Composite electrochemical catalysis utilizing mixed potential at the heterogeneous contact

本研究项目旨在开发一种新型的复合电化学催化剂，该催化剂可以利用具有离子-电子混合电导率的多孔氧化物电极、固体电解质和金属电极之间非均相界面上气体物种的反常反应活性。在微观尺度上，催化被认为是具有不对称电极结构的微尺度电池的混合物，利用所谓的混合电位，这与非均相界面上的空间电荷效应密切相关。在项目前期，考察了NdLt；2-X&GT；Ce_xCuO_4、掺钕CeO_2和Au粉末的混合物对NO/NO_2 Red-Ox反应的催化活性。与单组分催化剂相比，复合催化剂具有更高的催化活性。实验还表明，NiO、YSZ、Au复合粉末对NOx Red-Ox也具有强化催化作用。为了考察增强型催化…的作用机理考察了复合材料、三电极电化学池的更多反应。研究发现，反应速率决定步骤是NO_2和O_2在多孔氧化物上的有效吸附和电子转移反应与金电极上的简单电子转移反应的混合过程。由该模型推导出两种反应的交换电流密度。值得注意的是，可移动离子和吸附气体物种在非均相接触界面处积累的空间电荷的驰豫是催化反应选择性强化的基本机制。因此，氧化物的电子能带结构和电子输运性质在混合电势的形成中起着重要作用，这是理解复合电化学催化反常反应活性的关键之一。基于这些观点，通过光电子能谱对电子和离子输运性质以及电子能带结构的详细研究，对氧化物电极的可能候选者进行了调查。由于NOx的活化能很高，直接还原很困难，建议利用氧化物电极中的质子或溶解水进行间接还原反应。对氧化物质子导体也进行了详细的讨论。较少

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 … More 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