Mixed-potential theory characterized

Electrochemical corrosion systems can be characterized using the kinetic parameters previously described as Tafel slopes, exchange and limiting current densities. However, the mixed potential theory requires a mixed electrode system. This is shown in Eigure 5.1 for the classical pure zinc (Zn) electrode immersed in hydrochloric (NCl)acid solution [1,8-9]. This type of graphical representation of electrode potential and current density is known as Evans Diagram for representing the electrode kinetics of pure zinc. 

Clearly, in the subsystem resolution one could also consider all intermediate specifications of the molecular (constrained) equilibria, when only a part of the subsystems remains externally open (characterized by the fixed chemical potentials of a common reservoir) with the remaining, complementary set of subsystems being closed (characterized by the fixed subsystem numbers of electrons) [4,5]. Such mixed representations can be also naturally defined in the CSA approach. We would like to observe, that in the theory of chemical reactivity these partially opened situations do indeed arise, e.g., in the surface reactions, when one adsorbate is opened (chemisorbed) while the other reactant remains externally closed (physisorbed) on the catalyst surface, which acts as the electron reservoir for the reaction. 

---