Wj. Royea et al., FRUMKIN CORRECTIONS FOR HETEROGENEOUS RATE CONSTANTS AT SEMICONDUCTING ELECTRODES, Journal of electroanalytical chemistry [1992], 438(1-2), 1997, pp. 191-197
Frumkin corrections for semiconductor electrodes have been evaluated i
n both depletion and accumulation conditions. In conjunction with the
Gouy-Chapman-Stern model, a finite difference approach was used to cal
culate the potential drop in a depleted semiconductor and in the compa
ct and diffuse layers of the contacting solution as a function of the
potential applied to the solid/liquid interface. At potentials greater
than 30 mV positive of the flat-band potential E-fb the potential dro
p across the solution accounts for less than 3% of the total potential
drop across an n-type semiconductor of dopant density 1 X 10(15) cm(-
3) in a methanolic solution of 1.0 M LiCl. Under these conditions, the
concentration of a non-adsorbing, dipositively-charged redox species
at the outer Helmholtz plane does not vary from its concentration in t
he bulk of the solution by more than 2%. This relatively small concent
ration gradient and potential drop across the Helmholtz layer combine
to produce negligible Frumkin correction terms for kinetic data at dep
leted semiconductor electrodes compared to those for metallic electrod
es at the same applied potential relative to the potential of zero cha
rge. Under accumulation conditions, the potential drop across the solu
tion is more significant, and the concentration of redox species at th
e surface can be as much as twice as great as that in the bulk of the
solution. However, these conditions require an applied potential of -1
V relative to E-fb. Additionally, under all conditions that were simu
lated, the correction to the driving force used to evaluate the hetero
geneous rate constant does not exceed 2% of the uncorrected heterogene
ous rate constant. (C) 1997 Elsevier Science S.A.