Elucidating the Sintering Mechanisms and Synergistic Doping Effects in CuO/Fe₂O₃ Codoped Gd-Doped Ceria Electrolytes for Advanced Low-Temperature Solid Oxide Fuel Cells (LT-SOFCs)

This paper presents a study of the synergistic effects on sintering activity and the electrical performance of a CuO and Fe₂O₃ codoped gadolinium-doped ceria (GDC) electrolyte. The isothermal sintering behavior is investigated, and the viscous flow sintering mechanism is validated. The findings indicate that when the molar ratio of CuO to FeO_1.5 is 3:1, the sintering temperature can be reduced to 980 °C, which is approximately 450 °C lower than that of GDC (>1450 °C). The lowest sintering activation energy is found to be 389 kJ/mol when the molar ratio of CuO to FeO_1.5 is 3:1. Additionally, the concept named "macrodensification temperature" is proposed in this research to describe the connection of the densification process at the microstructure and macrostructure scale. The macrodensification temperature is further verified by quasi-<i>in situ</i> observation and isothermal testing, meanwhile, Cu-Fe-Gd-O and Cu-Ce-O phases, which are beneficial for low-temperature sintering are first found in this work. Moreover, when the molar ratio of CuO to FeO_1.5 is 3:1, the ionic conductivity reaches 0.041 S/cm@700 °C, which is 10% higher than that of GDC. The highest performance of the anode-supported cell is found when the electrolyte doping ratio of CuO to FeO_1.5 equals 3:1. The open-circuit voltage is observed to be 0.82 V@700 °C, accompanied by a high-power density of 1.2 W/cm²@700 °C. The cell performance with GDC as the electrolyte is found to be 0.8 W/cm²@700 °C. In conclusion, the combined effects of CuO and Fe₂O₃ doping in GDC may offer a promising avenue for enhancing electrolyte performance and extending its applications to low-temperature solid oxide fuel cells (LT-SOFCs).