Ln_1-xSr_xMnO₃(Ln=Pr, Nd, Sm and Gd) as the Cathode Material for Solid Oxide Fuel Cells

Abstract

The perovskite type manganite systems, Ln_1-xSr_xMnO₃ (Ln=La, Pr, Nd, Sm and Gd; 0.0≤x≤0.5) were studied as the electrode materials for solid oxide fuel cells (SOFC) from the view point of applications to the co-firing process of the electrolyte and electrode at higher temperature. The reactivity tests with yttria-stabilized zirconia (YSZ), no reaction product appeared between the Ln_1-xSr_xMnO₃ perovskite and YSZ even at a high annealing temperature of 1400°C when the lanthanoid elements were Pr, Nd and Sm and the Sr content was around 30% (x=0.3). The adjustment of the thermal expansion rate of Ln_1-xSr_xMnO₃ to YSZ, around x=0.1-0.2 in La_1-xSr_xMnO₃, 0.3 in Pr_1-xSr_xMnO₃ and Nd_1-xSr_xMnO₃ and more than 0.4 in Sm_1-xSr_xMnO₃ and Gd_1-xSr_xMnO₃. The electrical conductivity reached to 200 S/cm at 1000°C for all Ln_0.7Sr_0.3MnO₃ systems. The polarization measurements as an air electrode showed no significant dependence on the kind of lanthanoid elements. In the point of the electrode activity, high electrical conductivity, and low reactivity and good compatibility with YSZ, Pr_0.7Sr_0.3MnO₃ and Nd_0.7Sr_0.3MnO₃ are considered to be the most suitable electrode materials for the co-firing process.