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

Abstract Double-perovskites A 2 FeMoO 6− δ ( A  = Ca, Sr, Ba) have been investigated as potential anode materials for solid oxide fuel cells (SOFCs). At room temperature, A 2 FeMoO 6− δ 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 A MoO 4 . XPS has confirmed the coexistence of Fe 2+ –Mo 6+ and Fe 3+ –Mo 5+ electronic configurations. Moreover, a systematic shift from Fe 2+/3+ –Mo 6+/5+ to Fe 2+ –Mo 6+ configuration is seen with increasing A -site cation size. A 2 FeMoO 6− δ samples display distinct electrical properties in H 2 , which can be attributed to different degrees of degeneracy of the Fe 2+ –Mo 6+ and Fe 3+ –Mo 5+ configurations. Ca 2 FeMoO 6− δ is unstable in a nitrogen atmosphere, while Sr 2 FeMoO 6− δ and Ba 2 FeMoO 6− δ are stable up to 1200 °C. The thermal expansion coefficients of Sr 2 FeMoO 6− δ and Ba 2 FeMoO 6− δ are very close to that of La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3− δ (LSGM). The performances of cells with 300 μm thick LSGM electrolyte, double-perovskite SmBaCo 2 O 5+ x cathodes, and A 2 FeMoO 6− δ anodes follow the sequence Ca 2 FeMoO 6− δ 2 FeMoO 6− δ 2 FeMoO 6− δ . The maximum power densities of a cell with an Sr 2 FeMoO 6− δ anode reach 831 mW cm −2 in dry H 2 and 735 mW cm −2 in commercial city gas at 850 °C, respectively.