Abstract
The long-term stability of the oxygen exchange properties of the IT-SOFC cathode material La0.6Sr0.4CoO3-d vs. chromium poisoning is investigated at 600°C by in-situ measurements of the chemical surface exchange coefficient kchem and the chemical diffusion coefficient Dchem of oxygen by applying the dc-conductivity relaxation method. The as-prepared sample shows high values of kchem=3x10-4 cm s-1 and Dchem=1x10-6 cm2s-1, which are only negligibly affected by the treatment in a dry atmosphere for 1000 h without and with the presence of a Cr-source, respectively. However, humidification of the carrier gas results in a strong decrease in both kinetic parameters. Post-test surface analysis of the degraded samples by X-ray photoelectron spectroscopy identifies Cr- and Si-poisoning as well as significant Sr-enrichment within 150 nm depth as the origin of the degradation in a humid atmosphere.
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