PEM Fuel Cell Material ResearchPEM Fuel Cell Material Research

Michael Fowler, P.Eng., CEAChemical EngineeringUniversity of Waterloo

200 University Ave WestWaterloo, Ontario, Canada, N2L 3G1

519-888-4567 ext 3415mfowler@uwaterloo.ca

Areas of InterestAreas of InterestMichael Fowler – Assistant Profession in Chemical Engineering at University of Waterloo (since 2004)Currently supervising (or co-supervising) 7 Graduate students Principal Areas of Interest– Reliability of Fuel Cell Materials (MEAs), Stacks

and Systems– Membrane Electrode Accessibly Degradation

Studies– Conductive Polymers for Bi-polar Plates– Hydrogen Energy System Design and Modeling

Fuel Cell Testing Facilities

•6 Fuel Cell Test Stations For Research on PEMFC •One bench for System testing (2 @ 1.2 kW Nexa, on 1.5 kW Anuvu)•65 kW bench system for ChallengeX

Fuel Cell System Models

Reliability Modeling

Reliability Model of a Fuel Cell Stack and Hydrogen Power System

Identify the Failure Modes (Material Degradation and Failure)

Identify the Causes of MaterialDegradationand Failure

Recommendations for Improved Designs, Materials and Operation Strategies

Membrane Electrode Degradation Membrane Electrode Degradation (MEA)(MEA)

To understand the degradation of fuel cell materialsTo understand how operational conditions impact the mechanism and rate of degradationTo understand the 2-D distribution of the above over the active area of the MEAWhat is done in the Lab:– Performance Assessment– Diagnostics– Forensics

Current Work Current Work –– Performance Performance Assessment Assessment In-situ

– Durability, OCV Testing, Hydration Cycling

Current Work Current Work –– Performance Performance Assessment Assessment

Ex-Situ– Fenton’s/Perox 80 Tests– Hydration cycling– Creep

Current Work Current Work -- DiagnosticsDiagnostics

The main cell diagnostics are– CV, Crossover current, AC impedance,

Fluoride release rate,

Ex-situ testing also includes– Mass, FTIR, DMTA, Tensile testing

Current Work Current Work -- ForensicsForensics

Forensic work is necessary when trying to understand the impact of degradation– e.g. SEM, Cryo-microtome, Crossover

mapping, Catalyst removal

ModelingModeling

FEM stress modeling 2-D degradation model with OH radical and mechanical degradation.

Forensics: Forensics: -- Membrane Electrode AssemblyMembrane Electrode Assembly

Pinholes and GDL Degradation

Contamination, Polymer degradation And Erosion

Delamination

Gas Diffusion Layer (GDL)Gas Diffusion Layer (GDL)

Standard Performance Diagnostics

In-SituTestsLiquid Water Diagnostics

Project OutlineProject Outline

Full Fuel Cell

Pore Scale

Inherent GDL Properties

Behaviour of Water

Ex-SituTests

PEMFCPerformance

GDLProperties

Better GDL Design

GD

L Te

stin

gPE

M T

estin

gM

odel

ing

1

2

3 Effect of Liquid Water in Cell

Behaviour of Liquid Water in GDL

Degradation of Gas Diffusion LayerDegradation of Gas Diffusion LayerGDL Properties GDL Performance

•Capillary Pressure Curves

•Hydrophilic Pore Fraction

•Distribution of PTFE

•Gas and Liquid Permeability

•Thru Plane

•In Plane

•Relative Permeability

•Compression Effects

•Young’s Modulus

•Permeability

•Porosity

•In Situ Saturation Tests

•Current Interrupt, Water Collection, etc.

•Mass Transfer Tests

•Limiting Current, AC Impedance.

PEMFC Model

•Model water transport at the cell scale

•Use appropriate models and well known parameters

Hydrophobic GDLHydrophobic GDL

Water Flow

Conventional Wisdom:

PTFE treatment confines water to a subset of pores, assuring open pores for gas transport

Gas Flow

Hydrophilic Pores:

Pores into which water spontaneously imbibes.

Saturation:

Fraction of pores filled by waterGDL

Nafion Membrane

Catalyst Layer

Hydrophobic Pore

Hydrophilic Pore

Liquid Permeability Liquid Permeability –– Thru PlaneThru Plane

0 .0 E + 0 0

2 .0 E -0 6

4 .0 E -0 6

6 .0 E -0 6

8 .0 E -0 6

1 .0 E -0 5

1 .2 E -0 5

1 .4 E -0 5

1 .6 E -0 5

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 0 0 0 8 0 0 0 9 0 0 0

P re s s u re [P a ]

Flow

Rat

e [m

3 /s]

S G L 1 0 A A -2 -1 -1

S G L 1 0 A A -2 -1 -2

S G L 1 0 A A -2 -1 -3

S G L 1 0 A A -2 -1 -4

~ 3 Darcy

Mass transfer inMass transfer in--plane and throughplane and through--plane plane in GDLin GDL

Gas Permeability Gas Permeability –– In PlaneIn PlaneΔP

Gas Flow In Gas Flow Out

Applied Pressure

Spacer

GDL

Gas Permeability Gas Permeability –– Thru PlaneThru Plane

y = 2 .11995E -06xR 2 = 9 .99804E -01

0 .0E + 00

5 .0E -06

1 .0E -05

1 .5E -05

2 .0E -05

2 .5E -05

3 .0E -05

0 2 4 6 8 10

P resssu re D ro p [P a ]

Flow

Rat

e [m

3 /s]

K = 27 .5 D a rcy'sS G L 10B A

Characteristic of the channelsCharacteristic of the channels

Other MEA InitiativesOther MEA Initiatives

Innovative Catalysis Distribution in the ElectrodeLow Cost Conductive Polymers

F ill H o p p e r

R e s in H o p p e r

E x tru d e r P e l le t iz e r In je c t io n M o ld in g M a c h in e

M ix in g

M ix in g P ro c e s s M o ld in g P ro c e s sV irg in C o m p o n e n ts

P o ly p ro p y le n e

C a rb o n F ib e rV u lc a n B la c kA c e ty le n e B la c k

F i l l H o p p e r

R e s in H o p p e r

E x tru d e r P e l le t iz e r In je c t io n M o ld in g M a c h in e

M ix in g

M ix in g P ro c e s s M o ld in g P ro c e s sV irg in C o m p o n e n ts

P o ly p ro p y le n e

C a rb o n F ib e rV u lc a n B la c kA c e ty le n e B la c k

Conductive PolymersBiBi--Polar Plate DevelopmentPolar Plate Development

Solid Modeling of a Fuel Cell Plate

Injection Moldable Bi-Polar Plate

Design of a Hydrogen Retail Design of a Hydrogen Retail StationStation

Waterloo was the Honourable Mention winner in the National Hydrogen Association 2005 H2U Competition

Home Based Distributed Energy System – Fowler-Waterloo

ControlH2

Electrolyzer

Electricity

Water

Anode exit

Cathode exit (H20, air)

Home H2Storage

H2Compressor

Solar PV

H2 Fuel Tank Fuel Cell

Automobile

Compressed H2

Charger

Battery Load

LevelingDC /AC Inverter

Optional Fuel Cell Generator

Electricity

Electricity

Retainable Waste Heat Space

Heater

Hot Water Heater

Optional Absorption

Chillier AC

Household Loads

Optional Grid

Connection

Optional Solar

heating

Optional Adaptor Switch

(OSC)

DC/DC Converter

DC/DC Converter

Hydrator (Anode)

Hydrator (Cathode)Blower

Heat

ControlValve

Air

Electricity

Electricity

EnergyWater

PressureRegulator

Natural Gas Reformer Heat

H2

University of Waterloo Alternative Fuel Team

UWAFT is one of the 17 teams that have been accepted to compete in ChallengeX. Waterloo Finished First in the first year (2005) of this 3 year competition.

Currently, UWAFT will install 65 kWatt Hydrogenics fuel cell technology into the Chevy Equinox drive train.

UWAFT would like to thank GM and the US DOE for sponsoring this competition.

QuestionsQuestions

Michael Fowler, P.Eng., CEAChemical EngineeringUniversity of Waterloo

200 University Ave WestWaterloo, Ontario, Canada, N2L 3G1

519-888-4567 ext 3415mfowler@uwaterloo.ca

GDL ResearchGDL Research

In-SituTests

Objectives Objectives

Fuel CellModel

Pore ScaleModel

Ex-SituTests

GDLProperties

PEMFCPerformance

Better GDLs

Understand Fundamental Physics

Understand Complex Interactions

Explore Fundamental

Physics

Provide Model

Validation Identify Important Relationships

Provide Model Parameters

Improve PEM fuel cell performance through focused study of the Gas Diffusion Layer

1. Understand the behaviour of liquid water in the GDL

2. Elucidate the effects of liquid water in the GDL on fundamental mass transport properties

3. Develop a PEMFC model to effectively account for liquid water effects

4. Relate the performance of PEMFCs to fundamental GDL properties

Standard Performance Diagnostics

In-SituTestsLiquid Water Diagnostics

Project OutlineProject Outline

Full Fuel Cell

Pore Scale

Inherent GDL Properties

Behaviour of Water

Ex-SituTests

PEMFCPerformance

GDLProperties

Better GDL Design

GD

L Te

stin

gPE

M T

estin

gM

odel

ing

1

2

3 Effect of Liquid Water in Cell

Behaviour of Liquid Water in GDL

Background: Water in the GDLBackground: Water in the GDL

0

0.2

0.4

0.6

0.8

1

Effe

ctiv

e D

iffus

ivity

Fac

tor (

f)

Open AirDry GDL (70% Porosity)Slightly Wet GDL (10%)Very Wet GDL (50%)

(DAB)eff = f (ε,s) x DAB

Water Flow

Gas Transport

GDLNafion

Membrane

Catalyst Layer

Hydrophobic Pore

Hydrophilic Pore

HydrophilicHydrophilic--hydrophobic Dualityhydrophobic DualityCarbon Fibre

Hydrophilic Pore

Dual Wettability Pore

Hydrophobic Pore

PTFE Coating

PermeabilityPermeability

ΔP

Q

ΔP

Q

Thru-Plane In-Plane

Permeability ResultsPermeability Results

0.E+00

1.E-05

2.E-05

3.E-05

4.E-05

5.E-05

0 5 10 15 20

Pressure Drop [Pa]

Flow

Rat

e [m

3 /s]

SGL 10AA - 1

SGL 10AA - 2

SGL 10AA - 3

Toray 090 - 1

Toray 090 - 2

Toray 090 - 3

0.0E+00

5.0E-12

1.0E-11

1.5E-11

2.0E-11

2.5E-11

3.0E-11

3.5E-11

4.0E-11

4.5E-11

5.0E-11

0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88 0.9

Porosity

Perm

eabi

lity

[m2 ]

Data - 0Datal - 90Model - 0Model - 90

0.0E+00

2.0E-06

4.0E-06

6.0E-06

8.0E-06

1.0E-05

1.2E-05

1.4E-05

1.6E-05

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Pressure [Pa]

Flow

Rat

e [m

3 /s]

SGL 10AA-2-1-1

SGL 10AA-2-1-2

SGL 10AA-2-1-3

SGL 10AA-2-1-4

← In-plane with different compressions, simulating cell assembly conditions.

↓ Thru-plane with water, elucidating the effect of GDL hydrophobicity.

← Thru-plane with gas, characterizing absolute permeability.

Capillary Pressure: MIP vs. MSPCapillary Pressure: MIP vs. MSPOO

0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

1 .0

0 .8

0 .6

0 .4

0 .2

0 .01 0 21 0 11 0 01 0 -11 0 -21 0 -31 0 -4 1 0 -3 1 0 -2 1 0 -1 1 0 0 1 0 1 1 0 2 1 0 21 0 11 0 01 0 -11 0 -21 0 -3

O c ta n e - A ir C a p illa ry P re s s u re [B a r]

Non

-Wet

ting

Phas

e Sa

tura

tion

(a )

(b )

(c )

(d )

(e )

( f)

Gostick et al. (In Press)

Capillary Pressure: MSPCapillary Pressure: MSPWW vs. MSPvs. MSPOO

0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

1 .0

0 .8

0 .6

0 .4

0 .2

0 .01 0 21 0 11 0 01 0 -11 0 -21 0 -31 0 -4 1 0 21 0 11 0 01 0 -11 0 -21 0 -3 1 0 21 0 11 0 01 0 -11 0 -21 0 -3

W a te r - A ir C a p illa ry P re s s u re [B a r ]

Non

-Wet

ting

Phas

e Sa

tura

tion

(b )

(a ) (c )

(d )

(e )

( f)

Gostick et al. (In Press)

Capillary Pressure: Model FitsCapillary Pressure: Model Fits

1 0 -2 1 0 -1 1 0 0 1 0 10 .0

0 .2

0 .4

0 .6

0 .8

1 .0

1 0 11 0 01 0 -11 0 -2 1 0 -2 1 0 -1 1 0 0 1 0 1

Non

-Wet

ting

Phas

e Sa

tura

tion

W a te r - A ir C a p illa ry P re s s u re [B a r ]

(a ) (b ) (c )

van Genuchten model Brooks-Corey modelGostick et al. (In Press)

E-Tek Cloth ‘A’ Toray 090 SGL 10BA

Capillary Pressure: Microporous LayerCapillary Pressure: Microporous Layer

0 .0 0 0

0 .0 0 5

0 .0 1 0

0 .0 1 5

0 .0 2 0

0 .0 0 0

0 .0 0 5

0 .0 1 0

0 .0 1 5

0 .0 2 0

2 3 4 5P o re R a d iu s ( lo g 1 0 r ) [n m ]

1 0 11 0 01 0 -11 0 -21 0 -31 0 -40 .0

0 .1

0 .2

0 .3

0 .4

0 .5

0 .6

0 .7

0 .8

0 .9

1 .0

Non

-Wet

ting

Phas

e Sa

tura

tion

1 0 B A

1 0 B B

A ir -W a te r C a p illa ry P re s s u re [B a r]

Pore

Vol

ume

[cc/

cc]

(a )

(b )

(c )

Gostick et al. (In Press)

Capillary Pressure: Microporous LayerCapillary Pressure: Microporous Layer

10110010-110-210-30.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Air-Water Capillary Pressure [Bar]

Non

-wet

ting

Phas

e Sa

tura

tion

SGL 10BBSGL 10BASGL10BASGL10BA + MPLMPL

Gostick et al. (In Press)

Polarization Losses: ContributionsPolarization Losses: Contributions

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.5 1 1.5 2

Current Density [A/cm2]

Ove

rpot

entia

l [V]

Open Circuit VoltageActivationActivation and OhmicActivation, Ohmic and Concentration

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2

Current Density [A/cm2]

Pow

er D

ensi

ty [W

/cm

2 ]

Open Circuit Voltage

Activation

Activation and Ohmic

Activation, Ohmic and Concentration

VCELL = ER – VACT – ViR – VCONC

Polarization Losses: Mass TransferPolarization Losses: Mass Transfer

0

0 .2

0 .4

0 .6

0 .8

1

1 .2

0 0 .5 1 1 .5

C u rre n t D e n s ity [A /c m 2]

Ove

rpot

entia

l [V]

N o n e

M in o r

M o d e ra te

S e v e re

0

0 .2

0 .4

0 .6

0 .8

1

1 .2

0 0 .5 1 1 .5

C u rre n t D e n s ity [A /c m 2]

Wat

t Den

sity

[W/c

m2 ]

N o n e

M in o r

M o d e ra te

S e v e re

FEM Lab Model: 2D UFT FEM Lab Model: 2D UFT No under-land compression.

FEM Lab Model: 2D UFTFEM Lab Model: 2D UFTWith under-land compression. Reduced mean pore size and reduced permeability

MEA Degradation ResearchMEA Degradation Research

DEGRADATION FAILURE MODES DEGRADATION FAILURE MODES (leading to degradation of performance or (leading to degradation of performance or durabilitydurability))

• Kinetic or activation loss in the anode or cathode catalyst –Loss of Apparent Catalytic Activity

• Ohmic or resistive increases in the membrane or other components –Loss of Conductivity

• Decrease in the mass transfer rate of in the reactants flow channel or electrode –Loss of Mass Transfer Rate of

Reactants

Performance Assessment Performance Assessment VOLTAGE DEGRADATION MODESVOLTAGE DEGRADATION MODES

Diagnostics:Diagnostics:Voltage Performance at End of LifeVoltage Performance at End of Life

Outliners and Instability

Change in slope of degradation

Increase in Variability

Objectives of the overall researchObjectives of the overall research

To understand the mechanisms and factors leading to failureTo understand how manufacturing and operational conditions influence the dominant degradation modeTo design better membranes and control strategies to mitigate material limitations.

Reliability JargonReliability JargonDurability - ability to resist permanent change in performance over time, i.e. degradation or irreversible degradation. This phenomena is related to ageing. Reliability - The ability of an item to perform the required function, under stated conditions, for a period of time. Combination of degradation, and failure modes that lead to catastrophic failure.Stability - recoverable function of efficiency, voltage or current density decay or reversible degradation.

Degradation CategoriesDegradation CategoriesFactors influencing operational reliability

Inherent reliability

MaterialProperties Defects Assembly Maintenance Operation

Thermal Chemical Mechanical

Degradation Mechanism

Stability Power Lifetime

Performance Impact

Factors Influencing ReliabilityFactors Influencing ReliabilityThese include: Inherent Reliability– component properties (conductivity, mechanical

strength) – component defects (cracks, catalyst clusters) – Manufacturing (cell compression, MEA

manufacturing)Other Influencing Factors– operational environment (humidity, start stop)– Maintenance (stack deconstruction)

After these are specified the way in which the cell will degrade is determined.

Degradation MechanismDegradation MechanismThermal Degradation

Thermal decomposition

Chemical Degradation Radical attack ContaminationCatalytic area lossCatalyst migration

Mechanical DegradationPinching Creep Erosion DelaminationGDL Compression

Performance ImpactPerformance ImpactUltimately what we want out of a fuel cell is POWER!In general the impact of the degradation mechanism can be categorized into three impacts– Catalytic area loss– Conductivity loss– Mass transport ability loss

The importance of one degradation mode over another is based on how much it impacts performance and lifetimeVoltage, Current, powerStability, catastrophic failureLifetime

Reliability testing Reliability testing Durability testing at Waterloo consists of three main steps:Performance Evaluation

Polarization curves, voltage, current, power, efficiency (and degradation of these), lifetime Performance data is not enough

DiagnosticsCyclic voltametry, crossover, impedance, fluoride release rate, HELIOX tests, current decay, current interrupt

ForensicsElectron microscopy, pinhole mapping, infrared spectroscopy, mechanical property analysis, de-catalyzation

MEA Features in New MembranesMEA Features in New MembranesManufacturing plays a crucial role in durabilityInherent reliabilityHere is where defects and morphology can be controlled

CrackingDelaminationThickness variationsGDL MP layer morphologyNafion clustersPlatinum clustersMacroscopic orientation

CrackingCracking

Causes and Impacts of Causes and Impacts of CrackingCracking

Impacts– Location for defect propagation to

a pinhole– Areas of catalytic inactivity– Increased resistance in the catalyst

layer– Flooded areas– Areas for catalyst erosion

DelaminationDelamination

Causes and Impacts of Causes and Impacts of DelaminationDelamination

Impacts– Vulnerable location for further delamination– Increased resistance between the layers– Flooded areas– Imbalance in current and ion flow on the

membrane

Thickness VariationsThickness Variations

Causes and Impacts of Thickness Causes and Impacts of Thickness VariationsVariations

Impacts– Crossover– Mechanical weak spot– Shorting– Pinholes

Fresh

GDL DegradationGDL Degradation

2000 hours of external ageing

GDL DegradationGDL Degradation

GDL DegradationGDL Degradation

Morphology impacts degradation The manufacturers have control over morphologyImpacts– Loss of PTFE = more water

accumulation– Increased flooding

Nafion Clusters

NafionNafion ClustersClusters

Cluster IdentificationCluster IdentificationBackscattered electron detectorBright spots were shown to be platinum clusters

200nm

Causes and Impacts of ClustersCauses and Impacts of Clusters

Impacts– Increased resistance to ion transport– Reduction of active catalyst area– Hot spots/cold spots

Macroscopic Orientation of Macroscopic Orientation of MaterialMaterial

Causes and Impacts of Causes and Impacts of OrientationOrientation

Impacts– Contact resistance variation– Mechanical Stress variations– Less control over morphology

ConclusionsConclusionsThere are many different morphological features in an MEAThese are created largely during the manufacturing process Some of these features will have a clear impact on the performance and reliability of the fuel cellSince they are created at the manufacturing level, thus there is the potential to control them

Future WorkFuture WorkShowing links between morphological features and degradationExamining pin hole formation and the role of mechanical stressEstablishing links between operating conditions and the mechanism of degradation and failureDesigning better membranes and control strategies