Transition metal oxides (FeO(1.5) and COO) were added to Gd-doped ceria (Gd(0.1)Ce(0.9)O(2-delta), 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 presintered anode substrate by screen-printing method and then co-sintered to form the electrolyte/anode bilayer. The cathode, which is made of La(0.6)Sr(0.4)Fe(0.8)Co(0.2)O(3) 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 degrees C. At 500 degrees C, the chargetransfer 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. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.