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Development of mixed-conducting ceramic membranes for hydrogen separation.

Description: SrCeO{sub 3}- and BaCeO{sub 3}-based proton conductors have been prepared and their transport properties have been investigated by impedance spectroscopy in conjunction with open circuit voltage and water vapor evolution measurements. BaCe{sub 0.8}Y{sub 0.2}O{sub 3-{delta}} exhibits the highest conductivity in a hydrogen-containing atmosphere; however, its electronic conductivity is not adequate for hydrogen separation in a nongalvanic mode. In an effort to enhance ambipolar conductivity and improve interfacial catalytic properties, BaCe{sub 0.8}Y{sub 0.2}O{sub 3-{delta}} cermets have been fabricated into membranes. The effects of ambipolar conductivity, membrane thickness, and interfacial resistance on permeation rates have been investigated. In particular, the significance of interfacial resistance is emphasized.
Date: May 18, 1998
Creator: Guan, J.
Partner: UNT Libraries Government Documents Department

Development of proton-conducting membranes for separating hydrogen from gas mixtures

Description: Thin and dense ceramic membranes fabricated from mixed protonic/electronic conductors can provide a simple, efficient means of separating hydrogen from gas streams and offer an alternative to existing methods of hydrogen recovery. Because mixed electronic/protonic conductors internally transport not only hydrogen (and thus provide the means to separate hydrogen from other gaseous components) but also electrons, hydrogen separation could be achieved in a non-Galvanic mode of operation (i.e., without the need for external electrodes, circuitry, and/or power supply). To be suitable as a hydrogen-permeable membrane, a material must exhibit sufficiently high electronic and protonic conductivities, and these conductivities must be approximately equal to one another to maximize hydrogen permeation through the material. In addition, the material must have sufficient mechanical integrity to withstand normal operating stresses and must be chemically stable under a wide range of gas atmospheres. This talk summarizes results obtained in Argonne`s effort to develop material for use as a hydrogen separation membrane. The transport properties of BaCe{sub 0.95}Y{sub 0.05}O{sub 3{minus}{alpha}} (5%-BCY) and SrCe{sub 0.95}Y{sub 0.05}O{sub 3{minus}{alpha}} (5%-SCY) were characterized by impedance spectroscopy, gas permeation, and open-cell voltage measurements. In this presentation, the authors describe the materials selection, synthesis, characterization, and performance evaluation of mixed-conducting dense ceramic membranes for hydrogen separation applications.
Date: September 1, 1997
Creator: Balachandran, U.; Guan, J.; Dorris, S.E. & Liu, M.
Partner: UNT Libraries Government Documents Department

Development of proton-conducting membranes for hydrogen separation

Description: The objective of this project is to develop dense ceramic membranes that can efficiently and economically separate hydrogen from gaseous mixtures (e.g., syngas, coal gas, etc.). Toward this end, materials with suitable electronic and protonic conductivities will be identified, and methods for fabricating thin, dense ceramic membranes from such materials will be developed. The chemical and mechanical stability of the membranes will be determined to estimate the expected lifetime of the membranes. Scoping-level evaluations will be performed to identify potential applications of proton membrane technology. Areas that will be evaluated include overall market scale, typical site operating scale, process integration opportunities and issues, and alternative-source economics. The literature on mixed electronic/protonic conductors was surveyed to identify suitable candidate materials. SrCe{sub 1{minus}x}M{sub x}O{sub 3{minus}{delta}} and BaCe{sub 1{minus}x}M{sub x}O{sub 3{minus}{delta}} (where M is a fixed-valent dopant such as Ca, Y, Yb, In, Nd, or Gd) were selected for further investigation on the basis of their reported total conductivities and proton transference numbers.
Date: July 1, 1998
Creator: Balachandran, U.; Guan, J. & Dorris, S.E.
Partner: UNT Libraries Government Documents Department

Development of mixed-conducting dense ceramic membranes for hydrogen separation.

Description: The electronic transference numbers of BCY were relatively low when compared with the protonic numbers. At 800 C, a hydrogen flux of only 0.02 cm{sup 3}/min/cm{sup 2} was obtained in an {approx} 2-rnm-thick BCY sample by short-circuiting the two Pt electrodes. We have developed a novel composite system with improved electronic transport, and preliminary measurements indicate that the new membrane materials can be used in a nongalvanic mode to separate hydrogen from gas mixtures. A maximum flux of 0.12 cm{sup 3}/min/cm{sup 2} has been measured at 800 C in the composite material operated in the nongalvanic mode. Currently, work is underway to further enhance the hydrogen flux in the composite membrane materials.
Date: April 17, 1998
Creator: Balachandran, U.; Bose, A. C.; Guan, J. & Stiegel, G. J.
Partner: UNT Libraries Government Documents Department

Mixed-conducting dense ceramics for gas separation applications.

Description: Mixed-conducting (electronic and ionic conducting) dense ceramics are used in many applications, including fuel cells, gas separation membranes, batteries, sensors, and electrocatalysis. This paper describes mixed-conducting ceramic membranes that are being developed to selectively remove oxygen and hydrogen from gas streams in a nongalvanic mode of operation (i.e., with no electrodes or external power supply). Ceramic membranes made of Sr-Fe-Co oxide (SFC), which exhibits high combined electronic and oxygen ionic conductivities, can be used for high-purity oxygen separation and/or partial oxidation of methane to synthesis gas (syngas, a mixture of CO and H{sub 2}). The electronic and ionic conductivities of SFC were found to be comparable in magnitude. Steady-state oxygen permeability of SFC has been measured as a function of oxygen-partial-pressure gradient and temperature. For an {approx}3-mm-thick membrane, the oxygen permeability was {approx}2.5 scc{center_dot}cm{sup {minus}2}{center_dot}min{sup {minus}1} at 900 C. Oxygen permeation increases as membrane thickness decreases. Tubular SFC membranes have been fabricated and operated at 900 C for {approx}1000 h in converting methane into syngas. The oxygen permeated through the membrane reacted with methane in the presence of a catalyst and produced syngas. We also studied the transport properties of yttria-doped BaCeO{sub 3{minus}{delta}} (BCY) by impedance spectroscopy and open-cell voltage (OCV) measurement. Total conductivity of the BCY sample increased from {approx}5 x 10{sup {minus}3} {Omega}{sup {minus}1}{center_dot}cm{sup {minus}1} to {approx}2 x 10{sup {minus}2} {Omega}{sup {minus}1}{center_dot}cm{sup {minus}1}, whereas the protonic transference number decreased from 0.87 to 0.63 and the oxygen transference number increased from 0.03 to 0.15 as temperature increased from 600 to 800 C. Unlike SFC, in which the ionic and electronic conductivities are nearly equivalent BCY exhibits protonic conductivity that is significantly higher than its electronic conductivity. To enhance the electronic conductivity and therefore to increase hydrogen permeation, metal powder was combined with the BCY to form a cermet membrane, ...
Date: June 22, 1999
Creator: Balachandran, U.; Dorris, S. E.; Dusek, J. T.; Guan, J.; Liu, M.; Ma, B. et al.
Partner: UNT Libraries Government Documents Department