Redox behaviour, chemical compatibility and electrochemical performance of Sr 2MgMoO 6 − δ as SOFC anode

Abstract

The double perovskite Sr 2MgMoO 6 − δ (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 Sr 2MgMoO 6 − δ have been determined as a function of the oxygen partial pressure by coulometric titration and impedance spectroscopy techniques. The chemical compatibility of Sr 2MgMoO 6 − δ with most of the typical electrolytes commonly used in SOFCs i.e. La 0.8Sr 0.2Ga 0.8Mg 0.2O 3 − δ (LSGM), Ce 0.8Gd 0.2O 2 − δ (CGO) and Zr 0.84Y 0.16O 2 − δ (YSZ), was investigated. Reactivity between SMM and all these electrolytes has been found above 1000 °C, although the reaction is most severe with ZrO 2-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 LSGM 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 °C for SMM/CGO/LSGM/LSCF and SMM/LSGM/LSCF electrolyte-supported cells, respectively; with 600-μm-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 CH 4 atmospheres showed that the surface of SMM powders is mainly formed by SrMoO 4 and metal carbonates.