Alumina and transition metals were added to Gd-doped ceria and the electrical properties of doped ceria were studied. For 10 mol% Gd-doped ceria (GDC), 1 at.% transition metals (Fe, Co, Ni, Cu, or Ga) were added as a sintering aid and 1, 2, 5, 10, and 20 at.% alumina was added as a possible strengthening media. The electrical conductivity was measured as a function of temperature (250-700 degrees C) in air. The open circuit voltage (OCV) and the impedance spectra of the cell in dual atmosphere (air on one side, hydrogen on another side) were measured as a function of time. Samples added with both 1 at.% Cu and 2 at.% alumina showed good sinterability without much loss of electrical conductivity. The time-dependence of the OCV value and the impedance spectra showed that either the alumina-added or the Cu and alumina co-added sample exhibited the slower degradation of OCV and the less electrode polarization than GDC. The results indicate that Cu and alumina addition improved the stability of the cell. (C) 2009 Elsevier B.V. All rights reserved.