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

Abstract In this paper, the ionic conductivities of La 0.54 Sr 0.44 Co 0.2 Fe 0.8 O 3-δ and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ were measured by electron-blocked alternating current impedance analysis technique. The results show that the oxygen ion conductivity of La 0.54 Sr 0.44 Co 0.2 Fe 0.8 O 3-δ is nearly five times higher than that of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ , which makes La 0.54 Sr 0.44 Co 0.2 Fe 0.8 O 3-δ 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 La 0.54 Sr 0.44 Co 0.2 Fe 0.8 O 3-δ and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ begin to react with 8YSZ([Y 2 O 3 ] 0.08 ·[ZrO 2 ] 0.92 ) at 850 °C, but La 0.54 Sr 0.44 Co 0.2 Fe 0.8 O 3-δ with a faster reaction rate. The thermal expansion experiments manifest that the two LSCFs have approximate thermal expansion coefficients, being about 14 × 10 −6 –15 × 10 −6  K −1 from 500 °C to 700 °C, which is moderately higher than that of 8YSZ.