Understanding and Optimizing the H2/Br2 R edox 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 2 nd MRES Northeastern, August 19, 2014
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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
-‐ 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
Current Density (mA/cm2)
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
Outline • Introduc.on
– Performance – Cost
• Bromide crossover – Efficiency – Degrada.on
• Flow baQery performance – Bromide and water return – Cycling behavior
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
Minimal effect on -‐ contact resistance -‐ Nafion conduc.vity
0 500 1000 1500 2000 25000
250
500
750
1000
1250
1500
Current Density (mA/cm2)
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)