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RESEARCH PAPERS

Stresses in Proton Exchange Membranes Due to Hygro-Thermal Loading

[+] Author and Article Information
Yaliang Tang, Michael H. Santare, Anette M. Karlsson

Department of Mechanical Engineering, University of Delaware, Newark, DE 19716

Simon Cleghorn, William B. Johnson

 Gore Fuel Cell Technologies, Elkton, MD 21922

J. Fuel Cell Sci. Technol 3(2), 119-124 (Oct 23, 2005) (6 pages) doi:10.1115/1.2173666 History: Received June 20, 2005; Revised October 23, 2005

Durability of the proton exchange membrane (PEM) is a major technical barrier to the commercial viability of polymer electrolyte membrane fuel cells (PEMFC) for stationary and transportation applications. In order to reach Department of Energy objectives for automotive PEMFCs, an operating design lifetime of at least 5000h over a broad temperature range is required. Reaching these lifetimes is an extremely difficult technical challenge. Though good progress has been made in recent years, there are still issues that need to be addressed to assure successful, economically viable, long-term operation of PEM fuel cells. Fuel cell lifetime is currently limited by gradual degradation of both the chemical and hygro-thermomechanical properties of the membranes. Eventually the system fails due to a critical reduction of the voltage or mechanical damage. However, the hygro-thermomechanical loading of the membranes and how this effects the lifetime of the fuel cell is not understood. The long-term objective of the research is to establish a fundamental understanding of the mechanical processes in degradation and how they influence the lifetime of PEMFCs based on perfluorosulfuric acid membrane. In this paper, we discuss the finite element models developed to investigate the in situ stresses in polymer membranes.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

The calculated temperature profile inside the unit fuel cell assuming a constant anode/GDE temperature of 85°C and cathode/GDE temperature of 86°C

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Figure 2

Two different geometries have been modeled where the flow field has either (a) aligned or (b) alternating gas channels. The mechanical boundary conditions are noted in the figure. In addition, two additional boundary conditions (not shown) for case (a) and (b) were imposed by subjecting the stack to either constant displacement or constant load clamping at the top.

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Figure 3

In-plane stress (σxx) distributions in the membrane for constant load of the stack for the aligned and alternating geometries

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Figure 4

Out-plane stress (σzz) distributions in the membrane for constant load of the stack for the aligned and alternating geometries

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Figure 5

Shear stress (σxz) distributions in the membrane for constant load of the stack for the aligned and alternating geometries

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Figure 6

A comparison of the stress distributions in the membrane along the upper surface of the membrane when using either constant load or constant displacement clamping methods for the two different gas channel alignments

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Figure 7

The effect of thickness on the maximum in-plane stress (σxx) in the membrane is greater in the case of aligned flow fields under fixed displacement clamping than in the other cases studied

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Figure 8

The effect of thickness on the maximum out-plane stress (σzz) in the membrane is greater when the under fixed displacement clamping than when under fixed load displacement

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Figure 9

The maximum shear stress (σxz) in the membrane is relatively low in all cases, but highest when the flow fields are in the alternating geometry under fixed displacement clamping conditions

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Figure 10

The effects of anisotropy of the membrane swelling coefficient on the stress distributions in the membrane in aligned assembly

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Figure 11

The effects of anisotropy of the membrane swelling coefficient on the stress distributions in the membrane in alternating assembly

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