Synthesis and characterization of nickel doped LSM as possible cathode materials for LT-SOFC application

Abstract

Doping lanthanum strontium manganite with Ni2+ at Mn site for 10–30 mol% was investigated as cathode material for LT-SOFC application. Nanopowders were prepared using a simple solution combustion technique and only after calcination at 1200 °C phase purity was obtained. While TEM analysis confirmed particle size around 30 nm, the DLS study showed average most probable size as 13 nm. The SEM-EDAX analysis revealed porous nanopowder of all the studied compositions. It also confirmed composition of the cathode material. In symmetric cell configuration, using lanthanum gallate as electrolyte, oxygen reduction reaction (ORR) and hence polarization resistance (RP) was studied in detail in the temperature range 500–800 °C. The composition La0.7Sr0.3Mn0.8Ni0.2O3 (LSMN7382) showed lowest RP value of 0.117–0.039 Ω-cm2 in the temperature range 500–800 °C. In contrast, La0.7Sr0.3MnO3 (LSM731) showed much higher RP value. Among the cathodes with Sr2+doping variation in La site, 30 mol% showed the best performance. The electrical conductivity of ∼80% dense electrolyte pellets were studied and highest conductivity of 70 S/cm at 800 °C was observed for LSMN7382 among the all compositions. Generation of hole takes place due to the charge compensation in Mn3+ to Mn4+ conversion while doping Sr2+ as well as Ni2+. At 30 mol% Ni2+ doping (LSMN7373), the decrease of conductivity may be attributed to the secondary phase formation. A detailed electrical circuit analysis of the impedance spectrum indicates that charge transfer polarization resistance is the key to control the interface performance. Such high ORR performance by nickel doping can be explained due to Mn4+ converted to Mn3+ at high temperature and thus creating oxygen vacancy to enhance ORR ionic path on the cathode surface.