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Anion-Exchange Membranes with ImprovedStability for Energy Applications
Dr. Bernd Bauer
FuMA-Tech GmbH
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A leading supplier of ionomers, ion-exchange membranes and separators for:
- Electro-chemical water treatment technologies,
- Energy conversion in fuel cells
- Energy storage in Batteries
- Hydrogen production from renewable energies using water electrolysis
2 operation sites in Germany
25 employees in energy technologies
Leading and patented know-how in the production of ion-exchange membranes for various electro-membrane applications
Our Vision
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The FUMATECH Historyin Anion-Exchange Membranes
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1982 Fraunhofer- Institute FhIGB (membrane process technology)Development of bipolar membranesR&D initiated by Prof. Heiner Strathmann
Why chemical resistant AEM
+++++++++
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+ -
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+++++++++
+++++++++
MX
X- M+
MX
X-
H+
HX
OH-
MOHrepeating unit
+++++++++
---------
+++++++++
---------
++ --
---------
+++++++++
+++++++++
MXMX
X-X- M+
MXMX
X-X-
H+H+
HXHX
OH-
MOHrepeating unit
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55
1984 Alkaline stable anion-exchange layer based on
chloromethylated polystyrene and later on
poly(para-vinylbenzylchloride)-co-styrene (25/75)
quaternization with trimethylamine
ultra-high molecular weight needed for film formation
1986 R&D on the alkaline stability of cationic head groups
identification of degradation products
identification of degradation mechanism
variation of the head group:
1-benzyl-1-azonia-4-aza-bicyclo(2.2.2)-octane
The anion-layer in bipolar membranes
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c a t io n - s e le c t iv e la y e r a n io n - s e le c t iv e la y e r
c r o s s l in k e d p o ly e le c t r o ly t e
H O O C
C O O H N
O
C H 3
C H3
C O
N
S
C H3
N
C H 3
O
O
C H2
O C O S
C H3
C H3
O
OC H
2
Å N
N
O C
C H2
O
S
O
N a O3
S
O
O
C
O
OO
C
O
O
O
OC
c a ta ly ticin te rp h a s e
3 0 µ m9 0 µ m
Bipolar Single Film Multilayer Membrane
Development of Bipolar Membranes
6th International Symposium on Synthetic Membranes in Science and Industry (1986),
Desalination, 68 (1988) 279-292
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777
Bipolar Membranes (type FBM® ) are used in various industrial applications
for several years:
a) Lactic acid production
7% NaOH @ 30°C
b) KOH production
16% KOH @ 45°C
c) LiOH production (Lithium battery recycling)
7% LiOH @ 45°C
Warranty on membranes? Water goes in – warranty goes out !
NEW APPLICATIONS with bipolar membranes :
1) FBM in energy conversion: Microbial fuel cells
2) Energy storage in bipolar membrane flow batteries
Bipolar Membranes in Energy Conversion
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Chemical Resistant Anion-Exchange Membranes
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999
What is needed in energy applications?
1) Alkaline stability
2) Hydrolytic stability
3) Oxidation stability
4) Stability in strong acids
For safety of operation:
The ideal membrane should be prepared starting from a film !
Most obviously, grafting is the best technology.
However, scale-up has never been shown successfully so far:
Chain transfer reactions and formation of snake-in-the-cage ionomers
Chemical resistant AEM
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1010
The best compromise on safety:
1) Homogeneous membranes, mechanically reinforced with- porous separators (ePTFE, UHMWPE, …)- woven or non-woven fabrics (PK, PTFE)
2) Homogeneous membranes with side-chain functionality
Polymeric alkylation agent (PVBC, …) vs. polymeric amine (P4VP, …)
1987 Replacement of PVBC by low-cost polyepichlorohydrineand PECH-copolymers
1988 Replacement of PECH by chloromethylated polyethersulfone
1989 Research on bromination of polyphenyleneoxide
1996 Sterically hindered Polyamines and N-heterocyclic
Chemical resistant AEM
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SO O
O O
SO O
O O
NN
N
N
NN
Alkaline stable anion-exchange membranes
Diaza(bicyclo-octane) – DABCO - polyethersulfone anion exchange membranes(after conditioning with caustic at elevated temperatures)
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Alkaline stable membranes need strict mono-quaternization bis-quaternization is limited for cross-linking only
Challenge:pKb and reactivity of both N-groups is similar
Reaction control in industrial production is more difficult
Non-selective alkylation groups such as benzylchloride (e.g. PVBC, chloromethylated polysulfone) or benzylbromide (e.g. brominatedPPO) cannot be used without protection chemistry.
Aliphatic alkylchlorides (e.g. polyepichlorohydrine) are possible, but full conversion is difficult and remaining –CH2Cl will cause ageing.
Challenges with DABCO
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Various chemistries are en vogue and partially commercial:
FAA: aromatic ionomer, DABCO for alkaline applications
FAA-1: aromatic ionomer for alkaline applications
FAA-2: aliphatic ionomer, DABCO
FAA-3: hydrolytical stable, side-chain functionality, aromatic
FAA-4: hydrolytical stable, stabilized side-chain functionality, aromatic
FAP: sterically hindered aromatic polyamine, oxidation resistant
FAAM: N-heterocycle, APBI copolymer for strong alkaline applications
Alkaline stable anion-exchange membranes are not necessarily stable
in alkaline fuel cells and vice versa !
Alkaline stable anion-exchange membranes
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Membrane Temperature Conductivity / mS.cm-1
FAA-3 25 25
FAA-3 70 62
FAA-3 rf 25 22
FAA-3 rf 70 60
FAAM doped in 8M KOH to 100% d.l.
25 18
FAAM doped in 8M KOH to 100% d.l.
70 45
Characterization of FAA-3
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Ionic mobilities in water
Dσ 10-5 cm2/s
OH- 5.3
HCO3- 1.2
CO32- 0.9
Reduction of conductivity by carbonate formation and reduced swelling
Characterization of FAA-3
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FAAM is currently used in liquid alkaline electrolysers to replace
porous separators (Zirfon, etc. )
- Small hydrogen generators for gold welding
- Hydrogen storage from renewables
- Hydrogen for methanization (power-to-gas)
FAA-3 platform is tested (preliminary stage) in
- alkaline fuel cells,
- alkaline PEM electrolysers and
- zinc-air batteries
Alkaline stable anion-exchange membranes
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Redox-Flow Batteries
1988 cross-linked Poly-(4-vinylpyridine)-co-styrene membrane for
iron-chromium RFB.
1998 Sterically hindered aromatic polyamine for all vanadium RFB
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18
2+ + + 2+ 3+
4+ → 5+ −3+ − → 2+
Vanadium-Redox-Flow Batteries
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Cation exchange membranes Anion exchange membranes
Low selectivity
High conductivity
High electrolyte transfer
High oxidation stability
High cost for PFSA
High selectivity
Medium conductivity
Low electrolyte transfer
Medium to good oxidation stability
Medium to low cost
Guideline for membrane’s choice
Cation-exchange vs. Anion-exchange
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TypeCoulomb
efficiency
Energy
efficiency
Specific
resistance
(mOhm.cm2)
Osmotic
permeability
(µl/cm2.hr)
Electro-osmotic
permeability
(µl/cm2.hr)
FAP-450 96-99 % 87-91 % 725 1,7 0,9-4,1
FAP-375 94-98 % 85-89 % 540 2,4 1,3-6,2
VPX-20 98-99,5 % 85-92 % 850 0,6 0,4-1,4
F-940rf 85-92 % 78-83 % 410 0,3 < 3,7-8,3
Overview of results
Vanadium-Redox-Flow Batteries
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Depending on requested operation conditions, one can decide for
- High current density including fast charging. Membrane of lower selectivity, but higher conductivity: F-940RF
- Maximum selectivity in order to simplify electrolyte management: VPX 20
- Best trade off with broad range of operating conditions: FAP-450
All membrane are well proven on chemical durability and mechanicalintegrity.
Remaining problem: total cost of ownership, which is the business case?
Vanadium-Redox-Flow Batteries