A method and apparatus for operating an intermediate-temperature solid-oxide fuel cell stack with a mixed ionic/electronic conducting electrolyte in order to increase its efficiency. The required power output of the solid-oxide fuel cell stack is determined and one or more operating conditions of the solid fuel cell...

The fabrication of ceria based electrolytes to densities greater than 97 % of the theoretical achievable density at temperature below 1200°C, preferably approximately 1000°C, is disclosed. The electrolyte has a concentration of divalent cations minus an adjusted concentration of trivalent cations of between 0.01 mol...