Abstract
La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) symmetric-electrode cells with Gd0.1Ce0.9O1.95 (GDC) electrolytes were aged in ambient air at temperatures ranging from 550 to 800 °C for times up to 1400 h, without current/polarization. Electrochemical impedance spectroscopy measurements, taken periodically during the tests at a testing temperature of 700 °C for cells aged ³ 700 °C, showed a continuous increase in polarization resistance. Focused ion beam-scanning electron microscopy (FIB-SEM) 3D tomography showed that the LSCF electrode did not coarsen measurably even at the highest ageing temperature, 800 °C, ruling out LSCF microstructural changes as the mechanism behind the resistance increase. On the other hand, Sr surface segregation, determined by chemical etching with inductively coupled plasma-optical emission spectrometry (ICP-OES) detection, was found to increase with increasing ageing temperature > 650 °C. The effect of Sr surface segregation on the oxygen surface exchange and diffusion processes is quantified by comparing the measured electrochemical and microstructural data.
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