Mechanics of proton exchange membranes : time, temperature, and hydration dependence of the stress-strain behavior of persulfonated polytetrafluorethylene

Fuel cells are an important part of the future strategy for reducing dependence on fossil fuels as the world's supplies become more limited and greenhouse gasses become more of a concern. Proton Exchange Membrane Fuel Cells (PEMFC), in which protons from hydrogen gas are passed across a membrane to react with oxygen gas producing electricity, with water as the only waste product, are a cleaner and potentially more efficient chemical energy conversion method. However, the current usefulness of PEMFC is limited by the lifespan and high cost of the fuel cell unit, and more specifically the membrane electrode assembly (MEA). At the center of most contemporary MEA is a thin membrane (- 25 - 100pm thick) of persulfonated polytetrafluoroethylene manufactured by Dupont and known commercially as Nafion. Nafion has the unique quality of being microphase separated into hydrophobic and hydrophilic domains composed of backbone rich and sulfonic acid side chain rich regions respectively. This polymer electrolyte membrane is responsible for rapidly conducting the protons from the hydrogen side to the oxygen side while preventing electrons, hydrogen, and oxygen from passing through. Because of this selective permeability requirement it is important that the membrane possess good mechanical durability so that it does not form pinholes during operation (something which it has been shown to do experimentally). The goal of this thesis was to develop an understanding of the mechanical properties of Nafion as well as a comprehensive material model that captures all the features that are important to how a membrane deforms in an operational fuel cell, including the time, temperature, and hydration dependence of the elastic regime, yield, strain hardening, and stress relaxation at low to moderate strains.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Silberstein, Meredith N

Advisor dc:contributor.advisor

• Mary C. Boyce.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/43125

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/43125