The effect of Sr doping at the A-sites on the performance of La0.5Gd0.5Ba1-xSrxCo2O5+δ materials for intermediate-temperature solid oxide fuel cells

The effects of Sr doping on the crystal structures, thermal expansion behaviors, defect chemistries, electrical and electrochemical properties of the perovskite materials, La0.5Gd0.5Ba1-xSrxCo2O5+delta (LGBCOSr-x, x=0-0.5), were systematically analyzed and discussed. The X-ray diffraction (XRD) investigation revealed that LGBCOSr-x undergoes a phase transformation from tetragonal (x=0.1) to cubic (x=0.5), and the materials exhibit good thermochemical compatibility with Ce0.9Gd0.1O1.95 (GDC) under 1100 degrees C. Partial replacement of Ba with Sr is found helpful in decreasing the thermal expansivity of LGBCOSr-x and increasing the ability of oxygen vacancy formation in the materials. The latter could be attributed to the enhancement in the overall electrical conductivity and oxygen transport process in terms of low cathodic polarization resistance in LGBCOSr-x materials with high Sr doping content. Further analysis on the AC impedance spectroscopy assisted with the DRT (distribution of relaxation times) methodology suggested that the charge transfer sub-process is a predominant step in the oxygen transport processes across the LGBCOSr-x materials. These findings indicate that La0.5Gd0.5Ba1-xSrxCo2O5+delta is a promising cathode material for intermediate temperature solid oxide fuel cells.