Validating the application of semiconductor-ionic conductor in solid oxide fuel cells as electrolyte membrane

Electronic leakage is an unavoidable problem in solid oxide fuel cells (SOFCs) when the electrolyte has electronic conductivity. However, SOFCs using semiconductor-ionic conductor membrane (SIM) have been proved to deliver high open circuit voltage (OCV) and power output. This study seeks to understand the reason for the SIM fuel cell (SIMFC) to deliver high performance from a traditional view. The composition of semiconductor La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) and ionic conductor Sm-doped cerium oxide (SDC) is used as the SIM layer of SOFC. The electronic conductivity of the membrane is evaluated using both Ag and LiNi0.8Co0.15Al0.05O2-delta (NCAL) symmetrical electrodes. The dependency of electronic conductivity on the content of LSCF satisfies the percolation theory. Besides, NCAL electrode is found to remarkably influence the conductivity of the membrane after operating in fuel cell environment, which is proved to be due to the formation of melting alkali metal compounds in the SIM layer during cell operation. In addition, the relation of cell performance and the electrical resistance of the membrane is analyzed by utilizing a simplified model. This study provides important support for using SIM electrolyte to deliver high cell performance.