【作者】 高启君；

【导师】 王宇新；

【作者基本信息】 天津大学 ， 化学工程， 2009， 博士

【摘要】 直接甲醇燃料电池(DMFC)是一种极具广泛潜在应用价值的燃料电池。其发展面临两大难题:一是阳极催化剂对甲醇反应的催化活性低;二是通常使用的全氟磺酸质子交换膜的成本高且阻醇性能差。因此开发出低成本、高性能的替代膜是DMFC研究的重要课题之一。本论文在开发价格低廉的新型阻醇质子交换膜和耐高温质子交换膜方面进行了探索和尝试。聚醚醚酮(PEEK)是一种价格较低、性能优良的聚芳醚酮类聚合物。其磺化后可用来制备DMFC质子交换膜。高电导率要求磺化聚醚醚酮(SPEEK)的磺化度要高,但高磺化度会使膜的尺寸稳定性变差。为解决这个矛盾,需要对SPEEK进行改性。我们首次将羟基磷灰石(HA)、功能化二氧化硅(二氧化硅溶胶(SiO2)及带有磺酸基团的二氧化硅(SiOx–S))分别掺杂到较高磺化度的SPEEK中制备复合膜。研究表明,掺杂物与SPEEK之间发生氢键作用,因此复合膜的溶胀被有效地抑制,膜的阻醇性能、可使用温度都得到显著地提高。使用温度的提高使SPEEK高电导率的特性得以发挥,因此复合膜在高温时具有很高的电导率。我们还首次考察了复合膜在高温不同湿度下的电导率。结果表明,掺杂物的加入能显著提高复合膜在低湿度时的电导率。酚酞型聚醚砜(PES–C)经磺化后而制备的磺化酚酞型聚醚砜(SPES–C)质子交换膜,即使磺化度达到70%时,其在沸水中的溶胀度也很小(<13%)。膜的磺化度高,电导率高,但机械强度变差。我们首次将磺化度相对低的SPES–C及未磺化的PES–C分别混入高磺化度的SPEEK中制备共混膜。实验发现,通过控制SPEEK的磺化度及SPES–C、PES–C的混入量,可以制得尺寸稳定性好、电导率高、阻醇性能优良的共混膜。与具有相同离子交换容量的纯SPEEK膜相比,共混膜的阻醇性能及尺寸稳定性能更好。我们首次在SPEEK/PES–C共混溶液浇铸成膜过程中施加垂直膜面的电场,初步探索电场参数(场强、频率、波形、直流/交流)对膜性能的影响。研究发现,电场作用能够改变共混膜的微观结构,使膜在沿着电场方向上产生定向,从而大大提高膜沿着电场方向上的电导率;电场作用还能改变膜的含水率及阻醇性能。更多还原

【Abstract】 Direct methanol fuel cell (DMFC) is a novel power technology and is expected to find wide applications in areas from mobile phones to electric rehicles. Two obstacles, however, need to be surmounted before its commercialization. One is low methanol oxidation activity at the anode, and the other is methanol crossover from the anode to the cathode through the membrane. Therefore, developing new membranes to deal with the obstacles has been an important research subject in the fuel cell field. In this study, new methanol barrier and high temperature membranes for DMFC are explored.Sulfonated poly(ether ether ketone) (SPEEK) membranes are very promising alternative to Nafion membrane in DMFC for their high conductivity and better methanol resistance. However, in SPEEK membranes, there exits conflicts among ionic conductivity, methanol resistance and dimensional stability. The demand of high proton conductivity calls for the membranes to have a high degree of sulfonation (DS) and work at elevated temperature. Such membranes at elevated temperature, however, tend to swell excessively or even dissolve, thereby lowers applicable temperature.In order to overcome the conflicts, insolvable hydroxyapatite (HA) and functionalized silica (silica sol (SiO2) and silica with sulfonic acid groups (SiOx–S)) were incorporated into the SPEEK matrix with relative high DS to prepare novle composite membranes, respectively. Results show that the hydrogen bond happened between the adulterants and the polymers, which helps to reduce the swelling and methanol permeability of the composite membranes, and improve their dimensional stability. For the composite membranes, high conductivity can be achieved as the applicable temperature is improved. For the hygroscopic property of the adulterants, the conductivity of composie membranes under low relative humidity at high temperature(>100℃) was improved efficiently.Phenolphthalein poly(ether sulfone) (PES–C) is an engineering thermoplastic with high temperature resistance, and can be sulfonated to prepare SPES–C proton exchage membranes. The SPES–C membrane swelled somewhat (<13%) in boiling water, even with DS as high as 70%. The demand of high proton conductivity calls for SPES–C membranes to have a high degree of sulfonation (DS), which decreases mechanical strength of the membranres. In order to improve the properties of SPEEK membrane with high DS, SPES–C with a relative low DS (DS=53.7%) and PES–C were chosen and blended into SPEEK matrix to fabricate SPEEK/SPES–C and SPEEK/PES–C blend membranes, respectively. Results show that by controlling the DS of SPEEK and blend proportion, the blend membranes with dimensinoal stability, high conductivity and excellent methanol resistance can be fabricated. Furthermore, compared with pure SPEEK membrane with the same ion–exchange capacity, the blend membrane has better methanol resistance and dimensional stability.An electric field perpendicular to the membrane plane was applied during the course of preparing SPEEK/PES–C membranes by solution casting, and the influence of the electric parameters (e.g., electric field strength (E), frequency (f), waveform and DC/AC electric field) on the blend membranes’performance was explored preliminary. Results show that the electric field can change the membranes’microstructures, and can induce the membranes to orient along the electric field direction, thus improving obviously the trans–plane conductivity of the blend membranes. Furthermore, the electric field can also change the water content and the methanol permeability of the blend membranes.更多还原