Evaluation of Sc2O3-CeO2-ZrO2 electrolyte-based tubular fuel cells using activated charcoal and hydrogen fuels

Solid oxide fuel cells (SOFCs), as energy conversion devices, can use a variety of gaseous (hydrogen, methane, ammonia, carbon monoxide) and solid carbon fuels derived from coal and biomass. A critical component of SOFCs is the oxygen-ion conducting electrolyte material. Yttria-stabilised zirconia (YSZ) is a state-of-the-art electrolyte material often used in SOFCs; it has excellent stability in both reducing and oxidising atmospheres, good mechanical strength and compatibility with electrodes. However, YSZ electrolyte has low ionic conductivity, which leads to high voltage losses in electrolyte-supported SOFCs. Scandia-stabilised zirconia has much higher conductivity, but the phase assemblage is complex, with many phases having detrimental effect on the conductivity. Additions of a small quantity of dopants, such as ceria, appear to stabilise the cubic structure. In this work, we investigate the electrochemical performance of ceria-stabilised scandia-zirconia electrolyte supported tubular fuel cells using hydrogen fuel, and directly compare its electrochemical performance with YSZ-electrolyte supported cells using Ce0.9Gd0.1O2-Ag composite electrodes for both types of cells. The electrolyte conductivity and phase assemblage of ceria stabilised scandia-zirconia have been investigated. We also analysed the electrochemical performance of a tubular cell using activated charcoal as a fuel, and nitrogen and carbon dioxide as purge gases. Electrochemical impedance spectroscopy was used to investigate rate-limiting processes and other factors affecting the fuel oxidation reaction.