Preliminary investigation of the higher-order ruddlesden-popper phases for IT-SOFC cathodes, Lan+1NinO3n+1 (n = 2 and 3)

Abstract

The Ruddlesden-Popper phase, La2NiO4+δ, has generated much interest as an alternative cathode material to the conventionally used perovskite-based materials, La1-xSrxBO3 (B = Mn, Co), particularly in the intermediate temperature range (873-1073 K). This is largely due to a combination of good electrical conductivity with high oxide-ion diffusion coefficients in this temperature range. In a previous study, however, the degradation of La2NiO4+δ into a mixed Ni2+/Ni3+ impurity phase was reported when subjected to prolonged heating at 1173 K for two weeks. This has been attributed to the favourable stability of the Ni3+ ion at lower temperatures (T < 1273 K) compared to the predominant Ni2+ present in this phase. We report here the results of an investigative study of the higher-order, mixed Ni2+/Ni3+ Ruddlesden-Popper phases Lan+1Ni nO3n+1 (n = 2 and 3) for possible use as cathodes in intermediate temperature solid oxide fuel cells. Details regarding the preparation and subsequent characterization of the Lan+1Ni nO3n+1 (n = 2 and 3) phases by x-ray diffraction, oxygen content determination, electrical conductivity, thermal stability and area specific resistance measurements on symmetrical LSGM cells are presented.