Effects of Co Doping on the Electrochemical Performance of Double Perovskite Oxide Sr2MgMoO6−δ as an Anode Material for Solid Oxide Fuel Cells

Double-perovskite materials of composition Sr2Mg1–x Co x MoO6−δ (SMCMO, x = 0 to 0.7) were evaluated as potential SOFC anode materials. Their lattice structures, electrical and ionic conductivity, thermal expansion coefficient (TEC), and electrochemical performance were investigated as a function of Co content. Co doping was found to increase the TEC of the Sr2MgMoO6−δ material; however, the TEC was within the range of the commonly used La0.8Sr0.2Ga0.8Mg0.2O3‑δ (LSGM) electrolyte. SMCMO also showed good chemical compatibility with the LSGM electrolyte at temperatures below 1300 °C. Both the electronic and ionic conductivity increased with increasing Co doping. To investigate the effect of Co doping on the conduction properties of SMCMO, we performed first-principle calculations. From these results, the weak Co–O bond is considered to be responsible for the enhanced ionic conductivity of SMCMO materials. The substitution of Co was also found to increase the sinterability of SMCMO, resulting in a decrease in the polarization resistance of the SMMO electrode. Single-cell tests indicated the potential ability of the Co-doped SMMO to be used as SOFC anodes.