DURABLE, LOW-SWELLING REINFORCED ION EXCHANGE MEMBRANES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the priority benefit of US provisional patent application no. 63/417,173, filed on October 18, 2022, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] Composite ion exchange membranes composed of an extruded ion exchange material and woven reinforcement material have improved swelling in all three dimensions.

BACKGROUND

[0003] In a water electrolysis system, an ion exchange membrane is fixed between an oxygen electrode and hydrogen electrode, allowing the transport of protons through the pores in the membrane and allowing the hydrolysis of water. Because the ion exchange membrane is in constant contact with water, it must be capable of performing in a wet state.

[0004] Typical ion exchange membranes swell under conditions of contact with water or alcohol, which leads to decreased selectivity of the ion exchange membrane and, ultimately, decreased durability. Ionomer membranes using PTFE reinforcements are known for chloralkali applications but have swelling in the range of 7-8% in the machine and transverse directions of the films.

[0005] Additionally, low resistance is desired. For this reason, low Equivalent Weight (EW) polymers and membranes have been targeted. However, low EW polymers are consistent with low molecular weight polymers and thus are consistent with lower durability, especially when subjected to water or water/alcohol mixtures.

SUMMARY

[0006] The present invention describes composite membranes, catalyst coated membranes, and water electrolysis systems having improved swelling and durability when subjected to the conditions of a water electrolysis system. [0007] The present invention relates to a reinforced ion exchange membrane comprising a woven reinforcement and an ion exchange material, where the woven reinforcement is made from a material with a tensile modulus of at least 1 GPa, measured by ASTM D638; the ion exchange material is a fluorinated ionomer having sulfonate groups and having an ion exchange ratio less than about 13.2; the woven reinforcement has a first side and a second side opposite the first side, and the woven reinforcement has extruded ion exchange material layers on both the first side and second side. In one aspect, the reinforced ion exchange membrane expands less than about 60.0% in the Z direction after immersing in boiling water for 1 hour. In another aspect, the reinforced ion exchange membrane has an average thickness of about 30-150 pm. The present invention also relates to catalyst coated membranes made from the reinforced ion exchange membranes of the invention, having a cathode catalyst layer on one side of the reinforced ion exchange membrane and an anode catalyst layer on another side of the reinforced ion exchange membrane; and to water electrolysis systems using the catalyst coated membranes.

[0008] The present invention also relates to a process for forming a reinforced ion exchange membrane comprising a woven reinforcement and an ion exchange material, the process comprising extruding fluorinated ionomer precursor in at least one layer, contacting the fluorinated ionomer precursor layer in a flowable state with a woven reinforcement to form a composite membrane precursor, and treating the composite membrane precursor to form a reinforced ion exchange membrane, where the woven reinforcement is made from a material with a tensile modulus of at least 1 GPa, measured by ASTM D638; the ion exchange material is a fluorinated ionomer having sulfonate groups and having an ion exchange ratio less than about 13.2; the woven reinforcement has a first side and a second side opposite the first side, and the woven reinforcement has extruded ion exchange material layers on both the first side and second side. In one aspect, the reinforced ion exchange membrane expands less than about 60.0% in the Z direction after immersing in boiling water for 1 hour. In another aspect, the reinforced ion exchange membrane has an average thickness of about 30-150 pm. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 illustrates the three dimensions of a membrane, as they relate to a film or membrane role.

[0010] FIG. 2 illustrates a cross-section view of a catalyst coated membrane.

[0011] FIG. 3 illustrates the creep performance of Example 1 , Comparative Example A, and Comparative Example H.

[0012] FIG. 4 illustrates the conductivity and water electrolysis performance of Example 4 and Comparative Example K.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Features of the embodiments of the present invention described in the Detailed Description of the Invention can be combined in any manner. All tradenames are designated by capitalization of the brand name.

Definitions

[0014] As used herein, machine direction (MD) refers to the in-plane direction of a film parallel to a direction of travel or wind-up on a roll of the membrane during manufacture of the film, as depicted in FIG. 1.

[0015] As used herein, transverse direction (TD) refers to the in-plane direction of a film perpendicular to the machine direction, as depicted in FIG. 1.

[0016] As used herein, Z direction (ZD) refers to the direction through the thickness of the film, as depicted in FIG. 1.

[0017] The present invention relates to a reinforced ion exchange membrane comprising a woven reinforcement and an ion exchange material, where the woven reinforcement is made from a material with a tensile modulus of at least 1 GPa, measured by ASTM D638; the ion exchange material is a fluorinated ionomer having sulfonate groups and having an ion exchange ratio less than about 13.2; the woven reinforcement has a first side and a second side opposite the first side, and the woven reinforcement has extruded ion exchange material layers on both the first side and second side.

[0018] The woven reinforcement may be any woven material capable of providing the reinforced ion exchange membrane with a high modulus and low swelling in the machine and transverse directions. In one aspect, the woven reinforcement is made from a material with a tensile modulus of at least about 1 GPa, as measured by ASTM D638. If the tensile modulus is too high to be adequately measured by ASTM D638, such as above 20 GPa, an alternative method such as ASTM D3039/3039M. In another aspect, the woven reinforcement is made from a material with a tensile modulus of at least about 1 .5 GPa, as measured by ASTM D638; in another aspect, a tensile modulus of at least about 1 .8 GPa; in another aspect, a tensile modulus of at least about 2.0 GPa; in another aspect, a tensile modulus of at least about 2.5 GPa; in another aspect, a tensile modulus of at least about 3.0 GPa; in another aspect, a tensile modulus of at least about 3.5 GPa, and in another aspect, a tensile modulus of at least about 3.8 GPa; or any value, range, or sub-range therebetween. Examples of materials having a high enough tensile modulus to provide improvements in swelling in both machine and transverse directions are liquid crystal polymer, polyphenylene sulfide, glass, quartz, or polyaryl ether ketone (PAEK). Specific polyaryl ether ketones include, but are not limited to, polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), or polyether ketone ether ketone ketone (PEKEKK).

[0019] In one aspect, the woven reinforcement is in the form of a plain weave. As used herein, plain weave refers to a style of weave where the weft fiber alternates over and under the warp fiber, such that both sides of the woven material have the same fiber pattern. In one aspect, the woven reinforcement has a symmetrical weave pattern, such that the weave has the same fiber spacing in one position as when it is turned 180° in the same plane. In another aspect, the distance between fiber centers is about 150-240 pm; in another aspect, about 170-220 pm; in another aspect, about 180-210 pm; and in another aspect, about 190-200 pm; all defined as measuring the average distance from one fiber center to the distance of the next fiber center. In one aspect, the woven reinforcement has an open area of about 50- 80%; in another aspect, about 60-75%; and in another aspect, about 65-75%. Open area can be defined as:

L x w % Open Area = — - — — x 100%

(C _L x C _w ) where L is distance from one fiber center to the next fiber center in one direction, W is the distance from one fiber center to the next fiber center in a direction orthogonal to L, CL is the distance from one open area center to the next open area center in one direction, and Gw is the distance from one open area center to the next open area center in a direction orthogonal to CL.

[0020] To optimize resistance of the reinforced ion exchange membranes, it is preferred that the ion exchange material is a fluorinated ionomer having sulfonate groups. As used herein, sulfonate or sulfonic acid groups refers to either sulfonic acid groups or salts of sulfonic acid, preferably alkali metal or ammonium salts. Preferred functional groups are represented by the formula -SO3X wherein X is H, Li, Na, K or N(R ¹ )(R ² )(R ³ )(R ⁴ ), where R ¹ , R ² , R ³ , and R ⁴ are the same or different and are H, CH3, or C2H5. In exemplary embodiments, the fluorinated ionomer containing sulfonate or sulfonic acid groups is of the type available under the trade name of Nation™ (The Chemours Company FC, LLC, Wilmington, DE).

[0021] For example, the fluorinated ionomer may contain the repeat unit:

-[CF2-CF((CF2)b-(O-(CF2CFRf)c) _a -O-(CF ₂ CFR'f)dSO3X)]- where b is 0 or 1 ; c is an integer from 2 to 8; a is 0, 1 , or 2; d is an integer from 1 to 8; Rf and R' _f are independently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms; a = 0, 1 or 2; and X is H, Li, Na, K or N(R ¹ )(R ² )(R ³ )(R ⁴ ) where R ¹ , R ² , R ³ , and R ⁴ are the same or different and are H, CH3 or C2H5. For clarity, it is noted that the segment ((CF2)b-(O-(CF2CFRf) _c ) _a -O-(CF2CFR'f)dSO3X) in the structure above is the pendant chain from the perfluorinated polymer backbone. Branched pendant chains having multiple sulfonic acid groups are also emcompassed.

[0022] In one aspect, the fluorinated ionomer is a copolymer made from two or more monomers. For example, it is a copolymer of a sulfonic acid-containing monomer with tetrafluoroethylene (TFE), resulting in a repeat unit -[CF2-CF2]-, or with other comonomers. For example, monomers having pendant phosphonic acid groups may also be incorporated into the fluorinated ionomer to yield a fluorinated ionomer containing both sulfonic acid groups and phosphonic acid groups.

[0023] A class of preferred fluorinated ionomers containing sulfonate or sulfonic acid groups include a highly fluorinated, most preferably perfluorinated, carbon backbone with a side chain represented by the formula -(O-CF ₂ CFR ^f ) _a -O- CF2CFR ^,f SOsX, where R ^f and R ^,f are independently selected from F, Cl, or a perfluorinated alkyl group having 1 to 10 carbon atoms, a = 0, 1 or 2, and X is H, Li, Na, K or N(R ¹ )(R ² )(R ³ )(R ⁴ ), where R ¹ , R ² , R ³ , and R ⁴ are the same or different and are H, CH3, or C2Hs. Preferred fluorinated ionomers containing sulfonate or sulfonic acid groups may include, for example, polymers disclosed in U.S. Patent No. 3,282,875, in U.S. Patent No. 4,358,545, or in U.S. Patent No. 4,940,525.

[0024] One preferred fluorinated ionomer containing sulfonate or sulfonic acid groups includes a perfluorocarbon backbone and a side chain represented by the formula -O-CF ₂ CF(CP3)-O-CF2CF2SO3X, where X is as defined above. When X is H, the side chain is -O-CF2CF(CF3)-O-CF2CF2SO3H. Fluorinated ionomers containing sulfonate or sulfonic acid groups of this type are disclosed in U.S. Patent No. 3,282,875 and may be made by copolymerization of tetrafluoroethylene (TFE) and the perfluorinated vinyl ether CF2=CF-O-CF2CF(CF3)-O-CF2CF2SO2F, perfluoro(3,6 dioxa-4 methyl 7 octenesulfonyl fluoride) (PSEPVE, also called long side-chain or LSC), followed by conversion to sulfonate groups by hydrolysis of the sulfonyl fluoride groups and conversion to the proton form if desired for the particular application.

[0025] One preferred fluorinated ionomer containing sulfonate or sulfonic acid groups is of the type disclosed in U.S. Patent No. 4,358,545 and U.S. Patent No. 4,940,525, which has the side chain -O-CF2CF2SO3X, where X is as defined above. This fluorinated ionomer containing sulfonate or sulfonic acid groups may be made by copolymerization of TFE and the perfluorinated vinyl ether CF ₂ =CF-O- CF2CF2SO2F, perfluoro(3 oxa-4-pentenesulfonyl fluoride) (PFSVE, also called short side-chain or SSC), followed by hydrolysis and conversion to the proton form if desired for the particular application. When X is H, the side chain is -O- CF2CF2SO3H.

[0026] In some embodiments, the ion exchange material has an ion exchange ratio of less than about 13.2. As used herein, ion exchange ratio (IXR) refers to the number of carbon atoms in the ionomer backbone in relation to the number of cation exchange groups. In some embodiments, the IXR of an ionomer can be related to its equivalent weight (EW) by the equation EW = (50 x IXR) + MW _SC -19, where MW _SC is the molecular weight of the side chain of the ionomer. In one aspect, the ion exchange material has an IXR less than about 13.2; in another aspect, less than about 12.7; in another aspect, less than about 12.1 ; and in another aspect, less than about 11 .7; or any value, range, or sub-range therebetween. In one aspect, the ion exchange material has an IXR of at least 7.1 ; in another aspect, at least 8.1 ; in another aspect, at least 9.1 ; and in another aspect, at least 10.1 ; or any value, range, or sub-range therebetween.

[0027] In some embodiments, the ion exchange material has an equivalent weight (EW) less than about 1000; alternatively, less than about 980; alternatively, less than about 950; alternatively, less than about 930, or any value, range, or sub-range therebetween. In one aspect, the ion exchange material has an EW of at least about 530; alternatively, at least about 580; alternatively, at least about 630; alternatively, at least about 680, or any value, range, or sub-range therebetween. As used herein, (EW) refers to the weight of the ionomer in proton form required to neutralize one equivalent of NaOH.

[0028] In one aspect, the ion exchange material contains the long side chain and has an EW less than about 1000; alternatively, less than about 980; alternatively, less than about 950; alternatively, less than about 930, or any value, range, or subrange therebetween. In one aspect, the ion exchange material has an EW of at least about 700; alternatively, at least about 750; alternatively, at least about 800; alternatively, at least about 950, or any value, range, or sub-range therebetween. The IXR for a fluorinated ionomer with the side chain -O-CF2-CF(CF3)-O-CF2-CF2- SO3H, i.e. , produced from a copolymer of TFE and PSEPVE, can be related to EW using the following formula: 50 IXR + 344 = EW.

[0029] In another embodiment, the ion exchange material contains the short side chain and has an EW less than about 840; alternatively, less than about 810; alternatively, less than about 785; alternatively, less than about 765, or any value, range, or sub-range therebetween. In one aspect, the ion exchange material has an EW of at least about 530; alternatively, at least about 580; alternatively, at least about 630; alternatively, at least about 680, or any value, range, or sub-range therebetween. The IXR for a fluorinated ionomer with the side chain -O- CF2CF2SO3H, i.e., produced from a copolymer of TFE and PFSVE, can be related to equivalent weight using the following formula: 50 IXR + 178 = EW.

[0030] The woven reinforcement has a first side and a second side opposite the first side, where the woven reinforcement has extruded ion exchange material layers on both the first and second sides. As shown in FIG. 2, the woven reinforcement layer 3 has ion exchange material on either side to form the reinforced membrane 1 . In one aspect, the woven reinforcement is centered in the Z direction within the reinforced ion exchange membrane.

[0031] Ion exchange materials having lower IXR values are thought to have difficulty with polymer coalescence due to their low molecular weights, thus leading to decreased durability in alcohol, water, and water/alcohol mixtures, especially at elevated temperatures. However, the ion exchange material layers of the present invention have shown improved durability and swelling, partially due to the processing method. The present invention also relates to a process for forming a reinforced ion exchange membrane comprising a woven reinforcement and an ion exchange material, the process comprising extruding fluorinated ionomer precursor in at least one layer, contacting the fluorinated ionomer precursor layer in a flowable state with a woven reinforcement to form a composite membrane precursor, and treating the composite membrane precursor to form a reinforced ion exchange membrane, where the woven reinforcement is made from a material with a tensile modulus of at least 1 GPa, measured by ASTM D638; the ion exchange material is a fluorinated ionomer having sulfonate groups and having an ion exchange ratio less than about 13.2; the woven reinforcement has a first side and a second side opposite the first side, and the woven reinforcement has extruded ion exchange material layers on both the first side and second side. In one aspect, the reinforced ion exchange membrane expands less than about 60.0% in the Z direction after immersing in boiling water for 1 hour. In another aspect, the reinforced ion exchange membrane has an average thickness of about 30-150 pm.

[0032] The ion exchange materials are melt extruded and then laminated in a flowable state with the woven reinforcement, thus improving polymer coalescence and durability. In one aspect, the contacting or lamination step occurs above the T _g of the fluorinated ionomer precursor. In another aspect, the contacting or lamination step occurs above the T _g but below the T _m of the fluorinated ionomer precursor. T _g and T _m can be measured by rheological measurements, for example, using a parallel plate rheometer. The ion exchange materials are extruded in the melt processible form, usually an ion exchange polymer precursor. The term “fluorinated ionomer precursor” is used to define the melt-processible pre-hydrolyzed form of the fluorinated ionomer, such as the sulfonyl fluoride form. The extruded film can then be laminated at elevated temperature with the woven reinforcement to fuse the polymer and woven layer together into a composite film according to typical lamination methods, such as by using a lamination roll, belt laminator, or a vacuum lamination process. In one aspect, one layer of fluorinated ionomer precursor is extruded, and the woven reinforcement is laminated with the single layer of precursor such that the woven reinforcement migrates to the interior of the fluorinated ionomer precursor, forming a woven reinforcement with fluorinated ionomer precursor layers on both the first side and second side. In another aspect, two or more fluorinated ionomer precursor layers are extruded, and the woven reinforcement is laminated between two or more layers to form a woven reinforcement with fluorinated ionomer precursor layers on both the first side and second side. The term “extruded ion exchange material layers” is hereby intended to mean ion exchange material layers that have been formed by melt extrusion of the corresponding fluorinated ionomer precursor.

[0033] The composite film may then be treated by hydrolysis in an aqueous alkali metal hydroxide solution and, optionally, subsequently acidified to convert the sulfonyl fluoride groups to sulfonic acid or sulfonate groups. Alkali metal hydroxides include but are not limited to NaOH or KOH. During the hydrolysis step, a water- soluble organic solvent may be employed in the hydrolysis solution, such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2- pyrrolidinone, N-ethyl-2-pyrrolidone, methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butylcarbitol, hexyloxyethanol, octanol, propylene glycol methyl ether, ethylene glycol, ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2- aminoethoxyethanol, 2-aminoethoxyethanol, and 2-amino-2-methyl-1 -propanol.

[0034] In one aspect, the final reinforced ion exchange membranes may have an average thickness of about 30-150 pm; in another aspect, an average thickness of about 30-120 pm; in another aspect, an average thickness of about 30-100 pm; in another aspect, an average thickness of about 30-80 pm; and in another aspect, an average thickness of about 30-60 pm.

[0035] The reinforced ion exchange membranes resist expansion in all three dimensions after subjecting to conditions simulating an extreme water electrolysis system environment. In one aspect, the reinforced ion exchange membrane expands less than 2% in the machine direction and expands less than 2% in the transverse direction after immersing the reinforced ion exchange membrane in boiling water for 1 hour. The % expansion is calculated by comparing lengths of membrane before and after subjecting to boiling water, or in the case of measuring the Z direction, comparing thicknesses of membrane before and after subjecting to boiling water. In another aspect, the reinforced ion exchange membrane expands less than 1 .5% in the machine direction and expands less than 1 .5% in the transverse direction after immersing the reinforced ion exchange membrane in boiling water for 1 hour; in another aspect, the ion exchange membrane expands less than 1 .0% in the machine direction and expands less than 1 .0% in the transverse direction; and in yet another aspect, the ion exchange membrane expands less than 0.5% in the machine direction and expands less than 0.5% in the transverse direction. Comparing the % expansion in the Z direction is also an aspect of the invention. In one aspect, the reinforced ion exchange membrane expands less than about 60% in the Z direction after immersing in boiling water for 1 hour; in another aspect, the reinforced ion exchange membrane expands less than about 58% in the Z direction; in another aspect, the reinforced ion exchange membrane expands less than about 55% in the Z direction; in another aspect, the reinforced ion exchange membrane expands less than about 53% in the Z direction.

[0036] The reinforced ion exchange membranes are used in catalyst coated membranes, having multiple layers of functional materials. Such catalyst coated membranes may be used in electrolytical systems, for example, a water electrolysis system. In one aspect, the invention relates to a catalyst coated membrane comprising the reinforced ion exchange membrane, where the catalyst coated membrane comprises a cathode catalyst layer on one side of the reinforced ion exchange membrane and an anode catalyst layer on another side of the reinforced ion exchange membrane. A catalyst coated membrane may comprise a cathode catalyst layer (CCL) on one side of the ion exchange membrane and an anode catalyst layer (ACL) on another side of the ion exchange membrane. For example, in one embodiment shown in FIG. 2, a cathode catalyst layer 4 is in direct contact with an ion exchange membrane 1 , and the reinforced ion exchange membrane 1 is in further direct contact with anode catalyst layer 2 to make catalyst coated membrane 5. The ion exchange membrane 1 has a woven reinforcement layer 3 embedded within the ion exchange membrane. The catalyst coated membrane may contain multiple layers of the same material, and it may contain additional layers of functional materials, such as gas diffusion layers, porous transport layers, or bipolar plates.

[0037] The CCL and ACL may be applied to the ion exchange membrane in the form of a catalyst ink. Catalyst ink compositions often include a catalyst component and a polymer binder, where the polymer binder often includes fluorinated ionomers such as those described above. The polymer used in the CCL and ACL may be the same or different from the polymer used as the fluorinated ionomer of the ion exchange membrane. Catalyst components may include but are not limited to metal particles or carbon-supported metal particles. Specific metals may include but are not limited to platinum, ruthenium, gold, silver, palladium, iridium, rhodium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, and alloys thereof. Solvents, such as those mentioned for use in the ion exchange dispersion, may be used to aid in application of the catalyst ink to the ion exchange membrane. The CCL and ACL materials may be applied to the ion exchange membrane by any suitable means, including brushing, spraying, notch bar coating, fluid die coating, rod coating, slot-fed knife coating, three-roll coating, or decal transfer.

EXAMPLES

Test Methods

[0038] The following test methods and materials were used in the examples herein.

[0039] The invention is illustrated in the following examples which do not limit the scope of the invention as described in the claims. The following test methods and materials were used in the examples herein.

[0040] All solvents and reagents, unless otherwise indicated, are available from Sigma-Aldrich, St. Louis, MO.

[0041] NAFION D2021 and NAFION D2020 are dispersions made from chemically stabilized perfluorosulfonic acid I PTFE copolymers in the acid form having an EW of 1000 g/mol and 920 g/mol, respectively; NAFION N2050 is a PTFE-reinforced extruded membrane made from chemically stabilized perfluorosulfonic acid I PTFE copolymers in the acid form having an EW of 920 g/mol; NAFION N113 is an unreinforced extruded membrane made from chemically stabilized perfluorosulfonic acid / PTFE copolymers in the acid form having an EW of 1000 g/mol; NAFION N115 is an unreinforced extruded membrane made from chemically stabilized perfluorosulfonic acid I PTFE copolymers in the acid form having an EW of 1000 g/mol; NAFION N117 is an unreinforced extruded membrane made from chemically stabilized perfluorosulfonic acid I PTFE copolymers in the acid form having an EW of 1000 g/mol; and NAFION NR212 is an unreinforced dispersion cast membrane made from chemically stabilized perfluorosulfonic acid I PTFE copolymers in the acid form having an EW of 1000 g/mol; all available from The Chemours Company, Wilmington, DE. The sulfonate ionomer precursor (copolymer of CF2=CF2 and perfluorinated vinyl ether CF ₂ =CF-O-CF2CF(CF ₃ )-O-CF2CF ₂ SO2F, EW 920, IXR 11 .5) was also under the NAFION brand, available from The Chemours Company, Wilmington, DE.

[0042] FUMASEP FS-990-PK is a PEEK-reinforced short side-chain perfluorinated cation exchange membrane having an EW of 980 g/mol; FUMASEP F-10120-PK is a PEEK-reinforced long side-chain perfluorinated cation exchange membrane having an EW of 1000 g/mol; and AQUIVION E98-09S is a chemically stabilized unreinforced perfluorosulfonic acid ionomer membrane having an EW of 950 g/mol and made of the acid form of a copolymer of TFE/sulfonyl fluoride vinyl ether (CF2=CF-O-CF2CF2-SO2F); all available from The Fuel Cell Store, College Station, TX.

Expansion Testing

[0043] A 150 mm x 150 mm membrane sample was conditioned at 23 °C and 50% relative humidity for 24 hours. Black marks were then placed 100 mm apart from one another in both the machine and transverse direction of the membrane, and the thickness was recorded. The membrane was placed in boiling water for 1 hour and then removed. The distance between the marks in both the machine and transverse direction was recorded along with the new thickness after boiling. % Expansion was calculated as: where Lb = Length (or thickness) after boiling and L _a = Length (or thickness) before boiling. Expansion in the Z direction was calculated using the same equation, where the length used corresponds to the thickness before and after boiling. The lengths Lb and L _a were taken at 3 points and averaged. [0044] Volumetric expansion was calculated as: where Vb = volume after boiling and V _a = volume before boiling. For example, for a membrane having a starting volume of 1 .00 mm x 1 .00 mm x 1 .00 mm (1 .00 mm ³ ) and a post-boiling volume of 1.10 mm x 1.23 mm x 1.18 mm (1.60 mm ³ ), the volumetric expansion would be 60%.

Creep Performance (Blister Test)

[0045] In order to measure the long term, biaxial creep performance of these membranes in water, an instrument was built functionally equivalent to the one described from the paper of Yongqiang Li et al, “Fatigue and creep to leak tests of proton exchange membranes using pressure-loaded blisters” in the Journal of Power Sources, 194 (2009) 873-879. Of importance is the diameter of the blisters in this design being one inch.

[0046] Samples were pre-soaked in water such that any swelling that occurs in the machine or transverse dimensions was done before fixing in the device. A sample holder was used that allowed 8 samples to be measured simultaneously. Samples were loaded and maintained in a fully immersed state for the duration of the test. The samples were then pressurized to a setpoint and the time is recorded for each sample until rupture occurs.

Thickness

[0047] Three thickness measurements were taken with a ProGage thickness measurement gauge available from Thwing-Albert Instrument Company, West Berlin, NJ. The reported thickness represents an average of the three measurements.

Water Electrolysis Performance Testing

[0048] Catalyst coated membranes were made by decal transferring Greenerity E300 electrodes onto the membranes at 150 °C and 3000 pounds pressure on a 3” x 3” membrane. These catalyst-coated membranes were then run on a Scribner water electrolysis test station at 80 °C and ambient cathode and anode cell pressures.

After an industry-standard 4.5 hours break-in, polarization curves were measured from 0.01 A/cm ² up to 4 A/cm ² Examples 1-3

[0049] A 4 foot (1 .2 meter) wide sulfonate ionomer precursor (copolymer of CF ₂ =CF ₂ and perfluorinated vinyl ether CF ₂ =CF-O-CF ₂ CF(CF3)-O-CF ₂ CF ₂ SO ₂ F, EW 920, IXR 11 .5) was first extruded at 270 °C using a single-screw extruder, a die block, film die, chill roll, and take-up roll. The sulfonate ionomer precursor was melt laminated with a PEEK reinforcing fabric to form a composite film. The PEEK reinforcing fabric used was a plain weave fabric having fibers of approximately 38 pm in diameter, a center-to-center fiber spacing of about 195 pm, open area of about 70%.

[0050] The laminated films were hydrolyzed in a solution of DMSO I KOH / water as is taught in the art. The films were then acidified in a solution of 20% nitric acid in water before being dried to remove excess water. The final membranes were tested according to the Test Methods above to give the results of Tables 1 and 3.

Table 1. Creep Performance of Example 1

Comparative Example A

[0051] A base layer of Nation™ dispersion D2021 was cast with a doctor blade onto a PET substrate and allowed to dry to form a first layer. A PEEK reinforcing fabric was then placed on top of the base layer and two more layers of Nation™ D2021 were applied such that the final dry membrane thickness of the composite was 80.0 pm. The PEEK reinforcing fabric used was a plain weave fabric having fibers of approximately 38 pm in diameter, a center-to-center fiber spacing of about 195 pm, open area of about 70%. The final composite was then placed into a vacuum oven at 190 °C to coalesce the ionomer. The composite membranes were tested according to the Test Methods above to give the results in Tables 2 and 3.

Table 2. Creep Performance of Comparative Example A Comparative Example B

[0052] Comparative Example A was repeated, except Nation™ D2020 was used as the dispersion.

Comparative Examples C-J

[0053] Membranes FUMASEP FS-990-PK (Comparative Example C), FUMASEP F-10120-PK (Comparative Example D), AQUIVION E98-09S (Comparative Example E), NAFION N2050 (Comparative Example F), NAFION N113 (Comparative

Example G), NAFION N115 (Comparative Example H), NAFION N117 (Comparative Example I), and NAFION NR212 (Comparative Example J) were obtained and tested according to the Test Methods above to give the results of Tables 3 and 4.

Table 3. Characteristics and Expansion Performance of Examples

Table 4. Creep Performance of Comparative Example H

[0054] Comparative Examples A and B represent dispersion cast membranes using the same reinforcement as Examples 1-3. Comparative Examples C-D represent commercial composite membranes having similar reinforcement to Examples 1-3. Although each sample has low expansion in the machine and transverse directions, the composite membranes of Examples 1-3 show unexpectedly low expansion in the thickness direction of the membranes. This performance is visible in Comparative Examples A, C, and D, having a higher IXR, but it is especially visible in Comparative Example B, which has the same IXR as Examples 1-3. Here it is shown that the combination of low IXR and process allow for unexpectedly low expansion in all three dimensions of the membranes.

[0055] Comparative Examples E and G-l represent commercial unreinforced extruded membranes, Comparative Example J represents a commercial unreinforced dispersion cast membrane, and Comparative Example F represents a composite membrane of similar IXR and process having a different reinforcement material. Although the expansion is relatively low in the Z direction of the membranes of Comparative Examples E-J, the expansion in the machine and transverse directions are high. Here it is shown that the choice in reinforcement allows for unexpectedly low expansion in all three dimensions of the membranes.

[0056] The creep performance of the illustrative examples was shown using the blister test. Example 1 shows the significantly improved creep relative to an unreinforced extruded membrane. Where Example 1 can survive for 848 minutes at 42 psi of applied pressure, unreinforced Comparative example H only lasts 148 minutes at a much lower pressure of 32 psi. Comparative example A, containing a higher IXR polymer dispersion cast membrane, only lasts 329 minutes. This shows the performance benefit of the illustrative example, namely the improved creep performance over an unreinforced extruded film and over a dispersion cast reinforced film that both contain higher IXR polymers. The illustrative examples show improved durability and performance.

Example 4

[0057] Example 1 was repeated to form a construction where the PEEK cloth was between the 1 .6 mil film above the cloth and a 1 .6 mil film below the cloth. The PEEK reinforcing fabric used was a plain weave fabric having fibers of approximately 38 pm in diameter, a center-to-center fiber spacing of about 195 pm, open area of about 70%. This construction was placed into an isobaric vacuum press, Lauffer press UVL 50/1. A composite membrane was formed by heating the construction to 210 °C and applying 15 psi of pressure to laminate the extruded, sulfonyl fluoride films into the PEEK cloth. Afterwards, this material was hydrolyzed using DMSO, KOH, and water and then acid exchanged using 20% nitric acid in water. This produced an extruded, composite membrane consisting of 920 equivalent weight polymer (IXR 11 .5) and a thickness of 110 micron when measured at 50% RH.

[0058] A portion of the sample was measured in the expansion test and showed a swelling of 29.5% in the Z direction. This sample was run in a water electrolysis test station and the polarization curve was measured. The voltage at 2 A/cm ² was 1.754925 V.

Comparative Example K

[0059] Comparative Example K represents a direct comparison to Example 4, using a dispersion cast membrane rather than extruded membrane. A composite membrane was cast using a commercially available PFSA dispersion containing the same 920 EW ionomer as Example 4 in water and alcohol. A doctor blade applied a controlled level of dispersion to a polyethylene terephthalate (PET) backer, and the dispersion was dried in a 10% relative humidity chamber without heat. A second coating layer was applied, and the PEEK cloth was lain into the wet dispersion before placing the composite into a 10% relative humidity chamber. This final construction was then annealed at 175 °C for four minutes. This produced a composite membrane of an identical PEEK cloth fabric, 920 equivalent weight polymer, and 1 10 micron thickness as Example 4, but formed through a solution or dispersion casting process.

[0060] A portion of the sample was measured in the expansion test and showed a swelling of 58.0% in the Z direction. This sample was run in a water electrolysis test station and the polarization curve was measured. The voltage at 2 A/cm ² was 1.782388 V.

[0061] It can be seen that Comparative Example K had significantly more swelling in the Z direction than Example 4, indicating an unexpected difference in dispersion cast membranes versus extruded membranes. Additionally, polarization curves were measured from 0.01 A/cm ² to 4 A/cm ² on Example 4 and Comparative Example K. Highlighting the difference in resistance of the two membranes, Example 4 shows a voltage of 1 .63 V at 1 A/cm ² and a voltage of 1 .97 V at 4 A/cm ² , while Comparative Example K has a voltage of 1 .64 V at 1 A/cm ² and a voltage of 2.03 at 4 A/cm ² . The lower voltage at high current density and difference in slope of the polarization curves highlights the unexpectedly higher conductivity and improved performance for Example 4.