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Understanding the stability of positive electrode materials for aqueous organic
redox flow batteries
Sri Narayan
Bo Yang, Advaith Murali, Vinayak Krishnamurthi and G.K. Surya Prakash
University of Southern California, Los Angeles, CA
Presentation ID# 405
Session Topic : Flow Batteries
DoE Office of Electricity
Peer Review Meeting
October 27, 2021
1
Goals and Objectives
Overall Goal
Advance the understanding of an All-Organic Water-based RFBs for cost-effective large-scale energy storage.
Specific Objectives
• Understand the mechanisms of degradation to formulate design rules for new molecules
• Design and demonstrate inexpensive positive side organic molecules that can be cycled repeatedly without degradation
2
Advances Made at USC in RFBs
• First ever aqueous all-organic redox flow batteries based on quinone derivatives (BQDS/AQDS) in acidic media.
• Mitigated crossover by molecular design and symmetrical cycling.
• Demonstrated cycling of Michael-Reaction resistant positive side materials (DHDMBS)
• Scale up and demonstration (ITN) of 1kW/2KWh all-organic redox flow batteries (DHDMBS/AQDS) 4000 Ah/ 4.5 h per cycle with <0.01% loss/hour.
• Developed Iron sulfate/AQDS system for stable cycling over 1000 cycles with < 8 x10-6
%/hour. 3
Capacity Degradation Modes and Rates
4
(5x 10-4 %/ hour)
• For realizing LCOS of < 5 cents/kWh degradation rates must be < 5x10-4
%/hour (<500 ppm %/hour)
Michael Reaction (1,4-addition) with a nucleophile such as water, hydroxide ion or phenoxide ion. • Loss of capacity• Decrease of cell voltage
Desulfonation or loss of the sulfonic acid group• Loss of solubility • Decrease of cell voltage
• Capacity loss in water-based organic systems arises from two major processes: 1. Chemical transformations
2. Molecular crossover
Michael Reaction or 1,4-Addition
• Occurs more readily on electron-deficient systems
5
In Acid
In Alkali
Desulfonation Processes (alkaline medium)
7
• Oxidative Hydroxy-desulfonation
• Nucleophilic (SNAR) Hydroxy-desulfonation
Technical Approach
• To reduce the propensity for Desulfonation and Michael Reactions
- Examine the effect of substitution by alkyl and phenyl groups on benzoquinone rings
- Examine these reactivities in bi-functional molecules
• Adding functional groups to increase solubility without increasing reactivity.
• Developing procedures for in-house synthesis of compounds
• Follow the stability changes by NMR and GC-MS to determine effects of long-term cycling
• Electrochemical kinetics testing using RDE and CV on glassy carbon/graphite
• Establishing solubility in charged and discharged state
• Establish decay rates by extended cycling in symmetric cell configuration in flow cells (25 cm2)
8
Tasks to Address Challenges
• Task 1. Synthesis, purification and scale-up of materials.
• Task 2. Electrochemical characterization of charge/discharge reversibility and electrode potential.
• Task 3. Characterization of solubility and diffusion coefficient
• Task 4. Crossover rate studies
• Task 5. Passive and active durability studies using flow cell and electrolysis
• Task 6. Reporting, Reviews and Publication
9
Accomplishments in the past year
• Several promising benzoquinone derivatives have been synthesized and tested in acid and alkaline media.
• Preliminary results show these molecules possess distinct reactivity and stability based on the substituent groups.
• Verified that anthraquinone-based molecules can be stabilized to make positive side materials and also allow for bifunctional activity to achieve high cell voltage.
• Verified the long-term cycling behavior of stabilized redox materials.
10
Three Classes of Benzoquinone-derivedPositive Side Materials
11
Alkyl-substituted
Aryl-substituted Anthraquinone–derived
Studies on 6-methyl hydroquinone-3-sulfonic acid (MMS)
12
MMS
Synthesis
• Cyclic voltammogramssuggest excellent reversibility.
• Slow chemical transformations are not captured in a CV.
Cycling studies on MMS
13
0
1
2
3
4
5
0 50 100 150 200 250
Cap
acit
y , A
h
Cycle #
Cycling of MMS/ AQDS cell in Acid Medium100 mA/cm2, 25 cm2 , Graphite Felts
Charge
Discharge
CV at 50 mV/s,Graphite Electrodein 1 M Sulfuric Acid
Starting Material
After 516 cycles
MMS-1 MMS-2
After 516 cycles: Significant Loss of the Aromatic Protons and appearance of multiple aliphatic peaks
NMR Analysis-Starting Material
Polymerization of MMS
• Shown: dimerization
• Process can continue (chain propagation) to form redox active oligomers
14
CV Characterization of O3MMS, O4MMS, O3MDS
15
-4.00E-05
-3.00E-05
-2.00E-05
-1.00E-05
0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.00E-05
6.00E-05
-1 -0.5 0 0.5 1
Cu
rren
t (A
)
Potential (V vs MSE)
O3MMS, 1M H2SO4, GC, 50mV/second
-2.00E-05
-1.50E-05
-1.00E-05
-5.00E-06
0.00E+00
5.00E-06
1.00E-05
1.50E-05
2.00E-05
2.50E-05
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Cu
rren
t (A
)
Potential (V vs MSE)
O3MDS, 1M H2SO4, GC, 50mV/second
-3.00E-05
-2.00E-05
-1.00E-05
0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
-1 -0.5 0 0.5 1Cu
rren
t (A
)
Potential (V vs MSE)
O4MMS, 1M H2SO4, GC, 50mV/second
O3MMS
O3MDS
O4MMS
Tertiary-Butyl Substituted Orthobenzoquinonemonosulfonic acid (O4TBMS)
16
00.5
11.5
22.5
33.5
44.5
0 50 100 150 200
Cap
acit
y (A
h)
cycle number
Cha cap
Discha Cap
-8.00E-05
-6.00E-05
-4.00E-05
-2.00E-05
0.00E+00
2.00E-05
4.00E-05
6.00E-05
8.00E-05
1.00E-04
1.20E-04
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Cu
rren
t (A
)
Potential (V vs MSE)
O4TBMS, 1M H2SO4, GC, 50mV/second
Synthesis1M O4TBMS/ 1M AQDS cell cycled at 100 mA/cm2 in sulfuric acid
Potential shift to positive values upon sulfonation
NMR Analysis confirms fast single step hydroxylation
Aryl-Substituted benzoquinonesPHQS, PHQDS, Aryl sulfones
17
Aryl sulfones
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300
Cap
acit
y (A
h)
cycle number
Positive 100mL 1M PHQS, 1M H2SO4, Negative 100mL 1M AQDS, 1M H2SO4, E750, felt, centrifugal pump, 100mA/cm2
charge cap
discha cap
OH
OH
SO3H
-4.00E-05
-2.00E-05
0.00E+00
2.00E-05
4.00E-05
6.00E-05
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Cu
rre
nt
(A)
Potential (V vs MSE)
PHQS, 1M H2SO4, GC, 50mV/second
-4.00E-05
-3.00E-05
-2.00E-05
-1.00E-05
0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.00E-05
6.00E-05
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1Cu
rren
t (A
)
Potential (V vs MSE)
PHQDS, 1M H2SO4, GC, 50mV/second
PHQS
PHQDSCycling of PHQS /AQDS cell in 1M sulfuric acid at 100 mA/cm2
OH
OH
OH
SO3H
Bifunctional Anthraquinone –Derived Molecules-Alizarin Red in Alkaline Media
18
O
O
OH
OH
SO3H
O
O
OH
OH
SO3H
O
O
O
O
SO3H
Charge
Discharge
O
O
O
O
SO3H
O
O
OH
OH
SO3H
OH
Michael Reaction
O
O
OH
OH
SO3H
OH
O
O
OH
OH
OH
OH
KOH
-8.00E-05
-6.00E-05
-4.00E-05
-2.00E-05
0.00E+00
2.00E-05
4.00E-05
6.00E-05
8.00E-05
1.00E-04
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6Cu
rre
nt
(A)
Potential (V vs MMO)
Alizarin Red, 1M KOH, GC, 50mV/second
Hydroxydesulfonation of Alizarin Red
19
NMR Analysis of cycled Alizarin Red Confirms the formation of the tetrahydroxylatedproduct
Purpurin-a viable pathway to using anthraquinone derivatives
20
0
0.2
0.4
0.6
0.8
1
1.2
-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
Ce
ll V
olt
age
(V
olt
s)
Capacity (Ah)
40mMPurpurin/200mM AQDS 1M NaOH, 200mA
O
O
OH
OH
OH
OH
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10 15 20 25 30 35
Cap
acit
y (A
h)
Cycle number
40mMPurpurin/200mM AQDS 1M NaOH, 200mA, 400 mL on each side
Ch. Cap.
Disch. Cap.
HydroxylatedPurpurin can be cycled in alkali without noticeable degradation
O
O
OH
OH
SO3H
OH
O
O
OH
OH
OH
OH
KOH
Other Promising Bifunctional Molecules StudiedCompound Structure E1/2 (Volts) vs MMO Bi-functional Material
Potential
1,2,4-trihydroxy anthraquinone
O
O
OH
OH
OH
-0.84 V Yes, 840 mV difference
1,4-dihydroxy anthraquinone
O
O
OH
OH
-0.63 V Yes, 880 mV difference
1,2-dihydroxy anthraquinone
O
O
OH
OH
-0.73 V Yes, 1 V difference
1,2-dihydroxy, 3-sulfonic acid anthraquinone
O
O
OH
OH
SO3H
-0.75 V Yes, 930 mV difference
21
Potential to increase cell voltage by substitution
Next Steps
• Increase the solubility of stable redox molecules to ensure high concentrations.
• Develop methods of sulfonation for the non-participating ring.
• Complete the characterization in alkaline media
• Down-select molecules for full-cell testing
• Pursue further molecular designs to avoid oligomer formation.
• Explore the bifunctional nature of stabilized redox molecules in full cell.
22
Acknowledgements
• Dr. Imre Gyuk , DoE’s Office of Electricity.
• Drs. Wei Wang, David Reed and Vincent Sprenkle at PNNL
• University of Southern California, Loker Hydrocarbon Research Institute for post-doctoral fellow and graduate student support.
23