Fiber materials, methods of making and using the same

Abstract

A method for preparing a membrane, comprising: dispersing preformed polymer nanofibers in at least one first solvent to form a dispersion; spraying or coating the dispersion on a surface of a substrate to form a nanofiber-based structure on the surface of the substrate; and evaporating the at least one first solvent in the nanofiber-based structure to produce the membrane, wherein the membrane has pores.

Description

[0001] Declaration of Rights to Federally Funded Research This invention was made with government funding from the U.S. Department of Energy under contract numbers DE-EE0007215, DE-EE0008418, and DE-AR000103, to which the government holds certain rights. Cross-referencing of related patent applications

[0002] This application claims priority and benefit to U.S. Provisional Patent Application No. 63 / 528,092, filed July 21, 2023.

[0003] This application is also a continuation-in-part of U.S. Patent Application No. 17 / 341,487, filed June 8, 2021, which claims priority and benefit to U.S. Provisional Patent Application No. 63 / 035,918, filed June 8, 2020.

[0004] This application is also a continuation-in-part of U.S. Patent Application No. 18 / 567,888, filed December 7, 2023, which is the U.S. national phase application of PCT Patent Application No. PCT / US2021 / 061967, filed December 6, 2021; which in turn is a continuation-in-part of U.S. Patent Application Serial No. 17 / 341,487, filed June 8, 2021, and claims priority and benefit from that U.S. Patent Application Serial No. 17 / 341,487, which in turn claims priority and benefit from U.S. Provisional Patent Application Serial No. 63 / 035,918, filed June 8, 2020.

[0005] The full contents of all the aforementioned patent documents are incorporated herein by reference. Technical Field

[0006] This invention generally relates to the field of materials, and more specifically to the production and application of charged polymer fibers and particle-polymer fibers, which are produced by electrospinning or by specific methods that do not require the application of an electric field, such as centrifugal spinning or air jet spinning. The resulting fibers are dispersed in a solvent, polymer solution, or polymer melt, and then further formed into a film. Background Technology

[0007] Typically, polymers or polymer-particle nanofiber mats / bundles are used directly in devices. For example, porous nanofiber polymer mats can be used as microfiltration membranes and filters, while fiber mat bundles can serve as tissue engineering scaffolds. However, to date, there are no reports on techniques for redispersing one or more fiber mats or fiber bundles in a solvent, polymer solution, or polymer melt, followed by the preparation of thin films from this dispersion via spraying or coating processes. Summary of the Invention

[0008] The technical solution of this invention is particularly applicable to centrifugal spinning and air jet spinning, both of which generate nanofiber bundles during the spinning process. In traditional processes, relatively coarse fiber bundles cannot be directly used to prepare nanofiber thin layers (fiber mats) with a thickness on the order of 25–150 micrometers, while this invention at least overcomes this technical limitation.

[0009] In one aspect, the present invention relates to a method for preparing composite unipolar films or three-dimensional (3D) interfacial bipolar films containing one or more pre-fabricated nanofibers. The nanofibers are composed of one or more polymers, or are composed of one or more polymers combined with one or more particles. The nanofibers are spread into thin films by a spraying or coating process. The nanofibers are pre-prepared by an electrospinning process, or by a nanofiber spinning process without the application of an electric field (such as centrifugal spinning, air jet spinning [1-4]). Therefore, the subject matter of the invention includes polymer fibers and particle-polymer fibers, methods for preparing the fibers, processes for distributing the fibers to form thin mats / layers, the use of the fibers in the preparation of films, and the use of the films in devices or processes.

[0010] A porous film can be formed by spraying or coating a pre-fabricated nanofiber dispersion and allowing the solvent to evaporate. By applying compression pressure, heating, contacting with liquid or gaseous solvents, or a combination of these methods, the voids between the fibers can be eliminated or significantly reduced, thereby obtaining a dense film.

[0011] In one embodiment, the method for preparing the membrane includes: dispersing pre-made polymer nanofibers in at least one first solvent to form a dispersion; spraying or coating the dispersion onto the surface of a substrate to form a nanofiber-based structure on the substrate; and evaporating to remove at least one first solvent from the nanofiber-based structure to obtain the membrane; wherein the membrane has pores.

[0012] In one embodiment, prior to the spraying or coating step, the method further includes adding nanoparticles to the dispersion.

[0013] In one embodiment, the substrate on which the pre-formed nanofiber dispersion is sprayed or coated is a pre-formed polymer film.

[0014] In one embodiment, the membrane is a porous nanofiber felt.

[0015] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated charged anion exchange or cation exchange polymer nanofibers; the method further comprises: impregnating the porous nanofiber felt with a solution of a non-charged polymer containing one or more non-charged polymers, wherein the one or more non-charged polymers are dispersed in at least one second solvent; evaporating to remove the at least one second solvent from the impregnated porous nanofiber felt, thereby obtaining a nanofiber-based anion exchange membrane or cation exchange membrane.

[0016] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated non-charged polymer nanofibers; the method further comprises: spraying or coating the dispersion onto a surface to form a porous film; after evaporating and removing the solvent, impregnating the porous nanofiber felt with a solution of a cation exchange polymer or anion exchange polymer containing one or more cation exchange polymers or anion exchange polymers, wherein the one or more cation exchange polymers or anion exchange polymers are dispersed in at least one third solvent; and removing the at least one third solvent from the impregnated porous nanofiber felt to obtain a nanofiber-based anion exchange membrane or cation exchange membrane.

[0017] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced cation exchange membrane onto a nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0018] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated cation exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced anion exchange membrane onto a nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0019] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated anion-exchange polymer nanofibers and one or more prefabricated cation-exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion-exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced cation-exchange membrane onto a nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion-exchange polymer membrane and the cation-exchange membrane.

[0020] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated anion-exchange polymer nanofibers and one or more prefabricated cation-exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation-exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced anion-exchange membrane onto a nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion-exchange polymer membrane and the cation-exchange membrane.

[0021] In one embodiment, charged and / or uncharged polymer nanofibers comprise hydrocarbon polymers.

[0022] In one embodiment, the non-charged polymer nanofibers include polysulfone, polyethersulfone, polyamide-imide, polyvinylidene fluoride, and / or polyphenylene ether.

[0023] In one embodiment, the charged polymer nanofibers comprise cation exchange polymers and / or anion exchange polymers.

[0024] In one embodiment, the cation exchange polymer has sulfonate or carboxylate cation exchange groups.

[0025] In one embodiment, the charged polymer nanofibers comprise sulfonated polyether ether ketone, sulfonated polysulfone, sulfonated polyphenylene ether, sulfonated polyether sulfone, or sulfonated polyarylene ether sulfone cation exchange sites.

[0026] In one embodiment, the anion exchange polymer has a tetraalkylammonium, imidazolium, cycloammonium, benzimidazolium, phosphonium, or piperidinium anion exchange group.

[0027] In one embodiment, charged and / or uncharged polymer nanofibers comprise fluoropolymers.

[0028] In one embodiment, the cation exchange polymer nanofibers comprise a fluorinated polymer having sulfonic acid ion exchange sites.

[0029] In one embodiment, the one or more prefabricated charged and / or uncharged polymer nanofibers are cross-linked fibers.

[0030] In one embodiment, the one or more prefabricated charged and / or uncharged polymer nanofibers contain nanoparticles.

[0031] In one embodiment, the nanoparticles are one or more of titanium dioxide (TiO2), aluminum oxide (Al2O3), aluminum hydroxide (Al(OH)3), nanodiamond, nanographene oxide, and zirconium hydroxide (Zr(OH)4).

[0032] In one embodiment, the pre-fabricated polymer nanofibers are prepared in advance by a method that does not require the application of an electric field before being formed into a dispersion.

[0033] In one embodiment, the pre-fabricated polymer nanofibers are prepared by centrifugal spinning or air jet spinning.

[0034] In one embodiment, the pre-fabricated polymer nanofiber comprises two or more different types of polymer nanofibers, and these fibers are prepared simultaneously during the spinning process.

[0035] In one embodiment, the pre-fabricated polymer nanofibers are made from a spinning solution containing a charged or uncharged polymer and a carrier polymer.

[0036] In one embodiment, the carrier polymer includes polyethylene oxide, polyvinylpyrrolidone, or polyacrylic acid.

[0037] In one embodiment, a dispersion of one or more prefabricated nanofibers contains nanoparticles suspended in a dispersion solvent.

[0038] In one embodiment, the nanoparticles suspended in the dispersion solvent are one or more of titanium dioxide, aluminum oxide, aluminum hydroxide, nanodiamond, nanographene oxide, and zirconium hydroxide.

[0039] In some aspects, the present invention also relates to a cation exchange membrane, anion exchange membrane, and / or bipolar membrane prepared by the methods disclosed above.

[0040] In other respects, the present invention further relates to an electrochemical device and / or an electrodialysis cell comprising one or more unipolar cation and anion exchange membranes and / or bipolar membranes prepared by the methods disclosed above.

[0041] In another aspect of the invention, a membrane is provided comprising a pre-formed polymer nanofiber network; the pre-formed polymer nanofibers comprising one or more pre-formed non-charged polymer nanofibers, one or more pre-formed charged polymer nanofibers, or a combination thereof.

[0042] In one embodiment, the prefabricated polymer nanofibers comprise nanoparticles.

[0043] In one embodiment, the prefabricated polymer nanofiber network is formed by spraying or coating a dispersion containing the prefabricated polymer nanofibers onto a substrate surface, wherein the prefabricated polymer nanofibers are dispersed in at least one first solvent; and then evaporating to remove the solvent.

[0044] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated charged polymer nanofibers; the membrane further comprises a non-charged polymer impregnated in the prefabricated polymer nanofiber network, thereby producing a nanofiber-based anion exchange membrane or a cation exchange membrane.

[0045] In one embodiment, the prefabricated polymer nanofibers comprise one or more of the prefabricated non-charged polymer nanofibers; the membrane further comprises a cation exchange polymer or anion exchange polymer impregnated in the prefabricated polymer nanofiber network, thereby producing a nanofiber-based anion exchange membrane or cation exchange membrane.

[0046] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0047] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated cation exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0048] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers and one or more prefabricated cation exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0049] In one embodiment, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers and one or more prefabricated cation exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0050] In one embodiment, charged and / or uncharged polymer nanofibers comprise hydrocarbon polymers.

[0051] In one embodiment, the non-charged polymer nanofibers include polysulfone, polyethersulfone, polyamide-imide, polyvinylidene fluoride, and / or polyphenylene ether.

[0052] In one embodiment, the charged polymer nanofibers comprise cation exchange polymers and / or anion exchange polymers.

[0053] In one embodiment, the cation exchange polymer has sulfonate or carboxylate cation exchange groups.

[0054] In one embodiment, the charged polymer nanofibers have sulfonated polyether ether ketone, sulfonated polysulfone, sulfonated polyphenylene ether, sulfonated polyether sulfone, or sulfonated polyarylene ether sulfone cation exchange sites.

[0055] In one embodiment, the anion exchange polymer has benzyltrialkylammonium, imidazoline, cycloammonium, benzimidazolium, phosphonium, piperidinium, quaternary ammonium, or benzyldimethylhexylammonium anion exchange groups.

[0056] In one embodiment, charged and / or uncharged polymer nanofibers comprise fluoropolymers.

[0057] In one embodiment, the cation exchange polymer nanofibers comprise a fluorinated polymer having sulfonic acid ion exchange sites.

[0058] In one embodiment, the one or more prefabricated charged and / or uncharged polymer nanofibers are cross-linked fibers.

[0059] In one embodiment, the one or more prefabricated charged and / or uncharged polymer nanofibers contain nanoparticles.

[0060] In one embodiment, the nanoparticles are one or more of titanium dioxide, aluminum oxide, aluminum hydroxide, nanodiamond, nanographene oxide, and zirconium hydroxide.

[0061] In one embodiment, the pre-fabricated polymer nanofibers are prepared in advance by a method that does not require the application of an electric field before being formed into a dispersion.

[0062] In one embodiment, the pre-fabricated polymer nanofibers are prepared by centrifugal spinning or air jet spinning.

[0063] In one embodiment, the pre-fabricated polymer nanofiber comprises two or more different types of polymer nanofibers, and these fibers are prepared simultaneously during the spinning process.

[0064] In one embodiment, the pre-fabricated polymer nanofibers are made from a spinning solution containing a charged or uncharged polymer and a carrier polymer.

[0065] In one embodiment, the carrier polymer includes polyethylene oxide, polyvinylpyrrolidone, or polyacrylic acid.

[0066] In one embodiment, two or more dispersions composed of different pre-fabricated polymer nanofibers or polymer-particle nanofibers are used. These dispersions are deposited layer by layer and / or repeatedly using a spraying or coating process. Then, a suitable process is used to close some or all of the voids between the deposited fibers, thus fabricating a layered porous membrane, a layered semi-porous membrane, or a layered dense membrane. Dispersion A and dispersion B can be deposited multiple times to obtain a membrane with an ABABAB repeating layered structure; similarly, dispersions A, B, C, and D can be deposited to obtain a membrane with an ABCD, ABCABCD, or CDABABABDC type layered structure. This multilayer structure can be deposited on a pre-fabricated polymer anion exchange membrane, a pre-fabricated polymer cation exchange membrane, or an inert substrate that can be peeled off from the final membrane.

[0067] In some embodiments, the solvent comprises a single-component solvent or a mixture of two or more liquids.

[0068] Other aspects of the present invention will be illustrated by the following description of preferred embodiments in conjunction with the accompanying drawings. However, various modifications and variations may be made to the present invention without departing from the spirit and scope of the novel concept. Attached Figure Description

[0069] The accompanying drawings illustrate one or more embodiments of the invention and, together with the written description, serve to illustrate the principles of the invention. In each drawing, the same reference numerals may be used to refer to the same or similar elements in the embodiments.

[0070] Figure 1 Scanning electron microscope (SEM) images of electrospun polymer fibers and centrifugally spun fibers according to embodiments of the present invention are shown. The fibers are composed of a perfluorosulfonic acid cation exchange polymer and polyethylene oxide.

[0071] Figure 2 SEM images of polymer-particle fibers of embodiments of the present invention at different magnifications are shown. The fibers are prepared by centrifugal spinning and are composed of perfluorosulfonic acid cation exchange polymer, polyethylene oxide and iron-nitrogen-carbon (Fe-NC) catalyst particles. Detailed Implementation

[0072] The invention will now be described more fully below with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention more thorough and complete, and to fully convey the scope of the invention to those skilled in the art. The same reference numerals throughout refer to the same elements.

[0073] The terms used in this specification generally have their ordinary meanings in the art, in the context of this invention, and in the specific context in which each term is used. Certain terms used to describe the invention are discussed below or elsewhere in the specification, thereby providing additional guidance to those skilled in the art regarding the description of the invention. For convenience, certain terms may be highlighted, for example, using italics and / or quotation marks. The use of highlighting does not affect the scope and meaning of the terms. In the same context, the scope and meaning of a term are the same whether it is highlighted or not. It is understood that the same thing can be expressed in more than one way. Therefore, alternative language and synonyms may be used instead of any one or more terms discussed herein, and have no particular significance in whether the terms are elaborated or discussed herein. Synonyms for certain terms are provided. One or more synonyms do not preclude the use of other synonyms for description. The use of examples anywhere in this specification, including examples of any terms discussed herein, is merely illustrative and in no way limits the scope and meaning of the invention or any exemplary terminology. Similarly, the invention is not limited to the various embodiments given in this specification.

[0074] It will be understood that, as used in the description herein and throughout the claims, the terms “a,” “an,” and “the” include the plural form unless the context clearly specifies otherwise. Furthermore, it will be understood that when an element is referred to as “located on another element,” it may be located directly on the other element, or there may be intermediate elements present. Conversely, when an element is referred to as “located directly on another element,” there are no intermediate elements present. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0075] It will be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, without departing from the teachings of the invention, the first element, component, region, layer, or portion discussed below may be referred to as the second element, component, region, layer, or portion.

[0076] Furthermore, relative terms such as “lower” or “bottom” and “upper” or “top” may be used herein to describe the relationship between one element and another shown in the accompanying drawings. It should be understood that relative terms are intended to include different orientations in the device other than those shown in the accompanying drawings. For example, if the device in one of the drawings is flipped, an element described as being “lower” than the other element will be oriented “upper” than the other element. Thus, the exemplary term “lower” can encompass both “lower” and “upper” orientations, depending on the specific orientation in the drawing. Similarly, if the device in one of the drawings is flipped, an element described as being “below” or “under” the other element will be oriented “above” the other element. Thus, the exemplary terms “below” or “under” can encompass both “upper” and “lower” orientations.

[0077] It should also be understood that the terms “comprises and / or comprising,” “includes and / or including,” “has and / or having,” “carry and / or carrying,” “contains and / or containing,” or “involve and / or involving,” etc., are open-ended, meaning they include, but are not limited to, those mentioned above. When used in this invention, they specify the presence of the stated features, regions, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof.

[0078] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will be further understood that terms (such as those defined in common dictionaries) should be interpreted as having the same meaning as they have in the context of the relevant technology and this invention, and should not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0079] As used herein, “about,” “approximately,” or “roughly” generally means within 20%, preferably within 10%, and more preferably within 5%, of a given value or range. The values ​​given herein are approximate and are meant to be inferred unless explicitly stated otherwise.

[0080] As used in this disclosure, the phrase "at least one of A, B, and C" should be interpreted as representing the logic (A or B or C) using non-exclusive logic OR. It should be understood that one or more steps within the method may be performed in different orders (or simultaneously) without altering the principles of the invention.

[0081] The following description is merely exemplary in nature and is not intended to limit the invention, its application, or its uses. The broad teachings of the invention can be implemented in many forms. Therefore, while the invention includes specific examples, its true scope should not be so limited, as other modifications will become apparent upon study of the drawings, specification, and the following claims. For clarity, the same reference numerals will be used in the drawings to identify similar elements. It should be understood that one or more steps within the method may be performed in a different order (or simultaneously) without altering the principles of the invention.

[0082] In one aspect, the present invention relates to the preparation of porous nanofiber mats using pre-formed fibers, which are obtained by electrospinning, centrifugal spinning, air jet spinning, or other nanofiber preparation methods not involving an electric field. The nanofibers may be composed of non-charged polymers or ion-exchange polymers (cation-exchange polymers or anion-exchange polymers). One or more pre-formed fibers are dispersed in a suitable solvent (such as a water-alcohol mixture), with surfactants selectively added to assist in the formation of the dispersion or improve its stability. Subsequently, the fiber-containing dispersion is coated onto a surface using a spraying or liquid coating process (such as slot die coating, bar coating, gravure coating, spin coating, or blade coating). This surface may be an inert polymer film, an inert nonwoven fabric, or a polymer material (such as a cation-exchange polymer film or anion-exchange polymer film) that can form part of the final membrane. A sufficient amount of the dispersion solution is deposited, and after the solvent evaporates, a porous nanofiber mat of a certain thickness is formed. Subsequently, a polymer solution can be impregnated into the voids between the fibers. For example, for non-charged polymer nanofibers, anion-exchange polymer solutions or cation-exchange polymer solutions can be impregnated between the non-charged fibers.

[0083] After one or more impregnation and solvent evaporation steps, a dense composite membrane is obtained, wherein the pre-made nanofibers are dispersed in a cation exchange polymer matrix or anion exchange polymer matrix.

[0084] In another aspect of the invention, pre-fabricated anion-exchange fibers and / or cation-exchange fibers are dispersed in a suitable solvent, and the solution is subsequently deposited onto a surface by a spraying or coating process. After the solvent evaporates, a non-charged polymer solution is impregnated between the fibers. After one or more impregnation and solvent evaporation steps, a dense composite polymer film is formed, wherein the anion-exchange nanofibers and / or cation-exchange nanofibers are dispersed in a non-charged polymer matrix.

[0085] The prefabricated fiber may contain one or more different types of nanoparticles, or the impregnation solution may contain nanoparticles. Furthermore, the fiber itself may be composed of two or more polymers, and the impregnation solution may be composed of two or more polymers.

[0086] In another aspect of the invention, pre-prepared uncharged polymer fibers are dispersed in anion-exchange polymer solution or cation-exchange polymer solution; the solution is obtained by dispersing the anion-exchange polymer or cation-exchange polymer in a suitable organic solvent, and the organic solvent does not dissolve the pre-prepared nanofibers. To prevent dissolution of the nanofibers, the nanofibers may optionally be cross-linked. Alternatively, anion-exchange polymer microdroplets (micelles) or cation-exchange polymer microdroplets (micelles) may be dispersed together with the pre-prepared nanofibers in a solvent (such as a water-alcohol mixture). Subsequently, the nanofiber dispersion is sprayed or coated onto a surface, and after the solvent evaporates, a composite film is obtained, wherein the uncharged fibers are dispersed in an ion-exchange polymer matrix. Similarly, pre-prepared ion-exchange polymer nanofibers may be dispersed in a solution of uncharged or charged polymers; the solvent used must be able to dissolve the uncharged or charged polymers, but not the anion-exchange polymer fibers or cation-exchange polymer fibers. Subsequently, the dispersion is sprayed or coated onto a surface, and after the solvent evaporates, a composite film is formed, wherein the ion-exchange fibers are dispersed in a non-charged polymer matrix.

[0087] The surface on which the dispersion is sprayed or coated can be an inert polymer film, a nonwoven fabric, a pre-deposited pre-fabricated nanofiber layer, or a pre-fabricated polymer film.

[0088] In another aspect of the invention, pre-fabricated anion exchange fibers and cation exchange fibers are dispersed in a suitable solvent, with or without the addition of surfactants, and nanoparticles (such as titanium dioxide, aluminum oxide, nanodiamond, nanographene oxide, and / or aluminum hydroxide) are added; wherein the mass fractions of the anion exchange fibers, cation exchange fibers, and nanoparticles are all variable. This mixture is sprayed or cast / coated onto a smooth surface, which may be a pre-fabricated dense anion exchange membrane or a dense cation exchange membrane. After deposition is complete and the solvent evaporates, a second pre-fabricated dense film is placed on the dual-fiber deposition felt, the second film having the opposite charge properties to the fiber-deposited film. Subsequently, the entire three-layer structure is hot-pressed to melt one type of fiber in the intermediate layer and fuse the outer film with the intermediate layer. A bipolar membrane was ultimately fabricated, which has a three-dimensional interface layer composed of interlocking anion exchange fibers and cation exchange fibers, with outer membranes connected to both sides of the interface layer; one outer membrane is composed of anion exchange polymer, and the other outer membrane is composed of cation exchange polymer. This pre-fabricated dense outer membrane can be a composite ion exchange membrane, i.e., a membrane composed of anion exchange polymer or cation exchange polymer and dispersed non-charged polymer nanofibers. An example of such a membrane is as follows: a dispersion of anion exchange fibers and cation exchange fibers containing titanium dioxide nanoparticles is sprayed onto a pre-fabricated dense anion exchange polymer film; subsequently, a pre-fabricated cation exchange polymer membrane is placed on top of the sprayed fiber mat; the entire three-layer structure is then subjected to hot pressing. A slightly modified method involves spraying a pre-fabricated anion exchange polymer fiber dispersion containing dispersed particles onto a pre-fabricated dense anion exchange membrane; subsequently, placing a pre-fabricated dense cation exchange membrane on top of the fiber layer; and subjecting the entire structure to a hot-pressing treatment at a pressure and temperature sufficient to soften the cation exchange membrane and allow it to flow between the pre-fabricated anion exchange fibers, while ensuring that the temperature and pressure are not sufficient to damage the sprayed anion exchange fiber network.

[0089] The charged polymer nanofibers are prepared by electrospinning, wherein the spinning solution contains anion-exchange polymers, cation-exchange polymers, or blends of two or more charged polymers. Optionally, a carrier polymer is added to the spinning solution. The apparatus for preparing the fibers can be an electrospinning apparatus, a centrifugal spinner, an air jet spinning apparatus, or a spinning device without an applied electric field.

[0090] Without intending to limit the scope of protection of the present invention, exemplary embodiments of the present invention will be described below.

[0091] In some embodiments, the method for preparing the membrane includes: dispersing pre-made polymer nanofibers in at least one first solvent to form a dispersion; spraying or coating the dispersion onto the surface of a substrate to form a nanofiber-based structure on the substrate; and evaporating to remove at least one first solvent from the nanofiber-based structure, thereby obtaining the membrane, wherein the membrane has pores.

[0092] In some embodiments, prior to the spraying or coating step, nanoparticles are added to the dispersion.

[0093] In some embodiments, the membrane is a porous nanofiber felt.

[0094] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated charged anion exchange or cation exchange polymer nanofibers; the method further comprises: impregnating the porous nanofiber felt with a solution of a non-charged polymer containing one or more non-charged polymers, wherein the one or more non-charged polymers are dispersed in at least one second solvent; removing the at least one second solvent from the impregnated porous nanofiber felt to obtain a nanofiber-based anion exchange membrane or cation exchange membrane.

[0095] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated non-charged polymer nanofibers; the method further comprises: impregnating a cation exchange polymer solution or anion exchange polymer solution containing one or more cation exchange polymers or anion exchange polymers into the porous nanofiber felt, wherein the one or more cation exchange polymers or anion exchange polymers are dispersed in at least one third solvent; evaporating to remove the at least one third solvent from the impregnated porous nanofiber felt, thereby obtaining a nanofiber-based anion exchange membrane or cation exchange membrane.

[0096] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced cation exchange membrane onto the nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0097] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated cation exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced anion exchange membrane onto the nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0098] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers and one or more prefabricated cation exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced cation exchange membrane onto the nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0099] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers and one or more prefabricated cation exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the method further comprises: hot-pressing the prefabricated dense homogeneous or fiber-reinforced anion exchange membrane onto the nanofiber felt to obtain a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0100] In some embodiments, charged and / or uncharged polymer nanofibers include hydrocarbon polymers.

[0101] In some embodiments, the non-charged polymer nanofibers include polysulfone, polyethersulfone, polyamide-imide, polyvinylidene fluoride, and / or polyphenylene ether.

[0102] In some embodiments, charged polymer nanofibers include cation exchange polymers and / or anion exchange polymers.

[0103] In some embodiments, the cation exchange polymer has sulfonate or carboxylate cation exchange groups.

[0104] In some embodiments, the charged polymer nanofibers include sulfonated polyether ether ketone, sulfonated polysulfone, sulfonated polyphenylene ether, sulfonated polyether sulfone, or sulfonated polyarylene ether sulfone cation exchange sites.

[0105] In some embodiments, the anion exchange polymer has benzyltrialkylammonium, imidazolonium, cycloammonium, benzimidazolium, phosphonium, piperidinium, quaternary ammonium, or benzyldimethylhexylammonium anion exchange groups.

[0106] In some embodiments, charged and / or uncharged polymer nanofibers include fluoropolymers.

[0107] In some embodiments, the cation exchange polymer nanofibers comprise fluoropolymers having sulfonic acid ion exchange sites.

[0108] In some embodiments, the one or more prefabricated charged and / or uncharged polymer nanofibers are cross-linked fibers.

[0109] In some embodiments, the one or more prefabricated charged and / or uncharged polymer nanofibers contain nanoparticles.

[0110] In some embodiments, the nanoparticles are one or more of titanium dioxide, aluminum oxide, aluminum hydroxide, nanodiamond, nanographene oxide, and zirconium hydroxide.

[0111] In some embodiments, the pre-fabricated polymer nanofibers are prepared by a method that does not require the application of an electric field before being prepared into a dispersion.

[0112] In some embodiments, the pre-fabricated polymer nanofibers are prepared by centrifugal spinning or air jet spinning.

[0113] In some embodiments, the pre-fabricated polymer nanofibers comprise two or more different types of polymer nanofibers, and these fibers are prepared simultaneously during the spinning process.

[0114] In some embodiments, the pre-formed polymer nanofibers are prepared from a spinning solution containing a charged or uncharged polymer and a carrier polymer.

[0115] In some embodiments, the carrier polymer includes polyethylene oxide, polyvinylpyrrolidone, or polyacrylic acid.

[0116] In some embodiments, the prefabricated nanofibers are dispersed in a solvent, and the solvent also contains one or more suspended nanoparticles.

[0117] In some embodiments, the suspended nanoparticles are one or more of titanium dioxide, aluminum oxide, aluminum hydroxide, nanodiamond, nanographene oxide, and zirconium hydroxide.

[0118] In some aspects, the present invention also relates to a cation exchange membrane, anion exchange membrane, and / or bipolar membrane prepared by the methods disclosed above.

[0119] In other respects, the present invention further relates to an electrochemical device and / or an electrodialysis cell comprising one or more unipolar cation and anion exchange membranes and / or bipolar membranes prepared by the methods disclosed above.

[0120] In another aspect of the invention, a membrane is provided comprising a pre-formed polymer nanofiber network; the pre-formed polymer nanofibers comprising one or more pre-formed non-charged polymer nanofibers, one or more pre-formed charged polymer nanofibers, or a combination thereof.

[0121] In some embodiments, the prefabricated polymer nanofibers comprise nanoparticles.

[0122] In some embodiments, the prefabricated polymer nanofiber network is formed by spraying or coating a dispersion containing the prefabricated polymer nanofibers onto a substrate surface, wherein the prefabricated polymer nanofibers are dispersed in at least one first solvent; and then evaporating to remove the solvent.

[0123] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated charged polymer nanofibers; and the membrane further comprises a non-charged polymer impregnated in the prefabricated polymer nanofiber network, thereby producing a nanofiber-based anion exchange membrane or a cation exchange membrane.

[0124] In some embodiments, the prefabricated polymer nanofibers comprise one or more of the prefabricated non-charged polymer nanofibers; and the membrane further comprises a cation exchange polymer or anion exchange polymer impregnated in the prefabricated polymer nanofiber network, thereby producing a nanofiber-based anion exchange membrane or a cation exchange membrane.

[0125] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0126] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated cation exchange polymer nanofibers, and the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0127] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated anion-exchange polymer nanofibers and one or more prefabricated cation-exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced anion-exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced cation-exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion-exchange polymer membrane and the cation-exchange membrane.

[0128] In some embodiments, the prefabricated polymer nanofibers comprise one or more prefabricated anion exchange polymer nanofibers and one or more prefabricated cation exchange polymer nanofibers, wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the membrane further comprises a prefabricated dense homogeneous or fiber-reinforced anion exchange membrane hot-pressed onto the prefabricated polymer nanofiber network, thereby producing a bipolar membrane; the bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

[0129] In some embodiments, charged and / or uncharged polymer nanofibers include hydrocarbon polymers.

[0130] In some embodiments, the non-charged polymer nanofibers include polysulfone, polyethersulfone, polyamide-imide, polyvinylidene fluoride, and / or polyphenylene ether.

[0131] In some embodiments, charged polymer nanofibers include cation exchange polymers and / or anion exchange polymers.

[0132] In some embodiments, the cation exchange polymer has sulfonate or carboxylate cation exchange groups.

[0133] In some embodiments, the charged polymer nanofibers have sulfonated polyether ether ketone, sulfonated polysulfone, sulfonated polyphenylene ether, sulfonated polyether sulfone, or sulfonated polyarylene ether sulfone cation exchange sites.

[0134] In some embodiments, the anion exchange polymer has benzyltrialkylammonium, imidazolonium, cycloammonium, benzimidazolium, phosphonium, piperidinium, quaternary ammonium, or benzyldimethylhexylammonium anion exchange groups.

[0135] In some embodiments, charged and / or uncharged polymer nanofibers include fluoropolymers.

[0136] In some embodiments, the cation exchange polymer nanofibers comprise fluoropolymers having sulfonic acid ion exchange sites.

[0137] In some embodiments, the one or more prefabricated charged and / or uncharged polymer nanofibers are cross-linked fibers.

[0138] In some embodiments, the one or more prefabricated charged and / or uncharged polymer nanofibers contain nanoparticles.

[0139] In some embodiments, the nanoparticles are one or more of titanium dioxide, aluminum oxide, aluminum hydroxide, nanodiamond, nanographene oxide, and zirconium hydroxide.

[0140] In some embodiments, the pre-fabricated polymer nanofibers are prepared in advance by a method that does not require the application of an electric field before being formed into a dispersion.

[0141] In some embodiments, the pre-fabricated polymer nanofibers are prepared by centrifugal spinning or air jet spinning.

[0142] In some embodiments, the pre-fabricated polymer nanofibers comprise two or more different types of polymer nanofibers, and these fibers are prepared simultaneously during the spinning process.

[0143] In some embodiments, the pre-formed polymer nanofibers are prepared from a spinning solution containing a charged or uncharged polymer and a carrier polymer.

[0144] In some embodiments, the carrier polymer includes polyethylene oxide, polyvinylpyrrolidone, or polyacrylic acid.

[0145] In some embodiments, dispersions composed of two or more different pre-fabricated polymer nanofibers or polymer-particle nanofibers are used. These dispersions are deposited layer by layer and / or repeatedly using a spraying or coating process. Then, a suitable process is used to close some or all of the voids between the deposited fibers, thus fabricating a layered porous membrane, a layered semi-porous membrane, or a layered dense membrane. Dispersion A and dispersion B can be deposited multiple times to obtain a membrane with an ABABAB repeating layered structure; similarly, dispersions A, B, C, and D can be deposited to obtain a membrane with an ABCD, ABCABCD, or CDABABABDC type layered structure. This multilayer structure can be deposited on a pre-fabricated polymer anion exchange membrane, a pre-fabricated polymer cation exchange membrane, or an inert substrate that can be peeled off from the final obtained membrane.

[0146] In some embodiments, one or more pre-fabricated uncharged nanofibers are dispersed in a solvent to form a solution / dispersion; the solution is then spread into a thin layer by a spraying or coating process (such as slot die coating, wire rod coating, gravure coating, or blade coating); after the solvent evaporates, a porous fiber layer containing a fiber network is obtained. This porous fiber layer can be used directly as a porous fiber membrane, or further subjected to hot pressing to eliminate the voids between fibers, thereby obtaining a dense membrane.

[0147] In some embodiments, one or more pre-fabricated non-charged nanofibers are dispersed in a solvent containing solid nanoparticles and / or dispersed polymer particles / micelles to form a solution / dispersion; the solution is then spread into a thin layer by a spraying or coating process (such as slot die extrusion coating, wire rod coating, gravure coating, or doctor blade coating); after the solvent evaporates, a porous fiber layer is obtained; the porous layer can be further hot-pressed to obtain a dense film.

[0148] In some embodiments, one or more pre-fabricated non-charged polymer nanofibers are dispersed in a solution or dispersion of one or more charged polymers to form a polymer solution; solid nanoparticles may be selectively added to the polymer solution; the polymer solution is then spread into a thin layer by a spraying or coating process (such as slot die extrusion coating, wire rod coating, gravure coating, or blade coating); after solvent evaporation, a porous fiber layer is obtained; and the pores are then eliminated by hot pressing and / or solvent contact treatment to finally obtain a dense composite membrane, wherein the nanofibers are dispersed throughout the membrane polymer matrix.

[0149] In some embodiments, one or more pre-fabricated non-charged polymer nanofibers are dispersed in a polymer solution of one or more cation exchange polymers or one or more anion exchange polymers; the polymer solution is then spread into a thin layer by a spraying or coating process (such as slot die extrusion coating, wire rod coating, gravure coating or doctor blade coating); after solvent evaporation, a dense nanofiber composite cation exchange membrane or anion exchange membrane is obtained, wherein the non-charged fibers are dispersed throughout the charged polymer film.

[0150] In some embodiments, one or more pre-fabricated cation exchange fibers, one or more pre-fabricated anion exchange nanofibers, or a mixture of pre-fabricated cation exchange fibers and pre-fabricated anion exchange nanofibers are dispersed in a polymer solution or polymer dispersion of one or more non-charged polymers; the polymer solution is then spread into a thin layer by a spraying or coating process (such as slot die coating, wire rod coating, gravure coating, or blade coating); after solvent evaporation, a dense nanofiber composite cation exchange membrane or anion exchange membrane is obtained, wherein the ion exchange polymer nanofibers are dispersed throughout the non-charged polymer film.

[0151] In some embodiments, one or more pre-fabricated cation exchange fibers, one or more pre-fabricated anion exchange nanofibers, or a mixture of pre-fabricated cation exchange fibers and pre-fabricated anion exchange nanofibers are dispersed in a polymer solution or polymer dispersion of one or more non-charged polymers, and then a thin layer is formed by spraying or coating processes. After solvent evaporation, the resulting porous fiber layer is used as a three-dimensional interface layer in the bipolar membrane preparation process. Furthermore, the dispersion of cation exchange fibers and anion exchange fibers may contain dispersed solid nanoparticles, including titanium dioxide, aluminum oxide, nanodiamond, nanographene oxide, and / or aluminum hydroxide.

[0152] In some embodiments, nanofibers are prepared by electrospinning, centrifugal spinning, air jet spinning, or other fiber spinning processes that utilize an electric field.

[0153] In some embodiments, during the spinning process, two or more different nanofibers are prepared simultaneously by equipping each fiber with a separate spinneret / spinneret and polymer solution.

[0154] In some embodiments, a porous layer (optionally containing dispersed solid nanoparticles) composed of cation exchange fibers and anion exchange fibers is sandwiched between a dense cation exchange membrane and a dense anion exchange membrane, followed by hot pressing to obtain a three-layer bipolar membrane with a three-dimensional nanofiber interface layer.

[0155] In some embodiments, the polymer solution for fiber spinning comprises a hydrocarbon polymer with a fixed-charge group, and the polymer is dissolved in a solvent; wherein the fixed-charge group may be a positively charged group or a negatively charged group.

[0156] In some embodiments, the polymer solution for fiber spinning comprises a hydrocarbon polymer having anion exchange groups of benzyltrialkylammonium, imidazoline, cycloammonium, benzimidazolium, phosphonium, piperidinium, quaternary ammonium, or benzyldimethylhexylammonium.

[0157] In some embodiments, the backbone of the anion exchange polymer comprises polyphenylene ether, polyethersulfone, polyarylethersulfone, or other hydrocarbon polymers containing aromatic rings.

[0158] In some embodiments, the polymer solution for fiber spinning comprises a polyphenylene ether polymer with benzyltrialkylammonium positively charged ion-exchange groups.

[0159] In some embodiments, the polymer solution for fiber spinning comprises a polyphenylene ether polymer with benzyl dimethylhexylammonium fixed charge groups.

[0160] In some embodiments, the polymer solution used for fiber spinning comprises a hydrocarbon polymer with negatively charged ion-exchange groups of sulfonate or carboxylate.

[0161] In some embodiments, the polymer solution used for fiber spinning comprises charged perfluoropolymers or charged hydrocarbon polymers, as well as non-charged polymers (such as polyethylene oxide, polyacrylic acid, polyvinylidene fluoride, or polyvinylpyrrolidone).

[0162] In some embodiments, the polymer solution contains a low-boiling-point solvent.

[0163] In some embodiments, the polymer solution comprises two or more polymers.

[0164] In some embodiments, one or more polymers in the charged or uncharged fibers are cross-linked.

[0165] In some embodiments, solid particles are added to the polymer solution used for fiber spinning. These particles may include one or more of the following: (1) supported metal particles, the carrier comprising carbon, graphite, silicon dioxide, aluminum oxide, titanium dioxide, or other oxide materials, the metal comprising one or more platinum group metals (platinum, palladium, ruthenium, iridium, rhodium, osmium), platinum group metal alloys (platinum-cobalt alloys or platinum-nickel alloys), silver (Ag) particles, silver alloy particles, nickel (Ni) particles, nickel alloy particles, iron (Fe) particles, iron alloy particles, or combinations thereof; (2) zeolite; (3) silicon dioxide; (4) stone (5) Metal oxides (such as LiCoO4 or IrO2); (6) Noble metals or their alloys (such as platinum black or platinum ruthenium black); (7) Platinum group metal-free (PGM-free) powders, including metal-nitrogen groups (MNxCy), nitrogen-carbon groups (CNx), nitrogen-doped carbon materials (M@NxCy) coated with inorganic metal species, or combinations thereof; (8) Catalyst particles with controllable core-shell structure and morphology; and / or (9) One or more of the following particles: titanium dioxide, aluminum oxide, nanodiamond, nanographene oxide and / or aluminum hydroxide.

[0166] In some embodiments, the fiber is used to prepare a bipolar membrane for use in flow batteries, carbon dioxide electrochemical reduction reactors, electrodialysis cells or electrodialysis stacks for acid and alkali preparation, or other electrochemical devices.

[0167] In the above embodiments, the solvent may be a single-component solvent or a mixed solvent composed of two or more liquids.

[0168] Without intending to limit the scope of protection of this invention, further exemplary embodiments of the invention and related experimental results are given below according to embodiments of the invention. It should be noted that the titles or subtitles used in the examples are merely for convenience of the reader and do not limit the scope of protection of this invention in any way. Furthermore, certain theories are proposed and disclosed herein. However, as long as the invention is implemented according to the invention without considering any specific theory or course of action, regardless of whether such theories are correct or not, the scope of the invention should not be limited.

[0169] Example 1: Fibers containing perfluorosulfonic acid ionomer and polyethylene oxide (PEO) Add 25 wt.% Nafion®-PEO (mass ratio 95:5) methanol-water solution (methanol and water by mass percentages of 60 wt.% and 40 wt.%, respectively) to a double-needle centrifugal spinning machine with a central chamber (see...). Figure 1 The spinneret is available in 24G or 26G specifications. The spinning speed is approximately 10,000 rpm, and the solution flow rate is approximately 360 ml / h. The distance from the spinneret to the collector is typically 20-30 cm, but a shorter distance is also possible. Figure 2A comparison of scanning electron microscope (SEM) images of electrospun and centrifugally spun fibers is shown; the electrospun fibers were prepared using a single-needle spinneret at a solution flow rate of 0.25 ml / h. This example aims to demonstrate that charged ionomer fibers can be prepared from an alcohol-water dispersion of perfluorosulfonic acid ionomer using a PEO-supported polymer via centrifugation, and that the morphology of these fibers is similar to that of the electrospun fibers.

[0170] Figure 1 Scanning electron microscope (SEM) images of Nafion® / PEO fibers prepared by electrospinning or centrifugal spinning are shown. It is evident that centrifugal spinning can produce fibers with regular morphology. This example discloses for the first time a technical solution for preparing perfluorosulfonic acid nanofibers using a centrifugal spinning machine.

[0171] Example 2: Fibers containing particles and polymer binders Fibers containing Fe-NC powder (purchased from Pajarito Powder), perfluorosulfonic acid ionomer (Nafion® from Chemours), and polyethylene oxide (PEO) were prepared using a centrifugal spinning machine. The spinning solution had a solid content of 11.4 wt.%, with the following mass percentages of components: catalyst 52.5 wt.%, Nafion® 37.3 wt.%, and PEO 10.2 wt.%. The solvent was a mixture of dichloromethane, methanol, and water (54.5 wt.% + 41.0 wt.% + 4.5 wt.%). The spinning temperature was maintained at approximately 30-40°C, and the spinning speed was approximately 10,000 rpm. Scanning electron microscopy (SEM) images of the resulting centrifugally spun fibers are shown below. Figure 2 As shown.

[0172] Figure 2 SEM images of particles + polymer fibers prepared by centrifugal spinning are shown, wherein the particles are platinum group metal (PGM-free) catalyst powder (containing Fe-NC) purchased from Pajarito Powder.

[0173] This example discloses for the first time a technical solution for preparing nanofibers using a mixture of perfluorosulfonic acid ionomer, polyethylene oxide, and nanoparticles. The Fe-CN powder used in this example has been proven to be a highly efficient platinum-free group metal catalyst for the oxygen reduction reaction in proton exchange membrane fuel cells. Therefore, the fibers prepared in this example can be used to prepare fiber felt electrodes for fuel cells or other electrochemical devices. Furthermore, the use of Fe-CN powder in this example also aims to illustrate how to incorporate nanoparticles into ion exchange polymer fibers to prepare a three-dimensional intercalated fiber interface layer for bipolar membranes.

[0174] The above description of exemplary embodiments of the present invention is for illustrative purposes only and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Various modifications and variations can be made based on the above teachings.

[0175] While various alternative embodiments have been shown in this invention, those skilled in the art will understand that certain improvements and modifications can be made without departing from the basic scope of protection of this invention discussed and set forth above and below (including the claims and drawings). Furthermore, the above embodiments and the appended claims are for illustrative purposes only and are not intended to limit the scope of protection of this invention to the disclosed elements.

[0176] This disclosure includes references and discussions of various sources (including patents, patent applications, and publications). These references are cited and / or discussed solely for the purpose of clarifying the contents of this disclosure and do not imply that any of them constitutes "prior art" to the disclosure herein. All references cited and discussed in this specification are incorporated herein by reference in their entirety as if they were cited individually.

[0177] References [1] C. Chen, M. Dirican, X. Zhang, centrifugal Spinning-High RateProduction of Nanofibers, in Electrospinning: Nanofabrication andApplications, in Micro and Nano Technologies, Bin Ding, Xianfeng Wang andJianyong Yu (Eds.), Elsevier, 2019. [2] X. Zhang and Y. Lu, Centrifugal Spinning: An Alternative Approach to Fabricate Nanofibers at High Speed ​​and Low Cost, Polymer Reviews, 54, 677-701 (2014). [3] B. E. Kwak, H. J. Yoo, E. Lee, and D. H. Kim, Large-ScaleCentrifugal Multispinning Production of Polymer Micro- and Nanofibers forMask Filter Application with a Potential of Cospinning Mixed MulticomponentFibers, ACS Macro Lett., 10, 382-388 (2021). [4] Y. Lu, Y. Li, S. Zhang, G. Xu, K. Fu, H. Lee, X. Zhang, Parameterstudy and characterization for polyacrylonitrile nanofibers fabricated viacentrifugal spinning process, European Polymer Journal, 49, 3834-3845 (2013).

Claims

1. A method of making a film, comprising: Pre-fabricated polymer nanofibers are dispersed in at least one first solvent to form a dispersion. The dispersion is sprayed or coated onto the surface of a substrate to form a nanofiber-based structure on the substrate. The membrane is prepared by evaporating and removing at least one first solvent from the nanofiber-based structure; wherein the membrane has pores.

2. The method according to claim 1, further comprising adding nanoparticles to the dispersion prior to the spraying or coating step.

3. The method according to claim 1 or 2, wherein the membrane is a porous nanofiber felt.

4. The method according to claim 3, wherein the prefabricated polymer nanofibers comprise one or more prefabricated charged anion-exchange or cation-exchange polymer nanofibers; the method further comprises: The porous nanofiber felt is impregnated with a solution of one or more uncharged polymers, wherein the one or more uncharged polymers are dispersed in at least one second solvent. The at least one second solvent in the impregnated porous nanofiber felt is removed by evaporation to obtain a nanofiber-based anion exchange membrane or a cation exchange membrane.

5. The method of claim 3, wherein the prefabricated polymer nanofibers comprise one or more prefabricated non-charged polymer nanofibers; the method further comprises: A cation exchange polymer solution or anion exchange polymer solution containing one or more cation exchange polymers or anion exchange polymers is impregnated into the porous nanofiber felt, wherein the one or more cation exchange polymers or anion exchange polymers are dispersed in at least one third solvent; The at least one third solvent in the impregnated porous nanofiber felt is removed by evaporation to obtain a nanofiber-based anion exchange membrane or a cation exchange membrane.

6. The method of claim 3, wherein the pre-fabricated polymer nanofibers comprise one or more pre-fabricated anion-exchange polymer nanofibers, and wherein the substrate comprises a pre-fabricated dense homogeneous or fiber-reinforced anion-exchange film; the method further comprises: A bipolar membrane is prepared by hot-pressing a pre-fabricated dense homogeneous or fiber-reinforced cation exchange membrane onto the nanofiber felt. The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer film and the cation exchange film.

7. The method of claim 3, wherein the pre-fabricated polymer nanofibers comprise one or more pre-fabricated cation exchange polymer nanofibers, and wherein the substrate comprises a pre-fabricated dense homogeneous or fiber-reinforced cation exchange membrane; the method further comprises: A bipolar membrane is prepared by hot-pressing a pre-fabricated dense homogeneous or fiber-reinforced anion exchange membrane onto the nanofiber felt. The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer film and the cation exchange film.

8. The method of claim 3, wherein the pre-fabricated polymer nanofibers comprise one or more pre-fabricated anion-exchange polymer nanofibers and one or more pre-fabricated cation-exchange polymer nanofibers, and wherein the substrate comprises a pre-fabricated dense homogeneous or fiber-reinforced anion-exchange film; the method further comprises: A bipolar membrane is prepared by hot-pressing a pre-fabricated dense homogeneous or fiber-reinforced cation exchange membrane onto the nanofiber felt. The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer film and the cation exchange film.

9. The method of claim 3, wherein the pre-fabricated polymer nanofibers comprise one or more pre-fabricated anion-exchange polymer nanofibers and one or more pre-fabricated cation-exchange polymer nanofibers, and wherein the substrate comprises a pre-fabricated dense homogeneous or fiber-reinforced cation exchange membrane; the method further comprises: A bipolar membrane is prepared by hot-pressing a pre-fabricated dense homogeneous or fiber-reinforced anion exchange membrane onto the nanofiber felt. The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange membrane and the cation exchange membrane.

10. The method according to any one of claims 1-9, wherein the charged and / or uncharged polymer nanofibers comprise hydrocarbon polymers.

11. The method of claim 10, wherein the non-charged polymer nanofibers comprise polysulfone, polyethersulfone, polyamide-imide, polyvinylidene fluoride, and / or polyphenylene ether.

12. The method of claim 10, wherein the charged polymer nanofibers comprise cation exchange polymers and / or anion exchange polymers.

13. The method of claim 12, wherein the cation exchange polymer has sulfonate or carboxylate cation exchange groups.

14. The method of claim 13, wherein the charged polymer nanofibers comprise sulfonated polyether ether ketone, sulfonated polysulfone, sulfonated polyphenylene ether, sulfonated polyether sulfone, or sulfonated polyarylene ether sulfone cation exchange sites.

15. The method of claim 12, wherein the anion exchange polymer has benzyltrialkylammonium, imidazolium, cycloammonium, benzimidazolium, phosphonium, piperidinium, quaternary ammonium, or benzyldimethylhexylammonium anion exchange groups.

16. The method according to any one of claims 1-9, wherein the charged and / or uncharged polymer nanofibers comprise fluoropolymers.

17. The method of claim 16, wherein the cation exchange polymer nanofibers comprise fluoropolymers having sulfonic acid ion exchange sites.

18. The method according to any one of claims 1-9, wherein the one or more prefabricated charged and / or uncharged polymer nanofibers are cross-linked fibers.

19. The method according to any one of claims 1-9, wherein the one or more prefabricated charged and / or uncharged polymer nanofibers contain nanoparticles.

20. The method according to claim 19, wherein the nanoparticles are one or more of titanium dioxide (TiO2), aluminum oxide (Al2O3), aluminum hydroxide (Al(OH)3), nanodiamond, nanographene oxide, and zirconium hydroxide (Zr(OH)4).

21. The method of claim 1, wherein the pre-formed polymer nanofibers are pre-formed by a method that does not require the application of an electric field before forming the dispersion.

22. The method according to claim 21, wherein the pre-fabricated polymer nanofibers are prepared by centrifugal spinning or air jet spinning.

23. The method of claim 21, wherein the pre-fabricated polymer nanofibers comprise two or more different types of polymer nanofibers, and the different types of polymer nanofibers are prepared simultaneously during the spinning process.

24. The method of claim 21, wherein the pre-formed polymer nanofibers are prepared from a spinning solution containing a charged or uncharged polymer and a carrier polymer.

25. The method of claim 23, wherein the carrier polymer comprises polyethylene oxide, polyvinylpyrrolidone, or polyacrylic acid.

26. A cation exchange membrane or anion exchange membrane, prepared by the method according to claim 4 or 5.

27. A bipolar membrane prepared by the method according to any one of claims 6-9.

28. An electrochemical device, comprising: One or more membranes prepared using the method described in any one of claims 1-25.

29. An electrodialysis cell, comprising: Monopolar cation and anion exchange membranes and / or bipolar membranes prepared by the method according to any one of claims 1-25.

30. A membrane comprising: A prefabricated polymer nanofiber network; wherein the prefabricated polymer nanofibers comprise one or more prefabricated non-charged polymer nanofibers, one or more prefabricated charged polymer nanofibers, or a combination thereof.

31. The membrane of claim 30, wherein the pre-fabricated polymer nanofibers comprise nanoparticles.

32. The membrane according to claim 30 or 31, wherein the pre-formed polymer nanofiber network is formed by spraying or coating a dispersion containing the pre-formed polymer nanofibers onto a substrate surface, wherein the pre-formed polymer nanofibers are dispersed in at least one first solvent; and subsequently evaporating to remove the solvent.

33. The membrane of claim 32, wherein the prefabricated polymer nanofibers comprise one or more of the prefabricated charged polymer nanofibers; the membrane further comprises: Non-charged polymer impregnated in the pre-fabricated polymer nanofiber network; The membrane thus prepared is a nanofiber-based anion exchange membrane or a cation exchange membrane.

34. The membrane of claim 32, wherein the prefabricated polymer nanofibers comprise one or more of the prefabricated non-charged polymer nanofibers; the membrane further comprises: A cation exchange polymer or anion exchange polymer impregnated in the pre-fabricated polymer nanofiber network; The membrane thus prepared is a nanofiber-based anion exchange membrane or a cation exchange membrane.

35. The membrane of claim 32, wherein the pre-fabricated polymer nanofibers comprise one or more of the pre-fabricated anion exchange polymer nanofibers, and wherein the substrate comprises a pre-fabricated dense homogeneous or fiber-reinforced anion exchange membrane; the membrane further comprises: Hot-pressed composite onto the prefabricated dense homogeneous or fiber-reinforced cation exchange membrane on the prefabricated polymer nanofiber network; The membrane thus prepared is a bipolar membrane; The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer membrane and the cation exchange membrane.

36. The membrane of claim 32, wherein the prefabricated polymer nanofibers comprise one or more of the prefabricated cation exchange polymer nanofibers, and wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the membrane further comprises: Hot-pressed composite onto the prefabricated dense homogeneous or fiber-reinforced anion exchange membrane on the prefabricated polymer nanofiber network; The membrane thus prepared is a bipolar membrane; The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer film and the cation exchange film.

37. The membrane of claim 32, wherein the pre-fabricated polymer nanofibers comprise one or more pre-fabricated anion-exchange polymer nanofibers and one or more pre-fabricated cation-exchange polymer nanofibers, and wherein the substrate comprises a pre-fabricated dense homogeneous or fiber-reinforced anion-exchange membrane; the membrane further comprises: Hot-pressed composite onto the prefabricated dense homogeneous or fiber-reinforced cation exchange membrane on the prefabricated polymer nanofiber network; The membrane thus prepared is a bipolar membrane; The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer film and the cation exchange film.

38. The membrane of claim 32, wherein the prefabricated polymer nanofibers comprise one or more prefabricated anion-exchange polymer nanofibers and one or more prefabricated cation-exchange polymer nanofibers, and wherein the substrate comprises a prefabricated dense homogeneous or fiber-reinforced cation exchange membrane; the membrane further comprises: Hot-pressed composite onto the prefabricated dense homogeneous or fiber-reinforced anion exchange membrane on the prefabricated polymer nanofiber network; The membrane thus prepared is a bipolar membrane; The bipolar membrane has a three-dimensional interface layer composed of interpenetrating and tightly interlocked prefabricated nanofibers, and the interface layer is sandwiched between the anion exchange polymer film and the cation exchange film.

39. The membrane according to any one of claims 30-38, wherein the charged and / or uncharged polymer nanofibers comprise hydrocarbon polymers.

40. The membrane of claim 39, wherein the non-charged polymer nanofibers comprise polysulfone, polyethersulfone, polyamide-imide, polyvinylidene fluoride, and / or polyphenylene ether.

41. The membrane of claim 39, wherein the charged polymer nanofibers comprise cation exchange polymers and / or anion exchange polymers.

42. The membrane according to claim 41, wherein the cation exchange polymer has sulfonate or carboxylate cation exchange groups.

43. The membrane of claim 42, wherein the charged polymer nanofibers comprise sulfonated polyether ether ketone, sulfonated polysulfone, sulfonated polyphenylene ether, sulfonated polyether sulfone, or sulfonated polyarylene ether sulfone cation exchange sites.

44. The membrane according to claim 41, wherein the anion exchange polymer has benzyltrialkylammonium, imidazolium, cycloammonium, benzimidazolium, phosphonium, piperidinium, quaternary ammonium or benzyldimethylhexylammonium anion exchange groups.

45. The membrane according to any one of claims 30-38, wherein the charged and / or uncharged polymer nanofibers comprise fluoropolymers.

46. ​​The membrane of claim 45, wherein the cation exchange polymer nanofibers comprise a fluorinated polymer having sulfonic acid ion exchange sites.

47. The membrane according to any one of claims 30-38, wherein the one or more prefabricated charged and / or uncharged polymer nanofibers are cross-linked fibers.

48. The membrane according to any one of claims 30-38, wherein the one or more prefabricated charged and / or uncharged polymer nanofibers contain nanoparticles.

49. The membrane according to claim 48, wherein the nanoparticles are one or more of titanium dioxide (TiO2), aluminum oxide (Al2O3), aluminum hydroxide (Al(OH)3), nanodiamond, nanographene oxide, and zirconium hydroxide (Zr(OH)4).

50. The membrane of claim 32, wherein the pre-fabricated polymer nanofibers are pre-fabricated by a method that does not require the application of an electric field before forming the dispersion.

51. The membrane according to claim 50, wherein the pre-fabricated polymer nanofibers are prepared by centrifugal spinning or air jet spinning.

52. The membrane according to claim 50, wherein the pre-fabricated polymer nanofibers comprise two or more different types of polymer nanofibers, and the different types of polymer nanofibers are prepared simultaneously during the spinning process.

53. The membrane according to claim 50, wherein the pre-formed polymer nanofibers are prepared from a spinning solution containing a charged or uncharged polymer and a carrier polymer.

54. The membrane of claim 53, wherein the carrier polymer comprises polyethylene oxide, polyvinylpyrrolidone, or polyacrylic acid.

55. A porous, semi-porous, or dense membrane comprising a multilayer structure of two or more different polymers, the layers being prepared by sequentially depositing different dispersions: pre-formed polymer fibers or polymer-particle fibers, or polymer fibers containing solid particles or polymer particles; the final multilayer membrane being prepared by a hot pressing step or other method that removes some or all of the interfiber voids.

56. An electrochemical device comprising one or more membranes according to any one of claims 30-55.

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