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

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.