Polymer Blend Proton Exchange Membranes
R. A. Weiss and M. T. ShawUniversity of Connecticut
May 25, 2004
This presentation does not contain any proprietary or confidential information.
Objective
Develop new membranes based on polymer blends for operation at temperatures of 120°C or higher
Budget
DOE Funding FY04 = $ 95,000
Technical Barriers and Targets
DOE Technical Barriers For Fuel Cell ComponentsO. Stack Material and Manufacturing CostsP. DurabilityR. Thermal and Water
DOE TechnicalTargets for Membranes (Automotive) for 2005
Membrane conductivity (operating temperature) ~ 0.1 S/cm Operating temperature ≥ 120°CMembrane cost ~ $50/kWMembrane durability > 4000 hHydrogen/oxygen cross-over (MEA) ~ 5 mA/cm2
Survivability ~ -20 °C
ApproachDevelop high temperature PEMs with controlled
morphology using acid-base polymer blends
1. Thermodynamics: develop a percolated ionic pathway at the interface of a spinodal morphology of a polymer blend comprising a sulfonated polyketone and a polyimide or similar second component
2. Electro-dynamics: Orient a dispersed phase of the conductive sulfo-polyketone in a polyimide matrix by applying an electric field during membrane casting
50 µmE
Project SafetyHandling and disposing of SO3: normal handling procedures for strong acids; disposal by neutralization
Handling of hydrogen: normal handling procedures of high-pressure gas; high-flow-rate ventilation
Handling and disposing of solvents:normal OSHA/EPA procedures used
Project Timeline
Phase II Phase IIIPhase I10/02 – 10/03 10/03 – 10/04 10/04 – 12/06
Phase I: Feasibility1 Optimize preparation of sulfonated PEKK (SPEKK) ionomers2 Prepare/Evaluate SPEKK/polyether imide (PEI) blend membranesPhase II: Morphology Development3 Develop spinodal structure for SPEKK/PEI membranes and
characterize membrane performance4 Develop procedure for orienting SPEKK/PEI membranes and
characterize membrane performance5 MEA production and testingPhase III: System Optimization6 Optimize membrane composition and morphology for high
temperature SPEKK/PEI PEM7 Design and evaluate other blend PEMs
1 2 3 4 5 6 7
Technical Accomplishments/Progress
Developed Membranes Based on Poly(ether ketone ketone)
High temperature stability (Tg ~ 155°C; Tm ~ 360°C)Excellent mechanical properties (engineering thermoplastic)Excellent chemical and solvent resistanceExcellent oxidative stabilityAdequate resistance to desulfonation
O C
O
C
O
n
Technical Accomplishments/Progress
O C
O
C
O
n+ nSO3/H2SO4 + H2On
nO C
O
C
O
SO3H
kS
kD
Optimized procedure for preparing sulfonated PEKK (SPEKK)
Time (h)
0 20 40 80
IEC
(meq
/g)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
19oC
42oC
52oC52oC63oC
74oC
)/exp1( τtaIEC −−=IEC = IEC∞[1-exp(-t/τ)]
open symbols → PEKK T/I = 8/2closed symbols → PEKK T/I = 6/4
Proton Conductivity of SPEKK
Technical Accomplishments/Progress
SPEKKs:For IEC ~ 1.8 – 2.1 meq/g,conductivity ~ 10-1 S/cmWater insoluble when IEC < 2.3 meq/g20-150 µm membranes can be cast from NMP or DMAc
0.001
0.010
0.100
1.000
1.3 1.5 1.7 1.9 2.1 2.3 2.5IEC (meq/g)
σ(S
/cm)
AC 2ptDC 4ptAC 4pt
Immersed in H2O
98% RH
Nafion 112 (immersed): 0.09 S/cmNafion 112 (98% R.H.): 0.06 S/cm
Methanol Crossover for SPEKK in MEA
0.05
0.07
Resistance(ohm cm2)
(H2/O2, 80 oC)
0.40
0.22
Methanol Crossover(A/cm2)
(1M MeOH, 80 oC)
Nafion
SPEKK(1.8 meq/g)
SPEKK membranes:Good proton conductivity (~ 0.1 S/cm)Improved methanol permeability resistance vs. Nafion
Technical Accomplishments/Progress
Current Density (mA/cm2)
0 250 500 750 1000
Cel
l Vol
tage
(V)
0.0
0.2
0.4
0.6
0.8
1.080°C / 75% R.H. (H2/O2)
IEC2.0 meq/g
1.2 meq/g
MEA Performance of SPEKK PEMs
Technical Accomplishments/Progress
Reasonably good MEA performance
N
O
O
O C
CH3
CH3
O
O
O
N
n
O O C
O
n
SO
O
OH
e- donor
e- acceptor
SO
O
OH PEI
SPEEK
Blends of SPEKK with Poly(ether imide) (PEI)
Strong H-bonding interactions are expectedIonomer provides acid groups for proton conductivityRelatively hydrophobic PEI provides mechanical integrity
Technical Accomplishments/Progress
PEI
Hypotheses:Ion-rich interphase provides pathway for proton conductivityPercolated conductive path present before water is added
Amount of water required for conductivity will be less than forconventional ionomer membrane
SPEKK/PEI Blend PEMs
Technical Accomplishments/Progress
SO3H
SO3H
SO3H
SPEKK
O=
O=
O=
ion-richinterphase
50% SPEKK/50% PEI
50 µm
H2O
Effect of PEI content on conductivity (RT)
Technical Accomplishments/Progress
Increasing PEI concentration:Lowers conductivity (but still > 0.01 S/cm for cPEI < 30%Reduces water concentrationImproves mechanical properties of wet membrane
wt% PEI0 10 20 30 40 50 60
σ (
S/c
m)
0.001
0.01
0.1
IEC = 1.9
IEC = 1.6
Controlling the Blend Morphology: Film Casting T
Dispersed phase size decreases with casting temperatureDispersed phase size increases with increasing PEI
Technical Accomplishments/Progress
Ternary Phase Diagram
SPEKK0 20 40 60 80 100
NMP
0
20
40
60
80
100
PEI
0
20
40
60
80
100
cloudy
Casting Temp (oC)30 40 50 60 70 80 90 100 110
Dis
pers
ed P
hase
Siz
e ( µ
m)
0.1
1
10
PEI (wt%)0 20 40 60 80 100
Dis
pers
ed P
hase
Siz
e (µ
m)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Controlling the Blend Morphology: Electric Field Alignment
Technical Accomplishments/Progress
20% SPEKK 20% SPEKK
Cast without Electric Field Cast with Electric Field E = 0.5 kV/cm; f = 20 Hz
SPEKK dispersed phase can be oriented by applying an AC electricfield across the membrane during processing (solution or melt)
Controlling the Blend Morphology: Electric Field Alignment
Technical Accomplishments/Progress
E
Oriented at 200°C; E = 10 kV/cm; f = 20 Hz
30/70 SPEKK/PEI
4
5
6
7
8
9
10
0 1 2 3 4 5 6
Log (f, Hz)lo
g (l ρ
* l, Ω
-cm
) Unaligned
Aligned
Electric field alignment of SPEKK phase significantly increases the membrane conductivty
Impedance Spectroscopy
Interactions and Collaborations
Oxford Performance Materials (OPM): SPEKK development and blend membrane development; MEA fabrication and testing
Leveraging Resources:
Fundamental studies of the thermodynamics of ionomer blends
$1.1M1994-02NSF (UConn)
Development of equipment for electric field orientation of polymer films during film preparation
$75K2003-04Connecticut Global Fuel Cell Center (UConn)
Ongoing: Development of methods for controlling domain structure of polymer blends for PEM applications using thermodynamics and electric fields
$191K2003-05DOE (UConn)
Ongoing: sPEKK and sPEKK blend based MEAs. (subcontract to UConn)
$250K2003-05DOE Inventions & Innovations (OPM)
Development of reproducible process for sulfonation of PEKK. Demonstrated feasibility of SPEKK PEMs for direct methanol fuel cells.
$375K2001-03Connecticut Innovations, Inc. (UConn and OPM)
Development of sulfonated PEKK. Initial evaluation of sulfonated PEKK for PEM fuel cell applications.
$375K1999-01Connecticut Innovations, Inc. (UConn and OPM)
Outputs/ObjectivesAwardDatesAgency
Future Plans
Remainder of FY 2004:Develop ternary phase diagrams for SPEKK/PEI/solvent, using different solvents
Produce membranes with spinodal structure
Optimize equipment and procedures for electric field orientation of membranes
Fabricate MEAs with controlled morphology blend membranes