A composite electrolyte containing a Li/Na carbonate eutectic and a doped ceria phase is employed in a direct carbon fuel cell (DCFC). A four-layer pellet cell, viz, cathode current collector (silver powder), cathode (lithiated NiO/electrolyte), electrolyte and anode current collector layers (silver powder), is fabricated by a co-pressing and sintering technique. Activated carbon powder is mixed with the composite electrolyte and is retained in the anode cavity above the anode current collector. The performance of the single cell with variation of cathode gas and temperature is examined. With a suitable CO2/O-2 ratio of the cathode gas, an operating temperature of 700 degrees C. a power output of 100 mW cm(-2) at a current density of 200 mA cm(-2) is obtained. A mechanism of O2- and CO32- binary ionic conduction and the anode electrochemical process is discussed. (C) 2010 Elsevier B.V. All rights reserved.