Sr2Fe1.5Mo0.5O6 as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells with La0.8Sr0.2Ga0.87Mg0.13O3 Electrolyte

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Abstract
The performance of Sr2Fe1.5Mo0.5O6 (SFMO) as a cathode material has been investigated in this study. The oxygen ionic conductivity of SFMO reaches 0.13 S cm−1 at 800°C in air. The chemical diffusion coefficient (D chem) and surface exchange constant (k ex) of SFMO at 750°C are 5.0 × 10−6 cm2 s−1 and 2.8 × 10−5 cm s−1, respectively, suggesting that SFMO may have good electrochemical activity for oxygen reduction. SFMO shows a thermal expansion coefficient (TEC) of 14.5 × 10−6 K−1 the temperature range of 200–760°C in air. The polarization resistance of the SFMO cathode is 0.076 Ω cm2 at 800°C in air under open-circuit conditions measured on symmetrical cells with La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolytes. Dependence of SFMO cathode polarization resistance on the oxygen partial pressure and the cathode overpotentials at different temperatures are also studied. SFMO shows an exchange current density of 0.186 A cm−2 at 800°C in air. Single cells with the configuration of Ni-La0.4Ce0.6O2 (LCO)|LCO|LSGM|SFMO show peak power densities of 349, 468, and 613 mW cm−2 at 750, 800, and 850°C, respectively using H2 as the fuel and ambient air as the oxidant. These results indicate that SFMO is a promising cathode candidate for intermediate-temperature solid oxide fuel cells with LSGM electrolyte.