Patent Application
20240279824
The present invention relates to a membrane electrode assembly for polymer electrolyte membrane water electrolysis and a water electrolyzer.
In the so-called power-to-gas technology for storing surplus electricity for later use by converting it into a gas, use of polymer electrolyte membrane water electrolyzers (PEM water electrolyzers) has been explored.
For example, Patent Document 1 discloses a polymer electrolyte membrane water electrolyzer having a membrane electrode assembly comprising an anode and a cathode each having a catalyst layer and a polymer electrolyte membrane sandwiched between the anode and the cathode.
Recent years have seen a demand for water electrolyzers with higher performance, specifically speaking, water electrolyzers which enable low voltage electrolysis.
The present inventor assessed a water electrolyzer having the membrane electrode assembly disclosed in Patent Document 1 and found that it can operate at a low electrolysis voltage but decomposition of the fluorinated polymer contained in the membrane electrode assembly may occur.
In view of the above-mentioned circumstances, the present invention aims to provide a membrane electrode assembly for polymer electrolyte membrane water electrolysis and a water electrolyzer with which a low electrolysis voltage can be achieved and decomposition of the fluorinated polymer contained can be suppressed.
As a result of extensive studies on the above-mentioned problem, the present inventor has found that a membrane electrode assembly for polymer electrolyte membrane water electrolysis which comprises an anode catalyst layer, a cathode catalyst layer and a polymer electrolyte membrane sandwiched between the anode catalyst layer and the cathode catalyst layer can produce the desired effects when cerium ions are contained in a region overlapping the cathode catalyst layer when the membrane electrode assembly for polymer electrolyte membrane water electrolysis is observed from the normal direction of the surface, and when the amount of substance of cerium ions in the region and the amount of substance of the ion exchange groups of the fluorinated polymer contained in the cathode catalyst layer satisfy a predetermined relation, and has accomplished the present invention.
Namely, the present inventor has found the following solutions to the above-mentioned problem.
[1] A membrane electrode assembly for polymer electrolyte membrane water electrolysis, which comprises:
According to the present invention, it is possible to provide a membrane electrode assembly for polymer electrolyte membrane water electrolysis and a water electrolyzer with which a low electrolysis voltage can be achieved and decomposition of the fluorinated polymer contained can be suppressed.
The following definitions of terms apply throughout the specification and claims unless otherwise noted.
An “ion exchange group” is a group containing at least one ion which can be exchanged for a different ion, such as a sulfonic acid functional group and a carboxylic acid functional group, which will be mentioned below.
A “sulfonic acid functional group” means a sulfonic acid group (—SO3H) or a sulfonate group. The sulfonate group may, for example, be (—SO3−)Ma+, (—SO3−)2Mb2+ or (—SO3−)3Mc3+, where Ma+ is an alkali metal ion or a quaternary ammonium cation, Mb2+ is a bivalent metal ion, and Mc3+ is a trivalent metal ion, and when there are two ligands, the number of ion exchange groups is counted as 2, and when there are three ligands, the number of ion exchange groups is counted as 3.
A “carboxylic acid functional group” means a carboxylic acid group (—COOH) or a carboxylate group. The carboxylate group may, for example, be (—COO−)Ma+, (—COO−)2Mb2+ or (—COO−)3Mc3+, where Ma+ is an alkali metal ion or a quaternary ammonium cation, Mb2+ is a bivalent metal ion, and Mc3+ is a trivalent metal ion, and when there are two ligands, the number of ion exchange groups is counted as 2, and when there are three ligands, the number of ion exchange groups is counted as 3.
A “precursor membrane” is a membrane containing a polymer having groups convertible to ion exchange groups.
A “group convertible to an ion exchange group” means a group which can be converted to an ion exchange group by treatments such as hydrolysis and conversion to an acid form.
A “group convertible to a sulfonic acid functional group” means a group which can be converted to a sulfonic acid functional group by treatments such as hydrolysis and conversion to an acid form.
A “group convertible to a carboxylic acid functional group” means a group which can be converted to a carboxylic acid functional group by treatments such as hydrolysis and conversion to an acid form.
A “unit” in a polymer means an atomic group derived from one molecule of a monomer by polymerization. A unit may be an atomic group directly formed by a polymerization reaction, or may be an atomic group having a partially different structure obtained by polymerization followed by partial modification.
A numerical range expressed by using “to” includes the figures before and after “to” as the lower limit and the upper limit. In a series of numerical ranges mentioned herein, the upper limit or lower limit of a numerical range may be replaced by the upper limit or lower limit of another numerical range in the same series. The upper limit or lower limit of any numerical range herein may be replaced by a figure in the Examples.
The membrane electrode assembly for polymer electrolyte membrane water electrolysis (hereinafter referred to also simply as a “membrane electrode assembly”) of the present invention comprises a polymer electrolyte membrane containing a fluorinated polymer (hereinafter referred to also simply as a “fluorinated polymer (I)”) having ion exchange groups, a cathode catalyst layer containing a fluorinated polymer (hereinafter referred to also simply as a “fluorinated polymer (II)”) having ion exchange groups, provided on one side of the polymer electrolyte membrane, and an anode catalyst layer provided on the other side of the polymer electrolyte membrane. In the membrane electrode assembly of the present invention, when observed from the normal direction of the surface, cerium ions are contained in a region overlapping the cathode catalyst layer. Further, the membrane electrode assembly of the present invention satisfies the relation of the after-mentioned formula (X).
With the membrane electrode assembly of the present invention, a low electrolysis voltage can be achieved and decomposition of the fluorinated polymer contained in the membrane electrode assembly can be suppressed, when applied to a water electrolyzer, presumably, though not for sure, for the following reason.
In operation of a water electrolyzer, hydrogen peroxide may sometimes be generated in the system. If OH radicals generated from hydrogen peroxide react with the fluorinated polymer contained in the polymer electrolyte membrane or the cathode catalyst layer, the fluorinated polymer will be decomposed.
To overcome this problem, the present inventor has found that by using a membrane electrode assembly containing cerium ions, decomposition of the fluorinated polymer can be suppressed. That is, it is estimated that the OH radicals are quenched by cerium ions and as a result, decomposition of the fluorinated polymer can be suppressed.
While the above advantage is brought by the cerium ions, on the other hand, according to the content of the cerium ions, proton conductivity of the fluorinated polymer having ion exchange groups in the polymer electrolyte membrane or in the catalyst layer decreases, thus increasing the electrolysis voltage in some cases. Thus, achievement of a low electrolysis voltage and suppression of decomposition of the fluorinated polymer are in a trade-off relationship.
To overcome this problem, the present inventor has found the following. That is, in observation of the membrane electrode assembly from the normal direction of the surface, when the amount of substance of cerium ions contained in a region overlapping the cathode catalyst layer, and the amount of substance of ion exchange groups of the fluorinated polymer (fluorinated polymer (II)) contained in the cathode catalyst layer, satisfy the following formula (X), a low electrolysis voltage can be achieved even when the membrane electrode assembly contains cerium ions.
In the formula (X), ACe is the amount of substance (mol) of cerium ions contained in the above region, AIEG_C is the amount of substance (mol) of ion exchange groups of the fluorinated polymer (fluorinated polymer (II)) contained in the cathode catalyst layer.
“3” of the “ACe×3” means the valence of the cerium ions.
The cations (for example H+ in a case where the ion exchange groups are —SO3H) in the fluorinated polymer (fluorinated polymer (II)) contained in the cathode catalyst layer, are replaced with cerium ions present in the vicinity of the cathode catalyst layer. In the water electrolyzer, water is transported from the anode side toward the cathode side, and thus cerium ions contained in the membrane electrode assembly are likely to collect on the cathode side. Accordingly, in the above formula (X), the focus is on the relation between the amount of substance (mol) of ion exchange groups of the fluorinated polymer contained in the cathode catalyst layer, and the amount of substance (mol) of cerium ions contained in the above region.
The above formula (X) is an indicator of possibility of replacement of the cations constituting the ion exchange groups of the fluorinated polymer (II) with cerium ions. For example, a value of (ACe×3)/AIEG_C of 1 or more means that all the cations in the ion exchange groups of the fluorinated polymer (II) may be replaced with cerium ions.
The present inventor has estimated as follows. Even when all the cerium ions contained in the above region replace the cations constituting the ion exchange groups of the fluorinated polymer (II), ion exchange groups which have not been replaced with cerium ions remain to a certain extent, whereby favorable proton conductivity of the fluorinated polymer (II) is achieved, and thus a low electrolysis voltage can be achieved.
In the formula (X), (ACe×3)/AIEG_C is 0.90 or less, and with a view to further lowering the electrolysis voltage, it is preferably 0.80 or less, more preferably 0.60 or less, further preferably 0.50 or less.
In the formula (X), (ACe×3)/AIEG_C is, with a view to further suppressing decomposition of the fluorinated polymer, preferably 0.01 or more, more preferably 0.10 or more, further preferably 0.30 or more.
ACe is, with a view to further suppressing decomposition of the fluorinated polymer, preferably 0.02 μmol or more, more preferably 0.20 μmol or more, further preferably 0.60 μmol or more.
ACe is, with a view to further lowering the electrolysis voltage, preferably 2.00 μmol or less, more preferably 1.90 μmol or less, further preferably 1.40 μmol or less.
AIEG_C is, with a view to further lowering the electrolysis voltage and achieving sufficient strength of the catalyst layer, preferably 1.00 μmol or more, more preferably 1.50 μmol or more.
AIEG_C is, with a view to further lowering the electrolysis voltage, preferably 25.00 μmol or less, more preferably 10.00 μmol or less, further preferably 8.00 μmol or less.
ACe and AIEG_C are obtained by the method mentioned in Examples described later.
The electrolyte membrane contains a fluorinated polymer (I).
The thickness of the electrolyte membrane is preferably 30 μm or more.
The thickness of the electrolyte membrane is preferably 200 μm or less, more preferably 150 μm or less, further preferably 100 μm or less.
When the electrolyte membrane has a multilayer structure, the thickness of the electrolyte membrane is the sum of the thicknesses of the respective electrolyte layers.
The thickness of an electrolyte membrane is measured on a magnified cross-sectional image of the electrolyte membrane (for example, at an objective lens magnification of 50) taken by a laser microscope (model “VK-X1000”, manufactured by KEYENCE CORPORATION).
The ion exchange capacity of the fluorinated polymer (I) is preferably 1.10 meq/g dry resin or more, more preferably 1.25 meq/g dry resin or more, further preferably 1.40 meq/g dry resin or more, to provide a water electrolyzer with a lower electrolysis voltage.
The ion exchange capacity of the fluorinated polymer (I) is preferably 1.90 meq/g dry resin or less, more preferably 1.80 meq/g dry resin or less, in view of the strength of the membrane electrode assembly.
The fluorinated polymer (I) may be a single species or a laminate or mixture of two or more species.
Though the electrolyte membrane may contain a polymer other than the fluorinated polymer (I), it is preferred to practically consist of the fluorinated polymer (I) to further lower the electrolysis voltage. Practically consist of the fluorinated polymer (I) means that the content of the fluorinated polymer (I) is 95 mass % or higher to the total mass of the polymers in the electrolyte membrane. The upper limit of the content of the fluorinated polymer (I) is 100 mass % to the total mass of the polymers in the polymer electrolyte membrane.
Specific examples of the polymers other than the fluorinated polymer (I) include polyazole compounds selected from the group consisting of polymers of heterocyclic compounds containing at least one ring-constituting nitrogen atom and polymers of heterocyclic compounds containing at least one ring-constituting nitrogen atom and at least one ring-constituting oxygen and/or sulfur atom.
Specific examples of the polyazole compounds include polyimidazole compounds, polybenzimidazole compounds, polybenzobisimidazole compounds, polybenzoxazole compounds, polyoxazole compounds, polythiazole compounds and polybenzothiazole compounds.
In view of the oxidation resistance of the electrolyte membrane, other polymer may be a polyphenylene sulfide resin or a polyphenylene ether resin.
The fluorinated polymer (I) has ion exchange groups. Specific examples of the ion exchange groups include sulfonic acid functional groups and carboxylic acid functional groups, and sulfonic acid functional groups are preferred to attain a lower electrolysis voltage when the electrolyte membrane is applied to a water electrolyzer.
Hereinafter, a fluorinated polymer having sulfonic acid functional groups (hereinafter referred to also as a fluorinated polymer (S)) will be discussed mainly.
The fluorinated polymer (S) preferably has units based on a fluoroolefin and units based on a fluorine-containing monomer having a sulfonic acid functional group.
The fluoroolefin may, for example, be a C2-3 fluoroolefin having at least one fluorine atom in the molecule. Specific examples of the fluoroolefin include tetrafluoroethylene (hereinafter referred to also as “TFE”), chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride and hexafluoropropylene. Among them, TEE is preferred in view of the production cost of the monomer, the reactivity with other monomers and the ability to give an excellent fluorinated polymer (S).
The fluoroolefin may be a single species or a combination of two or more species.
The units based on a fluorine-containing monomer having a sulfonic acid functional group are preferably units represented by the formula (1).
—[CF2—CF(-L-(SO3M)n)]- Formula (1)
In the formula (1), L is a (n+1)-valent perfluorinated hydrocarbon group which may contain an ethereal oxygen atom.
The ethereal oxygen atom may be located at the end of the perfluorinated hydrocarbon group or between carbon atoms.
The number of carbon atoms in the (n+1)-valent perfluorinated hydrocarbon group is preferably 1 or more, more preferably 2 or more and is preferably 20 or less, more preferably 10 or less.
L is preferably a (n+1)-valent perfluorinated aliphatic hydrocarbon group which may contain an ethereal oxygen atom, particularly preferably a divalent perfluoroalkylene group which may contain an ethereal oxygen atom with n=1 or a trivalent perfluorinated aliphatic hydrocarbon group which may contain an ethereal oxygen atom with n=2.
The divalent perfluoroalkylene group may be linear or branched.
In the formula (1), M is a hydrogen atom, an alkali metal or a quaternary ammonium cation. When there are two M's, they may be identical to or different from one another.
In the formula (1), n is an integer of 1 or 2.
The units represented by the formula (1) are preferably units represented by the formula (1-1), units represented by the formula (1-2), units represented by the formula (1-3) or units represented by the formula (1-4), and to further lower the electrolysis voltage when the electrolyte membrane is applied to a water electrolyzer, more preferably units represented by the formula (1-3) or units represented by the formula (1-4).
In the above formula, Rf1 is a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and preferably 20 or less, more preferably 10 or less.
In the above formula, Rf2 is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and preferably 20 or less, more preferably 10 or less.
In the above formula, Rf3 is a single bond or a perfluoroalkylene group which may contain an oxygen atom between carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and preferably 20 or less, more preferably 10 or less.
In the above formula, r is an integer of 0 or 1.
In the above formula, m is an integer of 0 or 1.
M is a hydrogen atom, an alkali metal or a quaternary ammonium cation. When there are two or more M's, they may be identical to or different from one another.
The units represented by the formula (1-1) and the units represented by the formula (1-2) are more preferably units represented by the formula (1-5).
—[CF2—CF(—(CF2)x—(OCF2CFY)y—O—(CF2)z—SO3M)]- Formula (1-5):
In the formula (1-5), x is an integer of 0 or 1, y is an integer of from 0 to 2, z is an integer of from 1 to 4, and Y is F or CF3, and M is as defined above.
Specific examples of units represented by the formula (1-1) include the following units wherein w is an integer of from 1 to 8, x is an integer of from 1 to 5, and M is as defined above.
—[CF2—CF(—O—(CF2)w—SO3M)]—
—[CF2—CF(—O—CF2CF(CF3)—O—(CF2)w—SO3M)]—
—[CF2—CF(—(O—CF2CF(CF3))x—SO3M)]—
Specific examples of units represented by the formula (1-2) include the following units wherein w is an integer of from 1 to 8, and M is as defined above.
—[CF2—CF(—(CF2)w—SO3M)]—
—[CF2—CF(—CF2—O—(CF2)w—SO3M)]—
The units represented by the formula (1-3) are preferably units represented by the formula (1-3-1) wherein M is as defined above.
In the formula (1-3-1), Rf4 is a linear C1-6 perfluoroalkylene group, Rf5 is a single bond or a linear C1-6 perfluoroalkylene group which may contain an oxygen atom between carbon atoms, and r and M are as defined above.
Specific examples of the units represented by the formula (1-3-1) include the following units.
The units represented by the formula (1-4) are preferably units represented by the formula (1-4-1) wherein Rf1, Rf2 and M are as defined above.
Specific examples of the units represented by the formula (1-4-1) include the following units.
The fluorine-containing monomer having a sulfonic acid functional group may be a single species or a combination of two or more species.
The fluorinated polymer (I) may include units based on an additional monomer other than the units based on the fluoroolefin and the units based on the fluorine-containing monomer having a sulfonic acid functional group.
Specific examples of the additional monomer include CF2═CFRf6 (wherein Rf6 is a C2-10 perfluoroalkyl group), CF2═CF—ORf7 (wherein Rf7 is a C1-10 perfluoroalkyl group) and CF2═CFO(CF2)vCF═CF2 (wherein v is an integer of from 1 to 3).
The content of the units based on the additional monomer is preferably 30 mass % or less to all the units in the fluorinated polymer (I) to secure a certain level of ion exchange performance.
With a view to lowering the electrolysis voltage, the content of the fluorinated polymer (I) is, to the total mass of the electrolyte membrane, preferably from 80 to 100 mass %, more preferably from 90 to 100 mass %.
The electrolyte membrane may further include a reinforcing material to improve the strength of the electrolyte membrane.
Specific examples of the reinforcing material include a porous body, fibers, a woven fabric and a non-woven fabric.
The reinforcing material is preferably made of at least one material selected from the group consisting of polytetrafluoroethylene (hereinafter referred to also as “PTFE”), a tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (hereinafter referred to also as “PEA”), polyether ether ketone and polyphenylene sulfide.
In a case where the electrolyte membrane includes the reinforcing material, the amount of the reinforcing material to the total mass of the electrolyte membrane is preferably 3 mass % or more, more preferably 5 mass % or more, and preferably 50 mass % or less, more preferably 40 mass % or less, further preferably 30 mass % or less.
The electrolyte membrane may further contain components other than the above. Specific examples of such components include cerium ions. Details of cerium ions will be described later.
In a case where the electrolyte membrane contains cerium ions, the ratio of the amount of substance of cerium ions to the amount of substance of ion exchange groups of the fluorinated polymer (I) in the electrolyte membrane, is preferably 1 mol % or less, more preferably 0.5 mol % or less, further preferably 0.4 mol % or less.
Examples of a method for producing the electrolyte membrane include a method of producing a membrane (hereinafter referred to also as a “precursor membrane”) containing a polymer (hereinafter referred to also as a “fluorinated polymer (I′)”) of a fluorinated monomer (hereinafter referred to also as a “fluorinated monomer (I′)”) having a group convertible to an ion exchange group, and a reinforcing material used as the case require, and then converting the groups convertible to ion exchange groups in the precursor membrane to ion exchange groups. By this method, the electrolyte membrane can be obtained.
Further, as a method for producing an electrolyte membrane containing cerium ions, a method of immersing the electrolyte membrane obtained as above in a solution containing a water-soluble cerium salt, and then drying the membrane to obtain an electrolyte membrane containing cerium ions. Specific examples of the water-soluble cerium salt include cerium acetate, cerium chloride, cerium nitrate, cerium sulfate and cerium carbonate.
The fluorinated polymer (I′) is preferably a polymer (hereinafter referred to also as a “fluorinated polymer (S′)”) of a fluorinated monomer (hereinafter referred to also as a “fluorinated monomer (S′)”) having a group convertible to a sulfonic acid functional group, particularly preferably a copolymer of a fluoroolefin and a fluorine-containing monomer having a group convertible to a sulfonic acid functional group.
Next, the fluorinated polymer (S′) will be described.
The copolymerization for production of the fluorinated polymer (S′) may be carried out by any known technique such as solution polymerization, suspension polymerization or emulsion polymerization.
The fluoroolefin may be any of those mentioned previously and is preferably TEE in view of the production cost of the monomer, the reactivity with other monomers and the ability to give an excellent fluorinated polymer (S).
The fluoroolefin may be a single species or a combination of two or more species.
The fluorinated monomer (S′) may be a compound having at least one fluorine atom in the molecule, and having an ethylenic double bond and a group convertible to a sulfonic acid functional group.
The fluorinated monomer (S′) is preferably a compound represented by the formula (2) in view of the production cost of the monomer, the reactivity with other monomers and the ability to give an excellent fluorinated polymer (S).
CF2═CF-L-(A)n Formula (2):
L and n in the formula (2) are as defined above.
A is a group convertible to a sulfonic acid functional group. The group convertible to a sulfonic acid functional group is preferably a functional group convertible to a sulfonic acid functional group by hydrolysis. Specific examples of the group convertible to a sulfonic acid functional group include —SO2F, —SO2Cl and —SO2Br.
The compound represented by the formula (2) is preferably a compound represented by the formula (2-1), a compound represented by the formula (2-2), a compound represented by the formula (2-3) or a compound represented by the formula (2-4).
Rf1, Rf2, r and A in the formulae are as defined above.
The compound represented by the formula (2-1) and the compound represented by the formula (2-1) are preferably compounds represented by the formula (2-5).
CF2═CF—(CF2)x—(OCF2CFY)y—O—(CF2)z—SO3M Formula (2-5)
M, x, y, z and Y in the formula are as defined above.
Specific examples of the compound represented by the formula (2-1) include the following compounds wherein w is an integer of from 1 to 8, and x is an integer of from 1 to 5.
CF2═CF—O—(CF2)w—SO2F
CF2═CF—O—CF2CF(CF3)—O—(CF2)w—SO2F
CF2═CF—[O—CF2CF(CF3)]x—SO2F
Specific examples of the compound represented by the formula (2-2) include the following compounds wherein w is an integer of from 1 to 8.
CF2═CF—(CF2)w—SO2F
CF2═CF—CF2—O—(CF2)w—SO2F
The compound represented by the formula (2-3) is preferably a compound represented by the formula (2-3-1).
Rf4, Rf5, r and A in the formula are as defined above.
Specific examples of the compound represented by the formula (2-3-1) include the following compounds.
The compound represented by the formula (2-4) is preferably a compound represented by the formula (2-4-1).
Rf1, Rf2 and A in the formula are as defined above.
Specific examples of the compound represented by the formula (2-4-1) include the following compound.
The fluorinated monomer (S′) may be a single species or a combination of two or more species.
For production of the fluorinated polymer (S′), in addition to the fluoroolefin and the fluorinated monomer (S′), an additional monomer may be used. The additional monomer may be any of those mentioned previously.
The ion exchange capacity of the fluorinated polymer (I′) can be adjusted by changing the content of groups convertible to ion exchange groups of the fluorinated polymer (I′).
The precursor membrane may be formed, for example, by extrusion.
When the precursor membrane includes a reinforcing material, the precursor membrane may be formed by forming membranes (I′) containing a fluorinated polymer (I′), and then laminating a membrane (I′), a reinforcing material and a membrane (I′) in this order by laminating rolls or by a vacuum lamination apparatus.
The conversion of groups convertible to ion exchange groups of the precursor membrane to ion exchange groups may be carried out, for example, by hydrolyzing the precursor membrane or converting the precursor membrane to the acid form.
In particular, it is preferred to contact the precursor membrane with an aqueous alkaline solution.
Contact of the precursor membrane with an aqueous alkaline solution may be made, for example, by immersing the precursor membrane in the aqueous alkaline solution or by spraying the aqueous alkaline solution onto the surface of the precursor membrane.
The temperature of the aqueous alkaline solution is preferably from 30 to 100° C., more preferably from 40 to 100° C. The duration of the contact between the precursor membrane and the aqueous alkaline solution is preferably from 3 to 150 minutes, more preferably from 5 to 50 minutes.
The aqueous alkaline solution preferably comprises an alkali metal hydroxide, a water-miscible organic solvent and water.
The alkali metal hydroxide may be sodium hydroxide or potassium hydroxide.
Herein, the water-miscible organic solvent is an organic solvent which easily dissolves in water, and specifically, preferred is an organic solvent with a solubility of 0.1 g or more in 1,000 ml of water (20° C.), and more preferred is an organic solvent with a solubility of 0.5 g or more. The water-miscible organic solvent preferably contains at least one member selected from the group consisting of aprotic organic solvents, alcohols and amino alcohols, and more preferably contains an aprotic organic solvent.
The water-miscible organic solvent may be a single species or a combination of two or more species.
Specific examples of the aprotic organic solvents include dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and dimethyl sulfoxide is preferred.
Specific examples of the alcohols include methanol, ethanol, isopropanol, butanol, methoxyethoxyethanol, butoxyethanol, butyl carbitol, hexyloxyethanol, octanol, 1-methoxy-2-propanol and ethylene glycol.
Specific examples of the amino alcohols include ethanolamine, N-methylethanolamine, N-ethylethanolamine, 1-amino-2-propanol, 1-amino-3-propanol, 2-aminoethoxyethanol, 2-aminothioethoxyethanol and 2-amino-2-methyl-1-propanol.
The concentration of the alkali metal hydroxide in the aqueous alkaline solution is preferably 1 mass % or more, more preferably 3 mass % or more, and preferably 60 mass % or less, more preferably 55 mass % or less.
The content of the water-miscible organic solvent in the aqueous alkaline solution is preferably 1 mass % or more, more preferably 3 mass % or more, and preferably 60 mass % or less, more preferably 55 mass % or less.
The concentration of water in the aqueous alkaline solution is preferably from 39 to 80 mass %.
After the contact of the precursor membrane with an aqueous alkaline solution, the aqueous alkaline solution may be removed. The aqueous alkaline solution may be removed, for example, by washing the precursor membrane which has been contacted with the aqueous alkaline solution with water.
After the contact of the precursor membrane with an aqueous alkaline solution, the resulting membrane may be brought in contact with an aqueous acidic solution to convert the ion exchange groups to the acid form.
Contact of the precursor membrane with an aqueous acidic solution may be made, for example, by immersing the precursor membrane in the aqueous acidic solution or by spraying the aqueous acidic solution onto the surface of the precursor membrane.
The aqueous acidic solution preferably contains an acid component and water.
Specific examples of the acid component include hydrochloric acid and sulfuric acid.
The anode catalyst layer may, for example, be a layer containing a catalyst and a polymer having ion exchange groups.
Specific examples of the catalyst include a supported catalyst having platinum, a platinum alloy or a platinum-based core-shell catalyst supported on a carbon carrier, an iridium oxide catalyst, an iridium oxide alloy-based catalyst and an iridium oxide-based core-shell catalyst. As the carbon carrier, carbon black powder may be mentioned.
As the polymer having ion exchange groups, a fluorinated polymer having ion exchange groups may be mentioned. Specific examples of the fluorinated polymer having ion exchange groups may be the same as those of the fluorinated polymer (I) contained in the electrolyte membrane including the preferred embodiments.
The mass of the catalyst per 1 cm2 of the anode catalyst layer is preferably 0.05 mg/cm2 or more, more preferably 0.10 mg/cm2 or more, further preferably 0.20 mg/cm2 or more, and preferably 2.00 mg/cm2 or less, more preferably 1.50 mg/cm2 or less, further preferably 1.00 mg/cm2 or less.
The mass ratio of the catalyst to the polymer having ion exchange groups of the anode catalyst layer (mass of catalyst/mass of polymer having ion exchange groups) is preferably from 1 to 4.
The anode catalyst layer may further contain components other than the above. Specific examples of such components include cerium ions. Details of cerium ions will be described later.
The anode catalyst layer may be produced, for example, by using an anode catalyst ink containing the catalyst, the polymer having ion exchange groups, a solvent (water, an organic solvent), a water-soluble cerium salt used as the case requires, and the like, in accordance with a known method.
The thickness of the anode catalyst layer is, with a view to achieving more excellent effects of the present invention, preferably 5 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less, particularly preferably 15 μm or less.
The thickness of the anode catalyst layer is an arithmetic mean of arbitrary 20 points measured on a cross-sectional image of a membrane electrode assembly cut along the thickness direction with a laser microscope.
The cathode catalyst layer may, for example, be a layer containing a catalyst and the fluorinated polymer (II).
The specific examples of the catalyst are the same as those of the catalyst contained in the anode catalyst layer, including the preferred embodiments.
The specific examples of the fluorinated polymer (II) may be the same as those of the fluorinated polymer (I) including the preferred embodiments.
The mass of the catalyst per 1 cm2 of the cathode catalyst layer is preferably 0.05 mg/cm2 or more, more preferably 0.10 mg/cm2 or more, and is preferably 1.00 mg/cm2 or less, more preferably 0.50 mg/cm2 or less, further preferably 0.40 mg/cm2 or less.
The mass ratio of the catalyst to the fluorinated polymer (II) in the cathode catalyst layer (mass of catalyst/mass of fluorinated polymer (II)) is preferably 0.3 or higher, and is preferably 1.0 or lower, more preferably 0.7 or lower, further preferably 0.5 or lower.
The cathode catalyst layer may further contain components other than the above. Specific examples of such components include cerium ions. Details of cerium ions will be described later.
In a case where the cathode catalyst layer contains cerium ions, the ratio of the amount of substance of cerium ions to the amount of substance of ion exchange groups of the fluorinated polymer (II) in the cathode catalyst layer, is preferably 0.1 mol % or more, more preferably 0.3 mol % or more, and is preferably 15 mol % or less, more preferably 10 mol % or less.
The cathode catalyst layer may be produced, for example, by using a cathode catalyst ink containing the catalyst, the fluorinated polymer (II), a solvent (water, an organic solvent) and a water-soluble cerium salt used as the case requires, in accordance with a known method.
The thickness of the cathode catalyst layer is, with a view to achieving more excellent effects of the present invention, preferably 5 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less, particularly preferably 15 μm or less.
The method for measuring the thickness of the cathode catalyst layer is the same as the method for measuring the thickness of the anode catalyst layer.
A gas diffusion layer (anode gas diffusion layer, cathode gas diffusion layer) serves to uniformly diffuse the gas in a catalyst layer and also serves as a current collector. Specific examples of a gas diffusion layer include carbon paper, carbon cloth, carbon felt, a sintered product of titanium oxide fiber and a sintered product of titanium oxide particles. A sintered product of titanium oxide may be plated with platinum or the like, if necessary.
The cathode gas diffusion layer preferably has a water-repellent finish of PTFE or the like.
Although the membrane-electrode assembly shown in
Cerium ions are contained in a region overlapping the cathode catalyst layer when the membrane electrode assembly is observed from the normal direction of the surface. The cerium ions present in the region are likely to collect in the vicinity of the cathode catalyst layer, by transport of water when the water electrolyzer is run.
The above region will be described in detail with reference to
As shown in
In the example shown in
The cerium ions may be contained in the above region, and is preferably contained in at least one of the polymer electrolyte membrane present in the above region and the cathode catalyst layer present in the above region.
So long as the cerium ions are contained in the above region, they may be contained in other regions.
The cerium ions contained in the above region are preferably trivalent cerium ions.
Specific examples of a method of introducing the cerium ions to the above region, include a method of using an electrolyte membrane containing cerium ions, and a method of using a cathode catalyst layer containing cerium ions.
A membrane electrode assembly may be produced, for example, by using a laminate comprising an anode catalyst layer and a release liner (such as an ETFE sheet) and a laminate comprising a cathode catalyst layer and a release liner (such as an ETFE sheet), bonding the catalyst layers (anode catalyst layer and cathode catalyst layer) to both sides of the electrolyte membrane, and releasing the release liners.
Each laminate may have a gas diffusion layer between the catalyst layer and the release liner so that the gas diffusion layer (anode gas diffusion layer, cathode gas diffusion layer) is arranged on the opposite side of the catalyst layer from the electrolyte membrane.
The catalyst layers may be formed by applying a catalyst layer ink to the surface to be coated (such as the surface of release liners), followed by drying, if necessary. The catalyst layer ink is a dispersion of a polymer having ion exchange groups and a catalyst in a dispersion medium.
The membrane electrode assembly of the present invention is used in a polymer electrolyte membrane water electrolyzer.
The water electrolyzer of the present invention has the above-described membrane electrode assembly, a water supply member to supply water to the anode catalyst layer side, and a power supply member to electrically connect the anode catalyst layer side and the cathode catalyst layer side.
In the water electrolyzer of the present invention, upon application of a direct-current voltage by the power supply member in a state where water is supplied to the anode catalyst layer side by the water supply member, on the anode catalyst layer side, water is decomposed to generate oxygen and protons. On the cathode catalyst layer side, protons transported to the cathode catalyst layer side by means of the electrolyte membrane gain electrons to generate hydrogen.
With the water electrolyzer of the present invention, which has the above-described membrane electrode assembly, decomposition of the fluorinated polymer contained in the membrane electrode assembly can be suppressed, and a low electrolysis voltage can be achieved.
The water electrolyzer of the present invention may have the same constitution as a known water electrolyzer (for example, an oxygen recovery member to recover the generated oxygen and a hydrogen recovery member to recover the generated hydrogen) except that it has the above members.
Now, the present invention will be described in further detail with reference to Examples. Ex. 1-1 to 1-10 and Ex. 2-1 to 2-3 are Examples for preparation of membrane (layer), Ex. 3-1 to 3-10 are Examples of the present invention, and Ex. 4-1 to 4-3 are Comparative Examples. It should be understood that the present invention is by no means restricted thereto.
The weight of a fluorinated polymer was measured after 24 hours of incubation in a glove box purged with dry nitrogen, as the dry mass of the fluorinated polymer. Then, the fluorinated polymer was soaked in 2 mol/L aqueous sodium chloride at 60° C. for 1 hour. The fluorinated polymer was washed with ultrapure water and recovered, and the solution in which the fluorinated polymer had been soaked was titrated with 0.1 mol/L aqueous sodium hydroxide to determine the ion exchange capacity of the fluorinated polymer (meq/g dry resin).
In the tables appearing later, IEC (meq/g) means ion exchange capacity (meq/g dry resin).
The thickness of a polymer electrolyte membrane was measured on a magnified cross-sectional image of the electrolyte layer (at an objective lens magnification of 50) taken by a laser microscope (model “VK-X1000”, manufactured by KEYENCE CORPORATION) at a temperature of 23° C. under a relative humidity of 50% RH.
The amount of substance (mol) of ion exchange groups of the fluorinated polymer was calculated by dividing the milliequivalent of ion exchange groups obtained from the following formula, by the ionic charge number of the ion exchange groups. For example, in a case where the ion exchange groups are sulfonic acid groups, the ionic charge number is 1.
The dry mass (g) of the fluorinated polymer was obtained as follows.
In a case where the dry mass of the fluorinated polymer was to be measured by using a membrane (for example an electrolyte membrane), the membrane was cut into 7 cm×7 cm and dried in a glove box in a stream of dry nitrogen for 72 hours, and its mass was measured in the glove box.
In a case where the dry mass of the fluorinated polymer was to be measured by using a dispersion of the fluorinated polymer (for example, a dispersion of the fluorinated polymer used for production of cathode catalyst layer), the dry mass of the fluorinated polymer in the dispersion was calculated based on the solid concentration (mass %) of the dispersion and the mass of the dispersion.
“AIEG_C”, which is the amount of substance of ion exchange groups of the fluorinated polymer contained in the cathode catalyst layer, was calculated by the above method using a dispersion of the fluorinated polymer to be used for production of the cathode catalyst layer.
The method for measuring the amount of substance of cerium ions using a membrane (for example an electrolyte membrane) was as follows.
First, a membrane cut into a size of 4 cm×4 cm was soaked in 10 mL of hydrochloric acid at 80° C. for 3 hours to extract cerium ions from the membrane. The membrane was taken out, and the cerium ion concentration in the hydrochloric acid was analyzed by ICP spectrometry to obtain the amount of substance (mol) of cerium ions contained in the membrane.
The amount of substance of cerium ions using a dispersion of the fluorinated polymer (for example a dispersion of the fluorinated polymer to be used for production of the cathode catalyst layer) was calculated based on the mass of a cerium salt added for production of the dispersion.
“ACe”, which is the amount of substance of cerium ions contained in the region overlapping the cathode catalyst layer when the membrane electrode assembly is observed from the normal direction of the surface, was measured in the same manner as the above measurement of the amount of substance of cerium ions using a membrane except that a sample having only the region overlapping the cathode catalyst layer cut from the membrane electrode assembly was used.
The sample is obtained by cutting off the peripheral edge portion (that is, a portion on which no cathode catalyst layer is provided) of the membrane electrode assembly, and has the same size (4 cm×4 cm) as the cathode catalyst layer. The sample contains the cathode catalyst layer, the electrolyte membrane and the anode catalyst layer.
A membrane electrode assembly was sandwiched between sintered products of titanium fiber (manufactured by Bekaert) having a 0.25-mm thickness and a 60% porosity so that the electrode area would be under a pressure of 1.5 MPa and mounted in a single cell having an electrode area of 16 cm2 with platinum-coated titanium plates having straight channels as separators and evaluated.
Next, pure water at 60° C. and ordinary pressure with an electrical conductivity of 1.0 μS/cm or less was supplied to both the anode catalyst layer side and the cathode catalyst layer side to fully hydrate the polymer electrolyte membrane and the ionomers in the electrodes at a flow rate of 50 mL/min for 8 hours. Then, supply of water to the cathode catalyst layer side was terminated, and water electrolysis was carried out by supplying pure water at 60° C. with electrical conductivity of 1.0 μS/cm or less to the anode catalyst layer side at a flow rate of 50 mL/min with back pressures on the anode catalyst layer side and on the cathode catalyst layer side kept at ordinary pressure, while the electric current was kept at 16 A (current density 1 A/cm2) during 4 hours of preliminary run and then increased from 0 A to 48 A (current density from 0 to 3 A/cm2) stepwise by 2 A at intervals of 5 minutes for measurement of electrolysis voltage under current control by a high current potentio/garvanostat HCP-803 (manufactured by Biologic). The electrolysis voltage at 48 A (current density 3 A/cm2) was rated on the following scale.
A membrane electrode assembly was sandwiched between sintered products of titanium fiber (manufactured by Bekaert) having a 0.25-mm thickness and a 60% porosity so that the electrode area would be under a pressure of 1.5 MPa and mounted in a single cell having an electrode area of 16 cm2 with platinum-coated titanium plates having straight channels as separators and evaluated.
Next, pure water at 60° C. and ordinary pressure with an electrical conductivity of 1.0 μS/cm or less was supplied to both the anode catalyst layer side and the cathode catalyst layer side to fully hydrate the polymer electrolyte membrane and the ionomers in the electrodes at a flow rate of 50 mL/min for 8 hours. Then, water electrolysis was carried out by supplying pure water at 60° C. with electrical conductivity of 1.0 μS/cm or less to the anode catalyst layer side at a flow rate of 50 mL/min with back pressures on the anode catalyst layer side and on the cathode catalyst layer side kept at ordinary pressure, while the electric current was kept at 16 A (current density 1 A/cm2) during 4 hours of preliminary run, and then by supplying pure water to the anode catalyst layer side at a flow rate of 150 mL/min with back pressures on the anode catalyst layer side and on the cathode catalyst layer side kept at 50 kPa while the current density was kept at 1 A/cm2 for 1000 hours, under current control by a high current potentio/garvanostat HCP-803 (manufactured by Biologic).
The drainage discharged from the cathode catalyst layer side over a period from 500 hours to 1000 hours after the start of preliminary run was sampled. The amount of fluoride ions contained in the drainage was determined by ion chromatography and averaged to calculate the average fluoride ion amount per unit electrode area per unit time and rated as the fluorine release rate on the following scale. A smaller fluorine release rate indicates that decomposition of the fluorinated polymer is more suppressed.
A polymer in acid form obtained by copolymerization of TEE and PSVE followed by hydrolysis and acid treatment (ion exchange capacity: 1.25 meq/g dry resin) was dispersed in a solvent of water/ethanol in a ratio of 40/60 (mass %) to obtain a dispersion having a solid content of 20.0% (hereinafter referred to also as “Dispersion X”). Dispersion X was applied onto an ethylene-tetrafluoroethylene copolymer (ETFE) sheet having a thickness of 100 μm with a die coater, dried at 80° C. for 15 minutes and heated at 160° C. for 30 minutes to obtain an electrolyte membrane. The amount of the liquid composition to be applied was adjusted so that the dry thickness of the electrolyte membrane would be 100 μm.
Into a PEA container, ultrapure water (100 g) and the electrolyte membrane having a size of 10 cm×15 cm were put so that the electrolyte membrane was soaked in ultrapure water. A 9.8 mmol/L aqueous cerium(III) nitrate (1.79 g) was further added, and the container was left at rest under normal pressure for 16 hours. 16 hours later, liquid in the container was thrown away, and the electrolyte membrane was washed with ultrapure water. After washing, the membrane was taken out, sandwiched between filter paper and air-dried for 3 days to obtain polymer electrolyte membrane M-1.
The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups of the polymer electrolyte membrane M-1, calculated from the amount of substance of cerium ions and the amount of substance of ion exchange groups (sulfonic acid groups) obtained by the above method, is shown in Table 1. In tables, the ratio of the amount of substance of cerium ions to the amount of substance of ion exchange groups is abbreviated as “Ce/IEG (mol %) in electrolyte membrane”.
Polymer electrolyte membrane M-2 was obtained in the same manner as in Ex. 1-1 except that the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 1.15 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-3 was obtained in the same manner as in Ex. 1-1 except that the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 0.26 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-4 was obtained in the same manner as in Ex. 1-1 except as follows. That is, a dispersion (hereinafter referred to also as “Dispersion Y”) obtained by dispersing a polymer in acid form obtained by copolymerization of TFE and PSVE followed by hydrolysis and acid treatment (ion exchange capacity: 1.10 meq/g dry resin) in a solvent of water/ethanol in a ratio of 40/60 (mass %) to have a solid content of 26.0%, was used as a dispersion for forming the polymer electrolyte membrane, and the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 1.01 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-5 was obtained in the same manner as in Ex. 1-1 except as follows. That is, a dispersion obtained by dispersing a polymer in acid form obtained by copolymerization of TFE and P2SVE followed by hydrolysis and acid treatment (ion exchange capacity: 1.95 meq/g dry resin) in a solvent of water/propanol in a ratio of 30170 (mass %) to have a solid content of 13.0%, was used as a dispersion for forming the polymer electrolyte membrane, the amount of the dispersion to be applied was adjusted so that the dry thickness of the electrolyte membrane would be 50 μm to obtain a 50 μm-thick electrolyte membrane, and the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added to introduce cerium ions to the electrolyte membrane was changed to 0.99 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-6 was obtained in the same manner as in Ex. 1-1 except as follows. That is, a dispersion obtained by dispersing a polymer in acid form obtained by copolymerization of TFE and PSVE followed by hydrolysis and acid treatment (ion exchange capacity: 1.38 meq/g dry resin) in a solvent of water/ethanol in a ratio of 40/60 (mass %) to have a solid content of 20.0%, was used as a dispersion for forming the polymer electrolyte membrane, and the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 1.27 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-7 was obtained in the same manner as in Ex. 1-1 except that the woven fabric-reinforced electrolyte membrane as described in Example 1 of WO2020/162511 was used as the polymer electrolyte membrane, and the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 1.03 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-8, containing no cerium ions, was obtained in the same manner as in Ex. 1-1 except that no 9.8 mmol/L aqueous cerium(III) nitrate was added. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-9 was obtained in the same manner as in Ex. 1-1 except that the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 6.50 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
Polymer electrolyte membrane M-10 was obtained in the same manner as in Ex. 1-1 except that the amount of the 9.8 mmol/L aqueous cerium(III) nitrate added was changed to 3.19 g. The ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups is shown in Table 1.
A platinum-loaded carbon powder catalyst having a platinum content of 46 mass % (11 g) (“TEC10E50E”, manufactured by TANAKA Kikinzoku Kogyo K.K.) was mixed with water (59.4 g) and ethanol (39.6 g) in an ultrasonic homogenizer to obtain a catalyst dispersion.
The catalyst dispersion was mixed with a mixture (29.2 g) preliminarily obtained by kneading Dispersion Y (20.1 g), ethanol (11 g) and ZEORORA H (6.3 g) (manufactured by ZEON CORPORATION), and then further mixed with water (3.66 g) and ethanol (7.63 g) with a paint conditioner for 60 minutes to obtain a cathode catalyst ink having a solid content of 10.0 mass %.
The cathode catalyst ink was applied onto an ETFE sheet with a die coater, dried at 80° C. and heated at 150° C. for 15 minutes to obtain cathode catalyst layer decal D-1 having a platinum content of 0.4 mg/cm2.
Dispersion Y (50 g) and cerium(III) carbonate octahydrate (0.43 g) were mixed at room temperature for 3 days to obtain a dispersion, which was heated at 160° C. for 3 hours to remove the solvent, and the ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups (sulfonic acid groups) of the obtained fluorinated polymer is shown in Table 2. In tables, the ratio of the amount of substance of cerium ions to the amount of substance of ion exchange groups is abbreviated as “Ce/IEG (mol %) in cathode catalyst layer”.
Cathode catalyst layer decal D-2 was obtained in the same manner as in Ex. 2-1 except that 20.1 g of the above obtained dispersion was added instead of Dispersion Y as the polymer dispersion used for the cathode catalyst ink.
Dispersion Y (50 g) and cerium(III) carbonate octahydrate (0.014 g) were mixed at room temperature for 3 days to obtain a dispersion, which was heated at 160° C. for 3 hours to remove the solvent, and the ratio (mol %) of the amount of substance of cerium ions to the amount of substance of ion exchange groups (sulfonic acid groups) of the obtained fluorinated polymer is shown in Table 2.
Cathode catalyst layer decal D-3 was obtained in the same manner as in Ex. 2-1 except that 20.1 g of the above obtained dispersion was added instead of Dispersion Y as the polymer dispersion used for the cathode catalyst ink.
Dispersion Y (33.0 g) was mixed with ethanol (18.06 g) and ZEORORA H (10.58 g) (manufactured by ZEON CORPORATION) in a planetary centrifugal mixer (THINKY MIXER, manufactured by THINKY CORPORATION) at 2200 rpm for 5 minutes. The resulting composition (54.06 g) was mixed with ethanol (46.44 g) and water (75.75 g), further with an iridium oxide catalyst (40.0 g) having an iridium content of 74.8 mass % and a specific surface area of 100 m2/g (manufactured by TANAKA Kikinzoku Kogyo K.K.). The resulting mixture was ground in a planetary bead mill (rotational speed 300 rpm) for 90 minutes to obtain an anode catalyst ink having a solid content of 22 mass %.
The anode catalyst ink was applied onto an ETFE sheet with an applicator so that the iridium content would be 1.0 mg/cm2, dried at 80° C. for 10 minutes and heated at 150° C. for 15 minutes to obtain anode catalyst layer decal.
Polymer electrolyte membrane M-1 cut into 7 cm×7 cm, anode catalyst layer decal cut into 4 cm×4 cm and cathode catalyst layer decal D-1 cut into 4 cm×4 cm were hot-pressed at a pressing temperature of 150° C. under a pressure of 3 MPA for 10 minutes so that the catalyst layer side of anode catalyst layer decal would face one side of polymer electrolyte membrane M-1, and the catalyst layer side of cathode catalyst layer decal D-1 would face the other side of polymer electrolyte membrane M-1. After cooling to 70° C., followed by removal of the pressure, the resulting laminate was taken out, and the ETFE sheets in anode catalyst layer decal and cathode catalyst layer decal were peeled off to obtain a membrane electrode assembly having an electrode area of 16 cm2. The membrane electrode assembly was evaluated by measuring the electrolysis voltage and fluorine release rate. The evaluation results are shown in Table 3.
Membrane electrode assemblies were obtained in the same manner as in Ex. 3-1 except that polymer electrolyte membranes M-2 to M-7 were used instead of polymer electrolyte membrane M-1. The evaluation results are shown in Table 3.
Membrane electrode assemblies were obtained in the same manner as in Ex. 3-1 except that polymer electrolyte membrane M-8 was used instead of polymer electrolyte membrane M-1 and cathode catalyst layer decal D-2 or D-3 was used instead of cathode catalyst layer decal D-1. The evaluation results are shown in Table 3.
A membrane electrode assembly was obtained in the same manner as in Ex. 3-1 except that polymer electrolyte membrane M-3 was used instead of polymer electrolyte membrane M-1 and cathode catalyst layer decal D-2 was used instead of cathode catalyst layer decal D-1. The evaluation results are shown in Table 3.
Membrane electrode assemblies were obtained in the same manner as in Ex. 3-1 except that polymer electrolyte membranes M-9, M-10 and M-8 were respectively used instead of polymer electrolyte membrane M-1. The evaluation results are shown in Table 3.
In each of the membrane electrode assemblies in Ex. 3-1 to 3-10, cerium ions were contained in the region overlapping the cathode catalyst layer when the membrane electrode assembly is observed from the normal direction of the surface.
It was confirmed from the results in Table 1 that when the membrane electrode assemblies in Ex. 3-1 to 3-10 of the present invention were used, as compared with Ex. 4-1 to 4-3, a low electrolysis voltage can be achieved, and decomposition of the fluorinated polymer contained can be suppressed.
This application is a continuation of PCT Application No. PCT/JP2022/041156, filed on Nov. 4, 2022, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-182813 filed on Nov. 9, 2021. The contents of those applications are incorporated herein by reference in their entireties.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-182813 | Nov 2021 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/041156 | Nov 2022 | WO |
| Child | 18650655 | US |
