Double-Perovskite Anode Materials Sr2MMoO6 (M = Co, Ni) for Solid Oxide Fuel Cells

Double-perovskites Sr 2 MMoO 6 (M = Co, Ni) have been investigated as anode materials for a solid oxide fuel cell. At room temperature, both Sr 2 CoMoO 6 and Sr 2 NiMoO 6 are tetragonal ( I 4 /m ). X-ray absorption spectroscopy confirmed the presence of Co 2+ /Mo 6+ and Ni 2+ /Mo 6+ pairs in the oxygen-stoichiometric compounds. The samples contain a limited concentration of oxygen vacancies in the reducing atmospheres at an anode. Reoxidation is facile below 600 °C; they become antiferromagnetic at low temperatures T N = 37 and 80 K for M = Co and Ni, respectively. As an anode with a 300 μm thick La 0.8 Sr 0.2 Ga 0.83 Mg 0.17 O 2.815 electrolyte and SrFe 0.2 Co 0.8 O 3−δ as a cathode, Sr 2 CoMoO 6 exhibited maximum power densities of 735 mW/cm 2 in H 2 and 527 mW/cm 2 in wet CH 4 at 800 °C; Sr 2 NiMoO 6 shows a notable power output only in dry CH 4 . The high performance of Sr 2 CoMoO 6 in wet CH 4 may be due to its catalytic effect on steam reforming of methane, but some degradation of the structure that occurred in CH 4 obscures identification of the catalytic reaction processes at the surface. However, the stronger octahedral-site preference of Ni 2+ versus Co 2+ can account for the lower performance of the M = Ni anode.