Durable ion exchange membranes with additives

Abstract

Described herein are durable polymer electrolyte membranes comprising an additive blend with at least two components, wherein at least one of the at least two components is an organic additive. Also described herein are methods for manufacturing said polymer electrolyte membranes. Also described herein are durable polymer electrolyte membrane-electrode assemblies comprising at least one electrode, at least one inorganic additive in or on the at least one electrode and a polymer electrolyte membrane with at least one an organic additive.

Description

DURABLE ION EXCHANGE MEMBRANES WITH ADDITIVES FIELD OF THE INVENTION

[0001] This disclosure relates to polymer electrolyte membranes, and, in particular, toa composite membrane having an additive blend with at least one organic additive and presenting a surprisingly high durability compared with analogous membranes withoutthe additive blend. BACKGROUND OF THE INVENTION

[0002] Polymer Electrolyte Membranes (PEMs) are critical components in many applications, such as fuel cells, electrolyzers, flow batteries, and humidifiers. Forenvironmental, practical, and cost reasons, is desirable to produce PEMs capable ofwithstanding many use cycles in electrochemical devices without suffering from chemical degradation or decrease in performance. This is particularly true for applications where membranes are thin (e.g., less than 15 µm).

[0003] Low chemical stability of membrane-electrode assemblies (MEAs) remains amajor obstacle to commercialization of polymer electrolyte membrane fuel cells (PEMFCs) for fuel cell electric vehicles (FCEVs).

[0004] As discussed in Oh, K-H.; et al. J. Alloys and Compounds 2022, 928, 167227,and Kwon, T.; et al. Materials Today 2022, 58, 135, the chemical stability of PEMs isa key property because the PEM plays a crucial role such as proton conductor and reactant barrier between the two electrodes in electrochemical applications. In fuel cell and water electrolysis applications, the PEM undergoes chemical degradation by thehydroxyl radicals or hydrogen peroxides generated from the gas crossover, and those reactive chemicals can attack a weak point of the polymer backbone. To address thisproblem cerium oxide nanoparticles and cerium ions have been introduced in PEMs toprotect the membrane from chemical degradation. However, the PEMs suffer from performance degradation as a result of reduced proton transport, thermodynamic losses, and oxygen diffusion when cerium ions migrate toward electrodes. In addition,Ce3+, while initially exchanged with proton on the ionomer –SO3H groups, can migrateto inactive areas, further decreasing the timeframe of oxidative stability provided by the additive.

[0005] A number of organic additives have been applied to PEMFC applications using solution casting methods, and membrane thicknesses ranging from 30 to 55µm. Thewater solubility of organic additives is an issue because of diffusion and leaching,similar to the use of cerium ion. The reversibility of organic antioxidants is alsochallenging, the limited duration of stability reported indicates that the organic antioxidants reported do not regenerate well under fuel cell operating conditions. As also described in Agarwal, T.; et al. Adv. Funct. Mater. 2023, 2308856, the organic additive work reported to date has been limited, and many did not use the DOE- recommended open-circuit voltage (OCV) hold test protocol. There remains an urgentneed for further protection from chemical degradation of PEMs for electrochemicalapplications in order to promote widescale adoption of PEMFCs as a clean source of energy. SUMMARY OF THE INVENTION

[0006] It is well known in biological systems that mixtures of antioxidants can produce three outcomes as a result of interactions between antioxidants: synergistic,antagonistic, and additive effects (for example, see Tomczyk, M.O. Phytochem. Rev. 2020, 19, 63-103). Synergistic effects result in a higher degree of antioxidant activitythan the sum of each antioxidant acting separately; antagonistic effects result in antioxidant activity less than the sum of each antioxidant acting separately, and additive effects result in antioxidant activity that is the sum of each antioxidant acting separately. The operating environment of a fuel cell membrane is obviously muchdifferent than those of living organisms, but the inventors have discovered thatcombinations of organic or inorganic and organic additives dispersed in PEMs alsointeract to improve the durability of the membranes significantly by both additive and synergistic effects, without affecting the performance of the PEM. In particular, theinventors have discovered that synergistic additive blends comprising at least two additives wherein at least one of the two additives is an organic additive into a PEM, can significantly improve the chemical durability of the PEM. The inventors have alsodiscovered that the durability of MEAs is significantly improved when the MEA comprises at least two additives wherein at least one of the two additives is an organicadditive. In MEAs the at least two additives may be present in the PEM or alternatively the at least one organic additive may be present in a PEM of the MEA and at least one inorganic additive may be present in or on an electrode of the MEA.

[0007] According to a first aspect there is provided a PEM comprising an ion exchangematerial (IEM) and an additive blend. The additive blend may comprise at least twoadditives. At least one of the at least two additives may be an organic additive selected from a peroxide decomposition catalyst, a radical scavenger, a free radical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer.

[0008] The PEM may comprise one or more layers of porous reinforcement. The PEMmay comprise two or more layers of porous reinforcement and the material of at least two of the layers of porous reinforcement may be the same or it may be different. The reinforcement may comprise a polymeric material. The reinforcement may comprise a porous reinforcement. The reinforcement may be a woven reinforcement. The reinforcement may comprise a nanofiber mat.

[0009] Within the context of this disclosure, the total content of the porous reinforcement within the PEM may be presented in terms of total mass of the porousreinforcement (e.g., porous polymer reinforcement) in the composite membrane perthe total area of the composite membrane (g / m2). The PEM may comprise one or moretypes of porous polymer reinforcement. For example, the PEM may comprise a singletype of porous polymer reinforcement (e.g., ePTFE membrane). The porous polymerreinforcement may be present in a single reinforcing layer or in two or more reinforcing layers. The PEM may comprise at least two reinforcing layers, and each reinforcinglayer may comprise a different type of porous polymeric material (e.g., fluorinated,partially fluorinated, perfluorinated polymers and non-fluorinated polymers). The PEM may comprise at least two reinforcing layers and a first of the at least two reinforcing layers may comprise a single type of porous reinforcement (e.g., ePTFE membrane)and a second of the at least two reinforcing layers may comprise a single type of porous reinforcement different from the porous reinforcement of the first of the at least tworeinforcing layers (e.g. non-fluorinated polymer, such as hydrocarbon polymer).

[0010] In embodiments in which the PEM has two or more reinforcing layers, acomposition of all reinforcing layers may be the same. Alternatively, a composition of at least two of the reinforcing layers may be different.

[0011] The total content of the porous reinforcement in the PEM may be at least about5 vol% based upon the total volume of the PEM. The porous reinforcement may bepresent in an amount from about 5 vol% to about 65 vol% based on the total volumeof the PEM (in a single layer or spread across two or more layers of porousreinforcement). The porous reinforcement may be present in an amount from about 5vol % to about 60 vol %, or from about 5 vol% to about 50 vol%, or from about 5 vol%to about 40 vol%, or 5 vol% to 30 vol %, or 10 vol % to 30 vol %, or 10 vol % to 40 vol%, or 5 vol % to 10 vol %, or 10 vol % to 25 vol %, or 15 vol % to 30 vol %, or 20 vol% to 40 vol %, or 5 vol % to 7 vol %, or 10 vol % to 15 vol %, or from about 50 vol %to about 65 vol % based on the total volume of the PEM (in a single layer or spreadacross two or more layers of porous reinforcement).

[0012] Embodiments have been described using volume-based values instead of weight-based values in order to provide a way for meaningful comparison between composite membranes comprising ionomers and porous reinforcements of different densities. According to the scientific literature, volume-based normalization is moreappropriate for the description of transport phenomena, like proton conduction, forPEM used in fuel cells (for example, see: Kim, Y. S.; Pivovar, B. S. Annu. Rev. Chem.Biomol. Eng. 2010, 1, 123–148). More specifically, weight-based measurements maybe used to make comparisons between polymer electrolytes, but they have significant limitations when correlated to proton conductivity. These limitations arise in part because different polymers can have significantly different densities and because conduction occurs over length scales more appropriately represented by volume- based measurements rather than weight-based measurements.

[0013] The porous reinforcement may be a polymeric reinforcement comprising at least one of: a perfluorinated polymer, a partially fluorinated polymer, or a non-fluorinated polymer. The polymeric reinforcement may comprise a fluorinated orpartially fluorinated polymer selected from polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (ETFE), expanded polytetrafluoroethylene (ePTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (ePVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eETFE) and mixtures thereof. In some embodiments, the fluorinated or partially fluorinated polymer is expandedpolytetrafluoroethylene (ePTFE).

[0014] The polymeric reinforcement may comprise a non-fluorinated polymer, e.g. a polymeric hydrocarbon based porous reinforcement. The polymeric hydrocarbon based porous reinforcement may comprise a polyolefin. The polymeric hydrocarbonbased porous reinforcement may comprise one or more polymers selected from the list comprising: Polyethylene (PE), Polypropylene (PP), Polysulfone, Polyethersullfone(PES), Polystyrene (PS), Polycarbonate (PC), polybutyl terephthalate (PBT), and mixtures thereof.

[0015] The non-fluorinated polymer may comprise one or more polymers selected from the list comprising Poly ether ether ketone (PEEK), Poly ether ketone (PEK), Poly ether ketone ketone(PEKK), Poly aryl ether ketone (PAEK) and other variants as well as sulfonated versions thereof, Polyimide (PI), Polyamide (PA), a Liquid crystalpolymer (LCP), a Polyphenylene (PP) and / or a derivative thereof (e.g., Polyphenylene sulfide (PPS)), Polyetherimide (PEI), Polyamideimide (PAI), Polyethylene terephthalate (PET), Polybenzimidazole (PBI), and mixtures thereof.

[0016] The polymeric reinforcement may comprise a non-fluorinated polymer selected from the list comprising Polyethylene (PE), Polypropylene (PP), Polysulfone, Polyethersullfone (PES), Polystyrene (PS), Polycarbonate (PC), polybutyl terephthalate (PBT), Poly ether ether ketone (PEEK), Poly ether ketone (PEK), Poly ether ketone ketone(PEKK), Poly aryl ether ketone (PAEK) and other variants as well as sulfonated versions thereof, Polyimide (PI), Polyamide (PA), a Liquid crystal polymer (LCP), a Polyphenylene (PP) and / or a derivative thereof (e.g., Polyphenylene sulfide (PPS)), Polyetherimide (PEI), Polyamideimide (PAI), Polyethylene terephthalate (PET), Polybenzimidazole (PBI), and mixtures thereof.

[0017] The reinforcement may comprise at least two porous reinforcement layers (e.g. porous polymeric reinforcement layers). The porous reinforcement layers may be thesame or they may be different. At least two of the porous reinforcement layers may bein direct contact. In some embodiments, at least two of the porous reinforcement layersmay not be in direct contact.

[0018] The IEM may be at least partially embedded within the at least one layer ofporous reinforcement rendering the at least one layer of porous reinforcement occlusive.

[0019] The IEM may be fully embedded within the porous reinforcement. The IEM mayinclude more than one IEM in the form of a mixture of IEMs. In other embodiments, theIEM may include more than one layer of IEM. The layers of IEM may be formed of thesame IEM. Alternatively, the layers of IEM may be formed of different IEMs. At leastone of the layers of IEM may comprise a mixture of IEMs. The IEM may include anionomer. The at least one ionomer may include a proton conducting polymer. Theproton conducting polymer may include perfluorosulfonic acid.

[0020] The porous reinforcement may have a first surface and a second surface. TheIEM may form a layer on the first surface, on the second surface, or both on the firstsurface and the second surface. The IEM may be partially embedded within the porousreinforcement leaving a non-occlusive portion of the porous reinforcement closest to the first surface, second surface or both. The non-occlusive portion may be free of anyof the IEM. The non-occlusive portion may include a coating of IEM to an internalsurface of the porous reinforcement.

[0021] The IEM may have low equivalent weight (i.e. high acid content).The IEM mayhave an equivalent volume equal to or less than 460 cc / mole eq (or an equivalent weight equal to or less than 920 g / mol for an IEM with density of 2.0 g / cc), optionallywherein the IEM has an equivalent volume of about 350 cc / mol eq (or an equivalentweight of 700 g / mol an IEM with density of 2.0 g / cc).

[0022] The total average equivalent volume of IEM may be from about 240 cc / mol eqto about 1200 cc / mol eq. The average equivalent volume of the IEM may be from about240 cc / mole eq to about 720 cc / mole eq. The average equivalent volume of the IEM may be from about 350 cc / mole eq to about 475 cc / mole eq. The total average equivalent volume of IEM may comprise the total volume of IEM distributed betweenall the IEM layers of the composite membrane.

[0023] The additive blend may comprise at least one of: a synthetic antioxidant, a natural non-enzymatic antioxidant, and a radical scavenger. The synthetic antioxidantmay comprise a phenolic antioxidant (e.g. BHA, BHT, TBHQ).

[0024] The synthetic antioxidant may comprise a nano-antioxidant (e.g. an oxide, ametal nanoparticle, an antioxidant functionalised nanoparticle).

[0025] The organic additive may comprise a nonenzymatic antioxidant selected from: a quinone, a hydroquinone, a quinone-hydroquinone, a polyphenol selected from a flavonoid, a stilbene, and a phenolic acid; a coumarin, a chromone, an alkaloid, a catecholamine, a vitamin, a carotenoid, a phosphonic acid, a carboxylic acid, a phenolic and heterocyclic derivative radical scavenger, derivatives or mixtures thereof.

[0026] The organic additive may be selected from alizarin, purpurin, quinizarin, anthrarufin, rufigallol, thymol blue, alizairin-3-methyliminodiacetic acid, quercetin, myricetin, morin, kaempferol, baicalein, naringenin, naringenin chalcone, (E)-3-(e,4- dihydroxyphenyl)-1-(2,3,4-trihydroxyphenyl)prop-2-ene-1-one (a flavonoid), genistein,luteolin, eriodictyol, hesperetin, hesperidin, quercetagetin, catechin, epicatechin, epigallocatechin, epigallocatechin gallate, taxifolin, caffeic acid, sinapic acid, ferulicacid, rosmarinic acid, coumaric acid, caftaric acid, gallic acid, tannic acid, propylgallate, ellagic acid, 2,3,4-trihydroxybenzophenone, esculetin, 7,8-dihydroxy-4- methylcourmarin, daphnetin, 6,7-dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, 7,8- dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, curcumin, bis-demethylcurcumin, dopamine, usnic acid, hydroxylated chromone-3-carboxylic acid, resveratrol, polyhydroxystilbenes such as (E) 2',5',3,4-tetrahydroxystilbene and (E) 3',4',3,4- tetrahydroxystilbene, avenanthramide derivatives, terephthalic acid, syringic acid, 2,6-dimethoxy-1,4-benzoquinone, tert-butylhydroquinone, derivatives thereof and / ormixtures thereof. The organic additive may be selected from alizarin, purpurin, caffeic acid, propyl gallate, quercetin, catechin, esculetin, resveratrol, curcumin,epigallocatechin gallate, epicatechin, derivatives thereof, hesperetin, and mixtures orderivatives thereof.

[0027] A derivative of organic additives described herein may comprise a product ofreaction of one or more components of the additive blend. For example, a derivative of the organic additive may comprise an oxidation product, a hydrolysis product, an adduct, a covalently-bound complex of at least two additives, a dimer, an oligomer, a polymer or a product of reaction between one or more components of the additive blend. The product of reaction may a compound comprising at least two additives hydrogen bound, covalently modified, in a supermolecular complex, forming a polymer,a dimer, a trimer, an oligomer. These products of reaction may be formed throughradical coupling to a ring of the additive, as a result of oxidative addition to a doublebond a flavonoid, in a Friedel craft oxidation reaction, and the like.

[0028] Without wishing to be bound by theory, the component or components of the additive blend may react at the conditions for processing the polymer electrolyte membrane. For example, since the pH of the ion exchange material is acidic, dissolving or suspending the component or components of the additive blend in it may cause oneor more additives to oxidise or react with each other and may lead to the formation of oxidation products, covalently-bound reaction products, dimers, oligomers and / or polymers. The processing temperatures employed in the manufacture of polymer electrolyte membranes may also contribute to this effect. Derivatives of the additiveblend (e.g. products of reaction, covalently-bound compounds, dimers, oligomers, polymers, salts, ionic forms, and the like) are also encompassed by the additive blend. For example, when quercetin and / or catechin are present in the additive blend of the polymer electrolyte membrane and, after the membrane has been manufactured, an nuclear magnetic resonance (NMR) test or mass spectrum of the components of the membrane is taken, the characteristic signals of chatechin and / or quercetin may notbe observed and instead peaks characteristic of oxidation products and / or oligomers may be found.

[0029] These derivatives of the additives also comprise antioxidant or radical scavenger function of the additive blend and lead to the improvements of stability as discussed herein. In some instances, the antioxidant or radical scavenger capability of the derivatives is greater than that of the starting materials. In polymer electrolyte membranes containing the blends discussed herein, the antioxidant or antioxidants present in the blend may be in the original form in which they are introduced to the membrane, or may be present as a derivative (as discussed above) formed during themanufacture of the composite membrane.

[0030] The additive blend may comprise at least one inorganic additive. The at leastone inorganic additive may comprise a metal, its oxide or its salt, or mixtures thereof.

[0031] The at least one inorganic additive may comprise a metal selected from Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form, or their oxides, or their salts, or mixtures thereof. The inorganic additive may comprise cerium oxide (ceria). A salt of the at least one inorganic additivemay comprise an anion selected from nitrate, acetate, acetylacetonate, carbonate, orsulfate. A salt of the at least one inorganic additive may not comprise a halide anion.

[0032] The inorganic additive may comprise nanoparticles, nanotubes, nanorods, or mixtures thereof. The at least one inorganic additive may comprise metal nanoparticles. The metal nanoparticles may be selected from: Au (gold) nanoparticles, Pd (palladium) nanoparticles, Pt (platinum) nanoparticles, or mixtures thereof.

[0033] The at least one inorganic additive may be supported in a carrier. The carrier may be carbon black.

[0034] The additive blend may comprise at least two different organic additives. The additive blend may comprise two different organic additives, three different organic additives, four different organic additives, five different organic additives, or six different organic additives. The at least two organic additives may be physically mixed in the additive blend. The additive blend may comprise at least two different organicadditives and at least an inorganic additive.

[0035] The additive blend may comprise a physical mixture of compounds selected from the list comprising:A quinone-hydroquinone type antioxidant and a polyphenolic acid antioxidant such as but not limited to alizarin and caffeic acid; alizarin and propyl gallate; purpurin and propyl gallate; purpurin and caffeic acid; A quinone-hydroquinone antioxidant and a flavonoid such as but not limited to purpurin and quercetin; A polyphenolic acid antioxidant and a flavonoid such as but not limited to caffeic acid and quercetin, propyl gallate and quercetin; A stilbene and a flavonoid such as but not limited to resveratrol and catechin; A polyphenol and a flavonoid such as but not limited to curcumin and quercetin, curcumin and catechin; Aflavonoid antioxidant and a flavonoid antioxidant of a different subtype, such as butnot limited to catechin and quercetin; A flavonoid antioxidant and a coumarin, such as but not limited to quercetin and esculetin; or mixtures or derivatives thereof.

[0036] The additive blend may further comprise an inorganic additive. The inorganic additive may be selected from cerium, manganese, cobalt, zinc, aluminium, zirconium, oxides thereof, and / or combinations thereof. The inorganic additive may be present in any of its oxidation states. The inorganic additive may be present in more than one oxidation state. The inorganic additive may be present in ionic or salt form. The additiveblend may comprise Ce3+.

[0037] The at least one organic additive may be present in the membrane in a concentration of from about 0.5 mol % to about 20 mol % relative to the sulfonic acid group of the ionomer. The at least one organic additive may be present in the membrane in a concentration of from about 2 mol % to about 12 mol %, or from about 4 mol % to about 8 mol %, or from about 5 mol % to about 7 mol %, or from about 4 mol % to about 5 mol %, or from about 5 mol % to about 7 mol %, or from about 6 mol % to about 8 mol %, relative to the ionomer exchange site (e.g. relative to sulphonic acid groups when the ionomer is PFSA).

[0038] The total content of organic additive (e.g., total antioxidant content (i.e.,obtained by the sum of the contents of each organic additive)) in the membrane may be up to about 20 mol%, or up to about 16 mol %, or up to about 15 mol %, or up to about 14 mol %, or up to about 11 mol %, optionally wherein the total content of organic additive in the membrane is from about 4 mol% to about 11 mol %.

[0039] The at least one inorganic additive may be present in the membrane in a concentration of about 0.02 mol % to about 5 mol %, or from about 1 mol % to about3 mol %, or from about 2.5 mol% to about 3.5 mol %, or about 2 mol%. As discussed hereinabove, the inorganic additive may comprise at least one of Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form,or their oxides, or their salts, or mixtures thereof. In some embodiments, the inorganic additive may comprise Ce3+.

[0040] The PEM may comprise at least one layer of porous reinforcement and at leastone layer of IEM. The PEM may comprise a layer of IEM at either side of the at leastone layer of porous reinforcement. The PEM may comprise a first layer and a secondlayer of IEM and the IEMs of the first layer of IEM and the second layer of IEM may bethe same or different.

[0041] The IEM may comprise a proton conducting polymer selected from a non-fluorinated ionomer, a perfluorinated ionomer and a partially fluorinated ionomer, optionally wherein the at least one layer of ionomer comprises PFSA.

[0042] The additives of the additive blend may be dissolved, suspended, or dispersed in the IEM.

[0043] The PEM may comprise more than one layer of IEM and the additive blend maybe present in each layer of IEM of the membrane, or it may be present only on somelayer or layers of IEM. The additive blend may present in one or both external layers of IEM but not in internal layers of IEM. The additive blend may be present in an internallayer or layers of IEM. The additive blend may be present in all layers of IEM of thePEM.

[0044] The polymer electrolyte membrane may have a thickness at 50 % RH of atleast about 20 µm, or from about 20 µm to about 200 µm, or from about 40 µm to about 200 µm, or from about 60 µm to about 200 µm, or from about 80 µm to about 200 µm, or from about 100 µm to about 200 µm, or from about 120 µm to about 200 µm, or fromabout 140 µm to about 200 µm, or from about 160 µm to about 200 µm, or from about 180 µm to about 200 µm, or from about 50 µm to about 150 µm, or from about 20 µm to about 40 µm, or from about 40 µm to about 60 µm, or from about 40 µm to about 80µm, or from about 50 µm to about 80 µm, or from about 60 µm to about 80 µm, or fromabout 70 µm to about 80 µm, or from about 50 µm to about 75 µm, or from about 70 µm to about 90 µm, or from about 80 µm to about 100 µm. The PEM may be anelectrolyzer membrane or a redox flow battery membrane.

[0045] The polymer electrolyte membrane may have a thickness at 50 % RH of about1 to 50 µm at 50 % RH, or from about 20 µm to about 40 µm, or from about 1 µm to about 30 µm or from about 1 µm to about 20 µm, or from about 1 µm to about 10 µm,or from about 5 µm to about 20 µm, or from about 10 µm to about 20 µm, or from about 5µm to about 10 µm. The PEM may have a thickness at 50% RH of from about 1 µmto about 17 µm. The PEM may be a fuel cell membrane or a redox flow batterymembrane.

[0046] The polymer electrolyte membrane may have a thickness at 50 % RH fromabout 100 µm to about 300 µm, or from about 150 µm to about 300 µm, or from about200 µm to about 300 µm, or from about 250 µm to about 300 µm, or from about 100 µm to about 200 µm, or from about 100 µm to about 150 µm, or from about 150 µm to about 250 µm at 50 % RH. The polymer electrolyte membrane may have a thicknessat 50 % RH from about 50 µm to about 150 µm, or from about 75 µm to about 150 µm, or from about 100 µm to about 150 µm, or from about 125 µm to about 150 µm, or from about 50 µm to about 100 µm, or from about 50 µm to about 75 µm, or from about 75 µm to about 100, or from about 75 µm to about 125 µm at 50 % RH.

[0047] The polymer electrolyte membrane may be an electrolyzer polymer electrolyte membrane. The polymer electrolyte membrane may additionally comprise a recombination catalyst. The recombination catalyst may be present at least in a location (e.g. layer of IEM) configured to be disposed adjacent an anode of an electrolyzer composite MEA. Preferably, the recombination catalyst is configured to be disposed closer to an anode than to a cathode of an electrolyzer polymer electrolyte MEA. The recombination catalyst may be mixed with ion exchange material (IEM), and / or it may be present on a recombination catalyst support material, such as carbon particulate. In some embodiments, at least some of the recombination catalyst is configured to be in contact with the anode in a MEA. In an electrolyzer MEA, the recombination catalyst may be part of the MEA but not be present in the polymer electrolyte membrane. The recombination catalyst may be present in at least oneelectrode (e.g. as a layer or as part of the electrode). The polymer electrolyte membrane may or may not comprise recombination catalyst. The recombination catalyst may comprise a platinum group metal (Group 10 metal) such as platinum, palladium, iridium, rhodium, ruthenium or osmium; alloys of platinum group metals; and mixed oxides of platinum group metals with other metals such as cerium and titanium, and mixtures thereof; or wherein the recombination catalyst comprises one or more of Pt, Ir, Ni, Co, Pd, Ti, Sn, Ta, Nb, Sb, Pb, Mn, and Ru, their oxides andmixtures thereof. The recombination catalyst may be present at a loading of less than 0.10 mg / cm2 in the composite electrolyte membrane (e.g. a loading of from 0.0001 mg / cm2 to 0.09 mg / cm2). The electrolyzer composite membrane may further comprisea fluid diffusion layer selected from a felt, a paper or a woven material, a carbon / carbon-based diffusion layer, titanium porous sintered powder mesh / plates / Fibers / Felts, a stainless steel mesh, or mixtures thereof.

[0048] In a second aspect there is provided a MEA comprising a polymer electrolytemembrane as disclosed herein and at least one electrode.

[0049] In a third aspect there is provided a MEA comprising: a) a polymer electrolyte membrane comprising an organic additive selected from aperoxide decomposition catalyst, a radical scavenger, a free radical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer; and b) at least one electrode;wherein the MEA comprises an inorganic additive.

[0050] The at least one inorganic additive may be present in or on the at least oneelectrode. The inorganic additive may be present in the polymer electrolyte membraneand in or on the at least one electrode. The at least one inorganic additive may bepresent in a layer deposited on the at least one electrode. The at least one inorganic additive may comprise a metal, its oxide or its salt, or mixtures thereof.

[0051] The at least one inorganic additive may comprise a metal selected from Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form, or their oxides, or their salts, or mixtures thereof. The inorganic additive may comprise Ce3+. The at least one inorganic additive may comprise cerium oxide (ceria). A salt of the at least one inorganic additive may comprise an anionselected from nitrate, acetate, acetylacetonate, carbonate, or sulfate. A salt of the at least one inorganic additive may not comprise a halide anion.

[0052] The inorganic additive may comprise nanoparticles, nanotubes, nanorods, or mixtures thereof. The at least one inorganic additive may comprise metal nanoparticles.

[0053] The metal nanoparticles may be selected from: Au (gold) nanoparticles, Pd (palladium) nanoparticles, Pt (platinum) nanoparticles, or mixtures thereof. Inembodiments in which the at least one inorganic additive is present in or on at least one electrode, the inorganic additive present in or on the electrode may not be a metal nanoparticle.

[0054] The at least one inorganic additive may be supported in a carrier. The carrier may be carbon black.

[0055] In embodiments in which the at least one inorganic additive is present on at least one electrode, the inorganic additive may be cerium manganese oxide, cerium oxide, cerium nitrate, cerium carbonate, cerium sulfate, cerium acetate, manganeseoxide, manganese nitrate, manganese carbonate, manganese sulfate, manganese acetate.

[0056] The at least one inorganic additive may be present in the membrane-electrode assembly in a concentration of about 0.02 mol % to about 5 mol %, or from about 1mol % to about 3 mol %, or from about 2.5 mol% to about 3.5 mol %, or about 2 mol%.

[0057] The additive blend may comprise at least one of: a synthetic antioxidant, a natural non-enzymatic antioxidant, and a radical scavenger. The synthetic antioxidant may comprise a phenolic antioxidant (e.g. BHA, BHT, TBHQ).

[0058] The synthetic antioxidant may comprise a nano-antioxidant (e.g. an oxide, a metal nanoparticle, an antioxidant functionalised nanoparticle).

[0059] The organic additive may comprise a nonenzymatic antioxidant selected from: a quinone, a hydroquinone, a quinone-hydroquinone, a polyphenol selected from a flavonoid, a stilbene, and a phenolic acid; a coumarin, a chromone, an alkaloid, a catecholamine, a vitamin, a carotenoid, a phosphonic acid, a carboxylic acid, a phenolic and heterocyclic derivative radical scavenger, derivatives or mixtures thereof.

[0060] The organic additive may be selected from alizarin, purpurin, quinizarin, anthrarufin, rufigallol, thymol blue, alizairin-3-methyliminodiacetic acid, quercetin, myricetin, morin, kaempferol, baicalein, naringenin, naringenin chalcone, (E)-3-(e,4- dihydroxyphenyl)-1-(2,3,4-trihydroxyphenyl)prop-2-ene-1-one (a flavonoid), genistein, luteolin, eriodictyol, hesperetin, hesperidin, quercetagetin, catechin, epicatechin, epigallocatechin, epigallocatechin gallate, taxifolin, caffeic acid, sinapic acid, ferulicacid, rosmarinic acid, coumaric acid, caftaric acid, gallic acid, tannic acid, propyl gallate, ellagic acid, 2,3,4-trihydroxybenzophenone, esculetin, 7,8-dihydroxy-4- methylcourmarin, daphnetin, 6,7-dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, 7,8- dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, curcumin, bis-demethylcurcumin, dopamine, usnic acid, hydroxylated chromone-3-carboxylic acid, resveratrol, polyhydroxystilbenes such as (E) 2',5',3,4-tetrahydroxystilbene and (E) 3',4',3,4- tetrahydroxystilbene, avenanthramide derivatives, terephthalic acid, syringic acid, 2,6- dimethoxy-1,4-benzoquinone, tert-butylhydroquinone, derivatives thereof and / or mixtures thereof. The organic additive may be selected from alizarin, purpurin, caffeic acid, propyl gallate, quercetin, catechin, esculetin, resveratrol, curcumin, epigallocatechin gallate, epicatechin, hesperetin, derivatives thereof, and mixturesthereof. The organic additive may comprise a product of reaction between one or morecomponents of the blend described herein.

[0061] The additive blend may comprise a physical mixture of compounds selected from the list comprising: A quinone-hydroquinone type antioxidant and a polyphenolic acid antioxidant such as but not limited to alizarin and caffeic acid; alizarin and propyl gallate; purpurin and propyl gallate; purpurin and caffeic acid; A quinone-hydroquinone antioxidant and a flavonoid such as but not limited to purpurin and quercetin; A polyphenolic acid antioxidant and a flavonoid such as but not limited to caffeic acid and quercetin, propyl gallate and quercetin; A stilbene and a flavonoid such as but not limited to resveratrol and catechin; A polyphenol and a flavonoid such as but not limited to curcumin and quercetin, curcumin and catechin;A flavonoid antioxidant and a flavonoid antioxidant of a different subtype, such as but not limited to catechin and quercetin; A flavonoid antioxidant and a coumarin, such as but not limited to quercetin and esculetin; or mixtures or derivatives thereof. Derivatives of the physical mixtures of compounds may comprise products of reaction an organic additive with itself or between themixtures of the compounds which occur during the processing of the polymer electrolyte membrane (e.g. in acidic conditions when the ion exchange material is acidic and optionally at high temperatures when the polymer electrolyte membrane is heated to dry).

[0062] The at least one organic additive may be present in the membrane in a concentration of from about 0.5 mol % to about 20 mol % relative to the sulfonic acid group of the ionomer. The at least one organic additive may be present in the membrane in a concentration of from about 2 mol % to about 12 mol %, or from about 4 mol % to about 8 mol %, or from about 5 mol % to about 7 mol %, or from about 4 mol % to about 5 mol %, or from about 5 mol % to about 7 mol %, or from about 6 mol % to about 8 mol %, relative to the ionomer exchange site (e.g. relative to sulphonic acid groups when the ionomer is PFSA).

[0063] The total content of organic additive (e.g., total antioxidant content (i.e., obtained by the sum of the contents of each organic additive)) in the membrane may be up to about 20 mol%, or up to about 16 mol %, or up to about 15 mol %, or up to about 14 mol %, or up to about 11 mol %, optionally wherein the total content of organic additive in the membrane is from about 4 mol% to about 11 mol %.

[0064] The at least one inorganic additive may be present in the membrane-electrode assembly in a concentration of about 0.02 mol % to about 5 mol %, or from about 1mol % to about 3 mol %, or from about 2.5 mol% to about 3.5 mol %, or about 2 mol%. As discussed hereinabove, the inorganic additive may comprise at least one of Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form, or their oxides, or their salts, or mixtures thereof. In some embodiments, the inorganic additive may comprise Ce3+.

[0065] The construction and materials of the polymer exchange membrane (PEM) of the third aspect may be the same as that of the first aspect. Therefore, the description of the materials and structure of the PEM of the first aspect apply here too (e.g.definition of IEM, reinforcement, additive blend components, etc). However, in the MEA of the third aspect, there is an inorganic additive which may be present only in or on at least one electrode, or only in the PEM, or both on the PEM and at least one electrode.

[0066] In the MEA of the second or the third aspects, the polymer electrolyte membrane may be in contact with the at least one electrode. The polymer electrolyte membrane may be in contact with two electrodes. The polymer electrolyte membranemay be attached to the at least one electrode. The polymer electrolyte membrane mayadhered to the at least one electrode. The polymer electrolyte membrane may beattached to the at least one electrode. The polymer electrolye membrane may bepressed against the at least one electrode. The polymer electrolyte membrane may be fused to the at least one electrode. The polymer electrolyte membrane may be sandwiched between an anode disposed adjacent to a first external recombinationcatalyst layer, and a cathode disposed adjacent to a second external bottom layer ofIEM. The MEA may comprise only one of the two electrodes (anode or cathode). The at least one electrode may comprise fibers. The at least one electrode may be a fibrous electrode. The at least one electrode may be doped with fibers. The at least one electrode may comprise carbon fibers. The carbon fibers may have a diameter fromabout 5 to about 30 µm. The at least one electrode may comprise a porous layer (typical pore size 1-200 micron). The porous layer may comprise, among others, a felt, a paper, or a woven material. The at least one electrode may be selected from Pt / Co / Pd / doped graphene / MoSx (Cathode); RuO2 / IrO2 / Ir&Ru bimetallic oxides, Ir / Pt bimetallic oxides, Ti, Sn, Ta, Nb, Sb, Pb, Mn Oxides mixed with Ir or Ru Oxides. The electrode may comprise a catalyst support selected from carbon (e.g. Carbon Black / CNTs), or carbon nanoparticles doped with N,P,S or B). The at least oneelectrode may comprise doped carbon fibers. a first electrode and a second electrode,optionally wherein the first electrode forms an anode and the second electrode forms acathode. The anode may be in contact with the recombination catalyst. The MEAmay be an electrolyzer MEA.

[0067] The MEA of the second or third aspects may be a redox flow batterymembrane-electrode assembly comprising: a positive electrode with a first surface and a second surface; and apolymer electrolye membrane (PEM) as described hereinabove,wherein the electrode and the PEM are in contact with each other.

[0068] The redox flow battery MEA may comprise an electrode layer attached to a firstsurface of the composite membrane and a second electrode layer attached to a second surface of the composite membrane. The electrode may be a porous layer having apore size from about 1 to about 200 µm. The electrode may be selected from a felt, a paper or a woven material. The electrode may comprise doped carbon fibers.

[069] The MEA may be a fuel cell MEA comprising:a composite membrane as described hereinabove, wherein the composite membrane has a first surface and a second surface; a first layer of electrode catalyst adhered to the first surface of the composite membrane; and a second layer of catalyst adhered to the second surface of the composite membrane.

[0070] In the fuel cell MEA, the first and second layers of electrode catalyst may be nanoporous layers having a pore size of up to about 100 nm. The first and second electrode catalyst layers are adhered to the composite membrane.

[0071] In the fuel cell MEA, the first and second layers of electrode catalyst comprise: one or more ionomers; a catalyst support such as carbon black; and platinum.

[072] The MEA may be an electrolyzer membrane-electrode assembly comprising:the composite membrane described herein having a layer of catalyst laminated on the composite membrane; an electrode; and a gas diffusion layer disposed between the composite membrane and the electrode.

[073] In a further aspect there is provided an electrochemical device comprising acomposite membrane as described hereinabove or a membrane electrode assemblyas described hereinabove. The electrochemical device may be a fuel cell, a redox flow battery or an electrolyzer.

[074] In yet a further aspect there is provided a method of manufacturing a PEMcomprising the steps of:a) coating a backer layer with a first IEM by providing a backer layer and depositing aliquid layer of a first ionomer, wherein the first ionomer optionally comprises an additive blend having at least one organic additive; b) depositing a first reinforcing layer comprising a porous reinforcement over the liquid layer of the first IEM and allowing the porous reinforcement of the first reinforcing layerto become imbibed or at least partially imbibed with the first IEM and optionally theadditive blend (where present);c) optionally drying the laminate; and d) coating the imbibed first reinforcing layer with a liquid layer of a second IEM solution,optionally wherein the second IEM solution comprises an additive blend comprising atleast one organic additive; and e) drying the laminate.

[0075] The method may further comprise the step f) of depositing a second porous reinforcement layer over the liquid layer of the second ionomer and allowing the porous structure of the second reinforcement layer to become imbibed or at least partially imbibed with the second ionomer (and optionally the additive blend where present)before the drying step e). The method may further comprise coating the imbibedsecond porous reinforcement layer with a liquid layer of a third ionomer solution. Thethird ionomer solution may optionally comprise an additive blend comprising at leastone organic additive. In other words, the method may optionally further comprise coating the outermost surface of the laminate which is furthest away from the backer with a third liquid layer of ionomer and allowing porous reinforcement layer to become at least partially imbibed with ionomer (and additive blend where present), optionally drying the laminate.

[0076] The method further may further comprise the steps of depositing subsequent porous reinforcement layers over layers of solution of ionomer (and optionally additiveblend), allowing the porous structure to become imbibed with the ionomer (andoptionally additive blend), optionally applying a further layer of ionomer solution, and drying the membrane to form a laminate. For example, for PEMs comprising threeporous reinforcement layers, a third liquid layer of ionomer solution may be deposited over the imbibed second reinforcing layer and applying a third porous reinforcement layer over the layer of third liquid layer of ionomer solution, and then the laminate may be dried. In some embodiments, the process may comprise adding even further ionomer and porous reinforcement layers, and drying the laminate.

[0077] The PEM may be manufactured by sequential coating and / or lamination of thedifferent components of the membrane. The manufacturing process may comprise drying steps after some or all of the coating or lamination steps. In some embodiments, the manufacturing process may comprise only a single drying step at the end of the process.

[0078] In embodiments in which two porous reinforcement layers are in contact with each other, the process described above is modified to omit the step of coating the porous reinforcement layer with another solution of ionomer before applying a further porous reinforcement layer. For example, in the process described above, step d) would be omitted.

[0079] In the method described herein all the first, second and optionally third and subsequent ionomers may be the same or they may be different.

[0080] In the method described herein an additive blend may be added to any one of the of IEM(s) (e.g. the additive blend may be present in a layer of pure IEM and / or itmay be imbibed into a porous reinforcement together with the IEM). In some embodiments, additive blend is present in all layers of IEM and / or imbibed into one ormore layer(s) of porous reinforcement. In other embodiments, additive blend is present in more than one layer of IEM but not all layers. In yet other embodiments, additiveblend is present only in one layer of IEM. The additive blend (where present in more than one layer of IEM) may be the same in all layers of IEM, or it may be different in at least two of the layers of IEM.

[0081] In the method, at least one of the ionomers may comprise the additive blend. The additive blend may be present in all layers of ionomer. Alternatively, the additive blend may be present in some layers of ionomer but not others. The additive blend may be added to the ionomer by any suitable means. For example, the additive blend may be mixed with the ionomer prior to deposition of the ionomer to form the composite / laminate. The ionomer may be purchased commercially comprising all or some of the components of the blend. In that case, the blend may be further completed by adding any missing components / ingredients of the blend to the ionomer. The blendor at least some components of the blend may be added to the ionomer by any suitable means. For example, they may be provided in a suitable carrier (e.g. carbon black, organic solvent, or any other carrier) and they may be dispersed, dissolved, or otherwise mixed with the ionomer. In other embodiments, the ionomer layer or layersmay be deposited on the composite / laminate and the additive blend may be subsequently deposited on the layer of ionomer.

[0082] In a further aspect there is provided PEM directly obtained by the methoddescribed herein. Definitions

[0083] Various definitions used in the present disclosure are provided below.

[0084] As used herein, the terms “ionomer” and “IEM” refer to a cation exchange material. Mixtures of IEMs may also be employed. IEM may be perfluorinated orhydrocarbon-based. Suitable IEMs include, for example, perfluorosulfonic acid polymers, perfluorocarboxylic acid polymers, perfluorophosphonic acid polymers, styrenic ion exchange polymers, fluorostyrenic ion exchange polymers, polyarylether ketone ion exchange polymers, polysulfone ion exchange polymers, bis(fluoroalkylsulfonyl)imides, (fluoroalkylsulfonyl)(fluorosulfonyl)imides, polyvinyl alcohol, polyethylene oxides, divinyl benzene, metal salts with or without a polymer, and mixtures thereof. In exemplary embodiments, the IEM comprises perfluorosulfonicacid (PFSA) polymers made by copolymerization of tetrafluoroethylene and perfluorosulfonyl vinyl ester with conversion into proton form.

[0085] As used herein, the “equivalent volume” of an ionomer or IEM refers to thevolume of the ionomer per sulfonic acid group. The equivalent volume (EV) of theionomer refers to the EV if that ionomer were pure and in its proton form at 0% RH, with negligible impurities.

[0086] As used herein, the term “porous reinforcement” refers to a polymeric matrix that supports the IEM, adding structural integrity and durability to the resulting composite membrane. In some exemplary embodiments, the porous reinforcement / porous reinforcement comprises expanded polytetrafluoroethylene(ePTFE) having a node and fibril structure. In other exemplary embodiments, the porous reinforcement / porous reinforcement comprises track etched polycarbonatemembranes having smooth flat surfaces, high apparent density, and well-defined poresizes.

[0087] As used herein, an interior volume of a porous reinforcement is referred to as“substantially occluded” when said interior volume has structures that is characterizedby low volume of voids, less than 10% by volume, and being highly impermeable togases, Gurley numbers larger than 10000 s. Conversely, interior volume of porousreinforcement / porous reinforcement is referred to as “non-occluded” when said interiorvolume has structures that is characterized by large volume of voids, more than 10%by volume, and being permeable to gases, Gurley numbers less than 10000 s.Water and Solids Concentration of Solutions of Ion Exchange Material (IEM)

[0088] Herein, the terms “solution” and “dispersion” are used interchangeably when referring to IEMs. This test procedure is appropriate for solutions in which the IEM is in proton form, and in which there are negligible quantities of other solids. Percent water of stock ionomer dispersions was measured by Karl Fischer titration using a Metrohm 915 KF Ti-Touch. Solid concentrations were determined by drawing a volume of 2 cubic centimeters of IEM solution into a syringe and the mass of the syringe with solution was measured via a balance in a solids analyzer (obtained from CEM Corporation, USA). The mass of two pieces of glass fiber paper (obtained from CEM Corporation, USA) was also measured and recorded. The IEM solution was then deposited from the syringe into the two layers of glass fiber paper. The glass fiber paper with the ionomer solution was placed into the solids analyzer and heated up to 160°C to remove the solvent liquids. The mass of the glass fiber paper and residual solids was recorded when the mass stopped changing with respect to increasing temperature and time. It is assumed that the residual IEM contained no water (i.e., it is the ionomer mass corresponding to 0% RH). After that, the mass of the emptied syringe was measured and recorded using the same balance as before. The ionomer solids in solution was calculated according to the following formula:Equivalent Weight (EW) of an IEM

[0089] The following test procedure is appropriate for IEM comprised of a single ionomer resin or a mixture of ionomer resins that is in the proton form (i.e., that contains negligible amounts of other cations), and that is in a solution that contains negligible other ionic species, including protic acids and dissociating salts. If these conditions are not met, then prior to testing the solution must be purified from ionic impurities according to a suitable procedure as would be known to one of ordinary skill in the art,or the impurities must be characterized and their influence on the result of the EW test must be corrected for.

[0090] As used herein, the EW of an IEM refers to the case when the IEM is in its proton form at 0 % RH with negligible impurities. The IEM may comprise a single ionomer or a mixture of ionomers in the proton form. An amount of IEM solution with solids concentration determined as described above containing 0.2 grams of solids was poured into a plastic cup. The mass of the ionomer solution was measured via a conventional laboratory scale (obtained from Mettler Toledo, LLC, USA). Then, 5 ml of deionized water and 5 ml of 200 proof denatured ethanol (SDA 3C, Sigma Aldrich, USA) is added to ionomer solution in the cup. Then, 55 ml of 2N sodium chloride solution in water was added to the IEM solution. The sample was then allowed to equilibrate under constant stirring for 15 minutes. After the equilibration step, the sample was titrated with 1N sodium hydroxide solution. The volume of 1N sodium hydroxide solution that was needed to neutralize the sample solution to a pH value of 7 was recorded. The EW of the IEM (EWIEM) was calculated as:

[0091] When multiple IEMs were combined to make a 1+ composite membrane, the average EW of the IEMs in the composite membrane was calculated using the following formula:where the mass fraction of each IEM is with respect to the total amount of all IEMs. This formula was used both for composite membranes containing ionomer blends and for composite membranes containing ionomer layers. Equivalent Volume (EV) of an IEM

[0092] As used herein, the Equivalent Volume of the IEM refers to the EV if that IEM were pure and in its proton form at 0 % RH, with negligible impurities. The EV was calculated according to the following formula:

[0093] The Equivalent Weight of each IEM was determined in accordance with the procedure described above. The IEMs used in these applications were perfluorosulfonic acid ionomer resins the volumetric density of perfluorosul fonic acid ionomer resin was taken to be 1.96 g / cc at 0 % RH. Thickness of composite membrane

[0094] The composite membranes were equilibrated in the room in which the thickness was measured for at least 1 hour before measurement. Composite membranes were left attached to the substrates on which the composite membranes were coated. For each sample, the composite membrane on its coating substrate was placed on a smooth, flat, level marble slab. A thickness gauge (obtained from Heidenhain Corporation, USA) was brought into contact with the composite membrane and the height reading of the gauge was recorded in six different spots arranged in grid pattern on the membrane. Then, the sample was removed from the substrate, the gauge was brought into contact with the substrate, and the height reading was recorded again in the same six spots. The thickness of the composite membrane at a given relative humidity (RH) in the room was calculated as a difference between height readings of the gauge with and without the composite membrane being present. The local RH was measured using an RH probe (obtained from Fluke Corporation). The thickness at 0% RH was calculated using the following general formula:where the parameter corresponds to the water uptake of the IEM in terms of moles of water per mole of acid group at a specified RH. For PFSA ionomer, the values for any RH in the range from 0 to 100% in gas phase were calculated according the following formula:BRIEF DESCRIPTION OF THE DRAWINGS:

[0095] Figures 1A-1G show a cross sectional side view of a composite membrane inaccordance with some aspects of the invention;

[0096] Figures 2A-2C show a cross sectional side view of a composite membrane inaccordance with some aspects of the invention;

[0097] Figures 2D-2F show a cross sectional side view of a composite membrane inaccordance with some aspects of the invention;

[0098] Figure 2G shows a cross sectional side view of a composite membrane inaccordance with some aspects of the invention. The dots represent the additive blend which is dispersed throughout the ionomer and embedded in the reinforcement layers as well. In some embodiments the dots may additionally represent a recombination catalyst.

[0099] Figure 2H shows a cross sectional view of a composite membrane in accordance with some aspects of the invention. In this embodiment the membrane comprises an additive blend and / or a recombination catalyst (represented by dots)disposed solely in an external layer of ionomer, while the rest of the ionomer does not have additive blend and / or recombination catalyst.

[0100] Figure 2I shows a cross sectional view of a MEA for an electrolyzer comprisinga polymer electrolyte membrane in accordance with some aspects of the inventionsandwiched between an anode disposed adjacent to a recombination catalyst layer,and a cathode disposed adjacent to the second external bottom layer of IEM.

[0101] Figure 2J shows a cross-sectional view of a MEA according to the third aspectcomprising a polymer electrolyte membrane in accordance with some aspects of theinvention sandwiched between an anode and a cathode, wherein the anode comprisesa layer of inorganic additive.

[0102] Figures 3A-3C show cross sectional side views unreinforced compositemembranes in accordance with some aspects of the invention.

[0103] Figures 4A-4C show exemplary flow diagrams of processes for constructingexemplary composite membranes in accordance with some aspects of the invention.

[0104] Figure 5 shows a comparison of the chemical durability of PEMs forcomparative examples of no additive (A, Example 1.1), Ce3+(B, Example 1.2 and C, Example 1.3), and inventive examples containing Ce3+and one organic additive. B & D is Example 2.2. B & F is Example 3.2. B & H is the average of Examples 5.1, 5.2, and 5.3. C & F is Example 4.1. The chemical durability of the PEMs was measured asfluoride loss at 100h during OCV hold test (95 degrees C / 30%RH, 272kPa both sides,H2 / Air 100 / 200 sccm with electrode loadings of 0.1 mgPt / cm2on each side). Error bars represent the minimum and maximum of the data.

[0105] Figure 6 shows the results of a performance study on the PEMs of Figure 5.).Polarization is shown on the primary axis for the test condition at 80 degrees C withan inlet relative humidity of 33%. Low loading electrodes, 0.1 mgPt / cm2, were used onboth sides. The secondary axis shows the ohmic resistance measured during the polarization curve.

[0106] Figure 7 shows a comparison of the chemical durability of PEMs forcomparative examples of no additive (A, Example 1.1) and Ce3+(B, Example 1.2), and inventive examples containing two organic additives with no Ce3+: for D & E is Example6.1, for D & F is Example 7.1, for D & J is Example 8.1. The chemical durability of thePEMs was measured as fluoride loss at 100h during OCV hold test (95 degrees C / 30%RH, 272kPa both sides, H2 / Air 100 / 200 sccm with electrode loadings of 0.1 mgPt / cm2on each side). Error bars represent the minimum and maximum of the data.

[0107] Figure 8 shows the results of a performance study on the PEMs of Figure 7.Polarization is shown on the primary axis for the test condition at 80 degrees C with an inlet relative humidity of 33%. Low loading electrodes, 0.1 mgPt / cm2, were used on both sides. The secondary axis shows the ohmic resistance measured during the polarization curve.

[0108] Figure 9 shows a comparison of the chemical durability of PEMs forcomparative examples of no additive (A, Example 1.1) and Ce3+(B, Example 1.2), and inventive examples containing two organic additives with Ce3+. B & D & E is Example 10.1. B & D & F is Example 12.1. B & D & I is the average of Examples 14.1 and 14.2. B & D & J is Example 11.1. B & F & H is the average of Examples 9.1, 9.2, 9.3, and 9.4. B & G & I is the average of Examples 13.1, 13.2, 13.3, 13.4, 13.5, and 13.6. The chemical durability of the PEMs was measured as fluoride loss at 100h during OCVhold test (95 degrees C / 30% RH, 272kPa both sides, H2 / Air 100 / 200 sccm withelectrode loadings of 0.1 mgPt / cm2on each side). Error bars represent the minimum and maximum of the data.

[0109] Figure 10 shows the results of a performance study of the PEMs of Figure 9,with the exception of B & D & I, Examples 14.1 and 14.2. Polarization is shown on theprimary axis for the test condition at 80 degrees C with an inlet relative humidity of33%. Low loading electrodes, 0.1 mgPt / cm2, were used on both sides. The secondary axis shows the ohmic resistance measured during the polarization curve. DETAILED DESCRIPTION OF THE INVENTIONComposite Membranes

[0110] As shown in Figures 1A-1D, a PEM 100 is provided that includes a porouspolymer reinforcement 105 and an IEM (e.g. ionomer) 110 impregnated in the porouspolymer reinforcement 105. That is, the porous polymer reinforcement 105 is imbibedwith the IEM 110. The IEM 110 may substantially impregnate the porous polymerreinforcement 105 so as to render the interior volume substantially occlusive (i.e. theinterior volume having structures that is characterized by low volume of voids and being highly impermeable to gases). For example, by filling greater than 90% of theinterior volume of the porous reinforcement 105 with the IEM 110, substantial occlusionwill occur and membrane will be characterized by Gurley numbers larger than 10000 s. As shown in Figures 1A-1D, the IEM 110 is securely adhered to the internal andexternal surfaces of the porous reinforcement 105, e.g., the fibrils and / or nodes of theporous reinforcement forming an imbibed layer 104.

[0111] In some embodiments, the IEM 110, in addition to being impregnated in theporous reinforcement 105 in the imbibed layer 104, is provided as one or moreadditional layers 115 (e.g., referred also as “butter coat (BC)”) on one or more external surfaces of the imbibed layer 104 (Figures 1A-1C). In other embodiments, the IEM 110is only provided impregnated in the porous reinforcement 105 within the imbibed layer104, i.e., without any additional layers, (FIG. 1D). Nonetheless, the composite membrane 100 is characterized by the porous reinforcement 105 occupying at least 5vol % of the total volume (e.g. from about 5 vol% to about 65 vol %) of the compositemembrane 100, which total volume includes the volume of any additional layers 115, if present. The porous reinforcement may be present in an amount from 5 vol% to 50vol% based on the total volume of the PEM (in a single layer or spread across two ormore layers of porous reinforcement). The porous reinforcement may be present in an amount from 5 vol% to 40 vol%, or 5 vol% to 30 vol %, or 10 vol % to 30 vol %, or 10 vol % to 40 vol %, or 5 vol % to 10 vol %, or 10 vol % to 25 vol %, or 15 vol % to 30 vol %, or 20 vol % to 40 vol %, or 5 vol % to 7 vol %, or 10 vol % to 15 vol % based on the total volume of the PEM (in a single layer or spread across two or more layers ofporous reinforcement).

[0112] In additional embodiments, part of the porous reinforcement 105 (e.g. topsurface area or bottom surface area) may include a non-occlusive (i.e. the interior volume having structures that is characterized by high volume of voids and being highly permeable to gases) layer 112 that is free or substantially free of the IEM 110 (FIGS.1E-1F). The location of the non-occlusive layer 112 is not limited to the top surfacearea of the porous reinforcement 105. As provided above, the non-occlusive layer 112may be provided on a bottom surface area of the porous reinforcement 105.

[0113] Yet in other embodiments, the non-occlusive layer 112 may include a small amount of the IEM 110 present in an internal surface of the porous reinforcement 105as a thin node and fibril coating. However, the amount of the IEM 110 may be or maynot be large enough to render the porous reinforcement 105 occlusive, thereby formingthe non-occlusive layer 112.

[0114] In some embodiments, the composite membrane 100 may be provided on a support layer 114 (FIG. 1G). The support layer 114 may include a backer, a releasefilm such as, for example, cycloolefin copolymer (COC) layer. In some embodiments,the composite membrane 100 may be released (or otherwise uncoupled) from the support layer 114 prior to being incorporated in a MEA.

[0115] FIGS. 1A-1G illustrate exemplary composite membranes 100 that include a single type of IEM 110. However, the application is not limited to compositemembranes 100 having a single type of IEM 110 or a single imbibed layer 104.

[0116] As illustrated in Figures 2A-2H, the composite membrane 200 may also includea plurality, e.g., two or more, imbibed layers 104a and 104b. In the embodiment of FIG.2A, a first imbibed layer 104a may be formed by imbibing the porous reinforcement 105 with the IEM 110, and a second imbibed layer 104b may be formed by imbibingthe porous reinforcement 105 with the same IEM 110. For example, IEM may beimbibed into a first side of the porous reinforcement to form the first imbibed layer 104a,and the same IEM may be imbibed into a second side of the porous reinforcement,opposite the first side, to form the second imbibed layer 104b. In the embodiment of FIG. 2B, the first imbibed layer 104a may be formed by imbibing the porous reinforcement 105 with a first IEM 110a, and the second imbibed layer 104b may beformed by imbibing the porous reinforcement 105 with a second IEM 110b that isdifferent from the first IEM 110a. In this aspect, a first IEM may be imbibed into a firstside of the porous reinforcement to form the first imbibed layer 104a, and a secondIEM may be imbibed into a second side of the porous reinforcement, opposite the firstside, to form the second imbibed layer 104b.

[0117] In some embodiments, one or more of the IEM 110, the first IEM 110a and / orthe second IEM 110b may be provided as one or more additional layers 115 on one ormore external surfaces of the imbibed layers 104a and / or 104b (Figures 2A-2C),including optionally between imbibed layers 104a and 104b, as shown in Figures 2C,2F, and 2G.

[0118] As illustrated in Figures 2D-2F, the composite membrane 300 may also includea plurality, e.g., two or more, imbibed layers 104c and 104d formed by two (or more) different porous reinforcements 105a and 105b. In some embodiments, the firstimbibed layer 104c may be formed by imbibing a first porous reinforcement 105a withthe IEM 110, and the second imbibed layer 104b may be formed by imbibing a secondporous reinforcement 105b with the same IEM 110 (FIG. 2D). In other embodiments,the first imbibed layer 104c may be formed by imbibing a first porous reinforcement 105a with a first IEM 110a, and the second imbibed layer 104b may be formed byimbibing a second porous reinforcement 105b with a second IEM 110b. As shown inFIGS. 2D-2F, the first porous reinforcement 105a may be different than the secondporous reinforcement 105b. The first IEM 110a may be the same as or different fromthe second IEM 110b.

[0119] In some embodiments, the first IEM 110a and the second IEM 110b may beprovided as one or more additional layers 115 on one or more external surfaces of the imbibed layers 104c and 104d such that the first porous reinforcement 105a is in directcontact with the second porous reinforcement 105b (Figures 2D-2E). In someembodiments, the first IEM 110a and the second IEM 110b may be provided as oneor more additional layers 115 between the imbibed layers 104c and 104d such that the first porous reinforcement 105a may not be in direct contact with the second porousreinforcement 105b (Figure 2F).

[0120] All of the PEMs shown in the figures comprise an additive blend comprising atleast two additives (represented as triangles 120). At least one of the at least twoadditives may be an organic additive selected from a peroxide decomposition catalyst, a radical scavenger, a free radical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer. The additive blend may be present in at least one of the layers of the composite membrane. The additive blend may be dispersed, dissolved, or otherwise added to the IEM. Insome embodiments the additive blend 120 is present in more than one layer (e.g. composite membranes of Figures 1A, 1C, 1E, 1G, 2A, 2B, 2D, and 2E), and in other cases the additive blend is present in a discrete layer or layers of the composite membrane (e.g. in the composite membranes of Figures 1B, 1D, 2C, and 2F). Theadditive blend 120 may also become imbibed in the porous reinforcement 105 as shown in Figures 1A, 1C, 1D, 1E, 1F, 1G, 2A, 2B 2D, 2E, 2D, 2G, and 2H.

[0121] The additive blend may comprise at least one of: a synthetic antioxidant, a natural non-enzymatic antioxidant, and a radical scavenger. The synthetic antioxidant may comprise a phenolic antioxidant (e.g. BHA, BHT, TBHQ).

[0122] The synthetic antioxidant may comprise a nano-antioxidant (e.g. an oxide, a metal nanoparticle, an antioxidant functionalised nanoparticle).

[0123] The organic additive may comprise a nonenzymatic antioxidant selected from: a quinone, a hydroquinone, a quinone-hydroquinone, a polyphenol selected from a flavonoid, a stilbene, and a phenolic acid; a coumarin, a chromone, an alkaloid, a catecholamine, a vitamin, a carotenoid, a phosphonic acid, a carboxylic acid, a phenolic and heterocyclic derivative radical scavenger, derivatives or mixtures thereof.

[0124] The organic additive may be selected from alizarin, purpurin, quinizarin, anthrarufin, rufigallol, thymol blue, alizairin-3-methyliminodiacetic acid, quercetin, myricetin, morin, kaempferol, baicalein, naringenin, naringenin chalcone, (E)-3-(e,4- dihydroxyphenyl)-1-(2,3,4-trihydroxyphenyl)prop-2-ene-1-one (a flavonoid), genistein, luteolin, eriodictyol, hesperetin, hesperidin, quercetagetin, catechin, epicatechin, epigallocatechin, epigallocatechin gallate, taxifolin, caffeic acid, sinapic acid, ferulicacid, rosmarinic acid, coumaric acid, caftaric acid, gallic acid, tannic acid, propyl gallate, ellagic acid, 2,3,4-trihydroxybenzophenone, esculetin, 7,8-dihydroxy-4- methylcourmarin, daphnetin, 6,7-dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, 7,8- dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, curcumin, bis-demethylcurcumin, dopamine, usnic acid, hydroxylated chromone-3-carboxylic acid, resveratrol, polyhydroxystilbenes such as (E) 2',5',3,4-tetrahydroxystilbene and (E) 3',4',3,4- tetrahydroxystilbene, avenanthramide derivatives, terephthalic acid, syringic acid, 2,6- dimethoxy-1,4-benzoquinone, tert-butylhydroquinone, derivatives thereof and / or mixtures thereof. The organic additive may be selected from alizarin, purpurin, caffeic acid, propyl gallate, quercetin, catechin, esculetin, resveratrol, curcumin, epigallocatechin gallate, epicatechin, hesperetin, derivatives thereof, and mixtures thereof.

[0125] The additive blend may comprise at least one inorganic additive. The at least one inorganic additive may comprise a metal, its oxide or its salt, or mixtures thereof.

[0126] The at least one inorganic additive may comprise a metal selected from Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, and Zn in the ionic form, or their oxides, or their salts, or mixtures thereof. The inorganic additive may comprise cerium oxide (ceria).

[0127] The inorganic additive may comprise nanoparticles, nanotubes, nanorods, or mixtures thereof. The at least one inorganic additive may comprise metal nanoparticles. The metal nanoparticles may be selected from: Au (gold) nanoparticles, Pd (palladium) nanoparticles, Pt (platinum) nanoparticles, or mixtures thereof.

[0128] The at least one inorganic additive may be supported in a carrier. The carries may be carbon black.

[0129] The additive blend may comprise at least two different organic additives. The additive blend may comprise two different organic additives, three different organic additives, four different organic additives, five different organic additives, or six different organic additives. The at least two organic additives may be physically mixed in the additive blend. The additive blend may comprise at least two different organic additives and at least an inorganic additive.

[0130] The additive blend may comprise a physical mixture of compounds comprising from: A quinone-hydroquinone type antioxidant and a polyphenolic acid antioxidant such as but not limited to alizarin and caffeic acid; alizarin and propyl gallate; purpurin and propyl gallate; purpurin and caffeic acid; A quinone-hydroquinone antioxidant and a flavonoid such as but not limited to purpurin and quercetin; A polyphenolic acid antioxidant and a flavonoid such as but not limited to caffeic acid and quercetin, propyl gallate and quercetin; A stilbene and a flavonoid such as but not limited to resveratrol and catechin; A polyphenol and a flavonoid such as but not limited to curcumin and quercetin, curcumin and catechin; A flavonoid antioxidant and a flavonoid antioxidant of a different subtype, such as but not limited to catechin and quercetin; A flavonoid antioxidant and a coumarin, such as but not limited to quercetin and aesculetin; or mixtures thereof.

[0131] The additive blend may further comprise an inorganic additive. The inorganic additive may be selected from cerium, manganese, cobalt, zinc, aluminium, zirconium, oxides thereof, and / or combinations thereof. The inorganic additive may be present in any of its oxidation states. The inorganic additive may be present in more than oneoxidation state. The inorganic additive may be present in ionic or salt form. The additive blend may comprise Ce3+.

[0132] The at least one organic additive may be present in the membrane in a concentration of from about 0.5 mol % to about 20 mol % relative to the sulfonic acid group of the ionomer. The at least one organic additive may be present in the membrane in a concentration of from about 2 mol % to about 12 mol %, or from about 4 mol % to about 8 mol %, or from about 5 mol % to about 7 mol %, or from about 4 mol % to about 5 mol %, or from about 5 mol % to about 7 mol %, or from about 6 mol % to about 8 mol %, relative to the ionomer exchange site (e.g. relative to sulphonic acid groups when the ionomer is PFSA).

[0133] The total content of organic additive (e.g. total antioxidant content (i.e. obtained by the sum of the contents of each organic additive)) in the membrane may be up to about 20 mol%, or up to about 16 mol %, or up to about 15 mol %, or up to about 14 mol %, or up to about 11 mol %, optionally wherein the total content of organic additive in the membrane is from about 4 mol% to about 11 mol %.

[0134] The at least one inorganic additive may be present in the membrane in a concentration of about 0.5 mol % to about 5 mol %, or from about 1 mol % to about 3 mol %, or from about 2.5 mol% to about 3.5 mol %, or about 2 mol%. As discussed hereinabove, the inorganic additive may comprise at least one of Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form, or their oxides, or their salts, or mixtures thereof. In some embodiments, the inorganic additive may comprise Ce3+.

[0135] The additives of the additive blend may be dissolved, suspended, or dispersed in the IEM. In embodiments in which there is more than one layer of IEM, the additive blend may be present on some but not all of the layers of IEM. The additive blend may be present in at least one of the layers of IEM, and in some embodiments it is present in all layers of IEM.

[0136] In some embodiments in which the composite membrane is an electrolyzer composite membrane, may additionally comprise a recombination catalyst 130 (see dots in Figures 2G, 2H, 2I). When recombination catalyst is present, it may be present at least in a location (e.g. layer of IEM) configured to be disposed adjacent an anode of an electrolyzer composite MEA. Preferably, the recombination catalyst is configured to be disposed closer to an anode than to a cathode of an electrolyzer composite MEA.The recombination catalyst may be mixed with IEM, and / or it may be present on a recombination catalyst support material, such as carbon particulate. In some embodiments, at least some of the recombination catalyst is configured to be in contact with the anode in a MEA. The recombination catalyst may comprise a platinum group metal (Group 10 metal) such as platinum, palladium, iridium, rhodium, ruthenium or osmium; alloys of platinum group metals; and mixed oxides of platinum group metals with other metals such as cerium and titanium, and mixtures thereof; or wherein the recombination catalyst comprises one or more of Pt, Ir, Ni, Co, Pd, Ti, Sn, Ta, Nb, Sb, Pb, Mn, and Ru, their oxides and mixtures thereof. The recombination catalyst may bepresent at a loading of less than 0.10 mg / cm2in the composite electrolyte membrane (e.g. a loading of from 0.0001 mg / cm2to 0.09 mg / cm2).

[0137] Figure 2G shows a cross sectional side view of a composite membrane in accordance with some aspects of the invention. The triangles 120 represent theadditive blend and the dots 130 represent the recombination catalyst which are dispersed throughout the ionomer and embedded in the reinforcement layers 105a and 105b as well. In this embodiment the membrane comprises two imbibed reinforcement layers 104c and 104d comprising a porous reinforcement layer 105a, 105b (which maybe the same or different (i.e. they may have the same or different material, thickness, properties, etc.) and IEM within the pores. The membrane also comprises two externallayers of IEM 115 and an internal layer of IEM 115 separating the two imbibedreinforcement layers 104c,d. The IEM comprises additive blend 120 dispersed ordissolved therein and both the IEM and the additive blend become embedded in theimbibed reinforcement layers 104c,d.

[0138] Figure 2H shows a cross sectional view of a composite membrane in accordance with some aspects of the invention. In this embodiment the membrane comprises an additive blend 120 (represented by triangles) dispersed across the entire membrane except for an outermost external layer of ionomer which contains a recombination catalyst 130 (represented by dots), while the rest of the ionomer does not have additive blend and / or recombination catalyst.

[0139] Figure 2I shows a cross sectional view of a MEA 600 for an electrolyzercomprising a composite membrane in accordance with some aspects of the invention sandwiched between an anode disposed adjacent to the recombination catalyst layer, and a cathode disposed adjacent to the second external bottom layer of IEM. In otherembodiments the MEA comprises only one of the two electrodes (anode or cathode). The electrode(s) may be attached to the composite membrane. The electrode(s) maycomprise a porous layer. The electrode(s) may comprise carbon fibers. The carbonfibers may have a diameter from about 5 to about 30 µm.

[0140] In the composite membrane of the MEA of Figure 2I the recombination catalyst 130 is present only in the outermost layer of ionomer 115a, which also contains the additive blend 120 (triangles). The other layers of the composite membrane (ionomer layers 115c, 115d, 115b and imbibed layers 104a, 104b, and 104c also comprise the additive blend 120. The recombination catalyst 130 is present in the outermost ionomer layer 115a which is in contact with the anode 650a and the cathode 650b is in contact with the outermost ionomer layer 115b which is furthest from the recombination catalyst.

[0141] Figure 2J shows an exemplary membrane-electrode assembly (MEA) 800 according to the third aspect of the invention. The MEA has two electrodes in this case (an anode 850a and a cathode 850b), but in some embodiments it may comprise only one electrode (cathode or anode). The MEA also comprises a polymer electrolyte membrane 700 having an additive blend 120a (triangles). The other layers of thecomposite membrane 700 (ionomer layers 115, 115, 115 and imbibed layers 104c, 104d and reinforcement layers 105a, 105b also comprise the additive blend 120a). Insome embodiments (not shown), the reinforcement layers may not be present. In other embodiments (not shown), only one layer of reinforcement is present.

[0142] In embodiments like that of Figure 2J, at least one of the electrodes comprises an inorganic additive or an inorganic additive blend. In this embodiment, the anode 850a comprises a layer of inorganic additive 120b (hexagons). However, in other embodiments it is the cathode 850b or both the anode 850a and the cathode 850b which comprise inorganic additive.

[0143] In this embodiment, the inorganic additive or inorganic additive blend 120b depicted in this embodiment is not present in the polymer electrolyte membrane 700. However, the additive blend 120a of the PEM may also comprise inorganic additive inaddition to the at least one organic additive. The inorganic additive present in or on the electrode may be the same or different to inorganic additive present in the PEM. The additive blend 120a of the PEM comprises 1, 2 or more organic additives and may comprise no inorganic additive or one or more inorganic additives.

[0144] Embodiments of MEA according to the present invention comprise at least twoadditives. At least one organic additive must be present in a PEM of the MEA, and asecond or further additives may also be present in the PEM and / or, when a second or further additive is an inorganic additive, it may be present in or on an electrode of the MEA.

[0145] MEAs according to the present invention may present increased durabilitycompared to MEAs without additive blends as disclosed herein.

[0146] Figure 3A shows an example of an exemplary unreinforced PEM having a layer115a of IEM and comprising an additive blend 120. The membrane has noreinforcement in this embodiment.

[0147] Figure 3B shows an example of another unreinforced PEM, but in this case it comprises two layers 115a, 115b of IEM. One of the two layers of IEM comprises anadditive blend 120 and the other IEM layer 115b does not have additive blend. Figure3C shows an unreinforced composite membrane like that of Figure 3C but in this case both IEM layers 115a and 115b have additive blend 120.

[0148] The composite membranes of Figures 1-4 may have a thickness at 50 % RHof at least about 20 µm, or from about 20 µm to about 200 µm, or from about 40 µm to about 200 µm, or from about 60 µm to about 200 µm, or from about 80 µm to about 200 µm, or from about 100 µm to about 200 µm, or from about 120 µm to about 200 µm, or from about 140 µm to about 200 µm, or from about 160 µm to about 200 µm, or from about 180 µm to about 200 µm, or from about 50 µm to about 150 µm, or from about 20 µm to about 40 µm, or from about 40 µm to about 60 µm, or from about 40 µm to about 80 µm, or from about 50 µm to about 75 µm, or from about 80 µm to about 100 µm. The PEM may be an electrolyzer membrane or a fuel cell membrane.

[0149] The composite membranes may have a thickness at 50 % RH of about 1 to 50µm at 50 % RH, or from about 20 µm to about 400 µm, or from about 1 µm to about 30 µm or from about 1 µm to about 20 µm, or from about 1 µm to about 1 µm, or from about 5 µm to about 20 µm, or from about 10 µm to about 20 µm, or from about 5 µm to about 10 µm. The PEM may have a thickness at 50% RH of from 1 µm to about 17µm. The PEM may be a fuel cell or a redox flow battery membrane.

[0150] The composite membranes may have a thickness at 50 % RH from about 100µm to about 300 µm, or from about 150 µm to about 300 µm, or from about 200 µm to about 300 µm, or from about 250 µm to about 300 µm, or from about 100 µm to about 200 µm, or from about 100 µm to about 150 µm, or from about 150 µm to about 250 µm at 50 % RH. The membrane may have a thickness at 50 % RH from about 50 µmto about 150 µm, or from about 75 µm to about 150 µm, or from about 100 µm to about 150 µm, or from about 125 µm to about 150 µm, or from about 50 µm to about 100 µm, or from about 50 µm to about 75 µm, or from about 75 µm to about 100, or from about 75 µm to about 125 µm at 50 % RH.Porous reinforcement

[0151] A suitable porous reinforcement structure depends largely on the application inwhich the composite membrane is to be used. The porous reinforcement structurepreferably has good mechanical properties, is chemically and thermally stable in the environment in which the composite membrane is to be used, and is tolerant of any additives used with the IEM for impregnation.

[0152] As used herein, the term "porous reinforcement layer" is intended to refer to a layer having a thickness of at least 0.05 micron, optionally from 0.05 to 100 or from 1to 50 microns, and having an average pore size from 0.05 to 20 microns, e.g., from 0.05 to 1 microns. The pores of the porous reinforcement layer may have an averagepore size from about 0.01 to about 100 µm, e.g., from about 0.05 µm to about 20 µmor from about 0.1 µm to about 1 µm.

[0153] A suitable porous reinforcement layer 105 for electrochemical applications mayinclude porous polymeric materials. The porous polymeric materials may include a fluoropolymer, a chlorinated polymer, a non-fluorinated polymer (e.g. a hydrocarbon-based polymer), a polyamide, a polycarbonate, a polyacrylate, a polysulfone and / orderivative thereof, polyethylene, polypropylene, polyvinylidene fluoride (PVDF), apolyaryl ether ketone, a polybenzimidazole, poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene-co-hexafluoropropylene). In some embodiments, the porous reinforcement 105 includes a perfluorinated porous polymeric material. Theperfluorinated porous polymeric material may include polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (ePTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (ePVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE) or mixtures thereof.

[0154] In some embodiments, the porous polymeric structure 105 includes a non-fluorinated polymer (e.g. a polymeric hydrocarbon-based reinforcement). The non- fluorinated material maybe selected from the list comprising Polyethylene (PE),Polypropylene (PP), Polysulfone, Polyethersullfone (PES), Polystyrene (PS), Polycarbonate (PC), polybutyl terephthalate (PBT), Poly ether ether ketone (PEEK),Poly ether ketone (PEK), Poly ether ketone ketone(PEKK), Poly aryl ether ketone (PAEK) and other variants as well as sulfonated versions thereof, Polyimide (PI), Polyamide (PA), a Liquid crystal polymer (LCP), a Polyphenylene (PP) and / or a derivative thereof (e.g., Polyphenylene sulfide (PPS)), Polyetherimide (PEI), Polyamideimide (PAI), Polyethylene terephthalate (PET), Polybenzimidazole (PBI), and mixtures thereof.. Examples of suitable perfluorinated porous polymeric materials for use in electrochemical applications include ePTFE made in accordance with theteachings of U.S. Patent No.8,757,395, which is incorporated herein by reference in its entirety, and commercially available in a variety of forms from W. L. Gore & Associates, Inc., of Elkton, Md. Ion Exchange Material

[0155] A suitable IEM may be dependent on the application in which the compositemembrane is to be used. The IEM may have a low equivalent weight (e.g., equal to orless than 460 cc / eq). The IEM may be is chemically and thermally stable in theenvironment in which the composite membrane is to be used. A suitable ionomer forelectrochemical applications may include an IEM such as a proton conducting polymeror a cation exchange material. The IEM may perfluorocarboxylic acid polymers,perfluorophosphonic acid polymers, styrenic ion exchange polymers, fluorostyrenic ion exchange polymers, polyarylether ketone ion exchange polymers, polysulfone ion exchange polymers, bis(fluoroalkylsulfonyl)imides, (fluoroalkylsulfonyl)(fluorosulfonyl)imides, polyvinyl alcohol, polyethylene oxides, divinyl benzene, metal salts with or without a polymer and mixtures thereof. Examples of suitable perfluorosulfonic acid polymers for use in fuel cell applications include Nafion® (E.I. DuPont de Nemours, Inc., Wilmington, Del., US), Flemion® (Asahi Glass Co. Ltd., Tokyo, JP), Aciplex® (Asahi Chemical Co. Ltd., Tokyo, JP), Aquivion® (SolvaySolexis S.P.A, Italy), and 3MTM(3M Innovative Properties Company, USA) which are commercially available perfluorosulfonic acid copolymers. Other examples of suitable perfluorosulfonic acid polymers for use in fuel cell applications include perfluorinated sulfonyl (co)polymers such as those described in U.S. Pat. No. 5,463,005.RESULTS AND DISCUSSION Properties of the Composite Membrane

[0156] Table 1 summarizes additives used for the experimental section and the labelused for each. For CeX3, X may be nitrate, acetate, acetylacetonate, carbonate, orsulfate. The results for performance improvement are summarized in Table 2.Table 1. Legend of additives used and label. Label AdditiveA NoneB Cerium in ionomerC CeX3D QuercetinE CatechinF Caffeic AcidG Propyl GallateH AlizarinI PurpurinJ EsculetinK CurcuminL ResveratrolM Epigallocatechin gallate NHesperetinO EpicatechinTable 2. Summary of performance improvement vs. control. ImprovementExample LabelAntioxidant Antioxidant Antioxidant Rel. FRR at 100 1 2 3 hours vs Control Comparative examples 1.1 A (Control) None None None 11.2 B B (2mol%) None None 127.7x1.3 C C (3.3mol%) None None 118.8xOrganic additive and cerium 2.1 B & D B (2mol%) D (4.1mol%) None 139.8x2.2 B & D B (2mol%) D (8mol%) None 455.9x3.1 B & E B (1mol%) E (5mol%) None 363.2x3.2 B & E B (1mol%) E (8mol%) None 734.8x4.1 B & F B (2mol%) F (4mol%) None 150.4x4.2 B & F B (2mol%) F (8mol%) None 306.1x4.3 B & F B (3.3mol%) F (9.9mol%) None 126.8x5.1 C & F C (3.3mol%) F (9.9mol%) None 375.8x6.1 B & H B (2mol%) H (4.1mol%) None6.2 B & H B (2mol%) H (4.0mol%) None 445.1x6.3 B & H B (2mol%) H (4.1mol%) None7.1 B & L B (1mol%) L (4 mol%) None 781.4x8.1 B & M B (1mol%) M (9 mol%) None 1279x9.1 B & N B (1mol%) N (8 mol%) None 1045.8x10.1 B & N B (1mol%) O (8 mol%) None 460.3xTwo organic antioxidants (no cerium) 11.1 D & E None D (4mol%) E (5mol%) 309.4x12.1 D & F None D (4mol%) F (5mol%) 23.3x13.1 D & J None D (4mol%) J (5mol%) 16.5xTwo organic antioxidants and cerium 14.1 B & F & H B (2mol%) F (5-6mol%) H (4mol%)14.2 B & F & H B (2mol%) F (5mol%) H (4mol%)14.3 B & F & H B (2mol%) F (5mol%) H (4mol%)497.7x 14.4 B & F & H B (2mol%) F (6mol%) H (4.1mol%)14.5 B & F & H B (2mol%) F (8mol%) H (3mol%) 193.6x15.1 B & D & E B (2mol%) D (4mol%) E (5mol%) 740.0x16.1 B & D & J B (2mol%) D (4mol%) J (5mol%) 393.8x17.1 B & D & F B (2mol%) D (4mol%) F (5mol%) 777.4x17.2 B & D & F B (2mol%) D (4mol%) F (8mol%) 263.4x18.1 B & G & I B (2mol%) G (5mol%) I (4.3mol%)18.2 B & G & I B (2mol%) G (5mol%) I (4.3mol%)18.3 B & G & I B (2mol%) G (5mol%) I (4.3mol%)18.4 B & G & I B (2mol%) G (5mol%)I (4.7- 381.1x 4.75mol%) 18.5 B & G & I B (2mol%) G (5mol%) I (4.75mol%)18.6 B & G & I B (2mol%) G (5mol%) I (4.7mol%)18.7 B & G & I B (2mol%) G (5mol%) I (4.7mol%) 241.2x19.1 B & D & I B (2mol%) D (5mol%) I (4.7mol%)19.2 B & D & I B (2mol%) D (5mol%) I (4.3mol%)499.3x 20.1 B & D & K B (2mol%) D (4mol%) K (5mol%) 595.7x21.1 B & D & K B (1mol%) E (5mol%) L (4mol%) 1001.7x22.1 B & E & L B (1mol%) E (5mol%) K (4mol%) 790.7x

[0157] The additive blends disclosed herein improve the durability, as measured by fluoride release during accelerated stress testing, of the PEM. The performance improvement depends significantly on the concentration and type of the additive (mol%), the type of cerium used, how the ionomer dispersions were formed, and finally, the processing conditions used to fabricate membranes. As seen in Table 3, Ce3+added alone at 2 mol% improves the durability by a factor of 128. Single organic antioxidant blended with inorganic Ce3+can improve the durability up to a factor of 445 compared membranes prepared with no additive. Two organic additives blended with no Ce3+improved the durability by a factor of 309 compared to no additive. Overall, the most significant improvement in durability was found when two organic antioxidants were blended with Ce3+, up to a factor of 777.

[0158] As mentioned earlier, mixtures of antioxidants may undergo different interactions, affecting antioxidant activity positively in an additive or synergistic manner, or negatively, in an antagonistic manner. While the mechanism(s) responsiblefor antioxidant effects are not yet understood, synergistic responses can be explained by: regeneration of the stronger antioxidant by the weaker antioxidant; formation of stable intermolecular complexes between the antioxidants that deliver higherantioxidant activity that the individual species; formation of dimers and adducts and / ornew phenolic compounds with higher antioxidant power; solubility differences between the antioxidants which may affect phase distribution.

[0159] Table 3 shows results of the performance of select individual antioxidants, binary, and ternary blends. This data shows that none of the organic antioxidants aloneshown here come close to the improvement provided by Ce3+ alone. Single organicantioxidants blended at 4 – 8.7 mol% appear to vary from additive to synergistic withCe3+ blended at 2 mol%.. All ternary blends show significant, and sometimes dramatic,synergistic interactions between the antioxidants. On average, ternary blends withcerium show about 3.4x more potential synergy than binary blends of organic additive with cerium.Table 3. Antioxidant Interactions Based on Relative FRR at 100 hours.Antioxidant Antioxidant Antioxidant Sum of Improvement Interaction 1 2 3 Individual over A Antioxidants None None None 1 1 -B (2) None None 127.7 127.7 -D (4) None None 2.1 2.1 -H (4) None None -1.2 -1.2 -G (4) None None 1.1 1.1 -F (4) None None 3.5 3.5 -I (4) None None 2.0 2.0 -I (8.7) None None 3.7 3.7 -D (4) B (2) None 129.8 139.8 SynergisticH (4) B (2) None 126.5 224.3 SynergisticI (8.7) B (2) None 131.4 177.4 SynergisticF (4) B (2) None 131.2 150.5 SynergisticD (4) G (5) B (2) 130.9 441.1 SynergisticD (4) F (5) B (2) 133.3 777.4 SynergisticH (4) G (5) B (2) 127.6 353.4 SynergisticI (4.25) G (5) B (2) 130.8 450.2 SynergisticI (4.72) G (5) B (2) 132.5 743.8 SynergisticI (4.25) F (5) B (2) 133.2 534.5 SynergisticI (4.72) F (5) B (2) 134.9 847.8 Synergistic

[0160] As seen from the results table, the organic additive blends disclosed hereinincrease the durability of PEMs synergistically compared to membranes of similarstructure but not having organic additive blends.

[0161] Figure 5 shows a comparison of the chemical durability of PEMs forcomparative examples of no additive (A, Example 1.1), Ce3+(B, Example 1.2 and C, Example 1.3), and inventive examples containing Ce3+and one organic additive. B & D is Example 2.2. B & F is Example 3.2. B & H is the average of Examples 5.1, 5.2, and 5.3. C & F is Example 4.1. The chemical durability of the PEMs was measured asfluoride loss at 100h during OCV hold test (95 degrees C / 30%RH, 272kPa both sides, H2 / Air 100 / 200 sccm with electrode loadings of 0.1 mgPt / cm2on each side). Error bars represent the minimum and maximum of the data. The graph shows that a single organic additive blended with inorganic Ce3+drastically lowers the fluoride release of the composite compared to no additive. Furthermore, improved durability was observed compared to Ce3+ only, indicating that the organic additives act to reduce thenumber of radicals that attack the ionomer. This result was observed across twodifferent forms of Ce3+(Label B and C).

[0162] Figure 6 shows the results of a performance study on the PEMs of Figure 5.Polarization is shown on the primary axis for the test condition at 80 degrees C with an inlet relative humidity of 33%. Low loading electrodes, 0.1 mgPt / cm2, were used on both sides. The secondary axis shows the ohmic resistance measured during the polarization curve. Comparable performance is observed across the additive blendscompared to the no additive and Ce3+examples. The performance difference can be attributed to the difference in membrane resistance across the samples. The membrane resistance is thought to be within 2 sigma of a comparative sample. No kinetic impact is seen with the organic additives, indicating that the additives do not reduce the catalytic activity.

[0163] Figure 7 shows a comparison of the chemical durability of PEMs forcomparative examples of no additive (A, Example 1.1) and Ce3+(B, Example 1.2), and inventive examples containing two organic additives with no Ce3+ D & E is Example6.1. D & F is Example 7.1. D & J is Example 8.1. The chemical durability of the PEMswas measured as fluoride loss at 100h during OCV hold test (95 degrees C / 30% RH, 272kPa both sides, H2 / Air 100 / 200 sccm with electrode loadings of 0.1 mgPt / cm2on each side). Error bars represent the minimum and maximum of the data. This graphshows that blending two organic additives provides a clear improvement in the durability of the composite to no additive. Comparable durability was observed compared to Ce3+only, indicating that the organic additives act to reduce a similar number of radicals that attack the ionomer as Ce3+.

[0164] Figure 8 shows the results of a performance study of the performance of on the PEMs of Figure 7. Polarization is shown on the primary axis for the test condition at 80degrees C with an inlet relative humidity of 33%. Low loading electrodes, 0.1 mgPt / cm2, were used on both sides. The secondary axis shows the ohmic resistance measured during the polarization curve. Results show that durability can be maintained as inFigure 7, with no performance loss compared to samples with just Ce. Without wishing to be bound by theory, the comparable performance of examples 1.1 and 1.2 may be due to the fact that the amount of Ce in a thin membrane doesn't severely impactperformance.

[0165] Figure 9 shows a comparison of the chemical durability of PEMs forcomparative examples of no additive (A, Example 1.1) and Ce3+(B, Example 1.2), andinventive examples containing two organic additives with Ce3+. B & D & E is Example 10.1. B & D & F is Example 12.1. B & D & I is the average of Examples 14.1 and 14.2.B & D & J is Example 11.1. B & F & H is the average of Examples 9.1, 9.2, 9.3 and9.4. B & G & I is the average of Examples 13.1 - 13.6. The chemical durability of thePEMs was measured as fluoride loss at 100h during OCV hold test (95 degrees C / 30%RH, 272kPa both sides, H2 / Air 100 / 200 sccm with electrode loadings of 0.1 mgPt / cm2on each side). Error bars represent the minimum and maximum of the data. The graph shows that two organic additives blended with inorganic Ce3+drastically clowers the fluoride release of the composite compared to no additive. Furthermore, improved durability was observed compared to Ce3+only, indicating that the organic additives act to reduce the number of radicals that attack the ionomer.

[0166] Figure 10 shows the results of a performance study of the PEMs of Figure 9,with the exception of B & D & I, Examples 14.1 and 14.2. Polarization is shown on theprimary axis for the test condition at 80 degrees C with an inlet relative humidity of 33%. Low loading electrodes, 0.1 mgPt / cm2, were used on both sides. The secondary axis shows the ohmic resistance measured during the polarization curve. Comparableperformance is observed across the additive blends compared to the no additive and Ce3+examples. The performance difference can be attributed to the difference in membrane resistance across the samples. The membrane resistance is thought to be within 2 sigma of a comparative sample. No kinetic impact is seen with the organic additives, indicating that the additives do not reduce the catalytic activity. MEMBRANE PREPARATION General Procedure

[0167] The ionomer dispersion, such as prepared in the examples below, is formed into a membrane prototype by applying to a polymeric support using any process known in the art, including but not limited to the process described in U.S. Pat. No. RE37,707 to Bahar et. al. The polymeric support (porous reinforcement) having amicrostructure of micropores, may be any such material known in the art, including but not limited to porous fluorinated, or non-fluorinated polymers such as (but not limited to) a fluoropolymer, a chlorinated polymer, a non-fluorinated polymer (e.g. ahydrocarbon-based polymer), a polyamide, a polycarbonate, a polyacrylate, a polysulfone and / or derivative thereof, a copolyether ester, polyethylene, polypropylene, polyvinylidene fluoride (PVDF), a polyaryl ether ketone, a polybenzimidazole, poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene-co-hexafluoropropylene). The porous reinforcement can include a perfluorinated porous polymeric material. Selected from the list comprising: polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (ePTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidene fluoride (ePVDF), expanded poly(ethylene-co-tetrafluoroethylene) (eEPTFE) or mixtures thereof. The porous polymeric structure may include a non- fluorinated polymer (e.g. a polymeric hydrocarbon-based reinforcement) selected from the list comprising Polyethylene (PE), Polypropylene (PP), Polysulfone, Polyethersullfone (PES), Polystyrene (PS), Polycarbonate (PC), polybutyl terephthalate (PBT), Poly ether ether ketone (PEEK), Poly ether ketone (PEK), Poly ether ketone ketone(PEKK), Poly aryl ether ketone (PAEK) and other variants as well as sulfonated versions thereof, Polyimide (PI), Polyamide (PA), a Liquid crystal polymer (LCP), a Polyphenylene (PP) and / or a derivative thereof (e.g., Polyphenylene sulfide (PPS)), Polyetherimide (PEI), Polyamideimide (PAI), Polyethylene terephthalate (PET), Polybenzimidazole (PBI), and / or a mixture thereof. A particularlypreferable polymeric support is expanded PTFE, such as those described in U.S.Pat. No.3,953,566 to Gore, in U.S.Pat. No.6,613,203 Hobson et. al., or in U.S. Pat. No. 5,814,405 to Branca, et. al. Preferably, the polymeric support should be sufficientlystrong and / or heavy so that the final solid polymer electrolyte (SPE) has a failure force(defined more fully below) of greater than 115 g.

[0168] Figures.4A-4C show exemplary flow diagrams of processes 410, 420 and 430 for constructing exemplary composite membranes (e.g., the composite membrane 100 discussed with respect to Figures 1A-1G, the composite membrane 200 discussed with respect to Figures 2A-2C or the composite membrane 300 discussed with respectto Figures 2D-2F) in accordance with various aspects of the disclosure. The flow diagrams illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present disclosure. In some alternative implementations, where it makes logical sense to do so, the functions noted in each block may occur out of the order noted in the figure. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality, process, or end product involved.

[0169] Referring to Figure 4A, exemplary flow diagram of process 410 illustrates a method for forming a composite material having a fully imbibed porous reinforcement and two additional layers of IEM. The process 410 incudes providing a supportstructure like a backer. Suitable support structures may comprise woven materialswhich may include, for example, scrims made of woven fibers of expanded porous polytetrafluoroethylene; webs made of extruded or oriented polypropylene or polypropylene netting, commercially available from Conwed, Inc. of Minneapolis, Minn.; and woven materials of polypropylene and polyester, from Tetko Inc., of Briarcliff Manor, N.Y. Suitable non-woven materials may include, for example, a spun-bonded polypropylene from Reemay Inc. of Old Hickory, Tenn. In other aspects, the support structure can include web of polyethylene (“PE”), polystyrene (“PS”), cyclic olefin copolymer (“COC”), cyclic olefin polymer (“COP”), fluorinated ethylene propylene (“FEP”), perfluoroalkoxy alkanes (“PFAs”), ethylene tetrafluoroethylene (“ETFE”), polyvinylidene fluoride (“PVDF”), polyetherimide (“PEI”), polysulfone (“PSU”), polyethersulfone (“PES”), polyphenylene oxide (“PPO”), polyphenyl ether (“PPE”), polymethylpentene (“PMP”), polyethyleneterephthalate (“PET”), or polycarbonate (“PC”). In some aspects, the support structure also includes a protective layer, which can include polyethylene (PE), polystyrene (“PS”), cyclic olefin copolymer (“COC”), cyclic olefin polymer (“COP”), fluorinated ethylene propylene (“FEP”), perfluoroalkoxy alkanes (“PFAs”), ethylene tetrafluoroethylene (“ETFE”), polyvinylidene fluoride (“PVDF”), polyetherimide (“PEI”), polysulfone (“PSU”), polyethersulfone (“PES”), polyphenylene oxide (“PPO”), polyphenyl ether (“PPE”), polymethylpentene (“PMP”), polyethyleneterephthalate (“PET”), or polycarbonate (“PC”). In yet other aspects, support structure optionally may include a reflective layer that includes a metal substrate (e.g., an aluminum substrate). The specific metal chosen may vary widely so long as it is reflective. A non-limiting list of exemplary metals includes: aluminum, beryllium, cerium, chromium, copper, germanium, gold, hafnium, manganese, molybdenum, nickel, platinum, rhodium, silver, tantalum, titanium, tungsten, zinc, or alloys such as Inconel or bronze. The reflective layer optionally comprises a mixture or alloy of two or more metals, optionally two or more of the metals listed above. The reflective layer optionally can include a high reflectivity polymeric multilayer film such as VikuitiTMEnhanced Specular Reflector available from 3M company. In yet another example, the reflective layer optionally can include a high reflectivity non-metal inorganic dielectric multilayer film comprised of materials such as, for example, magnesium fluoride, calcium fluoride, titanium dioxide, silicon dioxide.

[0170] At step 440, a first ionomer solution is applied as a layer of controlled thickness to the support structure in a single or multiple pass ionomer coating technique includingforward roll coating, reverse roll coating, gravure coating, doctor coating, kiss coating, slot die coating, slide die coating, as well as dipping, brushing, painting, drawdown barcoating, meyer bar coating, and spraying. The first ionomer solution may be preparedby dissolving an IEM in a solvent. The first ionomer solution may comprise IEM and asolvent, and optionally additional components such as a surfactant. The first ionomer solution may further comprise an additive blend comprising at least two components, wherein at least one of the two additives is an organic additive selected from a peroxide decomposition catalyst, a radical scavenger, a free radical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer. The additive blend may be as described hereinabove for the PEMs. In some embodiments, the IEM is a cation exchange material. The choice of solvent maydepend, in part, on both the composition of the ionomer and the composition of the porous substrate.

[0171] At step 442, an untreated porous reinforcement layer is laminated over at least a portion of the first ionomer solution by any conventional technique, such as, for example, hot roll lamination, ultrasonic lamination, adhesive lamination, contact lamination or forced hot air lamination so long as the technique does not damage theintegrity of the untreated porous reinforcement structure. In some embodiments, theuntreated porous reinforcement structure comprises ePTFE having a porous polymericstructure. The porous reinforcement structure can be characterized by uniform structure and composition throughout its entire thickness. In other aspects, structure and composition of porous polymeric reinforcement structure can vary throughout itsthickness. The prepared or obtained porous reinforcement may have a thickness of less than 200 microns, for example from 1 microns to 50 microns at 0% relative humidity. The mass per unit area of the untreated porous reinforcement may be greater than 0.05 g / m2, for example from 0.3 g / m2to 20 g / m2at 0% relative humidity.

[0172] For example, a carrier support like a backer can be continuously fed from a roller unwind station via alignment and tension rollers to a coating station. The ionomer solution can be applied as a layer of controlled thickness onto the surface of the carrier support (backer) by suitable coating means, such as, for example, a doctor blade. The untreated porous reinforcement may be continuously fed from a roller unwind station to an alignment roller and contacts the coated carrier support and is impregnated with ionomer solution. Alternatively, the carrier support can be eliminated and the layer of ionomer solution can be directly applied to the untreated porous reinforcement.

[0173] At step 444, the treated porous reinforcement layer (imbibed with the IEM solution optionally comprising the additive blend) is placed into an oven to dry and finalize construction of a composite membrane. The oven temperature may be greaterthan 60° C, for example from 60° to 200° C or from 120° to 180° C. Drying the treated porous reinforcement in the oven causes the IEM to become securely adhered to theinternal membrane surfaces, and optionally the external membrane surfaces, e.g., the fibrils and / or nodes of the porous reinforcement.

[0174] At step 446, a second ionomer solution may be coated over the dried composite material. Similar to step 440, the second ionomer solution may be applied as a layerof controlled thickness to the composite material in a single or multiple pass ionomer coating technique including forward roll coating, reverse roll coating, gravure coating,doctor coating, kiss coating, slot die coating, slide die coating, as well as dipping,brushing, painting, drawdown bar coating, meyer bar coating, and spraying. Thesecond ionomer solution may be prepared by dissolving an IEM in a solvent. Thesecond ionomer solution may comprise IEM and a solvent, and optionally additionalcomponents such as a surfactant. The second ionomer solution may comprise an additive blend having at least two additives, wherein at least one of the two additives is an organic additive selected from a peroxide decomposition catalyst, a radical scavenger, a free radical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer. The additive blend may be dissolved, suspended or otherwise dispersed in the ionomer solution. In some embodiments, the ionomer solution may be purchased comprising some or all of the components of the additive blend. In embodiments in which commercial ionomer solution comprising some components of the additive blend is employed, the method may comprise adding further components of the additive blend to the commercial additive solution until the additive blend is complete. The IEM is a cation exchangematerial. In some embodiments, the second ionomer solution may be the same as thefirst ionomer solution. Alternatively, the second ionomer solution may be different thanthe first ionomer solution.

[0175] At step 448, the structure is placed into an oven to dry and finalize construction of the composite membrane 100, similar to step 444.

[0176] Referring now to Figure 4B, exemplary flow diagram of process 420 illustrates a method for forming a composite material having two fully imbibed porous reinforcements in contact with each other and two additional layers of IEM. Theprocess 420 incudes providing a support structure (e.g. backer), such as a woven material, similar to the process 410.

[0177] At step 450, a first ionomer solution is applied as a layer of controlled thickness to the support structure (backer) similar to step 440 of the process 410. The descriptionof step 450 is omitted here as it is identical to step 440 of the process 410, described above.

[0178] At step 452, a first untreated porous reinforcement (layer 1) is laminated over a first portion of the first ionomer solution and a second untreated porous reinforcement layer (layer 2) is laminated over the same portion of first ionomer solution on top of layer 1 by any conventional technique, such as, hot roll lamination, ultrasonic lamination, adhesive lamination, contact lamination or forced hot air lamination so long as the technique does not damage the integrity of the untreated porous reinforcements. In some embodiments, the first and second untreated porous reinforcements compriseePTFE having a porous structure. In some embodiments, the material of the second untreated porous reinforcement layer may be the same as the material of the first untreated porous reinforcement layer. Alternatively, the materials of the first andsecond reinforcement layers may be different. The first and second porous reinforcement layers can be characterized by uniform structure and composition throughout its entire thickness. In other aspects, structure and composition of first and second porous reinforcement layers can vary throughout its thickness.

[0179] Steps 454-458 are similar to steps 444-448 of the process 410. Accordingly,the description of steps 454-458 is omitted here.

[0180] Referring now to Figure 4C, exemplary flow diagram of process 430 illustrates a method for forming a composite material having two fully imbibed porous reinforcement layers and two additional layers of IEM and that are separated from eachother by another layer of IEM. The process 430 incudes providing a support structure(e.g. backer), such as a woven material, similar to processes 410 and 420.

[0181] Steps 460-466 of the process 430 are identical to steps 440-446 of the process 410, respectively. Accordingly, the description of steps 460-466 is omitted here.

[0182] At step 468, a second untreated porous reinforcement layer is laminated over at least a portion of the second ionomer solution by any conventional technique, such as, hot roll lamination, ultrasonic lamination, adhesive lamination, contact lamination, or forced hot air lamination so long as the technique does not damage the integrity of the untreated porous substrate. In some embodiments, the second untreated porousreinforcement comprises ePTFE having a porous reinforcement. In someembodiments, the second untreated porous reinforcement layer may be the same as the first untreated porous reinforcement layer. Alternatively, the second untreatedporous reinforcement layer may be different than the first untreated porous reinforcement layer. The first and second porous reinforcement layers can be characterized by uniform structure and composition throughout their entire thickness.In other aspects, structure and composition of first and second porous reinforcement layers can vary throughout its thickness.

[0183] At step 470, the treated porous reinforcement layer is placed into an oven to dry, similar to step 444 of the process 410.

[0184] At step 474, a third ionomer solution may be coated over the dried composite material, similar to step 460. In some embodiments, the third ionomer solution may bethe same as the first and / or the second ionomer solutions (optionally containing the same additive blend, a different additive blend, or no additive blend). Alternatively, thethird ionomer solution may be different than the first and second ionomer solutions.

[0185] At step 474, the treated porous reinforcement is placed into an oven to dry and finalize construction of the composite membrane 300, similar to step 448.

[0186] The processes 410, 420 and 430 may be repeated as desired in order to form a multi-layer composite membrane.

[0187] In some embodiments (not shown), the PEM may comprise no reinforcementand therefore it may consist of one or more layers of ionomer, wherein at least one of the layers of ionomer comprises the additive blend. In order to manufacture an unreinforced PEM a liquid layer of IEM (e.g. ionomer dissolved in a suitable solvent)may be deposited on a substrate (e.g. backer) by any suitable method. The liquid layer of IEM may comprise the additive blend as disclosed herein. Said additive blend maybe dissolved, suspended or otherwise dispersed in the IEM solution prior to depositingthe solution on the substrate, or it may be disposed on the liquid layer of IEM alreadylaid on the substrate. In some embodiments, if the solution of IEM is availablecommercially comprising some but not all of the components of the additive blend, the missing components of the additive blend would be added to the solution before laying the liquid layer of ionomer on the substrate, or dispersed on the liquid layer of ionomer after laying it on the substrate. The liquid layer of ionomer would then be dried and optionally further liquid layers of ionomer (same or different, with or without additiveblend) may be laid on top and subsequently dried to form the unreinforced PEM as inFigure 3.

[0188] When the imbibing steps are completed, an additional heating step at an elevated temperature may optionally be applied using an oven, infrared heater, forced air heater of the like. The temperature of this heating step is between about 100degrees C and about 200 degrees C and preferably between about 120 degrees C,and about 190 degrees C. The SPE is held at the elevated temperature for betweenabout 1 minute and about 10 minutes, and preferably for between about 1 minutes and about 3 minutes. Finally, the completed SPE membrane is collected, and removedfrom the thin polymer film before use. The removal may be accomplished by simplypulling the SPE off the thin polymer film, either in air or in water.

[0189] As is well understood by one of ordinary skill in the art, the process described above and in Figure 11 can be automated using roll goods, and automated pay-off andcollection systems so that each step is accomplished in a continuous fashion, and the final product is a roll of SPE supported on a thin polymer film. TEST PROCEDURES Microporous ePTFE Membrane Characterization: Bubble Point

[0190] The Bubble Point was measured according to the procedures of ASTM F316- 86. Isopropyl alcohol was used as the wetting fluid to fill the pores of the test specimen. The Bubble Point is the pressure of air required to create the first continuous stream of bubbles detectable by their rise through the layer of isopropyl alcohol covering the microporous polymer matrix. This measurement provides an estimation of maximum pore size. Non-contact thickness

[0191] A sample of microporous polymer structure was placed over a flat smooth metal anvil and tensioned to remove wrinkles. Height of microporous polymer structure on anvil was measured and recorded using a non-contact Keyence LS-7010M digital micrometer. Next, height of the anvil without microporous polymer matrix was recorded. Thickness of the microporous polymer structure was taken as a difference between micrometer readings with and without microporous structure being present on the anvil.Mass-per-area

[0192] Each Microporous Polymer structure was strained sufficient to eliminate wrinkles, and then a 10 cm2piece was cut out using a die. The 10 cm2piece was weighed on a conventional laboratory scale. The mass-per-area (M / A) was then calculated as the ratio of the measured mass to the known area. This procedure was repeated 2 times and the average value of the M / A was calculated. Apparent density of microporous layer

[0193] Apparent density of microporous polymer structure was calculated using the non-contact thickness and mass-per-area data using the following formula:Open-Circuit Voltage (OCV) Hold Testing

[0194] Because the inventive membranes typically last a very long time (thousands of hours) under normal fuel cell operating conditions, an accelerated test protocol was used to establish membrane lifetimes. A description of this test protocol follows.

[0195] Materials to be tested were prepared as outlined below in the examples, and then made into membrane electrode assemblies (MEAs). Electrodes supported on a backer, 5 x 5 cm, containing 0.1 mg / cm2of platinum supported on a ketjen black carbon with ionomer distributed throughout the thickness were obtained from W. L. Gore & Associates, Inc., Elkton, M.D. The electrodes were applied to the membrane using a decal transfer method described in the following text. A metal tray, 62.9 cm x 46.4 cm, was used as the work surface and then transferred to a heated press (PHI Hydraulics 50U2418-1UH0 / 1A-X-M1-S5, City of Industry, C.A.). Only the top plate of the press is heated. A 0.25 in thick sheet of silicone foam covered the metal tray to ensure a uniform distribution of pressure during the pressing step. On top of the foam was a layer of 5 mil (1271 µm) Kapton® polyimide film, followed by a layer of 10 mil ePTFEto ease sample release after the hot-pressing steps. The first electrode was laid on the ePTFE sheet with the catalyst-coated side facing up. The membrane on backer material was placed on top of the electrode with the backer-side facing up. These materials were covered with a 10 mil sheet of ePTFE, transferred to the heated press, and pressed for 3 seconds at 150 degrees C and 16 tons. The tray was removed and the ePTFE cover sheet was removed. Next, the membrane backer was removed fromthe membrane. The second electrode was placed on the membrane with the catalyst- coated side facing the membrane and centered over the first electrode. The ePTFE cover sheet was place over the lay-up and the metal tray was transferred to the heated press. The materials were pressed for 3 minutes at 150 degrees C and 16 tons. The tray was removed and the ePTFE cover sheet was removed. The electrode backer was removed from the top side, the MEA was flipped, and the electrode backer was removed from the first electrode, which serves as the cathode during operation.

[0196] Two 1.0 mil (25.4 µm) polyethylene terephthalate (PET) films (available fromCS Hyde Company, Lake Villa, I.L.), hereafter referred to as the sub-gasket, with an open window of 4.8 x 4.8 cm, were aligned on each side of the MEA. The MEA and sub-gaskets were placed between two sheets of 2 mil (50.8 µm) polyethylene and cut to a final part size of 7.62 x 7.26 cm using custom steel-rule dies and a manual die press (Lucris MA Series III, Ocean View, Queensland, Australia). With the sub-gaskets, the resulting MEA active area was 23.04 cm2.

[0197] For testing, the sub-gaskets and MEA were assembled into cell hardware using the procedure outlined below. The cell hardware consisted of sealed graphite blocks with triple-serpentine flow channels on both the anode and cathode sides. The path length is 5 cm, and the groove dimensions are 0.70 mm wide x 0.84 mm deep. The design was provided by Fuel Cell Technologies, Inc., Albuquerque, N.M. The gasdiffusion media (GDM) used was a Carbel® CL macro-layer with a Carbel® MP 30Zmicroporous layer, both obtained from W.L. Gore & Associates, Inc., Elkton, M.D. Cells were assembled with two 10 mil (254 µm) PTFE gaskets, and one to two 1.5 - 2.0 mil(38.1-50.8 µm) PET films, hereafter referred to as the spacer. The gaskets and spacers each have a square window of 5 x 5 cm.

[0198] The anode side of the cell hardware was placed with flow channels facing up on a workbench. One piece of the 10 mil (254 µm) ePTFE gasket and a PET spacer was placed on top of the graphite block. One set of the GDM was placed inside the gasket and spacer window with the MP-30Z layer facing up. The MEA with sub-gaskets were placed on top of the GDM, with the cathode-side up. If another spacer is being used, it would be placed on top of the sub-gasket, followed by another 10 mil (254 µm) ePTFE gasket. The second GDM is placed inside the gasket and spacer window with the MP-30Z layer facing down. The cathode side of the cell hardware was placed on top of the layered assembly with the flow channels facing down. The hardware was compressed with a total of eight bolts, all bolts had spring washers (Belleville disc springs, purchased from MSC Industrial Supply Co. (Cat #8777849)) to maintain afixed load on the cell during operation. The bolts were tightened to a fixed distance that previously had been established to provide a compressive pressure of 100-120 psi in the active area. Compression pressure was measured by using FujiFilm® LLW (SuperLow) pressure paper from Sensor Products, Inc., Madison, N.J.

[0199] The cell was connected to a fuel-cell test station. The purpose of the station is to supply humidified fuel and reactant to the cell at controlled dewpoints; control the gas flow rates, cell temperature, and pressure; and control and / or record the current and / or voltage for various operating conditions. Gasses were humidified by bubbling dry gas through heated water; hereafter referred to as humidifier bottle. The humidity at the cell inlet during testing was carefully controlled by maintaining the humidifier bottle temperatures and liquid level, and by heating all inlet lines between the station and the cell up to 105 degrees C to prevent any condensation in the lines. In all cases, the dew point of the gas delivered to the anode and / or cathode was calibrated by independently measuring the dew point with probes from Vaisala (HMT330, Vantaa, Finland). Two types of test stations were used. The first station type, Station Type 1, consisted of GlobeTech® gas units (GlobeTech®, Inc., Albuquerque, N.M.) withScribner load units 890B (Scribner Associates, Southern Pines, N.C.). The humidifier bottles in the GlobeTech® gas units were replaced by bottles purchased fromElectrochem Corporation, Woburn, M.A. The second station type, Station Type 2, consisted of gas units built in-house with Scribner load units 890e (Scribner Associates, Southern Pines, N.C.). The results do not depend on the station used.

[0200] The cells were conditioned at a cell temperature of 80 degrees C with inlet dew points of 80 degrees C (100 percent relative humidity) on both the anode and cathode. The outlet gas pressure of both sides was 25 psig. The gas supplied to the anode humidifier bottle was laboratory grade hydrogen at a flow rate 1.3 times greater than what is needed to maintain the rate of hydrogen conversion as determined by the current in the cell (i.e., 1.3 times stoichiometry). Filtered, compressed, and dried air was supplied to the cathode humidifier bottle at a flow rate of 2.0 times stoichiometry. The conditioning process involved cycling the cell at 80 degrees C between set potentials of 600 mV for 45 seconds, open-circuit voltage for 30 seconds, 300 mV for 60 seconds, and open-circuit voltage for 30 seconds. The cycle was repeated for four hours, at which time stable current responses had been established for at least 1 hour. To estimate initial performance a rapid polarization curve was taken by controlling the applied potential and applied current following the order of conditions and times in Table 4. The polarization curves varied based on station type due to incumbentprocedures stored on the computers. Station Type 1 held each condition for 60 seconds and was measured at 25psig. Station Type 2 held each condition at 15 seconds, unless otherwise indicated, and was measured at ambient pressure. The polarization curve on Station Type 2 is published in Edmundson, M. D. Tomiie, T. and Busby, F. C., ECS Transactions, 2010, 33, 1297 and denoted as “G1.” The type of polarization curve used does not impact lifetime testing. Table 4. Polarization curve procedures used on each station type, recorded after the condition step. Sequence Station Type 1Station Type 2 setpoints setpoints 1600 mV 200 mV (150 seconds)2 500 mV 300 mV3 400 mV 400 mV4 450 mV 300 mV5 550 mV 500 mV6 650 mV 400 mV7 750 mV 600 mV (30 seconds)8 850 mV 500 mV9 OCV 650 mV10 5 mA / cm2 600 mV (30 seconds)11 10 mA / cm2 400 mA / cm212 20 mA / cm2 650 mV13 30 mA / cm2 200 mA / cm2 (30 seconds)14 40 mA / cm2 65 mA / cm215 50 mA / cm2 20 mA / cm216 100 mA / cm2 10 mA / cm217 800 mV OCV18 700 mV 10 mA / cm219 20 mA / cm220 65 mA / cm221 200 mA / cm2 (30 seconds)22 400 mA / cm2

[0201] After the above procedure, the cells were set to the OCV hold life-test conditions. Specific test conditions were a cell temperature of 95 degrees C, 65 degrees C dew points for both hydrogen and air (30 percent relative humidity), with flows of 100 and 200 sccm, respectively. Outlet pressure was 25 psi for both sides. No current was flowing, the cell was operating at OCV.

[0202] Exhaust water from each test was collected in PTFE-lined stainless steel condenser bottles (304L-HDF4-500-T and 304L-HDF4-1000T, Swagelok, Solon Ohio)and analyzed for fluoride ions as means to evaluate the chemical degradation rate. This is a well-known technique to establish degradation of fuel-cell membranes that contain perfluorosulfonic acid ionomers. The anode and cathode condensates were collected separately for safety reasons and then combined for analysis. Water sampleswere collected about every 24 hours. Five grams of the mixed condensate were mixed with 5 grams of Total Ionic Strength Adjustment Buffer (TISAB II with CDTA 940909, Thermo Fisher Scientific, Chelmsford, M.A.), and the fluoride concentration in parts- per-billion, cF−, was determined using a calibrated ion-selective electrode (ORION (TM) 9609BNWP from Thermo Fisher Scientific, Chelmsford, M.A.). At each relative time of water collection, the fluoride release rate (FRR) in units of grams F- / cm2-hr was then calculated as,^× ^, where ^^^^ is the total mass of watercollected in grams, ∆^ is the time of collection in hours, and ^ is the active area of theMEA in cm2.

[0203] ^^^ =^^^^^^^^ ^^^× ∆^ × ^, ∆^^

[0204] The cumulative weight percent loss, ^^^, was calculated as, 100 + ^^^^^,where ^ is the relative time since the start of the test, ^^^^,^^^^^^^, is the mass per areaof initial fluorine content of the membrane in g / cm2. The cumulative weight percent loss of fluorine at 100h was then interpolated from the data and used as comparison metric across samples. Fuel Cell Performance Testing

[0205] Because fuel-cell stacks are subject to a wide range of cell temperatures and relative humidities, a robust beginning-of-life test was used to evaluate the current- voltage performance of MEAs containing the inventive membrane. A detailed description of the test protocol can be found in Edmundson, M. D. Tomiie, T. and Busby, F. C., ECS Transactions, 2010, 33, 1297.

[0206] Materials to be tested were prepared as outlined below in the examples, and then made into MEAs following the same procedure and components described in the OCV Hold Testing Method. A low cathode loading of 0.1 mg / cm2of platinum supportedon a ketjen black carbon was purposefully chosen to increase the likelihood of observing a performance impact due to the presence of the additives.

[0207] No sub-gaskets were applied to the MEA. The MEA was placed between twosheets of polyethylene and cut to a final part size of 7.62 x 7.26 cm using custom steel- rule dies and a manual die press (Lucris MA Series III, Ocean View, Queensland, Australia).

[0208] For testing, the MEA was assembled into cell hardware using the procedure outlined below. The cell hardware is the same as described in the OCV Hold Testing Method. The GDM used was a carbon paper with a microporous layer, CNW10A, obtained from W.L. Gore & Associates, Elkton, MD. Cells were assembled with multiplelayers of discrete PET gaskets (ranging in thickness from 38 to 125 microns), having asquare window of 5.0 cm x 5.0 cm, such that the GDM is compressed by 20 – 30%of the original thickness. The resulting MEA active area was 25 cm2.

[0209] The soft-components were first assembled and cold-pressed in a house-built metal jig to ensure alignment of all layers. The jig was placed face-up on a workbench. The previously determined number and thickness of PET gaskets were place on the bottom. Then, one GDM was placed inside the gaskets, in a shallow pocket inside the jig, with the microporous layer facing up. The MEA was placed on top of the GDM with anode-side down. Then, the previously determined number and thickness of PET gaskets were place on the top. A metal frame for the jig with a 25cm2window was placed on top of the gaskets. The second GDM was placed inside the frame, with the microporous layer facing down. A metal block was placed inside the frame. The entire assembly was cold pressed (Bosch Rexroth Corporation W-26188-2080) to 30 psi for 30 seconds.

[0210] To build the cell, the anode side of the cell hardware was placed with flow channels facing up on a workbench. The cell components were removed from the jig as one piece and placed on top of the flow channels, with the cathode side facing up. The cathode side of the cell hardware was placed on top of the layered assembly with the flow channels facing down. The hardware was compressed with a total of eight bolts, all bolts were torqued to 6 N-m.

[0211] The cell was connected to a fuel-cell test station. The purpose and operation of the station is the same as described in the OCV Hold Testing Method. The humidity at the cell inlet during testing was carefully controlled by maintaining the humidifierbottle temperatures and liquid level, and by heating all inlet lines between the station and the cell to 100 degrees C to prevent any condensation in the lines. The test station consisted of GlobeTech gas unit (GlobeTech, Inc., Albuquerque, N.M.) with a Scribner load unit 890B (Scribner Associates, Southern Pines, N.C.). The humidifier bottles in the GlobeTech gas units were replaced by bottles purchased from Electrochem Corporation, Woburn, M.A.

[0212] The conditioning and test protocol performed was the same as described in the publication. At each point along the polarization curve, the current-interrupt technique is used to obtain the ohmic resistance of the fuel cell, this is typically shown on a secondary-axis. In this technique the current is interrupted for a very short time interval (on the order of a few milliseconds) and resulting voltage is recorded. The differencebetween the cell voltage before and after the current interrupt, divided by the current, is the cell resistance. Representative data from the protocol was chosen to exemplifythe performance impact of the additives on fuel-cell performance. The selected data was from the P3 condition, described in the protocol, with a cell temperature of 80 degrees C and inlet dew points of 55 degrees C. Backpressure of 50 kPag was applied to both sides of the cell. Hydrogen and air stoichiometries of 1.3 and 2.0 were used, respectively. A G2+ polarization curve sequence, described in Figure 1 of the publication, was used to measure the performance, and took about 80 minutes. The ohmic resistance obtained from current interrupt was also recorded at this condition. This condition was chosen as representative of hot-dry conditions, relevant to the way many fuel-cell stacks operate, without being limited by other sources of loss (such as anode dry out). No change in the results was observed when considering other operating conditions. EXAMPLES

[0213] Without intending to limit the scope of the present invention, the SPEs and method of production of the present invention may be better understood by referring to the following examples. A legend of the additives used and labels can be found inTable 2. A summary of examples is provided in Table 3.

[0214] Materials: Ionomer dispersions were purchased from Asahi Glass Company(IW111-700 and IW111-700NPC, EW 720, typically 19-20wt% solids in about water- ethanol (approximately 1:1). The organic antioxidants quercetin hydrate, catechinhydrate, alizarin, purpurin, propyl gallate, caffeic acid (3,4-dihydroxycinnamic acid), curcumin, hesperetin, epicatechin, and esculetin (6,7-dihydroxycoumarin) werepurchased from Sigma Aldrich and used as received unless noted as “purified” in the examples below. Resveratrol and epigallocatechin gallate were purchased fromAmbeed, Inc, and used as received. Alizarin and purpurin from Sigma Aldrich were purified according to procedures found in Armarego and Chai, Purification ofLaboratory Chemicals, 6thEd, 2009, Elsevier, page 357 and 335, respectively. Purpurin was also purchased from Fisher Scientific, and purified by stirring an ethyl acetate solution (2g / 250mL) with Amerchrom 50WX4 hydrogen form beads (Sigma Aldrich, 3g, washed with 0.1M H2SO4 then DI-water before use) for 30 minutes, followed by filtration, washing with water, drying over sodium sulfate (Sigma Aldrich), filtration, and solvent removal (rotary evaporator and vacuum pump). Quercetinhydrate and catechin hydrate were estimated from TGA to contain two moles of water, and the hydrate molecular weight was used in calculations. Ethanol (Absolute, 200proof, 99.5+%) was purchased from ThermoFisher Scientific. Dimethylformamide(DMF) and 1-pentanol and were purchased from Sigma Aldrich, and used as received. Cerium salts were purchased from Sigma Aldrich and used as received. A Branson2510 ultrasonic bath was used at times to aid in the dissolution of organic additives. Mole percent (mol%) refers to the moles of additive relative the ionomer -SO3H group.In the following examples an ePTFE membrane with mass per area of 4.0 g / m2, athickness of 11.5 µm, an apparent density of 0.3483 g / cc and a bubble point of 77.95psi was used as microporous polymer matrix. Examples of suitable perfluorinated porous polymeric materials for use in fuel cell applications include ePTFE made in accordance with the teachings of U.S. Patent No.8,757,395, which is incorporated herein by reference in its entirety, and commercially available in a variety of forms from W. L. Gore & Associates, Inc., of Elkton, Md.Example 1 Comparative Example 1.1

[0215] An ionomer dispersion of IW111-700 (20.0g, 19.64% solids; 40.10% water; 40.26% ethanol) was diluted with 19.28 g of ethanol in a jar equipped with a magnetic stir bar and PTFE-lined cap. The mixture was stirred overnight at ambient temperature,then formed into a SPE membrane as described above, 8.4-8.5µm thick with twoionomer layers and one ePTFE layer in the middle. Comparative Example 1.2

[0216] A control dispersion containing 10 wt% solids and 2 mol% cerium ion (Ce3+) relative to the sulfonic acid group of the ionomer was prepared as follows. A solutionof IW111-700NPC (8.05g; 19.80% solids; 38.64% water; 41.56% ethanol; 0.1905% Ce3+) was combined with a solution of IW111-700 (11.913g, 19.64% solids; 40.10% water; 40.26% ethanol) and diluted with 19.49 g of ethanol in a 120mL jar equipped with a magnetic stirring bar and PTFE-lined cap. The resulting mixture was stirredovernight at ambient temperature, then formed into a SPE membrane as describedabove, 8.4 µm thick with two ionomer layers and one ePTFE layer in the middle. Comparative Example 1.3

[0217] A control dispersion containing 10wt% solids and 3.3mol% cerium ion relative to the sulfonic acid group of the ionomer was prepared as follows. Cerium nitratehexahydrate (0.0993 g) was dissolved in 2.65 g of distilled water in a jar equipped with amagnetic stir bar and PTFE-lined cap. To this was added 25.92 g of IW111-700(19.29% solids, 40.31% water, balance ethanol). While the mixture was stirring, 22.30g of ethanol were added, and the mixture was allowed to stir overnight at ambient temperature. Membrane prototypes, 8.2-8.3 µm, with thick with two ionomer layers andone ePTFE layer in the middle were prepared as described above. Example 2 Inventive Group Example 2.1

[0218] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0951 g (4.05 mol%) of quercetin hydrate. Ethanol (25.10g) was added and themixture was stirred until the quercetin hydrate dissolved completely, about ten minutes. To this was added 10.05 g of IW111-700NPC (19.92% solids, 39.94% water, balance ethanol), and 14.93 g of IW111-700 (19.64% solids; 40.10% water). The resultingionomer dispersion was stirred overnight and then formed into membrane prototypes 8.3 µm thick with two ionomer layers and one ePTFE layer in the middle, as described above. Inventive Group Example 2.2

[0219] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.1879 g (8 mol%) of quercetin hydrate. Ethanol (26.10g) was added and the mixturewas stirred until the quercetin hydrate dissolved completely, about 10 minutes. To thiswas added 10.25 g of IW111-700NPC (19.92% solids, 42.1% water, balance ethanol), and 15.309 g of IW111-700 (19.45% solids; 42.11% water). The dispersion was stirredovernight and then formed into membrane prototypes, 8.35µm thick, with two ionomer layers and one ePTFE layer in the middle, as described above. Example 3 Inventive Group Example 3.1

[0220] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0682 g (5 mol%) of catechin hydrate and 11.65 g of ethanol. The mixture was stirreduntil the additives dissolved completely (ca.10 minutes). To this was added 3.06 g of IW111-700NPC (19.85% solids, 41.25% water, balance ethanol), 12.168 g of IW111-700 (19.71% solids; 38.42% water), and 3.8 g distilled water. The dispersion wasstirred about 1 hour and then formed into membrane prototypes, 8.2 µm thick, with twoionomer layers and one ePTFE layer in the middle, as described above. Inventive Group Example 3.2

[0221] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.2182 g (8 mol%) of catechin hydrate and 30.8 g of ethanol. The mixture was stirreduntil the additives dissolved completely (ca. 10 minutes). To this was added 6.15 g ofIW111-700NPC (19.85% solids, 41.25% water, balance ethanol), 24.2 g of IW111-700(19.71% solids; 38.42% water), and 0.9 g distilled water. The dispersion was stirredabout 1 hour and then formed into membrane prototypes, 8.3 µm thick, with twoionomer layers and one ePTFE layer in the middle, as described above. Example 4 Inventive Group Example 4.1

[0222] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0492 g (4 mol%) of caffeic acid. Ethanol (24.75 g) was added, and the mixture wasstirred until the caffeic acid dissolved completely, about 10 minutes. To this was added10.05 g of IW111-700NPC (19.92% solids, 39.94% water, balance ethanol), and 14.93 gof IW111-700 (19.64% solids; 40.10% water). The dispersion was stirred overnightand then formed into membrane prototypes, 8.1-8.2 µm thick, with two ionomer layers and one ePTFE layer in the middle, as described above.Inventive Group Example 4.2

[0223] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.1001 g (8 mol%) of caffeic acid. Ethanol (26.20g) was added and the mixture wasstirred until the caffeic acid dissolved completely, about 10 minutes. To this was added10.25 g of IW111-700NPC (19.8% solids, 38.64% water, balance ethanol), and 15.309 gof IW111-700 (20.40% solids; 42.29% water). The dispersion was stirred overnightand then formed into membrane prototypes, 8.6 µm thick, with two ionomer layers and one ePTFE layer in the middle, as described above. Inventive Group Example 4.3

[0224] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.1239 g (9.9 mol%) of caffeic acid. Ethanol (26.3 g) was added and the mixture wasstirred until the caffeic acid dissolved completely, about 10 minutes. To this was added10.25 g of IW111-700NPC (19.8% solids, 38.64% water, balance ethanol), and 14.78 gof IW111-700 (20.23% solids; 39.26% water). This ratio of IW111-700NPC andIW111-700 provided cerium(III) at 3.3 mol%. The dispersion was stirred one hour andthen formed into membrane prototypes, 8.3-8.5 µm thick, with two ionomer layers and one ePTFE layer in the middle, as described above. Example 5 Inventive Group Example 5.1

[0225] Cerium(III) nitrate hexahydrate (0.0993 g, 3.3 mol%) was added to a jar equipped with a magnetic stir bar and PTFE-lined cap. Distilled water (3g) was addedand the mixture was swirled until dissolved, a couple of minutes. In a separate vial,0.1239 g of caffeic acid (9.9 mol%) was dissolved in 7 g of ethanol. The ethanol solutionof caffeic acid was added dropwise to the aqueous solution of cerium(III) nitrate. Thismixture was added to IW111-700 (25.92 g, 19.29% solids, 40.31% water, balance ethanol) with stirring. Ethanol (15.5 g) was then added and the homogeneous, peach-colored dispersion was stirred overnight. The dispersion was then formed intomembrane prototypes, 8.3-8.5 µm thick, with two ionomer layers and one ePTFE layer in the middle, as described above.Example 6 Inventive Group Example 6.1

[0226] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0676 g (4.1 mol%) of alizarin. Ethanol (24.9g) was added and the mixture wassonicated for 10 minutes. To this was added 10.05 g of IW111-700NPC (19.92% solids,39.94% water, balance ethanol), and 14.93 g of IW111-700 (19.64% solids; 40.10% water). The dispersion was stirred overnight and then formed into membraneprototypes, 8.5-8.6 µm thick, with two ionomer layers and one ePTFE layer in themiddle, as described above. Inventive Group Example 6.2

[0227] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0667 g (4.05mol%) of purified alizarin. Ethanol (24.9 g) was added and the mixturewas sonicated for 10 minutes. To this was added 10.25 g of IW111-700NPC (19.92%solids, 42.10% water, balance ethanol), and 15.436 g of IW111-700 (19.29% solids; 40.31% water). The dispersion was stirred overnight and then formed into membraneprototypes, 7.8-7.9 µm hick, with two ionomer layers and one ePTFE layer in themiddle, as described above. Inventive Group Example 6.3

[0228] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0688 g (4.1 mol%) of alizarin and 22.80 g of ethanol. The mixture was stirred untilthe additives dissolved completely, using a sonic bath to assist dissolution (10 minutes). To this was added 10.25 g of IW111-700NPC (19.92% solids, 42.1% water, balance ethanol), and 15.247 g of IW111-700 (19.53% solids; 42.00% water), and 2.285 g of 1-pentanol. The dispersion was sonicated in a bath for 10 minutes. The dispersion wasstirred overnight and then formed into membrane prototypes, 8.0 µm thick, with twoionomer layers and one ePTFE layer in the middle, as described above. Example 7 Inventive Group Example 7.1

[0229] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0380 g (4 mol%) of resveratrol and 11.58 g of ethanol. The mixture was stirred until the additives dissolved completely (ca. 10 minutes). To this was added 3.06 g ofIW111-700NPC (19.85% solids, 41.25% water, balance ethanol), and 12.168 g ofIW111-700 (19.71% solids; 38.42% water). The dispersion was stirred about 1 hour and then formed into membrane prototypes, 8.0 µm thick, with two ionomer layers andone ePTFE layer in the middle, as described above. Example 8 Inventive Group Example 8.1

[0230] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.2865 g (9 mol%) of epigallocatechin gallate and 20.8 g of ethanol. The mixture was stirred until the additives dissolved completely (ca.10 minutes). To this was added 5.1 gof IW111-700NPC (19.85% solids, 41.25% water, balance ethanol), and 20.281 g ofIW111-700 (19.71% solids; 38.42% water). The dispersion was stirred about 1 hour and then formed into membrane prototypes, 8.4 µm thick, with two ionomer layers andone ePTFE layer in the middle, as described above. Example 9 Inventive Group Example 9.1

[0231] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.1679 g (8 mol%) of hesperetin and 25.7 g of ethanol. The mixture was stirred untilthe additives dissolved completely (ca.10 minutes). To this was added 5.1 g of IW111-700NPC (19.85% solids, 41.25% water, balance ethanol), 20.191g of IW111-700 (19.71% solids; 38.42% water), and 0.6 g distilled water. The dispersion was stirredovernight and then formed into membrane prototypes, 8.5 µm thick, with two ionomerlayers and one ePTFE layer in the middle, as described above. Example 10 Inventive Group Example 10.1

[0232] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.1613 g (8 mol%) of epicatechin and 25.5 g of ethanol. The mixture was stirred until the additives dissolved completely (ca.10 minutes). To this was added 5.1 g of IW111- 700NPC (19.85% solids, 41.25% water, balance ethanol), 20.191g of IW111-700 (19.71% solids; 38.42% water), and 1.1 g distilled water. The dispersion was stirred overnight and then formed into membrane prototypes, 8.1 µm thick, with two ionomerlayers and one ePTFE layer in the middle, as described above.Example 11 Inventive Group Example 11.1

[0233] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.1136 g of catechin hydrate (5 mol%). Ethanol (27.35 g) was added and the mixture was stirred until the additives dissolved completely, typically about 10 minutes. To this was added 24.51 g of IW111-700(20.40% solids; 41.24% water). The dispersion was stirred overnight and then formedinto membrane prototypes, 8.0-8.4 µm thick, with two ionomer layers and one ePTFElayer in the middle, as described above. Example 12 Inventive Group Example 12.1

[0234] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.0626 g of caffeic acid (5 mol%). Ethanol(26.0 g) was added and the mixture was stirred until the additives dissolved completely,typically about 10 minutes. To this was added 24.405 g of IW111-700 (19.68% solids;42.34% water). The dispersion was stirred overnight and then formed into membraneprototypes, 7.9-8.1 µm thick, with two ionomer layers and one ePTFE layer in themiddle, as described above. Example 13Inventive Group Example 13.1

[0235] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.0619 g of esculetin (5 mol%). Ethanol(27.10 g) was added and the mixture was stirred until the additives dissolved completely, typically about 15 minutes. To this was added 24.285 g of IW111-700(20.59% solids; 42.31% water). The dispersion was stirred overnight and then formedinto membrane prototypes, 8.2-8.4 µm thick, with two ionomer layers and one ePTFElayer in the middle, as described above.Example 14 Inventive Group Example 14.1

[0236] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0667 g of purified alizarin (4 mol%) and 0.0751 g of caffeic acid (6 mol%). Ethanol(23.75 g) and 1-pentanol (1.8 g) were added and the mixture was sonicated 10 minutes until the additives dissolved. To this was added 10.25 g of IW111-700NPC (19.92%solids, 42.10% water, balance ethanol), and 15.436 g of IW111-700 (19.29% solids; 40.31% water). The dispersion was stirred overnight and then formed into membraneprototypes, 8.4-8.7 µm thick, with two ionomer layers and one ePTFE layer in themiddle, as described above. Inventive Group Example 14.2

[0237] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0667 g of purified alizarin (4 mol%) and 0.0626 g of caffeic acid (5 mol%). Ethanol(23.75 g) and 1-pentanol (1.8 g) were added and the mixture was sonicated 10 minutes until the additives dissolved. To this was added 10.25 g of IW111-700NPC (19.92%solids, 42.10% water, balance ethanol), and 15.436 g of IW111-700 (19.29% solids; 40.31% water). The dispersion was stirred overnight and then formed into membraneprototypes, 8.4-8.7 µm thick, with two ionomer layers and one ePTFE layer in themiddle, as described above. Inventive Group Example 14.3

[0238] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0667 g of purified alizarin (4 mol%) and 0.0626 g of caffeic acid (5 mol%). Ethanol(26.35 g) was added, and the mixture was sonicated 10 minutes until the additives dissolved. The solution of antioxidants in ethanol was stirred overnight at ambienttemperature. To this was added 10.25 g of IW111-700NPC (19.80% solids, 38.64%water, balance ethanol), and 14.78 g of IW111-700 (20.23% solids; 39.26% water). The dispersion was sonicated for 10 minutes, then stirred about 30 minutes and formed into membrane prototypes, 8.6-8.9 µm thick with two ionomer layers and one ePTFElayer in the middle, as described above. Inventive Group Example 14.4

[0239] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0688 g of alizarin (4.1 mol%) and 0.0751 g of caffeic acid (6mol%). Ethanol (24 g)and 1-pentanol (1.78 g) were added and the mixture was sonicated 10 minutes until the additives dissolved. To this was added 10.25 g of IW111-700NPC (19.92% solids,42.10% water, balance ethanol), and 15.247 g of IW111-700 (19.53% solids; 42.0% water). The dispersion was stirred overnight and then formed into membraneprototypes, 8.4 µm thick, with two ionomer layers and one ePTFE layer in the middle,as described above. Inventive Group Example 14.5

[0240] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0516 g of alizarin (3 mol%) and 0.1001 g of caffeic acid (8 mol%). Ethanol (24.05 g)and 1-pentanol (1.79 g) were added and the mixture was sonicated 10 minutes at 40°C until the additives dissolved. To this was added 10.25 g of IW111-700NPC (19.92%solids, 42.10% water, balance ethanol), and 15.247 g of IW111-700 (19.53% solids; 42.0% water). The dispersion was sonicated 10 minutes at 40°C, stirred for anadditional 30 minutes, and then formed into membrane prototypes, 8.5-8.6 µm thickwith two ionomer layers and one ePTFE layer in the middle, as described above. Example 15Inventive Group Example 15.1

[0241] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.1136 g of catechin hydrate (5 mol%).Ethanol (27.15 g) was added, and the mixture was stirred until the additives dissolved completely. To this was added 10.25 g of IW111-700NPC (19.82% solids, 43.17%water, balance ethanol), and 14.647 g of IW111-700 (20.40% solids; 41.24% water). The dispersion was stirred overnight and then formed into membrane prototypes, 8.0 µm thick, with two ionomer layers and one ePTFE layer in the middle, as describedabove. Example 16 Inventive Group Example 16.1

[0242] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.0619 g of esculetin (5 mol%). Ethanol(26.7g) was added and the mixture was stirred until the additives dissolved completely. To this was added 10.25 g of IW111-700NPC (19.82% solids, 43.17% water, balance ethanol), and 14.647 g of IW111-700 (20.40% solids; 41.24% water). The dispersionwas stirred overnight and then formed into membrane prototypes, 8.3 µm thick withtwo ionomer layers and one ePTFE layer in the middle, as described above. Example 17 Inventive Group Example 17.1

[0243] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.0626 g of caffeic acid (5 mol%). Ethanol(26.75g) was added and the mixture was stirred until the additives dissolved completely. To this was added 10.25 g of IW111-700NPC (19.82% solids, 43.17%water, balance ethanol), and 14.647 g of IW111-700 (20.40% solids; 41.24% water). The dispersion was stirred overnight and then formed into membrane prototypes, 8.5 µm thick with two ionomer layers and one ePTFE layer in the middle, as describedabove. Inventive Group Example 17.2

[0244] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.1001 g of caffeic acid (8 mol%). Ethanol(27.05 g) was added, and the mixture was stirred until the additives dissolved completely. To this was added 10.25 g of IW111-700NPC (19.82% solids, 43.17%water, balance ethanol), and 14.647 g of IW111-700 (20.40% solids; 41.24% water). The dispersion was stirred overnight and then formed into membrane prototypes, 8.5 µm thick, with two ionomer layers and one ePTFE layer in the middle, as describedabove. Example 18 Inventive Group Example 18.1

[0245] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0756 g of purpurin (Sigma Aldrich, 4.25mol%) and 0.0737 g of propyl gallate (5mol%). Ethanol (26.5 g) was added, and the mixture was stirred until the additives dissolved completely, using a sonic bath to assist dissolution (10 minutes). To this was added10.25 g of IW111-700NPC (19.80% solids, 38.64% water, balance ethanol), and 14.78g of IW111-700 (20.23% solids; 39.26% water). The dispersion was stirred for an hourand then formed into membrane prototypes, 9.2 µm thick, with two ionomer layers andone ePTFE layer in the middle, as described above. Inventive Group Example 18.2

[0246] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0756 g of purified purpurin (Sigma Aldrich, 4.25 mol%) and 0.0737 g of propyl gallate (5 mol%). Ethanol (25.65 g) was added, and the mixture was stirred about 30 minutesuntil the additives dissolved. To this was added 10.25 g of IW111-700NPC (19.92%solids, 42.10% water, balance ethanol), and 15.436 g of IW111-700 (19.29% solids; 40.31% water). The dispersion stirred overnight at ambient temperature and formedinto membrane prototypes, 8.6 µm thick, with two ionomer layers and one ePTFE layerin the middle, as described above. Inventive Group Example 18.3

[0247] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0756 g of purified purpurin (Sigma Aldrich, 4.25 mol%) and 0.0737 g of propyl gallate (5 mol%). Ethanol (23.82 g) and 1-pentanol (1.80 g) were added and the mixture wasstirred about 30 minutes until the additives dissolved. To this was added 10.25 g ofIW111-700NPC (19.92% solids, 42.10% water, balance ethanol), and 15.436 g of IW111-700 (19.29% solids; 40.31% water). The dispersion was sonicated for 10minutes, then stirred about 30 minutes and formed into membrane prototypes, 8.9-9.0 µm thick, with two ionomer layers and one ePTFE layer in the middle, as describedabove. Inventive Group Example 18.4

[0248] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0840 g of purpurin (Sigma Aldrich, 4.72 mol%) and 0.0737 g of propyl gallate (5 mol%). Ethanol (24.55 g) and DMF (1.0 g) were added, and the mixture was sonicatedusing a sonic bath at 40°C to assist dissolution (10 minutes). This mixture was stirredovernight at ambient temperature. To this was added 10.25 g of IW111-700NPC(19.99% solids, 45.29% water, balance ethanol), and 15.273 g of IW111-700 (19.45% solids; 42.11% water). The dispersion was stirred for an hour and then formed into membrane prototypes, 8.5-8.7 µm thick, with two ionomer layers and one ePTFE layerin the middle, as described above.Inventive Group Example 18.5

[0249] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0840 g of purified purpurin (Fisher Scientific, 4.72 mol%) and 0.0737 g of propyl gallate (5 mol%). Ethanol (26.80 g) was added, and the mixture was stirred until theadditives dissolved, about 10 minutes. To this was added 10.25 g of IW111-700NPC(19.94% solids, 41.33% water, balance ethanol), and 15.587 g of IW111-700 (20.40% solids; 42.29% water). The dispersion was sonicated for 10 minutes at 40°C, stirredovernight, and then formed into membrane prototypes, 9.2 µm thick, with two ionomerlayers and one ePTFE layer in the middle, as described above. Inventive Group Example 18.6

[0250] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0840 g of purpurin (Sigma Aldrich, 4.72 mol%) and 0.0737 g of propyl gallate (5 mol%). Ethanol (25.9 g) was added, and the mixture was sonicated 10 minutes at 40°C until the additives dissolved. To this was added 10.25 g of IW111-700NPC (19.92%solids, 42.10% water, balance ethanol), and 15.247 g of IW111-700 (19.53% solids; 42.0% water). The dispersion was sonicated for 10 minutes at 40°C, stirred for anadditional 30 minutes, and then formed into membrane prototypes, 8.8-9.2 µm, thick with two ionomer layers and one ePTFE layer in the middle, as described above. Inventive Group Example 18.7

[0251] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0845 g of purpurin (Sigma Aldrich, 4.75 mol%) and 0.1179 g of propyl gallate (8 mol%). Ethanol (25.7 g) and DMF (1.5 g) were added, and the mixture was sonicatedusing a sonic bath ambient temperature (10 minutes). To this was added 10.25 g of IW111-700NPC (19.99% solids, 45.29% water, balance ethanol), and 14.562 g of IW111-700 (20.40% solids; 42.29% water). The dispersion was stirred for 30min andthen formed into membrane prototypes, 8.5-8.6 µm thick, with two ionomer layers andone ePTFE layer in the middle, as described above. Example 19 Inventive Group Example 19.1

[0252] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0840 g of purpurin (Sigma Aldrich, 4.72mol%) and 0.1175 g of quercetin hydrate.DMF (2.0 g) was added, and the mixture was swirled until dissolved, a few minutes. Ethanol (23.95 g) was added slowly, and the mixture was sonicated for 10 minutes in an ultrasonic bath. To this was added 10.25 g of IW111-700NPC (19.99% solids,45.29% water, balance ethanol), and 15.273 g of IW111-700 (19.45% solids; 42.11% water). The dispersion was stirred overnight and then formed into membraneprototypes, 8.5 µm thick, with two ionomer layers and one ePTFE layer in the middle,as described above. Inventive Group Example 19.2

[0253] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0756 g of purpurin (Sigma Aldrich, 4.25 mol%) and 0.1175 g of quercetin (5 mol%). Ethanol (26.9 g) was added, and the mixture was sonicated for 10 minutes. Thesolution of antioxidants in ethanol was stirred overnight at ambient temperature. Tothis was added 10.25 g of IW111-700NPC (19.80% solids, 38.64% water, balance ethanol), and 14.78 g of IW111-700 (20.23% solids; 39.26% water). The dispersionwas stirred for about 30 minutes and formed into membrane prototypes, 8.3-8.6 µm thick, with two ionomer layers and one ePTFE layer in the middle, as described above.

[0254] While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to the skilled artisan. It may beunderstood that aspects of the invention and portions of various embodiments and various features recited above and / or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the variousembodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by the skilled artisan. Furthermore, the skilled artisan will appreciate that the foregoing descriptionis by way of example only and is not intended to limit the invention.Example 20 Inventive Group Example 20.1

[0255] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0940 g of quercetin hydrate (4 mol%) and 0.1279 g of curcumin (5 mol%). Ethanol (27.45g) was added and the mixture was stirred 15 minutes, followed by one minute in an ultrasonic bath (ambient temperature). To this was added 10.25 g of IW111- 700NPC (19.82% solids, 43.17% water, balance ethanol), and 14.512 g of IW111-700(20.40% solids; 41.24% water). The dispersion was stirred overnight and then formedinto membrane prototypes, 7.5 µm thick with two ionomer layers and one ePTFE layerin the middle, as described above. Example 21 Inventive Group Example 21.1

[0256] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0380 g (4 mol%) of resveratrol, 0.0682g (5mol%) of catechin, and 14.8 g of ethanol.The mixture was stirred until the additives dissolved completely (ca.10 minutes). To this was added 3.06 g of IW111-700NPC (19.85% solids, 41.25% water, balanceethanol), 12.168 g of IW111-700 (19.71% solids; 38.42% water), and 1.0 g distilledwater. The dispersion was stirred about 1 hour and then formed into membrane prototypes, 7.3 - 8.2 µm thick, with two ionomer layers and one ePTFE layer in themiddle, as described above. Example 22 Inventive Group Example 22.1

[0257] In a jar equipped with a magnetic stir bar and PTFE-lined cap was added 0.0614 g (4 mol%) of curcumin, 0.0682g (5mol%) of catechin, and 15 g of ethanol. Themixture was stirred until the additives dissolved completely (ca.10 minutes). To this was added 3.06 g of IW111-700NPC (19.85% solids, 41.25% water, balance ethanol), 12.168 g of IW111-700 (19.71% solids; 38.42% water), and 1.0 g distilled water. The dispersion was stirred about 1 hour and then formed into membrane prototypes, 7.7 µm thick, with two ionomer layers and one ePTFE layer in the middle, as describedabove.

[0258] As mentioned throughout the specification, mixtures of antioxidants may undergo different interactions, affecting antioxidant activity positively in an additive or synergistic manner, or negatively, in an antagonistic manner. While the mechanism(s)responsible for antioxidant effects are not yet understood, synergistic responses can be explained by: regeneration of the stronger antioxidant by the weaker antioxidant;formation of stable intermolecular complexes between the antioxidants that deliver higher antioxidant activity that the individual species; formation of dimers and adducts and / or new phenolic compounds with higher antioxidant power; solubility differences between the antioxidants which may affect phase distribution.

[0259] The organic antioxidants of this invention contain a variety of functional groups such as catechol, alcohol, carboxylic acid, phenol, ether, ketone, α,β-unsaturated ketones and carboxylic acids, and amine. Perfluorosulfonic acids present in the ionexchange material, both in monomeric and polymeric form, are strong acid catalysts used in organic synthesis to carryout functional group transformations and condensation reactions (Olah, G.A.; Iyer, P.S.; Surya Prakash, G.K. Synthesis 1986, 513). It is expected that under the conditions used for the formation of polymericmembranes (rapid drying in air using heat), organic antioxidants may undergo chemical reactions, which could deliver higher antioxidant power. Perfluorosulfonicacids are known to catalyze a wide variety of organic reactions including: acylation,alkylation of aromatics, and Friedel-Crafts related reactions, aldolization, ketolization, and ketalization, esterification, transesterification, and hydrolysis of esters, hydrolysis of ethers or saccharides, rearrangements, and conversion of nitriles to amides. (Gelbard, G. Ind. Eng. Chem. Res. 2005, 44, 8468 and there could be 100 more, easily).

[0260] The most likely reactions during the formation of proton exchange membranes according to the invention depend on the structure of the antioxidant. Antioxidants containing catechol groups are susceptible to aerobic oxidation. The oxidationprocess is affected by pH, with lower pH leading to a lower oxidation rate. However,studies have shown that dopamine may be polymerized at pH ~1 under hydrothermal conditions.(Zheng, W.; Fan, H.; Wang, L.; Jin, Z. Langmuir 2015, 31, 11671) Ceria has also been shown to be an effective oxidant that may catalyze oxidative dimerization / oligomerization, particularly during prototype fabrication.(Omran, B.; Baek, K-H. Molecules 2021, 26, 7031)

[0261] As a means of illustration, antioxidants containing carboxylate groups and phenol / catechol groups may undergo esterification / condensation reactions, or Friedel- Craft polymerization, as shown for caffeic acid (Example 3.1-3.3) in equation 1.Equation 1

[0262] Purpurin, and by analogy, alizarin, have been shown to add electrophiles at C3, and might react with caffeic acid if both antioxidants are present in the dispersion, such as in Examples 9.1-9.5

[0263] Quercetin has also been shown to undergo reactions with caffeic acid like those shown above (Examples 12.1,12.2), as shown in Equation 3. (Neto, A.S.; Veasco, I.T.; Pianowski, L.; Filho, N.O.S. PI0904460-4A2 17 / 11 / 2009 published 05 / 07 / 2011 (Brazilian patent, not sure how to cite it) Equation 3

[0264] The combination of quercetin and catechin (Example 10.1) could form the addition product shown in Equation 4, in addition to dimers and other oxidation products.Equation 4.

[0265] These examples are shown for illustration of the kinds of antioxidant interactions that may be possible and result in the observed synergistic performance improvements.

[0266] Therefore, it will be seen that the present invention provides proton exchange membranes and MEAs and electrochemical devices comprising said membranes and MEAs with improved durability compared to corresponding membranes, MEAs anddevices not containing the additives and blends described herein.

[0267] In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.

Claims

CLAIMS 1. A polymer electrolyte membrane comprising an ion exchange material and an additiveblend comprising at least two additives, wherein at least one of the at least two additives is anorganic additive selected from a peroxide decomposition catalyst, a radical scavenger, a freeradical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer.

2. A polymer electrolyte membrane according to claim 1, wherein the polymer electrolytemembrane comprises one or more layers of porous reinforcement.

3. A polymer electrolyte membrane according to any preceding claim, wherein theadditive blend comprises at least one of: a synthetic antioxidant, a natural non-enzymaticantioxidant, and a radical scavenger; optionally wherein one of:the synthetic antioxidant comprises a phenolic antioxidant (e.g. BHA, BHT, TBHQ); orthe synthetic antioxidant comprises a nano-antioxidant (e.g. an oxide, a metal nanoparticle, an antioxidant functionalised nanoparticle).

4. A polymer electrolyte membrane according to any preceding claim, wherein theorganic additive comprises a nonenzymatic antioxidant selected from: a quinone, ahydroquinone, a quinone-hydroquinone, a polyphenol selected from a flavonoid, a stilbene,and a phenolic acid; a coumarin, a chromone, an alkaloid, a catecholamine, a vitamin, acarotenoid, a phosphonic acid, a carboxylic acid, a phenolic and heterocyclic derivative radicalscavenger, or mixtures or derivatives thereof.

5. A polymer electrolyte membrane according to any preceding claim, wherein theorganic additive is selected from alizarin, purpurin, quinizarin, anthrarufin, rufigallol, thymol blue, alizairin-3-methyliminodiacetic acid, quercetin, myricetin, morin, kaempferol, baicalein,naringenin, naringenin chalcone, (E)-3-(e,4-dihydroxyphenyl)-1-(2,3,4-trihydroxyphenyl)prop- 2-ene-1-one (a flavonoid), genistein, luteolin, eriodictyol, hesperitin, hesperidin, quercetagetin,catechin, epicatechin, epigallocatechin, epigallocatechin gallate, taxifolin, caffeic acid, sinapicacid, ferulic acid, rosmarinic acid, coumaric acid, caftaric acid, gallic acid, tannic acid, propyl gallate, ellagic acid, 2,3,4-trihydroxybenzophenone, esculetin, 7,8-dihydroxy-4-methylcourmarin, daphnetin, 6,7-dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, 7,8-dihydroxy-3-(pyridin-2-yl)-2H-chromen-2-one, curcumin, bis-demethylcurcumin, dopamine, usnic acid, hydroxylated chromone-3-carboxylic acid, resveratrol, polyhydroxystilbenes such as (E) 2',5',3,4-tetrahydroxystilbene and (E) 3',4',3,4-tetrahydroxystilbene, avenanthramidederivatives, terephthalic acid, syringic acid, 2,6-dimethoxy-1,4-benzoquinone, tert-butylhydroquinone, derivatives thereof and / or mixtures thereof.

6. A polymer electrolyte membrane according to any preceding claim, wherein theorganic additive is selected from alizarin, purpurin, caffeic acid, propyl gallate, quercetin,catechin, esculetin, resveratrol, curcumin, epigallocatechin gallate, epicatechin, derivativesthereof, and mixtures or dervatives thereof.

7. A polymer electrolyte membrane according to any preceding claim, wherein theadditive blend comprises at least one inorganic additive.

8. A polymer electrolyte membrane according to claim 7, wherein the at least oneinorganic additive comprises a metal, its oxide or its salt, or mixtures thereof.

9. A polymer electrolyte membrane according to claim 7 or 8, wherein the at least oneinorganic additive comprises a metal selected from Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag,Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form, or their oxides, or their salts,or mixtures thereof, optionally wherein the inorganic additive comprises Ce3+ or cerium oxide(ceria).

10. A polymer electrolyte membrane according to any one of claims 7 to 9, wherein theinorganic additive comprises nanoparticles, nanotubes, nanorods, or mixtures thereof.

11. A polymer electrolyte membrane according to any one of claims 7 to 10, wherein theat least one inorganic additive comprises metal nanoparticles, optionally wherein the metalnanoparticles are selected from: Au (gold) nanoparticles, Pd (palladium) nanoparticles, Pt (platinum) nanoparticles, or mixtures thereof.

12. A polymer electrolyte membrane according to any one of claims 7 to 12, wherein theat least one inorganic additive is supported in a carrier, optionally wherein the carrier is carbon black.

13. A polymer electrolyte membrane according to any preceding claim, wherein theadditive blend comprises at least two different organic additives, optionally wherein the additive blend comprises two different organic additives, three different organic additives, four different organic additives, five different organic additives, or six different organic additives.

14. A polymer electrolyte membrane according to any preceding claim, wherein theadditive blend comprises at least two different organic additives and at least an inorganic additive.

15. A polymer electrolyte membrane according to claim 13 or 14, wherein the at least twoorganic additives are physically mixed in the additive blend.

15. A polymer electrolyte membrane according to claim 1, wherein the additive blendcomprises a physical mixture of compounds comprising:^ A quinone-hydroquinone type antioxidant and a polyphenolic acid antioxidant such asbut not limited to alizarin and caffeic acid; alizarin and propyl gallate; purpurin and propylgallate; purpurin and caffeic acid; ^A quinone-hydroquinone antioxidant and a flavonoid such as but not limited to purpurinand quercetin; ^A polyphenolic acid antioxidant and a flavonoid such as but not limited to caffeic acidand quercetin, propyl gallate and quercetin;^ A stilbene and a flavonoid such as but not limited to resveratrol and catechin;^ A polyphenol and a flavonoid such as but not limited to curcumin and quercetin,curcumin and catechin; ^A flavonoid antioxidant and a flavonoid antioxidant of a different subtype, such as butnot limited to catechin and quercetin; ^A flavonoid antioxidant and a coumarin, such as but not limited to quercetin andaesculetin; or a mixture or derivative thereof;optionally wherein the additive blend further comprises an inorganic additive, further optionally wherein the inorganic additive is selected from cerium, manganese, cobalt, zinc, aluminium, zirconium in the ionic form, in salt form, or oxides thereof, and / or combinations thereof.

16. A polymer electrolyte membrane according to any preceding claim, wherein theadditive blend comprises Ce3+.

17. A polymer electrolyte membrane according to any preceding claim, wherein the at leastone organic additive is present in the membrane in a concentration of from about 0.5 mol %to about 20 mol % relative to the sulfonic acid group of the ionomer, optionally from about 2mol % to about 12 mol %, or from about 4 mol % to about 8 mol %, or from about 5 mol % toabout 7 mol %, or from about 4 mol % to about 5 mol %, or from about 5 mol % to about 7mol %, or from about 6 mol % to about 8 mol %, relative to the ionomer exchange site (e.g.relative to sulphonic acid groups when the ionomer is PFSA).

18. A polymer electrolyte membrane according to any preceding claim, wherein the totalcontent of organic additive (e.g. total antioxidant content) in the membrane is up to about 20 mol%, or up to about 16 mol %, or up to about 15 mol %, or up to about 14 mol %, or up to about 11 mol %, optionally wherein the total content of organic additive in the membrane is from about 4 mol% to about 11 mol %.

19. A polymer electrolyte membrane according to any one of claims 7 to 18 whendepending from claim 7, wherein the at least one inorganic additive is present in the membranein a concentration of about 0.02 mol % to about 5 mol %, or from about 1 mol % to about 3mol %, or from about 2.5 mol% to about 3.5 mol %, or about 2 mol%, optionally wherein the inorganic additive comprises at least one of Ce, Mn, La, Ni, W, Co, Zr, Y, Mo, Nd, Ag, Pt, Ru, Pd, Rh, Ta, Ti, Ir, Pr, Tb, Dy, Au, Al, Zn in the ionic form, or their oxides, or their salts, ormixtures thereof , optionally wherein the inorganic additive is Ce3+.

20. A polymer electrolyte membrane according to any preceding claim, wherein theadditives of the additive blend are dissolved, suspended or dispersed in the ion exchange material.

21. A polymer electrolyte membrane according to any preceding claim, wherein themembrane comprises more than one layer of ion exchange material and the additive blend ispresent in each layer of ion exchange material of the membrane, or wherein the additive blend is present only on some layer or layers of ion exchange material, optionally wherein the additive blend is present in one or both external layers of ion exchange material but not in internal layers of ion exchange material, and / or wherein the additive blend is present in an internal layer of ion exchange material.

22. A polymer electrolyte membrane according to any preceding claim, wherein one of themembrane has a thickness at 50 % RH of at least about 20 µm, optionally from about 20 µmto about 200 µm, optionally wherein, the polymer electrolyte membrane is an electrolyzerpolymer electrolyte membrane; orthe membrane has a thickness at 50 % RH of about 1 to 50 µm at 50 % RH, optionallywherein the membrane has a thickness at 50% RH of from about 1 µm to about 17 µm, furtheroptionally wherein the polymer electrolyte membrane is a fuel cell or a redox flow batterymembrane.

23. A method of manufacturing a polymer electrolyte membrane comprising the steps of:a) coating a backer layer with a first ion exchange material by providing a backer layerand depositing a liquid layer of a first ion exchange material;b) depositing a first reinforcing layer comprising a porous reinforcement over theliquid layer of the first ion exchange material and allowing the porous reinforcement of the first reinforcing layer to become imbibed or at least partially imbibed with the first ion exchange material and additive blend; c) optionally drying the laminate; andd) coating the imbibed first reinforcing layer with a liquid layer of a second ion exchange material solution; and e) drying the laminate;wherein at least one of the first ion exchange material and / or the second ion exchange material comprises an additive blend having at least two additives and wherein at least one of the at least two additives is an organic additive.

24. A method according to claim 23, wherein the method further comprises the step f) ofdepositing a second reinforcing layer comprising a porous reinforcement over the liquid layerof the second ion exchange material and allowing the porous reinforcement of the secondreinforcing layer to become imbibed or at least partially imbibed with the second ion exchangematerial and additive blend before the drying step e), optionally wherein the method furthercomprises coating the imbibed second reinforcing layer with a liquid layer of a third ionexchange material solution, optionally wherein the third ion exchange material solutioncomprises an additive blend comprising at least one organic additive.

25. A method according to claim 234 or 24 wherein the method further comprises the stepsof depositing subsequent reinforcing layers comprising a porous reinforcement over layers ofsolution of ionomer (and optionally additive blend), allowing the porous reinforcement tobecome imbibed with the ionomer (and optionally additive blend), optionally applying a further layer of ionomer solution, and drying the membrane to form a laminate.

26. A method according to any one of claims 23 to 25, wherein all the first, second andoptionally third and subsequent ionomers are the same or wherein they are different.

27. A polymer electrolyte membrane directly obtained by the method of any one of claims23 to 26.

28. A membrane-electrode-assembly (MEA) comprising:a) a polymer electrolyte membrane according to any one of claims 1 to 22; b) at least one electrode.

29. A membrane-electrode-assembly (MEA) comprising:a) a polymer electrolyte membrane comprising an organic additive selected from aperoxide decomposition catalyst, a radical scavenger, a free radical decomposition catalyst, a self-regenerating antioxidant, a hydrogen donor primary antioxidant, an oligomer or a polymer; and b) at least one electrode,wherein the at least one electrode comprises an inorganic additive, optionally wherein theinorganic additive is Ce3+< / sup>.

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