A comparative study of Sm_0.5Sr_0.5MO _3-δ (M = Co and Mn) as oxygen reduction electrodes for solid oxide fuel cells

Sm_0.5Sr_0.5MO_3-δ (M = Co and Mn) materials are synthesized, and their properties and performance as cathodes for solid oxide fuel cells (SOFCs) on Sm_0.2Ce_0.8O _1.9 (SDC) and Y_0.16Zr_0.92O_2.08 (YSZ) electrolytes are comparatively studied. The phase structure, thermal expansion behavior, oxygen mobility, oxygen vacancy concentration and electrical conductivity of the oxides are systematically investigated. Sm _0.5Sr_0.5CoO_3-δ (SSC) has a much larger oxygen vacancy concentration, electrical conductivity and TEC than Sm _0.5Sr_0.5MnO_3-δ (SSM). A powder reaction demonstrates that SSM is more chemically compatible with the YSZ electrolyte than SSC, while both are compatible with the SDC electrolyte. EIS results indicate that the performances of SSC and SSM electrodes depend on the electrolyte that they are deposited on. SSC is suitable for the SDC electrolyte, while SSM is preferred for the YSZ electrolyte. A peak power density as high as 690 mW cm^-2 at 600°C is observed for a thin-film SDC electrolyte with SSC cathode, while a similar cell with YSZ electrolyte performs poorly. However, SSM performs well on YSZ electrolyte at an operation temperature of higher than 700°C, and a fuel cell with SSM cathode and a thin-film YSZ electrolyte delivers a peak power density of ∼590 mW cm^-2 at 800°C. The poor performances of SSM cathode on both YSZ and SDC electrolytes are obtained at a temperature of lower than 650°C.