Interfacial Phenomena in Mixed Conducting Membranes: Surface Oxygen Exchange‐ and Microstructure‐Related Factors

Abstract

The transport behavior of ions, such as O 2À anions or protons, driven by chemical potential gradient across dense mixed conducting membranes is governed by many factors. In this chapter, the effects of surface exchange and ceramic microstructure are addressed. The surface-related aspects are discussed involving selected theoretical approaches and modeling. Relevant experimental methods are briefly described. The influence of microstructure on the gas permeation processes is analyzed for several types of mixed conducting membranes. The relationships between the membranes stability and their microstructure and surface exchange kinetics are considered on the basis of existing experimental data. IntroductionSolid-state nonmetallic conducting materials have been extensively developed and applied for various solid electrochemical devices during the last century. A large number of works reveal the great interest of researchers in energy storage and conversion devices, sensors, gas separation membranes, and other electrochemical applications of solid-state conducting materials [1-3]. The charge carriers may include electrons (or holes), protons, nonmetallic anions (such as O 2À , Cl À , etc.), and metal cations (such as Li þ , Na þ , etc.). The major groups of ion-conducting materials are discussed in the first volume of this handbook. Mixed conductors are the materials that have more than one type of mobile charge carriers (see Chapter 3 of the first volume). The high-temperature electrochemical applications of mixed conductors are, in particular, electrodes for solid oxide fuel cells (SOFCs) and other electrochemical devices, and ceramic membranes for oxygen, hydrogen, and carbon dioxide separation. For these types of applications, the solid should have high values of both the ionic/protonic and electronic conductivities. The electrode applications have been reviewed by many researchers [4][5][6][7], including Chapter 12 of the first volume and Chapters 5, 6 and 9 of this book, and are thus outside the scope of this chapter focused on selected aspects of mixed conducting membranes for gas separation.Solid State Electrochemistry II: Electrodes, Interfaces and Ceramic Membranes. Edited by Vladislav V. Kharton.