Proton-conducting materials

Abstract

The present disclosure aims to provide a proton-conducting material that has good proton conductivity at high temperatures and good water resistance. [Solution] This embodiment is a proton-conducting material comprising a copolymer of a styrene sulfonic acid monomer, an alkyl (meth)acrylate monomer having an alkyl group with a hydroxyl group, and a polyfunctional (meth)acrylamide monomer.

Description

Technical Field

[0001] The present disclosure relates to a proton-conducting material. Further, the present disclosure preferably relates to a proton-conducting material that can be used for a solid electrolyte membrane used in a fuel cell.

Background Art

[0002] Conventionally, perfluorosulfonic acid resin membranes such as Nafion (registered trademark) have been used as solid electrolyte membranes for fuel cells. However, in order to achieve a high proton conductivity with a perfluorosulfonic acid resin membrane, the presence of water is indispensable, so it is necessary to use it at a temperature below the boiling point of water (100°C). Therefore, in conventional fuel cells using perfluorosulfonic acid resin membranes, a humidification system, a temperature control system, etc. for ensuring appropriate moisture have been introduced, and the enlargement of the fuel cell device and the increase in cost have become problems.

[0003] From such a situation, in recent years, the development of proton-conducting materials that can be used under non-humidified conditions has been attempted. As a solid electrolyte membrane that can be used under non-humidified conditions, for example, Patent Document 1 discloses an electrolyte membrane containing a strong acid such as phosphoric acid and a basic polymer such as polybenzimidazole.

[0004] Further, Patent Document 2 discloses a block copolymer having an A block that aggregates with each other at the use temperature to form a domain and a B block having a proton-accepting group, and a B block bridging between the domains, and a proton-conducting membrane containing a plasticizer that is a non-volatile acidic substance.

[0005] Also, an ion conductor composed of an inorganic porous membrane and an ionic liquid held in the inorganic porous membrane as described in Patent Document 3 is also known as an electrolyte membrane that can be used under non-humidified conditions.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-32275 [Patent Document 2] Japanese Patent Publication No. 2020-68130 [Patent Document 3] Japanese Patent Publication No. 2007-311311 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, when the electrolyte membranes disclosed in Patent Documents 1 to 3 are used in fuel cells, the components in the electrolyte membrane dissolve due to the generated water, which leads to unstable operation of the fuel cell and a decrease in power generation performance. Therefore, there is a need to develop proton-conducting materials that have properties that make it difficult for components in the electrolyte membrane to dissolve in water, i.e., water-resistant materials.

[0008] Furthermore, in fuel cells, operating temperatures exceeding 100°C are required to simplify the operating system and improve power generation performance (NEDO FCV / HDV Fuel Cell Technology Development Roadmap, February 2023). Therefore, from the perspective of high-temperature operating temperatures, there is a need to develop proton-conducting materials that exhibit excellent proton conductivity even at high temperatures (e.g., above 80°C).

[0009] Therefore, the present disclosure aims to provide a proton-conducting material that has good proton conductivity at high temperatures and good water resistance. [Means for solving the problem]

[0010] Therefore, after diligent research, the present inventors discovered that by employing a copolymer of a styrene sulfonic acid monomer, an alkyl (meth)acrylate monomer having a hydroxyl group alkyl group, and a polyfunctional (meth)acrylamide monomer, it is possible to provide a proton-conducting material that has good proton conductivity at high temperatures and good water resistance, leading to this disclosure.

[0011] Examples of embodiments of this embodiment can be expressed as follows.

[0012] (1) A proton-conducting material comprising a copolymer of a styrene sulfonic acid monomer, an alkyl (meth)acrylate monomer having an alkyl group with a hydroxyl group, and a polyfunctional (meth)acrylamide monomer. (2) The content of styrene sulfonic acid monomers is 10 to 90 mol% of the total amount of monomers. The content of alkyl methacrylate monomers is 10 to 90 mol% relative to the total amount of monomers. The proton-conducting material according to (1), wherein the content of the polyfunctional (meth)acrylamide monomer is 0.1 to 20 mol% of the total amount of monomer. (3) The proton-conducting material according to any one of (1) to (2), wherein the polyfunctional (meth)acrylamide monomer is a difunctional acrylamide monomer, a trifunctional acrylamide monomer, or a tetrafunctional acrylamide monomer. (4) The proton conducting material according to any one of (1) to (3), further comprising a polyalkylene oxide chain-containing compound in addition to the copolymer. (5) The proton-conducting material according to (4), wherein the polyalkylene oxide chain-containing compound is polyethylene glycol, polyglycerol polyglycidyl ether, or a Bis-MPA polyester superbranched polymer having a polyalkylene oxide chain. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide a proton-conducting material that has good proton conductivity at high temperatures and good water resistance. [Modes for carrying out the invention]

[0014] This embodiment is a proton-conducting material comprising a copolymer of a styrene sulfonic acid monomer, an alkyl (meth)acrylate monomer having an alkyl group with a hydroxyl group, and a polyfunctional (meth)acrylamide monomer.

[0015] This embodiment provides a proton-conducting material that exhibits good proton conductivity even at high temperatures. The styrene sulfonic acid monomer has a sulfo group (-SO3H) that can function as a proton source group, which is a group capable of releasing protons. The alkyl (meth)acrylate monomer having an alkyl group with a hydroxyl group has a hydroxyl group that can function as a proton channel. In the proton-conducting material according to this embodiment, the sulfo group that can function as a proton source group and the hydroxyl group that can function as a proton channel are in close proximity, thus exhibiting good proton conductivity. Furthermore, in this embodiment, by using a polyfunctional (meth)acrylamide monomer that can function as a crosslinking agent as a polymerization component, a crosslinked structure can be formed in the copolymer. This allows for good water resistance. Moreover, the amide group of the polyfunctional (meth)acrylamide monomer can easily coordinate protons and therefore can function as a proton channel, contributing to good proton conductivity. In addition, the proton-conducting material according to this embodiment preferably exhibits proton conductivity even at high temperatures and without humidity. For the reasons stated above, it is presumed that the proton-conducting material according to this embodiment will have proton conductivity even at high temperatures and good water resistance. In this specification, "unhumidified conditions" refers to an environment with a humidity of 5% RH or less.

[0016] While the electrolyte membranes disclosed in Patent Documents 1 to 3 can be used without humidification, the electrolyte membranes disclosed in Patent Documents 1 and 3 tend to have decreased proton conductivity in the medium-to-low temperature range below 100°C, and the electrolyte membrane disclosed in Patent Document 2 is difficult to use in the high-temperature range due to its low glass transition temperature. Therefore, when using the electrolyte membranes disclosed in Patent Documents 1 to 3, it is difficult to maintain high proton conductivity over a wide temperature range. In contrast, the embodiments of the proton conducting material of this disclosure can have good proton conductivity over a wide temperature range. When a proton conducting membrane with good proton conductivity over a wide temperature range is used in a fuel cell, the humidification system and temperature control system introduced into the fuel cell device can be further simplified, thereby enabling cost reduction of the fuel cell device.

[0017] In this disclosure, "unhumidified conditions" refers to an environment where the humidity is 5%RH or less.

[0018] The styrene sulfonic acid monomer (also referred to as component A in this specification) is not particularly limited, but examples include 4-styrene sulfonic acid or its salts. For example, by copolymerizing a salt such as sodium styrene sulfonate as the styrene sulfonic acid monomer with an alkyl (meth)acrylate monomer and a polyfunctional (meth)acrylamide monomer in water and then hydrogenating the mixture, a polymer having a crosslinked structure can be obtained in which a crosslinked structure derived from the polyfunctional (meth)acrylamide monomer is introduced into the main skeleton derived from the styrene sulfonic acid polymer and the alkyl (meth)acrylate monomer. Since sodium styrene sulfonate has higher polymerizability than styrene sulfonic acid, it is easier to form a skeleton of a desired molecular weight by carrying out the polymerization reaction using sodium styrene sulfonate.

[0019] Examples of the alkyl (meth)acrylate monomer having an alkyl group with a hydroxy group (also referred to as component B in this specification) include hydroxyalkyl (meth)acrylate. The hydroxyalkyl (meth)acrylate is not particularly limited, but for example, hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 2 to 4 carbon atoms is preferable. Examples of the hydroxyalkyl (meth)acrylate preferably include 2-hydroxyethyl acrylate (HEA) or 2-hydroxyethyl methacrylate (HEMA).

[0020] The polyfunctional (meth)acrylamide monomer (also referred to as component C in this specification) is a monomer having two or more acrylamide groups, and is not particularly limited. For example, N,N'-methylenebisacrylamide; N,N'-ethylenebisacrylamide; 1,2-dihydroxyethylenebisacrylamide; N,N'-{[(2-acrylamido-2-[(3-acrylamidopropoxy)methyl]propane-1,3-diyl)bis(oxy)]bis(propane-1,3-diyl)}diacrylamide (tetrafunctional acrylamide, FOM-03006); N,N',N''-triacryloyldiethylenetriamine (trifunctional acrylamide, FOM-03007); N,N',N'',N'''-tetraacryloyltriethylenetetramine (tetrafunctional acrylamide, FOM-03009) and the like can be mentioned.

[0021] Examples of commercially available polyfunctional acrylamide monomers include FOM-03008 (water-soluble bifunctional acrylamide), FOM-03007 (water-soluble trifunctional acrylamide), FOM-03006 (water-soluble tetrafunctional acrylamide), and FOM-03009 (water-soluble tetrafunctional acrylamide) (all manufactured by Fujifilm Wako Pure Chemical Corporation), E1086 (manufactured by Tokyo Chemical Industry Co., Ltd.) and the like.

[0022] Since the proton-conductive material according to this embodiment has a structure in which a sulfo group and a hydroxy group are close to each other, it has good proton conductivity. Further, since a crosslinked structure is formed by a polyfunctional (meth)acrylamide-based monomer, it has good water durability. Furthermore, the amide bond contained in the crosslinked structure serves as a proton channel and can contribute to good proton conductivity. Therefore, the proton-conductive material according to this embodiment has good water durability and can exhibit proton conductivity even at high temperatures, and preferably can exhibit proton conductivity even at high temperatures and under non-humidified conditions. In addition, since the proton-conductive material according to this embodiment is excellent in flexibility, it is possible to form a large-area thin film of the proton-conductive membrane.

[0023] The content of the styrene sulfonic acid-based monomer is, for example, 10 to 90 mol% with respect to the total amount of the monomers. The content of the styrene sulfonic acid-based monomer is preferably 10 mol% or more, 15 mol% or more, 20 mol% or more, 25 mol% or more, 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, 50 mol% or more, 55 mol% or more, or 60 mol% or more with respect to the total amount of the monomers. The content of the styrene sulfonic acid-based monomer is preferably 90 mol% or less, 89 mol% or less, 85 mol% or less, or 80 mol% or less with respect to the total amount of the monomers.

[0024] The content of the (meth)acrylic acid alkyl ester-based monomer is, for example, 10 to 90 mol% with respect to the total amount of the monomers. The content of the (meth)acrylic acid alkyl ester-based monomer is preferably 10 mol% or more, or 15 mol% or more with respect to the total amount of the monomers. The content of the (meth)acrylic acid alkyl ester-based monomer is preferably 90 mol% or less, 89 mol% or less, 85 mol% or less, 75 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, 50 mol% or less, 45 mol% or less, 40 mol% or less, or 35 mol% or less with respect to the total amount of the monomers.

[0025] The content of the polyfunctional (meth)acrylamide monomer is, for example, 0.1 to 20 mol% of the total amount of monomer. The content of the polyfunctional (meth)acrylamide monomer is preferably 0.1 mol% or more, 0.3 mol% or more, 0.5 mol% or more, or 1.0 mol% or more of the total amount of monomer. The content of the polyfunctional (meth)acrylamide monomer is preferably 20 mol% or less, 15 mol% or less, 10 mol% or less, or 5.0 mol% or less of the total amount of monomer.

[0026] The molar ratio of styrene sulfonic acid monomer content to alkyl (meth)acrylate monomer content (styrene sulfonic acid monomer: alkyl (meth)acrylate monomer) is, for example, 10:90 to 90:10, preferably 40:60 to 85:15, and preferably 50:50 to 80:20.

[0027] The molar ratio of the total content of styrene sulfonic acid monomers and alkyl (meth)acrylate monomers to the content of polyfunctional (meth)acrylamide monomers is, for example, 80:20 to 99:1, preferably 85:15 to 98:2, and preferably 90:10 to 97:3.

[0028] The copolymer may contain other monomers besides styrene sulfonic acid monomers, alkyl (meth)acrylate monomers, and polyfunctional (meth)acrylamide monomers, to the extent that they do not substantially impede the effects of this embodiment. Other monomers are not particularly limited, but examples include (meth)acrylic acid or styrene. The content of other monomers is, for example, 0 to 10 mol%, preferably 5.0 mol% or less, 3.0 mol% or less, and 1.0 mol% or less, relative to the total amount of monomers.

[0029] The amount of substance or mass of each monomer in the copolymer can be calculated from the amount of substance or mass of each monomer compound used in the synthesis of the copolymer.

[0030] The weight-average molecular weight Mw of the copolymer according to this embodiment is not particularly limited, but is, for example, 300 to 1,000,000, and preferably 1,000 to 50,000. When the weight-average molecular weight Mw is within the above range, proton conduction paths are more easily formed, and thus the proton conductivity of the proton conducting material can be effectively improved.

[0031] The copolymer in this embodiment can be formed by copolymerizing the above monomers. The copolymer may be a random copolymer, a block copolymer, or a graft copolymer, but a random copolymer is preferred in that it improves proton conductivity.

[0032] The above copolymer can be produced by known methods. For example, the monomer and polymerization initiator can be charged in water or an organic solvent, a polymerization reaction can be induced by light irradiation or heating, and the polymer can be obtained by reprecipitation or purification.

[0033] As a polymerization initiator, for example, a radical polymerization initiator can be used. While there are no particular limitations on the radical polymerization initiator, examples include 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHEMPP). The radical polymerization initiator is used dissolved in water or a buffer. The content of the radical polymerization initiator is, for example, 0.01 to 10% by mass, preferably 0.05 to 5% by mass, and preferably 0.1 to 3% by mass, relative to the total mass of the monomers.

[0034] The proton-conducting material according to this embodiment includes the copolymer described above. The copolymer content in the proton-conducting material is, for example, 90% by mass or more. The proton-conducting material may contain small amounts of other components, such as residual solvents and residual crosslinking components, as long as it does not impair its performance.

[0035] The proton-conducting material according to this embodiment preferably further contains a polyalkylene oxide chain-containing compound (also referred to as component D in this specification) in addition to the copolymer described above.

[0036] A polyalkylene oxide chain-containing compound is a compound that contains a polyalkylene oxide chain, which consists of structural units containing alkylene oxide, in its molecule, with the number of repeating alkylene oxide structural units being 3 to 300 (preferably 3 to 100). The polyalkylene oxide chain-containing compound does not contain vinyl groups and / or (meth)acrylic groups. It is preferable that the polyalkylene oxide chain-containing compound is not a polymer. The polyalkylene oxide chain-containing compound may also function as a crosslinking agent. Each alkylene group of the alkylene oxide structural unit may independently have a hydroxyl group or a glycidyl ether group as a substituent. In this embodiment, by making the copolymer a proton-conducting material having a structure containing a polyalkylene oxide chain-containing compound, the polyalkylene oxide chain portion of the polyalkylene oxide chain-containing compound functions as a proton channel, and proton conductivity can be more effectively improved. Furthermore, by including a polyalkylene oxide chain-containing compound in the proton-conducting material, a proton-conducting film with excellent flexibility can be provided. This makes it possible to create large-area thin films of proton-conducting films.

[0037] The weight-average molecular weight Mw of the polyalkylene oxide chain-containing compound is not particularly limited, but is preferably 300 to 600,000, preferably 500 to 500,000, preferably 700 to 400,000, and preferably 900 to 300,000. When the weight-average molecular weight Mw of the polyalkylene oxide chain-containing compound is 300 or higher, the durability of the proton-conducting material can be effectively improved. Furthermore, when the weight-average molecular weight Mw of the polyalkylene oxide chain-containing compound is below the above upper limit, the proton conductivity of the proton-conducting material can be effectively improved.

[0038] Examples of polyalkylene oxide chain-containing compounds include polyethylene glycol. The weight-average molecular weight Mw of polyethylene glycol is, for example, 300 to 100,000. The weight-average molecular weight Mw of polyethylene glycol is preferably 50,000 or less, preferably 30,000 or less, and preferably 10,000 or less.

[0039] Examples of polyalkylene oxide chain-containing compounds include polyglycerol polyglycidyl ether. The weight-average molecular weight Mw of polyglycerol polyglycidyl ether is, for example, 300 to 100,000. The weight-average molecular weight Mw of polyglycerol polyglycidyl ether is preferably 50,000 or less, preferably 30,000 or less, and preferably 10,000 or less. An example of a commercially available polyglycerol polyglycidyl ether is Denacol EX-521 (trade name, manufactured by Nagase & Co., Ltd.).

[0040] As a polyalkylene oxide chain-containing compound, a Bis-MPA polyester superbranched polymer having a polyalkylene oxide chain is a preferred example. This Bis-MPA polyester superbranched polymer has a structure in which polyester dendritic parts made of dimethylolpropionic acid (Bis-MPA) are attached to both ends of a polyalkylene oxide chain, and the terminals are hydroxyl (OH) functional groups. The number of terminal hydroxyl functional groups depends on the generation of the superbranched polyester. The generation is defined by the number of branching layers or the extent of branching from the core (polyalkylene oxide chain) to the terminal functional groups. For example, a second-generation Bis-MPA polyester superbranched polymer contains 16 hydroxyl groups, while a third-generation polymer contains 32 hydroxyl groups. Bis-MPA polyester hyperbranched polymers are commercially available from companies such as Polymer Factory and Sigma-Aldrich, and are sold under trade names such as (Hyperbranched bis-MPA PEG 20k, Hydroxyl Functional, Generation 3) and (Hyperbranched bis-MPA PEG 20k, Hydroxyl Functional, Generation 6).

[0041] The content of polyalkylene oxide chain-containing compounds in the proton-conducting material is not particularly limited, but for example, it is 0.01 to 5% by mass, 0.05 to 4% by mass, 0.1 to 3% by mass, and 0.5 to 1% by mass.

[0042] Copolymers containing polyalkylene oxide chain-containing compounds are not particularly limited, but for example, copolymers containing polyalkylene oxide chain-containing compounds can be obtained by polymerizing the monomer in the presence of the polyalkylene oxide chain-containing compound. That is, they can be obtained by polymerizing the monomer in water or an organic solvent containing the polyalkylene oxide chain-containing compound.

[0043] The proton conductivity of the proton-conducting material according to this embodiment is preferably 10 mS / cm or more, preferably 20 mS / cm or more, preferably 30 mS / cm or more, preferably 40 mS / cm or more, preferably 50 mS / cm or more, preferably 60 mS / cm or more, preferably 70 mS / cm or more, preferably 80 mS / cm or more, preferably 90 mS / cm or more, and preferably 100 mS / cm or more, in a humid environment at 100°C. The proton conductivity of the proton-conducting material is the proton conductivity in the film thickness direction of the proton-conducting material formed into a film.

[0044] The form of the proton-conducting material according to this embodiment is not particularly limited and may be, for example, a film, i.e., a proton-conducting membrane. The proton-conducting membrane can be used, for example, as a solid electrolyte membrane in a fuel cell.

[0045] The thickness of the proton-conducting film is adjusted as appropriate depending on the application and is not particularly limited, but for example, it is 0.1 to 5.0 mm.

[0046] When forming a proton-conducting material into a film, the process of removing the solvent from a solution or dispersion containing a copolymer can be performed by drying the liquid in a film state, for example, by a drop-casting method, thereby forming a film-like proton-conducting material. The method of removing the solvent is not particularly limited and includes methods such as drying at room temperature or on a hot plate at, for example, 60°C under an air atmosphere.

[0047] The solvent is not particularly limited, and for example, water, organic solvents, or mixtures thereof can be used. Water, alcohol, or mixtures thereof are preferably used as the solvent. Methanol is typically used as the alcohol. [Examples]

[0048] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0049] The film thickness of the proton-conducting films obtained in each example and the comparative conductive films obtained in each comparative example was measured using a micrometer (Mitutoyo Corp., model number: CLM1-15QM).

[0050] [Examples 1-3] (Manufacturing of proton-conducting films E1-E3) Scheme 1

[0051] [ka]

[0052] Copolymers to serve as proton-conducting materials were synthesized according to Scheme 1 described above. Specifically, 2-hydroxyethyl methacrylate (HEMA) and FOM-03007 (water-soluble trifunctional acrylamide) were added to a methanol solution of 4-styrene sulfonic acid (SSA), and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHEMPP) was added as a water-soluble initiator. The reaction was induced by irradiation with Xe lamp light for 5 hours to obtain a random copolymer gel of SSA, HEMA, and FOM-03007. The obtained copolymer gel was immersed in 3M hydrochloric acid and then washed with water. The washed copolymer gel was formed into a film by drop casting and vacuum-dried for 24 hours. Through these steps, proton-conducting films E1 to E3 were obtained.

[0053] In Example 1, 4-styrene sulfonic acid (SSA) was prepared by treating its sodium salt with a cation exchange resin. At the time of material preparation, the sum of the SSA content ([SSA]) and HEMA content ([HEMA]) was 1.5 mol / L. The ratio of the SSA content ([SSA]) to the HEMA content ([HEMA]) ([SSA] / [HEMA]) was 80 / 20. The ratio of the sum of the SSA content ([SSA]) and HEMA content ([HEMA]) to the FOM-03007 content ([FOM-03007]) ({[SSA]+[HEMA]} / [FOM-03007]) was 100 / 5. The ratio of the sum of the SSA content ([SSA]) and HEMA content ([HEMA]) to the HHEMPP content ([HHEMPP]) ({[SSA]+[HEMA]} / [HHEMPP]) was set to 100 / 2. Examples 2 and 3 were carried out under the same conditions as Example 1, except that the [SSA] / [HEMA] ratio was set to 50 / 50 or 20 / 80 instead of 80 / 20.

[0054] [Example 4] (Manufacturing of proton-conducting film E4) Scheme 2

[0055] [ka]

[0056] A copolymer serving as a proton-conducting material was synthesized according to Scheme 2 described above. In Scheme 2, 4-styrenesulfonic acid (SSA) was generated in situ by reacting sodium 4-styrenesulfonate (SS-Na) with sulfuric acid. Furthermore, [SSA] in Scheme 2 is shown assuming that all SS-Na was converted to SSA by reaction with sulfuric acid. In other words, [SSA] in Scheme 2 represents the concentration of sodium 4-styrenesulfonate ([SS-Na]) at the time of charging.

[0057] Polyethylene glycol (PEG-1000, Mn:1000) was added to an aqueous solution of sodium 4-styrenesulfonate (SS-Na) at a concentration of 5% by mass relative to the SS-Na. Sulfuric acid was then added to the aqueous solution to convert the SS-Na to 4-styrenesulfonic acid (SSA). Next, 2-hydroxyethyl acrylate (HEA) and FOM-03007 (water-soluble trifunctional acrylamide) were added to the aqueous solution, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHEMPP) was added as a water-soluble initiator. The reaction was induced by irradiation with Xe lamp light for 20 minutes to obtain a random copolymer gel of SSA, HEA, and FOM-03007. The obtained copolymer gel was immersed in 3M hydrochloric acid and then washed with water. The washed copolymer gel was formed into a film by drop casting and vacuum-dried for 24 hours. Through these steps, a proton-conducting film E4 was obtained.

[0058] Furthermore, at the time of preparation of the materials, the sum of the SSA content ([SSA]) and HEA content ([HEA]) was set to 1.0 mol / L. The ratio of the SSA content ([SSA]) to the HEA content ([HEA]) ([SSA] / [HEA]) was set to 80 / 20. The ratio of the sum of the SSA content ([SSA]) and HEA content ([HEA]) to the FOM-03007 content ([FOM-03007]) ({[SSA]+[HEA]} / [FOM-03007]) was set to 100 / 5. The ratio of the sum of the SSA content ([SSA]) and HEA content ([HEA]) to the HHEMPP content ([HHEMPP]) ({[SSA]+[HEA]} / [HHEMPP]) was set to 100 / 2.

[0059] [Example 5] A proton-conducting film E5 was obtained in the same manner as in Example 4, except that polyglycerol polyglycidyl ether (Denacol EX-521, manufactured by Nagase & Co., Ltd.) was used instead of polyethylene glycol.

[0060] [Example 6] A proton-conducting membrane E6 was obtained in the same manner as in Example 4, except that a bis-MPA polyester hyperbranched polymer (Hyperbranched bis-MPA PEG 20k, Hydroxyl Functional, Generation 6, manufactured by Polymer Factory Co., Ltd.) was used instead of polyethylene glycol.

[0061] [Comparative Example 1] A comparative conductive film C1 of Comparative Example 1, with the film thickness shown in Table 1, was obtained by drop-casting a solution containing polystyrene sulfonic acid (Mn: 7000) onto a 5 mm diameter steel electrode.

[0062] [Comparative Example 2] A Nafion film (product name: NR212, manufactured by Chemours, film thickness 0.31 mm), which is a perfluorosulfonic acid resin, was used as the comparative conductive film C2 in Comparative Example 2.

[0063] [evaluation] <Measurement of proton conductivity> A conductivity measurement cell was placed inside the chamber of a small environmental test chamber (ESPEC Corporation, model: SH-242), and characteristic impedance was measured using an impedance analyzer (YHP Corporation, model: 4194A) under the temperature and humidified or unhumidified conditions listed in Table 1, with a frequency sweep range of 100 Hz to 1 MHz. The measured value (Rm) was defined as the real component at the point where the capacitance component of the Nyquist plot of the characteristic impedance was minimized. The conductivity in the film thickness direction (σ) (unit: S / cm) was calculated using the following formula, based on the impedance characteristics (Ru) when the measurement cable was short-circuited, and the film thickness (d) and electrode area (S) of the sample. σ = d / {(Rm - Ru) × S} In the table, "No Humidification" indicates a relative humidity of 5%RH.

[0064] <Water durability> The proton-conducting films E1 to E6 obtained in Examples 1 to 6 were dried under vacuum at 80°C for 12 hours or more, and their weight (initial weight) was measured. Next, the dried proton-conducting films were immersed in hot water at 80°C for 24 hours, then dried under vacuum at 80°C for 5 hours, and their weight (weight after testing) was measured. The ratio (%) of the weight after testing to the initial weight was defined as the water resistance retention rate. In this test, a retention rate of 50% is presumed to be practical.

[0065] [Table 1]

[0066] Although the proton conductivity under high temperature and unhumidified conditions is not shown in the table for Comparative Examples 1 and 2, it is well known that the comparative conductive films in Comparative Examples 1 and 2 exhibit almost no proton conductivity at high temperatures. On the other hand, the proton conductive film of this embodiment showed good proton conductivity even under high temperature conditions, and also demonstrated good water resistance.

[0067] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range.

[0068] Although this embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and any design changes that do not depart from the gist of this disclosure are also included in this disclosure.

Claims

1. A proton-conducting material comprising a copolymer of a styrene sulfonic acid monomer, an alkyl (meth)acrylate monomer having a hydroxyl group alkyl group, and a polyfunctional (meth)acrylamide monomer.

2. The content of styrene sulfonic acid monomers is 10 to 90 mol% of the total amount of monomers. The content of alkyl methacrylate monomers is 10 to 90 mol% of the total amount of monomers. The proton-conducting material according to claim 1, wherein the content of the polyfunctional (meth)acrylamide monomer is 0.1 to 20 mol% of the total amount of monomer.

3. The proton-conducting material according to claim 1, wherein the polyfunctional (meth)acrylamide monomer is a difunctional acrylamide monomer, a trifunctional acrylamide monomer, or a tetrafunctional acrylamide monomer.

4. The proton-conducting material according to claim 1, further comprising a polyalkylene oxide chain-containing compound in addition to the copolymer.

5. The proton-conducting material according to claim 4, wherein the polyalkylene oxide chain-containing compound is polyethylene glycol, polyglycerol polyglycidyl ether, or a Bis-MPA polyester superbranched polymer having a polyalkylene oxide chain.

Images