Characterization and transport modeling of atypical porous materials

聚合物电解质膜燃料电池是目前唯一能够匹配汽车内燃机高功率、远距离和短加油时间的技术。本项目中提出的工作将详细研究同时发生在多孔电极所有组件中的多相传输过程。这将涉及到新的实验技术和先进的孔隙尺度建模。以前研究电极中复杂相互作用的所有努力都是基于体积平均建模方法，这些方法(A)需要大量的本构关系来描述这些非典型材料中未知且难以测量的多相传输特性，以及(B)由于在有限大小的区域中体积平均假设的失败以及此类模型不适用于毛细管驱动的过程，在理论上不能很好地表示传输过程。该项目将开发一种先进的孔隙网络建模框架，能够以孔隙尺度分辨率同时模拟所有相关的运移过程，以确保考虑离散水配置的临界影响。孔隙网络建模所需的实验确定的传输参数要少得多，而且实际上可以用来预测一些实验上无法获得的信息。这种建模方法需要的主要信息是孔隙度和毛管压力曲线等结构信息。将开发新的方法来获得燃料电池电极的所有组成层的信息。这项研究的结果将是人们期待已久的、亟需了解的水在电极中的传输机制以及影响的物理参数。这些信息的可获得性将有助于通过对所有相关现象的全面了解来设计电极结构和材料以实现最佳的燃料电池性能。

The polymer electrolyte membrane fuel cell is the only currently available technology capable of matching the capabilities of the automotive internal combustion engine for high power, long range and short refueling times. The work proposed in this project will investigate, in detail, the multiphase transport processes occurring in all components of the porous electrode simultaneously. This will involve both novel experimental techniques and advanced pore scale modeling. All previous efforts to study the complex interactions in the electrode have been based on volume average modeling approaches which (a) require numerous constitutive relationships describing the multiphase transport properties which are not known and are challenging to measure in these atypical materials and (b) are theoretically unsound representations of the transport processes due to the failure of the volume averaging assumption in finite size domains and the inapplicability of such models to capillarity driven processes. This project will develop an advanced pore network modeling framework capable of simulating all relevant transport processes simultaneously with pore scale resolution to ensure that the critical effects of discrete water configurations are considered. Pore network modeling requires significantly less experimentally determined transport parameters and in fact can be used to predict some experimentally inaccessible information. The main information required by this modeling approach is structural information such as porosity and capillary pressure curves. Novel approaches will be developed for obtaining this information for all constituent layers of the fuel cell electrode. The result of this study will be a long awaited and much needed understanding of water transport mechanisms in the electrode and the the physical parameters of influence. The availability of this information will enable design of electrode structure and materials for optimum fuel cell performance through a comprehensive understanding of all related phenomena.