Evaluation of W-containing Sr1 −xBaxFe0.75W0.25O3-δ (x = 0, 0.5, 1) anode materials for solid oxide fuel cells

In this work, W-containing Sr1 −xBaxFe0.75W0.25O3 −δ (x = 0, 0.5, 1) perovskite-related oxides have been for the first time evaluated in terms of their possible application as anode materials in solid oxide fuel cells. Crystal structure, thermal expansion coefficient, transport properties, oxygen content, chemical compatibility in relation to ceria-based electrolyte, and stability of the materials in reducing atmospheres have been studied. It was found that SrFe0.75W0.25O3 −δ and Sr0.5Ba0.5Fe0.75W0.25O3 −δ oxides show simple perovskite-type structure with cubic Pm-3m symmetry, while BaFe0.75W0.25O3 −δ exhibits hexagonal P63/mmc structure. Small grains (~ 2 μm) can be obtained for SrFe0.75W0.25O3 −δ compound with very simple, high-temperature synthesis process in air. Large oxygen nonstoichiometry changes of Δδ ≈ 0.36 were observed for SrFe0.75W0.25O3 −δ oxide upon heating in 5 vol.% H2 in argon. Seebeck coefficient and electrical conductivity measurements revealed that SrFe0.75W0.25O3 −δ oxide exhibits p-type conductivity in air and n-type conductivity under reducing conditions. This oxide presents relatively good chemical compatibility in relation to Ce0.8Gd0.2O1.9 electrolyte, and chemical stability in 5 vol.% H2 in argon up to at least 800 °C. Electrochemical impedance spectroscopy studies for SrFe0.75W0.25O3 −δ-based cells conducted in pure hydrogen and CH4 indicated the possibility of the application of SrFe0.75W0.25O3 −δ as the anode material in SOFCs.