Ferrite-based perovskites as cathode materials for anode-supported solid oxide fuel cells: Part II. Influence of the CGO interlayer

It was shown in part I (Variation of the cathode composition) [A. Mai, V.A.C. Haanappel, S. Uhlenbruck, F. Tietz, D. Stöver, Solid State Ionics 176 (2005), 1341], that an interlayer is needed between yttria-stabilised zirconia (YSZ) electrolytes and (La,Sr)(Co,Fe)O3−δ (LSCF) cathodes in order to prevent undesired chemical reactions between these materials. This interlayer makes it possible to benefit from the superior electrochemical properties of the LSCF perovskites in solid oxide fuel cells (SOFCs). In this study the influence of a Ce0.8Gd0.2O2−δ (CGO) interlayer on the electrochemical performance of LSCF-type SOFCs is investigated in more detail. For screen-printed and sintered interlayers the grain size as well as the sintering temperature affected the electrochemical performance. The use of a fine powder with a mean particle size of d50 = 0.2 μm and sintered at 1250 °C resulted in the best performance. Furthermore, reactive sputtering resulted in dense CGO interlayers at low deposition temperatures, which led to improved properties regarding diffusion inhibition and electrochemical performance. SOFCs with sputtered interlayers gave power densities of up to 0.9 W/cm2 at 700 °C and 0.7 V, with H2 + 3% H2O as fuel gas (approx. 10% fuel utilisation).