The Effect of Catalyst Layer Cracks on the Mechanical Fatigue of Membrane Electrode Assemblies

Mechanical fatigue testing has shown that MEAs (membrane electrode assemblies) fail at lower stresses than PEMs (proton exchange membranes) at comparable times under load. The failure of MEAs at lower stresses is influenced by the presence of mud cracks in the catalyst layers acting as stress concentrators. Fatigue testing of MEAs has shown that smaller-scale cracking occurs in the membrane within these mud cracks, leading to leaking during mechanical fatigue testing and the failure of the membrane. In addition, this testing of MEAs has further established that the cyclic pressurization pattern, which affects the viscoelastic behavior of the membranes, has a significant effect on the relative lifetime of the MEA. To investigate this behavior, pressure-loaded blister tests were performed at 90 °C to determine the biaxial fatigue strength of Gore-Primea® Series 57 MEAs. In these volume-controlled tests, the leak rate was measured as a function of fatigue cycles. Failure was defined as occurring when the leak rate exceeded a specified threshold. Post-mortem characterization FESEM (field emission scanning electron microscopy) was conducted to provide visual documentation of leaking failure sites. To elucidate the viscoelastic behavior of the MEA based on these results, testing was conducted using a DMA to determine the stress relaxation behavior of the membrane. This data was then used in a FEA program (ABAQUS) to determine its effect on the mechanical behavior of the MEAs. A linear damage accumulation model used the ABAQUS results to predict lifetimes of the membrane in the MEAs. The models showed that under volume-controlled loading, the stress decays with time and the stress dropped towards the edges of the blisters. The lifetimes of the MEAs varied depending on the cycling pattern applied. This is important for understanding failure mechanisms of MEAs under fatigue loading, and will help the fuel cell industry in designing membranes that better withstand imposed hygrothermal stresses experienced during typical operating conditions.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Macromolecular Science and Engineering

Department dc:contributor.department

Macromolecular Science and Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2010

Author dc:creator

• Pestrak, Michael Thomas

Chair dc:contributor.committeechair

• Case, Scott W.

Committee members dc:contributor.committeemember

• Dillard, David A.
• Ellis, Michael W.

• membrane electrode assembly
• Mechanical behavior
• fatigue lifetimes
• blister test
• proton exchange membranes

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-10202010-113758

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/35447