Kinetic Influence of the Electric Double Layer

Reactant concentrations Cyj in the bulk solution, as well as the Galvani potential between the electrode and the bulk solution (which is a constituent term in electrode potential E), appear in kinetic equations such as (6.8). However, the reacting particles are not those in the bulk solution but those close to the electrode surface, near the outer Helmholtz plane when there is no specific adsorption, and near the inner Helmholtz plane when there is specific adsorption. Both the particle concentrations and the potential differ between these regions and the bulk solution. It was first pointed out by Afexander N. Frumkin in 1933 that for this reason, the kinetics of electrochemical reactions should strongly depend on EDL structure at the electrode surface. 

Let / be the potential at the point where the reacting particle had been prior to the reaction, or where a product particle just generated by the reaction would be. This potential (which is referred to the potential in the bulk solution) has a value similar to potentials /2 or )/j, respectively, and gives rise to two effects important for the electrochemical reaction rates. 

The first effect is that of a concentration change of the charged reactant particles in the reaction zone this change is determined by Boltzmann s distribution law  

Depending on the signs of parameters Zj and /, the concentration in the reaction zone can be higher or lower than the bulk concentration. There is no change in the concentration of uncharged particles. 

The second effect is that of a change in the potentiaf difference effectively influencing the reaction rate. By its physical meaning, the activation energy should not be influenced by the full Galvani potential across the interface but only by the potential difference (cpo ) between the electrode and the reaction zone. Since the Galvani potential is one of the constituent parts of electrode potential E, the difference - j/ should be contained instead of E in Eq. (14.13)  

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