Effects of adsorbed ions on simple electrode reactions. Part 1.—Reduction of periodate ion in the presence of toluene-p-sulphonate anions

Abstract

The influence of adsorbed toluene-p-sulphonate ions on the rate of electroreduction of periodate ions at mercury has been studied as a function of electrode potential and bulk concentration of the adsorbing ions in solutions of constant ionic strength. The ratio of the reduction rate in the presence of adsorbed anions to that in their absence at constant potential was found to be a function of the surface concentration of the adsorbed species independent of electrode potential, bulk concentration of the adsorbing species and their orientation on the electrode surface. An analysis of the decelerating effect of the adsorbed ions in terms of an electrostatic model of the interface which considers discreteness-of-charge effects is presented. The results of the analysis indicate that the reacting anion pairs with non-adsorbed cations in the vicinity of the reaction site before entering the activated state.