We have examined the use of Cu-Ni alloys as anodes for the direct oxidation of methane in solid-oxide fuel cells (SOFC) at 1073 K. Ceramic-metal (cermet) composites having alloy compositions of 0, 10, 20, 50 and 100% Ni were exposed to dry methane at 1073 K for 1.5 h to demonstrate that carbon formation is greatly suppressed on the Cu-Ni alloys compared to that of pure Ni. Increased reduction temperatures also reduced the carbon formation on the alloys. The performance of a fuel cell made with a Cu(80%)-Ni(20%) cermet was tested in dry methane for 500 h and showed a significant increase in power density with time. Impedance spectra of similar fuel cells suggest that small carbon deposits are formed with time and that the increase in performance is due to enhanced electronic conductivity in the anode. Finally, the implications of the use of metal alloys for SOFC applications are discussed. © 2002 The Electrochemical Society. All rights reserved.

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.

A new method for fabrication of metal-cermet anodes in solid-oxide fuel cells (SOFCs) has been developed. Highly porous, yttriastabilized zirconia (YSZ) films were prepared using a mixture of zircon fibers (YSZp, Si-stabilized, and <0.3% Si) and normal YSZ powders (YSZd). The films remained highly porous following calcination up to 1550ЊC, after which either Cu or Ni could be incorporated by impregnation with the nitrate salts. For Cu cermets, the performance increased with metal loading to at least 40% Cu. At 800ЊC using H 2 as the fuel and a 230 m, YSZ electrolyte, the current-voltage (I-V) curves for either a Cu-or Ni-cermet anode formed using this new method were found to be identical to the I-V curve for a Ni cermet formed using traditional methods. Scanning electron microscopy showed that the anode films remained porous even with addition of Cu, so that additional modification was possible. Tests of this concept through the addition of ceria by impregnation with the Ce(NO 3 ) 3 led to an additional increase in the cell performance.

The apparent change in activation energy describing the parabolic rate constant for the passive oxidation of SiC is examined. New data are combined with reevaluated previous results to determine the influences of crystallinity, impurity contamination, and multiple flux mechanisms. The results suggest that the high-temperature transition from interstitialdominant to network-dominant oxygen transport is a property of amorphous SiO 2 scales and does not exist for cristobalite. Highly crystalline scales do not show this transition. Agreement among various studies also suggests that, for high-purity SiO 2 scales, there is no difference between the rates of interstitial oxygen transport in amorphous SiO 2 and in ␤-cristobalite.

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