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

质子交换膜燃料电池，也被称为聚合物电解质膜（PEM）燃料电池，正在开发用于运输，固定式燃料电池和便携式燃料电池的应用。PEM燃料电池将氢和氧的电化学反应中释放的化学能转化为电能，而不是直接燃烧氢气和氧气产生热能。其膜组件的结构由阳极和阴极组成，阳极和阴极由含有催化剂的电解质分开。一股氢气流被输送到阳极一侧，在那里它被催化地分裂成质子和电子。新形成的质子通过聚合物电解质膜渗透到阴极一侧。电子沿着外部电路移动到阴极一侧，产生燃料电池的电流输出。同时，一股氧气流被输送到阴极一侧，在那里氧分子与穿过聚合物电解质膜的质子和通过外部电路到达的电子发生反应，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，使其成为使用化石燃料作为能源的内燃机的理想替代品。该项目旨在开发更好的PEM燃料电池。PEM燃料电池的高功率密度操作通常受到催化剂层中高液态水饱和度的限制，这是由于添加的离子聚合物相具有高润湿性，从而为催化剂位点提供了三维离子通道。在这个EAGER项目中，根据最近对氟碳基离子聚合物界面特性的发现产生的假设，提出了一种简单的方法。它是在高相对湿度下的热处理导致聚合物表面具有高分数的磺酸基团和高度亲水性，而在干燥条件下的热处理导致聚合物表面具有小分数的磺酸基团和非常高分数的疏水性PTFE相。基于这些观察，我们假设，如果位于催化剂层孔隙中的离子聚合物涂层的外表面可以是疏水的，那么在催化剂表面产生的任何水，通过聚合物涂层扩散到聚合物涂层/气相界面，都将聚集并移动，而不会在聚合物涂层上形成一层。因此，氧气和氢气可以直接进入离子聚合物相和催化剂表面。如果这种形态能够实现，燃料电池的性能有望大大提高。为了验证这一假设，提出了两个任务：1)验证在干燥或低RH条件下热处理离子聚合物（例如，Nafion）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)确认修改膜？S的外表面润湿性不影响聚合物膜内的质子电导率，也不会对聚合物/催化剂界面产生不利影响。如果这种方法成功，它可能会改变PEM燃料电池的水管理，并导致性能更高、成本更低、更耐用的燃料电池的发展。这可能会加速燃料电池动力汽车的商业化，这是一种节能环保的交通系统。PI一直积极招收来自不同民族、种族、性别、地理、经济和家庭背景的学生，并为这些学生进入全球市场做好准备。PI还将组织访问当地的小学和中学，举办燃料电池和其他可再生能源示范讲习班。

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.