Degradation of La0.6Sr0.4Fe0.8Co0.2O3-? Oxygen Electrodes on Ce0.9Gd0.1O2-? Electrolytes during Reversing Current Operation

In order to assess the durability of La0.6Sr0.4Co0.2Fe0.8O3 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 Ce0.9Gd0.1O2-electrolyte cells at 700degC. 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.