The Effect of Sr Doping at the A-Sites on the Performance of La0.5gd0.5ba1− X Sr X Co2o5+ Δ Double Perovskite Materials

Abstract

La0.5Gd0.5Ba1−xSrxCo2O5+δ (x=0–0.5) perovskite cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) were prepared by a solid-state reaction method, and the crystal structures, thermal expansion coefficients, defect chemistries, and electrochemical properties of the cathode materials were studied. X-ray diffraction showed that with the doping level increase of Sr, the materials underwent a transformation from a tetragonal phase to a cubic phase. The materials retained good chemical compatibility with the Ce0.9Gd0.1O1.95 electrolyte at 1100°C. The thermal expansion coefficients decreased with the increase of Sr doping level, while the number of oxygen vacancies and the surface oxygen concentration increased. The conductivities of all the samples were measured above 100 S/cm at 400 to 700°C in air, and the conductivity of LGBCOSr-0.5 (x = 0.5, with a single perovskite) at 400°C reached up to 1034 S/cm. The cathodic polarization and characteristic capacitance obtained from the DRT (distribution of relaxation times) analysis of the electrochemical impedanceshowed that the addition of strontium improved the transport of oxygen ions and charge transfer in the cathodic redox processes. These results indicate that La0.5Gd0.5Ba0.5Sr0.5Co2O5+δ is a promising cathode material for IT-SOFCs.

Keywords: Solid oxide fuel cell, Cathode, Sr doping, Electrochemical performance, Active oxygen species