Synthesis and oxygen-permeation properties of thin YSZ/Pd composite membranes

Thin dense yttria-stabilized-zirconia (YSZ)/Pd composite (dual-phase) membranes were fabricated on porous YSZ membranes by a new approach that combines the reservoir method and chemical vapor deposition (CVD) technique. A thin porous YSZ layer was coated on a porous alumina support by dip coating the YSZ suspension. A continuous Pd phase was formed inside pores of the YSZ layer by the reservoir method. The residual pores of the YSZ/Pd layer were plugged with yttria/zirconia by CVD to ensure the gas tightness of the membranes. The oxygen-permeation fluxes through these composite (dual-phase) membranes, measured in situ in the CVD reactor, are 2.0 × 10^-8 and 4.8 × 10^-8 mol/cm² · s at 1,050°C when air and oxygen are used as the permeate gases, respectively. These oxygen-permeation values are about 1 order of magnitude higher than those of pure YSZ membranes prepared under similar conditions. The apparent activation energies for oxygen permeation at 900-1,050°C are 193 kJ/mol for thin YSZ/Pd composite (dual-phase) membranes and 124 kJ/mol for pure YSZ membranes. These results are explained in terms of relative importance of various mass-transfer steps for oxygen permeation and microstructure of the YSZ/Pd composite membranes prepared by this technique.