新能源材料结构和性能的同步辐射研究
发布时间：2019-03-10 21:24
【摘要】：随着全球经济和技术的快速发展,能源和环境已然成为国际社会面临最为严峻的两大基本问题。优化能源结构,发展高效的低碳清洁新能源是当今世界可持续发展的重要方向和途径。新能源材料作为新能源开发利用的关键,目前仍然处于蓄力发展阶段,还存在有转换效率低、能量密度低以及成本高等诸多问题。进一步拓展新能源材料的种类,选择合适的模型材料体系研究它们的结构、组成、性能之间的关系,对提升新能源生产利用水平以及实现其广泛应用都具有重要意义。本论文通过设计合成单原子催化剂和原子层厚度超薄纳米片作为研究高效新能源材料的切入点,明确其结构和性能之间的关系,旨在为优化设计新能源材料提供新的认识和思路。首先合成单活性位点钴/氮化碳光催化剂,实现高效、自发的太阳光驱动全解水产氢,并揭示其内在机制在于能有效地分离光生电子-空穴对。其次制备出原子层厚度金属锡超薄纳米片用于高效电催化还原二氧化碳,结合同步辐射X射线吸收精细结构谱学(XAFS)和电化学表征揭示其表面配位不饱和结构是有效稳定CO_2还原中间体CO_2-的关键。我们还利用原位XAFS实验技术揭示了 lcFe-Pt/SiO_2催化剂中Fe的单原子结构,深入研究了其对一氧化碳选择性氧化(PROX)催化反应的高活性机理。本论文的具体研究内容如下:1、单原子钴/氮化碳的光催化全解水研究光解水过程包含着复杂的多电子、多步骤反应,对催化剂材料的要求非常高,目前大多数光催化剂在没有牺牲剂的情况下很难实现全解水。本论文通过精确设计和构建一种单活性位点的钴/氮化碳光催化剂,来分离光生电子和空穴对,实现高效的全解水性能。利用氮化碳材料的空间限域效应合成原子级分散的复合结构,同步辐射XAFS和高角环形暗场像(HAADF-STEM)明确它形成了单位点的Co1-P4原子结构,紫外可见漫反射光谱(UV-visDRS)和同步辐射光电子能谱(SRPES)表征结果证实该复合结构在电子能带结构中形成了特殊中间态,它不仅极大地提高了材料的可见光吸收,而且能有效抑制光生电子-空穴对复合,成功将光生载流子寿命提高了约20倍。该光催化剂在模拟太阳光照、不加牺牲剂和贵金属的条件下全解水产氢速率达410.3 μmol h~(-1) g~(-1),其中500 nm波长处量子效率达到2.2 %。2、原子层厚度锡纳米片的电还原二氧化碳研究超薄纳米片材料因为特殊的二维电子限域效应,具有一系列特殊的物理和化学属性。本论文设计和制备出石墨烯限域二维Sn纳米片的类三明治结构,厚度仅为1.4nm。将其作为电催化剂还原CO_2,在~(-1).8Vvs.SCE (饱和甘汞电极)的电极电势条件下,电流密度达到21.1 mA cm-2,分别是Sn块材,15 nm Sn颗粒以及15nmSn颗粒/石墨烯物理混合物的13、2.5和2倍。通过对SnK边XAFS谱的分析和计算表明,Sn纳米片中Sn的近邻配位相比于Sn块材和纳米颗粒明显降低,存在明显的不饱和配位,最近邻Sn-Sn配位数从2.0和4.0分别减小为1.4和2.7。电化学测试进一步揭示该不饱和配位可以有效稳定CO_2还原中间体CO_2-,这为设计高效CO_2还原电催化剂提供了重要的实验依据。3、单原子Fe1-Pt/SiO_2的一氧化碳选择性氧化(PROX)研究原位XAFS技术是研究催化反应过程中动态催化剂结构变化的一种非常重要的方法,但通常情况下,它给出的是催化体系中所有吸收原子周围局域结构排布的平均信息,选择性分离获取催化剂表界面活性中心结构仍然面临着极大挑战。单原子催化剂在表现出高活性的同时还具有均一分散的催化活性位点,为原位XAFS研究结构和性能关系提供了简化的理想模型。本论文利用原子层沉积技术精确制备了 1 cFe-Pt/SiO_2单原子催化剂用于PROX反应,在198-380 K温度区间实现了 CO氧化的100%的选择性和转化率转化。基于原位同步辐射XAFS技术监测到在室温H2条件下1cFe-Pt/SiO_2中的Fe3+就可以被还原为Fe2+,并明确不同价态的Fe离子都主要以单原子形式存在。同时首次观察到在PROX反应条件下的活性位点是原子级分散的Pt-Fe1(OH)3物种,结合密度泛函理论计算进一步证实正是该结构导致了 1cFe-Pt/SiO_2单原子催化剂的高效PROX催化活性。
[Abstract]:With the rapid development of global economy and technology, energy and environment have become the two most serious problems facing the international community. Optimizing the energy structure and developing high-efficiency and low-carbon clean new energy is the important direction and way of the sustainable development in the world today. As the key to the new energy development and utilization, new energy materials are still in the development stage of energy storage, and there are many problems such as low conversion efficiency, low energy density and high cost. It is of great significance to further expand the kinds of new energy materials, to select the appropriate model material system to study their structure, composition and performance, and to improve the utilization level of new energy production and to realize its wide application. This paper, through the design and synthesis of single-atom catalyst and atomic layer thickness ultrathin nanosheet, is a breakthrough point for the study of high-efficiency new energy materials, and the relationship between its structure and performance is defined, and the aim of this paper is to provide a new understanding and thinking for the optimization of new energy materials. Firstly, a single active site cobalt/ carbon nitride photocatalyst is synthesized, so that high-efficiency and spontaneous sunlight driving is realized to fully solve the hydrogen, and the mechanism is that the photo-generated electron-hole pair can be effectively separated. X-ray absorption fine-structure spectroscopy (XAFS) and electrochemical characterization of the atomic layer are the key to the effective and stable CO _ 2 reduction of the intermediate CO _ 2. The monoatomic structure of Fe in the lcFe-Pt/ SiO _ 2 catalyst was also revealed by in-situ XAFS experiment, and the high activity mechanism of the catalytic reaction of the selective oxidation of carbon monoxide (PROX) was studied. The specific research contents of this thesis are as follows:1. The photodegradation water process of a single-atom-cobalt/ carbon-nitride-based photocatalytic water-photolysis process comprises a complex multi-electron and multi-step reaction, and the requirement on the catalyst material is very high. At present, most of the photocatalysts are difficult to achieve full solution without the agent. In this paper, through the precise design and construction of a single active site cobalt/ carbon nitride photocatalyst, the photo-generated electron and hole pairs are separated, and the high-efficiency full-solution water performance is realized. The composite structure, synchrotron radiation XAFS and high-angle annular dark field image (HAADF-STEM) of the carbon nitride material are used to synthesize the atomic-grade dispersed composite structure, and the Co1-P4 atomic structure of the unit point is defined by the synchrotron radiation XAFS and the high-angle annular dark field image (HAADF-STEM). The results of UV-visDRS and SRPES show that the composite structure forms a special intermediate state in the electron energy band structure, which not only greatly improves the visible light absorption of the material, but also can effectively inhibit the recombination of the photo-generated electron-hole pair, The success of the photo-generated carrier lifetime is increased by about 20 times. The photocatalyst has the full solution of the hydrogen rate of 410.3. mu. mol h to (-1) g-(-1) under the condition of simulating the sun light, without the addition of a condensing agent and a noble metal, wherein the quantum efficiency at the wavelength of 500 nm is 2.2%. The electroreducing carbon dioxide of the atomic layer thickness tin nanosheet has a series of special physical and chemical properties due to the special two-dimensional electron confinement effect. In this paper, the sandwich structure of the two-dimensional Sn nano-sheet of the graphene-limited domain is designed and prepared, and the thickness is only 1.4 nm. The current density was 21.1 mA cm-2 under the electrode potential of ~ (-1).8 V vs. SCE (saturated calomel electrode) as an electrocatalyst, and 13, 2.5 and 2 times of the physical mixture of Sn block,15 nm Sn particles and 15 nm Sn particles/ graphene, respectively. The analysis and calculation of the SnK-side XAFS spectrum show that the near-nearest-neighbor coordination of Sn in the Sn nano-sheet is obviously lower than that of the Sn-block material and the nano-particles, and has obvious unsaturated coordination, and the nearest neighbor Sn-Sn coordination number is reduced from 2.0 and 4.0 to 1.4 and 2.7, respectively. The electrochemical test further reveals that the unsaturated coordination can effectively and stably stabilize the CO _ 2-, which provides an important experimental basis for the design of a high-efficiency CO _ 2 reduction electric catalyst. In-situ XAFS technology is a very important method to study the change of dynamic catalyst structure in the process of catalytic reaction, but in general, It gives the average information of the local structure arrangement of all the absorption atoms in the catalytic system, and the selective separation and acquisition of the active center structure of the catalyst table still faces great challenges. The monoatomic catalyst also has a uniform dispersed catalytic activity site while exhibiting high activity, and provides a simplified ideal model for the in-situ XAFS study structure and performance relationship. In this paper,1 cFe-Pt/ SiO _ 2 monoatomic catalyst is prepared by atomic layer deposition technique for PROX reaction, and the selectivity and conversion rate of 100% of CO oxidation are realized in the temperature range of 198-380 K. Based on the in-situ synchrotron radiation XAFS technique, the Fe ~ (3 +) in 1 cFe-Pt/ SiO _ 2 at room temperature (H2) can be reduced to Fe 2 +, and the Fe ions in different valence states are mainly present in single atom form. At the same time, it was first observed that the active site under the condition of PROX was an atomic-grade dispersed Pt-Fe1 (OH)3 species, and in combination with the density functional theory, it was further confirmed that this structure resulted in the high-efficiency PROX catalytic activity of the 1 cFe-Pt/ SiO _ 2 monoatomic catalyst.
【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】：TB303
本文编号：2438040
[Abstract]:With the rapid development of global economy and technology, energy and environment have become the two most serious problems facing the international community. Optimizing the energy structure and developing high-efficiency and low-carbon clean new energy is the important direction and way of the sustainable development in the world today. As the key to the new energy development and utilization, new energy materials are still in the development stage of energy storage, and there are many problems such as low conversion efficiency, low energy density and high cost. It is of great significance to further expand the kinds of new energy materials, to select the appropriate model material system to study their structure, composition and performance, and to improve the utilization level of new energy production and to realize its wide application. This paper, through the design and synthesis of single-atom catalyst and atomic layer thickness ultrathin nanosheet, is a breakthrough point for the study of high-efficiency new energy materials, and the relationship between its structure and performance is defined, and the aim of this paper is to provide a new understanding and thinking for the optimization of new energy materials. Firstly, a single active site cobalt/ carbon nitride photocatalyst is synthesized, so that high-efficiency and spontaneous sunlight driving is realized to fully solve the hydrogen, and the mechanism is that the photo-generated electron-hole pair can be effectively separated. X-ray absorption fine-structure spectroscopy (XAFS) and electrochemical characterization of the atomic layer are the key to the effective and stable CO _ 2 reduction of the intermediate CO _ 2. The monoatomic structure of Fe in the lcFe-Pt/ SiO _ 2 catalyst was also revealed by in-situ XAFS experiment, and the high activity mechanism of the catalytic reaction of the selective oxidation of carbon monoxide (PROX) was studied. The specific research contents of this thesis are as follows:1. The photodegradation water process of a single-atom-cobalt/ carbon-nitride-based photocatalytic water-photolysis process comprises a complex multi-electron and multi-step reaction, and the requirement on the catalyst material is very high. At present, most of the photocatalysts are difficult to achieve full solution without the agent. In this paper, through the precise design and construction of a single active site cobalt/ carbon nitride photocatalyst, the photo-generated electron and hole pairs are separated, and the high-efficiency full-solution water performance is realized. The composite structure, synchrotron radiation XAFS and high-angle annular dark field image (HAADF-STEM) of the carbon nitride material are used to synthesize the atomic-grade dispersed composite structure, and the Co1-P4 atomic structure of the unit point is defined by the synchrotron radiation XAFS and the high-angle annular dark field image (HAADF-STEM). The results of UV-visDRS and SRPES show that the composite structure forms a special intermediate state in the electron energy band structure, which not only greatly improves the visible light absorption of the material, but also can effectively inhibit the recombination of the photo-generated electron-hole pair, The success of the photo-generated carrier lifetime is increased by about 20 times. The photocatalyst has the full solution of the hydrogen rate of 410.3. mu. mol h to (-1) g-(-1) under the condition of simulating the sun light, without the addition of a condensing agent and a noble metal, wherein the quantum efficiency at the wavelength of 500 nm is 2.2%. The electroreducing carbon dioxide of the atomic layer thickness tin nanosheet has a series of special physical and chemical properties due to the special two-dimensional electron confinement effect. In this paper, the sandwich structure of the two-dimensional Sn nano-sheet of the graphene-limited domain is designed and prepared, and the thickness is only 1.4 nm. The current density was 21.1 mA cm-2 under the electrode potential of ~ (-1).8 V vs. SCE (saturated calomel electrode) as an electrocatalyst, and 13, 2.5 and 2 times of the physical mixture of Sn block,15 nm Sn particles and 15 nm Sn particles/ graphene, respectively. The analysis and calculation of the SnK-side XAFS spectrum show that the near-nearest-neighbor coordination of Sn in the Sn nano-sheet is obviously lower than that of the Sn-block material and the nano-particles, and has obvious unsaturated coordination, and the nearest neighbor Sn-Sn coordination number is reduced from 2.0 and 4.0 to 1.4 and 2.7, respectively. The electrochemical test further reveals that the unsaturated coordination can effectively and stably stabilize the CO _ 2-, which provides an important experimental basis for the design of a high-efficiency CO _ 2 reduction electric catalyst. In-situ XAFS technology is a very important method to study the change of dynamic catalyst structure in the process of catalytic reaction, but in general, It gives the average information of the local structure arrangement of all the absorption atoms in the catalytic system, and the selective separation and acquisition of the active center structure of the catalyst table still faces great challenges. The monoatomic catalyst also has a uniform dispersed catalytic activity site while exhibiting high activity, and provides a simplified ideal model for the in-situ XAFS study structure and performance relationship. In this paper,1 cFe-Pt/ SiO _ 2 monoatomic catalyst is prepared by atomic layer deposition technique for PROX reaction, and the selectivity and conversion rate of 100% of CO oxidation are realized in the temperature range of 198-380 K. Based on the in-situ synchrotron radiation XAFS technique, the Fe ~ (3 +) in 1 cFe-Pt/ SiO _ 2 at room temperature (H2) can be reduced to Fe 2 +, and the Fe ions in different valence states are mainly present in single atom form. At the same time, it was first observed that the active site under the condition of PROX was an atomic-grade dispersed Pt-Fe1 (OH)3 species, and in combination with the density functional theory, it was further confirmed that this structure resulted in the high-efficiency PROX catalytic activity of the 1 cFe-Pt/ SiO _ 2 monoatomic catalyst.
【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】：TB303
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