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与汽车内燃机相媲美的技术，具有高功率、长距离和短加油时间的能力。本项目提出的工作将详细研究同时发生在多孔电极所有组分中的多相传输过程。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)需要许多描述多相传输特性的本构关系，这些特性是未知的，并且在这些非典型材料中很难测量；(b)由于在有限尺寸域中体积平均假设的失败以及这些模型的不适用性，理论上对传输过程的表述不合理到毛细管驱动的过程。该项目将开发一个先进的孔隙网络建模框架，能够同时模拟孔隙尺度分辨率下的所有相关输送过程，以确保考虑离散水配置的关键影响。孔隙网络建模需要的实验确定的输运参数要少得多，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取燃料电池电极的所有组成层的信息。这项研究的结果将是一个期待已久的和迫切需要的理解水在电极中的输送机制和影响的物理参数。这些信息的可用性将通过对所有相关现象的全面理解，使电极结构和材料的设计达到最佳燃料电池性能。

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.