The ionic conductivity, thermal expansion behavior, and chemical compatibility of La0.54Sr0.44Co0.2Fe0.8O3-δ as SOFC cathode material

In this paper, the ionic conductivities of La0.54Sr0.44Co0.2Fe0.8O3-delta and La0.6Sr0.4Co0.2Fe0.8O3-delta were measured by electron-blocked alternating current impedance analysis technique. The results show that the oxygen ion conductivity of La0.54Sr0.44Co0.2Fe0.8O3-delta is nearly five times higher than that of La0.6Sr0.4Co0.2Fe0.8O3-delta, which makes La0.54Sr0.44Co0.2Fe0.8O3-delta cathode more conductive than YSZ electrolyte. Consequently, the electrochemical reaction region is extended from the interface between the cathode and the electrolyte to the whole surface of the cathode grains, with a result of the cathode polarization overpotential being decreased and the cell electrical performance being improved. Besides, the XRD results show that both La0.54Sr0.44Co0.2Fe0.8O3-delta and La0.6Sr0.4Co0.2Fe0.8O3-delta begin to react with 8YSZ([Y2O3](0.08)center dot[ZrO2](0.92)) at 850 degrees C, but La0.54Sr0.44Co0.2Fe0.8O3-delta with a faster reaction rate. The thermal expansion experiments manifest that the two LSCFs have approximate thermal expansion coefficients, being about 14 x 10(-6)-15 x 10(-6) K-1 from 500 degrees C to 700 degrees C, which is moderately higher than that of 8YSZ. Crown Copyright (C) 2011 Published by Elsevier Masson SAS. All rights reserved.