PtRu合金催化剂电催化氧化甲醇的催化作用机理

发布时间：2018-04-10 21:20

本文选题：直接甲醇燃料电池 + PtRu合金　；参考：《太原理工大学》2017年硕士论文

【摘要】：直接甲醇燃料电池(DMFC)因能量转换效率与比能量较高,甲醇来源丰富,洁净环保,可低温快速启动的优势,使其可成为未来便携式产品应用的主流。目前DMFC的能量转换效率和功率密度与理论值存在差异,究其根本,是因为催化剂活性和稳定性达不到理想要求。明确催化机理对催化剂的发展至关重要。催化机理的研究可为提高催化剂性能,改进催化剂制备方法提供理论依据。PtRu合金是目前公认稳定性、电化学活性最好的合金催化剂之一,但其电催化甲醇氧化的机理一直存在争议,阻碍了催化剂研究的进一步发展。目前研究者们主张双功能机理或主张电子效应机理,虽然这两种机理从不同的角度出发,能够阐明Pt基纳米合金的一些实验现象,各有一定的说服力,但也都存在不能说明的问题。因此本论文对PtRu合金催化剂电催化氧化甲醇催化机理做了进一步探索,并提出PtRu合金催化剂电催化氧化甲醇是电子效应与双功能机理协同作用,对Pt基纳米金属新型催化剂的研发提供新的依据。本文采用液相还原法和两步化学还原法分别制备了直径相近、Pt/Ru原子比例不同的合金型PtRu/C和核壳型Ru@Pt/C催化剂,通过XRD、TEM、EDS、XPS等物理技术手段,对催化剂的晶体结构、表面元素组成进行了物理表征,说明两种催化剂中Pt、Ru原子间的电子效应的存在及其强度。通过CV、EIS、CA等测试手段对催化剂的电化学性能进行了表征。对比分析表征结果,进一步探究了合金型PtRu/C催化剂电催化氧化甲醇的催化作用机理。TEM表征,EDS,XPS实测催化剂Pt/Ru原子比以及0.5 mol/L硫酸溶液中的循环伏安曲线共同说明,制备的两类催化剂均为球形,粒径约9~11nm,Ru@Pt/C催化剂为核壳结构,Pt Ru/C催化剂为合金结构。XRD结果显示,Pt0.33Ru1/C中Pt原子呈非晶态结构,Pt0.5Ru1/C中Pt原子存在非晶态结构趋势,Ru1@Pt0.33/C中Pt原子形成微晶薄膜。通过分析XRD和XPS的结果推断出两种催化剂均存在电子效应。Pt原子呈晶态结构时,随Pt原子比增大,两种催化剂电子效应强度均减小,其中Pt1Ru1/C,Ru1@Pt0.5/C在各自体系中电子效应强度最高,相同Pt/Ru原子比下,两种催化剂电子效应近似相同。循环伏安、交流阻抗、计时电流测试结果说明,当Pt原子呈晶态结构时,随Pt原子比增大,两种催化剂催化活性均减小,Pt1Ru1/C,Ru1@Pt0.5/C催化剂在各自催化体系中性能最佳,这与电子效应强度随Pt原子比增大而减小的变化规律相一致。当Pt原子呈非晶态或微晶结构时,两种催化剂催化性能减弱。PtRu/C催化剂催化甲醇氧化反应级数大于Ru@Pt/C催化剂,证明两种催化剂催化机理不同。相同Pt/Ru原子比下,PtRu/C催化剂催化性能远优于Ru@Pt/C催化剂,两者电子效应近似相同,证明PtRu/C催化剂存在Pt、Ru活性位的“双功能活性中心”促进作用。综合以上实验结果本论文得出以下观点:PtRu合金催化剂电催化氧化甲醇是电子效应与双功能机理协同作用。
[Abstract]:Direct methanol fuel cell (DMFC) has the advantages of high energy conversion efficiency and specific energy, abundant methanol source, clean and environmental protection, and can be started quickly at low temperature, which makes it become the mainstream of portable products in the future.At present, the energy conversion efficiency and power density of DMFC are different from the theoretical values. The fundamental reason is that the activity and stability of the catalyst can not meet the ideal requirements.It is very important to clarify the catalytic mechanism for the development of catalysts.The study of catalytic mechanism can provide theoretical basis for improving the performance of catalyst and improving the preparation method of catalyst. PtRu alloy is recognized as one of the most stable alloy catalysts with the best electrochemical activity.However, the electrocatalytic mechanism of methanol oxidation has been controversial, which hinders the further development of catalyst research.At present, researchers advocate the bifunctional mechanism or the electronic effect mechanism, although the two mechanisms can elucidate some experimental phenomena of Pt-base nanocrystalline alloys from different angles, and each of them is persuasive.But there are also problems that cannot be explained.In this paper, the electrocatalytic oxidation mechanism of methanol over PtRu alloy catalyst is further explored, and it is suggested that the electrocatalytic oxidation of methanol over PtRu alloy catalyst is a synergistic effect of electron effect and bifunctional mechanism.It provides a new basis for the research and development of Pt-based nano-metal catalysts.In this paper, alloy type PtRu/C and core-shell type PtRu/C catalysts with similar diameter of Pt / Ru atom ratio were prepared by liquid phase reduction method and two-step chemical reduction method. The crystal structure of the catalyst was studied by means of physical techniques such as XRDX Tem Tem EDS.The physical characterization of the composition of the surface elements indicates the existence and intensity of the electron effect between the two kinds of catalysts.The electrochemical properties of the catalyst were characterized by means of CVN EIS-CA and so on.The mechanism of electrocatalytic oxidation of methanol over alloyed PtRu/C catalyst was studied. Tem characterization showed that the atomic ratio of Pt/Ru and cyclic voltammetry in 0.5 mol/L sulfuric acid solution were measured by EDSXPS.By analyzing the results of XRD and XPS, it is inferred that the electron effect intensity decreases with the increase of Pt atom ratio when both catalysts have electron effect. The electron effect intensity of Pt1Ru1Ru1 / CnRu@ Pt0.5% C is the highest in their respective systems.At the same Pt/Ru atomic ratio, the electron effects of the two catalysts are approximately the same.This is consistent with the law that the electron effect intensity decreases with the increase of Pt atomic ratio.When Pt atoms were amorphous or microcrystalline, the catalytic performance of the two catalysts was weakened. The catalytic order of methanol oxidation over PtRu- / C catalyst was higher than that of Ru@Pt/C catalyst, which proved that the catalytic mechanism of the two catalysts was different.At the same Pt/Ru atom ratio, the catalytic performance of PtRu-C catalyst is much better than that of Ru@Pt/C catalyst, and the electron effect of both catalysts is approximately the same. It is proved that there exists a "bifunctional active center" in the catalytic activity of PTR Ru in PtRu/C catalyst.Based on the above experimental results, the following points are obtained: the electrocatalytic oxidation of methanol over the 1: PtRu alloy catalyst is a synergistic effect of electron effect and bifunctional mechanism.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TM911.4

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