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US-20260128339-A1 - ELECTROCHEMICAL MEMBRANE

US20260128339A1US 20260128339 A1US20260128339 A1US 20260128339A1US-20260128339-A1

Abstract

This disclosure relates to polymer electrolyte membranes, and in particular, to a composite membrane having at least two reinforcing layers comprising a microporous polymer structure and a surprisingly high resistance to piercing. This disclosure also relates to composite membrane-assemblies and electrochemical devices comprising the composite membranes of the disclosure, and to methods of manufacture of the composite membranes.

Inventors

  • Joshua Bartels
  • Navya Jagarlamudi

Assignees

  • W. L. GORE & ASSOCIATES, INC.

Dates

Publication Date
20260507
Application Date
20251029

Claims (20)

  1. 1 . A composite membrane for an electrochemical device, comprising: a) at least two reinforcing layers, each of said at least two reinforcing layers comprising a microporous polymer structure; and b) an ion exchange material (IEM) at least partially imbibed within the microporous polymer structure of the at least two reinforcing layers and rendering the microporous polymer structure occlusive; wherein the normalized total content of microporous polymer structure within the composite membrane is at least 3.0 μm based on the total area of the composite membrane, wherein the normalized total content of the microporous polymer structure within the composite membrane is calculated with the following formula: [  ∑ M mps ⁢ 1 ⁢ in ⁢ each ⁢ reinforcing ⁢ layer / A composite ⁢ membrane ( g · m - 2 ) matrix ⁢ skeletal ⁢ density mps ⁢ 1 ( g · cm - 3 ) + ∑ M mps ⁢ 2 ⁢ in ⁢ each ⁢ reinforcing ⁢ layer / A composite ⁢ membrane ( g · m - 2 ) matrix ⁢ skeletal ⁢ density mps ⁢ 2 ( g · cm - 3 ) + ... + ∑ M mps ⁢ N ⁢ in ⁢ each ⁢ reinforcing ⁢ layer / A composite ⁢ membrane ( g · m - 2 ) matrix ⁢ skeletal ⁢ density mps ⁢ N ( g · cm - 3 ) ] · 10 - 6 ⁢ m 3 cm 3 wherein mps1 is microporous polymer structure 1, mps2 is microporous polymer structure 2, mpsN is microporous polymer structure N (if there are N different types of microporous polymer structures within the composite membrane).
  2. 2 . A composite membrane according to claim 1 , wherein the composite membrane has an average failure pressure of at least 150 psi.
  3. 3 . A composite membrane according to claim 1 , wherein the microporous polymer structure is present in a total content of at least 15 vol % based on the total volume of the composite membrane.
  4. 4 . A composite membrane according to claim 1 , wherein the composite membrane comprises at least three reinforcing layers.
  5. 5 . A composite membrane according to claim 1 , wherein a composition of the at least two reinforcing layers is the same or wherein a composition of the at least two reinforcing layers is different.
  6. 6 . A composite membrane according to claim 1 , wherein the microporous polymer structure comprises at least one fluorinated polymer.
  7. 7 . A composite membrane according to claim 6 , wherein the composite membrane has a total content of microporous polymer structure of at least 8 g·m −2 based on the sum of the mass per area of all the reinforcing layers present in the composite membrane.
  8. 8 . A composite membrane according to claim 1 , wherein one of: the at least two reinforcing layers are in direct contact; or the composite membrane comprises at least one internal layer of ion exchange material between the at least two reinforcing layers.
  9. 9 . A composite membrane according to claim 1 , wherein the at least two reinforcing layers are separated by a distance d, wherein the distance d is from 0.1 μm to 20 μm at 0% RH.
  10. 10 . A composite membrane according to claim 1 , wherein one of: the composite membrane comprises more than one layer of ion exchange material, wherein the layers of ion exchange material are formed of the same ion exchange material; or the ion exchange material comprises more than one layer of ion exchange material.
  11. 11 . A composite membrane according to claim 1 , wherein at least one of: the microporous polymer structure is fully imbibed with the ion exchange material; the microporous polymer structure of each of the at least two reinforcing layers has a first surface and a second surface, and wherein the ion exchange material forms a layer on at least one of the first surface or the second surface of each of the at least two reinforcing layers.
  12. 12 . The composite membrane as in claim 1 , wherein the microporous polymer structure of each of the at least two reinforcing layers has a first surface and a second surface, and wherein the microporous polymer structure is mostly imbibed with the ion exchange material, but comprises a region of un-imbibed or non-occlusive region of the microporous polymer structure closest to the first surface of at least one of the at least two reinforcing layers.
  13. 13 . A composite membrane according to claim 1 , wherein the average equivalent volume of the ion exchange material is from 240 cc/mole eq to 870 cc/mole eq.
  14. 14 . A composite membrane according to claim 1 , wherein the ion exchange material comprises at least one ionomer, or wherein the ion exchange material comprises at least one ionomer and wherein the at least one ionomer comprises a proton conducting polymer.
  15. 15 . A composite membrane according to claim 1 , wherein the composite membrane has a thickness at 0% RH of at least 10 μm.
  16. 16 . A membrane electrode assembly for an electrochemical device, comprising: at least one electrode; and the composite membrane according to claim 1 in contact with the at least one electrode.
  17. 17 . A membrane electrode assembly according to claim 16 , wherein the membrane electrode assembly is a redox flow battery membrane-electrode assembly comprising: a first electrode with a first surface and a second surface; a second electrode with a first surface and a second surface; and a composite membrane with a first surface and a second surface according to claim 1 , wherein the second surface of the first electrode is in contact with the first surface of the composite membrane and the first surface of the second electrode is in contact with the second surface of the composite membrane.
  18. 18 . The membrane electrode assembly according to claim 17 wherein the first electrode layer and/or the second electrode layer is a porous layer having a pore size from 1 to 200 μm.
  19. 19 . A membrane electrode assembly according to claim 16 , wherein the membrane electrode assembly is a fuel cell membrane electrode assembly or an electrolyzer electrode assembly; the membrane electrode assembly comprising: a composite membrane as described according to claim 1 , wherein the composite membrane has a first surface and a second surface; a first layer of electrode catalyst adhered to the first surface of the composite membrane; and a second layer of electrode catalyst adhered to the second surface of the composite membrane.
  20. 20 . A membrane electrode assembly according to claim 19 , wherein the first and second layers of electrode catalyst are nanoporous layers having a pore size of up to 100 nm.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of U.S. Non-Provisional application Ser. No. 18/021,988 filed Feb. 17, 2023 the national phase application of PCT Application No. PCT/IB2021/057600, internationally filed on Aug. 18, 2021, which claims the benefit of U.S. Provisional No. 63/067,665, filed Aug. 19, 2020, which are herein incorporated by reference in their entireties for all purposes. FIELD This disclosure relates to polymer electrolyte membranes, and in particular, to a composite membrane having at least two reinforcing layers comprising a microporous polymer structure and surprisingly high resistance to piercing. BACKGROUND Polymer Electrolyte Membranes (PEMs) are critical components in many applications, such as fuel cells, electrolyzers, redox flow batteries. In Fuel Cells, the Polymer Electrolyte Membrane (PEM) is part of a Membrane Electrode Assembly (MEA). The MEA is the core component of the fuel cell where the electrochemical reactions take place that generate power. A typical MEA comprises a PEM, two catalyst layers (i.e., the anode and the cathode, which are attached to opposite sides of the PEM), and two gas diffusion layers (GDLs) which are attached to the two outer surfaces of the catalyst layers. The PEM separates two reactant gas streams. On the anode side of the MEA, a fuel, e.g., hydrogen gas, is oxidized to separate the electrons and protons. The cell is designed so that the electrons travel through an external circuit while the protons migrate through the PEM. On the cathode side the electrons and protons react with an oxidizing agent (i.e., oxygen or air) to produce water and heat. In this manner, an electrochemical potential is maintained and current can be drawn from the fuel cell to perform useful work. Redox flow batteries use two soluble redox couples as electroactive materials to store energy via oxidation and reduction reactions. Typically, the redox flow batteries comprise two electrolyte reservoirs (cathiolyte and aniolyte) from which the electrolytes are circulated by pumps through an electrochemical cell stack. The cell stack usually comprises multiple cells connected in series or parallel to enable the electrochemical reaction to take place at inert electrodes. Each cell of the stack comprises an anode, a cathode and an ion exchange membrane separator (e.g. a polymer electrolyte membrane PEM) to allow diffusion of ions across the membrane separator while preventing the cross-mixing of the electrolyte solutions from the two reservoirs. Electrolyzers hydrolyze water to generate hydrogen and oxygen. The reactions that take place in an electrolyzer are very similar to the reaction in fuel cells, except the reactions that occur in the anode and cathode are reversed. In a fuel cell the anode is where hydrogen gas is consumed and in an electrolyzer the hydrogen gas is produced at the cathode. Bipolar electrolyzers (or PEM electrolyzers) use the same type of electrolyte separator as PEM fuel cells. The electrolyte separator is a thin, solid ion-conducting membrane, which is used instead of the thick, porous membrane separating aqueous solution employed in alkaline electrolyzers. High selectivity (via high conductance and/or low permeance), high durability, and low cost, are all desirable qualities in a PEM. However, as a matter of practical engineering, conflicts often arise in the optimization of these properties, requiring tradeoffs to be accepted. One can attempt to improve selectivity by increasing conductance via reduction in membrane thickness. Making a PEM thinner also lowers its cost because ionomer is expensive and less of it is used. However, thinner membranes have increased hydrogen permeation, which erodes any selectivity gains from increased proton conduction, and results in thinner membranes having similar or worse selectivity than thicker ones. In addition, thinner membranes also are weaker, frequently lacking sufficient mechanical durability for aggressive automotive conditions. Reducing the membranes physical thickness can also increase the susceptibility to damage or puncture from other electrochemical device components, leading to shorter cell lifetimes. Piercing of PEMs can be particularly problematic in Redox Flow Batteries (RFB), which employ electrode layers disposed at either side of the PEM. RFB electrode layers usually comprise a porous layer (typical pore size 1-200 micron). The porous layer may comprise, among others, a felt, a paper, or a woven material. RFB electrodes usually comprise carbon fibers which, upon compression of the electrode layer against the PEM during PEM-electrode assembly, can pierce the PEM. Therefore, access to membranes with higher proton conductance is restricted by membrane piercing resistance requirements. Ultimately, PEM electrochemical devices can fail because of pinholes that develop and propagate through the polymer electrolyte membranes. In addition, these devices can also fail if electr