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-delta (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 (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 degrees 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. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.