【摘要】：低溫燃料電池作為一種綠色能源轉(zhuǎn)換裝置已被廣泛應(yīng)用于軍事指揮、交通運(yùn)輸、無線電通訊、清潔電站、航天飛行、電動(dòng)汽車、便攜式移動(dòng)電源等領(lǐng)域。尤其在環(huán)境與能源問題日益突出的今天，對(duì)于燃料電池進(jìn)一步的研究與開發(fā)仍具有重大的社會(huì)意義與美好的應(yīng)用前景。雖然部分燃料電池(如質(zhì)子交換膜燃料電池)已經(jīng)實(shí)現(xiàn)了實(shí)際應(yīng)用，但其成本、工作性能、轉(zhuǎn)換效率仍需進(jìn)一步的改善。燃料電池電極上的催化劑材料(包括金屬納米粒子催化劑和催化劑載體)作為催化反應(yīng)的活性中心，是燃料電池中最核心的部件之一，它性能的優(yōu)劣直接影響著燃料電池的工作性能和轉(zhuǎn)換效率。其中，催化劑載體作為金屬納米粒子的支撐材料，其結(jié)構(gòu)與性能直接決定著金屬催化劑顆粒的粒徑大小、分散性、催化活性及穩(wěn)定性。炭黑作為一種傳統(tǒng)的燃料電池催化劑載體，具有較大的比表面積，然而其部分孔徑太小，不能與反應(yīng)液進(jìn)行充分的接觸，從而降低了催化劑的利用效率。另外，碳材料載體也容易被氧化腐蝕。因此，研究開發(fā)一種具有低成本、大比表面積、高穩(wěn)定性的新型催化劑載體對(duì)于燃料電池電極催化劑材料的進(jìn)一步發(fā)展十分有必要。 由于其獨(dú)特的物理與化學(xué)性能，導(dǎo)電高分子在燃料電池催化劑載體研究與應(yīng)用中逐漸引起了研究者們的關(guān)注與重視。與傳統(tǒng)的碳材料載體相比，導(dǎo)電高分子作為新型催化劑載體具有以下優(yōu)點(diǎn)：1)易形成三維多孔結(jié)構(gòu)，有較高的比表面積；2)通過官能團(tuán)的引入，可對(duì)其結(jié)構(gòu)及性能進(jìn)行改進(jìn)、調(diào)控；3)良好的電化學(xué)活性與高的抗氧化腐蝕能力；4)既能質(zhì)子導(dǎo)電又能電子導(dǎo)電的特性。另外，導(dǎo)電高分子的引入會(huì)為電荷在其表面與金屬催化劑間的傳遞提供低的歐姆電壓降，從而有利于電荷的傳輸與轉(zhuǎn)移；導(dǎo)電高分子較長的π電子共軛結(jié)構(gòu)與金屬納米顆粒間會(huì)產(chǎn)生一定的電子效應(yīng)，影響到金屬納米顆粒表面的電子分布，從而對(duì)其電催化活性及抗毒化性能產(chǎn)生影響。因此，導(dǎo)電高分子作為繼碳材料之后的一種新型催化劑載體為低溫燃料電池催化劑載體方面的研究開辟了一片新天地。本論文旨在設(shè)計(jì)、制備出幾種具有優(yōu)良性能的導(dǎo)電高分子，以此作為載體來負(fù)載貴金屬催化劑Pt或Pd納米顆粒，系統(tǒng)研究了所得催化劑對(duì)于甲醇、乙醇、甲酸的電催化氧化性能，并與商業(yè)催化劑進(jìn)行對(duì)比，評(píng)估了幾種新型導(dǎo)電高分子負(fù)載的貴金屬催化劑的電催化性能及其潛在的應(yīng)用價(jià)值，為新型高性能催化劑載體方面的研究和探索提供一些新思路及理論參考。本論文的主要研究內(nèi)容及結(jié)論概括如下： (1)以碳布(CC)為工作電極，首次實(shí)現(xiàn)了5-氨基吲哚(AIn)單體在硫酸水溶液中的電化學(xué)聚合，通過對(duì)其聚合機(jī)理的研究發(fā)現(xiàn)，AIn的聚合位點(diǎn)主要發(fā)生在C(2)與C(3)位，聚合物主鏈中結(jié)構(gòu)單元的連接方式有兩種，即2,3-式與2,2-3,3-式。實(shí)驗(yàn)結(jié)果表明：所得聚合物PAIn具有良好的電化學(xué)活性與穩(wěn)定性；與Pt/CC相比，Pt/PAIn/CC對(duì)于甲酸電化學(xué)氧化的催化活性、穩(wěn)定性以及抗毒化性能均得到提高，這要?dú)w因于PAIn載體的引入。因此，，PAIn有希望作為催化劑載體應(yīng)用于直接甲酸燃料電池領(lǐng)域。 (2)采用動(dòng)電位法對(duì)AIn與3,4-乙撐二氧噻吩(EDOT)兩種單體進(jìn)行了電化學(xué)共聚。實(shí)驗(yàn)結(jié)果表明：EDOT單體的引入很大程度上提高了AIn的電化學(xué)聚合效率與活性；共聚物主鏈結(jié)構(gòu)中，EDOT結(jié)構(gòu)單元的存在也明顯地提高了聚合物的氧化還原可逆性、電化學(xué)活性及穩(wěn)定性，從而有利于Pt顆粒在其表面的沉積與分散。與其它電極相比，Pt/P(AIn-co-EDOT)/CC對(duì)于甲酸氧化的電催化活性有所提高，但直接氧化路徑及其對(duì)于COads的抗毒化能力并沒有得到明顯的改進(jìn)。 (3)用石墨烯(GE)來修飾裸的玻碳電極(GC)，然后在該電極(GE/GC)的表面進(jìn)行5-氨基吲哚(AIn)的電化學(xué)聚合反應(yīng)。實(shí)驗(yàn)表明：AIn在GE表面的起始氧化電位較低、電化學(xué)活性及聚合效率明顯提高，且所得聚合物PAIn的電化學(xué)活性與穩(wěn)定性也得到明顯的提高。PAIn粗糙的表面形貌為Pt顆粒的沉積提供了較高的比表面積與較多的附著位點(diǎn)。與單純的PAIn相比，PAIn/GE負(fù)載的Pt顆粒對(duì)于甲醇的氧化具有較高的電催化活性與穩(wěn)定性。因此，在GE的輔助下高分子PAIn有希望作為金屬催化劑載體實(shí)現(xiàn)其在甲醇燃料電池方面的應(yīng)用。 (4)電化學(xué)法合成了聚芴(PF)及其三種衍生物聚9-羥基芴(PHF)、聚9-芴甲酸(PFCA)、聚9-羥基-9-芴甲酸(PHFCA)，并以所得聚合物為載體分別來負(fù)載Pt-Pd催化劑，研究了其對(duì)于甲酸的電催化氧化性能。實(shí)驗(yàn)表明：與PF、PHF、PHFCA相比，PFCA負(fù)載的Pt-Pd對(duì)于甲酸的氧化具有較高的電催化活性。分析其原因，一方面歸于PFCA特殊的表面形貌、良好的導(dǎo)電性能與電化學(xué)活性；另一方面源于PFCA分子結(jié)構(gòu)中的吸電子基團(tuán)羧基與Pt-Pd納米粒子之間的電子協(xié)同效應(yīng)，該協(xié)同效應(yīng)通過改變Pt-Pd納米粒子表面的電子分布進(jìn)而對(duì)甲酸在其表面的氧化路徑以及CO在其表面的吸附能產(chǎn)生影響。因此，主鏈中不含雜原子的導(dǎo)電高分子也可以作為載體來負(fù)載金屬催化劑顆粒電催化氧化有機(jī)小分子。 (5)采用化學(xué)“一鍋法”制備了Pd、聚3,4-乙撐二氧噻吩(PEDOT)、石墨烯(GE)的復(fù)合催化劑(Pd-PEDOT/GE)。其中，PEDOT為納米球狀，GE片層則將相鄰的PEDOT納米球包裹住，Pd納米粒子則均勻地分散在GE的表面以及PEDOT納米球的內(nèi)部及表面。GE的加入增強(qiáng)了Pd-PEDOT納米球間的聯(lián)絡(luò)并提高了其穩(wěn)定性；高導(dǎo)電性的GE也起著導(dǎo)線的作用，從而有利于電子在Pd-PEDOT/GE復(fù)合材料間的傳輸。Pd-PEDOT/GE對(duì)于乙醇的電化學(xué)氧化表現(xiàn)出高的電催化活性、穩(wěn)定性以及強(qiáng)的抗毒化性能，其主要原因要?dú)w于Pd納米粒子高的電化學(xué)活性表面積(ECSA)以及Pd納米粒子與PEDOT間的協(xié)同效應(yīng)。
[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.
【學(xué)位授予單位】：蘇州大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：O643.36;TM911.4

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