【作者】 阴强；

【导师】 孙康宁；

【作者基本信息】 山东大学 ， 材料学， 2008， 博士

【摘要】 在环境与能源备受人类关注的今天，具有能量转化率高（40-60％），污染少的质子交换膜燃料电池（PEMFC）的研究与开发越来越受到各国政府和科技人员的重视。双极板是其中的重要组成部分，其成本、重量分别占PEMFC的45％和80％，因此研究开发新型双极板材料、降低双极板的成本以及重量，对于促进燃料电池的商业化发展具有重要的意义。本研究在总结目前双极板材料及制备工艺的研究现状的基础上，根据美国能源部对树脂／石墨复合材料双极板的性能要求，以弯曲强度和导电率作为重点考虑的目标，利用廉价的石墨和酚醛树脂作为基体，以降低双极板材料的成本；采用碳纳米管对其进行增强，在保证导电性能的基础上，可提高复合材料的强度，利于制备薄的双极板，从而降低双极板体积和重量。主要研究内容如下：第一，采用粉体原材料、低温模压方式制备酚醛树脂／石墨复合材料，并系统研究复合材料的制备工艺对其性能的影响，从而确定复合材料的最佳制备工艺参数。首先，采用单因素实验法制备酚醛树脂／石墨复合材料，研究工艺参数对酚醛树脂／石墨复合材料的影响。结果发现：复合材料导电率随酚醛树脂的增加而增加，而弯曲强度则出现下降趋势；压制温度与时间对复合材料性能的影响相似，复合材料导电率随压制温度和时间的上升出现波浪上升的趋势，而弯曲强度出现先增加后减小的趋势；压力与石墨粒径对复合材料性能的影响相似，复合材料的导电率和弯曲强度均随着压力和石墨粒径的增加，出现先增加后减小的趋势；酚醛树脂为15wt％，压制温度为240℃，压制时间为60min，压力为30MPa，石墨粒径为105-150μm此时，复合材料的性能最佳：导电率为142s／cm，弯曲强度为61．6MPa。其次，以石墨含量、压制温度以及压制时间为主要研究对象，采用正交实验对复合材料制备工艺参数进一步优化。结果发现：石墨含量对复合材料的导电率与弯曲强度影响显著，压制时间与压制温度对复合材料的性能影响不显著；在单因素与正交试验中，复合材料的弯曲强度随着石墨含量的增加而减小，对于复合材料的导电率，单因素试验中，随石墨含量的增加而增加，而在正交实验中，却出现先增加后减小的趋势；确定复合材料的最佳工艺为：石墨含量为85wt％，压制时间和温度分别为100min、260℃，此时，复合材料导电率与弯曲强度分别为171．2 s／cm和59．7MPa。第二，成功制备碳纳米管增强酚醛树脂／石墨复合材料，并研究碳纳米管的表面处理以及含量对所研究的复合材料性能的影响，从而确定碳纳米管增强复合材料的最佳制备工艺参数。首先采用空气氧化法对碳纳米管进行纯化处理，利用透射电镜（TEM）、热重分析（TGA）对碳纳米管纯化前后进行观察和分析，碳纳米管经过纯化后，表面光洁，无缠绕现象，无定型碳等杂质得到了有效地去除。其次，首次采用Fenton/紫外线（ultraviolet，UV）对碳纳米管进行表面处理，并用处理后的碳纳米管来增强酚醛树脂／石墨复合材料。研究其工艺参数(Fenton试剂中Fe²⁺和H₂O₂的配比、pH值以及反应时间)对碳纳米管表面官能团以及复合材料性能的影响，并确立Fenton／UV处理方式的最佳工艺参数。结合红外光谱分析（FTIR）以及复合材料的性能，通过与不同的Fenton试剂法（Fenton、Fenton／超声波（ultrasonic，US））相比发现：紫外线的引入，不仅能够在碳纳米管表面引入更多的羟基官能团，而且能够引入少量的羧基官能团，可有效提高碳纳米管与基体之间的结合，从而提高了复合材料的性能。Fenton／UV处理方式中，其工艺条件是影响碳纳米管与基体之间界面结合的一个主要因素。结合FTIR、X射线衍射（XRD）手段以及复合材料的性能，研究Fenton／UV处理方式的工艺条件对碳纳米管表面结构和复合材料性能的影响，并确定Fenton／UV处理方式的最佳工艺条件为：Fe²⁺与H₂O₂之间的配比为1：40，pH=3以及反应时间为3h。再次，研究碳纳米管含量对复合材料性能的影响。结果发现：实验体系内，随着碳纳米管含量的增加，复合材料的弯曲强度和导电率出现增加的趋势；在碳纳米管含量为5wt％时，复合材料的性能达到最佳值：弯曲强度和导电率分别为81．2MPa和195．4s／cm，相比增强前复合材料性能分别提高了36．0％和14．1％。第三，以TEM、拉曼光谱（Raman spectra）手段，并结合FTIR研究Fenton试剂法对碳纳米管的改性机理。研究结果表明：Fenton试剂法对碳纳米管的改性机理是Fenton反应产生的羟基自由基优先利用其强亲电子加成性，与碳纳米管管壁的不饱和双键（C=C）发生电子加成反应，在碳管表面引入羟基；之后利用其强氧化性对羟基进行氧化，生成羧基，从而实现对碳纳米管的表面改性。第四，借助扫描电镜（SEM），研究碳纳米管复合材料的增强机理。碳纳米管与作为粘结剂的酚醛树脂结合处于强结合状态。复合材料的增强机制主要是具有皮芯结构碳纳米管的脱粘及“拔出效应”。第五，研究碳纳米管增强酚醛树脂／石墨复合材料弯曲强度的预估理论。利用碳纤维复合材料理论，考虑了碳纳米管的长度有效系数和取向系数的影响，从而给出所研究的复合材料的弯曲强度预估公式。复合材料弯曲预估公式在碳纳米管含量较低（<4wt％）时，复合材料弯曲强度的预估值与实测值较为吻合，能够较好地对复合材料的弯曲强度进行预估。更多还原

【Abstract】 More attention has been paid to the development and research of the polymer electrolyte membrane fuel cell（PEMFC） by internal and external conuntries, due to its high percent conversion of energy and little pollution. Bipolar plate is one of the most important components of PEMFC, which accounts for 45% and 80% of the stack cost and weight. So, developing new bipolar plate material and reducing its cost and weight can promote the industrialization of PEMFC.Carbon nanotubes（CNTs） reinforced phenol formaldehyde（PF） resin/graphite composite was prepared on the basis of summarizing current reasearch of bipolar plate material and preparation. According to property demand on resin/graphite bipolar plate by Department of Energy （USA）, the bending strength and conductivity were considered as major factor during the research. In my research, cheaper graphite and PF resin was used as matrix to reduce the cost of bipolar plate; CNTs was used to reinforce the PF resin/graphite composite to reduce the capacity and weight of bipolar plate. The main research content is as follows:Firstly, PF resin/graphite composite was prepared by low temperature and hot pressure molding formation. The effect of preparation technology on properties of composite was also studied, then the technological parameter of composite was optimized.PF resin/graphite composite was prepared by single-factor test at first. The effect of preparation technology on properties of composite was also studied. The results show that the conductivity decreases and bending strength increase with the increasing of PF resin content; that the effect of molding temprature on prperties of composite is similar to that of molding tempratur, the conductivity vary wave-like and bending strength will increase firstly and then decrease with the increasing of molding temprature and time; that the effect of molding pressure on prperties of composite is similar to that of graphite size, the conductivity and bending strength will increase firstly and then decrease with the increasing of pressure and graphite size; and the best conductivity and bending strength of the composite are 142 s/cm and 61.6 MPa, respectively, when its PF resin content is 15wt% and graphite size is 105 - 150μm molded at 240℃and 30MPa for 60min.Then, orthogonal test was used to keep on optimizing the technological parameter （graphite content, molding temprature and time）. The results show that the effect of graphite content on the properties of composite is obvious, the effects of curing temperature and time are not obvious; that the bending strength of composite reduces with the increasing of the graphite content in single-factor and orthogonal test; that the conductivity of composite increases with increasing of graphite content in single-factor test, but it increases firstly and then decreases with the increasing of the graphite content in orthogonal test; that the optimal association of conductivity is that graphite content is 85%, and that molding temprature and time are 260℃and 100min, when its conductivity and bending strength is 171.2 s/cm and 59.7MPa.Secondly, the CNTs reinforced PF resin/graphite composite was prepared, and the effects of CNTs ’s surface treatment and content on properties of composite were also studied to get the optimal preparation technological parameters.CNTs were purification treated by air oxydation treatment. The CNTs before and after purification treatment were observed by TEM and DTG, which showes that CNTs after purification are clear and smooth, that CNTs were purified effectively.Then, CNTs were surface treated by Fenton/ ultraviolet（UV）, which is the first time to be used in the surface treatment for CNTs, then was used to reinforce the PF resin/graphite composite. The effects of the technological parameters of Fenton/UV on surface of CNTs and properties of composite were also studied, which include the mached between Fe²⁺ and H₂O₂, the pH value in Fenton regents and reaction time.Compared with other Fenton regents reaction （Fenton、Fenton/US）by FTIR, Fenton/UV treatment can generate large quantity of hydroxyl groups and a little of carboxyl groups on the sidewall of CNTs, which can improve the interfacial binding between CNTs and matrix, then can improve the properties of composite.The technological conditions are important factors, which can effect the interface bonding between CNTs and matrix. The effects of technological conditions on surface of CNTs and properties of composite were studied by FTIR, XRD. On the basis of it, the best technological conditions are: M_Fe²⁺ : M_H2O = 1:40, pH=3 and reaction timeis 3h.Then, the effects of CNTs content on the properties of composite were studied. The results show that the conductivity and bending strength increase with the increasing of CNTs in the experiment system; that the best conductivity and bending strength of the composite are 81.2 MPa and 195.4 s/cm when CNTs content is 5wt%, respectively, which improved 36.0% and 14.1% compared with PF resin/graphite composite.Thirdly, the mechanism of Fenton regents reaction treated CNTs was studied by TEM, Raman spectra and FTIR. The results show that hydroxyl radical generated in the Fenton reation can attack the unsaturated bonds C=C on the sidewalls by electrophilic addition reaction, introducing hydroxyl groups on the sidewalls of CNTs; then the hydroxyl groups was oxidized to carboxyl groups by oxidation susceptibility of hydroxyl radical.Fourthly, the reinforcement mechanism of composite were studies by SEM. The results show that the boundary between CNTs and PF rensin is on strong bonding state; that the sticky point and "pull-out" effect of CNTs with skin-core structure is the reinforcement mechanism of composite.Fifthly, the bending strength forecast equation on the CNTs reinforced PF resin/graphite composite was concluded by using composite mechanical theory. The CNTs length cofficient, and CNTs oriental coefficient were considered and their analytic equations were also concluded, and the discreet value is inosculated with the experiment value when CNTs content is lower（<4wt%） for the bending strength of composite.更多还原