Life testing of LSM–YSZ composite electrodes under reversing-current operation

Abstract

Durability testing of solid oxide cell electrodes in reversing-current and constant-current operation modes is presented. (La_0.8Sr_0.2)_0.98MnO_3−δ–Zr_0.84Y_0.16O_2−γ (LSM–YSZ) symmetric cells were tested at 800 °C in air with current densities of 0.5 and 1.5 A cm⁻², with current cycle periods of 1 and 12 h. A continuous increase in both ohmic and polarization resistance was observed, via Electrochemical Impedance Spectroscopy (EIS), for cells tested with a reversing current of 1.5 A cm⁻², whereas cells tested at 0.5 A cm⁻² showed no measurable resistance increase. The resistance degradation was explained by delamination in the electrode, observed by post-test Scanning Electron Microscopy (SEM), near the interface with the electrolyte for the 1.5 A cm⁻² cells, but not for those tested at 0.5 A cm⁻². Current cycle period also impacted the degradation observed at 1.5 A cm⁻²: both the rate of resistance increase and the extent of post-test delamination decreased on going from constant current mode to a 12 h period to a 1 h period. The results indicate that lower current densities and reversing-current operation are desirable to maximize the lifetime of solid oxide cells.