Bipolar ionomer membrane

Abstract

A membrane useful for electrochemical or fuel cells is provided. The membranes can be formed of or include sulfonated polymers that are covalently or ionically bonded to multiple nitrogen-containing heterocyclic molecules, and the resulting membranes have excellent ionic conductivity and selectivity.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is dependent upon and claims priority to U.S. Provisional Application No. 62 / 290,692, filed February 3, 2016.

[0002] STATEMENT OF GOVERNMENT RIGHTS This invention was made with government support under Contract No. DE-SC0006457 awarded by the United States Department of Energy. The government has certain rights in this invention.

[0003] Field The present disclosure relates to ion exchange membranes for use in electrochemical applications, for example, for use as separators in electrochemical cells.

[0004] background Vanadium redox flow batteries (VRBs) are robust, multi-kWh, long-life flow batteries with an energy density of approximately 20 Wh / liter that can economically store large amounts of renewable energy in liquid form and are useful as storage for intermittent renewable power plants, such as wind and solar energy storage devices, or for off-peak power generation. VRBs function by pumping charged anolyte and catholyte from a storage tank through electrochemical half-cells separated by an ion-permeable membrane that contacts carbon felt anodes and cathodes on either side of the membrane. The cell discharges by the flow of electrons from the anolyte through a power load to the catholyte, while charge balance is maintained by the flow of ions, usually protons, through the ion-permeable membrane.

[0005] Negative half cell V 2+ ←→ V 3+ +e - Eo=-0.255V Positive half cell e - +VO2 + +2H + ←→ VO 2+ +H2O Eo=1.00V Overall VO2 + +2H + +V 2+ ←→ VO 2+ +H2O+V 3+ Effective (Net) Eo=1.255V Vanadium ions are released from the anolyte (V 3+ / V 2+ pair) and catholyte (VO 2+ / VO2 + pair), which greatly simplifies the battery and improves its lifespan, because if the separator leaks, there is no chemical cross-contamination since the composition of the leaking species is the same for both the anolyte and catholyte, only a change in charge state.

[0006] The key to enabling VRBs is an ion-conducting separator membrane. However, current VRBs have round-trip charge / discharge efficiencies of only 75–80% due to detrimental vanadium ion permeation through currently known separators. An ideal membrane would have low vanadium ion permeability, resistance to vanadium fouling, high proton conductivity, good oxidative and acid chemical stability, good mechanical strength, and low cost. Fluoropolymer copolymer cation-exchange membranes based on sulfonated tetrafluoroethylene, also known as perfluorosulfonic acid (PFSA) membranes or under the trade name Nafion®, are the current state-of-the-art VRB separators due to their relatively good chemical stability, long service life, good cyclability, high mechanical strength, and high proton conductivity.

[0007] However, PFSA membranes have many drawbacks, including high cost, vanadium fouling, and especially vanadium ion permeation. Vanadium ion permeation can discharge a charged VRB during idle periods and reduce coulombic efficiency during operation, resulting in self-discharge rates of as much as 6% and inefficiency dependent on the discharge current. Furthermore, vanadium ions have water of hydration, and permeation of vanadium ions through the membrane can alter the water balance of the VRB. Although fouling does not destroy the membrane, it requires periodic removal and cleaning. The relatively high cost of membranes also poses a fundamental challenge to reducing the overall cost of VRBs. Therefore, due to vanadium ion leakage, membrane fouling, and high cost, replacing PFSA membranes with alternative membranes that address these drawbacks is of great interest.

[0008] Bipolar membranes, consisting of a thin cationic coating on an anionic, cation-exchange, proton-conducting membrane, have demonstrated cation selectivity based on the Coulombic repulsion of cations with opposite charges (also known as the Donnan exclusion effect) following protonation in acidic media. The Donnan effect increases exponentially with permanent cation charge, so that multivalent cations are repelled to a greater extent than singly charged protons.

[0009] Ogumi reported the desorption of divalent Fe in acidic media in a bipolar membrane composed of 4-vinylpyridine plasma polymerized on cation-exchanged PFSA (Nafion®). 2+ and monovalent Li + demonstrated transport selectivity between 4-vinylpyridine and 4-vinylpyridine. 4-Vinylpyridine is protonated in an acidic medium, acquiring a positive charge that repels and inhibits the permeation of divalent cations more than monovalent cations. Sata reported that a bipolar membrane consisting of an aliphatic amine and a polyamine, such as polyethyleneimine, chemically grafted onto a PFSA film exhibited permselectivity for monovalent cations in seawater at continuous electrodialysis concentrations.

[0010] This principle has also been demonstrated in VRB membranes. Luo found that membranes composed of polyethyleneimine (PEI) grafted onto Nafion 117 exhibited significantly higher VO2 content than ungrafted Nafion 117. 2+ reported a 20-fold decrease in the transport of β-PHE. The net result was an increase in the Coulombic efficiency from 93.8% to 97.3% when comparing the 5% grafted PEI-Nafion 117® membrane with the unmodified Nafion 117® membrane. However, there was also an undesirable decrease of approximately 30% in the proton conductivity of the PEI-grafted membrane.

[0011] The primary and secondary amines in the bipolar membranes can have a relatively high basicity, e.g., a pKa greater than about 9, and when protonated can have a sufficiently strong Donnan effect to prevent undesirable levels of proton transport. Also, primary and secondary aliphatic amines and polyamines can have a V 5+ They may not be stable to oxidation by ions. Therefore, for the reasons stated above, it would be desirable to provide a bipolar VRB membrane that does not contain primary or secondary amines or polyamines.

[0012] Direct methanol fuel cells use proton-conducting membranes, such as PFSA and other sulfonated polymers. A problem these membranes face is self-discharge caused by methanol crossover through the membrane, which reduces the efficiency of the fuel cell.

[0013] Therefore, there is a need for new materials useful as separators in vanadium redox flow batteries or other applications requiring desirable ion permselectivity and dielectric constant.

[0014] overview The following summary is provided to facilitate understanding of some of the unique and innovative features of the present disclosure and is not intended to be a complete description. A complete understanding of the various aspects of the present disclosure can be obtained by taking the entire specification, claims, drawings, and abstract as a whole.

[0015] One object of the present invention is to provide a bipolar membrane that has the ion permselectivity and dielectric constant desired for VRB with reduced vanadium ion permeability while maintaining or improving proton conductivity. The bipolar membrane is optionally nonporous. Another object is to provide a bipolar membrane that has greater oxidative stability than monopolar membranes containing primary or secondary acyclic aliphatic amines. Yet another object is to provide a potentially lower-cost, optionally nonporous, composite membrane that includes a low-cost microporous support membrane, the pores of which are filled with a sulfonated polymer. Yet another object is to provide a potentially lower-cost, nonporous composite bipolar membrane that includes a low-cost microporous support membrane, the pores of which are filled with a bipolar composition.

[0016] According to one aspect of the present invention, a bipolar membrane is provided, comprising a sulfonated polymer, optionally a sulfonated polymer film, and a heterocyclic multi-nitrogen-containing molecule (hereinafter also referred to as a heterocyclic multi-nitrogen-containing molecule) chemically bonded to at least one surface of the sulfonated polymer, the heterocyclic multi-nitrogen-containing molecule being composed of two or more nitrogen atoms. After being bonded to the sulfonated polymer, the heterocyclic multi-nitrogen-containing molecule has a pKa of less than about 9.0. Prior to being chemically bonded to the surface of the sulfonated polymer, the heterocyclic nitrogen-containing molecule is optionally a molecule derived from the group consisting of adenine, aminoisoquinoline, aminobenzimidazole, 4-aminopiperidine, and aminoimidazopyridine. Optionally, any combination of the foregoing may also be used.

[0017] According to another aspect of the present invention, there is provided a composite bipolar membrane comprising a microporous support membrane, the pores of which are substantially filled with the bipolar composition described above.

[0018] Another embodiment of the invention is a composite bipolar membrane comprising a microporous support membrane, the pores of which are less than about 10 μm and which is substantially filled with the bipolar composition described above, and optionally, the microporous support film is composed of at least one polymer selected from the group consisting of polyolefins, polytetrafluoroethylene, polysulfones, polyethersulfones, polyesters, polyimides, polyamides, nitrocellulose, and mixed cellulose esters.

[0019] Another aspect of the invention is a non-porous composite bipolar membrane comprising a nonwoven support membrane, the pores of which are greater than about 10 μm and which are substantially filled with the bipolar composition described above, and the microporous support film is optionally composed of at least one polymer selected from the group consisting of polyolefins, polytetrafluoroethylene, polysulfones, polyethersulfones, polyesters, polyimides, polyamides, nitrocellulose, and mixed cellulose esters.

[0020] The present invention further relates to a method for producing the above-mentioned membrane or composite membrane.

[0021] Another aspect of the present invention is a vanadium redox flow battery incorporating the membrane described above.

[0022] In addition to incorporation into VRBs, the membranes or composite membranes provided herein can also be used in other flow batteries and fuel cells, particularly direct methanol fuel cells.

[0023] The embodiments illustrated in the drawings are illustrative and exemplary in nature and are not intended to limit the subject matter defined by the claims. The following detailed description of illustrative embodiments can be understood when read in connection with the following drawings, in which like structure is indicated with like reference numerals: [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram of a membrane according to some embodiments provided within the present application.

[0025] Detailed Description The following description is merely exemplary in nature and is not intended to limit the scope of the invention, its application, or methods of use, which may, of course, vary. The present invention is described with reference to non-limiting definitions and terms contained within this application. These definitions and terms are not intended to serve as limitations on the scope or practice of the invention, but are presented solely for purposes of illustration and description. While a method or composition is described as a sequence of individual steps or using specific materials, it is understood that the steps or materials are interchangeable and therefore the description may include multiple parts or steps arranged in numerous ways, as readily understood by those skilled in the art.

[0026] When an element is referred to as being "on" another element, it is understood that it can be directly on the other element or that there may be intervening elements between them, whereas when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0027] Although terms such as "first," "second," and "third" may be used herein to describe various elements, components, regions, layers, and / or sections, it is understood that these elements, components, regions, layers, and / or sections are not limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from other elements, components, regions, layers, or sections. Thus, a first "element," "component," "region," "layer," or "section" discussed below could be referred to as a second (or other) element, component, region, layer, or section without departing from the teachings herein.

[0028] The terminology used within this application is for the purpose of describing particular embodiments only and is not intended to be limiting. As used within this application, the singular forms "a," "an," "the," and "the" are intended to include the plural, including "at least one," unless the context clearly dictates otherwise. "Or" means "and / or." As used within this application, the term "and / or" includes any and all combinations of one or more of the associated listed items. The terms "comprises" and / or "comprising," as used within this specification, specify the presence of stated features, regions, integers, steps, operations, elements, components, and / or parts, but do not exclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof. The term "or combinations thereof" refers to combinations including at least one of the previously described elements.

[0029] Unless otherwise defined, all terms (including technical and scientific terms) used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the relevant art and in the context of this disclosure, and it is further understood that, unless specifically defined herein, they should not be interpreted in an idealized or overly formal sense.

[0030] Membranes are provided that have modified polymer structures, where the combination of the membrane material and the modifier dramatically improves the membrane's usefulness as a separator between half-cells in electrochemical cells or fuel cells. The provided membranes enhance or substantially consolidate the excellent proton transport capabilities of the underlying polymeric membrane material while reducing undesired ion transport across the membrane. Accordingly, an objective of the present disclosure is to provide membranes comprising heterocyclic multi-nitrogen-containing molecules covalently bonded to at least one surface or active group of a sulfonic acid-containing polymer. Bipolar membranes can be fabricated by any suitable chemical process for attaching, optionally covalently bonding, heterocyclic multi-nitrogen-containing molecules to sulfonic acid-containing polymers. In some embodiments, the heterocyclic multi-nitrogen-containing molecules contain amine or amide functional group substituents at one or more positions on the ring, and thus membranes can be formed using either sulfonamide coupling or an amination process via the formation of an acid-base salt via protonation of the unbonded electron pair in the amine. Thus, in some non-limiting embodiments, the amine reagent or precursor optionally contains a primary or secondary amine moiety for bonding to the sulfonic acid-containing polymer. While the following disclosure primarily relates to membranes for use in vanadium redox cells, it is understood that this is for illustrative purposes only and not limiting. The membranes can be used in other electrochemical cells or fuel cells, such as direct methanol fuel cells.

[0031] In some embodiments, the membrane is useful as a separator in a vanadium redox flow battery. Although vanadium ion permeability is very low in surface-aminated sulfonic acid polymers, it has been found that if the amine is a polymeric primary or secondary amine, such as polyethyleneimine or a polyamidoamine hyperbranched dendrimer, and if the amine has a pKa higher than about 9.0 after binding to the sulfonic acid polymer, the bipolar membrane may have unacceptably low proton permeability. Through extensive research, the inventors have found that if the amine is a heterocyclic multi-nitrogen-containing molecule, optionally a multi-nitrogen-containing heterocyclic amine, and / or has a pKa lower than about 9.0 after binding to the sulfonic acid polymer, both high proton permeability and low vanadium ion permeability can be achieved. Without being bound by any particular theory, it is believed that heterocyclic molecules with a pKa less than about 9.0 attached to sulfonic acid polymers have weaker Donnan repulsion after protonation in the acidic VRB electrolyte than modifier molecules with a pKa greater than about 9.0, thus achieving lower proton permeability while maintaining low vanadium ion rejection. Furthermore, without wishing to be bound by any particular theory, it is believed that replacing sulfonic acid protons on the membrane surface with one or more heterocyclic molecules with a pKa less than about 9.0 may enhance Grothaus proton "hopping" transport from one attached heterocyclic site to the next via a hydrogen bonding / breaking mechanism. Hydrated vanadium ions do not participate in Grothaus transport, likely due to vehicle transport, and therefore their permeation is not enhanced, favoring proton transport over vanadium cation transport.

[0032] Thus, provided is a membrane comprising a base material (e.g., in the form of a film or membrane), wherein the base material is or can include one or more polysulfonic acid polymers, and one or more surfaces of the base material can be coated on one or both sides with heterocyclic multi-nitrogen-containing molecules as modifiers. A schematic diagram of an exemplary membrane is shown in FIG. 1. As depicted, the base material 2 is coated and contacted or bonded with a modifier 4, exposing the heterocyclic multi-nitrogen inclusions on the surface of the base material. The heterocyclic multi-nitrogen-containing molecules optionally form a film layer on the surface, partially or completely penetrate the surface of the base material, or a combination thereof. The heterocyclic multi-nitrogen-containing molecular layer is optionally on the base material, or optionally directly on the base material. The heterocyclic multi-nitrogen-containing molecular layer is optionally substantially continuous or discontinuous on the surface of the base material. The reaction of the heterocyclic multi-nitrogen-containing molecule with the sulfonic acid polymer results in a certain degree of substitution of the heterocyclic amine for the sulfonic acid protons. The degree of substitution of the heterocyclic molecule for the protons can be 0.01% to 100%, or any value therebetween, optionally 0.1% to 80%, optionally 10% to 80%, or optionally 10% to 50%.

[0033] The membrane comprises one or more heterocyclic multi-nitrogen-containing molecules covalently, ionic, or otherwise bonded to a polysulfonic acid. The heterocyclic multi-nitrogen-containing molecule contains carbon and at least two nitrogen atoms in a ring structure. The heteroatom is optionally any heteroatom that provides basicity to the heterocycle. Illustrative examples of heteroatoms include nitrogen and phosphorus. Other suitable heteroatoms can also be included in the ring structure in some embodiments. The heterocyclic molecule contains at least one heterocyclic structure. Optionally, the modifier is an acyclic molecule having at least one phosphorus substituent and optionally having a pKa of 9.0 or less after attachment to the polysulfonic acid. In some embodiments, multiple rings, optionally multiple heterocycles, are included within the optionally multiple nitrogen-containing heterocyclic molecule, although it is not necessary to have each ring optionally contain one or more heteroatoms. In some embodiments, 1, 2, 3, 4, 5, or more heterocyclic or non-heterocyclic rings can be included within a multi-nitrogen-containing heterocyclic molecule. Optionally, the multi-nitrogen-containing heterocyclic molecule is not a polymer.

[0034] The provided membranes optionally have a plurality of nitrogen-containing heterocyclic molecules that have a pKa of 9.0 or less after attachment to the sulfonic acid polymer. Optionally, the pKa is 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, or 3.0, or less. In some embodiments, the pKa is 3.0 to 9.0, or any value or range therebetween, optionally 6.0 to 8.0. In some embodiments, the membranes do not include a modifier on the sulfonic acid-containing polymer and have a pKa of greater than 9.0 after attachment to the polymer.

[0035] The resulting membrane is optionally non-porous. A non-porous membrane has a Gurley air permeability of 86400 sec / 10 cc 0.20 in 2 In some embodiments, the membrane has a Gurley air permeability of 3600 sec / 10 cc 0.20 in 2 Above, 40000 seconds / 10cc 0.20in2 The above applies.

[0036] The provided membranes have a proton resistivity that is comparable to or reduced by the heterocyclic molecular modifier bonded to the polymer compared to polymer systems that do not contain the modifier. In some embodiments, the proton resistivity is 20 ohm cm. 2 Below, arbitrarily 1 ohm cm 2 In some embodiments, the proton resistivity is between 0.1 and 0.5 ohm cm 2 , optionally 0.2~0.4 ohm-cm 2 is.

[0037] The provided membranes optionally have reduced or substantially equivalent vanadium ion transport relative to membranes not modified with a heterocyclic molecular modifier. In some embodiments, the vanadium ion transport is 1.1×10 in 1.0 M vanadyl sulfate / 3 M sulfuric acid. -4 moles / day cm 2 The following is an arbitrary solution of 1.0 × 10 -5 moles / day cm 2 The following is the result.

[0038] The inventors have discovered that among heterocyclic, multi-nitrogen-containing amines that meet or provide the above-mentioned properties, some have much higher proton / vanadium ion permselectivities than others. In particular, bipolar membranes prepared by the direct reaction of the protonated form of perfluorosulfonic acid (PFSA) (e.g., Nafion®) with aqueous solutions of adenine, aminoisoquinoline, aminobenzimidazole, 4-aminopiperidine, or aminoimidazopyridine have demonstrated high vanadium ion rejection and, in the case of adenine and aminoimidazopyridine, desirable proton conductivity. The above-mentioned combinations of adenine, aminoisoquinoline, aminobenzimidazole, 4-aminopiperidine, and aminoimidazopyridine can also be used as precursors to heterocyclic, multi-nitrogen-containing molecules. In some embodiments, the sulfonic acid polymer is modified exclusively with amine-containing materials that are adenine, aminoisoquinoline, 4-aminopiperidine, aminobenzimidazole, aminoimidazopyridine, and combinations thereof. In some embodiments, the sulfonic acid polymer is modified exclusively with amine-containing molecules that are adenine, aminoimidazopyridine, or combinations thereof.

[0039] Attachment of a heterocyclic molecule containing multiple nitrogen atoms to a sulfonic acid polymer, optionally to one or more surfaces of the sulfonic acid polymer film, can be achieved either by sulfonamide coupling or acid-base salt formation (also referred to hereinafter as amination). These are non-limiting examples of mechanisms for attachment of a heterocyclic molecule to a sulfonic acid polymer. Exemplary attachments include those formed by or through sulfonamides, anhydrides, esters, or combinations thereof. Accordingly, a heterocyclic molecule containing multiple nitrogen atoms optionally includes one or more substituents containing functional groups suitable for attaching to a sulfonic acid polymer. Such substituents illustratively, but not limited to, amines, optionally primary or secondary amines, hydroxyls, or carboxylic acids. In some embodiments, a sulfonic acid polymer film is first modified with sulfonate groups, followed by attachment to one or more heterocyclic molecules bearing various functional groups. For example, the polymer is optionally modified by converting the sulfonate group to an acyl chloride using, for example, PCl or PCl, and then reacting with a substituent containing an acid, amine, or alcohol moiety on the heterocyclic molecule. Other suitable connections between the multiple nitrogen-containing heterocyclic molecule and the polymer are similarly suitable.

[0040] In some embodiments, heterocyclic molecules containing multiple nitrogens can contain substituents containing primary or secondary amines with unpaired nitrogen electrons available for either sulfonamide coupling or acid-base salt formation via protonation with sulfonic acid protons. Sulfonamide coupling can be achieved by several methods, including direct condensation, acid chloride coupling, or carbodiimide coupling. Direct condensation can be used in some embodiments due to its low cost, avoidance of toxic and corrosive reagents, and few reaction steps. Direct condensation consists of a reaction between protons from a sulfonic acid polymer and a solution of a heterocyclic amine. The reaction can result in the formation of sulfonamide couplings and the elimination of water. The reaction can be illustrated as follows: RSO3H+R'NH2 → RSO2NHR'+H2O where R is a sulfonic acid polymer-containing moiety and R' is a heterocyclic amine moiety.

[0041] Acid-base salt formation can also be achieved using conditions similar to those for sulfonamide coupling, resulting in proton transfer from the acid form of the sulfonic acid polymer to the unpaired electron of the heterocyclic amine. The reaction can be depicted as follows: RSO3H+R'NH2→ RSO3 - + NH3R' where R is a sulfonic acid polymer-containing moiety and R' is a heterocyclic amine moiety.

[0042] In both direct condensation and acid-base salt formation, multiple nitrogen-containing heterocyclic molecules are anchored onto sulfonated polymers with amine substituents.

[0043] In both direct condensation and acid-base salt formation, bipolar, multi-nitrogen-containing heterocyclic molecule-sulfonic acid polymer films can also be produced by directly coating a solution of multi-nitrogen-containing heterocyclic molecules onto a sulfonic acid polymer film or by immersing the sulfonic acid polymer film in a bath of a solution containing multi-nitrogen-containing heterocyclic molecules. In some embodiments, one side of the film can be temporarily blocked or masked to limit the attachment of heterocyclic molecules to one side of the film. After the reaction has proceeded to the desired extent, the excess multi-nitrogen-containing heterocyclic molecules can be washed off the sulfonated film.

[0044] The sulfonic acid polymer is optionally in the form of a film or membrane. In such cases, the sulfonic acid polymer film or membrane can be optionally pre-swollen before contacting with the multiple nitrogen-containing heterocyclic molecule, where the pre-swelling can be by immersion in a pure solvent (i.e., without the multiple nitrogen-containing heterocyclic molecule) used to dissolve it prior to reaction with the multiple nitrogen-containing heterocyclic molecule. This can prevent the sulfonic acid polymer from becoming physically distorted when immersed in the solution of the multiple nitrogen-containing heterocyclic molecule.

[0045] The solvent for the heterocyclic molecule for attachment to the sulfonic acid polymer is optionally an alcohol, a ketone, an ester, water, or a mixture thereof. In some embodiments, the solvent is water, optionally only water.

[0046] The sulfonic acid polymer is optionally selected from per(fluorosulfonic acid / polytetrafluoroethylene) copolymer, sulfonated polystyrene, sulfonated trifluoropolystyrene, sulfonated polystyrene-divinylbenzene copolymer, sulfonated styrene-butadiene, sulfonated polyparaphenylene, sulfonated poly(ether ether ketone), sulfonated poly(ether-ketone-ether-ketone-ketone), sulfonated polysulfone, sulfonated poly(ether sulfone), sulfonated The sulfonic acid polymer may be one or more of the group consisting of 2,6-dimethyl-1,4-phenylene oxide, sulfonated poly(phthalazinone ether ketone), sulfonated polyimide, sulfonated polyphosphazene and sulfonated polybenzimidazole, sulfonated polyphenylsulfone, poly(vinylidene fluoride)-graft-poly(styrenesulfonic acid), poly(arylene thioether ketone), poly(arylene thioether ketone ketone), and sulfonated polyfluorenyl ether ketone. In certain embodiments, the sulfonic acid polymer is per(fluorosulfonic acid / polytetrafluoroethylene) copolymer, or known under the tradenames Nafion® or Flemion®.

[0047] In some embodiments, the sulfonic acid polymer film or membrane has a thickness of 5 μm to 500 μm, or any value or range therebetween. Optionally, the sulfonic acid polymer film has a thickness of 15 μm to 200 μm.

[0048] In some embodiments, the sulfonic acid polymer film is laminated to a nonwoven, optionally a porous membrane, optionally providing additional strength to the sulfonic acid polymer film. Optionally, the sulfonic acid polymer is not in the form of a film, but instead is bonded to a nonwoven or porous membrane of various materials. Optionally, the sulfonic acid polymer is bonded to a porous membrane, filling some or all of the pores of the membrane with the sulfonic acid polymer, resulting in a membrane that is substantially non-porous as defined herein.

[0049] If the sulfonic acid polymer is sufficiently swollen in the reaction solvent and sufficient reaction time and temperature are provided, the amination process can proceed to a certain extent below the surface of the sulfonic acid polymer. The degree of substitution of sulfonate protons by the multiple nitrogen-containing heterocyclic molecule is primarily controlled by the concentration of the multiple nitrogen-containing heterocyclic amine in the reaction solvent, the reaction time, the reaction temperature, and the composition of the reaction solvent. In processes using the immersion method, the concentration of the multiple nitrogen-containing heterocyclic amine in the solution can be less than 10%, optionally less than 1% by weight. Optionally, the immersion time is from 1 second to 24 hours, optionally from 10 minutes to 10 hours. Optionally, the reaction temperature is above 0°C and below the boiling point of the solvent at 1.0 atmosphere, optionally above 30°C and below 100°C. The solvent for the multiple nitrogen-containing heterocyclic molecule can include or consist solely of water, alcohols, ketones, esters, amides, cyclic amides, or mixtures thereof. Optionally, the solvent for the multiple nitrogen-containing heterocyclic molecule is water, optionally only water.

[0050] The heterocyclic molecule containing multiple nitrogen atoms is optionally bound to the membrane on one or both sides of the membrane. In some embodiments, the reaction between the heterocyclic molecule containing multiple nitrogen atoms and the polymer can be carried out only on one side of the membrane, and this can be achieved by masking or blocking one side of the membrane with a material that is impermeable to the reaction solution. The material that provides masking or blocking is optionally a polymer sheet or film selected from the group consisting of polyolefin, butyl rubber, silicone rubber, and ethylene-propylene rubber.

[0051] In some embodiments, a nonporous composite membrane is provided comprising a nonwoven or microporous support film, which can be produced by impregnating the nonwoven or porous film with a solution of a sulfonated polymer, drying the solution, heat-treating the sulfonated polymer-impregnated film above the glass transition temperature of the sulfonated polymer, and finally coupling a plurality of nitrogen-containing heterocyclic molecules to the sulfonated polymer on at least one surface of the composite film. As a non-limiting example, a nonporous composite bipolar membrane can be produced by dip-coating or immersing a porous support film in a PFSA solution, such as D520 available from DuPont™ or Nafion® perfluorinated resin solution available from Sigma-Aldrich, drying the film at 60°C to 120°C, heat-treating the film at 80°C to 250°C, and finally coupling one or more nitrogen-containing heterocyclic molecules to one or both sides of the annealed film. The heat treatment temperature is optionally above the glass transition temperature of the sulfonated polymer, creating continuous, nonporous sulfonated polymer film bridges within the pores of the support film. The microporous support film optionally does not melt or flow at the drying or heat treatment temperatures used to produce the composite membrane. The microporous support film can comprise at least one polymer selected from the group consisting of polytetrafluoroethylene, polysulfone, polyethersulfone, polyester, polyimide, polyamide, polyolefin, nitrocellulose, cellulose, mixed cellulose esters, and combinations thereof. The average pore size (cross-sectional dimension) of the microporous support film is optionally 0.01 μm to 1000 μm, or any value or range therebetween, optionally 0.05 μm to 20 μm. The thickness of the support film is optionally 5 to 500 μm, or any value or range therebetween, optionally 15 to 200 μm.

[0052] The membranes provided herein are optionally used in electrochemical cells, fuel cells, or any other purpose where selective permeability is desired. In some embodiments, the membranes are incorporated into an electrochemical cell, such as a vanadium redox cell. The electrochemical cell optionally includes a negative half-cell and a positive half-cell. The negative half-cell includes an anode and an anolyte. The positive half-cell optionally includes a cathode and a catholyte. The membranes provided herein are disposed between the two half-cells to form a barrier between the anolyte and catholyte. The selective permeability of the membrane improves the function and efficiency of the cell by reducing the permeation of vanadium (or other reactants) through the membrane from one half-cell to the other while maintaining or improving ionic conductivity.

[0053] In some embodiments, the membrane is bound with multiple nitrogen-containing heterocyclic molecules on only one side of the membrane, and in such a situation, the side to which the multiple nitrogen-containing heterocyclic molecules are bound is optionally proximal to the negative half-cell of the battery to improve membrane performance.

[0054] In some embodiments, the electrochemical cell is or is part of a vanadium redox cell. Optionally, the anolyte and catholyte contain vanadium ions in various oxidation states. In vanadium oxide cells, the bond between the sulfonic acid polymer and the plurality of nitrogen-containing heterocycles is optionally an amide or amine-acid salt bond, optionally linked by a sulfonamide group.

[0055] In some embodiments, the membranes provided herein are included in a fuel cell. The fuel cell includes an anode, a cathode, and a membrane provided herein separating the anode and the cathode. In some embodiments, the membrane is bound to multiple nitrogen-containing heterocyclic molecules on only one side of the membrane. In such a situation, the side to which the multiple nitrogen-containing heterocyclic molecules are bound is optionally proximal to the anode side of the cell to improve membrane performance.

[0056] In some embodiments, the fuel cell is a direct methanol fuel cell, in which the bond between the sulfonic acid polymer and the plurality of nitrogen-containing heterocycles is optionally an amide or amine-acid salt bond, optionally bonded by a sulfonamide group, and optionally bonded through an acid anhydride or ester bond.

[0057] Various aspects of the present invention are illustrated by the following non-limiting examples, which are illustrative and do not limit any practice of the present invention. [Example]

[0058] experiment Proton resistivity Proton resistivity was measured in a four-probe, through-thickness cell with fixed conductivity, using a 2 M sulfuric acid electrolyte, 1.3 cm 2 The electrode area is measured using platinum electrodes. AC impedance is measured using an EGG Princeton Applied Research Potentiostat / Galvanostat Model 273A using a 10mV signal scanned from 600 kHz to 10 Hz. Bulk resistance is derived from the intersection of the low impedance of the high frequency semicircle on the real impedance axis of the impedance complex plane. The bulk resistance is then subtracted from the resistance of the test fixture without the membrane to obtain the resistance of the membrane. Resistivity is normalized to area and is expressed as area resistance in ohms cm. 2 Report as.

[0059] Vanadium ion transport On one side of the test membrane, 1.0 M vanadyl sulfate (VO 2+ The transport of vanadium ions is measured in a stationary diffusion cell with one side containing 1.0 M MgSO in 3 M sulfuric acid to balance the osmotic pressure, and the other side containing 1.0 M MgSO in 3 M sulfuric acid to balance the osmotic pressure. After a period of time, the concentration of vanadium in the MgSO chamber is measured spectrophotometrically. The leak of vanadium ions is measured by measuring the concentration of vanadium in the 1 cm 2 per day ( / cm 2Report as moles of vanadium (days).

[0060] Ion Exchange Capacity The ion exchange capacity (IEC) of the bipolar membrane is measured by acid-base titration. The IEC provides useful information regarding the number of accessible proton exchange sites in the film. The dried bipolar membrane is immersed in a saturated NaCl solution for 2 hours at 60°C, followed by 24 hours at 30°C to measure the ion exchange capacity of NaCl. + H + and released H + Acid-base titration was performed to determine the milliequivalents (mequiv.) of protons. -1 Measure the IEC by IEC=(H + The amount of the membrane is calculated by the formula: (milliequivalent of the amount of the membrane) / dry mass of the membrane = meq / gram.

[0061] porosity The porosity of the membrane is measured by a Gurley air permeability apparatus, with a Gurley number of 86400 sec / 10 cc 0.20 in 2 Films above this are considered non-porous.

[0062] Example 1 A 0.470 g perfluorosulfonic acid (PFSA) (Nafion® 117) film was blocked on one side with butyl rubber by mechanically attaching a butyl rubber membrane to one side of the film and aminated on only one side of the film. The blocked film was immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film was then immersed in 50 grams of a 0.05% aqueous 5-aminoisoquinoline solution (Alfa Aesar L01223) at 80°C for 3 hours, then rinsed with distilled water. The film had a proton area resistivity of 0.30 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.821 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 2.75 x 10 -5 moles / day cm 2 The transport of vanadyl ions is four times slower than that of unmodified PFSA, and the proton conductivity is comparable.

[0063] Example 2 A 0.470 g perfluorosulfonic acid (PFSA) (Nafion® 117) film was blocked on one side with butyl rubber by mechanically attaching a butyl rubber membrane to one side of the film and aminated on only one side of the film. The blocked film was immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film was then immersed in 50 grams of 0.125% aqueous 5-aminoisoquinoline solution (Alfa Aesar L01223) at 80°C for 3 hours, then rinsed with distilled water. The film had a proton sheet resistivity of 1.0 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.749 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 9.2 × 10 -6 moles / day cm 2 The transport of vanadyl ions is 12 times slower than that of the unmodified PFSA.

[0064] Example 3 A 0.470 g perfluorosulfonic acid (PFSA) (Nafion® 117) film was blocked on one side with butyl rubber by mechanically attaching a butyl rubber membrane to one side of the film and aminated on only one side of the film. The blocked film was immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film was then immersed in 50 grams of a 0.25% aqueous 5-aminoisoquinoline solution (Alfa Aesar L01223) at 80°C for 3 hours, then rinsed with distilled water. The film had a proton area resistivity of 1.3 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.67 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 5.7 × 10 -6 moles / day cm 2 The transport of vanadyl ions is 19 times slower than that of the unmodified PFSA.

[0065] Example 4 A 0.470 g film of perfluorosulfonic acid (PFSA) (Nafion® 117) is blocked with butyl rubber and aminated on only one side of the film. The blocked film is immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film is then immersed in 50 grams of a 0.25% aqueous adenine solution (Aldrich A8626) at 80°C for 2 hours, then rinsed with distilled water. The film has a proton area resistivity of 0.34 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.869 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 1.7 x 10 -5 moles / day cm 2 The transport of vanadyl ions is six times slower than that of unmodified PFSA, and the proton conductivity is comparable.

[0066] Example 5 A 0.470 g film of perfluorosulfonic acid (PFSA) (Nafion® 117) was plugged with butyl rubber and aminated on only one side of the film. The plugged film was immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film was then immersed in 50 grams of a 0.25% aqueous solution of 3-aminoimidazo(1,2)pyridine (Sigma Aldrich 685755) at 80°C for 3 hours, and then rinsed with distilled water. The film had a proton sheet resistivity of 0.30 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.702 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 5.9 x 10 -6 moles / day cm 2 The transport of vanadyl ions is 19 times slower than that of unmodified PFSA, and the proton conductivity is comparable.

[0067] Example 6 A 0.470 g film of perfluorosulfonic acid (PFSA) (Nafion® 117) is blocked with butyl rubber and aminated on only one side of the film. The blocked film is immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film is then immersed in 50 grams of a 0.25% aqueous solution of 2-aminobenzimidazole (Alfa-Aesar L02066) at 80°C for 3 hours, then rinsed with distilled water. The film has a proton area resistivity of 14.3 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.504 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 3.6 x 10 -7 moles / day cm 2 The transport of vanadyl ions is 312 times slower than that of the unmodified PFSA.

[0068] Example 7 A 0.470 g film of perfluorosulfonic acid (PFSA) (Nafion® 117) is plugged with butyl rubber and aminated on only one side of the film. The plugged film is immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film is then immersed in 50 grams of a 0.25% aqueous solution of 4-aminopiperidine (Alfa-Aesar L20127) at 80°C for 3 hours, then rinsed with distilled water. The film has a proton area resistivity of 0.21 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity 0.0 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid 2.3 x 10 -5 moles / day cm 2 The transport of vanadyl ions is eight times slower than that of the unmodified PFSA.

[0069] Example 8 Composite bipolar membrane Thickness 15μm, pore diameter 0.2μm, Gurley air permeability 2.2sec / 100cc 0.20in 2A 1 5 / 16 inch diameter polyester membrane disk (Sterlitech Corp., PET0247100) having a dry mass of 9 mg is immersed in 0.4 grams of a 15% perfluorosulfonic acid polymer solution (Ion Power Inc. EW1100) in a glass beaker for 10 minutes at room temperature. After immersion, excess solution is poured off and the wet membrane is dried at 80°C for 20 minutes. After drying, 1.0 gram of water is added to remove the membrane from the glass surface, and the membrane is then dried again at 80°C for 10 minutes. The dried membrane is heated to 130°C and placed between polytetrafluoroethylene (PTFE) (Teflon®) sheets at a pressure of 1 kilogram / in. 2 The membrane is then immersed in 50 grams of a 0.10% aqueous solution of 3-aminoimidazo(1,2)pyridine at 80°C for 3 hours, and then washed in distilled water. One side of the film is sealed with butyl rubber to amminate only one side of the film. The membrane has a mass of 26 mg, a thickness of 19 μm, and a Gurley air permeability of >86400 sec / 10 cc (0.20 in). 2 , and a proton area resistivity of 0.83 ohm cm in 2M sulfuric acid 2 , and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid: 3.95 × 10 -7 moles / day cm 2 The transport of vanadyl ions is 278 times slower than that of the unmodified PFSA.

[0070] Comparative Example 1 A 0.470 g perfluorosulfonic acid (PFSA) (Nafion® 117) film was aminated on one side only by mechanically attaching a butyl rubber membrane to one side of the film and then immersing the blocked film in 50 grams of distilled water at 80° C. for 2 hours. The film had a proton area resistivity of 0.29 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.849 meq / gram, and vanadium transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 1.1 x 10 -4 moles / day cm 2 It has.

[0071] Comparative Example 2 A 0.470 g perfluorosulfonic acid (PFSA) (Nafion® 117) film was aminated on one side only, capped with butyl rubber by mechanically attaching a butyl rubber membrane to one side of the film. The film was pre-swollen by immersing it in 50 grams of distilled water for 30 minutes at 80°C. The water-swollen film was then immersed in 50 grams of a 0.25% aqueous solution of 1200 MW polyethyleneimine (Polysciences Inc 24313) at 80°C for 3 hours, then rinsed with distilled water. The film had a proton sheet resistivity of 20 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.378 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 1.3 x 10 -6 moles / day cm 2 The transport of vanadyl ions is 87 times slower than that of the unmodified PFSA.

[0072] Comparative Example 3 A 0.470 g perfluorosulfonic acid (PFSA) (Nafion® 117) film was blocked on one side with butyl rubber by mechanically attaching a butyl rubber membrane to one side of the film and aminated on only one side of the film. The blocked film was immersed in 50 grams of distilled water for 30 minutes at 80°C to pre-swell the film. The water-swollen film was then immersed in 50 grams of a 0.25% aqueous solution of polyamidoamine hyperbranched dendrimer polyelectrolyte dendrimer, ethylenediamine core, generation 4.0 (Aldrich 412449) at 80°C for 2 hours, followed by rinsing with distilled water. The film had a proton sheet resistivity of 3.1 ohm cm in 2 M sulfuric acid. 2 , and ion exchange capacity of 0.789 meq / gram, and vanadyl ion transport in 1.0 M vanadyl sulfate / 3 M sulfuric acid of 1.0 x 10 -5 moles / day cm 2 The transport of vanadyl ions is 11 times slower than that of the unmodified PFSA.

[0073] Various modifications of the present disclosure in addition to those shown and described herein will be apparent to those skilled in the art, and such modifications are also intended to fall within the scope of the appended claims.

[0074] All reagents are understood to be available from sources known in the art unless otherwise noted.

[0075] List of various aspects 1. A sulfonated polymer; Heterocyclic molecules, optionally containing multiple nitrogen atoms; wherein said heterocyclic molecule is covalently bonded to said sulfonated polymer. 2. The membrane of embodiment 1, wherein the heterocyclic molecule has a pKa of less than 9.0, optionally between 3.0 and 9.0. 3. The membrane has a Gurley air permeability of 86,400 seconds / 10 cc 0.20 in 2 2. The membrane of embodiment 1, wherein 4. Proton resistivity is 20 ohm cm 2 2. The membrane of embodiment 1, wherein: 5. Vanadium transport was 1.1 x 10 in 1.0 M vanadyl sulfate / 3 M sulfuric acid. -4 moles / day cm 2 2. The membrane of embodiment 1, wherein: 6. The membrane of aspect 1, wherein the membrane has a thickness of 10 to 1000 μm. 7. The membrane of any combination of aspects 1-6, wherein the heterocyclic molecule is selected from the group consisting of adenine, aminoisoquinoline, aminobenzimidazole, aminoimidazopyridine, 4-aminopiperidine, and combinations thereof. 8. The sulfonated polymer is selected from the group consisting of per(fluorosulfonic acid / polytetrafluoroethylene) copolymer, sulfonated polystyrene, sulfonated trifluoropolystyrene, sulfonated polystyrene-divinylbenzene copolymer, sulfonated styrene-butadiene, sulfonated polyparaphenylene, sulfonated poly(ether ether ketone), sulfonated poly(ether-ketone-ether-ketone-ketone), sulfonated polysulfone, sulfonated poly(ether sulfone), and sulfonated 2,6-dimethyl-1,4-phenylene oxide. The membrane of any one of embodiments 1-6, comprising at least one polymer selected from the group consisting of sulfonated polyimides, sulfonated poly(phthalazinone ether ketones), sulfonated polyimides, sulfonated polyphosphazenes, sulfonated polybenzimidazoles, sulfonated polyphenylsulfones, poly(vinylidene fluoride)-graft-poly(styrenesulfonic acid), poly(arylene thioether ketones), poly(arylene thioether ketone ketones), and sulfonated polyfluorenyl ether ketones, and combinations thereof. 9. The membrane of any one of aspects 1 to 6 in any combination, wherein the polymer is in the form of a non-porous film. 10. The membrane of any one of embodiments 1 to 6, wherein the sulfonated polymer is associated with a nonwoven or microporous support film. 11. The membrane of embodiment 10, wherein the sulfonated polymer is contained within a plurality of pores in a nonwoven or microporous support film. 12. The membrane of aspect 10, wherein the support film comprises polytetrafluoroethylene, polysulfone, polyethersulfone, polyester, polyimide, polyamide, polyolefin, nitrocellulose, cellulose, mixed cellulose esters, or a combination thereof. 13. The membrane of embodiment 11, wherein the support film has pores with cross-sectional dimensions of 0.01 to 1000 μm. 14. A combination of aspects 1, 7 and 8. 15. A combination of aspects 2, 7 and 8. 16. A combination of aspects 1, 7, 8 and 9. 17. A combination of aspects 2, 7, 8 and 9. 18. A combination of aspects 1, 7, 8 and 10. 19. A combination of aspects 2, 7, 8 and 10. 20. A sulfonated polymer containing perfluorosulfonic acid; a heterocyclic molecule selected from the group consisting of adenine, aminoisoquinoline, aminobenzimidazole, aminoimidazopyridine, 4-aminopiperidine, and combinations thereof; wherein said heterocyclic molecule is covalently or ionically bonded to said sulfonated polymer. 21. The membrane has a flow rate of 86,400 seconds / 10 cc 0.20 in 2 Embodiment 20, having a larger Gurley air permeability number. 22. Proton resistivity is 20 ohm cm 2 The following is aspect 20. 23. Vanadium transport was 1.1 × 10 in 1.0 M vanadyl sulfate / 3 M sulfuric acid. -4 moles / day cm 2 The following is aspect 20. 24. Any one of aspects 20, 21, 22, and 23, or a combination thereof, wherein the thickness of the membrane is 10 to 1000 μm. 25. A sulfonated polymer containing perfluorosulfonic acid; a heterocyclic molecule selected from the group consisting of adenine, aminoimidazopyridine, and combinations thereof; wherein said heterocyclic molecule is covalently or ionically bonded to said sulfonated polymer. 26. A sulfonated polymer containing perfluorosulfonic acid; a heterocyclic molecule selected from the group consisting of adenine, aminoimidazopyridine, and combinations thereof; wherein said heterocyclic molecules are covalently or ionically bonded to said sulfonated polymer. 27. Any combination of embodiments 1-26, wherein the membrane is in an electrochemical cell or a fuel cell. 28. Any combination of embodiments 1-26, wherein the membrane is in a vanadium redox battery. 29. Any combination of embodiments 1-26, wherein the membrane is in a direct methanol fuel cell.

[0076] References 1. M.Gattrell, J.Park, B.MacDougall, J.Apte, S.McCarthy, and CWWu, “A study of the mechanism of the vanadium 4+ / 5+ redox reaction in acidic solutions,” Journal of the Electrochemical Society (J.Electrochem.Soc.), 2004, vol.151, no1, pp.A123-A130 2. S.Eckroad Vanadium Redox Flow Batteries An In-Depth Analysis 1014836 Technical Update, March 2007, Electric Power Research Institute 3. Zempachi Ogumi, Yoshiharu Uchimoto, Masanori Tsujikawa, Kazuaki Yasuda and Zen-Ichiro Takehara, Modification of Ion Exchange Membrane by Plasma Process. Journal of Membrane Science 54,(1990), 163-74 4. Qingtao Luo, Huaming Zhang, Jian Chen, Peng Qian and Yunfeng Zhai, Modification of Nafion® membrane using interfacial polymerization for vanadium redox flow battery applications. Journal of Membrane Science 311 (2008) 98-103 5. Tongwen Xu, Ion exchange membranes: State of their development and perspective. Journal of Membrane Science 263 (2005) 1-29 6. Toshikatsu Sata, Ryuji Izuo. Modification of transport properties of ion exchange membrane. 7. Morihiro Saito, Naoko Arimura, Kikuko Hayamizu, Tatsuhiro Okada, Mechanisms of Ion and Water Transport in Perfluorosulfonated Ionomer Membranes for Fuel Cells. J.Phys Chem B 2004, 108, 16064-70 8. U.S. Patent No. 4849311 Itoh, et al. July 18, 1989 9. U.S. Patent No. 5,547,551 (US5547551) August 20, 1996

[0077] The patents, publications, and applications mentioned in this specification are indicative of the level of those skilled in the art to which this invention pertains, and are herein incorporated by reference to the same extent as if each individual patent, publication, or application was specifically and individually indicated to be incorporated by reference.

[0078] The foregoing is a description of particular embodiments of the present invention and is not intended to be a limitation on its practice. The following claims, including all equivalents thereof, are intended to define the scope of the present invention.

Claims

[Claim 1] a nonwoven or microporous support film; a sulfonated polymer containing sulfonic acid groups; a heterocyclic molecule containing a primary amine substituent, said heterocyclic molecule being an aminoisoquinoline, adenine, aminoimidazopyridine, aminobenzimidazole, or 4-aminopiperidine; 1. A membrane for use as a separator in an electrochemical cell, comprising: The membrane, wherein a primary amine is covalently or ionically bonded to the sulfonic acid groups of the sulfonated polymer, and the sulfonated polymer is contained within a plurality of pores in a nonwoven or microporous support film.

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