EAGER: Engineering the Ionic Polymer Phase Surface Properties in a PEM Fuel Cell Catalyst Layer

Nguyen-1518755质子交换膜燃料电池，也称为聚合物电解质膜(PEM)燃料电池，正在为运输、固定式燃料电池和便携式燃料电池应用而开发。质子交换膜燃料电池将氢和氧在电化学反应中释放出来的化学能转化为电能，而不是直接燃烧氢和氧气气体来产生热能。它们的膜组件的结构由阳极和阴极组成，阴极由含有催化剂的电解液隔开。一股氢流被输送到阳极侧，在那里它被催化分解为质子和电子。新形成的质子通过聚合物电解质膜渗透到阴极侧。电子沿着外部电路传播到阴极侧，产生燃料电池的电流输出。同时，一股氧气被输送到阴极侧，在那里氧气分子与渗透到聚合物电解质膜的质子和通过外部电路到达的电子反应形成水分子。这种燃料电池在相对较低的温度下工作，体积小，重量轻，是使用化石燃料作为能源的内燃机的理想替代品。该项目的目标是开发更好的PEM燃料电池。PEM燃料电池的高功率密度运行通常受到催化层中高液态水饱和度的限制，这是因为添加了高润湿性的离子聚合物相以提供三维离子通道到催化剂位置。在这个迫不及待的项目中，一种简单的方法被提出，该方法基于最近对氟碳基离子聚合物界面性质的发现产生的假设。这是因为在高相对湿度下的热处理导致聚合物表面具有高比例的磺酸基团和高度的亲水性，而在干燥条件下的热处理导致聚合物表面具有少量的磺酸基团和很高比例的疏水聚四氟乙烯相。根据这些观察，假设如果位于催化剂层的孔中的离子聚合物涂层的外表面可以疏水，则在催化剂表面产生并通过聚合物涂层扩散到聚合物涂层/气相界面的任何水都将形成珠状并移动，而不在聚合物涂层上形成一层。因此，氧气和氢气将直接进入离子聚合物相和催化剂表面。如果能够实现这种形态，燃料电池的性能将有望得到极大的提高。为了验证这一假设，提出了两项任务：1)验证在干燥或低相对湿度条件下对离子聚合物(例如Nafion)进行热处理将导致具有永久疏水外表面的聚合物膜的假设，并确定形成永久疏水外表面的最佳热处理条件；2)证实了改性膜的S外表面润湿性不会影响聚合物膜内的质子导电性，也不会对聚合物/催化剂界面产生不利影响，如果该方法成功，可能会改变质子交换膜燃料电池中的水管理，从而开发出性能更高、成本更低、更耐用的燃料电池。这可能会加快燃料电池动力汽车的商业化进程，这是一种节能、环保的交通系统。PI一直在积极招收来自不同种族、种族、性别、地理、经济和家庭背景的学生，并一直在为这些学生进入全球市场做准备。PI还将组织对当地小学和中学的访问，举办燃料电池和其他可再生能源的示范研讨会。

Nguyen - 1518755Proton exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM) fuel cells, are being developed for transport, stationary fuel cell and portable fuel cell applications. A PEM fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy. The structure of their membrane assembly consists of an anode and a cathode that is separated by an electrolyte that contains a catalyst. A stream of hydrogen is delivered to the anode side where it is catalytically split into protons and electrons. The newly formed protons permeate through the polymer electrolyte membrane to the cathode side. The electrons travel along an external circuit to the cathode side creating the current output of the fuel cell. Meanwhile, a stream of oxygen is delivered to the cathode side where oxygen molecules react with the protons permeating through the polymer electrolyte membrane and the electrons arriving through the external circuit to form water molecules. Such fuel cells operate at relatively low temperatures, are small and lightweight, making them ideal as potential replacements for internal combustion engines that use fossil fuels as their energy source. This project is aimed at developing better PEM fuel cells.High power density operation in PEM fuel cells is often limited by high liquid water saturation levels in the catalyst layer due to high wettability of the ionic polymer phase that is added to provide three dimensional ionic access to the catalyst sites. In this EAGER project a simple approach is proposed based on a hypothesis generated from recent discoveries on interfacial properties of fluorocarbon-based ionic polymers. It is that heat treatment at high relative humidity leads to a polymer surface with a high fraction of sulfonic acid groups and a high degree of hydrophilicity, while heat treatment at dry conditions leads to a polymer surface with a small fraction of sulfonic acid groups and a very high fraction of the hydrophobic PTFE phase. Based on these observations, it is hypothesized that if the external surface of the ionic polymer coating located in the pores of the catalyst layers could be made hydrophobic, any water that is produced at the catalyst surface and diffuses through the polymer coating to the polymer coating/gas phase interface would bead and move away without forming a layer over the polymer coating. Therefore, oxygen and hydrogen gases would have direct access to the ionic polymer phase and catalyst surface. If this morphology could be achieved the fuel cell performance is expected to be greatly increased. To test this hypothesis, two tasks are proposed: 1) Validating the hypothesis that heat treating an ionic polymer (e.g., Nafion) in a dry or low RH condition will lead to a polymer film with a permanent hydrophobic external surface and determine the heat treatment conditions that are optimal for the formation of a permanent hydrophobic external surface; and 2) Confirming that modifying the membrane?s outer surface wetting property does not affect the proton conductivity within the polymer film, nor does it adversely affect the polymer/catalyst interface.If this approach is successful, it could transform water management in PEM fuel cells and lead to the development of higher performance, lower cost, and more durable fuel cells. This could accelerate the commercialization of fuel cell powered vehicles, an energy efficient and environmentally friendly transportation system. The PI has been actively recruiting students from different ethnic, racial, gender, geographical, economic and family backgrounds and has been preparing these students for the global market. The PI will also organize visits to local elementary schools and middle schools to host demonstration workshops on fuel cell and other renewable energy sources.