Roles of humidity and cathodic current in chromium poisoning of Sr-doped LaMnO3-based cathodes in solid oxide fuel cells

摘要

Performance degradation of cathodes caused by chromium deposition and poisoning is one of the major challenges to overcome for long-term operation of solid oxide fuel cells (SOFCs). To fundamentally understand the mechanisms of the degradation phenomenon, it is necessary to investigate the roles of humidity and cathodic current in chromium poisoning. In this study, anode-supported SOFCs, with Sr-doped LaMnO3 (LSM) based cathode are employed. These cells are electrochemically tested at 800 degrees C with and without chromia-forming interconnect. On identical cells, different cathode atmospheres (dry air or 10% humidified air) and current conditions (no current or 0.75 A/cm(2) cathodic current) are imposed. It is found that both humidity and cathodic current promote chromium poisoning. Microstructural characterizations also confirmed that larger amounts of chromium-containing deposits are present at the cathode/electrolyte interfaces of the cell tested with cathodic current and/or humidity. Free energy minimization calculations and thermogravimetric experiments are performed to determine the chromium vapor species that form over chromia-forming alloy interconnect and result in chromium deposition. Based on the experimental and computational results, the roles of humidity and cathodic current in chromium poisoning are evaluated, and a mechanism associated to chromium vapor species deposition at the cathode/electrolyte interface is proposed. (C) Performance degradation of cathodes caused by chromium deposition and poisoning is one of the major challenges to overcome for long-term operation of solid oxide fuel cells (SOFCs). To fundamentally understand the mechanisms of the degradation phenomenon, it is necessary to investigate the roles of humidity and cathodic current in chromium poisoning.