Bilayer polyelectrolyte membranes

Abstract

The present disclosure relates to a bilayer polyelectrolyte membrane, comprising a first layer and a second layer, wherein the first layer comprises a perfluorosulfonic acid, the second layer comprises a crosslinked sulfonated polymer, and wherein the first layer is disposed on the second layer. The present disclosure further relates to a method of making the bilayer polyelectrolyte membrane, as well as membrane electrode assembly and fuel cell comprising the bilayer polyelectrolyte membrane.

Description

BILAYER POLYELECTROLYTE MEMBRANESRELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 544062 filed October 13, 2023. The entire teachings of the above application are incorporated herein by reference.BACKGROUND OF THE INVENTION

[0002] Proton exchange membrane-based fuel cells (PEMFCs) are eco-friendly energy conversion devices that operate at low temperatures and are more efficient than existing internal combustion engines. With these advantages, PEMFCs have emerged as a popular alternative to fossil fuels in the transportation industry and have the potential for use in a wide range of applications, such as portable devices and stationary power supply systems.

[0003] The proton exchange membrane (PEM) which conducts protons and serves to separate the cathode and the anode is one of the most important elements of a PEMFC. PEMs significantly affect the overall performance of fuel cells; thus, improving the efficiency of a fuel cell requires a PEM that has high ionic conductivity and low fuel crossover, and exhibits high physicochemical and mechanical stability. Because a PEMFC uses a thin membrane as its electrolyte, these devices are more portable and compact than other types of fuel cells. However, the thin membrane can also allow the crossover of the fuel gas (H2), which negatively affects the cell efficiency. Accordingly, PEMs with high ionic conductivity and reduced hydrogen crossover are needed.SUMMARY OF THE INVENTION

[0004] In a first embodiment the invention is a bilayer polyelectrolyte membrane, comprising a first layer and a second layer, wherein the first layer comprises a perfluorosulfonic acid (PFSA) polymer, and the second layer comprises an admixture of a crosslinked sulfonated polymer and a filler polymer, and wherein the first layer is disposed on the second layer.

[0005] In a second embodiment, the invention is a method of making a bilayer polyelectrolyte membrane described herein with respect to the first embodiment and various aspects thereof, comprising: a) providing a first layer having a first side, and a solution or suspension comprising a sulfonated polymer, a filler polymer, and a crosslinking reagent, b) coating the first side of the first layer with the solution or suspension, thereby producing a coated first layer; c) exposing the coated first layer to conditions sufficient for the sulfonated polymer and the crosslinking reagent to undergo a crosslinking reaction, thereby producing the bilayer polyelectrolyte membrane.

[0006] In a third embodiment the invention is a membrane electrode assembly (MEA), comprising: the bilayer polyelectrolyte membrane described herein with respect to the first embodiment and various aspects thereof; a cathode; and an anode, wherein the bilayer electrolyte membrane is disposed between the anode and the cathode.

[0007] In a fourth embodiment the invention is a fuel cell, comprising one or more of the MEAs described herein with respect to the third embodiment and various aspects thereof and one or more gas flow bipolar plates.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing will be apparent from the following more particular description of example embodiments of the invention.

[0009] Figure l is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising an admixture of polyvinylidene fluoride (PVDF) and sulfonated polysulfonated polyphenyl sulfone (sPPS) crosslinked with hydroquinone.

[0010] Figure 2 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising an admixture of PVDF and sPPS crosslinked with hydroquinone.

[0011] Figure 3 is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nations® 211 coated with a 1.5 pm-thick layer comprising and admixture ofpolystyrene-polyacrylonitrile copolymer (PS-co-PAN) and sPPS crosslinked with hydroquinone.

[0012] Figure 4 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a1.5 pm-thick layer comprising and admixture of PS-co-PAN and sPPS crosslinked with hydroquinone.

[0013] Figure 5 is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising and admixture of polyvinyl chloride (PVC) and sPPS crosslinked with hydroquinone.

[0014] Figure 6 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a1.5 pm-thick layer comprising and admixture of PVC and sPPS crosslinked with hydroquinone.

[0015] Figure 7 is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising and admixture of polyacrylamide (PAAm) and sPPS crosslinked with hydroquinone.

[0016] Figure 8 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a1.5 pm-thick layer comprising and admixture of PAAm and sPPS crosslinked with hydroquinone.

[0017] Figure 9 is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising and admixture of polyvinyl alcohol (PVA) and sPPS crosslinked with hydroquinone.

[0018] Figure 10 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a1.5 pm-thick layer comprising and admixture of PVA and sPPS crosslinked with hydroquinone.

[0019] Figure 11 is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising and admixture of poly(4- vinylpyridine) (P4VP) and sPPS crosslinked with hydroquinone.

[0020] Figure 12 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a1.5 |im -thick layer comprising and admixture of P4VP and sPPS crosslinked with hydroquinone.

[0021] Figure 13 is a plot demonstrating fuel cell polarization of a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising and admixture of poly(etherimide) (PEI) and sPPS crosslinked with hydroquinone.

[0022] Figure 14 is a plot demonstrating cyclic voltammograms of a membrane comprising Nafion® 211 and a membrane comprising a layer of Nafion® 211 coated with a 1.5 pm-thick layer comprising and admixture of PEI and sPPS crosslinked with hydroquinone.

[0023] Figure 15 shows an additive value of area specific resistances (ASR) for a 25 pm Nafion® 211 membrane (dark grey) and a 1.5 pm thick membrane comprising an admixture of a filler polymer (PVDF, P4VP, PS-co-PAN, PAAm, PVC, or PVA) sPPS crosslinked with hydroquinone (light grey) and the ASR value measured for the bilayer membrane comprising a 25 pm thick layer of Nafion® 211 coated with a 1.5 pm thick coating comprising an admixture of the filler polymer and crosslinked sPPS.

[0024] Figure 16 shows aJH NMR spectrum of sPPS.

[0025] The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0026] A description of example embodiments of the invention follows.

[0027] Hydrogen crossover is an undesirable diffusion of hydrogen from the anode to the cathode through the membrane in a fuel cell. Hydrogen crossover can have at least three effects, including fuel efficiency reduction, cathode potential depression, and aggressive peroxide radical formation. The hydrogen which crosses the membrane can directly react with oxygen at the cathode surface, resulting in lowering of the cathode potential.Additionally, this direct reaction between H2 and O2 at the cathode can produce peroxide radicals, which not only attack the catalyst layer but also the membrane, causing significantcatalyst-layer and membrane degradation. In addition, it has been confirmed that the formation of hot-points or hydrogen peroxide by the highly exothermal chemical reaction between H2 and O2 can also lead to pinholes in membranes, destroying the MEA and causing safety problems. An accelerated sintering of catalysts could be also caused by the hydrogen crossover.

[0028] Lifetime is always one of the core concerns of proton exchange membrane fuel cell, especially in commercial utilization. Membrane failure caused by chemical degradation can lead to crash of the whole fuel cell system. Overall, hydrogen crossover accelerates thermal and chemical degradation of the membrane and, in turn, increases hydrogen crossover, accelerating a destructive cycle of the membrane decomposition.

[0029] Hydrogen crossover can be reduced by using thicker membranes; however, it reduces the efficiency due to the increased ionic ohmic resistance of the membrane (i.e., higher protonic resistance). Here, Applicant has unexpectedly discovered that a composite membrane comprising a layer of perfluorosulfonic acid (PFSA), such as Nafion®, and a coating layer comprising an admixture of a sulfonated crosslinked polymer and a filler polymer exhibits reduced hydrogen crossover while maintaining desirable membrane performance parameters. Further, the present disclosure unexpectedly demonstrates that a composite membrane comprising a layer of PFSA and a coating layer comprising an admixture of a sulfonated polymer and a filler polymer exhibits significant ionic conductivity.

[0030] In some embodiments, the present disclosure relates to a polyelectrolyte composite membrane which demonstrates reduced hydrogen crossover and improved membrane durability. The membrane comprises a layer of PFSA, such as Nafion®, and a coating comprising an admixture of a sulfonated crosslinked polymer and a filler polymer. In some embodiments the coating layer comprises a filler polymer, such as PVDF, P4VP, PS- co-PAN, PAAm, PVC, or PVA, homogeneously distributed within the sulfonated crosslinked polymer. The coating layer has lower hydrogen penetration compared to the PFSA, thus reducing hydrogen crossover through the membrane and improving membrane durability.

[0031] The plots in Figures 1, 3, 5, 7, 9, 11, and 13 show fuel cell polarization curves of a Nafion® 211 membrane and a membrane comprising Nafion® 211 coated with a 1.5 pm layer comprising a filler polymer distributed in sPPS crosslinked with hydroquinone (degree of crosslinking 30-50%). The data demonstrate that the coated membrane is fully functionalas a PEM as the cell would be unable to conduct electrical current without an associated proton current through the membrane since every electron the flows from the fuel cell must have an associated proton that moves through the membrane. Therefore, a generated current necessarily demonstrates proton conduction through the membrane.

[0032] The cyclic voltammograms in Figures 2, 4, 6, 8, 10, 12, and 14 show hydrogen crossover measurement of Nafion® 211 membrane and a membrane comprising Nafion® 211 coated with a 1.5 pm layer comprising a filler polymer distributed in sPPS crosslinked with hydroquinone (degree of crosslinking 30-50%). Remarkably, hydrogen crossover was reduced by addition of every examined filler polymer to the crosslinked sPPS matrix by as much as 75% from 1.33 mA / cm2(Nafion® 211 without a coating) to 0.34 mA / cm2(Nafion® 211 coated with 1.5 pm crosslinked sPPS+PVDF layer). These results shows that coatings comprising a filler polymer distributed in a matrix of a crosslinked sulfonated polymer decrease hydrogen crossover through PFSA-based membranes.

[0033] Increase in electrical resistance in composite systems comprising layers of materials is frequently observed in conductive systems and presents a significant barrier to layered geometries. To evaluate contact resistance in the composite polyelectrolyte membrane the area specific resistances (ASRs) of the following membranes were measured in a single cell fuel cell by electrochemical impedance spectroscopy. An additive ASR value was calculated by adding the ASR of a single layer of Nafion® 211 (25 pm thick) and the ASR value of a single 1.5 pm-thick layer comprising an admixture of crosslinked sPPS and a filler polymer. This additive ASR value was compared to the measured ASR value for a bilayer membrane (25 pm Nafion® 211 coated with 1.5 pm thick crosslinked sPPS+filler polymer layer). Surprisingly, the ASR of the bilayer membrane not only did not increase compared to the additive ASRs of a Nafion® 211 membrane and the crosslinked sPPS+filler polymer membrane, but in some cases stayed below the additive ASR value (e.g., when the filler polymer was P4VP). These results demonstrates that a layer comprising an admixture of crosslinked sPPS and a filler polymer and a Nafion® layer, surprisingly, show no contact resistance between each other, which means that a proton experiences no extra resistance by moving between the layers.Definitions

[0034] Numeric ranges are inclusive of the numbers defining the range. For example, “x is an integer from 5 to 14” means that x can be 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14. Measured and measureable values are understood to be approximate, taking into account significant digits and the error associated with the measurement. As used in this application, the terms “about” and “approximately” have their art-understood meanings; use of one vs the other does not necessarily imply different scope. Unless otherwise indicated, numerals used in this application, with or without a modifying term such as “about” or “approximately”, should be understood to encompass normal divergence and / or fluctuations as would be appreciated by one of ordinary skill in the relevant art. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of a stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0035] The term “bilayer polyelectrolyte membrane”, as used herein, refers to a membrane containing two layers disposed on top of each other, each layer comprising a polyelectrolyte. The two layers can adhere to each other through formation of chemical bonds or through Van der Waals interactions.

[0036] As used herein, the term “polysulfonated polymer” or “sulfonated polymer” refers to a polymer comprising a plurality of sulfonic acid or sulfonate salt groups: S(O)2OH or S(O)2O M+, where M+is a counterion.

[0037] As used herein, the term “degree of sulfonation” refers to the number of repeat units that have at least one sulfonic acid / sulfonate salt group. For example, 20% degree of sulfonation indicates a polymer that has 20 percent of its repeat units sulfonated, while 100% degree of sulfonation indicates every repeat unit in the polymer contains one sulfonic acid / sulfonate salt group. This may include polymers that contain multiple sulfonic acid / sulfonate salt groups per repeat unit (e.g., disulfonation, trisulfonation, tetrasulfonation, etc). In some embodiments, the sulfonated polymer can comprise on average 2 sulfonic acid groups per repeat unit, which corresponds to 200% degree of sulfonation. In some embodiments, the sulfonated polymer can comprise on average 2, 3, 4, or 5 sulfonic acid groups per repeat unit, which corresponds to 200%, 300%, 400%, or 500% degree of sulfonation, respectively. In some embodiments, the sulfonated polymer can comprise onaverage from 1.5 to 2.5 sulfonic acid groups per repeat unit, which corresponds to 150% to 250% degree of sulfonation.

[0038] The sulfonated polymers of the disclosure can also be characterized by the average number of sulfonic acid groups per repeat unit. For example, a sulfonated polyphenyl sulfone (sPPS) can comprise 1, 2, 3, 4, 5, 6, 7, or 8 sulfonic acid groups per repeat unit. For example, a repeat unit of sPPS can comprise 2 sulfonic acid groups:Alternatively, a repeat unit of sPPS can comprise 4 or 6 sulfonic acid groups:

[0039] In a given polymer, some repeat units can have, for example, 1 sulfonic acid group, some repeat units can have 2 sulfonic acid groups, and some repeat units can have 3 or more sulfonic acid groups. Accordingly, the number of sulfonic acid groups per repeat unit that is measured in a bulk polymer by analyzing, for example, itsJH NMR spectrum or ion exchange capacity, corresponds to the average number of sulfonic groups across all the repeat units of the polymer.

[0040] As used herein, the term “polyphenyl sulfone” refers to a polymer comprising the following repeat unit:

[0041] Sulfonated polyphenyl sulfone can comprise 1, 2, 3, 4, 5, 6, 7, or 8 sulfonic acid groups per repeat unit.

[0042] As used herein, the term “poly ether ether ketone” refers to a polymer comprising the following repeat unit:

[0043] Sulfonated polyether ether ketone can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 sulfonic acid groups per repeat unit.

[0044] As used herein, the term “polyphosphazine” refers to a polymer comprising the following repeat unit:

[0045] As used herein, the term “polybenzimidazole” refers to a polymer comprising the following repeat unit:

[0046] Sulfonated polybenzimidazole can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 sulfonic acid groups per repeat unit.

[0047] As used herein, the term “polyether sulfone”, also know as “polyarylethersulfone”, refers to a polymer comprising the following repeat unit:

[0048] Sulfonated polyether sulfone can comprise 1, 2, 3, 4, 5, 6, 7, or 8 sulfonic acid groups per repeat unit.

[0049] As used herein, the term “polyphenylene oxide” refers to a polymer comprising the following repeat unit:

[0050] Sulfonated polyphenylene oxide can comprise 1 or 2 sulfonic acid groups per repeat unit.

[0051] As used herein, the term “polyarylene ether ketone” refers to a polymer comprising one or more of the following repeat units:

[0052] Sulfonated polyarylene ether ketone can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 sulfonic acid groups per repeat unit.

[0053] As used herein, the term “poly(sulfone)” refers to a polymer comprising the following repeat unit:

[0054] Sulfonated poly(sulfone) (sPSU) can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 sulfonic acid groups per repeat unit.

[0055] As used herein, the term “poly(sulfide sulfone)” refers to a polymer comprising the following repeat unit:

[0056] Sulfonated poly(sulfide sulfone) can comprise 1, 2, 3, 4, 5, 6, 7, or 8 sulfonic acid groups per repeat unit.

[0057] As used herein, the term “polyimide” refers to a polymer comprising the following repeat unit:

[0058] Sulfonated polyimide can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 sulfonic acid groups per repeat unit.

[0059] As used herein, the term “poly(etherimide)” refers to a polymer comprising the following repeat unit:

[0060] Sulfonated poly(etherimide) can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18 sulfonic acid groups per repeat unit.

[0061] As used herein, the term “poly (4-phenoxybenzoyl-l,4-phenylene)” refers to a polymer comprising the following repeat unit:

[0062] Sulfonated poly (4-phenoxybenzoyl-l,4-phenylene) can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 sulfonic acid groups per repeat unit.

[0063] As used herein, the term “poly(4-vinylpyridine)” refers to a polymer comprising the following repeat unit:

[0064] As used herein, the term “polyvinylidene fluoride” refers to a polymer comprising the following repeat unit:

[0065] As used herein, the term “polystyrene polyacrylonitrile copolymer” refers to a polymer comprising the following repeat units:some embodiments, polystyrene polyacrylonitrile copolymer is a random copolymer. In some embodiments, polystyrene polyacrylonitrile copolymer is a block copolymer. A “block” copolymer refers to a structure comprising one or more sub-combination of repeat units. In some embodiments, the block copolymer is a diblock copolymer. A diblock copolymer comprises two blocks; a schematic generalization of such a polymer is represented by the following: [AaBb . . . ]m-[XxYy. . . ]n, wherein each capital letter stands for a repeat unit of a particular chemical composition, and wherein each subscript to a repeat unit represents the mole fraction of that unit in the particular block, the three dots indicate that there may be more (there may also be fewer) repeat units in each block and m and n indicate the molecular weight of each block in the diblock copolymer. In some instances, the number and the nature of each repeat unit is separately controlled for each block.

[0066] As used herein, the term “polyvinyl chloride” refers to a polymer comprising the following repeat unit:

[0067] As used herein, the term polyacrylamide” refers to a polymer comprising the following repeat unit:

[0068] As used herein, the term “polyvinyl alcohol” refers to a polymer comprising the following repeat unit:

[0069] Any of the polymer repeat units described above can have one or more hydrogen atoms substituted with a -CN, -NO2, -N3, -OH, F, Cl, Br, I, oxo, -SO2H, -SO3H, -ORaa, - NH(Raa)2, -N(Raa)2, -N(Raa)3+X‘, -SH, -SRaa, -C(=O)Raa, -CO2H, -CHO, -CO2Raa, - OC(=O)Raa, -OCO2Raa, -C(=O)N(Raa)2, -OC(=O)N(Raa)2, -NRaaC(=O)Raa, -NRaaCO2Raa, - NRaaC(=O)N(Raa)2, -C(=NRaa)Raa, -C(=O)NRaaSO2Raa, -NRaaSO2Raa, -SO2N(Raa)2, -SO2Raa, - SO2ORaa, -OSO2Raa, -S(=O)Raa, -OS(=O)Raa, -Si(Raa)3, -OSi(Raa)3, C1-12 alkyl, C1-12 alkoxyl, C1-12 haloalkyl, C3-12 cycloalkyl, 3-16 membered heterocyclyl, and Ce-12 aryl, wherein X is a counterion and each instance of Raais, independently, selected from H, -OH, C1-10 alkyl, C1-10 haloalkyl, C3-12 cycloalkyl, 5-16 membered heterocyclyl, and Ce-12 aryl, or two Raagroups are joined to form a 3-16 membered heterocyclyl.

[0070] As used herein, the term “polyalcohol” refers to an alcohol comprising more than one hydroxyl group. Examples of polyalcohols include, but are not limited to, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, glycerol, erythriol, xylitol, hydroquinone, catechol, resorcinol, and phloroglucinol. As used herein, the term “polyalcohol” does not refer to a polymer comprising more than one hydroxyl group. For example, the term “polyalcohol” does not refer to polyvinyl alcohol (PVA).

[0071] As used herein, the term “polyelectrolyte” refers to a polymer comprising repeat units bearing a charged or an ionizable group. Under a particular set of conditions a polyelectrolyte has a net negative or net positive charge. In some embodiments, a polyelectrolyte is or comprises a polycation; in some embodiments, a polyelectrolyte is or comprises a polyanion. Polycations have a net positive charge and polyanions have a net negative charge. The net charge of a given polyelectrolyte may depend on the surrounding chemical conditions, e.g., on the pH.

[0072] As used herein, the term “perfluorosulfonic acid” refers to a polymer represented by the following structural formula:where Rfrepresents a perfluoroalkylene or perfluorooxyalkylene group, and x and y the relative proportion of perfluoro monomer and sulfonated monomer respectively. As used herein, the terms “perfluoroalkylene” or “perfluorooxyalkylene” refer to an alkylene or an oxyalkylene groups in which all hydrogen atoms have been substituted with fluorines. A class of PFSAs is represented by the structural formula (I):Such PFSAs are usually categorized according to their side-chain length. For example, Aquivion® (formerly Dow SSC) PFSAs are commonly classified as short-side-chain (SSC) PFSAs, while Nafion® is considered as a long-side-chain (LSC) PFSA. Examples of commercial PFSAs include the following:

[0073] As used herein, the term “crosslinking” refers to formation of a covalent or ionic bond between a sulfonic acid group of the sulfonated polymer and the crosslinking reagent. For example, crosslinking refers to the formation of sulfonate esters as a result of the reaction between the sulfonic acid group of the sulfonated polymer and a polyol, such as hydroquinone, sulfonated hydroquinone, ethylene glycol, or propylene glycol. In some embodiments, crosslinking refers to the formation of sulfonamides as a result of the reaction between the sulfonic acid group of the sulfonated polymer and a polyamine. As used herein,the term “crosslinking” does not refer to formation of a covalent or ionic bond between the crosslinking reagent and any functional group in the polymer repeat unit other than a sulfonic acid group.

[0074] As used herein, the term “crosslinked polymer” refers to a polymer in which two or more non-adjacent repeat units of the same main chain are connected via a crosslinking moiety. The term “crosslinked polymer” also refers to two or more different main chains connected via a plurality of crosslinking moieties. As used herein, the term “crosslinked polymer” does not refer to formation of a covalent or ionic bond between the crosslinking reagent and any functional group in the polymer repeat unit other than a sulfonic acid group.

[0075] As used herein, the term “crosslinking moiety” refers a polyvalent, for example, divalent or trivalent, moiety which forms a covalent bond with one or more non-adjacent repeat units of the same polymer main chain or with one or more repeat units of different main chains. A crosslinking moiety can comprise charged groups, for example, an ammonium group or a metal ion, which form an electrostatic / ionic bond with a sulfonic acid group attached to the repeat unit of the sulfonated polymer.

[0076] As used herein, the term “crosslinking reaction” refers to a chemical reaction between a sulfonic acid group attached to the repeat units of the sulfonated polymer and a crosslinking reagent, resulting in formation of a covalent or electrostatic / ionic bonds between the polymer chains and the crosslinking reagent.

[0077] As used herein, the term “conditions sufficient for the polymer and the crosslinking reagent to undergo a crosslinking reaction” refers to the external stimuli (e.g. heat, UV light, microwave irradiation, presence of a chemical initiator, such as a radical initiator) as well as time necessary in order to form the crosslinked polymer.

[0078] As used herein, the term “repeat unit” (also known as a monomer unit) refers to a chemical moiety which periodically repeats itself to produce the complete polymer chain (except for the end-groups) by linking the repeat units together successively. A polymer can contain one or more different repeat units.

[0079] As used herein, the “main chain” of a polymer, or the “backbone” of the polymer, is the series of bonded atoms that together create the continuous chain of the polymer molecule. As used herein, a “side chain” of a polymer is the series of bonded atoms which are pendent from the main chain of a polymer.

[0080] As used herein, the term “a repeat unit comprising an aliphatic backbone” refers to a repeat unit having a backbone comprising an alkylene, alkenylene, alkynylene, carbocyclylene, heteroalkylene, heteroalkenylene, heteroalkynylene, or heterocyclylene moiety that connects to the adjacent repeat units. Repeat units comprising an aliphatic backbone do not include repeat units comprising an aromatic or a heteroaromatic moiety in their backbone. Examples of polymers comprising a repeat unit comprising an aliphatic backbone include but are not limited to PFSA, PAAm, PVA, PVDF, PS-co-PAN, P4VP, polyethylene, polypropylene, and PVC.

[0081] As used herein, “PFSA polymer and the matrix polymer form an interpenetrating network” refers to a porous matrix that contains PFSA polymer within its pores. A porous matrix can be impregnated with the PFSA polymer, for example, by soaking the matrix in a solution of the PFSA polymer or by spraying a solution of the PFSA polymer on the porous matrix. Alternatively, the porous matrix can be impregnated with a solution of the PFSA monomer, followed by a polymerization reaction within the pores of the matrix.

[0082] As used herein, “unsupported membrane” refers to a membrane that contains only the PFSA polymer layer and the crosslinked sulfonated polymer layer and does not contain any other layers, supports, or reinforcements.

[0083] As used herein, the term “continuous layer” refers to layer that does not contain gaps or openings, such that any point on the layer can be connected to any other point on the layer by a straight line, and each point of that straight line belongs to the layer.

[0084] As used herein, the term "alkyl" refers to a radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 10 carbon atoms ("Ci-io alkyl"). In some embodiments, an alkyl group has 1 to 9 carbon atoms ("C1-9 alkyl"). In some embodiments, an alkyl group has 1 to 8 carbon atoms ("C1-8 alkyl"). In some embodiments, an alkyl group has 1 to 7 carbon atoms ("C1-7 alkyl"). In some embodiments, an alkyl group has 1 to 6 carbon atoms ("C1-6 alkyl"). In some embodiments, an alkyl group has 1 to 5 carbon atoms ("C1-5 alkyl"). In some embodiments, an alkyl group has 1 to 4 carbon atoms ("C1-4 alkyl"). In some embodiments, an alkyl group has 1 to 3 carbon atoms ("C1-3 alkyl"). In some embodiments, an alkyl group has 1 to 2 carbon atoms ("C1-2 alkyl"). In some embodiments, an alkyl group has 1 carbon atom ("Ci alkyl"). In some embodiments, an alkyl group has 2 to 6 carbon atoms ("C2-6 alkyl"). Examples of C1-6 alkyl groups include methyl (Ci), ethyl (C2), propyl (C3) (e.g., n-propyl, isopropyl), butyl (C4) (g-g-, n-butyl, tert-butyl, sec-butyl, iso-butyl), pentyl (C5) e.g., n-pentyl, 3-pentanyl, amyl, neopentyl, 3- methyl-2-butanyl, tertiary amyl), and hexyl (Ce) (g-g-, n-hexyl). Additional examples of alkyl groups include n-heptyl (C7), n-octyl (Cs), and the like. Unless otherwise specified, each instance of an alkyl group is independently unsubstituted (an "unsubstituted alkyl") or substituted (a "substituted alkyl") with one or more substituents (e.g., halogen, such as F). In certain embodiments, the alkyl group is an unsubstituted C1-10 alkyl (such as unsubstituted C1-6 alkyl, e.g., -CH3 (Me), unsubstituted ethyl (Et), unsubstituted propyl (Pr, e.g., unsubstituted n-propyl (n-Pr), unsubstituted isopropyl (i-Pr)), unsubstituted butyl (Bu, e.g., unsubstituted n-butyl (n-Bu), unsubstituted tert-butyl (tert-Bu or t-Bu), unsubstituted sec-butyl (sec-Bu), unsubstituted isobutyl (i-Bu)). In certain embodiments, the alkyl group is a substituted C1-10 alkyl (such as substituted C1-6 alkyl, e.g., -CF3, Bn).

[0085] As used herein, the term "alkenyl" refers to a radical of a straight-chain or branched hydrocarbon group having from 2 to 10 carbon atoms and one or more carboncarbon double bonds (e.g., 1, 2, 3, or 4 double bonds) ("C2-10 alkenyl"). In some embodiments, an alkenyl group has 2 to 9 carbon atoms ("C2-9 alkenyl"). In some embodiments, an alkenyl group has 2 to 8 carbon atoms ("C2-8 alkenyl"). In some embodiments, an alkenyl group has 2 to 7 carbon atoms ("C2-7 alkenyl"). In some embodiments, an alkenyl group has 2 to 6 carbon atoms ("C2-6 alkenyl"). In some embodiments, an alkenyl group has 2 to 5 carbon atoms ("C2-5 alkenyl"). In some embodiments, an alkenyl group has 2 to 4 carbon atoms ("C2-4 alkenyl"). In some embodiments, an alkenyl group has 2 to 3 carbon atoms ("C2-3 alkenyl"). In some embodiments, an alkenyl group has 2 carbon atoms ("C2 alkenyl"). The one or more carboncarbon double bonds can be internal (such as in 2-butenyl) or terminal (such as in 1-butenyl). Examples of C2-4 alkenyl groups include, without limitation, vinyl (C2), 1 -propenyl (C3), 2- propenyl (C3), 1-butenyl (C4), 2-butenyl (C4), and the like. Examples of C2-6 alkenyl groups include the aforementioned C2-4 alkenyl groups as well as pentenyl (C5), hexenyl (Ce), and the like. Additional examples of alkenyl include heptenyl (C7), octenyl (Cs), and the like.Unless otherwise specified, each instance of an alkenyl group is independently unsubstituted (an "unsubstituted alkenyl") or substituted (a "substituted alkenyl") with one or more substituents. In certain embodiments, the alkenyl group is an unsubstituted C2-10 alkenyl. In certain embodiments, the alkenyl group is a substituted C2-10 alkenyl.

[0086] As used herein, the term "alkynyl" refers to a radical of a straight-chain or branched hydrocarbon group having from 2 to 10 carbon atoms and one or more carboncarbon triple bonds (e.g., 1, 2, 3, or 4 triple bonds) ("C2-10 alkynyl"). In some embodiments, an alkynyl group has 2 to 9 carbon atoms ("C2-9 alkynyl"). In some embodiments, an alkynyl group has 2 to 8 carbon atoms ("C2-8 alkynyl"). In some embodiments, an alkynyl group has 2 to 7 carbon atoms ("C2-7 alkynyl"). In some embodiments, an alkynyl group has 2 to 6 carbon atoms ("C2-6 alkynyl"). In some embodiments, an alkynyl group has 2 to 5 carbon atoms ("C2- 5 alkynyl"). In some embodiments, an alkynyl group has 2 to 4 carbon atoms ("C2-4 alkynyl"). In some embodiments, an alkynyl group has 2 to 3 carbon atoms ("C2-3 alkynyl"). In some embodiments, an alkynyl group has 2 carbon atoms ("C2 alkynyl"). The one or more carboncarbon triple bonds can be internal (such as in 2-butynyl) or terminal (such as in 1-butynyl). Examples of C2-4 alkynyl groups include, without limitation, ethynyl (C2), 1-propynyl (C3), 2- propynyl (C3), 1-butynyl (C4), 2-butynyl (C4), and the like. Examples of C2-6 alkynyl groups include the aforementioned C2-4 alkynyl groups as well as pentynyl (C5), hexynyl (Ce), and the like. Additional examples of alkynyl include heptynyl (C7), octynyl (Cs), and the like. Unless otherwise specified, each instance of an alkynyl group is independently unsubstituted (an "unsubstituted alkynyl") or substituted (a "substituted alkynyl") with one or more substituents. In certain embodiments, the alkynyl group is an unsubstituted C2-10 alkynyl. In certain embodiments, the alkynyl group is a substituted C2-10 alkynyl.

[0087] The term "aryl" refers to a radical of a monocyclic or polycyclic (e.g., bicyclic or tricyclic) 4n+2 aromatic ring system (e.g., having 6, 10, or 14 7t electrons shared in a cyclic array) having 6-14 ring carbon atoms and zero heteroatoms provided in the aromatic ring system ("Ce-i4 aryl"). In some embodiments, an aryl group has 6 ring carbon atoms ("Ce aryl"; e.g., phenyl). In some embodiments, an aryl group has 10 ring carbon atoms ("C10 aryl"; e.g., naphthyl such as 1-naphthyl and 2-naphthyl). In some embodiments, an aryl group has 14 ring carbon atoms ("C14 aryl"; e.g., anthracyl). "Aryl" also includes ring systems wherein the aryl ring, as defined above, is fused with one or more carbocyclyl or heterocyclyl groups wherein the radical or point of attachment is on the aryl ring, and in such instances, the number of carbon atoms continue to designate the number of carbon atoms in the aryl ring system. Unless otherwise specified, each instance of an aryl group is independently unsubstituted (an "unsubstituted aryl") or substituted (a "substituted aryl") with one or moresubstituents. In certain embodiments, the aryl group is an unsubstituted Ce-i4 aryl. In certain embodiments, the aryl group is a substituted Ce-i4 aryl.

[0088] The term “haloalkyl” refers to a substituted alkyl group, wherein one or more of the hydrogen atoms are independently replaced by a halogen, e.g, fluoro, bromo, chloro, or iodo. In some embodiments, the haloalkyl moiety has 1 to 12 carbon atoms (“C1-12 haloalkyl”). In some embodiments, the haloalkyl moiety has 1 to 6 carbon atoms (“C1-6 haloalkyl”). In some embodiments, the haloalkyl moiety has 1 to 4 carbon atoms (“C1-4 haloalkyl”). In some embodiments, the haloalkyl moiety has 1 to 3 carbon atoms (“C1-3 haloalkyl”). In some embodiments, the haloalkyl moiety has 1 to 2 carbon atoms (“C1-2 haloalkyl”). Examples of haloalkyl groups include -CHF2, -CH2F, -CF3, -CH2CF3, -CF2CF3, - CF2CF2CF3, -CCI3, -CFCh, -CF2CI, and the like.

[0089] The term “sulfonic acid group” refers to the following group: -S(O)2OH.

[0090] The term “sulfonate” refers to a salt or ester of sulfonic acid, -S(O)2OR, where R represents a cation, such as a metal or ammonium cation, or an aliphatic or aromatic substituent. Examples of sulfonates include salts such as lithium sulfonate, sodium sulfonate, potassium sulfonate, or ammonium sulfonate. In some embodiments, the term “sulfonate” refers to an ester of sulfonic acid, for example, an optionally substituted C1-12 alkyl sulfonate or an optionally substituted C6-12 aryl sulfonate. In some embodiments, R is a multivalent (e.g., bivalent or trivalent) radical forming a covalent or ionic bond with one or more sulfonic acid groups attached to the same or different sulfonated polymer chain, thus forming a crosslinking moiety together with the two or more -S(O)2O- groups to which it is attached.

[0091] The term “sulfonamide” refers to an amide of sulfonic acid, -S(O)2NRR’, where R and R’ is each a hydrogen or an optionally substituted aliphatic or aromatic substituent, such as optionally substituted C1-12 alkyl or an optionally substituted C6-12 aryl. In some embodiments, R and / or R’ is each a multivalent (e.g., bivalent or trivalent) radical forming a covalent or ionic bond with one or more sulfonic acid groups attached to the same or different sulfonated polymer chain, thus forming a crosslinking moiety together with the two or more - S(O)2O- groups to which it is attached.

[0092] Affixing the suffix "-ene" to a group indicates the group is a divalent moiety, e.g., alkylene is the divalent moiety of alkyl, alkenylene is the divalent moiety of alkenyl, alkynylene is the divalent moiety of alkynyl, heteroalkylene is the divalent moiety of heteroalkyl, heteroalkenylene is the divalent moiety of heteroalkenyl, heteroalkynylene is thedivalent moiety of heteroalkynyl, carbocyclylene is the divalent moiety of carbocyclyl, heterocyclylene is the divalent moiety of heterocyclyl, arylene is the divalent moiety of aryl, and heteroarylene is the divalent moiety of heteroaryl.

[0093] The term “substituted” refers to moieties having substituents replacing a hydrogen on one or more carbons of the backbone. It will be understood that “substitution” or “substituted with” includes the implicit proviso that such substitution is in accordance with permitted valence of the substituted atom and the substituent, and that the substitution results in a stable compound, e.g., which does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, etc. As used herein, the term “substituted” is contemplated to include all permissible substituents of organic compounds. In a broad aspect, the permissible substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and non-aromatic substituents of organic compounds. The permissible substituents can be one or more and the same or different for appropriate organic compounds. For purposes of this invention, the heteroatoms such as nitrogen may have hydrogen substituents and / or any permissible substituents of organic compounds described herein which satisfy the valences of the heteroatoms. Substituents can include any substituents described herein, for example, a halogen, a hydroxyl, a carbonyl (such as a carboxyl, an alkoxycarbonyl, a formyl, or an acyl), a thiocarbonyl (such as a thioester, a thioacetate, or a thioformate), an alkoxyl, a phosphoryl, a phosphate, a phosphonate, a phosphinate, an amino, an amido, an amidine, an imine, a cyano, a nitro, an azido, a sulfhydryl, an alkylthio, a sulfate, a sulfonate, a sulfamoyl, a sulfonamido, a sulfonyl, a heterocyclyl, an aralkyl, or an aromatic or heteroaromatic moiety. It will be understood by those skilled in the art that substituents can themselves be substituted, if appropriate. Unless specifically stated as “unsubstituted,” references to chemical moieties herein are understood to include substituted variants. For example, reference to an “aryl” group or moiety implicitly includes both substituted and unsubstituted variants.

[0094] The term "heteroalkyl" refers to an alkyl group, which further includes at least one heteroatom (e.g., 1, 2, 3, or 4 heteroatoms) selected from oxygen, nitrogen, or sulfur within (i.e., inserted between adjacent carbon atoms of) and / or placed at one or more terminal position(s) of the parent chain. In certain embodiments, a heteroalkyl group refers to a saturated group having from 1 to 20 carbon atoms and 1 or more heteroatoms within the parent chain ("heteroCi-20 alkyl"). In some embodiments, a heteroalkyl group is a saturatedgroup having 1 to 18 carbon atoms and lor more heteroatoms within the parent chain ("heteroCi-i8 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 to 16 carbon atoms andlor more heteroatoms within the parent chain ("heteroCi-i6 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 tol4 carbon atoms and 1 or more heteroatoms within the parent chain ("heteroCi-14 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 tol2 carbon atoms and 1 or more heteroatoms within the parent chain ("heteroCi-12 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having Ito 10 carbon atoms and lor more heteroatoms within the parent chain ("heteroCi-10 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 to 8 carbon atoms and 1 or more heteroatoms within the parent chain ("heteroCi-8 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 to 6 carbon atoms and 1 or more heteroatoms within the parent chain ("heteroCi-6 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 to 4 carbon atoms and 1 or 2 heteroatoms within the parent chain ("heteroCi-4 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 to 3 carbon atoms and 1 heteroatom within the parent chain ("heteroCi-3 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having Ito 2 carbon atoms and 1 heteroatom within the parent chain ("heteroCi-2 alkyl"). In some embodiments, a heteroalkyl group is a saturated group having 1 carbon atom and lheteroatom ("heteroCi alkyl"). In some embodiments, the heteroalkyl group defined herein is a partially unsaturated group having 1 or more heteroatoms within the parent chain and at least one unsaturated carbon, such as a carbonyl group. For example, a heteroalkyl group may comprise an amide or ester functionality in its parent chain such that one or more carbon atoms are unsaturated carbonyl groups. Unless otherwise specified, each instance of a heteroalkyl group is independently unsubstituted (an "unsubstituted heteroalkyl") or substituted (a "substituted heteroalkyl") with one or more substituents. In certain embodiments, the heteroalkyl group is an unsubstituted heteroCi-20 alkyl. In certain embodiments, the heteroalkyl group is an unsubstituted heteroCi-10 alkyl. In certain embodiments, the heteroalkyl group is a substituted heteroCi-20 alkyl. In certain embodiments, the heteroalkyl group is an unsubstituted heteroCi-10 alkyl.

[0095] The term "heteroalkenyl" refers to an alkenyl group, which further includes at least one heteroatom (e.g., 1, 2, 3, or 4 heteroatoms) selected from oxygen, nitrogen, or sulfur within (i.e., inserted between adjacent carbon atoms of) and / or placed at one or more terminalposition(s) of the parent chain. In certain embodiments, a heteroalkenyl group refers to a group having from 2 to 10 carbon atoms, at least one double bond, and 1 or more heteroatoms within the parent chain ("heteroC2-io alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 9 carbon atoms at

[0096] least one double bond, and 1 or more heteroatoms within the parent chain ("heteroC2-9 alkenyl").

[0097] In some embodiments, a heteroalkenyl group has 2 to 8 carbon atoms, at least one double bond, and 1 or more heteroatoms within the parent chain ("heteroC2-8 alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 7 carbon atoms, at least one double bond, and 1 or more heteroatoms within the parent chain ("heteroC2-7 alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 6 carbon atoms, at least one double bond, and 1 or more heteroatoms within the parent chain ("heteroC2-6 alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 5 carbon atoms, at least one double bond, and 1 or 2 heteroatoms within the parent chain ("heteroC2-5 alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 4 carbon atoms, at least one double bond, and 1 or 2 heteroatoms within the parent chain ("heteroC2-4 alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 3 carbon atoms, at least one double bond, and 1 heteroatom within the parent chain ("heteroC2-3 alkenyl"). In some embodiments, a heteroalkenyl group has 2 to 6 carbon atoms, at least one double bond, and 1 or

[0098] 2 heteroatoms within the parent chain ("heteroC2-6 alkenyl"). Unless otherwise specified, each instance of a heteroalkenyl group is independently unsubstituted (an "unsubstituted heteroalkenyl") or substituted (a "substituted heteroalkenyl") with one or more substituents. In certain embodiments, the heteroalkenyl group is an unsubstituted heteroC2-io alkenyl. In certain embodiments, the heteroalkenyl group is a substituted heteroC2-io alkenyl.

[0099] The term " heteroalky nyl" refers to an alkynyl group, which further includes at least one heteroatom (e.g., 1, 2, 3, or 4 heteroatoms) selected from oxygen, nitrogen, or sulfur within (i.e., inserted between adjacent carbon atoms of) and / or placed at one or more terminal position(s) of the parent chain. In certain embodiments, a heteroalkynyl group refers to a group having from 2 to 10 carbon atoms, at least one triple bond, and 1 or more heteroatoms within the parent chain ("heteroC2-io alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 9 carbon atoms, at

[0100] least one triple bond, and lor more heteroatoms within the parent chain ("heteroC2-9 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 8 carbon atoms, at least one triple bond, and lor more heteroatoms within the parent chain ("heteroC2-8 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 7 carbon atoms, at least one triple bond, and 1 or more heteroatoms within the parent chain ("heteroC2-7 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 6 carbon atoms, at least one triple bond, and 1 or more heteroatoms within the parent chain ("heteroC2-6 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 5 carbon atoms, at least one triple bond, and 1 or 2 heteroatoms within the parent chain ("heteroC2-5 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 4 carbon atoms, at least one triple bond, and 1 or 2 heteroatoms within the parent chain ("heteroC2-4 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 3 carbon atoms, at least one triple bond, and 1 heteroatom within the parent chain ("heteroC2-3 alkynyl"). In some embodiments, a heteroalkynyl group has 2 to 6 carbon atoms, at least one triple bond, and 1 or 2 heteroatoms within the parent chain ("heteroC2-6 alkynyl"). Unless otherwise specified, each instance of a heteroalkynyl group is independently unsubstituted (an "unsubstituted heteroalkynyl") or substituted (a "substituted heteroalkynyl") with one or more substituents. In certain embodiments, the heteroalkynyl group is an unsubstituted heteroC2-io alkynyl. In certain embodiments, the heteroalkynyl group is a substituted heteroC2-io alkynyl.

[0101] The term "carbocyclyl" or "carbocyclic" refers to a radical of a non-aromatic cyclic hydrocarbon group having from 3 to 14 ring carbon atoms ("C3-14 carbocyclyl") and zero heteroatoms in the non-aromatic ring system. In some embodiments, a carbocyclyl group has 3 to 10 ring carbon atoms ("C3-10 carbocyclyl"). In some embodiments, a carbocyclyl group has 3 to 8 ring carbon atoms ("C3-8 carbocyclyl"). In some embodiments, a carbocyclyl group has 3 to 7 ring carbon atoms ("C3-7 carbocyclyl"). In some embodiments, a carbocyclyl group has 3 to 6 ring carbon atoms ("C3-6 carbocyclyl"). In some embodiments, a carbocyclyl group has 4 to 6 ring carbon atoms ("C4-6 carbocyclyl"). In some embodiments, a carbocyclyl group has 5 to 6 ring carbon atoms ("C5-6 carbocyclyl"). In some embodiments, a carbocyclyl group has 5 to 10 ring carbon atoms ("C5-10 carbocyclyl"). Exemplary C3-6 carbocyclyl groups include, without limitation, cyclopropyl (C3), cyclopropenyl (C3), cyclobutyl (C4), cyclobutenyl (C4), cyclopentyl (C5), cyclopentenyl (C5), cyclohexyl (Ce), cyclohexenyl (Ce), cyclohexadienyl (Ce), and the like.

[0102] Exemplary C3-8 carbocyclyl groups include, without limitation, the aforementioned C3-6 carbocyclyl groups as well as cycloheptyl (C7), cycloheptenyl (C7), cycloheptadienyl (C7), cycloheptatrienyl (C7), cyclooctyl (Cs), cyclooctenyl (Cs), bicyclo[2.2.1]heptanyl (C7), bicyclo[2.2.2]octanyl (Cs), and the like. Exemplary C3-10 carbocyclyl groups include, without limitation, the aforementioned C3-8 carbocyclyl groups as well as cyclononyl (C9), cyclononenyl (C9), cyclodecyl (C10), cyclodecenyl (C10), octahydro- IH-indenyl (C9), decahydronaphthal enyl (C10), spiro[4.5]decanyl (C10), and the like. As the foregoing examples illustrate, in certain embodiments, the carbocyclyl group is either monocyclic ("monocyclic carbocyclyl") or polycyclic (e.g., containing a fused, bridged or spiro ring system such as a bicyclic system ("bicyclic carbocyclyl") or tricyclic system ("tricyclic carbocyclyl")) and can be saturated or can contain one or more carbon-carbon double or triple bonds. "Carbocyclyl" also includes ring systems wherein the carbocyclyl ring, as defined above, is fused with one or more aryl or heteroaryl groups wherein the point of attachment is on the carbocyclyl ring, and in such instances, the number of carbons continue to designate the number of carbons in the carbocyclic ring system. Unless otherwise specified, each instance of a carbocyclyl group is independently unsubstituted (an "unsubstituted carbocyclyl") or substituted (a "substituted carbocyclyl") with one or more substituents. In certain embodiments, the carbocyclyl group is an unsubstituted C3-14 carbocyclyl. In certain embodiments, the carbocyclyl group is a substituted C3-14 carbocyclyl.

[0103] In some embodiments, "carbocyclyl" is a monocyclic, saturated carbocyclyl group having from 3 to 14 ring carbon atoms ("C3-14 cycloalkyl"). In some embodiments, a cycloalkyl group has 3 to 10 ring carbon atoms ("C3-10 cycloalkyl"). In some embodiments, a cycloalkyl group has 3 to 8 ring carbon atoms ("C3-8 cycloalkyl"). In some embodiments, a cycloalkyl group has 3 to 6 ring carbon atoms ("C3-6 cycloalkyl"). In some embodiments, a cycloalkyl group has 4 to 6 ring carbon atoms ("C4-6 cycloalkyl"). In some embodiments, a cycloalkyl group has 5 to 6 ring carbon atoms ("C5-6 cycloalkyl"). In some embodiments, a cycloalkyl group has 5 to 10 ring carbon atoms ("C5-10 cycloalkyl"). Examples of C5-6 cycloalkyl groups include cyclopentyl (C5) and cyclohexyl (Ce). Examples of C3-6 cycloalkyl groups include the aforementioned C5-6 cycloalkyl groups as well as cyclopropyl (C3) and cyclobutyl (C4). Examples of C3-8 cycloalkyl groups include the aforementioned C3-6 cycloalkyl groups as well as cycloheptyl (C7) and cyclooctyl (Cs). Unless otherwise specified, each instance of a cycloalkyl group is independently unsubstituted (an "unsubstitutedcycloalkyl") or substituted (a "substituted cycloalkyl") with one or more substituents. In certain embodiments, the cycloalkyl group is an unsubstituted C3-14 cycloalkyl. In certain embodiments, the cycloalkyl group is a substituted C3-14 cycloalkyl.

[0104] The term "heterocyclyl" or "heterocyclic" refers to a radical of a 3- to 14- membered non-aromatic ring system having ring carbon atoms and 1 to 4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, and sulfur ("3-14 membered heterocyclyl"). In heterocyclyl groups that contain one or more nitrogen atoms, the point of attachment can be a carbon or nitrogen atom, as valency permits. A heterocyclyl group can either be monocyclic ("monocyclic heterocyclyl") or polycyclic (e.g., a fused, bridged or spiro ring system such as a bicyclic system ("bicyclic heterocyclyl") or tricyclic system ("tricyclic heterocyclyl")), and can be saturated or can contain one or more carboncarbon double or triple bonds. Heterocyclyl polycyclic ring systems can include one or more heteroatoms in one or both rings. "Heterocyclyl" also includes ring systems wherein the heterocyclyl ring, as defined above, is fused with one or more carbocyclyl groups wherein the point of attachment is either on the carbocyclyl or heterocyclyl ring, or ring systems wherein the heterocyclyl ring, as defined above, is fused with one or more aryl or heteroaryl groups, wherein the point of attachment is on the heterocyclyl ring, and in such instances, the number of ring members continue to designate the number of ring members in the heterocyclyl ring system. Unless otherwise specified, each instance of heterocyclyl is independently unsubstituted (an "unsubstituted heterocyclyl") or substituted (a "substituted heterocyclyl") with one or more substituents. In certain embodiments, the heterocyclyl group is an unsubstituted 3-14 membered heterocyclyl. In certain embodiments, the heterocyclyl group is a substituted 3-14 membered heterocyclyl.

[0105] In some embodiments, a heterocyclyl group is a 5-10 membered non-aromatic ring system having ring carbon atoms and 1-4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, and sulfur ("5-10 membered heterocyclyl"). In some embodiments, a heterocyclyl group is a 5-8 membered non-aromatic ring system having ring carbon atoms and 1-4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, and sulfur ("5-8 membered heterocyclyl"). In some embodiments, a heterocyclyl group is a 5-6 membered non-aromatic ring system having ring carbon atoms and 1- 4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, and sulfur ("5-6 membered heterocyclyl"). In some embodiments, the5-6 membered heterocyclyl has 1-3 ring heteroatoms selected from nitrogen, oxygen, and sulfur. In some embodiments, the 5-6 membered heterocyclyl has 1-2 ring heteroatoms selected from nitrogen, oxygen, and sulfur. In some embodiments, the 5-6 membered heterocyclyl has 1 ring heteroatom selected from nitrogen, oxygen, and sulfur.

[0106] Exemplary 3-membered heterocyclyl groups containing 1 heteroatom include, without limitation, aziridinyl, oxiranyl, and thiiranyl. Exemplary 4-membered heterocyclyl groups containing 1 heteroatom include, without limitation, azetidinyl, oxetanyl, and thietanyl. Exemplary 5-membered heterocyclyl groups containing 1 heteroatom include, without limitation, tetrahydrofuranyl, dihydrofuranyl, tetrahydrothiophenyl, dihydrothiophenyl, pyrrolidinyl, dihydropyrrolyl, and pyrrolyl-2, 5-dione. Exemplary 5- membered heterocyclyl groups containing 2 heteroatoms include, without limitation, dioxolanyl, oxathiolanyl and dithiolanyl. Exemplary 5-membered heterocyclyl groups containing 3 heteroatoms include, without limitation, triazolinyl, oxadiazolinyl, and thiadiazolinyl. Exemplary 6-membered heterocyclyl groups containing 1 heteroatom include, without limitation, piperidinyl, tetrahydropyranyl, dihydropyridinyl, and thianyl. Exemplary6-membered heterocyclyl groups containing 2 heteroatoms include, without limitation, piperazinyl, morpholinyl, dithianyl, and dioxanyl. Exemplary 6-membered heterocyclyl groups containing 3 heteroatoms include, without limitation, triazinyl. Exemplary 7- membered heterocyclyl groups containing 1 heteroatom include, without limitation, azepanyl, oxepanyl and thiepanyl. Exemplary 8-membered heterocyclyl groups containing 1 heteroatom include, without limitation, azocanyl, oxecanyl and thiocanyl. Exemplary bicyclic heterocyclyl groups include, without limitation, indolinyl, isoindolinyl, dihydrobenzofuranyl, dihydrobenzothienyl, tetrahydrobenzothienyl, tetrahydrobenzofuranyl, tetrahydroindolyl, tetrahydroquinolinyl, tetrahydroisoquinolinyl, decahydroquinolinyl, decahydroisoquinolinyl, octahydrochromenyl, octahydroisochromenyl, decahydronaphthyridinyl, decahydro- 1,8- naphthyridinyl, octahydropyrrolo[3,2-b]pyrrole, indolinyl, phthalimidyl, naphthalimidyl, chromanyl, chromenyl, lH-benzo[e][l,4]diazepinyl, l,4,5,7-tetrahydropyrano[3,4-b]pyrrolyl, 5,6-dihydro-4H-furo[3,2-b]pyrrolyl, 6,7-dihydro-5H- furo[3,2-b]pyranyl, 5,7-dihydro-4H- thieno[2,3-c]pyranyl, 2,3-dihydro-lH-pyrrolo[2,3-b]pyridinyl, 2,3-dihydrofuro[2,3- b]pyridinyl, 4, 5, 6, 7 -tetrahydro-lH-pyrrolo[2,3-b ]pyridinyl, 4,5,6,7-tetrahydrofuro[3,2- c]pyridinyl, 4,5,6,7-tetrahydrothieno[3,2-b]pyridinyl, 1,2, 3, 4- tetrahydro-1, 6-naphthyridinyl, and the like.

[0107] Exemplary carbon atom substituents include, but are not limited to, halogen, -CN, -NO2, -N3, -OH, F, Cl, Br, I, oxo, -SO2H, -SO3H, -ORaa, -NH(Raa)2, -N(Raa)2, -N(Raa)3+X’, - SH, -SRaa, -C(=O)Raa, -CO2H, -CHO, -CO2Raa, -OC(=O)Raa, -OCO2Raa, -C(=O)N(Raa)2, - OC(=O)N(Raa)2, -NRaaC(=O)Raa, -NRaaCO2Raa, -NRaaC(=O)N(Raa)2, -C(=NRaa)Raa, - C(=O)NRaaSO2Raa, -NRaaSO2Raa, -SO2N(Raa)2, -SO2Raa, -SO2ORaa, -OSO2Raa, -S(=O)Raa, - OS(=O)Raa, -Si(Raa)3, -OSi(Raa)3, C1-12 alkyl, C1-12 haloalkyl, 3-16 membered heterocyclyl, and C6-12 aryl, wherein X is a counterion and each instance of Raais, independently, selected from H, -OH, C1-10 alkyl, C1-10 haloalkyl, C3-12 cycloalkyl, 5-16 membered heterocyclyl, and C6-12 aryl, or two Raagroups are joined to form a 3-16 membered heterocyclyl.

[0108] In a first embodiment the invention is bilayer polyelectrolyte membrane, comprising a first layer and a second layer, wherein the first layer comprises a PFSA polymer, and the second layer comprises an admixture of a crosslinked sulfonated polymer and a filler polymer, and wherein the first layer is disposed on the second layer.

[0109] In a first aspect of the first embodiment, the PFSA polymer is a polymer comprising a repeat unit represented by structural formula (I):wherein x is an integer between 1 and 15, m is an integer between 0 and 2, n is an integer between 1 and 5, anda point of attachment to a neighboring repeat unit. For example, x is an integer between 5 and 14, m is 1 or 2, and n is 2 or 3. In certain cases, m is 1 and n is 2. In some embodiments, the PFSA polymer is a polymer comprising from about 500 to about 1500 repeat units represented by structural formula (I). For example, the PFSA polymer is a polymer comprising from about 600 to about 1400, from about 700 to about 1300, from about 800 to about 1200, or from about 900 to about 1100 repeat units represented by structural formula (I). For example, the PFSA polymer is a polymer comprising about 1000 repeat units represented by structural formula (I).

[0110] In a second aspect of the first embodiment, the admixture is a homogeneous admixture. The remainder of features and example features of the second aspect is as described above with respect to the first aspect of the first embodiment.In a third aspect of the first embodiment, the crosslinked sulfonated polymer comprises sulfonated polyphenyl sulfone (sPPS), sulfonated poly ether ether ketone (sPEEK), sulfonated polyphosphazene (sPOP), sulfonated polybenzimidazole (sPBI), sulfonated polyether sulfone (sPES), sulfonated polyphenylene oxide (sPPO), sulfonated polyarylene ether ketone (sPAEK), sulfonated poly(sulfone) (sPSU), sulfonated poly(sulfide sulfone), sulfonated polyimide (sPI), sulfonated poly(etherimide) (sPEI), sulfonated poly(amine), poly (4- phenoxybenzoyl-l,4-phenylene) (PPBP), or a combination thereof. In some embodiments, the crosslinked sulfonated polymer comprises sulfonated polyphenyl sulfone (sPPS), sulfonated polyether ether ketone (sPEEK), sulfonated polyphosphazene (sPOP), sulfonated polybenzimidazole (sPBI), sulfonated polyether sulfone (sPES), sulfonated polyarylene ether ketone (sPAEK), sulfonated poly(sulfone) (sPSU), sulfonated poly(sulfide sulfone), sulfonated polyimide (sPI), sulfonated poly(etherimide) (sPEI), sulfonated poly(amine), or a combination thereof. In some embodiments, the crosslinked sulfonated polymer comprises sPPS, sPEEK, sPOP, sPBI, sPES, sPAEK, sulfonated poly(sulfone), sulfonated poly(sulfide sulfone), sPI, sPEI, sulfonated poly(amine), sPPBP, or a combination thereof. For example, in certain embodiments, the crosslinked sulfonated polymer comprises sPPS, sPES, sPSU, sulfonated poly(sulfide sulfone), or a combination thereof. For example, the crosslinked sulfonated polymer comprises sPPS, sPES, sPSU, or a combination thereof. For example, the crosslinked sulfonated polymer comprises sPPS, sPEEK, sPOP, or sPBI. For example, the crosslinked sulfonated polymer comprises sPPS or sPSU. For example, the crosslinked sulfonated polymer comprises sPPS. The remainder of features and example features of the third aspect is as described above with respect to the first and second aspects of the first embodiment.

[0111] In a fourth aspect of the first embodiment, the crosslinked sulfonated polymer comprises a crosslinking moiety represented by one of the following structural formulas:wherein k is 0, 1, or 2; R1is selected from H,Ci-12 alkyl, Ci-n haloalkyl, Ce-i4 aryl, and Ce-i4 aryl(Ci-i2 alkylene); M2+is selected fromMg2+, Ca2+, Ba2+, and A1(X)2+, wherein X is halide, acetate, or nitrate; and the symbolrepresents a point of attachment of the crosslinking moiety to a repeat unit of the one or more first polymer. For example, in some embodiments, the crosslinking moiety is represented by one of the following structural formulas:For example, in some embodiments, the crosslinking moiety is represented by one of the following structural formulas:example, in some embodiments, the crosslinking moiety is represented by one of the following structural formulas:embodiments, the crosslinking moiety is represented by one of the following structuralFor example, in some embodiments, the crosslinking moiety is represented by the following structural formula:example, in some embodiments, the crosslinking moiety is represented by one of the following structural formulas:example, in some embodiments, the crosslinking moiety is represented by the following structural formula:. The remainder of features and example features of the fourth aspect is as described above with respect to the first through the third aspects of the first embodiment.

[0112] In a fifth aspect of the first embodiment, the first layer further comprises a porous matrix comprising a matrix polymer, wherein the PF SA polymer and the matrix polymer form an interpenetrating network. For example, the first layer comprises from about 50 wt.% to about 99 wt.% of PFSA polymer, from about 55 wt.% to about 98 wt.% of PFSA polymer, from about 60 wt.% to about 97 wt.% of PFSA polymer, from about 70 wt.% to about 96 wt.% of PFSA polymer, or from about 80 wt.% to about 96 wt.% of PFSA polymer. For example, the first layer comprises from about 70 wt.% to about 99 wt.% of PFSA polymer, such as from about 78 wt.% to about 95 wt.% of PFSA polymer. In some embodiments, the first layer comprises from about 50 wt.% to about 95 wt.% PFSA polymer. The remainder of features and example features of the fifth aspect is as described above with respect to the first through the fourth aspects of the first embodiment.

[0113] In a sixth aspect of the first embodiment, the matrix polymer is polytetrafluoroethylene (PTFE). For example, the matrix polymer is expanded PTFE(ePTFE). The remainder of features and example features of the sixth aspect is as described above with respect to the first through the fifth aspects of the first embodiment.

[0114] In a seventh aspect of the first embodiment, the degree of sulfonation of the crosslinked sulfonated polymer is from about 10% to about 400%. For example, in certain embodiments, the degree of sulfonation of the crosslinked sulfonated polymer is from about 10% to about 100%, from about 20% to about 100%, from about 30% to about 100%, from about 40% to about 100%, from about 50% to about 100%, from about 60% to about 100%, from about 70% to about 100%, from about 80% to about 100%, from about 50% to about 200%, from about 80% to about 200%, from about 100% to about 200%, from about 100% to about 250%, from about 150% to about 200%, from about 100% to about 300%, from about 100% to about 350%, from about 100% to about 400%, from about 150% to about 250%, from about 150% to about 300%, from about 150% to about 350%, from about 150% to about 400%, from about 200% to about 300%, from about 200% to about 350%, from about 200% to about 400%, or from about 250% to about 350%. For example, in certain embodiments, the degree of sulfonation of the crosslinked sulfonated polymer is about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 100%, about 120%, about 140%, about 160%, about 180%, about 200%, about 220%, about 240%, about 260%, about 280%, about 300%, about 320%, about 340%, about 360%, about 380%, or about 400%. In some embodiments, the crosslinked sulfonated polymer has degree of sulfonation from about 100% to about 300%. In some embodiments, the crosslinked sulfonated polymer has degree of sulfonation about 200%. Degree of sulfonation can be measured, for example, byJH NMR or by determining ion exchange capacity of the polymer by titration. The remainder of features and example features of the seventh aspect is as described above with respect to the first through the sixth aspects of the first embodiment.

[0115] In an eighth aspect of the first embodiment, the filler polymer is selected from PAAm, PVDF, PS-co-PAN, and PVC, the crosslinked sulfonated polymer is sPPS, and the sPPS comprises a crosslinking moiety represented by the following structural formula:. The remainder of features and example features of the thirteenth aspect is as described above with respect to the first through the twelfth aspects of the first embodiment.

[0116] The remainder of features and example features of the eighth aspect is as described above with respect to the first through the seventh aspects of the first embodiment.

[0117] In a ninth aspect of the first embodiment, the thickness of the first layer is from about 5 pm to about 200 pm. For example, the thickness of the first layer is about 5 pm, about 10 pm, about 15 pm, about 20 pm, about 25 pm, about 30 pm, about 35 pm, about 40 pm, about 45 pm, about 50 pm, about 55 pm, about 60 pm, about 65 pm, about 70 pm, about 75 pm, about 80 pm, about 85 pm, about 90 pm, about 95 pm, about 100 pm, about 110 pm, about 120 pm, about 130 pm, about 140 pm, about 150 pm, about 160 pm, or about 170 pm, about 180 pm, about 190 pm, or about 200 pm. For example, the thickness of the first layer is from about 5 pm to about 175 pm. For example, the thickness of the first layer is about 25 pm. The remainder of features and example features of the ninth aspect is as described above with respect to the first through the eighth aspects of the first embodiment.

[0118] In a tenth aspect of the first embodiment, the thickness of the second layer is from about 0.2 pm to about 175 pm. For example, the thickness of the second layer is about 0.2 pm, about 0.4 pm, about 0.6 pm, about 0.8 pm, about 1.0 pm, about 2.0 pm, about 3.0 pm, about 4.0 pm, about 5 pm, about 10 pm, about 15 pm, about 20 pm, about 25 pm, about 30 pm, about 35 pm, about 40 pm, about 45 pm, about 50 pm, about 55 pm, about 60 pm, about 65 pm, about 70 pm, about 75 pm, about 80 pm, about 85 pm, about 90 pm, about 95 pm, about 100 pm, about 110 pm, about 120 pm, about 130 pm, about 140 pm, about 150 pm, about 160 pm, or about 170 pm. For example, the thickness of the second layer is from about 0.2 pm to about 10 pm, from about 0.4 pm to about 5 pm, from about 0.6 pm to about 2 pm, from about 0.8 pm to about 1.5 pm. For example, the thickness of the second layer is from about 0.2 pm to about 10 pm. For example, For example, the thickness of the second layer is from about 0.5 pm to about 2 pm. For example, the thickness of the second layer is about 0.75 pm. For example, the thickness of the second layer is about 1 pm. For example, the thickness of the second layer is about 1.5 pm. Layer thickness is measured by cross-sectional scanning electron microscopy and / or optical absorption (in the IR). The remainder of features and example features of the tenth aspect is as described above with respect to the first through the ninth aspects of the first embodiment.

[0119] In an eleventh aspect of the first embodiment, the first layer is continuous. The remainder of features and example features of the eleventh aspect is as described above with respect to the first through the tenth aspects of the first embodiment.

[0120] In a twelfth aspect of the first embodiment, the membrane is unsupported. The remainder of features and example features of the twelfth aspect is as described above with respect to the first through the eleventh aspects of the first embodiment.

[0121] In a thirteenth aspect of the first embodiment, the filler polymer is selected fromPAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC, the crosslinked sulfonated polymer is sPPS, and the sPPS comprises a crosslinking moiety represented by the following structural formula:The remainder of features and example features of the thirteenth aspect is as described above with respect to the first through the twelfth aspects of the first embodiment.In a fourteenth aspect of the first embodiment, the membrane is unsupported, the PFSA is a polymer comprising a repeat unit represented by structural formula (I):wherein x is an integer between 5 and 14, m is 1 or 2, and n is 2 or 3; and further wherein the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC, the crosslinked sulfonated polymer is sPPS, the crosslinking moiety is represented by the following structural formula:has degree of sulfonation about200%, sPPS has degree of crosslinking about 40%, and the second layer is from about 0.5 pm to about 2 pm thick. The remainder of features and example features of the fourteenth aspect is as described above with respect to the first through the thirteenth aspects of the first embodiment

[0122] In a fifteenth aspect of the first embodiment, the first layer comprises a porous matrix comprising a matrix polymer, the PFSA polymer and the matrix polymer form an interpenetrating network, the crosslinked sulfonated polymer is sPPS, and the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC. The remainder of features and example features of the third aspect is as described above with respect to the firstand second aspects of the first embodiment. The remainder of features and example features of the fifteenth aspect is as described above with respect to the first through the fourteenth aspects of the first embodiment.

[0123] In a sixteenth aspect of the first embodiment, sPPs comprises a crosslinking moiety represented by one of the following structural formulas:The remainder of features and example features of the seventeenth aspect is as described above with respect to the first through the sixteenth aspects of the first embodiment.

[0124] In a seventeenth aspect of the first embodiment, the filler polymer is selected from PAAm, PVA, PVDF, PS-co-PAN, and PVC. The remainder of features and example features of the seventeenth aspect is as described above with respect to the first through the sixteenth aspects of the first embodiment.

[0125] In an eighteenth aspect of the first embodiment, the crosslinked sulfonated polymer comprises on average from about 0.5 to about 6 sulfonic acid, sulfonate, and sulfonamide groups, combined, per repeat unit. For example, the crosslinked sulfonated polymer comprises on average from about 0.5 to about 2, from about 1 to about 3, from about 1.5 to about 2.5 , from about 2 to about 4, from about 1.5 to about 3 , or from about 2 to about 1.5 sulfonic acid, sulfonate, and sulfonamide groups, combined, per repeat unit. For example, the crosslinked sulfonated polymer comprises on average about 0.5, about 1, about 1.5, about 2.0, about 2.5, or about 3 sulfonic acid, sulfonate, and sulfonamide groups, combined, per repeat unit. The remainder of features and example features of the eighteenth aspect is as described above with respect to the first through the seventeenth aspects of the first embodiment.

[0126] In a nineteenth aspect of the first embodiment, the degree of crosslinking of the crosslinked sulfonated polymer is from about 10% to about 95%. In some embodiments, the degree of crosslinking of the crosslinked sulfonated polymer is from about 20% to about 80%. In some embodiments, the degree of crosslinking of the crosslinked sulfonated polymer is from about 30% to about 50%. For example, the degree of crosslinking of the crosslinked sulfonated polymer is from about 15% to about 90%, from about 20% to about 80%, from about 20% to about 70%, from about 20% to about 60%, from about 20% to about 50%, fromabout 20% to about 45%, from about 20% to about 40%, from about 30% to about 50%, from about 25% to about 30%, or from about 30% to about 35%. For example, the degree of crosslinking of the crosslinked sulfonated polymer is about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, or about 95%. In some embodiments, the degree of crosslinking of the crosslinked sulfonated polymer is about 40%. Degree of crosslinking is measured, for example, by determining ion exchange capacity of the polymer by titration. The remainder of features and example features of the nineteenth aspect is as described above with respect to the first through the eighteenth aspects of the first embodiment.

[0127] In a twentieth aspect of the first embodiment, the PFSA polymer comprises a repeat unit represented by structural formula (I):wherein x is an integer between 5 and 14, m is 1 or 2, and n is 2 or 3; and the crosslinked sulfonated polymer comprises sPPS, and the crosslinking moiety is represented by one of the following structural formulas:The remainder of features and example features of the twentieth aspect is as described above with respect to the first through the nineteenth aspects of the first embodiment.

[0128] In a twenty-first aspect of the first embodiment, the membrane is unsupported, the filler polymer is selected from PAAm, PVDF, PS-co-PAN, and PVC; the crosslinked sulfonated polymer is sPPS, and the crosslinking moiety is represented by one of the following structural formulas:. The remainder of features and example features of the twenty-first aspect is as described above with respect to the first through the twentieth aspects of the first embodiment.

[0129] In a twenty-second aspect of the first embodiment, the PFSA polymer is a polymer comprising a repeat unit represented by structural formula (I):wherein x is an integer between 5 and 14, m is 1 or 2, and n is 2 or 3; the crosslinked sulfonated polymer comprises sPPS, and sPPS comprises a crosslinking moiety represented by one of the following structural formulas:The remainder of features and example features of the twenty-second aspect is as described above with respect to the first through the twenty -first aspects of the first embodiment.

[0130] In a twenty-third aspect of the first embodiment, the membrane is unsupported, the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC, and the crosslinked sulfonated polymer comprises a crosslinking moiety represented by the following structural formula:, the degree of sulfonation of the sPPS is about 200%, the degree of crosslinking of the sPPS is about 40%, and the thickness of the second layer is from about 0.5 pm to about 2 pm. The remainder of features and example features of the twenty-third aspect is as described above with respect to the first through the twenty-second aspects of the first embodiment.

[0131] In a twenty-fourth aspect of the first embodiment, the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC, and the crosslinked sulfonated polymer comprises a crosslinking moiety represented by the following structural formula:The remainder of features and example features of the twenty-fourth aspect is as described above with respect to the first through the twenty-third aspects of the first embodiment.

[0132] In a twenty-fifth aspect of the first embodiment, the first layer comprises a porous matrix comprising a matrix polymer, the PFSA polymer and the matrix polymer form an interpenetrating network, and the crosslinked sulfonated polymer comprises sPPS. For example, the crosslinked sulfonated polymer is sPPS. For example, the sPPS comprises a crosslinking moiety represented by one of the following structural formulas:the crosslinking moiety is represented by one of the following structural formulas:example, the crosslinking moiety is represented by the following structural formula:. The remainder of features and example features of the twenty-fifth aspect is as described above with respect to the first through the twenty -fourth aspects of the first embodiment.

[0133] In a twenty-sixth aspect of the first embodiment, the filler polymer comprises a repeat unit comprising an aliphatic backbone. In some embodiment, the filler polymer comprises a repeat unit having an aliphatic backbone. For example, in certain embodiments, the filler polymer comprises a repeat unit comprising a backbone consisting of substituted C2- 10 alkylene, such as substituted C2, C3, C4, Cs,, Ce, C7, Cs, C9, or C10 alkylene. In certain embodiments, the filler polymer comprises a repeat unit comprising a backbone consisting of substituted C2 alkylene. The remainder of features and example features of the twenty-sixthaspect is as described above with respect to the first through the twenty-fifth aspects of the first embodiment.

[0134] In a twenty-seventh aspect of the first embodiment, the filler polymer comprises polyacrylamide (PAAm), poly(N,N-dimethylacrylamide) (PDMA), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), poly(etherimide) (PEI), polyvinylidene fluoride (PVDF), poly(4-vinylpyridine) (P4VP), polystyrene-polyacrylonitrile co-polymer (PS-co-PAN), polyvinyl chloride (PVC), polyethylene, polypropylene, or a combination thereof. In some embodiments, the filler polymer comprises PAAm, PDMA, PVP, PEI, PVDF, P4VP, PS-co- PAN, PVC, or a combination thereof. In some embodiments, the filler polymer comprises PAAm, PDMA, PVP, PVDF, P4VP, PS-co-PAN, PVC, or a combination thereof. In some embodiments, the filler polymer comprises PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, PVC, or a combination thereof. In some embodiments, the filler polymer comprises PAAm, PVA, PVDF, PS-co-PAN, PVC, or a combination thereof. In some embodiments, the filler polymer comprises PAAm, PVA, PVDF, PS-co-PAN, PVC, or a combination thereof. In some embodiments, the filler polymer comprises PAAm, PVDF, PS-co-PAN, PVC, or a combination thereof. The remainder of features and example features of the twenty-seventh aspect is as described above with respect to the first through the twenty-sixth aspects of the first embodiment.

[0135] In a twenty-eighth aspect of the first embodiment, the second layer comprises from about 0.05 wt.% to about 70 wt.% of the filler polymer. For example, in certain embodiments, the second layer comprises from about 0.1 wt.% to about 50 wt.% of filler polymer. For example, in certain embodiments, the second layer comprises from about 1 wt.% to about 45 wt.% of filler polymer, from about 1 wt.% to about 35 wt.% of filler polymer, from about 1 wt.% to about 25 wt.% of filler polymer, from about 1 wt.% to about 15 wt.% of filler polymer, from about 1 wt.% to about 10 wt.% of filler polymer, from about2 wt.% to about 50 wt.% of filler polymer, from about 2 wt.% to about 40 wt.% of filler polymer, from about 2 wt.% to about 30 wt.% of filler polymer, from about 2 wt.% to about 20 wt.% of filler polymer, from about 2 wt.% to about 10 wt.% of filler polymer, from about3 wt.% to about 30 wt.% of filler polymer, from about 3 wt.% to about 20 wt.% of filler polymer, from about 3 wt.% to about 10 wt.% of filler polymer, from about 5 wt.% to about 50 wt.% of filler polymer, from about 5 wt.% to about 40 wt.% of filler polymer, from about 5 wt.% to about 30 wt.% of filler polymer, from about 5 wt.% to about 20 wt.% of fillerpolymer, from about 5 wt.% to about 10 wt.% of filler polymer, from about 10 wt.% to about 50 wt.% of filler polymer, from about 10 wt.% to about 40 wt.% of filler polymer, from about 10 wt.% to about 30 wt.% of filler polymer, from about 10 wt.% to about 20 wt.% of filler polymer, from about 20 wt.% to about 50 wt.% of filler polymer, from about 20 wt.% to about 40 wt.% of filler polymer, from about 20 wt.% to about 30 wt.% of filler polymer, from about 30 wt.% to about 50 wt.% of filler polymer, from about 30 wt.% to about 40 wt.% of filler polymer, or from about 40 wt.% to about 50 wt.% of filler polymer. For example, the second layer comprises about 0.1 wt.% of filler polymer, about 0.5 wt.%, about 1 wt.% , about 2 wt.%, about 3 wt.% of filler polymer, about 4 wt.% of filler polymer, about 5 wt.% of filler polymer, about 6 wt.% of filler polymer, about 7 wt.% of filler polymer, about 8 wt.% of filler polymer, about 9 wt.% of filler polymer, about 10 wt.% of filler polymer, about 12 wt.% of filler polymer, about 14 wt.% of filler polymer, about 16 wt.% of filler polymer, about 18 wt.% of filler polymer, about 20 wt.% of filler polymer, about 25 wt.% of filler polymer, about 30 wt.% of filler polymer, about 35 wt.% of filler polymer, about 40 wt.% of filler polymer, about 45 wt.% of filler polymer, about 50 wt.% of filler polymer, about 55 wt.% of filler polymer, about 60 wt.% of filler polymer, or about 65 wt.% of filler polymer. For example, in certain embodiments, the second layer comprises about 7 wt.% of filler polymer. For example, in certain embodiments, the second layer comprises about 8 wt.% of filler polymer. The remainder of features and example features of the twenty-eighth aspect is as described above with respect to the first through the twenty-seventh aspects of the first embodiment.

[0136] In a second embodiment, the invention is a method of making a bilayer polyelectrolyte membrane described herein with respect to the first embodiment and various aspects thereof, comprising: a) providing a first layer having a first side, and a solution or suspension comprising a sulfonated polymer, a filler polymer, and a crosslinking reagent, b) coating the first side of the first layer with the solution or suspension, thereby producing a coated first layer; c) exposing the coated first layer to conditions sufficient for the sulfonated polymer and the crosslinking reagent to undergo a crosslinking reaction, thereby producing the bilayer polyelectrolyte membrane.

[0137] In a first aspect of the second embodiment, the crosslinking reagent is selected from a polyalcohol, an amine, an azide, an epoxide, a thiol, or a compound comprising a terminal alkene or alkyne. For example, in certain embodiments, the crosslinking reagent is selected from hydroquinone, 2,5-dihydroxybenzenesulfonic acid, 2,5-dihydroxybenzene-l,4- disulfonic acid, biphenyl, glycerol, ethylene glycol, tetraglycidyl bis(p- aminophenyl)methane, phenylene diamine, 4,4’-thiobisbenzenethiol, and tetrafluoro styrene. For example, the crosslinking reagent is selected from hydroquinone, 2,5- dihydroxybenzenesulfonic acid, 2,5-dihydroxybenzene-l,4-disulfonic acid, biphenyl, glycerol, and ethylene glycol. For example, the crosslinking reagent is a polyalcohol, such as glycerol or ethylene glycol. For example, the crosslinking reagent is hydroquinone or 2,5- dihydroxybenzenesulfonic acid.

[0138] In a second aspect of the second embodiment, the conditions sufficient for the sulfonated polymer and the crosslinking reagent to undergo a crosslinking reaction comprise heating the coated first layer to a crosslinking temperature from about 180 °C to about 220 °C for a crosslinking time from about 1 hours to about 10 hours. For example, the crosslinking temperature is about 180 °C, about 190 °C, about 200 °C, about 210 °C, about 220 °C. For example, the crosslinking temperature about is about 200 °C and the crosslinking time is about 2 hours. For example, crosslinking time is about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours. For example, crosslinking time is about 2 hours. The remainder of features and example features of the second aspect is as described above with respect to the first aspect of the second embodiment.

[0139] In a third aspect of the second embodiment, coating the first side of the first layer with the solution or suspension comprises spray-coating the first side of the first layer with the solution or suspension. Alternatively, coating the first side of the first layer with the first solution or suspension comprises blade-coating, dip-coating, spin-coating, or flow-coating the first side of the first layer with the solution or suspension. In some embodiments, coating the first side of the first layer with the solution or suspension comprises blade-coating the first side of the first layer with the solution or suspension. The remainder of features and example features of the third aspect is as described above with respect to the first and second aspects of the second embodiment.

[0140] In a fourth aspect of the second embodiment, the solution or suspension comprises from about 0.005 wt.% to about 20 wt.% of the filler polymer. For example, in certain embodiments, the solution or suspension comprises from about from about 0.01 wt.% to about 0.5 wt.% of the filler polymer. In some embodiments, the suspension comprises from about from about 0.05 wt.% to about 1 wt.% of the filler polymer. In come embodiments, the suspension comprises from about from about 0.01 wt.% to about 2 wt.%, from about from about 0.01 wt.% to about 1 wt.%, from about from about 0.01 wt.% to about 0.5 wt.%, or from about from about 0.01 wt.% to about 0.1 wt.% of the filler polymer. For example, the suspension comprises about 0.8 wt.% of the filler polymer. For example, the suspension comprises about 1 wt.% to about 10 wt.% of the filler polymer, such as from about 1.3 wt.% to about 8 wt.%, from about 1.5 wt.% to about 3 wt.% , from about 3 wt.% to about 4 wt.%, from about 2.5 wt.% to about 3.5 wt.%, from about 2.5 wt.% to about 5.5 wt.%, or from about 3.0 wt.% to about 5.0 wt.% of filler polymer. The remainder of features and example features of the fourth aspect is as described above with respect to the first through third aspects of the second embodiment.

[0141] In a fifth aspect of the second embodiment, the solution or suspension comprises from about 0.05 wt.% to about 20 wt.% of the sulfonated polymer. For example, the solution or suspension comprises from about 0.1 wt.% to about 5 wt.% of the first polymer, such as about 0.75 wt.% of the first polymer. For example, the solution or suspension comprises about 0.2 wt.%, about 0.3 wt.%, about 0.4 wt.%, about 0.6 wt.%, about 0.7 wt.%, about 0.8 wt.%, about 0.9 wt.%, about 1.0 wt.%, about 2 wt.%, about 3 wt.%, about 4 wt.%, about 5 wt.%, about 6 wt.%, about 7 wt.%, about 8 wt.%, about 9 wt.%, about 10 wt.%, about 10 wt.%, about 12 wt.%, about 13 wt.%, about 14 wt.%, about 15 wt.%, about 16 wt.%, about 17 wt.%, about 18 wt.%, about 19 wt.%, or about 20 wt.% of the first polymer. In some embodiments, the suspension comprises from about from about 0.5 wt.% to about 2 wt.% of the first polymer. In come embodiments, the suspension comprises from about from about 0.05 wt.% to about 5 wt.%, from about from about 0.1 wt.% to about 3.0 wt.%, from about from about 0.2 wt.% to about 2.0 wt.%, or from about from about 0.3 wt.% to about 1.5 wt.% of the first polymer. The remainder of features and example features of the fifth aspect is as described above with respect to the first through fourth aspects of the second embodiment.

[0142] In a sixth aspect of the second embodiment, the solution or suspension comprises from about 0.01 wt.% to about 5 wt. % of the crosslinking reagent. For example, the solutionor suspension comprises from about 0.1 wt.% to about 1 wt.% of the crosslinking reagent. For example, the solution or suspension comprises about 0.01 wt.%, about 0.05 wt.%, about 0.1 wt.%, about 0.2 wt.%, about 0.3 wt.%, about 0.4 wt.%, about 0.6 wt.%, about 0.7 wt.%, about 0.8 wt.%, about 0.9 wt.%, about 1.0 wt.%, about 2 wt.%, about 3 wt.%, about 4 wt.%, or about 5 wt.% of the crosslinking reagent. For example, the solution or suspension comprises about 0.19 wt.% of the crosslinking reagent. The remainder of features and example features of the sixth aspect is as described above with respect to the first through the fifth aspects of the second embodiment.

[0143] In a seventh aspect of the second embodiment, the solution or suspension further comprises a solvent selected from water, alcohol, dimethylformamide, tetrahydrofuran, N- methylformamide, formamide, acetonitrile, dimethylacetamide, propylene carbonate, ethylene carbonate, N-methylpyrrolidone, dimethylsulfoxide, or a combination thereof. For example, in some embodiments, the solvent is dimethylacetamide. For example, in some embodiments, the solvent comprises water. For example, in some embodiments, the solvent is selected from dimethylacetamide and water. The remainder of features and example features of the seventh aspect is as described above with respect to the first through the sixth aspects of the second embodiment.

[0144] In a third embodiment the invention is a membrane electrode assembly (MEA), comprising: the bilayer polyelectrolyte membrane described herein with respect to the first embodiment and various aspects thereof; a cathode; and an anode, wherein the bilayer electrolyte membrane is disposed between the anode and the cathode.

[0145] In a first aspect of the third embodiment, the cathode is disposed on the first layer of the bilayer electrolyte membrane and the anode is disposed on the second layer of the bilayer electrolyte membrane. Alternatively, wherein the anode is disposed on the first layer of the bilayer electrolyte membrane and the cathode is disposed on the second layer of the bilayer electrolyte membrane.

[0146] In a fourth embodiment the invention is a fuel cell, comprising one or more of the MEAs described herein with respect to the third embodiment and various aspects thereof and one or more gas flow bipolar plates.ExamplesMaterialsNafion® PFSA membrane (NR-211) was purchased from Ion Power. Sulfuric acid (H2SO4) was purchased from Sigma-Aldrich (95-98%, CAS 7664-93-9). PPS (Solvay Radel R-5000, MW=5000) was purchased from Solvay. Hydroquinone was purchased from Sigma-Aldrich (>99%, CAS 123-31-9). PVDF (polyvinylidene fluoride, MW=534000) was purchased from Sigma-Aldrich (CAS 24937-79-9). P4VP (poly(4-vinylpyridine, MW=60000) was purchased from Sigma-Aldrich (CAS 25232-41-1). PS-co-PAN (polystyrene-polyacrylonitrile copolymer, 25 wt.% acrylonitrile, MW= 165000) was purchased from Sigma-Aldrich (CAS 9003-54-7). PAAm (polyacrylamide, MW=150000) was purchased from Sigma-Aldrich (CAS 9003-05-8). PVC (polyvinyl chloride, MW=233000) was purchased from Sigma- Aldrich (CAS 9002-86-2). PVA (polyvinyl alcohol, MW=31000-50000) was purchased from Sigma-Aldrich CAS(9002-89-5).Example 1. Sulfonation of PPS.

[0147] PPS was sulfonated by reacting the polymer with H2SO4. PPS resin was ground into a powder using an industrial grinder. PPS was dissolved in concentrated H2SO4 at a concentration 25 mg / mL and stirred at 60 °C for 10 hrs. The sulfonated polymer was precipitated by adding the reaction mixture dropwise to H2O at 0 °C. The resulting precipitated polymer was centrifuged and isolated. The sulfonated PPS (sPPS) was redispersed in H2O at room temperature and washed using dialysis until neutral pH was registered. The washed sPPS was dried on a hot plate to provide the final product. The yield of the reaction was determined by mass to be 91%. The resulting product had a titration determined ion exchange capacity (IEC) of 3.605 meq / g (2.0 sulfonic acids per repeat unit). The degree of sulfonation of sPPS can be tuned by adjusting the reaction time (1-8 hrs).

[0148] 'H NMR of the sulfonated polymers was measured at a concentration of about 10 wt.% in DMSO-d6 to confirm the polymer structure and degree of sulfonation. The1H NMR spectrum was acquired with a 500 MHz Bruker Ultrashield 500 Plus Spectrometer and processed using SpinWorks 4. The 'H NMR experiments were performed using a pulse angle of 30° and a pulse delay of 5s with 32 scans. The 'H NMR spectrum of the prepared sPPS is shown in Figure 10. Integration of the peaks as shown below in Table 1 was used to establish the number and positions of the sulfonic acid groups in the repeat unit as shown in Figure 4.

[0149] Table 1.JH NMR peak integrals for sPPS,JH NMR IEC values, and IEC value determined by titration.

[0150] Peaks were integrated and normalized by setting the peak integration of peak B to a value of 4, which is the number of B site protons per repeat unit (Table 1). The identity of peak B is assigned based on the steric and electronic protection of the B sites from sulfonation by the presence of the sulfone linkage. The number of sulfonic acid moieties per repeat unit was calculated by the ratio of peak integrations with peak C. Further, IEC values were calculated based on the peak integration values as follows. The value of IEC is related to the weight of material per sulfonic acid moieties. This is known as the effective weight (EW). Since the prepared sPPS has a monopolymer backbone, a ratio of the C peak integral (which matched the number of the sulfonic acid groups in the structure) with any hydrogen peak was used to calculate sulfonic acids per repeat unit using the following equation:S()3H...............RU

[0151] The number of sulfonic acid moieties per repeat unit was converted to EW according following equation:where MWRUis the molecular weight of the repeat unit (400 g / mol for PPS) and MWSOaHis the molecular weight of a sulfonic acid moiety (82 g / mol). EW was then converted to IEC as follows:1000 EC =EW

[0152] The obtained numbers for IEC based on each of the integrated peaks in theJH NMR spectrum of sPPS, as well as the average number, are in excellent alignment with theexperimental IEC value obtained by titration (see Table 1). This alignment demonstrates that there are no other significant sulfonation locations on the repeat unit, and that the sPPS contains two sulfonic acid moieties per repeat unit, which are located on the biphenyl portion of the backbone as shown in Figure 16.Example 2. Casting freestanding sPPS membranes.

[0153] A suspension of 1-5 wt.% sPPS, 0.1-0.5 wt.% filler polymer, and 0.5-2.5 wt.% hydroquinone in water or dimethylacetamide were added to a Kapton trough. The suspension was allowed to dry overnight. The dried sPPS / polymer membranes were crosslinked by condensation reaction with the hydroquinone by heating the membranes to 210 °C for 2 hours under flowing nitrogen to achieve a freestanding crosslinked sPPS / polymer membranes.Example 3. Preparation of bilayer Nafion® / sPPS+PVDF polyelectrolyte membrane.

[0154] A Sono-tek ExactaCoat coating system was used to spray-coat a mixture of sPPS, PVDF, and hydroquinone on a Nafion® membrane. The spraying solution consisted of 0.75 wt.% sPPS, 0.075 wt.% PVDF, 0.008 wt.% PFSA (as a compatiblizing agent), and 0.19 wt.% hydroquinone (1.3 hydroquinone per sPPS repeat unit) in dimethylacetamide. The solution was stirred for 30-60 min prior to use. The Nafion® membrane substrate was held under vacuum during deposition. The following parameters were used for the spray-coating: power 0.8-1.3 W, nozzle height 40 mm, temperature 60 °C, flow rate 0.25-0.5 mL / min. The number of polymer layers was adjusted for the desired coating thickness. 75 layers were applied to achieve 1.5 pm thick coating. The following ranges can be used for the spraycoating parameters: sPPS solution concentration: 0.05-20 wt.%; PVDF solution concentration: 0.005-20 wt.%; substrate temperature: 5-200 °C; nozzle height: 10-70 mm; flow rate: 0.251-4 mL / min; power: 0.8-5W; crosslinker amount: 0-6 molecules of hydroquinone per repeat unit of sPPS.Example 4. Preparation of bilayer Nafion® / sPPS+ PS-co-PAN polyelectrolyte membrane.

[0155] The same procedure as described in Example 3 was used to spray-coat a mixture of sPPS, PS-co-PAN, and hydroquinone on a Nafion® membrane. The spraying solutionconsisted of 0.75 wt.% sPPS, 0.083 wt.% PS-co-PAN, and 0.19 wt.% hydroquinone (1.3 hydroquinone per sPPS repeat unit) in dimethylacetamide.Example 5. Preparation of bilayer Nafion® / sPPS+ PEI polyelectrolyte membrane.

[0156] Spray-coating, The same procedure as described in Example 3 was used to spraycoat a mixture of sPPS, PEI, and hydroquinone on a Nafion® membrane. The spraying solution consisted of 0.75 wt.% sPPS, 0.083 wt.% PEI, 0.1 vol.% H2SO4, and 0.19 wt.% hydroquinone in spray solution (1.3 hydroquinone per sPPS repeat unit) in H2O.

[0157] Blade-coating, A MSK-AFA-III-HB tape casting coater system was used to deposit a mixture of sPPS, PEI, and hydroquinone on a Nafion® membrane. The coating solution consisted of consisted of 6.3 wt.% sPPS, 0.7 wt.% PEI, 0.843 vol.% H2SO4, and 1.59 wt.% hydroquinone (1.3 hydroquinone per sPPS repeat unit) in H2O. The solution was stirred for 30-60 min prior to use. The Nafion® membrane substrate was held under vacuum during deposition. The blade-coating was performed at 20 cm / min at room temperature. The blade height was adjusted for the desired coating thickness. Blade height 75 pm was used to achieve 1.5 pm thick coating.Example 6. Preparation of bilayer Nafion® / sPPS+ PVC polyelectrolyte membrane.

[0158] The same procedure as described in Example 3 was used to spray-coat a mixture of sPPS, PVC, and hydroquinone on a Nafion® membrane. The spraying solution consisted of 0.75 wt.% sPPS, 0.075 wt.% PVC, and 0.19 wt.% hydroquinone in spray solution (1.3 hydroquinone per sPPS repeat unit) in dimethylacetamide.Example 7. Preparation of bilayer Nafion® / sPPS+ P4VP polyelectrolyte membrane.

[0159] Spray-coating, The same procedure as described in Example 3 was used to spraycoat a mixture of sPPS, PEI, and hydroquinone on a Nafion® membrane. The spraying solution consisted of 0.75 wt.% sPPS, 0.083 wt.% P4VP, 0.05 vol.% H2SO4, and 0.19 wt.% hydroquinone in spray solution (1.3 hydroquinone per sPPS repeat unit) in H2O.

[0160] Blade-coating, The same procedure as described in Example 5 was used to bladecoat a mixture of sPPS, PEI, and hydroquinone on a Nafion® membrane. The coating solution consisted of consisted of 6.3 wt.% sPPS, 0.7 wt.% P4VP, 0.42 vol.% H2SO4, and 1.59 wt.% hydroquinone (1.3 hydroquinone per sPPS repeat unit) in H2O.Example 8. Preparation of bilayer Nafion® / sPPS+ PAAm polyelectrolyte membrane.

[0161] The same procedure as described in Example 3 was used to spray-coat a mixture of sPPS, PAAm, and hydroquinone on a Nafion® membrane. The spraying solution consisted of 0.75 wt.% sPPS, 0.083 wt.% PAAm, and 0.19 wt.% hydroquinone in spray solution (1.3 hydroquinone per sPPS repeat unit) in H2O.Example 9. Preparation of bilayer Nafion® / sPPS+ PVA polyelectrolyte membrane.

[0162] The same procedure as described in Example 3 was used to spray-coat a mixture of sPPS, PVA, and hydroquinone on a Nafion® membrane. The spraying solution consisted of 0.75 wt.% sPPS, 0.083 wt.% PVA, and 0.19 wt.% hydroquinone in spray solution (1.3 hydroquinone per sPPS repeat unit) in H2O.Example 10. Crosslinking of sPPS in the coating on Nafion® membrane.

[0163] The sPPS+filler polymer coatings on a Nafion® membrane were crosslinked using hydroquinone deposited on the Nafion® membrane. To perform the crosslinking the coated Nafion® membrane was heated to 200 °C for 2 hours under flowing nitrogen while being held under tension with tape to an aluminum mask to achieve a crosslinked coating. The resulting coatings were 30-50% crosslinked.Example 11. Determination of ion exchange capacity (IEC) and degree of crosslinking.

[0164] The ion exchange capacity (IEC) of the sPPS polymer and crosslinked sPPS membranes is measured by titration. A piece of polymer or membrane is dried in an oven for 12 hours at 100 °C under flowing nitrogen before being weighed to determine the mass of material (Wary). The dried material is soaked in 20 mL of 2M NaCl for 30 minutes before 10 pL of phenolphthalein is added. A standardized solution of NaOH (C\aon, 0.01M) is added dropwise until the solution becaomes tinted pink. The volume of NaOH solution added (V\aon) is recorded. IEC is then calculated as follows:

[0165] The degree of crosslinking (%) is defined as the fraction of sulfonic acid moieties that are reacted with a crosslinker molecule. Degree of crosslinking is calculated as follows:. 100Example 12. Preparation of membrane electrode assembly.

[0166] The composite polyelectrolyte membrane was used in a membrane electrode assembly (MEA) and tested in a single fuel cell with 5 cm2active area. For MEA preparation, a 3 inch x 3 inch membrane was placed between two gas diffusion electrodes (GDEs) with 0.2 mg Pt / cm2(20% Pt on Vulcan carbon) on Sigracet 22 BB, each with an area of 5 cm2. The GDEs had pre-deposited catalyst layer on the side of microporous layer and were implemented with the catalyst layer interfacing the membrane. 3 inch x 3 inch PTFE gaskets with 5 cm2windows were placed on each side of the membrane to encompass the gas diffusion electrodes to prevent the leak of reactant gases. The gasket thickness was adjusted to allow for 80% compression of the GDEs when the MEA is tightened between two fuel cell end plates.Example 13. Testing of bilayer polyelectrolyte membrane in a fuel cell.

[0167] The membrane performance was evaluated in a fuel cell via EE crossover measurement, fuel cell polarization curve, and accelerated stress test.

[0168] H2 crossover measurements H2 crossover was measured by performing cyclic voltammetry where cathode side electrode was scanned between 0.1 V and 0.8 V with a voltage scan rate of 2 mV / s at 80 °C and 100% RH with 0.4 1pm H2 flow on the anode side and 0.4 1pm Ar flow on the cathode side with no backpressure. Fuel cell polarization curve was measured by conducting constant voltage measurements from open circuit potential to 0.3 V back to open circuit potential at a 0.5 V increment between open circuit potential to 0.7 V and a 1 V increment between 0.7 V to 0.3 V at 80 °C at various RH values with 0.2 1pm H2 flow on the anode side and 0.2 1pm air or O2 flow on the cathode side with a backpressure of 50 kPag.

[0169] The results are shown in Figures 1, 3, 5, 7, 9, 11, and 13. The data show that a bilayer membrane comprising 1.5 pm thick crosslinked sPPS+filler polymer coating (crosslinked with hydroquinone; degree of crosslinking 30-50%) on a 25 pm Nafion® 211 layer functions as an effective PEM fuel cell membranes as noted by the generation of a polarization curve under H2 and air conditions.

[0170] Further, the bilayer membrane hydrogen crossover is suppressed by up to 75% with in a Nafion® 211 membrane coated with a 1.5 pm layer comprising hydroquinone crosslinked sPPS and a filler polymer (Figures 2, 4, 6, 8, 10, 12, and 14), which confirms that These results shows that low gas permeability coatings comprising a filler polymer distributed in a matrix of a crosslinked sulfonated polymer decrease hydrogen crossover through PFSA-based membranes.

[0171] Electrochemical impedance spectroscopy

[0172] Electrochemical impedance spectroscopy was performed at 150 mA / cm2with 75 mA / cm2excitation amplitude under EE pump mode. Measurements were performed at 80 °C and 100% RH with 0.05 1pm EE flow on the anode side and 0.05 1pm Ar flow on the cathode side with no backpressure.The data in Figure 15 unexpectedly demonstrate that in a bilayer membrane comprising a Nafion® 211 membrane coated with a 1.5 pm layer comprising crosslinked sPPS and a filler polymer, the sPPS-comprising layer and the Nafion® layer show no contact resistance between each other, which means that a proton experiences no extra resistance by moving between the layers. Contact resistance between hetero-materials is frequently observed in conductive systems and presents a significant barrier to layered geometries. Thus, a bilayer system comprising two materials layered on top of each other is expected to show a drop in ion conductivity due to interfacial / contact resistance. To evaluate contact resistance in the bilayer membrane, the area specific resistances (ASR) of a 25 pm Nafion® 211 membrane, a 1.5 pm thick freestanding membrane comprising crosslinked sPPS and a filler polymer, and a bilayer membrane comprising a 25 pm Nafion® 211 layer coated with a 1.5 pm thick coating comprising crosslinked sPPS and a filler polymer were measured in a single cell fuel cell. The results are shown in Figure 15. Unexpectedly, the ASR of the bilayer system was nearly equal to that of Nafion® 211 than the sum of the ASR values of the individual layers, demonstrating lack of contact resistance between the two polyelectrolyte layers.

[0173] Accelerated stress tests (ASTs)

[0174] Accelerated stress test includes an aggressive strenuous phase and a periodic hydration phase, with the duration of each phase amounting to 4.5 h and 0.5 h, respectively. During the aggressive strenuous phase the cell is set to 110 °C with 0.1 1pm EE flow on the anode and 0.1 1pm O2 flow on the cathode with no backpressure, and both gases at 30% RH.During the hydration phase the cell is set to 80 °C with 0.1 1pm H2 flow on the anode and 0.1 1pm O2 flow on the cathode with no backpressure, and both gases at 100% RH. H2 crossover is measured and exhaust water is collected periodically during the accelerated stress test.Example 14. Conductivity measurements of freestanding membranes.

[0175] Membrane conductivity was measured in 4-point probe geometry in a Scribner Bekktech BT-112 HT conductivity cell with an Admiral Squidstat potentiostat. Conductivity was assessed by current measurements during linear sweep voltammetry from -0.5 V to 0.5 V. Conductivity was then calculated from the current-voltage slope with sample thickness. Ionic conductivities of a 1.5 pm thick freestanding membrane comprising crosslinked sPPS and a filler polymer and a bilayer membrane comprising a 25 pm Nafion® 211 layer coated with a 1.5 pm thick coating comprising crosslinked sPPS and a filler polymer were measured in a single cell fuel cell, are shown in Table 2. Ionic conductivity of a 25 pm Nafion® 211 membrane is 0.206 S / cm.Table 2. Ionic conductivity of freestanding membranes.

[0176] The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.

[0177] While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A bilayer poly electrolyte membrane, comprising a first layer and a second layer, wherein: the first layer comprises a perfluorosulfonic acid (PFSA) polymer, and the second layer comprises an admixture of a crosslinked sulfonated polymer and a filler polymer, and wherein the first layer is disposed on the second layer.

2. The bilayer poly electrolyte membrane of Claim 1, wherein the admixture is a homogeneous admixture.

3. The bilayer poly electrolyte membrane of Claim 1 or 2, wherein the crosslinked sulfonated polymer comprises polysulfonated polyphenyl sulfone (sPPS), sulfonated polyether ether ketone (sPEEK), sulfonated polyphosphazene (sPOP), sulfonated polybenzimidazole (sPBI), sulfonated polyether sulfone (sPES), sulfonated polyphenylene oxide (sPPO), sulfonated polyarylene ether ketone (sPAEK), sulfonated poly(sulfone), sulfonated poly(sulfide sulfone), sulfonated polyimide (sPI), sulfonated poly(etherimide) (sPEI), sulfonated poly(amine), poly (4-phenoxybenzoyl-l,4-phenylene) (PPBP), or a combination thereof.

4. The bilayer polyelectrolyte membrane of Claim 3, wherein the crosslinked sulfonated polymer comprises sPPS, sPEEK, sPOP, sPBI, sPES, sPAEK, sulfonated poly(sulfone), sulfonated poly(sulfide sulfone), sPI, sPEI, sulfonated poly(amine), sPPBP, or a combination thereof.

5. The bilayer poly electrolyte membrane of Claim 4, wherein the crosslinked sulfonated polymer comprises sPPS, sPEEK, sPOP, or sPBI.

6. The bilayer polyelectrolyte membrane of Claim 5, wherein the crosslinked sulfonated polymer comprises sPPS.

7. The bilayer poly electrolyte membrane of any one of Claims 1-6, wherein the filler polymer comprises a repeat unit comprising an aliphatic backbone.

8. The bilayer poly electrolyte membrane of Claim 7, wherein the filler polymer comprises PAAm, PVA, PVDF, PS-co-PAN, P4VP, PVC, or a combination thereof.

9. The bilayer polyelectrolyte membrane of Claim 8, wherein the filler polymer comprises PAAm, PVDF, PVC, PS-co-PAN, or a combination thereof.

10. The bilayer polyelectrolyte membrane of any one of Claims 1-6, wherein the filler polymer comprises polyacrylamide (PAAm), poly(N,N-dimethylacrylamide) (PDMA), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), poly(etherimide) (PEI), polyvinylidene fluoride (PVDF), poly(4-vinylpyridine) (P4VP), polystyrene-polyacrylonitrile co-polymer (PS-co-PAN), polyvinyl chloride (PVC), polyethylene, polypropylene, or a combination thereof.

11. The poly electrolyte composite membrane of Claim 10, wherein the second layer comprises from about 0.1 wt.% to about 50 wt.% of the filler polymer.

12. The polyelectrolyte composite membrane of Claim 10, wherein the second layer comprises from about 1 wt.% to about 15 wt.% of the filler polymer.

13. The bilayer poly electrolyte membrane of any one of Claims 1-10, wherein the crosslinked sulfonated polymer comprises a crosslinking moiety represented by one of the following structural formulas:k is 0, 1, or 2;R1is selected from H, C1-12 alkyl, Ci-n haloalkyl, Ce-i4 aryl, and Ce-i4 aryl(Ci-i2 alkylene);M2+is selected from Mg2+, Ca2+, Ba2+, and A1(X)2+, wherein X is halide, acetate, or nitrate; and the symbolrepresents a point of attachment of the crosslinking moiety to a repeat unit of the one or more first polymer.

14. The bilayer polyelectrolyte membrane of Claim 13, wherein the crosslinking moiety is represented by one of the following structural formulas:

15. The bilayer polyelectrolyte membrane of Claim 14, wherein the crosslinking moiety is represented by one of the following structural formulas:

16. The bilayer poly electrolyte membrane of Claim 15, wherein the crosslinking moiety is represented by the following structural formula:

17. The bilayer poly electrolyte membrane of Claim 16, wherein the crosslinking moiety is represented by one of the following structural formulas:

18. The bilayer polyelectrolyte membrane of Claim 16, wherein the crosslinking moiety is represented by the following structural formula:

19. The bilayer polyelectrolyte membrane of any one of Claims 1-18, wherein the crosslinked sulfonated polymer has degree of sulfonation from about 100% to about 300%.

20. The bilayer poly electrolyte membrane of Claim 19, wherein the crosslinked sulfonated polymer has degree of sulfonation about 200%.

21. The bilayer polyelectrolyte membrane of any one of Claims 1-20, wherein the crosslinked sulfonated polymer comprises on average from about 1 to about 3 sulfonic acid, sulfonate, and sulfonamide groups, combined, per repeat unit.

22. The bilayer polyelectrolyte membrane of any one of Claims 1-21, wherein the crosslinked sulfonated polymer has degree of crosslinking from about 20% to about 80%.

23. The bilayer poly electrolyte membrane of Claim 22, wherein the crosslinked sulfonated polymer has degree of crosslinking about 40%.

24. The polyelectrolyte composite membrane of any one of Claims 1-23, wherein the first layer further comprises a porous matrix comprising a matrix polymer, and wherein the PFSA polymer and the matrix polymer form an interpenetrating network.

25. The bilayer poly electrolyte membrane of Claim 24, wherein the first layer comprises from about 50 wt.% to about 95 wt.% PFSA polymer.

26. The bilayer polyelectrolyte membrane of Claim 24 or 25, wherein the matrix polymer is polytetrafluoroethylene.

27. The bilayer polyelectrolyte membrane of Claim 26, wherein the matrix polymer is expanded polytetrafluoroethylene.

28. The bilayer poly electrolyte membrane of any one of Claims 1-27, wherein the first layer is from about 5 pm to about 175 pm thick.

29. The bilayer polyelectrolyte membrane of Claim 28, wherein the first layer is about 25 pm thick.

30. The bilayer polyelectrolyte membrane of any one of Claims 1-29, wherein the the second layer is from about 0.2 pm to about 10 pm thick.

31. The bilayer polyelectrolyte membrane of Claim 30, wherein the second layer is from about 0.5 pm to about 2 pm thick.

32. The bilayer poly electrolyte membrane of any one of Claims 1-31, wherein the first layer is continuous.

33. The bilayer polyelectrolyte membrane of any one of Claims 1-32, wherein the membrane is unsupported.

34. The bilayer polyelectrolyte membrane of any one of Claims 1-33 wherein the PFSA polymer comprises a repeat unit represented by structural formula (I):wherein x is an integer from 1 to 15, m is an integer from 0 to 2, n is an integer from 1 to 5, anda point of attachment to a neighboring repeat unit.

35. The bilayer poly electrolyte membrane of Claim 34, wherein x is an integer from 5 to 14, m is 1 or 2, and n is 2 or 3.

36. The bilayer polyelectrolyte membrane of Claim 34 or 35, wherein the PFSA polymer comprises from about 900 to about 1100 repeat units represented by structural formula (I).

37. The bilayer polyelectrolyte membrane of Claim 1, wherein: the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC, the crosslinked sulfonated polymer is sPPS, and the sPPS comprises a crosslinking moiety represented by the following structural formula:

38. The bilayer polyelectrolyte membrane of Claim 1, wherein: the membrane is unsupported, the PFSA is a polymer comprising a repeat unit represented by structural formula (I):(I), wherein x is an integer between 5 and 14, m is 1 or 2, and n is 2 or 3; and further wherein the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC, the crosslinked sulfonated polymer is sPPS, the crosslinking moiety is represented by the following structural formula:sPPS has degree of sulfonation about 200%, sPPS has degree of crosslinking about 40%, and the second layer is from about 0.5 pm to about 2 pm thick.

39. The bilayer polyelectrolyte membrane of Claim 1, wherein: the first layer comprises a porous matrix comprising a matrix polymer, the PFSA polymer and the matrix polymer form an interpenetrating network,the crosslinked sulfonated polymer is sPPS, and the filler polymer is selected from PAAm, PVA, PEI, PVDF, P4VP, PS-co-PAN, and PVC.

40. The bilayer polyelectrolyte membrane of Claim 39, wherein sPPS comprises a crosslinking moiety represented by one of the following structural formulas:

41. The bilayer polyelectrolyte membrane of Claim 1, wherein: the PFSA polymer comprises a repeat unit represented by structural formula (I):wherein x is an integer between 5 and 14, m is 1 or 2, and n is 2 or 3; and the crosslinked sulfonated polymer comprises sPPS, and the crosslinking moiety is represented by one of the following structural formulas:

42. The bilayer polyelectrolyte membrane of any one of Claims 41, wherein the filler polymer is selected from PAAm, PVA, PVDF, PS-co-PAN, and PVC.

43. A method of making a bilayer poly electrolyte membrane of any one of Claims 1-42, comprising:a) providing a first layer having a first side, and a solution or suspension comprising a sulfonated polymer, a filler polymer, and a crosslinking reagent, b) coating the first side of the first layer with the solution or suspension, thereby producing a coated first layer; c) exposing the coated first layer to conditions sufficient for the sulfonated polymer and the crosslinking reagent to undergo a crosslinking reaction, thereby producing the bilayer polyelectrolyte membrane.

44. The method of Claim 43, wherein the crosslinking reagent is selected from a polyalcohol, an amine, an azide, an epoxide, a thiol, or a compound comprising a terminal alkene or alkyne.

45. The method of Claim 43, wherein the crosslinking reagent is selected from hydroquinone, 2,5-dihydroxybenzenesulfonic acid, 2,5-dihydroxybenzene-l,4-disulfonic acid, biphenyl, glycerol, ethylene glycol, tetraglycidyl bis(p-aminophenyl)methane, phenylene diamine, 4,4’-thiobisbenzenethiol, and tetrafluoro styrene.

46. The method of Claim 45, wherein the crosslinking reagent is selected from hydroquinone, 2,5-dihydroxybenzenesulfonic acid, 2,5-dihydroxybenzene-l,4-disulfonic acid, biphenyl, glycerol, and ethylene glycol.

47. The method of Claim 46, wherein the crosslinking reagent is hydroquinone or 2,5- dihydroxybenzenesulfonic acid.

48. The method of any one of Claims 43-47, wherein the solution or suspension comprises from about 0.005 wt.% to about 20 wt.% of the filler polymer.

49. The method of Claim 48, wherein the solution or suspension comprises from about 0.01 wt.% to about 0.5 wt.% of the filler polymer.

50. The method of any one of Claims 43-49, wherein the solution or suspension comprises from about 0.05 wt.% to about 20 wt.% of the sulfonated polymer.

51. The method of Claim 50, wherein the solution or suspension comprises from about 0.1 wt.% to about 5 wt.% of the sulfonated polymer.

52. The method of any one of Claims 43-51, wherein the solution or suspension comprises from about 0.01 wt.% to about 5 wt.% of the crosslinking reagent.

53. The method of Claim 52, wherein the solution or suspension comprises from about 0.05 wt.% to about 1 wt.% of the crosslinking reagent.

54. The method of any one of Claims 43-53, wherein the conditions sufficient for the sulfonated polymer and the crosslinking reagent to undergo a crosslinking reaction comprise heating the coated first layer to a crosslinking temperature from about 180 °C to about 220 °C for a crosslinking time from about 1 hour to about 10 hours.

55. The method of Claim 54, wherein the crosslinking temperature is about 200 °C.

56. The method of Claim 54 or 55, wherein the crosslinking time is about 2 hours.

57. The method of any one of Claims 43-56, wherein coating the first side of the first layer with the solution or suspension comprises spray-coating the first side of the first layer with the solution or suspension.

58. The method of any one of Claims 43-57, wherein the solution or suspension further comprises a solvent selected from water, alcohol, dimethylformamide, tetrahydrofuran, N- methylformamide, formamide, acetonitrile, dimethylacetamide, propylene carbonate, ethylene carbonate, N-methylpyrrolidone, dimethylsulfoxide, or a combination thereof.

59. The method of Claim 58, wherein the solvent comprises dimethylacetamide or water.

60. A membrane electrode assembly (MEA), comprising: the bilayer poly electrolyte membrane of any one of Claims 1-42;a cathode; and an anode, wherein the bilayer electrolyte membrane is disposed between the anode and the cathode.

61. The MEA of Claim 60, wherein the cathode is disposed on the first layer of the bilayer electrolyte membrane and the anode is disposed on the second layer of the bilayer electrolyte membrane.

62. The MEA of Claim 60, wherein the anode is disposed on the first layer of the bilayer electrolyte membrane and the cathode is disposed on the second layer of the bilayer electrolyte membrane.

63. A fuel cell, comprising one or more of the MEAs of any one of Claims 60-62 and one or more gas flow bipolar plates.

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