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US-20260128341-A1 - REINFORCED ION-CONDUCTING MEMBRANE

US20260128341A1US 20260128341 A1US20260128341 A1US 20260128341A1US-20260128341-A1

Abstract

Reinforced ion-conducting membrane According to the present invention there is provided a reinforced ion-conducting membrane comprising: an ion-conducting polymer; and a porous mat of nanofibres. The porous mat of nanofibres is impregnated with the ion-conducting polymer. The nanofibres comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive. The cross-linked polymer comprises: a heterocyclic-based polymer backbone comprising basic functional groups, and linking chains linking at least two heterocyclic-based polymer backbones via linking groups. The porous mat of nanofibres has a tear index of at least 15 mN m 2 /g.

Inventors

  • Apoorva AMBARKAR
  • Silvain Buche

Assignees

  • Johnson Matthey Hydrogen Technologies Limited

Dates

Publication Date
20260507
Application Date
20231110
Priority Date
20221111

Claims (20)

  1. 1 . A reinforced ion-conducting membrane comprising: an ion-conducting polymer; and a porous mat of nanofibres, which is impregnated with the ion-conducting polymer; wherein the nanofibres comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprises: heterocyclic-based polymer backbones comprising basic functional groups, and linking chains linking at least two of the heterocyclic-based polymer backbones via linking groups wherein the linking chains have a different chemical structure to the heterocyclic-based polymer backbone; wherein the porous mat of nanofibres has a tear index of at least 15 mN m 2 /g.
  2. 2 . The reinforced ion-conducting membrane according to claim 1 , wherein each linking group (A) is independently selected from the group consisting of: wherein C 1 is chemically bonded to a heterocyclic-based polymer backbone.
  3. 3 . The reinforced ion-conducting membrane according to claim 1 , wherein the linking chains have a chemical formula selected from the group consisting of: wherein: A is the linking group, and each linking group A is independently selected from the group consisting of: R 1 is selected from the group consisting of: an aliphatic C 1-15 alkyl chain, preferably C 1-10 alkyl chain and more preferably C 1-6 alkyl chain; an alkoxy chain, for example a glycol chain such as [CH 2 CH 2 O] m , [CH 2 CH(CH 3 )O] m , [CH 2 CH 2 CH 2 O] m ; an aryloxy chain, or a combination thereof; X and Y are each independently selected from the group consisting of: O, [N(R 7 )], [OCH 2 CH 2 ] n , [OCH 2 CH(CH 3 )] n , [O(CH 2 ) 3 ] n and no atom; R 2 and R 7 are each independently selected from the group consisting of: H, C 1-5 alkyl chain, and (CH 2 ) p A, m and n are each independently in the range of and including 1 to 225, R 3 and R 4 are each independently selected from an aliphatic C 1-5 alkyl chain; an alkoxy chain, for example a glycol chain; or no atom; R a , R b , R c , R d , R 5 and R 6 are each independently selected from H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, or tert-butyl; and p is an integer in the range of and including 1 to 5.
  4. 4 . The reinforced ion-conducting membrane according to claim 2 , wherein the linking chains are selected from the group consisting of: wherein q is in the range of and including 1 to 225, and r is in the range of and including 1 to 225.
  5. 5 . A reinforced ion-conducting membrane according to claim 1 , wherein the linking chains are aliphatic.
  6. 6 . The reinforced ion-conducting membrane according to claim 5 , wherein the linking chains are linear or branched aliphatic chains.
  7. 7 . The reinforced ion-conducting membrane according to claim 2 , wherein C 1 is chemically bonded to a heteroatom of the heterocyclic-based polymer backbone.
  8. 8 . (canceled)
  9. 9 . The reinforced ion-conducting membrane according to claim 1 , wherein the basic functional groups comprise nitrogen-containing basic functional groups.
  10. 10 . The reinforced ion-conducting membrane according to claim 1 , wherein the heterocyclic-based polymer backbone is selected from the group consisting of: polybenzimidazoles, poly(pyridine)s, poly(pyrimidine)s, polybenzthiazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, polytriazoles, polyoxazoles, polybenzoxazoles, polythiazoles, polypyrazoles and derivatives thereof.
  11. 11 . The reinforced ion-conducting membrane according to claim 10 , wherein the heterocyclic-based polymer backbone is selected from the group consisting of: polybenzimidazoles, polytriazoles, polythiazoles, polydithiazoles and derivatives thereof.
  12. 12 . The reinforced ion-conducting membrane according to claim 1 , wherein the nanofibres are spun nanofibres.
  13. 13 . A reinforced ion-conducting membrane according to claim 1 , wherein the nanofibres further comprise a second polymer, wherein the second polymer is ionically non-conductive and has a different chemical composition to the heterocyclic-based polymer backbone.
  14. 14 . The reinforced ion-conducting membrane according to claim 13 , wherein the second polymer is selected from the group consisting of: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimides (PI), polyetherimide (PEI), poly(aryl ether ketone) (PAEK), poly(aryl ether sulfone), poly(phenylene sulfide) (PPS), polyvinylpyrrolidone (PVP).
  15. 15 . The reinforced ion-conducting membrane according to claim 1 , wherein the porous mat of nanofibres has an ultimate tensile strength of at least 25 MPa when measured in a machine direction and/or a transverse direction, wherein the machine direction and the transverse direction are perpendicular.
  16. 16 . The reinforced ion-conducting membrane according to claim 1 , wherein the ratio of ultimate tensile strength of the porous mat of nanofibres measured in a machine direction to ultimate tensile strength of the porous mat of nanofibres measured in a transverse direction is in a range of 0.5 to 2, wherein the machine direction and the transverse direction are perpendicular.
  17. 17 . The reinforced ion-conducting membrane according to claim 1 , wherein the porous mat of nanofibres has a strain at break of at least 5%, when measured in a machine direction and/or a transverse direction at a temperature of 20° C.±3° C., a relative humidity of 30-50% and at an extension rate of 20 mm/min, wherein the machine direction and the transverse direction are perpendicular.
  18. 18 . A reinforced ion-conducting membrane comprising: an ion-conducting polymer; and a porous mat of nanofibres, which is impregnated with the ion-conducting polymer; wherein the nanofibres comprise a cross-linked polymer, wherein the cross-linked polymer is ionically non-conductive and comprises: heterocyclic-based polymer backbones comprising basic functional groups, and linking chains linking at least two of the heterocyclic-based polymer backbones via linking groups, wherein the linking chains have a different chemical structure to the heterocyclic-based polymer backbone; wherein the porous mat has a mean average thickness of 10 μm or less and the reinforced ion-conducting membrane has a secant modulus at 8% strain of at least 30 MPa when measured in a machine direction at 80° C. and 90% RH, and a secant modulus at 8% strain of at least 30 MPa when measured in a transverse direction at 80° C. and 90% RH, wherein the machine direction and the transverse direction are perpendicular.
  19. 19 . (canceled)
  20. 20 . (canceled)

Description

FIELD OF THE INVENTION This invention relates to a reinforced ion-conducting membrane, such as a reinforced electrolyte membrane. In particular, this invention relates to a reinforced proton exchange membrane, and methods of manufacturing the same. The reinforced ion-conducting membrane can be suitable for use in electrochemical devices such as fuel cells and/or electrolysers. BACKGROUND OF THE INVENTION A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. A fuel, e.g. hydrogen, an alcohol such as methanol or ethanol, or formic acid, is supplied to the anode and an oxidant, e.g. oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode. Fuel cells are usually classified according to the nature of the electrolyte employed. Often the electrolyte is a solid polymeric membrane, in which the membrane is electronically insulating but ionically conducting. In the proton exchange membrane fuel cell (PEMFC) the membrane is proton conducting, and protons, produced at the anode, are transported across the membrane to the cathode, where they combine with oxygen to form water. An electrolyser is an electrochemical device for electrolysing water to produce high purity hydrogen and oxygen. Electrolysers can operate in both alkaline and acidic systems. Those electrolysers that employ a solid proton-conducting polymer electrolyte membrane, or proton exchange membrane (PEM), are known as proton exchange membrane water electrolysers (PEMWEs). Those electrolysers that utilise a solid anion-conducting polymer electrolyte membrane, or anion exchange membrane (AEM), are known as anion exchange membrane water electrolysers (AEMWEs). A principal component of the fuel cell or water electrolyser is the membrane electrode assembly (MEA). The MEA is typically composed of five layers. The central layer is the polymer ion-conducting membrane. On either side of the ion-conducting membrane there is an electrocatalyst layer, containing an electrocatalyst designed for the specific electrolytic reaction. Finally, adjacent to each electrocatalyst layer there is a gas diffusion layer, and/or a porous transport layer, which is porous and electrically conducting and allows the reactants to reach the electrocatalyst layer and conduct the electric current that is generated by the electrochemical reactions. Conventional ion-conducting membranes used in PEMFCs or PEMWEs are generally formed from sulphonated fully-fluorinated polymeric materials (often generically referred to as perfluorinated sulphonic acid (PFSA) ionomers). As an alternative to PFSA type ionomers, it is possible to use ion-conducting membranes based on partially fluorinated or non-fluorinated hydrocarbon sulphonated or phosphonated polymers. Recent developments in fuel cells and electrolysers require membranes to be thinner due to the advantages obtained (improved ionic conductivity, improved water transport etc) and thus, in order to provide the mechanical properties required to increase resistance to premature failure, a reinforcement, typically expanded polytetrafluoroethylene (ePTFE), is embedded within the membrane. Although such reinforced membranes often have lower proton conductivity when compared to an unreinforced membrane of the same thickness, the improvement in mechanical properties has enabled thinner membranes of lower electrical resistance to be used. Other types of reinforcement have also been proposed, for example as disclosed in WO2011/149732 and WO2016/020668. Li and Liu; J. Mater. Chem. A., 2013, 1, 1171 discloses polyelectrolyte composite membranes of polybenzimidazole and crosslinked polybenzimidazole-polybenzoxazine electrospun nanofibres for proton exchange membrane fuel cells. The membranes were doped with 85% phosphoric acid, which rendered the polymers of the composite membrane proton conductive (including the polymer of the nanofibres). It is desirable to develop reinforced ion-conducting membranes which have improved mechanical properties. SUMMARY OF THE INVENTION Although reinforced membranes such as those hereinbefore described have allowed thinner membranes to be used whilst maintaining mechanical strength, deficiencies still exist. In particular, limitations are seen in practical operation in which the conditions of humidity can vary quite significantly over short periods of time from relatively high levels (such as on start up from cold conditions) to quite dry levels (operation at maximum rated power density) where the membrane can degrade to a higher level than acceptable. In accelerated stress tests designed to mimic and accelerate this operation, a wet/dry cycling accelerated stress testing induces swelling/de-swelling of the