Investigation of La_1−xSm_x−ySr_yCoO_3−Δcathode for intermediate temperature solid oxide fuel cells

La_1−xSm_x−ySr_yCoO_3−δ(LSSC; x = 0.475, 0.650, 0.825, y = 0.35, 0.40, 0.45) compounds, which have the same compositions as the La_0.7Sr_0.3CoO_3−δ(LSC) and Sm_0.5Sr_0.5CoO_3−δ(SSC) mixture (corresponding mole ratio is 3:1, 1:1 and 1:3, respectively), are synthesized through a conventional solid-state reaction and characterized by X-ray diffraction, thermal expansion coefficient, X-ray photoelectron spectrometer and electrical conductivity measurement, as well as the electrochemical impedance spectra and single cell performance measurement. Interestingly, the experimental results reveal that with the linear increase of y in LSSC, the conductivity of the corresponding samples does not alter linearly but reaches a peak when y = 0.35, namely, the maximum electrical conductivity enhancing from 2148 S cm⁻¹(LSC, y = 0.30) and 1802 S cm⁻¹(SSC, y = 0.50) to 2750 S cm⁻¹ (y = 0.35). In addition, this turning point coincidently corresponds to the structure transition from hexagonal (y = 0.35) to orthorhombic (y = 0.40). Furthermore, comparing with LSC and SSC, the cathode polarization resistance (R_P) decreases by about 50% and 38%, respectively, after employing the LSSC (y = 0.40) compound as cathode at 800 °C and 0.21 atm p(O₂), which also leads to an increment of 49% and 31% respectively in peak power density. These results imply promising applications of such effective cathodes for intermediate temperature solid oxide fuel cells.