直接甲酸燃料电池高性能Pd电催化剂的制备及其催化行为的研究

发布时间：2018-01-24 22:24

本文关键词： 直接甲酸燃料电池高性能 Pd 电催化剂催化行为　出处：《西南大学》2014年博士论文　论文类型：学位论文

【摘要】：直接甲酸燃料电池(Direct Formic Acid Fuel Cell, DFAFC),具有能量转换效率高、安全可靠等特点,和氢氧燃料电池相比,具有明显的体积比能量优势,同时以液体甲酸为燃料,便于使用传统的汽油运输、储存和销售设备。因此在作为汽车动力以及便携式电源领域具有广阔的应用前景。然而DFAFC昂贵的价格极大地限制了其商业化发展,其中重要原因之一是该电池需要使用大量贵金属铂(Pt)催化剂,导致电池成本过高。因此,研究和制备具有高性能、低价位的阳极甲酸氧化和阴极氧还原(Oxygen reduction reaction, ORR)催化剂用于DFAFC,对加快其发展和应用具有重要的意义,但目前在研发中仍然存在很大的挑战。钯(Pd),具有和Pt相似的晶体结构和电子性能,价格相对便宜并且具有更高的抗一氧化碳(CO)中毒能力,从而成为一种有希望取代Pt的催化剂。近年来,纳米科学技术的进步和不断深入发展了在纳米尺度范围内设计和制备高性能催化剂的有效方法。本论文工作从纳米尺度设计和调控材料合成,发展了制备催化剂的新方法和研究催化剂碳载体以提高催化性能,制备出了一系列高性能Pd阴极和阳极电催化剂,进而对其纳米尺度的电催化行为进行了研究和讨论,发掘了电极过程动力学的科学内涵。第一章综述简要概述了燃料电池的原理、分类、特点和用途等。重点介绍了DFAFC催化剂及其反应机理,分析了当前催化剂常用的几种碳载体材料,同时也提出了DFAFC催化剂在科学和实践中的挑战。最后介绍了本论文的研究目的、主要内容以及创新点。第二章实验设计及表征方法本章介绍了实验过程中所使用的主要仪器和试剂,同时也分别描述了DFAFC催化剂的研究所使用的主要物理化学表征方法和电化学催化行为表征方法。第三章DNA调控的Pd纳米晶/碳纳米管催化剂及其氧还原催化行为的研究CNTs具有较大的比表面积以及良好的导电性和化学稳定性能,有作为优良催化剂载体的潜力。但是CNTs本身表面缺少活性基团,不利于金属颗粒的沉积。常用的方法是使用强酸回流来氧化CNTs,但会严重腐蚀CNTs并降低其导电性能。本论文研究通过DNA的芳香族碱基对和CNTs的石墨化表面的非共价ππ-ππ键相互作用对CNTs进行修饰,不仅保持了其原有的优良结构和导电性能,而且DNA规则排列的磷酸基团可以调控生长超小的,在CNTs表面均匀沉积的Pd纳米晶(平均粒径约是3.4nm),制备出了高性能Pd/DNA-CNTs催化剂。比较未经DNA调控制备的Pd/CNTs以及商业化Pd/C催化剂,Pd/DNA-CNTs展示出更好的ORR电催化活性和稳定性。这种使用DNA调控制备高性能催化剂的方法,应可以扩大应用到其它能源转换／存储系统中。第四章DNA修饰石墨烯并调控高活性Pd纳米晶作为甲酸氧化催化剂及其催化行为的研究Pt是DFAFC阳极常用的甲酸氧化催化剂,但是Pt的催化活性不够优良并且抗CO中毒能力较差。因此本论文研究选用DNA在具有高比表面积和优良导电性能的Graphene表面调控制备了高活性的Pd纳米晶作为甲酸氧化催化剂,即Pd-DNA@Graphene。通过TEM分析发现,平均粒径约5nm的Pd纳米晶均匀分散在Graphene表面。催化剂对甲酸氧化的电催化行为通过CV、LSV以及i-t等进行了研究。通过实验数据分析发现,Pd-DNA@Graphene催化剂展示出比Pd-Graphene和商业化Pd/C催化剂更高的峰电流密度和标准交换电流密度(i0)、更低的电荷转移电阻(Rct),说明我们制备的Pd-DNA@Graphene催化剂具有更好的甲酸氧化催化性能。另外,Pd-DNA@Graphene催化剂比Pd-Graphene和商业化Pd/C催化剂有更高的长时间运行稳定性。因此,我们制备的Pd-DNA@Graphene催化剂在DFAFC中具有较高的应用价值。第五章一步法制备超小Pd纳米晶/石墨烯催化剂及其甲酸氧化催化行为的研究由于传统制备Pd纳米催化剂的方法较为复杂、步骤冗繁,颗粒容易团聚并且难以实现均匀分散,严重影响了其ECSA,从而造成催化活性的降低。本论文研究使用甲酸作为还原剂在水热的条件下一步还原制备了平均粒径约4.3nm的超小的Pd纳米晶均匀分散在Graphene表面,制备出了高性能Pd@Graphene催化剂。和商业化Pd/C催化剂相比,Pd@Graphene催化剂对于甲酸氧化反应具有更高的峰电流密度和i0、更低的Rct以及更好的稳定性能。本论文也研究了Pd@Graphene催化剂的高效催化机制。这种一步法制备高效催化剂的方法,简单方便,容易实现,具有广泛的应用潜力。第六章不同纳米结构的碳材料作为载体制备的Pd催化剂及其对甲酸氧化催化行为影响的研究为了考察不同纳米结构的碳材料作为载体对制备的Pd催化剂甲酸氧化催化行为的影响,并选择出更高效的Pd催化剂,本论文研究分别选用零维的XC-72,一维的CNTs,二维的G以及三维的3D-RGO作为载体,制备了Pd@XC-72,Pd@CNTs,Pd@G以及Pd@3D-RGO催化剂并对其甲酸氧化催化行为进行了研究。和Pd@XC-72、Pd@CNTs以及Pd@G相比,Pd@3D-RGO不仅具有最大的比表面积和ECSA,而且还有最高的峰电流密度和i0、最低的Rct、最好的稳定性能。因此,Pd@3D-RGO是一种性能优良的甲酸氧化催化剂。另外,本论文研究不仅发现了三维的3D-RGO是一种比较理想的催化剂碳载体材料,而且也拓展了设计、合成和选择催化剂及其碳载体材料的应用基础理论。第七章结论和工作展望本章对论文研究得到的结论进行了总结并展望了这一领域以后要继续开展的研究工作。
[Abstract]:Direct formic acid fuel cell (Direct Formic Acid Fuel Cell, DFAFC), has high energy conversion efficiency, safe and reliable, compared with the fuel cell, has obvious advantages in energy and volume ratio, liquid acid as fuel, easy to use the traditional gasoline transportation, storage and sale of equipment. It has broad application prospects as in the automobile power and portable power. However, the DFAFC price greatly limit its commercial development, one of the most important reasons is the battery need to use a large number of precious metal platinum (Pt) catalyst, resulting in high battery cost. Therefore, the study and preparation of high performance anode and cathode oxygen, the oxidation of formic acid low price reduction (Oxygen reduction reaction, ORR) catalysts for DFAFC, has an important significance to accelerate its development and application, but the research still exists great challenges War. (Pd), PD and Pt has the similar crystal structure and electronic properties, the price is relatively cheap and has higher resistance to carbon monoxide (CO) poisoning ability, thus becoming a promising substitute for Pt catalyst. In recent years, nano science and technology progress and the development of effective design method in nanometer scale the range and preparation of high performance catalysts. This work from nano scale design and control materials, the development of a new method of preparing catalyst and catalyst carrier of carbon to improve the catalytic performance, preparation of a series of high performance Pd cathode and anode catalyst, and the electrocatalytic behavior of nano scale are studied and discussed, to explore the scientific connotation of electrode kinetics.
In the first chapter a brief overview of the principle of fuel cell, classification, characteristics and uses. Focusing on the DFAFC catalyst and its reaction mechanism, analyzes the current several commonly used carbon catalyst carrier materials, but also challenges the DFAFC catalyst in science and practice. Finally it introduces the research purpose, main content as well as innovation.
The second chapter is about experimental design and characterization. In this chapter, the main instruments and reagents used in the experiment are introduced. At the same time, the main physical and chemical characterization methods and Electrochemical Catalytic Behavior Characterization Methods of DFAFC catalysts are also described.
Study of CNTs Pd nanocrystals / third chapter DNA regulation of carbon nanotube catalyst and its catalytic behavior of oxygen reduction has a larger surface area and good conductivity and chemical stability, as the excellent catalyst carrier potential. But CNTs itself lack of surface active groups, is not conducive to the deposition of metal particles. The commonly used method is to use acid reflux to the oxidation of CNTs, but CNTs will be severe corrosion and reduce its electrical properties. This paper bases on the aromatic through DNA and CNTs graphite surface non covalent pi pi pi pi bond interaction of CNTs was modified, not only maintains the excellent original structure and electrical conductivity, and the phosphate group DNA regular arrangement can control the growth of ultra small, Pd in nanocrystalline CNTs uniformly deposited on the surface of the (average particle size is about 3.4nm), were prepared by the high performance Pd/DNA-CNTs catalyst without DNA control. The prepared Pd/CNTs and commercialized Pd/C catalysts show better ORR electrocatalytic activity and stability than Pd/DNA-CNTs. This method using DNA to control high performance catalysts should be extended to other energy conversion / storage systems.
The fourth chapter DNA modified graphene and the control of high activity of Pd nanocrystals as the formic acid oxidation catalyst and its catalytic behavior of Pt catalysts for DFAFC oxidation of formic acid is commonly used in the anode, but the catalytic activity of Pt is excellent and CO anti poisoning ability is poor. So this paper selects DNA in Graphene with high surface area and excellent conductive surface adjustment the controlled synthesis of Pd nanocrystals with high activity as formic acid oxidation catalyst, Pd-DNA@Graphene. is found through the analysis of TEM, Pd nanocrystals with an average particle size of about 5nm were uniformly dispersed on the surface of Graphene. The electrocatalytic behavior of catalyst for formic acid oxidation by CV, LSV and I-T were studied. Through the analysis of experimental data showed that the Pd-DNA@Graphene catalyst show the peak current density and higher standards than Pd-Graphene and commercial Pd/C catalyst exchange current density (I0), lower electric charge transfer Resistance (Rct), we illustrate the oxidation of formic acid catalytic performance of Pd-DNA@Graphene catalysts prepared has better. In addition, Pd-DNA@Graphene catalyst has long time running stability is higher than Pd-Graphene and commercial Pd/C catalyst. Therefore, the application value of our Pd-DNA@Graphene catalyzed by the agent is higher in DFAFC.
The fifth chapter is the research of one step preparation of ultra small Pd nanoparticles / graphene catalyst and its catalytic oxidation of formic acid behavior because the traditional methods of preparing Pd nano catalyst is more complex, cumbersome steps, easy to agglomerate particles and is difficult to achieve uniform dispersion, which seriously affected the ECSA, resulting in the decrease of catalytic activity. This paper use formic acid as reducing agent under hydrothermal conditions of one-step reduction preparation the average particle size of about 4.3nm ultra small Pd nanoparticles uniformly dispersed on the surface of Graphene was prepared by high performance Pd@Graphene catalyst. Compared with commercial Pd/C catalyst, Pd@Graphene catalyst has a peak current density and higher I0 for the oxidation of formic acid the reaction, lower Rct and better stability. This paper also studies the efficient catalytic mechanism of Pd@Graphene catalyst. This method of one step preparation of catalysts with high efficiency, simple and convenient, It is easy to realize and has wide application potential.
The sixth chapter on Pd catalysts for carbon materials with different nanostructures as carrier preparation and its effect on the catalytic oxidation of formic acid in order to investigate the behavior of carbon materials with different nanostructures as the effect of the support on the catalytic behavior of Pd catalyst for the oxidation of formic acid was prepared, and the choice of the Pd catalyst is more efficient, this paper selected zero dimension XC-72, one CNTs, two dimensional G and three-dimensional 3D-RGO as carrier, Pd@XC-72, prepared by Pd@CNTs, Pd@G and Pd@3D-RGO catalysts and studied its catalytic behavior. The oxidation of formic acid and Pd@XC-72, compared to Pd@CNTs and Pd@G, Pd@3D-RGO not only has the largest surface area and ECSA, but also the highest peak current the density and I0, the lowest Rct, stable performance best. Therefore, Pd@3D-RGO is an excellent catalyst for the oxidation of formic acid. In addition, this thesis not only found three dimension is 3D-RGO An ideal catalyst for carbon carrier, and it has also expanded the basic theory of the design, synthesis and selection of catalysts and their carbon carrier materials.
In the seventh chapter, the conclusion and work prospect are summarized and the future research work in this field is prospected.

【学位授予单位】：西南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O643.36;TM911.4

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