understanding and optimizing the h2/br2 r edox flow...

Understanding and Optimizing the H2/Br2 Redox Flow Battery for Grid-Scale Energy Sto

rage

Michael Tucker, Kyu Taek Cho, Vincent Battaglia, Venkat Sr

inivsan, and Adam Z. Weber

Environmental Energy Technologies Division Lawrence Berkeley National Laboratory

2nd MRES Northeastern, August 19, 2014

Outline •  Introduc.on

–  Performance –  Cost

•  Bromide crossover –  Efficiency –  Degrada.on

•  Flow ba?ery performance –  Bromide and water return –  Cycling behavior

•  Summary

Br2-‐H2 Flow Ba?ery Overview

$/kgVanadium (V2O5) 18Hydrogen 4-‐10Bromine 1

Porous Carbon Media (GDL) Catalyst Layer (CL)

1mm

High-‐power, low-‐cost system e-‐

H2 HBr/Br2

H2 à 2H+ + 2e (0.00V) Br2 + 2H+ + 2e à 2HBr (+ 1.09V)

Nega.ve Posi.ve

Aqueous Gas

Membrane

Porous Carbon Media Catalyst Layer Porous Carbon Media

H+

Br

-‐Porous electrode -‐Flow-‐Field Geometry -‐Cell Compression -‐Opera.ng pressure

Ecell = E0 -‐ηact -‐ηohm -‐ηmass

-‐Electrode material -‐Electrode ac.va.on -‐Electrode op.miza.on

-‐Membrane thickness -‐Electrolyte composi.on

-‐Electrolyte concentra.on -‐Opera.ng temperature and pressure

Cell Performance Cell Performance

Performance •  Greatly improved performance with op.miza.on of cell components

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.00.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

Cel

l vol

tage

(V)

Current Density (A/cm2)

Ambient temperature and pressure 0.9 M Br2 / 1 M HBr

Voltaic efficiency PD (W/cm2)

80 % 0.99 90 % 0.60

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0

0.2

0.4

0.6

0.8

1.0

1.2

GEN.1: Conventional cell (flow-by) GEN.2: Multi-layered electrode (flow-thru) GEN.3: Activated multi-layered electrode (flow-thru) GEN.4: With thinner (15µm) membrane

(flow-thru+activated multi-layered electrode)

Cel

l vol

tage

(V)


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Pow

er D

ensi

ty (W

/cm

2 )

K.Cho et al, Energy Technology, 1 (2013) 596 – 608

Performance

•  Trade-‐off between efficiency and rate capability as a func.on of membrane thickness

100 10000.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

N117

NR211

NR212

Energy

Voltage

Effi

cien

cy

Current (mA/cm2)

Coulombic

2.8MPH2 = 30psi

0 20 40 60 80 100 120 140 160 180 2000

5

10

15

20

25

30

Membrane Thickness (µm)

Sel

f-Dis

char

ge C

urre

nt (m

A/c

m2 )

2.8MPH2 = 30psi

Performance

Electrodes -‐ Br-‐ adsorp.on on Pt (-‐) -‐ Op.miza.on of (-‐) and (+) electrodes

100 10000.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Energy

Voltage

Effi

cien

cy

Current Density (mA/cm2)

Coulombic

Baseline

Improved

Membrane -‐ Pretreatment -‐ Crossover -‐ Type

Cycling -‐ closed hydrogen

Total U.liza.on

0 1 2 3 4 50.20

0.40

0.60

0.80

1.00

Br2

HBr

0.9 M Br2/ 1 M HBr at 300ml/minConst.Current: 3.5A (80% efficiency)

Cell: SPFF|25BC||Pt/C|N211||GFD-3|FLTHRUC

ell v

olta

ge (V

)

Discharge duration (hrs)

0.0

0.4

0.8

1.2

1.6

2.0

2.4

Con

cent

ratio

n (B

r 2 and

HB

r), m

ol/li

ter

4.597 hrs (Br2: 0.058 M HBr: 2.32 M)

Br2: 0.9 M HBr: 1.0 M

Bromine uBlizaBon: ~93%

Cost Model

Note: The cost model results shown here do not include components that may eventually be required to handle species crossover.

1200

1000

800

600

400

200

0

Bat

tery

sys

tem

cap

ital c

ost (

$/kW

h)

86420

Discharge time (hours)

Gen1 (ASR 0.50 Ohm-cm2) Gen2 (ASR 0.40 Ohm-cm2) Gen3 (ASR 0.32 Ohm-cm2) Gen4 (ASR 0.23 Ohm-cm2)

BOP costs: 37%

Stack costs: 37%

Assembly: 27%

Battery system capital cost = 737 $/kWh

Membrane: 38%

H2 electrode catal.: 3%

Electrodes (no catal): 12% GDL/Flow field: 5%

Bipolar plates: 33%

Gasket & sealing: 5%Endplates & tie rods: 3%

Stack cost = 270 $/kWh

Br liq. pump: 18%

Br tank: 14%

H2 tank: 16%Active matls.: 19%

Cooling: 19%

Other: 15%

BOP cost = 270 $/kWh

Cost Model •  Full-cell area-specific resistance (ASR) as a functions of HBr

concentration at 0% SOC and membrane thickness –  Ohmic losses are quite important to overall cost –  Do not want to operate at high HBr concentrations

•  Lower conductivity due to membrane dehydration •  Higher crossover

1000

800

600

400

200

0

Batte

ry s

yste

m c

apita

l cos

t ($/

kWh)

86420

HBr concentration at 0% SOC (M)

4h discharge

1h discharge

Cost minimum: 3.1 M HBr

Cost minimum: 4.8 M HBr

00.5

11.5

x 10-40

24

68

0

500

1000

1500

2000

Membrane Thickness (cm)HBr conc at 0% SOC (M)

Batte

ry s

yste

m c

apita

l cos

t ($/

kWh)

K.Cho et al, Energy Technology, 1 (2013) 596 – 608

•  Membrane characteriza.on

–  Conduc.vity decreases at higher HBr concentra.on –  Membrane dehydra.on

‘H’-‐glass cell

Membrane

Reference electrode

Conduc.vity

Ohmic Losses

Ahmet Kusoglu, Kyu Taek Cho, Rafael A. Prato, and Adam Z. Weber, Solid State Ionics, 252, 68-‐74 (2013).

Morphology



•  Bromide crossover –  Efficiency –  DegradaBon

•  Flow ba?ery performance –  Bromide and water return –  Cycling behavior

•  Summary

Membrane Transport Proper.es Charge Discharge

-‐ Ionic conduc.vity (H+) -‐ Electronic resistance -‐ Water permeability -‐ Br permeability -‐ Electro-‐osmo.c drag coeff. -‐ H2 permeability -‐ Br uptake

Br2-‐HBr (+)

H2 (-‐)

H+

H2O

Br-‐ Br3-‐ Br2

Br2-‐HBr (+)

H2 (-‐)

250-‐500mA/cm2

Crossover at OCV

0 20 40 60 80 1000

20

40

60

80

100

120

State of Charge (%)

Wat

er o

r Bro

min

e C

ross

over

Rat

e

(mg/

h/cm

2 )

0

20

40

60

H2O

Br

Br/H

2O C

ross

over

Rat

io (m

mol

/mol

)

Br/H2O

At OCV

Crossover Under Opera.on

•  Significant Br-‐ flux during charge •  Propor.onal to HBr concentra.on •  Correlated to water crossover

–  Should be returned to other electrode tank

15

0

10

20

30

40

50

60

70

5M HBr3M HBr1M HBr

Discharge

Charge

Discharge

Charge

Discharge

Charge

Cros

sove

r rat

e of

Br- (m

g/hr

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

5M HBr3M HBr1M HBr

Cro

ssov

er ra

te o

f H2O

dra

gged

by

H+

(mol

/mol

)

KT Cho, MC Tucker, et al, ChemPlusChem, accepted

NR212

During Charge

Br-‐ Crossover H2O Crossover

Collected during charge During discharge

IniBal level of water

Br- Crossover Causes Self-‐Discharge

𝐻↓2 (𝑔)⇄2𝐻↑+ (𝑎𝑞)+2𝑒↑−  𝐸↑0 =0.00 𝑉

𝐵𝑟↓3↑− (𝑎𝑞)+2𝑒↑− →3𝐵𝑟↑− (𝑎𝑞) 𝐸↑0 =1.06 𝑉

𝐵𝑟↓2 (𝑎𝑞)+2𝑒↑−  ⇄ 2𝐵𝑟↑− (𝑎𝑞) 𝐸↑0 =1.09𝑉

Crossover Br-‐ species are reduced at (-) electrode


Self-‐Discharge Limits Efficiency

H2 pressure effect

Self-‐discharge is propor.onal to Br concentra.on -‐ 10-‐25mA/cm2 equivalent current for useful concentra.ons

Not affected by H2 concentra.on

Limits overall Energy Efficiency at low current

Self-‐discharge appears as Coulombic inefficiency

à Desire membrane with high proton conduc.vity and low Br-‐crossover


Thickness (mm)

Self-‐discharge rate (mA/cm2)

N117 180 3 NR212 50 13 NR211 25 35

Effect of Membrane Pretreatment

100 1000

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Water 70°CBoiled

Energy

PH2 = 30psi

Voltage

Effi

cien

cy


Coulombic

2.8M

As-received

Pretreat Self-‐discharge mA/cm2

As-‐received 1.7 70°C water 3.4 Boiled 13.1

Thermal treatment: -‐ improves conduc.vity -‐ increases Br-‐crossover and self-‐discharge Good tradeoff with 70°C water soak

0 500 1000 15000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Current Density (mA/cm2)V

olta

ge (V

)

70°C Water

As-Received

BoiledNR212

(a)

0.0 0.1 0.2 0.30.0

0.1

ReZ(Ohm-cm2)

-ImZ

(Ohm

-cm

2 ) (b)

70°C Water

BoiledAs-Received

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6


Cel

l Vol

tage

(V)

Cell Polariza.on -‐ Limi.ng Current

0 1000 1500 500

Cell Poten.al

-‐ Symmetric charge/discharge -‐ ohmic-‐dominated

-‐ Sharp limi.ng current on discharge

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6


Cel

l Vol

tage

(V)

-0.4 0.0 0.4 0.8

H2 electrode vs. DHE (V)

V-‐steps 1mV/s

(-‐) Electrode

-‐ Br-‐/Br2 crossover to Pt H2 (-‐) electrode -‐ Br-‐ adsorbs on Pt at > 0.1V vs. DHE

à blocks H2 reac.on -‐ High Br-‐ coverage at high Pt poten.als

à No current -‐ Br-‐ reversible desorp.on

I-‐steps

(-‐) Pt Surface Coverage: H2 vs. Br-‐

0 100 200 300 4000.0

0.2

0.4

0.6

0.8

1.0

1.2

(-) vs DHE

H2 flowstopped 5sec

OCV

Charge200mA/cm2

Discharge200mA/cm2

OCV

Time (sec)

Vol

tage

(V)

OCV

CELL V

Increase Pt poten.al by H2 starva.on OCV and performance recover aner charge à complete Br-‐ stripping

Hydrogen Interrup.on

0 100 200 300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

1.2

D D D

OCVOCVOCV

(-) vs. DHE

Br2/HBr added to H2 bubbler

OCV

C

D

OCV

Time (sec)

Vol

tage

(V)

OCVCELL V

Increase Pt poten.al by Br-‐ poisoning OCV recovers aner charge Performance does not à irreversible Br-‐ adsorp.on

Br-‐dosing

Br Crossover à (-) Pt Deac.va.on/Dissolu.on

0 5 10 15 20 25 30 35 40 450.0

0.2

0.4

0.6

0.8

1.0

1.2

2mA/cm2

Time (h)

Vol

tage

(V)

0.2mA/cm2

No H2 flow, small cathodic current Hydrogen interrup.on -‐ no problem if Br flow off -‐ kills cell if Br flow on Crossover Br a?acks Pt -‐ increases Pt poten.al above dissolu.on threshold Protect with cathodic current -‐ generate H2 at Pt sites -‐ maintain low anode poten.al à prevent Pt dissolu.on

Effec.ve if: Cathodic current > Br crossover current

0 500 1000 15000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

After 0.2mA/cm2 hold


Vol

tage

(V)

After 2mA/cm2 hold

Fresh

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

FreshMEA

SPL ESPL DSPL CSPL B

Pt in fresh MEA Sample A: after 230 cycles Sample B: after 100 cycles Sample C: after 50-60 cycles Sample D: after 40-50 cycles Sample E: after 40-50 cycels

SPL A

Am

ount

of P

latin

um (m

g)

Pt dissolved in each electrolyte



•  Bromide crossover –  Efficiency –  Degrada.on

•  Flow baQery performance –  Bromide and water return –  Cycling behavior

•  Summary

Bromine Reten.on

0 5 10 15 20 25 30 35 400.00

0.25

0.50

0.75

1.00Condenser/pump

Batch collection - no condenser

Nor

mal

ized

Dis

char

ge C

apac

ity (m

Ah)

Cycle Number

Condenser/drain

Condenser/Drain

-‐ Possible to retain ~all Br

Condenser/Pump

Closed-‐Loop Experimental Setup

gas

Liq 1L

C A

Peristal.c Pump

H2 gas reservoir 5L

200 sccm

Diaphragm pump

130 mL/min

H2

5psi H2 Inlet regulator

10psi H2

Overpressure relief

Syringe pump

Match X-‐over

Liquid Recapture (op.onal)

Inlet valve

Cell: Fuel Cell Technologies housing Treadstone coated-‐steel flow fields

-‐ Serpen.ne anode -‐ Flow-‐through cathode

Hydrogen RecirculaBon

Cathode CirculaBon

Cycling with Liquid Return and Closed H2 Storage

0 25 50 75 100 1250

20

40

60

80

100

Cycle Number

Dis

char

ge C

apac

ity (A

h/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.5-1.2V400mA/cm2

Energy Efficiency

Voltage Efficiency

Effi

cien

cy

Capacity

Coulombic Efficiency

Hydrogen tank at ±5psi

Closed Bromine and Hydrogen loops Stable capacity -‐ Minimal loss of bromine High efficiency >75% energy efficiency at 400mA/cm2

No degrada.on of cell components

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.350.00

0.05

Cycle 122

ReZ(Ohm-cm2)

-ImZ

(Ohm

-cm

2)

Fresh

Selected cell materials and configura.on à High power density 1.4W/cm2 à Possible high energy efficiency

Limi.ng current behavior due to (-) polariza.on (flooding, H2 consump.on, Br crossover) à Alleviate with appropriate H2 pressure, (-) catalyst layer, compression Membrane allows water and Br- crossover à Mechanical return of crossover liquid enables stable cycling Br- crossover limits system efficiency via self-‐discharge à Appropriate pretreatment curtails crossover; >75% efficiency at 400mA/cm2

à Minimize impact on catalyst dissolu.on by cathodic protec.on

Very sensi.ve to: -‐ (-) Catalyst layer -‐ H2 pressure -‐ Membrane proper.es

Moderately or not sensi.ve to: -‐ (-) GDL type -‐ (+) catalyst surface area -‐ Compression

à Suggests (-) catalyst layer and membrane transport proper.es are most fruitul areas for further work

Summary

Tradeoff between coloumbic and voltaic efficiencies, in.mately related to the membrane

Acknowledgements •  Membrane characteriza.on

–  Rafael A. Prato (UC Santa Barbara), Ahmet Kusoglu (LBNL) •  Durability

–  Markus Ding, Karen Sugano •  Kine.c Measurements

–  Paul Ridgway (LBNL) •  Cost Model

–  Paul Albertus (Bosch) •  Funding

–  US DOE ARPA-‐E •  Robert Bosch Corp. •  TVN Systems K.T. Cho et al., J. Electrochem. Soc. 159 (2012) A1806

A. Kusoglu et al., Solid State Ionics, 252, 68-74 (2013)

K.T. Cho et al., Chempluschem, doi: 10.1002/cplu.201402043

K.T. Cho et al., Energy Technology 1 (2013) 557-557

M.C. Tucker, et al., J. Appl. Electrochem., under review

Understanding and Optimizing the H2/Br2 Redox Flow Battery for Grid-Scale Energy Sto

rage

Michael Tucker, Kyu Taek Cho, Vincent Battaglia, Venkat Sr

inivsan, and Adam Z. Weber

Environmental Energy Technologies Division Lawrence Berkeley National Laboratory

2nd MRES Northeastern, August 19, 2014

Back-‐up Slides

0 500 1000 1500 20000.0

0.2

0.4

0.6

0.8

1.0

1.2

3020105


Vol

tage

(V)

PH2 = 0psi

Hydrogen Pressure

With H2 Backpressure:

-‐ OCV goes up – H2 Nernst effect

-‐ Minimal change in slope (ASR)

-‐ Large increase in limi.ng current

Flow-‐through (+) Liquid

Flow-‐By (-‐)

H2 Gas

0 psig

30 psig

0-‐30 psig

(-‐)Electrode polariza.on affected by: -‐ (+) electrode pressure -‐ Hydrogen pressure (concentra.on) -‐ Electrode architecture

Typical: 200sccm H2 100mL/min Br2/HBr 0.9M:1M

0200400600800

Pow

er D

ensi

ty

(mW

/cm

2 )

PH2 = 30psiPH2 = 0psi

0 5 10 15 20 25 300.0

0.4

0.8

1.2

1.6

Lim

iting

Cur

rent

(A/c

m2 )

Hydrogen Pressure (psig)

(c)

0 500 1000 1500 2000 2500 30000.0

0.2

0.4

0.6

0.8

1.0

1.2


Vol

tage

(V)

BareCarbonBlack(+)

0 500 1000 1500 2000 25000

250

500

750

1000

1250

1500


Pow

er D

ensi

ty (m

W/c

m2 )

BareCarbonBlack (+)

0.0 0.1 0.2 0.30.00

0.05

ReZ(Ohm-cm2)

-ImZ(Ohm-cm2 )

Bare

Carbon(b)

0 500 1000 1500 2000 2500 30000.0

0.2

0.4

0.6

0.8

1.0

1.2


Vol

tage

(V)

BareCarbonBlack(+)

Pt/C(-)

0.0 0.1 0.2 0.30.00

0.05

ReZ(Ohm-cm2)

-ImZ(Ohm-cm2 )

Bare

CarbonPt/C(b)

Minimal effect on -‐ contact resistance -‐ Nafion conduc.vity

0 500 1000 1500 2000 25000

250

500

750

1000

1250

1500


Pow

er D

ensi

ty (m

W/c

m2 )

BareCarbonBlack (+)

Pt/C(-)

Catalyst Layers Bonded to Membrane (+) (-‐)

High S.A. carbon (+) does not help either ASR or limi.ng current -‐ (+) does not limit performance for bare membrane

Pt/C improves (-‐) polariza.on and ASR -‐ Peak power 1.27 W/cm2 (1.4 W/cm2 with 30psi backpressure)

-‐ no pooling between membrane and Pt/C -‐ ejects water be?er -‐ ion transfer at CL/Membrane improves

Effect of Compression and (+) Thickness

ASR improves with compression <77% needed for good contact resistance Pressure drop increases with compression -‐ mi.gated by more layers (or flow field design)

-‐ very high P for 66% -‐ low limi.ng current

(3) 83%

(4) 66%

0.0 0.5 1.0 1.50.0

0.2

0.4

0.6

0.8

1.0

1.2

(6) 77%(4) 79%(5) 76%(4) 66%

(3) 74%(3) 83%


Vol

tage

(V)

Long-‐Term Cycling Single-‐Pass H2

Closed-‐Loop H2 (Br accumulates)

KT Cho et al, ChemPlusChem, accepted

Stable cycling achieved -‐ H2 and Br2 retained -‐ Cell components durable

>70% efficiency at 350mA/cm2

350mA/cm2

0.5-‐1.2V

33

0 10 20 30 40 50 60 70 80 900

20

40

60

80

100

120

Cycle Number

Dis

char

ge C

apac

ity (A

h/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

92%

Energy Efficiency

Voltage Efficiency

Effi

cien

cy

Capacity

Coulombic Efficiency

100% *

* pump dead volume corrected

Thickness (µm)

Water Flux (mg/h/cm2)

Electro-‐osmo.c Drag Coefficient H2O/H+ (mol/

mol) Br Flux (mg/

h/cm2)

Selec.vity Br/H+

(mmol/mol) Br/H2O

(mmol/mol)

Self-‐Discharge from Coulombic Inefficiency (mA/

cm2)

Conduc.vity from AC impedance (S/

cm) NR212 Boiled 50 1040 3.1 228 153 49 13.1 0.08 NR212 70°C 50 790 2.4 41 28 12 3.4 0.07 NR212 AR 50 428 1.3 12 8 6 0.8 0.05

Aquivion E87-‐05S AR 50 469 1.4 16 11 8 1.0 0.07 Aquivion E98-‐05 AR 50 428 1.3 11 7 6 1.2 0.05 Gore 60111PC AR 60 469 1.4 12 8 6 0.9 0.04 3M 825EW AR 70 478 1.4 14 9 7 0.7 0.08

understanding and optimizing the h2/br2 r edox flow...

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