Surface-modified, dye-sensitized niobate nanosheets enabling an efficient solar-driven Z-scheme for overall water splitting

While dye-sensitized metal oxides are good candidates as H₂ evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remain low because of uncontrolled charge recombination reactions. Here, we show that modification of Ru dye-sensitized, Pt-intercalated HCa₂Nb₃O₁₀ nanosheets (Ru/Pt/HCa₂Nb₃O₁₀) with both amorphous Al₂O₃ and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO₃-based O₂ evolution photocatalyst and an I₃^-/I^- redox mediator, relative to an analogous system that uses unmodified Ru/Pt/HCa₂Nb₃O₁₀. By using the optimized photocatalyst, PSS/Ru/Al₂O₃/Pt/HCa₂Nb₃O₁₀, a maximum STH of 0.12% and an apparent quantum yield of 4.1% at 420 nm were obtained, by far the highest among dye-sensitized water splitting systems and comparable to conventional semiconductor-based suspended particulate photocatalyst systems.