Ln(1-x)Sr(x)MnO(3) (Ln = Pr, Nd, Sm and Gd) as the cathode material for solid oxide fuel cells

The perovskite type manganite systems, Ln(1-x)Sr(x)MnO(3) (Ln = La, Pr, Nd, Sm, and Gd; 0 less than or equal to x less than or equal to 0.5) were stud ied as the electrode materials for solid oxide fuel cells (SOFC) from the v iew point of applications to the co-firing process of the electrolyte and e lectrode at a higher temperature. The reactivity tests with yttria-stabiliz ed zirconia (YSZ) showed that the formation of the pyrochlore Ln(2)Zr(2)O(7 ) was suppressed for the perovskites having smaller lanthanoids than La, es pecially for the Pr1-xSrxMnO3 and Nd1-xSrxMnO3 systems. No reaction product appeared between the Ln(1-x)Sr(x)MnO(3) perovskite and YSZ even at a high annealing temperature of 1400 degrees C when the lanthanoid elements were P r, Nd and Sm and the Sr content was around 30% (x = 0.3). The adjustment of the thermal expansion rate of Ln(1-x)Sr(x)MnO(3) to YSZ needed more Sr sub stitution with an increase of the atomic number of lanthanoids. The Sr cont ents, x, showing comparable values with 8m/o YSZ were around x = 0.1-0.2 in La1-xSrxMnO3, 0.3 in Pr1-xSrxMnO3 and Nd1-xSrxMnO3 and more than 0.4 in Sm 1-xSrxMnO3 and Gd1-xSrxMnO3. The electrical conductivity, which may strongl y relate with the polarization of electrode reaction, showed about 200 S/cm at 1000 degrees C for all Ln(0.7)Sr(0.3)MnO(3) systems. The polarization m easurements as an air electrode showed no significant dependence on the kin d of lanthanoid elements. From the viewpoint of the electrode activity, hig h electrical conductivity, low reactivity and good compatibility with YSZ, Pr0.7Sr0.3MnO3 and Nd0.7Sr0.3MnO3 are considered to be the most suitable el ectrode materials for the co-firing process. (C) 1999 Elsevier Science BN. All rights reserved.