Abstract
The effects of Cr poisoning on the catalytic activity of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and the poisoning mechanism was investigated. AC impedance spectroscopy and temperature programmed isotopic exchange (TPX) were consistent in proving poisoning mainly degraded the surface catalytic activity as a passive layer evolved on the surface or near-surface region. The formation of small particles was clearly observed in scanning electron microscopy when LSCF was heat treated in the presence of Crofer22APU. Low angle X-ray diffraction identified these were SrCrO4. As a result of Sr diffusion to form SrCrO4 particles, it was found that a Sr-deficient phase was formed and a phase transition from rhombohedral to cubic perovskite occurred in the near surface region. While previous Cr poisoning studies on LSCF mostly emphasized the effects of SrCrO4 formation, the Sr deficient surface layer also significantly degrades the catalytic activity of LSCF due to reduction of oxygen vacancies and surface Co/Fe concentration.
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