Evaluation of mixed-conducting lanthanum-strontium-cobaltite ceramic membrane for oxygen separation

In this study, La₀₄Sr_0.6CoO3-s (LSC) oxide was synthesized via an EDTA-citrate com- plexing process and its application as a mixed-conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four-probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatog- raphy method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (D_v) and surface exchange coefficient (K_ex) for LSC membrane were derived by model regression. The importance ofsurface exchange kinetics at each side ofthe membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6-mm-thick La_0-4Sr _0-6CoO_3-s membrane was ∼4.0 × 10^-7 mol cm^-2 s^-1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10-^-5 mol cm^-2 s^-1 through a 5-/im-thick LSC membrane with ideal surface modification when operating at 950°C for air separation.