Electrolyte membrane, membrane-catalyst layer structure, membrane-electrode assembly, water electrolysis cell, water electrolysis device, and water electrolysis method

Abstract

Provided is an electrolyte membrane having good electrolytic performance and durability. This electrolyte membrane includes a block copolymer having a segment containing an ionic group (hereinafter referred to as "ionic segment") and a segment not containing an ionic group (hereinafter referred to as "nonionic segment"). The block copolymer has a saturated crystallinity of 1.0% or more as measured by wide-angle X-ray analysis. The electrolyte membrane has a co-continuous phase separation structure. In an average cycle length of the co-continuous phase separation structure observed by a transmission electron microscope, the ratio (L1 / L2) between an average cycle length (L1) in a membrane surface direction of the electrolyte membrane and an average cycle length (L2) of the film thickness direction of the same is 0.50 or more.

Description

Electrolyte membrane, membrane-catalyst layer assembly, membrane-electrode assembly, water electrolysis cell, water electrolysis device, and water electrolysis method

[0001] The present invention relates to an electrolyte membrane, a membrane-catalyst layer assembly, a membrane-electrode assembly, a water electrolysis cell, a water electrolysis device, and a water electrolysis method.

[0002] In recent years, due to environmental problems such as global warming, hydrogen has attracted attention as a clean energy source to replace fossil fuels. Hydrogen is expected to be a clean energy because it basically emits only water even when burned and does not emit carbon dioxide, which causes global warming.

[0003] The production of hydrogen is mainly carried out by electrolysis of water. As a method for producing hydrogen by electrolysis of water, alkaline water electrolysis and polymer electrolyte membrane (PEM) type water electrolysis are known. Among them, the PEM type water electrolysis method has the merit that it can be operated at a high current density and can flexibly cope with the output fluctuations of renewable energy.

[0004] The PEM type water electrolysis method is a method in which water is supplied to a water electrolysis cell in which an anode and a cathode are arranged opposite to each other with a diaphragm including a polymer electrolyte membrane interposed therebetween, and oxygen is generated at the anode and hydrogen is generated at the cathode. As the polymer electrolyte constituting the polymer electrolyte membrane, fluorine-based polymer electrolytes such as perfluorocarbon sulfonic acid have been generally known (for example, see Patent Document 1).

[0005] International Publication No. 2020 / 175677

[0006] In order to promote the spread of hydrogen energy, reduction of hydrogen production cost is required. In order to reduce the hydrogen production cost, it is effective to be able to maintain relatively high electrolysis performance for a long time in the same cell without replacing the water electrolysis cell. However, the technique described in Patent Document 1 was insufficient in terms of maintaining relatively high electrolysis performance for a long time.

[0007] Therefore, an object of the present invention is to provide an electrolyte membrane capable of maintaining good electrolysis performance for a long time in view of the above problems.

[0008] The above object of the present invention is achieved by the following invention: [1] An electrolyte membrane comprising a block copolymer having a segment containing an ionic group (hereinafter referred to as "ionic segment") and a segment not containing an ionic group (hereinafter referred to as "nonionic segment"), wherein the block copolymer has a saturated crystallinity of 1.0% or more as measured by wide-angle X-ray analysis, the electrolyte membrane has a cocontinuous phase separation structure, and the ratio (L2 / L1) of the average period length of the cocontinuous phase separation structure observed by a transmission electron microscope to the average period length in the film thickness direction (L2) of the electrolyte membrane is 0.50 or more. [2] The electrolyte membrane according to [1], wherein the ratio (L2 / L1) is 0.50 or more and 1.90 or less. [3] The electrolyte membrane according to [1] or [2], wherein the average period length (L1) in the film thickness direction is 15 nm or more and less than 90 nm. [4] The electrolyte membrane according to any one of [1] to [3], wherein the thickness of the electrolyte membrane is 20 μm or more and less than 200 μm. [5] The electrolyte membrane according to any one of [1] to [4], wherein the ionic segment and the nonionic segment each contain a hydrocarbon polymer. [6] The electrolyte membrane according to [5], wherein the hydrocarbon polymer is an aromatic hydrocarbon polymer. [7] The electrolyte membrane according to [6], wherein the aromatic hydrocarbon polymer is an aromatic polyetherketone polymer. [8] The electrolyte membrane according to any one of [1] to [7], wherein the number average molecular weight of the ionic segment is 30,000 or more. [9] A membrane-catalyst layer structure having an anode catalyst layer on one side and a cathode catalyst layer on the other side of the electrolyte membrane according to any one of [1] to [8], wherein the anode catalyst layer contains iridium and the cathode catalyst layer contains platinum.

[10] The membrane-catalyst layer structure according to [9], wherein the cathode catalyst layer contains platinum and ruthenium. A membrane-electrode assembly comprising electrode substrates arranged on both sides of the membrane-catalyst layer structure described in

[11] , [9], or

[10] . A water electrolysis cell comprising the membrane-electrode assembly described in

[12] ,

[11] . A water electrolysis apparatus comprising the water electrolysis cell described in

[13] ,

[12] .A water electrolysis method in which water is supplied to a water electrolysis cell internally partitioned into an anode and a cathode by an electrolyte membrane according to any one of

[14] [1]~[8], and water is electrolyzed to generate oxygen at the anode and hydrogen at the cathode, wherein the anode catalyst layer constituting the anode contains an iridium element, and the cathode catalyst layer constituting the cathode contains a platinum element.

[15] The water electrolysis method according to

[14] , wherein the cathode catalyst layer contains a platinum element and a ruthenium element.

[0009] According to the present invention, an electrolyte membrane capable of maintaining good electrolysis performance over a long period of time can be provided. Hereinafter, the performance of maintaining electrolysis performance over a long period of time may be referred to as "durability". That is, the electrolyte membrane of the present invention can achieve good electrolysis performance and good durability.

[0010] It is a schematic diagram of a phase separation structure in an electrolyte membrane. It is a schematic side view of an example of a film-forming apparatus for an electrolyte membrane according to an embodiment of the present invention. It is a cross-sectional schematic view showing an example of a water electrolysis cell that can be used in the present invention.

[0011] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be variously modified and implemented according to the purpose and application.

[0012] The electrolyte membrane according to an embodiment of the present invention includes a block copolymer (hereinafter sometimes simply referred to as "block copolymer") having a segment containing an ionic group (hereinafter referred to as "ionic segment") and a segment not containing an ionic group (hereinafter referred to as "non-ionic segment"), respectively. This block copolymer functions as a polymer electrolyte.

[0013] The block copolymer has a saturation crystallinity (hereinafter simply referred to as "saturation crystallinity") of 1.0% or more, as measured by wide-angle X-ray diffraction. Electrolyte membranes containing such block copolymers have improved durability. From the viewpoint of durability, the saturation crystallinity of the block copolymer is preferably 2.0% or more, more preferably 3.0% or more, even more preferably 4.0% or more, and particularly preferably 5.0% or more. The above saturation crystallinity is preferably 30.0% or less, more preferably 25.0% or less, even more preferably 23.0% or less, and particularly preferably 20.0% or less.

[0014] Saturated crystallinity refers to the degree of crystallinity at which crystallization can no longer proceed, i.e., the maximum degree of crystallinity. The saturated crystallinity of a block copolymer can be measured using a film made of the block copolymer.

[0015] Specifically, a film made of block copolymer is heated and pressed at 4.5 MPa at a temperature above the glass transition temperature (Tg) of the block copolymer. The degree of crystallinity is measured every 5 minutes by wide-angle X-ray diffraction, and the degree of crystallinity at which it stops changing is defined as the saturated degree of crystallinity. The appropriate heating temperature (T (°C)) during heating and pressing is Tg + 5°C.

[0016] The important aspect of the electrolyte membrane according to the embodiment of the present invention is that it contains a block copolymer having the characteristic of having a saturation crystallinity of 1.0% or more. For example, the crystallinity of the block copolymer when incorporated into a water electrolysis device does not necessarily need to reach the saturation crystallinity.

[0017] The degree of crystallinity of a block copolymer can be increased by heating it to a temperature above its glass transition temperature. In this case, the degree of crystallinity of the block copolymer may be increased to approximately the same level as the saturation degree of crystallinity, or it may be increased to approximately 1-99% of the saturation degree of crystallinity.

[0018] As described above, electrolyte membranes containing block copolymers with a saturation crystallinity of 1.0% or more exhibit improved durability, but tend to have reduced electrolytic performance. The inventors of this invention have conducted extensive research to improve the electrolytic performance of such electrolyte membranes and have found that the electrolytic performance is improved when the electrolyte membrane has a co-continuous phase separation structure, and the ratio (L2 / L1) of the average period length in the membrane plane direction (L1) to the average period length in the film thickness direction (L2) of this co-continuous phase separation structure is 0.50 or more.

[0019] [Phase Separation Structure of Electrolyte Membranes] The phase separation structure of electrolyte membranes can be confirmed by observation using a transmission electron microscope (TEM). When an electrolyte membrane forms a phase separation structure, it can be broadly classified into four types, as shown in Figure 1: co-continuous (M1), lamellar (M2), cylindrical (M3), and sea-island (M4).

[0020] In Figure 1, the white continuous phase (Phase 1) is formed by one segment selected from the ionic and nonionic segments, while the gray continuous or dispersed phase (Phase 2) is formed by the other segment. This phase separation structure is described, for example, in the Annual Review of Physical Chemistry, 41, 1990, p. 525.

[0021] In a co-continuous phase separation structure, hydrophilic and hydrophobic domains both form a continuous phase, and each of these continuous phases exhibits an intricate pattern. The presence of a co-continuous phase separation structure in an electrolyte membrane can be confirmed by the following method.

[0022] Specifically, a three-dimensional image obtained by TEM tomography observation is compared with three digital slice views taken from the length, width, and height directions. For example, in an electrolyte membrane containing a block copolymer having ionic and nonionic segments, if a co-continuous phase separation structure is formed, all three views will show that the hydrophilic domains containing ionic segments and the hydrophobic domains containing nonionic segments form a continuous phase, and each of the continuous phases exhibits an intricate pattern. Here, a continuous phase refers to a phase in which, macroscopically, individual domains are connected rather than isolated. However, it is acceptable for some parts to be unconnected.

[0023] In observing the phase separation structure, to clarify the aggregation state and contrast of ionic and nonionic segments, for example, the electrolyte membrane can be immersed in a 2% lead acetate aqueous solution for two days to exchange the ionic groups with lead, and then subjected to transmission electron microscopy (TEM) and TEM tomography observation.

[0024] The period length of a co-continuous phase separation structure can be expressed as the period size of the hydrophilic domain containing the ionic segment and the hydrophobic domain containing the nonionic segment. The period length of such a co-continuous phase separation structure can be estimated from the autocorrelation function obtained by image processing of the co-continuous phase separation structure obtained by transmission electron microscopy (TEM) observation.

[0025] Co-continuous phase separation structures are formed three-dimensionally, and their period lengths can be measured in both the direction of the electrolyte membrane and the direction of the film thickness. However, conventionally, when referring to the period length of a co-continuous phase separation structure, the period length in the direction of the membrane is often considered, and the period length in the direction of the film thickness has not received much attention. Possible reasons for this include the fact that measuring the period length in the direction of the film thickness requires measuring the membrane cross-section, which is more difficult than measuring it in the direction of the membrane, and that the period length in the direction of the film thickness is considerably smaller than the period length in the direction of the membrane.

[0026] Against this technological backdrop, the inventors focused on the period length in the film thickness direction of the co-continuous phase separation structure formed in the electrolyte membrane and found that the electrolytic performance is improved when the ratio (L2 / L1) of the average period length in the film surface direction (L1) to the average period length in the film thickness direction (L2) is 0.50 or higher. Hereinafter, the above ratio (L2 / L1) may be simply referred to as "L2 / L1".

[0027] From the viewpoint of electrolytic performance, L2 / L1 is preferably 0.55 or higher, more preferably 0.60 or higher, even more preferably 0.70 or higher, and particularly preferably 0.80 or higher. On the other hand, from the viewpoint of durability, it is preferably 1.90 or lower, more preferably 1.50 or lower, even more preferably 1.30 or lower, and particularly preferably 1.10 or lower.

[0028] The average period length (L1) in the film plane direction is preferably 15 nm or more and less than 90 nm, more preferably 20 nm or more and less than 80 nm, and particularly preferably 25 nm or more and less than 70 nm.

[0029] The average period length (L2) in the film thickness direction is preferably 10 nm or more and less than 80 nm, more preferably 15 nm or more and less than 70 nm, and particularly preferably 20 nm or more and less than 60 nm.

[0030] In the present invention, an electrolyte membrane containing a block copolymer having an ionic segment and a nonionic segment and a saturated crystallinity of 1.0% or more increases the L2 / L1 ratio by increasing the film thickness.

[0031] In other words, the electrolyte membrane according to the embodiment of the present invention preferably has a relatively large film thickness, in order to control L2 / L1 within the above-mentioned range. For example, the thickness of the electrolyte membrane is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 40 μm or more, and particularly preferably 50 μm or more. On the other hand, as the thickness of the electrolyte membrane increases, the membrane resistance increases and the electrolytic performance tends to decrease, so the film thickness is preferably less than 200 μm, more preferably less than 180 μm, even more preferably less than 160 μm, and particularly preferably less than 130 μm.

[0032] [Block Copolymer] A block copolymer has both an ionic segment and a nonionic segment. In the present invention, a segment is a partial structure in the block copolymer that originates from a macromonomer used in the synthesis of the block copolymer.

[0033] Although it is stated that nonionic segments do not contain ionic groups, they may contain small amounts of ionic groups as long as they are sufficiently small compared to the ion exchange capacity of the ionic segment. When a nonionic segment contains small amounts of ionic groups, the ion exchange capacity of the nonionic segment is preferably 1 / 10 or less of the ion exchange capacity of the ionic segment, more preferably 1 / 30 or less, particularly preferably 1 / 50, and most preferably contains no ionic groups at all.

[0034] Block copolymers are required to have a saturated crystallinity of 1.0% or higher and to be able to form a co-continuous phase separation structure. From this viewpoint, it is preferable that the ionic and nonionic segments constituting the block copolymer each contain hydrocarbon polymers. Here, hydrocarbon polymers do not include perfluorohydrocarbon polymers.

[0035] Furthermore, among hydrocarbon polymers, hydrocarbon polymers having aromatic rings in the main chain (hereinafter referred to as "aromatic hydrocarbon polymers") are preferred.

[0036] The aromatic rings contained in aromatic hydrocarbon polymers may include not only hydrocarbon aromatic rings but also heterocycles. Furthermore, some aliphatic units may constitute the polymer together with the aromatic ring units. Specific examples of aromatic hydrocarbon polymers include polymers having structures selected from polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene polymers, polyarylene ketone, polyether ketone, polyarylene phosphine foxide, polyetherphosphine foxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain together with aromatic rings. Among these, aromatic polyether polymers are preferred from the viewpoint of cost and polymerizability.

[0037] Aromatic polyether polymers are polymers mainly composed of aromatic rings in which at least ether bonds are included as a linking mechanism between aromatic ring units within the repeating unit. Examples of aromatic polyether polymers include, but are not limited to, aromatic polyethers, aromatic polyether ketones, aromatic polyetherimides, and aromatic polyethersulfones. From the viewpoint of saturated crystallinity, aromatic polyether ketone polymers are the most preferred.

[0038] Aromatic polyetherketone polymers are polymers primarily composed of aromatic rings, in which at least ether and ketone bonds are included in the linking mechanism of the aromatic ring units within the repeating unit. Aromatic polyetherketone polymers include aromatic polyetherketones, aromatic polyetheretherketones, aromatic polyetherketoneketones, aromatic polyetheretherketoneketones, aromatic polyetherketoneketones, aromatic polyetherketoneetherketoneketones, and aromatic polyetherketoneetherketoneketones.

[0039] As described above, the ionic segment and the non-ionic segment preferably each contain an aromatic polyether ketone polymer. The aromatic polyether ketone polymer constituting the ionic segment preferably contains a structure represented by the following general formula (S1). Further, the aromatic polyether ketone polymer constituting the non-ionic segment preferably contains a structure represented by the following general formula (S3).

[0040]

[0041] In the general formula (S1), Ar ８ to Ar ４ each independently represents a substituted or unsubstituted arylene group, and at least one of Ar １ to Ar ４ has an ionic group. Y １ and Y ２ each independently represents a ketone group or a protecting group that can be derived from a ketone group. * represents a bond with an adjacent segment.

[0042]

[0043] In the general formula (S3), Ar ５ to Ar ８ each independently represents a substituted or unsubstituted arylene group. However, none of Ar ５ to Ar ８ has an ionic group. Y ３ and Y ４ each independently represents a ketone group or a protecting group that can be derived from a ketone group. * represents a bond with an adjacent segment.

[0044] Here, examples of the arylene group represented by Ar １ to Ar ８ include a phenylene group, a naphthylene group, a biphenylene group, and the like. The arylene group represented by Ar １ to Ar ８ is preferably a phenylene group. At least one of Ar １ to Ar ４ is preferably a phenylene group having an ionic group. Further, Ar ５ to Ar８ The arylene group represented by may be substituted with groups other than ionic groups, but it is more preferable to be unsubstituted in terms of proton conductivity, chemical stability, and physical durability.

[0045] Y １ ~Y ４ The protecting groups that can be converted to the ketone group represented by are not particularly limited, but examples include those that yield a ketone group by hydrolysis. Examples of such protecting groups include ketal groups, acetal groups, or heteroatom analogs thereof (e.g., thioacetals and thioketals). Among these, ketal groups are preferred. These protecting groups are preferably converted to ketone groups by acid treatment (hydrolysis) after the electrolyte membrane has been formed.

[0046] The above-mentioned ionic group includes cases where it is in the form of a salt. Examples of cations that form such salts include any metal cation, ammonium cation, etc. There are no particular restrictions on the metal cation, but metals selected from Na, K, and Li are preferred because they are inexpensive and can be easily proton-substituted.

[0047] These ionic groups can be present in two or more types within the ionic segment. In particular, from the viewpoint of high proton conductivity, it is more preferable to include at least a group selected from sulfonic acid groups, sulfonimide groups, and sulfate groups, and from the viewpoint of raw material cost, it is especially preferable to include a sulfonic acid group.

[0048] The structure represented by general formula (S1) is preferably the structure represented by the following general formula (S2).

[0049]

[0050] In the general formula (S2), Y １ and Y ２ This is the Y of the general formula (S1). １ and Y ２ This is synonymous with M. １ ~M ４ Each of these independently represents a hydrogen atom, a metal cation, or an ammonium cation. １ ~n ４Each of these is independently either 0 or 1, and n １ ~n ４ At least one of them is 1. * indicates a connection with an adjacent segment.

[0051] Furthermore, from the standpoint of raw material availability and polymerizability, n １ = 1, n ２ = 1, n ３ = 0, n ４ = 0 or n １ = 0, n ２ = 0, n ３ = 1, n ４ It is most preferable that the value be 1.

[0052] The structure represented by general formula (S3) is preferably the structure represented by the following general formula (S4).

[0053]

[0054] In the general formula (S4), Y ３ and Y ４ This is the Y of the general formula (S3). ３ and Y ４ This is synonymous with the above. * indicates a connection with an adjacent segment.

[0055] The content of the constituent unit represented by general formula (S1) in the ionic segment is more preferably 20 mol% or more, even more preferably 50 mol% or more, and most preferably 80 mol% or more. Furthermore, the content of the structure represented by general formula (S3) in the nonionic segment is more preferably 20 mol% or more, more preferably 50 mol% or more, and even more preferably 80 mol% or more.

[0056] The block copolymer preferably contains one or more linker moieties that connect the ionic segment and the nonionic segment. Such a block copolymer is more likely to form a co-continuous-like phase separation structure.

[0057] The linker region described above is defined as a region that connects an ionic segment and a nonionic segment, and which has a different chemical structure from the ionic segment or the nonionic segment.

[0058] Linker moieties have the function of linking different segments while suppressing randomization of copolymers by ether exchange reactions, segment cleavage, and other side reactions that may occur during copolymer synthesis. Therefore, by using compounds that provide such linker moieties as raw materials for block copolymers, block copolymers can be obtained without reducing the molecular weight of each segment. Examples of compounds that provide linker moieties include, but are not limited to, decafluorobiphenyl, hexafluorobenzene, 4,4'-difluorodiphenylsulfone, and 2,6-difluorobenzonitrile.

[0059] By controlling the number-average molecular weight of the ionic and nonionic segments constituting the block copolymer, the saturation crystallinity and (L2 / L1) can be adjusted to the desired range described above. For example, from the viewpoint of polymerizability, the number-average molecular weight of the ionic segment is preferably 18,000 or more, more preferably 30,000 or more, even more preferably 34,000 or more, and particularly preferably 45,000 or more. There is no particular upper limit to the number-average molecular weight, but from the viewpoint of polymerizability, it is preferably 150,000 or less, more preferably 120,000 or less, even more preferably 110,000 or less, and particularly preferably 100,000 or less. On the other hand, the number-average molecular weight of the nonionic segment is preferably 5,000 or more, more preferably 8,000 or more, and particularly preferably 10,000 or more. There is no particular upper limit to the number-average molecular weight, but from the viewpoint of polymerizability, it is preferably 50,000 or less, more preferably 40,000 or less, and particularly preferably 30,000 or less.

[0060] Furthermore, when the number-average molecular weight of the ionic segment is Mn1 and the number-average molecular weight of the non-ionic segment is Mn2, it is preferable that the following formula (1) is satisfied. Such block copolymers are preferable from the viewpoint of adjusting the degree of saturated crystallinity and (L2 / L1) to the aforementioned range. 1.8 ≤ Mn1 / Mn2 ≤ 6.5 ... Formula (1).

[0061] The ion exchange capacity (IEC) of the block copolymer is preferably 1.5 meq / g or more, more preferably 1.8 meq / g or more, even more preferably 1.9 meq / g or more, and particularly preferably 2.0 meq / g or more, from the viewpoint of adjusting the degree of saturated crystallinity and (L2 / L1) to the aforementioned ranges. Furthermore, the above IEC is preferably 2.7 meq / g or less, more preferably 2.5 meq / g or less, even more preferably 2.3 meq / g or less, and particularly preferably 2.2 meq / g or less.

[0062] IEC refers to the molar amount of ion exchange groups introduced per unit dry mass of a block copolymer. IEC can be measured by elemental analysis, neutralization titration, etc. When the ion exchange group is a sulfonic acid group, it can also be calculated from the S / C ratio using elemental analysis, but measurement is difficult when sulfur sources other than sulfonic acid groups are present. Therefore, in this invention, IEC is defined as the value obtained by the neutralization titration method described later.

[0063] [Electrolyte Membrane] The polymer electrolyte contained in the electrolyte membrane according to the embodiment of the present invention preferably contains 60% by mass or more of block copolymer, more preferably 70% by mass or more, even more preferably 85% by mass or more, and particularly preferably 95% by mass or more, based on 100% by mass of the total amount of polymer electrolyte. The upper limit is 100% by mass.

[0064] Furthermore, the electrolyte membrane of the present invention preferably contains 50% by mass or more of block copolymer, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 95% by mass or more, based on 100% by mass of the total solid content of the electrolyte membrane. The upper limit is 100% by mass. The solid content referred to here is the component used in the manufacture of the electrolyte membrane, excluding the solvent.

[0065] To further improve durability, the electrolyte membrane may include a porous substrate such as a nonwoven fabric, porous film, or mesh fabric. One form of the electrolyte membrane that includes a porous substrate is a composite layer containing a porous substrate and a polymer electrolyte, with a non-composite layer containing the polymer electrolyte but not the porous substrate on one or both sides of the composite layer. Here, the polymer electrolyte includes at least a block copolymer.

[0066] In embodiments including a porous substrate, with the thickness of the electrolyte membrane being 100%, the thickness of the composite layer is preferably 10 to 90%, more preferably 20 to 80%, and particularly preferably 30 to 70%. Here, the thickness of the composite layer refers to the thickness of the porous substrate.

[0067] When the electrolyte membrane includes a porous substrate, from the viewpoint of electrolytic performance, the mass ratio of the porous substrate in the electrolyte membrane is preferably less than 50% by mass, more preferably less than 40% by mass, and particularly preferably less than 30% by mass, based on 100% by mass of the total solid content of the electrolyte membrane.

[0068] The electrolyte membrane may contain various additives, such as antioxidants, surfactants, radical scavengers, hydrogen peroxide decomposers, non-electrolyte polymers, elastomers, fillers, etc., as long as they do not impair the effects of the present invention.

[0069] [Method for forming an electrolyte membrane] The method for forming an electrolyte membrane preferably includes a coating step of applying a solution containing a block copolymer and a solvent onto a support film, and a drying step. The support film is not particularly limited, but for example, polyethylene terephthalate film is preferably used. The thickness of the support film is preferably in the range of 150 to 400 μm. The support film is ultimately peeled off and removed from the electrolyte membrane.

[0070] The solution used in the coating process is prepared by dissolving the block copolymer in a suitable solvent. Preferred solvents include aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphontriamide. The solid content concentration in the solution is preferably in the range of 1 to 40% by mass, more preferably in the range of 2 to 35% by mass, and particularly preferably in the range of 3 to 30% by mass. The thickness of the resulting electrolyte membrane can be adjusted by controlling the concentration and amount of this solution during the coating process.

[0071] The coating method is not particularly limited, and any known coating method can be used. Examples include dip coating, reverse coating, spray coating, bar coating, knife coating, direct roll coating, Meyer bar coating, gravure coating, rod coating, die coating, spin coating, extrusion coating, and curtain coating. Among these, a coating method in which the supply amount can be controlled in advance to achieve a predetermined coating amount, a so-called non-contact pre-metering coating method, is preferred. Examples of such coating methods include die coating, extrusion coating, and curtain coating. Among these, die coating is particularly preferred.

[0072] The drying process involves evaporating the solvent from the solution applied to the support film. Drying methods include using a floating dryer, a heating furnace, or a heating roll, either individually or in combination. Among these, a floating dryer is preferred. A floating dryer dries the support film, which is coated with the solution, by blowing heated air from both above and below, while it is being transported in a floating state.

[0073] It is preferable to set the drying temperature in stages, for example, to a relatively low temperature in the initial stage of drying and a relatively high temperature in the later stage of drying. Specifically, it is preferable to set the temperature to 50-90°C in the initial stage, 90-110°C in the middle stage, and 110-180°C in the later stage of drying. By performing the drying at a relatively low temperature in the initial stage and a relatively high temperature in the later stage, the L2 / L1 ratio tends to increase.

[0074] The above coating and drying processes are preferably carried out using a roll-to-roll method. The roll-to-roll method is a method in which the coating and drying processes are carried out while the support film unwound from the support film supply roll is transported, and then the support film with the electrolyte membrane formed on it is wound into a roll shape.

[0075] Figure 2 is a schematic side view of an example of a roll-to-roll film-forming apparatus. This apparatus includes an unwinding device 110, a coating device 120, a drying oven 130, and a winding device 140. A support film 112 is unwound from a support film supply roll 111 pivotally supported by the unwinding device 110, a solution (not shown) is applied to it by the coating device 120, and it is dried in the drying oven 130 to form an electrolyte film (not shown) on the support film 112. After that, it is wound into a roll by the winding device 140.

[0076] The electrolyte membrane formed as described above preferably undergoes an acid treatment step to carry out a proton substitution and / or deprotection reaction. The acid treatment step is preferably carried out with the electrolyte membrane laminated on a support film. The acid treatment step includes, for example, immersing the support film on which the electrolyte membrane is formed in an acidic solution, washing with water, and drying, in that order. As an acid treatment apparatus, for example, the apparatus described in Japanese Patent Application Publication No. 2011-194593 and International Publication No. 2017 / 141710 can be used.

[0077] [Membrane / Catalyst Layer Structure] The electrolyte membrane according to the embodiment of the present invention is preferably used in a water electrolysis device. The electrolyte membrane is incorporated into the water electrolysis cell of a water electrolysis device with a catalyst layer and an electrode substrate arranged on both sides thereof. An electrolyte membrane with catalyst layers arranged on both sides thereof is called a "membrane / catalyst layer structure," and an electrolyte membrane with electrode substrates arranged on both sides thereof is called a "membrane / electrode assembly."

[0078] The membrane / catalyst layer structure can be obtained, for example, by stacking an anode catalyst layer and a cathode catalyst layer on an electrolyte membrane. Hereinafter, the anode catalyst layer and the cathode catalyst layer will be collectively referred to as the "catalyst layer."

[0079] Methods for laminating a catalyst layer onto an electrolyte membrane include, for example, a coating method, a transfer method, or a combination of a coating method and a transfer method. These methods are not particularly limited, and known methods can be employed.

[0080] One possible coating method is to apply a coating solution for the catalyst layer to the electrolyte membrane using a known coating method.

[0081] One transfer method involves stacking a catalyst layer transfer sheet, which has a catalyst layer laminated on a transfer substrate, with an electrolyte membrane and then heating and pressing them together.

[0082] [Anode Catalyst Layer] The anode catalyst layer more preferably contains iridium. Iridium functions as a catalyst in the anode catalyst layer. Since the anode electrolyzes water to produce oxygen and protons, the anode catalyst is sometimes called an oxygen evolution catalyst. Iridium is useful as an oxygen evolution catalyst. In other words, the electrolytic performance of the anode catalyst layer is enhanced by containing iridium as a catalyst.

[0083] Catalysts containing iridium can include zero-valent iridium, iridium oxide, iridium carbide, iridium nitride, and others. Iridium oxide is preferred because it can maintain good electrolytic performance for a longer period of time. The catalyst containing iridium is preferably in the form of particles.

[0084] The iridium-containing catalyst may be catalyst-supported particles supported on a support made of a metal oxide such as titanium oxide, tin oxide, tantalum oxide, niobium oxide, zirconium oxide, or tungsten oxide. Since the anode in water electrolysis is in a high-potential environment, a support with relatively high electrochemical oxidation resistance is preferred. In this respect, the above-mentioned metal oxides are preferred because they have relatively high electrochemical oxidation resistance.

[0085] As for catalysts containing iridium, it is preferable to use iridium-containing particles alone, or catalyst-supported particles supported on a metal oxide carrier. Among these, it is particularly preferable to use iridium-containing particles alone.

[0086] Carbon particles, such as carbon black, are commonly known as carriers for catalyst-supported particles. However, carbon particles generally have low electrochemical oxidation resistance, and if they are included in too large a quantity, it can affect the durability of the catalyst layer. Therefore, it is preferable to reduce the carbon particle content in the anode catalyst layer. The carbon particle content in the anode catalyst layer is 0.1 mg / cm³. ２ Preferably less than 0.05 mg / cm³. ２ Less than 0.02 mg / cm³ is more preferable, and 0.02 mg / cm³ is preferable. ２ Less than 100% is even more preferable, and it is especially preferable that it contains none at all.

[0087] The iridium content in the anode catalyst layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, based on 100% by mass of the total amount of all metal elements contained in the anode catalyst layer. The upper limit is preferably 100% by mass or less.

[0088] The anode catalyst layer may further contain elements other than iridium as catalysts, such as precious metal elements (hereinafter referred to as "other precious metal elements"), including platinum, ruthenium, rhodium, palladium, gold, silver, and osmium. In water electrolysis, there is a risk of explosion due to the mixing of hydrogen into the oxygen produced at the anode by the back diffusion of hydrogen produced at the cathode. However, the above-mentioned other precious metal elements function as catalysts that produce water from hydrogen and oxygen, thus avoiding the risk of explosion. From this viewpoint, platinum and palladium are preferred as other precious metal elements, with platinum being particularly preferred. Catalysts containing platinum and palladium include those with zero valence, oxides, carbides, and nitrides, respectively. Among these, those with zero valence are preferred.

[0089] If other precious metal elements are present, the content of the other precious metal elements is preferably in the range of 1 to 90 parts by mass, more preferably in the range of 5 to 80 parts by mass, and particularly preferably in the range of 10 to 50 parts by mass, per 100 parts by mass of iridium.

[0090] In the anode catalyst layer, the mass of iridium element per unit area is 0.2 to 2.0 mg / cm². ２ A range of 0.4 to 1.5 mg / cm² is preferred. ２ A range of 0.6 to 1.3 mg / cm² is more preferable. ２ The range is particularly preferable.

[0091] The anode catalyst layer preferably further contains a polymer electrolyte. Hydrocarbon-based polymer electrolytes or fluorine-based polymer electrolytes can be used. Since the anode is in a high-potential environment in a water electrolysis device, it is preferable to use a fluorine-based polymer electrolyte, which has relatively good resistance to electrochemical oxidation, and perfluorocarbon sulfonic acid-based polymers are even more preferable.

[0092] When the anode catalyst layer contains a polymer electrolyte, the ratio (Ya) of the mass of iridium elements contained in the anode catalyst layer to the mass of the polymer electrolyte, i.e., "(mass of polymer electrolyte) / (mass of iridium elements)", is preferably 0.05 or higher, more preferably 0.07 or higher, and particularly preferably 0.1 or higher, from the viewpoint of electrolytic performance. Furthermore, from the viewpoint of the diffusibility of oxygen gas generated in the anode, the above ratio is preferably less than 0.5, more preferably less than 0.4, even more preferably less than 0.3, and particularly preferably less than 0.25.

[0093] From the viewpoint of electrolytic performance, the thickness of the anode catalyst layer is preferably 0.5 μm or more, more preferably 1 μm or more, and particularly preferably 3 μm or more. Furthermore, from the viewpoint of the diffusibility of oxygen gas generated in the anode and physical stability (such as cracking during operation), the above thickness is preferably 25 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less.

[0094] [Cathode Catalyst Layer] The cathode catalyst layer preferably contains platinum. Platinum functions as a catalyst in the cathode catalyst layer. In water electrolysis, the cathode reduces protons generated at the anode to produce hydrogen, so the cathode catalyst is sometimes called a proton reduction catalyst. Platinum is useful as a proton reduction catalyst.

[0095] As a catalyst containing platinum, a catalyst in which platinum is supported on carbon particles (hereinafter referred to as "platinum-supported carbon particles") is preferred from the viewpoint of electrolytic performance. Examples of the above carbon particles include carbon black such as furnace black, acetylene black, and Ketjen black, and carbon black obtained by graphitizing these carbon particles.

[0096] The platinum loading rate (ratio of the mass of platinum element to the mass of platinum-supported carbon particles) in platinum-supported carbon particles is preferably in the range of 20 to 70 mass%, more preferably in the range of 30 to 65 mass%, and particularly preferably in the range of 35 to 60 mass%.

[0097] The cathode catalyst layer is more preferably composed of platinum and ruthenium as catalysts. This is expected to further improve durability. From the viewpoint of durability, the mass ratio of platinum (Pt) to ruthenium (Ru) (Ru / Pt) is preferably 0.1 or higher, more preferably 0.2 or higher, even more preferably 0.3 or higher, and particularly preferably 0.4 or higher. On the other hand, from the viewpoint of electrolytic performance, it is preferably 2.0 or lower, more preferably 1.7 or lower, even more preferably 1.5 or lower, and particularly preferably 1.3 or lower.

[0098] Catalysts containing platinum and catalysts containing ruthenium may be used individually, or a platinum-ruthenium alloy may be used. From the viewpoint of durability, a platinum-ruthenium alloy is preferred. Furthermore, "platinum-ruthenium alloy-supported carbon particles" in which the platinum-ruthenium alloy is supported on carbon particles are preferred. The same carbon particles as described above can be used.

[0099] In the cathode catalyst layer, the mass of platinum element per unit area is 0.05 mg / cm², from the viewpoint of electrolytic performance. ２ The above is preferable, and 0.1 mg / cm³ ２ The above is more preferable, 0.2 mg / cm³ ２ The above is particularly preferable. Furthermore, the mass of the platinum element is 1.0 mg / cm³ from the viewpoint of cost. ２ Preferably less than 0.7 mg / cm³. ２ Less than 0.5 mg / cm³ is more preferable, and 0.5 mg / cm³ is preferable. ２ Less than is particularly preferable.

[0100] The mass of ruthenium element per unit area is 0.03 mg / cm², from the perspective of maintaining good electrolytic performance over a long period of time. ２ The above is preferred, and 0.05 mg / cm³ is preferred. ２ The above is more preferable, 0.1 mg / cm³ ２ The above is particularly preferable. Furthermore, the above content is 0.8 mg / cm³. ２ Preferably less than 0.6 mg / cm³. ２ Less than 0.4 mg / cm³ is more preferable, and 0.4 mg / cm³ is preferable. ２ Less than is particularly preferable.

[0101] The cathode catalyst layer preferably further contains a polymer electrolyte. As the polymer electrolyte, hydrocarbon-based polymer electrolytes or fluorine-based polymer electrolytes can be used. Among these, fluorine-based polymer electrolytes are preferred, and perfluorocarbon sulfonic acid-based polymers are even more preferred.

[0102] When the cathode catalyst layer contains a polymer electrolyte, the ion exchange capacity (IEC) of the polymer electrolyte is preferably less than 1.50 meq / g, more preferably less than 1.40 meq / g, and particularly preferably less than 1.30 meq / g. The lower limit is preferably 0.40 meq / g or more.

[0103] From the standpoint of electrolytic performance, the ion exchange capacity (hereinafter referred to as "IEC") of the polymer electrolyte contained in the cathode catalyst layer is important. ＣＡ The ion exchange capacity (hereinafter referred to as "IEC") of the polymer electrolyte contained in the polymer electrolyte membrane is the ion exchange capacity of the polymer electrolyte (hereinafter referred to as "IEC"). ＰＥ It is preferable that it be smaller than ( ). Specifically, IEC ＣＡ and IEC ＰＥ The ratio (IEC ＣＡ / IEC ＰＥ The ratio (IEC) is preferably 0.90 or less, more preferably 0.80 or less, even more preferably 0.70 or less, and particularly preferably 0.65 or less. ＣＡ / IEC ＰＥ The ratio is preferably 0.20 or higher, more preferably 0.30 or higher, even more preferably 0.35 or higher, and particularly preferably 0.40 or higher.

[0104] When the cathode catalyst layer contains a polymer electrolyte, the ratio (Yc) of the mass of platinum elements contained in the cathode catalyst layer to the mass of the polymer electrolyte, i.e., "(mass of polymer electrolyte) / (mass of platinum elements)", is preferably 0.25 or higher, more preferably 0.4 or higher, even more preferably 0.5 or higher, and particularly preferably 0.6 or higher, from the viewpoint of electrolytic performance. Furthermore, from the viewpoint of the diffusibility of hydrogen gas generated in the cathode, the above ratio is preferably less than 1.7, more preferably less than 1.5, even more preferably less than 1.3, and particularly preferably less than 1.1.

[0105] Furthermore, when platinum-supported carbon particles or platinum-ruthenium alloy-supported carbon particles are used as the catalyst for the cathode catalyst layer, the ratio (I / C) of the mass of the carbon particles (C) to the mass of the polymer electrolyte (I) is preferably less than 1.10, more preferably less than 1.00, even more preferably less than 0.95, and particularly preferably less than 0.90, from the viewpoint of electrolytic performance and durability. In addition, the ratio (I / C) is preferably 0.30 or higher, more preferably 0.40 or higher, even more preferably 0.50 or higher, and particularly preferably 0.60 or higher.

[0106] From the viewpoint of electrolytic performance, the thickness of the cathode catalyst layer is preferably 0.5 μm or more, more preferably 1 μm or more, and particularly preferably 3 μm or more. Furthermore, from the viewpoint of the diffusibility of hydrogen gas generated in the cathode and the physical stability of the catalyst layer (such as cracking during operation), the above thickness is preferably 25 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less.

[0107] In the membrane / catalyst layer structure, the thicknesses of the electrolyte membrane, anode catalyst layer, and cathode catalyst layer are as described above, but from the viewpoint of maintaining good electrolytic performance for a longer period of time, it is preferable to adjust the relationship between these thicknesses. For example, it is preferable that the thickness of the anode catalyst layer and / or cathode catalyst layer be 25% or less relative to 100% of the electrolyte membrane thickness. More specifically, the thickness of the anode catalyst layer is preferably 25% or less, more preferably 20% or less, and particularly preferably 15% or less, relative to 100% of the electrolyte membrane thickness. The lower limit is preferably 1% or more. The thickness of the cathode catalyst layer is preferably 25% or less, more preferably 20% or less, and particularly preferably 15% or less, relative to 100% of the electrolyte membrane thickness. The lower limit is preferably 1% or more.

[0108] In the film / catalyst layer structure, it is preferable that the above ratio (Ya) in the anode catalyst layer is 0.05 or more and less than 0.5, and the above ratio (Yc) in the cathode catalyst layer is 0.25 or more and less than 1.7. It is preferable that the above ratio (Ya) is smaller than the above ratio (Yc).

[0109] As an embodiment of the present invention, a membrane / catalyst layer structure having an anode catalyst layer on one side of the electrolyte membrane and a cathode catalyst layer on the other side, wherein the anode catalyst layer contains iridium and the cathode catalyst layer contains platinum, and among these, a membrane / catalyst layer structure in which the cathode catalyst layer contains both platinum and ruthenium is particularly preferred.

[0110] [Membrane-Electrode Assembly (MEA)] A membrane-electrode assembly is formed by arranging electrode substrates on both sides of the membrane-catalyst layer structure described above. That is, the membrane-electrode assembly has an anode catalyst layer and an anode electrode substrate on one side of the electrolyte membrane, and a cathode catalyst layer and a cathode electrode substrate on the other side.

[0111] The electrode substrate (which may also serve as a gas diffusion layer) is primarily intended for voltage application and is composed of a conductive material. For example, porous substrates made of metal or carbon can be used as electrode substrates. Examples of metal porous substrates include metal nonwoven fabrics, metal fiber sintered bodies, metal powder sintered bodies, and metal foam sintered bodies. Examples of carbon porous substrates include carbon felt, carbon paper, carbon cloth, and graphite particle sintered bodies.

[0112] As the anode electrode substrate, a porous metal substrate that exhibits excellent corrosion resistance in environments such as high potential, oxygen presence, and strong acidity is preferably used. From the above viewpoint, as the metal constituting the porous metal substrate, titanium, aluminum, nickel, stainless steel, and alloys mainly composed of at least one of these metals are preferred, and titanium and alloys mainly composed of titanium are particularly preferred.

[0113] As the cathode electrode substrate, a carbon porous substrate is preferred from the viewpoint of material cost and conductivity, and carbon paper is particularly preferred.

[0114] In a membrane-catalyst layer structure, the anode catalyst layer and the cathode catalyst layer can be laminated on an electrode substrate, either one or both. In the assembly process of the membrane-electrode assembly, the electrode substrate on which the catalyst layers are laminated and the electrolyte membrane are arranged, resulting in a configuration in which the anode catalyst layer and the cathode catalyst layer are positioned opposite each other with the electrolyte membrane in between. In other words, the membrane-catalyst layer structure is completed during the assembly process of the membrane-electrode assembly, and the present invention includes this embodiment.

[0115] In the above configuration, the anode catalyst layer and the cathode catalyst layer may be laminated on the electrode substrate, respectively. However, depending on the type of electrode substrate, sufficient adhesion to the catalyst layer may not be obtained, so it is preferable to select the appropriate type of electrode substrate. For example, a porous carbon substrate has relatively good adhesion to the catalyst layer. Therefore, a cathode catalyst layer may be laminated on a cathode electrode substrate suitable as a porous carbon substrate, and the anode catalyst layer may be laminated on the electrolyte membrane. As a method for laminating the catalyst layer onto the electrode substrate, the coating method or transfer method described above can be used.

[0116] [Water electrolysis cell and water electrolysis device] The water electrolysis cell includes the membrane-electrode assembly (MEA) and separator described above.

[0117] Figure 3 is a schematic cross-sectional view showing an example of a water electrolytic cell that can be used in the present invention. The water electrolytic cell 100 is divided into an anode 20 and a cathode 30 by an electrolyte membrane 10. Here, the anode 20 is composed of an anode catalyst layer 21 and an anode electrode substrate 22. The cathode 30 is composed of a cathode catalyst layer 31 and a cathode electrode substrate 32. These are sandwiched from both sides by separators 41 and 42.

[0118] The water electrolysis apparatus has multiple water electrolysis cells arranged together, and a power supply (not shown) is connected to the anode 20 and cathode 30 of each cell, to which a voltage is applied. The water electrolysis apparatus includes, as basic components, a water supply unit that supplies water to the water electrolysis cells, a power supply unit that supplies power to the water electrolysis cells, an oxygen discharge unit that discharges the generated oxygen, a hydrogen discharge unit that discharges the generated hydrogen, and a water discharge unit that discharges excess water after electrolysis.

[0119] The method of supplying water to the water electrolysis cell is not particularly limited, and known methods can be used. Specifically, methods such as supplying water to the anode, supplying water to the cathode, and supplying water to both the anode and the cathode can be used. In the above water supply methods, it is preferable to supply water from outside the water electrolysis cell using means such as a pump.

[0120] [Water Electrolysis Method] The water electrolysis method in the present invention is carried out using the water electrolysis cell and water electrolysis apparatus described above. That is, the water electrolysis method according to an embodiment of the present invention is a water electrolysis method in which water is supplied to a water electrolysis cell whose interior is divided into an anode and a cathode by an electrolyte membrane, and the water is electrolyzed to produce oxygen at the anode and hydrogen at the cathode, wherein the anode catalyst layer constituting the anode contains iridium as a catalyst, and the cathode catalyst layer constituting the cathode contains platinum as a catalyst. The electrolyte membrane, anode catalyst layer and cathode catalyst layer in this method can preferably be those described above.

[0121] As mentioned above, water can be supplied to the anode only, the cathode only, or both the anode and the cathode in a water electrolysis cell. In particular, it is preferable to supply water to at least the anode, where oxygen and protons are produced by the oxidation reaction of water.

[0122] The present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples. The measurement methods used in these examples are shown below. In the measurement methods described below, if measurement with block copolymers is difficult or if there are concerns about measurement accuracy, the following electrolyte membranes were used as samples instead of block copolymers.

[0123] (1) Molecular weight of polymers The number-average molecular weight and weight-average molecular weight of polymers were measured by GPC. A Tosoh Corporation HLC-8022 GPC was used as the instrument equipped with an ultraviolet detector and a differential refractometer, and a Tosoh Corporation TSKgelGuardColumnSuperH-H (inner diameter 4.6 mm, length 3.5 cm) was used as the guard column. Two Tosoh Corporation TSKgelSuperHM-H (inner diameter 6.0 mm, length 15 cm) columns were used as the GPC columns. Measurements were taken in N-methyl-2-pyrrolidone solvent (N-methyl-2-pyrrolidone solvent containing 10 mmol / L of lithium bromide) at a sample concentration of 0.1 mass%, a flow rate of 0.2 mL / min, a temperature of 40°C, and a measurement wavelength of 265 nm. The number-average molecular weight and weight-average molecular weight were determined by converting to standard polystyrene.

[0124] (2) Ion exchange capacity (IEC) of block copolymers The ion exchange capacity of block copolymers was measured by the neutralization titration methods shown in 1) to 4) below. Three measurements were taken, and the average value was used.

[0125] 1) The block copolymer was immersed in a 10% by mass sulfuric acid aqueous solution at 95°C for 24 hours to perform proton substitution. The proton-substituted block copolymer was thoroughly washed with pure water, wiped dry, and then vacuum-dried at 100°C for 12 hours or more to determine its dry weight.

[0126] 2) 50 mL of a 5% by mass sodium sulfate aqueous solution was added to the block copolymer obtained in step 1), and the mixture was allowed to stand for 12 hours for ion exchange.

[0127] 3) The sulfuric acid produced in step 2) was titrated using a 0.01 mol / L sodium hydroxide aqueous solution. A commercially available 0.1 w / v% titration phenolphthalein solution was added as an indicator, and the endpoint was defined as the point at which the solution turned a pale reddish-purple.

[0128] 4) IEC was calculated using the following formula.

[0129] IEC (meq / g) = [Concentration of sodium hydroxide solution (moles / mL) × Droplet volume (mL)] / Dry weight of sample (g).

[0130] (3) Measurement of the glass transition temperature Tg of the block copolymer Ten mg of the block copolymer was pre-dried in a DSC instrument at 110°C for 3 hours. Then, without removing the sample from the DSC instrument, the temperature was raised to 200°C under the following conditions, and temperature-modulated differential scanning calorimetry was performed during the heating stage. At this time, the glass transition temperature was defined as the midpoint of the two intersection points obtained from the two extensions of the baseline and the tangent to the endothermic curve.

[0131] DSC device: DSC7000X (manufactured by Hitachi High-Tech Corporation) Measurement temperature range: 30°C to 200°C Temperature control: AC temperature control Heating rate: 2°C / min Amplitude: ±3°C Applied frequency: 0.02 Hz Sample pan: Aluminum crimped pan measurement, pre-drying atmosphere: 100 mL / min nitrogen Pre-drying: 110°C, 3 hours.

[0132] (4) Measurement of the saturation crystallinity of the block copolymer Prior to measuring the saturation crystallinity of the block copolymer, a membrane sample made of the block copolymer was first prepared in the following manner.

[0133] <Preparation of film sample> A 25% by mass N-methylpyrrolidone (NMP) solution containing a dissolved block copolymer was pressure filtered using a glass fiber filter, then cast onto a glass substrate and dried at 100°C for 4 hours to obtain a film with a thickness of 10 μm. Next, this film was immersed in a 10% by mass sulfuric acid aqueous solution at 95°C for 24 hours to undergo proton substitution and deprotection reactions, and then thoroughly washed and dried by immersion in a large excess of pure water for 24 hours to obtain a film sample.

[0134] <Measurement of Saturated Crystallinity> A membrane sample was cut into a 5 cm x 5 cm square. This membrane sample was sandwiched between two polyimide films (50 μm thick). This was then heated and pressed in a heating press at a temperature of +5°C above the glass transition temperature of each block copolymer and a pressure of 4.5 MPa for 5 minutes. The degree of crystallinity was then measured. This process was repeated until the degree of crystallinity stopped changing, at which point it was defined as the saturated crystallinity. The method for measuring the degree of crystallinity is described below.

[0135] <Measuring crystallinity by wide-angle X-ray diffraction (XRD)> The sample after heating and pressing was placed in a diffractometer, and X-ray diffraction measurements were performed under the following conditions.

[0136] X-ray diffractometer: RIGAK RINT2500V X-ray: Cu-Kα X-ray output: 50kV-300mA Optical system: Focused optical system Scan rate: 2θ = 2° / min Scanning method: 2θ-θ Scanning range: 2θ = 5 to 60° Slits: Divergent slit -1 / 2°, receiving slit -0.15 mm, scattering slit -1 / 2° The X-ray diffraction measurement results were separated into each component by profile fitting, and the diffraction angle and integrated intensity of each component were determined. The degree of crystallinity was calculated using the integral intensities of the obtained crystalline peaks and amorphous halos from the following formula (2). Degree of crystallinity (%) = (sum of integral intensities of all crystalline peaks) / (sum of integral intensities of all crystalline peaks and amorphous halos) × 100 ... formula (2).

[0137] (5) Observation of phase separation structure by transmission electron microscope (TEM) A sample of the electrolyte membrane was immersed in a 2% by mass aqueous solution of staining agent (lead acetate) and left at 25°C for 72 hours. The stained sample was removed and embedded in epoxy resin. Using an ultramicrotome, an 80 nm thin section was cut from the sample at room temperature. The obtained thin section was collected on a Cu grid and subjected to TEM observation. The observation was performed at an acceleration voltage of 100 kV and the imaging magnification was 10,000 to 100,000 times. The above imaging magnification was set appropriately according to the size of the phase separation structure. The instrument used was the HT7700 (manufactured by Hitachi High-Tech Corporation).

[0138] The obtained TEM image was subjected to a Fast Fourier Transform (FFT), and the spatial frequencies in the film plane direction and film thickness direction were measured from the resulting ring-shaped FFT pattern. From this, the average period value in the film plane direction (L1) and the average period length in the film thickness direction (L2) were calculated, respectively. The spatial frequency was measured by measuring the distance from the center of the image to the center of the ring's thickness. Digital Micrograph (Gatan) was used for FFT and measurement.

[0139] (6) Observation of phase separation structure by transmission electron microscope (TEM) tomography The thin section samples prepared by the method described in (5) above were mounted on a collodion film and observed under the following conditions.

[0140] Equipment: Field emission electron microscope (HRTEM), JEOL Ltd. JEM 2100F Image acquisition: Digital Micrograph (Gatan) System: Marker method Acceleration voltage: 200kV Magnification: 30,000x Tilt angle: +61° to -62° Reconstruction resolution: 0.71nm / pixel Three-dimensional reconstruction was performed using the marker method with Au colloid particles attached to a collodion film as alignment markers. Using the markers as a reference, TEM images were taken by tilting the sample in 1° increments within the range of +61° to -62°. Based on a total of 124 TEM images obtained from this series of tilted images, CT reconstruction was performed to observe the three-dimensional phase separation structure.

[0141] (7) Measurement of the thickness of the electrolyte membrane and catalyst layer The cross-sections of the electrolyte membrane and catalyst layer were observed with a scanning electron microscope (SEM) according to the following conditions, and the thicknesses of the electrolyte membrane, anode catalyst layer, and cathode catalyst layer were measured from the obtained images.

[0142] Equipment: Field emission scanning electron microscope (FE-SEM) S-4800 (manufactured by Hitachi High-Technologies) - Acceleration voltage: 2.0 kV - Pretreatment: Cross-sectional samples prepared by the BIB method were coated with Pt and measured.

[0143] • BIB method: A cross-sectional sample preparation device using an argon ion beam. A shielding plate is placed directly above the sample, and an argon broad ion beam is irradiated from above to perform etching, thereby creating an observation surface and an analysis surface (cross-section).

[0144] (8) Evaluation of electrolytic performance In order to evaluate the electrolytic performance of the film-catalyst layer laminate, the film-electrode assembly was fabricated in the following manner.

[0145] [Membrane-Electrode Assembly] A membrane-electrode assembly was fabricated by laminating commercially available carbon paper as the cathode electrode substrate on the cathode catalyst layer side of the membrane-catalyst layer laminate prepared in the examples and comparative examples, and a commercially available porous titanium sintered plate as the anode electrode substrate on the anode catalyst layer side.

[0146] [Method for evaluating water electrolysis performance] The membrane / electrode assembly and edge seal (SB50A1P manufactured by Maxell Corporation) prepared above were subjected to the JARI standard cell "Ex-1" (electrode area 25 cm²) manufactured by Eiwa Co., Ltd. ２ The device was set to a specific configuration, and the cell temperature was set to 60°C. Deionized water with an electrical conductivity of 1 μS / cm or less was supplied to the anode and cathode at atmospheric pressure at a flow rate of 0.2 L / min, resulting in a current density of 1.3 A / cm². ２ A voltage was applied to achieve the desired result, and water electrolysis was performed for 1,000 hours. During operation, the applied voltage was measured every 25 hours, and the average applied voltage was calculated by averaging all measured values. A lower average applied voltage indicates that good electrolysis performance is maintained for a longer period of time. Furthermore, the voltage rise rate was calculated from the initial applied voltage and the applied voltage after 1,000 hours using Equation 2 below.

[0147] Voltage rise rate (%) = (V1 - V0) / V0 × 100 ... Equation 2 In the equation, V1 represents the applied voltage after 1,000 hours, and V0 represents the initial applied voltage.

[0148] [Synthesis of Block Copolymers] In the following synthesis example, the structure of the obtained compound is: １ The compound was confirmed using 1H-NMR. The purity of the compound was quantitatively analyzed using capillary electrophoresis (organic substances) and ion chromatography (inorganic substances).

[0149] <Synthesis Example 1> (Synthesis of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane (K-DHBP) represented by the following formula (G1)) 49.5 g of 4,4'-dihydroxybenzophenone, 134 g of ethylene glycol, 96.9 g of trimethyl orthoformate, and 0.50 g of p-toluenesulfonic acid monohydrate were charged into a 500 mL flask equipped with a stirrer, thermometer, and distillation tube to form a solution. The mixture was then kept warm and stirred at 78-82°C for 2 hours. The internal temperature was then gradually increased to 120°C and maintained at 120°C until the distillation of methyl formate, methanol, and trimethyl orthoformate had completely stopped. After the reaction mixture was cooled to room temperature, it was diluted with ethyl acetate. The organic layer was washed with 100 mL of 5% potassium carbonate aqueous solution, and after liquid-liquid extraction, the solvent was removed by distillation. 80 mL of dichloromethane was added to the residue to precipitate crystals, which were then filtered and dried to obtain 52.0 g of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane. The purity was 99.9%.

[0150]

[0151] <Synthesis Example 2> (Synthesis of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following formula (G2)) 109.1 g of 4,4'-difluorobenzophenone (Aldrich reagent) is mixed with fuming sulfuric acid (50% SO2). ３ The reaction was carried out at 100°C for 10 hours in 150 mL (Wako Pure Chemical Industries reagent). After the reaction was complete, the reaction solution was gradually added to a large amount of water, neutralized with NaOH, and then 200 g of sodium chloride (NaCl) was added to precipitate the product. The obtained precipitate was filtered off and recrystallized in an aqueous ethanol solution to obtain disodium-3,3'-disulfonate-4,4'-difluorobenzophenone. The purity was 99.3%.

[0152]

[0153] <Synthesis Example 3> (Synthesis of 3,3'-disulfonate sodium salt-4,4'-difluorodiphenylsulfone represented by the following formula (G3)) 109.1 g of 4,4-difluorodiphenylsulfone (Aldrich reagent) is mixed with fuming sulfuric acid (50% SO ３The reaction was carried out at 100°C for 10 hours in 150 mL (Wako Pure Chemical Industries reagent). After the reaction was complete, the reaction solution was gradually added to a large amount of water, neutralized with NaOH, and then 200 g of sodium chloride was added to precipitate the product. The obtained precipitate was filtered off and recrystallized in an aqueous ethanol solution to obtain 3,3'-disulfonate sodium salt-4,4'-difluorodiphenylsulfone. The purity was 99.3%.

[0154]

[0155] <Synthesis of block copolymer b1> Block copolymer b1 containing the following oligomer a2 as an ionic segment and the following oligomer a1 as a nonionic segment was synthesized according to the following procedure.

[0156] (Synthesis of nonionic oligomer a1 represented by the following general formula (G4)) In a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 16.59 g of potassium carbonate (Aldrich reagent, 120 mmol), 25.83 g (100 mmol) of K-DHBP obtained in Synthesis Example 1, and 20.73 g of 4,4'-difluorobenzophenone (Aldrich reagent, 95 mmol) were added. After purging the apparatus with nitrogen, 300 mL of N-methylpyrrolidone (NMP) and 100 mL of toluene were added, and the mixture was dehydrated at 150°C. The temperature was then raised to remove the toluene, and polymerization was carried out at 170°C for 3 hours. The reaction solution was added to a large amount of methanol and reprecipitation purification was performed to obtain the terminal hydroxyl form of nonionic oligomer a1. The number-average molecular weight of the terminal hydroxyl form of this nonionic oligomer a1 was 9,000.

[0157] In a 500 mL three-necked flask equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 1.1 g of potassium carbonate (Aldrich reagent, 8 mmol) and 9.0 g (1 mmol) of the terminal hydroxyl group of the nonionic oligomer a1 were added. After purging the apparatus with nitrogen, 100 mL of NMP and 30 mL of toluene were added, and the mixture was dehydrated at 100°C, then heated to remove the toluene. Furthermore, 1.1 g of hexafluorobenzene (Aldrich reagent, 6 mmol) was added, and the reaction was carried out at 105°C for 12 hours. The reaction solution was purified by adding it to a large amount of isopropyl alcohol and reprecipitation to obtain the nonionic oligomer a1 (terminal: fluoro group) shown in the following formula (G4). The number-average molecular weight of this nonionic oligomer a1 was 10,000.

[0158]

[0159] (Synthesis of ionic oligomer a2 represented by formula (G5) below) In a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube and Dean-Stark trap, 27.64 g of potassium carbonate (Aldrich reagent, 200 mmol), 12.91 g (50 mmol) of K-DHBP obtained in Synthesis Example 1, 9.31 g of 4,4'-biphenol (Aldrich reagent, 50 mmol), 41.60 g (98.5 mmol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone obtained in Synthesis Example 2, and 26.40 g of 18-crown-6 (Wako Pure Chemical Industries, 100 mmol) were added. After purging the apparatus with nitrogen, 300 mL of NMP and 100 mL of toluene were added, dehydration was performed at 150°C, the temperature was raised to remove the toluene, and polymerization was carried out at 170°C for 6 hours. The reaction solution was purified by adding it to a large amount of isopropyl alcohol and reprecipitation to obtain the ionic oligomer a2 (terminal: hydroxyl group) shown in the following formula (G5). The number-average molecular weight of this ionic oligomer a2 was 45,000. In formula (G5), M represents a hydrogen atom, Na, or K.

[0160]

[0161] (Synthesis of block copolymer b1) In a 2000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 49.0 g of ionic oligomer a2 and 12.3 g of nonionic oligomer a1 were added, and NMP was added so that the total amount of oligomers was 7% by mass. The reaction was carried out at 105°C for 24 hours. The reaction solution was added to a large amount of isopropyl alcohol / NMP mixture (mass ratio 2 / 1), reprecipitation was performed, and a large amount of isopropyl alcohol was purified to obtain block copolymer b1. The number average molecular weight of this block copolymer b1 was 160,000, and the weight average molecular weight was 400,000.

[0162] The saturated crystallinity of block copolymer b1 was 4.5%, the glass transition temperature was 163°C, and the IEC was 2.1 meq / g.

[0163] <Synthesis of block copolymer b2> Block copolymer b2 containing the following oligomer a4' as an ionic segment and the following oligomer a3 as a nonionic segment was synthesized according to the following procedure.

[0164] (Synthesis of nonionic oligomer a3 represented by the above general formula (G4)) In a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 16.59 g of potassium carbonate (Aldrich reagent, 120 mmol), 25.83 g (100 mmol) of K-DHBP obtained in Synthesis Example 1, and 21.40 g of 4,4'-difluorobenzophenone (Aldrich reagent, 98.1 mmol) were added. After purging the apparatus with nitrogen, 300 mL of N-methylpyrrolidone (NMP) and 100 mL of toluene were added, dehydration was performed at 150°C, the temperature was raised to remove the toluene, and polymerization was carried out at 170°C for 3 hours. The reaction solution was added to a large amount of methanol and reprecipitation purification was performed to obtain the terminal hydroxyl compound of nonionic oligomer a3. The number-average molecular weight of this terminal hydroxyl compound of nonionic oligomer a3 was 25,000.

[0165] In a 500 mL three-necked flask equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 1.1 g of potassium carbonate (Aldrich reagent, 8 mmol) and 25.0 g (1 mmol) of the terminal hydroxyl group of the nonionic oligomer a3 were added. After purging the apparatus with nitrogen, 100 mL of NMP and 30 mL of toluene were added, and the mixture was dehydrated at 100°C, then heated to remove the toluene. Furthermore, 1.1 g of hexafluorobenzene (Aldrich reagent, 6 mmol) was added, and the reaction was carried out at 105°C for 12 hours. The reaction solution was purified by adding it to a large amount of isopropyl alcohol and reprecipitation to obtain nonionic oligomer a3 (terminal: fluoro group) represented by the following general formula (G4). The number-average molecular weight of this nonionic oligomer a3 was 26,000.

[0166] (Synthesis of ionic oligomer a4 represented by the above general formula (G5)) In a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube and Dean-Stark trap, 27.64 g of potassium carbonate (Aldrich reagent, 200 mmol), 12.91 g (50 mmol) of K-DHBP obtained in Synthesis Example 1, 9.31 g of 4,4'-biphenol (Aldrich reagent, 50 mmol), 41.60 g (98.5 mmol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone obtained in Synthesis Example 2, and 18-clau 26.40 g of N-6 (100 mmol of Wako Pure Chemical Industries) was added. After purging the apparatus with nitrogen, 300 mL of NMP and 100 mL of toluene were added, and dehydration was performed at 150°C. The temperature was then raised to remove the toluene, and polymerization was carried out at 170°C for 6 hours. The reaction solution was added to a large amount of isopropyl alcohol and purified by reprecipitation to obtain ionic oligomer a4 (terminus: OM group) represented by the following general formula (G5). The number-average molecular weight of this ionic oligomer a4 was 45,000.

[0167] (Synthesis of ionic oligomer a4' represented by the general formula (G6) below) 0.56 g of potassium carbonate (Aldrich reagent, 400 mmol) and 49.0 g of ionic oligomer a2 were placed in a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap. After purging the apparatus with nitrogen, 500 mL of NMP was added, and the contents were dissolved at 60°C. Then, 19.8 g of hexafluorobenzene / NMP solution (1% by mass) was added. The reaction was carried out at 80°C for 18 hours to obtain an NMP solution containing ionic oligomer a4' (terminus: OM group) represented by the general formula (G6). The number-average molecular weight of this ionic oligomer a4' was 90,000. In the general formula (G6), M represents a hydrogen atom, Na, or K, and n represents an integer of 1 or more.

[0168]

[0169] <Synthesis of Block Copolymer b2> In a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 49.0 g of ionic oligomer a4' and 12.3 g of nonionic oligomer a3 were added, and NMP was added so that the total amount of oligomers was 7% by mass. The reaction was carried out at 105°C for 24 hours. The reaction solution was added to a large amount of isopropyl alcohol / NMP mixture (mass ratio 2 / 1), reprecipitation was performed, and the mixture was purified with a large amount of isopropyl alcohol to obtain block copolymer b2. The number average molecular weight of this block copolymer b2 was 160,000, and the weight average molecular weight was 390,000.

[0170] The saturated crystallinity of block copolymer b2 was 9.4%, the glass transition temperature was 160°C, and the IEC was 2.1 meq / g.

[0171] <Synthesis of block copolymer b3> Block copolymer b3 containing the following oligomer a6' as an ionic segment and the following oligomer a5 as a nonionic segment was synthesized according to the following procedure.

[0172] (Synthesis of nonionic oligomer a5 represented by the above general formula (G4)) The terminal hydroxyl derivative of oligomer a5 was obtained in the same manner as in the synthesis of the terminal hydroxyl derivative of oligomer a3, except that the amount of 4,4'-difluorobenzophenone used was 21.51 g. The number-average molecular weight of this terminal hydroxyl derivative of oligomer a5 was 29,000.

[0173] Nonionic oligomer a5 (terminal: fluoro group), represented by general formula (G4), was obtained in the same manner as the synthesis of oligomer a3, except that 29.0 g of the terminal hydroxyl group of oligomer a5 was used instead of the terminal hydroxyl group of oligomer a3. The number-average molecular weight of this nonionic oligomer a5 was 30,000.

[0174] (Synthesis of ionic oligomer a6 represented by the above general formula (G5)) Ionic oligomer a6 was obtained in the same manner as the synthesis of ionic oligomer a4, except that the amount of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone used was 41.38 g (98.0 mmol). The number-average molecular weight of this ionic oligomer a6 was 35,000.

[0175] (Synthesis of ionic oligomer a6' represented by the general formula (G7) below) 0.56 g of potassium carbonate (Aldrich reagent, 400 mmol) and 37.16 g of ionic oligomer a6 were placed in a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap. After purging the apparatus with nitrogen, 400 mL of NMP was added, and the contents were dissolved at 60°C. Then, 11.4 g of 2,6-difluorobenzonitrile / NMP solution (1% by mass) was added. The reaction was carried out at 80°C for 18 hours to obtain an NMP solution containing ionic oligomer a6' (terminus: OM group) represented by the general formula (G7). The number-average molecular weight of this ionic oligomer a6' was 70,000. In the general formula (G7), M represents a hydrogen atom, Na, or K, and n represents an integer of 1 or more.

[0176]

[0177] (Synthesis of block copolymer b3) Block copolymer b3 was obtained in the same manner as the synthesis of block copolymer b2, except that ionic oligomer a6' (37.16 g) was used instead of ionic oligomer a4' and nonionic oligomer a5 (12.39 g) was used instead of nonionic oligomer a3 (7.65 g). The number average molecular weight of this block copolymer b3 was 120,000 and the weight average molecular weight was 360,000.

[0178] The saturated crystallinity of block copolymer b3 was 17.8%, the glass transition temperature was 160°C, and the IEC was 1.9 meq / g.

[0179] <Synthesis of block copolymer b4> Block copolymer b4 containing the following oligomer a8 as an ionic segment and the following oligomer a7 as a nonionic segment was synthesized according to the following procedure.

[0180] (Synthesis of nonionic oligomer a7 represented by the above general formula (G4)) The terminal hydroxyl derivative of nonionic oligomer a7 was obtained in the same manner as the synthesis of the terminal hydroxyl derivative of nonionic oligomer a3, except that the amount of 4,4'-difluorobenzophenone used was 20.18 g. The number-average molecular weight of this terminal hydroxyl derivative of nonionic oligomer a7 was 5,000.

[0181] In a 500 mL three-necked flask equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap, 2.2 g of potassium carbonate (Aldrich reagent, 16 mmol) and 10.0 g of the terminal hydroxyl group of nonionic oligomer a7 were placed. After purging the apparatus with nitrogen, 100 mL of NMP and 30 mL of toluene were added, and the mixture was dehydrated at 100°C, followed by heating to remove the toluene. Furthermore, 2.2 g of hexafluorobenzene (Aldrich reagent, 12 mmol) was added, and the reaction was carried out at 105°C for 12 hours. The reaction solution was purified by adding it to a large amount of isopropyl alcohol and reprecipitation to obtain nonionic oligomer a7 (terminal: fluoro group) represented by general formula (G4). The number-average molecular weight of this nonionic oligomer a7 was 6,000.

[0182] <Synthesis of ionic oligomer a8 represented by the above general formula (G5)> In a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube and Dean-Stark trap, 27.64 g of potassium carbonate (Aldrich reagent, 200 mmol), 12.91 g (50 mmol) of K-DHBP obtained in Synthesis Example 1, 9.31 g of 4,4'-biphenol (Aldrich reagent, 50 mmol), 41.47 g (98.2 mmol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone obtained in Synthesis Example 2, and 18-crown-6 (26.40 g: Wako Pure Chemical Industries 100 mmol) were added. After purging the apparatus with nitrogen, 300 mL of NMP and 100 mL of toluene were added, dehydration was performed at 150°C, the temperature was raised to remove the toluene, and polymerization was carried out at 170°C for 6 hours. The reaction solution was purified by adding it to a large amount of isopropyl alcohol and reprecipitation to obtain ionic oligomer a8 (terminus: hydroxyl group) represented by general formula (G5). The number-average molecular weight of this ionic oligomer a8 was 42,000.

[0183] <Synthesis of block copolymer b4> Block copolymer b4 was obtained in the same manner as the synthesis of block copolymer b2, except that ionic oligomer a8 (43.57 g) was used instead of ionic oligomer a4' and nonionic oligomer a7 (6.81 g) was used instead of nonionic oligomer a3. The number average molecular weight of this block copolymer b4 was 130,000 and the weight average molecular weight was 400,000.

[0184] The saturated crystallinity of block copolymer b4 was 0.7%, the glass transition temperature was 157°C, and the IEC was 2.4 meq / g.

[0185] <Synthesis of block copolymer b5> Block copolymer b5 containing the following oligomer a10 as an ionic segment and the following oligomer a9 as a nonionic segment was synthesized according to the following procedure.

[0186] (Synthesis of nonionic oligomer a9 represented by the general formula (G8) below) The terminal hydroxyl compound of nonionic oligomer a9 was obtained in the same manner as the synthesis of the terminal hydroxyl compound of nonionic oligomer a3, except that 23.65 g of 4,4-difluorodiphenylsulfone was used instead of 4,4'-difluorobenzophenone. The number-average molecular weight of this terminal hydroxyl compound of nonionic oligomer a9 was 10,000.

[0187] Nonionic oligomer a9 (terminal fluoro group) represented by general formula (G8) was obtained in the same manner as the synthesis of nonionic oligomer a3, except that 10.0 g of the terminal hydroxyl group of nonionic oligomer a9 was used instead of the terminal hydroxyl group of nonionic oligomer a3. The number-average molecular weight of this nonionic oligomer a9 was 11,000. In general formula (G8), m represents an integer of 1 or more.

[0188]

[0189] (Synthesis of ionic oligomer a10 represented by the general formula (G9) below) Ionic oligomer a10 (terminus: OM group) represented by the general formula (G9) was obtained in the same manner as the synthesis of ionic oligomer a4, except that 44.94 g (98.1 mmol) of 3,3'-disulfonate sodium salt-4,4'-difluorodiphenylsulfone obtained in Synthesis Example 3 was used instead of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone. The number average molecular weight of this ionic oligomer a10 was 41,000. In general formula (G9), M represents a hydrogen atom, Na, or K, and n represents an integer of 1 or more.

[0190]

[0191] (Synthesis of block copolymer b5) Ionic oligomer a10 (45.76 g) and nonionic oligomer a9 (8.93 g) were placed in a 2,000 mL SUS polymerization apparatus equipped with a stirrer, nitrogen inlet tube, and Dean-Stark trap. NMP was added so that the total amount of oligomers was 7% by mass, and the reaction was carried out at 105°C for 24 hours. The reaction solution was added to a large amount of isopropyl alcohol / NMP mixture (mass ratio 2 / 1), reprecipitation was performed, and the mixture was purified with a large amount of isopropyl alcohol to obtain block copolymer b5. The number average molecular weight of this block copolymer b5 was 120,000, and the weight average molecular weight was 290,000.

[0192] The saturated crystallinity of block copolymer b5 was 0.0%, the glass transition temperature was 231°C, and the IEC was 2.4 meq / g.

[0193] <Synthesis of Block Copolymer b6> Referring to the methods described in Examples 7 and 21 of the brochure with international publication number WO2007 / 043274, block copolymer b6 was synthesized using Sumika Excel PES 5200P (manufactured by Sumitomo Chemical Co., Ltd.) to obtain a block copolymer b6 having an ionic segment represented by the following general formula G(10) and a nonionic segment represented by the following general formula G(11). This block copolymer b6 had a number average molecular weight of 140,000 and a weight average molecular weight of 290,000.

[0194] The saturated crystallinity of this block copolymer b6 was 0.0%, the glass transition temperature was 231°C, and the IEC was 2.4 meq / g.

[0195]

[0196]

[0197] <Synthesis of block copolymer b7> Block copolymer b7 containing oligomer a12 as an ionic segment and oligomer a11 as a nonionic segment was synthesized according to the following procedure.

[0198] Nonionic oligomer a11 was obtained in the same manner as the synthesis of nonionic oligomer a1, except that the amount of 4,4'-difluorobenzophenone used was 20.30 g. The number-average molecular weight of this nonionic oligomer a11 was 8,000.

[0199] Ionic oligomer a12 was obtained in the same manner as the synthesis of ionic oligomer a2, except that the amount of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone used was 41.31 g. The number-average molecular weight of this ionic oligomer a12 was 29,000.

[0200] Block copolymer b7 was obtained in the same manner as the synthesis of block copolymer b1, except that ionic oligomer a12 was used instead of ionic oligomer a2, and nonionic oligomer a11 was used instead of nonionic oligomer a1. The number-average molecular weight of this block copolymer b7 was 140,000, and the weight-average molecular weight was 340,000.

[0201] The saturated crystallinity of this block copolymer b7 was 3.8%, the glass transition temperature was 161°C, and the IEC was 2.0 meq / g.

[0202] <Synthesis of block copolymer b8> Block copolymer b8 containing oligomer a13 as an ionic segment and oligomer a12 as a nonionic segment was synthesized according to the following procedure.

[0203] Nonionic oligomer a12 was obtained in the same manner as the synthesis of nonionic oligomer a1, except that the amount of 4,4'-difluorobenzophenone used was 20.35 g. The number-average molecular weight of this nonionic oligomer a12 was 9,000.

[0204] Ionic oligomer a13 was obtained in the same manner as the synthesis of ionic oligomer a2, except that the amount of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone used was 41.39 g. The number-average molecular weight of this ionic oligomer a13 was 34,000.

[0205] Block copolymer b8 was obtained in the same manner as the synthesis of block copolymer b1, except that ionic oligomer a13 was used instead of ionic oligomer a2, and nonionic oligomer a12 was used instead of nonionic oligomer a1. The number-average molecular weight of this block copolymer b8 was 150,000, and the weight-average molecular weight was 360,000.

[0206] The saturated crystallinity of this block copolymer b8 was 4.0%, the glass transition temperature was 161°C, and the IEC was 2.1 meq / g.

[0207] [Example 1] An electrolyte membrane was prepared using the block copolymer b1 synthesized above in the following manner. The block copolymer b1 was dissolved in N-methyl-2-pyrrolidone (NMP), and the solution was further filtered under pressure using a glass fiber filter to prepare a solution with a solid content of 17% by mass. This solution was cast onto a PET film and dried at an initial drying temperature of 70°C, a mid-drying temperature of 100°C, and a final drying temperature of 120°C to obtain a film-like membrane. Furthermore, this membrane was immersed in a 10% by mass sulfuric acid aqueous solution at 80°C for 24 hours to undergo proton substitution and deprotection reactions, then thoroughly washed by immersion in a large excess of pure water for 24 hours, and dried to obtain an electrolyte membrane (thickness 100 μm).

[0208] [Example 2] An electrolyte membrane was prepared in the same manner as in Example 1, except that the thickness of the electrolyte membrane was changed to 50 μm.

[0209] [Example 3] An electrolyte membrane was prepared in the same manner as in Example 1, except that the thickness of the electrolyte membrane was changed to 30 μm.

[0210] [Comparative Example 1] An electrolyte membrane was prepared in the same manner as in Example 1, except that the thickness of the electrolyte membrane was changed to 10 μm.

[0211] [Example 4] An electrolyte membrane was prepared in the same manner as in Example 1, except that block copolymer b1 was changed to block copolymer b2 and the thickness of the electrolyte membrane was changed to 80 μm.

[0212] [Example 5] An electrolyte membrane was prepared in the same manner as in Example 1, except that block copolymer b1 was changed to block copolymer b3 and the thickness of the electrolyte membrane was changed to 70 μm.

[0213] [Comparative Example 2] An electrolyte membrane was prepared in the same manner as in Example 1, except that block copolymer b1 was changed to block copolymer b4 and the thickness of the electrolyte membrane was changed to 50 μm.

[0214] [Comparative Example 3] An electrolyte membrane was prepared in the same manner as in Example 1, except that block copolymer b1 was changed to block copolymer b5 and the thickness of the electrolyte membrane was changed to 50 μm.

[0215] [Comparative Example 4] An electrolyte membrane was prepared in the same manner as in Comparative Example 3, except that the thickness of the electrolyte membrane was changed to 20 μm.

[0216] [Comparative Example 5] An electrolyte membrane was prepared using the block copolymer b6 synthesized above in the following manner. The block copolymer b6 was dissolved in dimethyl sulfoxide and filtered under pressure through a polypropylene filter to obtain a solution with a polymer concentration of 13% by mass. This solution was cast onto a PET film and dried to obtain a film-like membrane. Furthermore, this membrane was immersed in 2N sulfuric acid for 2 hours, then immersed in a large excess of pure water for 24 hours to wash thoroughly, and dried to obtain an electrolyte membrane (thickness 30 μm).

[0217] [Example 6] An electrolyte membrane was prepared in the same manner as in Example 3, except that block copolymer b1 was changed to block copolymer b7.

[0218] [Example 7] An electrolyte membrane was prepared in the same manner as in Example 3, except that block copolymer b1 was changed to block copolymer b8.

[0219] [Evaluation] The morphology of the phase separation structure and the L2 / L1 ratio were observed and calculated for the electrolyte membranes obtained in the above examples and comparative examples. The results are shown in Table 1.

[0220]

[0221] [Preparation of Membrane / Catalyst Layer Structure 1] [Examples 101-104 and Comparative Examples 101-105] A membrane / catalyst layer laminate was prepared by laminating the following anode catalyst layer on one side of the electrolyte membrane prepared in the above examples and comparative examples, and the following cathode catalyst layer on the other side.

[0222] <Anode catalyst layer> Total solid content: Catalyst particles (IrO2 manufactured by Umicore) ２ The catalyst layer contained 10 parts by mass of catalyst Elyst Ir75 0480 (Ir content 75%) and 1.3 parts by mass of fluorine-based polymer electrolyte ("Nafion" (registered trademark) product number D2020, manufactured by Chemours K.K., IEC = 0.91 meq / g). The thickness of this anode catalyst layer was 8 μm.

[0223] <Cathode Catalyst Layer> The catalyst layer contains 10 parts by mass of catalyst particles (platinum-supported carbon particles TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. (platinum support rate 50% by mass)) and 4 parts by mass of fluorine-based polymer electrolyte ("Nafion" (registered trademark), product number D2020, IEC = 0.91 meq / g, manufactured by Chemours K.K.) as total solids. The ratio of the mass of carbon particles (C) to the mass of the polymer electrolyte (I) (I / C) is 0.80. The thickness of this cathode catalyst layer was 6 μm.

[0224] [Fabrication of Membrane / Catalyst Layer Structures 2] [Examples 111-116] Using the electrolyte membranes of Examples 1-6, the above-mentioned anode catalyst layer was laminated on one side of these electrolyte membranes, and the following cathode catalyst layer was laminated on the other side to create a membrane / catalyst layer laminate.

[0225] <Cathode Catalyst Layer> The catalyst layer contains 10 parts by mass of catalyst particles (platinum-ruthenium alloy-supported carbon particles TEC61E54 manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. (catalyst support rate 54% by mass, Pt / Ru mass ratio = 1 / 0.78)) as total solids, and 4 parts by mass of fluorine-based polymer electrolyte ("Nafion" (registered trademark) product number D2020, IEC = 0.91 meq / g manufactured by Chemours K.K.). The ratio of the mass of carbon particles (C) to the mass of the polymer electrolyte (I) (I / C) is 0.87. The thickness of this cathode catalyst layer was 12 μm.

[0226] [Evaluation] The electrolytic performance of the membrane and catalyst layer structures prepared as described above was evaluated using the method described in (8) above. The results are shown in Table 2.

[0227] In Comparative Examples 101 and 104, a significant voltage increase was observed before 1,000 hours had elapsed after the voltage was applied, making it impossible to evaluate the electrolytic performance.

[0228]

[0229] Phase 1 Phase 2 10 Electrolyte membrane 20 Anode 21 Anode catalyst layer 22 Anode electrode substrate 30 Cathode 31 Cathode catalyst layer 32 Cathode electrode substrate 41, 42 Separator 100 Water electrolysis cell 110 Unwinding device 111 Support film supply roll 112 Support film 120 Coating device 130 Drying oven 140 Winding device

Claims

An electrolyte membrane comprising a block copolymer having segments containing ionic groups (hereinafter referred to as "ionic segments") and segments not containing ionic groups (hereinafter referred to as "nonionic segments"), wherein the block copolymer has a saturated crystallinity of 1.0% or more as measured by wide-angle X-ray analysis, the electrolyte membrane has a co-continuous phase separation structure, and the ratio (L2 / L1) of the average period length of the co-continuous phase separation structure observed by a transmission electron microscope to the average period length in the film thickness direction (L2) of the electrolyte membrane is 0.50 or more. 　 The electrolyte membrane according to claim 1, wherein the ratio (L2 / L1) is 0.50 or more and 1.90 or less. 　 The electrolyte membrane according to claim 1, wherein the average period length (L1) in the direction of the membrane surface is 15 nm or more and less than 90 nm. 　 The electrolyte membrane according to claim 1, wherein the thickness of the electrolyte membrane is 20 μm or more and less than 200 μm. 　 The electrolyte membrane according to claim 1, wherein the ionic segment and the nonionic segment each contain a hydrocarbon polymer. 　 The electrolyte membrane according to claim 5, wherein the hydrocarbon polymer is a hydrocarbon polymer having an aromatic ring in its main chain (hereinafter referred to as "aromatic hydrocarbon polymer"). 　 The electrolyte membrane according to claim 6, wherein the aromatic hydrocarbon polymer is an aromatic polyether ketone polymer. 　 The electrolyte membrane according to claim 1, wherein the number-average molecular weight of the ionic segment is 30,000 or more. 　 A membrane-catalyst layer structure comprising an electrolyte membrane according to any one of claims 1 to 8, having an anode catalyst layer on one side and a cathode catalyst layer on the other side, wherein the anode catalyst layer contains iridium and the cathode catalyst layer contains platinum. 　 The film / catalyst layer structure according to claim 9, wherein the cathode catalyst layer contains platinum and ruthenium. 　 A film-electrode assembly comprising an electrode substrate disposed on both sides of the film-catalyst layer structure according to claim 9. 　 A water electrolysis cell comprising the membrane-electrode assembly described in claim 11. 　 A water electrolysis apparatus comprising the water electrolysis cell described in claim 12. 　 A water electrolysis method comprising supplying water to a water electrolysis cell whose interior is partitioned into an anode and a cathode by an electrolyte membrane according to any one of claims 1 to 8, and electrolyzing the water to produce oxygen in the anode and hydrogen in the cathode, wherein the anode catalyst layer constituting the anode contains an iridium element and the cathode catalyst layer constituting the cathode contains a platinum element. 　 The water electrolysis method according to claim 14, wherein the cathode catalyst layer contains platinum and ruthenium.

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