Electrode catalyst layer, membrane electrode assembly, water electrolysis apparatus, and organic hydride electrolysis synthesis apparatus

Abstract

The present invention provides an electrode catalyst layer, etc., that can lower the electrolytic voltage and suppress crack formation. [Solution] The electrode catalyst layer comprises a catalyst, a polymer electrolyte having proton conductivity or anion conductivity, and a polymer fibrous material. In the cross-section of the electrode catalyst layer, the proportion of the void area is 20% or more and 40% or less. In a Voronoi diagram with the centroid of each void in the cross-section of the electrode catalyst layer as the parent point, when the standard deviation of the area of ​​the Voronoi region is ASD and the arithmetic mean area of ​​the Voronoi region is AAV, the dispersion of the area of ​​the Voronoi region expressed as ASD / AAV is 0.50 or more and 0.90 or less.

Description

[Technical Field]

[0001] This disclosure relates to an electrode catalyst layer, a membrane electrode assembly, a water electrolysis apparatus, and an organic hydride electrolysis synthesis apparatus. [Background technology]

[0002] In recent years, there has been an accelerating movement to utilize hydrogen as a primary energy source, a CO2-free energy that can be produced from various resources, in order to achieve carbon neutrality. One promising method for producing such hydrogen is the electrolysis of water using renewable energy. Generally, there are several methods for electrolyzing water, including alkaline water electrolysis, proton exchange membrane (PEM) water electrolysis, anion exchange membrane (AEM) water electrolysis, and solid oxide water electrolysis. Among these, PEM water electrolysis is attracting attention as a method that enables miniaturization of water electrolysis equipment through high-efficiency operation, while AEM water electrolysis is attracting attention as a method that can be expected to reduce costs by using base metal catalysts.

[0003] A PEM-type water electrolysis apparatus generally comprises a pair of main electrodes and a membrane electrode assembly provided between them. The membrane electrode assembly includes a proton-conducting solid polymer electrolyte membrane, a first electrode catalyst layer provided on one surface of the solid polymer electrolyte membrane, and a second electrode catalyst layer provided on the other surface of the solid polymer electrolyte membrane. An AEM-type water electrolysis apparatus has a similar structure using an anion-conducting electrolyte membrane and has a similar membrane electrode assembly.

[0004] The above electrode catalyst layer is formed on the surface of a proton-conducting or anion-conducting electrolyte membrane, for example, by a coating method (see Patent Document 1 below).

[0005] Furthermore, organic hydride electrolysis synthesizers are attracting attention as transport carriers for hydrogen as a renewable energy source. One example of an organic hydride electrolysis synthesizer is one that, like a water electrolysis apparatus, comprises a pair of main electrodes and a membrane electrode assembly provided between them. The membrane electrode assembly has a proton-conducting solid polymer electrolyte membrane, a first electrode catalyst layer provided on one surface of the solid polymer electrolyte membrane, and a second electrode catalyst layer provided on the other surface of the solid polymer electrolyte membrane (see Patent Document 2 below). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-83085 [Patent Document 2] WO2022 / 091361 publication [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in conventional electrode catalyst layers, there is room for improvement in achieving both a lower electrolytic voltage required for water electrolysis or organic hydride electrolysis and suppression of crack formation.

[0008] This disclosure has been made in view of the above-mentioned problems, and aims to provide an electrode catalyst layer, etc., that can lower the electrolysis voltage and suppress crack generation. [Means for solving the problem]

[0009] As a result of diligent research, the present inventors have found that the above problem can be solved by identifying the void structure in the electrode catalyst layer containing a polymer fibrous material, leading to this disclosure.

[0010] [1] An electrode catalyst layer comprising a catalyst, a polymer electrolyte having proton conductivity or anionic conductivity, and a polymer fibrous material, In the cross-section of the electrode catalyst layer, the proportion of the void area is 20% or more and 40% or less. An electrode catalyst layer wherein, in a Voronoi diagram with the centroid of each void in the cross-section of the electrode catalyst layer as the generating point, the standard deviation of the area of ​​the Voronoi region is ASD, and the arithmetic mean area of ​​the Voronoi region is AAV, and the variance of the area of ​​the Voronoi region expressed as ASD / AAV is 0.50 or more and 0.90 or less. [2] The electrode catalyst layer according to [1], wherein in a cross-section of the electrode catalyst layer, in a Voronoi diagram with the centroid of the polymer fibrous material as the parent point, when the standard deviation of the area of ​​the Voronoi region is BSD and the arithmetic mean area of ​​the Voronoi region is BAV, the degree of dispersion of the area of ​​the Voronoi region expressed as BSD / BAV is 1.5 or less. [3] The electrode catalyst layer according to [1] or [2], wherein the proportion of the area of ​​the polymer fibrous material in the cross-section of the electrode catalyst layer is 2% or more and 15% or less. [4] The electrode catalyst layer according to any one of [1] to [3], wherein the average fiber diameter of the polymer fibrous material is 3 to 20 nm. [5] The electrode catalyst layer according to any one of [1] to [4], wherein the content of the polymer fibrous material is 10 parts by mass or less per 100 parts by mass of the catalyst. [6] The electrode catalyst layer according to any one of [1] to [5], wherein the polymer fibrous material has hydrogen bonding functional groups. [7] The electrode catalyst layer according to any one of [1] to [6], wherein the polymer fibrous material has hydrogen bonding functional groups in the repeating units. [8] The electrode catalyst layer according to any one of [1] to [7], wherein the polymer fibrous material is a cellulose nanofiber. [9] The electrode catalyst layer according to any one of [1] to [8], wherein the shear strength of the electrode catalyst layer is 0.08 N / mm or more.

[10] An electrode catalyst layer according to any one of [1] to [9], for use in water electrolysis or organic hydride electrolysis.

[11] A membrane electrode assembly for water electrolysis or organic hydride electrolysis, comprising an electrolyte membrane and an electrode catalyst layer according to any one of [1] to

[10] disposed on one or both sides of the electrolyte membrane.

[12] A polymer electrolyte membrane, and a membrane electrode assembly having a pair of electrode catalyst layers disposed on both sides of the polymer electrolyte membrane, A pair of current collectors provided so as to sandwich the membrane electrode assembly, A water electrolysis device, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer according to any one of [1] to

[11] .

[13] A polymer electrolyte membrane, and a membrane electrode assembly having a pair of electrode catalyst layers disposed on both sides of the polymer electrolyte membrane, A pair of current collectors provided so as to sandwich the membrane electrode assembly, An organic hydride electrolytic synthesis device, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer according to any one of [1] to

[11] . [Advantages of the Invention]

[0011] According to the present invention, an electrode catalyst layer or the like that can achieve both a reduction in electrolysis voltage and suppression of crack generation is provided. [Brief Description of the Drawings]

[0012] [Figure 1] It is a cross-sectional view showing an embodiment of the membrane electrode assembly of the present disclosure. [Figure 2] It is a diagram schematically and partially showing an example of the electrode catalyst layer of FIG. 1. [Figure 3] [[ID= It is a cross-sectional view showing an example of the catalyst of FIG. 2. [Figure 4] It is a cross-sectional view showing an embodiment of the water electrolysis device and the organic hydride electrolytic synthesis device of the present disclosure. [Embodiments for Carrying Out the Invention]

[0013] Hereinafter, embodiments of the present disclosure will be described in detail.

[0014] [Membrane Electrode Assembly 200 for Water Electrolysis or Organic Hydride Electrolytic Synthesis] First, an embodiment of the membrane electrode assembly 200 for water electrolysis or organic hydride electrolysis synthesis of the present disclosure will be described with reference to Figures 1 to 3. Figure 1 is a cross-sectional view showing an embodiment of the membrane electrode assembly 200 for water electrolysis or organic hydride electrolysis synthesis of the present disclosure, and Figure 2 is a diagram schematically and partially showing an example of the electrode catalyst layer 20 of Figure 1.

[0015] As shown in Figure 1, the membrane electrode assembly 200 for water electrolysis or organic hydride electrolysis comprises a polymer electrolyte membrane 10, an electrode catalyst layer 20 provided on one surface of the polymer electrolyte membrane 10, and an electrode catalyst layer 30 provided on the other surface of the polymer electrolyte membrane 10. The electrode catalyst layer 20 contains a catalyst 21, a polymer electrolyte 22, and a polymer fibrous material 23 (see Figure 2).

[0016] The polymer electrolyte membrane 10 and the electrode catalyst layer 20 will be described in more detail below.

[0017] (Polymer electrolyte membrane 10) In a PEM (proton exchange membrane) type water electrolysis apparatus and an organic hydride electrolytic synthesis apparatus, the polymer electrolyte membrane 10 is a proton-conducting polymer electrolyte membrane. A proton-conducting polymer electrolyte has a proton-conducting functional group. Examples of proton-conducting functional groups are sulfo groups (-SO3H), phosphonic acid groups (-PO3H2), and carboxyl groups (-COOH), and the proton-conducting functional group may also be in the form of a salt of a metal or the like.

[0018] Specific examples of proton-conducting polymer electrolyte membranes include fluorine-based polymer electrolyte membranes and hydrocarbon-based polymer electrolyte membranes. Examples of fluorine-based polymer electrolyte membranes include Nafion® from DuPont, Flemion® from Asahi Glass Co., Ltd., Aciplex® from Asahi Kasei Corporation, and Gore Select® from Gore Ltd. Examples of hydrocarbon-based polymer electrolyte membranes include sulfonated polyether ketones, sulfonated polyethersulfones, sulfonated polyetherethersulfones, sulfonated polysulfides, and sulfonated polyphenylenes.

[0019] In an AEM (anion exchange membrane type) water electrolysis apparatus, the polymer electrolyte membrane 10 is an anion-conducting polymer electrolyte membrane. An anion-conducting polymer electrolyte has anion-conducting functional groups. A typical example of anion conductivity is hydroxide ions (OH). - It is conductive.

[0020] An example of an anionic conductive functional group is the quaternary ammonium group (NR4 + ) Ammonium groups such as; primary to tertiary amino groups; quaternary phosphonium groups (PR4 + ) and other phosphonium groups; tertiary sulfonium groups (SR3 + ) is a sulfonium group, and the anionic conductive functional group may be in the form of a salt of a metal or the like. R is an organic group such as an alkyl group or an aryl group.

[0021] Examples of quaternary ammonium groups include trimethylammonium, imidazolium, and pyridinium groups. An example of an amino group is the dimethylamino group.

[0022] Examples of commercially available anion exchange membranes include A201 and A901 (both manufactured by Tokuyama Corporation); fumasep® FAA (e.g., FAB-3, FAA-3-50, FAA-3-PK-130, FAA-3-PP-75), FAB (all manufactured by fumatech); Sustainion® 37-50 (manufactured by Dioxide Materials Inc.); NEOSEPTA® ACM, AM-1, ACS, ACLE-5P, AHA, AMH (all manufactured by Astom Co., Ltd.); SELEMION® AMT, DSV, AAV, ASV, AHT, APS (all manufactured by Asahi Glass Co., Ltd.); Aciplex® A-501, A-231, A-101 (all manufactured by Asahi Kasei Corporation); and PiperION® A20-HCO3, A40-HCO3, A80-HCO3 (all manufactured by Versogen Inc.).

[0023] The thickness of the polymer electrolyte membrane 10 is not particularly limited, but is usually 20 to 250 μm, and preferably 20 to 80 μm. By keeping the thickness of the polymer electrolyte membrane 10 within the above range, the mechanical durability of the polymer electrolyte membrane 10 can be maintained, and the proton resistance (anion resistance) can be reduced to improve the electrolytic performance.

[0024] (electrode catalyst layer 20) The electrode catalyst layer 20 includes a catalyst 21, a polymer electrolyte 22, and a polymer fibrous material 23.

[0025] (1) Catalyst Catalyst 21 includes a catalyst (also referred to as an anode catalyst) that causes a reaction to generate oxygen from water at the anode of a water electrolysis device and an organic hydride electrolytic synthesis device, a catalyst (also referred to as a cathode catalyst) that carries out a reaction to generate hydrogen from water at the cathode of a water electrolysis device, or a catalyst (also referred to as a cathode catalyst) that causes the hydrogenation of organic compounds at the cathode of an organic hydride electrolytic synthesis device.

[0026] As the anode catalyst, metals belonging to the platinum group, metals other than the platinum group, or alloys, oxides, complex oxides, or carbides of these metals can be used. These can be used individually or in combination of two or more.

[0027] Among the anode catalysts mentioned above, ruthenium, rhodium, palladium, iridium, platinum, alloys containing at least one of these, and oxides thereof are preferred due to their high catalytic activity.

[0028] For example, iridium (Ir), platinum (Pt), rhodium (Rh), palladium (Pd), nickel (Ni) and its oxides (IrO) x RuO x , PdO x NiO x ), alloys of iridium (Ir) and ruthenium (Ru), and alloys of iridium (Ir) and titanium dioxide (TiO2) are preferably used. IrOx has prominent catalytic activity and is widely used.

[0029] Other preferred examples of the anode catalyst include composite oxides of cobalt and copper (e.g., CuCoO3, CuCoO x (x is a real number corresponding to the average oxidation number of the metal element), Cu x Co 3-x O4 (x is a real number where 0 < x < 3), Cu 0.7 Co 2.3 O4, etc.); composite oxides of nickel and cobalt (e.g., NiCo2O4, etc.); catalysts doped with iron in composite oxides of nickel and cobalt (NiCoO x :Fe (x is a real number corresponding to the average oxidation number of the metal element)); composite oxides of nickel and iron (e.g., NiFe2O4, etc.); composite oxides of ruthenium and lead (e.g., Pb2Ru2O 6.5 etc.); composite oxides of manganese, iron, and cerium (e.g., Ce 0.2 MnFe 1.8 O4, etc.); Ni-Fe alloys; Ni-Al alloys, etc. can be mentioned.

[0030] Also, as the cathode catalyst, for example, noble metals such as platinum, palladium, ruthenium, iridium, rhodium, osmium, base metals such as nickel, cobalt, molybdenum, or manganese, or oxides of these noble metals or base metals can be preferably employed. Other preferred examples of the cathode catalyst include platinum (e.g., platinum supported on carbon (Pt / C), and Pt black, etc.), cerium dioxide supported on activated carbon and nickel supported on lanthanum (III) oxide (Ni / CeO2-La2O3 / C), Ni-Mo alloys, Ni-Fe-Co alloys, Ni-Al-Mo alloys, etc. can be mentioned.

[0031] Catalysts are typically in particulate form. The average particle size of the primary particles of a particulate catalyst is preferably 100 nm or less, and more preferably 50 nm or less. In this case, the activity of the catalyst is further improved. The average particle size is the arithmetic mean of the area circle equivalent diameter of 20 particles in the SEM image. As will be described later, when the catalyst is supported on a conductive carrier, the average particle size of the carrier is preferably 100 nm or less, and more preferably 50 nm or less.

[0032] The catalyst 21 may be supported on a conductive support 21a, as shown in Figure 3. The support 21a can be any material that is conductive and capable of supporting the catalyst 21 without being eroded by the catalyst 21. Commonly used supports 21a include carbon, TiO2, Ti, SnO2, and Sn. The average particle size of the support is preferably 10 nm or larger. In this case, electron conduction paths are more easily formed. However, from the viewpoint of reducing the resistance of the electrode catalyst layer 30 and increasing the amount of catalyst supported, the average particle size of the support is preferably 1000 nm or less, and more preferably 100 nm or less. Here, the average particle size is the arithmetic mean of the area circle equivalent diameter of 20 particles in the SEM image.

[0033] In this embodiment, the catalyst 21 may or may not be supported on the carrier 21a.

[0034] (2) Polyelectrolytes (ionomers) The polymer electrolyte 22 is a proton-conducting or anion-conducting polymer electrolyte. These were explained in the section on polymer electrolyte membranes, so a further explanation is omitted here.

[0035] The polymer electrolyte 22 can function as a binder that connects the catalysts 21 together, the polymer fibrous material 23 together, and the catalysts 21 together with the polymer fibrous material 23. Furthermore, the polymer electrolyte 22 can function as a binder that connects at least one of the catalysts 21 and the polymer fibrous material 23 to the polymer electrolyte membrane 10.

[0036] The polymer electrolyte 22 may be the same polymer electrolyte as the polymer electrolyte membrane 10, or it may be a different polymer electrolyte. However, considering the interfacial resistance at the interface between the polymer electrolyte membrane 10 and the electrode catalyst layer 20, and the rate of dimensional change in the polymer electrolyte membrane 10 and the electrode catalyst layer 20 when humidity changes, it is preferable that the polymer electrolyte contained in the polymer electrolyte membrane 10 and the polymer electrolyte 22 contained in the electrode catalyst layer 20 are the same electrolyte or polymer electrolytes with similar coefficients of thermal expansion.

[0037] For example, to improve the adhesion between the electrode catalyst layer 20 and the polymer electrolyte membrane 10, if the constituent material of the polymer electrolyte 22 is a fluorine-based polymer electrolyte, it is preferable that the constituent material of the polymer electrolyte membrane 10 is also a fluorine-based polymer electrolyte. Furthermore, if the constituent material of the polymer electrolyte 22 is a hydrocarbon-based polymer electrolyte, it is preferable that the constituent material of the polymer electrolyte membrane 10 is also a hydrocarbon-based polymer electrolyte. If the constituent material of the polymer electrolyte 22 is a hydroxide ion conductive polymer electrolyte, it is preferable that the constituent material of the polymer electrolyte membrane 10 is also a hydroxide ion conductive polymer electrolyte.

[0038] The amount of polymer electrolyte 22 blended is preferably 10 to 100 parts by mass, and more preferably 20 to 70 parts by mass, per 100 parts by mass of catalyst. In this case, an intertwined structure of polymer fibers is suitably formed, which further increases the strength of the electrode catalyst layer 20 and further suppresses the occurrence of cracks. If the catalyst 21 contains a carrier 21b, the polymer fibers may be in the range of 1 part by mass or more and 20 parts by mass or less, based on the amount of carrier 21b in the catalyst 21 (100 parts by mass).

[0039] (3) Polymeric fibrous material The average fiber diameter of the polymer fibrous material 23 is not particularly limited, but is preferably 3 nm or more, more preferably 5 nm or more, preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less. In this case, the effect of suppressing crack formation in the electrode catalyst layer 20 with a smaller amount of additive can be obtained. Furthermore, the adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20 can be improved. As a result, the generation of voids due to delamination between the polymer electrolyte membrane 10 and the electrode catalyst layer 20 can be suppressed, and the increase in resistance of the membrane electrode assembly caused by these voids can be further suppressed. From the above, the membrane electrode assembly can further suppress the decrease in the electrolytic performance of water and organic hydrides.

[0040] The average fiber diameter of the polymer fibrous material 23 refers to the average diameter measured for the exposed cross-section of the polymer fibrous material 23 when the cross-section of the electrode catalyst layer 20 is observed using a scanning electron microscope (SEM). If the polymer fibrous material 23 is cut obliquely to its major axis, an elliptical cross-section is obtained; in this case, the diameter refers to the diameter of a perfect circle fitted along the minor axis of the ellipse. Furthermore, when observing the cross-section of the electrode catalyst layer 20 using an SEM, the surface of the polymer fibrous material 23 may be exposed instead of its cross-section. In this case, the diameter refers to the width of the fibers perpendicular to the major axis of the exposed polymer fibrous material 23. The average fiber diameter of the polymer fibrous material 23 refers to the arithmetic mean of the fiber diameters obtained by similarly measuring at at least 20 observation points.

[0041] For example, known methods such as ion milling and ultramicrotomes can be used to expose the cross-section of the electrode catalyst layer 20.

[0042] The average fiber length of the polymer fibrous material 23 is not particularly limited, but is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and even more preferably 4 μm or more. In this case, the polymer fibrous material 23 intertwines, forming voids of appropriate size within the electrode catalyst layer 20, and improving the mechanical properties of the electrode catalyst layer 20. However, the average fiber length of the polymer fibrous material 23 is preferably 100 μm or less, and more preferably 40 μm or less.

[0043] The average fiber length of the polymer fibrous material 23 is defined as the arithmetic mean of the fiber lengths obtained by measuring the lengths of at least 10 polymer fibrous materials 23. The average fiber length of the polymer fibrous material 23 in the electrode catalyst layer 20 can be determined by performing particle size distribution measurement using a solution in which the electrode catalyst layer 20 is dissolved in a solvent.

[0044] There are no particular limitations on the material of the polymeric fibrous material. For example, the polymeric fibrous material may be polyacrylonitrile nanofibers, polylactic acid nanofibers, or polycaprolactone nanofibers. The polymeric fibrous material may have functional groups capable of forming hydrogen bonds. "Capable of forming hydrogen bonds" means that it can form hydrogen bonds with other functional groups.

[0045] It is preferable that the polymeric fibrous material has functional groups capable of forming hydrogen bonds within its repeating units.

[0046] A functional group capable of forming hydrogen bonds may function as a hydrogen bond donor or as a hydrogen bond acceptor.

[0047] Examples of functional groups that function as hydrogen bond donors are hydroxyl groups (-OH) and NH bonds. In these functional groups, electron-rich oxygen or nitrogen atoms are directly bonded to hydrogen, so the hydrogen atom functions as a hydrogen bond donor.

[0048] Examples of functional groups that function as hydrogen bond acceptors include oxygen-containing functional groups such as carbonyl groups (>C=O), groups with ether bonds (-O-), groups with ester bonds (-COO-), and hydroxyl groups (-OH); nitrogen-containing functional groups such as amino groups (-NH2) and amide groups (-CO-NH2); and fluorine-containing functional groups such as -CF3. In these functional groups, the electron-rich oxygen, nitrogen, or fluorine atom is bonded to hydrogen, and therefore the oxygen, nitrogen, and fluorine atoms function as hydrogen bond acceptors.

[0049] Furthermore, hydroxyl groups and NH bonds can act as both donors and acceptors for hydrogen bonds.

[0050] From the viewpoint of promoting the formation of hydrogen bonds between polymeric fibrous materials, it is preferable that the functional group capable of forming hydrogen bonds is a hydroxyl group and / or an NH bond, or a combination of a functional group that functions as a donor and a functional group that functions as an acceptor.

[0051] Because the polymer fibrous material 23 contains functional groups capable of forming hydrogen bonds in its molecular structure, the polymer fibrous material can form a three-dimensional network structure in the electrode catalyst layer through hydrogen bonding and physical entanglement of fibers, making it less prone to cracking and increasing the durability of the electrode catalyst layer 20.

[0052] In order to efficiently form a three-dimensional network structure with a small amount of additive, it is preferable that the repeating units of the polymer fibrous material contain two or more functional groups capable of forming hydrogen bonds.

[0053] Furthermore, hydrogen bonding can occur between the hydrogen-bonding functional groups of the polymer fibrous material and oxygen atoms in the proton-conducting functional groups of the polymer electrolyte 22, or N atoms, H atoms in the anion-conducting functional groups, etc. This makes it easier for the polymer electrolyte 22 to exist around the polymer fibrous material, thus facilitating the formation of proton conduction paths.

[0054] Specific examples of such polymeric fibrous materials include cellulose nanofibers, chitin nanofibers, and chitosan nanofibers. Polymeric fibrous materials that can be dispersed in water or alcohol are preferable.

[0055] Examples of cellulose nanofibers include: cellulose nanofibers having hydroxyl groups and where the hydroxyl groups are not substituted; cellulose nanofibers in which at least a portion of the hydroxyl groups are substituted with carboxyl groups, acetyl groups or their derivatives, or carboxymethyl groups; sulfonated cellulose nanofibers; cellulose sulfate nanofibers; cellulose phosphate nanofibers: cellulose nanofibers in which at least a portion of the hydroxyl groups are substituted with C1-C10 alkyl groups or their derivatives, and any combination of these may be used. Cellulose nanofibers may be cellulose nanofibers having hydroxyl groups and where the hydroxyl groups are not substituted.

[0056] The shape of the polymer fibrous material 23 is not particularly limited; for example, it may have a hollow structure or a solid structure. Furthermore, the polymer fibrous material 23 contained in the electrode catalyst layer 20 may be only one type as described above, or a combination of two or more types.

[0057] The amount of polymer fibrous material blended is preferably 1 part by mass or more and 12 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of catalyst. In this case, an intertwined structure of polymer fibers is suitably formed, which further increases the strength of the electrode catalyst layer 20 and further suppresses the occurrence of cracks. When the catalyst 21 is supported on the carrier 21b, the polymer fibrous material may be in the range of 1 part by mass or more and 20 parts by mass or less, based on the carrier 21b in the catalyst 21 (100 parts by mass).

[0058] (Structure of the electrode catalyst layer 20) The electrode catalyst layer 20 has voids V, as shown in the catalyst layer structure in Figure 2. None of the catalyst 21, polymer electrolyte 22, or polymer fibrous material 23 are present in the voids V.

[0059] Furthermore, in a Voronoi diagram where the centroid of each void V in the cross-section of the electrode catalyst layer 20 is the generating point, when the standard deviation of the area of ​​the Voronoi region is ASD and the arithmetic mean area of ​​the Voronoi region is AAV, the variance of the area of ​​the Voronoi region expressed as ASD / AAV satisfies the condition of being between 0.50 and 0.90. This variance may be 0.55 or higher, 0.60 or higher, 0.85 or lower, or 0.80 or lower. Furthermore, in a Voronoi diagram where the centroid of each polymer fibrous material 23 in the electrode catalyst layer 20 is the generating point, when the standard deviation of the area of ​​the Voronoi region is BSD and the arithmetic mean area of ​​the Voronoi region is BAV, it is preferable that the variance of the area of ​​the Voronoi region expressed as BSD / BAV is 1.5 or less. This variance may be 0.80 or higher, 0.85 or higher, 0.90 or higher, 0.95 or higher, 1.0 or higher, 1.1 or higher, or 1.2 or higher.

[0060] First, we will explain the method for detecting voids and polymer fibrous material in the cross-section of the electrode catalyst layer. The voids V and polymer fibrous material in the cross-section of the electrode catalyst layer can be detected based on images obtained by observing the cross-section of the electrode catalyst layer with a scanning electron microscope (SEM). For example, the voids and polymer fibrous material can be extracted from an SEM observation image taken in a field of view that shows only the electrode catalyst layer at an observation magnification of approximately 10,000 to 20,000 times by image processing.

[0061] The conditions for acquiring electron microscope images are not particularly limited as long as the acceleration voltage does not damage the ionomer contained in the electrode catalyst layer, but an acceleration voltage of 0.5kV to 1kV is preferred. Also, during imaging, it is necessary to adjust the brightness and contrast of the image so that the brightness histogram falls within 0 to 255. Furthermore, the size of the voids and polymer fibrous material that can be detected depends on the size and magnification of the image to be saved, and a resolution of at least 0.02 μm / px is preferred. To reduce errors, it is preferable to image and measure similarly in at least 5 locations, preferably 10 locations or more. As for the method of exposing the cross-section of the electrode catalyst layer, there are no restrictions as long as the shape of the catalyst layer can be maintained during processing, and known methods such as ion milling and ultramicrotome can be used. The cross-section is a cross-section along the thickness direction.

[0062] Next, we will explain how to determine the dispersion of the area of ​​the Voronoi region in a Voronoi diagram where the centroid of each void V or polymer fibrous material 23 is the generating point.

[0063] A "Voronoi diagram" is a diagram that divides a plane into nearest neighbor regions (Voronoi regions) by drawing perpendicular bisectors (Voronoi division lines) between two adjacent generator points on a plane and connecting these perpendicular bisectors.

[0064] In this embodiment, a Voronoi diagram is obtained using the centroids of the voids V or polymer fibrous material 23 in the cross-section of the electrode catalyst layer as the generating points. The degree of dispersion of the area of ​​the Voronoi region with the centroid of the voids as the generating point is defined as ASD / AAV, where ASD is the standard deviation of the area of ​​the Voronoi region with the centroid of the voids as the generating point and AAV is the arithmetic mean area of ​​the Voronoi region with the centroid of the voids as the generating point. The degree of dispersion of the area of ​​the Voronoi region with the centroid of the polymer fibrous material as the generating point is defined as BSD / BAV, where BSD is the standard deviation of the area of ​​the Voronoi region with the centroid of the polymer fibrous material as the generating point and BAV is the arithmetic mean area of ​​the Voronoi region with the centroid of the polymer fibrous material as the generating point. The smaller these dispersion values ​​are, the higher the spatial dispersion of the voids or polymer fibrous material within the cross-section.

[0065] In this specification, a Voronoi diagram is created based on each of the above SEM images of at least five fields of view, and the standard deviation and arithmetic mean area are calculated based on the area of ​​all Voronoi regions included in each field of view.

[0066] In this embodiment, the ratio of the area of ​​voids in the cross-section of the electrode catalyst layer, that is, the ratio of the total area of ​​voids in the cross-section to the total area of ​​the cross-section, is 20% or more and 40% or less. This ratio of void area may be 22% or more, 24% or more, 26% or more, 28% or more, 38% or less, 36% or less, or 34% or less.

[0067] In this embodiment, the ratio of the area of ​​polymer fibrous material in the cross-section of the electrode catalyst layer, that is, the ratio of the total area of ​​fibrous material in the cross-section to the total area of ​​the cross-section, may be 2% or more and 15% or less. This ratio of fibrous material may be 2.5% or more, 3.0% or more, 4.0% or more, 5.0% or more, or 14% or less. Within these ranges, the effect of adding polymeric fibrous material can be obtained without increasing resistance. The calculation of the ratio of voids and polymer fibrous material area in the cross-section of the electrode catalyst layer is performed based on each of the above SEM images of at least five fields of view.

[0068] (Thickness of electrode catalyst layer 20) The electrode catalyst layer thickness is preferably between 1 μm and 10 μm. If the thickness is greater than 10 μm, cracking is more likely to occur. If the thickness is less than 1 μm, variations in layer thickness are likely to occur, and the catalyst material and polymer electrolyte (ionomer) are likely to become non-uniform. Cracking on the surface of the electrode catalyst layer and non-uniformity of thickness and material adversely affect durability during long-term operation.

[0069] The thickness of the electrode catalyst layer 20 can be measured, for example, by observing the cross-section of the film electrode assembly using a scanning electron microscope (SEM). For example, it is possible to measure the thickness of the electrode catalyst layer by measuring its length within a field of view that encompasses the entire catalyst layer at an observation magnification of approximately 1,000 to 10,000 times. To obtain a consistent thickness, it is preferable to perform similar measurements at at least 20 observation points. Known methods such as ion milling and ultramicrotome can be used to expose the cross-section of the film electrode assembly.

[0070] (Shear strength of electrode catalyst layer 20) The shear strength of the electrode catalyst layer can be 0.08 N / mm or higher, and may be 0.09 N / mm or higher. The shear strength of the electrode catalyst layer is the force per unit length observed when cutting a portion of the electrode catalyst layer to a depth of 1 μm from the surface of the electrode catalyst layer by moving a diamond cutting tool in the in-plane direction of the layer at a speed of 10 μm / sec. The width of the diamond cutting tool is 1 mm, the rake angle is 20°, and the relief angle is 10°.

[0071] (electrode catalyst layer 30) The electrode catalyst layer 30 is provided together with the electrode catalyst layer 20 so as to sandwich the polymer electrolyte membrane 10. The electrode catalyst layer 30 is not particularly limited as long as it contains a catalyst, but it is preferable that it further contains a polymer electrolyte and a fibrous material. The catalyst and polymer electrolyte, and their composition ratios, can be those exemplified in the section on the electrode catalyst layer 20. The electrode catalyst layer 30 may also satisfy the requirements of the electrode catalyst layer 20.

[0072] The electrode catalyst layer 30 may contain a catalyst, a polymer electrolyte, and a polymer fibrous material, similar to the electrode catalyst layer 20, but it may not contain the polymer fibrous material.

[0073] <Method for manufacturing a membrane electrode assembly> The method for manufacturing the membrane electrode assembly 200 includes an ink preparation step for preparing an ink and an electrode catalyst layer formation step for forming an electrode catalyst layer 20 by applying the ink to one side of the polymer electrolyte membrane 10.

[0074] <Ink preparation process> In the ink preparation process, the components constituting the electrode catalyst layer 20, namely the catalyst 21, the polymer electrolyte 22, and the polymer fibrous material 23, are mixed in the presence of a dispersion medium to prepare a catalyst ink. In other words, the ink contains a catalyst, a polymer electrolyte, a polymer fibrous material, and a dispersion medium.

[0075] The dispersion medium for the ink is not particularly limited as long as it does not erode the components constituting the electrode catalyst layer 20 and can dissolve the polymer electrolyte 22 in a highly fluid state or disperse it as a fine gel. However, it is desirable that the dispersion medium contains at least a volatile organic solvent. The dispersion medium for the ink may be water, alcohols, ketones, other polar solvents, ether-based solvents, etc. Specifically, examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, etc. Examples of ketones include acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, diisobutyl ketone, etc. Examples of polar solvents other than water, alcohols, and ketones include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, and 1-methoxy-2-propanol. Examples of ether-based solvents include tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, and dibutyl ether. The dispersion medium may be a mixed solvent obtained by mixing two or more of the above-mentioned solvents.

[0076] Furthermore, when using a lower alcohol as the dispersion medium, it is preferable to use a mixed solvent of the lower alcohol and water from the viewpoint of further suppressing the ignition of the dispersion medium. Moreover, from the viewpoint that the polymer electrolyte 22 is an ionomer, it is preferable that the dispersion medium contains water that is compatible with the ionomer, i.e., water with high affinity for the ionomer. The water content in the dispersion medium is not particularly limited as long as it does not cause the ionomer to separate, resulting in turbidity or gelation. When the catalyst 21 is supported on the carrier 21a, the ink may contain a dispersant in order to disperse the catalyst 21 and the carrier 21a in the ink. Examples of dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

[0077] The solid content in the ink is preferably 50% by mass or less. In this case, the occurrence of cracks on the surface of the electrode catalyst layer 20 is further suppressed. From the viewpoint of improving the film formation rate of the electrode catalyst layer 20, the solid content in the ink is more preferably 1% by mass or more and 20% by mass or less.

[0078] In the ink preparation process, each component constituting the electrode catalyst layer 20 may be mixed using a dispersion medium, and then dispersed as necessary. Alternatively, polymer fibrous material may be dispersed in a dispersion medium beforehand, then mixed with other materials, and dispersed as necessary. The dispersion process is not particularly limited as long as it can disperse each component contained in the electrode catalyst layer 20. Examples of such processes include processing with a planetary ball mill and roll mill, processing with a shear mill, processing with a wet mill, ultrasonic dispersion, and processing with a homogenizer.

[0079] Here, by adjusting the blending ratio of polymer electrolytes in the electrode catalyst layer of the ink, the blending ratio of polymer fibrous material in the electrode catalyst, the solvent composition of the catalyst ink, the dispersion strength during catalyst ink preparation, the heating temperature of the applied catalyst ink and its heating rate, the degree of dispersion of the area of ​​the Voronoi region in the Voronoi diagram, with the centroid of the voids in the cross-section of the electrode catalyst layer as the parent point, it is possible to adjust the degree of dispersion of the area of ​​the Voronoi region.

[0080] When a polymeric fibrous material contains functional groups capable of forming hydrogen bonds, the polymeric fibrous material can form a stable three-dimensional network structure through hydrogen bonding in addition to physical fibrous entanglement. Therefore, cracking of the electrode catalyst layer after drying can be suppressed, the dispersion stability of the catalyst in the ink is excellent, and the flow of the ink after coating can also be suppressed, resulting in excellent uniformity of the thickness of the coating film and the electrode catalyst layer after drying, as well as uniformity of the amount of catalyst supported.

[0081] When measured at 23°C using a cone-plate viscometer (rheometer), the ink preferably has a viscosity of 500 to 5000 mPa·s at a shear rate of 1 / s. In this case, the dispersion of the catalyst in the ink is particularly stable, and variations in thickness and catalyst load can be further suppressed. In addition, ink leveling occurs within a suitable range, contributing to the flatness of the electrode catalyst layer.

[0082] <Electrode catalyst layer formation process> In the electrode catalyst layer formation process, the ink obtained in the ink preparation process is applied to one side of the polymer electrolyte membrane 10, and then the electrode catalyst layer 20 is formed by performing a drying process to volatilize the dispersion medium.

[0083] In this configuration, the electrode catalyst layer 20 is formed directly on the surface of the polymer electrolyte membrane 10. This improves the adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20. Furthermore, since no pressure is required for bonding the electrode catalyst layer 20, the risk of the electrode catalyst layer 20 collapsing is suppressed.

[0084] Furthermore, since the polymer electrolyte membrane 10 generally has the characteristic of having a large degree of swelling and shrinkage, when ink is applied to the polymer electrolyte membrane 10, the volume change of the polymer electrolyte membrane 10 is larger compared to when the ink is applied to a support substrate to form an electrode catalyst layer 20, and then the electrode catalyst layer 20 is transferred to the polymer electrolyte membrane 10. For this reason, if the ink does not contain polymer fibrous material 23, cracks are likely to occur in the electrode catalyst layer 20. In contrast, when the ink contains polymer fibrous material 23, even if the volume of the polymer electrolyte membrane 10 changes significantly when the ink is applied directly to the polymer electrolyte membrane 10, the presence of polymer fibrous material 23 in the ink suppresses the occurrence of cracks in the electrode catalyst layer 20.

[0085] The method of applying the ink is not particularly limited, and various application methods can be used. From the viewpoint of applying the ink to the surface of the polymer electrolyte membrane 10 with a uniform film thickness, for example, the doctor blade method, die coating method, curtain coating method, dipping method, spray coating method, screen printing method, roll coating method, etc., can be preferably used.

[0086] The drying method used in the drying process is not particularly limited as long as it can volatilize the dispersion medium, and methods such as ovens, hot plates, hot air drying, and far-infrared radiation can be used. The drying temperature and drying time in the drying process can be appropriately selected depending on the materials that make up the ink. The drying temperature of the ink may be in the range of 40°C to 200°C, preferably in the range of 40°C to 120°C. The drying time of the ink may be in the range of 0.5 minutes to 1 hour, preferably in the range of 1 minute to 30 minutes.

[0087] Alternatively, instead of forming the electrode catalyst layer 20 by applying the ink to the surface of the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, the electrode catalyst layer 20 may be formed by applying the ink to the surface of a support substrate separate from the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, followed by a transfer process in which the electrode catalyst layer 20 is bonded to the polymer electrolyte membrane 10 and then the support substrate is peeled off.

[0088] The above-mentioned support substrate can be any material with good transferability, for example, a fluororesin can be used. Examples of fluororesins include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE). In addition, organic polymer compounds other than fluororesins, such as polyimide, polyethylene terephthalate, polyamide (nylon®), polysulfone, polyethersulfone, polyphenylene sulfide, polyether / etherketone, polyetherimide, polyarylate, and polyethylene naphthalate, can also be used as the substrate. The substrate may be in the form of a sheet or a film. For the above transfer process, for example, a transfer method using heat pressure bonding can be used.

[0089] After forming the electrode catalyst layer 20, the electrode catalyst layer 30 can be formed in the same manner.

[0090] <Water electrolysis apparatus and organic hydride electrolysis synthesis apparatus> An embodiment of the water electrolysis apparatus and organic hydride electrolysis apparatus of the present disclosure will be described with reference to Figure 4. Figure 4 is a cross-sectional view showing an embodiment of the water electrolysis apparatus or organic hydride electrolysis apparatus 300 of the present disclosure.

[0091] As shown in Figure 4, the water electrolysis apparatus or organic hydride electrolysis synthesis apparatus 300 of this embodiment comprises a membrane electrode assembly 200, an anode-side current collector 310 and a cathode-side current collector 320 provided so as to sandwich the membrane electrode assembly 200, and a DC power supply (not shown) electrically connected to the anode-side current collector 310 and the cathode-side current collector 320.

[0092] The anode-side current collector 310 is connected to a DC power supply so as to act as the anode, and the anode-side current collector 310 is bonded to the electrode catalyst layer 20 of the film electrode assembly 200. The cathode-side current collector 320 is connected to a DC power supply so as to act as the cathode, and the cathode-side current collector 320 is bonded to the electrode catalyst layer 30 of the film electrode assembly 200.

[0093] The current collector can be made of any conductive material. Specifically, examples include carbon paper, carbon nonwoven fabric, oxides, and metal plates. Examples of metal plates include titanium sintered bodies. Carbon paper may be water-repellent, and oxides and metal plates may be plated with precious metals. The current collector may be porous, or it may have channels for supplying or discharging gases and liquids. The current collector may function as a separator to hold liquids and gases supplied to or generated and discharged on the cathode and anode sides.

[0094] In a water electrolysis device, when water and voltage are supplied, in the case of a proton exchange membrane type, oxygen and protons are generated from water in the anode electrode catalyst layer, and the generated protons are converted to hydrogen in the cathode electrode catalyst layer. In the case of anion exchange membrane type, hydrogen and hydroxide ions are generated from water in the cathode electrode catalyst layer, and the generated hydroxide ions are converted to oxygen and water in the anode electrode catalyst layer. Ultrapure water or similar water is used.

[0095] In addition, in the case of an organic hydride electrolytic synthesis apparatus, when water, organic substances such as toluene, and voltage are supplied, oxygen and protons are generated from the water in the anode electrode catalyst layer, and the generated protons hydrogenate the organic substances in the cathode electrode catalyst layer, converting them into organic hydrides such as methylcyclohexane.

[0096] Since the water electrolysis apparatus and organic hydride electrolysis synthesis apparatus 300 are equipped with the membrane electrode assembly 200 described above, the occurrence of cracks in the electrode catalyst layer 20 of the membrane electrode assembly 200 is suppressed. Therefore, when water is supplied to the cathode-side electrode catalyst layer 20 and a voltage is applied between the pair of cathode-side current collectors 320 and anode-side current collectors 310 by the power supply, the potential distribution in the electrode catalyst layer 20 of the membrane electrode assembly 200 is suppressed, the decrease in water electrolysis performance is suppressed, and durability is improved.

[0097] In the water electrolysis apparatus and organic hydride electrolysis synthesis apparatus 300 of the present disclosure, the electrode catalyst layer 20 is provided on the anode side, but it may also be provided on the cathode side, or on both the anode and cathode sides.

[0098] (Effects and Benefits) According to this embodiment, since the proportion of the void area in the cross-section of the electrode catalyst layer 20 is relatively large, at 20-40%, the resistance to mass transport of reactants and products is reduced, thereby allowing the electrolysis voltage to be lowered.

[0099] Furthermore, because the electrode catalyst layer contains polymeric fibrous material, and because the degree of dispersion (ASD / AAV) of the area of ​​the Voronoi region in the Voronoi diagram, which uses the centroid of each void in the cross-section of the electrode catalyst layer as the parent point, is a particularly low value, indicating high structural uniformity of the electrode catalyst layer, it is thought that the electrode catalyst layer can exhibit high strength and suppress cracking even if the proportion of void area in the cross-section of the electrode catalyst layer is relatively large, at 20-40%.

[0100] Furthermore, the dispersion ratio ASD / AAV of the Voronoi region with the centroid of the voids as the generating point is a specific low value, and it is thought that the voids are distributed within the cross-section of the electrode catalyst layer with high spatial dispersion, allowing for efficient utilization of the volume of the electrode catalyst layer and thus enabling a lower electrolysis voltage.

[0101] Furthermore, the above-described electrode catalyst layer can improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer. Therefore, the generation of voids due to delamination between the polymer electrolyte membrane and the electrode catalyst layer can be suppressed, and the increase in resistance of the electrode catalyst layer caused by these voids can be further suppressed. For these reasons, a membrane electrode assembly equipped with the above-described electrode catalyst layer can further suppress the deterioration of electrolytic performance.

[0102] Furthermore, the reason why the above-mentioned electrode catalyst layer can improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer is thought to be as follows: Specifically, the stress applied to the electrode catalyst layer is effectively dispersed by the polymer fibrous material, which reduces the shear force at the interface between the electrode catalyst layer and the polymer electrolyte membrane.

[0103] Furthermore, if the polymeric fibrous material has functional groups capable of forming hydrogen bonds, when an electrode catalyst layer is formed by coating an ink onto one surface of a polymer electrolyte membrane, even if excessive stress is applied to the electrode catalyst layer due to the shrinkage of the electrode catalyst layer as the electrolyte membrane shrinks due to the discharge of water during drying after the polymer electrolyte membrane has swollen due to water infiltration, this stress is dispersed by the polymeric fibrous material having a three-dimensional network structure within the electrode catalyst layer. For this reason, it is thought that the occurrence of cracks in the electrode catalyst layer is further suppressed.

[0104] Furthermore, in this case, the polymer fibrous materials can form a three-dimensional network structure in the ink and electrode catalyst layer through hydrogen bonding and entanglement of fibers. When a voltage is applied to the electrode catalyst layer for water electrolysis or organic hydride electrolytic synthesis, areas of localized excessive stress may occur due to oxygen gas or hydrogen gas generated in the electrode catalyst layer. Even in such cases, the polymer fibrous materials with a three-dimensional network structure contained in the electrode catalyst layer distribute such excessive stress. Therefore, it is thought that the occurrence of cracks in the electrode catalyst layer is suppressed. In addition, although the viscosity of the paint often increases when added, if the TI (thixoindex) value is high, the apparent viscosity decreases due to the shear force during application with a die head, resulting in a good painted surface. After the shear force is removed, the viscosity returns to high, thus greatly contributing to preventing sagging and stabilizing the painted surface.

[0105] Furthermore, when the electrode catalyst layer contains a polymer fibrous material having functional groups capable of forming hydrogen bonds, it is believed that the polymer fibrous material can form a three-dimensional network structure through the entanglement of hydrogen atoms and fibers even in the ink before the electrode catalyst layer is formed, thereby increasing the viscosity of the catalyst ink. As a result, the dispersion of catalyst particles in the ink is stabilized, and the sedimentation of the catalyst in the ink is suppressed for a long period of time. Therefore, it is possible to suppress the change in the catalyst content in the coated ink over time, reduce variations in the amount of catalyst supported in the electrode catalyst layer, and suppress cracks in the electrode catalyst layer associated with variations in the amount of catalyst supported.

[0106] Furthermore, if the hydrogen-bonding functional groups of the polymer fibrous material 23 can bond with oxygen atoms in the proton-conducting functional groups of the polymer electrolyte 22, or with N atoms, H atoms in the anion-conducting functional groups, the polymer electrolyte 22 is more likely to be present around the polymer fibrous material 23, which can help in the formation of proton conduction paths. [Examples]

[0107] The contents of this disclosure will be described in more detail below using examples, but this disclosure is not limited to the following examples.

[0108] (Evaluation of the amount of cracks) In the following embodiment, the contrast value using transmitted light was measured as a method for determining the number of cracks. When transmitted light is shone from the back of the laminate, more light passes through defective areas such as cracks and pinholes. Therefore, the contrast between the black areas and the areas that appear white due to transmitted light can be used to determine the number of cracks. In this embodiment, the contrast value (number of black pixels / number of white pixels) in the transmitted light image was 10 3 Those exceeding 10 are called "many". 3 Less than was defined as "few".

[0109] (Measurement of shear strength of electrode catalyst layer) In the following examples, the shear strength of the catalyst layer was measured using a surface and interface physical property analyzer. A SAICAS DN type analyzer (manufactured by Daipla Wintes Co., Ltd.) was used for the measurement, and a diamond blade (width 1 mm, rake angle 20°, relief angle 10°) was used. Horizontal speed: 10μm / sec Cutting depth: 1 μm

[0110] (Analysis of the cross-sectional structure of the electrode catalyst layer) A cryocrosssection polisher (JEOL Ltd.) was used to expose the cross-section, and a scanning electron microscope SU8010 (Hitachi High-Technologies Corporation) was used for electron microscopy.

[0111] The size of the images to be analyzed had to be standardized, and the analysis was performed using images at 20,000x magnification and 1280 x 960 pixels. For void extraction, the Trainable Weka Segmentation function in ImageJ Fiji, a free software widely used for processing and analyzing electron microscope images, was used. In this embodiment, voids in the cross-section of the electrode catalyst layer are regions where none of the catalyst, conductive carrier, polymer electrolyte, or polymer fibrous material exist. However, for void extraction, regions where the outermost surface of the cross-section is a void and whose depth is deeper than the primary particle diameter of one catalyst particle were extracted as voids. If the depth of a void was less than or equal to the primary particle diameter of one catalyst particle, it was considered not to be a void. Specifically, more than 15 locations each were labeled as catalyst regions, polymer electrolyte regions, polymer fibrous material regions, and void regions, and segmentation was performed. Table 1 shows the degree of dispersion by Voronoi tessellation with voids as the parent point, the degree of dispersion by Voronoi tessellation with polymer fibrous material as the parent point, the proportion of voids in the cross-section of the electrode catalyst layer, the proportion of polymer fibrous material in the cross-section of the electrode catalyst layer, and the results of the power generation performance evaluation.

[0112] (Evaluation of water electrolysis performance) In the following examples, the IV measurement was performed using the following procedure to evaluate the water electrolysis performance of the membrane electrode assembly. A Pt-plated Ti mesh was incorporated as a power supply on both sides of the membrane electrode assembly to create an electrolytic cell for evaluation. Current density was 0-3 A / cm² at 50°C. 2 The voltage was measured when the current was applied in steps, and the voltage at 2.0 A / cm² was examined. A voltage of less than 1.90 V is preferable.

[0113] (Example 1) First, a catalyst ink was prepared by mixing a catalyst powder consisting of iridium oxide (product code "TEC77100", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst, a dispersion containing Nafion® (product name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries Ltd.) as a polymer electrolyte, and cellulose nanofiber (product name "BiNFi-s IMa 10002 Extremely Long", manufactured by Sugino Machine Co., Ltd.) as a polymer fibrous material in a solvent and dispersing it in a planetary ball mill for 60 minutes. The solvent used for the catalyst ink was a mixed solvent of ultrapure water and 1-propanol. The volume ratio of ultrapure water to 1-propanol was 30:70. At this time, the catalyst ink was adjusted so that the solid content in the catalyst ink was 10% by mass. The amount of polymer fibrous material added was 2.5 parts by mass per 100 parts by mass of catalyst. It was confirmed that the average fiber diameter of the polymer fibrous material was 10 nm and the average fiber length was 6 μm. The amount of polymer electrolyte added was set to 30 parts by mass per 100 parts by mass of catalyst.

[0114] As the polymer electrolyte membrane, we prepared a Nafion® membrane (trade name "N117", manufactured by DuPont).

[0115] Next, using a slit die coater, the catalyst ink is applied to one main surface of the polymer electrolyte membrane, with an iridium oxide load of 0.5 mg / cm² per unit area of ​​that main surface. 2 The material was coated using a die coating method. Then, it was dried in an 80°C oven to remove the solvent components from the catalyst ink, and a laminate of the electrode catalyst layer and the polymer electrolyte film was obtained. The thickness of the electrode catalyst layer was 10 μm.

[0116] Observation of the obtained laminate revealed that the amount of cracks in the electrode catalyst layer of Example 1 was "small". Furthermore, no delamination of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear strength of the electrode catalyst layer of the obtained laminate was measured using the method described above and was found to be 0.08 N / mm.

[0117] An electrode catalyst layer was laminated as a cathode on the back surface of the obtained laminate using the following procedure. A dispersion containing Pt-supported carbon particles (product number "TEC10E50E", Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst and Nafion® (product name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymer electrolyte was mixed in a solvent and dispersed for 60 minutes using a planetary ball mill to prepare a cathode catalyst ink. A mixed solvent of ultrapure water and 1-propanol was used as the solvent for the catalyst ink. The volume ratio of ultrapure water to 1-propanol was 30:70. Using a slit die coater, the above cathode catalyst ink was applied to the surface of the laminate on the side without the electrode catalyst layer, with a Pt support amount of 0.5 mg / cm² per unit area of ​​the main surface. 2 The material was coated using a die coating method. Then, it was dried in an 80°C oven to remove the solvent components from the catalyst ink, and a laminate of the electrode catalyst layer and the polymer electrolyte membrane was obtained. The electrolytic performance of the membrane electrode assembly obtained in this way was evaluated using the method described above. 2.0 A / cm 2 The electrolytic voltage at that point was 1.85V.

[0118] (Example 2) Except for the following points, the procedure was the same as in Example 1. The amount of polymer fibrous material blended was 5 parts by mass per 100 parts by mass of catalyst.

[0119] Observation of the obtained laminate revealed that the amount of cracks in the electrode catalyst layer of Example 2 was "small." Furthermore, no delamination of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear rate strength of the electrode catalyst layer of the obtained laminate was measured using the method described above and was found to be 0.10 N / mm. (2.0 A / cm) 2 The electrolytic voltage at that point was 1.87V.

[0120] (Example 3) Except for the following points, the procedure was the same as in Example 1. The amount of fibrous material blended was 10% by mass relative to 100% by mass of catalyst. Observation of the obtained laminate revealed that the amount of cracks in the electrode catalyst layer of Example 3 was "small." Furthermore, no delamination of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear rate strength of the electrode catalyst layer of the obtained laminate was measured using the method described above and was found to be 0.10 N / mm. (2.0 A / cm) 2 The electrolytic voltage at that point was 1.87V.

[0121] (Comparative Example 1) A catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained using the same method as in Example 1, except that it did not contain polymer fibrous material. Observation of the obtained laminate revealed that the amount of cracks in the electrode catalyst layer was "higher" than in Comparative Example 1. Furthermore, delamination of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear strength of the electrode catalyst layer in the obtained laminate was measured to be 0.04 N / mm. (2.0 A / cm) 2 The electrolytic voltage at that point was 1.94V.

[0122] (Comparative Example 2) A catalyst ink was obtained using the same method as in Example 1, except that the amount of polymeric fibrous material added was 15 parts by mass per 100 parts by mass of catalyst. Due to its high viscosity, it was difficult to coat the electrolyte membrane with the ink as a film of uniform thickness, and therefore an electrode catalyst layer could not be obtained.

[0123] (Comparative Example 3) Compared to Example 2, a catalyst ink and a laminate of the electrode catalyst layer and electrolyte membrane were obtained using the same method as in Example 2, except that the rotation speed and dispersion time in the dispersion process were reduced to create weaker dispersion conditions. Observation of the obtained laminate revealed that the amount of cracks in the electrode catalyst layer was "smaller" than in Comparative Example 3. Furthermore, delamination of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear strength of the electrode catalyst layer in the obtained laminate was measured to be 0.08 N / mm². (2.0 A / cm²) 2 The electrolytic voltage at that point was 1.91V.

[0124] (Comparative Example 4) Except for using polybenzimidazole polymer fibers (fiber diameter 200 nm, fiber length 15 μm) without hydroxyl groups and with a fiber diameter of 200 nm as the polymer fibrous material, a catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained by the same method as in Example 1.

[0125] Observation of the obtained laminate revealed that the amount of cracks in the electrode catalyst layer of Comparative Example 4 was "high." Furthermore, partial delamination of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear strength of the electrode catalyst layer of the obtained laminate was measured to be 0.05 N / mm. (2.0 A / cm) 2 The electrolytic voltage at that point was 1.93V.

[0126] The degree of Voronoi dispersion with respect to voids in the cross-section of the electrode catalyst layer for each example and comparative example, the degree of Voronoi dispersion with respect to polymer fibrous material as the parent point, the proportion of voids in the cross-section, the proportion of polymer fibrous material in the cross-section, and the evaluation results are shown in Table 1. [Table 1] [Explanation of symbols]

[0127] 10...Polymer electrolyte membrane, 20...Electrode catalyst layer, 21...Catalyst, 21a...Carrier, 22...Polymer electrolyte, 23...Polymer fibrous material, 30...Electrode catalyst layer, 200...Membrane electrode assembly, 300...Water electrolysis apparatus or organic hydride electrolysis synthesis apparatus.

Claims

1. An electrode catalyst layer comprising a catalyst, a polymer electrolyte having proton conductivity or anionic conductivity, and a polymer fibrous material, In the cross-section of the electrode catalyst layer, the proportion of the void area is 20% or more and 40% or less. An electrode catalyst layer wherein, in a Voronoi diagram with the centroid of each void in the cross-section of the electrode catalyst layer as the generating point, the standard deviation of the area of ​​the Voronoi region is ASD, and the arithmetic mean area of ​​the Voronoi region is AAV, and the variance of the area of ​​the Voronoi region expressed as ASD / AAV is 0.50 or more and 0.90 or less.

2. The electrode catalyst layer according to claim 1, wherein in a cross-section of the electrode catalyst layer, in a Voronoi diagram with the centroid of the polymer fibrous material as the parent point, when the standard deviation of the area of ​​the Voronoi region is BSD and the arithmetic mean area of ​​the Voronoi region is BAV, the dispersion of the area of ​​the Voronoi region expressed as BSD / BAV is 1.5 or less.

3. The electrode catalyst layer according to claim 1 or 2, wherein the area ratio of the polymer fibrous material in the cross-section of the electrode catalyst layer is 2% or more and 15% or less.

4. The electrode catalyst layer according to claim 1 or 2, wherein the average fiber diameter of the polymer fibrous material is 3 to 20 nm.

5. The electrode catalyst layer according to claim 1 or 2, wherein the content of the polymer fibrous material is 10 parts by mass or less per 100 parts by mass of the catalyst.

6. The electrode catalyst layer according to claim 1 or 2, wherein the polymeric fibrous material has hydrogen-bonding functional groups.

7. The electrode catalyst layer according to claim 1 or 2, wherein the polymeric fibrous material has hydrogen-bonding functional groups in its repeating units.

8. The electrode catalyst layer according to claim 1 or 2, wherein the polymer fibrous material is a cellulose nanofiber.

9. The electrode catalyst layer according to claim 1 or 2, wherein the shear strength of the electrode catalyst layer is 0.08 N / mm or more.

10. The electrode catalyst layer according to claim 1 or 2, for use in water electrolysis or organic hydride electrolysis synthesis.

11. A membrane electrode assembly for water electrolysis or organic hydride electrolysis synthesis, comprising an electrolyte membrane and an electrode catalyst layer according to claim 1 or 2 disposed on one or both sides of the electrolyte membrane.

12. A membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on both sides of the polymer electrolyte membrane, The film electrode assembly comprises a pair of current collectors provided so as to sandwich it, A water electrolysis apparatus in which at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in claim 1 or 2.

13. A membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on both sides of the polymer electrolyte membrane, The film electrode assembly comprises a pair of current collectors provided so as to sandwich it, An organic hydride electrolytic synthesis apparatus in which at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in claim 1 or 2.

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