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1 Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim ([email protected]) Los Alamos National Laboratory Los Alamos, NM, 87545 Project ID: FC043 2012 U.S. DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting May 14-18, 2012, Washington, D.C. This presentation does not contain any proprietary, confidential, or otherwise restricted information

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Page 1: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

1

Resonance-Stabilized Anion Exchange Polymer Electrolytes

Yu Seung Kim ([email protected])

Los Alamos National Laboratory Los Alamos, NM, 87545

Project ID: FC043

2012 U.S. DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting May 14-18, 2012, Washington, D.C.

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

Page 2: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

2

Timeline

Project start September 2009

Project end March 2012

Percent complete 100%

a. Polymer & ionomer synthesis (100%)

b. Catalyst preparation (100%)

c. MEA processing & testing (100%)

d. Degradation study (100%)

Budget

Total funding $ 1,320 K

Funding for FY10 $ 528 K

Funding for FY11 $ 330 K

No cost shared

Barriers

B. Cost

C. Electrode performance

A. Durability

Overview

Partners

Project lead Los Alamos National Laboratory Yu Seung Kim (PI)

Dae Sik Kim Andrea labouriau Hoon Jung

Subcontractor

Sandia National Laboratory Cy Fujiomoto (Ext. PI) Michael Hibbs

Jet Propulsion Laboratory Charles Hays (Ext. PI) Daniel Konopka Michael Johnson Michael Errico Poyan Bahrami

Interactions Cellera Technologies (Shimpshon Gottesfeld)

Advanced Industrial Science and Technology (Yoong-Kee Choe) Ovonic Fuel Cells (Rob Privette)

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 3: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

3

Relevance – Objectives, Technical Barriers, Technical Targets and Results

Demonstrate an improved alkaline membrane fuel cell (AMFC) performance and durability using advanced polymer electrolyte membranes, ionomers and non-precious catalysts

Major tasks

FY 09 & 10: Synthesis of anion exchange membranes and ionomers

FY 10 & 11: Characterization of catalyst and AMFC performance

FY 11 & 12: AMFC durability test and durability mechanism

ISSUES Technical Barriers Technical Target a FY 09-10 FY 10-11 FY 11-12 Result

Membrane Conductivity Stability Tensile properties

: > 50 mS/cm > 500 h in NaOH soln. 60 C Stress: > 10 MPa, Strain : > 10%

× ×

×

120 mS/cm 672 h

25 MPa, 30%

Ionomer Backbone structure Conductivity Stability

Perfluorinated > 50 mS/cm 20 mS/cmb > 500 h in NaOH soln.

×

–.

×

M-Nafion®-FA-TMG 20 mS/cm

7% after 72 h

Catalyst Element ORR activity

Non-precious metal or carbon > 0.9 V (E1/2)

– –

CNT/CNP cat. 0.95 V (E1/2)

AMFC per-formance

Maximum power Durability

> 200 mW/cm2 in H2/Air < 10% for 800 h

– –

×

466 mW/cm2

~50% for 300 hc

Technical Barriers, Targets and Results

a Values in the original proposal b Conductivity target for ionomer was lowered as we achieved MEA performance target with low conductive ionomers c Mostly due to the cation stability and water management issue; ionomer and polymer backbone degradation is negligible

Objectives

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 4: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

4

Strain (%)

NF-PAES

0 20 40 60 80 100

Str

ess

(M

Pa)

0

20

40

60

F-PAE

0 20 40 60 80 100

Str

ess

(M

Pa)

0

20

40

60 ATM-PP 1

0 20 40 60 80 100

Str

ess

(M

Pa)

0

20

40

60

Col 15 vs Col 16

Col 17 vs Col 18

Col 19 vs Col 20

ATM-PP 2

0 20 40 60 80 100

Str

ess

(M

Pa)

0

20

40

60

ATM-PP 3

0 20 40 60 80 100

Str

ess

(M

Pa)

0

20

40

60

90% RH

50% RH

10% RH

Strain (%)

Synthesis of Polyaromatic Anion Exchange Membranes for Durability Study

High molecular weight polyaromatic AEMs were prepared

Mechanical properties of the AEMs are strongly influenced by chemical structure and molecular weight

Highlight: Stress: > 25 MPa & Elongation: > 30% at 50% RH

Membrane mechanical milestone (> 10 MPa stress & 10% strain) achieved with F-PAE, NF-PAE and ATM-PP 3

Sample Coun-ter ion

Mw×103 a

(g/mol)

IEC (meq./g)

WU (wt.%)

b

(mS/cm)

F-PAE Cl- 150 2.5 99 46

NF-PAES Br- 87 2.2 43 15

ATM-PP1 Br- 61 1.7 72 30

ATM-PP 2 Br- 77 1.6 64 35

ATM-PP 3 Br- 196 1.7 70 37

Synthesis and properties of polyaromatic AEMs

a measured by GPC using the parent polymers b measured at 80 C using salt form membranes

Stress-strain behavior of AEM parent polymers

measured at 50 C under controlled RH conditions

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

BTMA : Benzyl TetraMethyl Ammonium

Page 5: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

5

0 10 20 30 40 50

0

5

10

15

20

25

a

de

f

ATM-PP 3 NF-PAES

Strain (%)

0 5 10 15 20 25 30 35

0

10

20

30

40

50

a

b

c

d

9609801000102010401060

NF-PAES c

C-H

1320135013801410

Ab

so

rban

ce

O-H C-O

C-O

C-H, S=O

NF-PAES b

NF-PAES d

NF-PAES a

C-H

Aryl-Ether Cleavage of Poly(arylene ether) AEMs*

FTIR results indicated phenol formation of poly(arylene ether) (PAE) based AEMs after membrane treatment Nucleophilic displacement takes place in the aryl-ether linkage of the PAE backbones

Mechanical properties of the AEMs are greatly influenced by the AEM backbone degradation

Highlight: No backbone degradation observed in poly(phenylene) AEMs

Proposed backbone degradation mechanism

Nucleophilic displacement of aryl-ether linkage

Mechanical property change after membrane treatment

Membrane treatment a: 0.5 M HCl (or HBr) for 30 min (or 2 h); b: 0.1 M NaOH for 1 h, room temp. after a;

c: 0.5 M NaOH for 30 min, room temp. after a d: 0.5 M NaOH for 1 h, 80 C after a e: 0.5 M HCl (or HBr) for 30 min (or 2 h) after d f: 0.5 M NaOH for 1 h 80 C after e g: 0.1 M NaOH for 2 h & 0.5 M NaOH for 100 h at 80 C

131013301350

Ab

so

rba

nc

e

9609801000102010401060

F-PAE a

F-PAE b

F-PAE c

F-PAE d

C-H

C-O C-O O-H C-H C-H C-H

Phenol formation (FTIR) after treatment

F-PAE

0 5 10 15 20 60 80 100

Str

ess (

MP

a)

0

10

20

30

40

50

a

b

c

d

e

Polymer Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

wavenumber (cm-1

)

96098010001020104010601320135013801410

Ab

so

rba

nc

e

C-O

C-O

C-H

ATM-PP bATM-PP c

ATM-PP d

ATM-PP g

O-H C-H

C-H

*C. Fujimoto et al. manuscript was submitted 2012

Page 6: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

6

ATM-PP 3

time (h)

0 50 100 150 200 250 300c

urr

en

t d

en

sit

y (

A/c

m2)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

HF

R (

Oh

m c

m2)

0.0

0.2

0.4

0.6

0.8

1.0

F-PAE

0 50 100 150 200 250 300

cu

rre

nt

de

ns

ity (

A/c

m2)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

HF

R (

Oh

m c

m2)

0.0

0.2

0.4

0.6

0.8

1.0

Impact of Polymer Structure on AMFC Performance*

The AEMs having low Mw (ca. < 100 K) showed poor AMFC performance due to the possible interfacial failure during MEA processing

Negligible interfacial issue for high Mw F-PAE and ATM-PP

F-PAE MEA showed catastrophic failure at 55h probably due to the AEM degradation

Highlight: No catastrophic failure for ATM-PP 3 MEA during 300 h life test

Effect of backbone degradation# Effect of molecular weight on AMFC performance

Polymer Degradation

Sample F-PAE ATM-PP1 ATM-PP 2 ATM-PP 3

Mw×103 a (g/mol) 150 61 77 196

HFR ( cm2) 0.23 1.67 1.23 0.21

Membrane: fluorinated poly(arylene ether) AEM (F-PAE, LANL) and poly(phenylene)-based AEMs with

three different molecular weight (ATM-PP, SNL); Test conditions: H2/O2 at 80 C

current density (A/cm2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6

ce

ll v

olt

(V

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

po

we

r d

en

sit

y (

W/c

m2)

0.00

0.05

0.10

0.15

0.20

0.25

F-PAE

current density (A/cm2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6

ce

ll v

olt

(V

)0.0

0.2

0.4

0.6

0.8

1.0

1.2

po

we

r d

en

sit

y (

W/c

m2)

0.00

0.05

0.10

0.15

0.20

0.25

ATM-PP 1

ATM-PP 2

ATM-PP 3

Membrane: F-PAE and ATM-PP 3; Test conditions: H2/O2 at constant

voltage of 0.3 V, at 80 C

# supporting information for analysis methodology

*C. Fujimoto et al. manuscript was submitted 2012

a measured by GPC using the parent polymers

Page 7: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

7

Stability of Perfluorinated Anion Exchange Ionomers

Phenyl guanidinium has much better stability than sulfone guanidinium under high pH conditions

Trace of degradation after the treatment for phenyl guanidinium functionalized perfluorinated ionomers is due to the hydrolysis of amide group rather than polymer backbone or cation degradation

Highlight: Stable perfluorinated ionomers were prepared by introducing electron donating spacer

Ionomer milestone (perfluorinated ionomer with conductivity > 20 mS/cm and stability) achieved

Sample IEC (meq./g)

WU (wt.%)

a

(mS/cm)

FY 11-12 M-Nafion®-FA-TMG 0.70 10 20

FY 10-11 M-Nafion®-TMG 0.90 18 45

Synthesis and properties of perfluorinated AEMs

a measured with hydroxide form at 80 C

Stability after soaking in 0.5 M NaOH at 80 C

1 2

3,4

Carbons in perfluoro carbon

Solid state 13C NMR

wavenumber (cm-1

)

1200140016001800

Tra

nsm

itta

nce

CNCO CH3

wavenumber (cm-1

)

1200140016001800

CN CH3

Before after 24 h

Before after 72 h

FY 11-12 FY 10-11

Polymer Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 8: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

8

Stability of Benzyl Tetramethyl Ammonium Cations (ex-situ)

Benzyl tetramethyl ammonium (BTMA) is stable at 60 C; However, ~ 10 % IEC loss after 9 days at 90 C was observed under high pH conditions

Anion conductivity loss of BTMA functionalized F-PAE and ATM-PP 3 was observed at 0.5 M NaOH at 80 C over 100 h

Polymer backbone degradation has a little impact on conductivity

Comparing the ether cleavage degradation of PAEs, the BTMA cation degradation was much slower

Anion conductivity change as a function of time*

Cation Degradation

Membrane: poly(phenylene) based AEM (ATM-PP, SNL) and

crosslinked polystyrene based AEM (AHA, Tokuyama) (cf.

PAE based AEMs became too brittle to handle after 1-2

days); Test conditions: 4 M NaOH (aqueous), no stirring; IEC

measured with back titration

Membrane: Poly(phenylene) based AEM (ATM-PP, SNL) and poly(arylene ether) based

AEM (F-PAE, LANL); Test procedures: 1st step: AEMs were prepared in their salt forms

and were immersed in 0.1 M NaOH at 80 C for 10, 30, 60 and 120 min and followed

by rinsing those in boiling water for 1 h to remove any residual NaOH; 2nd step: AEMs

were immersed in 0.5 M NaOH solution at 80 C for various time intervals

0.1 M NaOH 80oC

Time (min)

0 30 60 90 120

Co

nd

uc

tivit

y (

mS

/cm

)0

20

40

60

80

100

120

140

F-PAE

ATM-PP 3

0.5 M NaOH 80oC

Time (h)

0.1 1 10 100

F-PAE

ATM-PP 3

Time (days)

0 5 10 15 20 25 30

IEC

(m

eq

/g)

0.0

0.5

1.0

1.5

2.0

2.5

ATM-PP 90 C

ATM-PP 60 C

Tokuyama 60 C

4 M NaOH

IEC change as a function of time

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

*C. Fujimoto et al. manuscript was submitted 2012

Page 9: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

9

Stability Tetramethyl Guanidine Aqueous Solution (ex-situ)

Tetramethylguanidine (TMG) showed electro-catalytic activity; The current at 0.9 V is similar to conventional KOH electrolytes but is less favorable at lower potential due to the probable adsorption to the Pt surface

TMG and its byproducts can adsorb onto the Pt surface below ~0.8 V, obscuring the transition between typical kinetic and mass-limiting regions during oxygen reduction; This effect is especially pronounced at low rpm (low oxygen concentrations)

Highlight: The TMG electrolyte showed remarkable stability after two months, with some signs of increasing resistivity such as the positive potential shift of the H-desorption peak

Oxygen reduction reaction on Pt

ORR study: under O2 sparging with anodic and cathodic scans at a rate of 1 mV/s,

between a potential range of 1.0 V to ~ 0.2 V; A separate set of scans between 1.0

and 0.8 V for the kinetically limited region

H2O redox features of TMG Effect of rpm on oxygen reduction

CV Cycling: 0.0 to 1.1 V RHE (clockwise cycles) in 0.1 M TMG purged with sparging

and blanketing Ar gas; Durability test 2 L of 0.1 M TMG was mixed and allowed to

sit in open air for 2 months

*D. Konopka et al. Electrochem. Solid-State Lett, 15, B17 (2012)

Cation Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 10: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

10

Stability of Benzyl and Phenyl Guanidinium (ex-situ)

Benzylpentamethyl guanidinium was slowly decomposed while phenylpentamethyl guanidinium was stable under high pH conditions and elevated temperatures

Highlight: Phenylpentamethyl guanidinium was stable at 4 M NaOH, 90 C for 72 h

Stability of benzylpentamethyl guanidinium*

*M. Hibbs, C. Fujimoto, T. Lambert, D.S. Kim, Y.S. Kim, NAMS 2011, June 6, 2011

Stability of phenylpentamethyl guanidinium*

The relative areas of b and c peaks decrease drastically after NaOH. But b to c area ratio does not change

Cation Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 11: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

11

-50

-40

-30

-20

-10

0

10

20

30

Quantum Chemical Modeling for Guanidinium Degradation*

Alpha carbon in benzyl-guanidinium is weak site due to the nucelophilic substitution. Also hydrogen on the alpha carbon is very acidic

Activation energies of center carbon of benzyl and phenyl guanidinium for addition and carbonyl formation are similar

Next: The stability comparison with benzyl tetraalkyl ammonium is under investigation at AIST

*Yoong-Kee Choe, unpublished results, AIST

Benzyl-guanidinium (Addition + Carbonyl formation)

-50

-40

-30

-20

-10

0

10

20

30

Phenyl-guanidinium (Addition + Carbonyl formation)

-10

-5

0

5

10

15

20

12.2 kcal/mol

-20

-10

0

10

20

30

27.5 kcal/mol

28.0 kcal/mol

Benzyl-guanidinium (Nucleophilic substitution) Benzyl-guanidinium (Elimination reaction)

28.0 kcal/mol

Cation Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 12: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

12

Current density (A/cm2)

0.0001 0.001 0.01 0.1 1

EiR

-fre

e (

V)

0.80

0.85

0.90

0.95

1.00

1.05

1.10

Initial

after 300 h

Stability Comparison BTMA vs. Phenyl Guanidinium (in-situ)

The stability of phenylpentamethyl guanidinium and benzyltetramethyl ammonium functionalized PAEs were compared when used as ionomer in the catalyst layer

Spectroscopic results indicated that central carbon of pentamethyl guanidinium is the weakest site which is consistent with quantum chemical modeling

Highlight: Phenyl guanidinium cation was substantially more stable than BTMA after 300 h durability test (2 vs. 69 V/dec h)

Durability of ionomer (phenyl guanidinium vs. benzyl ammonium)

Sample IEC (meq./g)

WU (wt.%)

(mS/cm)

M-PAES-TMG 1.0 10 35

F-PAE 2.4 85 100

Cation functionalized ionomers

* Polymers were synthesized from FY 11 tasks

Membrane: Benzyl tetramethyl ammonium functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst:

Pt black (3 mg/cm2) for anode and cathode; Ionomer for catalyst layer: M-PAES-TMG and F-PAE; testing

conditions: H2/O2 at 60 C; Durability test: Constant voltage of 0.3 V for 300 h

Proposed phenyl pentamethyl guanidinium degradation mechanism

Addition and carbonyl formation Nucelophilic attack to the central carbon

M-PAES-TMG

Current density (A/cm2)

0.0001 0.001 0.01 0.1 1

EiR

-fre

e (

V)

0.80

0.85

0.90

0.95

1.00

1.05

1.10

Initial

after 300 h

Phenyl-guanidinium Benzyl ammonium

Tafel slope degradation rate

2 V/dec h

Tafel slope degradation rate

69 V/dec h

Cation Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 13: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

13

Potential/V vs. RHE

0.2 0.4 0.6 0.8 1.0 1.2

Cu

rren

t d

en

sit

y/m

A c

m-2

-3

-2

-1

0

Pt/C, 60 gPt

cm-2

CNT/CNP, 1.0 mg cm

-2

after 5,000 cycles

Stability of Pt and CNT/CNP Composite Catalyst (ex-situ)

Novel CNT/CNP composite catalyst was prepared from nitrogen containing compound and carbon black

Both Pt and CNT/CNP catalyst showed excellent stability under high pH conditions up to after 10,000 potential cycles

The CNT/CNP showed high activity after 5,000 potential cycles (ca. E1/2 = 0.95 V)

Highlight: Durability of electro-catalyst is no issue and the electrochemical activity of CNT/CNP catalyst is excellent

Catalyst ORR activity milestone (E1/2 > 0.9 V) achieved

Carbon Nanotube (CNT)

Carbon Nanoparticle (CNP)

RDE: E-TEK Pt/C, Pt loading: 60 μg cm-2; N-M-C, 1.0 mg cm-2; 0.1 M NaOH; 900 rpm; room temperature; Ag/AgCl (3 M NaCl) reference electrode; steady-state potential

program (OCP for 120 s first, then 20 mV steps, 25 s/step); Cycling: 0.6 -1.0 V, 50 mV s-1, O2-saturated solution

Cycling stability in 0.1 M NaOH

Catalyst Degradation

Potential/ V vs. RHE

0.2 0.4 0.6 0.8 1.0 1.2

Cu

rren

t d

en

sit

y/

mA

cm

-2

-4

-3

-2

-1

0

initial

3,000 cycles

5,000 cycles

Pt/C catalyst (60 g cm-2

)

Potential/ V vs. RHE

0.0 0.2 0.4 0.6 0.8 1.0 1.2Cu

rre

nt

de

ns

ity/

mA

cm

-2

-4

-2

0

2

4

CNT/CNP catalyst (1.0 mg cm-2

)

Potential/V vs. RHE

0.2 0.4 0.6 0.8 1.0 1.2

Cu

rren

t d

en

sit

y/m

A c

m-2

-4

-3

-2

-1

0

Potential/V vs. RHE

0.0 0.2 0.4 0.6 0.8 1.0 1.2Cu

rre

nt

de

nsit

y/ m

A c

m-2

-15

-10

-5

0

5

10

15

Initial

1000 cycles

3000 cycles

5000 cycles

10,000 cycles

Morphology and ORR activity of CNT/CNP catalyst

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 14: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

14

current density (A/cm2)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

cell

vo

lt (

V)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

HF

R (

oh

m c

m2)

0.0

0.1

0.2

0.3

0.4

0.5

0.6M-Nafion®-FA-TMG 80C

M-Nafion®-FA-TMG 60C

ATM-PP3 80C

ATM-PP3 60C

H2/O2 AMFC Performance

Membrane electrode assemblies for AMFC were prepared from LANL decal process using the AMFC materials

The MEA using M-Nafion®-FA-TMG showed superior performance to the MEA using ATM-PP 3

Highlight: Maximum power density reached to 577 mW/cm2 at 80 C under H2/O2 conditions

High AMFC performance using hydrocarbon AEM and resonance stabilized perfluorinated ionomer was demonstrated

Ionomer IEC (meq./g)

WU (wt.%)

a

(mS/cm)

HFR (ohm cm2) Maximum Power density (mW/cm2)

60 C 80 C 60 C 80 C

ATM-PP 3 1.7 100 120 0.215 0.174 206 335

M-Nafion®-FA- TMG 0.7 10 20 0.165 0.134 306 577

Materials for MEA fabrication

a measured with hydroxide form at 80 C

H2/O2 initial performance comparison between HC and PF ionomer AEM & hydrocarbon ionomer: ATM-PP 3

PF ionomer: M-Nafion®-FA-TMG

Membrane: BTMA functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst: Pt black (3 mg/cm2) for

anode and cathode; Ionomer for catalyst layer: M-Nafion-FA-TMG and ATM-PP 3

current density (A/cm2)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

po

we

r d

en

sit

y (

mW

/cm

2)

0

100

200

300

400

500

600

AMFC Performance & Degradation

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Page 15: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

15

60oC

current density (A/cm2)

0.0 0.2 0.4 0.6 0.8 1.0

cell

vo

lt (

V)

0.0

0.2

0.4

0.6

0.8

1.0

HF

R (

oh

m c

m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

H2/O

2

H2/Air, CO

2 390 ppm

80oC

current density (A/cm2)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

ce

ll v

olt

(V

)

0.0

0.2

0.4

0.6

0.8

1.0

HF

R (

oh

m c

m2)

0.0

0.1

0.2

0.3

0.4

0.5

0.6H

2/O

2

H2/Air, CO

2 10 ppm

H2/Air AMFC Performance

H2/CO2 free air AMFC performance showed excellent performance

Additional loss for H2/normal air (CO2 = 390 ppm) conditions was observed; The performance loss was significant at low current region, indicating some water management problems possibly due to the bicarbonate/carbonate issue at lower current density. Further study for the performance loss is required

Highlight: Maximum power density reached to 466 mW/cm2 at 80 C under H2/CO2 free Air conditions

H2/O2 vs. H2/CO2 free Air

Membrane: BTMA functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst: Pt black (3 mg/cm2) for anode and cathode; Ionomer for catalyst layer: M-Nafion®-FA-TMG

H2/O2 vs. H2/Air

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

AMFC Performance & Degradation

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16

X Data

0 2 4 6 8 10 12 14 16

cu

rre

nt

de

ns

ity (

A/c

m2)

0.0

0.2

0.4

0.6

0.8

Time (h)

0 2 4 6 8 10 12 14 16

HF

R (

oh

m c

m2)

0.0

0.1

0.2

0.3

0.4

at 0.6 V, 80oC

decay rate: -9.4 mA/cm2 h

decay rate: 2.7 mohm cm2/ h

Durability of BTMA-functionalized Poly(phenylene)s (in-situ)

The AMFC performance degradation depends on cell operating conditions; Large portion of current loss at low voltage conditions is due to water management issue which is recoverable loss.* However, HFR increase mostly reflects the AEM degradation

AEM degradation rate increased with decreasing cell voltage and increasing operating temperature

X Data

0 2 4 6 8 10 12 14 16

cu

rre

nt

de

ns

ity (

A/c

m2)

0.0

0.1

0.2

0.3

0.4

Time (h)

0 2 4 6 8 10 12 14 16

HF

R (

oh

m c

m2)

0.0

0.1

0.2

0.3

0.4

at 0.7 V, 80oC

decay rate: -2.5 mA/cm2 h

decay rate: 1.0 mohm cm2/ h

H2/O2, 80 C at 0.7 V

Membrane: BTMA functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst: Pt black (3 mg/cm2) for anode and cathode; Ionomer for catalyst layer: M-Nafion®-FA-

TMG; Life test conditions: constant voltage under full hydration

X Data

0 2 4 6 8 10 12 14 16

cu

rre

nt

de

ns

ity (

A/c

m2)

0.0

0.1

0.2

0.3

0.4

0.5

Time (h)

0 2 4 6 8 10 12 14 16

HF

R (

oh

m c

m2)

0.0

0.2

0.4

0.6

0.8

at 0.4 V, 95oC

decay rate: -19.0 mA/cm2 h

decay rate: 12.1 mohm cm2/ h

H2/Air, 95 C at 0.4 V H2/O2, 80 C at 0.6 V

*see supporting information

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

AMFC Performance & Degradation

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AMFC Degradation Summary

In general, the degradation rate of AMFC materials was faster under ex-situ conditions than under in-situ test; however other degradations such as membrane-electrode interface or water management issue played greater role in in-situ AMFC testing

Highlight: Materials developed from this project (appeared in yellow box) showed at least comparable durability to the state-of- the-art AMFC materials

Compo-nent

Type Degradation* (time, NaOH, Temp.)

Slide page

Polymer

Poly(arylene ether) Aryl ether linkage

Fast (g) (< 1 h, 0.5M, 80 C)

5

Poly(phenylene) Stable 5

Perfluorinated Stable 7

Amide linkage Slow (g) (72h, 0.5M, 80 C)

7

Cation

Tetramethyl guanidine aqueous soln.

Slow (g) (2 month, TMG 0.1 M, 25 C)

9

Benzyl tetra methylammonium

Slow (g) (< 100 h, 0.5 M, 80 C)

8

Sulfone penta methyl guanidinium

Fast (g) (< 1 h, 0.5 M, 80 C)

7

Benzyl penta methyl guanidinium

Moderate (g) (24 h 1M, 25 C)

10

Phenyl penta methyl guanidinium

Stable 10

Electro-catalyst

Platinum/carbon Stable 13

CNT/CNP Stable 13

Ex-situ testing in NaOH aqueous solution

Component Type Degradation (time, Temp.)

Slide page

Polymer

Poly(arylene ether) Moderate (c) (55h, 80 C)

6

Poly(phenylene) Stable 6

Cation

Benzyl tetramethyl ammonium (AEM)

moderate (g) (100h, 80 C)

16

Benzyl tetramethyl ammonium (ionomer)

Slow (g) (< 100h, 80 C)

12

Phenyl pentamethyl guanidinium (ionomer)

Slow (g) (72h, 90 C)

12

AEM-electrode interface

AEM with Mw < 100 K Unstable (c) 6

AEM with Mw > 100 K Stable 6

Electro-catalyst Platinum/carbon Stable 13

CNT/CNP Stable 13

Water management*

Hydrocarbon ionomer Fast (g) S

Perfluorinated ionomer Moderate (g)

In-situ AMFC testing

*g: gradual loss; c: catastrophic loss

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Relevance: Alkaline membrane fuel cells may enable non-precious metal catalysts and avoid or mitigate the shortcomings of traditional liquid AFCs

Approach: Develop highly stable and conductive anion exchange polymer electrolytes using resonance stabilized guanidinium cations and perfluorinated ionomer

Technical Accomplishments and Progress:

Demonstrated good H2/O2 and H2/air AMFC performance (> 450 and 550 mW/cm2, respectively) at 80 C

Established several synthetic pathways to prepare stable anion exchange polymer electrolytes and carbon based non-precious metal catalysts

Explored degradation phenomena for polymer backbones, cations and ionomers and ranked the stability both under ex-situ and in-situ conditions

Technology Transfer/Collaborations: Active partnership with Ovonic Fuel Cells and Cellera Inc.; Several patent applications were filed for technology transfer

Proposed Future Research: Catalyst-ionomer interaction and further improvement on stability, conductivity and mechanical properties of polymer electrolytes

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Project Summary

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19 2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

Technical Back-Up Slides

Page 20: Resonance-Stabilized Anion Exchange Polymer Electrolytes · Resonance-Stabilized Anion Exchange Polymer Electrolytes Yu Seung Kim (yskim@lanl.gov) Los Alamos National Laboratory Los

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Decoupling Degradation from in-situ AMFC testing AMFC Durability

2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review

0 5 10 15 20 25 30

cu

rre

nt

de

nsit

y (

A/c

m2)

0.0

0.1

0.2

0.3

0.4

Time (h)

0 5 10 15 20 25 30

HF

R (

oh

m c

m2)

0.0

0.1

0.2

0.3

0.4

1. Unrecoverable loss

2. Recoverable loss

3. Catastrophic failure

4. Unrecoverable loss(AEM related)

5. Recoverable loss(AEM related)

6. Catastrophic failure(AEM related)

1. Unrecoverable loss includes:

AEM degradation, ionomer degradation, catalyst degradation and interfacial degradation; AEM and ionomer cation degradation are the major contributors

2. Recoverable loss includes:

AEM dehydration and local flooding depending on operating conditions

3. Catastrophic failure is mostly due to:

AEM backbone failure (this failure accompanied by OCV decrease)

4. Unrecoverable loss (AEM related) includes:

AEM degradation and interfacial degradation: In all cases with few exception, AEM degradation

5. Recoverable loss (AEM related) is due to:

AEM dehydration

6. Catastrophic failure is mostly due to:

AEM backbone failure (this failure accompanied by OCV decrease)

Separated from current density and HFR behavior, the Ionomer degradation rate was measured from Tafel slope change

AMFC extended term test example General observation & in-situ methodology