FLUX-MATCHING CONDITIONS AT TIO2 PHOTOELECTRODES - IS INTERFACIAL ELECTRON-TRANSFER TO O-2 RATE-LIMITING IN THE TIO2-CATALYZED PHOTOCHEMICAL DEGRADATION OF ORGANICS
Jm. Kesselman et al., FLUX-MATCHING CONDITIONS AT TIO2 PHOTOELECTRODES - IS INTERFACIAL ELECTRON-TRANSFER TO O-2 RATE-LIMITING IN THE TIO2-CATALYZED PHOTOCHEMICAL DEGRADATION OF ORGANICS, Journal of physical chemistry, 98(50), 1994, pp. 13385-13395
A flux-matching condition has been applied to determine whether O-2 re
duction is rate-limiting under photocatalytic conditions for the degra
dation of CHCl3 at rutile TiO2 single-crystal electrodes. In this appr
oach, the potential dependence of the photooxidation current density i
s compared to the potential dependence of the current density for O-2
reduction. The potential at which the oxidation and reduction fluxes a
re equal determines the operating potential and the steady-state flux
that will flow through the crystal under no applied bias. If this flux
-matching condition occurs when the cathodic flux equals the flux of p
hotogenerated carriers, then the predicted quantum yield should approa
ch unity; otherwise, recombination should be significant in the TiO2.
Our measurements indicate that significant recombination will occur fo
r the oxidation of typical organic molecules in H2O over a range of pH
values. The data also indicate that Pt catalysis of O-2 reduction sho
uld be beneficial for the oxidation of organic molecules, as would the
use of alternate electron accepters such as Fe(CN)(6)(3-). The O-2 re
duction data and rotating disk electrode data collected in this work a
llow a quantitative comparison to theoretical estimates of the electro
n transfer rate constant for O-2 reduction at TiO2. We also present an
elucidation of the previously published theoretical treatments of TiO
2 charge transfer rate constants in view of the new data collected her
ein.