SM3+ -doped ceria (SDC) electrolytes growing various BaCe1-xSmxO3-x (BCS) layers over the electrolyte surface were investigated in order to develop high-performance solid oxide fuel cells in the temperature range of 600-900 degrees C. The BCS layers were grown by a solid-state reaction of the electrolyte substrate and a BaO film spin-coated previously over the substrate surface under different preparation conditions. The thickness of the layer was controlled with a precision of micrometer by the number of coats. The composition of the layer was optimized by the sintering temperature. As a result, a dense and microcrack-free BCS layer was formed over the electrolyte surface, and the junction between the electrolyte and layer was almost homogeneous. A hydrogen-air fuel cell with the improved electrolyte showed open-circuit voltages (OCVs) ranging from 857 (900 degrees C) to 1002 mV (600 degrees C). Furthermore, the peak power densities of this fuel cell were higher than those of a fuel cell with an uncoated SDC electrolyte. (c) 2004 Elsevier B.V. All rights reserved.