Oxygen ion conducting membrane

FIGURE 6.10 Different membrane concepts for oxygen-ion conducting membranes, (a) Dense mixed conducting membrane top-layer supported on an asymmetric macroporous support (b) dense self-supported mixed conducting membrane with graded porous interfaces and (c) solid electrolyte cell (oxygen pump). 

Figure6.2 Mixed electron-oxygen ion conducting membrane.

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... 

Atkinson, A. and Ramos, T.M.G.M. (2000) Chemically-induced stresses in ceramic oxygen ion-conducting membranes. Solid State Ionics, 129, 259-269. 

Certain requirements concerning mechanical performance and rehabihty must be fulfilled in all apphcations, e.g. thermally or electrically insulating materials (dense alumina for electronic circuit supports, thermally insulating closed-pore alumina or zirconia), catalyst supports, filter membranes and membrane supports (open-pore alumina), ionic conductors, oxygen sensors (dense zirconia) and oxygen-ion-conducting membranes in sohd oxide fuel cells, oxygen separators and catalytic membrane reactors (open-pore zirconia) [Atkinson ... 

For the pure oxygen ion conducting membrane, the electrons released from the chemical reactions have to be transported to the oxygen-rich side via an external circuit so as to precede the reaction and the oxygen permeation, as shown in Fig. 7.5c. In this case, electrical power is co-generated along with the production of valuable chemicals. Therefore, the membrane reactor operating in this mode is also called a solid oxide fuel cell type membrane reactor (SOFC-MR). 

B.C.H. Steele. Dense Ceramic ion conducting membranes in Oxygen ion and mixed conductors and their technological applications, (1997) Erice, Italy Kluwer. 

A fuel cell consists of an ion-conducting membrane (electrolyte) and two porous catalyst layers (electrodes) in contact with the membrane on either side. The hydrogen oxidation reaction at the anode of the fuel cell yields electrons, which are transported through an external circuit to reach the cathode. At the cathode, electrons are consumed in the oxygen reduction reaction. The circuit is completed by permeation of ions through the membrane. 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

For the purposes of review. Figure 1 illustrates the basic function of the cathode in a solid oxide fuel cell. Whether acting alone or as part of a stack of cells, each cell consist of a free-standing or supported membrane of an oxygen-ion-conducting electrolyte, often yttria-stabilized zirconia (YSZ). Oxygen, which is fed (usually as air) to one side of the membrane, is reduced by the cathode to oxygen ions via the overall half-cell reaction... 

Electrolysis of water — This is a process of electrochemical decomposition of water into -> hydrogen and -> oxygen. Apart from alkaline electrolyzers using 25% KOH solution [i], devices with polymer, or ceramic ion-conducting -> membranes have been developed for industrial applications [ii]. 

PEM technology was originally developed as part of the Gemini space program.16 In a PEM electrolyzer, the electrolyte is contained in a thin, solid ion-conducting membrane rather than the aqueous solution in the alkaline electrolyzers. This allows the H+ ion (proton) or hydrated water molecule (HsO+) to transfer from the anode side of the membrane to the cathode side, and separates the hydrogen and oxygen... 

Dense ceramic ion-conducting membranes (CICMs) are emerging as an important class of inorganic membranes based on fluorite- or perovskite-derived crystalline structures [18]. Most of the ion-conducting ceramics discovered to date exhibit a selective ionic oxygen transport at high temperatures >700°C. Ionic transport in these membranes is based on the following successive mechanisms [25] ... 

Ismail AF and David LIB. A review on the latest development of carbon membranes for gas separation. J. Membr. Sci. 2001 193 1-18. Kilner JA, Benson S, Lane J, and Waller D. Ceramic ion conductive membranes for oxygen separation. Chem. Ind. 1997 17 November 907-911. 

Perovskite-structured oxides with high electronic and oxygen ion conductivities could be used as a membrane alternative to solid electrolytes for oxygen separation. In such materials, both oxygen ions and electronic defects are transported in an internal circuit in the membrane material. 

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