Nanostructuring of SmBa0.5Sr0.5Co2O5+δ cathodes for reduced-temperature solid oxide fuel cells

Abstract

Here we report the fabrication of composite cathodes for reduced-temperature solid oxide fuel cells by impregnating aqueous solutions corresponding to SmBa0.5Sr0.5Co2O5 (SBSCO) into the porous La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) backbones. Examination of X-Ray diffraction patterns indicates that phase-pure SBSCO layered perovskite oxides can be only achieved at calcination temperatures ≥900 °C. Based upon impedance measurement of symmetric cells, the SBSCO–LSGM composites calcinated at 850 °C show a trade-off between the SBSCO phase purity and catalyst size, and thereby exhibit minimal cathode polarization resistances with respect to the infiltrate calcination temperature, e.g., 0.035 Ω cm2 at 550 °C and 0.12 Ω cm2 at 500 °C at the loadings of 21 wt%. Analysis of impedance spectra under varied oxygen partial pressures suggests that oxygen reduction reactions on the nano-scale SBSCO–LSGM composite are largely dominated by ionization of adsorbed oxygen atoms on the SBSCO surfaces. Thin LSGM electrolyte fuel cells with impregnated Ni anodes and SBSCO cathodes show high power densities of 1.5 W cm−2 at 600 °C and 0.70 W cm−2 at 500 °C.