La0.9Sr0.1Ga0.8Mg0.2O3 − δ-La0.6Sr0.4Co0.2Fe0.8O3 − θ composite cathodes for intermediate-temperature solid oxide fuel cells

Solid oxide fuel cells with thin La0.9Sr0.1Ga0.8Mg0.1O3 − 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 La0.6Sr0.4Co0.2Fe0.8O3 − 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 Rp, measured using impedance spectroscopy, varied little with firing temperature despite substantial changes in cathode microstructure as observed by scanning electron microscopy. Rp varied only slightly with LSCF content, reaching a minimum of ∼ 0.18 Ohm.cm2 at 650 °C for 40–60 wt.% LSCF fired at 1100 °C. The Rp value was stable over several hundred hours at a current density of 0.5 A/cm2. The temperature dependence of Rp yielded an activation energy of ≈ 1.7 eV for all compositions. Measurements versus oxygen partial pressure PO yielded Rp ∝ PO20.20. with LSCF-LSGM cathodes and thin LSGM electrolytes yielded a maximum power density of 0.57 W/cm2 at 650 °C.