Investigation of Graded La[sub 2]NiO[sub 4+δ] Cathodes to Improve SOFC Electrochemical Performance

Mixed ionic and electronic conducting (MIEC) oxides are promising materials for use as cathodes in solid oxide fuel cells (SOFCs) due to their enhanced electrocatalytic activity compared with electronic conducting oxides. In this paper, the MIEC oxide was prepared by the sol–gel route. Graded cathodes were deposited onto yttria-stabilized zirconia (YSZ) pellets by dip-coating, and electrochemical impedance spectroscopy studies were performed to characterize the symmetrical cell performance. By adapting the slurries, cathode layers with different porosities and thicknesses were obtained. A ceria gadolinium oxide (CGO) barrier layer was introduced, avoiding insulating phase formation and thus reducing resistance polarization of the cathode. A systematic correlation between microstructure, composition, and electrochemical performance of these cathodes has been performed. An improvement of the electrochemical performance has been demonstrated, and a reduction in the area specific resistance (ASR) by a factor of 4.5 has been achieved with a compact interlayer of between the dense electrolyte and the porous cathode layer. The lowest observed ASR of at was obtained from a symmetrical cell composed of a YSZ electrolyte, a CGO interlayer, an intermediate compact layer, a porous electrode layer, and a current collection layer of platinum paste.