Solution of transport equations in a mixed conductor—a generic approach

Abstract

Based on different assumptions and solution strategies, several approaches to solve the transport equations in electrochemical devices based on mixed-conducting solid electrolytes employing reversible electrodes have been reported. Presented in this article is a more general approach, minimizing the assumptions and linking the most elegant solution strategies. Coupling the basic equations for ionic and electronic fluxes to the boundary conditions at the electrodes, constraints imposed by an external circuit containing a resistive element and a voltage source and adopting an analytical solution generates a generic model, which can be applied to fuel cells, ion pumps and electrolyzers. The resultant model encompasses the characteristics of all the previous models, except that of Näfe, which is based on an erroneous formulation of “fictitious conductivity” of the external circuit. The model is extended to the study of fuel cell behavior under non-ideal conditions of electrode polarization.