导电高分子负载贵金属复合催化剂的制备及电催化性能研究

发布时间：2018-08-18 15:43

【摘要】：低温燃料电池作为一种绿色能源转换装置已被广泛应用于军事指挥、交通运输、无线电通讯、清洁电站、航天飞行、电动汽车、便携式移动电源等领域。尤其在环境与能源问题日益突出的今天，对于燃料电池进一步的研究与开发仍具有重大的社会意义与美好的应用前景。虽然部分燃料电池(如质子交换膜燃料电池)已经实现了实际应用，但其成本、工作性能、转换效率仍需进一步的改善。燃料电池电极上的催化剂材料(包括金属纳米粒子催化剂和催化剂载体)作为催化反应的活性中心，是燃料电池中最核心的部件之一，它性能的优劣直接影响着燃料电池的工作性能和转换效率。其中，催化剂载体作为金属纳米粒子的支撑材料，其结构与性能直接决定着金属催化剂颗粒的粒径大小、分散性、催化活性及稳定性。炭黑作为一种传统的燃料电池催化剂载体，具有较大的比表面积，然而其部分孔径太小，不能与反应液进行充分的接触，从而降低了催化剂的利用效率。另外，碳材料载体也容易被氧化腐蚀。因此，研究开发一种具有低成本、大比表面积、高稳定性的新型催化剂载体对于燃料电池电极催化剂材料的进一步发展十分有必要。由于其独特的物理与化学性能，导电高分子在燃料电池催化剂载体研究与应用中逐渐引起了研究者们的关注与重视。与传统的碳材料载体相比，导电高分子作为新型催化剂载体具有以下优点：1)易形成三维多孔结构，有较高的比表面积；2)通过官能团的引入，可对其结构及性能进行改进、调控；3)良好的电化学活性与高的抗氧化腐蚀能力；4)既能质子导电又能电子导电的特性。另外，导电高分子的引入会为电荷在其表面与金属催化剂间的传递提供低的欧姆电压降，从而有利于电荷的传输与转移；导电高分子较长的π电子共轭结构与金属纳米颗粒间会产生一定的电子效应，影响到金属纳米颗粒表面的电子分布，从而对其电催化活性及抗毒化性能产生影响。因此，导电高分子作为继碳材料之后的一种新型催化剂载体为低温燃料电池催化剂载体方面的研究开辟了一片新天地。本论文旨在设计、制备出几种具有优良性能的导电高分子，以此作为载体来负载贵金属催化剂Pt或Pd纳米颗粒，系统研究了所得催化剂对于甲醇、乙醇、甲酸的电催化氧化性能，并与商业催化剂进行对比，评估了几种新型导电高分子负载的贵金属催化剂的电催化性能及其潜在的应用价值，为新型高性能催化剂载体方面的研究和探索提供一些新思路及理论参考。本论文的主要研究内容及结论概括如下： (1)以碳布(CC)为工作电极，首次实现了5-氨基吲哚(AIn)单体在硫酸水溶液中的电化学聚合，通过对其聚合机理的研究发现，AIn的聚合位点主要发生在C(2)与C(3)位，聚合物主链中结构单元的连接方式有两种，即2,3-式与2,2-3,3-式。实验结果表明：所得聚合物PAIn具有良好的电化学活性与稳定性；与Pt/CC相比，Pt/PAIn/CC对于甲酸电化学氧化的催化活性、稳定性以及抗毒化性能均得到提高，这要归因于PAIn载体的引入。因此，，PAIn有希望作为催化剂载体应用于直接甲酸燃料电池领域。 (2)采用动电位法对AIn与3,4-乙撑二氧噻吩(EDOT)两种单体进行了电化学共聚。实验结果表明：EDOT单体的引入很大程度上提高了AIn的电化学聚合效率与活性；共聚物主链结构中，EDOT结构单元的存在也明显地提高了聚合物的氧化还原可逆性、电化学活性及稳定性，从而有利于Pt颗粒在其表面的沉积与分散。与其它电极相比，Pt/P(AIn-co-EDOT)/CC对于甲酸氧化的电催化活性有所提高，但直接氧化路径及其对于COads的抗毒化能力并没有得到明显的改进。 (3)用石墨烯(GE)来修饰裸的玻碳电极(GC)，然后在该电极(GE/GC)的表面进行5-氨基吲哚(AIn)的电化学聚合反应。实验表明：AIn在GE表面的起始氧化电位较低、电化学活性及聚合效率明显提高，且所得聚合物PAIn的电化学活性与稳定性也得到明显的提高。PAIn粗糙的表面形貌为Pt颗粒的沉积提供了较高的比表面积与较多的附着位点。与单纯的PAIn相比，PAIn/GE负载的Pt颗粒对于甲醇的氧化具有较高的电催化活性与稳定性。因此，在GE的辅助下高分子PAIn有希望作为金属催化剂载体实现其在甲醇燃料电池方面的应用。 (4)电化学法合成了聚芴(PF)及其三种衍生物聚9-羟基芴(PHF)、聚9-芴甲酸(PFCA)、聚9-羟基-9-芴甲酸(PHFCA)，并以所得聚合物为载体分别来负载Pt-Pd催化剂，研究了其对于甲酸的电催化氧化性能。实验表明：与PF、PHF、PHFCA相比，PFCA负载的Pt-Pd对于甲酸的氧化具有较高的电催化活性。分析其原因，一方面归于PFCA特殊的表面形貌、良好的导电性能与电化学活性；另一方面源于PFCA分子结构中的吸电子基团羧基与Pt-Pd纳米粒子之间的电子协同效应，该协同效应通过改变Pt-Pd纳米粒子表面的电子分布进而对甲酸在其表面的氧化路径以及CO在其表面的吸附能产生影响。因此，主链中不含杂原子的导电高分子也可以作为载体来负载金属催化剂颗粒电催化氧化有机小分子。 (5)采用化学“一锅法”制备了Pd、聚3,4-乙撑二氧噻吩(PEDOT)、石墨烯(GE)的复合催化剂(Pd-PEDOT/GE)。其中，PEDOT为纳米球状，GE片层则将相邻的PEDOT纳米球包裹住，Pd纳米粒子则均匀地分散在GE的表面以及PEDOT纳米球的内部及表面。GE的加入增强了Pd-PEDOT纳米球间的联络并提高了其稳定性；高导电性的GE也起着导线的作用，从而有利于电子在Pd-PEDOT/GE复合材料间的传输。Pd-PEDOT/GE对于乙醇的电化学氧化表现出高的电催化活性、稳定性以及强的抗毒化性能，其主要原因要归于Pd纳米粒子高的电化学活性表面积(ECSA)以及Pd纳米粒子与PEDOT间的协同效应。
[Abstract]:As a green energy conversion device, cryogenic fuel cell has been widely used in military command, transportation, radio communication, clean power station, aerospace flight, electric vehicle, portable mobile power supply and other fields. Especially in today's increasingly prominent environmental and energy problems, further research and development of fuel cell is still of great significance. Although some fuel cells (such as proton exchange membrane fuel cells) have been used in practical applications, their cost, performance and conversion efficiency still need to be further improved. Catalyst materials on fuel cell electrodes (including metal nanoparticle catalysts and catalyst supports) are used as catalytic reactions. The active center is one of the most important components in fuel cell, and its performance directly affects the performance and conversion efficiency of fuel cell. Among them, the structure and performance of catalyst carrier as the support material of metal nanoparticles directly determine the size, dispersion, catalytic activity and stability of metal catalyst particles. Carbon black, as a traditional carrier of fuel cell catalyst, has a large specific surface area. However, some of its pore sizes are too small to be fully contacted with the reaction liquid, thus reducing the utilization efficiency of the catalyst. New catalyst supports with high stability are necessary for the further development of fuel cell electrode catalyst materials.
Because of its unique physical and chemical properties, conducting polymers have attracted more and more attention in the research and application of fuel cell catalyst supports. Compared with traditional carbon materials, conducting polymers as new catalyst supports have the following advantages: 1) they are easy to form three-dimensional porous structure and have high specific surface area. 3) good electrochemical activity and high resistance to oxidation and corrosion; 4) conductive properties of both protons and electrons. In addition, the introduction of conductive polymers will provide a low ohmic voltage drop for the transfer of charge between the surface and the metal catalyst. Therefore, conducting polymer as a carbon material will have some effects on its electrocatalytic activity and anti-toxicity. A new type of catalyst carrier has opened up a new field for the study of catalyst support of low temperature fuel cell. This paper aims to design and prepare several conductive polymers with good performance, which can be used as support to support noble metal catalyst Pt or Pd nanoparticles, and systematically study the catalysts for methanol, ethanol and formic acid. Compared with commercial catalysts, the electrocatalytic performance and potential application value of several new conductive polymer supported noble metal catalysts were evaluated. Some new ideas and theoretical references were provided for the research and exploration of new high performance catalyst supports. The following are summarized as follows:
(1) Using carbon cloth (CC) as working electrode, the electrochemical polymerization of 5-aminoindole (AIn) monomer in sulfuric acid aqueous solution was firstly realized. It was found that the polymerization sites of AIn mainly occurred at C(2) and C(3) sites, and there were two ways to connect the structural units in the polymer main chain, namely, 2,3-and 2,2-3,3-formulas. Compared with Pt/CC, Pt/PAIn/CC has better catalytic activity, stability and anti-toxicity for the electrochemical oxidation of formic acid, which is attributed to the introduction of PAIn carrier. Therefore, PAIn is expected to be used as catalyst carrier in the field of direct formic acid fuel cells.
(2) The electrochemical copolymerization of AIn with 3,4-ethylenedioxythiophene (EDOT) was carried out by potentiodynamic method. The results showed that the introduction of EDOT monomer greatly improved the electrochemical polymerization efficiency and activity of AIn, and the presence of EDOT structural unit in the main chain of the copolymer also significantly improved the redox reversibility of the polymer. Compared with other electrodes, Pt / P (AIn-co-EDOT) / CC has higher electrocatalytic activity for formic acid oxidation, but the direct oxidation pathway and its antitoxicity to COads have not been improved significantly.
(3) Graphene (GE) was used to modify the bare glassy carbon electrode (GC), and then the electrochemical polymerization of 5-aminoindole (AIn) was carried out on the surface of the electrode (GE/GC). The experimental results showed that the initial oxidation potential of AIn on the surface of GE was low, the electrochemical activity and polymerization efficiency were obviously improved, and the electrochemical activity and stability of the polymer PAIN were also proved. The rough surface morphology of PAIn provides higher specific surface area and more attachment sites for the deposition of Pt particles. Compared with PAIN alone, PAIn/GE supported PT particles have higher electrocatalytic activity and stability for the oxidation of methanol. Therefore, the polymer PAIn with the assistance of GE is expected to be used as a support for metal catalysts. Its application in methanol fuel cell is realized.
(4) Polyfluorene (PF) and its three derivatives, poly (9-hydroxy fluorene) (PHF), poly (9-fluorenecarboxylic acid) (PFCA) and poly (9-hydroxy-9-fluorenecarboxylic acid) (PHFCA), were synthesized by electrochemical method. The electrocatalytic oxidation of formic acid on the Pt-Pd catalysts supported by PFCA was studied. The results showed that, compared with PF, PHF and PHFCA, PFCA-supported Pt-Pd catalyzed the oxidation of formic acid. Formic acid oxidation has high electrocatalytic activity, which is attributed to the special surface morphology, good conductivity and electrochemical activity of PFCA. On the other hand, it is attributed to the electronic synergistic effect between carboxyl groups of electron-absorbing groups and Pt-Pd nanoparticles in PFCA molecular structure. The synergistic effect can be attributed to the change of Pt-Pd nanoparticles. The distribution of electrons on the surface affects the oxidation path of formic acid on its surface and the adsorption energy of CO on its surface.
(5) Pd, poly (3,4-ethylenedioxythiophene) (PEDOT) and graphene (GE) composite catalysts (Pd-PEDOT/GE) were prepared by one-pot chemical method. PEDOT was nanosphere-like, GE lamellae encapsulated adjacent PEDOT nanospheres, and Pd nanoparticles were uniformly dispersed on the surface of GE and on the interior and surface of PEDOT nanospheres. The contact between Pd-PEDOT nanospheres and the stability of Pd-PEDOT nanospheres were improved, and the high conductivity GE also acted as a wire, which facilitated electron transport between Pd-PEDOT/GE composites. Pd-PEDOT/GE exhibited high electrocatalytic activity, stability and strong antitoxicity for the electrochemical oxidation of ethanol, mainly due to Pd nanoparticles. The electrochemical active surface area (ECSA) of rice seed and the synergistic effect between Pd nanoparticles and PEDOT.
【学位授予单位】：苏州大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O643.36;TM911.4

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