Miyatake Kenji, Chikashige Yohei, Higuchi Eiji, Watanabe Masahiro
Clean Energy Research Center, University of Yamanashi, 4 Takeda, Kofu 400-8510, Japan.
J Am Chem Soc. 2007 Apr 4;129(13):3879-87. doi: 10.1021/ja0672526. Epub 2007 Mar 13.
Poly(arylene ether sulfone)-based ionomers containing sulfofluorenyl groups have been synthesized for applications to polymer electrolyte membrane fuel cells (PEMFCs). In order to achieve high proton conductivity and chemical, mechanical, and dimensional stability, the molecular structure of the ionomers has been optimized. Tough, flexible, and transparent membranes were obtained from a series of modified ionomers containing methyl groups with the ion-exchange capacity (IEC) ranging from 1.32 to 3.26 meq/g. Isopropylidene tetramethylbiphenylene moieties were more effective than the methyl-substituted fluorenyl groups in giving a high-IEC ionomer membrane with substantial stability to hydrolysis and oxidation. Dimensional stability was significantly improved for the methyl-substituted ionomer membranes compared to that of the non-methylated ones. This new ionomer membrane showed comparable proton conductivity to that of the perfluorinated ionomer membrane (Nafion 112) under a wide range of conditions (80-120 degrees C and 20-93% relative humidity (RH)). The highest proton conductivity of 0.3 S/cm was obtained at 80 degrees C and 93% RH. Although there is a decline of proton conductivity with time, after 10 000 h the proton conductivities were still at acceptable levels for fuel cell operation. The membranes retained their strength, flexibility, and high molecular weight after 10 000 h. Microscopic analyses revealed well-connected ionic clusters for the high-IEC membrane. A fuel cell operated using the polyether ionomer membrane showed better performance than that of Nafion at a low humidity of 20% RH and high temperature of 90 degrees C. Unlike the other hydrocarbon ionomers, the present membrane showed a lower resistance than expected from its conductivity, indicating superior water-holding capability at high temperature and low humidity.
含磺芴基的聚亚芳基醚砜类离聚物已被合成用于聚合物电解质膜燃料电池（PEMFC）。为了实现高质子传导率以及化学、机械和尺寸稳定性，对离聚物的分子结构进行了优化。通过一系列离子交换容量（IEC）在1.32至3.26 meq/g范围内的含甲基改性离聚物制得了坚韧、柔韧且透明的膜。在制备具有高水解和氧化稳定性的高IEC离聚物膜方面，亚异丙基四甲基联苯部分比甲基取代的芴基更有效。与未甲基化的离聚物膜相比，甲基取代的离聚物膜的尺寸稳定性得到显著提高。在很宽的条件范围（80 - 120℃和20 - 93%相对湿度（RH））下，这种新型离聚物膜显示出与全氟离聚物膜（Nafion 112）相当的质子传导率。在80℃和93%RH条件下获得了最高0.3 S/cm的质子传导率。尽管质子传导率会随时间下降，但10000小时后质子传导率仍处于燃料电池运行可接受的水平。10000小时后膜仍保持其强度、柔韧性和高分子量。微观分析表明高IEC膜具有连接良好的离子簇。使用聚醚离聚物膜运行的燃料电池在20%RH的低湿度和90℃的高温下表现优于Nafion。与其他碳氢化合物离聚物不同，本膜显示出比根据其传导率预期更低的电阻，表明在高温低湿度下具有优异的持水能力。
