Water Management in PEM Fuel Cells by Material Engineering

摘要：质子交换膜（PEM）燃料电池依赖于适当的水管理来获得高功率密度和能量效率。在运行过程中，水被电渗透从阳极拖到阴极，导致阳极脱水。同时，除了通过电渗透从阳极输送水外，还通过氧还原反应在阴极生成水。当这些过程在阴极中产生的水没有被适当地去除时，它的积累会导致燃料电池性能下降，因为它阻塞了用于氧气运输的气孔，并在反应区形成了额外的运输屏障。传统上，水管理是通过系统工程来解决的，即通过在基本燃料电池系统中添加辅助系统来为阳极提供加湿并从阴极除去水。这种方法增加了系统的复杂性（例如可靠性和耐久性）和成本。此外，这些辅助系统降低了燃料电池系统的净功率输出，导致转换效率降低。知识优势：最近对PEM燃料电池中使用的一些组件的功能的发展和理解导致了如何在PEM燃料电池中实现水管理的范式转变。本文认为，如果使用性能合适的材料和正确的电极结构，通过电渗透输送到阴极的水可以被强制通过膜返回到阳极，从而在PEM燃料电池中实现零净跨膜水输送。这种方法消除了阳极气体加湿的需要，并最大限度地减少了阴极的除水要求，从而大大简化了PEM燃料电池系统。这些是这项工作在智力上的优点。为了更有效地实现上述目标，计划采用理论（建模）和实验工作相结合的方法。实验将用于测量PEM燃料电池的膜-电极组件（MEA）中使用的关键组件的两相输运特性。研究结果将用于研究这些组分的形态和润湿性质与两相输运性质之间的相关性。实验还将用于开发用于PEM燃料电池的催化剂层的四相（电子-离子-气-液）微观结构，该结构最适合两相（液体和气体）传输。同时，将开发一个完整的PEM燃料电池MEA的数学模型，该模型包含了从上述实验中获得的两相传输特性。一旦该模型的预测在实验中得到验证，该模型将用于优化研究，以确定在PEM燃料电池中实现零净水跨膜条件所需的电极配置以及组件的形态和表面特性。基于优化结果，将开发新的组件并在PEM燃料电池中进行测试，以验证实现零净水跨膜运输的条件。更广泛的影响：首先，这种利用材料工程实现最佳水管理的方法将显著降低PEM燃料电池系统的复杂性和成本，并有助于加速该技术的商业化。其次，这项工作的结果有望在基础科学和应用科学层面的其他领域产生影响。多孔介质中多相输运的认识适用于地质、核工程和石油工程等领域。PI还计划继续在他的研究团队中招募不同背景、性别和种族的本科生和研究生。他将燃料电池技术引入本科教育的努力得到了他所创立的公司所创造的教育工具（实验和文献）的认可。

ABSTRACTPI: Trung V. Nguyen Institution: University of KansasProposal Number: 0651758Title: WATER MANAGEMENT IN PEM FUEL CELLS BY MATERIAL ENGINEERINGProton Exchange Membrane (PEM) fuel cells depend on proper water management to obtain high power density and energy efficiency. During operation water is dragged from the anode to the cathode by electro-osmosis leading to dehydration at the anode. Concurrently, in addition to water being transported from the anode by electro-osmosis, water is also generated at the cathode by the oxygen reduction reaction. When the water created in the cathode by these processes is not properly removed, its accumulation leads to poor fuel cell performance because it blocks the gas pores used for oxygen transport and forms an additional transport barrier over the reactive area. Traditionally, water management has been addressed by system engineering, i.e., by adding auxiliary systems to the basic fuel cell system to provide humidification to the anode and removal of water from the cathode. This approach has added significant complexities (e.g. reliability and durability) and costs to the system. Furthermore, these auxiliary systems reduce the net power output of the fuel cell system leading to lower conversion efficiency.Intellectual Merit: Recent development and understanding of the functions of some of the components used in a PEM fuel cell have led to a paradigm shift as to how water management can be implemented in a PEM fuel cell. It is believed that if materials with the right properties and the correct electrode configuration are used, the water transported to the cathode by electro-osmosis can be forced back through the membrane to the anode to achieve the condition of zero-net-water-transport-across-the membrane in a PEM fuel cell. This approach eliminates the need for anode gas humidification and minimizes the water removal requirement at the cathode, allowing the PEM fuel cell system to be greatly simplified. These are the intellectual merits of this work.To achieve the objective stated above in a more efficient manner, a combined approach of theoretical (modeling) and experimental work is planned. Experiments will be conducted to measure the two-phase transport properties of the key components used in the membrane-and-electrode assembly (MEA) of a PEM fuel cell. The results will be used to develop correlations of the relationship between the morphological and wetting properties and the two-phase transport properties of these components. Experiments will also be conducted to develop a four-phase (electronic-ionic-gas-liquid) micro-structure for the catalyst layer used in PEM fuel cell that is optimal for two-phase (liquid and gas) transport. Concurrently, a mathematical model of a complete MEA of a PEM fuel cell that incorporates the two-phase transport properties obtained from the experiments above will be developed. Once the model's predictions are validated experimentally, the model will be used in an optimization study to determine the electrode configuration and the morphological and surface properties of the components needed to achieve the zero-net-water-transport-across-the-membrane condition in a PEM fuel cell. Based on the optimization results new components will be developed and tested in a PEM fuel cell to validate that the condition of zero-net-water-transport-across-the-membrane is achieved.Broader Impact: First, this approach of using materials engineering to achieve optimal water management should significantly lower the complexities and costs of the PEM fuel cell system and help accelerate the commercialization of this technology. Second, the results of this work are expected to have impacts in other areas at both the basic and applied science levels. The understanding of multi-phase transport in porous media is applicable in areas such as geology, nuclear engineering and petroleum engineering. The PI also plans to continue recruiting undergraduate and graduate students of various backgrounds, genders and ethnicity in his research team. His efforts to introduce fuel cell technology to the undergraduate education are well recognized by the educational tools (experimental and literature) created by a company that he founded.