Electric Double-Layer Effects on the Elementary Act of Electron Transfer

6 ELECTRIC DOUBLE-LAYER EFFECTS ON THE ELEMENTARY ACT OF ELECTRON TRANSFER 

In the crudest approximation, the effect of the efectrical double layer on electron transfer is taken into account by introduction of the electrostatic energy -e /i of the electron in the acceptor into the free energy of the transition AF [Frumkin correction see Eq. (34.25)], so that corrected Tafel plots are obtained in the coordinates In i vs. e(E - /i). Here /i is the average electric potential at the site of location of the acceptor ion. It depends on the concentration of supporting electrolyte and is small at large concentrations. Such approach implies in fact that the reacting ion represents a probe ion (i.e., it does not disturb the electric held distribution). 

A more sophisticated approach takes into account the fact that the presence of the reacting ion at a given point in the solution distorts the distribution of other ions of the electrolyte and thereby distorts the potential distribution. This phenomenon is called the effect of the micropotential. The average /i potential is then replaced by another average potential, calculated in the presence of the reacting ion at a given point. 

FIGURE 34.7 Dependence of the effective electron transmission coefficient on the electrochemical Landau-Zener parameter. 

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