Visible photoelectrochemical water splitting has been demonstrated for chemically linked Ru(II) polypyridyl chromophore-catalyst assemblies on nanoparticle TiO2 electrodes. In this presentation the results of nanosecond transient absorption measurements will be reported which, for the first time, explore the microscopic dynamics for the first two steps in the photo-activation of the assembly [(4,4’-PO3H2bpy)2Ru(BL)Ru(tpy’)(OH2)]4+ (1, -[RuII-RuII-OH2]4+; BL = 1,2-Bis(4’-methyl-[2,2’-bipyridin]-4-yl)ethane; tpy’ = 2,6-bis(1-methylbenzimidazol-2-yl)-pyridine) on both nanoparticle TiO2 and core/shell SnO2/TiO2 electrodes. A key result was that light excitation of the mixed-valence assembly at pH =1, -[RuII-RuIII-OH2]5+, resulted in excited state injection followed by back electron transfer to a -[RuII-RuIII-OH2]5+ assembly that had not undergone excited state injection. A slow process observed on a second time scale consistent with a one electron, two proton transfer reaction. TiO2|-[RuIII-RuIII-OH2]5+ TiO2|-[RuII-RuIV=O]2+ + 2 H+. The importance of this proton coupled electron transfer reaction for light driven water oxidation will be discussed.

Light-driven, multi-electron transfer activation of a water oxidation catalyst

252nd National Meeting (2016)

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