Journal of Membrane Science 320 (2008) 13–41 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Review Mixed ionic–electronic conducting (MIEC) ceramic-based membranes for oxygen separation J. Sunarso a , S. Baumann b , J.M. Serra c , W.A. Meulenberg b , S. Liu a , Y.S. Lin d , J.C. Diniz da Costa a,∗ a FIMLab - Films and Inorganic Membrane Laboratory, Division of Chemical Engineering, The University of Queensland, Brisbane, Qld 4072, Australia b Forschungszentrum J¨ ulich, Institute for Energy Research, IEF1, Materials Synthesis and Processing, 52425 J¨ ulich, Germany c Instituto de Tecnolog´ ıa Qu´ ımica (UPV-CSIC), 46022 Valencia, Spain d Department of Chemical Engineering, Arizona State University, Tempe, AZ 85287, USA article info Article history: Received 30 November 2007 Received in revised form 26 March 2008 Accepted 30 March 2008 Available online 15 April 2008 Keywords: Dense ceramic membrane Mixed ionic–electronic conduction Fluorite Perovskite Transport mechanisms Synthesis methods abstract Although Nernst observed ionic conduction of zirconia–yttria solutions in 1899, the field of oxygen sep- aration research remained dormant. In the last 30 years, research efforts by the scientific community intensified significantly, stemming from the pioneering work of Takahashi and co-workers, with the ini- tial development of mixed ionic–electronic conducting (MIEC) oxides. A large number of MIEC compounds have been synthesized and characterized since then, mainly based on perovskites (ABO 3-ı and A 2 BO 4±ı ) and fluorites (A ı B 1-ı O 2-ı and A 2ı B 2-2ı O 3 ), or dual-phases by the introduction of metal or ceramic ele- ments. These compounds form dense ceramic membranes, which exhibit significant oxygen ionic and electronic conductivity at elevated temperatures. In turn, this process allows for the ionic transport of oxygen from air due to the differential partial pressure of oxygen across the membrane, providing the driving force for oxygen ion transport. As a result, defect-free synthesized membranes deliver 100% pure oxygen. Electrons involved in the electrochemical oxidation and reduction of oxygen ions and oxygen molecules respectively are transported in the opposite direction, thus ensuring overall electrical neutral- ity. Notably, the fundamental application of the defect theory was deduced to a plethora of MIEC materials over the last 30 years, providing the understanding of electronic and ionic transport, in particular when dopants are introduced to the compound of interest. As a consequence, there are many special cases of ionic oxygen transport limitation accompanied by phase changes, depending upon the temperature and oxygen partial pressure operating conditions. This paper aims at reviewing all the significant and rele- vant contribution of the research community in this area in the last three decades in conjunction with theoretical principles. © 2008 Elsevier B.V. All rights reserved. Contents 1. Introduction ........................................................................................................................................... 14 2. General background .................................................................................................................................. 14 2.1. Current ceramic oxygen separation technology .............................................................................................. 14 2.2. Structure of ceramic membranes ............................................................................................................. 15 2.2.1. Fluorite compounds ................................................................................................................. 15 2.2.2. Perovskite compounds .............................................................................................................. 15 3. Defect theory ......................................................................................................................................... 15 4. Transport mechanisms ............................................................................................................................... 18 4.1. Limiting cases ................................................................................................................................. 18 4.1.1. Bulk-diffusion limited ............................................................................................................... 18 4.1.2. Surface-exchange reaction limited .................................................................................................. 20 4.2. Generalized transport equations ............................................................................................................. 21 ∗ Corresponding author. Tel.: +61 7 3365 6960; fax: +61 7 3365 4199. E-mail address: j.dacosta@eng.uq.edu.au (J.C. Diniz da Costa). 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.03.074