Solid-oxide fuel cells based on doped ceria electrolytes and operating at 500 degrees C are shown to be feasible. The operating regime of doped ceria electrolytes is discussed. It is shown that the ionic conductivity of ceria-based fuel cells is sufficiently high for operation with hydrogen fuel at low temperatures. The major challenges of fabricating a thin electrolyte by a conventional method and the development of high-performance cathodes capable of operating at 500-600 degrees C are addressed. Cells based on thin-film ceria electrolytes also exhibited good open-circuit voltages between 0.97 and 1 V. Cathode materials with high performance have been developed from pyrochlores, perovskites, and cermets of silver and doped bismuth oxide. The advantages and disadvantages of different cathode materials are discussed. The maximum power density obtained at 500 degrees C was 140 mW/cm(2).