G. A. Tsirlina, O. A. Petrii, Yu. I. Kharkats†, and A. M. Kuznetsov
Moscow State University, Vorob’evy gory, Moscow, 119899 Russia
Frumkin Institute of Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 117071 Russia
Received December 1, 1998
Abstract—Application of the slow-discharge theory for analyzing experimental data on the electron transfer
kinetics in the cases where the charge is distributed nonuniformly over species of the reagent and/or product is
considered. It is shown that, for real reagents whose size in some cases is commensurate with characteristic
thicknesses of the diffuse part of EDL, the corrected Tafel dependences (CTD) cannot be interpreted on the
basis of the approximation of point reagents. In particular, CTD constructed with ordinary techniques are
expected to be linear near the potential of zero charge (PZC). Substantial errors may also arise when heteroge-
neous rate constants are determined by extrapolating CTD. At the same time, the charge distribution makes no
impact on the reagent charge in the bulk solution calculated with the Frumkin–Petrii equation. Deviations of
CTD from linearity caused by the above effects are the strongest near PZC and substantially differ from those
predicted by the Marcus theory for point reagents. In a wide range of potentials (electrode charges), charge dis-
tributions of reagents and products do not affect the apparent transfer coefficient. However, they may substan-
tially alter the rate constant derived by extrapolating CTD. Special cases of charge distributions modeling reac-
tions that involve complex anions, functionally substituted organic molecules, and anion–cation pairs are con-
sidered.
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