Discreteness-of-charge effects in electrode kinetics. III. The electroreduction of aquopentamminochromium(III) cation in the presence of specifically adsorbed iodide anions

Abstract

The kinetics of electroreduction of the aquopentamminochromium(lI1) cation have been studied at a Hg electrode in acidified aqueous solutions of Nal + NaClOJ with an ionic strength of 0.25 M. The rate of reaction increased with increase in iodide concentration due to the accelerating effect of this anion when it is adsorbed on the electrode. Analysis of the double layer effect indicates that the rate acceleration is greater than that predicted by the Frumkin theory chiefly because the reaction site is closer to the electrode than to the outer Helmholtz plane.

Fifty years of studies of double layer effects in electrode kinetics—a personal view

“…Finally, p ≠ is the number of solvent molecules displaced by the activated complex on entering the inner layer. Several studies of discreteness-of-charge-effects involving contact adsorbed anions were carried out including the effect of adsorbed iodide anions on the electroreduction of tetrathionate anion [31], the effect of adsorbed nitrate anions on the electroreduction of hexamminocobalt(III) cation [32], and the effect of adsorbed iodide anions on the electroreduction of monofluoropentaquochromium(III) cation [33]. The final study involved the elecroreduction of monofluoropentamminocobalt(III) cation in the presence of adsorbed nitrate anions [34].…”

The Kinetics of Heterogeneous Electron Transfer Reactions in Polar Solvents

“…These results can also be partially attributed to discreteness-of- anions, the decelerating effect of the adsorbed charge is overestimated when discreteness-ofcharge effects are ignored, and the value ofy increases with increase in gs [ (130]. Further analysis of these data [130][131][132][133] led to a more detailed description of the double layer effect including the location of the reaction site with respect to adsorbed ions and counter ions.…”