Layered LnBaCo[sub 2−x]Cu[sub x]O[sub 5+δ] (0≤x≤1.0) Perovskite Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

The effects of Cu substitution on the crystal chemistry, thermal and electrical properties, and catalytic activity for the oxygen reduction reaction of the layered LnBaCo 2-x Cu x O 5+␦ ͑Ln = Nd and Gd, and 0 ഛ x ഛ 1.0͒ perovskite have been investigated.The LnBaCo 1.0 Cu 1.0 O 5+␦ compositions exhibit thermal expansion coefficients ͑TEC͒ of 16.4 ϫ 10 -6 °C -1 for Ln = Nd and 14.5 ϫ 10 -6 °C -1 for Ln = Gd in the range of 80-900°C.The LnBaCo 2-x Cu x O 5+␦ ͑x = 0.75 for Ln = Nd and x = 1.0 for Ln = Gd͒ cathodes exhibit low polarization resistance and fuel cell performance comparable to that of the well-known La 1-x Sr x CoO 3-␦ perovskite cathodes, but with an important advantage of lower TEC.The better performance of these Cu-substituted samples is partly due to the improved chemical stability with the La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 2.8 electrolyte at high temperatures ͑Ln = Gd͒ and a better matching of the TEC value with those of the standard electrolytes.With an electrolyte-supported single cell configuration ͑thickness = 0.50 mm͒, NdBaCo 1.25 Cu 0.75 O 5+␦ and GdBaCo 1.0 Cu 1.0 O 5+␦ exhibit higher maximum power densities of, respectively, 772 and 634 mW cm -2 at 800°C compared to that of the Cu-free ͑x = 0͒ sample ͑658 and 595 mW cm -2 ͒.