Correlationof Time-Dependent Oxygen Surface Exchange Kinetics with Surface Chemistryof La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ Catalysts

The Sr segregation at the surface of a perovskite La0.6Sr0.4Co0.2Fe0.8O3- (LSCF) oxygen electrode is detrimental to the electrochemical performance and durability of energy conversion devices such as solid oxide fuel cells (SOFCs). However, a quantitative correlation of degradation of the surface oxygen exchange kinetics with Sr precipitation formation at the LSCF surface is not clearly understood yet. Herein, the correlation of the time-dependent degradation mechanisms of the LSCF catalysts with respect to Sr segregation phenomena at the surface were investigated at 800 ℃ for a prolonged annealing time (~800 h) by combining in-situ electrochemical measurements, and ex-situ chemical and structural analyses at the multiscale. The in-situ monitored surface exchange coefficient (kchem) was found to drastically drop by ~86% over the 800 h, and it was accompanied with the formation of Sr-containing secondary phases on the bulk LSCF surface, as expected. However, the estimated coverage of Sr-segregation on the ...