Sm0.5Sr0.5Co0.4Ni0.6O3−δ–Sm0.2Ce0.8O1.9 as a potential cathode for intermediate-temperature solid oxide fuel cells

The mixed ionic and electronic conductors (MIECs) of Sm0.5Sr0.5Co0.4Ni0.6O3−δ (SSCN)–Sm0.2Ce0.8O1.9 (SDC) were investigated for potential application as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on an SDC electrolyte. Electrochemical impedance spectroscopy (EIS) technique was performed over the temperature range of 600–850 °C to determine the cathode polarization resistance which is represented by area specific resistance (ASR). To investigate the ORR mechanism, the impedance diagram for 70SSCN–30SDC was measured under applied cathodic voltage from E = 0.0 to E = −0.3 V. It indicated that the charge transfer dominated the rate-determining step at the temperature of 600 °C; whereas the diffusion or dissociative adsorption of oxygen dominated the rate-determining step at the temperature of 800 °C. In this study, the exchange current density (i0) for oxygen reduction reaction (ORR) was determined from the EIS data. The i0 value of 70SSCN–30SDC/SDC was 187.6 mA cm−2 which is larger than the i0 value of 160 mA cm−2 for traditional cathode/electrolyte, i.e. LSM/YSZ at 800 °C, indicating that the 70SSCN–30SDC composite cathode with a high catalytically active surface area could provide the oxygen reduction reaction areas not only at the triple-phase boundaries but also in the whole composite cathode.