贵金属纳米晶合成及其性能研究

发布时间：2018-08-08 19:50

【摘要】：作为化石能源的替代，燃料电池的产业化是全球的梦想。至今为止，Pt仍被认为是燃料电池的氧化和还原反应中最有效的电催化剂。然而，Pt对CO的低的抗毒性以及其高的成本限制了其广范应用。作为一个更有希望的方式，Pt-M双金属电催化剂由于协同效应，常显示超过其母体金属的电子和化学性能。这为具有增强选择性、活性、稳定性的新的电催化剂的开发提供了机会。例如，在以Xia小组先驱合成Pd@Pt之后，由于其优越的性能，双金属核/壳粒子的制备被研究者关注，也涌现出了诸多核-壳粒子的报道。但是目前为止，制备这种结构相对单金属是很困难的，由金属盐的还原速度不同而导致的复杂的合成条件。不仅如此，另外，在合成过程中所使用的结构诱导剂，由于其对金属晶面非常牢固的吸附性，后期难以去除。这使得合成的催化剂活性都不能达到预期的效果。针对以上问题，急需开发一种简单可行的，不使用结构诱导剂的制备高性能金属催化剂的合成方法。因此我们采取紫外光还原合成金属纳米粒子，不使用任何表面活性剂或结构诱导剂，通过自组装合成Pt纳米花和Pd@Pt双金属催化剂，呈现出优异的催化性能。利用银镜反应原理，使用葡萄糖作为还原剂还原氯金酸，在表面活性剂存在条件下制备单分散Au纳米粒子，使用紫外-可见光谱研究了在反应体系中添加表面活性剂对于所制备产物的形貌尺寸，稳定性产生的影响。结果表明，阴离子及非离子表面活性剂的添加有利于减缓银镜反应速度，阴离子型表面活性剂体系可获得尺寸为15nmAu纳米粒子簇，能获得一定的分散性；在非离子型表面活性剂体系中可获得5-10nm球形Au纳米粒子，分散性较好。这有望成为Au晶种合成其他双金属和多金属催化剂。通过一种简单，易操作的光诱导方法合成Pt纳米花状结构，并呈现出较好的甲醇氧化性能。在紫外光作用下，实验体系中不添加任何表面活性剂和结构诱导剂，用甲醇作还原剂还原H2PtCl6溶液，获得Pt纳米花状结构，通过调节甲醇与水的比例，甲醇的替代品，光强参数，前驱体的浓度得到最佳的实验参数来研究Pt纳米花形成因素，同时也研究随时间变化形貌的进化过程推断Pt纳米花形成机理。最后对甲醇催化性能的表征，，呈现出较高的催化活性：在酸性介质中Pt纳米花结构质量比活性是商业Pt/C的2.3倍，是商业Pt黑的3.9倍；在碱性介质中Pt纳米花结构的质量比活性是商业Pt/C的2.8倍，是商业Pt黑的5倍。在单金属基础上，我们研究Pd@Pt双金属催化剂的制备条件及甲醇催化性能的表征。首先对Pd晶种合成条件的调控，得到最佳合成晶种的条件，然后以Pd晶种为核，研究Pd@Pt合成的最佳实验条件，并调查前驱体量对形貌的影响，通过对随时间变化形貌的变化，推断出直接光照，甲醇还原金属纳米粒子的形成机理。另外借助XPS对催化剂表面价态和元素分布的调查。进一步验证最佳实验条件下得到的Pd@Pt具有高的催化活性和稳定性：在酸性介质中Pd@Pt纳米结构质量比活性是Pt纳米花结构的2.7倍，是商业Pt/C的6.4倍，是商业Pt黑的10.5倍；在碱性介质中Pd@Pt纳米结构的质量比活性是Pt纳米花结构的2.5倍，商业Pt/C的7.1倍，是商业Pt黑的12.5倍。
[Abstract]:As an alternative to fossil fuels, the industrialization of fuel cells is a global dream. Up to now, Pt is still considered the most effective electrocatalyst in the oxidation and reduction reactions of fuel cells. However, the low toxicity of Pt to CO and its high cost limit its wide application. As a more promising way, Pt-M bimetal electrocatalysis As a result of synergistic effects, it often displays the electronic and chemical properties that exceed the parent metal. This provides an opportunity for the development of a new electrocatalyst with enhanced selectivity, activity and stability. For example, the preparation of bimetallic core / shell particles has been paid attention to by the preparation of the Xia group precursor and the preparation of the bimetallic core / shell particles. There are many reports of nuclear shell particles. But so far, it is difficult to prepare this structure relative to the single metal, which is complicated by the different reduction rate of metal salts. In addition, the structural inducer used in the synthesis process is difficult to make in the later period because of its very strong adsorbability to the metal surface. Removal, which makes the catalytic activity of the synthesized catalyst fail to achieve the desired effect.
In view of the above problems, it is urgent to develop a simple and feasible synthesis method for the preparation of high performance metal catalysts without using structural inducers. Therefore, we adopt UV reduction to synthesize metal nanoparticles without any surface active agent or structural inducer, and present the synthesis of Pt nanoscale and Pd@Pt bimetallic catalysts by self assembled synthesis. Excellent catalytic performance.
Using the principle of silver mirror reaction, using glucose as reducing agent to reduce chlorosanic acid and the preparation of monodisperse Au nanoparticles under the presence of surfactants, the effects of adding surfactants on the morphology and stability of the prepared products in the reaction system are studied by UV visible spectra. The addition of ionic surfactants is beneficial to slow down the reaction speed of silver mirror. The anionic surfactant system can obtain the size of 15nmAu nanoparticles, which can obtain a certain dispersion. The 5-10nm spherical Au nanoparticles can be obtained in the nonionic surfactant system, and the dispersibility is better. This is expected to be the other double gold of the Au crystal. Genera and polymetallic catalysts.
The Pt nano flower structure was synthesized by a simple and easy to operate light induction method, and showed better methanol oxidation performance. Under ultraviolet light, no surfactant and structural inducer was added to the experimental system. The H2PtCl6 solution was reduced with methanol as a reductant, and the Pt nanostructure was obtained. The ratio of methanol to water was adjusted by adjusting the ratio of methanol to water. For example, the substitution of methanol, the light intensity parameters, the concentration of the precursor obtained the best experimental parameters to study the formation factors of Pt nanoscale, and also study the formation mechanism of Pt nanoscale with the evolution of the temporal change morphology. Finally, the catalytic activity of methanol shows a higher catalytic activity: the Pt nanoscale in the acid medium. The mass ratio activity is 2.3 times that of commercial Pt/C, 3.9 times as much as commercial Pt black, and the mass ratio of Pt nanoscale in alkaline medium is 2.8 times that of commercial Pt/C, and 5 times of commercial Pt black.
On the basis of single metal, we studied the preparation conditions of Pd@Pt bimetallic catalysts and the characterization of the catalytic performance of methanol. First, the conditions for the synthesis conditions of Pd crystals were regulated and the conditions for the optimum synthetic crystal species were obtained. Then the optimum experimental conditions for the synthesis of Pd@Pt were studied with the Pd crystal seed as the core, and the influence of the precursor volume on the morphology was investigated. The formation mechanism of direct illumination and methanol reduction of metal nanoparticles was deduced. In addition, the investigation of the surface valence and element distribution of the catalyst by XPS was used to further verify the high catalytic activity and stability of the Pd@Pt under the best experimental conditions: the mass ratio of Pd@Pt nanostructures in the acid medium was Pt 2.7 times the structure of the nanoscale, 6.4 times the commercial Pt/C and 10.5 times the commercial Pt black. The quality of the Pd@Pt nanostructure in the alkaline medium is 2.5 times more than the structure of the Pt nanometers, 7.1 times the commercial Pt/C, and 12.5 times the commercial Pt black.
【学位授予单位】：浙江理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TB383.1

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