Redox stability improvement in metal supported cells with strontium titanate based fuel electrodes: A step towards the next generation solid oxide cells

Kurzfassung

The state of the art nickel-zirconia cermet anode shows among others poor reliability in redox cycles, which might happen during on/off sequences and high sensitivity towards poisons. On the contrary, perovskite materials based on strontium titanate present a good dimensional stability during redox cycles. We report about redox stability improvement in metal supported cells with LST (La0.1Sr0.9TiO3-α) based anodes. LST powder was first produced by spray pyrolysis. Liquid precursors are mixed in stoichiometric ratios and atomised in a rotating furnace forming hollow spheres of metal oxides, allowing production of advanced electroceramic powders with good physico-chemical properties, reproducibility and suitable morphology. The particle size is typically submicronic (100-500 nm) and specific surface area in the range 1-50 m2/g. For the metal supported cells, LST (type A) or LST/NiO mixtures (type B) were infiltrated into a NiCrAl foam. The anode functional layer was made of LST mixed with Gd0.1Ce0.9O2-α (GDC) (type A), further modified with catalytic nickel for type B. Thin film electrolyte with thickness as low as 3µm was produced by wet ceramic processing and electron beam physical vapor deposition. Cathode was made of La0.6Sr0.4Co0.2Fe0.8O3-α. Cells as big as 9cm x 10cm were produced. At 750°C and 0.7 V, the power density of 5 cm x 5 cm cells was typically 100 mW / cm² and 400 mW / cm² for the type A and the type B, respectively. The redox behavior was further evaluated by exposing the anode to oxygen for 30 min at 750°C. With less than 2% variation for 50 redox cycles, the open circuit voltage showed an excellent stability suggesting that the electrolyte remain intact despite the harsh conditions. This demonstrates the robustness of this architecture compared to main stream anode supported cells and the suitability of SrTiO3 based perovskites to enhance the redox stability.