Ke. Pomykal et al., THEORETICAL AND EXPERIMENTAL UPPER-BOUNDS ON INTERFACIAL CHARGE-TRANSFER RATE CONSTANTS BETWEEN SEMICONDUCTING SOLIDS AND OUTER-SPHERE REDOX COUPLES, Journal of physical chemistry, 100(9), 1996, pp. 3652-3664
Theoretical expressions for the charge-transfer rate constant at a sem
iconductor/liquid junction have been modified to include the effects o
f adiabaticity and the existence of a Helmholtz layer at the solid/liq
uid interface. These expressions have yielded an estimate of the maxim
um interfacial charge-transfer rate constant, at optimal exoergicity,
for a semiconductor in contact with a random distribution of nonadsorb
ing, outer-sphere redox species. An experimental upper bound on this i
nterfacial charge-transfer rate constant has been obtained through the
determination of key energetic and kinetic properties for stable semi
conductor electrodes in contact with outer-sphere redox species. For t
his purpose, n-Si/CH3OH-dimethylferrocenium-dimethylferrocene, n-GaAs/
CH3CN-ferrocenium-ferrocene, and p-InP/CH3CN-cobaltocenium-cobaltocene
contacts were investigated using a combination of current density-pot
ential and differential capacitance-potential methods. The upper limit
s for the interfacial charge-transfer rate constant at these semicondu
ctor/liquid contacts were found to be consistent with the upper limits
predicted by theory. The current density-potential behavior of n-InP
and p-InP/Fe(CN)6(3-/4-)(aq) junctions was also examined in order to a
ssess the validity of prior kinetic measurements on these interfaces.