(La,Sr)MnO3–(Ce,Gd)O2−x composite cathodes for solid oxide fuel cells

Impedance spectroscopy was used to measure the oxygen reaction kinetics of composite cathodes consisting of La0.8Sr0.2MnO3 (LSM) and Ce0.8Gd0.2O2−x (GDC) on yttria-stabilized zirconia (YSZ) and GDC electrolytes. The LSM–GDC electrodes are analogous to the widely used LSM–YSZ cathodes but have potential advantages since LSM is non-reactive with GDC and the ionic conductivity of GDC is higher than that of YSZ. LSM–GDC cathodes with 0–60 wt.% GDC were characterized over a temperature range of 600–750°C at oxygen partial pressures between 10−3 and 1 atm. Using YSZ electrolytes, the low-current interfacial resistance was smallest for 50 wt.% GDC, where the value was 0.49 Ω cm2 at 750°C. This is two to three times lower than that for LSM–YSZ composite cathodes on YSZ with similar structure. The majority of the LSM–GDC cathodes appeared to be limited by adsorption, as well as oxygen ion transfer into the electrolyte.