Antioxidant-substituted sulfonated ion exchange membrane

Abstract

The disclosed technology relates to antioxidant-substituted sulfonic acid polymers and ion exchange membranes prepared therefrom. The binding of the antioxidant to the polymer can minimize the antioxidant's interference with ionic conductivity and prevent the antioxidant from leaching into other layers or catalysts.

Description

Technical Field

[0001] Background of the Invention The disclosed technology relates to antioxidant-substituted sulfonic acid polymers and ion exchange membranes prepared therefrom.

Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are promising technologies for enabling the diversification of drive trains for high-load vehicle applications and providing a clean fuel alternative to conventional combustion engines. The lifetime requirements and high demand placed on high-load PEMFCs lead to premature failure of the polymer electrolyte membrane (PEM), an important PEMFC component. Over time, free radical species generated during normal operation of a PEMFC chemically react with the PEM, compromising system performance by reducing mechanical integrity and proton conductivity. Current strategies to address this problem utilize some combination of end-group fluorination of perfluorosulfonic acid (PFSA) polymers and the use of suspended metal antioxidants (Ce or Mn). Unfortunately, unbound metal antioxidants cause an undesirable decrease in proton conductivity and leaching into other layers of the membrane electrode assembly (MEA), exposing the membrane to radical degradation and catalyst poisoning. These same problems can occur in anion exchange membranes.

[0003] There is a need for a polymer electrolyte membrane that can withstand attack by free radical species without the drawbacks associated with free radical scavengers such as simple ionically bound metal antioxidants that may be transported through the membrane.

Summary of the Invention

Means for Solving the Problems

[0004] The disclosed technology solves the problem of polymer electrolyte membrane (PEM) degradation from free radical species by covalently bonding an antioxidant to the PEM, either directly or via a linking group. The bonding of the PEM and the antioxidant also minimizes the antioxidant's interference with ionic conductivity and prevents the antioxidant from leaching into other layers or catalysts.

[0005] Accordingly, the disclosed technology provides a polymer composition comprising a sulfonic acid moiety, wherein the polymer composition comprises 0.2 to 25 mol% of an antioxidant directly or covalently bonded to the polymer via linking groups, relative to the sulfonic acid moiety.

[0006] Also provided are an ion exchange membrane prepared from a polymer composition, as well as a membrane electrode assembly and a fuel cell comprising the ion exchange membrane. [Modes for carrying out the invention]

[0007] Various preferred features and embodiments are described below by non-limiting examples.

[0008] This technology provides an antioxidant-substituted sulfonic acid polymer composition having a certain amount of antioxidant directly or covalently bonded to the sulfonic acid moiety of the polymer via linking groups. Methods for determining the content of the sulfonic acid moiety in the sulfonic acid polymer are well known in the art and include, for example, those based on monomer composition and those based on measurement of ion exchange capacity (IEC).

[0009] Sulfonic acid polymers are widely discussed in the literature and are not particularly limited here. Examples of sulfonic acid polymers include any sulfonate ion exchange polymer, i.e., polymers containing a sulfonic acid moiety. Sulfonic acid polymers may include, but are not limited to, perfluorosulfonic acid polymers, sulfonated poly(benzimidazole) polymers, sulfonated poly(etheretherketone) polymers, sulfonated polyvinyl chloride, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and poly(styrenesulfonate)(block-co)polymers, but the sulfonic acid may be any other sulfonic acid polymer currently known or to be developed in the future.

[0010] Antioxidants that may be covalently bonded directly to or via linking groups to the sulfonic acid portion of a sulfonic acid polymer can be any known antioxidant. Antioxidants are compounds that can inhibit the oxidative attack of aggressive chemical species on ion exchange materials, for example. Under the operating conditions of fuel cells, peroxides and other free radicals may be such aggressive chemical species. Therefore, radical scavengers or hydrogen peroxide decomposition catalysts are examples of suitable antioxidants.

[0011] Examples of radical scavenger antioxidants include, but are not limited to, hindered amines: hydroxylamines; arylamines; poly(arylamines); phenols; polyphenols; butylated hydroxytoluene; phosphites; benzofuranones; salicylic acid; azulenyl nitrones and their derivatives; tocopherols; 5,5-dimethyl-1-pyrroline-N-oxide; cyclic and acyclic nitrones; gold-chitosan nanocomposites; ascorbic acid; heteropoly acids; and molybdenum derivatives such as molybdenum dithiocarbamates, dithiophosphates, molybdenum sulfides, or molybdenum oxides.

[0012] Examples of hydrogen peroxide decomposition catalysts include, but are not limited to, lanthanide series metal cations, and in more specific embodiments, cerium and lanthanum, as well as mixtures thereof.

[0013] One suitable example of an inorganic antioxidant additive is MnO2. Other examples may include tungsten, vanadium, or antimony. Furthermore, one suitable example of an organic antioxidant additive is triphenylphosphine. In addition, organic / inorganic hybrid additives, as well as combinations of the aforementioned examples, are also suitable.

[0014] Other exemplary antioxidant functional groups include, but are not limited to, heteroaromatic groups: sulfides; disulfides; polysulfides; sulfurized olefins; zinc-based; dithiophosphates; dithiocarbamates; dithiophosphates; phosphines; phosphites; hydroquinones; catechols; quinones; flavins; chroman; chromanone; pyridyls; bipyridyls; diphenylamines; phenoxazines; phenothiazines; benzazepines; aminodibenzyls; lignins, lignosulfonates, and salicylates.

[0015] As will be understood by those skilled in the art, some antioxidants possess olefinic properties sufficient to be grafted onto polymer main chains or their side chains. Eugenol; isoeugenol; and N-(4-(phenylamino)phenyl)acrylamide are examples of antioxidants with olefinic properties.

[0016] Antioxidants containing reactive olefins may be directly grafted onto the sulfonic acid polymer with or without the use of protecting groups for the antioxidant moiety. The antioxidant can be grafted onto either the polymer backbone or side chains from the polymer backbone. Several methods, such as ozone or atom transfer radical polymerization (ATRP), may be used to initiate free radicals on the polymer backbone or side chains to graft the antioxidant. Alternatively, this may involve a radical initiator suitable for inducing radical formation on the polymer. Antioxidants containing reactive olefins (e.g., eugenol; isoeugenol; N-(4-(phenylamino)phenyl)acrylamide; etc.) may be reacted with the resulting radical moiety on the sulfonic acid polymer at a total concentration corresponding to a desired amount of antioxidant relative to the sulfonic acid moiety content. Protecting groups may optionally be required to prevent radical quenching by the antioxidant. The protecting groups may be any commonly encountered protecting groups that are readily removed (e.g., t-butyl ether; benzyl; carbonate; carbamate; silyl; etc.).

[0017] When antioxidants cannot be directly grafted onto the polymer backbone or side chains, "linking groups" are needed to crosslink the polymer and the antioxidant. Linking groups function to anchor the antioxidant to the polymer (i.e., the backbone, side chains, or sulfonic acid portion).

[0018] An example of a linking group is an electrophile. Sulfonic acid polymers can be functionalized with a suitable electrophile by radical grafting. The electrophile can be grafted onto either the polymer backbone or the side chains from the polymer backbone. Several methods, such as ozone or atom transfer radical polymerization (ATRP), may be used for grafting to initiate free radicals on the polymer backbone or side chains. Another method may involve a radical initiator suitable for inducing radical formation on the polymer. An electrophilic linking group containing a reactive olefin (e.g., maleic anhydride; acrylate ester; glycidol acrylate; acryloyl chloride; etc.) can be reacted with the resulting radical moiety on the sulfonic acid polymer at a total concentration corresponding to a desired amount of antioxidant relative to the sulfonic acid moiety content. The resulting electrophile-functionalized sulfonic acid polymer can then be further functionalized by adding a desired antioxidant, for example, by a nucleophilic reaction with the linking group.

[0019] Examples of electrophilic reagents include, but are not limited to, carbonyl acrylates such as maleic anhydride, epoxides, glycidol acrylates, alkyl halides, and acryloyl chlorides.

[0020] Conversely, the linking group may contain functional groups other than electrophiles that can bond to the antioxidant moiety. These functional groups may be, but are not limited to, nucleophilic carbon, oxygen, nitrogen, sulfur, or phosphorus atoms. Furthermore, the linking group may be bonded to the polymer at sites where radicals are initiated via functional groups other than olefins. One example is radical coupling with an aminooxyl radical, such as 2,2,6,6-tetramethylpiperidine-1-yl)oxyl or its derivatives.

[0021] Other linking groups include, for example, amines and aryl ethers. Amine and aryl ether linking groups are covalently bonded to the sulfonic acid moiety. Bonding of amine and aryl ether groups is generally achieved by first halogenating the sulfonic acid moiety. The sulfonic acid moiety on the polymer may be converted to a sulfonyl halide by reacting the polymer with a desired halide. Methods for halogenating the sulfonic acid moiety are well known in the art and include, for example, the use of halogenating agents such as SOCl2, POCl3, PCl, triphosgene, cyanuryl chloride, etc. In some examples, such as in the case of perfluorosulfonyl fluoride polymers, the halide may already be present on the sulfonic acid polymer. In either case, the sulfonyl halide moiety can be prepared into an antioxidant-substituted sulfonic acid polymer by one of two very similar methods: 1) reacting the sulfonyl halide moiety with one of the desired linking groups (i.e., amines and / or aryl ethers) to form a sulfonamide or sulfate ester, followed by nucleophilic addition of the sulfonamide / sulfate ester to the desired antioxidant; or 2) reacting a pre-linked amine-antioxidant or aryl ether-antioxidant group with the sulfonyl halide. The pre-linked amine-antioxidant or aryl ether-antioxidant groups may be purchased or prepared. The preparation of such pre-linked groups can be achieved by a simple reaction between the antioxidant functional group and a molecule containing a nucleophile. Examples include alkylation with alkylene oxides or mixtures thereof, such as ethylene oxide or propylene oxide, 2-hydroxyethyl acrylate, or any other electrophilic linking group whose reaction product with the antioxidant molecule and linking group results in a nucleophilic functionalized antioxidant.

[0022] The amine linking group is not particularly limited and may include primary and secondary amines, such as alkylamines and arylamines. For the purposes of this invention, ammonia is considered an amine.

[0023] The aryl ether linking group is not particularly limited and can include, for example, phenyl ether.

[0024] The linking group may be added to a polymer (main chain, side chain, or sulfonic acid moiety depending on the method used) that is already covalently bonded to the antioxidant, or the antioxidant may react on the linking group after the linking group is bonded to the polymer.

[0025] Furthermore, the linking group / antioxidant can be bonded to the sulfonic acid polymer as part of the completed sulfonic acid polymer or at a certain stage in the polymer preparation process. For example, the linking group / antioxidant may be added to a monomer containing a sulfonic acid moiety before the monomer is polymerized into the final polymer.

[0026] The antioxidant-substituted sulfonic acid polymer has an amount of antioxidant covalently bonded to the polymer directly or via a linking group to the sulfonic acid moiety of the polymer. As noted above, covalently bonding to the polymer means bonding to the polymer backbone itself, the side chains of the backbone, or to the sulfonic acid moiety. The reference to "relative to the sulfonic acid moiety" means that an amount of antioxidant is present for every 100 sulfonic acid moieties. In one embodiment, the antioxidant-substituted sulfonic acid polymer can have from about 0.2 to about 25 mol% antioxidant relative to the sulfonic acid moieties on the polymer; this means that for every 100 sulfonic acid moieties in the polymer, there can be from 0.2 to 25 antioxidant groups bonded directly or via a linking group to the polymer (i.e., the polymer backbone, side chain or sulfonic acid moiety). In some embodiments, the antioxidant-substituted sulfonic acid polymer can have from about 0.25 to about 22.5 mol% antioxidant relative to the sulfonic acid moieties covalently bonded to the polymer directly or via a linking group. In some embodiments, the antioxidant-substituted sulfonic acid polymer can have from about 0.3 to about 20 mol% antioxidant relative to the sulfonic acid moieties covalently bonded to the polymer directly or via a linking group. In some embodiments, the antioxidant-substituted sulfonic acid polymer can have from about 0.5 to about 18 mol% antioxidant relative to the sulfonic acid moieties covalently bonded to the polymer directly or via a linking group. In some embodiments, the antioxidant-substituted sulfonic acid polymer can have from about 0.75 to about 15 mol% antioxidant relative to the sulfonic acid moieties covalently bonded to the polymer directly or via a linking group.

[0027] The antioxidant-substituted sulfonic acid polymer can be formed into an ion exchange membrane by methods known in the art, such as casting, spraying, knife coating, extrusion, etc.

[0028] An ion exchange membrane prepared from an antioxidant-substituted sulfonic acid polymer may be included in a fuel cell, along with other components typically included in a fuel cell, such as bipolar plates, anodes and cathodes, and diffusion media.

[0029] The membranes are configured and sized to be suitable for use in, for example, fuel cells, electrolytic cells, electrodialysis machines, solar hydrogen generators, flow batteries, desalination units, sensors, desalination devices, water purifiers, wastewater treatment systems, ion exchangers, or CO2 separation devices, and may contain, for example, any of the antioxidant-substituted sulfonic acid polymers described herein.

[0030] Fuel cells, electrolytic cells, electrodialysis machines, solar hydrogen generators, flow batteries, desalination units, sensors, desalination devices, water purifiers, wastewater treatment systems, ion exchangers, and CO2 separation devices are also provided, and the fuel cells, electrolytic cells, electrodialysis machines, solar hydrogen generators, flow batteries, desalination units, sensors, desalination devices, water purifiers, wastewater treatment systems, ion exchangers, and CO2 separation devices are equipped with an exchange membrane containing an antioxidant-substituted sulfonic acid polymer.

[0031] A typical fuel cell may include an anode and a cathode separated by the aforementioned exchange membrane. The anode portion performs an anodic half-reaction, oxidizing the fuel and releasing electrons into the external circuit, producing oxidation products. The cathode portion performs a cathode half-reaction, reducing the oxidizer that consumes electrons from the external circuit. A gas diffusion layer (GDL) may be present, which serves to uniformly deliver the fuel and oxidizer across the anode and cathode, respectively. Charge neutrality is maintained by the flow of ions from anode to cathode for positive ions and from cathode to anode for negative ions. The exchange membrane is usually selected to be as thin as possible while maintaining the structural integrity and gas impermeability of the membrane.

[0032] While the primary application of antioxidant-substituted sulfonic acid polymers is energy conversion, such as in fuel cell exchange membranes, these exchange membranes can be used for many other purposes, including electrolytic cells (e.g., water / carbon dioxide / ammonia electrolytic cells), electrodialysis machines; ion exchangers; solar hydrogen generators; desalination units (e.g., seawater / brackish water desalination); desalination equipment (e.g., water desalination); water purifiers (e.g., ultrapure water production); wastewater treatment systems; concentration of electrolyte solutions in the fields of food, pharmaceuticals, chemicals, and biotechnology; electrolysis (e.g., chlor-alkali production and H2 / O2 production); energy storage (e.g., supercapacitors, metal-air batteries, and redox flow batteries); sensors (e.g., pH / RH sensors); and other applications where anion-conducting ionomers are advantageous.

[0033] The disclosed technology solves the problem of polymer electrolyte membrane (PEM) degradation from free radical species by covalently bonding an antioxidant to the PEM, either directly or via a linking group. The bonding of the PEM to the antioxidant also minimizes the antioxidant's interference with ionic conductivity and prevents the antioxidant from leaching into other layers or catalysts. Examples [Table 1] * A 5% by weight alcohol-based solution of Nafion® R-1000, as described in U.S. Patent No. 9,868,804. ** Sulfonated pentablock copolymer consisting of tert-butylstyrene-hydrogenated isoprene-sulfonated styrene: styrene-hydrogenated isoprene-tert-butylstyrene block *** As described in U.S. Patent No. 9,868,804 [Examples]

[0034] Example 1 Preparation of 4-hydroxybenzenesulfonyl chloride:

[0035] 5 g of sodium 4-hydroxybenzenesulfonate was mixed with 14.2 mL of thionyl chloride and 0.16 mL of DMF. The mixture was slowly heated to 60°C (gas generation was observed) and held for 4 hours. The reaction mixture was then cooled to 23°C and poured onto ice (exothermic). The mixture was then extracted three times with dichloromethane. The organic extracts were combined, dried over sodium sulfate, and concentrated under reduced pressure to obtain the final product as a yellow oil, which crystallized into a yellow needle-like substance when stored under vacuum.

[0036] Perfluorosulfonamide polymer preparation:

[0037] 5 g of Aquivion® P98-SO2F perfluorosulfonyl fluoride polymer pellets were mixed with 15 mL of NH3 (7 M ammonia) in methanol solution. The reaction vessel was sealed, and the reaction was allowed to proceed at room temperature for 48 hours. IR testing confirmed the conversion of the SO2F group by the disappearance of the indicator IR peak. The solid polymer was recovered and washed with a 3:1 mixture of methanol / DI H2O. The polymer was then added to an autoclave Parr reactor with 62 mL of DMF, and the system was heated to 220°C / 40 psi and stirred for 5 hours to disperse the polymer product. The polymer was then purified by precipitation and recovered as a powder.

[0038] Preparation of N-((4-hydroxyphenyl)sulfonyl)perfluorosulfonamide polymer

[0039] 1 g of perfluorosulfonamide polymer powder was mixed with 20 mL of DMF containing 1 equivalent of NEt3. The mixture was gently heated to disperse the polymer. The mixture was then cooled to room temperature, and 1.97 g of 4-hydroxybenzenesulfonyl chloride, followed by 2.3 g of triethylamine, was added dropwise. The reaction was allowed to proceed for 3 hours, after which the polymer product was precipitated by adding the reaction mixture dropwise to 300 mL of ethyl acetate. The precipitated solid was collected by vacuum filtration, washed with additional ethyl acetate, 0.5 M sulfuric acid, and 1 M KOH, and then dried under vacuum to obtain an off-white / yellowish-brown powder.

[0040] Example 2 N-(4-fluorobenzyl)sulfonamide pentablock copolymer

[0041] Dissolve 1.5 g of Nexar™ MD9150 sulfonated pentablock copolymer (t-butyl-styrene / hydrogenated isoprene / styrene / hydrogenated isoprene / tert-butyl-styrene) in 28 g of anhydrous THF. Add 0.3 g of 4-hydroxybenzylamine and stir the mixture for 30 minutes. Then add 0.295 g of trichlorotriazine (TCT), followed by 0.29 g of triethylamine. Stir the reaction mixture for 24 hours, then isolate the polymer by precipitation.

[0042] Testing of polymer electrolyte membranes can be performed both ex-situ and in-situ in a fuel cell system in operation. Ex-situ testing for performance and durability includes in-plane conductivity, water absorption measurement, swelling, mechanical strength, and Fenton oxidation using a Pt4 probe test cell. In-situ testing is performed in a fuel cell in operation, consisting of at least a polymer electrolyte membrane, electrodes, gas diffusion medium, flow field / bipolar plate, and current collector / end plate. Testing can be performed according to the Department of Energy standard outlined in the PEM single-cell testing procedure and may include polarization curves at various temperature / relative humidity levels, hydrogen crossover, HFR (high frequency resistance), ECSA (electrochemical surface area), CV (cyclic voltammetry), EIS (electrochemical impedance), chemical durability - OCV (open current voltage), and mechanical durability by RH cycle, as well as combined mechanical / chemical durability testing using simultaneous OCV and RH cycles.

[0043] Except in the examples or unless otherwise expressly indicated, all quantities in this description specifying the amount of material, reaction conditions, molecular weight, number of carbon atoms, etc., should be understood to be modified by the word “about.” It should be understood that the upper and lower limits of quantities, ranges, and ratios described herein can be combined independently. Similarly, the ranges and quantities for each element of the present invention can be used together with the ranges or quantities for any of the other elements.

[0044] As used herein, the transitional term “comprising,” which is synonymous with “including,” “contains,” or “characterized by,” is comprehensive or open-ended and does not exclude additional unlisted elements or method steps. However, in each “comprising” statement herein, the term is also intended to include, as alternative embodiments, the phrases “essentially from” and “consisting of,” where “consisting of” excludes any unspecified elements or steps, and “essentially from” allows for the inclusion of additional unlisted elements or steps that do not substantially affect the essential or basic and novel features of the composition or method under consideration.

[0045] A polymer composition comprising a sulfonic acid moiety, wherein the polymer contains, essentially consists of, or comprises an antioxidant in an amount of 0.2 to 25 mol% relative to the sulfonic acid moiety, directly or via linking groups and covalently bonded to the polymer.

[0046] Polymer compositions of the preceding paragraph, comprising, essentially comprising, or consisting of perfluorosulfonic acid polymers or mixtures thereof. Polymer compositions of the preceding paragraph, comprising, essentially comprising, or consisting of sulfonated poly(benzimidazole) polymers or mixtures thereof. Polymer compositions of the preceding paragraph, comprising, essentially comprising, or consisting of sulfonated poly(etheretherketone) polymers or mixtures thereof. Polymer compositions of the preceding paragraph, comprising, essentially comprising, or consisting of poly(styrenesulfonate)(block-co)polymers or mixtures thereof. Polymer compositions of the preceding paragraph, comprising, essentially comprising, or consisting of sulfonated polyvinyl chloride polymers or mixtures thereof. Polymer compositions of the preceding paragraph, comprising, essentially comprising, or consisting of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) polymers or mixtures thereof.

[0047] Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises an amine or aryl ether. A polymer composition of the preceding paragraph in which the amine contains, essentially consists of, or comprises a primary amine or a mixture thereof. A polymer composition of the preceding paragraph in which the amine contains, essentially consists of, or comprises a secondary amine or a mixture thereof. A polymer composition of the preceding paragraph in which the amine contains, essentially consists of, or comprises an alkylamine or a mixture thereof. A polymer composition of the preceding paragraph in which the amine contains, essentially consists of, or comprises an arylamine or a mixture thereof. A polymer composition of the first sentence of this paragraph in which the amine contains, essentially consists of, or comprises ammonia. A polymer composition of the first sentence of this paragraph in which the aryl ether contains, essentially consists of, or comprises a phenyl ether.

[0048] Any polymer composition of the preceding sentence in which the linking group contains, essentially consists of, or consists of an electrophile. A polymer composition of the preceding sentence in which the electrophile contains, consists of, or essentially consists of a carbonyl or a mixture thereof. A polymer composition of the preceding sentence in which the electrophile contains, consists of, or essentially consists of maleic anhydride. A polymer composition of the first sentence of this paragraph in which the electrophile contains, consists of, or essentially consists of an acrylate ester or a mixture thereof. A polymer composition of the first sentence of this paragraph in which the electrophile contains, consists of, or essentially consists of an epoxide or a mixture thereof. A polymer composition of the preceding sentence in which the electrophile contains, consists of, or essentially consists of a glycidol acrylate. A polymer composition of the first sentence of this paragraph in which the electrophile contains, consists of, or essentially consists of an alkyl halide or a mixture thereof. The polymer composition of the preceding sentence, wherein the electrophile contains, consists of, or essentially consists of acryloyl chloride.

[0049] Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises a nucleophilic carbon or a mixture thereof. Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises an oxygen atom. Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises a nitrogen atom. Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises a sulfur atom. Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises a phosphorus atom. Any polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises an aminooxyl radical or a mixture thereof. A polymer composition of the preceding paragraph in which the linking group contains, essentially consists of, or comprises 2,2,6,6-tetramethylpiperidine-1-yl)oxyl or a derivative thereof.

[0050] Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a radical scavenger or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a hindered amine or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a hydroxylamine or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises an arylamine or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a poly(arylamine) or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a phenol or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a polyphenol or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises butylated hydroxytoluene or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises phosphite or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises benzofuranone or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises salicylic acid or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises azlenylnitrone and its derivatives or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises tocopherol or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises 5,5-dimethyl-1-pyrroline-N-oxide or a mixture thereof. Any polymer composition of the preceding sentence, wherein the antioxidant contains, essentially consists of, or comprises a cyclic nitrone or a mixture thereof.A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises a noncyclic nitrone or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises gold-chitosan nanocomposite or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises ascorbic acid. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises a molybdenum-based antioxidant or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises molybdenum dithiocarbamate or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises molybdenum dithiophosphate or a mixture thereof. A polymer composition of any preceding sentence in which the antioxidant contains, essentially consists of, or comprises molybdenum sulfide or a mixture thereof. Any polymer composition of the preceding sentence, wherein the antioxidant contains molybdenum oxide or a mixture thereof, essentially consists of it, or consists of it.

[0051] Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a hydrogen peroxide decomposition catalyst or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a lanthanide series metal cation or a mixture thereof. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a cerium cation. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a lanthanum cation.

[0052] Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises an inorganic antioxidant. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a tungsten-containing antioxidant. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises a vanadium-containing antioxidant. Any polymer composition of the preceding sentence in which the antioxidant contains, essentially consists of, or comprises an antimony-containing antioxidant.

[0053] Any polymer composition of the Preamble comprising, essentially comprising, or comprising a heteroaromatic antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a sulfide antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a disulfide antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a polysulfide antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a sulfide olefin antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a zinc-based antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a dithiophosphate antioxidant. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a dithiocarbamate antioxidant, essentially consists of one or more of one. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a dithiophosphate antioxidant, essentially consists of one or more of one. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a phosphine antioxidant, essentially consists of one or more of one. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a triphenylphosphine, essentially consists of one or more of one. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a phosphite antioxidant, essentially consists of one or more of one. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a hydroquinone antioxidant, essentially consists of one or more of one. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a catechol antioxidant, essentially consists of one or more of one. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a quinone antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a flavin antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a chromane antioxidant.Any polymer composition of the Preamble comprising, essentially comprising, or comprising a chromanone antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a pyridyl antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a bipyridyl antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a diphenylamine antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a phenoxazine antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a phenothiazine antioxidant. Any polymer composition of the Preamble comprising, essentially comprising, or comprising a benzazepine antioxidant. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises an aminodibenkyl antioxidant, essentially consists of one or more aminodibenkyl antioxidants. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a lignin antioxidant, essentially consists of one or more lignin antioxidants. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a lignosulfonate antioxidant, essentially consists of one or more lignosulfonate antioxidants. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises a salicylate antioxidant, essentially consists of one or more salicylate antioxidants. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises eugenol, essentially consists of one or more eugenol. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises isoeugenol, essentially consists of one or more isoeugenol. Any polymer composition of the preceding paragraph, wherein the antioxidant comprises N-(4-(phenylamino)phenyl)acrylamide, essentially consists of one or more N-(4-(phenylamino)phenyl)acrylamide.

[0054] An ion exchange membrane comprising, consisting of, or essentially comprising any of the polymer compositions described in the preceding paragraph.

[0055] A process for preparing an antioxidant-substituted sulfonic acid polymer composition, comprising converting a sulfonic acid moiety to a sulfonyl halide, and subsequently covalently bonding the sulfonyl halide to one of the following: i) A linking group selected from the group consisting of amines and aryl ethers, followed by substitution of the linking group with an antioxidant, or ii) A linking group substituted with an antioxidant selected from the group consisting of substituted amines and substituted aryl ethers.

[0056] A process for preparing an antioxidant-substituted sulfonyl halide polymer composition, comprising covalently bonding a sulfonyl halide portion to one of the following: i) A linking group selected from the group consisting of amines and aryl ethers, followed by substitution of the linking group with an antioxidant, or ii) A linking group substituted with an antioxidant selected from the group consisting of substituted amines and substituted aryl ethers.

[0057] A process for preparing an antioxidant-substituted sulfonic acid polymer composition, comprising grafting a sulfonic acid-containing polymer with an electrophile to prepare a polymer having an electrophilic linking group, and subsequently incorporating a nucleophilic antioxidant into the electrophile.

[0058] A process for preparing an antioxidant-substituted sulfonic acid polymer composition, comprising grafting a sulfonic acid-containing polymer with an olefin-containing antioxidant to prepare an antioxidant-grafted sulfonic acid polymer.

[0059] Fuel cells equipped with the following: i) Bipolar plate, ii) Anode, iii) Cathode, iv) Dispersion medium, and v) The ion exchange membrane described in paragraph

[0046] .

[0060] For illustrative purposes, certain representative embodiments and details have been provided, but it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention. In this regard, the scope of the invention should be limited only by the following claims. The present invention provides, for example, the following items: (Item 1) A polymer composition comprising a sulfonic acid moiety, wherein the polymer contains 0.2 to 25 mol% of an antioxidant directly or covalently bonded to the polymer via linking groups, relative to the sulfonic acid moiety. (Item 2) The polymer composition according to item 1, wherein the polymer composition comprises a perfluorosulfonic acid polymer. (Item 3) The polymer composition according to item 1, wherein the polymer composition comprises a sulfonated poly(benzimidazole) polymer. (Item 4) The polymer composition according to item 1, wherein the polymer composition comprises a sulfonated poly(etheretherketone) polymer. (Item 5) The polymer composition according to item 1, wherein the polymer composition comprises a poly(styrene sulfonate) polymer. (Item 6) The polymer composition according to item 1, wherein the polymer composition comprises sulfonated polyvinyl chloride. (Item 7) The polymer composition according to item 1, wherein the polymer composition comprises a 2-acrylamido-2-methylpropanesulfonic acid (AMPS) polymer. (Item 8) The polymer composition according to any one of the preceding items, wherein the linking group contains, essentially consists of, or comprises an amine or an aryl ether. (Item 9) The polymer composition according to item 8, wherein the amine comprises ammonia. (Item 10) The polymer composition according to item 8, wherein the aryl ether comprises a phenyl ether. (Item 11) The polymer composition according to any one of the preceding items, wherein the linking group contains, essentially consists of, or comprises an electrophile. (Item 12) The polymer composition according to item 11, wherein the electrophile reagent contains a carboxyl-containing olefin. (Item 13) The polymer composition according to item 11, wherein the electrophile reagent comprises a dicarboxylic acid. (Item 14) The polymer composition according to item 11, wherein the electrophile reagent contains maleic acid. (Item 15) An ion exchange membrane comprising the polymer composition described in any one of the preceding items. (Item 16) It is a fuel cell, (a) Bipolar plate, (b) Anode, (c) Cathode, (d) Dispersion medium, and (e) A fuel cell comprising an ion exchange membrane as described in item 15.

Claims

1. A fuel cell, (a) Bipolar plate, (b) Anode, (c) Cathode, (d) Diffusion medium, and (e) An ion exchange membrane comprising a polymer composition comprising a sulfonic acid moiety, wherein the polymer composition comprises an antioxidant in an amount of 0.2 to 25 mol% relative to the sulfonic acid moiety, which is covalently bonded to the sulfonic acid moiety of the polymer composition, either directly or via linking groups. A fuel cell equipped with a fuel cell.

2. The fuel cell according to claim 1, wherein the polymer composition comprises a perfluorosulfonic acid polymer.

3. The fuel cell according to claim 1, wherein the polymer composition comprises a sulfonated poly(benzimidazole) polymer.

4. The fuel cell according to claim 1, wherein the polymer composition comprises a sulfonated poly(etheretherketone) polymer.

5. The fuel cell according to claim 1, wherein the polymer composition comprises a poly(styrene sulfonate) polymer.

6. The fuel cell according to claim 1, wherein the polymer composition comprises sulfonated polyvinyl chloride.

7. The fuel cell according to claim 1, wherein the polymer composition comprises a 2-acrylamido-2-methylpropanesulfonic acid (AMPS) polymer.

8. The fuel cell according to any one of claims 1 to 7, wherein the linking group contains or consists of an amine or an aryl ether.

9. The fuel cell according to claim 8, wherein the amine contains ammonia.

10. The fuel cell according to claim 8, wherein the aryl ether comprises a phenyl ether.

11. The fuel cell according to any one of claims 1 to 10, wherein the linking group contains or consists of an electrophile.

12. The fuel cell according to claim 11, wherein the electrophile reagent comprises a carboxyl-containing olefin.

13. The fuel cell according to claim 11, wherein the electrophile reagent comprises a dicarboxylic acid.

14. The fuel cell according to claim 11, wherein the electrophile reagent contains maleic acid.

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