Effects of transition metal oxides on the densification of thin-film GDC electrolyte and on the performance of intermediate-temperature SOFC

Transition metal oxides (FeO_1.5 and CoO) were added to Gd-doped ceria (Gd_0.1Ce_0.9O_2−δ, GDC) powder for preparing the thin-film electrolyte used in the anode-supported intermediate-temperature solid oxide fuel cell (SOFC). NiO–GDC anode substrate in a weight ratio of 65:35 was fabricated by the tape-casting method. Thin-film electrolyte was fabricated on the pre-sintered anode substrate by screen-printing method and then co-sintered to form the electrolyte/anode bilayer. The cathode, which is made of La_0.6Sr_0.4Fe_0.8Co_0.2O₃ and GDC (LSCF–GDC) in a weight ratio of 50:50, was screen-printed on the thus-prepared electrolyte surface and sintered to form a complete single cell. The effects of transition metal oxides on the densification of thin-film GDC electrolyte and on the performance of intermediate-temperature SOFC were studied. Results showed that the densification temperature of thin-film GDC electrolyte could not be further reduced by modifying it with transition metal oxides (FeO_1.5 and CoO) as sintering aids. Both the addition of Fe and Co to GDC enhanced the p-type conductivity of the electrolyte resulting in decreased ohmic resistance. However, they played different effects on the polarization behavior of the cells. Fe-loading decreased the single cell polarization resistance, thus greatly enhancing the charge-transfer process below 600 °C. At 500 °C, the charge-transfer resistance of the single cell with Fe-loaded GDC electrolyte is only 78% of that of the cell with pure GDC electrolyte. Conversely, Co-loading inhibited the charge-transfer process in the whole testing temperature range. Thus, it can be concluded that Fe-loaded GDC electrolyte is a promising electrolyte material for intermediate- and low-temperature SOFC.