Nanostructured Ni‐Based Cathode Materials for Intermediate Temperature SOFC

Ni substituted lanthanum strontium manganite, (La 0.8 Sr 0.2 ) 0.95 Mn 1-x Ni x O 3-d (x=0–0.5), was synthesized by ceramic route. X-ray diffraction revealed it to be a single phase up to 40 mole % Ni, but above x=0.4 two phases viz., La 2 NiO 4 and NiO start separating out. Even though it was prepared by ceramic route, the crystallite size was found to be ~20 nm. At 900°C, the rhombohedral phase of LSM could be retained only with very low Ni doping (x=0.1) and compositions between (La 0.8 Sr 0.2 ) 0.95 Mn 0.8 Ni 0.2 O 3-d (LSMNi 2 ) to (La 0.8 Sr 0.2 ) 0.95 Mn 0.6 Ni 0.4 O 3-d (LSMNi 4 ) were found to have orthorhombic symmetry. At 1400°C, all the compositions showed rhombohedral symmetry. The thermal expansion coefficients (a) in the temperature interval of 20–850°C of (La 0.8 Sr 0.2 ) 0.95 MnO 3-d , (La 0.8 Sr 0.2 ) 0.95 Mn 0.9 Ni 0.1 O 3-d and (La 0.8 Sr 0.2 ) 0.95 Mn 0.8 Ni 0.2 O 3-d were 10.08×10 -6 °C -1 , 11.82×10 -6 °C -1 and 13.59×10 -6 °C -1 , respectively. The thermal and chemical compatability of LSMNi 2 with ceria-based electrolytes, Ce 0.8 Gd 0.2 O 1.9 and Ce 0.8 Sm 0.2 O 1.9 was also studied using XRD and SEM technique.