Electrode properties of La_1-xSr_xCuO _2.5-δ as new cathode materials for intermediate-temperature SOFCs

Oxygen-deficient perovskite type oxides La_1-xSr _xCuO_2.5-δ (LSCu) have been synthesized in the composition range: 0.15≤x≤0.3. Due to their high oxygen vacancy concentration and good electrical conductivity, these materials are characterized as new positive electrode (cathode) materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The valence state of copper ions, thermal expansion, cathodic overpotential, reactivity with yttria-stabilized zirconia (YSZ) and polarization resistance (R_p) of the LSCu|YSZ interface are examined. At 800°C, the sample with the composition of La_0.7Sr_0.3CuO_2.5-δ exhibits the lowest overpotential of about 10 and 12.6mV at a current density of 150 and 200mAcm^-2, respectively. LSCu show no reaction against yttria-stabilized zirconia (8YSZ) at 800°C for 1000h. Reaction between LSCu and YSZ occurs, however, at 900°C for 10h. The formation of SrZrO ₃ is observed. Based on the results of ac impedance analyses, the polarization resistance of LSCu decreases from 0.85 to 0.25Ω at 800°C when the fraction of Sr is increased from 20 to 30%. The reduction of polarization resistance is improved by the presence of oxygen vacancies in LSCu. These oxygen vacancies provide numerous pathways for the diffusion of oxygen ions electrode surface to the triple phase boundary (TPB) and the electrode|electrolyte interface. Therefore, LSCu may be a very attractive cathode material for IT-SOFCs.