Ion exchange membrane containing asymmetric ion channel units

Abstract

The present invention relates to an ion exchange membrane containing asymmetric ion channel units, and the ion exchange membrane is based on covalent organic frameworks (COFs) and contains ion channel units having different diameters, degrees of hydrophilicity, and charge characteristics, such that an ion exchange membrane having both excellent ion conductivity and ion selectivity may be produced.

Description

ION EXCHANGE MEMBRANE CONTAINING ASYMMETRIC ION CHANNEL UNITS

[0001] The present invention relates to an ion exchange membrane containing asymmetric ion channel units.

[0002] An ion exchange membrane is a membrane that allows cations or anions to pass through and is classified as either a cation exchange membrane or an anion exchange membrane based on the electrostatic properties of its functional groups. An ion exchange membrane having excellent selectivity and conductivity inhibits permeation of ions with the same charge as that of the ion exchange membrane and allows selective permeation of ions with the opposite charge. Due to these characteristics, the ion exchange membrane is utilized in various applications such as a fuel cell, secondary battery, water electrolysis, and reverse electrodialysis power generation that require selective ion permeation.

[0003] A conventional ion exchange membrane utilizes a polymer-based material, which degrades performance in various applications due to its low ion selectivity and high membrane resistance. Therefore, many studies on development of a novel ion exchange membrane material have been actively conducted to solve these problems.

[0004] In the case of the conventional polymer material ion exchange membrane, since it has a thickness of tens to hundreds of micrometers, ion conductivity is low due to a long ion diffusion distance, and ion selectivity is not high due to uneven pore sizes. In particular, there is an increasing need to develop a novel ion exchange membrane material because a membrane structure partially collapses under acidic or basic conditions, resulting in membrane performance degradation.

[0005] In particular, a two-dimensional material-based ion exchange membrane may replace a polymer membrane because it can exhibit high ion selectivity and conductivity due to its abundant charge characteristics in a certain nano-sized pore structure, and therefore, the two-dimensional material-based ion exchange membrane is receiving much attention. A two-dimensional material-based membrane, unlike a conventional polymer membrane, has a significantly thin thickness of tens to hundreds of nanometers, resulting in low membrane resistance inside the ion channels. Additionally, pore sizes and charge characteristics can be controlled through various chemical reactions, allowing for easy modification of the membrane properties according to the application field, thereby enabling appropriate control of both conductivity and ion selectivity of the membrane.

[0006] For example, a covalent organic framework (COF) membrane is a two-dimensional material-based ion exchange membrane having a significantly small nanoscale thickness and a structure of numerous aligned one-dimensional channels. The COF membrane has low membrane resistance due to a significantly short ion diffusion distance and excellent ion selectivity due to constant pore sizes. However, when the COF membrane is used in an aqueous solution for a long period of time, there are limitations in that a channel structure is deformed or entering resistance of ions is still high due to small pores of several nanometers.

[0007] Therefore, there is an urgent need for research and development to induce an appropriate change in structure of aligned channels with high crystallinity and structural stability to lower the entering ion transport resistance and improve ion selectivity and ion conductivity.

[0008] An object of the present invention is to provide an ion exchange membrane with high crystallinity and structural stability, containing ion channel units in which covalent organic frameworks are asymmetrically arranged, in which the entering resistance of ions is reduced, and ion conductivity and ion selectivity are improved.

[0009] Another object of the present invention is to provide an ion exchange system including the ion exchange membrane.

[0010] Still another object of the present invention is to provide an electrochemical device including the ion exchange membrane.

[0011] Still another object of the present invention is to provide a method of producing the ion exchange membrane using a 3D printing method.

[0012] In order to achieve the above objects, the present inventors conducted studies to produce a covalent organic framework (COF) membrane with high crystallinity and structural stability, in which the entering resistance of ions is lowered and ion selectivity and ion conductivity are improved. They have found that when an ion exchange membrane is produced by gradually varying the pore size of the organic framework through a post-treatment with a strong alkaline solution, excellent ion conductivity is exhibited through an effective reduction in entering resistance due to the expansion of a pore diameter and hydrophilization. At the same time, a portion of the organic framework remains unchanged, and thus, high ion selectivity is maintained, such that an ion exchange membrane with both excellent ion conductivity and ion selectivity can be produced, thereby completing the present invention. Further, the present inventors have found that the ion conductivity and ion selectivity can be simultaneously improved by subjecting a covalent organic framework (COF) membrane according to another embodiment to an alkaline treatment and then forming asymmetric ion channels according to differences in hydrophilicity and charge characteristics by introduction of a polymer through an additional reaction.

[0013] In one general aspect, an ion exchange membrane contains ion channel units, wherein the ion channel unit has a structure in which a plurality of unit covalent organic frameworks is formed to be spaced apart in layers. The organic framework has a pore for an ion channel formed inside and ions move through the pores from an ion inlet of the ion channel unit toward an ion outlet of the ion channel unit. A diameter of an outer ion channel of the ion inlet (Dinput) and a diameter of an outer ion channel of the ion outlet (Doutput) of the ion channel unit are different (Dinput≠Doutput).

[0014] According to an embodiment of the present invention, a distance between the organic framework and a unit covalent organic framework located to be adjacent to and spaced apart from the organic framework may be 1 to 5 Å.

[0015] According to an embodiment of the present invention, an outer organic framework of the ion inlet of the ion channel unit may be hydrophilic.

[0016] According to an embodiment of the present invention, a diameter of the outermost organic framework of the ion inlet (Dinput_COF_1st) of the ion channel unit may be 3 to 25 nm.

[0017] According to an embodiment of the present invention, the organic framework may contain a repeating unit represented by the following Chemical Formula 1:

[0018] [Chemical Formula 1]

[0019]

[0020] in Chemical Formula 1,

[0021] A is a monocyclic or polycyclic compound,

[0022] -X- is a divalent linking group, and

[0023] R1to R4are each independently -H, C1-3 alkyl, -OH, -COOH, -COOM, -SO2M, -SO3M, -PO3M, or -PO4M, where M is a cationic metal.

[0024] According to an embodiment of the present invention, in Chemical Formula 1, -X- may be any one or a combination of two or more selected from the group consisting of a direct bond, -NH-, -N=N-, -N=C-, =CH-NH-, -NH-C(=O)-, -CH=CH-NH-, -OC(=O)-NH-, -CH2-C(=O)O-NH-, and -C(=O)NH-N=CH-.

[0025] According to an embodiment of the present invention, Chemical Formula 1 may be represented by the following Chemical Formula 2:

[0026] [Chemical Formula 2]

[0027]

[0028] in Chemical Formula 2,

[0029] R1to R4are each independently -H, C1-3 alkyl, -OH, or -COOH.

[0030] According to an embodiment of the present invention, the organic framework may have a polygonal structure containing the repeating unit of Chemical Formula 1 on one side and having a pore for an ion channel formed on the inside.

[0031] According to an embodiment of the present invention, the organic framework may contain a repeating unit represented by the following Chemical Formula 3:

[0032] [Chemical Formula 3]

[0033]

[0034] in Chemical Formula 3,

[0035] R1to R4are each independently -H, C1-3 alkyl, -OH, or -COOH.

[0036] According to an embodiment of the present invention, a diameter of an outer organic framework of the ion inlet (Dinput_COF) may be larger than a diameter of an outer organic framework of the ion outlet (Doutput_COF) (Dinput_COF> Doutput_COF).

[0037] According to an embodiment of the present invention, the diameter of the outer organic framework of the ion inlet (Dinput_COF) may be larger than a diameter of an inner organic framework of the ion channel unit (Dinner_COF) (Dinput_COF> Dinner_COF).

[0038] According to an embodiment of the present invention, the diameter of the outer organic framework of the ion outlet (Doutput_COF) may be equal to or smaller than the diameter of the inner organic framework of the ion channel unit (Dinner_COF) (Doutput_COF≤ Dinner_COF).

[0039] According to another embodiment of the present invention, the diameter of the outer ion channel of the ion inlet (Dinput) may be smaller than the diameter of the outer ion channel of the ion outlet (Doutput) (Dinput< Doutput).

[0040] According to another embodiment of the present invention, the diameter of the outer ion channel of the ion inlet (Dinput) may be smaller than a diameter of an inner ion channel of the ion channel unit (Dinner) (Dinput< Dinner).

[0041] According to another embodiment of the present invention, the diameter of the outer ion channel of the ion outlet (Doutput) may be equal to or larger than a diameter of an inner ion channel of the ion channel unit (Dinner) (Doutput≥ Dinner).

[0042] According to an embodiment of the present invention, the ion channel unit may further include an ionic polymer.

[0043] According to another embodiment of the present invention, the outer ion channel of the ion inlet may be more hydrophilic than the outer ion channel of the ion outlet due to an ionic polymer.

[0044] According to another embodiment of the present invention, the outer ion channel of the ion inlet may be more anionic than the outer ion channel of the ion outlet due to ionic polymer.

[0045] In another general aspect, an ion exchange system and ion exchange device using the ion exchange membrane are provided.

[0046] In still another general aspect, an electrochemical device including the ion exchange membrane is produced.

[0047] According to an embodiment of the present invention, the electrochemical device may be any one selected from a reverse electrodialysis power generation device, a fuel cell, and a secondary battery.

[0048] In still another general aspect, a method of producing an ion exchange membrane includes performing 3D printing on a monomer composition including a monomer for an organic framework and a solvent.

[0049] The ion exchange membrane according to an aspect of the present invention contains ion channel units composed of covalent organic frameworks (COFs) having an asymmetric pore diameter, in which entering resistance is effectively reduced due to expansion of the pore diameter of the organic framework and hydrophilicity, resulting in excellent ion conductivity. At the same time, the degree of hydrophilicity and the asymmetric charge characteristics of the channels are secured by a portion that remains unchanged during the gradual alkaline treatment process or by a polymer introduced through an additional reaction, resulting in high ion selectivity. As a result, an ion exchange membrane having both excellent ion conductivity and ion selectivity can be produced.

[0050] FIG. 1 is a schematic view illustrating a method of producing a COF membrane according to Production Examples 1 and 2.

[0051] FIG. 2 is a schematic view illustrating a method of producing an ion exchange membrane according to Production Example 1 and Examples 1 to 3.

[0052] FIG. 3 is a schematic view illustrating a method of producing an ion exchange membrane according to Production Example 2 and Examples 4 to 6.

[0053] FIG. 4 illustrates GIWAXS data (A) and Fourier-transform infrared spectroscopy (FT-IR) analysis spectrum (B) of the COF membrane according to an embodiment.

[0054] FIG. 5A is a pore distribution curve of the COF membrane produced according to Production Example 1, and FIG. 5B is a pore distribution curve of the COF ion exchange membrane produced according to Example 2.

[0055] FIG. 6 illustrates GIWAXS data (A), Fourier-transform infrared spectroscopy (FT-IR) analysis spectra (B), and contact angle data (C) of the COF membrane produced according to Production Example 1 and the ion exchange membranes according to Examples 1 to 3.

[0056] FIG. 7 is a depth profile obtained by analyzing the COF membrane produced according to Production Example 1 and the ion exchange membranes according to Examples 1 to 3 using X-ray photoelectron spectroscopy (XPS).

[0057] FIG. 8A illustrates GIWAXS data of the COF membrane produced according to Production Example 2 and the ion exchange membranes according to Examples 4 to 6, and FIG. 8B is a thermogravimetric analysis (TGA) graph of Examples 4 to 6 and PAA polymers used in Examples 5 and 6. FIG. 8C illustrates contact angle data according to Production Example 2 and Examples 4 to 6, and FIG. 8D illustrates surface charge characteristic data according to Examples 4 to 6.

[0058] FIG. 9 illustrates current-voltage graphs of the ion exchange membranes according to Production Example 1 (A), Examples 1 to 3 (B), and Production Example 2 and Examples 4 to 6 (C).

[0059] FIG. 10 illustrates power density graphs of the ion exchange membranes according to Example 1 to 6.

[0060] FIG. 11 is an image of an H-Cell used for reaction and evaluation.

[0061] Unless otherwise defined, all the technical terms and scientific terms used in the present specification have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The terms used in the description of the present specification are merely used to effectively describe a specific example, but are not intended to limit the present invention.

[0062] Unless the context clearly indicates otherwise, singular forms used in the present specification may be intended to include plural forms.

[0063] In addition, a numerical range used in the present specification includes upper and lower limits and all values within these limits, increments logically derived from a form and span of a defined range, all double limited values, and all possible combinations of the upper and lower limits in the numerical range defined in different forms. Unless otherwise specifically defined in the present specification, values out of the numerical range that may occur due to experimental errors or rounded values also fall within the defined numerical range.

[0064] In the present specification, the expression "comprise(s)" is intended to be an open-ended transitional phrase having an equivalent meaning to "include(s)", "contain(s)", "have (has)", and "are (is) characterized by", and does not exclude elements, materials, or steps, all of which are not further recited herein.

[0065] The term "diameter of ion channel" in the present specification means a diameter of a pore for an ion channel in a single ion channel unit, and the "diameter of organic framework" means a diameter of a pore of each of unit covalent organic frameworks. The diameter of the ion channel is distinct from the diameter of the organic framework, and the diameter of the organic framework does not vary due to additional components such as a polymer, but the diameter of the ion channel may vary.

[0066] Regarding the terms "outer" and "inner" in the present specification, based on the centrally located unit covalent organic framework with a direction of ion movement in the ion channel formed in the single ion channel unit as the central axis, a case where a reference object is located closer to the centrally located unit covalent organic framework is defined as "inner", and a case where a reference object is located more toward an ion inlet or an ion outlet is defined as "outer".

[0067] In the present specification, the term "substitution" may mean, but is not particularly limited to, that one or more hydrogens in a residue of a corresponding compound are substituted with a hydroxy group, a nitro group, a cyano group, an amino group, a carboxyl group, a linear or branched C1 to C6 alkyl group, a C1 to C6 alkylsilyl group, a C3 to C12 cycloalkyl group, a C6 to C12 aryl group, a C2 to C12 heteroaryl group, a C1 to C6 alkoxy group, a halogen group, or a C1 to C6 fluoroalkyl group.

[0068] Hereinafter, an ion exchange membrane according to an embodiment of the present invention will be described in more detail.

[0069] The present invention provides an asymmetric ion exchange membrane containing ion channel units, wherein the ion channel unit has a structure in which a plurality of unit covalent organic frameworks (hereinafter, referred to as "organic framework" or "COF") are formed to be spaced apart in layers. The organic framework has a pore for an ion channel formed inside and ions move through the pores from an ion inlet of the ion channel unit toward an ion outlet of the ion channel unit. A diameter of an outer ion channel of the ion inlet (Dinput) and a diameter of an outer ion channel of the ion outlet (Doutput) of the ion channel unit are different.

[0070] According to an embodiment of the present invention, in the ion exchange membrane, as illustrated in FIG. 2, a diameter of an outer organic framework of the ion inlet (Dinput_COF) may be larger than a diameter of an outer organic framework of the ion outlet (Doutput_COF) (Dinput_COF> Doutput_COF). That is, the diameter of the outer ion channel of the ion inlet (Dinput) may be larger than the diameter of the outer ion channel of the ion outlet (Doutput) (Dinput> Doutput). In this case, the diameter of the organic framework may vary proportionally to the diameter of the ion channel. In addition, the ion exchange membrane may be an asymmetric ion exchange membrane in which an ion inlet is more hydrophilic than an ion outlet.

[0071] According to another embodiment of the present invention, as illustrated in FIG. 3, the ion exchange membrane may be an asymmetric ion exchange membrane in which a diameter of an outer ion channel of an ion inlet (Dinput) is smaller than a diameter of an outer ion channel of an ion outlet (Doutput) (Dinput< Doutput). In addition, the ion exchange membrane may be an asymmetric ion exchange membrane in which an ion inlet may be more hydrophilic than an ion outlet or may have a stronger negative charge than the ion outlet.

[0072] According to an embodiment of the present invention, the ion channel unit has a structure in which two-dimensional organic frameworks are spaced apart or stacked in layers, in which an ion channel is formed by continuously connected pores located on the inside of the respective organic frameworks, and in this case, in an ion channel included in one ion channel unit, a portion through which ions enter is defined as an ion inlet, and a portion through which ions exit is defined as an ion outlet. The ion channel unit according to an embodiment effectively resolves the disadvantages of the conventional organic frameworks, such as narrow pore sizes and hydrophobicity, caused by excessive hydrophobic bonds, resulting in high entering resistance of ions and low ion conductivity. As the pore diameter of the organic framework is expanded through a simple post-treatment and an asymmetric ion channel in which the pore diameter and hydrophilicity of each organic framework gradually decrease from the ion inlet to the ion outlet (or the inside) is formed, the effect of the Debye length that is effectively controlled in the hydrophobic channels is utilized or the asymmetry of the channel is formed through an additional introduction of a polymer into the ion inlet, such that the entering resistance of ions is lowered, and at the same time, the portion where the polymer is introduced may act as an ion accumulation region, thereby significantly improving both ion conductivity and ion selectivity.

[0073] According to an embodiment of the present invention, the organic framework may contain a repeating unit represented by the following Chemical Formula 1.

[0074] [Chemical Formula 1]

[0075]

[0076] In Chemical Formula 1, A is a monocyclic or polycyclic compound, -X- is a divalent linking group, and R1to R4are each independently -H, C1-3 alkyl, -OH, -COOH, -COOM, -SO2M, -SO3M, -PO3M, or -PO4M, where M is a cationic metal.

[0077] According to an embodiment of the present invention, in Chemical Formula 1, A may be a monocyclic or polycyclic, aromatic or non-aromatic ring compound.

[0078] The monocyclic aromatic ring compound may be, for example, substituted or unsubstituted benzene, or an aromatic heterocyclic compound. However, the monocyclic aromatic ring compound of the present invention is not limited to the examples described above. As a non-limiting example, the monocyclic aromatic ring compound may be 1,3,5-triazine.

[0079] The polycyclic aromatic ring compound may be a substituted or unsubstituted C3 to C30 polycyclic aromatic ring compound, may be, for example, a substituted or unsubstituted C3 to C30 bicyclic aromatic ring compound such as naphthalene or azulene; a tricyclic aromatic ring compound such as anthracene, phenanthrene, or fluorene; a tetracyclic aromatic ring compound such as tetracene or pyrene; or a combination thereof, may be a polycyclic aromatic ring compound derived from these compounds, and may contain one or more heterocyclic rings. However, the polycyclic aromatic ring compound of the present invention is not limited to the examples described above.

[0080] The monocyclic non-aromatic ring compound may be, for example, substituted or unsubstituted C3 to C12 cycloalkane. However, the monocyclic non-aromatic ring compound of the present invention is not limited to the examples described above.

[0081] The polycyclic non-aromatic ring compound may be, for example, a polycyclic non-aromatic ring compound in which a plurality of monocyclic non-aromatic ring compounds is fused or non-fused, but is not limited to the examples described above.

[0082] In addition, A may be a compound in which a monocyclic or polycyclic aromatic ring compound and a monocyclic or polycyclic non-aromatic ring compound are fused or non-fused. Preferably, A may be a C3 to C50 or C6 to C20 monocyclic non-aromatic heterocyclic compound. Here, the meaning of hetero is that carbon in the cyclic compound is substituted with one or more heteroatoms selected from B, O, N, C(=O), P, P(=O), S, S(=O)2, and Si atoms.

[0083] According to an embodiment of the present invention, in Chemical Formula 1, -X- may be any one or a combination of two or more selected from the group consisting of a direct bond, -NH-, -N=N-, -N=C-, =CH-NH-, -NH-C(=O)-, -CH=CH-NH-, -OC(=O)-NH-, -CH2-C(=O)O-NH-, and -C(=O)NH-N=CH-. Specifically, -X- may be any one selected from -NH-, -N=C-, =CH-NH-, and -CH=CH-NH-.

[0084] According to an embodiment of the present invention, in Chemical Formula 1, R1to R4may be each independently -H, C1-3 alkyl, -OH, -COOH, or -COOM, and preferably may be hydrogen or -OH.

[0085] According to an embodiment of the present invention, the organic framework may have a polygonal structure, and preferably a hexagonal structure, containing the repeating unit of Chemical Formula 1 on one side and having a pore for an ion channel formed on the inside.

[0086] According to an embodiment of the present invention, Chemical Formula 1 may be represented by the following Chemical Formula 2.

[0087] [Chemical Formula 2]

[0088]

[0089] In Chemical Formula 2, R1to R4may be each independently -H, C1-3 alkyl, -OH, or -COOH, and preferably may be hydrogen or -OH.

[0090] According to an embodiment of the present invention, the organic framework may contain a repeating unit represented by the following Chemical Formula 3.

[0091] [Chemical Formula 3]

[0092]

[0093] In Chemical Formula 3, R1to R4may be each independently -H, C1-3 alkyl, -OH, or -COOH, and preferably may be hydrogen or -OH.

[0094] According to an embodiment of the present invention, the organic framework may have a polygonal structure containing the repeating unit of Chemical Formula 1, 2, or 3 on one side and having a pore formed on the inside. The polygon may include, for example, a regular or irregular triangle, square, pentagon, and hexagon, or a combination thereof, and is not particularly limited as long as a pore is provided on the inside. Specifically, the organic framework may have a hexagonal structure in which repeating units of Chemical Formula 1 are arranged horizontally to form two-dimensional sheet layers, the sheet layers form a layered structure, and pores are formed inside, and the pores may function as ion channels between the COF sheet layers. The ion exchange membrane according to an embodiment may exhibit higher ion conductivity compared to a conventional COF membrane due to its lower energy requirement for ion inflow and reduced entering resistance.

[0095] According to an embodiment of the present invention, a distance between the organic framework and a unit covalent organic framework located to be adjacent to and spaced apart from the organic framework may be 1 to 10 Å, 2 to 7 Å, 2 to 5 Å, or 2.5 to 4 Å In this case, the distance is calculated by confirming a crystalline peak in XRD or GIWAXS and calculating a d value based on nλ = 2dsinθ, which is Bragg's law, with a peak corresponding to a (001) plane as a reference, and reference is made to Non-Patent Document Nature Materials, 2021, 20, 1551-1558.

[0096] In an embodiment, a method of measuring the size of the diameter of the organic framework includes analyzing a pore size distribution through BET analysis or indirectly measuring a change in the size of the diameter by passing metal nanoparticles of known size. However, since it is difficult to measure the size of the diameter of the organic framework with significant accuracy, a value measured according to the above method or a commonly used or known method may be used.

[0097] In the ion exchange membrane according to an embodiment of the present invention, a diameter of an outer organic framework of the ion inlet (Dinput_COF) may be larger than a diameter of an outer organic framework of the ion outlet (Doutput_COF) (Dinput_COF> Doutput_COF). In addition, in the ion exchange membrane, the diameter of the outer ion channel of the ion inlet (Dinput) may be larger than the diameter of the outer ion channel of the ion outlet (Doutput) (Dinput> Doutput).

[0098] According to an embodiment of the present invention, the organic framework may have amphiphilicity including both hydrophilicity and hydrophobicity. The organic framework may be partially hydrolyzed and changed to hydrophilic through a simple post-treatment of a conventional organic framework. Specifically, the outer organic framework of the ion inlet of the ion channel unit may be hydrophilic. In this case, a pore diameter of the organic framework located in the hydrolyzed and hydrophilized portion may be wider than a pore diameter of a non-hydrolyzed organic framework.

[0099] According to an embodiment of the present invention, the diameter of the outer organic framework of the ion inlet (Dinput_COF) of the ion channel unit may be larger than a diameter of an inner organic framework (Dinner_COF) (Dinput_COF> Dinner_COF). In addition, the diameter of the outer ion channel of the ion inlet (Dinput) may be larger than a diameter of an inner ion channel (Dinner) (Dinput> Dinner). As illustrated in FIG. 2, Dinput_COFmeans a diameter of a pore of any organic framework located in an outer direction of the ion inlet relative to Dinner_COF, and means that the pore diameter gradually decreases from ion inlet to the ion outlet. However, the decrease in diameter may occur only in a very limited areas, as illustrated in Example 1 of FIG. 2, may occur throughout most of the ion channel units, as illustrated in Example 3 of FIG. 2, or may occur to an intermediate degree between Examples 1 and 3, as shown in Example 2 of FIG. 2. The decrease in diameter may be easily controlled according to a post-treatment time and a concentration of a post-treatment solution, but is not particularly limited.

[0100] According to an embodiment of the present invention, the diameter of the outer organic framework of the ion outlet (Doutput_COF) may be equal to or smaller than a diameter of an inner organic framework of the ion channel unit (Dinner_COF) (Doutput_COF≤ Dinner_COF). In addition, the diameter of the outer ion channel of the ion outlet (Doutput) may be equal to or smaller than the diameter of the inner ion channel of the ion channel unit (Dinner) (Doutput≤ Dinner). As illustrated in FIG. 2, Doutput_COFmeans a diameter of a pore of any organic framework located in an outer direction of the ion outlet relative to Dinner_COF, and means that the pore diameter is constant or gradually increases from the ion outlet to the ion inlet. However, the diameter may be constant from the vicinity of the ion outlet to the inside, and an increase in diameter may occur only in a significantly small portion of the ion inlet, as illustrated in Example 1 of FIG. 2, an increase in diameter may occur in most of the ion channel units from the ion outlet to the inside, as illustrated in Example 3 of FIG. 2, and an increase in diameter may occur to an intermediate degree between Examples 1 and 3, as illustrated in Example 2 of FIG. 2. The increase in diameter may be easily controlled according to a post-treatment time and a concentration of a post-treatment solution, but is not particularly limited.

[0101] According to an embodiment of the present invention, the diameter of the outer organic framework (Dinput_COF) or the outermost organic framework (Dinput_COF_1st) of the ion inlet of the ion channel unit may be 1 to 25 nm, 3 to 25 nm, 3 to 20 nm, 5 to 20 nm, or 5 to 10 nm. In addition, the diameter of the outer ion channel (Dinput) or the outermost ion channel of the ion inlet of the ion channel unit (Dinput_1st) may be 1 to 25 nm, 3 to 25 nm, 3 to 20 nm, 5 to 20 nm, or 5 to 10 nm.

[0102] According to an embodiment of the present invention, the diameter of the outer organic framework (Doutput_COF) or the outermost organic framework of the ion outlet of the ion channel unit (Doutput_COF_1st) may be 1 to 20 nm, 1.5 to 15 nm, 2 to 10 nm, or 2 to 5 nm. In addition, the diameter of the outer ion channel (Doutput) or the outermost ion channel of the ion outlet of the ion channel unit (Doutput_1st) may be 1 to 20 nm, 1.5 to 15 nm, 2 to 10 nm, or 2 to 5 nm.

[0103] According to an embodiment of the present invention, the diameter of the organic framework located inside the ion inlet and the ion outlet of the ion channel unit (Dinner_COF) may be smaller than the diameter of the outer organic framework of the ion inlet (Dinput_COF) and may be equal to or larger than the diameter of the outer organic framework of the ion outlet (Doutput_COF) (Dinput_COF> Dinner_COF≥Doutput_COF), and specifically, may be 1 to 20 nm, 2 to 15 nm, 2 to 10 nm, or 2 to 7 nm. In addition, the diameter of the ion channel located inside the ion inlet and the ion outlet of the ion channel unit (Dinner) may be smaller than the diameter of the outer ion channel of the ion inlet (Dinput) and may be equal to or larger than the diameter of the outer ion channel of the ion outlet (Doutput) (Dinput> Dinner≥ Doutput), and specifically, may be 1 to 20 nm, 2 to 15 nm, 2 to 10 nm, or 2 to 7 nm.

[0104] According to an embodiment of the present invention, the diameter of the organic framework located inside the ion inlet and the ion outlet of the ion channel unit (Dinner_COF) may be smaller than the diameter of the outermost organic framework of the ion inlet (Dinput_COF_1st) and may be equal to or larger than the diameter of the outermost organic framework of the ion outlet (Doutput_COF_1st) (Dinput_COF_1st> Dinner_COF≥ Doutput_COF_1st), and specifically, may be 1 to 20 nm, 2 to 15 nm, 2 to 10 nm, or 2 to 7 nm.

[0105] According to an embodiment of the present invention, the diameter of the ion channel located inside the ion inlet and the ion outlet (Dinner) of the ion channel unit may be smaller than the diameter of the outermost ion channel of the ion inlet (Dinput_1st) and may be equal to or larger than the diameter of the outermost ion channel of the ion outlet (Doutput_1st) (Dinput_1st> Dinner≥ Doutput_1st), and specifically, may be 1 to 20 nm, 2 to 15 nm, 2 to 10 nm, or 2 to 7 nm.

[0106] According to another embodiment of the present invention, since the organic framework may be entirely hydrolyzed starting from both sides of the ion inlet and ion outlet through a simple post-treatment of a conventional organic framework, both the outer organic framework of the ion inlet and the outer organic framework of the ion outlet of the ion channel unit may be hydrophilic. In this case, as illustrated in Example 4 of FIG. 3, the diameter of the pore of the inner organic framework (Dinner_COF) located between the outer organic framework of the ion inlet (Dinput_COF) and the outer organic framework of the ion outlet (Doutput_COF) may be similar to or relatively smaller than Dinput_COFand Doutput_COF. In addition, the diameter of the pore for the inner ion channel (Dinner) located between the outer ion channel of the ion inlet (Dinput) and the outer ion channel of the ion outlet (Doutput) may be similar to or relatively smaller than Dinputand Doutput.

[0107] According to another embodiment of the present invention, in the ion exchange membrane, an ionic polymer described below is introduced into the ion inlet to decrease the diameter of the outer ion channel of the ion inlet (Dinput), such that Dinputcan be controlled to be smaller than the diameter of the outer ion channel of the ion outlet (Doutput). The degree of decrease in diameter may be easily controlled according to conditions such as the degree of ionic polymer introduction and the molecular weight of the polymer, which will be described below, and is not particularly limited.

[0108] According to another embodiment of the present invention, as illustrated in Examples 5 and 6 of FIG. 3, in the ion exchange membrane into which the polymer is introduced, the diameter of the outer ion channel of the ion inlet (Dinput) may be smaller than the diameter of the outer ion channel of the ion outlet (Doutput) (Dinput< Doutput). In addition, in the ion exchange membrane, the diameter of the outer organic framework of the ion inlet (Dinput_COF) and the diameter of the outer organic framework of the ion outlet (Doutput_COF) may be similar to each other. That is, the diameter of the ion channel and the diameter of the organic framework may not vary proportionally.

[0109] According to another embodiment of the present invention, the diameter of the outer ion channel of the ion inlet (Dinput) of the ion channel unit may be smaller than the diameter of the inner ion channel of the ion channel unit (Dinner) (Dinput< Dinner). In addition, the diameter of the outer organic framework of the ion inlet (Dinput_COF) may be equal to or larger than the diameter of the inner organic framework (Dinner_COF) (Dinput_COF≥ Dinner_COF).

[0110] According to another embodiment of the present invention, the diameter of the outer ion channel of the ion outlet (Doutput) may be equal to or larger than the diameter of the inner ion channel of the ion channel unit (Dinner) (Doutput≥ Dinner). In addition, the diameter of the outer organic framework of the ion outlet (Doutput_COF) may be equal to or larger than the diameter of the inner organic framework of the ion channel unit (Dinner_COF) (Doutput_COF≥ Dinner_COF).

[0111] According to another embodiment of the present invention, the diameter of the outer ion channel of the ion inlet (Dinput) or the outermost ion channel of the outermost ion inlet (Dinput_1st) may be 1 to 25 nm, 1.5 to 20 nm, 2 to 15 nm, or 2 to 5 nm. In addition, the diameter of the outer organic framework (Dinput_COF) or the outermost organic framework (Dinput_COF_1st) of the ion inlet of the ion channel unit may be 1 to 25 nm, 3 to 25 nm, 3 to 20 nm, 5 to 20 nm, or 5 to 10 nm.

[0112] According to another embodiment of the present invention, the diameter of the outer ion channel (Doutput) or the outermost ion channel (Doutput_1st) of the ion outlet of the ion channel unit may be 1 to 25 nm, 1.5 to 20 nm, 2 to 15 nm, or 3 to 10 nm. In addition, the diameter of the outer organic framework (Doutput_COF) or the outermost organic framework (Doutput_COF_1st) of the ion outlet of the ion channel unit may be 1 to 25 nm, 3 to 25 nm, 3 to 20 nm, 5 to 20 nm, or 5 to 10 nm.

[0113] According to another embodiment of the present invention, an average diameter (pore size) of the pores of the organic frameworks may be 0.1 to 20.0 nm, and specifically, 1.0 to 10.0 nm or 2.0 to 5.0 nm, and may be easily controlled according to a post-treatment method, but is not limited thereto.

[0114] According to an embodiment of the present invention, the diameter of the inner organic framework (Dinner_COF) located between the ion inlet and the ion outlet of the ion channel unit may be 1 to 25 nm, 1.5 to 20 nm, 3 to 15 nm, 2 to 10 nm, or 2 to 5 nm.

[0115] According to another embodiment of the present invention, the ion channel of the ion inlet may be more hydrophilic than the ion channel of the ion outlet.

[0116] According to another embodiment of the present invention, the ion channel of the ion inlet may be more anionic than the ion channel of the ion outlet.

[0117] According to another embodiment of the present invention, the ion channel unit may further include an ionic polymer. When a highly hydrophilic polymer is introduced, the ion inlet of the ion channel unit may be more hydrophilic, and also, when the polymer exhibits stronger charge characteristics than the hydrolyzed organic framework, asymmetric charge characteristics are also imparted to the channel, which may improve ion selectivity.

[0118] According to another embodiment of the present invention, a weight average molecular weight of the anionic polymer may be 1,000,000 g / mol or less, 800,000 g / mol or less, or 1,000 g / mol or more. Alternatively, the weight average molecular weight of the anionic polymer may be 1,000 g / mol to 1,000,000 g / mol, 1,000 g / mol to 500,000 g / mol, or 1,500 g / mol to 200,000 g / mol.

[0119] According to another embodiment of the present invention, in the polymer introduction process, when the ionic polymer reacts with the ion inlet of the framework, the ionic polymer does not easily enter the channel; thus, the ionic polymer is concentrated at the ion inlet, and the insertion of the ionic polymer into the channel is suppressed, and as a result, an asymmetric membrane may be produced.

[0120] According to an embodiment of the present invention, the ionic polymer may strongly bind to the organic framework through covalent bonding, and may also be connected to the organic framework through non-covalent bonding such as hydrogen bonding or electrochemical bonding.

[0121] According to another embodiment of the present invention, the ionic polymer may be a polymer containing a cationic functional group or an anionic functional group, and specifically, may include any one or a combination of two or more selected from the group consisting of a carboxylic acid functional group, a sulfonic acid functional group, and a phosphoric acid functional group. The ionic polymer may be, but is not limited to, any one or a combination of two or more selected from polyvinylamidine, a derivative of polyvinylamidine, polyacrylic acid, a derivative of polyacrylic acid, polystyrene sulfonic acid, and a derivative of polystyrene sulfonic acid.

[0122] According to another embodiment of the present invention, the ionic polymer may be included in an amount of 1 to 80 parts by weight, 5 to 60 parts by weight, or 10 to 50 parts by weight, with respect to 100 parts by weight of the organic framework.

[0123] According to an embodiment of the present invention, the ion exchange membrane may be formed into a film by a certain process, and has an advantage of being able to be produced as a free-standing film that has excellent flexibility and may be produced into a large area. In this case, a thickness of the ion exchange membrane may be 0.1 to 100 μm, 1 to 50 μm, 1 to 1,000 nm, or 10 to 500 nm, and may be easily controlled according to the field to be applied.

[0124] According to an embodiment of the present invention, a current of the ion exchange membrane may be 1 μA or more, 3 μA or more, 5 μA or more, 7 μA or more, or 10 μA or more, and 100 μA or less, when a voltage is 1.5 V in 0.01 M NaCl in an ion conductivity test described below.

[0125] According to an embodiment of the present invention, a power density of the ion exchange membrane may be 1 W / m2or more, 2 W / m2or more, 3 W / m2or more, 4 W / m2or more, or 5 W / m2or more, and 50 W / m2or less, when measured at a NaCl concentration difference of 0.5 M / 0.01 M in a reverse electrodialysis power generation system test described below.

[0126] The present invention may provide an ion exchange system using the ion exchange membrane and an ion exchange device including the same. The ion exchange membrane can simultaneously achieve excellent ion conductivity and ion selectivity, and can be used to produce both an ion exchange system and an ion exchange device. The ion exchange membrane may be a cation exchange membrane or an anion exchange membrane. In the case of the cation exchange membrane, the inside of the channel is negatively charged, allowing selective permeation of cations and suppression of anion permeation. In the case of the anion exchange membrane, the inside of the channel is positively charged, allowing selective permeation of anions and suppression of cation permeation. The specific structure or conditions for this may utilize conventional or known technologies without limitation.

[0127] The present invention may provide an electrochemical device including the ion exchange membrane. The electrochemical device means any device or apparatus that performs an electrochemical reaction, and may include a secondary battery, a fuel cell, a solar cell, a power generation device, or any capacitor such as a supercapacitor device. The electrochemical device including the ion exchange membrane may exhibit more excellent properties than conventional technologies.

[0128] The present invention may be used in a reverse electrodialysis power generation system including the ion exchange membrane, and a reverse electrodialysis power generation device, a fuel cell, a secondary battery, or the like including the same. The ion exchange membrane according to an embodiment may exhibit high ion conductivity and ion selectivity with excellent stability through changes in physical channel size, surface charge, and hydrophilic / hydrophobic properties. Specifically, reverse electrodialysis, one of the salinity gradient power generation methods, applies the ion exchange membrane to a new and renewable energy technology with excellent potential to directly produce electrical energy through selective permeation of cations or anions by utilizing a difference in concentration between seawater and freshwater. This technology exhibits excellent power generation performance, and industrial water or acidic wastewater can be used instead of freshwater for reverse electrodialysis power generation, as the ion exchange membrane is structurally stable due to strong covalent bonding. Therefore, it is possible to efficiently reduce water resource treatment and power generation costs in an environmentally friendly manner. In addition, the reverse electrodialysis power generation system and the reverse electrodialysis power generation device including the same may use a structure of a conventional or known device without limitation.

[0129] In addition, the ion exchange membrane according to an embodiment may be used as a membrane for a secondary battery using its cation selective properties. When the ion exchange membrane is used as a membrane for a lithium-ion battery, a charging and discharging speed may be improved through a high theoretical lithium transfer number and ionic conductivity, and when the ion exchange membrane is used as a lithium-sulfur battery membrane, permeation of polysulfides may be suppressed and lithium may be selectively permeated through physical channel size and electrostatic effects, which may significantly improve the battery performance. Furthermore, when the ion exchange membrane is used as a membrane for a fuel cell, high conductivity of protons (H+) may be maintained for a long period of time with excellent electrochemical and acidic stability, such that power generation efficiency may be improved.

[0130] The present invention may provide a method of producing the ion exchange membrane, the method including producing ion channel units including covalent organic frameworks and then performing a post-treatment on the ion channel units. Here, as a method of synthesizing the covalent organic frameworks, a conventional or known method may be used, and for example, a membrane may be formed by producing ion channel units in which covalent organic frameworks containing the repeating unit of Chemical Formula 1, 2, or 3 are arranged in layers by subjecting an amine-based precursor and an aldehyde-based precursor to an imine bond reaction. In this case, as the synthetic reaction, interfacial polymerization may be used, but is not limited thereto.

[0131] Subsequently, the post-treatment may be an alkaline treatment, and the imine bond of the organic framework may be hydrolyzed through the alkaline treatment. An alkaline solution used in the case may be any one selected from potassium hydroxide, sodium hydroxide, and sodium hydride. A concentration of the alkaline solution may be 0.01 to 5 M, 0.05 to 3 M, 0.1 to 1 M, or 0.1 to 0.7 M, and in addition, a performance time of the alkaline treatment may be 10 minutes to 4 hours, 10 minutes to 2 hours, or 20 minutes to 1 hour. The degree of hydrolysis may be controlled according to the concentration or the performance time, and therefore, the concentration of the base solution or the performance time of the alkaline treatment may be easily controlled according to a target degree of hydrolysis.

[0132] The present invention may provide another method for producing the ion exchange membrane, which includes 3D printing a monomer composition. The monomer composition may include monomers for an organic framework, a catalyst and a solvent. Specifically, the method may include dissolving monomers for an organic framework and a catalyst in a solvent to prepare a monomer composition, and performing 3D printing on the monomer composition. In the performing of the 3D printing, crystallinity may be secured through temperature control, and a temperature range may be easily controlled according to the type of monomers and a catalyst.

[0133] As a non-limiting example of a monomer for a covalent organic framework (COF), 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde, 1,3,5-triformylbenzene, benzene-1,4-diboronic acid, 2,6-dihydroxyanthracene-9,10-dione, 2,5-dimethoxyterephthalohydrazide, 4,4'-biphenyldicarboxaldehyde, 3,3',5,5'-tetraaminobiphenyl, tetrakis(4-aminophenyl)methane, triphenylamine-based derivatives, benzene-1,3,5-tricarboxylic acid chloride, pyridine-2,6-dicarboxaldehyde, tris(4-formylphenyl)amine, and the like may be used, but are not limited thereto.

[0134] As a non-limiting example of the solvent, acetonitrile (ACN), ethyl acetate (EA), dichloromethane (DCM), tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), methanol, ethanol, chloroform, 1,4-dioxane, acetone, isopropanol, toluene, mesitylene and the like may be used, but are not limited thereto.

[0135] The method of producing the ion exchange membrane using 3D printing according to an embodiment features a simple and rapid process, ease of production, excellent work efficiency, and high commercialization potential due to the possibility of mass production, which may provide economic advantages.

[0136] Hereinafter, examples of the present invention will be described in detail with reference to the accompanying drawings. However, the examples are provided to enable those skilled in the art to easily implement the present invention, the present invention may be implemented in various forms, and the spirit of the present invention is not necessarily limited to the examples.

[0137] [Production Example 1]

[0138] 1,3,5-Tris(4-aminophenyl)benzene containing an amine group and p-toluene sulfonic acid catalyst were dissolved in a solution in which ultrapure water and acetonitrile were mixed in a volume ratio of 7:3, and 2,5-dihydroxyterephthalaldehyde containing an aldehyde group was dissolved in ethyl acetate, thereby preparing two solutions. The two solutions were subjected to an interfacial polymerization reaction at room temperature for 3 days, and a covalent organic framework film formed on a wall of a beaker was dropped by treating with a 0.1 M NaOH solution and then washed with ethanol, thereby obtaining a COF membrane having a thickness of 200 nm.

[0139] When the COF membrane of Production Example 1 was analyzed by GIWAXS, high crystallinity was observed (FIG. 4A), and successful synthesis of COF was confirmed through a newly formed imine peak in FT-IR analysis (FIG. 4B). FIG. 5A illustrates a pore distribution curve of the COF membrane of Production Example 1 according to BET analysis. Through this, it was confirmed that the COF membrane of Production Example 1 had a constant pore size of several nanometers.

[0140] [Production Example 2]

[0141] 1,3,5-Tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde were dissolved in dichloromethane, and a p-toluene sulfonic acid catalyst was dissolved in ultrapure water, thereby preparing two solutions. The two solutions were subjected to an interfacial polymerization reaction at room temperature for 5 days to obtain a COF membrane (COF_Bare) having a thickness of 200 to 300 nm according to Production Example 2. When the COF membrane of Production Example 2 was analyzed by GIWAXS, high crystallinity similar to that in Production Example 1 was exhibited, and the presence of imine bonds was confirmed in FT-IR analysis.

[0142] [Example 1]

[0143] Only one side of the COF membrane of Production Example 1 was subjected to a strong alkaline treatment with a NaOH solution (concentration: 0.5 M NaOH) at room temperature for 1 hour. In the alkaline treatment method, the synthesized COF membrane was placed on a polystyrene substrate and dried sufficiently, and then, the COF membrane was placed in contact with a 0.5 M NaOH solution so that the imine bonds were hydrolyzed only on one side of the membrane. Specifically, when the COF membrane is placed on a polystyrene substrate and then dried for a sufficient period of time, only one side of the COF membrane may be subjected to an alkaline treatment due to a hydrophobic interaction between the benzene groups of polystyrene and the benzene groups of COF. After the treatment was completed, the membrane was dried to produce an ion exchange membrane of A-COF-1 according to Example 1.

[0144] It was confirmed through GIWAXS analysis that the organic framework of the membrane was well maintained even after the alkaline treatment (FIG. 6A), and it was confirmed through FT-IR analysis that the hydrolysis reaction occurred successfully as the amine and aldehyde functional group peaks appeared again after the alkaline treatment (FIG. 6B). In addition, it was confirmed that the membrane was hydrophilized as the hydrolysis occurred due to the alkaline treatment and the contact angle value of the membrane decreased (FIG. 6C).

[0145] [Example 2]

[0146] In Example 1, a treatment was performed with a NaOH solution (concentration: 0.5 M) for 1 hour, followed by an additional treatment with a relatively weak NaOH solution (concentration :0.1 M) for 1 hour. Finally, an ion exchange membrane of A-COF-2 according to Example 2 was produced.

[0147] FIG. 5B illustrates a pore distribution curve of the ion exchange membrane (A-COF-2) according to Example 2 obtained by BET analysis. Through this, it was confirmed that a portion of the structure in the ion exchange membrane according to Example 2 was hydrolyzed by the alkaline treatment, and a certain number of nanometer-sized pores of the COF membrane according to Production Example 1 were decomposed; thus, additional pores were formed.

[0148] [Example 3]

[0149] The same procedures as that of Example 1 was performed, except that an alkaline treatment was performed with a NaOH solution (concentration: 0.5 M NaOH) at room temperature for 3 hours, and finally, an ion exchange membrane of A-COF-3 according to Example 3 was produced.

[0150] As a result of analyzing X-ray photoelectron spectroscope (XPS) depth profiles of the membranes of Examples 1 to 3, in Production Example 1, a ratio of N=C / N-H in N 1s spectra remained consistently high. In Example 1, however, the ratio decreased at the surface, and as the etching step was progressed, the ratio became similar to that of Production Example 1 toward the bottom surface. Based on the fact that when hydrolysis occurs in an imine bond-based COF, the N=C ratio decreases and the N-H ratio increases in the N 1s spectra, it was confirmed from the above results that the ion exchange membrane according to Example 1 is an asymmetric ion exchange membrane in which hydrolysis occurs gradually from the ion inlet, leading to gradual opening of the pores.

[0151] In addition, in Example 2, a more distinct decrease in the ratio at the surface was confirmed compared to Example 1, and it was confirmed that the asymmetry was well implemented in the ion exchange membrane. In Example 3, a consistently low ratio was observed when the etching step was progressed from the surface, it was confirmed that the pores opened uniformly, and hydrolysis occurred throughout the channels.

[0152] [Example 4]

[0153] The COF membrane of Production Example 2 was entirely subjected to a strong alkaline treatment using a NaOH solution (concentration: 0.5 M) at room temperature for one and a half hours, and the treated COF membrane was defined as COF_A. At this time, the COF_Bare membrane of Production Example 2 was completely immersed in the NaOH solution and both sides of the membrane were treated. It was confirmed that the membrane was hydrophilized as the hydrolysis occurred in the framework due to the alkaline treatment and the contact angle value of the membrane decreased (FIG. 8C).

[0154] As a result of analyzing XPS depth profiles of the membranes of Production Example 2 and Example 3 based on N 1s spectra, the N=C ratio in the entire N 1s was 83% in Production Example 2 and 53% in Example 3, and thus, it was confirmed that, in Example 3, hydrolysis occurred throughout the channels, and the COF diameter of Example 3 increased overall compared to Production Example 2.

[0155] [Example 5]

[0156] Only one side of the COF_A membrane of Example 4 was treated with a polyacrylic acid (weight average molecular weight (Mw): 100,000 g / mol) polymer solution (5 mM) at room temperature for 3 hours to finally produce COF_L according to Example 5. At this time, a polymer having a weight average molecular weight (Mw) of 100,000 g / mol was named PAA_L. At this time, in order to perform the polymer treatment on only one side of the membrane, the membrane was placed between cells of an H-cell and the polymer solution was injected into only one cell. At this time, the H-Cell is configured by connecting two glass wares as illustrated in FIG. 11, and the volume capacity of each glass ware is 8 mL. It was confirmed through GIWAXS analysis (FIG. 8A) that the organic framework of the membrane was well maintained even after the alkaline treatment and the polymer reaction, and the presence of binding between COF_A and the polymer (PAA_L) was confirmed through TGA analysis (FIG. 8B). In addition, it was confirmed that, as the polymer (PAA_L) was additionally introduced into COF_A, the contact angle value of the polymer-treated side decreased compared to the untreated side, and thus, the membrane was hydrophilized (FIG. 8C), and stronger surface charge characteristics were exhibited due to the introduction of a polymer having strong charge characteristics (FIG. 8D).

[0157] [Example 6]

[0158] The same procedure as that of Example 5 was performed, except that a polymer having a Mw of 2,000 g / mol was used instead of the PAA polymer having a Mw of 100,000 g / mol, and finally, an ion exchange membrane of COF_S according to Example 6 was produced. At this time, a polymer having a Mw of 2,000 g / mol was named PAA_S. As in Example 5, the crystallinity of the organic framework was confirmed through GIWAXS analysis (FIG. 8A), and the presence of binding between COF_A and the polymer (PAA_S) was confirmed through TGA analysis (FIG. 8B). In addition, it was confirmed that, as the polymer (PAA_S) was additionally introduced into COF_A, the contact angle value of the side treated with the polymer decreased compared to the side not treated with the polymer, and thus, the membrane was hydrophilized (FIG. 8C), and stronger surface charge characteristics were exhibited due to the introduction of a polymer having strong charge characteristics (FIG. 8D).

[0159] [Evaluation Example 1] Ion Conductivity Evaluation

[0160] The membrane was placed on the self-produced H-Cell as illustrated in FIG. 11, and 0.01 M NaCl was added to both sides, and then, an external voltage was applied and then a change was observed. The resulting current-voltage graph is illustrated in FIG. 9. 5 mL of NaCl electrolyte was added to each of side of the H-cell and an external voltage was applied in potentioStat with an Ag / AgCl electrode. The resulting current was measured to evaluate ion conductivity.

[0161] Specifically, the graph of Production Example 1, which is a comparative example, is illustrated in FIG. 9A, the graphs of Examples 1 to 3 are illustrated in FIG. 9B, and the graphs of Production Example 2 and Examples 4 to 6 are illustrated in FIG. 9C.

[0162] Comparing FIGS. 9A, 9B, and 9C, it was confirmed that the ionic conductivity of each of the COF membranes of Examples 1 to 6 was remarkably increased. This was because the internal membrane resistance was significantly reduced by the hydrophilic channels, and in particular, in the case of A-COF-2 in FIG. 9B, when hydrophobic channels with a limited area for movement of ions were formed at an appropriate ratio, since the electrical double layer (EDL) effect due to the Debye length, which is controlled by the ion concentration, was remarkably exhibited, a larger concentration gradient was implemented, and thus, an ion permeation behavior different from that of the symmetric membrane was formed, showing the highest ion conductivity among the COF membranes.

[0163] Referring to FIG. 9C, in the case of Examples 5 and 6, when the polymer is treated, asymmetry is exhibited on the both sides of the membrane. Due to the strong charge characteristics and hydrophilicity of the polymer, ions accumulate on the side where the polymer is present, increasing the ion selectivity of the membrane; thus, higher current and power density values may be obtained compared to when the channels exhibit uniform characteristics as a whole, as in Example 4. In this case, the degree of asymmetry imparted to the channels may vary depending on the length of the polymer.

[0164] [Evaluation Example 2] Reverse Electrodialysis Power Generation System Evaluation

[0165] The membrane was placed in the same H-Cell as in the ion conductivity evaluation, 5 ml of 0.5 M NaCl was added to one side and 0.01 M NaCl was added to the other side, and a change in power density was observed using the P = I2R formula based on the measured current values according to the external resistance using an Ag / AgCl electrode. This is an operating system similar to a reverse electrodialysis power generation system. The resulting graph is illustrated in FIG. 10. Specifically, the power density graphs of the ion exchange membranes according to Examples 1 to 3 are illustrated in FIG. 10A, and the power density graphs of the ion exchange membranes according to Examples 4 to 6 are illustrated in FIG. 10B.

[0166] In particular, in FIG. 10B, in the case of COF_L in Example 5, after the alkaline treatment was performed for one and a half hours, the reaction was carried out using a polymer solution with appropriate size and concentration, and therefore, the hydrophilic properties and surface charge of the membrane were strengthened in the area where the polymer was introduced, and the asymmetry was exhibited in the channels, facilitating the movement of ions. As a result, the ion selectivity of the membrane was improved by the polymer introduction, which resulted in excellent power density performance in reverse electrodialysis power generation.

[0167] Hereinabove, although the present invention has been described by limited embodiments in the present invention, the embodiments have been provided only for assisting in the entire understanding of the present invention. Therefore, the present invention is not limited to the embodiments. Various modifications and changes may be made by those skilled in the art to which the present invention pertains from this description.

[0168] Therefore, the spirit of the present invention should not be limited to the described embodiments, but the claims and all modifications equal or equivalent to the claims are intended to fall within the spirit of the present invention.

Claims

1.An ion exchange membrane comprising ion channel units,wherein the ion channel unit has a structure in which a plurality of unit covalent organic frameworks is formed to be spaced apart in layers,the organic framework has a pore for an ion channel formed on the inside,ions move through the pores from an ion inlet of the ion channel unit toward an ion outlet of the ion channel unit, anda diameter of an outer ion channel of the ion inlet (Dinput) and a diameter of an outer ion channel of the ion outlet (Doutput) of the ion channel unit are different (Dinput≠ Doutput).2.The ion exchange membrane of claim 1, wherein a distance between the organic framework and a unit covalent organic framework located to be adjacent to and spaced apart from the organic framework is 1 to 5 Å.3.The ion exchange membrane of claim 1, wherein an outer organic framework of the ion inlet of the ion channel unit is hydrophilic.4.The ion exchange membrane of claim 1, wherein a diameter of the outermost organic framework of the ion inlet (Dinput_COF_1st) of the ion channel unit is 3 to 25 nm.5.The ion exchange membrane of claim 1, wherein the organic framework contains a repeating unit represented by the following Chemical Formula 1:[Chemical Formula 1]in Chemical Formula 1,A is a monocyclic or polycyclic compound,-X- is a divalent linking group, andR1to R4are each independently -H, C1-3 alkyl, -OH, -COOH, -COOM, -SO2M, -SO3M, -PO3M, or -PO4M, where M is a cationic metal.6.The ion exchange membrane of claim 5, wherein, in Chemical Formula 1, -X- is any one or a combination of two or more selected from the group consisting of a direct bond, -NH-, -N=N-, -N=C-, =CH-NH-, -NH-C(=O)-, -CH=CH-NH-, -OC(=O)-NH-, -CH2-C(=O)O-NH-, and -C(=O)NH-N=CH-.7.The ion exchange membrane of claim 5, wherein Chemical Formula 1 is represented by the following Chemical Formula 2:[Chemical Formula 2]in Chemical Formula 2,R1to R4are each independently -H, C1-3 alkyl, -OH, or -COOH.8.The ion exchange membrane of claim 5, wherein the organic framework has a polygonal structure containing the repeating unit of Chemical Formula 1 on one side and having a pore for an ion channel formed on the inside.9.The ion exchange membrane of claim 1, wherein the organic framework contains a repeating unit represented by the following Chemical Formula 3:[Chemical Formula 3]in Chemical Formula 3,R1to R4are each independently -H, C1-3 alkyl, -OH, or -COOH.10.The ion exchange membrane of claim 1, wherein a diameter of an outer organic framework of the ion inlet (Dinput_COF) is larger than a diameter of an outer organic framework of the ion outlet (Doutput_COF) (Dinput_COF> Doutput_COF).11.The ion exchange membrane of claim 10, wherein the diameter of the outer organic framework of the ion inlet (Dinput_COF) is larger than a diameter of an inner organic framework (Dinner_COF) of the ion channel unit (Dinput_COF> Dinner_COF).12.The ion exchange membrane of claim 10, wherein the diameter of the outer organic framework of the ion outlet (Doutput_COF) is equal to or smaller than a diameter of an inner organic framework (Dinner_COF) of the ion channel unit (Doutput_COF≤ Dinner_COF).13.The ion exchange membrane of claim 1, wherein the diameter of the outer ion channel of the ion inlet (Dinput) is smaller than the diameter of the outer ion channel of the ion outlet (Doutput) (Dinput< Doutput).14.The ion exchange membrane of claim 13, wherein the diameter of the outer ion channel of the ion inlet (Dinput) is smaller than a diameter of an inner ion channel of the ion channel unit (Dinner) (Dinput< Dinner).15.The ion exchange membrane of claim 13, wherein the diameter of the outer ion channel of the ion outlet (Doutput) is equal to or larger than a diameter of an inner ion channel of the ion channel unit (Dinner) (Doutput≥ Dinner).16.The ion exchange membrane of claim 1, wherein the ion channel unit further includes an ionic polymer.17.The ion exchange membrane of claim 16, wherein an ion channel of the ion inlet is more hydrophilic than an ion channel of the ion outlet.18.The ion exchange membrane of claim 16, wherein an ion channel of the ion inlet is more anionic than an ion channel of the ion outlet.19.An ion exchange system using the ion exchange membrane of any one of claims 1 to 18.20.An electrochemical device using the ion exchange membrane of any one of claims 1 to 18.21.The electrochemical device of claim 20, wherein the electrochemical device is any one selected from a reverse electrodialysis power generation device, a fuel cell, and a secondary battery.22.A method of producing an ion exchange membrane, the method comprising performing 3D printing on a monomer composition including monomers for an organic framework, a catalyst, and a solvent.

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