Phase decomposition in the chromium- and silicon-poisoned IT-SOFC cathode materials La0.6Sr0.4CoO3-δ and La2NiO4 + δ

Chromium- and silicon-poisoned samples of the intermediate temperature solid oxide fuel cell (IT-SOFC) cathode materials La0.6Sr0.4CoO3-delta (LSC) and La2NiO4+delta (LNO) were investigated by transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDXS), electron energy loss spectroscopy (EELS), convergent beam electron diffraction (CBED), as well as by atomic force microscopy (AFM). Analytical TEM revealed phase decomposition of the original, oxygen exchange-active materials LSC and LNO, and the formation of secondary phases after 3500 h of testing at 700 degrees C. In the case of LSC, the phases SrCrO4, Co3O4, and CoCr2-xCoxO4 as well as a La-chromate phase with unknown stoichiometry were found in the near-surface region and at the grain boundaries. Transport of cations, especially Sr and Cr, along the grain boundaries seems to play a key role in the degradation of LSC. AFM was used to determine the three-dimensional shape including interplanar facet angles of SrCrO4 crystallites. In the case of the Sr-free material LNO, the formation of La-silicate and La-Ni-chromate phases was observed, which seems to proceed from the surface toward the bulk. Based on the experimental results, tentative mechanisms for the degradation processes are suggested. (C) 2016 Elsevier B.V. All rights reserved.