Interpretation of Defect and Gas-Phase Fluxes through Mixed-Conducting Ceramics Using Nernst-Planck-Poisson and Integral Formulations

This paper derives and demonstrates two models to represent defect transport through mixed-conducting ceramic membranes. The Nernst-Planck-Poisson (NPP) model is more general, but requires the computational solution of a boundary-value problem on a mesh network. The Integral method relies on more assumptions, but defect fluxes can be evaluated analytically based upon material properties and gas-phase composition at the membrane surfaces. Using examples based upon yttrium-doped barium zirconate, the two approaches are compared quantitatively. Under many circumstances the models deliver quantitatively similar results, but for situations where the membrane is exposed to large and/or multiple partial-pressure gradients, the predicted fluxes can deviate. The variations are the result of different physical assumptions and mathematical simplifications that are being used in the two models. (c) 2013 The Electrochemical Society. All rights reserved.