High temperature electrical conductivity and electrochemical investigation of La2-xSrxCoO4 nanoparticles for IT-SOFC cathode

Single-phase Ruddlesden popper of La2-xSrxCoO4 nanopowders with x = 0.7, 0.9, 1.1 and 1.3, were successfully synthesized by a modified sol-gel method. Structural stability and morphology of the prepared samples were examined using HT-XRD analysis, FE-SEM and SEM techniques. HT-XRD analysis of the samples, in the range of room temperature to 850 degrees C, revealed that the structure of all samples was tetragonal. The electrical conductivity measurements, in the range of room temperature to 850 degrees C, indicated that by increasing the temperature the electrical conductivity mechanism inverts from variable range hopping to the nearest-neighbor hopping of small polarons. In addition, it was found that by increasing Sr concentration the structure of the sintered samples becomes more stable. The electrochemical characterization was carried out using the impedance spectroscopy (EIS) measurements on symmetrical cells at three different temperatures, 650 degrees C, 750 degrees C and 850 degrees C. The area specific polarization resistance (ASR) of La2-xSxCoO4-CGO-La2-xSrxCoO4 symmetrical cell, in oxygen flow, was obtained about 1.07, 0.35, 0.33 and 0.43 Omega cm(2) at 850 degrees C for the samples with x = 0.7, 0.9, 1.1 and x = 1.3, respectively. According to our EIS results, the main rate-limiting step for La2-xSrxCoO4 cathode performance is the dissociation process of oxygen at the surface of cathode at 650 degrees C and the charge transfer limiting in the cathode/electrolyte at 750 degrees C and 850 degrees C. Our results showed that the samples with Sr contents of x = 0.9 and x = 1.1 can be the promising cathodes for IT-SOFC applications.