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Solid‐oxide fuel cells based on doped ceria electrolytes and operating at 500°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°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°C was 140 normalmW/cm2 . © 1999 The Electrochemical Society. All rights reserved.

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A family of sealant materials has been developed for use in the solid oxide fuel cell (SOFC) and in other applications in the temperature range of 800-1000 ± C. These materials are based on glasses and glass-ceramics in the SrO-La 2 O 3 -Al 2 O 3 -B 2 O 3 -SiO 2 system. The coefficients of thermal expansion (CTE) for these materials are in the range of 8-13 3 10 26 ͞ ± C, a good match with those of the SOFC components. These sealant materials bond well with the ceramics of the SOFC and, more importantly, form bonds that can be thermally cycled without failure. At the fuel cell operating temperature, the sealants have viscosities in the range of 10 4 -10 6 Pa-s, which allow them to tolerate a CTE mismatch of about 20% among the bonded substrates. The gas tightness of a sample seal was demonstrated in a simple zirconia-based oxygen concentration cell.

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