The electrochemical transfer-coefficient

In discussions of the kinetics of electrode reactions, the central issue is the manner in which the rate constants depend on the electrode potential. It is often stated ex cathedra that this dependence is exponential and that constant fractions of the electrode potential appear in the exponential terms; these fractions are characterized by the "transfer coefficient, α" or "symmetry factor, β". The impression is thereby given that we understand the physical nature of the "transfer" or "symmetry" that determines the magnitude of α or β. In fact, the terminology "transfer coefficient" was introduced in connection with a model for the electron transfer that is not accpted; and the interpretation of β as describing the symmetry of the energy barrier is inadequate since, by definition, β describes the change in the barrier as the potential changes, and not any property of the barrier at a particular potential. There is no adequate justification for an a priori introduction of the transfer coefficient as an implicitly potential-independent parameter.