La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 − δ-La 0.6Sr 0.4Co 0.2Fe 0.8O 3 − θ composite cathodes for intermediate-temperature solid oxide fuel cells

Abstract

Solid oxide fuel cells with thin La 0.9Sr 0.1Ga 0.8Mg 0.1O 3 − δ (LSGM) electrolytes have the potential to provide high power densities down to at least 600 °C. The present study was on a candidate cathode material for such SOFCs: composites containing La 0.6Sr 0.4Co 0.2Fe 0.8O 3 − θ (LSCF) and LSGM. Symmetrical cathodes with LSCF contents of 30–70 wt.% were fired at temperatures from 1000 to 1300 °C on both sides of bulk LSGM electrolytes. No secondary phases were detected by X-ray diffraction for the firing temperatures tested. Cathode polarization resistance R p, measured using impedance spectroscopy, varied little with firing temperature despite substantial changes in cathode microstructure as observed by scanning electron microscopy. R p varied only slightly with LSCF content, reaching a minimum of ∼ 0.18 Ohm.cm 2 at 650 °C for 40–60 wt.% LSCF fired at 1100 °C. The R p value was stable over several hundred hours at a current density of 0.5 A/cm 2. The temperature dependence of R p yielded an activation energy of ≈ 1.7 eV for all compositions. Measurements versus oxygen partial pressure P O yielded R p ∝ P O2 0.20. SOFCs with LSCF-LSGM cathodes and thin LSGM electrolytes yielded a maximum power density of 0.57 W/cm 2 at 650 °C.