Interfacial Electron Flow Control by Double Nano-architectures for Efficient Ru-Dye-Sensitized Hydrogen Evolution from Water

Interfacial electron flow is crucial for an efficient two-step (Z-scheme) solar water-splitting reaction. Dye-sensitization of a wide-gap oxide semiconductor has attracted considerable attention for decades as a means of producing hydrogen from water; however, it suffers from back electron transfer reactions at solid-solid and solid-solution interfaces. Here, we demonstrate that a combination of two nano-architectures, Ru-dye double layering and Pt cocatalyst intercalation to layered niobate semiconductor, effectively suppresses the back electron transfers at interfaces, leading to the complete oxidation of the [Co(bpy)(3)]-type electron mediator (bpy = 2,2'-bipyridine) as a result of efficient photocatalytic hydrogen production. Our systematic study on the Ru-dye double layers revealed that the double layering of two different Ru dyes and surface modification with the Zr4+ cation not only suppress the back electron transfer from an electron-injected semiconductor to oxidized dye but also accelerate the electron injection from the mediator to the oxidized dye. In addition, the re-reduction of the oxidized Co(III) mediator at the Pt cocatalyst surface was effectively suppressed by intercalation of Pt to the layered niobate semiconductor. The present work clearly shows that double nano-architectures controlling the surfaces of the semiconductor and cocatalyst have great potential for photo-induced charge separation at the solid-solution interface and expands the possibilities of layered semiconductor materials toward Z-scheme water splitting.