Post on 10-May-2018
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PEM Fuel Cell Design, Engineering, PEM Fuel Cell Design, Engineering, Modeling and Diagnostic IssuesModeling and Diagnostic Issues
Frano BarbirDirector of Fuel Cell Technology and Chief ScientistProton Energy Systems50 Inwood Road, Rocky Hill, CT 06067e-mail: fbarbir@protonenergy.comwww.protonenergy.com
NSF Workshop on Engineering Fundamentals of Low-Temperature PEM Fuel Cells, Arlington, VA, November 14-15, 2001
Hydrogen
Air
Collector Plate
Membrane
x
y
z
Cathode catalyst Gas diffuser
Anode catalyst Gas diffuser
Collector Plate
Gas channel
Gas channel
0.5
Cur
rent
Den
sity
(A/c
m2 )
-10
1 Z (mm)
0
2
4
6
8
X(cm
)
0.850.760.670.580.490.410.320.23
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yes
design
fabricate
test
requirements Knowledge:materialsprocessesinteractions
material characterizationquality control
Does it work?no
Fuel cell development processFuel cell development process
design
fabricate
test
model
Knowledge:materialsprocessesinteractions
requirements
diagnostics
Should it work?
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Role ofRole ofmodeling andmodeling anddiagnostics indiagnostics infuel cell fuel cell development development processprocess
Major componentsMajor components
MEA
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Bi-polarplate
end platebus plate
bi-polar collector plates
tie rod
MembraneCatalystCatalyst supportCatalyst layerGas diffusion layerGaskets/framesFlow fieldSeparator/connectorBus plates/terminalsEnd platesClamping mechanismFluid connectionsManifoldsCooling plates/arrangementsHumidification section (optional)
Stack design/engineering issuesStack design/engineering issues
Uniform distribution of reactants to each cellUniform distribution of reactants inside each cellUniform temperature distribution in each cellMinimal resistive losses
• good electrical contacts• selection of materials
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• Electro-osmotic drag removes water from the anode side. With thicker membranes, back diffusion of water is difficult - the anode side loses water content.0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
HF
RES
ISTA
NC
E (o
hm c
m2)
or C
ELL
VO
LTA
GE
(V)
CURRENT DENSITY (A/cm 2 )
Fg 3, TF69,109,74,117 Ox's
IncreasingMembraneThickness
(NeatOxygenCathodes)
Cell Resistance and Performance:PEM Thickness Effects
Materials Science and Technology DivisionPEFC Overview
electronic
cell resistancein-situ
(current interrupt)
100-150 mΩcm2
ionic40-60 mΩcm2
ex-situ20-30 mΩcm2
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Cell resistanceCell resistance
F
F
gold plate
sample
backing
backing
gold plate
press
press
mV
I
Electronic resistancemeasurement(ex-situ)
R = A VI
A
(mΩcm²)
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force
resi
stan
ce
contact resistance
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Resistance is a function of clamping forceResistance is a function of clamping force
electronic
ex-situcontact
bulk<1 mΩcm2
cell resistancein-situ
(current interrupt)
100-150 mΩcm2
20-30 mΩcm2
ionic40-60 mΩcm2
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Cell resistanceCell resistance
force
resi
stan
ce
contact resistance example of pressure distribution
forc
e
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Resistance is a function of clamping forceResistance is a function of clamping force
Stack design/engineering issuesStack design/engineering issues
Uniform distribution of reactants to each cellUniform distribution of reactants inside each cellUniform temperature distribution in each cellMinimal resistive losses
• good electrical contacts• selection of materials
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Account for thermal expansionNo crossover or overboard leaksMinimum pressure drop (reactant gases and coolant)No water accumulation pocketsDesign for manufacture/design for assembly
Difference between single cell and stackDifference between single cell and stack
Flow distributionActive areaTemperature control (heating/cooling)Temperature distributionCompression/electrical contactsLeak pathsAdjacent cell interference
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Modeling:Parameters and Processes (partial list)
O2H2Air
Flow-Fields - Convection -Two-Phase Flow
Gas Diffusion Layer - Gas Diffusivity - Porosity - Tortuosity - Electronic Conductivy - Gas Composition
Catalyst Layer - Ionic Conductivity - Electronic Conductivity - Gas Permeability - Reactant Solubility - Capacitance
Electro-catalyst - Exchange Current Density - Tafel Slope - Roughness Factor
Membrane - Water Content - Ionic Conductivity - Water Diffusivity - Electro-osmotic Drag - Hydraulic Permeability
Overall: Mass Balance - Heat Balance Cell Parameters
Fluid flowHeat transfer
Materials Science and Technology DivisionPEFC Overview
Modeling as a design toolModeling as a design tool
A model is approximation of the real world.
Every model is wrong!
Any model is as good as the assumptions it is built upon are valid!
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Concentration at the boundary is known
Local current density is known
Isothermal conditions
Heat transfer by conduction in the gas phase in negligible
Pressure is constant
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Assumptions used in fuel cell modelingAssumptions used in fuel cell modeling
1-D (y)2-D (x-y or z-y)2 2-D (x-y and z-y)3-D models (x-y-z)
One phaseTwo phase models
Hydrogen
Air
Collector Plate
Membrane
x
y
z
Cathode catalyst Gas diffuser
Anode catalyst Gas diffuser
Collector Plate
Gas channel
Gas channel
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Modeling Modeling domaindomain
DifferentDifferentmodels models
When someone presents the modeling results no one trusts those except the presenter/person who did themodeling.
except the presenter/personwho performed the experiment.
When someone presents the experimental resultseveryone trusts those
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Truths and myths about Truths and myths about experimental and modeling workexperimental and modeling work
0
500
1000
Y(X10
-3mm
)
-1
-0.5
0
0.5
1
Z (mm)
0
100
200
300
400
500
600
700
800
X (x10- 2 cm)
0.16800.14280.11760.09240.06720.0420
Oxygen mole fraction
Oxygen molar fractionconventional flow field vs. interdigitated flow field
0
0.5
1
Y(m
m)
0
0.5
1
1.5
2
Z (mm)
0
1
2
3
4
X (cm)
0.16800.12600.08400.0420
In
Oxygen molar fraction contours
0.0890.0990.1100.1100.1200.130
0.1400.150
0.160
0.160
0.170
0.170
0.18
0
0.180
0.180
0.190
0.190
0.20
0
0.200
X (cm)
Y(m
m)
0 1 2 3 4 5 6 7 80
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Gaschannel
Diffuser
Catalyst
0.0680.087
0.106
0.106
0.124
0.124
0.143
0.1
0.161
0.1
0.180
0.1
Z(mm)
Y(m
m)
0 0.25 0.5 0.75 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Collector plate gaschannel
catalyst
gasdiffuser
across x-y direction
across y-z direction
Current density distribution
0 . 5
Cur
rent
Den
sity
(A/c
m2 )
- 10
1 Z ( m m )
0
2
4
6
8
X( c m
)
0 . 8 50 . 7 60 . 6 70 . 5 80 . 4 90 . 4 10 . 3 20 . 2 3
Hydrogen
Air
Collector Plate
Membrane
x
y
z
Cathode catalyst Gas diffuser
Anode catalyst Gas diffuser
Collector Plate
Gas channel
Gas channel
Temperature profiles across the fuel cell
85
90
Temperature
( oC)
0
2
4
6
8
x
01
2y
92.7091.2789.8588.4286.9985.5784.1482.71
Temperature (oC)
0 0.5 1 1.5 2Y(mm)
80
82
84
86
88
90
92
94
Tem
pera
ture
(Co )
Near inletMiddle of channelNear exit
Cathode gas channel Anode gas channel
Diffuser
Diffuser
Membrane
Catalyst
Polarization curveCurrent interruptAC impedancePressure dropPolarization curve hysteresisComparative polarization curvesCurrent density mapping
design
fabricate
test
model
Knowledge:materialsprocessesinteractions
requirements
diagnostics
Should it work?
design
fabricate
test
model
Knowledge:materialsprocessesinteractions
requirements
diagnostics
Should it work?
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Diagnostics as a design toolDiagnostics as a design tool
Current density mappingCurrent density mapping
M. Potter, S.Shaw, P. Adcock, and J. McGuirk, Loughborough University,Computer Modelling of Solid Polymer Fuel Cells, 1998
S.J.C. Cleghorn, C.R. Derouin, M.S. Wilson, and S. Gottesfeld, A Printed Circuit Board Approach to Measuring Current Distribution in a Fuel Cell, J. Appl. Electrochem., 1997
Current density Current density mappingmapping
Polarization curveCurrent interruptAC impedancePressure dropPolarization curve hysteresisComparative polarization curvesCurrent density mappingTemperature mappingFlow visualizationNeutron imagingPost-mortem analyses
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Diagnostics as a design toolDiagnostics as a design tool
Development of new membrane materialLess expensiveRetains water or does not rely on water for proton
conductance
Development of new (less expensive) catalyst material
Effect of catalyst layer structure on fuel cell performance
Engineering of catalyst layer structure
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Fuel Cell R&D OpportunitiesFuel Cell R&D Opportunities
Investigation of surface quality and interface conductivity
Better understanding of thermal effects inside the fuel cell
temperature distributionphase change
Design of fuel cell as a heat exchanger
Design of a humidifier/heat exchanger
Investigation of 2-phase flow characteristics
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Fuel Cell R&D Opportunities Fuel Cell R&D Opportunities –– cont. (2)cont. (2)
Understanding of fuel cell degradation/aging/failure
Development of methods for accelerated life-testing
Development of diagnostic methods and tools
Development of standardized methods for characterization of fuel cell materials/subcomponents (pre-installation & post mortem)
Development of advanced control algorithms
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Fuel Cell R&D Opportunities Fuel Cell R&D Opportunities –– cont. (3)cont. (3)
AcknowledgmentAcknowledgment
My thanks to Dr. Hongtan Liu, Department ofMechanical Engineering, University of Miamifor letting me use his slides for this presentation.I also used the slides or materials from:• Mahlon Wilson, Los Alamos National Laboratory,• Simon Cleghorn, W.L.Gore&Assoc., (formerly with LANL)• Marcus Potter, University of Loughborough.
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