Electrochemical performance of SmBaCo ₂O _5+δ- Sm _0.2Ce _0.8O _1.9 as composite-cathode for intermediate temperature solid oxide fuel cells

The cathode powder of double perovskites-type SmBaCo ₂O _5+δ(SBCO) and electrolyte powder of fluorite-structure Sm _0.2Ce _0.8O _1.9(SDC) were synthesized by a citric acid-nitrates self-propagating combustion method. The composite-cathode was obtained by mixing and grinding the SBCO and SDC powders at a mass ratio of 3:2. The chemical compatibility, electrical conductivity and thermal expansion coefficient (TEC) of the composite-cathode (SBCO-SDC) were characterized by X-ray diffraction, direct current four-terminal method and thermal dilatometry, respectively. An anode-supporting fuel cell of Ni-SDC|SDC|SBCO-SDC was fabricated and the performance of the cell was analyzed. The cross-section microstructure and polarization of the cell were investigated using a scanning electron microscope (SEM) and AC impedance spectroscopy. The results indicate that there are no interactions between SBCO and SDC at 1000°C. The electrical conductivity of the SBCO-SDC composite-cathode reached to 369-234 S/cm at 450-800°C. The addition of SDC decreased the TEC of the composite-cathode. The single cell has an ideal microstructure and a good interface among anode, electrolyte and cathode. The polarization resistance of the electrodes was 0.031 Ω·cm ² at 650°C. The cell with an open-circuit potential of 0.77 V and a maximum output power density of 640 mW/cm ² was obtained when the humidified (about 3% H ₂O) hydrogen as a fuel and air as oxidant were used at 650°C. It was demonstrated that the SBCO-SDC composite-cathode could be used as a potential candidate cathode for intermediate temperature solid oxide fuel cell.