New Membranes for Aqueous BatteriesMichael A. Hickner

Associate Professor, Corning Faculty FellowDepartment of Materials Science and EngineeringAssociate Director – Materials Research Institute

The Pennsylvania State Universityhickner@matse.psu.edu

Hickner Research Group @ Penn State

2Industry Sponsors

EERE Award # DE-EE0006958ARPA-E Award # DE-AR0000121

Membranes in energy applications

3Environ. Sci. Technol. Lett. 2014

ACS Appl. Mater. Interfaces 2013J. Am. Chem. Soc. 2013

Flow Batteries

Reverse Osmosis

Fuel Cells

SaltWater

ACS Macro Lett. 2016

Electrodialysis

Disabb-Miller, Hickner, et al., Macromolecules 2013.Moore, Saito, Hickner, J. Mater. Chem. 2010.

Macromolecules 2010.

Li, Hickner, et al., J. Am. Chem. Soc. 2013.Leng, C-Y Wang, Hickner, et al., J. Am. Chem. Soc. 2012.

Zha, Disabb-Miller, Tew, Hickner, J. Am. Chem. Soc. 2012.

New membranes through polymer synthesis

Wang, Hickner, Polym. Chem. 2014.Wang, Hickner, Soft Matter. 2016.

4

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

10-2

10-1

100

I(q

) (au

)

q(nm-1)

q

2q

3q4q

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.410-3

10-2

10-1

100

I(q) (

au)

q(nm-1)

q

2q3q

4qHickner, et al.Soft Matter. 2016.

SDAPP3, 1.8 meq g-1Nafion, 0.91 meq g-1

Kreuer, J. Membrane Sci. 2001.

--

-

-

-- -

- - - ---

-

Membrane structure and function

Fujimoto, et al. Macromolecules 2005.Hickner, et al. Polymer 2006. 6

Good capacity maintenance with small channels

Chen, Hickner, Agar, Kumbur, ACS Appl. Mater. & Int. 2013.

Increasing vanadium crossover causes large capacity fade

7

Low permeability channels

High permeability channels

Vanadium Redox Flow Battery Capacity Fade

H2 → 2 H+ + 2 e-

½ O2 + 2 e- + 2 H+ → H2OH2 + ½ O2 → H2O

Polymer electrolyte membrane fuel cellsAnion Exchange Membrane (AEM)Proton Exchange Membrane (PEM)

QA Radel®Nafion®

H2 + 2 OH- → 2 H2O + 2 e-

½ O2 + H2O + 2 e- → 2 OH-

H2 + ½ O2 → H2O

PEM fuel cells need new catalysts that are stable at pH ~ 0

AEM fuel cells need new membranes that are stable at pH ~ 9-14

8

Water battery – reversible fuel cell

9

Need a very low-cost system with no precious metals in both fuel cell and electrolyzer modes.

Can optimize the material for anion exchange or cation exchange

10

Chemical structures of polymer backbones and cations for anion exchange membranes

11

12

1. Bromination of benzylic methyl groups

2. Quaternizationwith different cationic moieties

Need to evaluate ionic group and backbone stability

Chen, D., M. A. Hickner, “Degradation of Imidazolium and Quaternary Ammonium Functionalized Poly(fluorenyl ether ketone sulfone)s for Anion Exchange Membranes,” ACS Appl. Mater. Int. 2012.

Need to evaluate ionic group and backbone stability

Lifetime of anion-conducting polymers

Leng, Chen, Mendoza, Tighe, Hickner, Wang, “Solid-State Water Electrolysis with an Alkaline Membrane,” J. Am. Chem. Soc. 2012.

QA-Radel

QA-Radel 1

QA-Radel 2

QA-Radel 3

QA-Radel

What caused the short lifetime of the ionomer?

Ionomer testing with Tokuyama membrane

14

965 970 975 980 985 990

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Abso

rban

ce (a

.u.)

Wavenumber (cm-1)

0 h 2 h 4 h 6 h 8 h 10 h 11 h 21 h

AS-4

960 965 970 975 980 985

0.00

0.02

0.04

Abso

rban

ce (a

.u.)

Wavenumber (cm-1)

0 h 2 h 4 h 6 h 8 h 10 h 11 h 21 h

Thermal degradation of cast ionomers at 135˚C (low humidity)

• Ex-situ FTIR analysis of thermally degraded ionomers.• 974-977 cm-1 peak corresponds to asymmetric C-N+ stretching of QA

groups.

QA-Radel

15

Expected QA-based AEM degradation pathways

16

Stability ranking of AEMs

Nuñez, S. A. & Hickner, M. A. “Quantitative 1H NMR Analysis of Chemical Stabilities in Anion-Exchange Membranes,” ACS Macro Lett. 2013, 2, 49–52.

17

Sterics play a role in stabilizing membranes

Zhuang, et al. Acc. Chem Res. 2012 DOI: 10.1021/ar200201x

O

CH3

CH3

CH3

O100-x x

14

N

O

CH3

CH3

CH3

O100-x x

4

N

O

CH3

CH3

CH3

O100-x x

8

N

Hickner, et al. J. Am. Chem. Soc. 2013 DOI: dx.doi.org/10.1021/ja403671u18

PPO-based AEMs

O

CH3

CH3

CH3

O100-x x

14

N

O

CH3

CH3

CH3

O100-x x

4

N

O

CH3

CH3

CH3

O100-x x

8

N

Short Medium Long

C6 Dx C10 Dx C16 Dx

Li, N., Y. Leng, M. A. Hickner, C.-Y. Wang, “Highly Stable, Anion Conductive Comb-shaped Copolymers for Alkaline Fuel Cells,” J. Am. Chem. Soc. 2013, 135 (27), 10124–10133.

C denotes side chain length.D denotes functionalization, e.g. 40 = 0.4 cationic groups

per repeat unit.

19

Phase separation observed with longer alkyl side chains

d-spacingC16D40 3.3 nmC10D40 2.3 nm C6D40 1.7 nm

Roughly correspond to extended side chain lengths.

No separation observed for benzyltrimethyl ammonium (BTMA) cations – as seen in other aromatic AEMs.

20

d

Good conductivity and reasonable stability with alkyl side chains

21

Fuel cell power density and stability are reasonable but more development is needed

Still work to be done to optimize the fuel cell MEA construction and operating conditions

50 °C, air, Pt catalysts

100 mA/cm2 constant current

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20 30 40 50 60 70 8050

100

150

200

250

300

350

T (ºC)

T20NC6NC5N, IEC 2.52 T30NC6NC6, IEC 2.47 S60NC6, IEC 2.60

Wat

er u

ptak

e (w

t %)

(a)

20 30 40 50 60 70 80-40

0

40

80

120

160

200

240

T (oC)

T20NC6NC5N, IEC 2.52 D30NC6NC6, IEC 2.47 S60NC6, IEC 2.60

Swel

ling

degr

ee(%

)

(b)

Double and triple cation side chains constrain swelling with temperature increases

CH3

CH3

O

CH3

CH2

O

NBr

NBr

3m

X100-X

DxNC6NC6

CH3

CH3

O

CH3

CH2

O

NBr

4

SxNC6

X100-X

CH3

CH3

O

CH3

CH2

O100-X

NBr

NBr

n2

N Br

X

TxNC6NC5N

23

1.6 2.0 2.4 2.8 3.2 3.60

20

40

60

80

100

DF30

DF25

DF20

DF15

DF60

DF40DF20

DF30DF35

DF40

σ O

H - (m

S/cm

)

IEC (mmol/g)

TxNC6NC5N DxNC6NC6 SxNC6

OH- Conductivity with Increasing Cation NumberOverswelling decreases conductivity due to ion dilution.

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Microscopy Confirms Structured AEMs With Addition of Side Chains

BTMA40 S60NC6

D30 T20

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Microscopy Confirms Structured AEMs With Addition of Side Chains

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0 200 400 600 800 1000 1200 1400 16000.0

0.2

0.4

0.6

0.8

1.0

1.2

T20NC6NC5N D30NC6NC6 S60XN6

Current density (mA/cm2)

Cell

volta

ge (V

)

0

50

100

150

200

250

300

350

400

AEMFC @ 60oC, 0.1 MPa

Pow

er d

ensi

ty ( m

W/c

m2 )

H2/O2 Fuel Cell Performance

Many demonstrations of fuel cell performance with power densities between 150-500 mW/cm2.

There appears to be an optimization barrier to obtain higher power densities.

Triple cation side chain AEMs show reasonable fuel cell performance

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NegativePositiveV4+

V5+ V2+

V3+

H+

e2HVOOHVO 222 ++↔+ +++ ++ ↔+ 2VeV3

• Independently Tunable Power and Energy

• No Solid Reaction Indefinite Lifetime

• No Contamination due to Single Element (V)

• Fast Response• Low Energy density

Load

Stationary Application for Renewable

Smart Grid (Wind, Sun)

VRFB stores energy by employing vanadium redox reactions at two opposite electrodes that are separated by a proton ion exchange membrane.

281.7 M V in ~3.3 M H2SO4

Vanadium Redox Flow Battery (VRFB) require permselective or conductive-selective

membranes

http://global-sei.com/news/press/12/prs069_s.html

Sumitomo Electric – 200 kW CSP array and 1 MW * 5 h flow battery

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0 20 40 60 80 100 1200.00

0.01

0.02

0.03

0.04

0.05

0.06

Pretreated N117 DI water soaked N117 S-Radel

Conc

entra

tion

of V

O2+ [M

]

Time(hrs)

Lower V-ion permeability increases the efficiency of flow batteries

Low permeability of S-Radel

Kim, S., J. Yan, B. Schwenzer, J. Zhang, L. Li, J. Liu, Z. Yang, M. A. Hickner, Electrochem. Comm. 2010.and J. Appl. Electrochem. 2011.

S-Radel – small pores

Nafion – large pores

CF2 CF2 CF CF2

OCF2 CF

CF3

O(CF2)2 SO3H

x y n

S O

O

O n

O

HO3S R

R =

H or -SO3H

SDAPP3, 1.8 meq g-1Nafion, 0.91 meq g-1

Kreuer, J. Membrane Sci. 2001.

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-

-

-- -

- - - ---

-

Ionic pores in sulfonated polymers

Fujimoto, et al. Macromolecules 2005.Hickner, et al. Polymer 2006. 31

Small single-cycle gains add up in long-term testing

0 5 10 15 20 25 30 35 40 450.0

0.5

1.0

1.5

2.0

2.5

3.0

Capa

city

(Ah)

Cycles

S-Radel N117

• Due to higher ion selectivity of S-Radel, capacity loss per cycle of S-Radel was 6.4 mAhcycle-1, half of that of Nafion (13 mAh cycle-1).

• Lower capacity loss translates to ½ the maintenance interval for devices with S-Radelmembranes.

25 50 75 10070

75

80

85

90

95

100

Effic

ienc

y (%

)

Discharging current density (mA/cm2)

N117 Coulombic N117 Energy SRadel Coulombic SRadel Energy

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50 cycles

activearea

25 cycles

Degradation of aromatic PEMs in VRFBsActive area cracking and failure after extended cycling.

D. Chen, M. A. Hickner, Phys. Chem. Chem. Phys. 2013. 33

Improved cycling performance with fluorinated aromatic polymers

Chen, Kim, Li, Yang, Hickner, “Stable Fluorinated Sulfonated Poly(arylene ether) Membranes for Vanadium Redox Flow Batteries,” RSC Advances 2012, 2, 8087-8094.

Sulfonated fluorinated poly(arylene ether)(SFPAE)

O O

F

F F

F F

F F

F HO3S R

n

R =

H or -SO3H

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Low vanadium cation crossover due to Donnan exclusion

Need membranes with permselective properties for high H+

or SO42- conductivity and high Vn+ exclusion

35

Route to scale-up with commercial starting materials

36

Can widely vary the conductivity and permeability.

Transport selectivity = σ/P

Give us a handle to explore performance tradeoffs.

110016.921.6

Large-scale AEM synthesis

37

Need kg-scale AEM synthesis with m2 membrane capability

Good capacity maintenance with low IEC AEMs

Low IEC membranes are desirable for long cycle life with no electrolyte maintenance.

Chen, Hickner, Agar, Kumbur, ACS Appl. Mater. & Int. 2013.

increasing crossover

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Must balance conductivity and crossoverHigher power densities and low capacity fade with optimized

permselective membrane

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Optimized trade-off in conductivity and crossover

-110016.921.6

Transport selectivityσ/P

Conclusions

• Membranes offer a gateway to new energy storage and conversion devices with low cost – can see real performance improvements with optimized materials in targeted applications.

• There are lots of parameters in ionic polymers to influence ion and water transport.

block copolymers, new cationic groups, backbone polarity, crosslinking…

• There is more work to do in AEM technology especially in regards to cost and device performance.

• We need tools for targeted design of new membranes for unique flow battery chemistries.

• Teaming with polymer specialists can pay dividends!

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