Method for producing membrane-catalyst-layer assembly, membrane-catalyst-layer assembly, and water electrolysis apparatus

Abstract

To provide a technique capable of improving air permeability of a catalyst layer.SOLUTION: First, a catalytic ink is prepared by mixing catalytic particles, solvents and ionomers (S1). Next, the catalytic ink is applied to the surfaces of the electrolytic membrane (S2). Thereafter, the catalytic ink applied to the electrolytic membrane is dried (S3). Thus, a catalyst layer is formed on the surface of the electrolyte membrane. The diameters of the catalytic particles are not less than 50nm and not more than 300nm. The dried catalyst layer has aggregated portions in which a plurality of catalyst particles are aggregated, and void portions formed between the aggregated portions. This void portion can improve the gas permeability of the catalyst layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a membrane-catalyst layer assembly, a membrane-catalyst layer assembly, and a water electrolysis device. [Background technology]

[0002] Conventionally, a PEM (Proton Exchange Membrane) type water electrolysis device is known that produces hydrogen (H) by electrolyzing water (H2O). This type of water electrolysis device has a cell stack in which cells and separators are alternately stacked. Each cell has an electrolyte membrane and catalyst layers formed on both sides of the electrolyte membrane.

[0003] When the water electrolysis device is in use, a voltage is applied between the anode catalyst layer and the cathode catalyst layer, and water is supplied to the anode catalyst layer. This causes the following electrochemical reaction to occur between the anode catalyst layer and the cathode catalyst layer. As a result, hydrogen is discharged from the cathode catalyst layer. (Anode side) 2H2O → 4H + + O2+ 4e - (Cathode side) 2H + + 2e - → H2

[0004] A conventional water electrolysis device is described in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-023996 Summary of the Invention [Problem to be solved by the invention]

[0006] When the water electrolysis device is in use, as described above, water is converted into hydrogen ions (H + ), oxygen (O2), and electrons (e - ) is electrolyzed into the following: For this reason, it is necessary to supply liquid water to the catalyst layer on the anode side and discharge gaseous oxygen. However, if the catalyst layer has low gas permeability, oxygen will remain in the catalyst layer, and the remaining oxygen will hinder the supply of water. As a result, there is a problem that the efficiency of electrolysis on the anode side decreases.

[0007] Therefore, an object of the present invention is to provide a technique capable of improving the gas permeability of a catalyst layer. [Means for solving the problem]

[0008] The first invention is a method for manufacturing a membrane-catalyst layer assembly, comprising: a preparation step of preparing a catalyst ink by mixing catalyst particles, a solvent, and an ionomer; an application step of applying the catalyst ink to the surface of an electrolyte membrane; and a drying step of drying the catalyst ink applied to the electrolyte membrane, wherein the catalyst particles have a diameter of 50 nm or more and 300 nm or less, and the catalyst layer formed by the drying step has agglomeration portions where a plurality of the catalyst particles agglomerate, and void portions formed between the agglomeration portions.

[0009] A second invention is the production method of the first invention, wherein the diameter of the catalyst particles is 80 nm or more and 150 nm or less.

[0010] A third invention is the manufacturing method of the first or second invention, wherein the maximum width of the voids is 10 nm or more.

[0011] A fourth invention is the manufacturing method of any one of the first to third inventions, wherein the catalyst particles have template particles and catalyst powder supported on the template particles.

[0012] A fifth invention is the manufacturing method of the fourth invention, wherein the template particles are silica particles.

[0013] A sixth invention is the manufacturing method of the first or second invention, wherein a flocculant is further mixed in the preparation step.

[0014] A seventh aspect of the present invention is the manufacturing method of any one of the first to sixth aspects of the present invention, wherein the drying step involves drying the catalyst ink by heating.

[0015] An eighth aspect of the present invention is a membrane-catalyst layer assembly comprising an electrolyte membrane and a catalyst layer formed on a surface of the electrolyte membrane, wherein the catalyst layer contains a plurality of catalyst particles, each having a diameter of 50 nm or more and 300 nm or less, and the catalyst layer has aggregation portions where the plurality of catalyst particles are aggregated, and void portions formed between the aggregation portions.

[0016] A ninth aspect of the present invention is a water electrolysis apparatus, which comprises the membrane-catalyst layer assembly of the eighth aspect of the present invention. [Effects of the Invention]

[0017] According to the first to seventh inventions, by setting the diameter of the catalyst particles to 50 nm or more and 300 nm or less, a plurality of catalyst particles aggregate in the drying process. As a result, voids are formed in the catalyst layer. This improves the breathability of the catalyst layer.

[0018] In particular, according to the second aspect of the present invention, a plurality of catalyst particles can be more effectively aggregated in the drying step.

[0019] In particular, according to the third aspect of the present invention, the gas permeability of the catalyst layer can be further improved.

[0020] In particular, according to the fourth aspect of the present invention, the diameters of the catalyst particles can be made uniform with high precision by using template particles.

[0021] In particular, according to the sixth aspect of the present invention, by mixing an aggregating agent into the catalyst ink, it is possible to more effectively aggregate the catalyst particles in the drying step.

[0022] In particular, according to the seventh aspect of the present invention, the drying time of the catalyst ink can be shortened, which allows for more efficient formation of voids in the catalyst layer.

[0023] According to the eighth and ninth inventions, by setting the diameter of the catalyst particles to 50 nm or more and 300 nm or less, agglomeration portions and void portions are formed in the catalyst layer, thereby improving the breathability of the catalyst layer. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram of a water electrolysis device. [Figure 2] FIG. 1 is a schematic diagram of one cell and a pair of separators located on either side of the cell. [Figure 3] 1 is a flowchart showing a manufacturing procedure for an anode catalyst layer. [Figure 4] FIG. 2 is a schematic cross-sectional view of a catalyst particle. [Figure 5] FIG. 1 is a diagram showing an example of a manufacturing apparatus that performs a coating step and a drying step. [Figure 6] 1 is an image of a part of an anode catalyst layer taken with a scanning electron microscope. [Figure 7] 1 is an image of a part of an anode catalyst layer taken with a scanning electron microscope. [Figure 8] 1 is an image of a part of an anode catalyst layer taken with a scanning electron microscope. [Figure 9] 1 is a graph showing the current-voltage characteristics of a cell. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0026] <1. Water electrolysis device according to one embodiment> Fig. 1 is a schematic diagram of a PEM water electrolysis system 1 according to one embodiment of the present invention. This water electrolysis system 1 is a system for producing hydrogen by water electrolysis. As shown in Fig. 1, the water electrolysis system 1 includes a cell stack 30 composed of a plurality of cells 10 and a plurality of separators 20, and a power supply device 40 that applies a voltage to the cell stack 30. The cells 10 and the separators 20 are alternately stacked to form the cell stack 30.

[0027] 2 is a schematic diagram illustrating only one cell 10 and a pair of separators 20 located on either side of the cell 10 in the cell stack 30 of the water electrolysis device 1. As shown in FIG. 2, one cell 10 has an electrolyte membrane 51, an anode catalyst layer 61, a porous transport layer 62, a cathode catalyst layer 71, and a gas diffusion layer 72.

[0028] A laminate composed of the electrolyte membrane 51, the anode catalyst layer 61, and the cathode catalyst layer 71 is called a catalyst-coated membrane (CCM). A laminate composed of the electrolyte membrane 51, the anode catalyst layer 61, the porous transport layer 62, the cathode catalyst layer 71, and the gas diffusion layer 72 is called a membrane-electrode-assembly (MEA).

[0029] The electrolyte membrane 51 is a thin membrane (ion exchange membrane) having ion conductivity. The electrolyte membrane 51 of this embodiment is a membrane that exchanges hydrogen ions (H + ) is a proton exchange membrane that conducts a current. A fluorine-based or hydrocarbon-based polymer electrolyte membrane is used as the electrolyte membrane 51. Specifically, for example, a solid polymer electrolyte membrane containing perfluorocarbon sulfonic acid is used as the electrolyte membrane 51. The thickness of the electrolyte membrane 51 is, for example, 5 μm to 200 μm.

[0030] The anode catalyst layer 61 is a catalyst layer that causes water electrolysis on the anode side of the electrolyte membrane 51. The anode catalyst layer 61 is formed on the anode side surface of the electrolyte membrane 51. The anode catalyst layer 61 contains a large number of catalyst particles and an ionomer.

[0031] The catalyst particles are particles that have catalytic activity for causing the electrolysis of water. The catalyst particles include, for example, iridium (Ir), ruthenium (Ru), iridium oxide (IrOx), platinum (Pt), or an alloy of iridium (Ir) and ruthenium (Ru). As described below, the catalyst particles of this embodiment are formed by supporting catalyst powder on the surface of template particles.

[0032] The ionomer is an electrolyte polymer that covers the catalyst particles. The ionomer plays a role in transporting hydrogen ions generated by the electrolysis of water within the anode catalyst layer 61. For example, Nafion (perfluorocarbon sulfonic acid) is used as the ionomer. The ionomer has a polymer chain structure with ion exchange groups such as sulfonic groups. The hydrogen ions combine with water within the anode catalyst layer 61 to form oxonium ions (HO + ) Then, the oxonium ion propagates through the ion exchange groups of the ionomer.

[0033] When the water electrolysis device 1 is in use, water (H2O) is supplied to the anode catalyst layer 61. Then, a voltage is applied between the anode catalyst layer 61 and the cathode catalyst layer 71 by the power supply device 40. Then, due to the action of the voltage and the catalyst particles, the water is converted into hydrogen ions (H + ), oxygen (O2), and electrons (e - That is, in the anode catalyst layer 61, the following electrochemical reaction occurs: 2H2O → 4H + + O2+ 4e - (1)

[0034] The porous transport layer (PTL) 62 is a layer that uniformly supplies water from the separator 20 to the anode catalyst layer 61 and transports oxygen and electrons generated in the anode catalyst layer 61 to the separator 20. The porous transport layer 62 is laminated on the outer side of the anode catalyst layer 61 (the side opposite the electrolyte membrane 51). The porous transport layer 62 is made of a conductive and porous material. For example, a porous substrate made of metallic titanium or a titanium alloy is used for the porous transport layer 62.

[0035] The cathode catalyst layer 71 is a catalyst layer that causes a hydrogen reduction reaction on the cathode side of the electrolyte membrane 51. The cathode catalyst layer 71 is formed on the cathode side surface of the electrolyte membrane 51 (the surface opposite to the surface on which the anode catalyst layer 61 is formed). The cathode catalyst layer 71 contains a large number of catalyst particles. The catalyst particles are, for example, platinum (Pt) catalyst powder supported on the surface of carbon particles that serve as template particles. However, the catalyst particles may also contain trace amounts of ruthenium (Ru) or cobalt (Co).

[0036] When the water electrolysis device 1 is in use, hydrogen ions (H + ) and electrons (e - ) is supplied. Then, a voltage is applied between the anode catalyst layer 61 and the cathode catalyst layer 71 by the power supply device 40. This voltage and the action of the catalyst particles cause a reduction reaction in the cathode catalyst layer 71, producing hydrogen gas (H2) from the hydrogen ions and electrons. That is, the following electrochemical reaction occurs in the cathode catalyst layer 71: 2H + + 2e - → H2(2)

[0037] The gas diffusion layer (GDL) 72 is a layer that transfers electrons from the separator 20 to the cathode catalyst layer 71 and transfers hydrogen generated in the cathode catalyst layer 71 to the separator 20. The gas diffusion layer 72 is laminated on the outer side of the cathode catalyst layer 71 (the side opposite to the electrolyte membrane 51). The gas diffusion layer 72 is made of a conductive and porous material. For example, a porous substrate made of carbon (carbon paper) is used for the gas diffusion layer 72.

[0038] The separator 20 is a layer that transfers electrons between adjacent cells 10 and also forms paths for water, oxygen, and hydrogen. The separator 20 is interposed between the porous transport layer 62 and the gas diffusion layer 72 of adjacent cells 10. The separator 20 is made of a material that is electrically conductive and impermeable to gases and liquids. For example, a metal plate is used as the separator 20.

[0039] Separator 20 has an anode surface 21 in contact with porous transport layer 62 and a cathode surface 22 in contact with gas diffusion layer 72. A plurality of anode grooves 23 are formed on anode surface 21. Water is supplied from outside cell stack 30 to porous transport layer 62 through anode grooves 23 of separator 20. Oxygen generated in anode catalyst layer 61 passes through porous transport layer 62 and anode grooves 23 of separator 20, and is discharged to outside cell stack 30.

[0040] In addition, a plurality of cathode grooves 24 are formed on the cathode surface 22 of the separator 20. Hydrogen generated in the cathode catalyst layer 71 passes through the gas diffusion layer 72 and the cathode grooves 24 of the separator 20, and is discharged to the outside of the cell stack 30.

[0041] The power supply 40 is a device that applies a voltage to the above-mentioned cell stack 30. As shown in Fig. 1, the positive terminal of the power supply 40 is electrically connected to the separator 20 located at the end of the cell stack 30 closest to the anode. The negative terminal of the power supply 40 is electrically connected to the separator 20 located at the end of the cell stack 30 closest to the cathode. The power supply 40 applies a voltage required for water electrolysis to the cell stack 30.

[0042] When the water electrolysis device 1 is in use, water is supplied from the anode grooves 23 of the separator 20 through the porous transport layer 62 to the anode catalyst layer 61. Then, due to the voltage from the power supply 40 and the action of the catalyst particles in the anode catalyst layer 61, the water is decomposed into hydrogen ions, oxygen, and electrons. The hydrogen ions propagate through the electrolyte membrane 51 to the cathode catalyst layer 71. The oxygen passes through the porous transport layer 62 and the anode grooves 23 and is discharged to the outside of the cell stack 30. The electrons flow through the porous transport layer 62 and the separator 20 to the adjacent cell 10.

[0043] In the adjacent cell 10, the electrons pass through the gas diffusion layer 72 and reach the cathode catalyst layer 71. Then, in the cathode catalyst layer 71, the hydrogen ions and electrons combine to generate hydrogen. The generated hydrogen passes through the gas diffusion layer 72 and the cathode groove 24 and is discharged to the outside of the cell stack 30. In this way, hydrogen is produced.

[0044] 2. Method for manufacturing membrane-catalyst layer assembly The above-described anode catalyst layer 61 is an example of the "catalyst layer" of the present invention. The anode catalyst layer 61 is formed by applying a catalyst ink to the surface of the electrolyte membrane 51 and drying it. A method for manufacturing a membrane-catalyst layer assembly including the anode catalyst layer 61 will be described below.

[0045] Fig. 3 is a flowchart showing the procedure for manufacturing the anode catalyst layer 61. As shown in Fig. 3, when manufacturing the anode catalyst layer 61, first, a catalyst ink for the anode catalyst layer 61 is prepared (step S1: preparation step).

[0046] In the preparation process of step S1, multiple catalyst particles and an ionomer are added to a solvent and mixed by stirring. The solvent is water, alcohol, or both. The alcohol is, for example, methanol, ethanol, 1-propanol, or 2-propanol. The amount of solvent is, for example, such that the solids concentration in the catalyst ink is 1% or more and 20% or less. The weight ratio of the ionomer to the catalyst particles is, for example, 1 wt% or more and 50 wt% or less, preferably 10 wt% or more and 30 wt% or less.

[0047] FIG. 4 is a schematic cross-sectional view of a catalyst particle 80. As shown in FIG. 4, the catalyst particle 80 has a template particle 81 and a large number of catalyst powders 82 supported on the template particle 81. The template particle 81 is a substantially spherical support. The template particle 81 itself does not have catalytic activity. For example, silica (Si) particles are used for the template particle 81. The catalyst powder 82 is a molecule having catalytic activity, such as iridium (Ir), ruthenium (Ru), or iridium oxide (IrOx). The catalyst powder 82 is arranged so as to cover the surface of the template particle 81.

[0048] The particle diameter of the catalyst powder 82 (the average diameter of the catalyst powder 82 before preparing the catalyst ink) is, for example, about 2 to 3 nm. In contrast, the template particles 81 have a particle diameter larger than that of the catalyst powder 82. By using template particles 81 with a constant particle diameter, the particle diameter of the catalyst particles 80 can be made uniform with high precision. The diameter of the catalyst particles 80 is set to be 50 nm or more and 300 nm or less.

[0049] The diameter of the catalyst particles 80 refers to the average value of diameters measured using a laser diffraction / scattering particle size distribution analyzer (LA-920, manufactured by Horiba, Ltd.). When the catalyst particles 80 are produced using the template particles 81, the thickness of the catalyst powder 82 is very small, so the average value of the diameters of the template particles 81 may be considered to be the diameter of the catalyst particles 80.

[0050] The measurement sample used to measure the diameter of the catalyst particles 80 is prepared by adding the catalyst particles (or the template particles, if the catalyst particles 80 are prepared using the template particles 81) to methanol to a concentration of 1 mass % and dispersing the catalyst particles for 10 minutes using an ultrasonic disperser.

[0051] Next, the catalyst ink prepared in step S1 is applied to the surface of the electrolyte membrane 51 (step S2: application step). FIG. 5 is a diagram showing an example of a manufacturing apparatus 90 that performs the application step of step S2 and the drying step of step S3. The manufacturing apparatus 90 in FIG. 5 has a nozzle 91 that ejects the catalyst ink and a transport mechanism 92 that moves the electrolyte membrane 51 relative to the nozzle 91. The nozzle 91 may eject the catalyst ink in the form of a film from a slit-shaped outlet, or may eject the catalyst ink in the form of a spray.

[0052] The manufacturing apparatus 90 ejects catalyst ink from a nozzle 91 onto the surface of the electrolyte membrane 51 while transporting the electrolyte membrane 51 using a transport mechanism 92. In this way, the catalyst ink is applied to the surface of the electrolyte membrane 51.

[0053] After the application process of step S2 is completed, the catalyst ink applied to the electrolyte membrane 51 is dried (step S3: drying process). In the manufacturing apparatus 90 of FIG. 5, the electrolyte membrane 51 to which the catalyst ink has been applied is transported to a drying oven 93 by a transport mechanism 92. The temperature inside the drying oven 93 is higher than the ambient temperature, which promotes evaporation of the solvent in the catalyst ink. This dries the catalyst ink. As a result, an anode catalyst layer 61 is formed on the surface of the electrolyte membrane 51.

[0054] Thereafter, a water electrolysis device 1 is manufactured using a membrane-catalyst layer assembly including the electrolyte membrane 51 and the above-described anode catalyst layer 61. Specifically, a porous transport layer 62 and a gas diffusion layer 72 are added to a membrane-catalyst layer assembly composed of the electrolyte membrane 51, the anode catalyst layer 61, and the cathode catalyst layer 71, to manufacture a cell 10. Then, the cells 10 and separators 20 are alternately stacked to form a cell stack 30. Thereafter, a power supply 40 is connected to the cell stack 30, to manufacture the water electrolysis device 1.

[0055] 6 to 8 are images of a portion of the anode catalyst layer 61 taken with a scanning electron microscope (SEM). FIG. 6 is an image obtained when no template particles 81 were used (comparative example). FIG. 7 is an image obtained when template particles 81 were used and the diameter of the catalyst particles 80 was set to 100 nm (example). FIG. 8 is an image obtained when template particles 81 were used and the diameter of the catalyst particles 80 was set to 300 nm (example).

[0056] In the image of Fig. 6, catalyst powder with particle diameters of 2 to 3 nm is densely packed. Therefore, in the example of Fig. 6, the voids in the anode catalyst layer 61 are extremely small. Note that the lump in the center of Fig. 6 is used for focusing during imaging and is not a catalyst.

[0057] In contrast, in the examples of FIGS. 7 and 8 , the catalyst particles 80 have a particle diameter that is sufficiently larger than that of the catalyst powder 82. Specifically, while the diameter of the catalyst powder 82 is 2 to 3 nm, the diameter of the catalyst particles 80 in FIG. 7 is 100 nm, and the diameter of the catalyst particles 80 in FIG. 8 is 300 nm. Increasing the diameter of the catalyst particles 80 in this way makes it easier for the catalyst particles to aggregate together in the drying process of step S3. As a result, as shown in FIGS. 7 and 8 , aggregation portions 63 in which a plurality of catalyst particles 80 aggregate are formed in the anode catalyst layer 61. Furthermore, voids 64 are formed between the plurality of aggregation portions 63 in the anode catalyst layer 61. In other words, the anode catalyst layer 61 formed in the drying process has the aggregation portions 63 and the voids 64.

[0058] As described above, the manufacturing method of this embodiment makes it possible to obtain the anode catalyst layer 61 having the agglomeration portions 63 and the void portions 64. When the water electrolysis device 1 is in use, water is supplied to the anode catalyst layer 61, and the water is electrolyzed to generate gaseous oxygen. At this time, the anode catalyst layer 61 has good air permeability due to the large number of void portions 64, so that oxygen is efficiently discharged from the anode catalyst layer 61 and water is efficiently supplied to the anode catalyst layer 61. As a result, the efficiency of electrolysis in the anode catalyst layer 61 can be improved.

[0059] FIG. 9 is a graph showing the current-voltage characteristics when a voltage is applied from the power supply 40 to the cell 10 after fabrication while a fixed amount of water is supplied to the anode side. In the experiment shown in FIG. 9, iridium oxide (IrOx) was used as the catalyst for the anode catalyst layer 61. The horizontal axis of FIG. 9 represents the current density (A / cm ), which is the current value per unit area flowing through the cell 10. 2 9. The vertical axis of FIG. 9 represents the voltage value (V) applied between the anode and cathode of the cell 10 by the power supply device 40.

[0060] The power supply device 40 performs so-called constant current control, which controls the voltage value applied to the cell 10 so that the current flowing through the cell 10 becomes a specified current value. Therefore, as shown in Figure 9, when the specified current density is changed, the voltage value changes accordingly.

[0061] Case C0 in Fig. 9 shows the current-voltage characteristics when no template particles 81 are used (comparative example). Case C1 in Fig. 9 shows the current-voltage characteristics when template particles 81 are used and the diameter of the catalyst particles 80 is 50 nm (example). Case C2 in Fig. 9 shows the current-voltage characteristics when template particles 81 are used and the diameter of the catalyst particles 80 is 100 nm (example). Case C3 in Fig. 9 shows the current-voltage characteristics when template particles 81 are used and the diameter of the catalyst particles 80 is 300 nm (example).

[0062] The weight of the catalyst powder 82 used was the same in cases C0 to C3. Other conditions than the presence or absence of template particles 81 and the size of the template particles 81 were the same in cases C0 to C3.

[0063] When catalyst powder 82 with a particle diameter of 2 to 3 nm is used without using template particles 81, as in case C0, a relatively large voltage must be applied to cell 10. In contrast, when template particles 81 are used and the diameter of catalyst particles 80 is set to 50 nm or more and 300 nm or less, as in cases C1 to C3, the voltage applied to cell 10 is smaller than in case C0. That is, hydrogen is produced with less power in cases C1 to C3 than in case C0. This is thought to be because the aggregation of catalyst particles 80 described above forms voids 64 in anode catalyst layer 61, which allows oxygen to be efficiently discharged from anode catalyst layer 61 and water to be efficiently supplied to anode catalyst layer 61.

[0064] In cases C0 to C2, the larger the diameter of the catalyst particles 80, the smaller the voltage value applied to the cell 10. However, when the diameter of the catalyst particles 80 was set to 300 nm as in case C3, the voltage value applied to the cell 10 was larger than when the diameter of the catalyst particles 80 was set to 100 nm as in case C2. This may be because the diameter of the catalyst particles 80 was too large, which made it easier for the catalyst particles 80 to be regularly arranged, or because the proportion of the volume occupied by the template particles 81 increased, making it less likely for voids 64 to be formed.

[0065] From the above results, it can be said that it is desirable that the diameter of the catalyst particles 80 is 50 nm or more and 300 nm or less, and particularly about 100 nm. For example, it is thought that by making the diameter of the catalyst particles 80 80 nm or more and 150 nm or less, it is possible to more effectively aggregate the plurality of catalyst particles 80 in the drying step.

[0066] Furthermore, in the above manufacturing method, the catalyst ink is dried by heating in the drying step. Therefore, the catalyst ink dries in a shorter time than when heating is not performed. By shortening the drying time of the catalyst ink, the plurality of catalyst particles 80 can be arranged in the dried anode catalyst layer 61 so that they are not close-packed but have a suitable amount of voids 64. Therefore, the voids 64 can be formed well in the anode catalyst layer 61.

[0067] The maximum width of the voids 64 is preferably 10 nm or more. Specifically, the maximum width of the voids 64 is preferably about 10 nm to 3000 nm. Furthermore, the maximum width of the voids 64 is preferably larger than the diameter of the catalyst particles 80. This can further improve the breathability of the anode catalyst layer 61.

[0068] <3. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0069] In the above embodiment, the aggregation portions 63 were formed by adjusting the diameter of the catalyst particles 80 to 50 nm or more and 300 nm or less without adding an aggregating agent to the catalyst ink. In the experiments shown in FIGS. 6 to 9, an aggregating agent was also not added to the catalyst ink. However, an aggregating agent may be added to the catalyst ink to further promote aggregation of the catalyst particles 80. That is, the catalyst particles, solvent, ionomer, and aggregating agent may be mixed in the preparation process of step S1.

[0070] The flocculant may be either an inorganic flocculant or an organic flocculant, as long as it can aggregate the catalyst particles 80 and form voids 64 of about 10 nm to several μm.

[0071] In the above embodiment, silica particles are used as the template particles 81. However, the template particles 81 may be particles other than silica. For example, the template particles 81 may be particles of titanium dioxide (TiO) or carbon (C).

[0072] Alternatively, the catalyst particles 80 may be formed without using the template particles 81, using only catalyst molecules, with a diameter of 50 nm or more and 300 nm or less.

[0073] In the above embodiment, the agglomeration portions 63 and voids 64 are formed in the anode catalyst layer 61. However, the agglomeration portions 63 and voids 64 may be formed in the cathode catalyst layer 71 using a similar method. Forming the voids 64 in the cathode catalyst layer 71 allows gaseous hydrogen to be efficiently discharged from the cathode catalyst layer 71.

[0074] However, in the water electrolysis device 1, the reaction rate of electrolysis in the anode catalyst layer 61 is often slower than the reaction rate of the reduction reaction in the cathode catalyst layer 71. For this reason, there are situations in which the overall treatment rate of the water electrolysis device 1 is rate-determined by the reaction rate on the anode side. As in the above embodiment, forming voids 64 in the anode catalyst layer 61 to increase the reaction rate of electrolysis in the anode catalyst layer 61 can improve the reaction efficiency of the entire water electrolysis device 1. Therefore, in the water electrolysis device 1, forming a plurality of voids 64 in the anode catalyst layer 61 is of particularly great technical significance.

[0075] In the above embodiment, the present invention is described as being applied to a PEM (Proton Exchange Membrane) type water electrolysis apparatus 1. However, the present invention may also be applied to water electrolysis apparatuses other than PEM type, such as AEM (Anion Exchange Membrane) type water electrolysis apparatuses. In AEM type water electrolysis apparatuses, for example, nickel (Ni), cobalt (Co), iron (Fe), or the like is used as a catalyst.

[0076] In the above embodiment, the condensation sections 63 and voids 64 are formed in the catalytic layer of the cell 10 used in the water electrolysis device 1. However, the condensation sections and voids may be formed in the catalytic layer of a cell used in a fuel cell using a similar method. Forming voids in the catalytic layer on the anode side of the fuel cell can improve the hydrogen supply efficiency. Forming voids in the catalytic layer on the cathode side of the fuel cell can improve the water discharge efficiency and oxygen supply efficiency.

[0077] Furthermore, agglomeration portions and voids may be formed in the catalyst layer of a cell used in a liquid organic hydrogen carrier (LOHC) process for producing an organic hydride (e.g., toluene-methylcyclohexane) by hydrogenating an aromatic compound such as toluene, using a method similar to that described above.

[0078] Furthermore, the elements appearing in the above-described embodiments and modifications may be combined as appropriate or some may be deleted within the scope of not causing any contradiction. [Explanation of symbols]

[0079] 1: Water electrolysis device 10: Cell 20: Separator 21: Anode surface 22: Cathode surface 23: Anode groove 24: Cathode groove 30: Cell stack 40: Power supply 51: Electrolyte membrane 61: Anode catalyst layer 62: Porous transport layer 63:Agglutination part 64:Void part 71: Cathode catalyst layer 72: Gas diffusion layer 80: Catalyst particles 81: Template particle 82: Catalyst powder 90: Manufacturing equipment 91: Nozzle 92:Transport mechanism 93:Drying oven

Claims

1. A method for producing a membrane catalyst-layer assembly, comprising: a preparation step of preparing a catalyst ink by mixing catalyst particles, a solvent, and an ionomer; a coating step of coating the catalyst ink on a surface of an electrolyte membrane; a drying step of drying the catalyst ink applied to the electrolyte membrane; and The diameter of the catalyst particles is 50 nm or more and 300 nm or less, The catalyst layer formed by the drying step has aggregated portions where the catalyst particles are aggregated, and void portions formed between the aggregated portions.

2. The method of claim 1, The manufacturing method, wherein the diameter of the catalyst particles is 80 nm or more and 150 nm or less.

3. The manufacturing method according to claim 1 or claim 2, The manufacturing method, wherein the maximum width of the void portion is 10 nm or more.

4. The manufacturing method according to claim 1 or claim 2, The catalyst particles are template particles; a catalyst powder supported on the template particles; The manufacturing method of the present invention.

5. The manufacturing method according to claim 4, The method of manufacturing, wherein the template particles are particles of silica.

6. The manufacturing method according to claim 1 or claim 2, A manufacturing method wherein a flocculant is further mixed in the preparation step.

7. The manufacturing method according to claim 1 or claim 2, In the drying step, the catalyst ink is dried by heating.

8. A membrane-catalyst layer assembly, an electrolyte membrane; a catalyst layer formed on the surface of the electrolyte membrane; Equipped with the catalyst layer includes a plurality of catalyst particles; The diameter of the catalyst particles is 50 nm or more and 300 nm or less, The catalyst layer has an agglomeration portion where a plurality of the catalyst particles are agglomerated, and a void portion formed between the agglomeration portions.

9. A water electrolysis device comprising the membrane catalyst layer assembly according to claim 8.

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