Synthesis and characterization of suspension-derived, porous ion-conducting ceramic membranes

Porous, oxygen-ion-conducting ceramic membranes can have applications as supports for fuel cells, sensors, and thin membrane films, or as filters for membrane filtration. This paper reports on the preparation of unsupported and supported yttria-stabilized zirconia (YSZ) and yttria-doped bismuth oxide (BY) membranes with submicrometer pore sizes. Fluorite-structured BY powder that has been synthesized using the citrate method and commercial YSZ powder have been used to prepare stable aqueous suspensions. Unsupported and supported YSZ and BY membranes have been prepared from the stable suspensions of YSZ and BY. The supported BY membranes are crack free but contain small defects. Defect-free YSZ membranes that are supported on porous alumina have been prepared under controlled conditions. The average pore size is 100 nm, with a porosity of 57%, for an unsupported YSZ membrane (measured by mercury porosimetry), and 114 nm for a supported membrane (as estimated via helium permeation). The ionic conductivity of the YSZ membranes is 0.00044-0.01 S/cm in the temperature range of 600°-900 °C, which is lower than that of dense YSZ disks.