【作者】 魏永生；

【导师】 朱红； Hongtan Liu；

【作者基本信息】 北京交通大学 ， 光学， 2011， 博士

【摘要】 直接甲醇燃料电池(DMFC)是目前最具有市场应用前景的新能源之一。膜电极是直接甲醇燃料电池的核心部件,通过实验和模型模拟研究对于优化直接甲醇燃料电池的膜电极结构、提高电池的放电性能具有重要的研究意义。本论文从模型模拟和实验两个角度出发,旨在深入研究和识别膜电极的内部结构与电池宏观性能之间的构效关系。在直接甲醇燃料电池的参数统计分析和优化管理、膜电极关键材料的制备与表征、单电池的放电性能、模型模拟等方面分别做了系统性和具体化的研究与探讨,以提高膜电极的电池性能、稳定性和能源效率,为膜电极及电池结构优化设计提供指导。根据直接甲醇燃料电池参数的特性,将其划分为几何参数、物性参数、工作参数、常量参数四个类别。为了更好的对参数进行优化管理,我们建立参数分级模型,根据电池的性能与参数的偏导数函数将参数分成零级参数、一级参数、二级参数和三级参数。对于不同级别的参数,我们给予了相应的参数优化管理策略。该项研究工作为论文的研究方向做了有效的指导,确定研究工作的重点是在膜电极部分,并选择膜材料作为膜电极的关键材料进行研究。采用无机-有机杂化法对Nafion(?)进行改性,通过流延法制备得到了钛酸钠纳米管/Nafion(?)新型复合膜,并且对其微观结构和材料性能进行了表征和测试。研究结果表明,钛酸钠纳米管/Nafion(?)复合膜具有良好的高温保水能力,可以有效降低甲醇渗透系数高达一个数量级,同时提高相对选择性2-5倍,对钛酸钠纳米管/Nafion(?)新型复合膜的作用机理进行了探讨和分析。通过热压法制备了5wt.%钛酸钠纳米管含量的膜电极,测试和分析了复合膜的单电池放电性能。实验结果表明新复合膜的单电池性能要优于纯Nafion膜,同时考察了电池温度、阴极加湿温度、甲醇浓度、甲醇流速和空气流速5个操作参数对燃料电池性能的影响。电池阴极交流阻抗图谱结果表明Na2Ti3O7/Nafion(?)复合膜的阻抗明显低于Nafion(?)膜,成功降低了膜中的甲醇穿透,这主要是因为降低了电荷转移电阻,同时保护了阴极氧还原反应的有效面积。建立了直接甲醇燃料单电池模型,通过与实验数据的比较来验证模型和数值模拟方法的有效性。主要考察了甲醇的穿透的作用、阳极甲醇溶液和阴极氧气在膜电极中的浓度分布。结论是由于甲醇穿透的存在,在一定程度上降低了电池的性能。阳极甲醇进料浓度的增大会提高甲醇的穿透。改变电池的操作条件可以降低甲醇穿透的影响,从而提高电池性能。更多还原

【Abstract】 Direct methanol fuel cells (DMFC) are a promising power source for various applications. Membrane Electrode Assembly (MEA) is the key unit in direct methanol fuel cells. It is significant for optimizing the strugture of MEA and improving the cell performance in DMFC throuth experiment, model and the simulation study.This purpose of this dissertation is to further research and identify the structure-activity relationship between internal structure of MEA and macro properties of cell. Research is done from the model simulation and experimental two directions. Parameters statistical analysis and optimization management in Direct methanol fuel cell, preparation and characterization of the key materials of MEA, performance of single cell, model and simulation have been studied and discussed respectively and systemic for improving the cell performance, stability and energy efficiency. The expectation of this research is to provide the guidance in designing and optimizing the strugture of MEA and the cell.According to the characteristics, parameters in the direct methanol fuel cell are classified as geometric parameters, physical parameters, working parameters and constant parameters. In order to optimize the parameters of management, Grading Model are established according the cell performance unction partial derivative parameters, and the parameters are divided into primary parameters of level zero parameters, level 1 parameters, level 2 parameters and level 3 parameters. For different level of parameters, we give the corresponding parameter optimizing management strategy. The research work did effective guidance for thesis research direction and helped determing the research work is on MEA parts, and chose the membrane materials as film electrode materials for research.In this study, novel sodium titanate (Na2Ti3O7) nanotube/Nafion(?) composite membranes were prepared by a solution casting method. The properties of these composite membranes were measured to evaluate the applicability of these membranes in DMFCs. It was found that the addition of Na2Ti3O7 nanotubes enhanced the water uptake and reduced the methanol permeability of the composite membranes as high as 10 times. The new composite membrane was found to have significantly 2-5 times higher selectivity than a pure Nation(?) membrane and thus has good potential to outperform Nation(?) in DMFCs. The mechanism is also discussed and analyzed. With new composite membrane materials of 5wt.% Na2Ti3O7/Nafion(?) for proton exchange membrane, Membrane Electrode Assembly (MEA) was prepared using hot-pressing method, and been tested in single direct methanol fuel cell. Operation parameters of cell temperature, cathode humidifying temperature, methanol concentration, methanol flow rate and air flow rate have been employed to study on the effect of direct methanol fuel cells polarization curve. The AC impedance maps were tested and analyzed. The results show that the cell performance of new composite membrane is superior to that of the pure Nafion membrane, which blocked the methanol crossover successfully. The main reason is that the novel composite membrane decreases the charge transfer resistance, and protectes the effect surface in the reduction reactions of Oxgen in cathode.Established a model of single direct methanol fuel, model and numerical simulation method is effective which are validated through the comparison with experimental data. The effect of methanol crossover, anode methanol solution and the cathode oxygen concentration distributions in the MEA are investigated. The Conclusion is cell performance is reduced due to the existence of methanol penetrate. Increase of anode methanol feed concentration will enhance the methanol crossover. The methanol penetrable influence could be reduced through the operating conditions, and thus cell performance also could be improved.更多还原