Dramatically Enhanced Oxygen Fluxes in Fluorite-Rich Dual-Phase Membrane by Surface Modification

Dual-phase ceramic membranes with very high oxygen flux have been designed by taking into account the volume fraction of the fluorite phase, membrane thickness, and surface modification. The oxygen flux of Ce0.9Gd0.1O2-delta-La0.6Sr0.4Co0.2Fe0.8O3-delta (GDC-LSCF) dual-phase membranes has been systematically investigated as a function of membrane thickness and volume fraction of the fluorite phase with or without surface modification. The percolation threshold of the composites for electronic conduction has been determined to be about 20 vol % of LSCF by general effective-medium theory. The oxygen flux of uncoated fluorite phase-rich membrane (80 vol % GDC-20 vol % LSCF) with 30-mu m thickness exhibits a low oxygen flux (8.0 x 10(-3) mL. cm(-2).min(-1) at 850 degrees C) under an air/He gradient, indicating that the permeation is controlled by only the surface-exchange kinetics of GDC. With both sides coated with La0.6Sr0.4CoO3-delta (LSC), the flux of the membrane (3.6 mL.cm(-2).min(-1) at 850 degrees C) has been dramatically enhanced by about 3 orders of magnitude in comparison with the oxygen flux of the membrane with a nonmodified surface. This observation implies that surface modification has a decisive role in dramatically enhancing the contribution of the GDC to the fluorite rich dual-phase membrane.