Preparation, Characterization and Application of Praseodymium-doped Ceria-based Materials in Fuel Cells
Date Issued
2011
Date
2011
Author(s)
Chen, Mei-Ju
Abstract
Abstract
The thesis includes four parts. In the first part, optimal weight ratio of 50% of La0.6Sr0.4Co0.2Fe0.8O3 (6428LSCoF)
to Ce0.7Pr0.3O2-δ(30CPO) or Ce0.7Pr0.28Mg0.02O2-δ(28,2-CPMgO) composite cathodes can effectively reduce polarization resistance and result in high cell performance of the single cells assembled with 60NiO-20CGO anode, 20CGO electrolyte and the composite cathodes. The optimal cell performance of 0.74 V, 1110 mA/cm2 and 297 mW/cm2 was obtained at 700˚C on the cell with the 50% 28,2-CPMgO-6428LSCoF composite cathode. In the second part, it was found that the degree of suppression of electronic conductivity of doped ceria material increases with the amount of Pr dopant. Of Pr doped ceria materials, 25CPO has nearly the same conductivities in air and in reducing atmosphere, but the conductivity in reducing atmosphere declines with time. It was also found that co-doping small amount of Mg in CPO not only enhances the oxide ion conductivity in air, but also retains the conductivity in reducing atmosphere with time. The nearly equal conductivities under air and reducing atmosphere
could be obtained by the 2% Mg co-doped 25CPO (25,2-CPMgO) material. In the third part, the Pr doped ceria was introduced in between the anode and electrolyte as a buffer layer to impede the reduction of electrolyte during cell operation. The single cells with the buffer layers had better cell performances than that without the buffer layer. The optimal cell OCV, current density and power density of 0.8 V, 1090 mA/cm2 and 285 mW/cm2 were obtained on the cell with 25,2-CPMgO buffer layer and 50% 28,2-CPMgO-6428LSCoF composite cathode at 700˚C. Moreover, the OCV could be obtained for 140 h with only 3.75% degradation.
In the last part, Pr-doped CeO2 was used as the catalyst support of preferential oxidation (PROX) of CO.
The active sites and deactivation behaviors of CuO/CeO2 catalysts for the preferential oxidation (PROX) of CO
in H2-rich environment were examined by in-situ X-ray absorption spectroscopy. The CO conversion increased with
increasing reaction temperature, while the CO2 selectivity decreased, especially at temperatures higher than 120˚C.
100% CO conversions can be achieved over CuO/dx-CeO2 at 140-160˚C. In-situ Cu K-edge XAS revealed that CuO was reduced
to metallic Cu when the reaction temperature was higher than 120˚C, accompanying with the decline in CO2 selectivity. Thus, the active site for H2 oxidation to water would be metallic Cu, and the Cu2+ might be the active species for CO oxidation of to CO2. For Pr-doped ceria supported CuO catalysts, although the Pr-doped ceria materials have higher oxide ion conductivity than CeO2, it has a negative effect on the catalytic activity of CO preferential oxidation under H2-rich atmosphere. The best catalytic activity was obtained over the dd4-20CuCeO2-δ catalyst in CO preferential oxidation under H2-rich atmosphere. The T95 was 130˚C with S95 of 98%.
Keyword: SOFC, Pr-doped ceria, composite cathode, CO PROX, in-situ XAS and CuO/CeO2 catalyst.
Subjects
SOFC
Pr-doped ceria
composite cathode
CO PROX
in-situ XAS and CuO/CeO2 catalyst.
Type
thesis
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