Exchange current density
Oxygen reduction reaction a b s t r a c t
The mixed ionic and electronic conductors (MIECs) of Sm 0.5 Sr 0.5 Co 0.4 Ni 0.6 O 3Àd (SSCN)e Sm 0.2 Ce 0.8 O 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 600e850 C to determine the cathode polarization resistance which is represented by area specific resistance (ASR). To investigate the ORR mechanism, the impedance diagram for 70SSCNe30SDC was measured under applied cathodic voltage from E ¼ 0.0 to E ¼ À0.3 V. It indicated that the charge transfer dominated the ratedetermining 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 70SSCNe30SDC/SDC was 187.6 mA cm À2 which is larger than the i 0 value of 160 mA cm À2 for traditional cathode/electrolyte, i.e.
LSM/YSZ at 800 C, indicating that the 70SSCNe30SDC 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.