Electrochemical characterization of gradient Sm_(0.5)Sr_(0.5)CoO_(3-δ) cathodes on Ce_(0.8)Sm_(0.2)O_(1.9) electrolytes for solid oxide fuel cells

摘要

This study investigates Sm_(0.5)Sr_(0.5)CoO_(3-δ) (SSC)-Ce_(0.8)Sm_(0.2)O_(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.