Time-dependent performance of mixed-conducting SOFC cathodes

The time-dependent degradation of anode-supported Solid Oxide Fuel Cells (SOFCs) with La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathodes has been studied. Eight SOFCs have been tested over a period of 1000 h under different operation conditions to investigate the influence of different operation parameters on the degradation of the electrochemical performance. The cells were tested at 700 or 800 °C, at 0.3 or 0.6 A/cm2 and with 21% or 5% O2 at the cathode side and showed performance losses of 2–4% per 1000 h. While an elevated temperature and an elevated oxygen partial pressure had a negative influence on long-term performance, the current density did not have a clear effect. Material analysis of the cells showed a formation of SrZrO3 at the interface of the Ce0.8Gd0.2O2−δ interlayer and the yttria stabilized zirconia (8YSZ) electrolyte during sintering of the cathode. There are indications of a further formation of this phase during the electrochemical characterization obtained from X-ray diffraction analysis on LSCF–YSZ powder mixtures that were exposed to 800 °C for 200 h.