anion-exchange membranes with improved stability … · anion-exchange membranes with improved...

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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

+++++++++

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+++++++++

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++ --

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+++++++++

+++++++++

MXMX

X-X- M+

MXMX

X-X-

H+H+

HXHX

OH-

MOHrepeating unit

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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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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