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An anode-supported tubular solid oxide fuel cell ͑SOFC͒ with a thin electrolyte film for reduced temperature operation was fabricated by a wet cofire process. Instead of the traditional extrusion method, the anode substrate was formed by a tape-cast method. This allows design the substrate with some advantageous configurations that can improve the performance of SOFCs. Sc 2 O 3 and Y 2 O 3 -stabilized zirconia electrolyte films were fabricated on the substrate by a modified slurry dip-coating method and then cofired. In order to use (La 0.6 Sr 0.4 )CoO 3 cathode, a thin (CeO 2 ) 0.9 (GdO 1.5 ) 0.1 interlayer was also fabricated by the slurry dip-coating method. The fabricated tubular cell generated electricity successfully between 600 and 850°C. Power density of ca. 170 and 220 mW/cm 2 was achieved at 600 and 700°C, respectively, however, the ohmic resistance was larger than expected. Because (CeO 2 ) 0.9 (GdO 1.5 ) 0.1 interlayer was used, ohmic resistance could be high due to the formation of a layer of (Zr,Ce)O 2 solid solution at the zirconia/ceria interface. The gaseous diffusion resistance governed the performance between 700 and 850°C. Better performances of the anode-supported tubular SOFCs can be achieved by further optimizations for the zirconia/ceria interface, control of both porosity and thickness of the anode substrate, as well as improvement of the (La 0.6 Sr 0.4 )CoO 3 cathode.In order to make solid oxide fuel cells ͑SOFCs͒ suitable for practical use such as in compact cogeneration systems and transportation applications, reduced temperature SOFCs have been extensively studied. Operation at around 750°C or less retards materials degradation and hence prolongs stack lifetime, reducing cost by utilization of metallic materials, simplifying the system. Reducedtemperature SOFCs can be realized in two parallel ways: employing materials with high functional properties and/or fabricating SOFCs with novel thin-film concepts. Among basic SOFC designs, anodesupported SOFCs with thin-film electrolyte are better suited for operation at reduced temperature. Many groups have investigated the planar anode substrate SOFC due to its high specific power output and volumetric power density. However, works on tubular SOFCs have shown that the tubular designs have an advantage of being capable of coping with thermal stresses. 1 Siemens Westinghouse multiple tubular cell tests have been successfully conducted for almost 70,000 h. 2 Small-scale tubular SOFCs, as described by Kendall and Prica, 3 and Mizusaki et al., 4 could endure rapid heating/cooling and quickly respond to load variation within 1 min at an operating temperature of 800°C. Therefore, it can be expected that a tubular design can be applied to anode substrate SOFCs for cogeneration and transportation applications. 5-8 In such cases, a benefit on sealing the stack is expected because the sealing length can be reduced. 9 Previously, Kato et al. 7,8 estimated the performance at medium temperature of lightweight Ni porous substrate tubular SOFC with electroly...

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