發(fā)布時(shí)間：2018-08-16 14:56

【摘要】：在過(guò)去的幾十年里,質(zhì)子交換膜燃料電池(PEMFC)作為一種高效、環(huán)保的電化學(xué)能量轉(zhuǎn)化裝置得到了科學(xué)家們的廣泛關(guān)注。近些年,隨著研究的不斷深入,開(kāi)發(fā)能夠在高溫和低濕度環(huán)境下工作的PEMFC成為研究的熱點(diǎn)。與傳統(tǒng)的低溫質(zhì)子交換膜燃料電池(工作溫度100℃)相比,在100-200℃下操作的高溫質(zhì)子交換膜燃料電池(HT-PEMFC)具有很多優(yōu)勢(shì),例如,提高了催化劑對(duì)CO的耐受性,提高了催化劑效率以及簡(jiǎn)化了水/熱管理等。聚苯并咪唑(PBI)由于具有優(yōu)異的機(jī)械性能和熱穩(wěn)定性,以及具有可以同時(shí)作為質(zhì)子供體和受體的特殊堿性雜環(huán)結(jié)構(gòu),使其成為高溫質(zhì)子交換膜(HT-PEM)的候選材料。PBI本身的質(zhì)子傳導(dǎo)率很低,只有10-9 m S·cm-1,不能作為獨(dú)立的固體電解質(zhì)。磷酸(PA)是一種具有高熱穩(wěn)定性的良好電解質(zhì),它在200℃下的質(zhì)子傳導(dǎo)率高達(dá)800m S·cm-1。在20世紀(jì)90年代,Wainright等人首次將磷酸摻雜到PBI中制備了磷酸摻雜聚苯并咪唑(PA-PBI)型質(zhì)子交換膜,其在高溫下運(yùn)行表現(xiàn)出許多優(yōu)異的性能。這個(gè)里程碑式的研究,以及隨后的很多相關(guān)研究,使PA-PBI膜逐漸演變?yōu)樽罹邼摿Φ腍T-PEM候選材料。在過(guò)去的二十年里,最為廣泛研究的PBI基體是已經(jīng)商業(yè)化的聚[2,2'-間-(亞苯基)-5,5'-二苯并咪唑](m-PBI)。對(duì)于m-PBI來(lái)說(shuō),由于咪唑基團(tuán)間強(qiáng)烈的氫鍵作用導(dǎo)致其具有較差的溶解性,為了保證薄膜的均勻性,避免不溶性殘留物的存在,一般采用線性分子量相對(duì)較低(23-40 k Da,對(duì)應(yīng)于0.5-1.0 d L·g-1的特性粘度)的PBI來(lái)制備PA-PBI膜。但較低的分子量導(dǎo)致聚合物薄膜的機(jī)械性能相對(duì)較差,僅允許PBI薄膜獲得較低的磷酸摻雜量(通常每摩爾PBI重復(fù)單元摻雜6-10摩爾的磷酸分子),從而導(dǎo)致較低的質(zhì)子傳導(dǎo)率(100 m S·cm-1)。因此,研究者們采用了多種方法來(lái)提高膜的性能,包括接枝、交聯(lián)、無(wú)機(jī)摻雜、溶膠-凝膠法制膜以及新型PBI材料的合成等。雖然前期工作在提高PBI膜性能上作出了很多貢獻(xiàn),但是PA-PBI型高溫質(zhì)子交換膜若想實(shí)現(xiàn)商業(yè)化仍然面臨著幾個(gè)關(guān)鍵性的挑戰(zhàn),如更高的質(zhì)子傳導(dǎo)率、更優(yōu)異的機(jī)械性能和更穩(wěn)定的磷酸保持能力等。PA-PBI膜的質(zhì)子傳導(dǎo)率與膜的磷酸摻雜水平(ADL)息息相關(guān),我們可以直接通過(guò)提高PBI薄膜的磷酸摻雜水平來(lái)制備高傳導(dǎo)性的PA-PBI膜,但是,高的ADL會(huì)導(dǎo)致薄膜產(chǎn)生較大的尺寸溶脹,相應(yīng)的降低其機(jī)械強(qiáng)度,從而降低薄膜的耐久性。此外,在高的ADL下,磷酸容易從膜中流失,這也會(huì)影響燃料電池的性能和使用壽命。所以,研制能夠在高ADL即高質(zhì)子傳導(dǎo)率下保持良好尺寸穩(wěn)定性和機(jī)械穩(wěn)定性以及具有高酸保持能力的PBI膜材料,是目前PA-PBI型高溫質(zhì)子交換膜研究中所需要解決的關(guān)鍵問(wèn)題。針對(duì)以上問(wèn)題,本論文的研究主要包括以下四個(gè)部分:首先,我們?cè)O(shè)計(jì)并合成了兩種高分子量的含有柔性醚鍵和不對(duì)稱大體積側(cè)基(苯基和甲基苯基)的芳醚型PBI(Ph-PBI和Me-PBI),并且制備了相應(yīng)的磷酸摻雜膜。通過(guò)芳醚型PBI薄膜與已有的不含側(cè)基的聚[2,2'-(對(duì)-氧聯(lián)二苯基)-5,5'-聯(lián)苯并咪唑](OPBI)薄膜之間的性能比較,我們發(fā)現(xiàn),Ph-PBI和Me-PBI薄膜表現(xiàn)出與OPBI薄膜不同的磷酸摻雜行為,具有更高的磷酸摻雜水平、更好的尺寸和機(jī)械穩(wěn)定性以及更高的質(zhì)子傳導(dǎo)率和更加優(yōu)異的燃料電池性能。其中Ph-PBI在160℃下經(jīng)72 h的磷酸摻雜后,所得到的PA-PBI(Ph-72)膜在200℃、干態(tài)下的質(zhì)子傳導(dǎo)率為138 m S·cm-1,體積溶脹僅為188%,機(jī)械強(qiáng)度為9.7 MPa。Ph-72膜的H2/O2燃料電池在160℃、沒(méi)有加濕情況下的最大功率密度為279m W·cm-2�；�于上一部分工作中合成的具有優(yōu)異尺寸和機(jī)械穩(wěn)定性的Ph-PBI,為了進(jìn)一步提升PBI膜的傳導(dǎo)性能和電池性能,在研究的第二部分里,我們將2-氯甲基苯并咪唑接枝到Ph-PBI上,制備了一系列具有不同接枝度的聚苯并咪唑薄膜。額外的咪唑基團(tuán)的引入使Ph-PBI分子鏈上的堿性基團(tuán)增加,提高了Ph-PBI膜與磷酸分子之間的相互作用,進(jìn)而使膜獲得了更高的磷酸摻雜水平、更高的質(zhì)子傳導(dǎo)率以及更加優(yōu)異的電池性能。當(dāng)接枝度為20%時(shí),磷酸摻雜量為341%,PBI膜在200℃、干態(tài)下的傳導(dǎo)率達(dá)到212 m S·cm-1,拉伸強(qiáng)度為6.5 MPa。該膜的H2/O2燃料電池在160℃、沒(méi)有加濕情況下的最大功率密度為443 m W·cm-2。繼續(xù)提高接枝度,磷酸摻雜膜的強(qiáng)度變?nèi)�。在第三部分�?為了同時(shí)提高PA-PBI膜的質(zhì)子傳導(dǎo)率和機(jī)械強(qiáng)度,我們以Ph-PBI為基體,設(shè)計(jì)并合成了一種新型的含有咪唑基團(tuán)的交聯(lián)劑2,2'-雙(氯甲基)-5,5'-聯(lián)苯并咪唑,制備了一系列具有不同交聯(lián)度的交聯(lián)型PBI薄膜。交聯(lián)薄膜在高的磷酸摻雜水平下表現(xiàn)出比原始Ph-PBI膜和第二部分中的接枝薄膜更好的尺寸和機(jī)械穩(wěn)定性,從而獲得了更高的質(zhì)子傳導(dǎo)率和更優(yōu)異的燃料電池性能。所有磷酸摻雜交聯(lián)膜的機(jī)械強(qiáng)度均在10 MPa以上。當(dāng)交聯(lián)度為30%時(shí),交聯(lián)膜的ADL為354%,200℃、無(wú)水條件下的傳導(dǎo)率達(dá)到253 m S·cm-1,其H2/O2燃料電池在160℃、沒(méi)有加濕情況下的最大功率密度高達(dá)533 m W·cm-2。在研究的最后一部分,為了增強(qiáng)PA-PBI膜對(duì)磷酸的保持能力,我們將具有保酸性的多羥基納米Si O2粒子引入到上一部分所制備的具有優(yōu)異性能的交聯(lián)PBI膜中,制備了無(wú)機(jī)-有機(jī)復(fù)合型質(zhì)子交換膜(Si O2/PBI)。通過(guò)掃描電子顯微鏡研究了復(fù)合膜的斷面形貌。結(jié)果表明Si O2粒子均勻的分散在交聯(lián)的PBI基質(zhì)中。具有2 wt%Si O2含量的Si O2/PBI復(fù)合膜的磷酸摻雜水平為350%,其在200℃、無(wú)水條件下的質(zhì)子傳導(dǎo)率為244 m S·cm-1。該膜的H2/O2燃料電池在160℃、沒(méi)有加濕情況下的最大功率密度為497 m W·cm-2。隨著納米Si O2含量的增加,PBI膜的酸保持能力和傳導(dǎo)率穩(wěn)定性均有提高。綜上所述,我們從PBI基體結(jié)構(gòu)設(shè)計(jì)的角度出發(fā),制備了具有優(yōu)異尺寸和機(jī)械穩(wěn)定性的芳醚型PBI薄膜,通過(guò)引入更多的咪唑基團(tuán)和交聯(lián)膜的制備來(lái)進(jìn)一步提升PBI膜的傳導(dǎo)性能和機(jī)械強(qiáng)度,并通過(guò)無(wú)機(jī)-有機(jī)復(fù)合膜的制備來(lái)提升薄膜的保酸能力,最終獲得了一系列具有優(yōu)異綜合性能的PA-PBI型高溫質(zhì)子交換膜。
[Abstract]:In the past few decades, proton exchange membrane fuel cell (PEMFC) as a highly efficient and environmentally friendly electrochemical energy conversion device has attracted wide attention of scientists. In recent years, with the deepening of research, the development of PEMFC which can work in high temperature and low humidity environment has become a research hotspot. High temperature proton exchange membrane fuel cell (HT-PEMFC) operated at 100-200 C has many advantages over membrane fuel cell (100 C). For example, it improves the tolerance of catalyst to CO, improves the efficiency of catalyst and simplifies the water/heat management. Polybenzimidazole (PBI) has excellent mechanical properties and thermal stability. The proton conductivity of PBI itself is very low, only 10-9 m S. cm-1, and it can not be used as an independent solid electrolyte. Phosphoric acid (PA) is a good electrolyte with high thermal stability, it is at 200 C. In the 1990s, Wainright et al. first doped phosphoric acid into PBI to prepare phosphoric acid-doped polybenzimidazole (PA-PBI) proton exchange membranes, which exhibited many excellent performances at high temperatures. This landmark study, as well as many subsequent related studies, led to PA-PBI films one by one. In the past two decades, the most widely studied PBI substrates have been commercialized poly [2,2'-m-(phenylene)-5,5'-dibenzimidazole] (m-PBI). For m-PBI, the strong hydrogen bonding between imidazole groups leads to poor solubility in order to ensure uniformity of the films. PA-PBI films are prepared by PBI with relatively low linear molecular weight (23-40 K Da, corresponding to the intrinsic viscosity of 0.5-1.0 D L.g-1). However, the mechanical properties of the polymer films are relatively poor due to the lower molecular weight, which only allows the PBI films to obtain a lower phosphoric acid doping amount (usually repeated per mole of PBI). The proton conductivity (100 m S cm 1) is low due to the doping of 6-10 moles of phosphoric acid with the unit. Therefore, researchers have adopted a variety of methods to improve the performance of the membrane, including grafting, crosslinking, inorganic doping, sol-gel method and synthesis of new PBI materials. The PA-PBI high-temperature proton exchange membranes still face several key challenges if they are to be commercialized, such as higher proton conductivity, better mechanical properties and more stable phosphoric acid retention capacity. High conductivity PA-PBI films are prepared by phosphoric acid doping of the films. However, high ADL leads to large size swelling, which correspondingly reduces the mechanical strength and durability of the films. PBI membrane materials with good dimensional stability and mechanical stability and high acid retention ability under high ADL or high proton conductivity are the key problems to be solved in the study of PA-PBI high temperature proton exchange membrane. Two kinds of high molecular weight aryl ether PBI (Ph-PBI and ME-PBI) containing flexible ether bonds and asymmetric large-volume side groups (phenyl and methyl phenyl) were synthesized and the corresponding phosphoric acid doped films were prepared. Compared with OPBI films, Ph-PBI and Me-PBI films exhibit different phosphoric acid doping behaviors, higher phosphoric acid doping levels, better dimensional and mechanical stability, higher proton conductivity and better fuel cell performance. Among them, the PA-PBI (Ph-PBI) obtained by phosphoric acid doping of Ph-PBI at 160 C for 72 h has higher proton conductivity and better fuel cell performance. - 72) The proton conductivity of the membrane is 138 m S. cm - 1, the volume swelling is only 188%, and the mechanical strength of the membrane is 9.7 MPa. Ph - 72. The maximum power density of the H2 / O2 fuel cell is 279 m W. cm - 2 without humidification. Based on the Ph - PBI with excellent size and mechanical stability synthesized in the previous part of the work, in order to make progress In the second part of the study, we grafted 2-chloromethylbenzimidazole onto Ph-PBI and prepared a series of polybenzimidazole films with different grafting degrees. The introduction of additional imidazole groups increased the basic groups on the chain of Ph-PBI and increased the ratio of Ph-PBI film to phosphoric acid. When the grafting degree is 20%, the phosphoric acid doping content is 341%, the conductivity of PBI film is 212 m S. cm - 1, and the tensile strength is 6.5 MPa in dry state. In the third part, in order to improve both proton conductivity and mechanical strength of PA-PBI film, we designed and synthesized a novel crosslinking agent 2,2'-bis (chloromethyl) -5,5'-biphenyl containing imidazole group on the basis of Ph-PBI. A series of cross-linked PBI thin films with different crosslinking degrees were prepared. The cross-linked thin films exhibited better size and mechanical stability than the original Ph-PBI films and the grafted thin films in the second part at high phosphoric acid doping levels, resulting in higher proton conductivity and better fuel cell performance. The mechanical strength of the cross-linked membranes is above 10 MPa. When the degree of cross-linking is 30%, the ADL of the cross-linked membranes is 354%, and the conductivity of the cross-linked membranes is 253 m S. cm-1 under anhydrous condition. The maximum power density of the H2/O2 fuel cell is 533 m W. cm-2 under 160 ~C and no humidification condition. In the last part of the study, in order to enhance the protection of PA-PBI membrane to phosphoric acid. The acidic polyhydroxy nano-Si O2 particles were introduced into the crosslinked PBI films prepared in the previous part to prepare inorganic-organic composite proton exchange membranes (Si O2/PBI). The cross-section morphology of the composite films was studied by scanning electron microscopy (SEM). The results showed that the Si O2 particles were uniformly dispersed in the crosslinked PBI films. The phosphoric acid doping level of the SiO 2/PBI composite membrane with 2 wt% SiO 2 content is 350%, and its proton conductivity is 244 m S cm 1 at 200 C and anhydrous condition. The maximum power density of the H2/O 2 fuel cell with this membrane is 497 m W cm 2 at 160 C and without humidification. With the increase of the nano Si 2 content, the acid of the PBI membrane remains. In summary, we have prepared aryl ether PBI films with excellent size and mechanical stability from the point of view of the structure design of PBI matrix. By introducing more imidazole groups and cross-linking membranes, the conductivity and mechanical strength of PBI films have been further improved, and by Inorganic-Organic methods. A series of PA-PBI high temperature proton exchange membranes with excellent comprehensive properties were obtained.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TQ425.236

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