Life testing of 10 cm x 10 cm fuel-electrode-supported solid oxide cells in reversible operation

Reversible solid oxide cells (ReSOCs) can provide significant value by playing different roles - electrical generation or electricity storage - depending on the prevailing electrical grid requirements. Relatively few studies have focused on the life testing of solid oxide cells in this mode-switching operation, and much of that work has focused on small "button" cells. The present study describes electrochemical characterization and post-test characterization from an -2600 h life test of a 10 cm x 10 cm fuel-electrode-supported cell operated with periodically reversing current. The cell performance gradually decreased for the first -1000 h and then stabilized with low degradation rate until an abrupt test-ending gas crossover failure that resulted in open circuit voltage drop. Post-test characterization of the (La,Sr)CoO3-delta air-electrode showed evidence of Cr vapor contamination from stainless-steel manifolds and Ag contamination from current collection contacts. Partial delamination of the air-electrode and Gd-doped ceria interlayer was observed, along with fractures in the electrolyte near the fuel inlet that probably caused a drop in open circuit voltage near the end of the test. Ni-Ni connectivity was reduced in both the functional and support layers accompanied by Ni particle coarsening, especially at the fuel outlet.