【作者】 李俊升；

【导师】 潘牧；

【作者基本信息】 武汉理工大学 ， 新能源材料， 2010， 硕士

【摘要】 质子交换膜燃料电池(PEMFC)是一种通过电化学反应将燃料(如氢气)的化学能转化为电能的装置。质子交换膜燃料电池有着起动快,高效,低污染的特点,这一特点使其成为未来移动电源及备用电源的重要候选电源。目前,制约质子交换膜燃料电池商业化的主要是燃料电池的寿命问题。质子交换膜是燃料电池的核心组件。质子交换膜的物理退化被认为是燃料电池失效的重要原因之一。而已有的研究表明,提高强度可以提高可以改善膜的耐久性。通过热处理和纤维增强是提高膜的机械性能有效途径。但是热处理提高机械性能的机理并不清楚,而且对膜的导电性影响也令人担心。纤维增强虽然已有大量实际工作,但是理论上纤维增强的潜力和局限还没有研究报道。本文研究了ePTFE/Nafion复合膜中ePTFE相含量对膜机械性能的影响并评价了不同热处理工艺对膜Nafion 211膜机械性能及传导性能的影响。本文通过研究得到以下主要结论：(1)对Nafion膜进行120℃-160℃之间的热处理时可以提高膜的结晶度,但热处理引起的无规则热运动会破坏膜的团簇结构,从而降低膜的电导率。也就是说直接将Nafion膜进行热处理是行不通的。(2)对Na离子修饰的Nafion膜进行220℃-240℃之间的热处理也可以改善膜的机械性能。同时,由于Na离子的引入,膜内形成强大的静电网络。在静电网络的作用下,高温热处理时膜中离子团簇发生有序化重构,使膜中侧链活动性增强。这一结构变化导致了膜电导率的提高。对Na型Nafion膜进行2h的热处理(如在240℃)可以较好的平衡膜的强度和电导率关系,同时可以使膜的溶胀应力降至膜的安全疲劳应力值附近。这为Nafion膜的热处理提供了一条有效的途径。(2) ePTFE/Nafion复合膜的强度与复合膜中各相含量有紧密关系。ePTFE的引入不一定能对复合膜起到增强的作用,只有当复合膜中的ePTFE相含量高于其增强阈值时,ePTFE才能对复合膜进行增强,在本研究中,该阈值为20.7vol%。在ePTFE相含量高于此阈值含量时,复合膜强度随ePTFE相含量的升高而增大。复合膜屈服强度随膜中ePTFE含量变化的规律与抗拉强度随ePTFE含量变化的规律类似。更多还原

【Abstract】 Proton exchange membrane fuel cell (PEMFC) is a device converting the chemical energy of the fuel to electrical energy through electrochemical reaction. The characteristics of fast start-up, high efficiency and low emission make it the promising candidate for the mobile and stationary power.The major hurdle for the commercialization of fuel cell is the durability issue of the fuel cell. Proton exchange membrane is the key component of PEMFC. It is believed that the fast degradation of the proton exchange membrane would lead to the early failure of the PEMFC. Extensive researches have demonstrated the durability of the membrane could be enhanced by reinforcing the membrane with a base material or annealing. Although there are now many papers concerning to the fabrication and evaluation of the ePTFE reinforced composite PEM, no study has revealed the effect of ePTFE content on the mechanical behavior of the composite membrane. The durability of the membranes could be improved through annealing but the origin of the improvement in durability is still unknown. Besides, the annealed membranes may show a lower conductivity compared to the as-received membranes. In this thesis, we carefully investigated the effect of ePTFE content on the mechanical properties of the ePTFE/Nafion membrane and the annealing effect on Nafion 211 membrane. The conclusions have been drawn as followed:(1) Annealing Nafion 211 membrane between 120℃-160℃would help to increase the membrane crystallinity and the mechanical properties of the membrane could be enhanced as a result. But the annealing procedure may disturb the cluster structure in the membrane. Therefore, the conductivity of the membrane is lower after annealing. Annealing the Nafion 211 membrane in Na-form also improves the mechanical properties of the membrane. At the same time, the conductivity of the membrane is also improved because annealing with the introduction of Na +ion could reform the membrane to a structure with lower constrain to the side chain of the membrane. Annealing the Na-form membrane (i.e. at 240℃) could balance the mechanical properties and conductivity of the membrane. Besides, The durability of the membrane could be expected to be enhanced because the decrease of the humidity induced stress after annealing.(2) In the ePTFE/Nafion composite membrane, there is a PTFE phase content threshold value (ca. 22.7vol%, volume fraction) beyond which the composite membrane could be reinforced. The tensile strengthen of the composite membrane goes up with the growing phase content of the ePTFE when the ePTFE content is greater than the threshold value and the tensile strengthen of the composite membrane decreases with the growing ePTFE content when the ePTFE content does not reach the threshold value. The yield strengthens change of the composite membranes with the ePTFE content shows similar trend. The yield strengthens increase with the ePTFE content only when the relative ePTFE content is greater than the threshold value.更多还原