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首页> 外文学位 >Non-platinum group metal oxgyen reduction catalysts and their mechanism in both acid and alkaline media: The effect of the catalyst precursor and the ionomer on oxygen reduction.
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Non-platinum group metal oxgyen reduction catalysts and their mechanism in both acid and alkaline media: The effect of the catalyst precursor and the ionomer on oxygen reduction.

机译：非铂族金属氧还原催化剂及其在酸性和碱性介质中的机理：催化剂前体和离聚物对氧还原的影响。

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摘要

Non-platinum catalysts are an attractive strategy for lowering the cost of fuel cells, but much more development is needed in order to replace platinum, especially at the cathode where oxygen is reduced. Research groups worldwide have donated material for a study in which precursor structure to catalyst activity correlations are made. The donated samples have been divided into three classes based on their precursor; macrocyclic chelates, small molecule, and polymeric precursors. The precursor is one activity-dictating factor among many, but it is one of the most influential. It was found that macrocyclic chelates on average produced the most active catalysts, having the highest limiting, diffusion-limited, kinetic, and exchange current densities, as well as the lowest overpotentials and H2O2 production. This suggests that the M-N4 atomic structure of the precursor remains largely static throughout heat treatment, as the M-Nx motif is the accepted active site conformation. The other classes were somewhat less active, but the breadth of precursor materials that range in structure and functionality, as well as low associated costs, make them attractive precursor materials.;Careful precursor selection based on this analysis was applied to a new generation of catalyst derived from iron salt and 4-aminoantipyrine. An extensive investigation of the reduction of oxygen on the material performed in both acid and alkaline media, and it was found that reduction follows a two-step pathway. While the peroxide reducing step is also very fast, the first step is so rapid that, even at low active site density, the material is almost as active as platinum if all diffusion limitations are removed.;In addition to bottom-up catalyst design, the catalyst:ionomer complex, by which catalyst is incorporated into the membrane electrode assembly, also affects reductive kinetics. A series of novel anionically conductive ionomers have been evaluated using a well-described cyanamide derived catalyst, and the ionomeric influence on activity was mechanistically evaluated. It was found that the water-uptake percentage of the ionomer and the ion exchange capacity has a major role in catalyzing the reaction. The ionomer content of the complex must balance ionic and electrical charge transfer, as well as manage a certain degree of hydration at the active site.;In order for a catalyst to perform optimally in an operational fuel cell, design considerations must be addressed at the precursor, support, synthesis, morphological, and ionomer-complexing levels. If any level of design is neglected, catalytic performance will be sacrificed.
机译：非铂催化剂是降低燃料电池成本的一种有吸引力的策略，但是需要更多的开发来替代铂，尤其是在氧被还原的阴极。世界各地的研究小组已捐赠了用于研究的材料，其中将前体结构与催化剂活性进行了关联。捐赠的样品根据其前身分为三类。大环螯合物，小分子和聚合物前体。前体是许多活动中的一种决定活动的因素，但它是最有影响力的因素之一。已经发现，大环螯合物平均产生最高活性的催化剂，具有最高的极限，扩散极限，动力学和交换电流密度，以及最低的过电势和H 2 O 2产生。这表明前体的M-N4原子结构在整个热处理过程中基本上保持静态，因为M-Nx基序是公认的活性位点构象。其他类别的活性稍差，但是结构和功能范围广泛的前体材料的广泛性以及较低的相关成本使其成为有吸引力的前体材料。基于此分析精心选择的前体被应用于新一代催化剂衍生自铁盐和4-氨基安替比林。在酸性和碱性介质中对材料上的氧气还原进行了广泛的研究，发现还原遵循两步走的路径。尽管过氧化物还原步骤也非常快，但第一步是如此之快，以至于即使在低活性位点密度下，如果消除了所有扩散限制，该材料的活性也几乎与铂一样。催化剂：离聚物配合物（通过该配合物将催化剂结合到膜电极组件中）也影响还原动力学。已经使用一种众所周知的氰酰胺衍生的催化剂评估了一系列新型的阴离子导电离聚物，并通过机械方法评估了离聚物对活性的影响。发现离聚物的吸水率和离子交换容量在催化反应中起主要作用。配合物的离聚物含量必须平衡离子和电荷转移，并在活性部位控制一定程度的水合作用。为了使催化剂在可操作的燃料电池中发挥最佳性能，必须在设计时考虑到设计上的考虑。前体，载体，合成，形态和离聚物复合物水平。如果忽略任何设计水平，都会牺牲催化性能。

著录项

  • 作者

    Robson, Michael H.;

  • 作者单位

    The University of New Mexico.;

  • 授予单位 The University of New Mexico.;
  • 学科 Engineering Chemical.;Nanoscience.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 130 p.
  • 总页数 130
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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