Light-Driven Water Splitting by a Covalently Linked Ruthenium-Based Chromophore− Catalyst Assembly

The preparation and characterization of new Ru(II) polypyridylbased chromophore−catalyst assemblies, [(4,4′-PO3H2-bpy)2Ru(4-Mebpy-4′-epic)Ru(bda)(pic)] (1, bpy = 2,2′-bipyridine; 4-Mebpy-4′-epic = 4-(4-methylbipyridin-4′-yl-ethyl)-pyridine; bda = 2,2′-bipyridine-6,6′-dicarboxylate; pic = 4-picoline), and [(bpy)2Ru(4-Mebpy-4′-epic)Ru(bda)(pic)] (1′) are described, as is the application of 1 in a dye-sensitized photoelectrosynthesis cell (DSPEC) for solar water splitting. On SnO2/TiO2 core−shell electrodes in a DSPEC configuration with a Pt cathode, the chromophore−catalyst assembly undergoes light-driven water oxidation at pH 5.7 in a 0.1 M acetate buffer, 0.5 M in NaClO4. With illumination by a 100 mW cm−2 white light source, photocurrents of ∼0.85 mA cm−2 were observed after 30 s under a 0.1 V vs Ag/AgCl applied bias with a faradaic efficiency for O2 production of 74% measured over a 5 min illumination period. Photoelectrochemical water splitting and the production of fuels with energy harnessed from sunlight (“solar fuels”) will likely play an important role in our energy future. In this approach, energy from solar radiation drives production of a fuel such as H2, CO, or CH4, coupled with the oxidation of water to O2. 3 Dye-sensitized photoelectrosynthesis cells (DSPECs) have been shown to carry out solar-driven water splitting, and the improvement of this technology has focused on the development of higher-performing photoanodes. A DSPEC photoanode integrates a nanoparticulate wide-band-gap n-type semiconductor oxide film, such as nanoTiO2, with a molecular chromophore−catalyst assembly for carrying out light absorption and catalyzing the oxidation of water to O2 (eq 1). υ + → + + + − h 2H O 4 O 4H 4e (photoanode) 2 2