Anion-Exchange Membranes with Improved Stability for Energy Applications

Transcription

1 AnionExchange Membranes with Improved Stability for Energy Applications Dr. Bernd Bauer FuMATech GmbH 1

2 ur Vision A leading supplier of ionomers, ionexchange membranes and separators for: Electrochemical 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 knowhow in the production of ionexchange membranes for various electromembrane applications 2

3 The FUMATECH History in AnionExchange Membranes 3

4 Why chemical resistant AEM 1982 Fraunhofer Institute FhIGB (membrane process technology) Development of bipolar membranes R&D initiated by Prof. Heiner Strathmann repeating unit MX MH HX H H X M X MX 4 4

5 The anionlayer in bipolar membranes 1984 Alkaline stable anionexchange layer based on chloromethylated polystyrene and later on poly(paravinylbenzylchloride)costyrene (25/75) quaternization with trimethylamine ultrahigh 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: 1benzyl1azonia4azabicyclo(2.2.2)octane 5 5

6 Bipolar Single Film Multilayer Membrane catio n selective layer 90 µm ca ta lytic interphase anionselective layer 30 µm C CH 3 C S CH 3 C Na 3 S C S C CH 2 N CH 3 Å N CH 2 CH 3 N N CH 2 CH 3 C S CH 3 HC C HN crosslinked polyelectrolyte Development of Bipolar Membranes 6 6th International Symposium on Synthetic Membranes in Science and Industry (1986), Desalination, 68 (1988)

7 Bipolar Membranes in Energy Conversion Bipolar Membranes (type FBM ) are used in various industrial applications for several years: a) Lactic acid production 7% 30 C b) KH production 16% 45 C c) LiH production (Lithium battery recycling) 7% 45 C Warranty on membranes? Water goes in warranty goes out! NEW APPLICATINS with bipolar membranes : 1) FBM in energy conversion: Microbial fuel cells 2) Energy storage in bipolar membrane flow batteries 7 7

8 Chemical Resistant AnionExchange Membranes 8

9 Chemical resistant AEM What is needed in energy applications? 1) Alkaline stability 2) Hydrolytic stability 3) xidation 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. 9 However, scaleup has never been shown successfully so far: Chain transfer reactions and formation of snakeinthecage ionomers 9

10 Chemical resistant AEM The best compromise on safety: 1) Homogeneous membranes, mechanically reinforced with porous separators (eptfe, UHMWPE, ) woven or nonwoven fabrics (PK, PTFE) 2) Homogeneous membranes with sidechain functionality Polymeric alkylation agent (PVBC, ) vs. polymeric amine (P4VP, ) 1987 Replacement of PVBC by lowcost polyepichlorohydrine and PECHcopolymers 1988 Replacement of PECH by chloromethylated polyethersulfone 1989 Research on bromination of polyphenyleneoxide Sterically hindered Polyamines and Nheterocyclic 10

11 Alkaline stable anionexchange membranes Diaza(bicyclooctane) DABC polyethersulfone anion exchange membranes (after conditioning with caustic at elevated temperatures) S N N S N N N N 11 11

12 Challenges with DABC Alkaline stable membranes need strict monoquaternization bisquaternization is limited for crosslinking only Challenge: pk b and reactivity of both Ngroups is similar Reaction control in industrial production is more difficult Nonselective alkylation groups such as benzylchloride (e.g. PVBC, chloromethylated polysulfone) or benzylbromide (e.g. brominated PP) cannot be used without protection chemistry. Aliphatic alkylchlorides (e.g. polyepichlorohydrine) are possible, but full conversion is difficult and remaining CH 2 Cl will cause ageing

13 Alkaline stable anionexchange membranes Various chemistries are en vogue and partially commercial: FAA: aromatic ionomer, DABC for alkaline applications FAA1: aromatic ionomer for alkaline applications FAA2: aliphatic ionomer, DABC FAA3: hydrolytical stable, sidechain functionality, aromatic FAA4: hydrolytical stable, stabilized sidechain functionality, aromatic FAP: sterically hindered aromatic polyamine, oxidation resistant FAAM: Nheterocycle, APBI copolymer for strong alkaline applications Alkaline stable anionexchange membranes are not necessarily stable in alkaline fuel cells and vice versa! 13 13

14 Characterization of FAA3 Membrane Temperature Conductivity / ms.cm1 FAA FAA FAA3 rf FAA3 rf FAAM doped in 8M KH to 100% d.l. FAAM doped in 8M KH to 100% d.l

15 Characterization of FAA3 Ionic mobilities in water D σ 10 5 cm 2 /s H 5.3 HC C Reduction of conductivity by carbonate formation and reduced swelling 15 15

16 Alkaline stable anionexchange membranes 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 (powertogas) FAA3 platform is tested (preliminary stage) in alkaline fuel cells, alkaline PEM electrolysers and zincair batteries 16 16

17 RedoxFlow Batteries 1988 crosslinked Poly(4vinylpyridine)costyrene membrane for ironchromium RFB Sterically hindered aromatic polyamine for all vanadium RFB 17

18 VanadiumRedoxFlow Batteries

19 Guideline for membrane s choice Cationexchange vs. Anionexchange Cation exchange membranes Low selectivity High conductivity High electrolyte transfer High oxidation stability High cost for PFSA Anion exchange membranes High selectivity Medium conductivity Low electrolyte transfer Medium to good oxidation stability Medium to low cost 19

20 VanadiumRedoxFlow Batteries verview of results Type Coulomb efficiency Energy efficiency Specific resistance (mhm.cm 2 ) smotic permeability (µl/cm 2.hr) Electroosmotic permeability (µl/cm 2.hr) FAP % 8791 % 725 1,7 0,94,1 FAP % 8589 % 540 2,4 1,36,2 VPX ,5 % 8592 % 850 0,6 0,41,4 F940rf 8592 % 7883 % 410 0,3 < 3,78,3 20

21 VanadiumRedoxFlow Batteries Depending on requested operation conditions, one can decide for High current density including fast charging. Membrane of lower selectivity, but higher conductivity: F940RF Maximum selectivity in order to simplify electrolyte management: VPX 20 Best trade off with broad range of operating conditions: FAP450 All membrane are well proven on chemical durability and mechanical integrity. Remaining problem: total cost of ownership, which is the business case? 21