Energetics of Electron Transfer at the Nanocrystalline Titanium DioxideSemiconductor/Aqueous Solution Interface: pH Invariance of the Metal Based Formal Potential of a Representative Surface Attached Dye Couple

摘要

Mediator-based spectroelectrochemical assessment of the metal-centered formalpotential (E sub f(RU)) of a representative inorganic dye, Ru(4,4'-(CH2PO3)-2,2'-bipyridine)3 (10-), bound to a nanocrystalline titanium dioxide film shows that the potential is insensitive to changes in solution pH, despite significant shifts in the conduction band edge energy (E sub CB) of the underlying semiconductor electrode in response to the same environmental perturbations. The observations are important in the context of recent work showing that back electron reactivity for the same semiconductor/dye combination is pH independent over a 19 pH unit range, despite apparent changes in back reaction driving force of greater than 1.2 eV over the same interval (Yan, S.; Hupp, J. T. J Phys. Chem. 1996, 100, 6867). In particular, the spectroelectrochemical findings serve to rule out a suggested alternative interpretation of the unusual kinetic effects