Phase decomposition in the chromium- and silicon-poisoned IT-SOFC cathode materials La_0.6Sr_0.4CoO_3-δ and La₂NiO_4+δ

Chromium- and silicon-poisoned samples of the intermediate temperature solid oxide fuel cell (IT-SOFC)cathode materials La0.6Sr0.4CoO3-δ(LSC) and La2NiO4+δ(LNO) were investigated by transmission electronmicroscopy (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). AnalyticalTEM revealed phase decomposition of the original, oxygen exchange-active materials LSC and LNO, and the for-mation of secondary phases after 3500 h of testing at 700 °C. In the case of LSC, the phases SrCrO4,Co3O4,andCoCr2-xCoxO4as well as a La‐chromate phase with unknown stoichiometry were found in the near-surface regionand at the grain boundaries. Transport of cations, especially Sr and Cr, along the grain boundaries seems to play akey roleinthe degradation of LSC. AFMwasused todeterminethethree-dimensional shapeincludinginterplanarfacet angles of SrCrO4crystallites. 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 theexperimental results, tentative mechanisms for the degradation processes are suggested.© 2016 Elsevier B.V. All rights reserved.