The kinetics of electrode reactions. I and II

Abstract

In any surface reaction taking place in a Solution, it is clear that the concentration of the reactants in the vicinity of the surface must fall. If the concentration in the bulk of the solution remains constant, a steady state may finally be reached, in which the rate of replenishment of the solution in this region, from the bulk, is equal to the rate at which the reactant in question is used up. But, in general, such a state is only attained when the concentration at the surface is less than that in the rest of the solution. If the reaction considered is an electrode reaction, these concentration changes may affect the electrode potential. This question is therefore of importance in the study of overpotential, and of the kinetics of electrode processes generally. The overpotential at an electrode is defined as the potential difference between this electrode and a similar unpolarized reversible electrode in the same solution. In practice this reference electrode is usually situated outside the region affected by the concentration changes near the electrode at which the reaction is taking place. The measured potential difference between the two electrodes, i.e. the measured overpotential, may therefore include a term due to the concentration difference.