铂基纳米晶的可控合成及其电化学催化性能研究

发布时间：2018-07-29 20:04

【摘要】：在过去的几十年里,全球范围内化石燃料的大量使用在极大的提升了人们的生活水准同时,也带来了日益严重的环境问题。面对环境污染的加重以及能源危机的加剧,降低对非可再生资源例如石油以及化学能源的使用已经迫在眉睫。低温质子交换膜燃料电池能够零排放的将化学能转化成电能,是化石能源材料绝佳的替代物。由于贵金属Pt纳米晶催化剂的高效率,高稳定性,目前在燃料电池的催化剂使用中占据最重要的组成部分。然而考虑到Pt资源匮乏和昂贵的价格,寻找Pt的替代品提高催化剂的活性成为科学研究的热点。将其它金属与Pt形成合金是一种成为有效减少Pt的使用量的常用大方式。除了用其它金属替代Pt以外,设计合成具有特殊结构的纳米晶,例如中空结构,多级多孔结构等都是能够更好提升Pt使用价值的手段。除了考虑纳米晶的形貌,在纳米晶中引入缺陷位点也是一种绝佳的手段。因此,构建具有众多缺陷位点的多级结构纳米晶以及具有超高比表面积的中空结构都是解决Pt资源危机的理想手段。本论文报道了多种具有结构特异性的Pt基纳米晶的合成方法,并对其合成机理进行了系统研究。文中报道的几种Pt基催化剂,在燃料电池中非常重要的甲酸氧化和氧还原反应中展现出了优异的表现。本论文主要包括以下几方面的内容:1.我们介绍了一种的尺寸可控的多级结构Pt-Cu三角双锥结构的方法。实验中通过改变加入反应的KI的量,可以实现样品尺寸在110纳米到250纳米之间的调节。Cu2+离子的存在对形成具有{111}孪晶结构三角盘晶种至关重要。多级结构Pt-Cu三角双锥纳米晶相对于商用Pt/C催化剂在电化学甲酸氧化催化中表现出了更优异的性能。内部相互桥连的多级框架结构是提高材料催化性能的根本原因。2.我们合成了两种基于二十面体晶核生长的Pd-Pt-Cu三元金属纳米晶(大十二面体和大菱形二十面体)。这两种特殊结构的纳米晶的生长都是源于二十面体的晶核。当反应体系中KI量很少时,晶体生长优先于垂直于二十面体的孪晶界面处,形成大十二面体结构。随着KI的量增多,KI对于晶面的包覆作用大大增加,使得垂直于孪晶界面方向的生长受限直至被阻止。当KI量达到一定阈值以后,纳米晶在垂直于二十面体顶点的方向生长,从而得到大菱形二十面体结构。并且两种纳米晶都属于多枝结构,并且拥有大量暴露的孪晶界面基,作为一种理想催化剂进行氧还原性能测试,获得了优异的催化表现。3.我们通过氧化刻蚀不同比例的PdPt合金纳米晶立方体,得到了三种不同结构的中空结构。实验中发现,最终氧化刻蚀产物的形貌决定于初始反应的PdPt合金纳米晶两种元素的比值。在氧气存在的刻蚀条件下,纯Pd会被各向同性刻蚀,保留下来的Pt会进行迁移重排,Pt迁移和聚集的模式决定了最终的形貌。拥有高比表面的三种中空结构的Pd-Pt合金纳米催化剂的在电化学氧还原反应中表现出优异的催化性能。
[Abstract]:Over the past few decades, the massive use of fossil fuels worldwide has greatly increased the standard of living and a growing environmental problem. It is imminent to reduce the use of non renewable resources such as stone and chemical energy in the face of the aggravation of environmental pollution and the intensification of the energy crisis. The proton exchange membrane fuel cell (PEMFC) can convert chemical energy into electrical energy with zero emission. It is an excellent substitute for fossil energy materials. Because of the high efficiency and high stability of the Pt nanocrystalline catalyst, the most important component of the catalyst for fuel cells is occupied. However, the lack of Pt resources and the expensive price are taken into account. Looking for a substitute for Pt to improve the activity of the catalyst has become a hot spot of scientific research. It is a major way to effectively reduce the use of Pt by using other metals and Pt as an effective way to reduce the use of Pt. In addition to other metals instead of Pt, the design and synthesis of nanocrystals with special structures, such as hollow structures, multistage porous structures, etc. In addition to considering the morphology of nanocrystalline, the introduction of defect sites in nanocrystalline is also an excellent means. Therefore, the construction of multilevel structure nanocrystals with numerous defect sites and hollow structures with high specific surface area are ideal means to solve the crisis of Pt resources. This paper reports a variety of methods in this paper. The synthesis method of the structure specific Pt nanocrystalline crystal has been systematically studied. Several Pt based catalysts reported in this paper have shown excellent performance in the very important formic oxidation and oxygen reduction reactions in fuel cells. This paper mainly includes the following aspects: 1. we introduce one kind. The size controlled multistage structure Pt-Cu triangular double cone structure. By changing the amount of KI added to the reaction in the experiment, the existence of the sample size from 110 nanometers to 250 nanometers is essential to the formation of the {111} twin crystal triangulated disk crystals. The multistage structure Pt-Cu triangular biconical nanocrystals are relative to the quotient. The Pt/C catalyst has shown better performance in the oxidation of formic acid by electrochemical catalysis. The fundamental reason for improving the catalytic properties of the material is.2.. We have synthesized two kinds of Pd-Pt-Cu three Yuan metal nanocrystals based on the growth of twenty surface nuclei (large twelve face and diamond twenty sides). These two kinds of nanocrystals. The growth of nanocrystalline in the special structure is the nucleation of the twenty facets. When the reaction system has little KI, the crystal growth preceded the twin interface perpendicular to the twenty surface, forming a large twelve surface structure. As the amount of KI increased, the coating effect of KI on the crystal surface was greatly increased, making the growth perpendicular to the twin interface direction. When the limit was stopped, when the KI amount reached a certain threshold, the nanocrystalline crystal grew in the direction perpendicular to the vertex of the twenty surface body, thus the structure of the diamond shaped twenty surface body was obtained. And the two nanocrystals belonged to the multi branched structure and had a large number of exposed twins. As an ideal catalyst, the oxygen reduction performance test was obtained. Excellent catalytic performance.3. we obtained three different structures of hollow structures by oxidizing different PdPt alloy nanocrystalline cubes. In the experiment, it was found that the morphology of the final oxidation etching product was determined by the ratio of the initial reaction of the two elements of the PdPt alloy nanocrystals. Under the etching condition of oxygen, the pure Pd would be different. The retained Pt will rearrange the migration, and the mode of Pt migration and aggregation determines the final morphology. The three hollow structure Pd-Pt alloy nano catalysts with high specific surface exhibit excellent catalytic performance in the electrochemical oxygen reduction reaction.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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