Investigations on structures, thermal expansion and electrochemical properties of La0.75Sr0.25Cu0.5-xCoxMn0.5O3-delta (x=0, 0.25, and 0.5) as potential cathodes for intermediate temperature solid oxide fuel cells

A series of perovskite oxides have been investigated as excellent potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this paper, we take the La0.75Sr0.25Cu0.5-xCoxMn0.5O3-delta (LSCCM, x = 0, 0.25 and 0.5) system as subject, with Cu/Mn and/or Co/Mn on B-site and 25% Sr-substituted La ions on A-site, to investigate their structures, thermal stability and electrochemical properties. Pure rhombohedral crystal with space group R (3) over barc (no. 167) is identified by Rietveld refinement of X-ray diffraction data (XRD). It is found that the thermal expansion coefficient (TEC) is manageable when Co ion is incorporated, and the low TEC value ranges from 12.7 x 10(-6) to 15.4 x 10(-6) K-1 that are well compatible with prototypical electrolytes Zr0.84Y0.16O1.92 (YSZ) and Ce0.8Sm0.2O2-delta (SDC). The dc-conductivity is significantly enhanced from 36.5, 90.5 to 173.7 S cm(-1) at 850 degrees C with the increasing Co percent, and accordingly, polarization resistance (R-p) is determined as 0.1291, 0.0835 and 0.0486 V cm(2) at 800 degrees C. The high electrical conductivities and low resistances can be attributed to the strong B-O bond hybridization and oxygen vacancy formation at elevated temperatures with the introduction of Co ion, which is consistent with the results of first-principles calculation and thermogravimetric analysis. All these results demonstrate that LSCCM series are promising cathodes with controllable TEC for IT-SOFCs. (C) 2015 Elsevier Ltd. All rights reserved