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

Abstract

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−δ (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 R3¯c (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 12.7×10−6 to 15.4×10−6K−1 that are well compatible with prototypical electrolytes Zr0.84Y0.16O1.92 (YSZ) and Ce0.8Sm0.2O2−δ (SDC). The dc-conductivity is significantly enhanced from 36.5, 90.5 to 173.7 Scm−1 at 850°C with the increasing Co percent, and accordingly, polarization resistance (Rp) is determined as 0.1291, 0.0835 and 0.0486Ωcm2 at 800°C. The high electrical conductivities and low resistances can be attributed to the strong BO 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.