A dual-phase bilayer oxygen permeable membrane with hierarchically porous structure fabricated by freeze-drying tape-casting method

Abstract

A bilayer oxygen permeable membrane consisting of hierarchically porous Ce0.9Gd0.1O1.95-(La0.8Sr0.2)0.95MnO3−δ (GDC-LSM) support and dense GDC-LSM film has been fabricated by a combined freeze-drying tape-casting and screen-printing method followed by co-sintering. Two dimensional (2D) SEM-BSE and reconstructed three dimensional (3D) XCT images indicated that the porous GDC-LSM support (870-µm-thick) contains graded straight pores with low tortuosity factor, promoting fast gas diffusion in the support, while the dense GDC-LSM film with a thickness of 30µm provides a short path for the bulk transport of oxygen ions and electrons. However, the oxygen flux of the asymmetric GDC-LSM membrane is only 81% higher than that of the 900-µm-thick dense GDC-LSM symmetric membrane, indicating that the oxygen transport becomes limited by the surface oxygen exchange process for the GDC-LSM asymmetric membrane with a 30-µm-thick dense GDC-LSM film. When the permeate side surface is modified with Ce0.8Sm0.2O1.9-La0.6Sr0.4Co0.2Fe0.8O3−δ (SDC-LSCF), the oxygen permeation flux of the GDC-LSM asymmetric membrane is significantly enhanced from 0.105 to 0.780mLcm−2min−1, while the activation energy is substantially decreased from 219.6±8.7 to 138.1±3.3kJmol−1, due to enhanced surface oxygen exchange kinetics. Furthermore, the coated asymmetric membrane shows 1100% higher oxygen flux than the coated symmetric membrane. When the sweep gas is switched from helium to CO2, although the adsorption of CO2 on the permeate side surface leads to a slight decrease in oxygen permeation flux, a high oxygen permeation flux of 0.659mLcm−2min−1 can still be achieved, demonstrating that the coated GDC-LSM asymmetric membrane is promising for oxy-fuel combustion application.