【作者】 陈惠；

【导师】 刘洪波；

【作者基本信息】 湖南大学 ， 材料学， 2011， 博士

【摘要】 质子交换膜燃料电池(PEMFC)是一种将燃料和氧化剂的化学能直接转换成电能的连续发电装置,具有能量转换效率高、噪音低、结构简单、发电效率受负载变化影响小等优点,被公认为是21世纪最有发展前景的洁净、高效的发电技术。双极板是PEMFC的关键部件之一,其质量的好坏直接决定电池堆输出功率的大小和使用寿命的长短,其成本占电池堆总成本的40%左右,高成本正是PEMFC的商业化的一大障碍。寻找性能优良且成本低廉的双极板新材料和加工方法已成为燃料电池产业化技术研究中的重要课题。本论文着眼于PEMFC双极板的现实需要和未来发展,在开发高性能、价廉的燃料电池双极板材料和工艺方面进行了新的探索和尝试。本文首先采用人造石墨和酚醛树脂为主要原料制备复合材料双极板,对人造石墨/酚醛树脂复合材料的制备工艺进行了初步研究,探讨了原料配比、成型工艺和热处理工艺对复合材料双极板性能的影响,并建立了复合材料双极板成型的模压工艺。研究结果表明,采用人造石墨作导电原料所制备的双极板的电学性能与力学性能都较差,与实际应用存在很大的差距。在此基础上,作者对石墨原料和混料方式进行了筛选,选用天然鳞片石墨为导电原料,采用超声分散方法制备天然石墨/酚醛树脂复合材料,详细研究了复合材料的制备工艺、双极板的成型工艺和双极板的热处理工艺。研究结果表明,采用天然鳞片石墨制备的双极板各项性能比用人造石墨制备的双极板性能提高了很多,电导率和抗折强度都增大了3倍。采用超声分散技术可使复合材料各组分混合得更加均匀,极大地提高了复合材料双极板的综合性能。复合材料双极板的抗折强度随树脂含量的增大而增大,电导率随树脂含量的增大而减小,溶剂和炭黑的加入量、混料时间和固化温度存在最佳值,成型压力与保压时间对复合材料双极板的性能影响规律相同,随成型压力增大与保压时间的延长,双极板的电导率与抗强度都增大,适宜的成型压力为200MPa,保压时间为1分钟。针对天然石墨/酚醛树脂复合材料双极板存在强度较低的特点,本文提出了利用炭纤维增强和加入偶联剂的技术解决方案,重点研究了炭纤维加入量、不同炭纤维处理方法、偶联剂种类、偶联剂加入量和偶联剂的加入方式等对复合材料导电性能和力学性能的影响。研究结果表明,复合材料双极板的电导率随着炭纤维添加量的增加而不断降低,强度随着炭纤维添加量的增加先增大后减小。对炭纤维进行液相氧化处理,在同一温度下,双极板的电导率和抗折强度随着处理时间的延长而增大；在处理时间相同的条件下,双极板的电导率和抗折强度随着处理温度的升高而增大。偶联剂的加入能有效地改善双极板的力学性能,不同种类的偶联剂和不同的加入方式时,偶联剂的加入量都存在最佳值。本论文还在天然石墨／酚醛树脂复合材料双极板研究的基础上,对粘结剂树脂进行了改进,采用环氧改性的酚醛树脂为粘结剂,研究了树脂配比、树脂含量、石墨粒径、炭黑添加量、溶剂比、成型压力、保压时间以及热固化温度等因素对天然石墨/环氧改性酚醛树脂复合材料双极板结构和性能的影响。研究结果表明,在酚醛树脂体系中加入适量环氧树脂可显著改善复合材料双极板的性能,粘结剂的最佳用量有所减少,在最优的复合材料制备工艺、双极板的成型工艺和热处理工艺条件下,所制备的双极板的体积密度大于1.85g.cm-3,电导率大于120S.cm-1,抗折强度大于40MPa,均能达到美国能源部(DOE)提出的燃料电池双极板的使用标准。本文还利用膨胀石墨的优点,选用其作为导电原料,酚醛树脂为粘结剂制备复合材料双极板,对双极板的制备工艺进行了优化。研究表明,随膨胀石墨量的增加,双极板的电导率增加,强度不断减小,炭黑的加入方式对双极板性能有很大的影响。双极板作为燃料电池的重要组成部分,除了基本性能良好外,还需要满足其使用性能。为此,本文还对双极板的使用性能如润湿性、吸水性、热稳定性、热膨胀性、腐蚀性、阻气性和单电池性能进行了研究。结果表明,所研制复合材料双极板具有一定的亲水性,其接触角都在81°-86°之间,双极板的导电性和力学性能受吸水率影响较小。在燃料电池的工作温度范围(80-100℃)内其热稳定性能非常好。热膨胀系数也很小,数量级都为10-6K-1,这在PEMFC的工作温度范围内几乎不会因热膨胀而产生变形。模拟质子交换膜燃料电池工作环境的浸泡腐蚀实验表明,失重率在0.1-0.6%间,在电化学腐蚀中,腐蚀电流密度都小于5μA/cm2,耐腐蚀性能较好,能满足双极板的电池工作要求。模拟单电池试验表明,复合双极板在PEMFC运行环境下性能较稳定,以复合材料双极板组装的PEMFC单电池的开路电压为0.9V左右,在电流密度为1.56A.cm-2时可获得最大功率密度0.66W·cm-2。更多还原

【Abstract】 Proton Exchange Membrane Fuel Cell (PEMFC) is a device that directly converts the chemical energy of the fuel and oxidant into electrical energy. It is recognized as the most promising power generation technology in the21st century because of it’s high efficiency, low emission, simple structure, et al. Bipolar plate is a critical component of the PEMFC, which distributes fuel and oxidant to the membrane electrode and provides electronic connection between single cells. It’s quality directly affects the output power and life time of the cell stack, and it’s cost accounts for about40percent of the total cost of a cell stack, while the high cost of FC is a key obstacle to its wide application.Therefore, searching materials and manufacturing methods for high performance and low cost bipolar plate has been very important. With the above background, new materials and manufacturing methods for bipolar plates are explored in this study.The composite bipolar plates have been preparated firstly using of synthetic graphite and phenolic resin in this article. The preparation technology of synthetic graphite/phenolic resin composites was studied preliminarily. The influences of the raw material configuration, molding technology and heat treatment process on the performance of bipolar plates were investigated, and the forming molding technology of the composite bipolar plates was established. Research results show that the electrical property and mechanical property of bipolar plates preparated using synthetic graphite as conductive fillers are both low, and it can not meet the actual application requirements. On this basis, the author screened graphite raw materials and the mix method, and the natural graphite/phenolic resin composites was preparated using natural graphite as conductive aggregates and using ultrasound decentralized methods. The preparation technology of the composite bipolar plates forming process and heat treatment process was studied detaily. Research results indicate that the performances of bipolar plates preparated using the natural graphite were improved compared to those preparated using the synthetic graphite, and the conductivity and flexural strength are increased to3times respectively. Using ultrasound dispersion technology, composites components are mixed more uniform, and the comprehensive performance of composite bipolar plates are greatly improved. The flexural strength of composite bipolar plates increases and the conductivity decreases with increase of resin content.and the addition of carbon black and curing temperature have the optimal value. The influences of molding pressure and time on the performance of bipolar plates is the same. With the increase of molding pressure and the extension of holding time, conductivity and flexural strength of bipolar plates are increasing, and the suitable forming pressure is about200MPa, the holding time is1minute.For the natural graphite/phenolic resin composite bipolar plates have low mechanical performance, carbon fiber and coupling agent were used to reinforce composites strength. The influences of carbon fiber content, different carbon fiber processing methods, coupling agent species, coupling agent content and coupling agent added methods on the electrical conductivity and mechanical properties of composite were investigated respectively. Research results show that the conductivity of composite bipolar plates is decreased with the incease of carbon fiber content, the flexural strength is increased firstly and then decreased. Carbon fiber being liquid handling at the same temperature, the conductivity and flexural strength of bipolar plates increase with processing time increases, and at the same handing time, electrical conductivity and flexural strength of bipolar plates increase as the processing temperature increase. Adding Coupling agent, mechanical property of bipolar plates is effectively improved. Using different types coupling agent and a different adding way, the coupling agent content has the optimal value.On the basis of the study on the natural graphite/phenolic resin composite bipolar plates, the binder resin has been improved, and we used phenolic resin modified by epoxy resin as binder. The influences of resin ratio, resin content, graphite granularity, carbon black content, solvents ratio, molding pressure, molding time, curing temperature and other factors on the structure and properties of natural graphite/modified phenolic resin composite bipolar plates have been investigated. The results indicate that the mechanical properties of the bipolar plates significantly improved by adding suitable epoxy resin to the phenolic resin system. The optimum dosage of binder decrease. At optimal composite materials preparation technology, bipolar plate molding technology and heat treatment technology, the preparated bipolar plates have the density greater than1.85g/cm3, conductivity greater than120S/cm, flexural strength greater than40MPa, which have been able to meet the standards of U.S. Department of energy (DOE).The expanded graphite/phenolic resin composite bipolar plates have been preparated taking the advantage of expanded graphite and using it as a conductive aggregates, phenolic resin as binder. Results show that with the increase of expanded graphite content, conductivity of bipolar plates increases, while flexural strength decreases.the addition methods of carbon black has a great influence on bipolar plates performance.As an important component of the fuel cell, in addition to the basic performance, bipolar plate needs to meet the operational performance. Therefor, the operational performances of bipolar plates such as wettability, absorbent, thermal stability, thermal expansion, corrosiveness, gas impermeability and single-cell performance also have been investigated. Results show that the composite bipolar plates which were developed in this paper were hydrophilic. those contact angle is between81°-86°, there almost has no infulence of water absorption on the conductivity and strength of bipolar plates. In the range of fuel cell working temperature (80-100℃), thermal stability of bipolar plates is very good. Thermal expansion rate is also very low, the order of magnitude is10-6K-1. In PEMFC working temperature range, bipolar plates almost dosen’t becom deformation due to thermal expansion. In simulation cell working environment immersion corrosion, weightlessness is0.1-0.6%. In electrochemical corrosion, the corrosion current densitys are less than5pμA/cm2. In this research corrosion resistance of three bipolar plate is good, which can meet the need of bipolar plates. Simulation experiments of single cell show that the composite bipolar plates have a more stable performance in PEMFC run environment. For the PEMFC assembled with graphite/phenolic composite bipolar plates, the open-circuit voltage is about0.9V, and the maximum power density can reach to0.66W·cm-2at the current density of1.56A·cm-2更多还原