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Water Transport Exploratory Studies

2009 DOE Hydrogen Program ReviewMay 18-22, 2009Presented by: Rod Borup

Solicitation Partners:Los Alamos National Lab, National Institute of Standards and

Technology, Sandia National Lab, Oak Ridge National Lab, SGL Carbon, W.L. Gore, Case Western Reserve University

Additional Partners/Collaborations:University of Texas-Austin, Lawrence Berkeley National Lab, Nuvera

Fuel CellsFC_35_Borup

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project Overview

Barriers• Project initiated FY07

– Start March ’07• 4 year Project Duration

– End March ’11• ~> 50 % complete

Water management is critical for optimal operation of PEM Fuel Cells

• Energy efficiency• Power density• Specific power• Cost• Start up and shut down energy• Freeze Start Operation

• Total project funding– DOE Cost: $6,550,000

(over 4 yrs)– Cost Share: $290,811

• Funding for FY09LANL $1100kPartners (Univ. & Ind.) $200kOther National Labs $350k FY09 Total $1650k

• Direct collaboration with Industry, Universities and other National Labs (see list)

• Interactions with other interested developers

• Project lead: Los Alamos National Lab

Timeline

Partners

Budget

Collaboration: Organizations / Partners• Los Alamos National Lab: Rod Borup, Rangachary Mukundan, John

Davey, David Wood, Partha Mukherjee, Jacob Spendelow, Tom Springer, Tommy Rockward, Fernando Garzon, Mark Nelson

• Sandia National Laboratory: Ken Chen & C.Y Wang (PSU)

• Oak Ridge National Lab: Karren More

• Case Western Reserve University: Tom Zawodzinski

• SGL Carbon Group: Peter Wilde

• National Institute of Standards and Technology (no-cost): Daniel Hussey, David Jacobson, Muhammad Arif

• W. L. Gore and Associates, Inc.: Will Johnson, Simon Cleghorn (Purchase request basis)

• Lawrence Berkeley National Lab: Adam Weber, Haluna P. Gunterman (directly funded)

• Univ. Texas-Austin (additional sub-contract): Jeremy Meyers

• Nuvera: James Cross, Amedeo Conti (Technical Assistance – freeze workshop)

Relevance: Objectives

• Develop understanding of water transport in PEM Fuel Cells (non-design-specific) – Evaluate structural and surface properties of materials affecting water

transport and performance– Develop (Enable) new components and operating methods – Accurately model water transport within the fuel cell– Develop a better understanding of the effects of freeze/thaw cycles

and operation– Develop models which accurately predict cell water content and

water distributions– Work with developers to better state-of-art– Present and publish results

Approach• Experimentally measure water in situ operating fuel cells

– Neutron Imaging of water– HFR, AC impedance measurements– Transient responses to water, water balance measurements– Freeze measurement / low temperature conductivity

• Understand the effects of freeze/thaw cycles and operation• Help guide mitigation strategies.

• Characterization of materials responsible for water transport– Evaluate structural and surface properties of materials affecting water transport

• Measure/model structural and surface properties of material components • Determine how material properties affect water transport (and performance)• Evaluate materials properties before/after operation

• Modeling of water transport within fuel cells– Water profile in membranes, catalyst layers, GDLs– Water movement via electro-osmotic drag, diffusion, migration and removal

• Develop (enable) new components and operating methods– Evaluate materials effects on water transport

In situ Measurement of Membrane Water

• Membrane conductivity is a f(water content)( λ = # of Water molecules per # of sulphonic acid sites)• Large literature base measuring water in Nafion®

• Vast majority of studies were conducted ex situ

Prior Neutron Imaging and modeling based off of literature results show large discrepancy (Factor of 4 difference) A.Z.Weber, M.A. Hickner, Electrochimica Acta 53 (2008) 7668.• T. E. Springer, T. A. Zawodzinski, and S.

Gottesfeld, Polymer Electrolyte Fuel Cell Model, J. Electrochem. Soc., Vol. 138, No. 8, 1991 2334

(λ = 14 at Cathode interface)

• Zawodzinski, et al., J. Electrochem. Soc., Vol. 140, No. 4, April 1993

(λ as a f(RH) – λ = 14 RH=100, λ = 22 Liq.)

• J. T. Hinatsu, M. Mizuhata, and H. Takenaka, J. Electrochem. Soc., Vol. 141, No. 6, June 1994

(λ as a f(RH) at 80 oC by thermogravimetric)

• L.M. Onishi, J.M. Prausnitz and J. Newman, J. Phys. Chem. B 2007, 111, 10166-10173

(Membrane water content is a f(thermal history)λ = 13-14 (predried), λ = 21 +/- 1 (preboiled) (Suggest why 26 papers are ‘incorrect’)

Worked with NIST to in situ evaluate membrane water• Measured through-plane water content:

• Gore 18 micron membrane• N212• N117• N117 3-layer sandwich• 20 mil Nafion® Membrane• 40 mil Nafion® Membrane

Equilibrated with RH, Liquid water, under fuel cell operation, under H2 pump operation.

Water Profiles for Different Membrane Geometries3 x Nafion® 117

0

0.5

1

1.5

2

2.5

3

3.5

4

0 50 100 150 200

pixels

wat

er th

ickn

ess

OCV0.5 A, pump0.59 A, pump-0.57 A, pumpH2/O2, 0.15 A

40 Mil Nafion® MembraneN117λ = 14

(40 mil ~ 1000 micron)

Acknowledge: Steve Grot, Ion Power

18 μm Gore

20 Mil Nafion®

40 Mil Nafion®

• Interface between membranes is hydrophobic• Water peaks in the middle of each Nafion®

117 membrane slice • Interface between membrane and catalyst

layer maybe hydrophilic• Water peaks near each of the catalyst

layers (liquid water in catalyst layer pores)• Can clearly distinguish membrane profiles

• FWHM (≈ 100 μm) is much smaller than membrane thickness (≈ 585 – 1000 μm)

• Water gradient formed at saturated conditions by H2 pump

λ = 7.5 λ = 15.3

λ = 18.7

λ = 6

Water Gradient

(80 oC 175% RH)

Wat

er T

hick

ness

Wat

er T

hick

ness

Wat

er T

hick

ness

20 mil Nafion® Membrane(RH Equilibration, Fuel Cell and H2 Pump Operation)

0

0.5

1

1.5

2

2.5

3

-150 -100 -50 0 50 100 150

Pixel

mm

H2O

OCV0.1 A0.2 A

λ = 8.3

λ = 11.5

Fuel Cell Operation 100/100 % RH 40 C

• Water profile is not flat at OCV. due to edge effects.

• Middle 7 pixels vary by <4% for the 50/50 case and <5% for the 100/100 case.

• Single Nafion® 20 mil electrolyte• 6mg/cm2 Pt on cathode and anode• SGL Sigracet® 24 AA (Hydrophilic

no MPL)• Vertical setup

0

0.5

1

1.5

2

2.5

3

-150 -100 -50 0 50 100 150pixels

mm

/ H

2O

OCV0.1 A pump0.2 A pump0.5 A pump

λ = 8.3

λ = 11.5

Hydrogen Pump

• Membrane hydration is observed to be• λ = 5.0 (50/50%) and 8.3 (100/100%)• λ increases with water production (Fuel Cell) and with

H2 pump (liquid water formation, electro-osmotic drag)• Observed differences with 40 mil membrane at 80 oC

& super-saturated conditions• At 100/100, 0.1 A there is no discernible difference between

pump operation and normal operation• At 100/100, 0.2 A cathode flow field become wet when the

cell is operated in fuel cell, however not in H2 pump mode• Increasing pump current causes decreasing water on the

anode and increasing water on the cathode side.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-50 -30 -10 10 30 50

Pixel

mm

H2O

OCV0.1 A0.2 A

GDL GDLλ = 8.8

50/50 % RH, 40 C – Fuel Cell Operation

λ = 5

λ = 7.1

λ Comparison

0

4

8

12

16

20

24

40 60 80 100Relative Humidity

Lam

bda

(H2O

/SO

4-- )

40 C - THIS WORK80 C - THIS WORK40 C (Liquid) - THIS WORK80 C (Liquid) - THIS WORKTom Z (30 C)Tom Z (30 C - Liquid)Hinatsu (80C)

• Cathode under-saturated - Membrane water increases from λ ≈ 6 to λ ≈ 10 with current• Membrane water gradients observed, much less than in modeling literature• Reasonable agreement with some literature data at low RH

• Do not measure absolute reliance on ‘membrane thermal history’ • Membranes will equilibrate at different λ for 100% RH and liquid water•Observe higher λ at equivalent water activity at higher temperatures

• Other recent literature on in situ measurements of membrane water content:

λ Measurement Summary:λ ~ 10-12 at 100% RHλ ~ 18-24 liquid H2OFuel Cell current increases λ :

at 50/50 % RH’s 5 8.8at 100/100% 8.3 11.5(depends upon current)

Tsushima, Shoji, Water Transport Analysis by Magnetic Resonance Imaging, LANL/AIST Meeting, San Diego, 2008

A. Isopo, V. Rossi Albertini, An original laboratory X-ray diffraction method for in situ investigations on the water dynamics in a fuel cell proton exchange membrane, Journal of Power Sources 184 (2008) 23–28

0123456789

10

0 200 400 600 800 1000 1200Time (sec)

Wat

er C

onte

tnt (

mg/

cm2 )

-0.2

0

0.20.4

0.6

0.8

11.2

1.4

1.6

Res

ista

nce

( Ωcm

2 )

Channel Water (MEA + GDLs + Channels)Land Water (MEA + GDLs)HFR

0.5 amps 34 amps

Wetting TransientNeutron Images of Cell Wetting

During Current Transient

Minimum flows at 82cc/min and 333cc/min at the anode and cathode @ 0.5A. At 34A it is 1.2 and 2.0 stoich flows.

Wetting from 0.5A to 34A 40C and 0/0 inlet RH

Integrated Water Content from Neutron Images During Current

Transient

0

1

2

3

4

5

6

7

8

0 500 1000 1500 2000 2500

Time (sec)

Wat

er C

onte

tnt (m

g/cm

2 )

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Resistan

ce (

Ωcm

2 )

Channel Water (MEA + GDLs + Channels)

Land Water (MEA + GDLs)

HFR

34 amps

0.5 amps

Drying TransientDrying from 34A to 0.5A 40C and 0/0 inlet RH

Neutron Images of Cell Drying During Current Transient

Integrated Water Content from Neutron Images During Current

Transient

• Wetting response is faster (10 – 30 sec) than the reciprocal drying response (~ minutes) • Wetting response is the result of water produced at cathode which quickly back

diffuses to into the membrane. • Drying response requires water to move out of the MEA through wetted GDLs.

Segmented Polarization Data for Different Cathode GDLs

• Cathode GDL:– GDL 24BC (5/23 wt% PTFE substrate/MPL) – GDL 24B”C”5 (5/5 wt% PTFE

substrate/MPL)• Anode GDL:

– GDL 24BC (5/23 wt% PTFE substrate/MPL)

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.4 0.8 1.2 1.6Current Density (A/cm2)

Volta

ge (V

)

Segment 1 (GDL 24BC)Segment 5 (GDL 24BC)Segment 10 (GDL 24BC)Segment 1 (GDL 24BC5)Segment 5 (GDL 24BC5)Segment 10 (GDL 24BC5)

100% / 100% RH (A/C)

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2Current Density (A/cm2)

Volta

ge (V

)

Segment 1 (GDL 24BC)Segment 5 (GDL 24BC)Segment 10 (GDL 24BC)Segment 1 (GDL 24BC5)Segment 5 (GDL 24BC5)Segment 10 (GDL 24BC5)

50% / 50% RH (A/C)

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2Current Density (A/cm2)

Volta

ge (V

)

GDL 24BC, 100% / 100% RH (A/C)GDL 24BC5, 100% / 100% RH (A/C)GDL 24BC, 50% / 50% (A/C)GDL 24BC5, 50% / 50% RH (A/C)

Total Cell Performance

Best performance at inlet

Best performance at outlet

Segmented Cell Measurements show where Mass Transport losses dominate versus where IR losses, and kinetic occur

Performance of 2 GDLs~ identical

AC Impedance Data of Different Segmentsfor Different Cathode GDLs

• GDL 24BC5 maintains higher water content in catalyst layer at high V and high RH (i.e. lower impedance).

• GDL 24BC has better water management at low V and low RH.

-0.10

0.10

0.30

0.50

0.70

0.90

0.0 0.2 0.4 0.6 0.8 1.0 1.2Zr (Ω·cm2)

-Zj (Ω

·cm

2 )

GDL 24BC, Seg 1GDL 24BC5, Seg 1GDL 24BC, Seg 10GDL 24BC5, Seg 10

10 kHz120 mHz

12 Hz

Vcell = 0.84 V100% / 100% RH (A/C)

-0.10

0.10

0.30

0.50

0.70

0.90

0.0 0.3 0.6 0.9 1.2Zr (Ω·cm2)

-Zj (Ω

·cm

2 )

GDL 24BC, 0.84 VGDL 24BC5, 0.84 VGDL 24BC, 0.54 VGDL 24BC5, 0.54 V

100% / 100% RH (A/C)

Total Cell

10 kHz 120 mHz

12 Hz

-0.1

0.1

0.3

0.5

0.7

0.9

0.0 0.4 0.8 1.2

Zr (Ω·cm2)

-Zj (Ω

·cm

2 )

GDL 24BC, Seg 5GDL 24BC5, Seg 5GDL 24BC, Seg 10GDL 24BC5, Seg 10

10 kHz

120 mHz

8.3 Hz

Vcell = 0.54 V50% / 50% RH (A/C)

Charge x-ferResistance

Mass Transport problems

Less Mass Transport problems

Charge x-ferResistance

MTResistance

Interrelation of GDL, Catalyst and membrane

• Increasing ECSA loss with segment position due to greater water content• Greater increase in membrane crossover and lower ECSA for 24BC5 compared

with 24BC (over 308 hrs)– higher liquid water content in cathode catalyst layer with 24BC5.

• Demonstrates interrelated durability effects between GDL (water content), membrane and catalyst.

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1 2 3 4 5 6 7 8 9 10Segment No. (Channel Position)

Nor

mal

ized

Cro

ssov

er C

urre

nt

Den

sity

GDL 24BC (308 hr)

GDL 24BC5 (308 hr)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 500 1000 1500

Vo

ltag

e (

V)

/ H

FR

(Ω

cm2)

Time (s)

GoreTM MEA at 0.02 A cm-2

Start -10 oCStart -10 oC HFRstart -20 oCstart -20 oC HFR

Freeze: Low resolution imaging

0

5

10

15

20

25

30

35

0 500 1000 1500 2000

Water con

tent (μ

m cm

‐2)

Time (s)

Water density images @ ‐10 oC and ‐20 oCGoreTM Primea® MEA

Channel Average (‐10 oC)

Land Average (‐10 oC)

Channel Average (‐20 oC)

Land Average (‐20 oC)

-10 oCIncrease of HFR stops after a timeWater under land almost stops accumulatingWater accumulation mostly under channels

- 20 oCWater distribution always even between land/channelWater probably in the MEA or GDLHFR continuously increases

• Membrane hydration due to the generated current and back diffusion is dominant at sub-freezing temperatures

• Ice build up results in charge transfer and mass transfer resistance increases

Freeze: High resolution imaging

• Location of frozen water (ice) depends on operating temperature and current density• Water distribution closer to the cathode catalyst layer with:

• Decreasing temperature• Increasing current

• Greater water formation possible at higher temperatures and lower current densities

SerpentineCell

Distance (μm)

Wat

er (m

m)

‐0.06

0.04

0.14

0.24

0.34

1000 1500 2000Pixel

mm W

ater

m10C,0.225A/cm2

m20C,0.043A/cm2Anode

GDL CathodeGDL

MEA

1000

0.3

0.2

0.1

0.0

Freeze Durability

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2

Gore MEA/Paper GDL after Break-InGore MEA/Paper GDL after 4 starts at -10CLANL MEA/Cloth GDL after BreakinLANL MEA/Cloth GDL after 4 starts @-10Gore MEA/Cloth GDL after Break-InGore MEA/Cloth GDL after 4 starts @-10C

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2

Gore MEA/Paper GDL after Break-InGore MEA/Paper GDL after 11 startsLANL MEA/Cloth GDL after BreakinLANL MEA/Cloth GDL after 12 startsGore MEA/Cloth GDL after Break-InGore MEA/Cloth GDL after 10 starts

Durability after 4 starts @ -10C is dependant on MEAGore MEA/Cloth GDL loses 27% cathode ECSALANL MEA/Cloth GDL loses 7% cathode ECSAGore MEA/Paper GDL loses 46% cathode ECSA

Durability after ≥ 10 starts @ -10C > T > -40C is also dependant on MEAPaper GDL shows maximum lossin performanceMass transport losses in addition to kinetic losses

Current (A/cm2)

Current (A/cm2)

Volta

ge (V

)Vo

ltage

(V)

ESEM (Environmental SEM)GDL Cross-Section Water Mapping

• Fluorine distribution uneven• Fluorine at outer edges of GDL

• Less H2O in center of GDL

Fluorine

Exposed to 0.75 Torr H2O• Fluorine distribution uneven with carbon• Oxygen (Water) seems to align on carbon fibers

SGL GDL 24DC (24DI)

5% / 5% PTFEExposed to 1 Torr H2O

X-RAY Tomograph Image of water in GDL Pores

GDL

KaptonWater

MPL side against KaptonKapton

• Evaluate pore size density and distribution

• Observe GDL compression• Observe/monitor water

diffusion• Evaluate water wetting and

water diffusion pathways

Water Inside SGL GDL Pores

Water

(23% PTFE MPL, 20% Substrate) (5% PTFE MPL, 5% Substrate)

Water

MPL

Water

Significantly more water in GDL pores as cross-section approaches water layer

Modeling: Capillary Pressure SimulationCCM CL

Liquid water saturationLiquid water saturation

• LB model simulates liquid water transport through the CL, insight into underlying two-phase dynamics.

• Capillary pressure and relative permeability as functions of liquid water saturation are employed in macroscopic two-phase fuel cell models.

• Other modeling activities described in supplemental slides (Ken Chen Sandia; Adam Weber LBNL, Jeremy Meyers UTA) 0 20 40 60 80 1000

2

4

6

8

10

CCM

Liquid Water Saturation (%)

Cap

illar

y P

ress

ure

(ba

r)

0 20 40 60 80 1000

2

4

6

8

10

CCM

Liquid Water Saturation (%)

Cap

illar

y P

ress

ure

(ba

r)

P. P. Mukherjee et al., “Polymer Electrolyte Fuel Cell Modeling – a Pore-Scale Perspective,” Chapter in Progress in Green Energy, Springer, in press (2008).

Future WorkExperimental and Characterization• 3-D X-Ray tomography during operation observing water transport in GDL pores

• Identify hydrophobic pores vs. hydrophillic pores• Identify liquid water pathways in GDLs

• Incorporate 3-D X-ray tomography PSD into Capillary Pressure Simulation• Conduct segmented cell measurements varying the GDL PTFE loading as a function of cell

location and with counter-flow inlets configurations.• Measure the effect of compression and GDL substrate porosity• Better identify GDL loss of hydrophobicity degradation mechanism

• Surface characterization (TEM) and surface species identification (DRIFTS)• Measure capillary pressure in GDLs with concurrent counter flow of water and gas

• (Collaboration with LBNL LANL visiting student from LBNL)

Modeling• Develop a multiphase model for simulating ice formation and thawing during start-up, and

investigating the effects of cell design (e.g., catalyst-layer thickness, pore volume) on PEMFC startup under sub-zero temperatures.

• Using modeling parameters, correlate impact of diffusion-media wettability on fuel-cell performance and demonstrate agreement with NIST water images

• Effects to examine– Heterogeneous structures

• Separate hydrophobic and hydrophilic PSDs• Anisotropy• Structural and chemical changes within a GDL

– Compression– Transients including hysteresis

Summary of Technical AccomplishmentsProviding fundamental information on water transport

• Varying MPL and substrate Teflon® loadings and cell operating conditions• Using Neutron imaging, AC impedance to get data about water content and

performance• Use data to develop comprehensive GDL water transport model in addition to the

existing membrane/electrode model• Equilibrium water content in the membrane, how membrane water content changes

with RH, T, current and water production• Segmented cell operation

• How water varies as a function of GDLs, inlet RH, cell position, and the effect that water content has on membrane durability and catalyst durability

• Response of GDL and membrane water to transients• Fast membrane wetting• Slow GDL de-wetting, followed by membrane drying

• GDL Characterization• Profiling the GDL in 3-D• Observing the location in the GDL structure where water exists• Correlating water with Teflon® content in the GDL

• Freeze• Durability• Monitoring where water freezes as a function of operating variables

Thanks to

• U.S. DOE -EERE Hydrogen, Fuel Cells and Infrastructure Technologies Program for financial support of this work– Program Manager: Nancy Garland

Additional Slides

Milestones

Mon Yr Milestone

Dec 08 Demonstrate isothermal operations at -10oC, -20oC, -30oC and -40oC. Report on degradation due to sub-freezing isothermal operations.(ECS Transactions (2008), 16(2), 1939-1950)

Mar 09 Correlate water content data to ex situ membrane and electrode conductivity results(Neutron imaging of water content as f(RH, T, current)

Mar 09 Provide accurate water balance data to verify models(Modified: Provided water content in X,Y,Z as function of operating variables)

Mar 09 NIST to provide z-direction imaging capability (Go/No Go). (Using the cross-section (25 micron) and field view (150 micron) detectors to understand water content in 3-d).

Jun 09 Quantify effects of varying GDL hydrophobicity(Already have used multiple variation of GDL PTFE loadings, will continue to expand matrix)

√

√

√

√

√

Modeling Flow in Diffusion Media

• Goal is to model the impact of wettability and two-phase flow– Previous model framework* is being modified to include contact-

angle distribution• Input parameters

– 1. Fit the material properties to data (e.g., PSD of SGL24BC)

– 2. Fit a contact-angle distribution to capillary-pressure vs. saturation data

• Hysteresis needs to be considered• Majority of the curve (saturation) is due to

the GDL and not MPL pores

*A.Z. Weber, et al., JES, 151, A1715 (2004).

Data provided by J. Gostick

( ) θθΨ= ∫∫ dd)( rrVS

2-pt normal distribution

2-pt log-normal distribution

• Simulations of cathode DM– Explore two-phase flow effects and DM signature by setting oxygen flux and

changing liquid pressure at inlet (i.e., catalyst-layer side) • Mimics what happens in fuel-cell operation• Example: Equivalent oxygen flux set at 2 A/cm2 at 80°C, 100% RH, 1 bar, ΔT=1°C

– MPL can support higher pressures– Develop optimum DM structures

• Optimum contains separate small porehydrophobic network

– Optimization depends on operating regime


0.85

0.9

0.95

1

1.05

1.1

0 0.2 0.4 0.6 0.8 1

Pressure (b

ar)

Dimensionless DM distance

Liquid

Gas

Resistance mainly in MPL even though saturation dominated by GDLGas pressure as important as liquid pressure since capillary pressure is their difference

v = 0.04 cm/s

GDLMPL


• Future Work– Using modeling parameters, correlate impact of

diffusion-media wettability on fuel-cell performance and demonstrate agreement with NIST water images

– Effects to examine• Heterogeneous structures

– Separate hydrophobic and hydrophilic PSDs– Anisotropy– Structural and chemical changes within a GDL

• Compression• Transients including hysteresis

– Impact of boundary conditions

Pc vs. S

SGL

• 0% (blue) and 5% Teflon®

(purple) from Gostick• Red from Nguyen• Data from Mench not shown

Toray

• Data from Schwartz, Nguyen, Gostick, Darling

Unanswered Questions

• Is our approach okay?– Can we decouple the two effects…is it reasonable?

• Are there interfacial effects– CL, flooding and mass-transport resistance– Matching of pore sizes (capillary condensation, intrusion)– Droplet removal into the channel

• Impacted by CAD or PSD?

• Impact of other things– Anisotropy in properties– Different structural zones– Mechanical properties and compression– Changes in absolute permeability

• What to do with hysteresis• Aging?

– Same PSD (if Teflon® does not migrate) but change CAD to make it more hydrophilic

Calculating Properties

• Previous saturation

• Now

• Do the above using a Gauss-Legendre integration method so have

– A 20 term series is used and the wi’s and θi’s are calculated between the range 0 to 90 and 90 to 180

• Refinement is to use ± 4 standard deviations (σk) to increase accuracy

• fHI can be seen as

( ) ( ) ( )∑∑∫∫⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛ −−−+

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛ −+=−+=−+=

∞

k k

kk

k k

kk

r

r

srrf

fs

rrffrrVfrrVfSfSfS

2lnln

erf12

1 2lnln

erf12

d)(1d)(1 o,HO,c,rHI

o,HI,c,rHIHI

0HIHOHIHIHI

HO,c

HI,c

( ) ( ) ( )

∫∑∑∫∑

∫ ∑∫∫∫∫

+θ

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛−⎟⎟

⎠

⎞⎜⎜⎝

⎛ θγ−

+⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛σ

θ−θ−

πσ=

θ⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛ −ϑ+θΨ=θθΨ=θθΨ=

180

90

o,,

90

0

o,,

o,,c,

... d2

lncos2lnerf1

2

2

21exp

21

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Modeling Phase Change in a PEM Fuel Cell:(water vapor liquid water)

Motivation: it is critically important to elucidate the dynamic phenomena inside the PEM fuel cell: Where does water vapor condense? Where does liquid water evaporate? Under what process conditions do condensation/evaporation occur?

Ken S. Chen ([email protected]) • Sandia National Labs

Model geometry and cross sections for analysis

⇔

MEA

Cathode GDL(200μm)

Anode GDL (200μm)

AnodeChannelAnodeLand

Cathode Land

CathodeChannel

Cross-Section of the Cellin the flow direction (Section A)

In Plane Direction

Thro

ugh

Pla

neD

irect

ion

Flow Direction

100 mm

CCL 10μmMem 30μmACL 10μm 2.

45m

m

2 mm

0.5mm

1 mm

Section A(cross sectionIn flow direction)

Modeling results: computed temperature, saturation, phase-change rate

•Temperature is high above/below the channels whereas low above/below the lands due to higher conductivity of the bipolar plate.

• Evaporation takes place in the GDL underneath the channel near the channel-land boundary.

• Condensation mainly occurs within the cathode catalyst layer and in GDL near CL/GDL interface.

• Water also condenses on the cooler land surface.

temperature

355354.9354.8354.7354.6354.5354.4354.3354.2354.1354353.9353.8353.7353.6353.5353.4353.3353.2

Anode Side

Cathode Side

Cathode Channel

Anode Channel

CathodeBipolar Plate

AnodeBipolar Plate

AnodeBipolar Plate


saturation

0.260.250.240.230.220.210.20.190.180.170.160.150.140.130.120.110.10.090.080.070.060.050.040.030.020.01

Anode Side

Cathode Side

Cathode Channel

Anode Channel


AnodeBipolar Plate

AnodeBipolar Plate


Temperature contours Saturation contours

Phase-change rate contours(cathode side only)

*Reference: S. Basu, C.-Y. Wang, and K. S. Chen, “Phase change in a polymer electrolyte fuel cell”, accepted for publication in J. Electrochem. Soc.

Ph Ch Rate

2218141062

-2-6-10-14-18-22

Condensation at thecathode CL and GDL

Cathode Channel


Condensation atbipolar plate surface


GD

LC

L

Evaporation


Cathode Channel





Cathode Channel




(1.0A/cm2, Stoic (A/C) =2.0, RH=100%)

Ph Ch Rate

9.586.553.520.5

-1-2.5-4-5.5-7


Cathode Channel




GD

LC

L

Evaporation

Ph Ch Rate

2218141062

-2-6-10-14-18-22


Cathode Channel




GD

LC

L

Evaporation


Cathode Channel





Cathode Channel




Effect of Inlet Humidity on Phase-Change Rate (I =1.0A/cm2, Stoic =2.0, at Section A)

100% RH

45% RH

67% RH

25% RH

mg/cm3-sPh Ch Rate

2218141062

-2-6-10-14-18-22


Cathode Channel




GD

LC

L

Evaporation

mg/cm3-s

Ph Ch Rate

2218141062

-2-6-10-14-18


Cathode Channel




GD

LC

LEvaporation

mg/cm3-smg/cm3-s

• Water vapor condenses on the cooler land surfaces.• Condensation region at cathode CL & GDL shrinks in size as inlet humidity is lowered.• Evaporation regions increase in size when inlet humidity is lowered.

*Reference: S. Basu, C.-Y. Wang, K. S. Chen, accepted for publication in J. Electrochem. Soc.

Transient Water Management ModelingUT Austin On-going Work

membrane catalyst layer GDLcatalyst

layerGDL

slope related toGDL mass transportor MEA relaxation

HFR modeled by neglecting interfacialresistance, and by appropriate timescales oftransient processes: quasi-steady state ingas phase; liquid and polymer-phase waterprofile relaxation

Modeling of HFR Transient Response to Step in Current

water transport exploratory studies - energy.gov•energy efficiency •power density •specific...

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