Electrochemical characterization of gradient Sm 0.5Sr 0.5CoO 3− δ cathodes on Ce 0.8Sm 0.2O 1.9 electrolytes for solid oxide fuel cells

Abstract

This study investigates Sm 0.5Sr 0.5CoO 3− δ (SSC)–Ce 0.8Sm 0.2O 1.9 (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 ( R 2) and gas phase diffusion resistance ( R 3). Because the value of R 3 is always larger than R 2 and R 3 significantly dominates the total cathode polarization resistance ( R P) 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 ( i 0) 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.