Abstract

Fuel cells are a very promising technology for transportation applications in the future. Many companies are performing research in order to make the implementation of fuel cell- powered vehicles more feasible. One issue that needs to be addressed is the fact that fuel cell vehicles will be used in sub-freezing climates. Vehicles undergo frequent shut-down and startup events, and as such, freezing and thawing effects on fuel cell components become important when the vehicle is shut off and left standing in cold climates. When shut off, fuel cells will maintain water in the membrane electrode assembly (MEA) and gas diffusion layer (GDL) unless certain purging protocols are followed. Excessive purging will lead to membrane dryout and increased system costs. Understanding the effects of repeated freeze-thaw cycling on the GDL is critical in developing effective purging techniques. When the cell is subjected to sub-freezing temperatures, the water remaining in these media will freeze. This freezing could have a detrimental impact on the pore structure, fiber integrity, and binder effectiveness in the GDL, thereby decreasing the electrochemical active surface area of the electrolytes and hurting the overall performance of the cell. This thesis presents a numerical simulation to highlight the damage caused by freezing, followed by an experimental study to observe these effects in a GDL under a compressed state to represent actual fuel cell operating conditions. This study validates the damage incurred through freeze-thaw cycling and confirms the need for developing cost-effective purging protocols. Another finding of this study is the usefulness of electrical resistance measurement techniques in identifying freeze-thaw damage to the GDL.

Library of Congress Subject Headings

Fuel cell vehicles--Cold weather operation--Mathematical models; Fuel cells--Mathematical models

Publication Date

2007

Document Type

Thesis

Student Type

Graduate

Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Satish G. Kandlikar

Advisor/Committee Member

Steven Day

Advisor/Committee Member

Jeffrey Kozak

Comments

Physical copy available from RIT's Wallace Library at TL221.13 .P45 2007

Campus

RIT – Main Campus

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