Multifactor theoretical study on ionic transport numbers of mixed oxygen ionic-electronic conducting oxides determined by the electromotive force method

Abstract

The electromotive force (EMF) method is widely applied to measure the ionic transport numbers (ti) of mixed oxygen-ionic and electronic conducting oxides. However, the results determined by the EMF method are the average/apparent ti (tiapp), subjected to a given gradient of oxygen partial pressure (PO2), rather than ti at a specific PO2, making it challenging to reveal the accurate properties of materials. In this study, to clarify the impact of this issue, a precise defect distribution model of Gd doped CeO2 (GDC), considering defect equilibrium and local charge neutrality, is built. A multifactor theoretical analysis is conducted to compare tiapp and ti of the membrane at different sides. The modeling results reveal that a thick membrane is recommended for avoiding the influence of membrane thickness on tiapp. When there is a large difference of PO2 between two sides of the GDC membrane (PO2highPO2PO2lowPO2>1025), tiapp is inclined to ti at the side of high PO2. Only when both sides of the GDC membrane are reducing atmosphere, tiapp of the modified EMF method is approximately the average of ti at both sides. The findings of this study are instructive for the rational application of EMF methods.