We propose the use of porous substrates and thin films of oxygen permeable ceramics as a method for separating oxygen from air. The porosity and pore size of various Ce0.8Gd0.2O1.9 (CGO) porous substrates were modified in an attempt to optimize the oxygen permeable flux of CGO-CoFe2O4 thin films. The oxygen permeable flux density of the CGO-CoFe2O4 thin film coated on the porous CGO substrate was found to be 4.7 mu mol cm(-2) s(-1) under a O-2 partial pressure difference (-log(P-OII/ P-OI)) of 4.5 at 1000 degrees C. This value is about 20 times higher than that of the 1 mm thick bulk material. (C) 2004 The Electrochemical Society.