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

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)–LaCrO3) coating was measured as a function of membrane thickness and surface coating, under controlled PO2 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 CO2 content of CO gas stream of permeate side with gas chromatograph. Compared to the oxygen flux of YSZ with LaCrO3 coating, the oxygen flux with bi-layer (GDC–LaCrO3) coating increased more steeply with the decreasing membrane thickness. The GDC coated between YSZ and LaCrO3 may have prevented the La2Zr2O7 formation that is detrimental for the oxygen surface kinetics. The maximum oxygen flux was 4.2 × 10−7 mol/cm2·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 (Lc) 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.