若干种燃料电池催化剂的浸渍法制备及相关电催化研究

发布时间：2018-04-21 06:42

本文选题：燃料电池 + 催化剂　；参考：《武汉大学》2010年博士论文

【摘要】： 燃料电池具有高效、清洁等优点,被认为是未来的备选能源之一。以氢为燃料的质子交换膜燃料电池(PEMFC)已经达到相当高的技术水平,但氢气储运的困难和安全问题成为其商品化的主要障碍。研究者们在企图解决这一问题的同时,开始寻求新的燃料,直接甲醇燃料电池(DMFC)和直接甲酸燃料电池(DFAFC)成为研究的热点。Pt/C、PtRu/C和Pd/C是上述三种燃料电池最常用的催化剂。无论何种燃料电池,都需要适于规模生产的高效电催化剂的制备方法。本论文工作对最适合批量生产的浸渍法进行较全面的研究,探究控制催化剂品质的关键,最终获得了高分散的PtRu/C、Pt/C和Pd/C催化剂,并对其物理化学性质及相关电催化进行了研究。主要的工作内容与结论如下： 1、高分散、高载量PtRu/C催化剂的浸渍法制备及表征发展了一种简单的易实现规模化制备的催化剂合成方法,整个过程由“浸渍-干燥-氢气还原”三个步骤构成,无需过滤洗涤。即便采用含Cl-前驱体,也可获得分散度很高的金属载量为60wt%的PtRu/C催化剂。TEM分析表明,所制60wt%PtRu/C的金属粒径为1.5±0.5nm；通过EDAX, XRD, XPS和TGA/DTA等分析发现,制备的PtRu/C催化剂中含PtRu合金与非晶态RuOxHy。电催化研究表明,所制PtRu/C对甲醇氧化具有优越的性能,可能与催化剂中含非晶态RuOxHy有关。 2、PtRu/C催化剂的热重分析热重分析(TGA)是文献中用于指认PtRu催化剂中RuOxHy组分的常用实验方法,通常将150-600℃下的催化剂失重归结为RuOxHy的失水。我们通过TG-FTIR联用分析发现,在上述温度区间催化剂失重的主要产物是C02,没有发现可以检测的H2O。因此此温度范围内催化剂的失重应该归因于碳载体在PtRu催化下的氧化,而且氧的来源主要是催化剂中Pt表面的氧与氧化钌中的氧。此研究对PtRu/C催化剂的热重行为产生了不同于文献的认识,TGA并非分析PtRu/C催化剂中非合金钌组分的有效方法。 3、高分散Pt/C催化剂的浸渍法制备对Pt/C催化剂浸渍法制备过程中的关键实验参数进行探究,发现获得高分散Pt/C催化剂的关键因素包括：(1)采用大比表面积的载体有利于获得小粒径的Pt/C。(2)热浸渍和超声结合搅拌是我们的方法与传统浸渍法的重要区别,也是获得高分散Pt/C的关键。(3)氢气还原的温度须控制在80-150℃之间,过高的还原温度导致Pt粒径增大。(4)浸渍后凝胶态的含水量对Pt粒径有影响,水碳质量比在5-20范围内,催化剂的粒径为2.5nm左右。 4、Pd/C催化剂的浸渍法制备以PdCl2为前体,采用浸渍法制备Pd/C催化剂很难获得高的分散度。研究发现,Cl-的存在和还原气体的种类是影响Pd/C粒径的两大因素。采用Pd(NO3)2为前体,并以Ar+H2混合气或CO代替纯氢气作为还原剂,可以显著提高Pd/C催化剂的分散度。优化条件下制得的20wt%Pd/C的Pd粒径为3.5nm,10wt%Pd/C的Pd粒径为2.7nm。 5、Pd/C催化剂的电催化粒度效应研究对粒径分别为2.7、3.5、4.7、6.1、8.1nm的Pd/C催化剂进行氢氧化、氧还原、甲酸氧化等反应的粒度效应研究。结果表明,Pd粒径越小,催化剂与氧原子结合力越强,氧还原反应动力电流密度随着粒径增大而提高。对于氢氧化反应,随着粒径增加,反应交换电流密度增大；4.7nm Pd/C的氢氧化交换电流密度为0.21mAcm-2,约为Pt的百分之一。对于甲酸氧化反应,4.7nm的Pd/C催化剂具有最高的质量比活性和面积比活性。
[Abstract]:Fuel cells have the advantages of high efficiency and cleanliness, which are considered to be one of the future alternative energy sources. Proton exchange membrane fuel cells (PEMFC) with hydrogen as fuel have reached a high level of technology, but the difficulties and safety problems of hydrogen storage and transportation have become the main obstacle to its commercialization. In search of new fuel, direct methanol fuel cell (DMFC) and direct formic acid fuel cell (DFAFC) have become the hot.Pt/C of the research. PtRu/C and Pd/C are the most commonly used catalysts for these three fuel cells. All kinds of fuel cells need a preparation method suitable for large-scale production of high-efficiency electrocatalytic agents.
In this paper, the most suitable impregnation method for mass production is studied in a more comprehensive way. The key to control the quality of the catalyst is studied. The highly dispersed PtRu/C, Pt/C and Pd/C catalysts are finally obtained. The physical and chemical properties and related electrocatalysis are studied. The main work internal capacity and conclusion are as follows:
1. Preparation and characterization of highly dispersed and highly loaded PtRu/C catalyst by impregnation method
A simple and easy to realize synthesis method of catalyst is developed. The whole process is composed of three steps of "impregnation - drying - hydrogen reduction". No filtration is needed. Even using Cl- precursor, a PtRu/C catalytic agent with high dispersive metal load of 60wt% can also be obtained. The analysis of 60wt%PtRu/C metal The particle size is 1.5 + 0.5nm. Through the analysis of EDAX, XRD, XPS and TGA/DTA, it is found that the electrocatalysis of PtRu alloy and amorphous RuOxHy. in the prepared PtRu/C catalyst shows that the prepared PtRu/C has superior performance to methanol oxidation and may be related to amorphous RuOxHy in the catalyst.
Thermo gravimetric analysis of 2, PtRu/C catalyst
Thermogravimetric analysis (TGA) is a common experimental method used in the identification of RuOxHy components in PtRu catalysts in the literature. Usually, the weight loss of catalyst at 150-600 C is attributed to RuOxHy's loss of water. Through TG-FTIR combined analysis, we found that the main product of the weight loss of the catalyst at the above temperature range is C02, and the detected H2O. is not found so this temperature is found. The weight loss of the catalyst in the range should be attributed to the oxidation of the carbon carrier under the catalysis of PtRu, and the source of oxygen is mainly the oxygen on the Pt surface in the catalyst and the oxygen in the ruthenium oxide. This study is different from the literature on the thermogravimetric behavior of the PtRu/C catalyst. TGA is not an effective method for the analysis of the unalloyed ruthenium components in the PtRu/C catalyst.
3, preparation of highly dispersed Pt/C catalyst by impregnation method
The key experimental parameters in the preparation process of Pt/C catalyst impregnation method are explored, and the key factors for obtaining highly dispersed Pt/C catalysts include: (1) the important difference between our method and the traditional impregnation method is the important difference between our square method and the traditional impregnation method by using the carrier of large specific surface area to obtain the small particle size Pt/C. (2) and the ultrasonic combined agitation. The key to dispersing Pt/C. (3) the temperature of hydrogen reduction must be controlled at 80-150 degrees C, and the high reduction temperature leads to the increase of the particle size of the Pt. (4) the water content of the gelation state after impregnation has an effect on the particle size of Pt, and the water carbon mass ratio is within the range of 5-20, and the particle size of the catalyst is about 2.5nm.
4, preparation of Pd/C catalyst by impregnation method
It is difficult to obtain high dispersion by using PdCl2 as precursor to prepare Pd/C catalyst by impregnation. It is found that the existence of Cl- and the type of reducing gas are two factors affecting the particle size of Pd/C. Using Pd (NO3) 2 as the precursor and using Ar+H2 mixture or CO instead of pure hydrogen as a reductant, the dispersion of the Pd/C catalyst can be significantly improved. The diameter of Pd prepared by 20wt%Pd/C is 3.5Nm, and the diameter of 10wt%Pd/C Pd is 2.7nm..
Study on the effect of 5, Pd/C catalyst on the particle size of electrocatalysis
The particle size effect of hydrogen oxidation, oxygen reduction, formic acid oxidation, and so on. The results show that the smaller the Pd particle size, the stronger the binding force of the catalyst with oxygen atoms, the increase of the kinetic current density of the oxygen reduction reaction with the increase of the particle size. For the hydrogen oxidation reaction, the reaction with the particle size increases. The exchange current density increases; the hydrogen peroxide exchange current density of 4.7nm Pd/C is 0.21mAcm-2, about one percent of Pt. For the oxidation of formic acid, the Pd/C catalyst of 4.7nm has the highest mass ratio activity and area specific activity.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2010
【分类号】：TM911.4

【参考文献】