三苯基氧膦磺酸质子交换膜的制备与表征

【作者】 马旭辉；

【导师】 徐僖； 颜德岳；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 质子交换膜是质子交换膜燃料电池的关键材料。目前,PEMFC主要采用Nafion全氟膜。然而,Nafion在温度高温或湿度较低时,电导率急剧下降,甲醇渗透率过高,价格昂贵,难以满足PEMFC产业化应用要求。因此,人们转而寄希望于研制性能优良的非氟芳香族聚合物质子交换膜。本论文针对芳香族聚合物质子交换膜存在的两个主要问题,即在离子容量高时其耐氧化性不足和溶胀率较高,结合我课题组有关耐氧化性及耐溶胀的质子交换膜工作,设计并制备了一系列三苯基氧膦磺酸质子交换膜,同时较为全面地研究了其结构与性能的关系。对比研究了磺化聚芳醚三苯基氧膦基和磺化聚芳硫醚三苯基氧膦基质子交换膜的耐氧化性能,结果表明后者耐氧化性能比前者高得多,并阐述了机理;将二氮杂萘酮基团引入到产物中,制备了低溶胀率的三苯基氧膦基质子交换膜;将耐氧化性和耐溶胀性的基团引入到产物中,制备了耐氧化、低溶胀的三苯基氧膦基质子交换膜。具体内容如下:通过Grignard反应合成了二(4-氟苯基)苯基氧膦(BFPPO)单体,并将其磺化,合成了二(4-卤苯基)-3-磺酸钠苯基氧膦(sBFPPO)单体。将BFPPO与sBFPPO分别与多种二羟基或二巯基单体,如对苯二酚(HQ)、双酚A (Bis A)、4,4’-二苯酚(BP)、双酚F(Bis F)、1,5’-二羟基萘(NA)、4, 4’-二羟基二苯硫醚(DB)和4,4’-二巯基二苯硫醚(TB),直接共聚制备了一系列磺化聚芳(硫)醚三苯基氧膦,侧重考察了二羟基和二巯基单体结构单元对产物的耐氧化性能的影响。结果表明含双酚A和萘结构的产物,耐氧化性能最差。前者结构中含有α氢,C-H键键能较低,耐氧化性差;而后者结构中的萘环的芳香性比苯环差,耐氧化性能低;含HQ、BP、Bis F和DB单体单元结构的产物耐氧化性能较好。含DB和TB单体单元结构的产物分别为磺化聚芳醚三苯基氧膦和磺化聚芳硫醚三苯基氧膦。从结构上看,后者可以看成是前者的醚基团被硫醚基团取代后的“产物”,其耐氧化性能比前者好得多,这是因为后者的硫醚基团在Fenton试剂中被氧化成为砜或亚砜基团,而砜或亚砜基是钝化基团,钝化了与之相连的苯环,阻碍了降解反应(加成反应)。与磺化聚芳硫醚砜(酮)类似,磺化聚芳硫醚三苯基氧膦与磺化聚芳醚三苯基氧膦相比,前者耐氧化性能要好得多。以BFPPO、sBFPPO和4,4’-二巯基二苯硫醚为单体,通过改变BFPPO/sBFPPO的配比,合成了一系列不同磺化度的磺化聚芳硫醚三苯基氧膦,考察了IEC对产物性能的影响。结果表明,随着IEC的增加,产物热失重5%的温度(Td5)降低,而其分子量、玻璃化转变温度、吸水率、溶胀率以及质子传导率都增大。磺化度达90%和100%时,聚合物膜在70 oC就出现溶胀突变;磺化度为80%时,聚合物膜在80 oC出现溶胀突变,显著丧失力学强度。磺化度为70%的产物在90 oC也没出现溶胀,但其导电率偏低,为0.041 S/cm。磺化聚芳硫醚三苯基氧膦耐氧化性能虽好,但溶胀率仍然较高。通过将4-(4-羟基苯基)-2,3-二氮杂萘酮与二(4-氟苯)苯基氧膦和磺化二(4-氟苯)苯基氧膦单体共聚,制备了一系列磺化聚二氮杂萘酮醚三苯基氧膦。将二氮杂萘酮结构单元引入到产物结构中,形成强烈的分子间氢键,降低溶胀率。磺化聚二氮杂萘酮醚三苯基氧膦具有较低的溶胀率,并且其它性能良好。磺化度达100%时,其IEC为1.69 meq/g,在80oC下的溶胀率仅为19.5%,接近于Nafion 117的溶胀率(20%),而导电率达到0.19 S/cm,几乎为Nafion 117导电率的两倍。而前述IEC为1.60 meq/g的磺化聚芳硫醚三苯基氧膦在80oC下的溶胀率为70.1%,已经出现溶胀突变,显著丧失力学强度,其耐溶胀性能比磺化聚二氮杂萘酮醚三苯基氧膦差得多。与磺化聚二氮杂萘酮醚砜(酮)类似,磺化聚二氮杂萘酮醚三苯基氧膦具有很好的耐溶胀性能。结合上述硫醚基团的耐氧化性能和二氮杂萘酮基团的耐溶胀性能,设计并合成了既含硫醚又含二氮杂萘酮的二(4-苯基-2,3-二氮杂萘酮)硫醚单体,将其与磺化二(4-氟苯)苯基氧膦直接缩聚制备了磺化聚双二氮杂萘酮硫醚三苯基氧膦。作为对比,还合成了二(4-苯基-2,3-二氮杂萘酮)醚单体并制备了磺化聚双二氮杂萘酮醚三苯基氧膦。对比研究了其与磺化聚双二氮杂萘酮硫醚三苯基氧膦膜的耐氧化性能差异,并证实了后者具有更好的耐氧化性能。磺化聚双二氮杂萘酮硫醚三苯基氧膦与磺化聚双二氮杂萘酮醚三苯基氧膦的溶胀率在50oC以下随温度升高缓慢增加,此后略有降低,但基本平稳。两者溶胀性能好,形状稳定性高,80oC下的溶胀率很小,分别为6.6%和9.8%,这是由于其分子中都存在二氮杂萘酮结构单元,它与磺酸基上的氢原子之间形成了较强烈的氢键交联的缘故。与预期结果一致,磺化聚双二氮杂萘酮硫醚三苯基氧膦与磺化聚双二氮杂萘酮醚三苯基氧膦相比,前者耐氧化性能要好得多,这是由于前者硫醚基团在过氧化氢作用下氧化成了砜基,钝化了相连苯环的缘故。从分子设计着手,通过共聚将二氮杂萘酮单元和硫醚基团同时引入到产物中而制备的磺化聚双二氮杂萘酮硫醚三苯基氧膦既具有良好的耐氧化性能,又具有良好的溶胀性能,这为制备耐氧化又耐溶胀的质子交换膜材料提供了新思路。磺化聚双二氮杂萘酮硫醚三苯基氧膦与磺化聚双二氮杂萘酮醚三苯基氧膦的IEC分别为1.21和1.23 meq/g,质子导电率偏低,在80oC时分别为2.4×10-3 S/cm和7.0×10-3 S/cm,这一不足可通过提高IEC的方法改进。针对磺化聚芳硫醚三苯基氧膦具有良好的耐氧化性而耐溶胀性能不足的缺点,将二(4-氟苯)苯基氧膦、磺化二(4-氟苯)苯基氧膦和二巯基单体与2,2’-二(2-(4-氟苯基)苯并噁唑基)六氟丙烷共聚制备了含噁唑基团的磺化聚芳硫醚三苯基氧膦,将噁唑基团引入到产物结构中,从而与磺酸基形成氢键交联,减小溶胀。类似地,采用直接缩聚法制备了含腈基的磺化聚芳硫醚三苯基氧膦,将腈基引入到产物结构中,形成强烈的分子间相互作用,减小溶胀。含苯并噁唑基团的磺化聚芳硫醚三苯基氧膦的综合性能良好。IEC为1.68 meq/g的样品热失重5%的温度为391oC,玻璃化转变温度为277oC。80oC下的溶胀率和质子导电率分别为12.5%和0.13 S/cm。耐氧化性能良好,在50℃的Fenton试剂(3% H2O2 containing 2 ppm FeSO4)中开裂和完全溶解的时间分别为240和602分钟。含腈基的磺化聚芳硫醚三苯基氧膦的综合性能优良。IEC为1.56 meq/g的样品热失重5%的温度为374oC,玻璃化转变温度为241oC。80oC下的溶胀率和质子导电率分别为11.2%和0.13 S/cm。耐氧化性能良好,在60oC的Fenton试剂(3% H2O2 containing 2 ppm FeSO4)中开裂和完全溶解的时间分别为255和730分钟。TEM和AFM结果表明磺化聚合物膜具有亲水/疏水的微观相分离结构,它随着IEC的增加而变得更显著。IEC较高时,亲水相聚集增大,甚至形成连通性很好的质子传递通道,导电率因而较高,溶胀率也相对较大;但含二氮杂萘酮、苯并噁唑基团或腈基的磺化聚合物分子中存在强烈的分子间相互作用力,在IEC较高时溶胀率仍然较低。此外,上述三苯基氧膦磺酸质子交换膜结构中的氧磷基团具有良好的高温保湿能力和对无机纳米离子较强的吸附能力,可望在高温PEM和无机掺杂复合PEM领域中应用。更多还原

【Abstract】 Proton exchange membrane (PEM) is one of the key components of proton exchange membrane fuel cells (PEMFC). At present, Nafion is the state-of-the-art PEM. However, it shows some drawbacks such as low conductivity at high temperatures or low humidity, high methanol permeability, and expensive cost, which impede its broad applications. Therefore, great efforts have been made to develop non-fluorinated aromatic polymer PEM with excellent overall properties.The objective of this dissertation aims at the shortcomings of aromatic polymer proton exchange membranes, i.e., the poor oxidative stability and high swelling at high ion exchange capacity (IEC). A series of triphenyl phosphine oxide-containing PEM were designed and prepared according to our previous studies related to the oxidative stability and swelling of PEM. At the same time, the relationship between the structure and the properties was investigated in detail. The comparison studies of oxidative stability between sulfonated poly(arylene ether phosphine oxide)s and sulfonated poly(arylene thioether phosphine oxide)s demonstrated that the latter showed much better resistance to oxidation, and the reason was expounded; The triphenyl phosphine oxide-containing PEM with low swelling was prepared by incorporation of phthalazinone units; Finally, the triphenyl phosphine oxide based PEM, with low swelling as well as high oxidative stability, was synthesized by introduction of functional groups. The detailed content is narrated as follows.Bis(4-fluorophenyl)phenyl phosphine oxide (BFPPO) was synthesized by Grignard reaction, and sulfonated bis(4-fluorophenyl)phenyl phosphine oxide (sBFPPO) was prepared by sulfonation of BFPPO.A series of sulfonated poly(arylene thioether/ether phosphine oxide)s was prepared by direct polycondensation of sBFPPO and BFPPO with the diphenol-type or dimercapto-type monomers such as hydroquinone (HQ), bisphenol-A (Bis A), 4,4’-biphenol (BP), 4,4’-(Hexafluoroisopropylidene)diphenol (6F), 1,5-dihydroxynaphthalene (NA), 4,4’-dihydroxybiphenyl (DB), and 4,4’-thiobisbenzenethiol (TB), respectively. The structural effect of the diphenol-type or dimercapto-type monomers on the properties of the products was investigated. Sulfonated poly(arylene ether phosphine oxide)s derived from Bis A and NA show the worst oxidative stability among the products because the former possess theα-H with low bond strength and the latter have naphthalene rings with low energy of conjugation. In contrast, sulfonated poly(arylene ether phosphine oxide)s derived from HQ, BP, Bis F, and DB indicate better oxidation stability than the products from Bis A and NA. The structure of sulfonated poly(arylene ether phosphine oxide)s from DB is similar to that of sulfonated poly(arylene thioether phosphine oxide)s (sPATPO) from TB. The latter could be regarded as the“product”of the former provided that the ether unit of the former was replaced by the thioether unit. The studies illustrated that the latter exhibited much better oxidative stability than the former. This is due to the fact that the thioether unit of the former was oxidized into the sulfone or sulfoxide unit in Fenton reagent, which inactivated the adjacent benzene rings and thus retarded the degradation reaction (addition reaction). Similar to sulfonated poly(arylene thioether sulfone/ketone)s, sulfonated poly(arylene thioether phosphine oxide)s denote better oxidative stability than sulfonated poly(arylene ether phosphine oxide)s.A series of sulfonated poly(arylene thioether phosphine oxide)s (sPATPO) with various degrees of sulfonation was prepared by polycondensation of 4,4’-thiobisbenzenethiol with the mixture of sBFPPO and BFPPO at different ratios. The effect of IEC on the properties of the products was studied. The investigations demonstrated that the Td5 of the products decreased with increasing IEC and that the molecular weight, Tg, water uptake and swelling as well as proton conductivity of the products enhanced with the increase of IEC. The membranes with the sulfonation degrees of 90% and 100% show an abrupt swelling at 70 oC while the membrane with the sulfonation degrees of 80% indicates a sharp swelling at 80 oC, losing most of the mechanical strength. The membrane with a sulfonation degree of 70% exhibits no abrupt swelling even at 90 oC but a low conductivity of 0.041 S/cm. Therefore, sulfonated poly(arylene thioether phosphine oxide)s with high IEC denote excellent oxidative stability but high swelling.A series of sulfonated poly(phthalazinone ether phosphine oxide)s (sPPEPO) were prepared via polycondensation of 4-(4-hydroxyphenyl) phthalazinone with sBFPPO and BFPPO. The incorporation of phthalazinone units into the backbone leads to forming the powerful intermolecular H-bonds, decreasing the swelling of the products. sPPEPO show low swelling as well as other excellent properties. sPPEPO with a sulfonation degree of 100% exhibit a IEC of 1.69 meq/g and a swelling of 19.5% at 80oC, which are close to that (20%) of Nafion 117. Moreover, sPPEPO indicates a conductivity of 0.19 S/cm at 80oC, two times higher than that of Nafion 117. On the contrary, sulfonated poly(arylene thioether phosphine oxide)s, with a IEC of 1.60 meq/g, even denote a swelling of 70.1% at 80oC and thus lose most of the mechanical strength. Thus sPPEPO shows much lower swelling than sPATPO.In order to combine the excellent oxidative stability of thioether units and the dimensional stability of phthalainone units, bis(4-phenyl-2,3-phthalinone)thioether with both the thioether group and the phthalainone group was designed and synthesized, and sulfonated poly(diphthalazinone thioether phosphine oxide)s (sPDTPO) were prepared by direct polycondensation of bis(4-phenyl-2,3-phthalinone) -thioether and sBFPPO. For comparison, bis(4-phenyl-2,3-phthalinone)ether and sulfonated poly(diphthalazinone ether phosphine oxide)s (sPDEPO) were also prepared. The difference of the oxidative stability between sPDEPO and sPDTPO was studied, the results demonstrated that the latter show better oxidation stability than the former.The swelling of sPDTPO and sPDEPO increases with increasing temperature at the temperatures lower than 50 oC, then decreases slightly and remains steady. They show a low swelling of 6.6% and 9.8%, respectively. This is due to the fact that the phthalainone groups and sulfonic acid groups form the powerful intermolecular H-bonds. As expected, sPDTPO exhibit better oxidative stability than sPDEPO because the thioether unit was oxidized into the sulfone unit, which inactivates the adjacent benzene rings. From the viewpoint of molecular design, the thioether group and phthalainone group were introduced into the main chain of sPDTPO, endowing them with excellent oxidative stability and low swelling. This provides an idea for preparation of PEM with oxidative stability as well as low swelling. sPDTPO and sPDEPO have a IEC of 1.21 and 1.23 meq/g, while they indicate a conductivity of 2.4×10-3 and 7.0×10-3 S/cm, respectively. The low conductivity of sPDTPO could be improved by increasing IEC in the future work.In order to decrease the swelling of the family of sPATPO and still remain their oxidative stability, sPATPO containing benzoxazole groups (sPATPO-bo) were prepared by polycondensation of 2,2’-bis(2-(4-fulorophenyl)benzoxazole) -hexafuloropropane and sBFPPO with the dimercapto-type monomers . The benzoxazole unit was incorporated into the backbone of the products by polycondensation in order to produce the intermolecular H-bonds between the benzoxazole and sulfonic acid group, which made the products possess low swelling. Similarly, sPATPO containing nitrile groups (sPATPO-cn) were prepared by polycondensation of 2,6-difluorobenzonitrile and sBFPPO with 4,4’-thiobisbenzenethiol. The nitrile group was attached onto the main chain of the products, leading to form the powerful intermolecular interaction in the products and provide the products with low swelling.sPATPO-bo have excellent overall properties. sPATPO-bo with a IEC of 1.68 meq/g shows a T5d of 399 oC, a Tg of 277 oC, while it indicates a swelling of 12.5% and a conductivity of 0.13 S/cm at 80oC. Moreover, its membrane exhibits excellent oxidative stability, which starts to break into pieces after immersing in Fenton reagent for 240 min and completely dissolved after immersing in Fenton reagent for 602 min.sPATPO-cn exhibit excellent overall properties. sPATPO-cn with a IEC of 1.56 meq/g exhibits a T5d of 374 oC, a Tg of 241 oC and a swelling of 11.2% as well as a conductivity of 0.13 S/cm at 80oC. Besides, its membrane indicates excellent oxidative stability, which starts to break into pieces after immersing in Fenton reagent for 255 min and completely dissolved after immersing in Fenton reagent for 730 min.The results of TEM and AFM demonstrated that the above PEM show a nanophase separation morphology, which is composed of the hydrophilic and hydrophobic domains. The nanophase separation becomes more and more obvious with increasing IEC. The hydrophilic domains aggregate to form large domains and even to produce well connected proton channels as the IEC rises, often leading to high conductivity but high swelling. However, for the above-mentioned PEM containing phthalainone groups, benzoxazole groups, or nitrile groups, the swelling is still low at high IEC due to the powerful intermolecular interaction.Besides, the triphenyl phosphine oxide-containing PEM show excellent water retention at high temperatures and strong adhesion with inorganic particles, suggesting a good prospect in high temperature PEM and inorganic doped PEM.更多还原