Interfacial Electron Transfer Dynamics for [Ru(bpy)2((4,4′-PO3H2)2bpy)]2+ Sensitized TiO2 in a Dye-Sensitized Photoelectrosynthesis Cell: Factors Influencing Efficiency and Dynamics

Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [(Ru(bpy)2(4,4′-(PO3H2)2bpy)]2+ attached to TiO2 nanoparticle films, TiO2−RuII, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H2 production. In these experiments, laser flash excitation of TiO2−RuII and rapid injection lead to TiO2(e−)−RuIII with subsequent TiO2(e−)−RuIII → TiO2−RuII back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA4−) as irreversible electron transfer donors. With added TEOA or EDTA4−, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H2 production in the photoelectrosynthesis cell. Reduction of TiO2(e−)−RuIII by both TEOA and EDTA4− occurs with kD ∼ 106 M−1 s−1. EDTA4− is a more efficient scavenger by a factor of ∼3 because of a more favorable partition equilibrium between the film and the externa...