Selective membranes for water electrolysis applications and methods of making same

Abstract

A selective membrane is described that includes a porous polymer membrane and a selective material on at least one outer surface. A selective material comprising a composite material of an ion exchange polymer and zirconia particles (ZrO2) distributed throughout the ion exchange polymer may be applied as a liquid by a spray method. Selective membranes made by the methods described herein are suitable for alkaline water electrolysis applications.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 451,655, filed March 13, 2023, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Alkaline water electrolysis (AWE) plays a vital role in the hydrogen economy due to its well-known chemical properties. Improving the efficiency of alkaline water electrolyzers is crucial for meeting the low-cost goal of green hydrogen production. High current density operation is a major strategy for reducing operating costs. High current density is possible by reducing ohmic resistance, which is typically achieved through the use of thinner diaphragms, larger pore sizes, and / or shorter distances between the diaphragm and electrodes. However, these methods can have adverse consequences in terms of mechanical strength, gas cross-contamination, and gas blockage.

[0004] Besides the loss of mechanical strength, thinner membranes or those with larger pore sizes can lead to significant gas cross-linking, thus reducing coulombic efficiency and safety. It has been shown that reducing the gap between the electrode and the membrane to lower resistance results in significant voltage loss. Hydrogen and oxygen generated on the electrode are trapped between the electrode and membrane interface, reducing the active membrane area available for ion conduction. This reduced active area leads to an increase in ohmic resistance. Several methods have been developed to mitigate the gas blockage effect in electrolyzers. These methods include increasing flow rates through novel electrode architectures, materials, and hydrophobic diffusion layers. Additionally, various operating conditions, such as pressure oscillations, ultrasound, and magnetic fields, have been examined in laboratory experiments to reduce gas stagnation on the membrane surface.

[0005] The design of the electrodes, diaphragm, and electrolyzer determines the overall efficiency of the electrolyzer. High-pressure operation is required in water electrolyzers to improve efficiency. Porous diaphragms limit high-pressure operation.

[0006] In AWE applications, conventional non-porous ion exchange membranes with relatively small, narrow ion channels have proven inferior to porous membranes due to their high resistance. For example, Nafion membranes, with significantly smaller channel sizes than porous membranes... TM Membranes can lead to high ionic resistance. In addition, while porous membranes enable the transport of both cations and anions, cation exchange membranes that only allow the transport of cations limit the mobility of hydroxide ions (OH-). Summary of the Invention

[0007] A selective separator for alkaline water electrolysis (AWE) as described herein includes a porous separator layer or structure on which a selective material is applied as a coating to form the outermost surface of the selective separator. The selective material coating includes an ion exchange polymer and inorganic particles that provide good ion conductivity, low gas permeability, and improved gas release suitable for AWE processes.

[0008] An AWE porous selective separator can include a porous polyolefin separator layer and a selective material coating including an ion exchange polymer and inorganic particles, where the coating is on one or both opposing surfaces of the porous polyolefin separator. In one embodiment, a multi-layer selective separator includes a porous polyethylene (PE) layer and a selective material coating including a perfluorosulfonic acid ion exchange polymer and zirconium oxide particles forming the outermost layer of the multi-layer selective separator, where the particles are adhered to one or both opposing surfaces of the porous polyethylene. A method for manufacturing a selective separator includes spray coating a liquid blend of a selective material to form a thin selective layer on one or both surfaces of a porous PE support. The ratio of ion exchange polymer to inorganic particles in the selective material and the dry solids loading of the selective material on the porous polymeric separator are optimized for properties such as gas adhesion and / or gas permeability.

[0009] The novel AWE porous selective separators described herein have significantly reduced gas permeability and gas release properties without a significant increase in ionic resistance. A significant reduction in gas release angle is associated with enhanced gas release in use. Without wishing to be bound by theory, it is believed that the application of selective material to a porous separator advantageously provides for higher gas operating pressures, which can lead to, among other things, reduced operating costs in AWE applications. A challenge with AWE as compared to PEM water electrolyzers is a limited pressure range due to high gas crossover through the large pores of conventional separators. Thus, the pore size optimized by the application of novel selective materials and coating techniques advantageously results in reduced gas crossover through the separator. The novel porous selective separators described herein achieve minimal impact on the total ohmic resistance of the separator, where conventional approaches to reduce gas crossover result in increased ohmic resistance. Pore size can be selectively varied by varying particle size, ratio of ion exchange polymer to inorganic particles, and coating techniques. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a schematic of one embodiment of a high selective multi-layer separator.

[0011] Figure 2 is a top view of an image of one embodiment of a selective layer on a porous separator obtained by scanning electron microscopy (SEM).

[0012] Figure 3SEM image of a cross-sectional view of one embodiment of a porous selective membrane.

[0013] Figure 4 SEM image of a cross-sectional view of one embodiment of a porous selective membrane.

[0014] Figure 5 Schematic of one embodiment of an alkaline water electrolyzer. DETAILED DESCRIPTION

[0015] A novel porous selective membrane and its method of manufacture are described. The selective membrane is suitable for AWE applications, thereby providing improved gas release and gas permeation characteristics without significant changes in ionic resistance. As shown in Figure 1 The selective membrane (100) includes a porous polymeric membrane (101) having outer surfaces (105a and / or 105b) coated with a selective material (102a and / or 102b) that becomes the outermost layer (104a and 104b) of the selective membrane, which provides hydrophilicity, surface roughness, controlled pore size, pore diameter, and / or porosity percentage through the selective membrane to improve the efficiency of the porous membrane in the water electrolysis process.

[0016] In an embodiment, a selective membrane film is described that consists essentially of: 1) a porous polyolefin membrane as a free-standing membrane (101); and 2) a coating of a selective material (102a, 102b) comprising an ion exchange polymer (106) and inorganic particles (103) applied to at least one surface (105a, 105b) of the porous polyolefin membrane, wherein the selective material becomes the outermost layer of the selective membrane. The selective material can be applied to both the first and second opposing surfaces (105a, 105b) of the porous polymeric membrane. In one embodiment, the polyolefin is polyethylene (PE) and the selective material comprises an ion exchange polymer and zirconium oxide.

[0017] Porous polymeric separator

[0018] A porous separator suitable for use herein can comprise a polymer that does not have chemically reactive functional groups on the polymer structure. The porous polymeric separator can comprise a polyolefin, such as polyethylene (PE), including but not limited to ultra-high molecular weight polyethylene (UHMWPE), low density polyethylene (LDPE), and high density polyethylene (HDPE), or polypropylene (PP). In other embodiments, the porous polymeric separator can comprise a fluoropolymer suitable for water electrolysis applications, such as polytetrafluoroethylene (PTFE) or expanded polytetrafluoroethylene (ePTFE) or polyvinylidene fluoride (PVDF), polystyrene, polysulfone, polyether sulfone or polyarylether sulfone, polyphenylene sulfide (PPS), or combinations thereof, and can include materials under the trade name CELGARD® Celgard® (Agfa Gevaert N.V.) and under the trade name 5550, 3419S and 3420 (Celgard, LLC).

[0019] A porous separator can be hydrophobic or hydrophilic, as measured, for example, by the contact angle method described herein. The hydrophilicity of a porous separator polymer can be increased by adding an additive or inorganic material to the polymer, such as an ionic surfactant or metal oxide particulate, such as silica powder, forming a polymer composite. Metal oxides suitable for optimizing hydrophobicity or hydrophilicity include zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, and magnesium oxide, and combinations thereof. Other hydrophilic particulates that can be used include nitrides and carbides of Group IV elements of the periodic table. The inorganic particulate can have an average particle size in the range of about 0.5 pm to 5 pm, or 0.5 pm to 2 pm, or 0.15 pm to 1 pm, or in the range of 0.15 pm to 0.75 pm, as determined by laser diffraction particle size analysis. Composites of a hydrophobic polymer, such as polyethylene, and metal oxide particulate, such as titanium dioxide or zirconium oxide, integrated into and / or distributed throughout a polymer matrix can be used to form a hydrophilic porous polyethylene separator.

[0020] Prior to application of the selective material, the average pore size of the porous separator can be greater than about 0.1 pm, or less than about 4 pm, or from 0.1 pm to 4 pm, 0.1 pm to 2 pm, 0.1 pm to 1 pm, 0.5 pm to 4 pm, 0.5 pm to 3 pm, 0.5 pm to 2 pm, and 0.5 pm to 1 pm, as measured by a capillary flow porometer. In some embodiments, prior to application of the selective material coating, the porous separator comprises a microporous layer having an average pore size in the range of, for example, about 0.1 pm to 5 pm, or about 0.3 pm to 2 pm, such as about 0.1 pm, or about 0.5 pm, or about 1 pm. The microporous layer can comprise a microporous polymer, such as a fluoropolymer, such as microporous ePTFE.

[0021] Prior to coating with the selective material, the percent porosity of the porous polymeric separator material can be about 40% to 80%, or about 50% to 80%, or 60% to 80%, or 50% to 70% by volume. The pore size can be symmetrical or asymmetrical across the thickness of the porous polymeric separator of the selective separator construction. Further, the percent porosity can be uniform or non-uniform across the thickness of the porous polymeric separator. In some embodiments where the selective separator comprises a multi-layered porous polymeric separator, the pore size and percent porosity can independently be the same or can be different in each polymeric material layer. The pore size distribution of each layer of a multi-layered porous polymeric separator can independently be symmetrical or asymmetrical across the thickness of each layer, and the percent porosity of each layer is independently uniform or non-uniform across the layer.

[0022] By way of example and not limitation, the porous polymeric separator can be manufactured by casting, extrusion, or phase inversion, or can be woven or non-woven, including but not limited to woven or non-woven fabric, spunbond felt, mesh, web, or cast or extruded layer or film. The porous polymeric separator can comprise one or more than one layer, or other structure or form.

[0023] The porous separator can be reinforced or self-supporting. One or more reinforcing components can be integrated or embedded in the separator polymer, for example, to increase the mechanical strength, chemical durability, and / or dimensional stability of the final selective separator. Reinforcing components of a multi-layered porous selective separator can include a porous continuous reinforcing layer or discrete structures, optionally composed of a polymer such as PTFE, e.g., ePTFE, or PPS, polypropylene, polyphenylene sulfide, polyether ether ketone (PEEK), etc. Alternatively, the discontinuous reinforcing components can be in the form of reinforcing fibers or threads. Fabrics, including woven or non-woven carriers, can be embedded into the polymeric structure. The reinforcing components can comprise the same or different polymeric composition as the porous polymeric separator.

[0024] In some embodiments, the porous polymeric separator comprises a microporous ePTFE membrane bonded to a nonwoven fabric, wherein one or both opposing non-bonded surfaces of the ePTFE membrane and nonwoven fabric can be subjected to a surface hydrophilic treatment. The nonwoven fabric can include, but is not limited to, melt-spun PP or PE. In some embodiments, the ePTFE layer of the porous separator can have a thickness in the range of about 0.5 pm to about 2 pm, such as about 1 pm.

[0025] In embodiments, the porous polymeric separator is non-functionalized and does not comprise a functionalized polymer, such as an ion exchange polymer having sulfonic acid functionality or carboxylic acid functionality, or groups that can be converted to sulfonic acid functionality or carboxylic acid functionality, prior to application of the selective material. In one embodiment, wherein the porous separator comprises a reinforcing material, the reinforcing material does not comprise an ion exchange polymer having sulfonic acid functionality or carboxylic acid functionality. In further embodiments, neither the porous polymeric separator material nor the reinforcing material, if present, comprise an ion exchange polymer having sulfonic acid functionality or carboxylic acid functionality prior to coating with the selective material. In other embodiments, a surface treatment can be applied to impart surface functionality, such as hydrophilicity, to the underlying polymeric structure; in some embodiments, there is an ionic surface treatment, although neither the porous polymeric separator nor the reinforcing material, if present, comprise an ion exchange functionality. Surface hydrophilic treatments suitable for use herein include surface coating, plasma treatment, chemical grafting with sulfonate or phosphate functionality, UV irradiation, base treatment, and the like.

[0026] The porous polymeric separator can have a thickness of less than 300 pm, or less than 250 pm, or less than 200 pm, or less than 150 pm, or less than 100 pm, or the porous polymeric separator layer can have a thickness of 50 pm to 250 pm, or 50 pm to 225 pm, or 50 pm to 200 pm, or 75 pm to 225 pm, or 75 pm to 200 pm, or 75 pm to 150 pm. Thickness can be measured by SEM cross-section analysis by taking an average of at least 3 thickness measurements across the entire cross-section.

[0027] Selective material

[0028] A selective material mixture is applied to one or more outer surfaces (105a, 105b) of the porous polymeric separator. The selective material (102a, 102b) comprises an ion exchange polymer (106) and inorganic particles (103), such as inorganic particles that impart good ionic conductivity, low gas permeability, and improved gas release characteristics in the final selective separator compared to the same porous polymeric separator material without a selective material coating.

[0029] The ion exchange polymer can be a cation exchange polymer or an anion exchange polymer. Suitable cation exchange polymers for use herein can include one or more fluorinated polymers, such as perfluorinated or partially fluorinated alkyl compounds, including fluorinated hydrocarbon or aromatic polymers having ionic functional sites. The polymer composition can include perfluorosulfonic acid (PFSA), for example, sold under the trade name NAFION, including materials commonly known for use as solid polymer electrolyte membranes (PEM) in electrochemical devices. The selective polymer material can also include a multivalent PFSA composition. The selective polymer can be crosslinked, for example, by treatment or exposure to a physical or chemical crosslinking method, including but not limited to irradiation and / or free radicals. Alternatively, the selective polymer can be non-crosslinked, such that the non-crosslinked polymer is not exposed to a crosslinking method.

[0030] The ion exchange polymer backbone (the backbone of the polymer) can include units represented by the formula:

[0031]

[0032] where m is 1 to 6, and M is an alkali metal;

[0033]

[0034] where m is 1 to 6, and M is an alkali metal;

[0035]

[0036] where Q 1 is a perfluoroalkylene group optionally having ether oxygen atoms, Q 2 is a single bond or a perfluoroalkylene group optionally having ether oxygen atoms, R 1 is a perfluoroalkyl group optionally having ether oxygen atoms, X 1 is an oxygen atom, a nitrogen atom, or a carbon atom, a is 0 when X 1 is an oxygen atom, a is 1 when X 1 is a nitrogen atom, and a is 2 when X 1 is a carbon atom, Y is a fluorine atom or a monovalent perfluoroorganic group, r is 0 or 1, and M is an alkali metal; or

[0037]

[0038] where R 2 is a single bond or a C 1-6 straight-chain perfluoroalkylene group that can have ether oxygen atoms, and R 3 is a C 1-6a linear perfluoroalkylene group, m is 0 or 1, n is 1, and M is an alkali metal. In some embodiments, the ion exchange polymer backbone (backbone of the polymer) can include units represented by the formula:

[0039]

[0040] where m is 0, 1, or 2; n is 0, 1, or 2; R f1 is C 1-6 a linear perfluoroalkylene group; R f2 is C 1-6 a linear perfluoroalkylene group; and M is a cation, which can be a proton, an alkali metal, or a quaternary ammonium; or

[0041]

[0042] where m is 0, 1, or 2; n is 0, 1, or 2; R f1 is C 1-6 a linear perfluoroalkylene group; R f2 is R f1 is C 1-6 a linear perfluoroalkylene group; and M is a cation, which can be a proton, an alkali metal, or a quaternary ammonium. Suitable alkali metals and quaternary ammoniums for use herein include, but are not limited to, for example, K + , Na + , and Li + , and tetramethylammonium, respectively.

[0043] In other embodiments, the ion exchange polymer backbone comprises a polyphenylene ether, a polysulfone, a polyethylene, or a poly(aryl ether sulfone). The functional groups of the cation exchange polymer can include, but are not limited to, sulfonate functional groups, carboxylate functional groups, or phosphate functional groups. In embodiments, suitable ion exchange polymers for use herein include copolymers derived from the polymerization of tetrafluoroethylene (TFE) and perfluoro(alkyl vinyl ether) derivatives with sulfonyl fluoride, such as Nafion TM brand polymers.

[0044] Anion exchange polymers for use herein can have ion sites selected from the group consisting of ammonium, quaternary ammonium, piperidinium, imidazolium, guanidinium, benzimidazolium, pyrrolidinium, spirocyclic, or phosphonium functional groups, and derivatives thereof, to improve ion conductivity, chemical stability, and mechanical properties. In one embodiment, the AEM membrane comprises a selective material comprising a poly(aryl piperidinium) (Versogen, Inc., Newark, DE). In embodiments, suitable cation exchange polymers or anion exchange polymers or polyelectrolytes of which the selective material is composed have an anion exchange capacity of about 0.8 meq / g dry polymer to 2.5 meq / g dry polymer.

[0045] The selective material includes a liquid mixture of inorganic particles dispersed within a polymer and applied as a coating. Inorganic particles suitable for use in the selective material, such as metal oxides, include zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, and magnesium oxide, and combinations thereof. Other hydrophilic particles that can be used include nitrides and carbides of the Group IV elements of the periodic table. The inorganic particles can have an average particle size in the range of about 0.5 pm to 8 pm, 0.5 pm to 5 pm, or 0.5 pm to 2 pm, or 0.15 pm to 1 pm, or in the range of 0.15 pm to 0.75 pm, as determined by laser diffraction particle size analysis. In embodiments, the metal oxide particles can include a bimodal particle size distribution, such as 0.5 pm and 5 pm.

[0046] The liquid mixture including, for example, zirconium oxide particles and ion exchange polymer can be diluted to a viscosity optimized for the application technique selected. The diluent can include a volatile such as ethanol, n-propanol, or isopropanol. Methods of applying the selective material to the porous polymeric separator layer include, but are not limited to, spray coating techniques, application by doctor blade, Meyer bar, gravure coating, and the like. The coating coverage of the selective material on the outer surface of the porous polymeric separator provides a total combination of ionomer and inorganic solids of about 0.1 mg / cm 2 to 2 mg / cm 2 The dry solids loading of the porous polymeric separator, or loading, can be 0.5 mg / cm 2 to 1.5 mg / cm 2 and in one particular embodiment, the coverage is about 0.9 mg / cm 2 .

[0047] In some embodiments, the selective material coating can be applied to one or both opposing outer surfaces of the porous polymeric separator at a loading of about 0.9 mg / cm 2 of total dry solids weight of ionomer and inorganic particles per side of the porous polymeric support (i.e., ePTFE surface and nonwoven fabric surface). In one embodiment, the dry solids weight ratio of ionomer to inorganic particles can be in the range of 0.1 to 0.8, or 0.1 to 0.6, or 0.3 to 0.4. In other embodiments, the weight ratio of dry ion exchange polymer solids to Zr02 solids of the selective material is in the range of about 0.1 to 0.8, such as about 0.1 to 0.5.

[0048] In one embodiment, the selective material covers at most about 80%, or 90%, or 100% of the outer surface area of the porous separator, and the coated outer surface of the porous selective separator maintains sufficient porosity or permeability to achieve optimized ohmic resistance and gas crossover levels. While conventional liquid ion exchange polymers can form a continuous, non-porous coating that seals the pores of a porous polymer separator, in some embodiments disclosed herein, the addition of dispersed metal oxide particles, such as zirconium oxide, can prevent or disrupt the formation of a dense, continuous polymer matrix on the outer surface of the porous separator, such that the porous separator described herein retains at least some continuous open porosity that extends through and between the opposing outer surfaces of the selective separator. Thus, a selective material comprising an ion exchange polymer and inorganic particles can be applied to form a porous thin film on the surface of the porous polymer separator. In some embodiments, the porous polymer selective separator has a surface roughness in the range of about 0.1 pm to 4 pm when measured on the coated surface.

[0049] In some embodiments, the selective separators described herein have a gas permeability of less than 0.008 ft 3 / min*ft 2 when measured according to the methods provided herein. In other embodiments, the selective separators have a gas permeability of less than 0.007 ft 3 / min*ft 2 , or less than 0.005 ft 3 / min*ft 2 , or less than 0.004 ft 3 / min*ft 2 , or between 0.001 ft 3 / min*ft 2 and 0.008 ft 3 / min*ft 2 , or between 0.001 ft 3 / min*ft 2 and 0.007 ft 3 / min*ft 2 , or between 0.002 ft 3 / min*ft 2 and 0.004 ft 3 / min*ft 2 . In other embodiments, the gas permeability is less than 0.008 ft 3 / min*ft 2 , or between 0.001 ft 3 / min*ft 2 and 0.008 ft 3mOhm-cm 2 The selective separator between the anode and the cathode has an ionic resistance of less than 200 mOhm-cm, or less than 150 mOhm-cm 2 , or less than 100 mOhm-cm 2 .

[0050] A layer of porous selective material having a thickness of about 1 pm to 10 pm, or 4 pm to 10 pm, or less than 20 pm, can be formed on at least one outer surface of the porous polymeric separator, wherein the inorganic particles of the selective material are greater than or equal to 0.1 pm. The resulting selective separator has an acceptable ohmic resistance, for example, that is within 20% of the ohmic resistance of the porous polymeric separator material that makes up the selective separator, or + 10% of the ohmic resistance of the porous polymeric separator material that makes up the selective separator, when tested without the layer of selective material. In other embodiments, the selective separator is formed with an increase in ohmic resistance of no more than about 50% of the ohmic resistance of the porous polymeric separator material used to form the selective separator. +

[0051] In some embodiments, the application of selective material to the porous selective separator results in an increase in ohmic resistance of less than 200 mOhm-cm 2 , when tested by the test conditions described herein compared to a substantially identical porous separator material without the selective material coating. In some embodiments, the selective separator membrane with the selective material coating advantageously has an ionic resistance of less than 200 mOhm-cm 2 , or less than 180 mOhm-cm 2 , or less than 150 mOhm-cm 2 , while having a gas release angle of less than 20 degrees, or less than 10 degrees, when measured according to the methods described herein. In still further embodiments, the selective separator has a gas release angle of less than 20 degrees, a gas permeability of less than 0.008 ft 3 / min*ft 2 , and an ionic resistance of less than 200 mOhm-cm 2 , when tested according to the methods described herein.

[0052] ​In one embodiment, the selective separator membrane comprises a multi-layered porous polymeric separator having a uniform distribution of inorganic particles across the thickness of a layer of selective material applied to at least one surface of the porous polymeric separator. In further embodiments, the pores of a first layer of the multi-layered porous polymeric separator are substantially free of the selective material, e.g., where only an insignificant amount of inorganic particles penetrate the porous structure, e.g., as observed by SEM, and at least a second layer of the multi-layered porous polymeric separator is substantially penetrated by a selective material coating. In a particular embodiment comprising a multi-layered ePTFE microporous membrane / PP layer separator, the inorganic particles, such as zirconium oxide particles, form a uniform layer on the outer surface of the ePTFE membrane layer, while the zirconium oxide particles do not substantially penetrate into the ePTFE microstructure, and the selective coating mixture applied to the opposite surface substantially penetrates the pores of the nonwoven PP layer and coats the fibers of the nonwoven PP layer; and optionally, the zirconium oxide particles penetrate through the pores of the nonwoven PP layer to which they are applied, coating the portion of the ePTFE surface that is bonded to the PP layer, as opposed to the ePTFE outer surface.

[0053] With respect to the orientation of the porous selective separator within the electrolytic cell, the selective material can be applied to the outer surface of the porous polymeric separator facing the anode, the outer surface facing the cathode, or both the outer surface facing the anode and the outer surface facing the cathode. The interaction of the surfaces of the separator varies with the type of gas, and thus, the composition of the selective material applied to the surface facing the anode can differ from the composition of the selective material applied to the opposite surface of the porous polymeric separator facing the cathode. In embodiments, the selective material does not significantly affect the ionic resistance of the final porous separator.

[0054] An electrochemical cell for AWE applications is also provided, comprising an anode compartment, an anode located within the anode compartment, a cathode compartment, a cathode located within the cathode compartment, and a porous selective separator located between and separating the anode and the cathode, the electrochemical cell configured to hold a liquid electrolyte solution, and the porous selective separator providing ionic contact between the electrodes. In one embodiment, the porous selective separator is constructed from 1) a hydrophilic porous polymeric separator and 2) a selective material provided as a coating on at least one outer surface of the hydrophilic porous polymeric separator. In one embodiment, the polymeric material forming the porous polymeric separator structure consists essentially of a non-functional polymeric material; however, in some embodiments, a treatment material can be applied to the porous polymeric separator, and the treatment material can include a functional or non-functional composition that enhances or provides wettability to the porous polymeric structure made from the non-functional polymer. In some embodiments, the selective material layer forms the outermost surface of the selective separator surface, which includes a composite matrix of a discontinuous ion exchange polymer and inorganic particles (e.g., metal oxide particles) distributed throughout the ion exchange polymer. The average particle size of the inorganic particles of the selective material can range from about 0.1 pm to 4 pm, or 0.1 pm to 5 pm, or 0.1 pm to 6 pm, or 0.1 pm to 8 pm.

[0055] In Figure 5 In the schematic illustration of an embodiment of an alkaline water electrolyzer (500) for hydrogen production, the porous selective separator (501) separating the anode and cathode is operated in an alkaline electrolyte solution (502) such as a 25-40 wt% KOH aqueous solution. A first selective material coating (503) is provided on the outer surface (505) of the porous polymeric separator (504) adjacent to the anode, and a second selective material (503) coating is applied to the opposite outer surface of the porous polymeric separator adjacent to the cathode to form a porous selective separator that prevents gas stagnation on the surface and / or within the pores of the selective separator, which mitigates crossover of oxygen and hydrogen, and potassium and hydroxide ions are transported through the separator between the cathode and anode.

[0056] The selective material composition and solid loading of the selective material coating can be varied to adjust the surface energy and / or gas adhesion while maintaining low ionic resistance and low gas crossover. The selective material composition can be uniform or form a gradient of selectivity through the thickness of the selective layer.

[0057] A method of making a selective separator is provided, the method comprising the steps of: obtaining a porous polymeric separator; obtaining a selective material comprising an ion exchange polymer and a liquid composition of inorganic particles having an average particle size between 0.1 pm and 4 pm; and applying the liquid composition to one or both outer surfaces of the porous polymeric separator, thereby forming a selective layer, wherein the inorganic particles are uniformly distributed throughout the thickness of the selective layer without substantially permeating the thickness of the porous polymeric separator layer.

[0058] Test method

[0059] Ionic resistance in KOH: Ionic resistance was measured to determine the resistance of the sprayed AWE separator in a 30% KOH solution.

[0060] Sprayed separators were dried in an oven at about 90 °C. Measurements were made on conditioned separators. Conditioned separators were heated in 60 °C water for six hours. They were stored in 30% KOH overnight before testing.

[0061] Ionic resistance was characterized by four-probe impedance spectroscopy in a caustic electrolyte. Separator samples were placed between two chambers filled with 30% KOH. Impedance-resistance was measured at ambient conditions (about 22 °C) using an impedance analyzer on a BioLogic Potentiostat SP-240 (Lambda System). Impedance scans were frequency scans from 50 kHz to 1 MHz. Resistance values were determined manually from the impedance at the high frequency intercept in the Nyquist plot.

[0062] Maximum tilt angle of bubble release: The maximum tilt angle of bubble release was used to measure gas release on the surface of coated selective separators. The maximum angle at which a bubble will rest on the surface of an AWE separator through tilting was measured as follows.

[0063] Separators were heated in 60 °C water for six hours and stored in water after treatment. The separators were secured in a bubble capture pool and the pool was filled with water. A bubble was introduced at a tilt angle of 0 degrees (flat). The average bubble size was 2 mm diameter. The platform (pool holder) was tilted manually until the bubble moved from the separator surface. The maximum angle reached when the bubble moved was measured in triplicate and the average value was recorded.

[0064] Measurement of air permeability by Gurley Densometer

[0065] The porosity of the membrane was measured using a Gurley air permeability meter. Prior to testing, the membrane was dried in an oven at approximately 90°C for one hour, followed by immersion in water at 60°C for six hours. The membrane was then equilibrated overnight at 50% RH. The test was performed by measuring the time required for a given volume of air to pass through the sample. Triples of the membranes were tested, and the average value was expressed in feet. 3 / min*ft 2 Report. The standard deviation of all samples is... + 0.0002 or less.

[0066] Example

[0067] Coating preparation

[0068] A selective material mixture for coating porous polymers was prepared as follows. In preparing the selective material mixture, the components were added in the following order: zirconium oxide, ion-exchange polymer dispersion, and reagent-grade ethanol. The weight ratio of the ion-exchange polymer to solid ZrO2 was approximately 0.1 to 0.6 on a dry weight basis. (Nafion) TM The dispersion has approximately 10% by weight of perfluorosulfonic acid polymer (1000 EW) solids and approximately 90% by weight of water (dispersion Nafion). TM D1021, from The Chemours Company FC, LLC. A certain amount of ethanol is added to make the material suitable for the selected spray application.

[0069] Add the selective material mixture components to a 20 ml glass scintillation vial for mixing. Sonicate the vial (without shaking before sonication) for 5 minutes, then shake vigorously and sonicate again for another 5 minutes. Briefly shake the vial containing the selective material mixture using a vortex mixer before loading it into the application device.

[0070] Spray application technique

[0071] Before spraying, the sample porous polymer membrane is placed in the frame template and fixed around the periphery of the porous substrate with clamps.

[0072] use The VL-type spray gun kit is used to apply the selective material mixture. The selective material mixture is gravity-fed into the spray brush using a cut-off syringe that holds and supplies the mixture within the spray gun. Maintain an air pressure of 15 psi during application. For each substrate sample, spray an area of ​​approximately 12 cm × 12 cm.

[0073] Through Kapton TMSprayed on the membrane, the transfer rate of the selective material mixture determined gravimetrically was about 30 to 50 wt% to provide a nominal loading of about 0.9 mg / cm 2 .

[0074] Example 1

[0075] The AWE selective membrane membrane (200) was prepared by spraying the selective material mixture on only one outer surface of the porous PE substrate.

[0076] The PE substrate was a composite structure of silica powder and polyethylene with an average thickness of about 160 microns (from Entek). The selective coating mixture was prepared as described above containing ethanol as the solvent and Zr02 at a ratio of about 0.1 (Zr02 / dry ionomer) and Nafion TM perfluorosulfonic acid polymer (1000 EW dispersion). The average particle size of the Zr02 was about 0.8 pm as determined by laser diffraction particle size analysis (MEL Chemical, MS2 grade). The coating mixture was applied by the spraying method described herein. The hydrophilic particles of the selective material adhered to the PE porous membrane by the ion exchange polymer. The average thickness of the final selective membrane was about 167 pm.

[0077] The loading of the selective coating solids on the PE substrate was about 0.9 mg / cm 2 as measured gravimetrically. The gas release angle, gas permeability, and ionic resistance of the porous selective membrane were tested by the methods provided herein and compared to conventional materials. The results are provided in Table 1. Figure 2 SEM images of the AWE selective membrane membrane (200) are shown in FIG. 2, depicting a top view of the selective membrane showing the uniform application of the selective coating mixture (202) with small and large zirconium oxide particles (201a, 201b).

[0078] Example 2

[0079] A selective membrane was prepared substantially similar to Example 1; however, the selective material mixture was applied to both the anode-facing outer surface and the cathode-facing outer surface of the porous PE by spraying. The nominal loading of coating solids on each surface was about 0.9 mg / cm 2 .

[0080] The gas release angle, gas permeability, and ionic resistance of the porous selective membrane were tested by the methods provided herein and compared to conventional materials. The results are provided in Table 1. SEM images of the AWE selective membrane membrane (300) are shown in FIG. 3, depicting a top view of the selective membrane showing the uniform application of the selective coating mixture (302) with small and large zirconium oxide particles (301a, 301b).Figure 3 The diagram shows a cross-sectional view of the selective diaphragm, illustrating a uniform distribution of zirconia particles (304), which are considered to be white particles uniformly distributed across the entire thickness of the selective coating mixture (303), forming the outermost surface (301a, 301b) of the selective diaphragm membrane. Minimal permeation of the selective coating mixture permeates into and through the porous PE diaphragm structure (302), which remains substantially free of zirconia particles throughout the porous PE structure (302).

[0081] Example 3

[0082] The selective membrane preparation was essentially similar to that in Example 2; however, the porous membrane was a multilayer of ePTFE membrane laminated to a nonwoven polypropylene membrane, wherein the ePTFE / polypropylene substrate was obtained from Membrane Solutions, LLC (FPL100A12 hydrophilic PTFE membrane with a 1.0 μm pore size, a bubble point of 0.12 to 0.15 MPa at 23°C, a PP support layer, and bubble point testing reported using purified water as the wetting fluid). The selective material layer was applied to the porous membrane substrate by spraying the anode-facing and cathode-facing outer surfaces of the ePTFE / polypropylene substrate to form the selective membrane. The nominal loading of coating solids on each surface was approximately 0.9 mg / cm³. 2 .

[0083] SEM images of selective diaphragm membrane (400) in Figure 4 The diagram depicts a cross-sectional view of a uniform coating of selective coating mixture (401), in which zirconia particles are seen on the outer surface of the ePTFE membrane (402a) of the porous membrane layer (403), wherein minimal zirconia permeates the ePTFE microstructure and the selective coating mixture (401) is applied to the opposite surface, substantially permeating the pores of the nonwoven PP layer (404) and coating the fibers (405) of the nonwoven PP layer, wherein the zirconia particles are shown to reach the ePTFE surface (402b) opposite to the outer ePTFE surface (402a).

[0084] The weight ratio of the ion-exchange polymer to ZrO2 solids was approximately 0.4 on a dry weight basis. The gas release angle, gas permeability, and ion resistance of the porous selective membrane were tested using the methods presented herein and compared with conventional materials. The results are presented in Table 1. The final thickness measurements of the porous selective membrane ranged from approximately 170 μm to 220 μm when measured at 10 points.

[0085] Comparative Example 4

[0086] The polyethylene porous substrate used in Examples 1 and 2 was tested without any surface modification and without the addition of a selective material. The gas release angle, gas permeability, and ionic resistance of the substrate were tested by the methods provided herein and compared to conventional materials. The results are provided in Table 1. As reported in Table 1, the coated separators of Examples 1 and 2 showed a significant improvement in gas release angle compared to the uncoated plain PE, without a significant effect on the ionic resistance values, which were 71 mQcm 2 and 78 mQcm 2 , respectively, similar to the plain PE separator of Comparative Example 4 (PE).

[0087] Comparative Example 5

[0088] A comparative selective separator was prepared substantially similar to Example 2, however, the inorganic particles in the selective material mixture were Zr02nanoparticles with an average particle size of 100 nm. The nominal loading of the coating solids on each surface of the porous PE substrate was approximately 0.9 mg / cm 2 and the weight ratio of ion-exchange polymer to Zr02solids on a dry weight basis was approximately 0.11, substantially similar to Example 2. The coated substrate of Comparative Example 5 was tested for gas release angle, gas permeability, and ionic resistance by the methods provided herein and compared to conventional materials. The results provided in Table 1 show a significantly higher gas release angle (>45 degrees) compared to Example 2 (<2 degrees), without a significant change in ionic resistance (approximately 81 mQcm 2 compared to Example 2 (78 mQcm 2 ).

[0089] Comparative Example 6 and Comparative Example 7

[0090] An ePTFE / PP porous separator substrate according to Example 3 was prepared without any surface modification or selective material (Comparative Example 6), and with an ionomer of the selective material (Nafion TM ionomer) applied to the ePTFE side of the porous separator, without inorganic particles. The material was tested for gas release angle, gas permeability, and ionic resistance by the methods provided herein and compared to conventional materials. The results are provided in Table 1, which show a significantly higher gas release angle compared to Example 3, thus lower gas release from the surface; and Comparative Example 7 also shows a higher ionic resistance (217 mQcm 2 ) compared to Example 3 (approximately 136 mQcm 2 ), while Comparative Example 6 shows a high gas permeability, equivalent to a higher gas crossover.

[0091] Comparative Example 8

[0092] Nafion, based on perfluorosulfonic acid, was also tested. TM The membrane was compared with those of Examples 1 and 2. A 10 μm thick Nafion membrane cast on a 160 μm thick PE separator was tested using the methods provided herein. TM Nafion dispersion TM The gas release angle, gas permeability, and ion resistance of the NR220 membrane were compared with those of conventional materials. The results are provided in Table 1 and show a significantly higher ion resistance than any of the selective membranes prepared according to Examples 1 through 3. Visual observation indicates that Nafion... TM The polymer surface was not fully wetted in 30% KOH. While not wishing to be bound by theory, the high resistivity can be attributed to the Nafion in 30% KOH. TM Low water content in the polymer layer.

[0093] Comparative Example 9

[0094] get The membrane bleu (UTP500; Agfa-Gevaert N.V. Belgium) is a porous membrane and reference membrane in AWE technology. The resistance values ​​reported in Table 1 are from the literature (AGFA Technical Data Sheet). Obtained in Perl UTP 500).

[0095] Comparative Example 10

[0096] Obtain Nafion TM A 25 μm thick membrane (The Chemours Company FC, LLC, Wilmington, DE) was cast from the dispersion and tested as reported in Table 1. The dispersion-cast membrane exhibited significantly higher ion resistance than any of the selective membranes prepared according to Examples 1 through 3.

[0097] Table 1. Gas release angle and ionic resistance of separators .

[0098]

[0099] *Based on literature values ​​(AGFA technical data sheet) Perl UTP 500)

[0100] The porous selective separator of Example 1, with the first outer surface coated with the selective material, and Example 2, with both outer surfaces coated with the selective material, produced significantly lower gas release angles of approximately 3.9 degrees and approximately 1.4 degrees, respectively, compared to the sample of Comparative Example 4, which had the same porous selective separator material with no selective material layer applied thereon and which had a gas release angle of approximately 33 degrees. The material of Comparative Example 7, which included a separator of ion exchange polymer with sulfonic acid functionality, had a gas release angle of greater than 40 degrees. The lower gas release angles of Examples 1-3 described herein are beneficial to mitigate gas blockage at the membrane / electrode interface.

[0101] When compared to both Example 1 and Example 2, which each had a selective material layer composed of Zr02particles with a larger particle size (approximately 106 pm), the porous sample of Comparative Example 5, which had both outer surfaces coated with zirconia nanoparticles (particle size < 100 nm), showed a higher gas release angle (equivalent to lower gas release) and higher gas permeability (equivalent to higher gas crossover), while Example 1 and Example 2 maintained similar ion resistance values. Bubbles still attached to the surface of the Comparative Example 5 sample material at the maximum angle on the test instrument.

[0102] The porous selective separator of Example 3, which had an ePTFE layer laminated to a nonwoven polypropylene with both outer surfaces coated with the selective material, produced a low gas release angle of approximately 8.1 degrees on its outermost ePTFE surface. The plain porous polymeric separator of Comparative Example 6, which did not contain a selective layer, did not release gas at the maximum angle limit on the instrument (45 degrees) during testing. The lack of selective material on the ePTFE / PP structure resulted in a significant drop in gas permeability from approximately 2.48 ft 3 / min*ft 2 for the plain ePTFE / PP structure (Comparative Example 6) to approximately 0.0029 ft 3 / min*ft 2 for the ePTFE / PP structure with the selective layer (Example 3).

Claims

1. A selective separator for water electrolysis applications, the selective separator comprising: a porous polymeric separator layer having opposing first and second outer surfaces, and a selective material layer on at least one of the porous polymeric separator layer surfaces, the selective material layer comprising a composite of an ion exchange polymer and inorganic particles distributed throughout the ion exchange polymer, the inorganic particles having an average particle size in the range of 0.1 pm to 8 pm, wherein the selective material layer forms an outermost surface of the selective separator and has a gas release angle of less than 20 degrees.

2. A selective separator for water electrolysis applications, the selective separator comprising: a porous polymeric separator layer comprising a polymeric microporous membrane laminated onto a nonwoven porous material, and a selective material layer on at least one surface of the porous polymeric separator layer, the selective material comprising a composite of an ion exchange polymer and Zr02 particles, the ion exchange polymer comprising a perfluorinated sulfonic acid polymer, the Zr02 particles being uniformly distributed throughout the selective material layer, wherein the average Zr02 particle size is in the range of 0.1 pm to 4 pm, and the selective material is an outermost surface of the selective separator surface provided with the selective material.

3. A selective separator for water electrolysis applications, the selective separator consisting essentially of: a porous polymeric separator layer having a composite comprising a polymer and inorganic particles, the inorganic particles being in an amount sufficient to increase the hydrophilicity of the porous polymeric separator polymer, a selective material layer on at least one outer surface of the porous polymeric separator layer, the selective material comprising a composite of an ion exchange polymer containing perfluorosulfonic acid functional groups and zirconium oxide particles having an average particle size in the range of 0.1 pm to 5 pm distributed within the selective material, wherein the selective material layer is an outermost surface of the selective separator surface to which the selective material layer is applied.

4. The selective separator of any one of claims 1 to 3, wherein the porous polymeric separator layer comprises polyethylene, polypropylene, a fluoropolymer, PTFE, expanded PTFE, PVDF, polysulfone, polyphenylene sulfide, or a combination thereof.

5. The selective separator of claim 1, wherein the porous polymeric separator layer comprises a polymer composite comprising metal oxide microparticles selected from zirconium oxide, titanium oxide, bismuth oxide, cerium oxide, magnesium oxide, and combinations thereof, the metal oxide microparticles increasing the hydrophilicity of the polymer.

6. The selective separator of any one of claims 1 to 3, wherein the porous polymeric separator layer has an average pore size in the range of 0.1 pm to 5 pm.

7. The selective separator of any one of claims 1 to 3, wherein the porous polymeric separator layer is self-supporting.

8. The selective separator of any one of claims 1 to 3, wherein the selective separator has a gas release angle of less than 20 degrees, an ionic resistance of less than 200 mΩ-cm 2 , and a gas permeability of less than 0.008 ft 3 / min*ft 2 .

9. The selective separator of any one of claims 1 to 3, wherein the selective material layer is applied to both outer surfaces of the porous polymeric separator.

10. The selective membrane of claim 1, wherein the layer of selective material has a dry solid loading of 0.1 mg / cm 2 to 2 mg / cm 2 comprising an ion exchange polymer and inorganic particles.

11. The selective membrane of claim 1 or 2, wherein the layer of selective material has a dry solid loading of 0.1 mg / cm 2 to 2 mg / cm 2 comprising ion exchange polymer and Zr02 particles.

12. The selective separator of claim 1, wherein the solid weight ratio of ion exchange polymer to inorganic particles of the selective material layer is in the range of 0.1 to 0.

6.

13. The selective separator of claim 2 or 3, wherein the solid weight ratio of ion exchange polymer to Zr02 solids is 0.1 to 0.

8.

14. The selective separator of claim 1, wherein the inorganic particles of the selective material layer comprise at least one material selected from the group consisting of oxides, nitrides, and carbides of Group 4 or Group 14 elements, or mixtures thereof.

15. The selective separator of claim 1, wherein less than 20 wt% of the inorganic particles penetrate the pores of the porous polymeric separator.

16. The selective separator of any one of claims 1 to 3, wherein the thickness of the selective material layer on one of the porous polymeric separator surfaces is less than 20 pm.

17. The selective separator of any one of claims 1 to 3, wherein the average thickness of the selective material layer is in the range of 1 pm to 10 pm.

18. The selective separator of claim 1, wherein the ion exchange polymer is a cation exchange polymer.

19. The selective separator of claim 1, wherein the ion exchange polymer is an anion exchange polymer.

20. The selective separator of claim 1, wherein ion exchange polymer functional groups include, but are not limited to, sulfonate functional groups, carboxylate functional groups, or phosphate functional groups.

21. The selective separator of claim 1, wherein the ion exchange polymer is a perfluorinated sulfonic acid polymer.

22. The selective separator of any one of claims 1 to 3, wherein the ion exchange capacity of the ion exchange polymer is 0.8 meq / g dry polymer to 2.5 meq / g dry polymer.

23. The selective separator of any one of claims 1 to 3, further comprising zirconium oxide particles adhered to the selective separator by ionomer exchange polymer.

24. The selective separator of any one of claims 1 to 3, wherein the selective separator surface roughness is 0.1 pm to 4 pm.

25. The selective separator of any one of claims 1 to 3, wherein the thickness of the selective material layer on one or both outermost surfaces is less than or equal to 300 pm.

26. The selective separator of any one of claims 1 to 3, wherein the thickness of the selective material layer is less than 250 pm.

27. The selective separator of claim 2 or 3, wherein the gas release angle is less than 20 degrees when measured on the outermost surface of the selective separator.

28. The selective separator of any one of claims 1 to 3, wherein the outermost surface of the selective separator has a gas release angle of less than 10 degrees.

29. The selective separator of claim 1 having a first selective material layer on a surface facing the anode and a second selective material layer on a surface facing the cathode, and an amount of inorganic particles infiltrating the first selective material layer is different than an amount of inorganic particles infiltrating the second selective material layer.

30. The selective separator of claim 1 or 3, wherein the porous polymeric separator comprises at least two layers.

31. The selective separator of claim 30, wherein an average pore size of a first porous polymeric separator layer is smaller than an average pore size of a second porous polymeric separator layer.

32. The selective separator of claim 31, wherein the porous polymeric separator layers comprise a microporous membrane and a nonwoven fabric.

33. The selective separator of any one of claims 30 to 32, wherein the porous polymeric separator layers comprise an ePTFE layer and a nonwoven fabric layer.

34. The selective separator of any one of claims 30 to 33, wherein the porous polymeric separator layers comprise a nonwoven fabric between two outer layers of ePTFE.

35. The selective separator of any one of claims 32 to 34, wherein the nonwoven fabric comprises polypropylene or polyethylene.

36. The selective separator of claim 1, wherein the ohmic resistance is less than 100 mW-cm2 when measured at ambient temperature.

37. Use of the selective separator of any one of claims 1 to 36 in a water electrolyzer.

38. An electrochemical cell for alkaline water electrolysis (AWE) applications, the electrochemical cell comprising an anode compartment, an anode positioned within the anode compartment, a cathode compartment, a cathode positioned within the cathode compartment, the electrochemical cell configured to hold a liquid electrolyte, and a selective separator between the anode and the cathode, the selective separator comprising: a hydrophilic porous polymeric separator, and a selective material layer on at least one outer surface of the porous polymeric separator, the selective material layer comprising a composite of an ion exchange polymer and inorganic particles distributed throughout the ion exchange polymer, wherein the average inorganic particle size is in the range of 0.1 pm to 4 pm, and wherein the selective material layer forms an outermost surface of the selective separator surface to which the selective material layer is applied.

39. The electrochemical cell of claim 38, wherein the selective separator is in contact with at least one of the anode and the cathode.

40. The electrochemical cell of claim 38, wherein the selective separator is configured to be free of contact with the anode or the cathode.

41. A method of manufacturing a selective separator, the method comprising the steps of: obtaining a porous polymeric separator, obtaining a selective material comprising a liquid composition of an ion exchange polymer and inorganic particles having an average particle size between 0.1 pm and 4 pm, and applying the selective material to at least one outer surface of the porous polymeric separator. applying the liquid composition to one or both outer surfaces of the porous polymeric separator to form a selective layer that does not substantially penetrate the thickness of at least a portion of the porous polymeric separator layer, wherein the inorganic particles are uniformly distributed throughout the thickness of the selective layer.

42. The method of manufacturing a selective separator of claim 41, wherein the selective separator has a gas release angle of less than 20 degrees.

43. The method of claim 41, wherein the porous polymeric separator comprises polyethylene and the selective material comprises an ion exchange polymer and zirconium oxide particles.

44. The method of claim 41, comprising the step of forming a layer of selective material on an outer surface of the porous polymeric separator having a thickness of less than 10 pm.

45. The method of claim 41, comprising the step of forming a layer of selective material on at least one outer surface of the porous polymeric separator having a thickness of between 4 pm or 10 pm.

46. The method of claim 41, wherein the porous polymeric separator is formed from a polymer mixture comprising polyethylene and silica, and wherein the ion exchange polymer comprises perfluorosulfonic acid.

47. The method of claim 41, wherein the porous polymeric separator is formed by applying the selective material comprising a perfluorosulfonic acid polymer to a multi-layered porous polymeric separator comprising a microporous ePTFE membrane laminated to a nonwoven polypropylene.

48. The method of claim 41, comprising applying the selective material on the outer surface of the porous polymeric separator forming a coating having a dry solid loading of about 0.1 mg / cm 2 to 2 mg / cm 2 such that an outermost layer of the selective separator is formed.

49. The method of claim 47, wherein the selective material comprising the inorganic particles forms a layer on the microporous ePTFE membrane without substantially penetrating the microporous ePTFE, and the selective material penetrates the thickness of the nonwoven layer, wherein the inorganic particles coat the fibers of the nonwoven layer.

50. The method of claim 47, wherein the selective material comprises a perfluorosulfonic acid polymer and zirconium oxide particles.

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