Membranes and MEA's for Dry, Hot Operating Conditions
Steven Hamrock
May 19, 2009
FC_13_HamrockThis presentation does not contain any proprietary, confidential, or otherwise restricted information
3 Fuel Cell Components
2
Overview
Timeline• Project start 4/1/07• Project end 3/31/11• 50% complete
BarriersA. DurabilityC. Performance
Budget• Total Project funding $11.4 million
- $8.9 million - DOE- $2.5 million - contractor cost share
(22%)• Funding in FY 2008• $2.5 Million• Funding in FY 2009 • $2.5 Million
PartnersCase Western Reserve Univ.* Professors T. Zawodzinski and D. SchiraldiColorado School of Mines* Professor A. HerringUniv. of Detroit Mercy* Professor S. SchlickUniv. of Tennessee* Professor S. PaddisonGeneral Motors C. GittlemanBekktech Inc. T. Bekkedahl3M S. Hamrock (Project lead)
* denotes subcontractor
3
Project Objectives-Relevance• To develop a new proton exchange membrane with:
• higher proton conductivity• improved durabilityunder hotter and dryer conditions compared, to current membranes.
4
Project Approach• New polymers, fluoropolymers, non-fluorinated polymers and composite/hybrid systems
with increased proton conductivity and improved chemical and mechanical stability
• Developing new membrane additives for both increased conductivity and improved stability/durability under these dry conditions
• Experimental and theoretical studies of factors controlling proton transport both within the membrane and mechanisms of polymer degradation and membrane durability in an MEA
• New membrane fabrication methods for better mechanical properties and lower gas crossover.
• Focus on materials which can be made using processes which are scalable to commercial volumes using cost effective methods
• Testing performance and durability. Tests will be performed in conductivity cells, single fuel cells and short stacks using realistic automotive testing conditions and protocols.
• 2008/2009 Milestones
Q1 2008: 3M will develop new test methods and install and modify new equipment as appropriate. Screening of new materials will be underway.
Q3 2009: 3M will identify a first set of new, more conductive and durable materials.
5
Collaborations – Flow Of Samples And Information
Polymer Development3M, CWRU
Inorganic conductor/stabilizer developmentCSoM, 3M
Membrane Fabrication3M
Membrane Coating Process Development3M
Conductivity, Transport, Morphology Studies3M, CWRU, CSoM, UT
Fuel Cell Testing3M
Durability Testing3M
Ex Situ Stability TestsDetroit Mercy, 3M
Final MEA Fabrication3M
Stability ModelingUT
MEAs for Testing3M
Model Compound Stability Studies
CWRU
Performance and Durability Testing
3M
Short Stack Test
6
1.0E-03
1.0E-02
1.0E-01
1.0E+00
30 40 50 60 70 80 90 100Relative Humidity (%RH)
Con
duct
ivity
(S/c
m)
650 EW 700 EW825 EW 900 EW980 EW 1100 EW
Conductivity vs Relative Humidity @ 80CComparing to Nafion at 120C 230 kPa
1
10
100
1000
10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
Relative Humidity (%RH)
Con
duct
ivity
(mS/
cm)
3M 650EW (10-30-08) 120C
NRE-212 (3-20-07) 120C
Conductivity C alculatedbased on dry dimensions
and no swelling
Conductivity vs Relative Humidity @ 30C
1.0E-03
1.0E-02
1.0E-01
1.0E+00
30 40 50 60 70 80 90 100Relative Humidity (%RH)
Cond
uctiv
ity (S
/cm
)
650 EW 700 EW825 EW 900 EW 980 EW 1100 EW
• Conductivity vs. temperature for EW ionomers in 640 – 1100 EW range.
• The 2 lowest EW ionomers shown, 650 and 700 EW, meets DOE milestone for RT conductivity (ca. 80 mS/cm at 80%RH, 25C).
AC 4-point probe measurement.
Conductivity w/ Low EW
OCF2CF2CF2CF2
SO3H
(CF2CF)n(CF2CF2)m
3M Polymer
OCF2CF2CF2CF2
SO3H
(CF2CF)n(CF2CF2)m
3M Polymer
OCF2CF2CF2CF2
SO3H
(CF2CF)n(CF2CF2)m
OCF2CF2CF2CF2
SO3H
(CF2CF)n(CF2CF2)m
3M Polymer
Tim Bekkedahl - Bekktech
Low EW PFSA’s
• The 650 EW almost meets the 120ºC interim milestone (ca. 93 mS/cm at 120ºC, 50%RH)
7
1.0E-03
1.0E-02
1.0E-01
1.0E+00
20 30 40 50 60 70 80 90 100Relative Humidity (%RH)
Con
duct
ivity
(S/c
m)
3M PFSA, 800 EW
3M PFSA, 650 EW
3M PFSA, 580 EW
80ºC
Going To Even Lower Ew’s (<600) Can Provide Conductivity That Meets The DOE 2010/2015
Conductivity Targets At 80ºC• EW’s below about
600 will meet conductivity requirements at 80ºC, even at 40% RH.
• The conductivities at these very low EW’s are slightly higher than expected.
Low EW PFSA’s
Target %RH
8
Transport Pathways• Probed by NMR Diffusion and
Relaxation Studies• Plot shows Diffusion Coefficient vs.
Water Content for two samples• D levels off at low water content;
significantly higher for 700 EW than for other PFSA samples to date
Low EW PFSA’s
Lambda at 80C
0
2
4
6
8
10
12
14
16
18
0 20 40 60 80 100
Relative Humidity (%RH)
Lam
bda
(mol
es w
ater
/ m
oles
aci
d) 3M 700 EW3M 825 EW3M 900 EW3M 980 EW3M 1100 EWNafion 112 In the range from 700 to 1100 EW,
these polymers show similar water absorption at 80ºC.
Tortuosity or Intrinsic Interactions?
Diffusivity vs Activity chart
1.00E-07
1.00E-06
1.00E-05
1.00E-04
0 0.2 0.4 0.6 0.8 1Ac tivity (LiCl+H2O)
Dif
fusi
on C
oeff
icie
nt [
cm2/
s
EW 825
EW 700
9
• Lower EW ionomer have higher conductivity than CF3CF2CF2CF2SO3H (300 MW/EW) at a given lambda value, showing the importance of the phase separated morphology.
In- Plane Conductivity At 80ºC• At lower % RH or λ, the conductivity increases by a much larger factor when the EW is
lower compared to the more humidified state.• This is consistent with the hydrated acid groups being more accessible to one another in
the lower EW ionomer, allowing proton transport even with little or no “free” water.
Low EW PFSA’s
0.001
0.01
0.1
1
200 300 400 500 600 700 800 900 1000 1100 1200EW
S/cm
λ = 14λ = 9λ = 5λ = 3λ = 2
Perfluorobutanesulfonic acid
λ = 9
λ = 5
λ = 3
λ = 2
Large Increase 16.6 X
Small Increase 3.6 X
10
Wide Angle X-Ray Scattering• Crystalinity from TFE in the polymer backbone is important for good mechanical properties and low water solubility
• WAXS shows little crystalinity below about 800 EW
The Bad News - Loss of CrystalinityLow EW PFSA’s
11
More Bad News - Loss of Crystalinity
• Solubility is determined by boiling, filtering an aliquot of filtrate, and determining fraction of membrane “dissolved”.
• Solubility starts near where crystalinity is gone.
• Many mechanical properties parallel this effect
Understanding “true” solubility helps defining possible mechanical stabilization methods
Low EW PFSA’s
Membrane Solubility*
0
10
20
30
40
50
60
70
80
90
100
400 500 600 700 800 900 1000 1100 1200
Eq, Wt (g/mol)
% D
isso
lved Water Solubility
* Can vary w ith process conditions
Range where crystallinity index goes to zero
12
02468
101214161820
0 5000 10000 15000 20000
RH Cycles
Cros
s-ov
er (s
ccm
) .
730 EW730 EW3M Cast Nafion™ 10003M Cast Nafion™ 1000825 EW Process 1825 EW Process 1825 EW Process 1825 EW Process 2825 EW Process 3
RH CyclingLow EW ionomers do poorly in humidity cycle testing.Performance of 825 EW depends on membrane processing conditions.
Craig Gittleman - GM
Low EW PFSA’s
13
So, we can make low EW that can give great conductivity, but mechanical properties and
durability can be compromised.Some possible solutions:
blends crosslinking
reinforcementpolymer modifications
We are looking at all of these
Low EW PFSA’s
14
Blends of Water Soluble and Insoluble Ionomers
• In miscible blends of soluble and insoluble ionomers there is little to no evidence of the insoluble ionomer captivating the soluble ionomer.
• We are still evaluating blends with not-so-low EW ionomers and high EW ionomers or non-ionic polymers.
Low EW PFSA’s
583 and 1000EW blends
0
20
40
60
80
100
120
0 20 40 60 80 100 120Fraction of 583 EW polymer
% w
ater
sol
uble
15
Polymer Modification – one approach
• Bis-sulfonyl imides are very chemically stable and highly acetic.
• Aromatic R groups can be substituted with additional functionality for stable cross-linking and/or adding additional acid groups including HPA’s.
Imide sidechains
16
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
O
OO
H
• Changing the nature of the acid group
Sulfonic acid• Lowest EW limited by monomer MW
Imide sidechains
17
SF3CO
O
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
N
OO
H
• Changing the nature of the acid group
Perfluoro imides • Similar polymers prepared at Clemson via
polymerization of imide monomers with TFE*• Stronger acids than sulfonic acids
* Creager, S.E et.al., Electrochem. and Solid State Lett. 2(9) 434-436 (1999)
Imide sidechains
18
SO
O
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
N
OO
H
• Changing the nature of the acid group
Aromatic imides • Useful synthetic handle• Similar pKa to sulfonic acids• Very hydrolytically stable in aqueous acid at
elevated temperatures
Our interest is using this as a synthetic handle for attachment of
additional protogenic groups, cross-links, etc.
Imide sidechains
19
ClSO2
Polymer-SO2HN2 Polymer-SO2HNSO2
(sulfonamide)
Sulfonic acid
• 19F NMR of CF2group next to sulfur allows following the reaction
• This is a “poor” sample to show peak separation
Imide sidechains
20
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
30 40 50 60 70 80 90 100Relative Humidity (%RH)
Con
duct
ivity
(S/c
m)
Sulfonic acid, 800 EWSulfonic Acid 650 EWTrifluoromethyl imide,808 EWSPES 770 EWPhenyl imide, 802 EW
• Conversion of a 650 EW sulfonyl fluoride to the trifluoromethyl imide provided a 808 EW ionomer. The conductivity remained the same (stronger acid but higher EW) as the sulfonic acid
• Conversion of the same sulfonyl fluoride to the an 802 EW phenyl imide resulted in lower conductivity at lower %RH.
New Protogenic Groups
80ºC
Imide sidechains
21
SO
O
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
N
OO
HHO3S
• Changing the nature of the acid group
Aromatic imides • Multiple acid groups• Two examples have been prepared
Imide sidechains
22
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
20 30 40 50 60 70 80 90 100Relative Humidity (%RH)
Con
duct
ivity
(S/c
m)
3M PFSA, 800 EW3M PFSA, 650 EWOrtho Bis Acid, 550 EWMeta Bis Acid 550 EWPhenyl imide, 802 EWSPES 770 EWBPSH 100 (EW 280)
• Multiple acid groups allow raising the conductivity of starting ionomer• 800 EW starting PFSA precursor with crystalline backbone can be used to make
low EW ionomer with higher conductivity.• These swell much less in liquid water than the PFSA’s with the same EW
Multiple Acid Groups On A Single Side-chain
CF2CF2
CF2
O
CF2
CF2CF2
CF2
n
n
SN
S
OO
OO
HSO3H
CF2CF2
CF2
O
CF2
CF2CF2
CF2
n
n
SN
S
OO
OO
H
SO3H
Ortho bis acid
Meta bis acid
80ºC
Imide sidechains
23
Imide sidechains
Thermal Gravimetric Analysis
• As is the case with di-sulfonated aromatics, the ortho substitution is less thermally stable than the meta.
• Neutralized samples have much better stability.
Ortho bis acid
Meta bis acid
24
SO
O
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
N
OO
H
HO3S
HO3S
Future Work - Other Polymers Are Being Prepared And Evaluated For:•Adding higher levels of acid groups, sulfonic or inorganic (HPA)•Impact of imide on morphology•Cross-linking through multi imide groups, backbone or Zr phosphonate linkages
SO
O
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
N
OO
H
H2O3P
CF2
CFCF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S OO
X
R
R= OH or imide
SO
O
O2S
CF2
CF2
CF2
CF
O
F2C
CF2
F2C
CF2
S
N
OO
H
NHO2S
Polymer
Attach sulfonated oligomers and/or polymers
Imide sidechains
25
Phenylphosphonate Attached to SiW11 KegginAromatic phosphonates attach to lacunary HPA’s, potentiality allowing immobilization. Membranes must be stable to liquid water!
Imide sidechains
8.2 8.0 7.8 7.6 7.4 PPM
Phenyl phosphonate in DMSO
Modified Keggin in DMSO
Modified keggin in DMSO spiked with phenyl phosphonate
Linewidth differences indicative of slower rotating species (attached to keggin)
PO3H2
+2PO3H2
+2
HPA’s can increase proton conductivity and oxidative stability (AMR 2008)
26
Equilibrated morphologies: PFSA Chemistry
(PTFE in red,
–CF2SO3 – green
and water in blue)
D. Wu, S.J. Paddison, and J.A. Elliott, Energy and Environmental Science 1 284-293 (2008).
(Water density)
Simulation Box
(32 nm)3
• These mesoscale DPD simulations are able to capture differences in the hydrated morphology as both EW and monomer chemistry is changed.
• At the same EW and water content, the water domains in the 3M ionomer are larger and to some extent less connected than in the SSC ionomer.
Polymer morphology
λ = 16
27
Increasing EWD
ryB
oile
d
733 EW 825 EW 900 EW 1082 EW
Representative Morphologies from analysis of SAXS data
SAXS analysis shows structure which appears similar to mesoscale DPD simulations
Polymer morphology
28EW = 678, λ = 15
Water contour plots from simulations - Effects of the protogenic group on hydrated morphology
3M PFSA 3M PFSulfonylImideEW = 450, λ = 7.5
• Initail simulations have been done on the Ortho-bis acid with an EW of 450 and 600.
• Mesoscale DPD modeling suggest that polymer with an imide sidechain bearing 2 acidic protons may have a quite different structure
Polymer morphology
CF2CF2
CF2CF2
O
F2C
CF2
F2C
CF2
SO O
OH
CF2CF2
CF2CF2
O
F2C
CF2
F2C
CF2
SO O
NHS
O
O
SO3H
29
ESR: Competition Reactions for HO• in the Presence of DMPO as the Spin Trap
HO• + DMPO → DMPO/OH
HO• + A → A• (A is membrane or Ce(III), A• is membrane-derived fragment or Ce(IV))
][][1
DMPOkaka
vV
DMPO
=−
V and v are reaction rates for the formation of the DMPO/OH adduct in the absence and in the presence of the competitor A. Plot of vs gives the ratio , and a measure of the ability of the competitor to be attacked by hydroxyl radicals.
1−vV
][][
DMPOa
DMPOkka
kDMPO
ka
The formalism of “parallel reactions” leads to the expression:
Polymer Stability
30
Competition by Perfluorinated Membranes
Inhibition of DMPO/OH formation by the different membrane concentrations (0-10%) in Nafion® (A) and 3M membrane (B). [DMPO]= 9·10-
5 M, [H2O2]=9·10-3 M. Downward red arrow on the left shows the ESR signal that was monitored as a function of irradiation time. The black line on the right is for the formation of the DMPO/OH adduct in the absence of membranes.
3380 3400 3420 3440 3460
Magnetic Field / G
0%
2.5%
5%
7.5%
10%
0 5 10 15 20 25 300,0
0,2
0,4
0,6
0,8
1,0
Rel
ativ
e In
tens
ity o
f DM
PO
/OH
/ au
UV-Irradiation Time / s
3M/H2O2/DMPO/UV(B)
0%
2.5-10 %
0 5 10 15 20 25 300,0
0,2
0,4
0,6
0,8
1,0
Rel
ativ
e In
tens
ity o
f DM
PO
/OH
/ au
UV-Irradiation Time / s
Nafion/H2O2/DMPO/UV(A)
0%
2.5%5%
7.5%
10%
3380 3400 3420 3440 3460
Magnetic Field / G
0%
2.5%
5%
7.5%
10%
Polymer Stability
31
Reaction Rates of Nafion®, Stabilized Nafion® and 3M
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
0.2
0.4
0.6
0.8
1.0
1.2
(V/v
)-1
[SO-3]/[DMPO]
Nafion
Stabilized Nafion
3M
Slope ka•10-9 M-1s-1
Nafion® 1.124 4.0
Stab Nafion®
0.678 2.4
3M 0.034 0.17
ka (3M) / ka (Nafion®) ≈ 0.04
ka (S-Nafion®) / ka (Nafion®) ≈ 0.6
3M membranes appear more stable to attack by hydroxyl radicals compared to Nafion® and to stabilized (end group modified) Nafion®. We do not see such a large difference in longer term Fentons tests or fuel cell testing.
Polymer Stability
32
Ce(III) as Competitor
0 10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0
Inte
nsity
/ a.
u.
UV-Irradiation Time / s
No Ce(III)
1.2 mM
0.24 mM
0.48 mM
0.72 mM
0.96 mM
(A)
0 2 4 6 8 10 12 140.0
0.5
1.0
1.5
2.0
2.5
3.0
(V/v
) -1
[Ce(III)]/[DMPO]
Slope = 0.17
(B)
(A) Effect of Ce(III) addition on the formation of the DMPO/OH adduct in solutions (pH=5.3) containing the indicated Ce(III) concentrations. (B) Inhibition of DMPO/OH formation by addition of Ce(III). Slope = kce/kDMPO = 0.17, kDMPO = 3.6·109 M-1s-1
(deduced in competition kinetics with methanol as the competitor for hydroxyl radicals) and kCe = 6·108 M-1s-1. This value can be compared with kCe = 3·108 M-1s-1 quoted in Coms, F.D.; Liu, Han; Owejan, J.E. ECS Transactions 2008, 16, 1735-1747.
Polymer Stability
33
n
MC1 MC2
MC3
MC4 MC5
MC6
MC7 MC8
MC5‐S
Model Compounds and Degradation Test Conditions
100mM MC + Solvent + 100mM H2O2 : exposed to UV light for 1hr
100mM MC + Solvent + 11mM H2O2 + 1.25mM Fe(II) : Fenton’s degradation test
Technique: Liquid chromatography-Mass spectrometry (LC-MS)Biphenyl ColumnNegative-ion electrospray ionization MS
Polymer Stability
34
UV/Peroxide and Fenton’s Degradation Products of AMCs
AMC1
HO OHAMC4
AMC5‐S
AMC7
AMC8
AMC Structures Degradation Products
Polymer Stability
• Aromatic compounds do degrade in the presence of peroxides.
• Major products mono- or di-hydroxylated AMCs.
• No aromatic-ring breaking observed. • AMCs containing more that one
sulfonic acid groups may show loss of one of the sulfonic acid groups.
• No biphenyl link breaking observed in AMC4 ; extensive hydroxylation and dimerization observed.
• Ether link breaking observed in AMC5.
Progress on Aromatic Model Compounds Study
35
Electrode Resistance and Performance
• Lower EW membranes provide better Fuel cell performance under hotter, drier conditions.
• Not all due to Ohmic losses.• Our screening electrode resistance, as
determined by transmission line measurements (TLM), is the dominant resistance. TLM method yields membrane resistances consistent with conductivity values.
Fuel cell testingPerformance
0
10
20
30
40
50
60
70
80
90
100
95 100 105 110 115 120 125
Cell Temperature (C)
Res
ista
nce
(mO
hm-c
m2)
Electrode 10um 733ew PEM15um 733ew PEM25um 733ew PEM
H2Air CS2/2x/8080oCCounterflowAmbient Pressure
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
50
100
150
70 80 90 100 110 120 130
700 ew 1.0mil
800 ew 1.0mil
900 ew 1.2mil
1000 ew 1.2mil
1100 ew 1.2mil
RH %
Volta
ge (V
olts
)
@ 0
.5 A
mps
/cm
2 Outlet G
as RH
%
Cell Temperature (oC)
H2/Air CS 2.0
80oC DewpointsAmbient Pressure OutletsCounterflow
0.45
0.5
0.55
0.6
0.65
0.7
0.75
70 80 90 100 110 120 130
700ew 1.0mil800 ew 1.0mil900 ew 1.2mil1000 ew 1.2mil1100 ew 1.2mil
IR F
ree
Volta
ge (v
olts
)
@ 0
.5 a
mps
/cm
2
Cell Temperature (oC)
H2/Air CS 2.0
80oC DewpointsAmbient Pressure OutletsCounterflow
36
Oxidative Stability Gains
OCV, H2/Air, 95C, 7 PSIG, 50% RH
OCV, H2/O2, 90C, 0 PSIG, 30% RH
Fuel cell testingDurability
• Stabilizing additives can have a large effect on MEA lifetimes and fluoride release rates
• We continue to evaluate peroxide mitigation additives. Studies are ongoing to look at the effect of the location of the additive in the MEA.
• In addition, other variables have shown dramatic influences on FRR such as:
– Different PEM constructs.– Electrode effects.
37
Humidity Cycle Lifetime Durability Testing
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2000 4000 6000 8000 10000 12000Time (hours)
Volta
ge
825 EW - 20 Micron, 0.4/0.4 Disp. Cat., New additive
825 EW - 0.2/0.2 NSTF w/ 20 micron mechanically stabilized membrane
825 30 Micron, 0.4/0.4 Disp. Cat., 3M stablizing addtive
3M Cast Nafion 1000, 0.4/0.4 Disp. Cat.
• New additive package provides over 10,000 lifetime in automotive accelerated durability protocol
From AMR 2006
Fuel Cell Durability Testing
New Data
Test Point
J (A/cm
2)
Duration (m
in)
Stoich.
1 0.20 5 5
2 0.02 20 15
3 0.80 15 1.7
4 0.80 10 3
5 0.02 20 15
6 0.80 15 1.7
7 0.20 20 5
8 1.00 20 1.7
From AMR 2008(ran to >8,000 hours)
Cast Nafion® Control
Cell Temperature: 80 oCInlet Dew points: 64/64 oCOutlet Pressures: 175kPa
End of life = < 800 mV OCV w/ 7 PSIG anode overpressure.
Fuel cell testingDurability
38
New Durability ProtocolCycles/Day Cell Temp Conditions Description Time
1 80 Long scan @ 0.6A/cm2 to used collect fluoride data 4.5 hrs
1 80 Short anode overpressure OCV to monitor lifetime 5 min
4120 Hot Temperature Low RH to degrade MEA (up to 80ºC dewpoint)
15 hrs30 Low Temperature to Thermal and Humidity Cycle MEA
2 80 Load Cycle at Various RH to monitor performance 4.5 hrs
Our old protocol was getting too long as material stability improved. New protocol with higher temp conditions (up to 120ºC) shows MEA lifetimes of about 1,000 to 2000 h for MEA’s which have lifetimes >5,000 h. in old test (3-5 X faster).
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800 1000 1200 1400 1600 1800
Time (hours)
Volta
ge
0.00
0.20
0.40
0.60
0.80
1.00
1.20
Fluo
ride
Ion
Rele
ase
(ug/
dayc
m2)
GREEN COLORS STILL RUNNING
Data To Be Measured
Fuel cell testingDurability
39
Future Work• Continue preparation and evaluation of the conductivity and durability of low EW
PFSA’s, new imide containing polymers (Slide 15-24), cross-linked polymers (Slide 24) and membrane additives (Slide 25,36,37).
• Evaluate membranes crosslinked in both the hydrophilic and hydrophobic regions (Slide 24).
• Evaluate additional polymer blends for ionomer stabilization (Slide 14)• Continue to probe factors in transport using NMR relaxation and diffusion, SAXS,
conductivity and other spectroscopic measurements. Continue to develop a better understanding of effect of low lambda on proton transport (Slides 6-9, 20, 22, 26-28).
• Undertake first principles modeling of crystallinity through a comparison of different ionomers (Slides 26,28).
• Develop a better understanding of role of crystalinity on swelling in new polymers using X-ray scattering, mechanical properties testing and modeling (Slides 10-12, 26-28).
• Evaluate impact of new protogenic groups and additives on membrane oxidative and chemical stability using ESR, ex-situ tests and fuel cell tests (Slides 29-34,36-38).
• Investigate the structural basis for the higher stability of 3M membranes compared to Nafion® in ESR experiments. Better understand what this is telling us about membrane stability in a fuel cell (Slides 29-31).
• Evaluate additional stabilizers for perfluorinated membranes (Slides 29-31, 36-37).• Describe degradation pathways and rates for current group of model compounds and
correlate with membrane stability (Slides 33-34).• Design MEA’s for larger scale testing (Slide 35).
40
Summary3M
2009 Status 2010 target 2015 target
Conductivity at 120º C S/cm
0.146 (46%RH)
580 EW PFSA 0.1 0.1
Conductivity at 80º C S/cm
0.1 (40% RH)0.13 (50%RH) 0.50 (92%RH)580 EW PFSA 0.1 0.1
Conductivity at 30º C S/cm
0.1 (80% RH)580 EW PFSA 0.07 0.07
Conductivity at -20º C S/cm
0.014 S/cm700 EW PFSA 0.01 0.01
O2 cross-over mA/cm2
<0.520 micron 2 2
H2 cross-over mA/cm2
<220 micron 2 2
Durability w/ cycling hours
10,000 (80ºC) 1000 (120ºC)
825 EW PFSA5000 (80ºC) 2000 (120ºC)
5000 (80ºC) 5000 (120ºC)
• This project involves using experiment and theory to develop an understanding of factors controlling proton transport and the chemical/physical durability of the membranes.
• New materials are being synthesized based on this understanding, and evaluation of these materials will further our understanding.
• This “feedback loop” will ultimately allow for materials “designed” to meet performance and durability targets.
• Several approaches or pathways to improving membranes are being investigated. We expect the final membrane will have attributes resulting from some or all of these. We will not “down select” just one approach.