Reduced Temperature Sintering of GDC Electrolyte for IT-SOFCs

Abstract

Lanthanide material- (gadolinium or samarium) doped ceria (GDC or SDC) is considered one of the most advanced electrolyte materials for intermediate temperature (below 700 oC) SOFC (IT-SOFC) because of its high ionic conductivity at these temperatures. However, a high sintering temperature (above 1400 oC) is a disadvantage of the doped ceria. Metal oxides such as Fe oxide, Co oxide, Mn oxide, Li oxide, Ga oxide and Cu oxide were used as sintering aids to obtain the fully sintered electrolytes at a lower sintering temperature. In this study, the effect of a copper additive as a sintering aid to lower the sintering temperature for the construction of solid oxide fuel cells (SOFCs) was investigated. Gd-doped ceria (GDC) electrolyte with 0.25-10 mol% CuO sintering aid was prepared by reacting GDC power and copper nitrate solution followed by heating at 600 oC. The sintering of CuO-coated GDC powder was optimized by investigating linear shrinkage, microstructure, grain size, ionic conductivity, and activation energy of CuO-GDC electrolytes at temperatures ranging from 1100 to 1400 ¢ªC. The addition of Cu additive in GDC powder led to a decrease in the sintering temperature from 1400 to 1100 oC, which can result in the reduction of SOFC fabrication costs. For the GDC powder with 0.25 mol% Cu additive, linear shrinkage rates over the range of 1100 to 1400 oC were the highest (ca. 16.79-17.34 %). Regarding ionic conductivity, the 0.25 and 0.5 mol% Cu-added samples showed a higher value than the untreated GDC powder in the range of 550 to 750 oC, while the value for the 0.75 mol% Cu-added sample was lower. This result was evidenced by the occurrence of mechanical defects in body of the GDC samples with higher Cu contents (≥ 0.75 mol%). In addition, the activation energy of the CuO-GDC prepared in this work remained unchanged significantly. These results obtained in this study suggest that further investigations of proper sintering aids with the combination of different metal oxides and the optimization of GDC-electrolyte synthesis conditions may enable more stable and efficient SOFCs based on GDC. Figure 1