Sm 0.5Sr 0.5Co 0.4Ni 0.6O 3−δ–Sm 0.2Ce 0.8O 1.9 as a potential cathode for intermediate-temperature solid oxide fuel cells

Abstract

The mixed ionic and electronic conductors (MIECs) of Sm 0.5Sr 0.5Co 0.4Ni 0.6O 3−δ (SSCN)–Sm 0.2Ce 0.8O 1.9 (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 ( i 0) for oxygen reduction reaction (ORR) was determined from the EIS data. The i 0 value of 70SSCN–30SDC/SDC was 187.6 mA cm −2 which is larger than the i 0 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.