Surface Exchange Model for MIEC Membrane in Transient Stage

Abstract

Mixed Ionic and Electronic Conductors (MIECs) are promising membrane materials for oxygen separation from air at high temperature. The transient stage is critical due to the stress induced by the chemical and thermal strain. To predict this strain, the oxygen activity field through the membrane has to be known. While the diffusion is well described by the Wagner theory, no consensus has yet emerged regarding the surface exchange models proposed in the literature. Furthermore, these models describe the stationary state, and cannot be extended to the transient stage. A new macroscopic surface exchange model is proposed. This model takes into account the association/dissociation of oxygen and the high energetic cost of oxygen reduction/oxidation thanks to the balance of a transient species only present at the membrane surface. This model reproduces stationary and transient states