Investigation of Sm0.5Sr0.5CoO3−δ/Co3O4 composite cathode for intermediate-temperature solid oxide fuel cells

The electrochemical properties of an Sm0.5Sr0.5CoO3−δ/Co3O4 (SSC/Co3O4) composite cathode were investigated as a function of the cathode-firing temperature, SSC/Co3O4 composition, oxygen partial pressure and CO2 treatment. The results showed that the composite cathodes had an optimal microstructure at a firing temperature of about 1100 °C, while the optimum Co3O4 content in the composite cathode was about 40 wt.%. A single cell with this optimized C40-1100 cathode exhibited a very low polarization resistance of 0.058 Ω cm2, and yielded a maximum power density of 1092 mW cm−2 with humidified hydrogen fuel and air oxidant at 600 °C. The maximum power density reached 1452 mW cm−2 when pure oxygen was used as the oxidant for a cell with a C30-1100 cathode operating at 600 °C due to the enhanced open-circuit voltage and accelerated oxygen surface-exchange rate. X-ray diffraction and thermogravimetric analyses, as well as the electrochemical properties of a CO2-treated cathode, also implied promising applications of such highly efficient SSC/Co3O4 composite cathodes in single-chamber fuel cells with direct hydrocarbon fuels operating at temperatures below 500 °C.