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Research Papers

Polymer Electrolyte Fuel Cell Transport Mechanisms: A Universal Approach to Multilayer Two-Phase Modeling Through the General Transport Equation

[+] Author and Article Information
Pratap Rama

Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire LE11 3TU, UKp.rama@lboro.ac.uk

Rui Chen

Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire LE11 3TU, UK

J. Fuel Cell Sci. Technol 7(5), 051007 (Jul 16, 2010) (16 pages) doi:10.1115/1.4001004 History: Received April 20, 2009; Revised October 19, 2009; Published July 16, 2010; Online July 16, 2010

A mathematical multilayer, multispecies two-phase model for polymer electrolyte fuel cells (PEFCs) is presented based on fundamental molecular theory using the general transport equation (GTE). The GTE was previously developed and applied to bridge the gap that exists between the benchmark modeling philosophies in the literature for transport across the PEFC. In the current work, the GTE is applied with Darcy’s law to describe water transport and water uptake through the porous and quasiporous layers of a PEFC under single- and two-phase operating conditions. The characteristic transport equations and available material properties from the literature are translated into a single-cell fuel cell model, which is implemented using the object modeling technique. The PEFC model is applied to predict and validate the net water transport ratio and water content under a range of operating conditions. The numerical model exhibits good agreement with experimental data under both vapor- and liquid-equilibrated conditions. The model is then applied in a water transport study to determine the effects of cell compression on local water content, liquid water intrusion, water transport, and Ohmic resistance across nonreinforced polymer electrolyte membranes (PEMs) under two-phase operating conditions. The modeling results suggest that the presence of liquid water at the cathodic boundary of the PEM and a well-established liquid water network can affect water uptake and water transport and can reduce the Ohmic resistance of the PEM.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

PEFC structure for the one-dimensional two-phase model

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Figure 2

Comparison of simulated and experimental values of net water flux per proton for the 18 test cases (39,44)

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Figure 3

Specific resistance profiles across the PEM for simulated (black) and measured (points) results at 0.2 mA/cm2 (◆), 0.1 A/cm2 (▲), 0.2 A/cm2 (●), and 0.3 A/cm2 (◼) (63), and simulated water content profiles (gray)

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Figure 4

Simulated (line) and measured (points) water content profiles as a function of nondimensional PEM thickness for three levels of supply gas relative humidity: 92% (◼), 80% (▲), and 40% (●) (64)

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Figure 5

Water content profile (a) and water volume fraction (b) as a function of nondimensional position along the constrained PEM thickness for 0.0<χ<1.0. Note that the nondimensional position of 0 reflects the anodic PEM boundary and 1 reflects the cathodic boundary.

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Figure 6

Liquid pressure (a) and pore expansion profiles (b) as functions of nondimensional position along the constrained PEM thickness for 0.0<X<1.0

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Figure 7

Change in PEM thickness relative to the original thickness of the 25.4 μm as functions of degree of constraint

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Figure 8

Effect of PEM constraint on the average water content of the PEM

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Figure 10

Change in average and net water flux profiles as functions of degree of constraint

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Figure 11

Superficial gradient in water content as a function of degree of constraint

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Figure 12

Vapor- and liquid-phase components of net water transport as a function of position along PEM thickness for χ=0.6

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Figure 9

Ohmic resistance to proton transfer in the PEM as a function of degree of constraint

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