Fabrication and electrochemical characterisation of cathodes for solid oxide fuel cells

For the fabrication of solid oxide fuel cells (SOFC) screen-printing is used, because it allows quite easily up scaling of small laboratory process to larger volumes with comparatively low costs. The paste properties for screen-printed electrolyte supported cells include high electrochemically active powder mixtures and for the electrode production relevant attributes like viscosity and long-term stability for storage. Sr-doped LaMnO3 (LSM)-yttria-stabilized (YSZ) composites are at present the most used and researched materials for the cathode of the SOFC. In the present work the influence of the powder properties and the technology of the paste preparation on the performance of LSM/YSZ (ScSZ)-cathodes were investigated. The cathode resistance was measured by impedance spectroscopy at 950 - 800 deg C and different oxygen partial pressures. Optimized LSM/YSZ-electrodes were tested under real conditions with a symmetrically screen-printed cell, consisting of cathode and anode. Open-circuit voltage (OCV), V-I curves of the cells were measured in the temperature range of 850 to 950 deg C, using H2-50%H2O as fuel and air as oxidant. The polarization resistances of the electrodes were determined at open-circuit potential and under load by impedance spectroscopy.