Effect of the electrical double layer on the rate of electrode processes at high overvoltages: Comparing different theoretical approaches

The possibility of applying the slow-discharge theory of Frumkin to process es of the electron transfer is considered in a wide range of overvoltages t hat correspond to considerable variations in the formal and real transfer c oefficients. In connection with this, an analysis is conducted of dependenc es of the current on the supporting-electrolyte concentration and the reage nt charge that are predicted by the Marcus theory and the quantum-mechanica l theory of an elementary act which allows for the activation contribution of transfer from different electronic levels of the metal. It is shown that the Frumkin-Petrii equation for the charge of a reacting species is rigoro usly fulfilled in all considered approaches. A technique is proposed for co nstructing corrected Tafel dependences (CTD), which is based on the Marcus equation for the activation energy of a redox process. The fundamental diff erence between the marcusian and classical CTDs lies in a unique determinat ion of kinetic parameters without resorting to the formal transfer coeffici ent in an explicit form. By applying an optimization procedure, one can det ermine the total reorganization energy and estimate the transmission transf er coefficient. A simple criterion is found that allows one to determine th e region of applicability of the Marcus theory for the description of exper imental data. It is shown that the reduction of the ferricyanide ion on a m ercury electrode at negative charges of the surface occurs outside this reg ion and is presumably an activationless process.