纳米合金材料的制备及电催化甲醇和甲酸氧化性能研究

发布时间：2018-01-15 09:35

本文关键词：纳米合金材料的制备及电催化甲醇和甲酸氧化性能研究　出处：《南开大学》2014年博士论文　论文类型：学位论文

【摘要】：能源将是二十一世纪人类所面临的最大的挑战。随着氢能源消耗的增长,关于储氢和燃料电池的研究正在增多。在燃料电池的许多类型中,其中有一类是质子交换膜燃料电池,由于其污染小,能量密度高和低温操作,已经成为移动设备和便携设备的高效能源供给。质子交换膜燃料电池可以将储存在燃料分子的化学能转化为电能。在具体操作中,氧气从阴极供给,并且随着燃料分子在阳极低电位下的氧化而发生电化学还原反应。根据所用燃料的不同,质子交换膜燃料电池又被划分为直接氢燃料电池,直接甲醇燃料电池,和直接甲酸燃料电池等。目前,由于氢气储存比较难,价格也相对昂贵,所以对直接甲醇和甲酸燃料电池研究的比较多。铂基纳米颗粒被用作几乎所有燃料电池电极表面的电催化剂,但是铂基催化剂很容易被反应的中间体类CO物质所毒化。本论文将围绕催化剂的载体和反应活性中心两方面来展开研究工作,我们合成了Pt-基和Pd-基催化剂,并且利用X-射线衍射(XRD),场发射扫描电镜(FE-SEM),透射电镜(TEM),X射线光电子能谱(XPS),高角环形暗场像-扫描透射电子显微镜(HAADF-STEM)等表征技术,研究了质子交换膜燃料电池催化剂的合成及其电催化应用。论文主要内容分为三部分： (1) Pt-Cu二元壳核纳米合金催化剂的合成及其对甲醇反应的影响 Pt-Cu二元纳米晶体由于其较高的抗一氧化碳中毒性和自然界中丰富的Cu资源成为较有效的催化剂。通过电势替代法合成了PtCu3, PtCu2, PtCu, Pt3Cu纳米壳核结构,XRD表征得到Pt与Cu的边延部分形成了合金,并且随着Pt:Cu比的增加,合金化程度也越大。HAADF-STEM的结果得到Pt-Cu纳米颗粒成壳核结构,而且核主要是Cu元素,表面是丰富的Pt元素,并且是沿着Cu外延生长的。将PtCu3, PtCu2, PtCu和Pt3Cu纳米颗粒负载在碳黑上,研究其对甲醇的催化活性,发现PtCu2/C在甲醇氧化实验中表现了超强的电催化活性。在0.75V(参比于可逆氢电极,RHE)PtCu2/C质量和面积比活性是604.8mA mg-1Pt和9.4Am-2,这分别是工业商用催化Pt/C的3.3和4.1倍,其中商用催化剂的质量和面积比活性分别是185.5mA mg-1pt和2.3A m-2。甲醇氧化活性的提高可能由于Pt与Cu的协同作用及形成的壳核结构有关。 (2)铂基三元合金催化剂的合成及其对甲醇和甲酸电催化氧化反应的影响在氮气下,利用硼氢化钠还原法得到了碳载单金属Pt/C, Pd/C, Co/C双金属PtPd/C, PtCo/C, PdCo/C和不同比例的三金属PtPdCo/C催化剂,并且通过对每种催化剂做电化学测试得到了Pt, Pd和Co的最优比例。研究了他们的电催化甲醇和甲酸氧化反应,最后得到Pt0.35Pd0.35Co0.3/C的电催化甲醇和甲酸反应活性最高。得到的材料分别用X射线衍射(XRD),透射电镜(TEM)和X射线光电子能谱(XPS)做了表征。合金中三种金属的比例用原子吸收光谱得到了结果。XRD和XPS证明PtPdCo形成了三元合金,TEM图得出Pt0.35Pd0.35Co0.3合金平均粒径为2nm,粒径均匀,并高度均匀地分散在碳载体上,适合做电催化的催化剂。 (3) PdAu/graphene催化剂的制备及其对甲酸电催化反应的影响我们发明了一种新颖的,简便的,快捷的化学还原法把PdAu纳米粒子高效地负载到PAC功能化的氧化石墨烯表面上。即在PAC功能化的氧化石墨烯溶液中加入Na2PdCl4和HAuCl4混合液,通过NaBH4原位还原成PdAu合金纳米枝。XRD及HAADF-STEM证明PdAu形成了稳定的合金,而且PdAu合金成功地负载在石墨烯上了。通过催化剂性能的测试,合成的PdAu/graphene催化剂电化学活性比表面积增大了,对甲酸电催化氧化反应也有很高的活性。在甲酸电催化实验中,PdAu/graphene催化剂的活性是Pd/graphene和Pd/C催化剂的3.2和5.1倍。PdAu/graphene在碱性条件下对甲醇的电催化氧化活性与Pd/C相比,催化活性也有提高。最后我们对PdAu/graphene,Pd/graphene和Pd/C催化剂对CO的电催化活性进行了测试,通过对比,发现PdAu/graphene催化剂的氧化电位和起始电位都负移了,加快了CO的氧化过程,进一步证明了PdAu/graphene催化剂较高的电催化氧化甲酸活性。
[Abstract]:The energy will be the biggest challenge facing humanity in twenty-first Century. With the increase of energy consumption of hydrogen, research on hydrogen storage and fuel cell is increasing. In many types of fuel cell, in which a kind of proton exchange membrane fuel cell, because of its low pollution, high energy density and low temperature operation, has become a mobile equipment and portable equipment and efficient energy supply. The proton exchange membrane fuel cell can store energy into electrical energy in the chemical fuel molecules. In operation, the supply of oxygen from the cathode, and with the oxidation of fuel molecules at the anode low potentials and electrochemical reduction reaction. According to the different proton exchange fuel. Membrane fuel cell is divided into direct hydrogen fuel cell, direct methanol fuel cell, and direct formic acid fuel cells. At present, the hydrogen storage is more difficult, the price is also expensive to, So for direct methanol and formic acid fuel cell research more. Pt based nanoparticles are used as almost all surface electrode for fuel cell electrocatalysts, but platinum catalysts can easily be reaction substance CO intermediate class poisoning. This paper will focus on two aspects of the support and the reaction active center of catalyst to carry out the research work, we the synthesis of Pt- based and Pd- based catalyst, and using X- ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X ray photoelectron spectroscopy (XPS), high angle annular dark field image scanning transmission electron microscopy (HAADF-STEM) characterization, synthesis of proton exchange membrane fuel cell catalyst and its application in electric catalysis. The main content of this thesis is divided into three parts:
(1) synthesis of Pt-Cu two element shell nanoscale catalyst and its effect on the reaction of methanol
Pt-Cu two nano crystal catalyst due to effective Cu become rich in carbon monoxide poisoning and its anti nature high. PtCu3, synthesized by potential substitution method PtCu2, PtCu, Pt3Cu nano core-shell structure, obtained by XRD Pt and Cu edge extension part formed alloy, and with the Pt:Cu ratio increases. The greater the degree of alloying of.HAADF-STEM obtained Pt-Cu nanoparticles into core-shell structure, and nuclear Cu is the main element, the surface is rich Pt elements, and grow along the Cu extension. PtCu3, PtCu2, PtCu and Pt3Cu nanoparticles supported on carbon, study the catalytic activity of methanol, found PtCu2/C showed superior electrocatalytic activity for methanol oxidation in the experiment. In the 0.75V (reference to the reversible hydrogen electrode, RHE) PtCu2/C quality and area ratio is 604.8mA mg-1Pt activity and 9.4Am-2, which are Pt/C commercial industrial catalysis The 3.3 and 4.1 times of the commercial catalyst's mass and area specific activity are 185.5mA mg-1pt and 2.3A m-2. respectively. The increase of methanol oxidation activity may be related to the synergistic effect of Pt and Cu and the formation of putamen structure.
(2) synthesis of platinum based three element alloy catalyst and its effect on the electrocatalytic oxidation of methanol and formic acid
Under nitrogen, using sodium borohydride reduction method of the carbon supported single metal Pt/C, Pd/C, Co/C, PtCo/C, PtPd/C double metal, three metal PtPdCo/C catalyst PdCo/C and different proportion, and through the electrochemical test for each catalyst was Pt, the optimal ratio of Pd and Co. Their catalytic activity for methanol electro and the oxidation of formic acid, methanol and formic acid electro catalytic and finally get the highest activity of Pt0.35Pd0.35Co0.3/C. The materials were obtained by X ray diffraction (XRD), transmission electron microscopy (TEM) and X ray photoelectron spectroscopy (XPS) have been characterized. Three kinds of metal alloy in the proportion of the results of.XRD and XPS PtPdCo the formation of three element alloy by atomic absorption spectroscopy, TEM obtained Pt0.35Pd0.35Co0.3 alloy with an average diameter of 2nm, uniform particle size, uniform and highly dispersed on the carbon support, suitable for catalyst electrocatalytic.
(3) preparation of PdAu/graphene catalyst and its effect on the electrocatalytic reaction of formic acid
We have developed a novel, simple, fast chemical reduction method to load PdAu nanoparticles efficiently to graphene oxide surface functionalization of PAC. Adding Na2PdCl4 and HAuCl4 mixture in graphene oxide solution functionalization of PAC, reduced to PdAu.XRD and HAADF-STEM alloy nano branch that PdAu form stable alloy by in situ NaBH4 and PdAu alloy was successfully supported on graphene. Through the catalyst performance test, electrochemical synthesis of PdAu/graphene catalyst activity increase the surface area, also has very high activity for electrocatalytic oxidation of formic acid in formic acid electrocatalytic reaction. In the experiment, the activity of PdAu/graphene catalyst is 3.2 and 5.1 times.PdAu/graphene Pd/graphene and Pd/C catalysts under alkaline conditions on methanol electrocatalytic activity compared with Pd/C, the catalytic activity is improved. Finally we PdAu/gra Phene, Pd/graphene and catalytic activity of Pd/C catalysts for CO were measured, by contrast, found that the oxidation potential and the onset potential of PdAu/graphene catalyst shifted negatively, accelerate the oxidation process of CO, further proved that PdAu/graphene catalyst high electrocatalytic oxidation of formic acid activity.

【学位授予单位】：南开大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O643.32;TM911.4

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