Simulating Charge Transport in Solid Oxide Mixed Ionic and Electronic Conductors: Nernst-Planck Theory vs Modified Fick s Law

© The Author(s) 2016. Published by ECS. All rights reserved. With the assumption that the Fermi level (electrochemical potential of electrons) is uniform across the thickness of a mixed ionic and electronic conducting (MIEC) electrode, the charge-transport model in the electrode domain can be reduced to the modified Fick s first law, which includes a thermodynamic factor A. A transient numerical solution of the Nernst-Planck theory was obtained for a symmetric cell with MIEC electrodes to illustrate the validity of the assumption of a uniform Fermi level. Subsequently, an impedance numerical solution based on the modified Fick s first law is compared with that from the Nernst-Planck theory. The results show that Nernst-Planck charge-transport model is essentially the same as the modified Fick s first law model as long as the MIEC electrodes have a predominant electronic conductivity. However, because of the invalidity of the uniform Fermi level assumption for a MIEC electrolyte with a predominant ionic conductivity, Nernst-Planck theory is needed to describe the charge transport behaviors.