Investigation of the sudden drop of electrolyte conductivity at low temperature in ceramic fuel cell with Ni_0·8Co_0·15Al_0·05LiO₂ electrode

The sudden drop of ionic conductivity of GDC (Gd_0.1Ce_0·9O_1.95) electrolyte in ceramic fuel cells with NCAL (Ni_0·8Co_0·15Al_0·05LiO₂) as electrode at low temperature was studied. It is found that the peak power density (PPD) of the cell with GDC electrolyte decreases linearly with the decreasing of the operation temperature above 400 °C. However, when the operation temperature drops to 400 °C, the cell PPD decreases significantly. EIS results show that the ionic conductivity of the electrolyte decreases linearly with the decrease of cell operating temperature. When the temperature decreases to approximately 400 °C, the ionic conductivity of the electrolyte decreases from 0.251 S cm⁻¹ at 425 °C to 0.026 S cm⁻¹ at 400 °C. The rapid decrease of the electrolyte ionic conductivity is considered to be the direct cause of the sudden decrease of the PPD. According to the results of XPS, FTIR and TG-DSC, LiOH/Li₂CO₃ formed in the NCAL anode diffuses into the electrolyte and melts at 419 °C or above, which is the reason for the high ionic conductivity of the electrolyte. The reason for the sudden drop of ionic conductivity is that LiOH/Li₂CO₃ and other compounds solidify in molten salts below 419 °C.