Reduced-Temperature Firing of Solid Oxide Fuel Cells with YSZ/GDC Bilayer Electrolytes and Sr0.8La0.2TiO3-a Anode-Side Supports

Solid oxide fuel cells (SOFCs) supported on Ni cermets have some drawbacks including coking in hydrocarbon fuels, poisoning by sulfur fuel impurities, and poor redox stability. Prior work has shown that SOFCs with an electronically conducting oxide anode support can overcome these difficulties, even if the anode functional layer is a Ni cermet. In this work, fabrication of SOFCs with Sr_0.8La_0.2TiO_3-α (SLT) anode-side supports is demonstrated utilizing tape casting and co-firing at 1250^oC. This ~ 150^oC reduction in firing temperature compared to typical anode-supported cells was enabled by the use of Fe₂O₃ sintering aid. The reduced temperature enables the use of different materials combinations. For example, cells with a Ni–Gd_0.1Ce_0.9O_1.95 anode functional layer and Yttria-stabilized Zirconia (YSZ) – Gd-doped Ceria (GDC) bi-layer electrolyte have been prepared. Different amounts of Fe₂O₃ were added to the SLT, YSZ and GDC layers to achieve well-matched layer-to-layer shrinkage and avoid delamination. With 7.5mol.% Fe₂O₃ added to the SLT layer, 1mol% Fe₂O₃ added to the YSZ layer and 3mol.% Fe₂O₃ added to the GDC layer, the shrinkages were reasonably well matched and the electrolyte bi-layers were sufficiently dense to yield good open-circuit voltage of 1.043 V at 800^oC in air and humidified hydrogen. The cell yielded maximum power density of 577mWcm^-2 and total cell area specific resistance of 0.5Ωcm² at 800^oC; a portion of this resistance was from the SLT support. Electrochemical test results will be discussed in terms of the observed cell microstructure. In addition, results will be presented on Ni-free cells where the Ni-based anode functional layer was replaced by a mixed-conducting oxide functional layer, SrTi_0.3Fe_0.7O₃ (STF).