model of pem fuel cell cathode sarah hipple egee 520 may 3, 2007
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Model of PEM Fuel Cell Cathode
Sarah HippleEGEE 520
May 3, 2007
Introduction PEM Fuel Cell Structure
Platinum Electrodes Very effective at splitting hydrogen at the anode Less effective at splitting oxygen at the cathode
This Analysis: Focuses on transport of species through the Cathode Species Distribution Velocity of molecules
Governing Equations Darcy's Law
Conservation of mass & momentum balance Equation:
Maxwell-Stephan Equation Mass Balance Equation:
0
pp
RT
M
)()()(~
i1
uiTij
j
jjj
j
N
ji jii R
T
TD
p
pM
MM
M
M
MD
t
where
N
wO
w
w
O
O
MMM
M
11
andRT
pM
Boundary Conditions
RT
k F
FD
a
M
MMM
x eOO
OOOwOO 4exp
4
)21(2
RT
k F
FD
a
M
MMM
x eOO
OwwwOw 4exp
4
)21(2)21(2
RTk F
Fa
MMM
xp
O
OwO 4exp
4)21(2
(1)
(2)
(3)
Solution Parameters
Basic Operating Conditions:
T=80°C
Atmospheric Pressure
Solution: Velocity
Velocity:
Solution: Oxygen and Water Distribution
From the left:•Graph of oxygen mass fraction at 5 x values; •Image of Oxygen mass fraction distribution;•Image of water mass fraction distribution
ValidationComparison to work of Yi and Nguyen & He, Yi, and Nguyen
On the left: Pressure
On the right: Velocity Field
Parametric Study Oxygen Concentration at the Interface with the Polymer
Electrolyte Membrane Air as the cathodic feed (left image) Pure oxygen as the cathodic feed (right image)
Importance Drying out of the membrane (too much oxygen/air) Reduction of power output (too little oxygen/air) Carbon monoxide poisoning prevention
Conclusions This model agrees with other authors’
models This model can help determine species’
distributions and flow paths through the cathode in: The existing model A model with modified pressure, temperature,
porosity, dimensions, or cathodic feed
Image Sources Aguirre, Lauren. (2005, July). Nova: scienceNOW: How Fuel Cells
Work: PBS. URL www.pbs.org/wgbh/nova/sciencenow/3210/01-fcw.html (visited 2007, January 30)
Yi, Jung Seok, & Nguyen, Trung Van. (1998, April). An along-the-channel model for proton exchange membrane fuel cells. Journal of The Electrochemical Society, 145 (4), 1149-1159.
He, Wensheng, Yi, Jung Seok, & Nguyen, Trung Van. (2000, October). Two-phase flow model of the cathode of PEM fuel cells using interdigitated flow fields. American Institute of Chemical Engineers. AIChE Journal, 46 (10), 2053-2064.