Reduced Thermal Expansion and Enhanced Redox Reversibility of La0.5Sr1.5Fe1.5Mo0.5O6-δ Anode Material for Solid Oxide Fuel Cells

Abstract

High performance anode materials with suitable thermal and chemical expansions are highly desirable for solid oxide fuel cells. In this work, we report a promising anode material La0.5Sr1.5Fe1.5Mo0.5O6-δ (LSFM) synthesized in nitrogen at 1050 °C. Its phase stability, mechanical behavior, redox stability, and electrochemical performance were studied. The electrical conductivity of LSFM reaches 23 S cm-1 in 5% H2-95% N2 at 800 °C with excellent reversibility over three redox cycles. After lanthanum doping, the coefficient of thermal expansion (CTE) is reduced from 17.12 × 10-6 K-1 (SF1.5M) to 15.01 × 10-6 K-1 (LSFM), and this value can be lowered further with a higher lanthanum content. Dilatometry testing at 800 °C shows that the chemical expansion behavior of LSFM is highly reversible during the oxidation-reduction cycling. These results indicate that the thermal and chemical expansion of the crystal lattice can be reduced by a stronger metal-oxygen (M-O) bond strength, leading to an improvement in redox reversibility. The polarization resistance of the LSFM symmetrical cell at 800 °C in humidified hydrogen is 0.16 ω cm2, and the active region is ∼4.5 μm. The half-tear-drop-shaped impedance spectroscopy indicates an oxygen bulk diffusion and surface reaction colimited process. The maximum power density of the LSFM single cell reaches 1156 mW cm-2 at 800 °C within humidified H2. The new ceramic material LSFM is a promising anode for high performance solid oxide fuel cells.