Cr-poisoning in (La,Sr)(Co,Fe)O-3 cathodes after 10,000 h SOFC stack testing
Résumé
After 10,000 h solid oxide fuel cell (SOFC) stack operation, the Cr-poisoning situation in (La0.6Sr0.4) (Co0.2Fe0.8)O-3 (LSCF)-based cathode material is depicted in this work. Systematic Cr profiling by energy-dispersive X-ray spectroscopy (EDS), from post-operation samples taken at different locations within the air flow field, reveals Cr accumulation in electrochemically active cathode regions, although the major amount of Cr is trapped in inactive surface-proximal cathode regions; the 20 m LSCF current collector does not fully impede the Cr access to the functional cathode.
The distribution of Cr within the flow field reports on the severity of the sources and causes for Cr contamination: 1) Cr preferentially accumulates at sealing-proximal locations; this is explained by fuel-leakage through the sealing with subsequent water vapor generation in the cathode compartment, aggravating local Cr-poisoning via the Cr-oxyhydroxide vapor species; 2) high Cr amounts at air inlet regions point to system components located upstream of the cell to contribute to local Cr contamination; 3) the remaining main part of the cell experiences low Cr-poisoning; the protective solution to prevent Cr evaporation from the metallic interconnects thus appears to be adequate.
The detected low overall amounts of Cr contamination, partially correlated to the observed low performance degradation, encouragingly indicate 40,000 h operation, a prerequisite for stationary SOFC application, to be in reach for LSCF-based stacks. (C) 2012 Elsevier BM