Visible Photoelectrochemical Water Splitting Based on a Ru(II) Polypyridyl Chromophore and Iridium Oxide Nanoparticle Catalyst

Preparation of Ru­(II) polypyridyl–iridium oxide nanoparticle (IrOX NP) chromophore–catalyst assemblies on an FTO|nanoITO|TiO2 core/shell by a layer-by-layer procedure is described for application in dye-sensitized photoelectrosynthesis cells (DSPEC). Significantly enhanced, bias-dependent photocurrents with Lumencor 455 nm 14.5 mW/cm2 irradiation are observed for core/shell structures compared to TiO2 after derivatization with [Ru­(4,4′-PO3H2bpy)2(bpy)]2+ (RuP2) and uncapped IrOX NPs at pH 5.8 in NaSiF6 buffer with a Pt cathode. Photocurrents arising from photolysis of the resulting photoanodes, FTO|nanoITO|TiO2|−RuP2,IrO2, are dependent on TiO2 shell thickness and applied bias, reaching 0.2 mA/cm2 at 0.5 V vs AgCl/Ag with a shell thickness of 6.6 nm. Long-term photolysis in the NaSiF6 buffer results in a marked decrease in photocurrent over time due to surface hydrolysis and loss of the chromophore from the surface. Long-term stability, with sustained photocurrents, has been obtained by atomic layer deposition (ALD) of overlayers of TiO2 to stabilize surface binding of −RuP2 prior to the addition of the IrOX NPs.