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