Degradation of La_0.6Sr_0.4Fe_0.8Co_0.2O_3-δ oxygen electrodes on Ce_0.9Gd_0.1O_2-δ electrolytes during reversing current operation

In order to assess the durability of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ oxygen electrodes in reversible solid oxide cells, current switched ~1000 h galvanostatic (0.7, 1.0, and 1.5 A/cm²) life tests were performed on symmetrical Ce_0.9Gd_0.1O₂-electrolyte cells at 700°C. Cell operating voltage and resistance, the latter measured by impedance spectroscopy, were monitored throughout. Degradation was minimal for the 0.7 A/cm² case. For the higher current densities, the cell voltage and resistance increased with time, although the cell appeared to stabilize after ~500 h in the 1.5 A/cm² case. Post-test analyses showed no evidence of electrolyte cracking or delamination for any current. However, 3D imaging revealed measureable microstructural coarsening after 1.5 A/cm² operation that was not present after 0.7 A/cm² operation. Furthermore, the amount of Sr segregated onto LSCF surfaces was higher for the cells operated with current switching versus the as-prepared and zero-current cells. Analysis of the results suggest that much of the degradation was due to decreased oxygen surface exchange rate due to current-enhanced Sr segregation, with a smaller contribution due to microstructural coarsening. The possibility of extrapolating these accelerated tests to longer times is discussed.