Enhancing Performance of Stabilized Bismuth Oxide-Based Cathodes via Infiltration Process for LT-SOFCs

Solid oxide fuel cells (SOFCs) are the most efficient technology to directly convert chemical energy to electrical energy via electrochemical reactions. However, commercialization of SOFCs has been impeded due to the high cost associated with high temperature operation over 800 ^oC with conventional stabilized zirconia electrolytes. Thus, lowering the temperature of solid oxide fuel cells (SOFCs) is essential for the commercialization via availability to use cheap stainless steel interconnector, rapid start-up time, and higher mechanical and chemical stability, leading to significant reduction of system cost. To achieve this goal, at reduced temperatures the cathodic polarization mainly caused by oxygen reduction reaction at triple phase boundaries (TPBs) should be effectively reduced.

  At lower temperatures below 700 ^oC, however, the cathode polarization exponentially increases due to its thermally activated nature, thus dramatically decreasing the performance. Previously, stabilized bismuth oxide-based composite cathodes (ex: LSM-ESB) have been reported as promising cathodes for LT-SOFC applications with their low area specific resistance (ASR) at LT region. This high performance would be explained that LSM has low activation energy for dissociative adsorption of oxygen in ORR on its surface and that ESB has exceptionally high ionic conductivity as well as excellent surface exchange properties. Therefore, one can expect that the microstructural optimization of these cathode could further increase the cathode performance as well as enhance the their durability.

In this study, we employed the infiltration process to tailor the surface morphologies of stabilized bismuth oxide-based composite cathodes for enhancing surface activity and their stability to achieve higher SOFC performance. Through infiltration, for example, LSM was infiltrated on the porous ESB scaffold with different manners. The microstructural evolution and electrochemical performance was characterized and their cross-effect will be discussed.