LnBaCo[sub 2]O[sub 5+δ] Oxides as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

Abstract

LnBaCo2 O5+δ (Ln=Nd, Sm, Gd, and Y) oxides with a cation ordered perovskite structure have been investigated as cathode materials for intermediate-temperature solid oxide fuel cells (SOFCs). The oxygen content 5+δ, thermal expansion coefficient (TEC), and electrical conductivity (metallic) decrease with decreasing size of the Ln3+ ions from Ln=La to Y. While the decrease in TEC is due to the decreasing ionicity of the Ln-O bond, the decrease in electrical conductivity is due to the increasing oxide ion vacancies and a bending of the O-Co-O bonds. The power density of single-cell SOFCs fabricated with the LnBaCo2 O5+δ cathodes, La0.8 Sr0.2 Ga0.8 Mg0.2 O2.8 electrolyte, and Ni- Ce0.9 Gd0.1 O1.95 cermet anode decrease with decreasing size of the Ln3+ ions, partly due to a decreasing electrical conductivity. The LnBaCo2 O5+δ cathodes with an intermediate lanthanide ion such as Sm3+ offer a trade-off between catalytic activity and TEC. © 2008 The Electrochemical Society.