Al-Doped SrMoO₃ Perovskites as Promising Anode Materials in Solid Oxide Fuel Cells

Two perovskite materials with SrMo_1-xAl_xO_3- (x = 0.1, 0.2) compositions have been synthesized by reduction from the corresponding scheelite phases, with SrMo_1-xAl_xO_4- stoichiometry; the pertinent characterization shows that the defective perovskites can be used as anode materials in solid oxide fuel cells, providing maximum output power densities of 633 mW/cm² for x = 0.2. To correlate structure and properties, a neutron powder diffraction investigation was carried out for both perovskite and scheelite phases. Both perovskites are cubic, defined in the Pm-3m space group, displaying a random distribution of Mo and Al cations over the 1a sites of the structure. The introduction of Al at Mo positions produced conspicuous amounts of oxygen vacancies in the perovskite, detected by neutrons. This is essential to induce ionic diffusion, providing a mixed ionic and electronic conduction (MIEC), since in MIEC electrodes, charge carriers are combined in one single phase and the ionic conductivity can be one order of magnitude higher than in a conventional material. The thermal expansion coefficients of the reduced and oxidized samples demonstrated that these materials perfectly match with the La_0.8Sr_0.2Ga_0.83Mg_0.17O_3- electrolyte, La_0.4Ce_0.6O_2- buffer layer and other components of the cell. Scanning electron microscopy after the test in a real solid oxide fuel cell showed a very dense electrolyte and porous electrodes, essential requirements for this type of fuel. SrMo_1-xAl_xO_3- perovskites are, thus, a good replacement of conventional biphasic cermet anodes in solid oxide fuel cells.