La(Sr)Ga(Fe)O3 perovskite oxide as a new mixed ionic-electronic conductor for oxygen permeating membrane

Fe-doped La1-xSrxGaO3 exhibits a high conductivity (similar to1 S/cm) and a high oxygen permeation rate. In particular, the highest conductivity and the oxygen permeating rate were attained at La0.7Sr0.3Ga0.6Fe0.4O3 (LSGF). Although a surface catalyst is required, oxygen permeation rate from air to Ar was as high as 2.5 cm(3) std/min cm(2) at 1273 K and 0.3 mm membrane thickness. Oxygen permeation rate from air to Ar increased in the following order, La0.6Sr0.4CoO3 > La0.9Sr0.1CoO3 = Sm0.5Sr0.5CoO3 >> Sm0.6Sr0.4CoO3, as the surface catalyst. Since the p(O2) gradient becomes larger, the oxygen permeation rate drastically increased by changing from air-Ar to CH4-air condition. The products were only CO and H-2, having a molar ratio (H-2/CO ratio) of almost two. Electronic hole conduction was only observed in LSGF polarization measurement and the oxide ion conductivity estimated is as high as s = 0.6 S cm(-1) at 1073 K. At high p(O2), the main defect in LSGF is O-i" and Fe-Fe(.), and at intermediate p(O2), concentration of Fe-Fe(.) is balanced with that of O-i". The estimated transport number of oxide ion was ca. 0.6, which is in a good agreement with that estimated by the electromotive force in H-2-O-2 gas concentration cells. (C) 2002 The Electrochemical Society.