The role of redox mixed phases {ox _x (C _n red)_{1 −x} } in solid state electrochemical reactions and the effect of miscibility gaps in voltammetry

Abstract

A basic analysis is performed to establish the interrelations between the equilibria existing when one solid phase {ox} is transformed into another solid phase {C _n red} while both are in close contact with a solution containing both redox forms in the dissolved state. The transformation of the above solid phases by electrochemical reactions can be understood when the intermediate formation of mixed phases between {ox} and {C _n red} is taken into account. Such a description allows solid state electrochemical reactions to be modeled for the case of an infinite miscibility of oxidized and reduced solid compounds as well as for the case of systems with miscibility gaps. It is shown that miscibility gaps will lead to a splitting of both the anodic and cathodic voltammetric peaks and also to a distinct separation of the anodic and cathodic reactions on the potential scale in voltammetric experiments. This phenomenon can be called an immiscibility polarization.