Synthesis and characterization of Gd1−xSrxMnO3 cathode for solid oxide fuel cells

Gd1−xSrxMnO3 (0≤x≤0.6) is synthesized as the cathode material for solid oxide fuel cells (SOFC) using a citrate process. Properties of the oxides such as the crystal structure, electrical conductivity, thermal expansion coefficient (TEC) and reactivity with 8 mol% yttria-stabilized zirconia (8YSZ) or Ce0.8Gd0.2O1.9 (CGO) electrolyte are investigated. The crystal structure is orthorhombic (0≤x≤0.3), cubic (0.4≤x≤0.5) or tetragonal (x=0.6), as dictated by the composition. The electrical conductivity increases, but the activation energy for conduction decreases, with increasing Sr content. The TEC displays normal behavior for x≥0.3 and increases with increasing Sr content. When heated at 1300°C for 48 h, Gd1−xSrxMnO3 reacts with 8YSZ to produce SrZrO3, but does not react at all with CGO. The cathodic polarization of the mixed cathode, Gd0.6Sr0.4MnO3−δ–CGO, is reduced with increase in the CGO content. The maximum power density is about 210 mW/cm2 in the vicinity of 50 vol.% CGO in the mixed cathode at an operating temperature of 800°C.