Zirconia as a high temperature oxygen-permeating membrane : The effect of GDC and LaCrO3 surface coating

Abstract The high temperature oxygen-permeating membrane can be used as a hydrogen generator from steam or a deoxidation unit in steel melt. The oxygen flux of yttria-stabilized zirconia (YSZ) with bi-layer (GDC (Gd-doped ceria)–LaCrO 3 ) coating was measured as a function of membrane thickness and surface coating, under controlled P O 2 gradient (permeate side: ~ 3 × 10 −12  atm, feed side: 2 × 10 −12 ~ 2 × 10 −8  atm) in reducing atmosphere at 1600 °C. The oxygen flux was determined by measuring the change in CO 2 content of CO gas stream of permeate side with gas chromatograph. Compared to the oxygen flux of YSZ with LaCrO 3 coating, the oxygen flux with bi-layer (GDC–LaCrO 3 ) coating increased more steeply with the decreasing membrane thickness. The GDC coated between YSZ and LaCrO 3 may have prevented the La 2 Zr 2 O 7 formation that is detrimental for the oxygen surface kinetics. The maximum oxygen flux was 4.2 × 10 −7 mol/cm 2 ·s for the 200 μm-thick zirconia membrane with bi-layer coating. This value was ~ 26 times higher than the oxygen flux of the uncoated membrane. The Characteristic membrane thickness ( L c ) which divides the bulk diffusion and surface-exchange limits was calculated as small as ~ 50 μm. Thus, the oxygen flux can further be enhanced by reducing the electrolyte thickness.