Electrode catalyst layer, ink, membrane electrode assembly, water electrolysis device, and organic hydride electrolytic synthesis device

Abstract

This electrode catalyst layer comprises: a catalyst; a polymeric electrolyte that has proton conductivity or anion conductivity; and a polymeric fibrous material that has a functional group capable of forming a hydrogen bond.

Description

Electrode catalyst layer, ink, membrane electrode assembly, water electrolysis device, and organic hydride electrolysis device

[0001] The present disclosure relates to an electrode catalyst layer, an ink, a membrane electrode assembly, a water electrolysis device, and an organic hydride electrosynthesis device.

[0002] In recent years, CO2 that can be produced from various resources has been used to achieve carbon neutrality. ２ The movement to utilize hydrogen, a free energy source, as a primary energy source is accelerating. As a method for producing such hydrogen, a method of electrolyzing water using renewable energy is considered promising. Known methods for water electrolysis generally include 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 has attracted attention as a method that enables the miniaturization of water electrolysis equipment through highly efficient operation, and AEM water electrolysis as a method that is expected to reduce costs through the use of base metal catalysts.

[0003] A PEM water electrolysis device generally includes a pair of main electrodes and a membrane electrode assembly provided therebetween, the membrane electrode assembly including a proton-conductive solid polymer electrolyte membrane, a first electrode catalyst layer provided on one side of the solid polymer electrolyte membrane, and a second electrode catalyst layer provided on the other side of the solid polymer electrolyte membrane. An AEM water electrolysis device also has a similar structure using an anion-conductive electrolyte membrane and includes a similar membrane electrode assembly.

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

[0005] Furthermore, organic hydride electrolysis apparatuses have been attracting attention as a transport carrier for hydrogen, a renewable energy source. One example of an organic hydride electrolysis apparatus is known, similar to a water electrolysis apparatus, that includes a pair of main electrodes and a membrane electrode assembly disposed between them. The membrane electrode assembly includes a proton-conductive solid polymer electrolyte membrane, a first electrode catalyst layer disposed on one side of the solid polymer electrolyte membrane, and a second electrode catalyst layer disposed on the other side of the solid polymer electrolyte membrane (see Patent Document 2 below).

[0006] JP 2019-83085 A

[0007] However, conventional electrode catalyst layers have room for improvement in terms of both suppressing variations in catalyst loading and suppressing cracking (first problem).Furthermore, conventional electrode catalyst layers have room for improvement in terms of both lowering the electrolysis voltage required for water electrolysis or organic hydride electrosynthesis and suppressing cracking (second problem).

[0008] A part of the present disclosure has been made in consideration of the first problem, and has an object to provide an electrode catalyst layer etc. that can suppress cracking and / or variation in catalyst loading amount. Another part of the present disclosure has been made in consideration of the second problem, and has an object to provide an electrode catalyst layer etc. that can reduce electrolysis voltage and suppress cracking.

[0009] As a result of extensive research, the present inventors have discovered that the first problem can be solved by adding a specific polymeric fibrous material to the ink for forming the electrode catalyst layer, leading to the present disclosure.

[0010] [1] An electrode catalyst layer for water electrolysis or organic hydride electrosynthesis, comprising a catalyst, a proton-conducting or anion-conducting polymer electrolyte, and a polymer fibrous material having a functional group capable of forming a hydrogen bond. [2] The electrode catalyst layer according to [1], wherein the polymer fibrous material contains a functional group capable of forming a hydrogen bond in a repeating unit. [3] The electrode catalyst layer according to [1] or [2], wherein the functional group capable of forming a hydrogen bond is a hydroxyl group and / or an N—H bond. [4] The electrode catalyst layer according to any one of [1] to [3], wherein the polymer fibrous material is a cellulose-based nanofiber. [5] The electrode catalyst layer according to any one of [1] to [4], wherein the catalyst has a specific gravity of 5 or more. [6] The electrode catalyst layer according to any one of [1] to [5], wherein the polymer fibrous material has an average fiber diameter of 3 to 20 nm. [7] The electrode catalyst layer according to any one of [1] to [6], wherein the content of the polymer fibrous material is 1 to 12 parts by mass per 100 parts by mass of the catalyst. [8] The electrode catalyst layer according to any one of [1] to [7], wherein the shear strength of the electrode catalyst layer is 0.08 N / mm or more. [9] An ink for water electrolysis or organic hydride electrolysis, comprising a catalyst, a polymer electrolyte having proton conductivity or anion conductivity, and a polymer fibrous material having a functional group capable of forming a hydrogen bond.

[10] The ink according to [9], wherein the polymer fibrous material contains a functional group capable of forming a hydrogen bond in a repeating unit.

[11] The ink according to [9] or

[10] , wherein the functional group capable of forming a hydrogen bond is a hydroxyl group and / or an N—H bond.

[12] The ink according to any one of [9] to

[11] , wherein the specific gravity of the catalyst is 5 or more.

[13] The ink according to any one of [9] to

[11] , wherein the specific gravity of the catalyst is 5 or more at a shear rate of 1 s measured by a rheometer －１

[14] The ink according to any one of [9] to

[12] , wherein the viscosity at a shear rate of 1 s is 500 to 5,000 mPa·s. －１ The viscosity is 30 to 12,000 mPa·s, and the shear rate is 1 s －１ viscosity) / (shear rate 1000 s －１The ink according to any one of [9] to

[12] , having a TI value of 2.0 to 100(-), defined by the viscosity at 100°C (T=0.01°F).

[15] A membrane / electrode assembly for water electrolysis or organic hydride electrolysis, comprising a polymer electrolyte membrane and an electrode catalyst layer disposed on one or both sides of the polymer electrolyte membrane, wherein the electrode catalyst layer is the electrode catalyst layer of any one of [1] to [8].

[16] The membrane / electrode assembly according to

[15] , wherein the electrode catalyst layer is the electrode catalyst layer of [8].

[17] A water electrolysis device comprising: a membrane / electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on either side of the polymer electrolyte membrane, and a pair of current collectors disposed so as to sandwich the membrane / electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer of any one of [1] to [8].

[18] An organic hydride electrolytic synthesis apparatus comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on both sides of the polymer electrolyte membrane; and a pair of current collectors disposed to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer according to any one of [1] to [8].

[0011] As a result of extensive research, the inventors have discovered that the second problem can be solved by specifying the configuration of voids in an electrode catalyst layer containing a polymer fibrous material, leading to the present disclosure.

[0012] [B1] An electrode catalyst layer comprising a catalyst, a polymer electrolyte having proton conductivity or anion conductivity, and a polymer fibrous material, wherein the ratio of the area of ​​voids in a cross section of the electrode catalyst layer is 20% to 40%, and wherein, in a Voronoi diagram in which the centers of gravity of each void in the cross section of the electrode catalyst layer are used as generating points, when ASD is the standard deviation of the area of ​​the Voronoi regions and AAV is the arithmetic mean area of ​​the Voronoi regions, a dispersity of the area of ​​the Voronoi regions expressed by ASD / AAV is 0.50 to 0.90. [B2] The electrode catalyst layer according to [B1], wherein, in a Voronoi diagram in which the centers of gravity of the polymer fibrous material are used as generating points, when BSD is the standard deviation of the area of ​​the Voronoi regions and BAV is the arithmetic mean area of ​​the Voronoi regions, a dispersity of the area of ​​the Voronoi regions expressed by BSD / BAV is 1.5 or less. [B3] The electrode catalyst layer according to [B1] or [B2], wherein the polymeric fibrous material accounts for 2% or more and 15% or less of the area of ​​a cross section of the electrode catalyst layer. [B4] The electrode catalyst layer according to any one of [B1] to [B3], wherein the polymeric fibrous material has an average fiber diameter of 3 to 20 nm. [B5] The electrode catalyst layer according to any one of [B1] to [B4], wherein the content of the polymeric fibrous material is 10 parts by mass or less per 100 parts by mass of the catalyst. [B6] The electrode catalyst layer according to any one of [B1] to [B5], wherein the polymeric fibrous material has a hydrogen-bonding functional group. [B7] The electrode catalyst layer according to any one of [B1] to [B6], wherein the polymeric fibrous material has a hydrogen-bonding functional group in a repeating unit. [B8] The electrode catalyst layer according to any one of [B1] to [B7], wherein the polymeric fibrous material is a cellulose-based nanofiber. [B9] The electrode catalyst layer according to any one of [B1] to [B8], wherein the shear strength of the electrode catalyst layer is 0.08 N / mm or more. [B10] The electrode catalyst layer according to any one of [B1] to [B9], which is for water electrolysis or organic hydride electrolysis. [B11] A membrane electrode assembly for water electrolysis or organic hydride electrolysis, comprising an electrolyte membrane and the electrode catalyst layer according to any one of [B1] to [B10], disposed on one or both sides of the electrolyte membrane.[B12] A water electrolysis device comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on either side of the polymer electrolyte membrane, respectively; and a pair of current collectors disposed so as to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in any one of [B1] to [B11]. [B13] An organic hydride electrolysis device comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers disposed on either side of the polymer electrolyte membrane, respectively; and a pair of current collectors disposed so as to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in any one of [B1] to [B11].

[0013] According to one aspect of the present disclosure, there are provided an electrode catalyst layer and an ink, etc., which can simultaneously suppress the variation in the loading amount in the electrode catalyst layer and the occurrence of cracks. According to another aspect of the present disclosure, there are provided an electrode catalyst layer, etc., which can simultaneously suppress the occurrence of cracks and reduce the electrolysis voltage.

[0014] Fig. 2 is a cross-sectional view showing an embodiment of a membrane electrode assembly of the present disclosure. Fig. 3 is a diagram showing a schematic and partial view of an example of an electrode catalyst layer of Fig. 1. Fig. 4 is a cross-sectional view showing an example of a catalyst of Fig. 2. Fig. 5 is a cross-sectional view showing an embodiment of a water electrolysis device and an organic hydride electrolysis device of the present disclosure.

[0015] Hereinafter, embodiments of the present disclosure will be described in detail.

[0016] First Embodiment <Membrane Electrode Assembly 200 for Water Electrolysis or Organic Hydride Electrosynthesis> First, one embodiment of a membrane electrode assembly 200 for water electrolysis or organic hydride electrosynthesis according to the present disclosure will be described with reference to Figures 1 to 3. Figure 1 is a cross-sectional view showing one embodiment of a membrane electrode assembly 200 for water electrolysis or organic hydride electrosynthesis according to the present disclosure, Figure 2 is a schematic and partial view of an example of an electrode catalyst layer 20 in Figure 1, and Figure 3 is a cross-sectional view showing an example of a catalyst in the electrode catalyst layer 20 in Figure 2.

[0017] 1, a membrane electrode assembly 200 for water electrolysis or organic hydride electrolysis includes a polymer electrolyte membrane 10, an electrode catalyst layer 20 provided on one side of the polymer electrolyte membrane 10, and an electrode catalyst layer 30 provided on the other side of the polymer electrolyte membrane 10. The electrode catalyst layer 20 includes a catalyst 21, a polymer electrolyte 22, and a fibrous material 23 (see FIG. 2).

[0018] The polymer electrolyte membrane 10 and the electrode catalyst layer 20 will be described in more detail below.

[0019] (Polymer Electrolyte Membrane 10) The polymer electrolyte membrane 10 is a proton-conductive polymer electrolyte membrane in a PEM (proton exchange membrane) type water electrolysis device and an organic hydride electrolysis device. The proton-conductive polymer electrolyte has a proton-conductive functional group. An example of the proton-conductive functional group is a sulfo group (—SO ３ H), phosphonic acid group (-PO ３ H ２ ), a carboxyl group (—COOH), and the proton-conducting functional group may be in the form of a salt of a metal or the like.

[0020] Specific examples of the proton-conducting polymer electrolyte membrane include a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane. Examples of the fluorine-based polymer electrolyte membrane include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore Select (registered trademark) manufactured by Gore. Examples of the hydrocarbon-based polymer electrolyte membrane include polymer electrolyte membranes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene.

[0021] In an AEM (anion exchange membrane) type water electrolysis device, the polymer electrolyte membrane 10 is an anion-conducting polymer electrolyte membrane. The anion-conducting polymer electrolyte has an anion-conducting functional group. A typical example of anion conductivity is hydroxide ions (OH － ) conductive.

[0022] Examples of anion-conducting functional groups include quaternary ammonium groups (NR ４ ＋ ammonium groups such as primary, secondary, or tertiary amino groups; quaternary phosphonium groups (PR ４ ＋ phosphonium groups such as tertiary sulfonium groups (SR ３ ＋ The anion-conducting functional group may be in the form of a salt of a metal, etc. R is an organic group such as an alkyl group or an aryl group.

[0023] Examples of quaternary ammonium groups are trimethylammonium groups, imidazolium groups, pyridinium groups, etc. An example of an amino group is a dimethylamino group.

[0024] 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), and FAB (all manufactured by Fumatech); Sustainion™ 37-50 (Dioxide Materials); NEOSEPTA (registered trademark) ACM, AM-1, ACS, ACLE-5P, AHA, AMH (all manufactured by Astom Corporation); SELEMION (registered trademark) AMT, DSV, AAV, ASV, AHT, APS (all manufactured by Asahi Glass Co., Ltd.); Aciplex (registered trademark) A-501, A-231, A-101 (all manufactured by Asahi Kasei Corporation), PiperION (trademark) A20-HCO3, A40-HCO3, A80-HCO3 (all manufactured by Versogen), and the like can be mentioned.

[0025] 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. When the thickness of the polymer electrolyte membrane 10 is 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, thereby improving the electrolysis performance.

[0026] (Electrode catalyst layer 20 ) The electrode catalyst layer 20 includes a catalyst 21 , a polymer electrolyte 22 , and a fibrous material 23 .

[0027] (1) Catalyst The 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 the water electrolysis device and the organic hydride electrolysis device, a catalyst (also referred to as a cathode catalyst) that is responsible for a reaction to generate hydrogen from water at the cathode of the water electrolysis device, or a catalyst (also referred to as a cathode catalyst) that causes hydrogenation of an organic compound at the cathode of the organic hydride electrolysis device.

[0028] The anode catalyst may be a platinum group metal, a metal other than a platinum group metal, or an alloy, oxide, double oxide, or carbide of these metals, which may be used alone or in combination of two or more.

[0029] Among the above anode catalysts, ruthenium, rhodium, palladium, iridium, platinum, alloys containing at least one of these, and oxides of these are preferred because of their high catalytic activity.

[0030] For example, iridium (Ir), platinum (Pt), rhodium (Rh), palladium (Pd), nickel (Ni) and their oxides (IrO ｘ , RuO ｘ , PdO ｘ , NiO ｘ ), alloys of iridium (Ir) and ruthenium (Ru), and alloys of iridium (Ir) and titanium dioxide (TiO ２ ) alloys are particularly preferred. ｘ has outstanding catalytic activity and is widely used.

[0031] Other preferred examples of the anode catalyst include composite oxides of cobalt and copper (e.g., CuCoO ３ , CuCoO ｘ (x is a real number corresponding to the average oxidation number of the metal element), Cu ｘ Co ３－ｘ O ４ (x is a real number between 0 and 3), Cu ０．７ Co ２．３ O ４ etc.); composite oxides of nickel and cobalt (e.g., NiCo ２ O ４etc.); nickel and cobalt composite oxide catalysts doped with iron (NiCoO ｘ : Fe (x is a real number corresponding to the average oxidation number of the metal element); a composite oxide of nickel and iron (e.g., NiFe ２ O ４ etc.); Ruthenium and lead composite oxides (e.g., Pb ２ Ru ２ O ６．５ etc.); composite oxides of manganese, iron, and cerium (e.g., Ce ０．２ MnFe １．８ O ４ Ni—Fe alloy; Ni—Al alloy, etc.

[0032] The cathode catalyst may preferably be, for example, a noble metal such as platinum, palladium, ruthenium, iridium, rhodium, or osmium, a base metal such as nickel, cobalt, molybdenum, or manganese, or an oxide of these noble or base metals. Other preferred examples of the cathode catalyst include platinum (e.g., platinum supported on carbon (Pt / C) and Pt black), cerium dioxide supported on activated carbon, and nickel supported on lanthanum (III) oxide (Ni / CeO ２ -La ２ O ３ / C), Ni-Mo alloy, Ni-Fe-Co alloy, Ni-Al-Mo alloy, etc.

[0033] The catalyst is usually in particulate form. The average particle size of the primary particles of the particulate catalyst is preferably 100 nm or less, 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 diameters of the circles equivalent to the area of ​​20 particles in an SEM image. As will be described later, when the catalyst is supported on a conductive support, the average particle size of the support is preferably 100 nm or less, more preferably 50 nm or less.

[0034] There are no particular limitations on the specific gravity of the catalyst (or the catalyst-supported carrier when supported on a carrier), but it is preferably 5 or greater. The specific gravity of the catalyst or catalyst-supported carrier is the true density of the catalyst or catalyst-supported carrier divided by the density of water. For example, the specific gravity of iridium oxide is 11.7. When a metal catalyst or oxide catalyst with a high specific gravity is used, the catalyst ink is likely to settle, resulting in irregular loading amounts during long production periods and the likelihood of cracks occurring due to low viscosity, which may enhance the effects of this embodiment.

[0035] The catalyst 21 may be supported on a conductive support 21a as shown in Fig. 3. The support 21a may be made of a material that is conductive and capable of supporting the catalyst 21 without being eroded by the catalyst 21. Examples of such a support 21a include carbon, TiO ２ , Ti, SnO ２ , Sn are often used. The average particle size of the support is preferably 10 nm or more. In this case, an electron conduction path is easily formed. However, from the viewpoint of reducing the resistance value 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 diameters of the equivalent circle of the area of ​​20 particles in an SEM image.

[0036] In this embodiment, it is preferable that the catalyst 21 is not supported on the carrier 21 a. In such a case, the catalyst is likely to settle in the ink, and variations in the amount of catalyst supported in the electrode catalyst layer are likely to become a problem, thereby enhancing the effect of this embodiment.

[0037] (2) Polymer Electrolyte The polymer electrolyte 22 is a proton-conductive or anion-conductive polymer electrolyte. These have been explained in the section on the polymer electrolyte membrane, so further explanation will be omitted.

[0038] The polymer electrolyte 22 can function as a binder that binds between the catalysts 21, between the polymer fibrous materials 23, and between the catalysts 21 and the polymer fibrous materials 23. The polymer electrolyte can also function as a binder that binds at least one of the catalysts 21 and the polymer fibrous materials 23 to the polymer electrolyte membrane 10.

[0039] The polymer electrolyte 22 may be the same polymer electrolyte as that of the polymer electrolyte membrane 10, or may be a polymer electrolyte different from that of the polymer electrolyte membrane 10. However, taking into consideration 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 be the same electrolyte or polymer electrolytes having similar thermal expansion coefficients.

[0040] For example, when increasing 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, and 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.

[0041] The blending amount of the polymer electrolyte 22 is preferably 10 to 100 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of the catalyst. In this case, an entangled structure of the 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 contains the carrier 21b, the polymer fiber may be in the range of 1 part by mass to 100 parts by mass, based on the carrier 21b in the catalyst 21 (100 parts by mass).

[0042] (3) Polymeric Fibrous Material The polymeric fibrous material 23 has a functional group capable of forming a hydrogen bond. It is preferable that the polymeric fibrous material 23 has a functional group capable of forming a hydrogen bond in the repeating unit.

[0043] Being capable of forming hydrogen bonds means being able to form hydrogen bonds with other functional groups.

[0044] A functional group capable of forming a hydrogen bond may function as a hydrogen bond donor or as a hydrogen bond acceptor.

[0045] Examples of functional groups that function as hydrogen bond donors are the hydroxyl group (-OH) and the N-H bond, in which the electron-rich oxygen or nitrogen atom is directly bonded to hydrogen, allowing the hydrogen atom to function as the hydrogen bond donor.

[0046] Examples of functional groups that function as hydrogen bond acceptors include a carbonyl group (>C=O), a group having an ether bond (-O-), a group having an ester bond (-COO-), a functional group having an oxygen atom such as a hydroxyl group (-OH); an amino group (-NH ２ ), an amide group (—CO—NH ２ a functional group having a nitrogen atom, such as —CF ３ In these functional groups, oxygen, nitrogen, or fluorine atoms, which are electron-rich, are bonded to hydrogen, so the oxygen, nitrogen, and fluorine atoms function as hydrogen bond acceptors.

[0047] The hydroxyl group and the N—H bond can act as both a donor and an acceptor of a hydrogen bond.

[0048] 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 N-H bond, or a combination of a functional group that functions as a donor and a functional group that functions as an acceptor.

[0049] Because the polymer fibrous material 23 contains functional groups capable of forming hydrogen bonds in the molecular structure of the material, the polymer fibrous material can form a three-dimensional network structure in the electrode catalyst layer through hydrogen bonds and physical entanglement of the fibers, making cracks less likely to occur and increasing the durability of the electrode catalyst layer 20.

[0050] Furthermore, 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 N atoms, H atoms in the anion-conducting functional groups, through hydrogen bonds, making it easier for the polymer electrolyte 22 to exist in the vicinity of the polymer fibrous material 23 and helping to form a proton-conducting path.

[0051] Specific examples of such polymeric fibrous materials include cellulose nanofibers, chitin nanofibers, and chitosan nanofibers. Polymeric fibrous materials that can be dispersed in water, alcohol, or the like are preferred.

[0052] Examples of cellulose-based nanofibers include cellulose nanofibers that have hydroxy groups but the hydroxy groups are not substituted; cellulose nanofibers in which at least a portion of the hydroxy groups are substituted with carboxyl groups, acetyl groups or derivatives thereof, or carboxymethyl groups; sulfonated cellulose nanofibers; cellulose sulfate nanofibers; cellulose phosphate nanofibers; cellulose nanofibers in which at least a portion of the hydroxy groups are substituted with C1-C10 alkyl groups or derivatives thereof, and any combination of these is also acceptable. The cellulose-based nanofiber may be a cellulose nanofiber that has hydroxy groups but the hydroxy groups are not substituted.

[0053] The shape of the fibrous material 23 is not particularly limited, and may be, for example, a hollow structure or a solid structure. The fibrous material 23 contained in the electrode catalyst layer 20 may be one of the above-mentioned examples, or a combination of two or more types.

[0054] The average fiber diameter of the 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, a smaller amount of the fibrous material 23 can provide a thickening effect and further suppress cracks in the electrode catalyst layer 20. It can also improve the adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20. This can suppress the generation of voids due to peeling between the polymer electrolyte membrane 10 and the electrode catalyst layer 20, and further suppress the increase in resistance of the membrane electrode assembly due to these voids. From the above, the membrane electrode assembly can further suppress the deterioration of water electrolysis performance.

[0055] The average fiber diameter of the fibrous material 23 refers to the average value of diameters measured for the cross section of the exposed fibrous material 23 when the cross section of the electrode catalyst layer 20 is observed using a scanning electron microscope (SEM). When the fibrous material 23 is cut obliquely relative 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 the cross section of the electrode catalyst layer 20 is observed using an SEM, the surface of the fibrous material 23 may be exposed rather than the cross section of the fibrous material 23. In this case, the diameter refers to the width of the fibers perpendicular to the major axis of the exposed fibrous material 23. The average fiber diameter of the fibrous material 23 refers to the arithmetic mean value of fiber diameters obtained by similar measurements at at least 20 observation points.

[0056] The cross section of the electrode catalyst layer 20 can be exposed by a known method such as ion milling or ultramicrotome.

[0057] The average fiber length of the 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 fibrous material 23 becomes entangled, forming pores of an appropriate size in the electrode catalyst layer 20 and improving the mechanical properties of the electrode catalyst layer 20. However, the average fiber length of the fibrous material 23 is preferably 100 μm or less, more preferably 40 μm or less. The average fiber length of the fibrous material 23 refers to the arithmetic mean value of the fiber lengths obtained by measuring the lengths of at least 10 fibrous material pieces 23. The average fiber length of the fibrous material 23 in the electrode catalyst layer 20 can be determined by measuring the particle size distribution using a solution in which the electrode catalyst layer 20 is dissolved in a solvent.

[0058] The blending amount of the polymer fibrous material is preferably 1 part by mass or more and 12 parts by mass or less, more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the catalyst. In this case, an entangled structure of the 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 support 21b, the polymer fiber may be in the range of 1 part by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the support 21b in the catalyst 21.

[0059] (Thickness of electrode catalyst layer 20) The thickness of the electrode catalyst layer is preferably 1 μm or more and 10 μm or less. If the thickness is greater than 10 μm, cracks are likely to occur. If the thickness is less than 1 μm, the layer thickness is likely to vary, and the catalyst material and polymer electrolyte (ionomer) are likely to become non-uniform. Cracks on the surface of the electrode catalyst layer and non-uniformity in thickness and material have a negative impact on durability during long-term operation.

[0060] The thickness of the electrode catalyst layer 20 can be measured, for example, by observing the cross section of the membrane electrode assembly using a scanning electron microscope (SEM). For example, it can be measured by measuring the thickness of the electrode catalyst layer within a field of view that includes the entire catalyst layer at an observation magnification of about 1000 to 10000 times. In order to grasp the thickness without bias, it is preferable to measure it in the same way at at least 20 or more observation points. For example, known techniques such as ion milling and ultramicrotome can be used to expose the cross section of the membrane electrode assembly.

[0061] (Shear Strength of Electrode Catalyst Layer 20) The shear strength of the electrode catalyst layer can be 0.08 N / mm or more, and may be 0.09 N / mm or more. There is no particular upper limit, but it may be 1.0 N / mm or less, or 0.50 N / mm or less. The shear strength of the electrode catalyst layer is the force per unit length observed when a diamond blade is moved in the in-plane direction of the layer at a speed of 10 μm / sec to cut a portion of the electrode catalyst layer to a depth of 1 μm from the surface. The diamond blade has a width of 1 mm, a rake angle of 20°, and a clearance angle of 10°.

[0062] (Electrode catalyst layer 30) The electrode catalyst layer 30 is provided so as to sandwich the polymer electrolyte membrane 10 together with the electrode catalyst layer 20. There are no particular limitations on the electrode catalyst layer 30 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 composition ratios exemplified in the section on the electrode catalyst layer 20 can be used.

[0063] Like the electrode catalyst layer 20, the electrode catalyst layer 30 may contain a catalyst, a polymer electrolyte, and a polymer fibrous material having a functional group capable of forming a hydrogen bond, but it does not have to contain the polymer fibrous material.

[0064] <Method for manufacturing membrane electrode assembly> The method for manufacturing the membrane electrode assembly 200 includes an ink preparation step of preparing ink, and an electrode catalyst layer formation step of applying the ink to one surface of the polymer electrolyte membrane 10 to form the electrode catalyst layer 20.

[0065] Ink Preparation Step In the ink preparation step, the components that make up the electrode catalyst layer 20, i.e., the catalyst 21, the polymer electrolyte 22, and the polymer fibrous material 23 having a functional group capable of forming a hydrogen bond, are mixed in the presence of a dispersion medium to prepare a catalyst ink. That is, the ink contains the catalyst, the polymer electrolyte, the polymer fibrous material having a functional group capable of forming a hydrogen bond, and the dispersion medium.

[0066] The dispersion medium of the ink is not particularly limited as long as it does not corrode 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 of the ink may be water, alcohols, ketones, other polar solvents, ether-based solvents, etc. Specific examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol. 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, and diisobutyl ketone. Examples of polar solvents other than water, alcohols, and ketones include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol, etc. Examples of ether solvents include tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, etc. The dispersion medium may also be a mixed solvent of two or more of the above-mentioned solvents.

[0067] Furthermore, when a lower alcohol is used as the dispersion medium, a mixed solvent of a lower alcohol and water is preferably used from the viewpoint of further suppressing ignition of the dispersion medium. Furthermore, since the polymer electrolyte 22 is an ionomer, the dispersion medium preferably contains water that is compatible with the ionomer, i.e., water that has a high affinity for the ionomer. The water content of the dispersion medium is not particularly limited as long as it is sufficient to prevent the ionomer from separating and becoming cloudy or gelling. When the catalyst 21 is supported on the carrier 21a, the ink may contain a dispersant 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.

[0068] The solid content of the ink is preferably 50% by mass or less, which further suppresses the occurrence of cracks on the surface of the electrode catalyst layer 20. From the viewpoint of improving the film formation rate of the electrode catalyst layer 20, the solid content of the ink is more preferably 1% by mass or more and 20% by mass or less.

[0069] In the ink preparation process, the components constituting the electrode catalyst layer 20 may be mixed using a dispersion medium, and then a dispersion treatment may be performed as needed. The polymer fibrous material may be dispersed in a dispersion medium in advance, and then mixed with other materials, and a dispersion treatment may be performed as needed. The dispersion treatment is not particularly limited as long as it is a treatment that can disperse the components contained in the electrode catalyst layer 20. Examples of such treatments include treatment with a planetary ball mill and a roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and treatment with a homogenizer.

[0070] The ink contains a polymeric fibrous material containing a functional group capable of forming hydrogen bonds, which allows the polymeric fibrous material to form a stable three-dimensional network structure through physical entanglement of fibers as well as hydrogen bonding, thereby suppressing cracking of the electrode catalyst layer after drying, providing excellent dispersion stability of the catalyst in the ink, and suppressing ink flow after application, resulting in excellent thickness uniformity of the coated film and the electrode catalyst layer after drying, as well as excellent uniformity of the catalyst loading amount.

[0071] The ink preferably has a viscosity of 500 to 5,000 mPa·s at a shear rate of 1 / s when measured with a cone-and-plate viscometer (rheometer) at 23°C. In this case, the dispersion of the catalyst in the ink is particularly stabilized, further suppressing variations in thickness and catalyst loading. In addition, this range allows ink leveling to occur appropriately, contributing to the flatness of the electrode catalyst layer. In this specification, unless otherwise specified, viscosity refers to a value measured with a cone-and-plate viscometer (rheometer) at 23°C.

[0072] It is also preferable that the ink has a viscosity of 30 to 12,000 mPa·s at a shear rate of 1 / s and a thixotropic index value (hereinafter sometimes referred to as TI value) of 2.0 to 100(-). The thixotropic index value is defined as (viscosity at a shear rate of 1 / s) / (viscosity at a shear rate of 1,000 / s). The TI value may be 3 or greater, and in this case, the viscosity at a shear rate of 1 / s may be 100 to 8,000 mPa·s, or 500 to 5,000 mPa·s. The thixotropic index value may be 3.0 or greater, 4.0 or greater, or 80 or less. Such thixotropy can be easily imparted by including a polymeric fibrous material having a functional group capable of forming a hydrogen bond.

[0073] <Electrode catalyst layer forming process> In the electrode catalyst layer forming process, the ink obtained in the ink preparation process is applied to one side of the polymer electrolyte membrane 10, and then a drying process is performed to volatilize the dispersion medium, thereby forming the electrode catalyst layer 20.

[0074] At this time, the electrode catalyst layer 20 is formed directly on the surface of the polymer electrolyte membrane 10. This improves adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20. Furthermore, since pressure is not required to bond the electrode catalyst layer 20, crushing of the electrode catalyst layer 20 is also prevented.

[0075] Note that the polymer electrolyte membrane 10 generally has the characteristic of being subject to large degrees of swelling and shrinkage, and therefore, when ink is applied onto the polymer electrolyte membrane 10, the volume of the polymer electrolyte membrane 10 changes more significantly than when the ink is applied to a support substrate to form the electrode catalyst layer 20, and then the electrode catalyst layer 20 is transferred to the polymer electrolyte membrane 10. Therefore, if the ink does not contain the fibrous material 23, cracks are likely to occur in the electrode catalyst layer 20. In contrast, if the ink contains the fibrous material 23, the occurrence of cracks in the electrode catalyst layer 20 is suppressed because the ink contains the fibrous material 23, even if the volume of the polymer electrolyte membrane 10 changes significantly when the ink is applied directly onto the polymer electrolyte membrane 10.

[0076] The method for applying the ink is not particularly limited, and various application methods can be used. As the application method, for example, a doctor blade method, a die coating method, a curtain coating method, a dipping method, a spray coating method, a screen printing method, a roll coating method, etc. can be preferably used from the viewpoint of applying the ink to the surface of the polymer electrolyte membrane 10 with a uniform film thickness.

[0077] The drying method used in the drying treatment is not particularly limited as long as it can volatilize the dispersion medium, and methods using an oven, a hot plate, hot air drying, far infrared rays, etc. can be used. The drying temperature and drying time in the drying treatment can be appropriately selected depending on the materials constituting the ink. The ink drying temperature may be, for example, in the range of 40°C to 200°C, and preferably in the range of 40°C to 120°C. The ink drying time may be, for example, in the range of 0.5 minutes to 1 hour, and preferably in the range of 1 minute to 30 minutes.

[0078] 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 other than the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, and then bonding the electrode catalyst layer 20 to the polymer electrolyte membrane 10 and then performing a transfer process to peel off the support substrate.

[0079] The support substrate may be made of any material that has good transferability, and for example, a fluorine-based resin may be used. Examples of fluorine-based resins include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE). Furthermore, organic polymer compounds other than fluorine-based resins, such as polyimide, polyethylene terephthalate, polyamide (Nylon (registered trademark)), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate, may also be used as the substrate. The substrate may be in the form of either a sheet or a film. The transfer process may be, for example, a transfer method using thermocompression bonding.

[0080] After the electrode catalyst layer 20 is formed, the electrode catalyst layer 30 may be formed in the same manner.

[0081] <Water electrolysis device and organic hydride electrolysis device> One embodiment of the water electrolysis device and organic hydride electrolysis device according to the present disclosure will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view showing one embodiment of the water electrolysis device or organic hydride electrolysis device 300 according to the present disclosure.

[0082] As shown in FIG. 4 , the water electrolysis apparatus or organic hydride electrosynthesis apparatus 300 of this embodiment includes a membrane electrode assembly 200, an anode-side current collector 310 and a cathode-side current collector 320 disposed 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.

[0083] The anode-side current collector 310 is connected to a DC power supply to function as an anode, and the anode-side current collector 310 is joined to the electrode catalyst layer 20 of the membrane electrode assembly 200. The cathode-side current collector 320 is connected to a DC power supply to function as a cathode, and the cathode-side current collector 320 is joined to the electrode catalyst layer 30 of the membrane electrode assembly 200.

[0084] The current collector may be any conductive material. Specific examples include carbon paper, carbon nonwoven fabric, and oxide and metal plates. Examples of metal plates include titanium sintered bodies. The carbon paper may be water-repellent, and the oxide and metal plates may be plated with a precious metal. The current collector may be porous or may have flow paths for supplying or discharging gases or liquids. The current collector may function as a separator that retains liquids and gases supplied to the cathode and anode sides or generated and discharged.

[0085] In the case of a water electrolysis device, when water and voltage are supplied, oxygen and protons are generated from water at the electrode catalyst layer on the anode side in the case of a proton exchange membrane type, and the generated protons are converted to hydrogen at the electrode catalyst layer on the cathode side, while in the case of an anion exchange membrane type, hydrogen and hydroxide ions are generated from water at the electrode catalyst layer on the cathode side, and the generated hydroxide ions are converted to oxygen and water at the electrode catalyst layer on the anode side. Ultrapure water or other water is used as the water.

[0086] In the case of an organic hydride electrolytic synthesis device, when water, an organic substance such as toluene, and a voltage are supplied, oxygen and protons are generated from the water in the electrode catalyst layer on the anode side, and the generated protons hydrogenate the organic substance in the electrode catalyst layer on the cathode side, converting it into an organic hydride such as methylcyclohexane.

[0087] The water electrolysis device and organic hydride electrosynthesis device 300 includes the above-described membrane electrode assembly 200, and therefore the occurrence of cracks in the electrode catalyst layer 20 of the membrane electrode assembly 200 is suppressed. Therefore, when a voltage is applied between the pair of cathode-side current collector 320 and anode-side current collector 310 by a power source while water is supplied to the cathode-side electrode catalyst layer 20, the potential distribution in the electrode catalyst layer 20 of the membrane electrode assembly 200 is suppressed from being disturbed, the water electrolysis performance is suppressed from being deteriorated, and durability is improved.

[0088] In the water electrolysis device and organic hydride electrosynthesis device 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 side and the cathode side.

[0089] (Effects) According to the above embodiment, the occurrence of cracks in the electrode catalyst layer is suppressed. In addition, the variation in catalyst loading amount between the electrode catalyst layers is suppressed. The reason why the above effects are achieved is not clear, but the following reasons are thought to be the cause.

[0090] Since the electrode catalyst layer contains a polymer fibrous material with functional groups capable of forming hydrogen bonds, even if excessive stress is applied to the electrode catalyst layer due to shrinkage of the electrode catalyst layer caused by the polymer electrolyte membrane shrinking due to the discharge of water as it dries after swelling due to the infiltration of water when the electrode catalyst layer is formed by applying ink to one side of the polymer electrolyte membrane, the stress is dispersed by the polymer fibrous material with a three-dimensional network structure in the electrode catalyst layer, which is thought to be why cracks are suppressed in the electrode catalyst layer.

[0091] Furthermore, the polymeric fibrous materials can form a three-dimensional network structure in the ink and the electrode catalyst layer through hydrogen bonding and entanglement of the fibers. When voltage is applied to the electrode catalyst layer for water electrolysis or organic hydride electrosynthesis, excessive stress may occur locally in the electrode catalyst layer due to oxygen gas or hydrogen gas generated in the electrode catalyst layer. Even in such cases, the polymeric fibrous materials with a three-dimensional network structure contained in the electrode catalyst layer disperse such excessive stress. This is thought to prevent cracks from occurring in the electrode catalyst layer.

[0092] Furthermore, when polymeric fibrous substances are added to ink, viscosity often increases, but if the TI (thixotropic index) value is high, the apparent viscosity actually decreases due to shear forces during application with a die head, etc., resulting in a good coated surface, and then when the shear forces are no longer applied, the viscosity returns to high, which contributes greatly to preventing sagging and stabilizing the coated surface, and the shrinkage stress applied during drying is evenly distributed, making it less likely to crack. On the other hand, when the TI value exceeds 100, the viscosity changes with even a slight change in shear, making the ink difficult to handle and difficult to coat at high viscosity.

[0093] Furthermore, because the electrode catalyst layer contains a polymeric fibrous material with functional groups capable of forming hydrogen bonds, it is believed that the polymeric fibrous material can form a three-dimensional network structure through hydrogen bonding and entanglement of fibers even in the ink before the electrode catalyst layer is formed, which increases the viscosity of the catalyst ink. This stabilizes the dispersion of catalyst particles in the ink and prevents catalyst sedimentation in the ink over a long period of time. This prevents changes in the catalyst content in the applied ink over time, reduces variations in the catalyst loading in the electrode catalyst layer, and also prevents cracks in the electrode catalyst layer due to variations in the catalyst loading.

[0094] The electrode catalyst layer of the present disclosure has few cracks and / or little variation in catalyst loading, and therefore provides uniform performance in a water electrolysis device or an organic hydride electrosynthesis device equipped with a membrane electrode assembly having the same. Specifically, performance variation is reduced in a water electrolysis device or an organic hydride electrosynthesis device equipped with the membrane electrode assembly 200, and when used as a stack, the voltage applied to each membrane electrode assembly is constant, thereby improving the durability of the water electrolysis device and the organic hydride electrosynthesis device. Furthermore, even in a single membrane electrode assembly, disturbance of the potential distribution in the electrode catalyst layer 20 is suppressed, which prevents a decrease in the water electrolysis performance of the electrolysis device or the synthesis performance of the organic hydride electrosynthesis device, thereby improving the durability of the device.

[0095] Furthermore, 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 N atoms, H atoms in the anion-conducting functional groups, through hydrogen bonds, making it easier for the polymer electrolyte 22 to exist in the vicinity of the polymer fibrous material 23 and helping to form a proton-conducting path.

[0096] Furthermore, the electrode catalyst layer can also improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer. This can prevent the generation of voids due to peeling between the polymer electrolyte membrane and the electrode catalyst layer, and further prevent an increase in the resistance of the electrode catalyst layer due to these voids. For these reasons, a membrane electrode assembly including the electrode catalyst layer can further prevent a decrease in electrolysis performance.

[0097] The reason why the electrode catalyst layer can improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer is thought to be as follows: The stress applied to the electrode catalyst layer is effectively dispersed by the fibrous material, which makes it possible to reduce the shear force at the interface between the electrode catalyst layer and the polymer electrolyte membrane.

[0098] (Examples of First Embodiment) Hereinafter, the contents of the first embodiment will be described more specifically using examples, but the present disclosure is not limited to the following examples.

[0099] (Evaluation of crack amount) In the following examples, the contrast value of transmitted light was measured as a method for determining the amount of cracks. When transmitted light is irradiated from the back side of the laminate, more light is transmitted through defective areas such as cracks and pinholes, so the contrast between black areas and areas that appear white in transmitted light can be used to determine the amount of cracks. In this example, the contrast value (number of black pixels / number of white pixels) in the transmitted light image was measured to determine the amount of cracks. ３ Anything over 10 is considered "many"; ３ Less than was considered "few."

[0100] (Evaluation of Viscosity of Catalyst Ink) The viscosity was measured using a rheometer (HAAKE VtiQ Air, manufactured by Thermo Fisher Scientific). The shear rate was changed under the following conditions: Measurement temperature: 23°C Measurement jig: cone plate (diameter 40 mm, angle 2°) Shear rate: 1000 to 1 sec －１ (Sweep from high shear rate) Number of data points: 10 points

[0101] (Measurement of Shear Strength of Electrode Catalyst Layer) In the following examples, the strength of the catalyst layer was measured using a surface / interface physical property analyzer. For the measurement, a SAICAS DN type (manufactured by Daipla Wintes Co., Ltd.) was used, and a diamond blade (width 1 mm, rake angle 20°, relief angle 10°) was used. Horizontal speed: 10 μm / sec Cutting depth: 1 μm

[0102] (Evaluation of Water Electrolysis Performance) In the following examples, the water electrolysis performance of the membrane electrode assembly was evaluated by IV measurement according to the following procedure. Pt-plated Ti mesh was installed on both sides of the membrane electrode assembly as a power feeder to prepare an electrolysis cell for evaluation. The current density was 0 to 3 A / cm at 50°C. ２ The voltage when applied in steps of 2.0 A / cm ２ The voltage at

[0103] Example 1 First, a catalyst powder made of iridium oxide (product number "TEC77100", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst, a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cellulose nanofiber (product name "BiNFi-s IMa 10002 Kyokucho", manufactured by Sugino Machine Co., Ltd.) as a polymer fibrous material were mixed in a solvent, and the mixture was dispersed for 60 minutes using a planetary ball mill to prepare a catalyst ink. The solvent 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. The catalyst ink was adjusted so that the solid content in the catalyst ink was 10% by mass. The blend amount of the fibrous material was 5 parts by mass per 100 parts by mass of the catalyst. The fibrous material was confirmed to have an average fiber diameter of 10 nm and an average fiber length of 6 μm. The blending amount of the polymer electrolyte was set to 30 parts by mass per 100 parts by mass of the catalyst.

[0104] The viscosity of the catalyst ink thus obtained was measured using a rheometer (HAAKE VtiQ Air, manufactured by Thermo Fisher Scientific) as described above. The shear rate was varied under the following conditions: Measurement temperature: 23°C Measurement jig: cone plate (diameter 40 mm, angle 2°) Shear rate: 1000 to 1 sec －１ (Sweep from high shear rate) Number of data points: 10 As a result of the measurements as described above, the viscosity at a shear rate of 1 / s was 1000 mPa s, and the viscosity at a shear rate of 1000 / s was 17.9 Pa s, and the TI was 56.

[0105] The catalyst ink thus prepared was filled into a container, and the solid content was measured at 1 / 5 of the liquid height from the liquid surface immediately after filling and after 24 hours. The solid content maintenance rate was as shown in the table.

[0106] As the polymer electrolyte membrane, a Nafion (registered trademark) membrane (product name "N117", manufactured by DuPont) was prepared.

[0107] Next, using a slit die coater, the catalyst ink was applied to one main surface of the polymer electrolyte membrane so that the amount of iridium oxide carried per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the thickness of the electrode catalyst layer was 8.2 μm. The solvent component in the catalyst ink was removed by drying in an oven at 80° C., yielding a laminate of the electrode catalyst layer and the polymer electrolyte membrane.

[0108] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Example 1 was "small." Furthermore, in the laminate, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed. The shear strength of the electrode catalyst layer of the obtained laminate was measured in the same manner as above and was found to be 0.10 N / mm.

[0109] Coating onto the polymer electrolyte membrane using a slit die coater was repeated for 6 hours. The catalyst loading amount contained in the laminate obtained by coating 6 hours after the start of coating was measured using a fluorescent X-ray spectrometer, and the ratio to the loading amount contained in the laminate obtained by coating at the start of coating (loading amount maintenance rate) was confirmed. The results are shown in the table below.

[0110] An electrode catalyst layer was laminated as a cathode on the back surface of the obtained laminate using the following procedure. Pt-supported carbon particles (product number "TEC10E50E", Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst and a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a solvent and dispersed for 60 minutes using a planetary ball mill to prepare a cathode catalyst ink. The solvent 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. Using a slit die coater, the cathode catalyst ink was applied to the surface of the laminate on the side without the electrode catalyst layer so that the amount of Pt supported per main surface area was 0.5 mg / cm. ２The catalyst ink was applied by die coating so that the solvent component in the catalyst ink was removed by drying in an oven at 80°C, yielding a laminate of an electrode catalyst layer and a polymer electrolyte membrane. The electrolytic performance of the membrane electrode assembly thus obtained was evaluated by the method described above. ２ The electrolysis voltage at this point was 1.86V.

[0111] Example 2 First, a catalyst powder made of iridium oxide (product number "TEC77100", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst, a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cellulose nanofiber (product name "BiNFi-s IMa 10002 Kyokucho", manufactured by Sugino Machine Co., Ltd.) as a polymer fibrous material were mixed in a solvent, and the mixture was dispersed for 60 minutes using a planetary ball mill to prepare a catalyst ink. The solvent 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. The catalyst ink was adjusted so that the solid content in the catalyst ink was 10% by mass. The blend amount of the fibrous material was 5 parts by mass per 100 parts by mass of the catalyst. The fibrous material was confirmed to have an average fiber diameter of 10 nm and an average fiber length of 3 μm. The blending amount of the polymer electrolyte was set to 30 parts by mass per 100 parts by mass of the catalyst.

[0112] The viscosity of the catalyst ink thus obtained was measured in the same manner as above, and was found to be 800 mPa·s at a shear rate of 1 / s and 200 Pa·s at a shear rate of 1000 / s, giving a TI of 4.0.

[0113] The catalyst ink thus prepared was filled into a container, and the solid content was measured at 1 / 5 of the liquid height from the liquid surface immediately after filling and after 24 hours. The solid content maintenance rate was as shown in the table.

[0114] As the polymer electrolyte membrane, a Nafion (registered trademark) membrane (product name "N117", manufactured by DuPont) was prepared.

[0115] Next, using a slit die coater, the catalyst ink was applied to one main surface of the polymer electrolyte membrane so that the total amount of iridium oxide carried per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the thickness of the electrode catalyst layer was 8.3 μm. The solvent component in the catalyst ink was removed by drying in an oven at 80° C., yielding a laminate of the electrode catalyst layer and the polymer electrolyte membrane.

[0116] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Example 2 was "small." Furthermore, in the laminate, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed. The shear strength of the electrode catalyst layer of the obtained laminate was measured in the same manner as above and was found to be 0.08 N / mm.

[0117] Coating onto the polymer electrolyte membrane using a slit die coater was repeated for 6 hours. The catalyst loading amount contained in the laminate obtained by coating 6 hours after the start of coating was measured using a fluorescent X-ray spectrometer, and the ratio to the loading amount contained in the laminate obtained by coating at the start of coating (loading amount maintenance rate) was confirmed. The results are shown in the table below.

[0118] Example 3: First, a catalyst powder consisting of iridium oxide (product number "TEC77100", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was mixed with a dispersion containing Nafion® (trade name "Nafion® DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymer electrolyte, and chitin nanofiber (trade name "BiNFi-s SFo 2002 Chitin", manufactured by Sugino Machine Co., Ltd.) as a polymer fibrous material in a solvent. The mixture was dispersed in a planetary ball mill for 60 minutes to prepare a catalyst ink. The solvent for the catalyst ink was a mixture of ultrapure water and 1-propanol. The volume ratio of ultrapure water to 1-propanol was 30:70. The catalyst ink was adjusted so that the solids content in the catalyst ink was 10% by mass. The amount of fibrous material was 5.0% by mass relative to 100% by mass of catalyst. The average fiber diameter of the fibrous material was confirmed to be 10 nm. Furthermore, when the ink was evaluated in the same manner as in Example 1, the viscosity was 165 mPa s at a shear rate of 1 / s. Furthermore, the viscosity at a shear rate of 1000 / s was 16.5 Pa s, and the TI was 10. Furthermore, the prepared catalyst ink was filled into a container, and the solid content at 1 / 5 of the liquid height from the liquid surface was measured immediately after filling and after 24 hours. The solid content retention rate was as shown in the table.

[0119] On the other hand, a Nafion (registered trademark) membrane (product name "N117", manufactured by DuPont) was prepared as a polymer electrolyte membrane.

[0120] Next, using a slit die coater, the catalyst ink was applied to one main surface of the polymer electrolyte membrane so that the amount of iridium oxide carried per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the thickness of the electrode catalyst layer was 8.1 μm. The solvent component in the catalyst ink was removed by drying in an oven at 80° C., yielding a laminate of the electrode catalyst layer and the polymer electrolyte membrane.

[0121] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Example 1 was "low." Furthermore, no peeling 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 in the same manner as above, and was found to be 0.08 N / mm. Coating of the polymer electrolyte membrane using a slit die coater was repeated over a period of 6 hours. The catalyst loading amount contained in the laminate obtained by coating 6 hours after the start of coating was measured using an X-ray fluorescence spectrometer, and the ratio to the loading amount contained in the laminate obtained by coating at the start of coating (loading amount maintenance rate) was confirmed, and the results are shown in the table below.

[0122] An electrode catalyst layer was laminated as a cathode on the back surface of the obtained laminate using the following procedure. Pt-supported carbon particles (product number "TEC10E 50E", Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst and a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a solvent and dispersed for 60 minutes using a planetary ball mill to prepare a cathode catalyst ink. The solvent 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. Using a slit die coater, the cathode catalyst ink was applied to the surface of the laminate on the side without the electrode catalyst layer so that the amount of Pt supported per main surface area was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the solvent component in the catalyst ink was removed by drying in an oven at 80°C, yielding a laminate of an electrode catalyst layer and a polymer electrolyte membrane. The electrolytic performance of the membrane electrode assembly thus obtained was evaluated by the method described above. ２ The electrolysis voltage at this point was 1.87V.

[0123] Comparative Example 1 A catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained in the same manner as in Example 1, except that the fibrous material was not included. The thickness of the electrode catalyst layer was 7.4 μm.

[0124] The viscosity of the resulting catalyst ink was measured in the same manner, and was found to be 8 mPa·s at a shear rate of 1 / s. Furthermore, the viscosity at a shear rate of 1000 / s was 20.0 Pa·s, resulting in a TI of 0.4. The prepared catalyst ink was filled into a container, and the solid content was measured at 1 / 5 of the liquid height from the liquid surface immediately after filling and 24 hours later. The solid content retention rate was as shown in the table. Observation of the resulting laminate revealed that the amount of cracking in the electrode catalyst layer of Comparative Example 1 was "large." Furthermore, partial peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The ink was repeatedly applied to the polymer electrolyte membrane using a slit die coater over a period of 6 hours. The amount of catalyst supported in the laminate obtained by coating 6 hours after the start of coating was measured using an X-ray fluorescence spectrometer. The ratio (retention rate) of the amount of catalyst supported in the laminate obtained by coating at the start of coating to the amount of catalyst supported in the laminate obtained by coating at the start of coating was confirmed, and the results were as shown in the table. The shear strength of the electrode catalyst layer of the resulting laminate was measured and found to be 0.04 N / mm.

[0125] An electrode catalyst layer was laminated as a cathode on the back surface of the obtained laminate using the following procedure. Pt-supported carbon particles (product number "TEC10E50E", Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst and a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a solvent and dispersed for 60 minutes using a planetary ball mill to prepare a cathode catalyst ink. The solvent 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. Using a slit die coater, the cathode catalyst ink was applied to the surface of the laminate on the side without the electrode catalyst layer so that the amount of Pt supported per main surface area was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the solvent component in the catalyst ink was removed by drying in an oven at 80°C, yielding a laminate of an electrode catalyst layer and a polymer electrolyte membrane. The electrolytic performance of the membrane electrode assembly thus obtained was evaluated by the method described above. ２ The electrolysis voltage at this point was 1.91V.

[0126] Comparative Example 2 A catalyst ink was obtained in the same manner as in Example 1, except that the blending amount of the fibrous material was changed to 15 parts by mass per 100 parts by mass of the catalyst.

[0127] The viscosity of the catalyst ink was measured in the same manner, and was found to be 9000 mPa s at a shear rate of 1 / s. Furthermore, the viscosity at a shear rate of 1000 / s was 11250 Pa s, resulting in a TI of 0.8. The high viscosity made it difficult to coat the ink onto the electrolyte membrane as a film of uniform thickness, and an electrode catalyst layer could not be obtained.

[0128] Comparative Example 3 A catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained in the same manner as in Example 1, except that carbon fiber (fiber diameter 150 nm, fiber length 6 μm, manufactured by Resonac) with a fiber diameter of 200 nm and no functional groups capable of forming hydrogen bonds, such as hydroxyl groups, was used as the fibrous material. The thickness of the electrode catalyst layer was 8.2 μm.

[0129] The viscosity of the resulting catalyst ink was measured in the same manner, and was found to be 200 mPa·s at a shear rate of 1 / s. Furthermore, the viscosity at a shear rate of 1000 / s was 133 Pa·s, resulting in a TI of 1.5. The prepared catalyst ink was filled into a container, and the solid content was measured at 1 / 5 of the liquid height from the liquid surface immediately after filling and after 24 hours. The solid content retention rate was found to be as shown in the table.

[0130] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Comparative Example 3 was "large." Furthermore, partial peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. The shear rate of the electrode catalyst layer of the obtained laminate was measured and found to be 0.05 N / mm.

[0131] Second Embodiment <Membrane Electrode Assembly 200 for Water Electrolysis or Organic Hydride Electrosynthesis> One embodiment of a membrane electrode assembly 200 for water electrolysis or organic hydride electrosynthesis according to the present disclosure will be described with reference to Figures 1 to 3. Figure 1 is a cross-sectional view showing one embodiment of a membrane electrode assembly 200 for water electrolysis or organic hydride electrosynthesis according to the present disclosure, and Figure 2 is a diagram showing a schematic and partial view of an example of the electrode catalyst layer 20 of Figure 1.

[0132] 1, a membrane electrode assembly 200 for water electrolysis or organic hydride electrolysis includes a polymer electrolyte membrane 10, an electrode catalyst layer 20 provided on one side of the polymer electrolyte membrane 10, and an electrode catalyst layer 30 provided on the other side of the polymer electrolyte membrane 10. The electrode catalyst layer 20 includes a catalyst 21, a polymer electrolyte 22, and a polymer fibrous material 23 (see FIG. 2).

[0133] The polymer electrolyte membrane 10 and the electrode catalyst layer 20 will be described in more detail below.

[0134] (Polymer Electrolyte Membrane 10) The polymer electrolyte membrane 10 is a proton-conductive polymer electrolyte membrane in a PEM (proton exchange membrane) type water electrolysis device and an organic hydride electrolysis device. The proton-conductive polymer electrolyte has a proton-conductive functional group. An example of the proton-conductive functional group is a sulfo group (—SO ３ H), phosphonic acid group (-PO ３ H ２ ), a carboxyl group (—COOH), and the proton-conducting functional group may be in the form of a salt of a metal or the like.

[0135] Specific examples of the proton-conducting polymer electrolyte membrane include a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane. Examples of the fluorine-based polymer electrolyte membrane include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Corporation, and Gore Select (registered trademark) manufactured by Gore. Examples of the hydrocarbon-based polymer electrolyte membrane include polymer electrolyte membranes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene.

[0136] In an AEM (anion exchange membrane) type water electrolysis device, the polymer electrolyte membrane 10 is an anion-conducting polymer electrolyte membrane. The anion-conducting polymer electrolyte has an anion-conducting functional group. A typical example of anion conductivity is hydroxide ions (OH － ) conductive.

[0137] Examples of anion-conducting functional groups include quaternary ammonium groups (NR ４ ＋ ammonium groups such as primary, secondary, or tertiary amino groups; quaternary phosphonium groups (PR ４ ＋ phosphonium groups such as tertiary sulfonium groups (SR ３ ＋ The anion-conducting functional group may be in the form of a salt of a metal, etc. R is an organic group such as an alkyl group or an aryl group.

[0138] Examples of quaternary ammonium groups are trimethylammonium groups, imidazolium groups, pyridinium groups, etc. An example of an amino group is a dimethylamino group.

[0139] 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), and FAB (all manufactured by Fumatech); Sustainion™ 37-50 (Dioxide Materials); NEOSEPTA (registered trademark) ACM, AM-1, ACS, ACLE-5P, AHA, AMH (all manufactured by Astom Corporation); SELEMION (registered trademark) AMT, DSV, AAV, ASV, AHT, APS (all manufactured by Asahi Glass Co., Ltd.); Aciplex (registered trademark) A-501, A-231, A-101 (all manufactured by Asahi Kasei Corporation), PiperION (trademark) A20-HCO3, A40-HCO3, A80-HCO3 (all manufactured by Versogen), and the like can be mentioned.

[0140] 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. When the thickness of the polymer electrolyte membrane 10 is 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, thereby improving the electrolysis performance.

[0141] (Electrode Catalyst Layer 20 ) The electrode catalyst layer 20 includes a catalyst 21 , a polymer electrolyte 22 , and a polymer fibrous material 23 .

[0142] (1) Catalyst The 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 the water electrolysis device and the organic hydride electrolysis device, a catalyst (also referred to as a cathode catalyst) that is responsible for a reaction to generate hydrogen from water at the cathode of the water electrolysis device, or a catalyst (also referred to as a cathode catalyst) that causes hydrogenation of an organic compound at the cathode of the organic hydride electrolysis device.

[0143] The anode catalyst may be a platinum group metal, a metal other than a platinum group metal, or an alloy, oxide, double oxide, or carbide of these metals, which may be used alone or in combination of two or more.

[0144] Among the above anode catalysts, ruthenium, rhodium, palladium, iridium, platinum, alloys containing at least one of these, and oxides of these are preferred because of their high catalytic activity.

[0145] For example, iridium (Ir), platinum (Pt), rhodium (Rh), palladium (Pd), nickel (Ni) and their oxides (IrO ｘ , RuO ｘ , PdO ｘ , NiO ｘ ), alloys of iridium (Ir) and ruthenium (Ru), and alloys of iridium (Ir) and titanium dioxide (TiO ２ ) alloys are particularly preferred. ｘ has outstanding catalytic activity and is widely used.

[0146] Other preferred examples of the anode catalyst include composite oxides of cobalt and copper (e.g., CuCoO ３ , CuCoO ｘ (x is a real number corresponding to the average oxidation number of the metal element), Cu ｘ Co ３－ｘ O ４ (x is a real number between 0 and 3), Cu ０．７ Co ２．３ O ４ etc.); composite oxides of nickel and cobalt (e.g., NiCo ２ O ４ etc.); nickel and cobalt composite oxide catalysts doped with iron (NiCoO ｘ : Fe (x is a real number corresponding to the average oxidation number of the metal element); a composite oxide of nickel and iron (e.g., NiFe ２ O ４ etc.); Ruthenium and lead composite oxides (e.g., Pb ２ Ru ２ O ６．５ etc.); composite oxides of manganese, iron, and cerium (e.g., Ce ０．２ MnFe １．８ O ４ Ni—Fe alloy; Ni—Al alloy, etc.

[0147] The cathode catalyst may preferably be, for example, a noble metal such as platinum, palladium, ruthenium, iridium, rhodium, or osmium, a base metal such as nickel, cobalt, molybdenum, or manganese, or an oxide of these noble or base metals. Other preferred examples of the cathode catalyst include platinum (e.g., platinum supported on carbon (Pt / C) and Pt black), cerium dioxide supported on activated carbon, and nickel supported on lanthanum (III) oxide (Ni / CeO ２ -La ２ O ３ / C), Ni-Mo alloy, Ni-Fe-Co alloy, Ni-Al-Mo alloy, etc.

[0148] The catalyst is usually in particulate form. The average particle size of the primary particles of the particulate catalyst is preferably 100 nm or less, 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 diameters of the circles equivalent to the area of ​​20 particles in an SEM image. As will be described later, when the catalyst is supported on a conductive support, the average particle size of the support is preferably 100 nm or less, more preferably 50 nm or less.

[0149] The catalyst 21 may be supported on a conductive support 21a as shown in Fig. 3. The support 21a may be made of a material that is conductive and capable of supporting the catalyst 21 without being eroded by the catalyst 21. Examples of such a support 21a include carbon, TiO ２ , Ti, SnO ２ , Sn are often used. The average particle size of the support is preferably 10 nm or more. In this case, an electron conduction path is easily formed. However, from the viewpoint of reducing the resistance value 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 diameters of the equivalent circle of the area of ​​20 particles in an SEM image.

[0150] In this embodiment, the catalyst 21 may or may not be supported on a carrier 21a.

[0151] (2) Polymer Electrolyte (Ionomer) The polymer electrolyte 22 is a proton-conductive or anion-conductive polymer electrolyte. These have been explained in the section on the polymer electrolyte membrane, so further explanation will be omitted.

[0152] The polymer electrolyte 22 can function as a binder that bonds between the catalysts 21, between the polymer fibrous materials 23, and between the catalysts 21 and the polymer fibrous materials 23. The polymer electrolyte 22 can also function as a binder that bonds at least one of the catalysts 21 and the polymer fibrous materials 23 to the polymer electrolyte membrane 10.

[0153] The polymer electrolyte 22 may be the same polymer electrolyte as that of the polymer electrolyte membrane 10, or may be a polymer electrolyte different from that of the polymer electrolyte membrane 10. However, taking into consideration 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 be the same electrolyte or polymer electrolytes having similar thermal expansion coefficients.

[0154] For example, when increasing 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, and 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.

[0155] The blending amount of the polymer electrolyte 22 is preferably 10 to 100 parts by mass, more preferably 20 to 70 parts by mass, per 100 parts by mass of the catalyst. In this case, an entangled structure of the 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 contains the carrier 21b, the polymer fibers may be present in an amount of 1 part by mass or more and 20 parts by mass or less, based on the amount of the carrier 21b in the catalyst 21 (100 parts by mass).

[0156] (3) Polymer 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, even with a smaller amount added, the effect of further suppressing the occurrence of cracks in the electrode catalyst layer 20 can be obtained. It is also possible to improve the adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20. This can suppress the occurrence of voids due to peeling between the polymer electrolyte membrane 10 and the electrode catalyst layer 20, and further suppress the increase in resistance of the membrane electrode assembly due to these voids. From the above, the membrane electrode assembly can further suppress the deterioration of the electrolysis performance of water and organic hydrides.

[0157] The average fiber diameter of the polymer fibrous material 23 refers to the average value of diameters measured for the cross section of the exposed polymer fibrous material 23 when the cross section of the electrode catalyst layer 20 is observed using a scanning electron microscope (SEM). When the polymer fibrous material 23 is cut obliquely relative 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 the cross section of the electrode catalyst layer 20 is observed using an SEM, the surface of the polymer fibrous material 23 may be exposed rather than the cross section of the polymer fibrous material 23. 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 value of fiber diameters obtained by similar measurements at at least 20 observation points.

[0158] The cross section of the electrode catalyst layer 20 can be exposed by a known method such as ion milling or ultramicrotome.

[0159] 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 becomes entangled, forming voids of an appropriate size in 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.

[0160] The average fiber length of the polymer fibrous material 23 refers to the arithmetic mean value of the fiber lengths obtained by measuring the lengths of at least 10 strands of the polymer fibrous material 23. The average fiber length of the polymer fibrous material 23 in the electrode catalyst layer 20 can be determined by measuring the particle size distribution using a solution in which the electrode catalyst layer 20 is dissolved in a solvent.

[0161] There are no particular limitations on the material of the polymeric fibrous material. For example, the polymeric fibrous material may be polyacrylonitrile nanofiber, polylactic acid nanofiber, or polycaprolactone nanofiber. The polymeric fibrous material may have a functional group capable of forming a hydrogen bond. Being capable of forming a hydrogen bond means that a hydrogen bond can be formed with another functional group.

[0162] The polymeric fibrous material preferably has a functional group capable of forming a hydrogen bond in the repeating unit.

[0163] A functional group capable of forming a hydrogen bond may function as a hydrogen bond donor or as a hydrogen bond acceptor.

[0164] Examples of functional groups that function as hydrogen bond donors are the hydroxyl group (-OH) and the N-H bond, in which the electron-rich oxygen or nitrogen atom is directly bonded to hydrogen, allowing the hydrogen atom to function as the hydrogen bond donor.

[0165] Examples of functional groups that function as hydrogen bond acceptors include a carbonyl group (>C=O), a group having an ether bond (-O-), a group having an ester bond (-COO-), a functional group having an oxygen atom such as a hydroxyl group (-OH); an amino group (-NH ２ ), an amide group (—CO—NH ２ a functional group having a nitrogen atom, such as —CF ３ In these functional groups, oxygen, nitrogen, or fluorine atoms, which are electron-rich, are bonded to hydrogen, so the oxygen, nitrogen, and fluorine atoms function as hydrogen bond acceptors.

[0166] The hydroxyl group and the N—H bond can act as both a donor and an acceptor of a hydrogen bond.

[0167] 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 N-H bond, or a combination of a functional group that functions as a donor and a functional group that functions as an acceptor.

[0168] Because the polymer fibrous material 23 contains functional groups capable of forming hydrogen bonds in the molecular structure of the material, the polymer fibrous material can form a three-dimensional network structure in the electrode catalyst layer through hydrogen bonds and physical entanglement of the fibers, making cracks less likely to occur and increasing the durability of the electrode catalyst layer 20.

[0169] In order to efficiently form a three-dimensional network structure with a small amount of additive, it is preferable that the repeating unit of the polymeric fibrous material contains two or more functional groups capable of forming hydrogen bonds.

[0170] Furthermore, the hydrogen-bonding functional groups of the polymer fibrous material can bond with oxygen atoms in the proton-conducting functional groups of the polymer electrolyte 22, or N atoms, H atoms in the anion-conducting functional groups, through hydrogen bonds, making it easier for the polymer electrolyte 22 to exist in the vicinity of the polymer fibrous material and helping to form a proton-conducting path.

[0171] Specific examples of such polymeric fibrous materials include cellulose nanofibers, chitin nanofibers, and chitosan nanofibers. Polymeric fibrous materials that can be dispersed in water, alcohol, or the like are preferred.

[0172] Examples of cellulose-based nanofibers include cellulose nanofibers that have hydroxy groups but the hydroxy groups are not substituted; cellulose nanofibers in which at least a portion of the hydroxy groups are substituted with carboxyl groups, acetyl groups or derivatives thereof, or carboxymethyl groups; sulfonated cellulose nanofibers; cellulose sulfate nanofibers; cellulose phosphate nanofibers; cellulose nanofibers in which at least a portion of the hydroxy groups are substituted with C1-C10 alkyl groups or derivatives thereof, and any combination of these is also acceptable. The cellulose-based nanofiber may be a cellulose nanofiber that has hydroxy groups but the hydroxy groups are not substituted.

[0173] The shape of the polymer fibrous material 23 is not particularly limited, and may be, for example, a hollow structure or a solid structure. The polymer fibrous material 23 contained in the electrode catalyst layer 20 may be only one of the above-mentioned examples, or may be a combination of two or more types.

[0174] The blending amount of the polymeric fibrous material is preferably 1 part by mass or more and 12 parts by mass or less, more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the catalyst. In this case, an entangled structure of the polymeric 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 support 21b, the polymeric fibrous material may be in the range of 1 part by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the support 21b in the catalyst 21.

[0175] (Structure of Electrode Catalyst Layer 20) As shown in the structure of the catalyst layer in Fig. 2, the electrode catalyst layer 20 has voids V. The voids V are free of the catalyst 21, polymer electrolyte 22, and polymer fibrous material 23.

[0176] In a Voronoi diagram in which the center of gravity of each void V in the cross section of the electrode catalyst layer 20 is used as a 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 dispersity of the area of ​​the Voronoi region expressed as ASD / AAV satisfies 0.50 to 0.90. This dispersity may be 0.55 or more, 0.60 or more, 0.85 or less, or 0.80 or less. Furthermore, in a Voronoi diagram in which the center of gravity of each of the polymer fibrous materials 23 in the electrode catalyst layer 20 is used as a 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 dispersity of the area of ​​the Voronoi region expressed as BSD / BAV be 1.5 or less. The dispersity may be 0.80 or more, 0.85 or more, 0.90 or more, 0.95 or more, 1.0 or more, 1.1 or more, or 1.2 or more.

[0177] First, a method for detecting voids and polymer fibrous material portions in the cross section of an electrode catalyst layer will be described. The voids V and polymer fibrous material portions in the cross section of an electrode catalyst layer can be detected based on an image of the cross section of the electrode catalyst layer observed with a scanning electron microscope (SEM). For example, the voids and polymer fibrous material portions can be extracted by image processing from an SEM observation image taken in a field of view that captures only the electrode catalyst layer at an observation magnification of about 10,000 to 20,000 times.

[0178] 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; for example, an acceleration voltage of 0.5 kV to 1 kV is preferred. Furthermore, during imaging, the brightness and contrast of the image must be adjusted so that the brightness histogram falls within a range of 0 to 255. Furthermore, the size of the voids and polymeric 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 minimize errors, it is preferable to similarly image and measure at least five or more, preferably 10 or more, fields of view. The method for exposing the cross section of the electrode catalyst layer is not limited as long as it maintains the shape of the catalyst layer during processing; for example, known methods such as ion milling and ultramicrotome can be used. The cross section refers to a cross section along the thickness direction.

[0179] Next, a method for determining the degree of dispersion of the area of ​​the Voronoi region in a Voronoi diagram using the center of gravity of each void V or polymeric fibrous material 23 as the generating point will be described.

[0180] A "Voronoi diagram" is a diagram in which a plane is divided into the regions (Voronoi regions) closest to each of the generating points by drawing perpendicular bisectors (Voronoi division lines) on the line connecting two adjacent generating points on the plane and connecting the perpendicular bisectors.

[0181] In this embodiment, a Voronoi diagram is obtained using the centers of gravity of the voids V or the polymer fibrous material 23 in the cross section of the electrode catalyst layer as the respective generating points. The degree of dispersity of the areas of the Voronoi regions having the centers of gravity of the voids as the generating points is defined as ASD / AAV, where ASD is the standard deviation of the areas of the Voronoi regions having the centers of gravity of the voids as the generating points and AAV is the arithmetic mean area of ​​the areas of the Voronoi regions having the centers of gravity of the voids as the generating points. The degree of dispersity of the areas of the Voronoi regions having the centers of gravity of the polymer fibrous material as the generating points is defined as BSD / BAV, where BSD is the standard deviation of the areas of the Voronoi regions having the centers of gravity of the polymer fibrous material as the generating points and BAV is the arithmetic mean area of ​​the areas of the Voronoi regions having the centers of gravity of the polymer fibrous material as the generating points. The smaller these dispersity values, the higher the spatial dispersity of the voids or polymer fibrous material distributed within the cross section.

[0182] In this specification, a Voronoi diagram is created based on each of the above SEM images of at least five or more fields of view, and the standard deviation and arithmetic mean area are calculated based on the areas of all Voronoi regions included in each field of view.

[0183] In this embodiment, the ratio of the area of ​​voids in the cross section of the electrode catalyst layer, i.e., the ratio of the area of ​​all voids in the cross section to the total area of ​​the cross section, is 20% or more and 40% or less. This ratio of the area of ​​voids may be 22% or more, 24% or more, 26% or more, 28% or more, 38% or less, 36% or less, or 34% or less.

[0184] In this embodiment, the area ratio of the polymeric fibrous material in the cross section of the electrode catalyst layer, i.e., the ratio of the area of ​​the total fibrous material in the cross section to the total area of ​​the cross section, may be 2% or more and 15% or less. This fibrous material ratio may be 2.5% or more, 3.0% or more, 4.0% or more, 5.0% or more, or 14% or less. When it is within these ranges, the effect of adding the polymeric fibrous material can be obtained without increasing resistance. The area ratios of the voids and polymeric fibrous material in the cross section of the electrode catalyst layer are calculated based on each of the above SEM images of at least five or more fields of view.

[0185] (Thickness of electrode catalyst layer 20) The thickness of the electrode catalyst layer is preferably 1 μm or more and 10 μm or less. If the thickness is greater than 10 μm, cracks are likely to occur. If the thickness is less than 1 μm, the layer thickness is likely to vary, and the catalyst material and polymer electrolyte (ionomer) are likely to become non-uniform. Cracks on the surface of the electrode catalyst layer and non-uniformity in thickness and material have a negative impact on durability during long-term operation.

[0186] The thickness of the electrode catalyst layer 20 can be measured, for example, by observing the cross section of the membrane electrode assembly using a scanning electron microscope (SEM). For example, it can be measured by measuring the thickness of the electrode catalyst layer within a field of view that includes the entire catalyst layer at an observation magnification of about 1000 to 10000 times. In order to grasp the thickness without bias, it is preferable to measure it in the same way at at least 20 or more observation points. For example, known techniques such as ion milling and ultramicrotome can be used to expose the cross section of the membrane electrode assembly.

[0187] (Shear Strength of Electrode Catalyst Layer 20) The shear strength of the electrode catalyst layer can be 0.08 N / mm or more, and may be 0.09 N / mm or more. The shear strength of the electrode catalyst layer is the force per unit length observed when a diamond blade is moved in the in-plane direction of the layer at a speed of 10 μm / sec to cut a portion of the electrode catalyst layer to a depth of 1 μm from the surface. The diamond blade has a width of 1 mm, a rake angle of 20°, and a clearance angle of 10°.

[0188] (Electrode catalyst layer 30) The electrode catalyst layer 30 is provided so as to sandwich the polymer electrolyte membrane 10 together with the electrode catalyst layer 20. There are no particular limitations on the electrode catalyst layer 30 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 composition ratios can be those exemplified in the electrode catalyst layer 20. The electrode catalyst layer 30 may satisfy the requirements of the electrode catalyst layer 20.

[0189] The electrode catalyst layer 30 may contain a catalyst, a polymer electrolyte, and a polymer fibrous material, like the electrode catalyst layer 20, but may not contain the polymer fibrous material.

[0190] <Method for manufacturing membrane electrode assembly> The method for manufacturing the membrane electrode assembly 200 includes an ink preparation step of preparing ink, and an electrode catalyst layer formation step of applying the ink to one surface of the polymer electrolyte membrane 10 to form the electrode catalyst layer 20.

[0191] Ink Preparation Step In the ink preparation step, the components constituting the electrode catalyst layer 20, i.e., 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. That is, the ink contains the catalyst, the polymer electrolyte, the polymer fibrous material, and the dispersion medium.

[0192] The dispersion medium of the ink is not particularly limited as long as it does not corrode 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 of the ink may be water, alcohols, ketones, other polar solvents, ether-based solvents, etc. Specific examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol. 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, and diisobutyl ketone. Examples of polar solvents other than water, alcohols, and ketones include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1-methoxy-2-propanol, etc. Examples of ether solvents include tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, etc. The dispersion medium may also be a mixed solvent of two or more of the above-mentioned solvents.

[0193] Furthermore, when a lower alcohol is used as the dispersion medium, a mixed solvent of a lower alcohol and water is preferably used from the viewpoint of further suppressing ignition of the dispersion medium. Furthermore, since the polymer electrolyte 22 is an ionomer, the dispersion medium preferably contains water that is compatible with the ionomer, i.e., water that has a high affinity for the ionomer. The water content of the dispersion medium is not particularly limited as long as it is sufficient to prevent the ionomer from separating and becoming cloudy or gelling. When the catalyst 21 is supported on the carrier 21a, the ink may contain a dispersant 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.

[0194] The solid content of the ink is preferably 50% by mass or less, which further suppresses the occurrence of cracks on the surface of the electrode catalyst layer 20. From the viewpoint of improving the film formation rate of the electrode catalyst layer 20, the solid content of the ink is more preferably 1% by mass or more and 20% by mass or less.

[0195] In the ink preparation process, the components constituting the electrode catalyst layer 20 may be mixed using a dispersion medium, and then a dispersion treatment may be performed as needed. The polymer fibrous material may be dispersed in a dispersion medium in advance, and then mixed with other materials, and a dispersion treatment may be performed as needed. The dispersion treatment is not particularly limited as long as it is a treatment that can disperse the components contained in the electrode catalyst layer 20. Examples of such treatments include treatment with a planetary ball mill and a roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and treatment with a homogenizer.

[0196] Here, by adjusting the blending ratio of the polymer electrolyte in the ink electrode catalyst layer, the blending ratio of the polymer fibrous material in the electrode catalyst, the solvent composition of the catalyst ink, the dispersion strength when preparing the catalyst ink, the heating temperature and heating rate of the applied catalyst ink, etc., it is possible to adjust the degree of dispersion of the areas of the Voronoi regions in a Voronoi diagram with the centers of gravity of the voids in the cross section of the electrode catalyst layer as the generating points.

[0197] When the polymeric fibrous material contains a functional group capable of forming hydrogen bonds, the polymeric fibrous material can form a stable three-dimensional network structure through hydrogen bonding in addition to physical entanglement of the fibers, which can prevent cracking of the electrode catalyst layer after drying, as well as providing excellent dispersion stability of the catalyst in the ink and suppressing ink flow after application, resulting in excellent thickness uniformity of the coated film and the electrode catalyst layer after drying, as well as excellent uniformity of the catalyst loading amount.

[0198] The ink preferably has a viscosity of 500 to 5,000 mPa·s at a shear rate of 1 / s when measured at 23°C using a cone-plate viscometer (rheometer). In this case, the dispersion of the catalyst in the ink is particularly stabilized, further suppressing variations in thickness and catalyst loading. In addition, this range allows ink leveling to occur appropriately, contributing to the flatness of the electrode catalyst layer.

[0199] <Electrode catalyst layer forming process> In the electrode catalyst layer forming process, the ink obtained in the ink preparation process is applied to one side of the polymer electrolyte membrane 10, and then a drying process is performed to volatilize the dispersion medium, thereby forming the electrode catalyst layer 20.

[0200] At this time, the electrode catalyst layer 20 is formed directly on the surface of the polymer electrolyte membrane 10. This improves adhesion between the polymer electrolyte membrane 10 and the electrode catalyst layer 20. Furthermore, since pressure is not required to bond the electrode catalyst layer 20, crushing of the electrode catalyst layer 20 is also prevented.

[0201] Note that the polymer electrolyte membrane 10 generally has the characteristic of being subject to large degrees of swelling and shrinkage, and therefore, when ink is applied onto the polymer electrolyte membrane 10, the volume of the polymer electrolyte membrane 10 changes more significantly than when the ink is applied to a support substrate to form the electrode catalyst layer 20, and then the electrode catalyst layer 20 is transferred to the polymer electrolyte membrane 10. Therefore, if the ink does not contain the polymer fibrous material 23, cracks are likely to occur in the electrode catalyst layer 20. In contrast, if the ink contains the polymer fibrous material 23, the occurrence of cracks in the electrode catalyst layer 20 is suppressed because the ink contains the polymer fibrous material 23, even if the volume of the polymer electrolyte membrane 10 changes significantly when the ink is applied directly onto the polymer electrolyte membrane 10.

[0202] The method for applying the ink is not particularly limited, and various application methods can be used. As the application method, for example, a doctor blade method, a die coating method, a curtain coating method, a dipping method, a spray coating method, a screen printing method, a roll coating method, etc. can be preferably used from the viewpoint of applying the ink to the surface of the polymer electrolyte membrane 10 with a uniform film thickness.

[0203] The drying method used in the drying treatment is not particularly limited as long as it can volatilize the dispersion medium, and methods using an oven, a hot plate, hot air drying, far infrared rays, etc. can be used. The drying temperature and drying time in the drying treatment can be appropriately selected depending on the materials constituting the ink. The ink drying temperature may be, for example, in the range of 40°C to 200°C, and preferably in the range of 40°C to 120°C. The ink drying time may be, for example, in the range of 0.5 minutes to 1 hour, and preferably in the range of 1 minute to 30 minutes.

[0204] 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 other than the polymer electrolyte membrane 10 and then performing a drying process to volatilize the dispersion medium, and then bonding the electrode catalyst layer 20 to the polymer electrolyte membrane 10 and then performing a transfer process to peel off the support substrate.

[0205] The support substrate may be made of any material that has good transferability, and for example, a fluorine-based resin may be used. Examples of fluorine-based resins include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE). Furthermore, organic polymer compounds other than fluorine-based resins, such as polyimide, polyethylene terephthalate, polyamide (Nylon (registered trademark)), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate, may also be used as the substrate. The substrate may be in the form of either a sheet or a film. The transfer process may be, for example, a transfer method using thermocompression bonding.

[0206] After the electrode catalyst layer 20 is formed, the electrode catalyst layer 30 may be formed in the same manner.

[0207] <Water electrolysis device and organic hydride electrolysis device> One embodiment of the water electrolysis device and organic hydride electrolysis device of the present disclosure will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view showing one embodiment of the water electrolysis device or organic hydride electrolysis device 300 of the present disclosure.

[0208] As shown in FIG. 4 , the water electrolysis apparatus or organic hydride electrosynthesis apparatus 300 of this embodiment includes a membrane electrode assembly 200, an anode-side current collector 310 and a cathode-side current collector 320 disposed 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.

[0209] The anode-side current collector 310 is connected to a DC power supply to function as an anode, and the anode-side current collector 310 is joined to the electrode catalyst layer 20 of the membrane electrode assembly 200. The cathode-side current collector 320 is connected to a DC power supply to function as a cathode, and the cathode-side current collector 320 is joined to the electrode catalyst layer 30 of the membrane electrode assembly 200.

[0210] The current collector may be any conductive material. Specific examples include carbon paper, carbon nonwoven fabric, and oxide and metal plates. Examples of metal plates include titanium sintered bodies. The carbon paper may be water-repellent, and the oxide and metal plates may be plated with a precious metal. The current collector may be porous or may have flow paths for supplying or discharging gases or liquids. The current collector may function as a separator that retains liquids and gases supplied to the cathode and anode sides or generated and discharged.

[0211] In the case of a water electrolysis device, when water and voltage are supplied, oxygen and protons are generated from water at the electrode catalyst layer on the anode side in the case of a proton exchange membrane type, and the generated protons are converted to hydrogen at the electrode catalyst layer on the cathode side, while in the case of an anion exchange membrane type, hydrogen and hydroxide ions are generated from water at the electrode catalyst layer on the cathode side, and the generated hydroxide ions are converted to oxygen and water at the electrode catalyst layer on the anode side. Ultrapure water or other water is used as the water.

[0212] In the case of an organic hydride electrolytic synthesis device, when water, an organic substance such as toluene, and a voltage are supplied, oxygen and protons are generated from the water in the electrode catalyst layer on the anode side, and the generated protons hydrogenate the organic substance in the electrode catalyst layer on the cathode side, converting it into an organic hydride such as methylcyclohexane.

[0213] The water electrolysis device and organic hydride electrosynthesis device 300 includes the above-described membrane electrode assembly 200, and therefore the occurrence of cracks in the electrode catalyst layer 20 of the membrane electrode assembly 200 is suppressed. Therefore, when a voltage is applied between the pair of cathode-side current collector 320 and anode-side current collector 310 by a power source while water is supplied to the cathode-side electrode catalyst layer 20, the potential distribution in the electrode catalyst layer 20 of the membrane electrode assembly 200 is suppressed from being disturbed, the water electrolysis performance is suppressed from being deteriorated, and durability is improved.

[0214] In the water electrolysis device and organic hydride electrosynthesis device 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 side and the cathode side.

[0215] (Effects) According to this embodiment, the proportion of the void area in the cross section of the electrode catalyst layer 20 is relatively large at 20 to 40%, which reduces the resistance to the mass transport of reactants and products, thereby allowing the electrolysis voltage to be lowered.

[0216] Furthermore, because the electrode catalyst layer contains a polymeric fibrous material, and because the degree of dispersion ASD / AAV of the areas of the Voronoi regions in a Voronoi diagram in which the centers of gravity of the voids in the cross section of the electrode catalyst layer are used as generating points is a specific low value and the structure of the electrode catalyst layer is highly uniform, it is believed that even if the proportion of the area of ​​voids in the cross section of the electrode catalyst layer is relatively large at 20 to 40%, the electrode catalyst layer can exhibit high strength and cracks can be suppressed.

[0217] Furthermore, the degree of dispersion ASD / AAV of the area of ​​the Voronoi region with the center of gravity of the void as the generating point is a particularly low value, and the voids are distributed with high spatial dispersion within the cross section of the electrode catalyst layer. This is thought to enable efficient use of the volume of the electrode catalyst layer and a lower electrolysis voltage.

[0218] Furthermore, the electrode catalyst layer can also improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer. This can prevent the generation of voids due to peeling between the polymer electrolyte membrane and the electrode catalyst layer, and further prevent an increase in the resistance of the electrode catalyst layer due to these voids. For these reasons, a membrane electrode assembly including the electrode catalyst layer can further prevent a decrease in electrolysis performance.

[0219] The reason why the electrode catalyst layer can improve the adhesion between the polymer electrolyte membrane and the electrode catalyst layer is thought to be as follows: The polymer fibrous material effectively disperses the stress applied to the electrode catalyst layer, thereby reducing the shear force at the interface between the electrode catalyst layer and the polymer electrolyte membrane.

[0220] Furthermore, when the polymer fibrous material has functional groups capable of forming hydrogen bonds, even if excessive stress is applied to the electrode catalyst layer due to shrinkage of the electrode catalyst layer caused by the polymer electrolyte membrane shrinking due to the discharge of moisture when the electrolyte membrane is dried after swelling due to the penetration of moisture when the polymer electrolyte membrane is coated with ink to form an electrode catalyst layer, the stress is dispersed by the polymer fibrous material having a three-dimensional network structure in the electrode catalyst layer, which is thought to further suppress the occurrence of cracks in the electrode catalyst layer.

[0221] Furthermore, in this case, the polymeric fibrous materials can form a three-dimensional network structure in the ink and the electrode catalyst layer through hydrogen bonding and fibrous entanglement. When voltage is applied to the electrode catalyst layer for water electrolysis or organic hydride electrosynthesis, excessive stress may occur locally in the electrode catalyst layer due to oxygen gas or hydrogen gas generated in the electrode catalyst layer. Even in such cases, the polymeric fibrous materials with a three-dimensional network structure contained in the electrode catalyst layer disperse such excessive stress. This is thought to suppress the occurrence of cracks in the electrode catalyst layer. Furthermore, although the addition of a cellulose ester often increases the viscosity of the paint, a high thixotropic index (TI) value actually reduces the apparent viscosity due to shear forces during application with a die head, resulting in a good coating surface. The viscosity then returns to high when the shear forces are no longer applied, significantly contributing to preventing sagging and stabilizing the coating surface.

[0222] Furthermore, when the electrode catalyst layer contains a polymeric fibrous material having functional groups capable of forming hydrogen bonds, the polymeric fibrous material can form a three-dimensional network structure through hydrogen bonding and entanglement of fibers even in the ink before the electrode catalyst layer is formed, which is thought to increase the viscosity of the catalyst ink. This stabilizes the dispersion of catalyst particles in the ink and suppresses catalyst sedimentation in the ink over a long period of time. This suppresses changes in the catalyst content in the applied ink over time, reduces variations in the catalyst loading in the electrode catalyst layer, and is thought to suppress cracking in the electrode catalyst layer due to variations in the catalyst loading.

[0223] Furthermore, if the hydrogen-bonding functional group of the polymer fibrous material 23 can bond with an oxygen atom in the proton-conducting functional group of the polymer electrolyte 22, or an N atom, H atom in the anion-conducting functional group, by hydrogen bonding, the polymer electrolyte 22 is more likely to be present in the vicinity of the polymer fibrous material 23, which can help form a proton conduction path.

[0224] (Examples of the Second Embodiment) Hereinafter, the content of the second embodiment will be described more specifically using examples, but the present disclosure is not limited to the following examples.

[0225] (Evaluation of crack amount) In the following examples, the contrast value of transmitted light was measured as a method for determining the amount of cracks. When transmitted light is irradiated from the back side of the laminate, more light is transmitted through defective areas such as cracks and pinholes, so the contrast between black areas and areas that appear white in transmitted light can be used to determine the amount of cracks. In this example, the contrast value (number of black pixels / number of white pixels) in the transmitted light image was measured to determine the amount of cracks. ３ Anything over 10 is considered "many"; ３ Less than was considered "few."

[0226] (Measurement of Shear Strength of Electrode Catalyst Layer) In the following examples, the shear strength of the catalyst layer was measured using a surface / interface physical property analyzer. For the measurement, a SAICAS DN type (manufactured by Daipla Wintes Co., Ltd.) was used, and a diamond blade (width 1 mm, rake angle 20°, clearance angle 10°) was used. Horizontal speed: 10 μm / sec Cutting depth: 1 μm

[0227] (Analysis of Cross-Sectional Structure of Electrode Catalyst Layer) A cryo-cross-section polisher (JEOL Ltd.) was used to expose the cross-section, and a scanning electron microscope SU8010 (Hitachi High-Technologies Corporation) was used as the electron microscope.

[0228] The size of the images to be analyzed had to be uniform, and analysis was performed using 20,000x magnification, 1,280 x 960 pixel images. The Trainable Weka Segmentation function in ImageJ Fiji, free software widely used for processing and analyzing electron microscope images, was used to extract voids. In this embodiment, voids in the cross section of the electrode catalyst layer refer to regions where none of the catalyst, conductive support, polymer electrolyte, or polymer fibrous material is present. For void extraction, the outermost surface of the cross section was considered to be a void, and a portion with a depth greater than one primary particle diameter of the catalyst particle was extracted as a void. If the depth of a void was one primary particle diameter or less of the catalyst particle, it was not considered to be a void. Specifically, 15 or more regions each of the catalyst region, polymer electrolyte region, polymer fibrous material region, and void region were labeled, and segmentation was performed. Table 1 shows the dispersion obtained by the Voronoi tessellation method using voids as the kernel points, the dispersion obtained by the Voronoi tessellation method using polymer fibrous materials as the kernel points, the proportion of voids in the cross section of the electrode catalyst layer, the proportion of polymer fibrous materials in the cross section of the electrode catalyst layer, and the results of the power generation performance evaluation.

[0229] (Evaluation of Water Electrolysis Performance) In the following examples, the water electrolysis performance of the membrane electrode assembly was evaluated by IV measurement according to the following procedure. Pt-plated Ti mesh was installed on both sides of the membrane electrode assembly as a power feeder to prepare an electrolysis cell for evaluation. The current density was 0 to 3 A / cm at 50°C. ２ The voltage when applied in steps of 2.0 A / cm ２ The voltage at this point was checked. A voltage of less than 1.90 V is preferable.

[0230] Example 1 First, a catalyst powder made of iridium oxide (product number "TEC77100", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst, a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and cellulose nanofiber (product name "BiNFi-s IMa 10002 Kyokucho", manufactured by Sugino Machine Co., Ltd.) as a polymer fibrous material were mixed in a solvent, and the mixture was dispersed in a planetary ball mill for 60 minutes to prepare a catalyst ink. The solvent 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. The catalyst ink was adjusted so that the solids content in the catalyst ink was 10% by mass. The amount of polymer fibrous material was 2.5 parts by mass per 100 parts by mass of the catalyst. The polymer fibrous material was confirmed to have an average fiber diameter of 10 nm and an average fiber length of 6 μm. The blending amount of the polymer electrolyte was set to 30 parts by mass per 100 parts by mass of the catalyst.

[0231] As the polymer electrolyte membrane, a Nafion (registered trademark) membrane (product name "N117", manufactured by DuPont) was prepared.

[0232] Next, using a slit die coater, the catalyst ink was applied to one main surface of the polymer electrolyte membrane so that the amount of iridium oxide carried per area of ​​the main surface was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the thickness of the electrode catalyst layer was 10 μm. The solvent component in the catalyst ink was removed by drying in an oven at 80° C., yielding a laminate of the electrode catalyst layer and the polymer electrolyte membrane.

[0233] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Example 1 was "small." Furthermore, in the laminate, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed. The shear strength of the electrode catalyst layer of the obtained laminate was measured by the above-mentioned method and was found to be 0.08 N / mm.

[0234] An electrode catalyst layer was laminated as a cathode on the back surface of the obtained laminate using the following procedure. Pt-supported carbon particles (product number "TEC10E50E", Tanaka Kikinzoku Kogyo Co., Ltd.) as a catalyst and a dispersion containing Nafion (registered trademark) as a polymer electrolyte (product name "Nafion (registered trademark) DE2020", Fujifilm Wako Pure Chemical Industries, Ltd.) were 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 cathode catalyst ink was applied to the surface of the laminate on the side without the electrode catalyst layer so that the amount of Pt supported per main surface area was 0.5 mg / cm. ２ The catalyst ink was applied by die coating so that the solvent component in the catalyst ink was removed by drying in an oven at 80°C, yielding a laminate of an electrode catalyst layer and a polymer electrolyte membrane. The electrolytic performance of the membrane electrode assembly thus obtained was evaluated by the method described above. ２ The electrolysis voltage at this point was 1.85V.

[0235] Example 2 The same procedure as in Example 1 was carried out except for the following points: The blending amount of the polymeric fibrous material was set to 5 parts by mass per 100 parts by mass of the catalyst.

[0236] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Example 2 was "small." Furthermore, in the laminate, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed. The shear rate strength of the electrode catalyst layer of the obtained laminate was measured by the above-mentioned method and was found to be 0.10 N / mm. 2.0 A / cm ２ The electrolysis voltage at this point was 1.87V.

[0237] (Example 3) The same as Example 1 was performed except for the following points. The blending amount of the fibrous material was set to 10% by mass relative to 100% by mass of the catalyst. When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Example 3 was "low." Furthermore, in the laminate, no peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed. The shear rate strength of the electrode catalyst layer of the obtained laminate was measured by the above-mentioned method and was found to be 0.10 N / mm. 2.0 A / cm ２ The electrolysis voltage at this point was 1.87V.

[0238] (Comparative Example 1) A catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained in the same manner as in Example 1, except that the polymer fibrous material was not included. When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Comparative Example 1 was "large." In addition, peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. When the shear strength of the electrode catalyst layer of the obtained laminate was measured, it was 0.04 N / mm. 2.0 A / cm ２ The electrolysis voltage at this point was 1.94V.

[0239] Comparative Example 2 A catalyst ink was obtained in the same manner as in Example 1, except that the blending amount of the polymer fibrous material was 15 parts by mass per 100 parts by mass of the catalyst. The viscosity was high, making it difficult to apply the ink to the electrolyte membrane as a film of uniform thickness, and an electrode catalyst layer was not obtained.

[0240] (Comparative Example 3) A catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained by the same method as in Example 2, except that the rotation speed during the dispersion treatment was lower and the dispersion treatment time was shorter, making the dispersion conditions weaker than in Example 2. When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Comparative Example 3 was "low." Furthermore, peeling of the electrode catalyst layer from the polymer electrolyte membrane was observed in the laminate. When the shear strength of the electrode catalyst layer of the obtained laminate was measured, it was 0.08 N / mm. 2.0 A / cm ２ The electrolysis voltage at this point was 1.91V.

[0241] Comparative Example 4 A catalyst ink and a laminate of an electrode catalyst layer and an electrolyte membrane were obtained in the same manner as in Example 1, except that polybenzimidazole polymer fibers (fiber diameter 200 nm, fiber length 15 μm) having no hydroxy groups and a fiber diameter of 200 nm were used as the polymer fibrous material.

[0242] When the obtained laminate was observed, the amount of cracks in the electrode catalyst layer of Comparative Example 4 was "large." In addition, partial peeling 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 and found to be 0.05 N / mm. ２ The electrolysis voltage at this point was 1.93V.

[0243] The Voronoi dispersion coefficients with the voids in the cross section of the electrode catalyst layer as the generating points, the Voronoi dispersion coefficients with the polymer fibrous material as the generating points, the proportion of voids in the cross section, the proportion of polymer fibrous material in the cross section, and the evaluation results for each of the examples and comparative examples are shown in Table 2.

[0244] 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 device or organic hydride electrolysis device

Claims

1. An electrode catalyst layer for water electrolysis or organic hydride electrolysis, comprising a catalyst, a polymer electrolyte having proton conductivity or anion conductivity, and a polymer fibrous material having functional groups capable of forming hydrogen bonds.

2. The electrode catalyst layer according to claim 1, wherein the polymer fibrous material contains a functional group capable of forming a hydrogen bond in the repeating unit.

3. The electrode catalyst layer according to claim 1 or 2, wherein the functional group capable of forming a hydrogen bond is a hydroxyl group and / or an N--H bond.

4. The electrode catalyst layer according to claim 1 or 2, wherein the polymeric fibrous material is a cellulose-based nanofiber.

5. The electrode catalyst layer according to claim 1 or 2, wherein the specific gravity of the catalyst is 5 or more.

6. The electrode catalyst layer according to claim 1 or 2, wherein the polymeric fibrous material has an average fiber diameter of 3 to 20 nm.

7. The electrode catalyst layer according to claim 1 or 2, wherein the content of the polymeric fibrous material is 1 to 12 parts by mass per 100 parts by mass of the catalyst.

8. 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.

9. An ink for forming an electrode catalyst layer for water electrolysis or organic hydride electrolysis, comprising a catalyst, a polymer electrolyte having proton conductivity or anion conductivity, and a polymer fibrous material having a functional group capable of forming a hydrogen bond.

10. The ink according to claim 9, wherein the polymeric fibrous material contains functional groups capable of forming hydrogen bonds in the repeating units.

11. The ink according to claim 9 or 10, wherein the functional group capable of forming a hydrogen bond is a hydroxyl group and / or an N--H bond.

12. The ink according to claim 9 or 10, wherein the specific gravity of the catalyst is 5 or more.

13. Shear rate 1s measured by a rheometer －１ The ink according to claim 9 or 10, having a viscosity of 500 to 5,000 mPa·s at 200° C.

14. Shear rate 1s －１ The viscosity is 30 to 12,000 mPa·s, and the shear rate is 1 s －１ viscosity) / (shear rate 1000 s －１ The ink according to claim 9 or 10, wherein the TI value, defined as the viscosity at room temperature (T1) of the ink is 2.0 to 100(-).

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

16. The membrane electrode assembly according to claim 15, wherein the electrode catalyst layer is the electrode catalyst layer according to claim 8.

17. A water electrolysis device comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on either side of the polymer electrolyte membrane; and a pair of current collectors arranged to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in claim 1 or 2.

18. An organic hydride electrolytic synthesis apparatus comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on either side of the polymer electrolyte membrane; and a pair of current collectors arranged to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in claim 1 or 2.

19. An electrode catalyst layer comprising a catalyst, a polymer electrolyte having proton conductivity or anion conductivity, and a polymer fibrous material, wherein the ratio of the area of ​​voids in a cross section of the electrode catalyst layer is 20% or more and 40% or less, and when the standard deviation of the area of ​​the Voronoi regions in a Voronoi diagram having the center of gravity of each void in the cross section of the electrode catalyst layer as a generating point is ASD and the arithmetic mean area of ​​the Voronoi regions is AAV, the dispersion of the area of ​​the Voronoi regions expressed by ASD / AAV is 0.50 or more and 0.90 or less.

20. An electrode catalyst layer as described in claim 19, wherein in a Voronoi diagram in a cross section of the electrode catalyst layer, the center of gravity of the polymer fibrous material is used as a generating point, and when the standard deviation of the area of ​​the Voronoi regions is BSD and the arithmetic mean area of ​​the Voronoi regions is BAV, the degree of dispersion of the area of ​​the Voronoi regions expressed by BSD / BAV is 1.5 or less.

21. The electrode catalyst layer according to claim 19 or 20, wherein the polymeric fibrous material accounts for 2% or more and 15% or less of an area in a cross section of the electrode catalyst layer.

22. The electrode catalyst layer according to claim 19 or 20, wherein the polymeric fibrous material has an average fiber diameter of 3 to 20 nm.

23. The electrode catalyst layer according to claim 19 or 20, wherein the content of the polymeric fibrous material is 10 parts by mass or less per 100 parts by mass of the catalyst.

24. The electrode catalyst layer according to claim 19 or 20, wherein the polymeric fibrous material has a hydrogen-bonding functional group.

25. The electrode catalyst layer according to claim 19 or 20, wherein the polymeric fibrous material has a hydrogen-bonding functional group in the repeating unit.

26. The electrode catalyst layer according to claim 19 or 20, wherein the polymeric fibrous material is a cellulose-based nanofiber.

27. The electrode catalyst layer according to claim 19 or 20, wherein the shear strength of the electrode catalyst layer is 0.08 N / mm or more.

28. The electrode catalyst layer according to claim 19 or 20, which is used for water electrolysis or organic hydride electrosynthesis.

29. A membrane electrode assembly for water electrolysis or organic hydride electrolysis, comprising an electrolyte membrane and an electrode catalyst layer according to claim 19 or 20 disposed on one or both sides of the electrolyte membrane.

30. A water electrolysis device comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on either side of the polymer electrolyte membrane; and a pair of current collectors arranged to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in claim 19 or 20.

31. An organic hydride electrolytic synthesis apparatus comprising: a membrane electrode assembly having a polymer electrolyte membrane and a pair of electrode catalyst layers arranged on either side of the polymer electrolyte membrane; and a pair of current collectors arranged to sandwich the membrane electrode assembly, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer described in claim 19 or 20.