Samaria-doped ceria ͑SDC͒ electrolyte-supported solid oxide fuel cells ͑SOFCs͒ with Cu-SDC and Cu-CeO 2 -SDC anode composites were fabricated. Current-voltage and impedance-spectroscopy measurements were used to characterize their performance at temperatures between 600 and 700°C. The cells demonstrated the ability to directly utilize not only hydrogen (H 2 ) but also dry butane (C 4 H 10 ) fuel. At 700°C, the maximum power density of a cell with a Cu-CeO 2 -SDC anode composite was 246 and 170 mW/cm 2 for H 2 and C 4 H 10 fuels, respectively. Impedance spectra suggested that for butane fuel, the anode resistance significantly limits the overall cell performance. It was shown that the addition of pure ceria to the anode significantly increased the catalytic activity for oxidation reactions and decreased the anode resistances.
Solid oxide fuel cells ͑SOFC͒ with samaria-doped ceria ͑SDC͒ electrolytes were prepared with anodes made from either Cu, ceria, and SDC or Au, ceria, and SDC. These cells were tested in H 2 and n-butane fuels at 650°C. The similarity of performance (V-I) curves and impedance results for cells made with Au and Cu suggests that both metals are simply electronic conductors in the anode and that Cu does not play a catalytic role in direct-oxidation anodes made with Cu. The addition of ceria is shown to play an important role in improving anode performance, either through improved catalytic activity or mixed ion-electronic conductivity.
The microstructure, thermal expansion, mechanical property, and ionic conductivity of samaria-doped ceria (SDC) prepared by coprecipitation were investigated in this paper. The results revealed that the average particle size ranged from 10.970.4 to 13.570.5 nm, crystallite dimension varied from 8.670.3 to 10.770.4 nm, and the specific surface area distribution ranged from 62.671.8 to 76.772.2 m 2 /g for SDC powders prepared by coprecipitation. The dependence of lattice parameter, a, versus dopant concentration, x, of Sm 31 ion shows that these solid solutions obey Vegard's rule as a (x) 5 5.408910.10743x for Ce 1Àx Sm x O 2À1/2x . For SDC ceramics sintered at 15001C for 5 h, the bulk density was over 95% of the theoretical density; the maximum ionic conductivity, r 8001C 5 (22.371.14) Â 10 À3 S/cm with minimum activation energy, E a 5 0.8970.02 eV, was found in the Ce 0.80 Sm 0.20 O 1.90 ceramic. A dense Ce 0.8 Sm 0.2 O 1.9 ceramic with a grain size distribution of 0.5-4 lm can be obtained by controlling the soaking time at 15001C. When the soaking time was increased, the microhardness of Ce 0.8 Sm 0.2 O 1.9 ceramic increased, the toughness slightly decreased, which was related to grain growth with the soaking time.
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