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

Preparation of Ru(II) polypyridyl–iridium oxide nanoparticle (IrO X NP) chromophore–catalyst assemblies on an FTO| nano ITO|TiO 2 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/cm 2 irradiation are observed for core/shell structures compared to TiO 2 after derivatization with [Ru(4,4′-PO 3 H 2 bpy) 2 (bpy)] 2+ (RuP 2 ) and uncapped IrO X NPs at pH 5.8 in NaSiF 6 buffer with a Pt cathode. Photocurrents arising from photolysis of the resulting photoanodes, FTO| nano ITO|TiO 2 |−RuP 2,IrO 2, are dependent on TiO 2 shell thickness and applied bias, reaching 0.2 mA/cm 2 at 0.5 V vs AgCl/Ag with a shell thickness of 6.6 nm. Long-term photolysis in the NaSiF 6 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 TiO 2 to stabilize surface binding of −RuP 2 prior to the addition of the IrO X NPs.