Measurement of Polarization Resistances of LSCF/YSZ/LSCF Symmetrical Cell Using Alternating Current (AC) and Direct Current (DC) Techniques

Abstract

Solid oxide fuel cells (SOFCs) are electrochemical devices, which can efficiently convert the chemical energy stored in fuels such as CH4 and H2 to electrical energy. SOFCs are of great significance for the next generation of clean energy storage and conversion. Yttria stabilized zirconia (YSZ) is a common solid oxide electrolyte used in SOFCs since it has outstanding oxygen ion conductivity, especially when operated at a high temperature (>800°C). Lanthanum strontium cobalt iron oxide (LSCF) is a mixed ionic-electronic conductor (MIEC), which offers both good electronic conductivity and good oxygen ion conductivity. Electrochemical impedance spectroscopy (EIS) is typically used to study the electrochemical performance of SOFCs. However, when using the common two-electrode EIS, the electrode processes at the cathode and anode cannot be studied separately. To study the electrode processes at the cathode and anode, a three-electrode EIS (two-electrode EIS with one pseudo-reference electrode) was performed on an LSCF/YSZ/LSCF bar-shaped symmetrical cell with platinum strip electrodes as probes. The point-by-point sum of the EIS spectra across the cathode and probe and across the anode and probe was found to match the impedance across the cathode and the anode. Also, polarity was switched, and it was found that the two electrodes do not necessarily have identical polarization resistance. Direct current (DC) measurements were also used to measure the polarization resistance of two electrodes separately with good agreement with the EIS results.