Comparison of solid oxide fuel cell (SOFC) electrolyte materials for operation at 500 °C

Abstract

Solid oxide fuel cells (SOFCs) operating at low temperature (~500 °C) enable new fields of application, such as auxiliary power units (APUs) or power generation for mobile applications. However, the state-of-the-art electrolyte material currently used in intermediate-temperature SOFCs (yttria-stabilized zirconia (YSZ)) does not provide sufficiently high ionic conductivity for low temperature applications. When looking for alternatives, the conductivity values for each material found in widely cited literature can be confusing, as the reported values are sometimes in conflict with each other. Therefore, we present a systematic comparison of the conductivity of the three most popular, commercially available electrolyte materials, i.e., YSZ, scandia-stabilized zirconia (ScSZ), and gadolinium-doped ceria (GDC). By using electrochemical impedance spectroscopy (EIS) to characterize the ionic conductivities, we find that at 500 °C, GDC has a higher ionic conductivity (5.8 × 10−3 S cm−1) than ScSZ (2.5 × 10−3 S cm−1) and YSZ (1.1 × 10−3 S cm−1). The properties of the starting powders, powder processing and the microstructure after sintering were considered. This conductivity comparison can be used as a guide when deciding on electrolyte materials for different SOFC applications, especially when the fabrication of different thickness of the electrolyte layer has to be considered and rectify misleading information in the literature.