Redox behaviour, chemical compatibility and electrochemical performance of Sr2MgMoO6-δ as SOFC anode

The double perovskite Sr2MgMoO6-delta (SMM) has been proposed as a potential anode material for direct hydrocarbon oxidation in solid oxide fuel cells (SOFCs). The oxygen nonstoichiometry and electrical conductivity dependence of Sr2MgMoO6-delta, have been determined as a function of the oxygen partial pressure by coulometric titration and impedance spectroscopy techniques. The chemical compatibility of Sr2MgMoO6-delta with most of the typical electrolytes commonly used in SOFCs i.e. La0.8Sr0.2Ga0.8Mg0.2O3-delta (LSGM), Ce-0.8Gd0.2O2-delta (CGO) and Zr0.84Y0.16O2-delta (YSZ), was investigated. Reactivity between SMM and all these electrolytes has been found above 1000 degrees C, although the reaction is most severe with ZrO2-based electrolytes. Area-specific polarisation resistance of the SMM/LSGM/SMM symmetrical cells indicates that the polarisation resistance increases with the firing temperature of the electrodes due to chemical interaction between USGM and SMM layers. A CGO buffer layer between the anode and electrolyte was also used to prevent an excessive interdiffusion of ionic species between these components, resulting in better performance. Power densities of 330 and 270 MW cm(-2) were reached at 800 degrees C for SMM/CGO/LSGM/L.SCF and SMM/LSGM/LSCF electrolyte-supported cells, respectively; with 600-mu m-thick LSGM electrolyte, using humidified H-2 as fuel and air as oxidant. XPS and XRPD studies on SMM powders annealed in air and diluted CH4 atmospheres showed that the surface of SMM powders is mainly formed by SrMoO4 and metal carbonates. (C) 2009 Elsevier B.V. All rights reserved.