Short stack and full system test using a ceramic A-site deficient strontium titanate anode

摘要

Doped strontium titanates have been widely studied as potential anode materials in solid oxide fuel cells (SOFCs). The high n-type conductivity that can be achieved in these materials makes them well suited for use as the electronically conductive component in SOFC anodes. This makes them a potential alternative to nickel, the presence of which is a major cause of degradation due to coking, sulphur poisoning and low tolerance to redox cycling. As the electrocatalytic activity of strontium titanates tends to be low, impregnation with oxidation catalysts, such as ceria and nickel is often required to obtain anode performances that can compete with Ni-YSZ cermets. Here the stability issues due to nickel should be reduced due to the small loadings and its non-structural function. In this study, a lanthanum and calcium co-doped A-site deficient strontium titanate (LSCTA-) was used as the anode material in cells with an active area of 100 cm~2. Cell performance was tested in both short (5 cell) stack configuration, as well as a full HEXIS Galileo system (nominally 1 kW AC). Various impregnates, such as nickel and ceria, were used in this approach with promising results. The system test initially produced 70% of the nominal output power and is to the authors’ knowledge the first all-oxide SOFC test on this scale. The strontium titanate backbone provides sufficient electronic conductivity to ensure acceptable ohmic losses. Power densities up to 200 mA/cm~2 could be obtained at 900°C, which compares well with Ni-cermet based anodes. Degradation is however severe at 900°C, due to impregnate coarsening, but operation at 850°C minimises this effect. Short stacks could be stably operated for 1600 hours with an output power of 100 mA/cm~2. Stacks are redox stable, but sulphur tolerance is determined by the electrocatalysts.