Membranes and MEA's for Dry, Hot Operating Conditions by DeptEnergy

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									  Membranes and MEA's for Dry,
    Hot Operating Conditions
                                 Steven Hamrock
                                Fuel Cell Components
                                  June 10, 2008




                                                                                                  FC13
This presentation does not contain any proprietary, confidential, or otherwise restricted information
                                   Overview
                Timeline                                 Barriers
•   Project start 4/1/07                       A. Durability
•   Project end 3/31/11                        C. Performance
•   25% complete

                Budget                                  Partners
•   Total Project funding $11.4 million       Case Western Reserve Univ.
     - $8.9 million - DOE                     Professors T. Zawodzinski and D.
                                              Schiraldi
     - $2.5 million - contractor cost share
                                              Colorado School of Mines
       (22%)
                                              Professor A. Herring
•   Funding in FY 2007                        University of Detroit Mercy
•   $0.8 Million (6 months)                   Professor S. Schlick
•   Funding in FY 2008                        University of Tennessee
                                              Professor S. Paddison
•   $1.2 Million (6 Months)


                                                                                 2
                               Project Objectives
•   To develop a new proton exchange membrane with:
     • higher proton conductivity
     • improved durability
     under hotter and dryer conditions compared, to current membranes.

                                      Milestones
•   Year 1, Quarter 4: Complete the development of all pertinent testing methods and install and
    modify new equipment as appropriate. Screening of new materials developed as part of Task
    1 will be underway.
•   Year 2, Quarter 4: Complete the identification of a first set of new, more conductive and
    durable materials.
•   Year 3, Quarter 2: Go/no-go decision based on progress toward meeting DOE 2010
    Membrane Technical Targets (this decision point coincides with the end of Budget Period
    1). Membrane will have shown improvement over baseline material and measurable progress
    indicating a pathway to meeting DOE Membrane Technical Targets. The broad material
    classes showing the higher promise will be identified, based on performance in ex situ and
    single cell tests, and optimization of the final membrane structure and composition will begin.
•   Year 4, Quarter 2: 3M will down select for the best performing catalyst/GDL/process based
    on performance in ex situ testing and single cell testing. Go/no-go decision for starting
    Subtask 4.1, Stack Fabrication and Testing.
•   Year 4, Quarter 3: 3M will have assembled a short stack with the best stack components and
    prepared the stack for independent testing at DOE designated entity.
                                                                                                      3
                        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.


                                                                                      4
                        Project Approach
•   Task 1 Membrane Subcomponent         •   Task 2 MEA Fabrication and Testing
    Development                              (MEA fabrication, performance and
     – Subtask Materials Development         durability test method development,
       (Polymer development,                 initial performance testing,
       conductivity enhancing additive       accelerated durability testing)
       development and stabilizing       •   Task 3 Final MEA Design and
       additive development)                 Integration (membrane fabrication,
     – Subtask Studies for                   catalyst interface optimization and
       Downselection (conductivity,          integration, final MEA optimization
       membrane physical properties,         and fabrication)
       failure and degradation           •   Task 4 Final Fuel Cell Testing (stack
       mechanisms)                           fabrication and testing, durability and
     – Subtask Membrane Fabrication          performance testing)
       Process Development               •   Task 5 Project Management,
                                             Deliverables and Reporting (building
                                             and testing short stack, reporting)



                                                                                   5
              Conductivity w/ Low EW                                                      (CF 2 CF) n(CF 2CF 2)m
•          Conductivity vs. temperature for EW ionomers in 640
           – 980 EW range.
•          The lowest EW ionomer tested so far, 640 EW,                                          OCF 2 CF 2 CF 2 CF 2
           shows a conductivity of about 30 mS/cm at 120˚ C,
           80˚ C DP, ambient pressure, very dry conditions, and
           meets DOE milestone for RT conductivity (ca. 80                                                   SO3 H
           mS/cm at 80%RH, 25C).                                                                   3M Polymer
                              %RH
                                                                                          Conductivity versus Relative
              100              50                 25                                          Humidity @ 25°C
           1.00                                                               1.00
                               3M PFSA   640 EW
                               3M PFSA   730 EW                                              640 EW



                                                        Conductivity (S/cm)
                               3M PFSA   830 EW                                              825 EW
                               3M PFSA   900 EW
                               3M PFSA   980 EW
    S/cm




           0.10                                                               0.10




           0.01                                                               0.01
                  80         100                  120                                60      70        80        90      100
                           Temp (°C)                                                         Relative Humidity (%RH)
                                                                                                                           6
                                         AC 4-point probe measurement.
                                                       Polymer Research
Polymer Modification – one                                                                             •   A few example prepared w/ low
approach                                                                                                   MW starting polymer.
                                                                                                       •   Fluorocarbon/aromatic imides are
     CF2
           CF 2
                        CF2                                             CF 2
                                                                                         CF 2              very chemically stable and highly
                                                                                                           acetic.
                                                                               CF2
                                 CF                                                              CF


                                   O                                                               O   •   Aromatic groups will be
                        F2C
                                                        NH 3
                                                                                         F2C               substituted with additional
                                CF2                                                             CF 2       functionality for stable cross-
                    F 2C                                                             F2C                   linking and/or adding additional
                            CF 2                                                            CF 2           acid groups including HPA’s.
                    O       S        O                                               O      S      O
                            F                                                               N
                                                                                      H            H
       CF 2
                            CF 2
              CF2
                                       CF
                                                     1) RSO 2X, R 3N
                                                                                                                 Polymer
                                         O

                            F2C                                2) H +

                                                                                                                     CF2
                                   CF 2
                                                                                                                   O2S         SO2
                        F2C
                                         O
                                                                                                                           N
                                 CF 2            R
                                             S
                                                 O                                                                         H
                        O        S        N
                                 O               H



                                                                                                                                               7
                                         CF2
                                                         CF2
• Changing the nature of                       CF2
                                                                CF

  the acid group                                                 O

                                                         F2C


                                                               CF2

                                                     F2C

     Sulfonic acid                                         CF2

     • Lowest EW limited by monomer MW               O     S     O

                                                           O
                                                                H




                                                                     8
                                             CF2
                                                              CF2
• Changing the nature of                           CF2
                                                                     CF

  the acid group                                                      O

                                                              F2C


                                                                    CF2

                                                         F2C

     Perfluoro imides                                           CF2

     • Similar material prepared by                       O     S     O
        DesMarteau via polymerization of                 O
        imide monomers with TFE                                 N
                                                   F3C   S           H
     • Stronger acids than sulfonic acids                O
     • This example has been prepared, not
        tested yet.



                                                                          9
                                                                                                             CF2
                                                                                                                              CF2
 • Changing the nature of                                                                                          CF2
                                                                                                                                     CF

   the acid group                                                                                                                     O
 Aromatic imides                                                                                                              F2C
 • Useful synthetic handle
 • Similar pKa to sulfonic acids                                                                                                    CF2
 • Excellent thermal, hydrolytic and oxidative
    stability. Further stability testing underway.                                                                       F2C

                                                                                                                                CF2
• Starting with a low                                   Conductivity versus Relative Humidity @ 25C

  MW, 640 EW                               1.000                                                                          O     S     O
                                                                       785 EW Bz imide
  sulfony fluoride, a                                                                                                    O
                                                                       800 EW Sulfonic acid                                     N
  785 EW imide
                     Conductivity (S/cm)




                                                                                                                         S           H
                                           0.100
  ionomer was                                                                                                            O
  prepared.
• This material has                        0.010


  similar conductivity
  to an 800 EW PFSA                        0.001

  control at 25ºC.                                 40       50        60        70       80
                                                                     Relative Humidity (%RH)
                                                                                                  90   100


                                                                                                                                          10
                                               CF2
                                                                CF2
• Changing the nature of                             CF2
                                                                       CF

  the acid group                                                        O

                                                                F2C


                                                                      CF2

                                                           F2C

     Aromatic imides                                              CF2

     • Multiple acid groups                   HO3S          O     S     O
     • This example has been prepared                      O
                                                                  N
     • starting with a 640 EW polymer, this                S           H
        ionomer should have an EW of 430.                  O




                                                                            11
                                                CF2
                                                                 CF2
• Changing the nature of                              CF2
                                                                        CF

  the acid group                                                         O

                                                                 F2C


                                                                       CF2

 Aromatic imides                                            F2C

 • Multiple acid groups                                            CF2
 • EW could be < 280 !!
                                         HO3S                O     S     O
 • By increasing and/or changing                            O
    size and shape of pendant          HO3S
                                                                   N
                                                            S           H
    group, we hope to increase free
    volume of ionic regions,                               O
                                                        SO3H
    increasing water retention under
    hotter, drier conditions.

One possible example – has not been prepared
                                                                             12
                                                 CF2
                                                                  CF2
• Changing the nature of                               CF2
                                                                         CF

  the acid group                                                          O

                                                                  F2C


              Linking group                                             CF2

             (HPA’s Zircania)                                F2C

  Aromatic imides                                                   CF2

  • Phosphonic acid groups can allow:                         O     S     O
     • Attachment of HPA’s,                  H2O3P           O
                                                                    N
     • Attachment of zirconia particles                      S           H
        or zirconyl phosphate particles                      O
        for increased conductivity, better
        mechanical properties, or latent
        cross-link.


                                                                              13
                                    CF2
                                                      CF2
• Changing the nature of                   CF2
                                                             CF

  the acid group                                              O

                                                      F2C


         Cross-linking group                                CF2
                                    Polymer
                                                 F2C
                                    O2S
     Aromatic imides                                    CF2
                                          NH
     • Crosslinking the ionic       O2S           O     S     O
        region can allow lower                   O
        EW’s to be more stable                          N
                                                 S           H
        and prevent disruption of                O
        ionic structure at
        temperatures approaching
        Tα.



                                                                  14
               Cross-linking polymers – Objectives
•   Minimize swelling at high hydration levels.
•   Increase/eliminate α transition.
•   Conductivity and mechanical properties can be compromised above this transition
•   Improve mechanical properties.

• Compare properties of crosslinking hydrophobic matrix vs ionic domain.
   – Measure water uptake and conductivity.
   – Measure durability              1.E+06                        Std. PFSA E'                                1

                                                                   3M Membrane E'                              0.9
      • wet/dry cycling              1.E+05                        Std. PFSA Tan Delta                         0.8
                                                                   3M Membrane Tan Delta
         – H2O2                                                                                                0.7


         – Single cell tests         1.E+04                                                                    0.6




                                                                                                                     Tan Delta
                                         E' (PSI)



                                                                                                               0.5

                                                    1.E+03                                                     0.4

     Changing or cross-linking                                                                                 0.3


     the acid group may also                        1.E+02                                                     0.2


     have a big impact on Tα. A                                                   Tα                           0.1

                                                    1.E+01                                                     0
     higher Tα may improve                                   25   50   75   100        125   150   175   200
                                                                              Temp (C)
     conductivity at higher
                                                       Relevant previous work - DMA of Nafion™ and
     temperatures.                                     3M Membrane (Both 1,000 EW) showing Tα
                                                                                                                   15
Crosslinked ionomer using cure site monomer
Crosslinking the hydrophobic matrix
                                                                                 Cure Rheology
                                                                 Sample #1& 2, LM9-767 & 844, 175C, time s c an, 3-20-08

                                                      10 4                                                                                                            178. 0
                                                                 ¬*

 CF2CF2       CF2CF    CF2CF                                             Sample #1 LM 9- 767, 175C , time s can, 3- 20- 08
                                                                         Sample #2 LM 9- 844, 175C , time s can, 3- 20- 08

          n                    ~0.03
                O        O                                                                                                                                            177.0

                                                                      x : 18.0 [s ]                                                       x : 1797.0 [s]
                                                                      y : 2176.0 [P]
                CF2      CF2                                                                                                              y : 2523.0 [P]
                                                                                                                 x : 1207.0 [ s]                                      176.0
                                                                                                                 y : 2303.1 [P]




                                                                                                                                                                              Temp (
                                           )
                CF2      CF2




                                                                                                                                                                                [°C]
                                               [ P]
                                           ¬* (
                CF2      x
                         Br




                                                                                                                                                                                 )
                                                                                                                                                                      175.0


                CF2                                                                                               x : 607.0 [s ]
                                                                                                                                              x: 1507.0 [s ]
                                                                                                                                              y: 2419.7 [P]
                                                                                                                  y : 1986.6 [P]
                                                                                  x : 201.0 [s ]
                SO3H                                                              y : 1532.7 [P]
                                                                                                                                                                      174.0

                                                                                                         T emp
                                                                      x : 77.0 [s ]                               Sample #1 LM 9- 767, 175C , time sc an, 3- 20- 08
                                                                                                                  Sample #2 LM 9- 844, 175C , time sc an, 3- 20- 08

Ionomer with Cure Site Monomer                        10   3

                                                           0.0   300.0
                                                                      y : 1188.1 [P]

                                                                                 600.0           900.0             1200.0          1500.0          1800.0
                                                                                                                                                                      173.0
                                                                                                                                                                  2100.0
                                                                                                         tim e [s]


                                                        Melt viscosity increase shows polymer
• Standard fluoroelastomer cure                         is being cross-linked in SO2F form.
  systems for initial
  experiments.                     Swelling Experiments based on x-y dimensions SO3H form
• This is being used to                  Sample               Water Glycol Methanol
  understand the effects of
  cross-linking. More stable      Uncrosslinked Sample         30.6       63.3     soluble
                                  Crosslinked Sample           24.4       52.4      73.7
  cross-links will be developed
  if this approach is           Swelling measurements show hydrolyzed samples are
  successful.                   cross-linked.                                           16
                Polymer Research
New polymer structures with hydrocarbon polymers
  • Hydrocarbon ionomers with fluorochemical
    acids attached for improved conductivity.
     – Initial coupling reactions have been run.
     – Can be made into composites with PFSA’s?
  • Prepare ‘hybrid’ polymers with perfluorinated
    and aromatic regions as hydrophobic and
    hydrophilic portions
     – Initial reactions have been run.
     – Durable linkages are key.


                                                    17
                 Example: Side-chain addition
•   Model reactions carried out                                                     O
                                                                                        F
                                                                   O2
    on small                                                       S
                                                                                       S O
                                                                                    F2C
    molecules to test                                                           *       CF2
                                           *                   O            O        F2C
•   Friedel-Crafts acylation                                                                  O
                                                                                         F
    unsuccessful                                                        HO3S
                                  1.   n-BuLi, THF, -70C
•   Lithiation/Electrophilic      2.   Acylfluoride                         CF2
                                  3.   KOH                               F2C
    Addition (at right)           4.   H2SO4
                                                                           CF2
                                                                        O
    successful                                                                O2
                                                                              S

                                                                                         *
                                                           *        O                O



    •   Cross-linking occurred in all trials and products formed gels and were
        partially soluble
    •   In one case IEC=0.66 meq/g was obtained (Target was 0.86) and
        conductivity was around 80 mS/cm

                                                                                              18
    Studies of Transport in Polymer Electrolytes
•   This activity is just getting started; collaborative between Case Western and
    Colorado School of Mines.
•   Use NMR relaxation and diffusion to probe local and long-range motion
•   Extend analysis as function of protogenic group, water content, equivalent
    weight, polymer composition, blockiness etc.
•   Look for:
     – tortuosity analysis
     – chain to chain hand-off? interaction?
           • use polarization transfer, 2-D methods
           • sidechain mobility: C-13 relaxation
     – changes in activation energies
           • threshold for increase as f(EW)?
•   Eventually implement Electrophoretic NMR
•   First samples will be 3M PFSA of varying EW

                                                                                    19
Phosphonic Acids containing Bis sulfonyl imide
                                      Br                   (O Et) 2 O P                   (O H) 2 O P



       Br           Br
                                                S O2                            SO2                          S O2
                                                       Phosphonation                   Hydrolysis
              +                -HCl
                                           HN
                                                S O2
                                                                           HN
                                                                                S O2
                                                                                                        HN
                                                                                                             S O2
       S O2N H2     S O 2 Cl


                                      Br                    (O Et) 2 O P                  (O H) 2 O P

Zirconyl phosphate structure                                          This bis-phosphonate has been prepared.
where imides control distance
between platelets?                                      We will attempt to attach this molecule to
                                                        HPA’s to generate chains or oligamers. These
                                                        may immobilize the HPA’s
                                                              H

                                                                                                              SO2
                                                              N      SO2




= SO2NHSO2                                                                                                          20
               Impact of HPA salts on conductivity
•   Addition of Ce and
    other cations can
                                                                              %RH
    improve membrane
                                                            100               50                    25
    oxidative stability, but
                                                     1.00
    lower membrane
    conductivity and fuel                                           Constant 80º C dewpoint

    cell performance,                                0.10
    particularly under hot,    Conductivity (S/cm)
    dry conditions.
                                                     0.01
•   Addition of HPA’s
    can mitigate this.                                            Control 825 EW
                                                                  CSM 10% Ce
•   Studies of the effects                           0.00         CSM 10% Ce 5% HPA
    of HPA’s immobilized                                          CSM 10% Ce 10% HPA
    via different routes on                                       CSM 10% Ce 20% HPA
                                                     0.00
    conductivity are
                                                            80     90           100           110        120
    ongoing
                                                                         Temperature (C)

                                                                                                          21
Carbon-centered Adducts in Nafion™ and
3M in Aqueous Solutions
                                                                          Me                                    Me                Ηβ
                                                                                             H +R
                                                                          Me                                    Me                R
Oxygen Radicals Formed by UV-irradiation, DMPO as                                     N                                   N

the Spin Trap                                                                         O                                   O
                                                                              DMPO Spin Trap                     DMPO/R Adduct

         3M (3.5%)/H2O2/DMPO/UV                                 Nafion (2.8%)/H2O2/DMPO/UV)
                                       Experimental: UV 6 min
                                                                                                        Experimental: UV 14 min



                                              Simulation
                                                                                                                     Simulation



                                            DMPO/OH 70%                                                        DMPO/OH 50%


                                           DMPO/CCR 30%                                                       DMPO/CCR 45%


                                                                                                          DMPO degradation 5%
 3450   3460   3470   3480   3490   3500    3510   3520
                  Magnetic Field / G                            3450   3460    3470       3480   3490    3500     3510     3520
                                                                                   Magnetic Field / G

  Carbon-centered radical (CCR) and •OH radical adducts were detected. The magnetic
  parameters for the CCR adducts in Nafion™ and 3M solutions are different, suggesting:
  (a) formation of different radicals, and (b) attack of •OH radicals on the side chain.
 Effect of Ce(III) on the Intensity of the
 Chain End Radical RCF2CF2•
   Nafion™ Membranes with Constant Fe(III) Concentration

              Nafion, 120 K, after UV 40 min                                               2.5
Integrated Intensity




                                                             Normalized Intensity / a.u.
   453                            Fe(III) 10%, Ce(III) 90%
                                                                                           2.0
   873                            Fe(III) 10%, Ce(III) 70%
   744                            Fe(III) 10%, Ce(III) 50%
                                                                                           1.5
   296                            Fe(III) 10%, Ce(III) 35%
   1123                           Fe(III) 10%, Ce(III) 20%
   707                            Fe(III) 10%, Ce(III) 10%                                 1.0
   4101                           Fe(III) 10%, Ce(III) 5%
   3924                           Fe(III) 10%, Ce(III) 0%
                                                                                           0.5
   0                               Fe(III) 0%, Ce(III) 10%

                                                                                           0.0

   3100    3200   3300   3400   3500   3600     3700                                             0       20      40       60       80   100
                  Magnetic Field / G                                                                 Ce(III) % (constant Fe(III) 10%)

         The chain end radical is not generated when the membrane contains only Ce(III), and
         no Fe(III).
         For a constant 10 % neutralization by Fe(III), Ce(III) is an effective stabilizer of
         membrane fragmentation when the degree of neutralization by Ce(III) is ≥10%.
                                                                                                                                              23
Model Compounds –
Approach and recent progress
•       Developed initial approach to testing aromatic sulfonic acid model compounds
         – Initial evaluation of MC’s has begun.
         – Many aromatic sulfonic acids and other model compounds readily degrade in
            Fenton’s reagent solution
         – Systematically ‘harvesting’ small molecule analogs from synthetic activity to
            explore degradation pathways
         – Considering oxidation, hydrolysis and other degradation modes
•       Recently received new LC/MS for rapid turnaround on degradation product analysis
•       Extensive analysis of perfluorosulfonic acid degradation products, 19F NMR carried out
•       Developing new methods to explore other possible degradation pathways
         – Could sulfonate cleavage be more favorable in presence of Pt?
•       Collaboration beginning between Case Western and Detroit-Mercy
                                                                                  Li
                    O                            O                                    H
                                                                          O                       O
                                                                                      N
    F               S             F                                           S               S
                                                                                                      CF2
                    O                                                             O       O
                                                     O
                                                                                                      CF3

        HO                       OH                  S   OH

                                                     O

                                                                                                            24
Bond Dissociation Energies of 3M fragment

                                                 F2
                                                            Fluoride    Energy of C-F bond
  • Nafion™, 3M ionomer                                      bond      dissociation (kcal/mol)
    and the short side chain                    F1
                                                               F1              103.60
    (Dow) ionomer have                                         F2              114.92
    been investigated.                F4
                                                      F3
                                                               F3              108.78
  • All show, qualitatively,                                   F4              105.14
    that the C-S bond is the     F6
                                                 F5
                                                               F5              102.77
    weakest. Possible sight                                    F6              105.43
    of side-chain attack?
  • An investigation into the                              Bond type       Energy of bond
                                                                       dissociation (kcal/mol)
    energetics and kinetics of                  C2
                                                             C6-S              61.15
    reaction of the fragments              C1

                                                            C5-C6              79.96
    with hydroxyl radicals                 O


                                                            C4-C5              75.77
    has begun.
                                           C3

                                           C4
                                                            C3-C4              80.96
                                           C5                O-C3              81.26
                                  C6
                                                            C1-C2              76.83
                                       S




                                                                                                 25
  Meso-scale modeling of Morphology
         Dissipative Particle Dynamics (DPD) simulations




SSC   EW = 678
                     3M

        λ = 11                       • Nafion™, 3M ionomer and the short side
                                       chain ionomer have been investigated.
                                     • It appears that the longer side in the 3M
                                       membrane results in larger water domains
                                       with higher density than the SSC PFSA
                                       membrane.
       (λ = 16                       • Need to account for backbone crystalinity.
                                     • Add other protogenic groups (size and
                                       acidity?).
                                                                               26
                  Test Method Development
Performance Testing
      • Developed Humidity Performance Test - Hold the dew point constant at
        80°C and gradually raise cell temperature from 80 to 120°C (Record
        performance and impedance)

Durability Testing Protocol Development
•   95ºC OCV Hold
     • One station running this protocol and we have begun to run samples.
•   SHIVA 1 Automotive Protocol
     • Protocol carried over from previous automotive development.
     • Four Cells commissioned. One sample set started.
•   SHIVA 2 Automotive Protocol with 120ºC Excursion
     • Equipment upgrade complete
     • New protocol currently being tested
•   Mechanical Membrane Humidity Cycle
     • Equipment upgrade complete
     • New protocol currently being tested

                                                                               27
Fuel Cell Testing                                                                                         0.7


                                                                                                          0.6
Down selection of screening electrode                                                                                                                                V1
                                                                                                                                                                     HFR V1

• Time was spent evaluating different




                                                                 Cell Voltage (volts)
                                                                                        @ 0.5 Amps/cm 2
                                                                                                          0.5                                                        V2
                                                                                                                                                                     HFR V2
  electrodes for increased performance in the                                                             0.4        H /Air CS 2.0
                                                                                                                                                                     V3

  screening of MEAs. We do not want the                                                                                  2
                                                                                                                     Ambient Pressure
                                                                                                                                                                     HFR V3
                                                                                                                                                                     V4
  electrode to limit evaluation of new PEMs.                                                              0.3
                                                                                                                     x/8080 C
                                                                                                                             o                                       HFR V4

• Cursor study of such electrode variables as:                                                            0.2
                                                                                                                     Counter Flow


   – I/C ratio                                                                                            0.1
   – Ionomer EW
   – GDL type                                                                                              0
                                                                                                                70           80       90    100        110      120       130

   – Catalyst type                                                                                                                 Cell Temperature ( C)
                                                                                                                                                         o


• We have down-selected V2 for our                                                                                                                     1000 ew 30 um
                                                                                                                                                       1000 ew 5um
  screening process.                                                                                                                                   644 ew 25um
                                                                                                                                                       733 ew 30 um
                                                                                                   0.7
                                                                                                                                                       825 ew CSM additive 30um


 Performance Gains                                                                                 0.6




                                                 Cell Voltage (Volts)
 •   Over 300 samples have been screened

                                                                           2
                                                                               @ 0.5 Amps/cm
     for performance.                                                                              0.5


 •   Gains in performance seen with –                                                              0.4
      – Thinner PEMS
      – Lower ew                                                                                   0.3
                                                                                                                 H /Air CS 2.0 70oC Dewpoint Inlets
                                                                                                                     2

      – New Chemistries                                                                            0.2
                                                                                                                 Ambient Pressure Outlets Co-Flow

                                                                                                          80                 85        90         95         100          105
      – New Additives                                                                                                             Cell Temperature ( C)
                                                                                                                                                        o
                                                                                                                                                                                  28
                                                      Oxidative Stability/Durability Gains
                                                                                                                                                                                  Oxidative Stability
                                                                                                                                                                                   o
                                                                                                                                                                H O 90 C 30%RH Ambient Pressure OCV
                                                                                                                                                                          2   2

•                            We have screened over 200 samples                                                                      10000
                             over our contract so far.
•                            Variables showing an influence on




                                                                                                   Flouride Release Rate




                                                                                                                                                                                                                           CSM HPA Additive B




                                                                                                                                                                                                                                                CSM HPA Additive C
                                                                                                                                                    No Additive Control
                             FRR include:




                                                                                                                                                                                                       Multilayer No Add
                                                                                                                                         1000




                                                                                                                                                                                       3M Additive A
                                                                                                                               (ug/day/cm )
                              – Additives




                                                                                                                           2
                              – Different PEM constructs.                                                                                     100

                              – Electrode effects.
                                                                                                                                              10

                                       0.8                                                     6


                                       0.7                                                                                                     1
                                                                                               5

                                       0.6
Cell Voltage (Volts)




                                                                                                            FRR (ug/day/cm )
                       2
                       @ 0.4 amps/cm




                                                                                               4
                                       0.5                                                                                                          •                         Additive A in 825 EW 3M
                                       0.4
                                                 H /Air CS 2.5/2
                                                  2                                            3
                                                                                                                                                                              membrane also provides
                                                      o
                                                 120 C 80/95%RH inlet                                                                                                         about 1,000 hours lifetime
                                       0.3                               2
                                                 Counter Flow 30psig 102cm
                                                                                               2
                                                                                                                                                                              at 120º C.
                                                                                                                                                    •                         Relatively high humidity
                                                                                                                           2




                                       0.2
                                                                                               1                                                                              and pressure.
                                       0.1
                                                                                                                                                    •                         Future testing will be done
                                        0                                                      0                                                                              at lower pressure, drier
                                             0            200      400   600   800   1000   1200
                                                                                                                                                                              conditions.
                                                                     Time (hours)
                                                                                                                                                                                                                                                                     29
                                      Future Work
•   Continue preparation and evaluate conductivity and durability of low EW and new imide
    containing polymers.
•   Prepare and test membranes crosslinked in both the hydrophilic and hydrophobic regions.
•   Produce low EW/MW ionomer segments for ‘Hybrid’ polymers.
•   Demonstrate synthesis of aromatic membrane or monomer unit with perfluorosulfonic acid side
    chain and ‘Hybrid’ polymers: Key focus on creating stable ‘links’.
•   Probe key factors in transport using NMR relaxation and diffusion, SAXS, QCM measurements,
    conductivity and other spectroscopy measurements. Develop better understanding of effect of
    low lambda on proton transport.
•   Prepare and test zirconyl analogs of new polymers and small molecules.
•   Immobilize stabilizing metal ions/HPA through synthesis of novel HPA as stand alone insoluble
    salts or grafting to ionomer backbone or inorganic nanoparticle.
•   Describe degradation pathways for current group of model compounds.
•   Quantify the intensity of the •OH radicals in the Fenton reaction based on Ce cations in aqueous
    solutions.
•   Quantify the intensity of the carbon-centered radicals (CCRs) generated in the Fenton reaction in
    aqueous solutions in the presence of model compounds.
•   Assess mechanism of Ce stabilization in dry 3M and Nafion™ membranes.
•   Complete hydrated morphology comparison of the three PFSA ionomers: Nafion™, SSC, and 3M
    ionomer. EW comparison and degree of hydration (λ=3-20)
•   Undertake first principles modeling of crystallinity through a comparison of the three PFSA
    ionomers and aromatic backbone ionomers with perfluorinated sulfonic acid side chains.
•   Complete chemical stability comparison of Nafion™, SSC, and 3M ionomer. (1) Bond
    dissociation energies; (2) Kinetics and thermodynamics of reaction with hydroxyl and peroxyl
    radicals.
•   Begin longer term single cell durability testing.
                                                                                                        30
• This project involves using              Summary
  experiment and theory to
  develop an understanding of
  factors controlling proton                                  2008 Status    2010 target    2015 target
  transport and the                 Conductivity
  chemical/physical durability of    at 120º C       S/cm    0.03 (25%RH)        0.1            0.1
  the membranes.
• New materials are being           Conductivity             0.05 (50%RH)
                                      at 80º C       S/cm    0.29 (100%RH)       0.1            0.1
  synthesized based on this
  understanding, and evaluation     Conductivity               0.08 (80%
  of these materials will further     at 30º C       S/cm        RH)*            0.07           0.07
  our understanding.                Conductivity
• This “feedback loop” will          at -20º C       S/cm      Not tested        0.01           0.01
  ultimately allow for materials     O2 cross-
  “designed” to meet                   over         mA/cm2     Not tested         2              2
  performance and durability
                                     H2 cross-
  targets.
                                       over         mA/cm2        <2              2              2
• Several approaches or pathways
  to new membranes are being        Durability w/            > 5000 (80ºC)   5000 (80ºC)    5000 (80ºC)
  investigated. We expect the        cycling**      hours    <1000 (120ºC)   2000 (120ºC)   5000 (120ºC)
  final membrane will combine
  some or all of these. We will      * tested at 25ºC
  not “down select” just one         ** not same EW membrane as conductivity test
  approach.
                                                                                                       31

								
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