Electrode catalyst layer and membrane electrode assembly

Abstract

To provide an electrode catalyst layer capable of reducing cracks during formation and further enabling high efficiency and high durability of water electrolysis.SOLUTION: An electrode catalyst layer for ion-exchange membrane water electrolysis comprises a catalyst, a conductive particulate matter, a polymer electrolyte, and a fibrous matter. In a cross section along a thickness direction of the electrode catalyst layer, when three regions obtained by dividing the thickness of the electrode catalyst layer into three equal parts are defined as a region 1, a region 2, and a region 3 in order from one surface side of the electrode catalyst layer, and porosities of the region 1, the region 2, and the region 3 are defined as V1, V2, and V3, respectively, V1<V2<V3 is satisfied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst layer constituting a membrane electrode assembly for ion-exchange membrane water electrolysis. [Background technology]

[0002] In recent years, the development of hydrogen-related technologies has accelerated in an effort to achieve decarbonization. To promote the social implementation of hydrogen, it is necessary to reduce the cost of hydrogen supply, and it is expected that hydrogen production using water electrolysis equipment will become more widespread. Water electrolysis equipment produces hydrogen by electrolyzing water using electricity (renewable energy).

[0003] There are two main types of water electrolysis equipment: alkaline water electrolysis and proton exchange membrane water electrolysis. In recent years, the spread of proton exchange membrane water electrolysis has accelerated due to its high efficiency and ability to be miniaturized, but its high cost remains an issue. Therefore, anion exchange membrane water electrolysis has attracted attention as a new method because it can produce hydrogen inexpensively. In particular, anion exchange membrane water electrolysis using hydrocarbon electrolyte membranes has been actively developed due to its potential for low cost.

[0004] Anion exchange membrane water electrolysis is equipped with a membrane electrode assembly in which an anion exchange membrane, which is an electrolyte membrane, is sandwiched between a pair of electrodes consisting of an anode-side electrode catalyst layer and a cathode-side electrode catalyst. When electric power is applied from the outside to the anode and cathode, hydrogen is generated by the following electrochemical reaction:

[0005] Cathode: 2H2O + 4e → 4OH - + H2 (1) Anode: 4OH - → 2H2O + O2+ 4e (2) At the cathode, water and electrons produce hydroxide ions and hydrogen (Reaction 1). The hydroxide ions pass through the electrolyte membrane and move to the anode. At the anode, the hydroxide ions produce water, oxygen, and electrons (Reaction 2). Water can also be supplied to the cathode from the anode through the electrolyte membrane (dry cathode type).

[0006] Currently, in order to reduce the cost of hydrogen production, there is a demand for improving the efficiency and durability of ion (proton or anion) exchange membrane water electrolysis.

[0007] To address the above-mentioned problems, Patent Document 1 proposes a method of forming an electrode catalyst layer by a coating method using a hydrocarbon electrolyte as the electrolyte membrane. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-83085 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 1 describes that an electrode catalyst layer free from cracks and peeling can be formed by adjusting the composition of the paste for forming an electrode catalyst layer. However, even when the paste for forming an electrode catalyst layer described in Patent Document 1 is used, cracks and peeling may occur in the electrode catalyst layer. Furthermore, although the content of the paste solvent is described, there is no description of the structure of the electrode catalyst layer, and its effects have not been specifically verified.

[0010] The invention was made in consideration of these circumstances, and aims to provide an electrode catalyst layer that can reduce cracking and peeling during formation and that enables high efficiency and durability of water electrolysis. [Means for solving the problem]

[0011] [1] An electrode catalyst layer for ion exchange membrane water electrolysis, The catalyst includes a catalyst, a conductive particulate material, a polymer electrolyte, and a fibrous material. In a cross-section along the thickness direction of the electrode catalyst layer, three regions obtained by equally dividing the thickness of the electrode catalyst layer are defined as Region 1, Region 2, and Region 3 in order from one surface side of the electrode catalyst layer. When the porosity of Region 1, Region 2, and Region 3 is V1, V2, and V3, respectively, an electrode catalyst layer satisfying V1 < V2 < V3.

[0012] [2] The electrode catalyst layer according to [1], wherein V2 / V1 is 1.01 or more.

[0013] [3] The electrode catalyst layer according to [1] or [2], wherein V3 / V1 is 1.05 or more.

[0014] [4] The electrode catalyst layer according to any one of [1] to [3], wherein at least a part of the conductive particulate material supports the catalyst.

[0015] [5] The electrode catalyst layer according to any one of [1] to [4], wherein the fibrous material exhibits at least one of electronic conductivity or ionic conductivity.

[0016] [6] An electrode catalyst layer comprising an anode-side electrode catalyst layer, an ion exchange membrane, and a cathode-side electrode catalyst layer in this order, wherein at least one of the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer is the electrode catalyst layer according to any one of [1] to [5], A membrane electrode assembly, wherein the surface of the electrode catalyst layer on the Region 1 side is arranged to face the ion exchange membrane. [Advantages of the Invention]

[0017] According to one aspect of the present invention, it is possible to reduce cracks and peeling during formation, and further provide an electrode catalyst layer capable of enhancing the efficiency and durability of water electrolysis. [Brief Description of the Drawings]

[0018] [Figure 1]FIG. 2 is an enlarged schematic view of the inside of a cathode-side electrode catalyst layer according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a cross section along the thickness of an electrode catalyst layer according to one embodiment of the present invention. [Figure 3] 1 is an exploded perspective view schematically illustrating a membrane electrode assembly having an electrode catalyst layer for a water electrolysis cell according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] It should be noted that the present invention is not limited to the embodiments described below, and modifications such as design changes may be made based on the knowledge of those skilled in the art, and such modified embodiments are also included in the scope of the present invention.

[0021] (electrode catalyst layer) As shown in FIG. 1, an electrode catalyst layer 12 for ion exchange membrane water electrolysis according to an embodiment of the present invention (hereinafter referred to as this embodiment) includes a catalyst 21, a conductive granular material 22, a polymer electrolyte 23, and a fibrous material 24.

[0022] <Catalyst> As the catalyst 21, platinum group elements, metals, alloys thereof, oxides, double oxides, etc. can be used. Platinum group elements include platinum, palladium, ruthenium, iridium, rhodium, and osmium. Examples of metals include iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Among these, platinum and platinum alloys are preferred for proton exchange membrane water electrolysis. Furthermore, platinum, nickel and their alloys, and iron and their alloys are preferred for anion exchange membrane water electrolysis. Furthermore, the particle size of these catalysts 21 is preferably 0.5 to 20 nm because if the particle size is too large, the activity of the catalyst 21 decreases, and if the particle size is too small, the stability of the catalyst 21 decreases. A particle size of 1 to 5 nm is even more preferred.

[0023] <Conductive particulate matter> The conductive granular material 22 is a particle having conductivity and an aspect ratio of less than 5. The aspect ratio of the conductive material is expressed by the ratio of the major axis to the minor axis in a transmission electron microscope image. Any material may be used as the conductive granular material as long as it is not affected by the catalyst 21. A specific example of the conductive granular material 22 is carbon particles. If the particle size of the conductive granular material 22 is too small, it becomes difficult to form an electron conduction path. If the particle size is too large, the electrode catalyst layer becomes thick, increasing resistance and resulting in reduced output characteristics. Therefore, a particle size of approximately 10 to 1,000 nm is preferable. A particle size of 10 to 100 nm is even more preferable. The particle size of the conductive granular material is expressed by the diameter of a circle equivalent to the area in a transmission electron microscope image. Furthermore, as shown in FIG. 1, by supporting the catalyst 21 on a conductive granular material 22 with a high surface area, the catalyst 21 can be supported at a high density, thereby improving catalytic activity.

[0024] It is not necessary to support the catalyst 21 on the conductive granular material 22. For example, the catalyst 21 may be supported on the fibrous material 24, or the catalyst 21 may be supported on both the conductive granular material 22 and the fibrous material 24. The voids formed in the fibrous material 24 can serve as a discharge path for hydrogen produced by water electrolysis. Here, when the catalyst 21 is supported on the fibrous material 24, a water electrolysis reaction also occurs in the hydrogen discharge path. On the other hand, supporting the catalyst 21 on the conductive granular material 22 makes it possible to distinguish between the reaction points at the three-phase interface between the conductive granular material 22, the catalyst 21, and the polymer electrolyte 23 and the hydrogen discharge path through the spaces formed by the fibrous material 24, which is preferable because it enables efficient water electrolysis in the electrode catalyst layer.

[0025] <Polymer electrolyte> The polymer electrolyte 23 may be any material that has ion conductivity, but considering the adhesion between the electrode catalyst layer 12 and the ion exchange membrane described below, it is preferable to select a material of the same quality as the ion exchange membrane. For example, fluororesin or hydrocarbon resin can be used for the polymer electrolyte 23. For example, fluororesin includes Nafion (manufactured by Chemours, registered trademark) and Flemion (manufactured by Asahi Glass Co., Ltd., registered trademark), and hydrocarbon resin includes fumasep (manufactured by Fumatech, registered trademark), engineering plastic, or copolymers thereof with ion exchange groups introduced. Among these, hydrocarbon resin is preferable because it is expected to reduce costs.

[0026] The amount of the polymer electrolyte may be in the range of 1 part by mass to 100 parts by mass, based on the conductive granular material 22 (100 parts by mass).

[0027] <Fibrous material> Any material may be used as the fibrous material 24 as long as it can maintain its fibrous shape without being affected by the catalyst 21 and the polymer electrolyte 23. In order to reduce the resistance of the electrode catalyst layer 12, the fibrous material 24 preferably exhibits electronic conductivity or ionic (anionic or cationic) conductivity. The term "fibrous" refers to a material having an aspect ratio, defined as fiber length / fiber diameter, of 10 or more.

[0028] As the fibrous material 24 exhibiting electron conductivity, carbon fibers such as carbon fibers, carbon nanofibers, and carbon nanotubes, or conductive polymers can be used.

[0029] An example of the ionic conductive fibrous material 24 is a fiber made by processing a polymer electrolyte into a fibrous form. A fluororesin or a hydrocarbon resin can be used as the polymer electrolyte, for example. For example, the fluororesin can be Nafion (manufactured by Chemours, registered trademark) or Flemion (manufactured by Asahi Glass Co., Ltd., registered trademark), and the hydrocarbon resin can be fumasep (manufactured by Fumatech, registered trademark), engineering plastic, or a copolymer thereof to which an ion exchange group has been introduced.

[0030] As the fiber diameter of the fibrous material 24, 0.5 to 500 nm is preferable, and 10 to 300 nm is more preferable. By setting it within the above range, the pores in the electrode catalyst layer can be increased, and higher output can be achieved.

[0031] The fiber length of the fibrous material 24 is preferably 1 to 200 μm, and more preferably 1 to 50 μm. By setting it within the above range, the strength of the electrode catalyst layer 12 can be increased, and the occurrence of cracks during formation can be suppressed. Also, the pores in the electrode catalyst layer 12 can be increased, and higher output can be achieved.

[0032] By including the fibrous material 24, cracks do not occur during the formation of the electrode catalyst layer, and it is possible to increase the pores in the anode side and the anode side electrode catalyst layer.

[0033] From the viewpoint of increasing the porosity of the electrode catalyst layer, the addition amount of the fibrous material is preferably 0.5 to 300 parts by mass with respect to 100 parts by mass of the conductive particulate material. It may be 1 part by mass or more, or 10 parts by mass or more. If the addition amount of the fibrous material becomes too large, the porosity increases and the dischargeability of the generated hydrogen improves, but the thickness of the electrode catalyst layer becomes thick and the performance tends to deteriorate. If the addition amount of the fibrous material becomes too small, the porosity becomes small and the generated hydrogen tends to stay in the electrode catalyst layer.

[0034] (Porosity of the cross-section of the electrode catalyst layer) FIG. 2 shows a schematic view of a cross-sectional plane along the thickness direction of the electrode catalyst layer 12. In the cross-section along the thickness direction of the electrode catalyst layer 12, three regions with a thickness of T / 3 obtained by dividing the thickness T of the electrode catalyst layer 12 into three equal parts are defined as region 1, region 2, and region 3 in order from one surface 12X side of the electrode catalyst layer to the other surface 12Y.

[0035] In the present embodiment, when the porosity of region 1, region 2, and region 3 is V1, V2, and V3, respectively, V1 < V2 < V3 is satisfied.

[0036] V2 / V1 may be 1.01 or more, 1.02 or more, or 1.03 or more.

[0037] V3 / V1 may be 1.05 or more, may be 1.07 or more, or may be 1.10 or more.

[0038] The range of V1 is preferably 3 to 30%.

[0039] The range of V3 is preferably 10 to 45%.

[0040] The porosity in the cross section of the electrode catalyst layer can be measured based on an image of the cross section of the electrode catalyst layer observed with a scanning electron microscope (SEM). Well-known techniques such as ion milling and ultramicrotome can be used to expose the cross section of the electrode catalyst layer. It is preferable to cool the electrode catalyst layer when exposing the cross section. This can reduce damage to the polymer electrolyte contained in the electrode catalyst layer.

[0041] The void area can be extracted by image processing from SEM images taken at magnifications of approximately 5,000 to 20,000. The void ratio is the ratio of the void area to the area of ​​the electrode catalyst layer in a cross-sectional scanning electron microscope image.

[0042] The conditions for acquiring electron microscope images are an acceleration voltage that does not change the electrode catalyst layer structure, and an acceleration voltage of 1 kV to 3 kV is preferred. The brightness and contrast of the acquired images are adjusted so that the image brightness histogram falls within a range of 0 to 255. The resolution of the acquired images is preferably 0.02 μm / px or higher. Considering the variability of the measurement results, it is preferable to acquire images from at least five or more locations, and preferably ten or more locations, in each region and calculate the average porosity.

[0043] (Method of manufacturing electrode catalyst layer) Next, an example of a method for producing the electrode catalyst layer will be described.

[0044] As shown in FIG. 2, the electrode catalyst layer can be manufactured by preparing a slurry for the electrode catalyst layer, applying the prepared slurry for the electrode catalyst layer to the surface of the ion exchange membrane 11, and drying it.

[0045] The slurry for the electrode catalyst layer contains a catalyst, a conductive particulate material, a polymer electrolyte, a fibrous material, and a solvent.

[0046] The solvent is not particularly limited, but is preferably one that can disperse or dissolve the polymer electrolyte. Commonly used solvents include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol, ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, and diisobutyl ketone, tetrahydrofuran, tetrahydropyran, dioxane, and diethylene glycol dimethyl ether. Other examples of solvents that may be used include ethers such as ether, anisole, methoxytoluene, diethyl ether, dipropyl ether, and dibutyl ether, amines such as isopropylamine, butylamine, isobutylamine, cyclohexylamine, diethylamine, and aniline, esters such as propyl formate, isobutyl formate, amyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, and butyl propionate, as well as acetic acid, propionic acid, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Examples of glycol and glycol ether solvents include ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diacetone alcohol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol.

[0047] Among these, from the viewpoint of satisfying V1 < V2 < V3, it is preferable to use a mixture of water and ethanol.

[0048] Examples of the method for coating the slurry for the electrode catalyst layer on the ion exchange membrane 11 include, but are not particularly limited to, the doctor blade method, die coating method, dipping method, screen printing method, laminator roll coating method, spraying method, and the like.

[0049] Examples of the drying method for the slurry for the electrode catalyst layer include hot air drying, IR drying, and the like. Here, when the ink for forming the electrode catalyst layer is applied to the ion exchange membrane and dried at a low temperature, the solvent in the coating film moves to the ion exchange membrane, and accordingly, the ionomer also moves. Therefore, in terms of porosity, the voids become larger in order from the region 1 on the ion exchange membrane 11 side to the region 3 on the opposite side, that is, it is easy to satisfy V1 < V2 < V3. Specifically, the drying temperature may be, for example, about 70°C.

[0050] On the other hand, when the ink for forming the electrode catalyst layer is applied to the ion exchange membrane 11 and dried at a high temperature (for example, 90°C), the ionomer concentration on the surface of the coating film tends to be high, and it is difficult to achieve V1 < V2 < V3.

[0051] The drying time is 0.5 minutes to 1 hour, preferably about 1 minute to 30 minutes.

[0052] In addition, from the viewpoint of setting V1 < V2 < V3, in addition to the drying temperature, conditions such as the amount of polymer electrolyte, the amount of fibrous substance added, fiber length, temperature gradient, and pressing pressure in the film thickness direction after drying may be appropriately adjusted. Also, the porosity can be adjusted by overcoating electrode catalyst layer slurries with different compositions.

[0053] (Membrane Electrode Assembly) As shown in FIG. 3, the membrane electrode assembly 10 for water electrolysis of the present embodiment has a three-layer structure. This membrane electrode assembly 10 includes an anode-side electrode catalyst layer 12A, an ion exchange membrane 11, and a cathode-side electrode catalyst layer 12C in this order. At least one or both of the anode-side electrode catalyst layer 12A and the cathode-side electrode catalyst layer 12C is the above-mentioned electrode catalyst layer 12. If at least the cathode-side electrode catalyst layer 12C is the above-mentioned electrode catalyst layer 12, it is highly effective.

[0054] Here, as shown in FIG. 2, the electrode catalyst layer 12 is arranged so that the surface 12X on the side of the region 1 with the smallest porosity faces the ion exchange membrane 11, and the surface 12Y on the side of the region 3 with the largest porosity faces the opposite side from the ion exchange membrane 11.

[0055] (Method for manufacturing membrane electrode assembly) An example of a method for producing a membrane electrode assembly will be described.

[0056] In particular, by applying the above-described method for manufacturing the electrode catalyst layer 12, the electrode catalyst layer 12 having the above-described porosity distribution can be formed with the surface 12X on the region 1 side facing the ion exchange membrane 11.

[0057] Alternatively, the electrode catalyst layer 12 may be formed on a transfer substrate, peeled off from the transfer substrate, and transferred to the ion exchange membrane 11 by thermocompression bonding or the like to form the electrode catalyst layer.

[0058] (Mechanism of action) The electrode catalyst layer 12 according to this embodiment can reduce cracks and peeling during the formation of the electrode catalyst layer, and further enables high efficiency and durability of water electrolysis.

[0059] The reason for this is not clear, but it is thought that one of the reasons is that the addition of a fibrous material reduces cracking and peeling during formation, and that in the membrane electrode assembly, the porosity of the electrode catalyst layer can be increased with increasing distance from the ion exchange membrane in the thickness direction, thereby improving the discharge of hydrogen gas and oxygen gas from the ion exchange membrane side to the opposite side of the ion exchange membrane.

[0060] Therefore, the electrode catalyst layer of this embodiment is extremely suitable for application to, for example, ion-exchange membrane water electrolysis. [Example]

[0061] Next, an embodiment based on the present invention will be described.

[0062] [Calculation of void ratio] The cross section of the electrode catalyst layer was extracted using a cryo-CP (cross-section polisher). SEM images were taken using a scanning electron microscope SU8010 (Hitachi High-Technologies Corporation) at 1,500x magnification and 2 microns / 403 pixels, with brightness and contrast adjusted so that the image brightness histogram was within the range of 0 to 255. SEM images were taken at least five times at each of three locations divided into three sections in the thickness direction of the electrode catalyst layer, and these were used to calculate the porosity.

[0063] To extract voids, we used the Trainable Weka Segmentation function in ImageJ Fiji, a free software widely used for processing and analyzing electron microscope images. Voids in the cross section of the electrode catalyst layer are defined as areas where no catalytic material, conductive granular material, ionomer, or fibrous material is present, and voids were determined and extracted on the outermost surface of the cross section. Specifically, we labeled at least 15 areas each for conductive granular material and catalytic material, ionomer, fibrous material, and void regions, and then performed segmentation.

[0064] [Electrolytic performance test] The membrane electrode assembly was sandwiched between gas diffusion layers and incorporated into a water electrolysis cell for evaluation. Current densities were 0-3 A / cm. 2 Water electrolysis was carried out at an electrolysis temperature of 60°C, and the cell voltage was measured. Performance was evaluated at a current density when the cell voltage was 1.7V. Proton exchange membrane water electrolysis Anode: Pure water Cathode: Pure water Anion exchange membrane water electrolysis Anode: Pure water Cathode: 1 wt% KOH aqueous solution

[0065] The electrolysis performances of Comparative Examples 1 and 2 are relative values ​​with Example 1 being 100, the electrolysis performance of Comparative Example 3 is relative values ​​with Example 2 being 100, the electrolysis performances of Comparative Examples 4 and 5 are relative values ​​with Example 3 being 100, and the electrolysis performance of Comparative Example 6 is relative values ​​with Example 4 being 100.

[0066] [Electrolytic durability test (peeling)] Current density 1A / cm 2 After performing water electrolysis for 200 hours at 400°C, the membrane electrode assembly was removed from the water electrolysis cell and checked for peeling of the electrode catalyst layer by visual inspection and cross-sectional observation using an SEM.

[0067] Example 1 [Production of cathode-side catalyst ink] The catalyst, polymer electrolyte, and fibrous material shown below were mixed in a solvent and dispersed for 30 minutes using a planetary ball mill to prepare a catalyst ink. The solvent used for the catalyst ink was a mixed solvent of ultrapure water and ethanol. The volume ratio of ultrapure water to ethanol was 0.3:0.7. The catalyst ink was adjusted so that the solid content in the catalyst ink was 12% by mass.

[0068] Catalyst: Platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) Polymer electrolyte: Fluorine-based polymer electrolyte (Nafion® dispersion) Fibrous material: Carbon nanofiber (manufactured by Showa Denko, product name "VGCF", fiber diameter approximately 150 nm, fiber length approximately 10 μm) · Blending ratio: For the catalyst ink, the carbon mass of the platinum-supported carbon was 1, the mass of the polymer electrolyte (solid content) was 0.4, and the mass of the fibrous material was 0.25.

[0069] [Production of anode-side catalyst ink] The catalyst and electrolyte shown below were mixed in a solvent and dispersed for 30 minutes using a planetary ball mill to prepare a catalyst ink. The solvent used for the catalyst ink was a mixed solvent of ultrapure water and 1-propanol. The volume ratio of ultrapure water to 1-propanol was 0.3:0.7. The catalyst ink was adjusted so that the solid content in the catalyst ink was 20% by mass.

[0070] Catalyst: Iridium oxide Polymer electrolyte: Fluorine-based polymer electrolyte (Nafion® dispersion) Mixing ratio: The catalyst ink has a catalyst particle mass of 1 and an electrolyte (solid content) mass of 0.3.

[0071] [Fabrication of Membrane Electrode Assembly] The cathode catalyst ink was applied to one side of a proton exchange membrane (fluorine-based polymer electrolyte membrane) using an applicator and dried in an oven at 70°C to form a cathode electrode catalyst layer. The coating amount was 1.0 mg / cm. 2 The amount was set to be:

[0072] Next, the anode catalyst ink was applied to the surface opposite to the surface on which the cathode catalyst layer was formed, and the applied ink was dried in an oven to form an anode catalyst layer, thereby obtaining a membrane electrode assembly. The amount of the anode catalyst ink applied was 1.0 mg / cm. 2 The electrode catalyst layer of the obtained membrane electrode assembly was divided into three parts in the thickness direction, and the porosity of each part (V1, V2, and V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the cathode side electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode side electrode catalyst layer.

[0073] <Comparative Example 1> A membrane electrode assembly of Comparative Example 1 was obtained using the same procedure as in Example 1, except that a mixture of ultrapure water and 1-propanol in a volume ratio of 0.5:0.5 was used as the solvent for the cathode-side catalyst ink, and the drying temperature in the oven after coating was set to 90°C. The electrode catalyst layer of the obtained membrane electrode assembly was divided into three sections in the thickness direction, and the porosity of each section (V1, V2, V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer.

[0074] <Comparative Example 2> A membrane electrode assembly of Comparative Example 2 was obtained in the same manner as in Example 1, except that no fibrous material was used in the cathode catalyst ink. Numerous cracks occurred in the cathode catalyst layer of the obtained membrane electrode assembly. Furthermore, significant peeling of the cathode catalyst layer from the ion exchange membrane was observed after water electrolysis evaluation.

[0075] <Example 2> A membrane electrode assembly of Example 2 was obtained using the same procedure as in Example 1, except that resin fibers (fiber diameter: approximately 200 nm, fiber length: approximately 20 μm) having an azole structure were used as the fibrous material in the cathode-side catalyst ink, and the mass of the fibrous material was set to 0.05 relative to the carbon mass of the platinum-supported carbon. The electrode catalyst layer of the obtained membrane electrode assembly was divided into three sections in the thickness direction, and the porosity of each section (V1, V2, V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer.

[0076] <Comparative Example 3> A membrane electrode assembly of Comparative Example 3 was obtained using the same procedure as in Example 2, except that a mixture of ultrapure water and 1-propanol in a volume ratio of 0.5:0.5 was used as the solvent for the cathode-side catalyst ink, and the drying temperature in the oven after coating was 90°C. The electrode catalyst layer of the obtained membrane electrode assembly was divided into three sections in the thickness direction, and the porosity of each section (V1, V2, and V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer.

[0077] Example 3 [Production of cathode-side catalyst ink] The catalyst, polymer electrolyte, and fibrous material shown below were mixed in a solvent and dispersed for 30 minutes using a planetary ball mill to prepare a catalyst ink. The solvent used for the catalyst ink was a mixed solvent of ultrapure water and ethanol. The volume ratio of ultrapure water to ethanol was 0.3:0.7. The catalyst ink was adjusted so that the solid content in the catalyst ink was 12% by mass.

[0078] Catalyst: Platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) Polymer electrolyte: hydrocarbon-based anion exchange electrolyte Fibrous material: Carbon nanofiber (manufactured by Showa Denko, product name "VGCF", fiber diameter approximately 150 nm, fiber length approximately 10 μm) Mixing ratio: For the catalyst ink, the mass of the platinum-supported carbon was 1, the mass of the electrolyte (solid content) was 0.4, and the mass of the fibrous material was 0.25.

[0079] [Production of anode-side catalyst ink] The catalyst and electrolyte shown below were mixed in a solvent and dispersed for 30 minutes using a planetary ball mill to prepare a catalyst ink. The solvent used for the catalyst ink was a mixed solvent of ultrapure water and 1-propanol. The volume ratio of ultrapure water to 1-propanol was 0.3:0.7. The catalyst ink was adjusted so that the solid content in the catalyst ink was 20% by mass.

[0080] Catalyst: Iridium oxide Polymer electrolyte: hydrocarbon-based anion exchange electrolyte Blending ratio: The catalyst ink had a catalyst particle mass of 1 and a polymer electrolyte (solid content) mass of 0.3.

[0081] [Fabrication of Membrane Electrode Assembly] The cathode catalyst ink was applied to one side of an anion exchange electrolyte membrane (hydrocarbon-based polymer electrolyte membrane) using an applicator and dried in an oven at 70°C to form a cathode electrode catalyst layer. The coating amount was 1.0 mg / cm. 2 Next, the anode-side catalyst ink was applied to the surface opposite to the surface on which the cathode-side electrode catalyst layer was formed, and the applied ink was dried in an oven to form an anode-side electrode catalyst layer, thereby obtaining a membrane electrode assembly. The amount of the anode-side catalyst ink applied was 1.0 mg / cm of catalyst. 2 The electrode catalyst layer of the obtained membrane electrode assembly was divided into three parts in the thickness direction, and the porosity of each part (V1, V2, and V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode side electrode catalyst layer.

[0082] <Comparative Example 4> A membrane electrode assembly of Comparative Example 4 was obtained using the same procedure as in Example 3, except that a mixed solution of ultrapure water and 1-propanol in a volume ratio of 0.5:0.5 was used as the solvent for the cathode-side catalyst ink, and the drying temperature in the oven after coating was 90°C. The electrode catalyst layer of the obtained membrane electrode assembly was divided into three sections in the thickness direction, and the porosity of each section (V1, V2, V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer.

[0083] <Comparative Example 5> A membrane electrode assembly of Comparative Example 5 was obtained in the same manner as in Example 3, except that no fibrous material was used in the cathode-side catalyst ink. Numerous cracks occurred in the cathode-side electrode catalyst layer of the obtained membrane electrode assembly. Furthermore, significant peeling from the ion exchange membrane was observed after water electrolysis evaluation.

[0084] Example 4 A membrane electrode assembly of Example 4 was obtained using the same procedure as in Example 3, except that resin fibers (fiber diameter: approximately 200 nm, fiber length: approximately 20 μm) having an azole structure were used as the fibrous material in the cathode-side catalyst ink, and the mass of the fibrous material was set to 0.05 relative to the carbon mass of the platinum-supported carbon. The electrode catalyst layer of the obtained membrane electrode assembly was divided into three sections in the thickness direction, and the porosity of each section (V1, V2, V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer.

[0085] <Comparative Example 6> A membrane electrode assembly of Comparative Example 6 was obtained using the same procedure as in Example 4, except that a mixture of ultrapure water and 1-propanol in a volume ratio of 0.5:0.5 was used as the solvent for the cathode-side catalyst ink, and the drying temperature in the oven after coating was 90°C. The electrode catalyst layer of the obtained membrane electrode assembly was divided into three sections in the thickness direction, and the porosity of each section (V1, V2, and V3 from the ion exchange membrane side) was measured. Furthermore, no cracks or peeling from the ion exchange membrane were observed in the electrode catalyst layer of the obtained membrane electrode assembly. Even after water electrolysis evaluation, no cracks or peeling from the ion exchange membrane were observed in the cathode-side electrode catalyst layer.

[0086] V1, V2, V3 and the results obtained in each example and comparative example are shown in Table 1. In the examples, there was no peeling or cracking during formation, the water electrolysis performance was high, and no peeling from the electrolyte membrane was observed even after the electrolysis performance evaluation.

[0087] [Table 1] [Explanation of symbols]

[0088] 11... ion exchange membrane, 10... membrane electrode assembly, 12C... cathode side electrode catalyst layer, 12A... anode side electrode catalyst layer, 12... electrode catalyst layer.

Claims

1. An electrode catalyst layer for ion exchange membrane water electrolysis, comprising: The catalyst includes a catalyst, a conductive particulate material, a polymer electrolyte, and a fibrous material. In a cross section of the electrode catalyst layer taken along the thickness direction, three regions obtained by dividing the thickness of the electrode catalyst layer into three equal parts are designated as region 1, region 2, and region 3, in this order from one surface side of the electrode catalyst layer, When the porosities of the regions 1, 2, and 3 are V1, V2, and V3, respectively, An electrode catalyst layer that satisfies V1<V2<V3.

2. The electrode catalyst layer according to claim 1 , wherein V2 / V1 is 1.01 or more.

3. 3. The electrode catalyst layer according to claim 1, wherein V3 / V1 is 1.05 or more.

4. The electrode catalyst layer according to claim 1 or 2, wherein the conductive particulate material supports at least a portion of the catalyst.

5. 3. The electrode catalyst layer according to claim 1, wherein the fibrous material exhibits at least one of electronic conductivity and ionic conductivity.

6. An electrode catalyst layer including, in this order, an anode-side electrode catalyst layer, an ion exchange membrane, and a cathode-side electrode catalyst layer, at least one of the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer is the electrode catalyst layer according to claim 1 or 2; a membrane electrode assembly, wherein the surface of the electrode catalyst layer on the region 1 side is disposed so as to face the ion exchange membrane;

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