Effects of chromium poisoning on the long-term oxygen exchange kinetics of the solid oxide fuel cell cathode materials La0.6Sr0.4CoO3 and Nd2NiO4

The influence of chromium poisoning on the long-term stability of the oxygen exchange kinetics of the promising IT-SOFC cathode materials La0.6Sr0.4CoO3−δ (LSC) and Nd2NiO4+δ (NDN) is investigated in-situ by dc-conductivity relaxation experiments. The as-prepared LSC and NDN samples show high chemical oxygen surface exchange coefficients kchem. After the deposition of a 10 nm thick Cr-layer onto the surface, kchem of LSC decreases to 50% of the initial value. Additional chromium deposition of 20 nm on LSC leads to a further decrease of kchem to 27% of the initial value. In contrast, the effect of a 10 nm thick Cr-layer on kchem of NDN is negligible. Even with additional 20 nm of chromium and a total testing time of 1750 h, the nickelate retains a kchem of 60% of the initial value. X-ray photoelectron spectroscopy (XPS) of the degraded. LSC shows a significantly altered surface cation composition with Sr-enrichment down to 30 nm depth while XPS analysis of the degraded NDN reveals a thin surface zone of approximately 30 nm containing nickel and chromium. In contrast to LSC, the changes in the surface composition of NDN due to Cr-poisoning ultimately had only a minor influence on the surface exchange properties.