Electrochemical Performance of SrMg_0.1Mo_0.9O₃‑Based Composites for Solid Oxide Fuel Cell Anodes

The electrochemical performance of porous composites of Gd_0.1Ce_0.9O_2−δ/SrMg_0.1Mo_0.9O_3−δ is investigated for the anode application under a typical fuel environment of solid oxide fuel cells (SOFCs). Nanosized powder of SrMg_0.1Mo_0.9O_3−δ possessing a cubic perovskite phase is synthesized using the solution-combustion method. Composites having the composition of xGd_0.1Ce_0.9O_2−δ/SrMg_0.1Mo_0.9O_3−δ (where x is a weight fraction of Gd_0.1Ce_0.9O₂₋δ ranging from 0.5 to 0.8) are prepared using a traditional mixing method. At 850 °C, the DC electrical conductivity of SrMg_0.1Mo_0.9O_3−δ under moist 20% H₂/N₂ is 617 S·cm^–1 which declines to ∼105 S·cm^–1 for 0.6Gd_0.1Ce_0.9O_2−δ/SrMg_0.1Mo_0.9O_3−δ. Symmetric cells are fabricated using dense disks of yttria-stabilized zirconia as an electrolyte with a thin Gd_0.1Ce_0.9O_2−δ buffer layer coated on both faces. An optimized slurry of the composite electrode is blade-coated on the dense buffer layer and subsequently sintered at 950 °C in air. Scanning electron microscopy reveals a porous microstructure with an electrode layer thickness of ∼14 μm. A single-phase SrMg_0.1Mo_0.9O_3−δ electrode exhibits an area-specific resistance of 0.28 Ω·cm², which is less than 6 times the value offered by undoped SrMoO₃ at 800 °C in 3% H₂O/H₂. The optimum Gd_0.1Ce_0.9O_2−δ addition (x = 0.7) to SrMg_0.1Mo_0.9O_3−δ resulted in a significantly low area-specific resistance of 0.09 Ω·cm² at 800 °C. The performance of the optimized electrode composite is also evaluated by modifying the microstructure of the Gd_0.1Ce_0.9O_2−δ buffer layer. Interestingly, the symmetrical cell with a porous buffer layer further reduces the electrode area-specific resistance to 0.065 Ω·cm². The observed results are ascribed to the penetration of electrocatalyst SrMg_0.1Mo_0.9O_3−δ particles inside the porous buffer layer during the blade-coating. This possibly extends the triple-phase boundary length and facilitates the charge-transfer reaction. The electrochemical performance attained in the present study is far superior to the other Ni-free ceramic anodes reported earlier, which highlights the promise of 0.7Gd_0.1Ce_0.9O_2−δ/SrMg_0.1Mo_0.9O_3−δ for the SOFC anode.