Date of Completion

8-6-2014

Embargo Period

8-1-2015

Major Advisor

Wilson Chiu

Associate Advisor

Brice Cassenti

Associate Advisor

Tai-Hsi Fan

Associate Advisor

Kyle Grew

Associate Advisor

William Mustain, Ugur Pasaogullari

Field of Study

Mechanical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Fuel cell technology has many promising characteristics which make it an attractive prospect for an environmentally friendly energy conversion device. Some of the benefits of using these devices include high efficiencies, diversity in applicability and scalability, high energy densities, and the ability to use a wide variety of fuels. However, continuing limitations which are a constant thrust in basic research include improving performance, system cost, and longevity. One promising fuel cell type, the polymer electrolyte fuel cell, is a low temperature fuel cell which generally scales from the portable power level up to small back-up power units or automobile engines. Two basic types of these cells are the proton and anion exchange membrane fuel cells (PEMFC and AEMFC). These fuel cells make use of a solid polymer membrane as the ion conducting electrolyte. Like other fuel cells, polymer electrolyte membrane fuel cells are the subject of intensive research to improve their overall performance while reducing cost and degradation. The polymer membrane material itself is the subject of many studies since the membrane must have high ionic conductivity while maintaining durability for the fuel cell to function. The situation is further complicated because the ionic conductivity is linked intimately to the hydration state of the membrane. Keeping the delicate water balance of the system such that the membrane is hydrated but the electrodes are not flooded is a constant struggle. Naturally, the transport behavior occurring within the membrane in respect to water, ions, and gases are of great interest since this all contributes to the performance of the fuel cell. This work presents several studies of polymer electrolyte membranes, both PEM and AEM, for each of the aforementioned species types. These studies include measuring water diffusivity and gas permeability as well as modeling transport during ion exchange processes and cell operation. Due to the complicated heterogeneous nature of not only the polymer electrolyte membranes, but also many other fuel cell materials, popular effective medium theories are investigated. These analytical theories are useful as they provide homogeneous approximations of transport properties in complicated systems. The theories are extended to allow for added complexity in the systems studied in the form of multiple material types and anisotropic behaviors.

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