Performance of composite cathode Sr_0.95Ti_0.05Co_0.95O_3-δ-Sm_0.2Ce_0.8O_1.9 used in intermediate temperature SOFCs

A cathode powder of Sr_0.95Ti_0.05Co_0.95O_3-δ (STC) and an electrolyte powder of 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 the STC and SDC powders in a mass ratio of 7:3. The chemical compatibility, electrical conductivity and thermal expansion coefficient of the composite cathode were characterized by X-ray diffraction (XRD), direct current four-terminal method and thermal dilatometer, respectively. The XRD results show that a pure cubic STC perovskite phase can be obtained at 900 ℃ and no second phase is formed in the composite cathode at the operating temperature. The polarization resistance of the electrode is only 0.05 Ω∙cm² at 650 ℃. The anode-supported solid oxide fuel cells of NiO-SDC│SDC│STC-SDC were fabricated. The electrochemical performances were examined at 450-650 ℃ with humidified hydrogen (about 3% H₂O) as a fuel and air as an oxidant. It is demonstrated that the anode-supported half cells can be sintered at 1 350 ℃ with a dense electrolyte layer and porous electrodes, and the single cell with an open circuit voltage of 0.82 V and the maximum power density of 721 mW/cm² at 650 ℃ can be obtained. These results indicate that STC-SDC is a promising composite cathode candidate for IT-SOFC with SDC electrolyte.