Catalyst layer for electrochemical devices, membrane electrode assembly for electrochemical devices, and electrochemical device

Abstract

To provide a catalyst layer for electrochemical devices suitable for suppressing the increase in the diffusion resistance of reactants such as oxygen.SOLUTION: A disclosed catalyst layer for electrochemical devices 100 has a first main surface 10a and a second main surface 10b at the opposite side of the first main surface 10a. The catalyst layer includes: multiple conductive columns 11 extending from the first main surface 10a toward the second main surface 10b, and catalyst particles 12 supported on the multiple conductive columns 11. Defining the end of the conductive column 11 positioned on the main surface 10a side as a first end 11a, and when the distance D11a between the first ends 11a adjacent to each other is measured, there is a cross-section of the catalyst layer 100 parallel to the thickness direction T10 in which 30% or more of the measured values are 20 nm or less.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present disclosure relates to a catalyst layer for an electrochemical device, a membrane electrode assembly for an electrochemical device, and an electrochemical device.

Background Art

[0002] Patent Document 1 discloses a membrane / electrode assembly for a fuel cell, which includes an electrolyte membrane, at least one electrode disposed on at least one surface of the electrolyte membrane, the electrode including a conductive nanocolumnar body oriented substantially perpendicular to the surface direction of the electrolyte membrane, and a catalyst supported on the conductive nanocolumnar body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, it has been desired to suppress an increase in diffusion resistance of reactants such as oxygen in a catalyst layer for an electrochemical device such as a fuel cell.

[0005] An object of the present disclosure is to provide a catalyst layer for an electrochemical device, a membrane electrode assembly for an electrochemical device, and an electrochemical device suitable for suppressing an increase in diffusion resistance of reactants such as oxygen.

Means for Solving the Problems

[0006] The catalyst layer for an electrochemical device in the present disclosure is a catalyst layer having a first main surface and a second main surface opposite to the first main surface, a plurality of conductive columnar bodies extending from the first main surface toward the second main surface, and catalyst particles supported on the plurality of conductive columnar bodies, comprising defining an end portion of the conductive columnar body located on the first major surface side as a first end portion, and when measuring a distance between the adjacent first end portions, there exists a cross-section of the catalyst layer parallel to the thickness direction in which 30% or more of the obtained measurement values are 20 nm or less.

[0007] On another aspect, the membrane electrode assembly for an electrochemical device in the present disclosure an anode, a cathode, an electrolyte membrane disposed between the anode and the cathode, comprising the cathode includes the catalyst layer for an electrochemical device of the present disclosure, in the cathode, the first major surface of the catalyst layer for an electrochemical device is in contact with the electrolyte membrane.

[0008] On yet another aspect, the electrochemical device in the present disclosure comprises the membrane electrode assembly for an electrochemical device of the present disclosure.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to suppress an increase in diffusion resistance of reactants such as oxygen in the catalyst layer for an electrochemical device.

Brief Description of the Drawings

[0010]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 7

[0011] (Findings and the like on which the present disclosure is based) For the purpose of improving the efficiency of fuel cells, the development of technologies for promoting the electrochemical reaction of the cathode catalyst layer has been studied. In order to promote the electrochemical reaction of the cathode catalyst layer, it is considered as issues to smoothly supply reactants such as oxygen to the cathode catalyst layer, smoothly discharge water as a product substance from the cathode catalyst layer, and increase the reaction field in the cathode catalyst layer. In order to solve these issues, for example, a catalyst layer in which conductive columnar bodies such as carbon nanotubes supporting catalyst particles are integrated while being oriented in a direction substantially perpendicular to the plane direction of the electrolyte membrane has been proposed (for example, Patent Document 1). The catalyst layer as shown in Patent Document 1 is provided on one surface of the electrolyte membrane, and includes a conductive columnar body oriented in a direction substantially perpendicular to the plane direction of the electrolyte membrane, catalyst particles supported on the conductive columnar body, and an electrolyte resin. The conductive columnar body is coated with the electrolyte resin.

[0012] In the catalyst layer as shown in Patent Document 1, when the conductive columnar bodies are highly integrated to increase the reaction field, the gaps (pores) formed between the conductive columnar bodies become narrow. Therefore, water as a product substance stays in the pores, increasing the diffusion resistance of reactants, particularly oxygen. Under such circumstances, the inventors first focused on promoting the discharge of water as a product substance, and came to constitute the subject matter of the present disclosure in order to control the capillary pressure of water in the pores for realizing it.

[0013] The present disclosure provides a catalyst layer for an electrochemical device, a membrane electrode assembly for an electrochemical device, and an electrochemical device suitable for suppressing an increase in the diffusion resistance of reactants such as oxygen.

[0014] Hereinafter, embodiments will be described in detail with reference to the drawings. However, a more detailed description than necessary may be omitted. For example, a detailed description of well-known matters or a redundant description of substantially the same configuration may be omitted. This is to avoid making the following description overly redundant and to facilitate the understanding of those skilled in the art.

[0015] The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0016] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to FIGS. 1A to 5.

[0017] [1-1. Configuration] FIG. 1A is a schematic cross-sectional view of a catalyst layer 100 for an electrochemical device according to Embodiment 1. FIG. 1A is a cross-sectional view of the catalyst layer 100 parallel to the thickness direction T10. FIG. 1B is a partially enlarged view of region A in FIG. 1A. The catalyst layer 100 has a first main surface 10a and a second main surface 10b opposite to the first main surface 10a in the thickness direction T10. The catalyst layer 100 includes a plurality of conductive columnar bodies 11 extending from the first main surface 10a toward the second main surface 10b, and catalyst particles 12 supported on the plurality of conductive columnar bodies 11. Pores 11p are formed between adjacent conductive columnar bodies 11.

[0018] As shown in FIG. 1A, the end of the conductive columnar body 11 located on the first main surface 10a side is defined as the first end 11a, and the end of the conductive columnar body 11 located on the second main surface 10b side is defined as the second end 11b. In the catalyst layer 100 according to Embodiment 1, when measuring the distance D11a between adjacent first ends 11a, there exists a cross-section of the catalyst layer 100 parallel to the thickness direction T10, where 30% or more of the obtained measured values are 20 nm or less.

[0019] FIG. 2A is a diagram for explaining the movement of reactants, electrons, and product substances in the catalyst layer 100 in Embodiment 1. FIG. 2A is an example in the case where the catalyst layer 100 is used as the cathode catalyst layer of a fuel cell. In FIG. 2A, it is assumed that the first main surface 10a of the catalyst layer 100 is in contact with an electrolyte membrane (not shown), and a hydrogen-containing gas is used as the anode gas and an oxygen-containing gas is used as the cathode gas. As shown in FIG. 2A, the oxygen-containing gas (O2) supplied from the cathode gas diffusion layer side (the upper side in FIG. 2) can move in the catalyst layer 100 along the pores 11p. Protons (H + ) that have moved from the electrolyte membrane side (the lower side in FIG. 2) can move in the catalyst layer 100 along the liquid water. In the catalyst layer 100, the oxygen-containing gas reacts with electrons (e - ) and protons that have moved through the external circuit, and as a result, water is generated.

[0020] In the catalyst layer 100 in Embodiment 1, there is a cross-section of the catalyst layer 100 that satisfies the following requirements (i) and (ii). (i) The cross-section is parallel to the thickness direction T10 of the catalyst layer 100. (ii) When the distance D11a between the adjacent first ends 11a is measured, 30% or more of the obtained measurement values are 20 nm or less.

[0021] With such a configuration, as shown in FIG. 1A, the plurality of conductive columnar bodies 11 are likely to have a structure in which the adjacent first ends 11a are close to each other. When the adjacent first ends 11a are close to each other, the pores 11p between the conductive columnar bodies 11 having such first ends 11a can have a shape F11 that expands from the first main surface 10a toward the second main surface 10b. A capillary pressure that attempts to raise the liquid level in the direction from the first main surface 10a to the second main surface 10b can act on the pores 11p having the shape F11.

[0022] The capillary pressure acting on the pore 11p having the shape F11 will be specifically described with reference to FIG. 2B. FIG. 2B is a partially enlarged view of the region B in FIG. 2A. As shown in FIG. 2B, the capillary pressure P represented by the following formula (1) acts on the pore 11p having the shape F11 c acts.

[0023]

Equation

[0024] In formula (1), r is the inner diameter r of the pore 11p having the shape F11, θ is the contact angle of water, and σ is the surface tension of water.

[0025] The capillary pressure P acting on the pore 11p having the shape F11 c causes the water generated in the pore 11p having the shape F11 to be pushed upward in the direction from the first main surface 10a to the second main surface 10b. As a result, the discharge of the water generated in the pore 11p having the shape F11 from the catalyst layer 100 is promoted, so that the clogging of the pore 11p by water is suppressed. As a result, an increase in the diffusion resistance of the reactants, particularly oxygen, in the catalyst layer 100 is suppressed.

[0026] The presence of a cross-section of the catalyst layer 100 that satisfies the above requirements (i) and (ii) can be confirmed, for example, by the following method. First, a sample is prepared in which a cross-section of the catalyst layer 100 parallel to the thickness direction T10 is exposed. A cross-sectional image of the sample is obtained using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). For all of the plurality of first ends 11a included in the obtained cross-sectional image, the distance D11a is measured. As shown in FIGS. 1A and 1B, the distance D11a is the distance between the outer surfaces 11c of the mutually adjacent first ends 11a in the cross-section of the catalyst layer 100 parallel to the thickness direction T10. When the mutually adjacent first ends 11a are in contact, the distance D11a is regarded as 0 nm. For example, when 30 or more of the 100 measurement data of the distance D11a in the cross-section of the catalyst layer 100 parallel to the thickness direction T10 have a distance D11a of 20 nm or less, it can be regarded that there is a cross-section of the catalyst layer 100 that satisfies the above requirements (i) and (ii).

[0027] In the catalyst layer 100, when measuring the distance D11a between the mutually adjacent first ends 11a, there may be a cross-section of the catalyst layer 100 parallel to the thickness direction T10 in which 40% or more of the obtained measurement values are 20 nm or less, or there may be a cross-section of the catalyst layer 100 parallel to the thickness direction T10 in which 50% or more of the obtained measurement values are 20 nm or less.

[0028] In the catalyst layer 100, when measuring the distance D11a between the mutually adjacent first ends 11a, there may be a cross-section of the catalyst layer 100 parallel to the thickness direction T10 in which 99% or less of the obtained measurement values are 20 nm or less, or there may be a cross-section of the catalyst layer 100 parallel to the thickness direction T10 in which 95% or less of the obtained measurement values are 20 nm or less.

[0029] In the catalyst layer 100 in Embodiment 1, in a cross-section of the catalyst layer 100 parallel to the thickness direction T10, a plurality of first ends 11a are arranged at unequal intervals along the first main surface 10a, and the plurality of second ends 11b may be arranged at equal or unequal intervals along the second main surface 10b. According to such a configuration, the adjacent first ends 11a can take a structure approaching each other. When the adjacent first ends 11a take a structure approaching each other, the pores 11p between the conductive columnar bodies 11 having such first ends 11a can have a shape F11 that expands from the first main surface 10a toward the second main surface 10b. Therefore, the discharge of water generated in the pores 11p having the shape F11 from the catalyst layer 100 is promoted.

[0030] In this specification, "equal intervals" means equal intervals including, in addition to completely equal intervals, errors generally acceptable in the technical field and not contrary to the gist of the technology of the present disclosure. "Unequal intervals" means all intervals other than equal intervals.

[0031] In a cross-section of the catalyst layer 100 parallel to the thickness direction T10, a plurality of first ends 11a are arranged at unequal intervals along the first main surface 10a, and the plurality of second ends 11b may be arranged at equal intervals along the second main surface 10b. According to such a configuration, the adjacent first ends 11a tend to take a structure approaching each other. Therefore, the pores 11p between the conductive columnar bodies 11 having such first ends 11a tend to have a shape F11 that expands from the first main surface 10a toward the second main surface 10b.

[0032] For example, as shown in FIG. 1A, the plurality of second ends 11b may be arranged along the second main surface 10b so as to be separated from each other by a distance D11b.

[0033] For example, as shown in FIGS. 1A and 1B, a plurality of first end portions 11a may be arranged to alternately repeat a first distance d1 and a second distance d2 along the first main surface 10a. In this case, the first distance d1 may correspond to the distance D11a from the nearest first end portion 11a to the first end portion 11a. That is, for the first distance d1 and the second distance d2, d1 < d2 may hold.

[0034] The arrangement of the plurality of second end portions 11b on the second main surface 10b is not particularly limited. On the second main surface 10b, the plurality of second end portions 11b may be arranged at equal intervals from each other, or may be arranged at unequal intervals from each other. As an aspect in which the plurality of second end portions 11b are arranged at equal intervals from each other on the second main surface 10b, for example, the second end portions 11b are respectively arranged at the lattice points of a square lattice, and one side of the square lattice is parallel to one side of the catalyst layer 100; the second end portions 11b are respectively arranged at the lattice points and the center point of the square lattice, and one side of the square lattice is parallel to one side of the catalyst layer 100, and the like. For example, when the plurality of second end portions 11b are arranged at the lattice points of a square lattice on the second main surface 10b, on the first main surface 10a, the plurality of first end portions 11a may not be arranged at the lattice points of the square lattice.

[0035] As described above, in the catalyst layer 100, the plurality of conductive columnar bodies 11 extend from the first main surface 10a toward the second main surface 10b. The plurality of conductive columnar bodies 11 may include a conductive columnar body 11 oriented at an angle α with respect to the first main surface 10a. All of the plurality of conductive columnar bodies 11 may be oriented at an angle α with respect to the first main surface 10a.

[0036] In this specification, as shown in FIG. 1B, the angle α is the smallest angle within the range greater than 0° and less than or equal to 90° between the first main surface 10a of the catalyst layer 100 and the outer surface 11c of the first end portion 11a of the conductive column 11 in the cross-section of the catalyst layer 100 parallel to the thickness direction T10. In this specification, among the surfaces of the conductive column 11, the longitudinal surface is defined as the outer surface 11c of the conductive column 11, and the lateral surface among the surfaces of the conductive column 11 is defined as the end surface 11d of the conductive column 11.

[0037] The angle α can be obtained, for example, by the following method. In the cross-sectional image obtained by the same method as above, for any number (for example, 1000) of the first end portions 11a, the smallest angle within the range greater than 0° and less than or equal to 90° between the first main surface 10a and the outer surface 11c of the first end portion 11a is measured. The average of the measured values can be regarded as the angle α.

[0038] The plurality of conductive columns 11 may include conductive columns 11 oriented in a direction perpendicular to the first main surface 10a. All of the plurality of conductive columns 11 may be oriented in a direction perpendicular to the first main surface 10a.

[0039] In this specification, the "perpendicular direction" means a direction in which the angle α with respect to the reference plane is greater than 80° and less than or equal to 90°. That is, the angle α may be greater than 80° and less than or equal to 90°.

[0040] The angle α may be greater than 0° and less than or equal to 80°. The angle α may be greater than or equal to 10° and less than or equal to 60°, and may also be greater than or equal to 10° and less than or equal to 30°.

[0041] In the catalyst layer 100 in Embodiment 1, the plurality of conductive columns 11 may have a number density of 10 2 or more per square centimeter 9 on the first main surface 10a. According to such a configuration, while realizing a high integration of the conductive columns 11, it is possible to suppress an increase in the diffusion resistance of reactants, particularly oxygen.

[0042] The plurality of conductive columnar bodies 11 may have a number density of 10 or more per 1 cm on the first main surface 10a, and may further have a number density of 10 or more. 2 per 10 cm, and may further have a number density of 10 or more. 11 cm.

[0043] The upper limit of the number density of the plurality of conductive columnar bodies 11 can be appropriately set according to, for example, the diameter of the conductive columnar bodies 11. For example, when the diameter of the conductive columnar bodies 11 is 10 nm, the plurality of conductive columnar bodies 11 may have a number density of less than 10 per 1 cm on the first main surface 10a. 2 per 12 cm.

[0044] The dimension in the longitudinal direction of the conductive columnar body 11 can be, for example, 1 μm or more and 100 μm or less. The dimension in the short direction orthogonal to the longitudinal direction of the conductive columnar body 11 can be, for example, 10 nm or more and 200 nm or less. When the conductive columnar body 11 has a cylindrical shape or a columnar shape such as a carbon nanotube, the dimension in the short direction of the conductive columnar body 11 means the diameter of the conductive columnar body 11.

[0045] The aspect ratio of the conductive columnar body 11 can be, for example, 5 or more and 100,000 or less. The aspect ratio of the conductive columnar body 11 is a value obtained by dividing the distance in the longitudinal direction of the conductive columnar body 11 by the distance in the short direction of the conductive columnar body 11. The aspect ratio of the conductive columnar body 11 can be obtained, for example, by the following method. In the TEM image or SEM image obtained by the same method as above, for any number (for example, 100) of conductive columnar bodies 11, the distance in the longitudinal direction and the distance in the short direction are measured, and the aspect ratio is calculated. The average of the calculated values can be regarded as the aspect ratio of the conductive columnar body 11.

[0046] The conductive column 11 is formed of a conductive material such as carbon. As the conductive column 11, for example, a conductive long material such as a carbon nanotube or a carbon fiber can be used. Thus, the conductive column 11 may include a carbon nanotube. When a carbon nanotube is used as the conductive column 11, a structure in which adjacent first ends 11a approach each other is easily realized in the cross section of the catalyst layer 100 parallel to the thickness direction T10. The carbon nanotube may have a single-layer structure or a multi-layer structure.

[0047] From the viewpoint of improving the catalytic activity and heat resistance, the catalyst particles 12 may be particles containing a noble metal such as platinum or a platinum alloy. Examples of the platinum alloy include an alloy of platinum and at least one selected from the group consisting of cobalt, nickel, ruthenium, and palladium. Each of the catalyst particles 12 may contain at least one noble metal selected from the group consisting of platinum, palladium, iridium, ruthenium, and rhodium.

[0048] The average particle diameter of the catalyst particles 12 is not particularly limited. From the viewpoints of catalyst utilization rate and durability, the average particle diameter of the catalyst particles 12 may be 1 nm or more and 30 nm or less. The average particle diameter is calculated, for example, from a transmission electron microscope (TEM) image of the catalyst particles 12. In the TEM image, the equivalent diameters of an arbitrary number (for example, 10) of catalyst particles 12 are measured. The average value of the equivalent diameters can be regarded as the average particle diameter of the catalyst particles 12. The equivalent diameter means the diameter of a circle having the same area. The same applies to other materials.

[0049] The catalyst layer 100 in Embodiment 1 may include an electrolyte resin and further include a coating layer that covers at least a part of the surface of each of the plurality of conductive columns 11. The electrolyte resin is an electrolyte having proton conductivity. The coating layer can connect the catalyst particles 12 and the conductive column 11 in a state where proton conduction is possible. Therefore, when the catalyst layer 100 includes a coating layer made of an electrolyte resin, an increase in the diffusion resistance of protons can be suppressed in addition to oxygen.

[0050] As the electrolyte resin contained in the coating layer, a polymer electrolyte having ion conductivity can be used. As the electrolyte resin contained in the coating layer, a perfluorocarbon sulfonic acid-based polymer material having a sulfonic acid group, a hydrocarbon-based polymer material, or the like can be used. As the electrolyte resin contained in the coating layer, a perfluorosulfonic acid resin may be used. The perfluorosulfonic acid resin exhibits excellent proton conductivity. The electrolyte resin contained in the coating layer typically includes a perfluorocarbon sulfonic acid-based polymer electrolyte having a sulfonic acid group.

[0051] The electrolyte resin contained in the coating layer 13 is also called an ionomer.

[0052] Hereinafter, examples of the catalyst layer further including the coating layer 13 containing the electrolyte resin will be described using Modifications 1 to 3. In Modifications 1 to 3, the same reference numerals may be used for elements common to the catalyst layer 100 described above, and detailed descriptions thereof may be omitted.

[0053] (Modification 1) FIG. 3 is a schematic cross-sectional view of the catalyst layer 101 in Modification 1. In the catalyst layer 101, the coating layer 13 includes a first coating portion 13a that covers the outer surface 11c of the first end portion 11a.

[0054] In the example shown in FIG. 3, when it is assumed that the first main surface 10a of the catalyst layer 101 is in contact with an electrolyte membrane (not shown) and a hydrogen-containing gas is used as the anode gas and an oxygen-containing gas is used as the cathode gas, the oxygen-containing gas supplied to the catalyst layer 101 from the cathode gas diffusion layer side (the upper side in FIG. 3) can move along the pores 11p. Protons moving from the electrolyte membrane side (the lower side in FIG. 3) can move along the coating layer 13. In the catalyst layer 101, the oxygen-containing gas reacts with electrons and protons that have moved through the external circuit, and as a result, water is generated.

[0055] According to the catalyst layer 101 in Modification 1, since the structure of the first end portion 11a can be controlled by the first covering portion 13a, in the cross-section of the catalyst layer 100 parallel to the thickness direction T10, a structure in which adjacent first end portions 11a approach each other can be realized. Therefore, the pores 11p between the conductive columnar bodies 11 having such first end portions 11a are likely to have a shape F11 that expands from the first main surface 10a toward the second main surface 10b. Accordingly, the discharge of water generated in the pores 11p having the shape F11 from the catalyst layer 100 is likely to be promoted.

[0056] As shown in FIG. 3, the covering layer 13 in Modification 1 may be the first covering portion 13a that covers the outer surface 11c of the first end portion 11a. In other words, the catalyst layer 101 may include only the first covering portion 13a that covers the outer surface 11c of the first end portion 11a as the covering layer 13.

[0057] As shown in FIG. 3, the covering layer 13 may not be formed in the pores 11p having the shape F11.

[0058] (Modification 2) FIG. 4 is a schematic cross-sectional view of the catalyst layer 102 in Modification 2. In the catalyst layer 102, the thickness of the covering layer 13 decreases from the first end portion 11a toward the second end portion 11b.

[0059] In the example shown in FIG. 4, when it is assumed that the first main surface 10a of the catalyst layer 102 is in contact with an electrolyte membrane (not shown) and a hydrogen-containing gas is used as the anode gas and an oxygen-containing gas is used as the cathode gas, the oxygen-containing gas supplied to the catalyst layer 102 from the cathode gas diffusion layer side (the upper side in FIG. 4) can move along the pores 11p. Protons that have moved from the electrolyte membrane side (the lower side in FIG. 4) can move along the covering layer 13. In the catalyst layer 102, the oxygen-containing gas reacts with electrons and protons that have moved through the external circuit, and as a result, water is generated.

[0060] According to the catalyst layer 102 in Modification 2, since the structure of the first end portion 11a can be controlled by the coating layer 13, in the cross-section of the catalyst layer 100 parallel to the thickness direction T10, a structure in which adjacent first end portions 11a approach each other can be realized. Therefore, the pores 11p between the conductive columnar bodies 11 having such first end portions 11a tend to have a shape F11 that expands from the first main surface 10a toward the second main surface 10b. Accordingly, the discharge of water generated in the pores 11p having the shape F11 from the catalyst layer 100 is likely to be promoted. In addition, since the electrolyte resin is arranged with a distribution, an oxygen diffusion path and a proton diffusion path can be secured in the pores 11p while suppressing the blockage of the pores 11p by the electrolyte resin.

[0061] As shown in FIG. 4, the coating layer 13 of Modification 2 may include a first coating portion 13a.

[0062] The coating layer 13 of Modification 2 does not have to cover the entire surface of each of the plurality of conductive columnar bodies 11.

[0063] As shown in FIG. 4, the coating layer 13 does not have to be formed in the pores 11p having the shape F11.

[0064] In the example shown in FIG. 4, the coating layer 13 does not cover the outer surface 11c of the second end portion 11b. However, the coating layer 13 may cover the outer surface 11c of the second end portion 11b.

[0065] (Modification 3) FIG. 5 is a schematic cross-sectional view of the catalyst layer 103 in Modification 3. In the catalyst layer 103, the coating layer 13 includes a second coating portion 13b that covers the end face 11d of the first end portion 11a.

[0066] In the example shown in FIG. 5, assuming that the first main surface 10a of the catalyst layer 103 is in contact with an electrolyte membrane (not shown) and a hydrogen-containing gas is used as the anode gas and an oxygen-containing gas is used as the cathode gas, the oxygen-containing gas supplied to the catalyst layer 102 from the cathode gas diffusion layer side (the upper side in FIG. 5) can move along the pores 11p. Protons moving from the electrolyte membrane side (the lower side in FIG. 5) can move along the coating layer 13. In the catalyst layer 103, the oxygen-containing gas reacts with electrons and protons that have moved through the external circuit, and as a result, water is generated.

[0067] According to the catalyst layer 103 in Modification 3, since the structure of the first end portion 11a can be controlled by the second covering portion 13b, in the cross section of the catalyst layer 100 parallel to the thickness direction T10, a structure in which adjacent first end portions 11a approach each other can be realized. Therefore, the pores 11p between the conductive columnar bodies 11 having such first end portions 11a tend to have a shape F11 that expands from the first main surface 10a toward the second main surface 10b. Accordingly, the discharge of water generated in the pores 11p having the shape F11 from the catalyst layer 100 is easily promoted. In addition, by the second covering portion 13b located on the first main surface 10a side, when the electrolyte membrane and the catalyst layer 103 are joined, which will be described later, the first end portion 11a of the conductive columnar body 11 can be suppressed from piercing the electrolyte membrane. Thereby, quality defects such as pinholes and tears in the electrolyte membrane are suppressed.

[0068] As shown in FIG. 5, the coating layer 13 in Modification 3 may include a first covering portion 13a. The first covering portion 13a and the second covering portion 13b may be integrated.

[0069] The coating layer 13 of Modification 3 does not have to cover the entire surface of each of the plurality of conductive columnar bodies 11.

[0070] In the example shown in FIG. 5, the coating layer 13 does not cover the outer surface 11c of the second end portion 11b. However, the coating layer 13 may cover the outer surface 11c of the second end portion 11b.

[0071] In the catalyst layer 103 in Modification 3, the first end portion 11a may be joined to an electrolyte membrane, which will be described later, via the second coating portion 13b.

[0072] The catalyst layers 100, 101, 102, and 103 described above can be manufactured, for example, by the following method.

[0073] First, a plurality of conductive columnar bodies 11 are formed on a substrate. As a method of forming a plurality of conductive columnar bodies 11 on a substrate, for example, after supporting metal fine particles on a substrate on which a metal thin film is formed, a method of growing carbon nanotubes on the substrate using a thermal CVD method, a plasma CVD method, or the like can be mentioned. When the metal fine particles are arranged at a high density, the carbon nanotubes can grow vertically with respect to the substrate by supporting each other during the growth of the carbon nanotubes.

[0074] Next, catalyst particles are supported on the carbon nanotubes on the substrate. The method of supporting a catalyst on the carbon nanotubes is not particularly limited. For example, either a wet method or a dry method may be used.

[0075] Next, if necessary, a material containing an electrolyte resin is coated on the carbon nanotubes on the substrate. The method of coating a material containing an electrolyte resin on the carbon nanotubes is not particularly limited. For example, a solution containing a precursor of the electrolyte resin may be impregnated into the carbon nanotubes and dried, and then polymerized by irradiation with radiation such as ultraviolet rays or heating. For example, by adjusting the amount of the material containing the electrolyte resin, a structure in which the adjacent first end portions 11a approach each other can be realized.

[0076] Finally, an electrolyte membrane is disposed on the carbon nanotubes on the substrate and hot-pressed to peel the substrate from the carbon nanotubes. Thereby, a catalyst layer can be obtained in which the first main surface 10a of the catalyst layer is disposed in contact with the electrolyte membrane.

[0077] (Embodiment 2) Hereinafter, Embodiment 2 will be described with reference to FIGS. 6A to 7.

[0078] [2-1. Configuration] FIG. 6A is a schematic cross-sectional view of a membrane electrode assembly 200 for an electrochemical device according to Embodiment 2. FIG. 6B is a partially enlarged view of region C in FIG. 6A. FIG. 7 is a schematic cross-sectional view of an electrochemical device 300 according to Embodiment 2. The electrochemical device 300 includes a membrane electrode assembly 200, an anode separator 301, a cathode separator 302, and a power source 307. The membrane electrode assembly 200 is disposed between the anode separator 301 and the cathode separator 302.

[0079] In the present embodiment, the electrochemical device 300 may be used in a fuel cell. In this way, a fuel cell with high power generation performance and high efficiency can be obtained.

[0080] In the example shown in FIG. 7, the electrochemical device 300 is a polymer electrolyte fuel cell (PEFC) that generates electricity by receiving a supply of a hydrogen-containing gas G1 as an anode gas and an oxygen-containing gas G3 as a cathode gas. The electrochemical device 300 may be used as other electrochemical devices such as a hydrogen purification device for purifying hydrogen and a water electrolysis device for electrolyzing water, in addition to a fuel cell.

[0081] As shown in FIG. 6A, the membrane electrode assembly 200 has an anode 202, an electrolyte membrane 201, and a cathode 203. The electrolyte membrane 201 is disposed between the anode 202 and the cathode 203. The anode 202 is joined to one surface of the electrolyte membrane 201. The cathode 203 is joined to the other surface of the electrolyte membrane 201.

[0082] The anode 202 has an anode catalyst layer 204 and an anode gas diffusion layer 205. The anode catalyst layer 204 is disposed between the electrolyte membrane 201 and the anode gas diffusion layer 205. The cathode 203 has a cathode catalyst layer 206 and a cathode gas diffusion layer 207. The cathode catalyst layer 206 is disposed between the electrolyte membrane 201 and the cathode gas diffusion layer 207.

[0083] The electrolyte membrane 201 conducts proton conduction between the anode catalyst layer 204 and the cathode catalyst layer 206. The electrolyte membrane 201 is made of a polymer material having proton conductivity and gas barrier properties. Typically, the electrolyte membrane 201 is a perfluorocarbon sulfonic acid-based or hydrocarbon-based polymer electrolyte membrane having sulfonic acid groups. The electrolyte membrane 201 may be a perfluorosulfonic acid-based polymer electrolyte membrane. The perfluorosulfonic acid-based polymer electrolyte membrane exhibits excellent proton conductivity and exists stably even in the power generation environment of the electrochemical device 300.

[0084] The electrolyte membrane 201 has a surface in contact with the anode catalyst layer 204 and a surface in contact with the cathode catalyst layer 206. These surfaces are flat surfaces. When the surface of the electrolyte membrane 201 is a flat surface, the drainage property on the surface of the electrolyte membrane 201 is good. The "flat surface" means a surface that has not been processed to provide unevenness.

[0085] The anode catalyst layer 204 has a function of promoting an electrochemical reaction that dissociates hydrogen into protons. The anode catalyst layer 204 includes a conductive material and catalyst particles supported on the conductive material. The anode catalyst layer 204 may cover at least a part of the surface of the conductive material and include a coating layer made of an electrolyte resin.

[0086] The membrane electrode assembly 200 may include, as the anode catalyst layer 204, the catalyst layers 100, 101, 102, or 103 described in Embodiment 1.

[0087] The anode gas diffusion layer 205 has a function of supplying the hydrogen-containing gas G1 to the anode catalyst layer 204 and a function of receiving electrons from the anode catalyst layer 204. The anode gas diffusion layer 205 is composed of a material having gas permeability, water repellency, and conductivity. The anode gas diffusion layer 205 has, as a main material, for example, a porous body having conductivity. Examples of the porous body include a carbon fiber aggregate such as carbon paper.

[0088] The cathode catalyst layer 206 has a function of promoting an electrochemical reaction that generates water from protons and oxygen. The cathode catalyst layer 206 includes a conductive material and catalyst particles supported on the conductive material. The cathode catalyst layer 206 may include a coating layer made of an electrolyte resin that covers at least a part of the surface of the conductive material.

[0089] In the present embodiment, the cathode 203 includes the catalyst layers 100, 101, 102, or 103 described in Embodiment 1. That is, the membrane electrode assembly 200 includes the catalyst layers 100, 101, 102, or 103 described in Embodiment 1 as the cathode catalyst layer 206. FIG. 6B is an example in the case where the membrane electrode assembly 200 includes the catalyst layer 100 as the cathode catalyst layer 206. As shown in FIG. 6B, the first main surface 10a of the cathode catalyst layer 206 is in contact with the electrolyte membrane 201. According to such a configuration, the discharge of water generated in the pores 11p from the cathode catalyst layer 206 is promoted, so that the blockage of the pores 11p by water is suppressed. As a result, an increase in the diffusion resistance of reactants, particularly oxygen, in the cathode catalyst layer 206 is suppressed. Thereby, the power generation performance of the electrochemical device 300 using the membrane electrode assembly 200 can be improved.

[0090] Although not shown, when the cathode catalyst layer 206 further includes a coating layer 13 made of an electrolyte resin, the electrolyte membrane 201 and the plurality of conductive columnar bodies 11 may be adhered by the coating layer 13.

[0091] The cathode gas diffusion layer 207 has a function of supplying an oxygen-containing gas to the cathode catalyst layer 206 and a function of transferring electrons to the cathode catalyst layer 206. The cathode gas diffusion layer 207 is composed of a material having gas permeability, water repellency, and conductivity. The cathode gas diffusion layer 207 mainly has, for example, a porous body having conductivity. Examples of the porous body include a carbon fiber aggregate such as carbon paper.

[0092] The anode catalyst layer 204 may have the same structure as that of the cathode catalyst layer 206 or may have a different structure.

[0093] As shown in FIG. 7, the anode separator 301 has an anode gas inlet 303, an anode gas outlet 304, and an anode gas flow path 301g. The anode gas flow path 301g is a groove-shaped gas flow path that guides the hydrogen-containing gas G1 to the anode 202. The anode gas inlet 303 is provided at the upstream end of the anode gas flow path 301g. The anode gas outlet 304 is provided at the downstream end of the anode gas flow path 301g. The hydrogen-containing gas G1 is introduced from the outside into the anode gas flow path 301g through the anode gas inlet 303. The unreacted hydrogen-containing gas G2 is discharged from the anode gas flow path 301g to the outside through the anode gas outlet 304.

[0094] The cathode separator 302 has a cathode gas inlet 305, a cathode gas outlet 306, and a cathode gas flow path 302g. The cathode gas flow path 302g is a groove-shaped gas flow path that guides the oxygen-containing gas G3 to the cathode 203. The cathode gas inlet 305 is provided at the upstream end of the cathode gas flow path 302g. The cathode gas outlet 306 is provided at the downstream end of the cathode gas flow path 302g. The oxygen-containing gas G3 is introduced from the outside into the cathode gas flow path 302g through the cathode gas inlet 305. The unreacted oxygen-containing gas G4 is discharged from the cathode gas flow path 302g to the outside through the cathode gas outlet 306.

[0095] The shapes of the anode gas flow path 301g and the cathode gas flow path 302g are not particularly limited. The anode gas flow path 301g and the cathode gas flow path 302g may each have a serpentine shape. The serpentine shape is the shape of a flow path in which one or more flow paths meander in a plane. When the anode gas flow path 301g and the cathode gas flow path 302g have the above-described shapes, gas can be supplied to the entire catalyst layers 204 and 206 at a constant flow rate. As a result, gas can easily reach all of the catalyst particles.

[0096] The anode separator 301 and the cathode separator 302 are made of a conductive material. The anode separator 301 and the cathode separator 302 may each be made of a conductive material such as carbon or metal. In order to prevent corrosion, the anode separator 301 and the cathode separator 302 may be provided with a corrosion-resistant coating such as resin or plating.

[0097] [2-2. Operation] Regarding the electrochemical device 300 configured as described above, its operation and action will be described below with reference to FIG. 7.

[0098] A hydrogen-containing gas G1 is supplied from the anode gas inlet 303 to the anode gas flow path 301g of the anode separator 301. The hydrogen-containing gas G1 is a humidified hydrogen gas. As a result, the hydrogen-containing gas G1 is supplied to the anode catalyst layer 204 through the anode gas diffusion layer 205. An oxygen-containing gas G3 is supplied from the cathode gas inlet 305 to the cathode gas flow path 302g of the cathode separator 302. The oxygen-containing gas G3 is humidified air. As a result, the oxygen-containing gas G3 is supplied to the cathode catalyst layer 206 through the cathode gas diffusion layer 207. A current is applied by the power source 307 between the anode catalyst layer 204 to which the hydrogen-containing gas G1 is supplied and the cathode catalyst layer 206 to which the oxygen-containing gas G3 is supplied.

[0099] In the anode catalyst layer 204 supplied with the hydrogen-containing gas G1, an oxidation reaction occurs in which hydrogen (H2) dissociates into protons (H + ) and electrons (e - ) according to the electrochemical reaction represented by the following formula (I). The protons pass through the electrolyte membrane 201 and move to the cathode catalyst layer 206. The electrons dissociated in the anode catalyst layer 204 move from the anode 202 toward the cathode 203 through an external circuit (not shown) and reach the cathode catalyst layer 206. In the cathode catalyst layer 206, a reduction reaction occurs in which water (H2O) is generated by an electrochemical reaction of protons, oxygen (O2), and electrons according to the electrochemical reaction represented by the following formula (II). The protons used in this reduction reaction are the protons that dissociated by the oxidation reaction in the anode catalyst layer 204 shown in the following formula (I) and passed through the electrolyte membrane 201 to move to the cathode catalyst layer 206.

[0100] H2→2H + +2e - (I) 4H + +O2+2e - →2H2O (II)

[0101] (Other Embodiments) As described above, as examples of the technology disclosed in the present application, Embodiments 1 to 2 have been described. However, the technology in the present disclosure is not limited thereto, and can also be applied to embodiments with changes, additions, omissions, etc. Further, it is also possible to combine the respective components described in the above embodiments and modification examples to form a new embodiment.

[0102] Note that the above embodiments are for exemplifying the technology in the present disclosure, and various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or their equivalents.

[0103] (Supplementary Note) With the description of the above embodiments, the following technology is disclosed.

[0104] (Technology 1) A catalyst layer having a first main surface and a second main surface opposite to the first main surface, a plurality of conductive columnar bodies extending from the first main surface toward the second main surface; catalyst particles supported on the plurality of conductive columnar bodies; and comprising defining an end portion of the conductive columnar body located on the first main surface side as a first end portion, and when measuring the distance between adjacent first end portions, there exists a cross-section of the catalyst layer parallel to the thickness direction in which 30% or more of the obtained measurement values are 20 nm or less. A catalyst layer for an electrochemical device.

[0105] According to the catalyst layer for an electrochemical device of Technique 1, an increase in diffusion resistance of reactants, particularly oxygen, is suppressed.

[0106] (Technique 2) When defining an end portion of the conductive columnar body located on the second main surface side as a second end portion, a plurality of the first end portions are arranged at unequal intervals along the first main surface, and a plurality of the second end portions are arranged at equal intervals along the second main surface. The catalyst layer for an electrochemical device according to Technique 1. According to such a configuration, an increase in diffusion resistance of reactants, particularly oxygen, in the catalyst layer is suppressed.

[0107] (Technique 3) The plurality of conductive columnar bodies have a number density of 10 2 or more per 1 cm 9 on the first main surface. The catalyst layer for an electrochemical device according to Technique 1 or 2. According to such a configuration, while realizing high integration of the conductive columnar bodies, an increase in diffusion resistance of reactants, particularly oxygen, in the catalyst layer can be suppressed.

[0108] (Technique 4) A catalyst layer for an electrochemical device according to any one of Technologies 1 to 3, further comprising a coating layer containing an electrolyte resin and covering at least a part of the surface of each of the plurality of conductive columnar bodies. According to such a configuration, an increase in the diffusion resistance of protons can be suppressed in addition to oxygen.

[0109] (Technology 5) The catalyst layer for an electrochemical device according to Technology 4, wherein the coating layer includes a first coating portion that covers the outer surface of the first end portion. According to such a configuration, an increase in the diffusion resistance of reactants, particularly oxygen, in the catalyst layer is suppressed.

[0110] (Technology 6) When an end portion of the conductive columnar body located on the second main surface side is defined as a second end portion, the thickness of the coating layer decreases from the first end portion toward the second end portion. The catalyst layer for an electrochemical device according to Technology 4 or 5. According to such a configuration, an increase in the diffusion resistance of reactants, particularly oxygen, in the catalyst layer is suppressed. In addition, while suppressing the clogging of pores by the electrolyte resin, an oxygen diffusion path and a proton diffusion path can be secured in the pores.

[0111] (Technology 7) The catalyst layer for an electrochemical device according to any one of Technologies 4 to 6, wherein the coating layer includes a second coating portion that covers the end face of the first end portion. According to such a configuration, an increase in the diffusion resistance of reactants, particularly oxygen, in the catalyst layer is suppressed. In addition, quality defects such as pinholes and breaks in the electrolyte membrane are suppressed.

[0112] (Technology 8) The catalyst layer for an electrochemical device according to any one of Technologies 4 to 7, wherein the conductive columnar body includes carbon nanotubes. According to such a configuration, an increase in the diffusion resistance of reactants, particularly oxygen, in the catalyst layer is suppressed.

[0113] (Technology 9) An anode, A cathode, An electrolyte membrane disposed between the anode and the cathode, comprising The cathode includes a catalyst layer for an electrochemical device according to any one of Technologies 1 to 8, In the cathode, the first main surface of the catalyst layer for the electrochemical device is in contact with the electrolyte membrane. A membrane electrode assembly for an electrochemical device.

[0114] According to the membrane electrode assembly for an electrochemical device of Technology 9, the power generation performance of an electrochemical device using the membrane electrode assembly can be improved.

[0115] (Technology 10) An electrochemical device comprising the membrane electrode assembly for an electrochemical device according to Technology 9, An electrochemical device.

[0116] According to the electrochemical device of Technology 10, an electrochemical device excellent in power generation performance can be realized.

Industrial Applicability

[0117] The present disclosure is useful for electrochemical devices such as fuel cells, hydrogen purification devices, and water electrolysis devices.

Explanation of Signs

[0118] 100, 101, 102, 103 Catalyst layer 10a First main surface 10b Second main surface 11 Conductive columnar body 11a First end 11b Second end 11c Outer surface 11d End face 11p Pore 12 Catalyst particle 13 Coating layer (electrolyte resin) 13a First coating portion 13b Second coating portion D11a Distance between the first ends 11a d1 First distance d2 Second distance D11b Distance between the second ends 11b T10 Thickness direction 200 Membrane electrode assembly 201 Electrolyte membrane 202 Anode 203 Cathode 204 Anode catalyst layer 205 Anode gas diffusion layer 206 Cathode catalyst layer 207 Cathode gas diffusion layer 300 Electrochemical device 301 Anode separator 301g Anode gas flow path 302 Cathode separator 302g Cathode gas flow path 303 Anode gas inlet 304 Anode gas outlet 305 Cathode gas inlet 306 Cathode gas outlet 307 Power source

Claims

1. A catalyst layer having a first main surface and a second main surface opposite to the first main surface, a plurality of conductive columnar bodies extending from the first main surface toward the second main surface, catalyst particles supported on the plurality of conductive columnar bodies, comprising: defining an end portion of the conductive columnar body located on the first main surface side as a first end portion, and when measuring the distance between adjacent first end portions, there exists a cross-section of the catalyst layer parallel to the thickness direction in which 30% or more of the obtained measurement value is 20 nm or less, A catalyst layer for an electrochemical device.

2. When defining an end portion of the conductive columnar body located on the second main surface side as a second end portion, a plurality of the first end portions are arranged at unequal intervals along the first main surface, and a plurality of the second end portions are arranged at equal intervals along the second main surface, The catalyst layer for an electrochemical device according to Claim 1.

3. The plurality of conductive columnar bodies have a number density of 10 or more per 1 cm 2 on the first main surface. 9 ​ The catalyst layer for an electrochemical device according to Claim 1.

4. Further comprising a coating layer containing an electrolyte resin and covering at least a part of the surface of each of the plurality of conductive columnar bodies, The catalyst layer for an electrochemical device according to Claim 1.

5. The coating layer includes a first coating portion covering the outer surface of the first end portion, The catalyst layer for an electrochemical device according to Claim 4.

6. When defining an end portion of the conductive columnar body located on the second main surface side as a second end portion, the thickness of the coating layer decreases from the first end portion toward the second end portion, The catalyst layer for an electrochemical device according to Claim 4.

7. The coating layer includes a second coating portion covering the end face of the first end portion, The catalyst layer for an electrochemical device according to Claim 4.

8. The conductive columnar body includes carbon nanotubes, The catalyst layer for an electrochemical device according to Claim 4.

9. An anode, A cathode, An electrolyte membrane disposed between the anode and the cathode, comprising: The cathode includes the catalyst layer for an electrochemical device according to any one of Claims 1 to 8, In the cathode, the first main surface of the catalyst layer for an electrochemical device is in contact with the electrolyte membrane, A membrane electrode assembly for an electrochemical device.

10. An electrochemical device comprising the membrane electrode assembly for an electrochemical device according to Claim 9. An electrochemical device.

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