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

Double-perovskites A2FeMoO6−δ (A = Ca, Sr, Ba) have been investigated as potential anode materials for solid oxide fuel cells (SOFCs). At room temperature, A2FeMoO6−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 AMoO4. 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. A2FeMoO6−δ samples display distinct electrical properties in H2, which can be attributed to different degrees of degeneracy of the Fe2+–Mo6+ and Fe3+–Mo5+ configurations. Ca2FeMoO6−δ is unstable in a nitrogen atmosphere, while Sr2FeMoO6−δ and Ba2FeMoO6−δ are stable up to 1200 °C. The thermal expansion coefficients of Sr2FeMoO6−δ and Ba2FeMoO6−δ are very close to that of La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM). The performances of cells with 300 μm thick LSGM electrolyte, double-perovskite SmBaCo2O5+x cathodes, and A2FeMoO6−δ anodes follow the sequence Ca2FeMoO6−δ < Ba2FeMoO6−δ < Sr2FeMoO6−δ. The maximum power densities of a cell with an Sr2FeMoO6−δ anode reach 831 mW cm−2 in dry H2 and 735 mW cm−2 in commercial city gas at 850 °C, respectively.