Effects of Anionic Polymer Modification of Dye-Sensitized Niobate Photocatalysts on Solar-Driven Z-Scheme Overall Water Splitting

Pt-intercalated calcium niobate nanosheets (Pt/HCa2Nb3O10) sensitized by a Ru(II) complex dye are good photocatalysts for producing H-2 from aqueous solutions containing I- as a reversible electron donor. These materials are applicable to Z-scheme overall water splitting in combination with a WO3-based O-2-evolving photocatalyst under simulated sunlight. In this work, the effects of anionic polymer modification of the dye-sensitized nanosheets are examined by adsorbing sodium poly(styrenesulfonate) (PSS), sodium polyacrylate, sodium polymethacrylate (PMA), or sodium poly(4-styrenesulfonic-co-maleic acid) onto the dye-sensitized nanosheet surface. For half-cell H-2-evolution reaction in the presence of NaI, all of the polymers have a positive impact on the activity under visible light at lower light intensity, whereas only PMA is effective under high light-intensity condition. For Z-scheme overall water splitting with PtOx/H-Cs-WO3, PSS and PMA give almost the same solar-to-hydrogen energy conversion efficiencies (0.12% +/- 0.01%) under optimized conditions. However, PMA operates better than PSS at relatively low and high NaI concentrations, which are in general disadvantageous for the H-2- and O-2-evolving components of the Z-scheme, respectively.