 [SiW 11 O 39 Mn II (H 2 O)] ⋅ nH 2 O ( Mn II ‐POM )‐as redox‐reversible electron donors, to induce effective photocatalyst‐donor electrostatic attraction. Surface‐phosphonate‐comprising H + ‐DSP completely one‐electron oxidized V IV ‐POM with 0.39 % apparent quantum yield in the initial hour ( i AQY) in both HCl and phosphate buffer aqueous solutions. Conversely, the Zr 4+ ‐DSP i AQY decreased to 0.05 % in HCl aq. Considering that the 0.39 % i AQY was retained when replacing V IV ‐POM with Mn II ‐POM in HCl aq, we supposed that energy transfer deactivation from photoexcited PS* to surface‐immobilized V IV ‐POM is the plausible origin of the lower i AQY, owing to the stronger visible‐light absorptivity of V IV ‐POM . This suggests that accumulation of visible‐light‐transparent electron mediator on the photocatalyst surface is an effective approach for one‐directional electron transfer in Z‐scheme water‐splitting photocatalysis.