钴基金属有机框架结构材料的合成及其电化学性能研究
发布时间：2019-05-22 23:12
【摘要】：随着能源材料的发展,氢气由于其清洁、零污染等优点被视为一类高效的新型能源载体。而碱性条件下的水分解被认为是一种非常具有应用前景的制氢方法,它包括两个半反应,即在阴极发生的析氢反应和在阳极发生的析氧反应。但是,在整个水分解系统中,由于电催化析氧反应是一个4电子反应过程,因此,析氧反应的发生需要克服更大的动力学能垒。所以,发展高效的析氧电催化剂成为提高全水分解性能的一个主要研究方向。近年来,金属有机框架结构材料(metal-organic frameworks)由于其较好的物理稳定性、化学稳定性以及规则有序的孔道、骨架结构,逐渐代替了传统的多孔材料并广泛地应用于各类反应中。鉴于现有的析氧电催化剂仍然具有析氧过电位大,制备方法复杂等缺点,本论文结合金属有机框架结构材料(MOFs)的结构优点和应用基础,创新性地合成了不同的钴基金属有机框架结构材料(MOFs)和其衍生物并将获得的MOFs材料应用于电催化析氧反应中,同时研究其在析氧反应中的理论意义和实际应用价值。本文主要分为以下几个工作:1.近年来,鉴于MOFs-基材料的大的比表面积和可调的孔道结构等优点,MOFs-基材料被逐步应用在电催化析氧反应中。然而,通常的MOFs-基催化剂的制备方法是使用Nafion将电极材料涂覆在玻璃碳电极上以待测试。这就使得电极材料在析氧反应中的电子和质子传输被Nafion膜阻碍,因而导致MOFs-基催化剂的有效催化活性降低。因此,优化活性材料的电荷传输性能成为了设计MOFs-基析氧电催化剂的关键。在本工作中,我们合成了超薄的MOFs材料(ZIF-67)纳米片并将其原位生长在高导电的Ti@TiO_2/Cd S基底上以此来优化整个电极的电荷传输能力。所获得的Ti@TiO_2/Cd S/ZIF-67电极具有的独特的三维结构,不仅提高了电子转移的速率而且提高了ZIF-67材料的稳定性。而ZIF-67作为一类由Co盐和2-甲基咪唑配位形成的多孔材料,由于咪唑配体中所含的高电负性的N原子产生的诱导效应,使得Co离子的价态升高,从而进一步提高了Ti@TiO_2/Cd S/ZIF-67电极的析氧反应的能力。鉴于以上结论,我们将合成的Ti@TiO_2/Cd S/ZIF-67电极应用于碱性条件下的析氧反应,与其他MOFs-基的电催化剂相比,它展示了一个非常小的Tafel斜率(42m V/dec)及良好的稳定性,这进一步说明了Ti@TiO_2/Cd S基底良好的导电性。这些实验数据及结论为研究高效的析氧电化学催化剂开辟了一条新的研究思路。2.电催化水分解作为一种高效的、大规模的产氢方式,日益受到科研工作者的广泛关注。然而,作为电催化水分解的一个半反应,析氧反应的发生需要克服更大的动力学能垒。因此,发展高效的析氧电催化剂成为提高电催化全水分解性能的一个主要研究方向。考虑到金属有机框架材料(metal-organic frameworks,MOFs)规则有序的孔道结构、稳定的骨架及大的比表面积等优点,在本工作中,我们采用一步磷化法在N2气氛下将水热合成的双金属有机框架结构材料(Co Fe-MOFs)转化生成Co-Fe-P复合物,并把它作为新的电催化剂应用于电催化析氧反应中。通过对钴、铁比例的进一步优化,我们所得到的Co-Fe-P-1.7电极具有比钴铁层状双氢氧化物(Co Fe-LDH)以及Co Fe-MOFs-1.7电极更优越的析氧性能。同时,我们将造成这一结果的原因进行了详细的分析并得出以下结论:正是由于Co和Fe两种金属之间的协同效应、Co-Fe-P-1.7中高价态的Co离子的存在、大的电化学活性表面积(ECSA)以及暴露在Co/Fe磷化物表面上的纳米线,使得Co-Fe-P-1.7在1.0 M KOH中展示了优异的电催化析氧性能,包括:在10 m A/cm~2处的过电位为244 m V、小Tafel斜率(58 m V/dec)以及良好的稳定性。此外,在1.0 M KOH溶液中,我们将所获得的Co-Fe-P-1.7修饰在Ni网上并作为在二电极体系下水分解的阳极和阴极,其在10 m A/cm~2的电流密度下的全水分解电压为1.60 V,以上研究都为发展高效的MOFs-基双功能化的催化剂提供了实验借鉴和研究思路。3.通过水热法合成了钴/铁双金属有机框架结构(Co Fe-MOF-74),同时比较了不同的Fe掺入量对Co Fe-MOF-74的析氧性能的影响;继而将所得到的Co Fe-MOF-74电极和商业的Pt/C负载在Ni网上进行了全水分解实验,发现组合的催化剂具有良好的水分解性能,这为发展高效的MOFs-基析氧催化剂提供了实验借鉴和研究思路。
[Abstract]:With the development of energy materials, hydrogen is considered as a new type of new energy carrier because of its cleaning and zero pollution. The decomposition of water under alkaline conditions is considered to be a very promising method of hydrogen production, which consists of two half-reactions, the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode. However, in the whole water decomposition system, since the electrocatalytic oxygen evolution reaction is a 4-electron reaction process, the occurrence of the oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property. In recent years, metal-organic framework has been widely used in various reactions due to its good physical stability, chemical stability and regular and ordered pore and framework structure. In view of the defects of the existing oxygen evolution electrocatalyst still has the defects of large oxygen evolution potential, complex preparation method and the like, the present paper combines the structural advantages and the application foundation of the metal organic framework structure material (MOFs), The organic framework material (MOFs) and its derivatives are synthesized and the obtained MOFs material is applied to the electrocatalytic oxygen evolution reaction, and the theoretical and practical application value in the oxygen evolution reaction is also studied. This paper is mainly divided into the following work:1. In recent years, with the advantages of large specific surface area and adjustable pore structure of the MOFs-based materials, the MOFs-based materials are gradually applied in the electrocatalytic oxygen evolution reaction. However, the usual method for preparing the MOFs-based catalyst is to use Nafion to coat the electrode material on the glassy carbon electrode for testing. This allows the electron and proton transport of the electrode material in the oxygen evolution reaction to be blocked by the Nafion membrane, thus leading to a reduction in the effective catalytic activity of the MOFs-based catalyst. Therefore, the charge transfer performance of the optimized active material becomes the key to the design of MOFs-based oxygen-based electrocatalyst. In this work, we synthesized ultra-thin MOFs (ZIF-67) nanosheets and grown them in situ on a highly conductive Ti@TiO_2/ Cd S substrate to optimize the charge transport capacity of the entire electrode. The obtained Ti@TiO_2/ Cd S/ ZIF-67 electrode has a unique three-dimensional structure, not only improves the rate of electron transfer, but also improves the stability of the ZIF-67 material. ZIF-67 is a kind of porous material which is formed by co-salt and 2-methyl detomidine, and because of the induced effect of the high electronegativity of N atoms, the valence state of Co ion is increased, thus further improving the oxygen evolution reaction capability of the Ti@TiO_2/ Cd S/ ZIF-67 electrode. In view of the above conclusion, we apply the synthesized Ti@TiO_2/ Cd S/ ZIF-67 electrode to the oxygen evolution reaction under alkaline conditions, which shows a very small Tafel slope (42 m V/ dec) and good stability as compared to the other MOFs-based electrocatalysts. This further illustrates the good electrical conductivity of the Ti@TiO_2/ Cd S substrate. These experimental data and conclusions have opened up a new way to study the efficient oxygen evolution electrochemical catalyst. Electrocatalytic water decomposition is an efficient and large-scale method of hydrogen production, and is increasingly concerned by scientific researchers. However, as one and a half of the electrocatalytic water decomposition, the occurrence of oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of an efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property of electrocatalysis. in consideration of that well-ordered pore structure of the metal-organic framework material (MOFs), the stable skeleton and the large specific surface area and the like, The Co-Fe-P composite was synthesized by a one-step phosphorization method in the atmosphere of N2, and the Co-Fe-P composite was transformed into a new electrocatalyst. By further optimizing the ratio of cobalt and iron, the Co-Fe-P-1.7 electrode obtained has better oxygen evolution performance than that of the cobalt-iron layered double hydroxide (Co Fe-LDH) and the Co Fe-MOFs-1.7 electrode. At the same time, the cause of this result is analyzed in detail and the conclusion is drawn that Co-Fe-P-1.7 has the Co-Fe-P-1.7 high valence Co ion in the co-Fe-P-1.7 due to the synergistic effect between the two metals of Co and Fe. The large electrochemically active surface area (ECSA) and the nanowires exposed to the Co/ Fe phosphide surface, such that the Co-Fe-P-1.7 exhibited excellent electrocatalytic oxygen evolution performance in 1.0 M KOH, including an overpotential at 10 m A/ cm-2 of 244 m V, a small Tafel slope (58 m V/ dec), and good stability. in addition, in a 1.0 M KOH solution, we modify the obtained Co-Fe-P-1.7 on the Ni line and act as an anode and a cathode for water decomposition in a two-electrode system, with a full water decomposition voltage of 1.60 V at a current density of 10 m A/ cm-2, The above research has provided the experimental reference and the research thinking for the development of efficient MOFs-based bifunctional catalyst. Co Fe-MOF-74 (Co Fe-MOF-74) was synthesized by hydrothermal method, and the effect of different Fe doping amount on the oxygen evolution of Co Fe-MOF-74 was compared. It is found that the combined catalyst has good water decomposition property, which provides the experimental reference and the research idea for the development of efficient MOFs-based oxygen evolution catalyst.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2
本文编号：2483360
[Abstract]:With the development of energy materials, hydrogen is considered as a new type of new energy carrier because of its cleaning and zero pollution. The decomposition of water under alkaline conditions is considered to be a very promising method of hydrogen production, which consists of two half-reactions, the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode. However, in the whole water decomposition system, since the electrocatalytic oxygen evolution reaction is a 4-electron reaction process, the occurrence of the oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property. In recent years, metal-organic framework has been widely used in various reactions due to its good physical stability, chemical stability and regular and ordered pore and framework structure. In view of the defects of the existing oxygen evolution electrocatalyst still has the defects of large oxygen evolution potential, complex preparation method and the like, the present paper combines the structural advantages and the application foundation of the metal organic framework structure material (MOFs), The organic framework material (MOFs) and its derivatives are synthesized and the obtained MOFs material is applied to the electrocatalytic oxygen evolution reaction, and the theoretical and practical application value in the oxygen evolution reaction is also studied. This paper is mainly divided into the following work:1. In recent years, with the advantages of large specific surface area and adjustable pore structure of the MOFs-based materials, the MOFs-based materials are gradually applied in the electrocatalytic oxygen evolution reaction. However, the usual method for preparing the MOFs-based catalyst is to use Nafion to coat the electrode material on the glassy carbon electrode for testing. This allows the electron and proton transport of the electrode material in the oxygen evolution reaction to be blocked by the Nafion membrane, thus leading to a reduction in the effective catalytic activity of the MOFs-based catalyst. Therefore, the charge transfer performance of the optimized active material becomes the key to the design of MOFs-based oxygen-based electrocatalyst. In this work, we synthesized ultra-thin MOFs (ZIF-67) nanosheets and grown them in situ on a highly conductive Ti@TiO_2/ Cd S substrate to optimize the charge transport capacity of the entire electrode. The obtained Ti@TiO_2/ Cd S/ ZIF-67 electrode has a unique three-dimensional structure, not only improves the rate of electron transfer, but also improves the stability of the ZIF-67 material. ZIF-67 is a kind of porous material which is formed by co-salt and 2-methyl detomidine, and because of the induced effect of the high electronegativity of N atoms, the valence state of Co ion is increased, thus further improving the oxygen evolution reaction capability of the Ti@TiO_2/ Cd S/ ZIF-67 electrode. In view of the above conclusion, we apply the synthesized Ti@TiO_2/ Cd S/ ZIF-67 electrode to the oxygen evolution reaction under alkaline conditions, which shows a very small Tafel slope (42 m V/ dec) and good stability as compared to the other MOFs-based electrocatalysts. This further illustrates the good electrical conductivity of the Ti@TiO_2/ Cd S substrate. These experimental data and conclusions have opened up a new way to study the efficient oxygen evolution electrochemical catalyst. Electrocatalytic water decomposition is an efficient and large-scale method of hydrogen production, and is increasingly concerned by scientific researchers. However, as one and a half of the electrocatalytic water decomposition, the occurrence of oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of an efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property of electrocatalysis. in consideration of that well-ordered pore structure of the metal-organic framework material (MOFs), the stable skeleton and the large specific surface area and the like, The Co-Fe-P composite was synthesized by a one-step phosphorization method in the atmosphere of N2, and the Co-Fe-P composite was transformed into a new electrocatalyst. By further optimizing the ratio of cobalt and iron, the Co-Fe-P-1.7 electrode obtained has better oxygen evolution performance than that of the cobalt-iron layered double hydroxide (Co Fe-LDH) and the Co Fe-MOFs-1.7 electrode. At the same time, the cause of this result is analyzed in detail and the conclusion is drawn that Co-Fe-P-1.7 has the Co-Fe-P-1.7 high valence Co ion in the co-Fe-P-1.7 due to the synergistic effect between the two metals of Co and Fe. The large electrochemically active surface area (ECSA) and the nanowires exposed to the Co/ Fe phosphide surface, such that the Co-Fe-P-1.7 exhibited excellent electrocatalytic oxygen evolution performance in 1.0 M KOH, including an overpotential at 10 m A/ cm-2 of 244 m V, a small Tafel slope (58 m V/ dec), and good stability. in addition, in a 1.0 M KOH solution, we modify the obtained Co-Fe-P-1.7 on the Ni line and act as an anode and a cathode for water decomposition in a two-electrode system, with a full water decomposition voltage of 1.60 V at a current density of 10 m A/ cm-2, The above research has provided the experimental reference and the research thinking for the development of efficient MOFs-based bifunctional catalyst. Co Fe-MOF-74 (Co Fe-MOF-74) was synthesized by hydrothermal method, and the effect of different Fe doping amount on the oxygen evolution of Co Fe-MOF-74 was compared. It is found that the combined catalyst has good water decomposition property, which provides the experimental reference and the research idea for the development of efficient MOFs-based oxygen evolution catalyst.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2
【参考文献】
相关期刊论文 前1条
1 宋国强;王志清;王亮;李国儒;黄敏建;银凤翔;;MOF(Fe)的制备及其氧气还原催化性能[J];催化学报;2014年02期
，本文编号：2483360
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