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

Abstract

The electrochemical performance of porous composites of Gd0.1Ce0.9O2−δ/SrMg0.1Mo0.9O3−δ is investigated for the anode application under a typical fuel environment of solid oxide fuel cells (SOFCs). Nanosized powder of SrMg0.1Mo0.9O3−δ possessing a cubic perovskite phase is synthesized using the solution-combustion method. Composites having the composition of xGd0.1Ce0.9O2−δ/SrMg0.1Mo0.9O3−δ (where x is a weight fraction of Gd0.1Ce0.9O2−δ ranging from 0.5 to 0.8) are prepared using a traditional mixing method. At 850 °C, the DC electrical conductivity of SrMg0.1Mo0.9O3−δ under moist 20% H2/N2 is 617 S·cm–1 which declines to ∼105 S·cm–1 for 0.6Gd0.1Ce0.9O2−δ/SrMg0.1Mo0.9O3−δ. Symmetric cells are fabricated using dense disks of yttria-stabilized zirconia as an electrolyte with a thin Gd0.1Ce0.9O2−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 SrMg0.1Mo0.9O3−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 Gd0.1Ce0.9O2−δ addition (x = 0.7) to SrMg0.1Mo0.9O3−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 Gd0.1Ce0.9O2−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 SrMg0.1Mo0.9O3−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 0.7Gd0.1Ce0.9O2−δ/SrMg0.1Mo0.9O3−δ for the SOFC anode.