设计贵金属Au、Ag纳米结构高指数晶面及调制催化性质研究

发布时间：2018-03-27 20:37

本文选题：贵金属纳米催化剂　切入点：高指数晶面　出处：《吉林大学》2017年博士论文

【摘要】：全球人口不断增加,能源需求日益扩大,气候变化和环境问题日趋严重,如何保护我们赖以生存的地球家园,可谓是迫在眉睫!催化降解污染物、发展可持续清洁能源是解决上述问题的有效手段。燃料电池及氢能源是目前最具应用前景的清洁能源,但无论是催化降解污染物,还是发展燃料电池或氢能源都需要高效的催化剂。因此,如何提高催化剂的催化性能和节约应用成本是技术应用的核心问题。也就是说设计优化催化剂的组成成分、纳米结构、形貌、裸露晶面及大小尺寸是提高催化剂催化性能的关键所在。金Au、银Ag贵金属纳米催化剂,具有生物相容性、稳定性,是常用高效、持久的催化剂,在催化降解有机污染物、汽车尾气处理及CO2催化还原应用中都取得了出色的效果。大量的实验证明,催化剂裸露的表面晶面直接影响着催化剂的催化反应速率及激活势垒。高指数晶面,相对于低指数的基础晶面,存有大量的台阶面、晶体缺陷及丰富的低配位原子,具有更好的催化活性。本文重点发展简单、绿色、经济的水相合成方式,通过选择不同的还原剂、调控溶液的p H环境、控制反应动力学、可控设计合成出富有高指数晶面的多孔Au、Ag纳米结构及多面体,优化并提升催化降解有机污染物(p-硝基苯酚等)、葡萄糖燃料电池及电解水析氢性能,揭示贵金属纳米催化剂的形貌、尺寸、结构与催化性能的构效关系。开展了如下的研究内容:1.多孔Ag的可控制备及其催化性能研究。我们实现了对多孔Ag纳米晶的形貌、尺寸、结晶性及孔径分布的可控制备,并优化提升了其催化性能。多孔Ag催化性能的优化主要是通过调控以下参数实现的:多孔Ag的比表面积及在多孔结构表面的台阶steps、突起ledges和缺陷kinks处的Ag原子数目。这部分工作,我们主要是发展了一种简单的两步法合成体系。通过调节溶液的p H环境来调控多孔Ag的形貌及尺寸(形貌可实现梭形及四边形的可控合成,尺寸可实现2.5mm到36mm的调控);通过调节热处理的温度、升温速率、加热时间调控多孔Ag纳米晶的结晶性、表面缺陷及孔径分布。随后,在p-硝基苯酚等有机污染物催化降解应用中,我们探究了多孔Ag的形貌与性能的构效关系。研究结果表明:多孔Ag在催化降解有机污染物时表现出优异的催化活性。其中,4mm的四边形多孔Ag的催化活性最好,其反应速率可达到6.43*10-2 s-1,并且在多次循环利用后仍保持较高的催化活性。多孔Ag的高催化活性主要归结于:规则形貌(梭形或者四边形)、多孔结构、高比表面积、优异的渗透性、离子迁移率以及丰富的高指数晶面等高活性位点。鉴于多孔Ag上述的结构优势,相信其在电化学催化、传感和驱动器等实际应用中存在潜在的应用前景。2.多孔Au的可控制备及其GOR催化性能研究。我们创造性地发展了低温动力学方式,成功合成出多孔Au纳米结构。此合成方法突破了经典图尔克维奇(Turkevich)利用柠檬酸钠热还原氯金酸制备Au的方式。其中,低温合成条件改变了柠檬酸根在Au表面的吸附方式,获得表面“清洁”的多孔Au纳米晶。基于多孔Au的结构特点,我们探究了其表面结构与催化性能的关系。研究表明,表面“清洁”的多孔Au在葡萄糖电催化氧化中取得出色的催化效果,其催化氧化电流密度可高达9 A cm-2 g-1,是Turkevich-Au(0.45 A cm-2g-1)的20倍,也是当前所报道的最优值(2.65 A cm-2g-1)的3.4倍。多孔Au的高催化性能,主要归结于以下两方面:1)多孔Au具有清洁的表面、能够自由传输电子、最大化地暴露其活性位点;2)多孔Au具有大的电化学比表面积、多孔结构、良好的离子迁移率、丰富的高指能面及原子台阶位steps等高活性位点。高性能多孔Au在葡萄糖电催化氧化中的成功应用,为葡萄糖燃料电池在未来生活中的实际应用提供了广阔的商业应用前景。3.可控制备二十面体Au及其HER性能研究。我们继续发展了低温动力学的方式,成功制备出表面“清洁”的多重孪晶二十面体Au。同时,通过调控反应时间,设计合成出截角二十面体Au。(截角)二十面体Au具有丰富的孪晶界及边角原子等高活性位点。将二十面体Au应用到电解水HER催化反应中,我们发现随着测试循环次数的增加,二十面体Au的催化活性随之增加(过电位、Tafel斜率、电阻都随之降低)。30 000次循环后,二十面体Au的催化活性基本可以和商业Pt-C相媲美。初步的研究结果表明:催化剂的晶体缺陷能够显著增强其催化活性,多重孪晶中存在可调的应力应变;外加电位提供外部动力压缩了Au的晶格参数、使d带电子上移、优化了Au-H键能、提高了电解水HER性能。
[Abstract]:Increasing of global population, energy demand is growing, climate change and environmental problems become increasingly serious, how to protect the survival of our planet, it is imminent! The catalytic degradation of pollutants, the sustainable development of clean energy is an effective means to solve the above problems. The fuel cell and hydrogen energy is the most promising clean energy, but no matter is the catalytic degradation of pollutants, or the development of fuel cells and hydrogen energy need efficient catalyst. Therefore, how to improve the performance of the catalyst and save the application cost is a key problem in technology application. That is to say design optimization of composition, catalyst of nano structure, morphology, size and size of bare crystal surface is the key to improve the catalytic performance the catalyst. Au gold and silver Ag noble metal nano catalyst, biocompatibility, stability, is efficient, durable catalyst, In the photocatalytic degradation of organic pollutants and applications have achieved excellent results processing and automobile exhaust catalytic reduction of CO2. A large number of experiments show that the catalyst surface crystal exposed directly affects the catalytic reaction rate of the catalyst and the activation barrier. High index surfaces, relative to the low number of basic crystal surface, there are a lot of stepped surface and the crystal defects and rich low coordination atoms, has better catalytic activity. This paper focuses on the development of simple, green, aqueous synthesis economy, by choosing a different reducing agent, control solution P H environment control, reaction kinetics, controllable synthesis of rich design of high index surfaces of porous Au nanostructures, Ag and the polyhedron, and enhance the optimization of catalytic degradation of organic pollutants (p- nitro phenol), glucose fuel cell and water electrolysis hydrogen evolution performance, reveal the morphology of noble metal nano catalyst size, structure and catalytic The structure-activity relationship of performance. The research contents are as follows: 1. porous Ag can be prepared and their catalytic properties. We realize the control of morphology, porous Ag nano crystal size, crystallinity and pore size distribution can be controlled, and optimized to enhance the catalytic performance of porous Ag. Optimization of catalytic properties of the main the regulation is realized by the following parameters: the porous surface area of Ag and steps on the steps of porous structure on the surface, the number of Ag atoms ledges and kinks processes. This defect is the main part of the work, we developed a simple two step synthesis system. By adjusting the P of the solution to control the morphology and size of H porous Ag (controlled synthesis, morphology can be fusiform and quadrilateral size can achieve 2.5mm to 36mm control); by adjusting the heat treatment temperature, heating rate, heating time regulation of crystalline porous nanocrystalline Ag, and surface defects The pore size distribution in p-. Subsequently, p-nitrophenol catalytic degradation of organic pollutants such as application, we explore the structure-activity relationship of the morphology and properties of porous Ag. The results showed that the porous Ag exhibits excellent catalytic activity in the catalytic degradation of organic pollutants. The best catalytic activity of the porous Ag quadrilateral 4mm, the the reaction rate of 6.43*10-2 can reach s-1, and still maintain high catalytic activity in the repeated recycling. High catalytic activity of porous Ag is mainly due to the rules of morphology (fusiform or quadrilateral), porous structure, high surface area, excellent permeability, ion mobility and rich high index surfaces etc. high active site. In view of the advantages of porous structure of Ag, believes in electrochemical catalysis, applications of porous.2. Au potential practical application of sensor and driver in the preparation of catalytic performance and GOR control. We creatively developed low-temperature dynamics, the successful synthesis of Au nano porous structure. This method breaks through the classical Turk Vecchi (Turkevich) using sodium citrate reduction of HAuCl4 Au preparation method. The synthesis conditions of low temperature change of citrate adsorption on the Au surface, porous nanocrystalline Au surface "clean". Based on the structure characteristics of porous Au, we explore the relationship between the surface structure and catalytic performance. The results show that the porous Au surface cleaning has excellent catalytic effect on glucose oxidation, the oxidation current density can be as high as 9 A cm-2 g-1, Turkevich-Au (0.45 A cm-2g-1) 20 times, but also the optimal reported value (2.65 A cm-2g-1) 3.4 times. The high catalytic performance of porous Au, mainly due to the following two aspects: 1) porous Au have a clean surface, can be free The electronic transmission, to maximize the exposure of the active site; 2) porous Au has large electrochemical specific surface area, porous structure, good ion mobility, which can rich the surface and high atomic steps steps active site. The successful application of high performance porous Au in glucose oxidation of glucose the fuel cell in the future practical application in life provides the business prospects of.3. can be prepared in twenty face Au and HER properties of the control. We continue to develop the low temperature dynamics, the prepared multiple twin surface cleaning of twenty sides of Au. at the same time, by adjusting the reaction time, the design and synthesis of a truncated Au. (truncated) twenty face twenty face body Au has twin boundaries and high angle edge rich atom active site. The Au is applied to the twenty surface water electrolysis reaction catalyzed by HER, we found that with the number of test cycles Increase the catalytic activity of twenty surface Au increased (overpotential, Tafel slope, resistance decreased.30) after 000 cycles, the catalytic activity of twenty surface Au can be comparable to Pt-C and business. The preliminary results show that the crystal defects of catalyst can significantly enhance the catalytic activity, stress and strain adjustable multiple twins; applied potential provides external power compression of the lattice parameters of Au, with d electronic shift, optimize the Au-H bond energy, improve the performance of HER water electrolysis.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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