| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 1999: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1998: ¥2,800,000 (Direct Cost: ¥2,800,000)
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| Research Abstract |
The present research project was aimed to develop a novel composite electrochemical catalysis which can utilize anomalous reactivity of gas species at the heterogeneous interface among porous oxide electrode with ion-electron mixed conductivity, solid electrolyte, and metallic electrode. In a microscopic scale, the catalysis is regarded as the mixture of microscaled cells with asymmetric electrode configuration that utilize so-called mixed potential, which is closely related to the space charge effect at the heterogeneous interface. In the early stage of the project, the mixture of Nd_<2-X>Ce_XCuO_4, Nd-doped CeO_2, and Au powder were examined for the catalytic activity to the NO/NO_2 Red-Ox reaction. The composite catalysis showed enhanced activity for the reaction compared to those of single component ones. It is also shown that the composite of NiO, YSZ, Au powder also showed the enhanced catalytic reaction for NOx Red-Ox. In order to examine the mechantism of the enhanced catalytic
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reaction of composites, electrochemical cells with three electrodes were examined. We found that the rate determinant steps are the mixed process of the competent absorption of NO_2 and O_2 on porous oxide and electron transfer reaction, and the simple electron transfer reaction on the Au electrode. The exchange current density of both reactions are deduced from the model. It should be noted that the relaxation of space charge, built-up at the interface of heterogeneous contact interface by both mobile ion and the adsorbed gas species is the essential mechanism for the selective enhancement of the catalytic reaction. Therefore the electronic band structure and electronic transport properties of oxides are estimated as playing important role in the formation of the mixed potential, that is one of the key to understand the anomalous reactivity of composite electrochemical catalysis. Based on these view points, the survey of possible candidates for the oxide electrode is conducted in accordance with the detailed investigation of electronic and ionic transport properties and electronic band structure by means of the photoelectron spectroscopy. As the direct reduction of NOx is difficult because of the very high activation energy, it is proposed the utilization of the proton or dissolved water in oxide electrode for the indirect reduction reaction. The detailed discussion on the oxide protonic conductors are also conducted. Less
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