Interfacial long-term effects of LSCF cathodes at medium current densities

In this work, two solid oxide fuel cells (SOFCs) were tested at 750 °C but at different testing times in order to study the long-term voltage behavior and identify voltage degradation mechanisms. The main objective here is to determine if the normally observed Sr segregation continues at the electrolyte/ceria interface or remains constant over different testing times at medium current densities. Distribution of relaxation times (DRT) analysis is extended to long-term impedance spectroscopy (IS) data to address any possible concerns with the complex non-linear least square fitting (CNLS) analysis. For the long-term cell test, no significant change in performance is observed based upon the initial and final voltage-current density curves. DRT analysis on this cell shows five distinct processes. The CNLS data analysis proved to be a little more complex as resulting resistances are somewhat scattered. The cell ohmic resistance increased from about 0.2 to 0.23 Ω cm 2 . The total cell polarization resistance stabilizes from about 1.2 to 1.15 Ω cm 2 . Energy dispersive x-ray spectroscopy (EDS) data indicate that Sr has increased at the electrolyte/ceria interface when compared to a green cell. However, the EDS data for the short-term cell test suggest that most of the Sr migration has occurred in the initial stages of testing and most likely due to the initial electrochemical performance characterization.