Membrane-catalyst layer assembly and water electrolysis apparatus

Abstract

To provide a technique capable of reducing usage amount of a catalyst while securing a surface area of the catalyst that promotes bonding of hydrogen and oxygen, and also suppressing a decrease in a reaction rate of electrolysis.SOLUTION: A third catalyst that promotes bonding of hydrogen and oxygen is disposed on an anode side of an electrolyte membrane 51. Even when hydrogen generated on a cathode side permeates the electrolyte membrane 51 and enters the anode side, the hydrogen can be bonded with oxygen generated on the anode side and converted into water by an action of the third catalyst. Thereby, the hydrogen concentration in the gas discharged from the anode side can be reduced. Particles of the third catalyst have a hollow structure having a cavity inside. Therefore, usage amount of the third catalyst can be reduced while securing a surface area of the particles. Furthermore, since the particles of the third catalyst have openings, movement of water, hydrogen, and oxygen on the anode side is not easily inhibited. Therefore, a decrease in a reaction rate of electrolysis on the anode side can also be suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to 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] In PEM water electrolysis devices, hydrogen ions (H +) passes through the electrolyte membrane and moves to the catalyst layer on the cathode side. Therefore, in order to increase the efficiency of hydrogen production, it is desirable to reduce the thickness of the electrolyte membrane and reduce the ionic resistance of the electrolyte membrane.

[0007] However, if the thickness of the electrolyte membrane is reduced, some of the hydrogen generated in the catalyst layer on the cathode side may permeate the electrolyte membrane and enter the anode side. In this case, the hydrogen may be mixed with the oxygen discharged from the anode side. To improve the safety of the water electrolysis device 1, it is necessary to keep the hydrogen concentration in the gas discharged from the anode side within an acceptable range.

[0008] To address this issue, for example, a platinum catalyst could be placed on the anode side, allowing hydrogen entering the anode side from the cathode side through the electrolyte membrane to combine with oxygen on the anode side and convert it into water. However, platinum is expensive, and the manufacturing cost of the water electrolysis device increases depending on the amount of platinum used. Furthermore, there is concern that placing platinum on the anode side may inhibit the movement of water, hydrogen, and oxygen, slowing the electrolysis reaction rate.

[0009] Therefore, an object of the present invention is to provide a technology that can reduce the amount of catalyst used while ensuring the surface area of ​​the catalyst that promotes the bonding of hydrogen and oxygen, and that can also prevent a decrease in the electrolysis reaction rate. [Means for solving the problem]

[0010] In order to solve the above problems, a first invention of the present application is a membrane-catalyst layer assembly for use in a water electrolysis device, comprising: an electrolyte membrane; a first catalyst layer provided on the anode side of the electrolyte membrane and containing a first catalyst that promotes water electrolysis; a second catalyst layer provided on the cathode side of the electrolyte membrane and containing a second catalyst that promotes a hydrogen reduction reaction; and a plurality of third catalyst particles provided on the anode side of the electrolyte membrane that promote the combination of hydrogen and oxygen, wherein the third catalyst particles have a hollow structure with a cavity inside and a plurality of openings that connect the cavity to the outside of the particle.

[0011] A second invention of the present application is the membrane-catalyst layer assembly of the first invention, wherein the particles of the third catalyst are substantially spherical and have the cavity inside.

[0012] A third invention of the present application is the membrane-catalyst layer assembly of the first or second invention, which has a third catalyst layer containing particles of the third catalyst between the electrolyte membrane and the first catalyst layer.

[0013] A fourth invention of the present application is the membrane-catalyst layer assembly of the third invention, wherein the third catalyst layer contains an ionomer.

[0014] A fifth invention of the present application is the membrane-catalyst layer assembly of the first or second invention, wherein the first catalyst layer contains particles of the third catalyst.

[0015] A sixth aspect of the present invention is the membrane-catalyst layer assembly of any one of the first to fifth aspects, wherein the third catalyst contains platinum.

[0016] A seventh invention of the present application is the membrane-catalyst layer assembly of the sixth invention, wherein the third catalyst contains platinum and cobalt.

[0017] An eighth aspect of the present invention is a water electrolysis apparatus, comprising the membrane-catalyst layer assembly of any one of the first to seventh aspects of the present invention. [Effects of the Invention]

[0018] According to the first to eighth aspects of the present invention, even if hydrogen generated on the cathode side permeates the electrolyte membrane and enters the anode side during use of the water electrolysis device, the hydrogen can be combined with oxygen generated on the anode side by the action of the third catalyst to convert the hydrogen into water, thereby reducing the hydrogen concentration in the gas discharged from the anode side.

[0019] The third catalyst particles have a hollow structure with internal cavities. This allows the amount of third catalyst used to be reduced while maintaining the particle surface area. Furthermore, the third catalyst particles have multiple openings, which do not impede the movement of water, hydrogen, and oxygen on the anode side. This also prevents a decrease in the electrolysis reaction rate on the anode side.

[0020] In particular, according to the second aspect of the present invention, the specific surface area of ​​the third catalyst can be made larger.

[0021] In particular, according to the third aspect of the present invention, hydrogen that permeates the electrolyte membrane from the cathode side and enters the anode side can be more reliably brought into contact with the third catalyst, and the amount of hydrogen that enters the first catalyst layer can be further reduced.

[0022] In particular, according to the fourth aspect of the present invention, the conductivity of the third catalyst layer can be improved.

[0023] In particular, according to the fifth aspect of the present invention, there is no need to form a third catalyst layer, separate from the first catalyst layer, on the anode side of the electrolyte membrane.

[0024] In particular, according to the sixth aspect of the present invention, the particles of the third catalyst have a hollow structure, which makes it possible to reduce the amount of expensive platinum used.

[0025] In particular, according to the seventh aspect of the present invention, the amount of platinum used can be reduced compared to when the third catalyst is made of platinum alone. [Brief explanation of the drawings]

[0026] [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] FIG. 3 is a diagram schematically illustrating particles of a third catalyst. [Figure 4] FIG. 3 is a diagram schematically illustrating a method for producing particles of a third catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0028] <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. The 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 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.

[0029] 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, a first catalyst layer 61, a porous transport layer 62, a second catalyst layer 71, a gas diffusion layer 72, and a third catalyst layer 80.

[0030] A laminate composed of the electrolyte membrane 51, the first catalyst layer 61, the second catalyst layer 71, and the third catalyst layer 80 is called a catalyst-coated membrane (CCM). Also, a laminate composed of the electrolyte membrane 51, the first catalyst layer 61, the porous transport layer 62, the second catalyst layer 71, the gas diffusion layer 72, and the third catalyst layer 80 is called a membrane-electrode-assembly (MEA).

[0031] 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.

[0032] The first catalyst layer 61 is a catalyst layer that causes water electrolysis on the anode side of the electrolyte membrane 51. In this embodiment, the first catalyst layer 61 is formed on the anode side of the electrolyte membrane 51 via a third catalyst layer 80, which will be described later. The first catalyst layer 61 contains a plurality of first catalyst particles and an ionomer.

[0033] The first catalyst is a catalyst that promotes the electrolysis of water. The first catalyst particles are made of, for example, iridium (Ir), ruthenium (Ru), iridium oxide (IrOx), or an alloy of iridium (Ir) and ruthenium (Ru). The first catalyst particles may be supported on a support. For example, titanium dioxide (TiO2) or carbon (C) is used as the support.

[0034] The ionomer is an electrolyte polymer that covers the particles of the first catalyst. The ionomer plays a role in transporting hydrogen ions generated by the electrolysis of water within the first 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 bond with water within the first catalyst layer 61 to form oxonium ions (HO + ) Then, the oxonium ion propagates through the ion exchange groups of the ionomer.

[0035] When the water electrolysis apparatus 1 is in use, water (H2O) is supplied to the first catalyst layer 61. Then, a voltage is applied between the first catalyst layer 61 and the second catalyst layer 71 by the power supply 40. Then, due to the voltage and the action of the first catalyst, the water is converted into hydrogen ions (H + ), oxygen (O2), and electrons (e -That is, in the first catalyst layer 61, the following electrochemical reaction occurs: 2H2O → 4H + + O2+ 4e - (1)

[0036] The porous transport layer (PTL) 62 is a layer that uniformly supplies water from the separator 20 to the first catalyst layer 61 and transports oxygen and electrons generated in the first catalyst layer 61 to the separator 20. The porous transport layer 62 is laminated on the outer side of the first 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.

[0037] The second catalyst layer 71 is a catalyst layer that causes a hydrogen reduction reaction on the cathode side. The second catalyst layer 71 is formed on the cathode side surface of the electrolyte membrane 51 (the surface opposite to the surface on which the first catalyst layer 61 is formed). The second catalyst layer 71 contains a large number of carbon particles that support second catalyst particles. The second catalyst is a catalyst that promotes a hydrogen reduction reaction. The second catalyst particles are, for example, platinum (Pt) particles. However, the second catalyst particles may also be platinum particles mixed with a small amount of ruthenium or cobalt particles.

[0038] When the water electrolysis device 1 is in use, hydrogen ions (H + ) and electrons (e - ) is supplied. Then, a voltage is applied between the first catalyst layer 61 and the second catalyst layer 71 by the power supply 40. This voltage and the action of the second catalyst cause a reduction reaction in the second catalyst layer 71, producing hydrogen gas (H2) from the hydrogen ions and electrons. That is, the following electrochemical reaction occurs in the second catalyst layer 71: 2H + + 2e - → H2(2)

[0039] The gas diffusion layer (GDL) 72 is a layer that transmits electrons from the separator 20 to the second catalyst layer 71 and also transmits hydrogen generated in the second catalyst layer 71 to the separator 20. The gas diffusion layer 72 is laminated on the outer side of the second 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.

[0040] 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.

[0041] 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 first catalyst layer 61 passes through porous transport layer 62 and anode grooves 23 of separator 20, and is discharged to outside cell stack 30.

[0042] In addition, a plurality of cathode grooves 24 are formed on the cathode surface 22 of the separator 20. Hydrogen generated in the second 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.

[0043] 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.

[0044] When the water electrolysis device 1 is in use, water is supplied from the anode groove 23 of the separator 20 through the porous transport layer 62 to the first catalyst layer 61. Then, due to the voltage from the power supply 40 and the action of the catalyst particles in the first catalyst layer 61, the water is decomposed into hydrogen ions, oxygen, and electrons. The hydrogen ions propagate through the electrolyte membrane 51 to the second catalyst layer 71. The oxygen passes through the porous transport layer 62 and the anode groove 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.

[0045] In the adjacent cell 10, the electrons pass through the gas diffusion layer 72 and reach the second catalyst layer 71. Then, in the second 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.

[0046] <2. Third catalyst layer> Some of the hydrogen generated on the cathode side may permeate the electrolyte membrane 51 and enter the anode side. In this case, the hydrogen is mixed with the oxygen discharged from the anode side. To improve the safety of the water electrolysis device 1, it is necessary to keep the hydrogen concentration in the gas discharged from the anode side within a predetermined allowable range.

[0047] Therefore, the water electrolysis device 1 of this embodiment has a third catalyst layer 80 for converting hydrogen, which has permeated the electrolyte membrane 51 from the cathode side and entered the anode side, into water. The third catalyst layer 80 is interposed between the anode side surface of the electrolyte membrane 51 and the first catalyst layer 61. The third catalyst layer 80 contains a plurality of third catalyst particles 81. The third catalyst is a catalyst that promotes the bonding of hydrogen and oxygen. For example, platinum (Pt) is used as the third catalyst.

[0048] In this way, even when hydrogen generated on the cathode side permeates the electrolyte membrane 51 and enters the anode side, the hydrogen comes into contact with the third catalyst in the third catalyst layer 80. In addition, a portion of the oxygen generated in the first catalyst layer 61 is also supplied to the third catalyst layer 80. As a result, the hydrogen and oxygen combine with each other through the action of the third catalyst to produce water. That is, the following chemical reaction occurs in the third catalyst layer 80. 2H2+ O2→ 2H2O (3)

[0049] Through the above reaction, hydrogen that has permeated the electrolyte membrane 51 from the cathode side and entered the anode side is converted into water. Therefore, the hydrogen concentration in the gas discharged from the anode side can be reduced. Specifically, the hydrogen concentration in the gas discharged from the anode side can be reduced to 4 vol.% or less, more preferably 2 vol.% or less.

[0050] FIG. 3 is a schematic diagram of a particle 81 of the third catalyst. The particle 81 has a diameter R of, for example, approximately 50 to 500 nm. As shown in FIG. 3, the third catalyst particle 81 has a hollow structure with a cavity 811 inside. This makes it possible to reduce the amount of platinum used as the third catalyst while ensuring the surface area of ​​the particle 81. Ensuring the surface area of ​​the particle 81 makes it easier for hydrogen to come into contact with the third catalyst. Furthermore, reducing the amount of expensive platinum used can reduce the manufacturing cost of the water electrolysis device 1.

[0051] In particular, in this embodiment, the particles 81 of the third catalyst are substantially spherical (capsule-shaped) with an internal cavity 811. This allows the specific surface area of ​​the third catalyst to be larger than that of other hollow structures such as fiber shapes.

[0052] As shown in FIG. 3, the third catalyst particle 81 has a plurality of openings 812. The openings 812 connect the cavity 811 to the outside of the particle 81. Therefore, the third catalyst particle 81 is less likely to obstruct the movement of water, hydrogen, and oxygen on the anode side. This allows the reaction (3) to occur efficiently. The third catalyst layer 80 also prevents a decrease in the rate of the reaction (1).

[0053] 4 is a diagram schematically illustrating a method for producing a third catalyst particle 81. When producing the third catalyst particle 81, first, a spherical template particle 90 is prepared as shown in FIG. 4(a). The template particle 90 is made of, for example, silica (Si) particles. Next, the surface of the template particle 90 is modified with poly(diallyldimethylammonium chloride: PDDA).

[0054] 4(b), a third catalyst is supported on the template particle 90. Specifically, the third catalyst is supported on the template particle 90 by a polyol method using tetraethylene glycol as a reducing agent and the third catalyst as a metal precursor. As a result, molecules 813 of the third catalyst are aligned along the surface of the template particle 90.

[0055] Next, the third catalyst supported on the template particle 90 is subjected to supercritical treatment to improve the strength of the third catalyst. The template particle 90 is then dissolved. Specifically, the silica particles supporting the third catalyst are immersed in an aqueous sodium hydroxide solution and heated at 80°C for 1 hour to dissolve the silica particles. This results in particles 81 with a hollow structure in which third catalyst molecules 813 are arranged in a roughly spherical shape, as shown in FIG. 4(c). The portions of the surface of the template particle 90 where the third catalyst was not supported become openings 812.

[0056] During production of the water electrolysis device 1, a catalyst solution is prepared by adding the third catalyst particles 81 produced by the above-described method to a solvent and stirring them. The solvent is water or alcohol. The catalyst solution is then applied to the anode side surface of the electrolyte membrane 51. The catalyst solution may be applied by discharging the catalyst solution through a slit-shaped outlet or by discharging the catalyst solution in a spray form. The catalyst solution may also be applied to the first catalyst layer 61 before it is bonded to the electrolyte membrane 51.

[0057] In this embodiment, instead of mixing third catalyst particles 81 into the first catalyst layer 61, a third catalyst layer 80 separate from the first catalyst layer 61 is provided closer to the electrolyte membrane 51 than the first catalyst layer 61. This allows hydrogen that permeates the electrolyte membrane 51 from the cathode side and enters the anode side to more reliably come into contact with the third catalyst. Furthermore, the amount of hydrogen that enters the first catalyst layer 61 can be further reduced.

[0058] If the amount of the third catalyst is too small, the effect of converting hydrogen into water by the reaction (3) above will be reduced. On the other hand, if the amount of the third catalyst is too large, the effect of converting hydrogen into water will reach an upper limit, and the thickness of the third catalyst layer 80 will be unnecessarily large. From this perspective, it is desirable that the weight ratio of the third catalyst (e.g., platinum) to the first catalyst (e.g., iridium) be, for example, 0.01 wt% or more and 0.4 wt% or less. It is more desirable that the weight ratio of the third catalyst to the first catalyst be 0.2 wt% or more and 0.3 wt% or less.

[0059] The third catalyst layer 80 may contain an ionomer. The inclusion of an ionomer can improve the electrical conductivity of the third catalyst layer 80. Therefore, the third catalyst layer 80 can further suppress the decrease in the reaction rate of the above item (1).

[0060] <3. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0061] <3-1. First modified example> In the above embodiment, the third catalyst layer 80 is formed on the anode side of the electrolyte membrane 51, separately from the first catalyst layer 61. However, the first catalyst layer 61 may contain particles 81 of the third catalyst. That is, the first catalyst layer 61 containing the first catalyst and the third catalyst may be formed on the anode side surface of the electrolyte membrane 51 without providing the third catalyst layer 80.

[0062] In this way, it is not necessary to perform two coating processes on the anode side surface of the electrolyte membrane 51, namely, a coating process for forming the third catalyst layer 80 and a coating process for forming the first catalyst layer 61. This reduces the number of steps in manufacturing the water electrolysis device 1.

[0063] <3-2. Second modified example> In the above embodiment, platinum is used as the third catalyst. However, the third catalyst may contain platinum and cobalt (Co). Even when an alloy of platinum and cobalt is used as the third catalyst, the reaction (3) above can be carried out satisfactorily. Furthermore, by including cobalt in the third catalyst, the amount of platinum used can be reduced compared to when the third catalyst is composed of platinum alone. Therefore, the manufacturing cost of the water electrolysis device 1 can be further reduced. The weight ratio of platinum to cobalt is preferably about 1:1 to 3:1.

[0064] The third catalyst may also contain platinum and iron (Fe). Even when an alloy of platinum and iron is used as the third catalyst, the reaction (3) above can be carried out satisfactorily. Furthermore, by including iron in the third catalyst, the amount of platinum used can be reduced compared to when the third catalyst is composed of platinum alone. This can further reduce the manufacturing cost of the water electrolysis device 1. The weight ratio of platinum to iron is preferably about 1:1.

[0065] <3-3.Third modified example> In the above embodiment, the third catalyst particles 81 have a substantially spherical shape with an internal cavity 811. However, the shape of the third catalyst particles 81 may be a shape other than a spherical shape. For example, in the above-described method for producing particles 81, fibrous particles 81 having an internal cavity 811 may be produced by using fibrous template particles instead of the spherical template particles 90.

[0066] <3-4. Other variations> In the above embodiment, the third catalyst layer 80 is provided between the electrolyte membrane 51 and the first catalyst layer 61. However, the third catalyst layer 80 may be provided between the first catalyst layer 61 and the porous transport layer 62.

[0067] 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]

[0068] 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: 1st catalyst layer 62: Porous transport layer 71:Second catalyst layer 72: Gas diffusion layer 80:Third catalyst layer 81: Third catalyst particles 90: Template particle 811: hollow 812 :Aperture 813: Molecules of the third catalyst

Claims

1. A membrane catalyst layer assembly for use in a water electrolysis device, comprising: an electrolyte membrane; a first catalyst layer provided on the anode side of the electrolyte membrane and including a first catalyst that promotes water electrolysis; a second catalyst layer provided on the cathode side of the electrolyte membrane and including a second catalyst that promotes a hydrogen reduction reaction; a plurality of third catalyst particles provided on the anode side of the electrolyte membrane to promote the combination of hydrogen and oxygen; Equipped with The third catalyst particles are It has a hollow structure with a cavity inside, a plurality of openings communicating the cavity with the outside of the particle; Membrane / catalyst layer assembly.

2. The membrane-catalyst layer assembly according to claim 1, a membrane-catalyst layer assembly, wherein the particles of the third catalyst are substantially spherical and have the cavity therein;

3. 3. The membrane-catalyst layer assembly according to claim 1 or 2, a third catalyst layer between the electrolyte membrane and the first catalyst layer, the third catalyst layer containing particles of the third catalyst; A membrane-catalyst layer assembly having the above structure.

4. The membrane-catalyst layer assembly according to claim 3, The membrane-catalyst layer assembly, wherein the third catalyst layer contains an ionomer.

5. 3. The membrane-catalyst layer assembly according to claim 1 or 2, a membrane-catalyst layer assembly, wherein the first catalyst layer contains particles of the third catalyst.

6. 3. The membrane-catalyst layer assembly according to claim 1 or 2, The membrane-catalyst layer assembly, wherein the third catalyst contains platinum.

7. The membrane-catalyst layer assembly according to claim 6, The membrane-catalyst layer assembly, wherein the third catalyst contains platinum and cobalt.

8. A water electrolysis device comprising the membrane catalyst layer assembly according to claim 1 or 2.

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