Novel Approaches to Immobilized Heteropoly Acid (HPA) Systems for High Temperature,

Low Relative Humidity Polymer-Type Membranes

Andrew M. HerringColorado School of Mines

Mathew H Frey3M Corporate Research Materials Laboratory

5/19/09 FC_11_Herring

This presentation does not contain any proprietary, confidential, or otherwise restricted information

2

Overview

• April 1st 2006• March 31st 2011• 60% Complete

– C Performance– B Cost – A Durability

• Total project funding– DOE - $1,500K– Contractor - $375K

• Funding for FY08– $313K ($46K)

• Funding for FY09 to date– $300K ($45 K)

Timeline

Budget

Barriers

• 3M - Industrial• Project lead - CSM

Partners

3

Objectives•Overall

•Fabricate a hybrid HPA polymer (polyPOM) from HPA functionalized monomers with:

– σ >0.1 S cm-1 at 120°C and 25%RH

• 2008 •Synthesis and optimization of hybrid HPA polymers for conductivity from RT to 120ºC with an understanding of chemistry/morphology conductivity relationships using model system

• 2009 •Optimize hybrid polymers in more practical systems for proton conductivity and mechanical properties

4

Go/No-Go 08/09Month/Year Milestone or Go/No-Go Decision

Jan 09 Demonstrate conductivity of 100 mS cm-1 at 50% RH and 120ºC –30ºC 60% RH 120 mS cm-1

80ºC 100% RH >300 mS cm-1

Comparable to PFSA membranes under FC operating conditions120ºC 40-50%RH >100 mS cm-1

Feb 09 Deliver membrane to topic 2 awardee –Lower conductivity, unfortunately hard to control model film quality and durability at high HPA loadings

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RelevanceObjective• To fabricate PEMs with a proton conductivity

<100 ms cm-1 for operation in a vehicular system up to 120ºC with no inlet RH

• Films were synthesized that meet this DOE performance target at temperatures > RT

• Future work will address both cost and durability targets

6

Collaborators

3M• Corporate Materials Research

laboratory– Matthew Frey (Sub)

• Fuel Cell Components Group– Steven Hamrock (Consultant)

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Unique Approach• Materials Synthesis

based on HPA Monomers, Novel “High and Dry” proton conduction pathways mediated by organized HPA moieties – A NEW Ionomer System

• Task 2.1: Synthesis and Optimization of hybrid HPA polymers for 120ºC conductivity for Go/No Go Decision - Complete

• Task 2.2 – Synthesis and selection of protonic additive for hybrid HPA polymers for 120ºC conductivity for Go/No Go Decision -Complete

• Task 3.1 – Down Selection of potential practical approaches – 10% complete

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Generation I Model System: Acrylate Co-Monomers

• Polymer system in a kit• Allows Chemistry to be varied• Effect of Morphology can be studied• Full Disclosure• But…

– Ester linkage unstable to hydrolysis– Oxidizable CH2 groups and an oxidizing super acid moiety – The formulation is not optimized and becomes brittle eith time

• Residual unpolymerized volatile butyl acrylate acts a plasticizer and is continually being lost from the film.

• The morphology of these materials is hard to control and may indeed be changing during testing.

– For UV cured films, although solid films are obtained, the degree of polymerization may vary between the surface and the interior of the film

– In previous work, we showed that under very dry conditions, approaching 0% RH, some of the protons became unsolvated and irreversibly bound to the HPA structure.

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Design Space for Model System

• We can control chemistry• Need to understand morphology

100%PO

M m

onomer content

Vinyl methacrylate styrenyl ethylstyrenyl

POM monomer, so far all based on HSiW11

Butyl AcrylateHydroxyethyl Acrylate

-COOH-SO3H

-X?

Best HT performance, to date

Best RT performanceto date

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Technical Accomplishments: Poly POMs Cross-linked

• PolyPOM75v/BA• ρ= 2.58 g cm-3

• ≈100 μm

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Poly POM 75v Morphology(Phase Separation at loadings >50wt% HPA)

AFM SAXS

12

Water content decreases for PolyPOM75v with RH

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PolyPOM75v, 100%RH

• Proton Conductivity higher than Nafion®

• Very High Proton Conductivity calculated from Nernst-Einstein Equation

RTFcDz 22

=σ

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P(SiW1180V-co-BA-co-HDDA), 50%RH

-3.50

-3.00

-2.50

-2.00

-1.50

-1.00

0.00250 0.00255 0.00260 0.00265 0.00270 0.00275 0.00280 0.00285 0.00290 0.00295

1/T (K-1)

ln(C

ondu

ctiv

ity)

Actual Conductivity

Extrapolated Regression

Theoretical Conductivity

Linear ( )

(70 oC, 60 mS/cm)

(80 oC, 82 mS/cm)

(95 oC, 109 mS/cm)

(120 oC, 173 mS/cm)

(144 oC, 77 mS/cm)

(120 oC, 37 mS/cm)30% RH

(110 oC, 121 mS/cm)

(100 oC, 106 mS/cm)

Regression

EA - 22.97 kJ/mole

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High Proton Conductivity can be Obtained at 120ºC

0.010

0.100

1.000

40 45 50 55 60

Relative Humidity (%RH)

Con

duct

ivity

(S/c

m) 75% vinyl-HPA (Initiator 1)

80% vinyl-HPA (Initiator 1)75% vinyl-HPA (Initiator 1)80% vinyl-HPA (Initiator 1)75% vinyl-HPA (Initiator 1)85% vinyl-HPA (Initiator 1)85% vinyl-HPA (Initiator 1)85% vinyl-HPA (Initiator 1 + 2)85% vinyl-HPA (Initiator 1 + 2)

Measurements made at 3M (single condition)Data are averages of figures collected after 70 to 110 min. at condition

TestEquity oven, atmospheric pressureBekktech sample fixture

(Balance of compositions, in all cases, is 90:10 n-butylacrylate:hexanediol diacrylate)

Michael Emery, 3M

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Thermal vs UV changes Morphology

Thermal - clusters UV - networks

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Dramatic Differences in Transport for Thermal vs UV cured PolyPOM80v

1H

UV polymerization

Polymerization D(0) x 105 D(∞) x 105 σ(0) σ(∞)Method (cm2 s-1) (cm2 s-1) (mS cm-1) (mS cm -1)

Thermal 0.84 0.13 65 10

UV 2.48 0.95 191 73

13C CPMAS

Thermal polymerization

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Future Work – 3M

X X

XX

BrA

ZA

Z Z

Z Z

Na2WO4+

Na2SiO3+

HCl

K8[SiW11O39]•14H2O

Details are withheldas proprietary

(not on this slide)

1 2

4

3

5

1

2

3

4

5

New to 3M (took 2 tries)

Core 3M chemistry

Extension of 3M chemistry

Core CSM chemistry

Extension of CSM chemistry

Changes w.r.t. Phase I• Different backbone• New linkage• Different film-forming process

Features• More durable (chem & mech)• Expected to be easier to mfr.• Crosslinkable• Expecting better reproducibility

2nd Generation HPA Hybrid Electrolyte

Preformed Polymer

2nd polymer also on the drawing board.

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Future Work - CSM

Continue to Fabricate Hybrid Polymers from monomeric building blocks

• Eliminate ester and CH2 functionalities from Monomers

• Improve Morphology – Channels vs Clustering– Monomer System A– Monomer System B– Monomer System C

• Down select at end of Year 4• Optimize for end of Year 5

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0

50

100

150

200

250

20 30 40 50 60 70 80 90 100 110 120T (oC)

(mS

cm-1

)

PolyPOM75v (100% RH)Nafion 112 (100% RH)polyPOM80v (50% RH)

polyPOM98m60% RH

(PolyPOM85v 47% RH - 3M)(PolyPOM80v 40% RH - CSM)

Summary

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Summary

April 2008 RT milestone Exceeded August 2008

Met DOE 2010 target January 2009

H+ conductivity 300 ms/cm 100%RH 80ºC

126 ms/cm60%RH, 31ºC

100 ms/cm47%RH at 120ºC

0

50

100

150

200

250

20 30 40 50 60 70 80 90 100 110 120T (oC)

(mS

cm-1

)

PolyPOM75v (100% RH)Nafion 112 (100% RH)polyPOM80v (50% RH)

polyPOM98m60% RH

(PolyPOM85v 47% RH - 3M)(PolyPOM80v 40% RH - CSM)