基于高温热解金属有机框架化合物的氧还原电催化剂研究

发布时间：2018-05-24 11:40

本文选题：燃料电池 + 氧还原反应　；参考：《湖南大学》2015年硕士论文

【摘要】：质子交换膜燃料电池(PEMFCs)由于具有能量密度高、操作温度低和污染物排放量少的优势引起了人们的普遍关注,有望应用在便携式电子产品和交通工具中。阴极电催化剂作为燃料电池的核心部分,极大地影响电极反应的过电位,电化学反应的速率以及电池的输出电压和稳定性。目前应用最多的氧还原催化剂为碳材料负载铂基纳米粒子,由于催化剂具有价格昂贵,稳定性差以及无法克服“甲醇渗透”的缺点,因而无法实现质子交换膜燃料电池大规模的应用。本文以金属有机框架化合物(MOF)为前躯体,在氮气或氧气氛围中对不同类型的MOF进行热处理,得到了立方体状Co3O4与酸化碳管的复合材料(Co3O4/Ao-CN T)、氮掺杂的多孔石墨碳(NMGCs)以及包埋了铂纳米粒子(Pt NPs)的多面体介孔碳(Pt NPs@NMCs)。通过多种分析检测方法,对材料的微观形貌、晶体结构以及氧还原(ORR)性能进行研究。本论文的具体工作如下:(1)在ZIF-8配位生长的过程中,Pt N Ps连续吸附到生长的ZIF-8表面,ZIF-8配位结束以后,Pt NPs均匀镶嵌在整个ZIF-8内部。经过一步高温碳化,得到包埋了Pt NPs的氮掺杂多面体介孔碳(Pt NPs@NMCs)。通过SEM、TEM、XRD、XPS、Raman等分析方法对催化剂的表观形貌、晶体结构、孔隙分布以及元素组成进行了分析,并在0.5 M H2SO4溶液中考察了Pt N Ps@N MCs的电化学性能。结果表明,Pt NPs@NMCs的比表面积为1226 m2 g-1,孔径分布为3.9 nm,氮掺杂含量为5.4 At.%,粒径为3.7 nm的Pt NPs均匀分散在整个介孔碳材料内部。电化学测试结果表明,Pt NPs@NMCs除了能有效催化氧还原之外,还具有优异的稳定性和抗甲醇性能。(2)以钴基金属有机框架化合物ZIF-67为碳源、氮源和模板,在氮气中高温碳化,利用中心金属钴的催化作用形成了石墨结构的多孔碳材料(NMGCs)。利用SEM、TEM、XRD、BET和Rama n对N MGCs的形貌特征和晶体结构进行研究,并用CV、LSV和I-t测试方法考察了NMGCs在0.1 M KOH中的氧还原性能。结果表明,NMGCs保留了前驱物ZIF-67的多面体形貌、比表面积大(576 m2 g-1)、N掺杂含量多(6.14 wt.%)、尺寸均一(300 nm)、并且石墨化程度很高。氧还原测试结果表明,NMGCs按照直接四电子途径催化氧气还原,与Pt/C催化性能相当。此外,还具有优异的稳定性和抗甲醇性能。(3)在空气中直接氧化ZIF-67、酸化碳管与ZIF-67的复合物,制备了立方体状的Co3O4和Co3O4/Ao-CN T复合物催化剂。利用SEM、XRD、TGA对材料形貌结构进行了表征,用CV、LSV和I-t电化学测试技术研究了催化剂在0.1 M KOH中的氧还原催化性能。结果表明,与酸化碳管复合以后,Co3O4/Ao-CN T的电化学反应阻抗变小,催化ORR性能提高,起峰电位虽然比Pt/C负,但具有优异的稳定性和抗甲醇性能。
[Abstract]:Proton exchange membrane fuel cell (PEMFCs) has attracted much attention due to its advantages of high energy density, low operating temperature and low pollutant emission. It is expected to be used in portable electronic products and vehicles. As the core part of fuel cell, cathode electrocatalyst greatly affects the overpotential of electrode reaction, the rate of electrochemical reaction, the output voltage and stability of the cell. At present, the most widely used oxygen reduction catalyst is carbon material supported platinum-based nanoparticles, because the catalyst is expensive, stable and unable to overcome the shortcomings of "methanol permeation". Therefore, the proton exchange membrane fuel cell (PEMFC) can not be used on a large scale. In this paper, different types of MOF were heat-treated in nitrogen or oxygen atmosphere using organometallic frame compound (MOF) as precursor. Cubic Co3O4 and acidated carbon tube composites, such as Co _ 3O _ 4 / Ao-CN _ T, N-doped porous graphite carbon (NMGCs), and polyhedron mesoporous carbon (Pt-NPs) coated with platinum nanoparticles, have been obtained. The microstructure, crystal structure and ORR properties of the materials were studied by various analytical methods. The specific work of this thesis is as follows: (1) during the ZIF-8 coordination growth, Pt-NPs are continuously adsorbed to the surface of the grown ZIF-8 (ZIF-8). After the completion of the coordination, the Pt NPs is uniformly embedded in the whole ZIF-8. After one step of carbonization at high temperature, the nitrogen-doped polyhedron carbon oxide (PNPs) deposited in Pt NPs was obtained. The apparent morphology, crystal structure, pore distribution and elemental composition of the catalyst were analyzed by means of SEMTEMX Ps@N MCs Raman analysis. The electrochemical properties of Pt N Ps@N MCs were investigated in 0.5 M H2SO4 solution. The results show that the specific surface area of Pt NPs@NMCs is 1226 m ~ 2 g ~ (-1), the pore size distribution is 3.9 nm, the nitrogen doping content is 5.4At.and the particle size is 3.7nm Pt NPs is uniformly dispersed in the whole mesoporous carbon material. The electrochemical test results showed that Pt NPs@NMCs not only can effectively catalyze oxygen reduction, but also has excellent stability and methanol resistance. (2) Cobalt-based organometallic frame compound ZIF-67 was used as carbon source, nitrogen source and template as carbon source, and carbonized in nitrogen at high temperature. A porous carbon material with graphite structure was formed by the catalytic action of cobalt in the center. The morphology and crystal structure of N MGCs were studied by SEMTEMX RDET and Rama n, and the oxygen reduction properties of NMGCs in 0. 1 M KOH were investigated by CVLSV and I-t measurements. The results show that NMGCs retain the polyhedron morphology of the precursor ZIF-67, with a large specific surface area of 576 m ~ 2 g ~ (-1) and N doping content of 6.14 wt.The size is homogeneous to 300 nm ~ (-1), and the graphitization degree is very high. The results of oxygen reduction test showed that NMGCs catalyzed oxygen reduction by direct four-electron pathway, which was comparable to that of Pt/C. In addition, ZIF-67 was oxidized directly in air, and the complex of ZIF-67 and carbon tube was acidified. Cube-like Co3O4 and Co3O4/Ao-CN T complex catalysts were prepared. The morphology and structure of the catalyst were characterized by SEMX KOH TGA. The catalytic performance of the catalyst for oxygen reduction in 0. 1 M KOH was studied by CVN LSV and I-t electrochemical test techniques. The results show that the electrochemical reaction impedance of Co _ 3O _ 4 / Ao-CN _ T decreases, the catalytic ORR performance is improved, and the peak initiation potential is negative than that of Pt/C, but it has excellent stability and methanol resistance.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TM911.4

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