Proton conductor, method for producing same, and electrochemical cell

Abstract

Disclosed is a proton conductor which includes a metal organic structure that has proton conductivity, a resin, and a dispersant. The metal organic structure has metal ions and a crosslinkable ligand that is coordinated to the metal ions. The metal organic structure contains molecules or ions, which have proton conductivity. It is preferable that the dispersant is a polymer dispersant which includes a resin affinity unit and a polar unit that has a polar group. It is also preferable that the dispersant contains a polymer dispersant which has a comb-shaped structure and / or a block polymer structure.

Description

Proton conductor, method for producing the same, and electrochemical cell

[0001] The present invention relates to a proton conductor and a method for producing the same. The present invention also relates to an electrochemical cell.

[0002] Conventionally, electrochemical cells such as polymer electrolyte fuel cells and water electrolysis devices have been known. ２ As part of efforts to prevent global warming by reducing CO2 emissions, electrochemical cells with higher energy efficiency have been attracting attention. One method for improving the energy efficiency of electrochemical cells is to increase the proton conductivity of the proton conductor used as the electrolyte membrane. In particular, proton conductors with high proton conductivity at temperatures above 100°C are required to be applicable to chemical reactions requiring higher temperature conditions. However, sulfonated tetrafluoroethylene, which is widely used in this field, has a problem in that the proton conduction pathways shrink at temperatures above 100°C, significantly reducing its conductivity.

[0003] Various attempts have been made to improve the proton conductivity of proton conductors at high temperatures of 100°C or higher. For example, Patent Document 1 describes a coordination polymer containing metal ions, oxoanions, and proton-coordinating molecules. This document states that such a coordination polymer has high ionic conductivity even at high temperatures. Patent Document 2 describes a conductive membrane containing a proton conductor containing metal ions, oxoanions, and proton-coordinating molecules, and a resin filler containing an engineering plastic. This document also states that such a conductive membrane has high ionic conductivity even at high temperatures. Patent Document 3 describes a proton conductor composed of a coordination polymer containing chromium ions, Cr-MIL-101, and phosphoric acid. This document also states that such a proton conductor has excellent ionic conductivity and structural stability even at high temperatures.

[0004] US Patent Application Publication No. 2014 / 0011103 JP 2016-004621 A US Patent Application Publication No. 2019 / 0386327

[0005] As described above, although various proton conductors have been proposed, none of them have sufficient proton conductivity at high temperatures, and there is room for improvement in application to reactions requiring reaction temperatures of 100° C. or higher. Therefore, an object of the present invention is to provide a proton conductor having high proton conductivity at high temperatures of 100° C. or higher.

[0006] The present invention provides a proton conductor comprising a metal organic framework having proton conductivity, a resin, and a dispersant, wherein the metal organic framework has metal ions and bridging ligands coordinated to the metal ions, and the metal organic framework includes molecules or ions having proton conductivity.

[0007] The present invention also provides a method for producing a proton conductor, which comprises casting a mixed liquid containing a resin, a metal organic framework having proton conductivity, a dispersant, and a solvent to form a wet membrane, and removing the solvent from the wet membrane, wherein the metal organic framework has metal ions and bridging ligands coordinated to the metal ions, and the metal organic framework includes molecules or ions having proton conductivity.

[0008] The present invention will be described below based on preferred embodiments. The proton conductor of the present invention comprises a metal organic framework (hereinafter also referred to as "MOF"), a resin, and a dispersant. The MOF is a metal complex having metal ions and bridging ligands coordinated to the metal ions, and has proton conductivity. The resin is used to improve the heat resistance of the MOF. Details of the MOF and the resin will be described later. The proton conductor of the present invention preferably comprises a MOF and a dispersant dispersed in a matrix made of a resin. The proton conductor having such a form can further enhance the effects of the resin and the dispersant described later.

[0009] First, the dispersant contained in the proton conductor of the present invention will be described. As a result of the inventors' investigations, it was found that proton conductors consisting only of MOFs and resins have room for improvement in proton conductivity, particularly at high temperatures of 100°C or higher. However, by further incorporating a dispersant, it was found that the proton conductivity of the proton conductor at high temperatures can be improved. The reason for this is unclear, but the inventors speculate as follows. Generally, in proton conductors, it is necessary for particles consisting of proton-conducting MOFs (hereinafter simply referred to as "MOF particles") to be connected to each other in order to exhibit proton conductivity. However, in proton conductors that do not contain a dispersant, the dispersibility of the MOF particles dispersed in the resin is insufficient, resulting in uneven distribution of the MOF particles. This results in poor connection between the MOF particles and reduced proton conductivity. On the other hand, the proton conductor of the present invention contains a dispersant, which improves the dispersibility of the MOF particles and allows the MOF particles to be more uniformly distributed within the proton conductor. This increases the connectivity between the MOF particles and improves the proton conductivity of the proton conductor.

[0010] The dispersant is not particularly limited as long as it can achieve the effects of the present invention, and known dispersants can be used. In particular, from the viewpoint of ease of handling in a suitable method for producing the proton conductor of the present invention, which will be described later, the dispersant is preferably a liquid at room temperature (25°C). However, when the dispersant is dissolved in a solvent, which will be described later, the dispersant may be a solid at room temperature. To more reliably obtain the above-described effects in the temperature range in which the proton conductor is used, the dispersant is preferably a liquid at 0°C or higher and 400°C or lower, more preferably 20°C or higher and 300°C or lower, and even more preferably 100°C or higher and 250°C or lower, under atmospheric pressure (1 atm). Furthermore, it is preferable that the dispersant does not substantially decompose within the above temperature range.

[0011] Preferred dispersants include, for example, low-molecular-weight dispersants (surfactants) and polymer dispersants. Examples of surfactants include anionic, cationic, amphoteric, and nonionic surfactants. As the polymer dispersant, a dispersant having a weight-average molecular weight of preferably 500 to 100,000, more preferably 700 to 80,000, and even more preferably 900 to 65,000 can be used. In particular, from the viewpoint of preventing the proton conductivity of the MOF from being inhibited due to complete coverage of the MOF surface or complete blocking of the pores in the MOF, it is preferable that the dispersant has a large molecular weight, i.e., a polymer dispersant.

[0012] The dispersant preferably contains a resin affinity unit and a polar unit having a polar group. By using such a dispersant, the MOF particles are bonded to the polar unit, while the resin affinity unit enhances the dispersibility of the MOF particles bonded to the dispersant, thereby effectively improving the dispersibility of the MOF particles. The resin affinity unit has a structure that enhances affinity with the resin. To enhance affinity with the resin, the resin affinity unit preferably has hydrophobic properties. Examples of the resin affinity unit include polyalkylene glycol structures such as polyethylene glycol structures, polypropylene glycol structures, and polybutylene glycol structures, as well as polyurethane structures, polyester structures, unsaturated polyamide structures, phosphate ester structures, polycarboxylic acid structures and salts thereof, polyalkylamine structures and salts thereof, polycarboxylic acid ester structures, hydroxyl group-containing polycarboxylic acid ester structures, polysiloxane structures, and modified polyacrylate structures. From the viewpoint of enhancing the bonding strength with the MOF particles, the polar unit preferably has one or more polar groups selected from the group consisting of carboxy groups, amino groups, sulfo groups, ester groups, ether groups, ketone groups, and hydroxyl groups. The polar group may be ionized, for example, a carboxylate formed by ionizing a carboxy group.

[0013] The dispersant preferably has a comb structure and / or a block polymer structure. A comb structure refers to a structure including a main chain and molecular chains arranged in a comb shape relative to the main chain. An example of a comb structure is a structure including a main chain including polar units and resin affinity units arranged in a comb shape relative to the main chain. An example of a dispersant having a block polymer structure is a structure in which a structure including polar units and a structure including resin affinity units are arranged in separate blocks.

[0014] Specific examples of dispersants that can be preferably used in the present invention include polymeric polycarboxylic acid dispersants, polymeric amine dispersants, and polymeric polyester dispersants.

[0015] Commercially available dispersants can also be used. Examples of such dispersants include Marialim FA-1150AM-08 (manufactured by NOF Corporation), Marialim AKM-0531 (manufactured by NOF Corporation), S-reem AD-3172M (manufactured by NOF Corporation), S-reem C-2095I (manufactured by NOF Corporation), S-reem C-2093I (manufactured by NOF Corporation), S-reem 221P (manufactured by NOF Corporation), Hinoact T-9100 (manufactured by Kawaken Fine Chemicals), Hinoact KF-1300M (manufactured by Kawaken Fine Chemicals), Ajisper PN411 (manufactured by Ajinomoto Fine-Techno Co., Ltd.), and Ajisper PN111 (manufactured by Ajinomoto Fine-Techno Co., Ltd.).

[0016] The dispersant may or may not have proton conductivity.

[0017] The proton conductor of the present invention preferably contains 0.3% by mass or more and 40% by mass or less of a dispersant, more preferably 0.5% by mass or more and 30% by mass or less, even more preferably 0.6% by mass or more and 20% by mass or less, and particularly preferably 0.8% by mass or more and 20% by mass or less. By setting the dispersant content to 0.3% by mass or more, the effect of the dispersant in increasing the proton conductivity of the proton conductor can be more reliably obtained. Furthermore, by setting the dispersant content to 40% by mass or less, the content of proton-conductive MOF can be sufficiently ensured, thereby increasing the proton conductivity of the proton conductor.

[0018] From the same viewpoint, the mass ratio of the dispersant to the MOF (dispersant / MOF) contained in the proton conductor is preferably 0.020 or more and 1.0 or less, more preferably 0.040 or more and 0.50 or less, even more preferably 0.070 or more and 0.30 or less, and particularly preferably 0.070 or more and 0.20 or less.

[0019] Next, the MOF contained in the proton conductor of the present invention will be described. As described above, the MOF is a metal complex having a metal ion and a bridging ligand coordinated to the metal ion. As the MOF, any MOF commonly used in this field can be used without particular limitation, as long as it has proton conductivity.

[0020] As used herein, the phrase "having proton conductivity" means that the MOF conducts protons or oxonium ions when a potential gradient is applied to the MOF.

[0021] The metal ions contained in the MOF are not particularly limited, but are preferably one or more selected from the group consisting of zinc ions, chromium ions, aluminum ions, magnesium ions, manganese ions, iron ions, cobalt ions, nickel ions, copper ions, yttrium ions, and zirconium ions, and more preferably one or more selected from the group consisting of zinc ions, chromium ions, aluminum ions, iron ions, cobalt ions, nickel ions, copper ions, and zirconium ions. By using such metal ions, an MOF with excellent stability at high temperatures of 100°C or higher can be obtained.

[0022] The bridging ligand contained in the MOF is not particularly limited, but from the viewpoint of further enhancing the chemical stability of the MOF, the bridging ligand preferably contains a multidentate ligand having two or more coordination sites capable of coordinating with a metal ion. Examples of the bridging ligand include phosphoric acid, polycarboxylic acid, amino acid, polyamine, nitrogen-containing heteroaromatic compound, and anions thereof, as well as oxide ions (O ２－ ) can be preferably used. The term "these anions" refers to anions generated by deprotonation of the acidic functional groups in the crosslinkable ligands exemplified above, and when there are multiple acidic protons in the ligand, includes anions generated by deprotonation of only some of the protons and anions generated by deprotonation of all of the protons. For example, the anion of phosphate refers to phosphate ion, hydrogen phosphate ion, and dihydrogen phosphate ion.

[0023] The polycarboxylic acid refers to a compound having two or more carboxy groups, and examples thereof include dicarboxylic acids, tricarboxylic acids, and tetracarboxylic acids. Examples of dicarboxylic acids include oxalic acid, butanedioic acid, (E)-butenedioic acid, benzene-1,4-dicarboxylic acid, benzene-1,3-dicarboxylic acid, 2-bromo-1,4-benzenedicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 2,5-dihydroxy-1,4-benzenedicarboxylic acid, (2E,4E)-hexa-2,4-dienedioic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,4-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, pyrene-2,7-dicarboxylic acid, 4,5,9,10-tetrahydropyrene-2,7-dicarboxylic acid, and 1H-pyrazole-3,5-dicarboxylic acid. Examples of tricarboxylic acids include benzene-1,3,5-tricarboxylic acid, biphenyl-3,4',5-tricarboxylic acid, and 1,3,5-tris(4-carboxyphenyl)benzene. Examples of tetracarboxylic acids include biphenyl-3,3',5,5'-tetracarboxylic acid.

[0024] The amino acid is a compound containing at least one amino group and at least one carboxy group in the molecule. In this specification, the term "amino group" refers to a primary amino group (-NH ２ ), secondary amino group (-NHR １ ) and a tertiary amino group (—NR １ R ２ Examples of amino acids include 2-amino-1,4-benzenedicarboxylic acid, aspartic acid, and glutamic acid.

[0025] The polyamine refers to a compound having two or more amino groups, and examples thereof include diamine, triamine, and tetraamine. Examples of diamines include piperazine and 1,4-diazabicyclo[2.2.2]octane. Examples of triamines include biphenyl-3,4',5-triamine and 1,3,5-tris(4-aminophenyl)benzene. Examples of tetracarboxylic acids include biphenyl-3,3',5,5'-tetraamine.

[0026] The nitrogen-containing heteroaromatic compound is a compound having at least one nitrogen atom on its heteroaromatic ring, and the nitrogen atom can coordinate to a metal ion via its unshared electron pair. Examples of the nitrogen-containing heteroaromatic compound include (i) a compound having two or more nitrogen atoms on a heteroaromatic ring, or (ii) a compound having one or more nitrogen atoms on a heteroaromatic ring and one or more functional groups capable of coordinating to a metal ion, such as a carboxy group and an amino group. The two or more nitrogen atoms contained in the compound (i) may be present on a single heteroaromatic ring, or may be present separately on two or more different heteroaromatic rings. Examples of the compound (i) include adenine, 4,4'-bipyridine, pyrimidine, pyrazine, 1,2,4-triazole, 1,3,5-triazine, imidazole, 5,6-dimethylbenzimidazole, 1H-benzimidazole, and 2-methyl-1H-imidazole. Examples of the compound (ii) include pyridine-4-carboxylic acid and pyridine-3-carboxylic acid.

[0027] The crosslinking ligand is not limited to those exemplified above. For example, the crosslinking ligand may be a derivative of the compound exemplified above. In this specification, the term "derivative" refers to a compound in which a part of the chemical structure is replaced with another atom or atomic group, and examples thereof include a compound in which one or more hydrogen atoms in the chemical structure are replaced with a hydrocarbon group having 1 to 4 carbon atoms. Specific examples of derivatives of imidazole include 2-methylimidazole, 2-ethylimidazole, histamine, and histidine.

[0028] The MOF may have a non-bridging ligand. A non-bridging ligand refers to a ligand that is coordinated to only one metal ion in the MOF. The MOF may also have components other than the metal ion and the ligand, such as a non-coordinating counter ion. A non-coordinating counter ion refers to a counter ion that does not form a direct coordinate bond with the metal ion. From the viewpoint of improving the proton conductivity of the MOF, when the MOF has a non-bridging ligand, it is preferable to use a molecule or ion having proton conductivity, as described below, as the non-bridging ligand. From the same viewpoint, when the MOF has a non-coordinating counter ion, it is preferable to use an ion having proton conductivity, as described below, as the non-coordinating counter ion.

[0029] The MOF preferably contains a molecule or ion having proton conductivity. As used herein, the term "molecule or ion having proton conductivity" refers to a molecule or ion that can conduct protons or oxonium ions when a potential gradient is applied to the molecule or ion.

[0030] The phrase "MOF contains molecules or ions having proton conductivity" can mean any of the following: (1) A form in which one or more of the bridging ligands, non-bridging ligands, and non-coordinating counter ions constituting the MOF correspond to molecules or ions having proton conductivity; (2) A form in which the MOF forms pores, and the pores are filled with molecules or ions having proton conductivity.

[0031] In the form (2), the MOF before being filled with proton-conducting molecules or ions does not necessarily have to have proton conductivity. Furthermore, in the form (2), the proton-conducting molecules or ions may be present so as to fill all of the pores of the MOF, or may be present in only some of the pores of the MOF, as long as the MOF has proton conductivity. In this specification, depending on the context, the term "MOF" may refer to a metal complex whose pores are filled with proton-conducting molecules or ions, or may refer to a metal complex before its pores are filled with proton-conducting molecules or ions.

[0032] The MOFs of the present invention may include one or more molecules or ions that have proton conductivity.

[0033] Examples of molecules having proton conductivity include those exemplified above as crosslinking ligands (excluding those in which all coordination sites are occupied by metal ions), as well as amines such as primary amines, secondary amines, and tertiary amines. Primary amines include, for example, alkylamines such as methylamine, ethylamine, and propylamine; and aromatic primary amines such as aniline and toluidine. Secondary amines include, for example, dialkylamines such as dimethylamine, diethylamine, dipropylamine, pyrrolidine, piperidine, and morpholine; and aromatic secondary amines such as N-methylaniline and N-methyltoluidine. Tertiary amines include, for example, trialkylamines such as trimethylamine, triethylamine, 1-alkylpyrrolidine (e.g., 1-methylpyrrolidine), 1-alkylpiperidine (e.g., 1-methylpiperidine), and 4-alkylmorpholine (e.g., 4-methylmorpholine); and aromatic tertiary amines such as N,N-dimethylaniline and N,N-dimethyltoluidine.

[0034] Examples of proton-conductive ions include proton-conductive cations and proton-conductive anions. Examples of proton-conductive cations include protonated forms of the various amines and nitrogen-containing heteroaromatic compounds exemplified above; and quaternary ammonium salts such as tetraalkylammonium salts. Examples of proton-conductive anions include anions of the compounds exemplified above as bridging ligands (excluding those in which all coordination sites are occupied by metal ions), sulfate ions, and hydrogen sulfate ions. Among these, phosphate ions, hydrogen phosphate ions, and dihydrogen phosphate ions are preferred due to their high chemical stability against protons. Derivatives of these ions can also be used as proton-conductive molecules or ions. Regardless of which molecule or ion is used as the proton-conductive molecule or ion, the number of carbon atoms is preferably 0 to 30, more preferably 0 to 25, and even more preferably 0 to 20.

[0035] From the viewpoint of proton conductivity, particularly preferred molecules or ions having proton conductivity include one or more selected from the group consisting of phosphate ion, hydrogen phosphate ion, dihydrogen phosphate ion, imidazole, imidazolium ion, benzimidazole, benzimidazolium ion, pyridine, pyridinium ion, trialkylamine, tetraalkylammonium salt, sulfate ion, hydrogen sulfate ion, and derivatives thereof.

[0036] In the case of the above-mentioned form (1), from the viewpoint of obtaining sufficient proton conductivity, a total of 2 moles or more of molecules or ions having proton conductivity (bridging ligands, non-bridging ligands, or non-coordinating counterions) are preferably contained per mole of metal ion, more preferably 4 moles or more, and even more preferably 5 moles or more. Furthermore, from the viewpoint of facilitating the synthesis of the MOF, it is practical to set the content of molecules or ions having proton conductivity to, for example, 10 moles or less per mole of metal ion. Similarly, in the case of the above-mentioned form (2), from the viewpoint of obtaining sufficient proton conductivity, the content of molecules or ions having proton conductivity in the MOF containing molecules or ions having proton conductivity is preferably 10 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more. Furthermore, considering the pore volume of the MOF, it is practical to set the content of molecules or ions having proton conductivity to 50 mass% or less relative to the MOF containing molecules or ions having proton conductivity.

[0037] The content of the MOF in the proton conductor is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 60% by mass or less. By setting the content of the MOF to 10% by mass or more, the content of the proton-conductive MOF can be sufficiently ensured, thereby obtaining the effect of increasing the proton conductivity of the proton conductor. Furthermore, by setting the content of the MOF to 80% by mass or less, the effect of sufficiently increasing the heat resistance of the proton conductor can be obtained. In the above embodiment (2), the mass of the MOF used to calculate the "MOF content" also includes the mass of the proton-conductive molecules or ions filled in the pores of the MOF.

[0038] Next, the resin contained in the proton conductor of the present invention will be described. The resin has the effect of improving the heat resistance of the MOF that constitutes the proton conductor. There are no particular restrictions on the resin that can be used in the present invention, but from the viewpoint of more reliably obtaining the above-mentioned effects, it is preferable that the resin does not substantially decompose at temperatures of preferably 250°C or less, more preferably 350°C or less, and even more preferably 500°C or less.

[0039] In view of the above, preferred examples of the resin include one or more selected from the group consisting of polyamideimide, polysulfone, polyphenylsulfone, polyvinylidene fluoride, polyimide, polyvinyl butyral, and cellulose ester.

[0040] The content of the resin in the proton conductor is preferably 15% by mass or more and 85% by mass or less, more preferably 20% by mass or more and 75% by mass or less, and even more preferably 30% by mass or more and 65% by mass or less. By setting the content of the resin to 15% by mass or more, the heat resistance of the proton conductor can be sufficiently improved. Furthermore, by setting the content of the resin to 85% by mass or less, the content of the proton-conductive MOF can be sufficiently ensured, thereby improving the proton conductivity of the proton conductor.

[0041] Similarly, from the viewpoint of enhancing the heat resistance and proton conductivity of the proton conductor in a balanced manner, the mass ratio of the MOF to the resin (MOF / resin) in the proton conductor is preferably 0.40 or more and 3.0 or less, more preferably 0.50 or more and 2.0 or less, and even more preferably 0.60 or more and 1.5 or less.

[0042] The proton conductor may contain components other than the MOF, resin, and dispersant, as long as the effects of the present invention are not impaired.

[0043] Although there are no particular limitations on the shape of the proton conductor, when it is used as an electrolyte membrane of an electrochemical cell, for example, it is advantageous to have a membrane shape. In this case, the membrane thickness of the proton conductor is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 300 μm or less, and even more preferably 40 μm or more and 200 μm or less. By setting the membrane thickness of the proton conductor within this range, it is possible to obtain the effect of keeping the resistance low while ensuring flexibility.

[0044] The proton conductor of the present invention can be used as an electrochemical cell by disposing it between an anode and a cathode. Since the proton conductor of the present invention has high proton conductivity at high temperatures, such an electrochemical cell can be suitably used for electrochemical reactions that require high temperatures.

[0045] Next, a preferred method for producing the proton conductor of the present invention will be described. This production method comprises the following steps: (A) preparing a proton-conductive MOF; (B) preparing a mixed solution containing a resin, a proton-conductive MOF, a dispersant, and a solvent; and (C) casting the mixed solution to form a wet membrane and removing the solvent from the wet membrane.

[0046] <Step A> As the MOF, for example, one synthesized by a well-known method or a commercially available product can be used. Furthermore, when the MOF is in the form (2) above, a MOF before being filled with proton-conductive molecules or ions is prepared, and then a step of filling the pores of the MOF with proton-conductive molecules or ions is carried out. Filling can be carried out by either a dry method or a wet method. When filling by a dry method, for example, the MOF and the proton-conductive molecules or ions may be mixed in a mortar. Alternatively, the MOF and the proton-conductive molecules or ions may be mixed using a ball mill, a planetary mixer, a grinder, or the like. Filling can also be carried out by introducing vapor of the proton-conductive molecules or ions into a container containing the MOF at high temperature. From the viewpoint of ease of operation, filling is preferably carried out by a dry method, particularly mortar mixing. Regardless of the method used for filling, filling may be carried out in an air atmosphere or an inert gas atmosphere.

[0047] <Step B> In step B, the resin, MOF, dispersant, and solvent may be mixed in any order. For example, the MOF and resin may be mixed, and then the solvent and dispersant may be added sequentially to prepare a mixed solution. Alternatively, the resin and solvent may be mixed in advance, and then the MOF and dispersant may be added sequentially to prepare a mixed solution. Alternatively, three or more components may be mixed simultaneously.

[0048] The solvent used to prepare the mixed solution may be appropriately selected taking into consideration the solubility of the resin in the solvent, etc., but from the viewpoint of resin solubility, aprotic polar solvents are preferably used. Examples of aprotic polar solvents include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), acetone, and cyclopentanone. These solvents may be used alone or in combination of two or more.

[0049] The content of the solvent is not particularly limited, but by appropriately adjusting the content of the solvent, it is possible to obtain the effects of increasing the fluidity of the mixed liquid to improve moldability, and of increasing the viscosity of the mixed liquid to make it easier to control the film thickness of the proton conductor.

[0050] The resulting mixture may be degassed under reduced pressure, if necessary. In this case, the pressure for the degassing treatment is preferably 0.2 kPa or more and 80 kPa or less, more preferably 5 kPa or more and 30 kPa or less. The degassing treatment can be carried out, for example, at room temperature. The time for the degassing treatment is preferably 15 minutes or more and 2 hours or less, more preferably 30 minutes or more and 1 hour or less.

[0051] <Step C> Once the mixed solution is obtained, it is then cast onto a substrate to form a wet film. Examples of substrates that can be used include glass plates, metal plates, resin plates, and resin sheets. There are no particular limitations on the method for casting the mixed solution; for example, a wet film with a uniform thickness can be easily obtained by using an applicator. Alternatively, a wet film can be obtained by dripping the mixed solution onto the substrate.

[0052] The wet membrane is then dried to remove the solvent and obtain a proton conductor. Drying can be carried out under atmospheric pressure or reduced pressure. Drying is preferably carried out at a temperature below the decomposition temperature of the MOF and resin, and, if the MOF has a melting point, preferably at a temperature below its melting point. More specifically, when drying is carried out under atmospheric pressure, the drying temperature is preferably 100°C to 200°C, more preferably 120°C to 180°C, and even more preferably 130°C to 150°C. The drying time is preferably 15 minutes to 24 hours, more preferably 30 minutes to 12 hours, and even more preferably 1 hour to 8 hours. When drying is carried out under atmospheric pressure, drying can be carried out under an inert gas atmosphere or in the air. There are no particular limitations on the heating means. For example, heating means such as hot air blowing, infrared radiation, and heating in a heating furnace can be used.

[0053] The membrane thickness of the proton conductor can be adjusted, for example, by the following method. When an applicator is used to cast the mixed solution to form a wet membrane, the membrane thickness can be adjusted by appropriately selecting the applicator gap. When a wet membrane is obtained by dripping the mixed solution onto a substrate, the membrane thickness can be adjusted by appropriately selecting the amount of dripping per unit area. The proton conductor thus obtained can be peeled off from the substrate, if necessary, and then used for various purposes.

[0054] The above-described embodiments of the present invention encompass the following technical concepts. [1] A proton conductor comprising a metal organic framework having proton conductivity, a resin, and a dispersant, wherein the metal organic framework has metal ions and bridging ligands coordinated to the metal ions, and the metal organic framework contains molecules or ions having proton conductivity. [2] The proton conductor according to [1], wherein the dispersant is a polymer dispersant containing a resin affinity unit and a polar unit having a polar group. [3] The proton conductor according to [1] or [2], wherein the dispersant contains a polymer dispersant having a comb structure and / or a block polymer structure. [4] The proton conductor according to any one of [1] to [3], wherein the proton conductor contains 1 part by mass or more and 40 parts by mass or less of the dispersant per 100 parts by mass of the metal organic framework. [5] The proton conductor according to any one of [1] to [4], wherein the resin is one or more selected from the group consisting of polyamideimide, polysulfone, polyphenylsulfone, polyvinylidene fluoride, polyimide, polyvinyl butyral, and cellulose ester. [6] The proton conductor according to any one of [1] to [5], wherein the metal ion is one or more selected from the group consisting of zinc ion, chromium ion, aluminum ion, magnesium ion, manganese ion, iron ion, cobalt ion, nickel ion, copper ion, yttrium ion, and zirconium ion. [7] The proton conductor according to any one of [1] to [6], wherein the molecule or ion having proton conductivity is one or more selected from the group consisting of phosphate ion, hydrogen phosphate ion, dihydrogen phosphate ion, imidazole, imidazolium ion, benzimidazole, benzimidazolium ion, pyridine, pyridinium ion, trialkylamine, tetraalkylammonium salt, sulfate ion, hydrogen sulfate ion, and derivatives thereof. [8] The proton conductor according to any one of [1] to [7], wherein the crosslinkable ligand is at least one selected from the group consisting of phosphoric acid, polycarboxylic acid, amino acid, polyamine, nitrogen-containing heteroaromatic compound, and anion and oxide ion thereof.[9] The proton conductor according to any one of [1] to [8], wherein the metal organic framework and the dispersant are dispersed in a matrix made of the resin.

[10] An electrochemical cell comprising a solid electrolyte membrane containing the proton conductor according to any one of [1] to [9], disposed between an anode and a cathode.

[11] A method for producing a proton conductor, comprising casting a mixed liquid containing a resin, a metal organic framework having proton conductivity, a dispersant, and a solvent to form a wet membrane, and removing the solvent from the wet membrane, wherein the metal organic framework has metal ions and bridging ligands coordinated to the metal ions, and the metal organic framework includes molecules or ions having proton conductivity.

[0055] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0056] The synthesis of the MOFs used in the examples and comparative examples described below was carried out as follows.

[0057] (Synthesis of ZnPIm) ZnPIm was synthesized as follows according to the method described in J. Am. Chem. Soc. 2012, 134, 7612-7615. 81 mg of zinc oxide, 136 mg of imidazole, 205 μL of 85% phosphoric acid, and 500 μL of ethanol were weighed and mixed in a mortar for 15 minutes. The white powder was then collected, washed with ethanol, and dried overnight at 100° C. to obtain ZnPIm. ZnPIm has the composition formula: [Zn(HPO ４ ) (H ２ P.O. ４ ) ２ ](ImH ２ ) ２ It is an MOF having a structure represented by the formula: ２ represents an imidazolium ion. ZnPIm has a zinc ion as the metal ion, a hydrogen phosphate ion and a dihydrogen phosphate ion as bridging ligands, and an imidazolium ion as a non-coordinating counter ion. The hydrogen phosphate ion, the dihydrogen phosphate ion, and the imidazolium ion are all ions that have proton conductivity.

[0058] (Synthesis of ZnP_dmBIm) ZnP_dmBIm was synthesized as follows according to the method described in J. Mater. Chem. A, 2014, 2, 10404-10409. 81 mg of zinc oxide, 205 μL of 85% phosphoric acid, 292 mg of 5,6-dimethylbenzimidazole, and 500 μL of ethanol were weighed and mixed in a mortar for 15 minutes. The brownish-white powder was then collected, washed with ethanol, and dried overnight at 80°C. ZnP_dmBIm has the composition formula: [Zn(HPO ４ ) (H ２ P.O. ４ ) ２ ](H ２ dmBIm) ２ It is an MOF having a structure represented by the formula: ２ dmBIm represents a 5,6-dimethylbenzimidazolium ion. ZnP_dmBIm has a zinc ion as the metal ion, a hydrogen phosphate ion and a dihydrogen phosphate ion as bridging ligands, and a 5,6-dimethylbenzimidazolium ion as a non-coordinating counter ion. The hydrogen phosphate ion, dihydrogen phosphate ion, and 5,6-dimethylbenzimidazolium ion are all ions that have proton conductivity.

[0059] (Synthesis of MIL(20)-1) MIL(20)-1 was synthesized as follows according to the method described in RSC Adv. 2017, 7, 403-407. First, 15 mg of MIL-101(Cr) (manufactured by Atomis) was dried at 180°C under reduced pressure for 6 hours. Next, it was mixed with 85 mg of imidazole trifluoromethanesulfonate (manufactured by Sigma-Aldrich) in a mortar for 15 minutes under a nitrogen atmosphere. MIL-101(Cr) has the composition formula: Cr ３ O (C ８ H ４ O ４ ) ３It is an MOF having a structure represented by the formula F, which has chromium ions as metal ions, terephthalate (anion of benzene-1,4-dicarboxylic acid) and oxide ions as bridging ligands, and fluoride ions as non-bridging ligands. MIL(20)-1 is a compound in which the pores of MIL-101(Cr) are filled with imidazole trifluoromethanesulfonate, and the imidazolium ions are ions with proton conductivity. MIL(20)-1 contains 27% by mass of imidazolium ions.

[0060] (Synthesis of MIL(10)-1) MIL(10)-1 was synthesized as follows according to the method described in RSC Adv. 2017, 7, 403-407. First, 24 mg of MIL-101(Cr) (manufactured by Atomis) was dried at 180°C for 6 hours under reduced pressure. Next, 68 mg of imidazole trifluoromethanesulfonate (manufactured by Sigma-Aldrich) was mixed in a mortar for 15 minutes under a nitrogen atmosphere. MIL(10)-1 is a compound in which the pores of MIL-101(Cr) are filled with imidazole trifluoromethanesulfonate, and the imidazolium ion is a proton-conducting ion. MIL(10)-1 contains 23% by mass of imidazolium ions.

[0061] (Synthesis of DMAS_ZnoxRe) DMAS_ZnoxRe was synthesized as follows according to the method described in Angew. Chem. 2014, 126, 2676. 143 mg of zinc sulfate heptahydrate, 158 mg of oxalic acid, and 6 mL of dimethylformamide were weighed and mixed, then placed in an autoclave and heated at 160°C for 4 days. The mixture was then cooled to room temperature over 24 hours, and the resulting solid was filtered, washed with DMF, and vacuum dried at 120°C. DMAS_ZnoxRe has the composition formula: [(Me ２ NH ２ ) ３ (SO ４ )] ２ [Zn ２ (ox) ３In the formula, Me represents a methyl group, and ox represents an oxalate ion. DMAS_ZnoxRe has a zinc ion as the metal ion, an oxalate ion as the bridging ligand, and a dimethylaminium ion and a sulfate ion as non-coordinating counter ions. Both the dimethylaminium ion and the sulfate ion are proton-conducting ions.

[0062] (Resins and Dispersants) The resins and dispersants used in the examples and comparative examples described below are as follows. <Resins> Polyamideimide (PAI 4000 TF manufactured by Solvey, hereinafter also referred to as "PAI") Polysulfone (PSU P-1700 NT11 manufactured by Solvey, hereinafter also referred to as "PSU") Polyvinyl butyral (Mowital B 75H manufactured by Kuraray, hereinafter also referred to as "PVB") Polyvinylidene fluoride (PVDF 6013 / 1001 manufactured by Solvey, hereinafter also referred to as "PVDF") Glass fiber reinforced polyamideimide (Torlon 5030 polyamideimide manufactured by Solvey, hereinafter also referred to as "5030") Cellulose ester (L-20 manufactured by Daicel Corporation, hereinafter also referred to as "L-20") <Dispersants>・Marialim FA-1150AM-08 (manufactured by NOF Corporation, polymeric polycarboxylic acid dispersant with a comb-shaped structure, aqueous solution containing 50% active ingredient) ・Sleem AD-3172M (manufactured by NOF Corporation, polymeric amine dispersant with a comb-shaped structure, active ingredient 100%) ・Hinoact T-9100 (manufactured by Kawaken Fine Chemicals Co., Ltd., polymeric polyester dispersant with a comb-shaped structure, active ingredient 100%) ・Ajisper PN411 (manufactured by Ajinomoto Fine-Techno Co., Ltd., polymeric neutral dispersant, active ingredient 100%) ・Sleem 221P (manufactured by NOF Corporation, low-molecular-weight dispersant, active ingredient 100%)

[0063] Example 1 (Production of Proton Conductor) 1.00 g each of ZnPIm and PAI were weighed out and mixed in a mortar. Next, 4.25 g of DMF and 0.20 g of Marialim FA-1150AM-08 (containing 0.10 g of active ingredient) were added dropwise in that order, and the mixture was mixed until a uniform paste was formed to obtain a mixed solution. The mixed solution was transferred to a Teflon (registered trademark) beaker, placed in a vacuum desiccator, and depressurized to 10 kPa. The mixture was then degassed for 30 minutes. The degassed mixed solution was then dropped onto a glass plate and applied with an applicator to form a wet film. The applicator gap was adjusted to achieve the film thickness of the proton conductor shown in Table 1. The wet film was then dried in air at 140°C for 3 hours to obtain a proton conductor. [Examples 2 to 9 and Comparative Examples 1 to 9] Proton conductors were obtained in the same manner as in Example 1, except that the type and mass of the MOF, the type and mass of the resin, the type and mass of the dispersant, the type and mass of the solvent, and the membrane thickness of the proton conductor were changed as shown in Tables 1 and 2. Note that no dispersant was used in any of the comparative examples.

[0064] Examples 10 to 16 and Comparative Example 10: ZnPIm was used as the MOF, PVDF as the resin, a mixed solvent of NMP / acetone = 43 / 57 (mass ratio) as the solvent, and the dispersants listed in Table 3 were used. First, 0.50 g of PVDF and 9.92 g of the mixed solvent were mixed. Next, 0.33 g of ZnPIm and the amount of dispersant listed in Table 3 were sequentially added to this. The mixture was mixed in a mortar to obtain a mixed solution. The mixed solution was transferred to a Teflon (registered trademark) beaker and placed in a vacuum desiccator, where the pressure was reduced to 10 kPa and degassed for 1 hour. Next, the degassed mixed solution was dropped onto a glass plate to form a wet membrane. The amount of mixed solution dropped per unit area was adjusted to achieve a proton conductor membrane thickness as listed in Table 3. The wet membrane was dried in air at 140°C for 3 hours to obtain a proton conductor. Note that no dispersant was used in Comparative Example 10.

[0065] Examples 17 to 22 and Comparative Example 11 DMAS_ZnoxRe was used as the MOF. The mass of the MOF, the type and mass of the resin, the type and mass of the solvent, the type and mass of the dispersant, and the membrane thickness of the proton conductor were changed as shown in Table 4. Except for the above, proton conductors were obtained in the same manner as in Example 1. In Example 21, a mixed dispersant of ESLime 221P / AJISPER PN411 = 50 / 50 (mass ratio) was used as the dispersant. In Comparative Example 11, no dispersant was used.

[0066] Example 23 DMAS_ZnoxRe was used as the MOF. The mass of the MOF, the type and mass of the resin, the type and mass of the solvent, the type and mass of the dispersant, and the membrane thickness of the proton conductor were changed as shown in Table 4. Except for the above points, proton conductors were obtained in the same manner as in Examples 10 to 16 and Comparative Example 10. The solvent used was a mixed solvent of NMP / acetone = 43 / 57 (mass ratio).

[0067] [Evaluation] The proton conductors obtained in the examples and comparative examples were evaluated as follows.

[0068] (Measurement of Proton Conductor Film Thickness) The film thickness of the proton conductor was measured using a digital length measuring device (DIGIMICRO STAND MS-1C manufactured by Nikon Corporation). The average value of the thicknesses at five points was taken as the film thickness of the proton conductor.

[0069] (Measurement of Proton Conductivity) A circular test piece with a diameter of 10 mm was cut from the proton conductor, and platinum paste (TR-7905, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was applied to both sides in a 3 mm x 3 mm area and dried at 140°C for 1 hour to form electrodes on both sides of the test piece. Next, an AC voltage of 100 mV was applied between the two electrodes under a nitrogen gas flow (200 mL / min), and complex impedance analysis was performed in the frequency range of 10 Hz to 5 MHz (TOYO Corporation SOLARTRON 1260 IMPEDANCE / GAIN-PHASE ANALYZER). Proton conductivity (S / cm) was calculated from the total resistance component (intragranular resistance + grain boundary resistance). The proton conductivity was measured at the temperatures listed in Tables 1 to 4. The proton conductivity of Comparative Example 11 was recorded as "unmeasurable" because the proton conductor had low durability and collapsed during evaluation.

[0070] (Measurement of mechanical loss tangent (tanδ)) A square test piece measuring 5 mm × 50 mm was cut out from the proton conductor, and tensile vibration measurement was carried out using a dynamic viscoelasticity measuring device (DMS6100 manufactured by Seiko Instruments Inc.). Measurement was carried out under a nitrogen flow (200 mL / min), at a frequency of 1 Hz, and at a temperature increase rate of 5°C / min from 35°C, and the temperature at which a peak was obtained from the obtained tanδ graph was read. Note that for the proton conductors of Example 6 and Comparative Examples 6 and 7, no peak was observed in the measurement, and therefore the results are listed as "measurable" in Tables 1 and 2.

[0071] The evaluation results are shown in Tables 1 to 4. In these tables, "mass of dispersant" refers to the mass of the active ingredient of the dispersant, and does not include the mass of water as a solvent when the dispersant is used in the form of an aqueous solution. Furthermore, "dispersant content" in Tables 1, 3, and 4 refers to the percentage of the mass of the dispersant relative to the total mass of the MOF, resin, and dispersant. Furthermore, in Tables 1 to 4, "film thickness" refers to the film thickness of the proton conductor. In Tables 1 to 4, "-" means not measured.

[0072]

[0073]

[0074]

[0075]

[0076] As can be seen from a comparison between Examples 1 to 9 listed in Table 1 and Comparative Examples 1 to 9 listed in Table 2, the proton conductors of each Example using a dispersant had higher proton conductivity at high temperatures of 110°C or higher than the proton conductors of each Comparative Example prepared under the same conditions except that no dispersant was used. This indicates that the dispersant has the effect of improving proton conductivity at high temperatures. Furthermore, as shown in Table 3, even when the type and amount of dispersant were changed (Examples 10 to 16), it was found that proton conductivity at high temperatures was higher than when no dispersant was used (Comparative Example 10). Furthermore, as shown in Table 4, all of the proton conductors of Examples 17 to 23 using DMAS_ZnoxRe as the MOF had satisfactory proton conductivity at high temperatures. The proton conductor of Comparative Example 11, which did not use a dispersant, had low durability and proton conductivity measurements were not possible. In other words, the proton conductor of Comparative Example 11 was a proton conductor with low practical utility. Furthermore, when the mechanical loss tangent (tanδ) values ​​are compared between the Examples and Comparative Examples, it can be seen that the values ​​of tanδ are smaller in the Examples in which a dispersant was used. The value of tanδ is thought to represent the glass transition temperature (Tg), which means that the proton conductors of the Examples have higher flexibility. Such proton conductors are more practical because they are less likely to break when incorporated into an electrochemical cell, for example.

[0077] According to the present invention, a proton conductor having high proton conductivity at high temperatures of 100° C. or higher is provided.

Claims

1. A proton conductor comprising a metal organic framework having proton conductivity, a resin, and a dispersant, wherein the metal organic framework has metal ions and bridging ligands coordinated to the metal ions, and the metal organic framework contains molecules or ions having proton conductivity.

2. The proton conductor according to claim 1, wherein the dispersant is a polymer dispersant containing a resin affinity unit and a polar unit having a polar group.

3. The proton conductor according to claim 1, wherein the dispersant comprises a polymer dispersant having a comb structure and / or a block polymer structure.

4. The proton conductor according to any one of claims 1 to 3, comprising 0.3 mass % or more and 40 mass % or less of the dispersant.

5. The proton conductor according to any one of claims 1 to 3, wherein the resin is at least one selected from the group consisting of polyamideimide, polysulfone, polyphenylsulfone, polyvinylidene fluoride, polyimide, polyvinyl butyral and cellulose ester.

6. The proton conductor according to any one of claims 1 to 3, wherein the metal ion is at least one selected from the group consisting of zinc ions, chromium ions, aluminum ions, magnesium ions, manganese ions, iron ions, cobalt ions, nickel ions, copper ions, yttrium ions and zirconium ions.

7. The proton conductor according to any one of claims 1 to 3, wherein the molecule or ion having proton conductivity is one or more selected from the group consisting of phosphate ion, hydrogen phosphate ion, dihydrogen phosphate ion, imidazole, imidazolium ion, benzimidazole, benzimidazolium ion, pyridine, pyridinium ion, trialkylamine, tetraalkylammonium salt, sulfate ion, hydrogen sulfate ion, and derivatives thereof.

8. The proton conductor according to any one of claims 1 to 3, wherein the bridging ligand is at least one selected from the group consisting of phosphoric acid, polycarboxylic acid, amino acid, polyamine, nitrogen-containing heteroaromatic compound, and anion and oxide ion thereof.

9. The proton conductor according to any one of claims 1 to 3, wherein the metal organic framework and the dispersant are dispersed in a matrix made of the resin.

10. An electrochemical cell comprising a solid electrolyte membrane containing the proton conductor according to any one of claims 1 to 3 disposed between an anode and a cathode.

11. A method for producing a proton conductor, comprising casting a mixed liquid containing a resin, a metal organic framework having proton conductivity, a dispersant, and a solvent to form a wet membrane, and removing the solvent from the wet membrane, wherein the metal organic framework has metal ions and bridging ligands coordinated to the metal ions, and the metal organic framework contains molecules or ions having proton conductivity.

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