The non-integer cyclovoltammetric electron-exchange numbers of reversible redox reactions of adsorbates: theoretical considerations

Two types of non-integer electron-exchange numbers from uniform and reversible surface-redox reactions without side reactions have been distinguished. The first being the apparent number, napp, of the apparent faradaic charge corresponding to cyclovoltammetric peak areas above the interpolated baseline, and the second the thermodynamically defined surface-redox valency, n', of Nernstian slopes of cyclovoltammetric peak potentials depending on different solution pH. An analytical expression has been derived for napp based on a simplified capacitive equivalent circuit and for n' using the potential-dependent free adsorption energies of the reactants involved. It should be pointed out that the different experimental values of napp and n' refer to the same integer number of electrons per molecule oxidized or reduced.