Sur la définition locale des potentiels chimiques dans les systèmes électrochimiques

The electrochemical potential of a component is usually defined as the derivative of the electrochemical free energy of the whole system. With this global definition it is impossible to give a simple relation between the electrochemical potential at a point in the system and the physical properties at the same point (as temperature, concentrations and polarisation of the molecules a. g.). On the contrary, the local method, which was elaborated by the authors in collaboration with I. PRIGOGINE, consists in writing the entropy and energy balances in each volume element. This method allows one to define the chemical potential for each component as a function of the local variables. This expression, which is a generalisation of one proposed by GUGGENHEIM for dielectrics, shows clearly the effect of the electric field and polarisation of the molecules. The equilibirum state then corresponds to uniform electrochemical potentials. These are composed of three terms representing respectively the ordinary chemical potential in absence of electric field, the influence of polarisation and the influence of electric potential. When the system is made up of homogeneous conducting phases, the polarisation term acts only at the interfaces. In the bulk of each homogeneous conducting phase, the chemical potential is simply the potential which would exist at equilibrium in an electrically neutral system without field. The authors discuss the effect of dipoles on the galvani electric tension and on the distribution of the components in the layers. They show the deficiencies of the global definition and recall the physical meaning of the division of the electrochemical potential into a chemical term and a term related to the electric potential. The purely local phenomena are controlled by the chemical term. Copyright © 1954 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim