Oxygen separation MIEC membranes

Sunarso J, Baumann S, Serra JM, Meulenberg WA, Liu S, Lin YS, and Diniz da Costa JC. Mixed ionic-electronic conducting (MIEC) ceramic-based membranes for oxygen separation. J. Membr. Sci. 2008 320 13-41. 

It is known that the MIEC membranes inevitably undergo a kinetic demixing/ decomposition process under oxygen separation conditions. When an oxygen ion conductive membrane is exposed to an oxygen chemical potential... 

MIEC Perovskites as Oxygen Separation Membrane Materials for the Oxy-fuel Combustion Power Production... 

It should be noted that mixed rate control is often reported in the literature on MIEC for oxygen separation in three cases when the membrane thickness is very close to its critical value, when the oxygen permeation flux values no longer seem to progress in a linear manner and when the oxygen permeation is co-controlled by both bulk diffusion and surface exchange processes (as shown in the illustration in Figure 4.3) [10]. To better... 

Figure 4.3 Schematic of the counter-current oxygen transport mechanism of a symmetric (dense) MIEC membrane exploited for oxygen separation applications (a) and the change in oxygen permeation flux with the membrane thickness (b). fSource Reproduced from Ref [ 10], with permission from Elsevier)...

Figure 4.15 (a) 3D CAD model and (b) a photo of a demonstration unit equipped with MIEC membranes for oxygen separation. fSource Reproduced with permission from Ref [92], Copyright 2012, Ralf Kriegel and Ingolf Voigt)... 

Oxygen separation by using a membrane is expected to be a real possibility, thanks to developments in mixed ionic and electronic conductors (MIECs). With mixed ionic and electronic conduction, oxide-ion conductors selectively permeate oxygen as a form of oxide ion. The mixed oxide-ion and electronic conductors used for this purpose are referred to as oxygen-permeable membranes. An oxygen-permeable membrane subjected to an oxygen potential gradient at elevated temperatures of around 700—1000 °C leads to the ambipolar conduction of oxide ions and electrons, as shown... 

Sunarso J, Mixed Ionic-electronic Conducting (MIEC) Ceramic-based Membranes for Oxygen Separation, Journal of Membrane Science, 320,13-41 (2008). 

Determination of nonstoichiometry in oxides is a key point in the search for new materials for electrochemical applications. In recent decades, owing to their current and potential applications (electrodes in fuel cells, insertion electrodes, membranes of oxygen separation, gas sensors, catalytic materials, etc.), various methods of precise characterization of MfECs have been proposed, either the measurement of the defect concentrations and the stoichiometric ratio as functions of the oxide composition, of the surroxmding oxygen pressure and of temperature, or the transport properties. There are different methods to determine the electrical properties of MIECs and, more specifically, the ionic and electronic contributions. The most appropriate method depends on different parameters, i.e., the total electrical conductivity of the studied oxides, the ionic and electronic transport numbers, the... 

CMRs. It is well established that MIECs are inherently catalytic to oxidation reactions. Therefore, MIEC-derived membranes may serve as both catalyst and oxygen separator, and no other catalysts are used in the dense ceramic MRs. Since chemical reactions take place on the membrane surface, it is required to have a much more porous membrane surface so as to contain a sufficient quantity of active sites. This can be achieved in the membrane preparation process, or by coating a porous membrane material after preparation. The main potential problems for this configuration are that the membrane may not have sufficient catalytic activity and the catalytic selectivity cannot he modulated with respect to the reactions considered. 

Due to its adjustable transport properties, suitably doped ceria may be used as an electrolyte (which must be an electronic insulator and a good ion conductor), as discussed in depth in Section 12.5, or as a dense oxygen separation membrane (which needs to be a MIEC). A dense oxygen separation membrane must conduct both... 

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