Hyperstoichiometric La1.9Sr0.1NiO4+δ mixed conductor as novel cathode for intermediate temperature solid oxide fuel cells

The materials La2-x,SrNiO4+delta (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+delta 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 (200 bar, 650 degrees C). As a result, the O-2- treated La1.9Sr0.1NiO4+delta exhibited an increase of the amount of interstitial oxygens (delta= 0.17) but with improved electronic properties. The polarization resistances measured for these materials vary between 8 Omega cm(2) and 0.1 Omega cm(2) in air at the temperature range of 700-975 degrees C. This remarkable behavior enables us to propose this material as an alternative cathode for IT-SOFC.