Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells IV. On the Ohmic Loss in Anode-Supported Button Cells with LSM or LSCF Cathodes

Anode-supported solid oxide fuel cells with a variety of yttria-stabilized zirconia (YSZ) electrolyte thicknesses were fabricated by tape casting and lamination. Preparation of the YSZ electrolyte tapes with various thicknesses was accomplished by using doctor blades with different gaps between the precision machined, polished blade and the casting surface. The green tape was cut into disks, sintered at 1385 degrees C for 2 h, and subsequently creep-flattened at 1350 degrees C for 2 h. Either (La, Sr)(Co, Fe)O(3) (LSCF) with an Sm(0.2)Ce(0.8)O(1.9) (SDC) interlayer or an (La(0.8)Sr(0.2))(0.98)MnO(3) (LSM) + YSZ composite was used as the cathode material for the fuel cells. The ohmic resistances of these anode-supported fuel cells were characterized by electrochemical impedance spectroscopy at temperatures from 500 to 750 degrees C. A linear relationship was found between the ohmic resistance of the fuel cell and the YSZ electrolyte thickness at all the measuring temperatures for both LSCF and LSM + YSZ cathode fuel cells. The ionic conductivities of the YSZ electrolyte, derived for the fuel cells with LSM + YSZ or LSCF cathodes, were independent of the cathode material and cell configuration. The ionic conductivities of the YSZ electrolyte were slightly lower than that of the bulk material possibly due to Ni doping into the electrolyte. The fuel cell with an SDC interlayer and an LSCF cathode showed a larger intercept resistance than the fuel cell with an LSM + YSZ cathode, which was possibly due to the imperfect contact between the SDC interlayer and the YSZ electrolyte and the migration of Zr into the SDC interlayer to form an insulating solid solution during cell fabrication. Calculations of the contribution of the YSZ electrolyte to the total ohmic resistance showed that YSZ was still a satisfactory electrolyte at temperatures above 650 degrees C. Explorations should be directed to reduce the intercept resistance to achieve significant improvement in cell performance. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3417064] All rights reserved.