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

Double-perovskites Sr2MMoO6 (M = Co, Ni) have been investigated as anode materials for a solid oxide fuel cell. At room temperature, both Sr2CoMoO6 and Sr2NiMoO6 are tetragonal (I4/m). X-ray absorption spectroscopy confirmed the presence of Co2+/Mo6+ and Ni2+/Mo6+ 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 degrees 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 mu m thick La0.8Sr0.2Ga0.83Mg0.17O2.815 electrolyte and SrFe0.2Co0.8O3-delta as a cathode, Sr2CoMoO6 exhibited maximum power densities of 735 mW/cm(2) in H-2 and 527 mW/cm(2) in wet CH4 at 800 degrees C; Sr2NiMoO6 shows a notable power output only in dry CH4. The high performance of Sr2CoMoO6 in wet CH4 may be due to its catalytic effect on steam reforming of methane, but some degradation of the structure that occurred in CH4 obscures identification of the catalytic reaction processes at the surface. However, the stronger octahedral-site preference of Ni2+ versus Co2+ can account for the lower performance of the M = Ni anode.