Crystal chemistry and electrochemical properties of Ln(Sr,Ca)3(Fe,Co)3O10 intergrowth oxide cathodes for solid oxidefuel cells

Abstract

Ln(Sr,Ca)₃(Fe,Co)₃O₁₀ (Ln = La, Nd, and Gd) oxides crystallizing in a perovskite-related intergrowth structure have been synthesized and explored as new cathode materials for solid oxide fuel cells (SOFC). The crystal structures of the Ln(Sr,Ca)₃(Fe,Co)₃O₁₀ samples could be refined based on the tetragonal space groupI4/mmm. The substitution of Co for Fe in LnSr₃(Fe,Co)₃O₁₀ (Ln = La and Nd) increases the amount of oxygen loss on heating, thermal expansion coefficient (TEC), total electrical conductivity, and cathode performance in SOFC. In particular, the Ln = Nd samples exhibit superior cathode performances in SOFC compared to those obtained with the Ln = La or Gd samples in LnSr₃(Fe,Co)₃O₁₀. Further improvement in the cathode performance and a decrease in the TEC value have been realized by a substitution of less electropositive Ca for Sr in NdSr_3−yCa_yFe_1.5Co_1.5O₁₀, demonstrating that NdSr_2.5Ca_0.5Fe_1.5Co_1.5O₁₀ (NSCFC) is the optimum composition among the Ln(Sr,Ca)₃(Fe,Co)₃O₁₀ samples investigated. The improved performance of NSCFC is attributed to the decreased lattice distortion in the perovskite layer, which is beneficial to enhance the oxide-ion conductivity.