Hyperstoichiometric La1.9Sr0.1NiO4+δ Mixed Conductor as Novel Cathode for Intermediate Temperature Solid Oxide Fuel Cells

Abstract

The materials La2−xSrxNiO4+δ(x=0,0.1) with K2NiF4 structure have been studied in order to explore their potential use as cathodes for intermediate temperature solid oxide fuel cells. The introduction of Sr in the La2NiO4+δ lattice produces an enhancement of the electric conductivity but is accompanied by a decrease of ionic transport species. Neutron powder diffraction data show a transition from orthorhombic to tetragonal symmetry with the incorporation of Sr in the LaO sublattice. Excess oxygen determined by iodometric titration shows that strontium insertion generates a decrease of the interstitial oxygen. In order to avoid the concomitant decrease of the ionic conductivity, the system underwent heat treatments under high oxygen pressure (200bar, 650°C). As a result, the O2− treated La1.9Sr0.1NiO4+δ exhibited an increase of the amount of interstitial oxygens (δ=0.17) but with improved electronic properties. The polarization resistances measured for these materials vary between 8Ωcm2 and 0.1Ωcm2 in air at the temperature range of 700–975°C. This remarkable behavior enables us to propose this material as an alternative cathode for IT-SOFC.