(Invited) Z-Scheme Water Splitting Using Dye-Sensitized Metal Oxide Nanosheets

Abstract

Solar water splitting by a heterogeneous photocatalyst, producing H2 and O2, is a potential solution for realizing large-scale H2 production. 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 remains low because of uncontrolled charge recombination reactions. Here it is shown 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. The Al2O3 and PSS modifiers, which have previously been shown to suppress back electron transfer reactions in a dye-sensitized H2 evolution photocatalyst, enabled operation of the Z-scheme system even at low intensity of simulated sunlight without a decrease in the STH values. 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 also comparable to conventional semiconductor-based suspended particulate photocatalyst systems.