An Insulating AlO Overlayer Prevents Lateral Hole Hopping Across Dye-Sensitized TiO Surfaces.

Three chromophores of the general form [Ru(bpy')(4,4'-(POH)-2,2'-bipyridine)], where bpy' is 4,4'-(C(CH))-2,2'-bipyridine (Ru(dtb)P); 4,4'-(CHO)-2,2'-bipyridine (Ru(OMe)P), and 2,2'-bipyridine (RuP) were anchored to mesoporous thin films of TiO nanocrystallites at saturation surface coverages to investigate lateral self-exchange Ru intermolecular hole hopping in 0.1 M LiClO/CHCN electrolytes. Hole hopping was initiated by a potential step 500 mV positive of the (Ru) potential or by pulsed laser (532 nm, 8 ns fwhm) excitation and monitored by visible absorption chronoabsorptometry and time-resolved absorption anisotropy measurements, respectively.

A donor-chromophore-catalyst assembly for solar CO reduction.

We describe here the preparation and characterization of a photocathode assembly for CO reduction to CO in 0.1 M LiClO acetonitrile. The assembly was formed on 1.

Halide Photoredox Chemistry.

Halide photoredox chemistry is of both practical and fundamental interest. Practical applications have largely focused on solar energy conversion with hydrogen gas, through HX splitting, and electrical power generation, in regenerative photoelectrochemical and photovoltaic cells. On a more fundamental level, halide photoredox chemistry provides a unique means to generate and characterize one electron transfer chemistry that is intimately coupled with X-X bond-breaking and -forming reactivity.

Barriers for interfacial back-electron transfer: A comparison between TiO and SnO/TiO core/shell structures.

Temperature dependent kinetics for back-electron transfer (BET) from electrons in TiO or SnO/TiO core/shell nanoparticles to oxidized donor-bridge-acceptor (D-B-A) sensitizers is reported over a 110° range. Two D-B-A sensitizers (CF-p and CF-x) were utilized that differed only by the nature of the bridging ligand: a xylyl spacer that largely insulated the two redox active centers and a phenyl bridge that promoted strong electronic coupling and an adiabatic electron transfer mechanism. An Arrhenius analysis revealed that the activation energies were significantly larger for the core/shell oxides, E = 32 ± 4 kJ/mol, compared to TiO alone, E = 22 ± 6 kJ/mol.

Optimization of Photocatalyst Excited- and Ground-State Reduction Potentials for Dye-Sensitized HBr Splitting.

Dye-sensitized bromide oxidation was investigated using a series of four ruthenium polypyridyl photocatalysts anchored to SnO/TiO core/shell mesoporous thin films through 2,2'-bipyridine-4,4'-diphosphonic acid anchoring groups. The ground- and excited-state reduction potentials were tuned over 500 mV by the introduction of electron withdrawing groups in the 4 and 4' positions of the ancillary bipyridine ligands. Upon light excitation of the surface-bound photocatalysts, excited-state electron injection yielded an oxidized photocatalyst that was regenerated through bromide oxidation.

Fundamental Factors Impacting the Stability of Phosphonate-Derivatized Ruthenium Polypyridyl Sensitizers Adsorbed on Metal Oxide Surfaces.

A series of 18 ruthenium(II) polypyridyl complexes were synthesized and evaluated under electrochemically oxidative conditions, which generates the Ru(III) oxidation state and mimics the harsh conditions experienced during the kinetically limited regime that can occur in dye-sensitized solar cells (DSSCs) and dye-sensitized photo-electrosynthesis cells, to further develop fundamental insights into the factors governing molecular sensitizer surface stability in aqueous 0.1 M HClO. Both desorption and oxidatively induced ligand substitution were observed on planar fluorine-doped tin oxide (FTO) electrodes, with a dependence on the E Ru(III/II) redox potential dictating the comparative ratios of the processes.

Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex.

The complex [Ru(deeb)(bpz)] (RuBPZ, deeb = 4,4'-diethylester-2,2'-bipyridine, bpz = 2,2'-bipyrazine) forms a single ion pair with bromide, [RuBPZ, Br], with K = 8400 ± 200 M in acetone. The RuBPZ displayed photoluminescence (PL) at room temperature with a lifetime of 1.75 μs.

Dye-Sensitized Hydrobromic Acid Splitting for Hydrogen Solar Fuel Production.

Hydrobromic acid (HBr) has significant potential as an inexpensive feedstock for hydrogen gas (H) solar fuel production through HBr splitting. Mesoporous thin films of anatase TiO or SnO/TiO core-shell nanoparticles were sensitized to visible light with a new Ru polypyridyl complex that served as a photocatalyst for bromide oxidation. These thin films were tested as photoelectrodes in dye-sensitized photoelectrosynthesis cells.