Electrochemical characterization of gradient Sm0.5Sr0.5CoO3−δ cathodes on Ce0.8Sm0.2O1.9 electrolytes for solid oxide fuel cells

This study investigates Sm0.5Sr0.5CoO3−δ (SSC)–Ce0.8Sm0.2O1.9 (SDC) composite cathodes with a gradual change in composition from electrolyte to the cathode in an attempt to discover a potential approach applicable to solid oxide fuel cells (SOFCs). The gradual change in composition from electrolyte to cathode shows the decline in charge transfer resistance (R2) and gas phase diffusion resistance (R3). Because the value of R3 is always larger than R2 and R3 significantly dominates the total cathode polarization resistance (RP) at temperatures within the range of 750–850 °C, i.e., in this temperature range, the rate-determining step is dominated by the diffusion or dissociative adsorption of oxygen. The functionally gradient cathode with a graded interface between cathode and electrolyte reveals both a higher exchange current density (i0) and a lower activation energy for oxygen reduction reaction (ORR), which suggests that the ORR kinetics can be improved by using the configuration of a functionally gradient cathode.