MEA and Stack Durability for PEM Fuel Cells · 2006 DOE Hydrogen Program Review MEA & Stack Durability for PEM Fuel Cells 3M/DOE Cooperative Agreement No. DE-FC36-03GO13098 Project
Post on 13-Jul-2019
224 Views
Preview:
Transcript
2006 DOE Hydrogen Program Review
MEA & Stack Durability for PEM Fuel Cells
3M/DOE Cooperative Agreement No. DE-FC36-03GO13098
Project ID # FC8
3 Mike Hicks
3M Company May 16, 2006
This presentation does not contain any proprietary or confidential information
Overview
Timeline • 9/1/2003 – 6/30/2007* • 70% complete * Revised end date subject to
DOE approval
Budget • Total $10.1 M
– DOE $8.08 M – Contractor $2.02 M
• Funding received in FY05: $2.43 M
• Funding for FY06: $2.60 M
Barriers & Targets • A. Durability: 40k hrs
Team Members • Plug Power • Case Western Reserve
University • University of Miami
Consultant • Iowa State University
MEA & Stack Durability for PEM Fuel Cells 2 3 Fuel Cell Components
Objectives Develop a pathway/technology for stationary PEM fuel cell systems for enabling
DOE’s 2010 objective of 40,000 hour system lifetime to be met
Goal: Develop an MEA with enhanced durability – Manufacturable in a high volume process – Capable of meeting market required targets for lifetime and cost – Optimized for field ready systems – 2000 hour system demonstration
Focus to Date • MEA characterization and diagnostics • MEA component development • MEA degradation mechanisms • MEA nonuniformity studies • Hydrogen peroxide model • Defining system operating window • MEA and component accelerated tests • MEA lifetime analysis
MEA & Stack Durability for PEM Fuel Cells 3 3 Fuel Cell Components
Approach To develop an MEA with enhanced durability ….
Optimize MEAs and Components for Durability
Optimize System Operating Conditions to Minimize
Performance Decay
• Utilize proprietary 3M Ionomer • Improved stability over baseline ionomer
• Utilize ex-situ accelerated testing to age MEA components • Relate changes in component physical properties to changes in MEA
performance • Focus component development strategy
• Optimize stack and/or MEA structure based upon modeling and experimentation
• Utilize lifetime statistical methodology to predict MEA lifetime under ‘normal’ conditions from accelerated MEA test data
MEA & Stack Durability for PEM Fuel Cells 4 3 Fuel Cell Components
Accomplishments GDL Characterization
• Developed new test equipment to measure capillary pressure in GDLs Membrane
• Completed investigation of reinforced membranes – reinforcement may not be necessary for membrane durability
• Identified membrane failure mode and implemented solution to mitigate it • Ongoing monitoring of membrane properties in accelerated tests
Membrane Degradation Mechanism • Analyzed experimental and literature data – more than just end group degradation • Utilized ionomer model compounds to identify likely ‘points of attack’ and provide insight
into ionomer degradation mechanism • Developed initial hydrogen peroxide model to study peroxide in operating fuel cell
MEA Nonuniformity Studies • Completed 121-channel segmented cell and investigated the effects of flow rate, load
setting and GDL type; determined high gas stoichiometry yields current uniformity • Utilized theoretical 3D fuel cell model to investigate effects of catalyst, membrane and
GDL nonuniformity; determined that electrode defects result in highly, nonuniform current distribution
System Test • Initiated Saratoga system test with a preliminary, durable MEA design
MEA Lifetime Modeling • Demonstrated that load profile affects MEA durability • Developed initial lifetime prediction model to estimate MEA lifetime relative to DOE’s 2010
stationary system goals • Related initial fluoride ion to lifetime – method to increase sample throughput
MEA & Stack Durability for PEM Fuel Cells 5 3 Fuel Cell Components
GDL Characterization – Capillary Pressure Background Solution • Measured GDL permeability in humid and • Design your own instrument
dry air • CWRU has designed, machined and • Humid air yields lower gas permeability assembled the sample holders, load cell
• Pores fill with water and strain sensor • CWRU collaborated with Porous Materials
Problem Inc, Ithaca, NY to fabricate the instrument • Need technique to characterize water • PMI will integrate the syringe pump, the
transport in GDL pores press and automation• There are no available instruments for
measuring capillary pressures for hydrophobic porous media
• measuring Capillary Forces in hydrophobic GDLs
• GDLs
Developed an instrument for
New method to characterize
MEA & Stack Durability for PEM Fuel Cells 6 3 Fuel Cell Components
Reinforced Membrane Activities Membrane Stress Model Evaluation of Various Reinforcing Members
Highest Stress Lowest Stress
Lands
Channels
Hypothesis 0 20 40 60 80
100 120 140 160 180 200
0 5 10 15 20 25 30 35 40
Tear (MPa)
Impe
danc
e (m
Ωcm
2 )
conductivity than neat Nafion
with 3M Ionomer
- Need reinforcing member to carry stress to eliminate mechanical failure or reduce mechanical failure rate
Desired Result – stronger and higher
Lines – 3M Cast Nafion® Membrane Symbols – Various reinforced membranes
RH Cycle Test to Evaluate HypothesisTest Conditions: 80°C Cycle equally between 0 and 150% RH
MEA (electrode and GDL) made Time to failure with: (hours) DuPont™ Nafion® (NR-111)1 260 – 330 Ion Power™ Nafion® (N111-IP)1 1330 + Gore™ Primea®1 400 – 470 3M Cast Nafion® (1000 EW) 1200 +
• Neat membrane most durable
props and durability • predict
mechanical durability • predict
mechanical durability • Less shrinking does not correlate to
more mechanical durability
• No relationship between mechanical
Tensile test does not
Tear resistance does not
• What is the benefit of reinforcement? 1. Gittleman et al, Fall AIChE Meeting, October 2005.
MEA & Stack Durability for PEM Fuel Cells 7 3 Fuel Cell Components
Mitigation of Membrane Edge Failure in Modules Problem • In module testing, observe infant
Active Area
Site of mortality of MEAs due to edge failure at edge the membrane – catalyst interface failure
Solution • Developed edge protection component
for MEA
Rel
ativ
e M
EA F
ailu
re R
ate 120
100
80
60
40 No Failures
20
0
w/o Edge Protection w/ Edge Protection
• failure mode
• solution to significantly reduce infant mortality failure rate
Identified MEA
Implemented a
MEA & Stack Durability for PEM Fuel Cells 8 3 Fuel Cell Components
3M Ionomer Membrane Properties vs Decay Membrane Aging Procedure
Pre-condition w/
Received H+ Form Membrane H+ Form
H2SO4 (0.1M) Ion exchange w/ FeSO4 (0.1M) 70°C, 1 hour Fe(II) Form
70°C, 1 hour
Degraded MembraneFe(II) Form
H2O2 (0.1M) 70°C, ~ 35 hours H2SO4 (0.1M) Ion exchange w/
70°C, 2 hours
• Measure degraded membrane properties over time
‘As Received’ ‘H+ Form’ ‘Degraded Sample @ 125 hrs’
132°C
125°C
131°C
Mechanical
20 40 60 80 100 120 140 160 180 0.0
0.1
0.2
0.3
0.4
0.5
0.6
Tan
delta
Temperature [C]
• experiments in progress
• after 125 hrs
0 100 200 300 400 500 600 0
20
40
60
80
100
120
Wei
ght [
%]
Temperature [C]
Thermal Gravimetric
Dynamic
Analysis
Aging
No change Analysis
MEA & Stack Durability for PEM Fuel Cells 9 3 Fuel Cell Components
Membrane Decay Mechanism Via Model Compounds 208th ECS Meeting, Abstract 1195,
Non-zero intercept
mechanism(s)
F-ge
nera
ted‘Conventional Wisdom’: Los Angeles, CA, October 2005
• H2O2 generated during fuel cell operation
• HO⋅ or other radicals are attacking species
• -COOH end group unzipping primary route 0
0
• Demands other degradation
[ -COOH] Investigate alternative degradation mechanism(s) via
model compounds • • reactive sites •
Utilize analytical capabilities Better isolation of effect from different Age MCs via Fenton’s test or UV light (200 - 2400 nm @ 100W)
MC1 MC2 MC3 O O O
F F2 F2 F F2 F2 F2 F2 F2 F2 F2HO C C O C C CF3 HO C C O C C C C SO3H HO C C C C SO3H
CF3 CF3
MC4 MC7 MC8
F3C F2 C C6 OH F3C
F2 C O
F2 C
F2 C
F2 C SO3H F3C
F2 C O
F2 C
F C O
F2 C
F2 C SO3H
O CF3
MEA & Stack Durability for PEM Fuel Cells 10 3 Fuel Cell Components
MC3 > MC1 ≈ MC2 > MC4 > MC7 & MC8 MC3 MC1 MC2
Model Compounds Relative Degradation Rates
HO C
O
F2 F2 F2 > C F C O
O
CF3
HO F2 F2
≈ HO C F C O
CF3
O
F2 F2 F2 F2 C C C SO3H C C CF3 C C C C SO3H
MC4 MC7 MC8
O F2
O F2 F
C O
CF3
F2 F2F2 F2C OH
O
F2 F2 F2> C C C SO3HCF3C F3C C C C C SO3H ≈ F3C C>6
• effect
products? •
& MC2 •
hydrolysis
• COOH containing MCs exhibit low stability • Comparison of MC3 & MC4
Is it really a reactivity effect or solubility
• Is there a change in reactivity hydrolysis
Hydrolysis observed (by NMR) for MC1
Need to evaluate MC7 & MC8 for
Identified MC1 & MC2 Reaction Products O O O
C C F3C
COH F3C CF2
MC3 Isomer Degradation6 7 11
O CF3O F F 1 3
HO CF2 CF2
CF2 4 CF 10 SO3H
2 SO3H HO CF SO3H HO
O CF3 F F 8 95
• Same degradation rate • Decarboxylation is rate determining step
MEA & Stack Durability for PEM Fuel Cells 11 3 Fuel Cell Components
Membrane Decay Mechanism – Hydrogen Peroxide Model Objective • To define simple model to study peroxide behavior in an MEA Equations:
(CH O ) = Rate of production electrochemical +Chemical recombination )d (dt 2 2
+ Rate of consumption ⎛
+ electrochemical reductionIonomer degradation + catalytic disproportionation ⎞
⎜ ⎟⎜ ⎟⎝ ⎠
+ Transport through the electrode Diffusion +Convection )(
Peroxide to membrane
Peroxide Concentration Profile as f(L) O2 inlet No peroxide 0.75 V = η
Z= Z= 0 1
Experiments to Determine Input Parameters 1. Rate of Peroxide Production2. Rate of Peroxide Disproportionation
• Model provides insight into hydrogen peroxide distribution in an operating fuel cell and the degradation of ionomer by hydrogen peroxide
Geometry Model Output
MEA & Stack Durability for PEM Fuel Cells 12 3 Fuel Cell Components
MEA Nonuniformity Studies Motivation - MEA Durability • Is MEA durability a function of current
distribution/uniformity?
Cur
rent
Den
sity
(A/c
m2 )
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Increasi urrentng avg. cV. Gurau, H. Liu and S. Kakac, “A Two Dimensional Non-Isothermal Mathematical Model for Proton Exchange Membrane Fuel Cells,” AIChE Journal, Vol. 44 (11), pp. 2410 – 2422, 1998
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Dimensionless Channel Length
Approach • Measure experimentally – segmented cell • Theoretical modeling
MEA & Stack Durability for PEM Fuel Cells 13 3 Fuel Cell Components
Segmented Cell
Inlet
Outlet A B C D E F G H I J K
1 2 3 4 5 6 7 8 9 10 11
0 5 10 15 20 25
Volta
ge (V
)
Current (A)
100 sccm Air 200 sccm Air 500 sccm Air
1000 sccm Air
210 sccm O2
50 cm2, 121 segments
Validation of Cell Design
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95 Filled Symbols – Sum of Individual Segments Hollow Symbols – Fuel Cell (Segments shorted together)
Frac
tion
of T
otal
Cur
rent
at 0
.66
V (S
egm
ent C
urre
nt/T
otal
Cur
rent
) Effect of Air Flow Rate on Current Distribution
O2 Utilization = 0.99 0.96 0.56 0.31
200 sccm100 sccm 500 sccm 1000 sccm0.00
0.04
0.08
0.12
0.16
0.20
0.24
Inlet Outlet MEA & Stack Durability for PEM Fuel Cells 14 3 Fuel Cell Components
• •
at high stoichiometry for uniformity •
load
Cell design validated Design fuel cell systems to operate
Recently completed 121 channel
MEA & Stack Durability for PEM Fuel Cells 15 3 Fuel Cell Components
0
0.1
0.2
0.3
0.4
0.5
0.6
curr
entd
ensi
ty
0
0.2
0.4
0.6
0.8
x
1
1.02
1.04
1.06
y
0.78590.68110.57630.47160.36680.26200.15720.0524
CL +1
0
0.1
0.2
0.3
0.4
0.5
0.6
curren
tden
sity
0
0.2
0.4
0.6
0.8
x
1
1.02
1.04
1.06
y
0.58900.51050.43200.35340.27490.19630.11780.0393
CL -1
0
0.2
0.4
0.6
0.8
1
1.2
curr
entd
ensi
ty
0
0.2
0.4
0.6
0.8
x
1
1.02
1.04
1.06
y
1.13380.98260.83140.68030.52910.37790.22680.0756
CL +3
0
0.1
0.2
0.3
0.4
0.5
0.6
curren
tden
sity
0
0.2
0.4
0.6
0.8
x
1
1.02
1.04
1.06
y
0.58900.51050.43200.35340.27490.19630.11780.0393
CL -1/2
Hydrogen
Air
Collector Plate
Membrane
x
y
z
Cathode catalyst layerGas diffusion layer
Anode catalyst layer Gas diffusion layer
Collector Plate
Gas channel
Gas channel
MEA Nonuniformity StudiesVariables Investigated• Ionic Conductivity• Catalyst Loading• GDL Porosity• Electrode Thickness• Membrane Thickness• GDL Thickness
Electrode Thickness
• Surface defects resulted in highly non-uniform current distribution
MEA & Stack Durability for PEM Fuel Cells 16 3 Fuel Cell Components
Objective – Investigate possible interaction between system design and durable MEA design
0
10
20
30
40
50
60
70
80
0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
Stack DC voltage System Efficiency
Cell Ratio
Saratoga System Test – First Durable MEA TestingSt
ack
Volta
ge (V
) Sy
stem
Effi
cien
cy (%
)
Stac
k C
ell R
atio
Run Hours• No negative MEA – System interaction• Program approach validated
System Restarts
Statistical MEA Lifetime Predictions from Accelerated Test Data
00
0.50.5
Solid Lines Dashed Lines
I (A
/cm
2 )
0
0.5
Dotted Lines
I (A
/cm
2 ) Modified Load CycleConstant Load Cycle
I (A
/cm
2 )Near-OCV Load Cycle
Time Time Time
MEA & Stack Durability for PEM Fuel Cells 17 3 Fuel Cell Components
Model Assumes • • • • Class model load profiles
Accelerated Lifetime (Hrs)
Frac
tion
Faili
ng
Decreasing Stress
Predicted Lifetime 70°C 100% RH
• ibution • • •
.001
.003
.005
.01
.02
.03
.05
.1
.2
.3
.5
.7
.9 .98
10^01 10^02 10^03 10^04 10^05 10^06
Censored data No censored data
Baseline Components
.001
.003
.005
.01
.02
.03
.05
.1
.2
.3
.5
.7
.9 .98
10 20 50 100 500
Frac
tion
Faili
ng
Comparison of MEA Designs
~ 4x New 3M PEM MEAs
Baseline MEAs
Weibull distribution Arrhenius for temp Humidity model for RH
Lifetime probability distrReasonable predictive values No OCV load cycle offers ~ 13X lifetime improvement New MEAs with 3M ionomer ~ 4x more durable
200 1000
Accelerated Lifetime (Hrs)
Fluoride Ion Mapping of Accelerated Test Data 1.0E+05
Acc
eler
ated
Life
time
(Hrs
)
Predicted Lifetime New 3M PEM MEAs 70°C 100% RH Hollow symbols: In-Progress
R2 = 0.77
R2 = 0.89
R2 = 0.83
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
0.00 0.01 0.10 1.00 10.00
Initial Fluoride Release (μg/min)
I (A
/cm
2 ) • 3M PEM MEAs under accelerated, near-OCV load cycle test conditions
• Time
Pathway towards ~ 20,000 hour MEA lifetime with
Means to increase sample throughput
Near-OCV Load Cycle
MEA & Stack Durability for PEM Fuel Cells 18 3 Fuel Cell Components
0
0.5
Future Work – To the End of the Project MEA & Stack Development & Testing
• MEA Component optimization & integration – 3M • Saratoga stack tests – Plug Power • Complete MEA evaluation in modules/single cells – Plug Power • Select ‘Final’ stack and MEA design and test – Plug Power/3M
MEA Degradation Studies • Peroxide model – CASE
• Incorporate realistic kinetic and transport parameters • Model compounds – CASE
• Determine degradation kinetic constants • MEA nonuniformity studies – 3M/Plug/University of Miami
• Determine operating conditions/MEA designs that yield current distribution uniformity
• Post mortem analysis – CASE/Plug Power • Mechanical properties-morphology relationship – CASE
MEA Statistical Lifetime Predictions • MEA lifetime modeling – 3M/Plug Power
MEA & Stack Durability for PEM Fuel Cells 19 3 Fuel Cell Components
Project Summary Relevance:
Approach:
Progress:
Developing MEA and system technologies to meet DOE’s year 2010 stationary durability objective of 40,000 hour system lifetime. Providing insight to MEA degradation mechanisms.
Two phase approach (1) optimize MEAs and components for durability and (2) optimize system operating conditions to minimize performance decay.
Demonstrated pathway towards 20,000 hour MEA lifetime with 3M PEM MEAs under accelerated ‘near-OCV’ load cycle test conditions. Initiated durable MEA-stack system tests.
DOE 2010 FY ’05 FY ’06 Goal (hrs)
Accelerated Lifetime Predictions (hrs) 16,000 > 20,000 40,000
Technology Transfer/Collaborations: Active partner with CWRU, Plug Power and the University of Miami. Presented 9 presentations and 2 papers on work related to this project in last 12 months.
Future Work: Complete studies on MEA degradation mechanism. Select ‘final’ MEA and stack design and test system for 2,000 hours.
MEA & Stack Durability for PEM Fuel Cells 20 3 Fuel Cell Components
Publications and Presentations • M. Yandrasits, “Mechanical property measurements of PFSA membranes at elevated temperatures and
humidities,” 2nd International Conference on Polymer Batteries and Fuel Cells, Las Vegas, NV, June 2005. • D. Stevens, M. Hicks, G. Haugen, J. Dahn, “Ex situ and in situ stability studies of PEMFC catalysts: Effect of
carbon type and humidification on degradation of the carbon,” J. Electrochem. Soc., 152 (12), A2309 (2005). • D. Schiraldi and C. Zhou, “Chemical durability studies of PFSA polymers and model compounds under mimic
fuel cell membrane conditions,” 230th ACS Meeting, Washington, D.C., August 2005. • M. Hicks, D. Pierpont, P. Turner, T. Watschke, M. Yandrasits, “Component Accelerated Testing and MEA
Lifetime Modeling,” 2005 Fuel Cell Testing Workshop, Vancouver, BC, September 2005. • J. Dahn, D. Stevens, A. Bonakdarpour, E. Easton, M. Hicks, G. Haugen, R. Atanasoski, M. Debe, “Development
of Durable and High-Performance Electrocatalysts and Electrocatalyst Support Material,” 208th Meeting of The Electrochemical Society, Los Angeles, CA, October 2005.
• D. Pierpont, M. Hicks, P. Turner, T. Watschke, “Accelerated Testing and Lifetime Modeling for the Development of Durable Fuel Cell MEAs,” 208th Meeting of The Electrochemical Society, Los Angeles, CA, October 2005 (presentation and paper).
• M. Hicks, K. Kropp, A. Schmoeckel, R. Atanasoski, “Current Distribution Along a Quad-Serpentine Flow Field: GDL Evaluation,” 208th Meeting of The Electrochemical Society, Los Angeles, CA, October 2005 (presentation and paper).
• G. Haugen, D. Stevens, M. Hicks, J. Dahn, “Ex-situ and In-situ Stability Studies of PEM Fuel Cell Catalysts: the effect of carbon type and humidification on the degradation of carbon supported catalysts,” 2005 Fuel Cell Seminar, Palm Springs, CA, November 2005.
• D. Pierpont, M. Hicks, P. Turner, T. Watschke, “New Accelerated Testing and Lifetime Modeling Methods Promise Development of more Durable MEAs,” 2005 Fuel Cell Seminar, Palm Springs, CA, November 2005.
• M. Hicks, R. Atanasoski, “3M MEA Durability under Accelerated Testing,” 2005 Fuel Cell Durability, Washington, DC, December 2005.
• Z. Qi, Q. Guo, B. Du, H. Tang, M. Ramani, C. Smith, Z. Zhou, E. Jerabek, B. Pomeroy, J. Elter, "Fuel Cell Durability for Stationary Applications - From Single Cells to Systems,” 2005 Fuel Cell Durability, Washington, DC, December 2005.
MEA & Stack Durability for PEM Fuel Cells 21 3 Fuel Cell Components
Response to 2005 Reviewer’s Comments • Need to evaluate catalyst degradation; how does catalyst degradation affect
overall MEA durability? – Reported results of ‘commercial’ Pt/C catalyst durability and degradation at 2004
HFCIT Review – Project not focused on development of Pt/C catalyst; separate 3M/DOE project
focused on catalyst durability (3M NSTF catalyst) • Need additional characterization of membrane physical properties and effect of
aging on these properties – Initiated task on measuring membrane mechanical properties & morphology as a
function of aging • Need to relate effect of component improvements to overall MEA improvements.
What component improvement added most value to MEA lifetime? – Integration of components is critical in terms of obtaining good MEA durability – Considering possible patent applications
• Need to work on reinforced membranes. – Have evaluated reinforced membranes; results to be presented in the future – Development out of scope of project – some work done at expense to 3M
• Better description of lifetime model – Using std lifetime statistical analysis techniques; see W.Q. Meeker and L.A.
Escobar, Statistical Methods for Reliability Data, John Wiley and Sons, Inc. (1998) • Need to address other targets (cost/performance) in concert with durability
– Reported performance at the 2005 DOE Hydrogen Program Review – Cost not a primary objective; it is used as a metric when deciding options
• Too much emphasis on fluoride ion release. – Disagree – Very strong relationship between fluoride release and MEA lifetime
MEA & Stack Durability for PEM Fuel Cells 22 3 Fuel Cell Components
Critical Assumptions and Issues • Validation of lifetime model analysis method
• Testing baseline samples at ‘normal’ test conditions • Comparison to field test data
• Increasing sample throughput of improved durability MEAs • New, durable MEAs last too long • Use initial fluoride ion release as metric (reduces test time) • Plug Power test equipment online (adds more test equipment)
• Understanding role of peroxide • Initial peroxide lifetime model established
• Demonstrate benefit of new, more durable MEAs • Start lifetime accelerated tests of new MEAs • Apply lifetime model to new MEAs
MEA & Stack Durability for PEM Fuel Cells 23 3 Fuel Cell Components
top related