Polymer, electrolyte membrane, membrane electrode assembly, fuel cell, and water electrolysis device

Abstract

The purpose is to provide a polymer capable of forming an electrolyte membrane having excellent ability to suppress gas permeation, an electrolyte membrane having excellent ability to suppress gas permeation, and a membrane electrode assembly, a fuel cell, and a water electrolysis device, all using the electrolyte membrane. A polymer has a structural unit represented by formula (1). In the formula, R1 is a C1-12 alkyl group having an ion exchange group, R2 is a halogen atom or an optionally substituted hydrocarbon group, m1 is an integer of 0-3, Ar1 is an aromatic group optionally having a halogen atom or a hydrocarbon group as a substituent, or a group in which an aromatic group optionally having a halogen atom or a hydrocarbon group as a substituent is linked via a single bond, and carbon atoms constituting the aromatic group bond to a fluorene skeleton.

Description

Polymers, electrolyte membranes, membrane electrode assemblies, fuel cells, and water electrolysis devices

[0001] The present disclosure relates to a polymer, an electrolyte membrane, a membrane electrode assembly, a fuel cell, and a water electrolysis device.

[0002] Water electrolysis (water electrolysis) can convert electricity into hydrogen without generating carbon dioxide, so it has attracted attention as a power-hydrogen storage system that stores renewable energy as hydrogen energy. Water electrolysis methods include alkaline water electrolysis, solid alkaline water electrolysis, and solid polymer water electrolysis.

[0003] An example of non-pressurized hydrogen solid alkaline water electrolysis is shown in Figure 1. In the example shown in Figure 1, when a voltage is applied to both electrodes while supplying an electrolyte to the anode 82 side and the cathode 83 side, the following reaction occurs at the cathode 83, generating hydrogen gas: 2H ２ O + 2e － →2OH － +H ２ Hydroxide ion (OH － ) permeates the electrolyte membrane 81 and moves to the anode 82. The following reaction occurs at the anode 82, generating oxygen gas: － →H ２ O+1 / 2O ２ +2e － The generated hydrogen and oxygen are discharged together with the electrolyte, and after the water is separated in a gas-liquid separator, the hydrogen gas is stored in a storage tank, etc. In the example of Figure 1, the generated hydrogen gas is at normal pressure, so it needs to be pressurized by a compressor, etc., when stored in the storage tank.

[0004] Figure 2 shows another example of hydrogen-pressurized solid alkaline water electrolysis. In the example of Figure 2, water or electrolyte is supplied to the anode 82 side, and water molecules permeate the electrolyte membrane 81 and move to the cathode 83. Reactions similar to those in Figure 1 occur at each electrode, and high-concentration hydrogen is discharged at the cathode 83. In the example of Figure 2, the generated hydrogen gas is gradually pressurized. Therefore, it does not need to be compressed when stored in a storage tank. Considering the power required for the compressor, hydrogen-pressurized solid alkaline water electrolysis makes it easy to achieve high efficiency in hydrogen production. The same is true for other electrolysis methods, and gas-pressurized water electrolysis is being considered.

[0005] The present inventors have disclosed a polymer applicable to electrolyte membranes for solid alkaline water electrolysis, etc. in Patent Document 1. The polymer in Patent Document 1 is a polyphenylene-based polymer that does not have an ether bond in its main chain, and therefore has excellent durability against alkali.

[0006] Japanese Patent Application Laid-Open No. 2021-042351

[0007] To improve water electrolysis performance, it is necessary to make the electrolyte membrane thinner. However, a thinner electrolyte membrane poses a problem in that generated gases tend to permeate the electrolyte membrane, particularly in gas-pressurized water electrolysis devices.

[0008] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a polymer capable of forming an electrolyte membrane excellent in gas permeation suppression ability, an electrolyte membrane excellent in gas permeation suppression ability, and a membrane electrode assembly, a fuel cell, and a water electrolysis device using the electrolyte membrane.

[0009] The present disclosure includes the following aspects: [1] A polymer having a constitutional unit represented by the following formula (1): However, R １ are each independently an alkyl group having 1 to 12 carbon atoms and an ion exchange group, and R ２ are each independently a hydrocarbon group which may have a substituent or a halogen atom, m1 is each independently an integer of 0 to 3, Ar １ is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to a fluorene skeleton. [2] The polymer according to [1], further comprising a structural unit represented by the following formula (2): However, R ３ are each independently an alkyl group having 1 to 12 carbon atoms which may have a halogen atom as a substituent, and R ４ are each independently a hydrocarbon group which may have a substituent or a halogen atom, m2 is each independently an integer of 0 to 3, Ar １is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton. １ is represented by any one of the following formulas (3a) to (3d):

[0022] The polymer according to [1] or [2]: However, R ５ each independently represents a hydrogen atom, a hydrocarbon group which may have a substituent, or a halogen atom; Ar ２ is a phenylene group, a biphenylene group, a terphenylene group, or a divalent naphthalene, a divalent anthracene, or a divalent carbazole, each of which may have a halogen atom or a hydrocarbon group as a substituent, and * indicates a bonding position. [4] The polymer according to [3], wherein the formula (3d) is represented by any one of the following formulas (4a) to (4j): However, R ５ are each independently a hydrogen atom, a hydrocarbon group which may have a substituent, or a halogen atom, and * indicates a bonding position. [5] The polymer according to any one of [1] to [4], wherein the ion exchange groups are each independently represented by any one of the following formulas (N1) to (N12): However, R ６ are each independently an alkyl group having 1 to 6 carbon atoms, and R ７ are each independently an alkyl group having 1 to 6 carbon atoms or an aryl group which may have a substituent, and * indicates a bonding position. [6] A polymer represented by the following formula (11): However, R １１ are each independently an alkyl group having 6 to 12 carbon atoms and an ion exchange group, and R １３ are each independently an alkyl group having 1 to 8 carbon atoms, and R １２ and R １４ each independently represents a hydrocarbon group which may have a substituent, or a halogen atom; m11 and m12 each independently represents an integer of 0 to 3; Ar １１is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton, m is a molar ratio and is 0.1 to 0.9, and n is 1 or more. [7] A polymer represented by the following formula (21): However, R ２１ are each independently an alkyl group having 1 to 12 carbon atoms and an ion exchange group, and R ２２ and each independently represent a hydrocarbon group which may have a substituent or a halogen atom; m21 each independently represent an integer of 0 to 3; Ar ２１ is a group represented by the following formula (3d), p is 1 or more, R ５ each independently represents a hydrocarbon group which may have a substituent, or a halogen atom; Ar ２ is a phenylene group, a biphenylene group, a terphenylene group, or a divalent naphthalene, a divalent anthracene, or a divalent carbazole, each of which may have a halogen atom or a hydrocarbon group as a substituent. [8] An electrolyte membrane comprising the polymer according to any one of [1] to [7]. [9] A membrane electrode assembly comprising the electrolyte membrane according to [8].

[10] A fuel cell comprising the electrolyte membrane according to [8].

[11] A water electrolysis device comprising the electrolyte membrane according to [8].

[0010] The present disclosure provides a polymer capable of forming an electrolyte membrane with excellent gas permeation suppression ability, an electrolyte membrane with excellent gas permeation suppression ability, and a membrane electrode assembly, a fuel cell, and a water electrolysis device that use the electrolyte membrane.

[0011] Fig. 1 is a schematic diagram showing an example of non-pressurized hydrogen-type solid alkaline water electrolysis; Fig. 2 is a schematic diagram showing an example of pressurized hydrogen-type solid alkaline water electrolysis; Fig. 3 is a schematic cross-sectional view showing an example of a main part of a fuel cell; Fig. 4 is a graph showing the results of gas permeability evaluation; Fig. 5 is an X-ray diffraction spectrum of an electrolyte membrane; Fig. 6 is a graph showing the results of ion conductivity measurement; Fig. 7 is a graph showing the results of radical durability evaluation; Fig. 8 is a graph showing the results of alkaline durability evaluation.

[0012] The present invention will be described below through embodiments. For clarity, the following description and drawings have been simplified as appropriate. Furthermore, matters necessary for implementing the present invention that are not specifically mentioned in this specification can be understood as design matters for those skilled in the art based on the prior art in the relevant field. In this specification, the term "to" indicating a numerical range includes the upper and lower limits unless otherwise specified. In this disclosure, "polymer" includes "copolymer" unless otherwise specified. In this disclosure, "ion exchange group" refers to a functional group that is dissociative and capable of ion exchange. In this disclosure, when a compound, polymer, group, etc. is represented by a specific formula (X), the compound, polymer, group, etc. represented by formula (X) may be referred to as compound (X), polymer (X), or group (X), respectively. When the same symbol is present in a chemical formula, the same symbol may represent the same structure or different structures within the scope specified in the specification.

[0013] [Polymer] The polymer according to this embodiment is a polymer having a constitutional unit represented by the following formula (1). However, R １ are each independently an alkyl group having 1 to 12 carbon atoms and an ion exchange group, and R ２ are each independently a hydrocarbon group which may have a substituent or a halogen atom, m1 is each independently an integer of 0 to 3, Ar １ is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton.

[0014] The structural unit (1) is a wholly aromatic hydrocarbon having a main chain that does not have an ether bond, and has a fluorene skeleton and an Ar group having an aromatic ring. １and are arranged alternately. Furthermore, at least a portion of the fluorenes have an alkyl group having an ion exchange group, and at least another portion of the fluorenes have a relatively short-chain alkyl group. This polymer has excellent chemical durability against alkalis, radicals, and the like because the main chain does not have an ether bond. Furthermore, this polymer is prone to π-π stacking between polymers, which reduces gas permeability. Therefore, an electrolyte membrane obtained from this polymer has excellent chemical durability and gas permeation suppression effects, and even when made into a membrane thinner than conventional membranes, the permeation of hydrogen and oxygen generated by water electrolysis is suppressed.

[0015] R １ is an alkyl group having 1 to 12 carbon atoms and having an ion exchange group as a substituent. １ The alkyl group in R is preferably a linear or branched alkyl group, more preferably a linear alkyl group. The number of carbon atoms in the alkyl group may be 1 to 12, preferably 3 to 12, more preferably 4 to 12, and even more preferably 6 to 10. １ Examples of the substituent that may be possessed by the group include an ion exchange group described below, a halogen atom, a hydroxyl group, and the like.

[0016] R １ The ion exchange group of the polymer is a functional group that has dissociation properties and is capable of ion exchange. When proton conductivity is to be imparted to the electrolyte membrane, the ionic group is preferably an acidic group. Examples of the acidic group include a sulfonic acid group (—SO ３ H group), phosphate group (-H ２ P.O. ４Preferably, the ionic group is a quaternary ammonium group (--COOH group) or a carboxylic acid group, more preferably a sulfonic acid group. The H in the acidic group may be dissociated or may be substituted with an alkali metal ion, alkaline earth metal ion, or the like. When anion conductivity is to be imparted to the electrolyte membrane, the ionic group is preferably a quaternary ammonium group or an imidazolium group, more preferably a quaternary ammonium group. From the viewpoint of alkali durability, the quaternary ammonium group is preferably a quaternary alkylammonium group. The quaternary alkylammonium group also includes groups in which alkyl groups bonded to nitrogen atoms are bonded to each other to form a ring structure, and may be, for example, an azaadamantyl group or a quinuclidinium group.

[0017] Specific examples of preferred ion exchange groups include groups represented by the following formulae (N1) to (N12). However, R ６ are each independently an alkyl group having 1 to 6 carbon atoms, and R ７ are each independently an alkyl group having 1 to 6 carbon atoms or an aryl group which may have a substituent, and * indicates the bonding position.

[0018] R ６ ~R ７ The alkyl group of R may be linear, branched, or cyclic. ７ Examples of the aryl group include a phenyl group and a naphthyl group, with a phenyl group being preferred. Examples of the substituent that the aryl group may have include a linear or branched alkyl group having 1 to 4 carbon atoms, a halogen atom, and a hydroxyl group.

[0019] One R １ In the formula, the number of ion exchange groups is preferably one. The ion exchange group is preferably located at the end of the alkyl group. １ Ha*-L １ -R ９ Preferably, L is a group represented by the formula: １ is an alkylene group having 1 to 12 carbon atoms which may have a substituent, and R ９ is an ion exchange group. １ , L １may have a substituent other than an ion exchange group. Examples of such a substituent include a halogen atom and a hydroxyl group, and examples thereof include a fluorine atom and a chlorine atom.

[0020] R ２ R is a hydrocarbon group which may have a substituent, or a halogen atom. ２ The halogen atom in R is preferably a fluorine atom or a chlorine atom. ２ Examples of the hydrocarbon group in R include an alkyl group and an aryl group. The alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and examples include a methyl group, an ethyl group, an n-butyl group, and a tert-butyl group. Examples of the substituent that the alkyl group may have include a halogen atom and a hydroxyl group. ２ The aryl group in R is exemplified by a phenyl group, a naphthyl group, etc., and a phenyl group is preferred. Examples of the substituent that the aryl group may have include a linear or branched alkyl group having 1 to 4 carbon atoms, a halogen atom, and a hydroxyl group. ２ Each m1 independently represents an integer of 0 to 3, preferably 0 to 2, and more preferably 0 or 1.

[0021] Ar １is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond. The aromatic ring constituting the aromatic group may be a carbocyclic ring or a heterocyclic ring. Specific examples of the aromatic ring include a benzene ring, as well as condensed polycyclic aromatic hydrocarbons such as a naphthalene ring, a tetralin ring, an indene ring, a fluorene ring, an anthracene ring, and a phenanthrene ring; 5-membered heterocyclic rings such as furan, thiophene, pyrrole, oxazole, thiazole, imidazole, and pyrazole; 6-membered heterocyclic rings such as pyran, pyrone, pyridine, pyrone, pyridazine, pyrimidine, and pyrazine; and condensed polycyclic heterocyclic rings such as benzofuran, thionaphthene, indole, carbazole, coumarin, benzo-pyrone, quinoline, isoquinoline, acridine, phthalazine, quinazoline, and quinoxaline. Examples of groups in which aromatic groups are linked via a single bond include polyphenyls such as biphenyl and terphenyl, and groups in which aromatic groups are linked via other bonds in addition to a single bond, such as carbazole.

[0022] The aromatic group may have a halogen atom or a hydrocarbon group as a substituent. Examples of the halogen atom include a fluorine atom and a chlorine atom. Examples of the hydrocarbon group include an alkyl group and an aryl group. The alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and examples include a methyl group, an ethyl group, an n-butyl group, and a tert-butyl group. Examples of the substituent that the alkyl group may have include a halogen atom and a hydroxyl group. Examples of the aryl group include a phenyl group and a naphthyl group, and the aryl group may have a linear or branched alkyl group having 1 to 4 carbon atoms, a halogen atom, or a hydroxyl group as a substituent. Ar １ In the above formula, the substituent of the aromatic group is preferably a halogen atom or an alkyl group.

[0023] Ar １ In the formula (1), a carbon atom constituting the aromatic group is bonded to the fluorene skeleton in the formula (2) described below by a single bond. １In the above, it is preferable that a fluorine atom is substituted at the α-position relative to the carbon atom bonded to the fluorene skeleton. Furthermore, by using a compound having such a structure as a raw material, the synthesis of the present polymer becomes easy and it becomes possible to obtain a polymer with a high molecular weight.

[0024] Ar １ is preferably a group represented by any one of the following formulas (3a) to (3d). However, R ５ each independently represents a hydrogen atom, a hydrocarbon group which may have a substituent, or a halogen atom; Ar ２ represents a phenylene group, a biphenylene group, a terphenylene group, or a divalent naphthalene, a divalent anthracene, or a divalent carbazole, each of which may have a halogen atom or a hydrocarbon group as a substituent, and * represents a bonding position.

[0025] As the group represented by formula (3d), a group represented by any one of the following formulae (4a) to (4j) is preferred.

[0026] R in formulas (3a) to (3d) and formulas (4a) to (4j) ５ are each independently preferably a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group, more preferably a hydrogen atom, a fluorine atom, or a methyl group. ５ is preferably a hydrogen atom or an alkyl group.

[0027] The polymer of the present disclosure may have a structural unit other than the structural unit represented by formula (1). Examples of the structural unit include a structural unit represented by the following formula (2). However, R ３ are each independently an alkyl group having 1 to 12 carbon atoms which may have a halogen atom as a substituent, and R ４ are each independently a hydrocarbon group which may have a substituent or a halogen atom, m2 is each independently an integer of 0 to 3, Ar １is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton.

[0028] R ３ is an alkyl group having 1 to 12 carbon atoms which may have a halogen atom as a substituent. ３ The alkyl group in is preferably a linear or branched alkyl group, more preferably a linear alkyl group. The alkyl group may have 1 to 12 carbon atoms, preferably 3 to 12, more preferably 4 to 12, and even more preferably 6 to 10.

[0029] R ４ R each independently represents a hydrocarbon group which may have a substituent, or a halogen atom. ４ Specific examples of R ２ The preferred embodiments are also the same as those of the above. ４ Each m2 is independently an integer of 0 to 3, preferably 0 to 2, and more preferably 0 or 1. １ is the same as that in formula (1), and preferred embodiments are also the same.

[0030] The polymer having the structural unit (1) is preferably a polymer represented by the following formula (11) or formula (21), in view of being more excellent in chemical durability and gas permeation inhibiting ability.

[0031] <Polymer (11)> Polymer (11) is represented by the following formula (11).

[0032] However, R １１ are each independently an alkyl group having 6 to 12 carbon atoms and an ion exchange group, and R １３ are each independently an alkyl group having 1 to 8 carbon atoms, and R １２ and R １４ each independently represents a hydrocarbon group which may have a substituent, or a halogen atom; m11 and m12 each independently represents an integer of 0 to 3; Ar １１is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton, m is a molar ratio and is 0.1 to 0.9, and n is 1 or more.

[0033] R １１ ~R １４ , m11, m12 and Ar １１ respectively represent R in the structural units (1) and (2). １ ~R ４ , m1, m2 and Ar １ For specific structures, refer to these. １１ and R １３ By setting the carbon number of the above specific combination, the polymer can be formed into an electrolyte membrane having excellent chemical durability and gas permeation suppression ability.

[0034] m represents the molar ratio of the structural unit (1) to the structural unit (2), and may be 0.1 to 0.9, preferably 0.15 to 0.85, and more preferably 0.2 to 0.8. n is a number of 1 or greater, and is, for example, an integer of 1 to 10,000, or an integer of 2 to 5,000.

[0035] The order in which the structural units (1) and (2) are linked is not particularly limited, and the copolymer may be a random copolymer, a block copolymer in which the structural units (1) and (2) are arranged in blocks, an alternating copolymer in which the structural units (1) and (2) are arranged alternately, or a partial combination of these.

[0036] <Polymer (21)> Polymer (21) is represented by the following formula (21).

[0037] However, R ２１ are each independently an alkyl group having 1 to 12 carbon atoms and an ion exchange group, and R ２２ and each independently represent a hydrocarbon group which may have a substituent or a halogen atom; m21 each independently represent an integer of 0 to 3; Ar ２１is a group represented by the formula (3d), and p is 1 or more.

[0038] R ２１ ~R ２２ , m21 and Ar ２１ are each R in the structural unit (1). １ ~R ２ , m1 and Ar １ For specific structures, refer to these. ２１ By using the group (3d), the polymer can be formed into an electrolyte membrane having superior chemical durability and gas permeation suppression ability.

[0039] The polymer having the structural unit (1) may further contain other structural units as long as the effects of the present invention are not impaired. Examples of the other structural units include a structure in which a group convertible to an ion exchange group remains unreacted in the production method described below. The proportion of the other structural units is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less of the total structural units of the polymer.

[0040] The weight-average molecular weight of the polymer having the structural unit (1) can be adjusted as appropriate and can be, for example, in the range of 10,000 to 1,000,000, but from the viewpoints of film-forming properties, film strength, etc., it is preferably 30,000 or more, and more preferably 100,000 or more. The weight-average molecular weight is a polystyrene-equivalent value measured by GPC (gel permeation chromatography).

[0041] The polymer has a high ionic conductivity due to its high ionic functional group density (IEC). The IEC of the polymer is 0.5 meq g －１ More than 4.0 meq.g －１ The following is achieved. The ionic conductivity of the present polymer is preferably 50 mS / cm or more at 80°C and saturated humidity. Generally, polymers with high ionic conductivity have a high water content and often swell significantly when hydrated, but the present polymer also has good swelling resistance.

[0042] [Method for Producing Polymer] There are no particular limitations on the method for producing a polymer having the structural unit (1). For example, a method for producing a polymer having the structural unit (1) by reacting the following compound (31), compound (32), and H-Ar １ According to the following method, a polymer having a high molecular weight (for example, a weight average molecular weight of 100,000 or more) can be synthesized relatively easily.

[0043] However, X １ are each independently Br or I; R ３１ are each independently an alkyl group having 1 to 12 carbon atoms and having an ion exchange group or a group convertible to an ion exchange group as a substituent, and R ３２ are each independently an alkyl group having 1 to 12 carbon atoms which may have a halogen atom as a substituent. １ represents Ar in the formulas (1) and (2). １ is the same as:

[0044] R ３１ Examples of the group that can be converted into an ion exchange group in include a halogen atom, a sulfonate group, a phosphate group, a carboxylate group, an imidazole group, and an amino group.

[0045] The polymerization of the compound (31) and the compound (32) with the compound (33) can be carried out using, for example, a Pd complex, a ligand, a carboxylic acid (RCO ２ The reaction can be carried out by reacting compound (31) and compound (32) with compound (33) in a solvent in the presence of palladium complex (Pd) and a base. ２ (dba) ３ CHCl ３ , P(o-C ６ H ４ -OMe) ３ , pivalic acid (PivOH), Cs ２ CO ３and dry THF are preferably used. Here, dba means dibenzylideneacetone. The reaction time and reaction temperature in the reaction step can also be set appropriately, and can be, for example, 1 to 48 hours and 80 to 140°C.

[0046] Next, R ３１ When the structural unit (1) has a group that can be converted into an ion exchange group, it is converted into an ion exchange group after polymerization to obtain the structural unit (1). For methods of converting to an ion exchange group, see the examples described below and the methods described in JP-A-2020-169287 and JP-A-2021-042351.

[0047] [Electrolyte Membrane] The electrolyte membrane of the present disclosure is characterized by including a polymer having the structural unit (1) (hereinafter also referred to as polymer (1)). An electrolyte membrane using this polymer is excellent in chemical durability, ionic conductivity, and membrane mechanical strength, and can be suitably used as an electrolyte membrane for fuel cells and water electrolysis devices. In addition, the electrolyte membrane is also excellent in gas permeation suppression performance, so that gas permeation can be suppressed even when used at a thinner thickness than conventional membranes, allowing for the production of a water electrolysis device with higher performance.

[0048] The electrolyte membrane can be produced by a general membrane-forming method, for example, by dissolving the polymer (1) in a solvent in which it can be dissolved (e.g., dimethyl sulfoxide, alcohol, an aqueous alcohol solution, etc.) to prepare a polymer solution, forming a coated film using a known coating means, and drying the coated film. When the electrolyte membrane is a membrane made of the polymer (1), the membrane thickness may be appropriately adjusted in the range of 0.5 to 200 μm, preferably 1 to 150 μm, and more preferably 1 to 100 μm.

[0049] Furthermore, a pore-filling membrane in which the present polymer is filled into the pores of a porous substrate may be used as the electrolyte membrane. One example of a method for producing a pore-filling membrane is a method in which the polymer (1) is applied to a porous substrate and then dried. Examples of methods for applying the polymer (1) to a porous substrate include preparing a solution of the polymer (1) and then using a dipping method, a spray method, a spin coating method, a barcode method, and the like. The polymer (1) solution is permeated into the porous substrate, and then dried to obtain a pore-filling membrane. The fact that the polymer (1) has been filled into the porous substrate can be confirmed, for example, by Raman analysis.

[0050] In the porous substrate, at least some of the pores preferably form through-holes in order to improve ionic conductivity. The porous substrate is preferably in the form of a nonwoven fabric or a porous film in order to provide mechanical strength, and a porous film is more preferred. The porosity of the porous substrate (= void volume / bulk volume × 100 (%)) is preferably 30 to 95% in order to achieve both mechanical strength and ionic conductivity, more preferably 40 to 80%, and even more preferably 45 to 70%. The film thickness of the porous substrate is preferably 5 to 200 μm in order to achieve both mechanical strength and ionic conductivity, more preferably 7 to 100 μm, and even more preferably 10 to 50 μm. The pore size of the porous substrate is preferably 10 to 10,000 nm in average diameter, more preferably 10 to 1,000 nm, in order to fill and retain the polymer (1) and in order to achieve mechanical strength.

[0051] [Membrane Electrode Assembly and Water Electrolysis Apparatus] A membrane electrode assembly according to the present disclosure includes the electrolyte membrane, an anode catalyst, and a cathode catalyst. Also, a water electrolysis apparatus according to the present disclosure includes the membrane electrode assembly.

[0052] The configurations of a membrane electrode assembly and a water electrolysis device will be described with reference to FIG. 3 . FIG. 3 is a schematic cross-sectional view showing an example of a water electrolysis device. The water electrolysis device 1 shown in the example of FIG. 3 includes an electrolyte membrane 5, an anode electrode 10 disposed on one side of the electrolyte membrane 5, a cathode electrode 20 disposed on the other side, a power source 7 connected to the anode electrode 10 and the cathode electrode 20, and a water supply unit that supplies water or an alkaline aqueous solution to the cathode electrode 20. The anode electrode 10 is sufficient to have at least an anode catalyst 11 and may further include a first diffusion layer 12. The cathode electrode 20 is sufficient to have at least a cathode catalyst 21 and may further include a second diffusion layer 22. The membrane electrode assembly 8 is sufficient to have at least an anode catalyst 11 disposed on one side of the electrolyte membrane 5 and a cathode catalyst 21 disposed on the other side. In the example of FIG. 3 , a cell 6 is further configured including separators 13 and 23 on the outer sides of the anode electrode 10 and the cathode electrode 20, respectively. The water electrolysis device 1 may be a single cell 6 or may be a stack of a plurality of cells 6. The water supply unit may supply water to at least one of the cathode and the anode.

[0053] When the water electrolysis device is a solid alkaline water electrolysis device, for example, when a voltage is applied to both electrodes while water or an alkaline aqueous solution is supplied to the anode electrode 10 side, water is also supplied to the cathode electrode side, and the following reaction occurs on the cathode electrode 20 side, generating hydrogen gas: 2H ２ O + 2e － →2OH － +H ２ Hydroxide ion (OH － ) passes through the electrolyte membrane 5 and moves to the anode electrode 10. At the anode electrode 10, the following reaction occurs, generating oxygen gas: － →H ２ O+1 / 2O ２ +2e － The generated hydrogen and oxygen are discharged from the cell 6 through gas flow paths 14, 24 provided in the separators 13 and 23, respectively. The gas flow paths are connected to a storage tank or the like via a gas-liquid separator (not shown), and the hydrogen and oxygen are each stored in the storage tank or the like after water is separated from them in the gas-liquid separator.

[0054] The water supplied to the water electrolysis apparatus may be pure water or an alkaline aqueous solution. By using an alkaline aqueous solution, water electrolysis can be performed more efficiently than with pure water. The solute in the alkaline aqueous solution is not particularly limited, and may be, for example, potassium hydroxide of 1 M or less.

[0055] The anode electrode 10 includes at least an anode catalyst 11 and may further include a first diffusion layer 12. The anode catalyst 11 is preferably a metal or a metal alloy. The metal or metal alloy can be appropriately selected from known metals and metal compounds, such as platinum, cobalt, nickel, palladium, iron, silver, gold, copper, iridium, molybdenum, rhodium, chromium, tungsten, manganese, and ruthenium, as well as metal compounds, metal oxides, and alloys containing two or more of these metals. Furthermore, the anode catalyst 11 is preferably a porous body in terms of the contact area with water and the diffusion of water and gas. Examples of porous catalysts include metal particle links formed by fusion-bonding particles of the above-mentioned metals, foams of the above-mentioned metals, and porous bodies such as felt (nonwoven fabric) and mesh-like bodies formed from wire- or fibrous metals. The anode catalyst 11 may be used by coating the surface of the above-mentioned metal with a known electrolyte polymer (ionomer). On the other hand, in this embodiment, ionic conductivity is achieved by the movement of water (solution) within the membrane electrode assembly 8, and therefore excellent ionic conductivity is achieved without using an electrolyte polymer. Furthermore, by not coating the anode catalyst with an electrolyte polymer, catalytic activity is further improved.

[0056] The anode electrode 10 may further include a first diffusion layer 12 in addition to the anode catalyst 11. The first diffusion layer 12 can be appropriately selected from known gas diffusion layers, and examples thereof include a foam metal layer such as nickel foam and a porous carbon layer.

[0057] The cathode electrode 20 includes at least a cathode catalyst 21 and may further include a second diffusion layer 22. The cathode catalyst 21 is preferably a metal or a metal alloy. The metal or metal alloy can be appropriately selected from known metals and metal compounds, such as platinum, cobalt, nickel, palladium, iron, silver, gold, copper, iridium, molybdenum, rhodium, chromium, tungsten, manganese, and ruthenium, as well as metal compounds, metal oxides, and alloys containing two or more of these metals. Furthermore, the cathode catalyst 21 is preferably a porous body in terms of the contact area with water and the diffusion of water and gas. Examples of porous catalysts include metal particle links formed by fusion bonding particles of the above-mentioned metals, foams of the above-mentioned metals, and porous bodies such as felt (nonwoven fabric) and mesh-like bodies formed from wire- or fibrous metals. The cathode catalyst 21 may be used by coating the surface of the above-mentioned metal with a known electrolyte polymer. On the other hand, in this embodiment, ionic conductivity is achieved by the movement of the alkaline aqueous solution within the membrane electrode assembly 8, and therefore, excellent ionic conductivity is achieved without using an electrolyte polymer. Furthermore, by not coating the cathode catalyst with an electrolyte polymer, catalytic activity is further improved.

[0058] The cathode electrode 20 may further include a second diffusion layer 22 in addition to the cathode catalyst 21. The second diffusion layer 22 can be appropriately selected from known gas diffusion layers, and examples thereof include a foam metal layer such as nickel foam and a porous carbon layer.

[0059] The water electrolysis apparatus may have separators 13, 23 on the outside of the anode electrode 10 and the cathode electrode 20, respectively. The separators do not need to be platinum-coated or the like, and may be made of an appropriate material such as carbon or stainless steel. When the separators 13, 23 are conductive, the separator 13 may serve as a first main electrode and the separator 23 may serve as a second main electrode, and a power source 7 may be connected to the first main electrode and the second main electrode to apply a voltage to the cathode and the anode.

[0060] The separators 13, 23 may have gas flow channels 14, 24. Oxygen generated at the anode electrode 10 and hydrogen generated at the cathode electrode 20 are discharged through the gas flow channels 14, 24, respectively, and stored in a storage tank or the like.

[0061] The power supply 7 is not particularly limited and can be appropriately selected from known DC power supplies. Because the water electrolysis apparatus has excellent response to input power, it can be suitably used with renewable energy sources such as solar power generation and wind power generation, which have large fluctuations in input power.

[0062] Another electrolysis technique is to electrolyze carbon dioxide to produce formic acid. For example, protons produced at the anode are transferred to the cathode through an electrolyte membrane, where they react with carbon dioxide supplied to the cathode to produce formic acid. The reaction formula at each electrode is as follows: Anode: 2H ２ O → O ２ + 4H ＋ + 4e － Cathode: CO ２ + 2H ＋ + 2e － → HCOOH

[0063] [Fuel Cell] The fuel cell of the present disclosure is characterized by including the electrolyte membrane described above. The electrolyte membrane can be suitably used in both solid alkaline fuel cells and polymer electrolyte fuel cells.

[0064] When the electrolyte membrane is applied to a solid alkaline fuel cell, an anion-conducting electrolyte membrane is used as the electrolyte membrane. The configuration of the solid alkaline fuel cell can be a conventionally known configuration. For example, a membrane electrode assembly is formed by disposing a cathode on one side of the electrolyte membrane and an anode on the other side, and oxygen is supplied to the cathode and fuel is supplied to the anode, and OH generated at the cathode is decomposed. －The hydrogen ions migrate to the anode through the electrolyte membrane, where they generate water, thereby generating electricity. The fuel can be appropriately selected from conventionally known fuels, and examples include, but are not limited to, hydrogen, methanol, ethanol, ethylene glycol, formate, hydrazine, sodium borohydride, and ammonia. The reactions at each electrode when hydrogen, methanol, and formate are used as representative fuels are shown below. Fuel cell using hydrogen: Anode: 2OH － + H ２ → 2H ２ O Cathode: O ２ + 2H ２ O + 4e － → 4OH － ・Fuel cell using methanol Anode: 6OH － + CH ３ OH → CO ２ + 5H ２ O Cathode: O ２ + 2H ２ O + 4e － → 4OH － ・Fuel cell using formate Anode: HCOO － + 3OH － → 2H ２ O + CO ３ ２－ + 2e － Cathode: O ２ + 2H ２ O + 4e － → 4OH －

[0065] Furthermore, when the electrolyte membrane is applied to a polymer electrolyte fuel cell, a proton-conductive electrolyte membrane is used as the electrolyte membrane. The configuration of the polymer electrolyte fuel cell can be a conventionally known configuration. For example, a membrane electrode assembly is formed by disposing a cathode on one side of the electrolyte membrane and an anode on the other side, oxygen is supplied to the cathode, fuel is supplied to the anode, and protons generated at the anode move to the anode via the electrolyte membrane, where water is generated, thereby generating electricity. The fuel can be appropriately selected from known fuels, and specific examples include the same fuels as those exemplified in the solid alkaline fuel cell. As a representative example, the reactions at each electrode when hydrogen is used as fuel are shown below. Anode: H ２ → 2H ＋ + 2e － Cathode: O ２ + 4H ＋ + 4e － → 2H ２ O

[0066] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0067] [Preparation of Polymers] Polymers (I) to (VI) represented by the following formulae were prepared: Polymers (V) to (VI) are comparative examples.

[0068]

[0069] [Production of Electrolyte Films] Each of the above polymers (I) to (VI) was dissolved in dimethyl sulfoxide to prepare a solution (20 mg / ml). Each of these solutions was cast onto a glass substrate and dried by heating at 100°C to form a film. The substrate was then immersed in water to peel the polymer film from the substrate. After washing several times with pure water, the film was dried in vacuum at 80°C for 6 hours to obtain electrolyte membranes 1 to 6. The thickness of these electrolyte membranes was 15 to 30 μm.

[0070] [Evaluation] (Measurement of IEC, water content, and area change rate) For electrolyte membranes 1 to 6, the water content and area change rate in water at 80°C after ion exchange with OH- were measured. The measurement results are shown in Table 1. The lower the water content, the better the swelling resistance can be evaluated. In addition, the ionic functional group density (IEC) of polymers (I) to (VI) was １ The values ​​calculated from the H-NMR measurement results are shown in Table 1.

[0071]

[0072] (Gas Permeability Evaluation) The hydrogen permeability of electrolyte membranes 1 to 6 was measured at a relative humidity (RH) of 90% and a temperature of 80° C. The results are shown in FIG.

[0073] (X-ray Diffraction Evaluation) X-ray diffraction measurements were carried out at room temperature for the electrolyte membranes 3 and 5. The results are shown in FIG.

[0074] (Measurement of ionic conductivity) Cl of electrolyte membranes 1 to 6 － The ionic conductivity of ions was measured. The ionic conductivity was calculated from the electrical resistance measured by AC impedance measurement. In-plane AC impedance measurement was performed using platinum electrodes and the two-terminal method. The electrode distance for measuring the voltage was 5 mm to 15 mm, and the low-current and low-voltage electrodes were contacted on the opposite side of the electrolyte membrane relative to the high-current and high-voltage electrodes. The electrolyte membrane together with the platinum electrodes was sandwiched between two slide glasses, and both ends of the slide glasses were fixed with clips. The electrolyte membrane was placed in a thermostatic chamber (Espec SH-241 Bench-Top Type Temperature & Humidity Chamber) and allowed to stabilize for at least 2 hours at a humidity of 100 RH and at a constant temperature (40 ° C to 80 ° C). The measurement was then performed. The AC impedance was measured using a Solartron 1260 (manufactured by Solartron, UK) under the conditions of an AC amplitude of 10 to 100 mV and a frequency ranging from 100,000 Hz to 1 Hz. The results are shown in FIG.

[0075] (Radical durability evaluation) For the electrolyte membrane 3 and the electrolyte membrane 5, 3 wt % H ２ O２ and 2 μg / g FeSO ４ A Fenton test was carried out using a Fenton reagent containing the compound at 80° C. The result of the residual weight after 12 hours and photographs showing the state before and after the measurement are shown in FIG.

[0076] (Evaluation of Alkali Durability) Electrolyte Membranes 3 and 5 were immersed in an 8M NaOH solution at 80°C. After a predetermined time had elapsed, the membranes were removed and immersed in pure water for 3 hours. The ionic conductivity of the electrolyte membranes was measured under conditions of 40°C and 95% RH, after which the membranes were immersed in an 8M NaOH solution and the same procedure was repeated. The results are shown in Figure 8.

[0077] [Results] The electrolyte membrane of Comparative Example 6 had excellent swelling resistance but insufficient gas permeation suppression effect. The electrolyte membrane of Comparative Example 5 had excellent gas permeation suppression effect but insufficient swelling resistance. Electrolyte membranes 1 to 4, which used polymers (I) to (IV) corresponding to the polymer represented by formula (1), were shown to have both swelling resistance and gas permeation suppression and to be excellent in chemical durability. In particular, electrolyte membrane 3, in which a peak (indicated by the arrow in FIG. 5) derived from a π-π stack (corresponding to a distance of 4.2 Å) of a long-range ordered structure was observed in the X-ray diffraction analysis shown in FIG. 5, exhibited the lowest gas permeability.

[0078] This application claims priority based on Japanese Patent Application No. 2024-105291, filed on June 28, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0079] 1: Water electrolysis device, 5: Electrolyte membrane, 6: Cell, 7: Power source, 8: Membrane electrode assembly, 10: Anode electrode, 11: Anode catalyst, 12: First diffusion layer, 13: Separator, 14: Gas flow path, 20: Cathode electrode, 21: Cathode catalyst, 22: Second diffusion layer, 23: Separator, 24: Gas flow path, 81: Electrolyte membrane, 82: Anode, 83: Cathode.

Claims

1. A polymer having a structural unit represented by the following formula (1): However, R １ are each independently an alkyl group having 1 to 12 carbon atoms and an ion exchange group, and R ２ are each independently a hydrocarbon group which may have a substituent or a halogen atom, m1 is each independently an integer of 0 to 3, Ar １ is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton.

2. The polymer according to claim 1, further comprising a structural unit represented by the following formula (2): However, R ３ are each independently an alkyl group having 1 to 12 carbon atoms which may have a halogen atom as a substituent, and R ４ are each independently a hydrocarbon group which may have a substituent or a halogen atom, m2 is each independently an integer of 0 to 3, Ar １ is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton.

3. The Ar １ The polymer according to claim 1, wherein the polymer is represented by any one of the following formulas (3a) to (3d): However, R ５ each independently represents a hydrogen atom, a hydrocarbon group which may have a substituent, or a halogen atom; Ar ２ represents a phenylene group, a biphenylene group, a terphenylene group, or a divalent naphthalene, a divalent anthracene, or a divalent carbazole, each of which may have a halogen atom or a hydrocarbon group as a substituent, and * represents a bonding position.

4. The polymer according to claim 3, wherein the formula (3d) is represented by any one of the following formulas (4a) to (4j): However, R ５ are each independently a hydrogen atom, a hydrocarbon group which may have a substituent, or a halogen atom, and * indicates the bonding position.

5. The polymer according to claim 1, wherein the ion exchange groups are each independently represented by any one of the following formulas (N1) to (N12): However, R ６ are each independently an alkyl group having 1 to 6 carbon atoms, and R ７ are each independently an alkyl group having 1 to 6 carbon atoms or an aryl group which may have a substituent, and * indicates the bonding position.

6. A polymer represented by the following formula (11): However, R １１ are each independently an alkyl group having 6 to 12 carbon atoms and an ion exchange group, and R １３ are each independently an alkyl group having 1 to 8 carbon atoms, and R １２ and R １４ each independently represents a hydrocarbon group which may have a substituent, or a halogen atom; m11 and m12 each independently represents an integer of 0 to 3; Ar １１ is an aromatic group which may have a halogen atom or a hydrocarbon group as a substituent, or a group in which aromatic groups which may have a halogen atom or a hydrocarbon group as a substituent are linked via a single bond, and a carbon atom constituting the aromatic group is bonded to the fluorene skeleton, m is a molar ratio and is 0.1 to 0.9, and n is 1 or more.

7. A polymer represented by the following formula (21): However, R ２１ are each independently an alkyl group having 1 to 12 carbon atoms and an ion exchange group, and R ２２ and each independently represent a hydrocarbon group which may have a substituent or a halogen atom; m21 each independently represent an integer of 0 to 3; Ar ２１ is a group represented by the following formula (3d), p is 1 or more, R ５ each independently represents a hydrogen atom, a hydrocarbon group which may have a substituent, or a halogen atom; Ar ２ is a phenylene group, a biphenylene group, a terphenylene group, or a divalent naphthalene, a divalent anthracene, or a divalent carbazole, each of which may have a halogen atom or a hydrocarbon group as a substituent.

8. An electrolyte membrane comprising the polymer according to any one of claims 1 to 7.

9. A membrane electrode assembly comprising the electrolyte membrane according to claim 8.

10. A fuel cell comprising the electrolyte membrane according to claim 8.

11. A water electrolysis device comprising the electrolyte membrane according to claim 8.

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