Investigation of Shorting by Penetration in Pem Fuel Cell Membranes
Fox, Christopher James
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Electrical shorting through the proton exchange membrane (PEM) is a form of early failure commonly found in PEM fuel cells. In order to improve the durability and thus the commercial potential for PEM fuel cells, this form of failure must be understood and mitigated. This research investigates whether complete penetration is the most likely cause of shorting and establishes general parameters (force, contact pressure, temperature, and time) that lead to shorting in a typical PEM material, NafionÂ® NRE211. Data was obtained from a novel indentation apparatus that was coupled with an electrical circuit to assess the force and depth of penetration at which shorting occurs in a PEM at temperatures ranging from 70ï °C to 100ï °C. The results show that shorting occurs when full penetration is reached, based on both displacement at shorting, and resistance of the electrical circuit at shorting. In addition, a finite element model was created in a commercial finite element tool (Abaqus) in an attempt to predict time to penetration under loads and geometric configurations typically found in PEM fuel cells. The finite element model was investigated for use with standard Abaqus material modules (e.g. two-layer viscoplastic and hyperelastic-viscoelastic) describing NafionÂ® behavior. The results suggest that the standard material models do not sufficiently describe NafionÂ® behavior in this particular application and suggest the need for alternative material models that capture both the viscous and plastic nature of NafionÂ®.
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