同步辐射原位XAFS实验方法表征燃料电池催化剂在工作状态下的结构变化

发布时间：2018-02-10 21:14

本文关键词： PEMFC 原位 XAFS 催化剂结构变化　出处：《中国科学院研究生院(上海应用物理研究所)》2016年博士论文　论文类型：学位论文

【摘要】：质子交换膜燃料电池(PEMFC)由于其构造简单,能量密度高,能量转化效率高,环境友好等优点,作为化学电源被广泛的应用。在氢-氧PEMFC中,氢阳极的反应速率很快,阳极纳米Pt/C催化剂具有很高的催化活性和稳定性,氧阴极的反应速率较慢,氧电极的电势更负,因此如何提高燃料电池的阴极催化剂活性并且降低催化剂的成本,成为燃料电池的研究热点之一。Pt具有催化活性高和稳定性好是质子交换膜燃料电池最常用的催化剂,但是Pt催化剂高昂的成本、较短的使用寿命极大地阻碍了其大规模的商业应用。在Pt中掺杂非贵金属元素如Fe、Co、N i等,有助于提高Pt催化剂的稳定性和催化活性,同时也减少Pt的使用量,降低燃料电池的成本。但是在催化反应过程中,Pt中掺杂的另外一种组分增强Pt的催化反应机理尚不完全清楚。基于同步辐射的X射线吸收精细结构(XAFS)方法具有元素特征选择性,可以分别获得燃料电池双金属纳米催化剂中两种金属原子的局域几何结构和电子结构,同时该方法也适合研究原位条件下燃料电池催化剂的结构变化,可以与透射电镜(TEM)和X射线衍射(XRD)其它表征技术联用,提供更丰富的结构信息,包括价态、配位数、键长等。本文依托上海同步辐射装置(SSRF),在BL14W1线站开展了燃料电池催化剂的原位XAFS方法研究,发展了燃料电池催化剂的原位XAFS实验方法,同时结合一系列的非原位表征方法如TEM、XRD、XAFS等,系统的研究了Pt基双金属纳米催化剂在催化反应过程中的结构变化,以及双金属组分在催化反应过程中的相互作用关系。主要的研究内容和结果如下:(1)依托上海光源X射线吸收精细结构谱学线站B L14W1,建立并发展了用于氢-氧PEMFC原位XAFS实验的测试装置,以Pt/C纳米催化剂作为PEMFC的阴极催化剂,Pd/C作为燃料电池的阳极催化剂,采集在工作状态下的阴极催化剂的XAFS数据,同步监测燃料电池的C-V曲线和功率密度曲线,观察到Pt/C催化剂在反应过程中不同电位下氧化态的变化,在高电位下Pt/C催化剂的表面存在较强的Pt-O键,Pt-O键的存在降低了Pt/C催化氧化还原反应(ORR)的活性,该研究同时也验证了我们所建立的实验装置和研究方法的可行性和可靠性.(2)利用已经建立的原位X AFS方法表征了三种商业燃料电池催化剂:HS-Pt/C,JM-Pt/C,JM-Pt Ru/C。随着电压的逐渐降低,HS-Pt/C和JM-Pt/C在催化反应过程中都逐渐被还原,但是JM-Pt Ru/C在高电位时逐渐被还原,在低电位逐渐被氧化。影响催化活性的关键因素是零价态Pt的含量,Pt-O键的存在能够抑制Pt/C催化剂的活性,Ru的存在没有增强Pt催化ORR的活性,反而占据了Pt的催化剂活性中心,导致JM-Pt Ru/C催化剂的活性下降。(3)在Pt中掺杂过渡金属元素C o形成的Pt C o/C双金属纳米催化剂,与商业Pt/C催化剂相比,由于Co的存在能够影响Pt的氧化程度,使得金属Pt晶格变小,Pt-Pt键长缩短,导致Pt Co/C具有更小的纳米尺寸,减小了Pt-Pt键之间的距离,从而提高Pt Co/C纳米催化剂中Pt的催化活性。过渡金属Co有比Pt更多的d带空位,原位XAFS实验揭示了Pt Co/C在催化反应过程中Pt的d电子向过渡金属Co的转移过程,Pt的d带空位的增加,有利于提高Pt催化O RR反应的性能。综上所述,本文依托上海光源X射线吸收谱学线站BL14W1搭建了原位燃料电池催化剂实验测试装置,优化了实验条件,实现了在线XAFS数据的采集。建立了包括测试装置的研制搭建、测试技术的优化、在线数据的采集分析在内的用于PEMFC催化剂结构研究的一套原位XAFS实验方法,为国内相关研究领域的科研人员利用上海光源开展燃料电池原位XAFS研究提供了新的方法。
[Abstract]:Proton exchange membrane fuel cell (PEMFC) because of its simple structure, high energy density, high energy conversion efficiency, environment friendly and other advantages, is widely used as chemical power. In hydrogen oxygen PEMFC, the reaction rate of hydrogen anode quickly, anode nano Pt/C catalyst has high catalytic activity and stability, reaction the rate of oxygen, the oxygen electrode potential is more negative, so how to improve the fuel cell cathode catalyst activity and reduce the cost of the catalyst, the fuel cell become one of research hotspots of.Pt has a high catalytic activity and stability are good catalysts for proton exchange membrane fuel cell is the most commonly used, but the Pt catalyst is high cost, short the service life greatly hindered the large-scale commercial applications. Doping in Pt non noble metal elements such as Fe, Co, N, I etc., is helpful to improve the stability and catalytic activity of Pt catalyst, at the same time Also reduce the amount of use of Pt, reduce the cost of fuel cells. But during the catalytic reaction of Pt doped in another component to enhance the catalytic reaction mechanism of Pt is still not entirely clear. The synchrotron radiation X ray absorption fine structure (XAFS) method is selected based on element characteristics, can obtain geometric local structure and the electronic structure of two kinds of fuel cell Nanobimetallic catalyst in metal atoms respectively at the same time, this method is also suitable for changes in the structure of fuel cell catalyst of in situ conditions, and transmission electron microscopy (TEM) and X ray diffraction (XRD) combined with other characterization techniques, provide more structure information, including the valence states. The coordination number and bond length. This paper is based on the Shanghai synchrotron radiation facility (SSRF), the station carried out research on the method of in situ XAFS fuel cell catalyst in the BL14W1 line, the development of in situ XAFS experimental method of fuel cell catalyst, At the same time, combined with a series of in situ characterization methods such as TEM, XRD, XAFS, and systematic study of the structural change of Pt based bimetallic catalysts in the catalytic reaction in the process of interaction between the two metal components and the catalytic reaction process. The main research contents and results are as follows: (1) based on the Shanghai light source X ray absorption fine structure spectrum line station B L14W1, set up and test device for hydrogen oxygen PEMFC in situ XAFS experimental development, with nanometer Pt/C as cathode catalyst PEMFC, Pd/C as the anode catalyst of fuel cell, XAFS data collection of cathode catalyst in the working condition, the synchronous monitoring of fuel the battery of C-V curve and power density curve, observed changes in oxidation state under different potentials of Pt/C catalyst in the reaction process, the high potential surface of Pt/C catalyst has strong Pt-O bonds, Pt-O bonds are falling Low Pt/C catalytic oxidation reduction reaction (ORR) activity, the study also verified the feasibility and reliability of experimental apparatus and research method established by us. (2) by in situ X AFS method has been established to characterize three kinds of commercial fuel cell catalyst: HS-Pt/C, JM-Pt/C, JM-Pt, Ru/C. gradually decreases with voltage HS-Pt/C, and JM-Pt/C in the catalytic reaction process was gradually reduced, but the JM-Pt Ru/C was gradually reduced in high potential, low potential is gradually oxidized. The key factors affecting the catalytic activity of the content is zero valence state of Pt, the presence of Pt-O bonds can inhibit the activity of Pt/C catalyst, Ru had no obvious enhancement of Pt catalyst the activity of ORR, but occupy the active centers of the catalyst Pt, resulting in a decline in the activity of the catalyst. JM-Pt Ru/C (3) Pt C o/C bimetallic catalyst for the formation of doping transition metal element C o in Pt, and commercial Pt/C Compared with the catalyst, due to the presence of Co can affect the degree of oxidation of Pt, makes the metal lattice Pt Pt-Pt smaller, shorten the bond length, resulting in Pt Co/C has a smaller nano size and reduced the Pt-Pt distance between the keys, so as to improve the catalytic activity of Pt catalyst in Co/C nano Pt. There are more than Pt d with vacancy transition metal Co, XAFS in situ experiments revealed that Pt Co/C during the catalytic reaction of Pt d to the electronic transfer process of transition metal Co, D increased with Pt vacancy, is beneficial to improve the catalytic performance of Pt O RR reaction. In summary, this paper relies on the Shanghai light source X ray absorption spectroscopy in situ fuel line station BL14W1 the battery test device of catalyst structures, the experimental conditions were optimized to achieve online XAFS data acquisition was established. The development includes the testing device structures, optimization test technology, PEMFC catalyst for online data acquisition and analysis, A set of in-situ XAFS experimental methods for structural research, which provides a new method for researchers in the field of domestic research, using Shanghai light source to carry out in situ XAFS research of fuel cell.

【学位授予单位】：中国科学院研究生院(上海应用物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O643.36;TM911.4

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