Double-perovskites A2FeMoO6-δ (A = Ca, Sr, Ba) as anodes for solid oxide fuel cells

Double-perovskites A(2)FeMoO(6-delta) (A = Ca, Sr, Ba) have been investigated as potential anode materials for solid oxide fuel cells (SOFCs). At room temperature, A(2)FeMoO(6-delta) compounds crystallize in monoclinic, tetragonal, and cubic structures for A = Ca, Sr, and Ba, respectively. A weak peak observed at around 880 cm(-1) in the Raman spectra can be attributed to traces of AMoO(4). XPS has confirmed the coexistence of Fe2+-Mo6+ and Fe3+-Mo5+ electronic configurations. Moreover, a systematic shift from Fe2+/3+-Mo6+/5+ to Fe2+-Mo6+ configuration is seen with increasing A-site cation size. A(2)FeMoO(6-delta) samples display distinct electrical properties in H-2, which can be attributed to different degrees of degeneracy of the Fe2+-Mo6+ and Fe3+-Mo5+ configurations. Ca2FeMoO6-delta is unstable in a nitrogen atmosphere, while Sr2FeMoO6-delta and Ba2FeMoO6-delta are stable up to 1200 degrees C. The thermal expansion coefficients of Sr2FeMoO6-delta and Ba2FeMoO6-delta are very close to that of La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM). The performances of cells with 300 mu m thick LSGM electrolyte, double-perovskite SmBaCo2O5+x cathodes, and A(2)FeMoO(6-delta) anodes follow the sequence Ca2FeMoO6-delta < Ba2FeMoO6-delta < Sr2FeMoO6-delta. The maximum power densities of a cell with an Sr2FeMoO6-delta anode reach 831 mW cm(-2) in dry H-2 and 735 mW cm(-2) in commercial city gas at 850 degrees C, respectively. (C0 2010 Elsevier B.V. All rights reserved.