Actual activation energy of electrode process under mixed kinetics conditions

Abstract

In the case of a single-electron reaction with account for slow diffusion of reagents, equations for actual (experimentally determined) activation energies of two types were derived and analyzed: real energy A f, i.e., the energy measured at a constant electrode polarization value η = const) and formal energy (Ω_f, i.e., the value measured at a constant value of potential vs. an ambiguously chosen reference electrode E = const). It is found that under the conditions of a sufficiently significant deviation from equilibrium, the actual activation energy A _f is the weighted arithmetic mean of the diffusion activation energy and the sum of A ₀ + αFη (where A ₀ is the real activation energy of the discharge stage at polarization of η = 0); herewith, the weighting coefficients are the corresponding values of the current of the discharge stage and the limiting diffusion current. A similar relationship is also obtained for Ω_f. It is found that the A _f, η- and Ω_f, E-curves can in a number of cases feature regions with the negative A _f and Ω_f values in the mixed kinetics range.