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In view of its important role as raw materials in various energy and environment fields, pure oxygen has been widely required. The present cryogenic distillation, polymeric membrane and pressure swing adsorption (PSA) air separation methods are either energy-intensive or producing non-high purity oxygen. The comparative analysis of the inorganic dense ceramic-based oxygen transport membranes (OTMs) with these traditional oxygen production technologies and the H 2 /O 2 production by electrolysis of water shows irreplaceable advantages. The oxygen transport mechanism has been elaborated further to reveal the theoretical basis for the development of OTMs. The dual-phase membranes that have been widely studied are divided into three types according to the conduction paths of oxygen ions and electrons. Based on a review of the different types of OTM materials experienced in the past 30 years, its applications such as oxygen-enriched combustion involving H 2 and membrane reactors have been discussed. Finally, challenges and future directions are analyzed according to potential industrial design directions and competitive technologies of OTMs. • Progress of oxygen transport membrane architecture and materials is presented. • Dual-phase membrane is subdivided into three types by particle conduction paths. • Electrolytic water, membrane and traditional O 2 production ways are analyzed. • The development history and application of membrane are summarized in detail. • Membrane reactor to produce pure H 2 (>99.99%) for fuel cell is discussed. [ABSTRACT FROM AUTHOR]

Oxygen permeation measurements are performed on dense samples of CaTi 0.85 Fe 0.15 O 3− δ , CaTi 0.75 Fe 0.15 Mg 0.05 O 3− δ and CaTi 0.75 Fe 0.15 Mn 0.10 O 3− δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O 2 permeability of CaTi 1− x Fe x O 3− δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 °C with feed side oxygen partial pressures between 0.01 and 1 bar. The O 2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.2×10 −3 ml min −1 cm −1 at 900 °C and 0.21 bar O 2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x =0.2. While the O 2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 °C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O 2 permeability, i.e., oxygen vacancies and electronic charge carriers. [ABSTRACT FROM AUTHOR]

Abstract: Although Nernst observed ionic conduction of zirconia–yttria solutions in 1899, the field of oxygen separation 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 initial 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 (ABO3−δ and A2BO4±δ ) and fluorites (A δ B1−δ O2−δ and A2δ B2−2δ O3), or dual-phases by the introduction of metal or ceramic elements. 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 neutrality. 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 relevant contribution of the research community in this area in the last three decades in conjunction with theoretical principles. [Copyright &y& Elsevier]

CO 2 uphill permeation is interpreted as being in accordance with the recently developed permeation model. The model allows the conditions to be qualified for the occurrence of the phenomenon. [ABSTRACT FROM AUTHOR]