Catalyst layer for electrochemical device, membrane electrode assembly for electrochemical device, electrochemical device, and method for manufacturing catalyst layer for electrochemical device

Abstract

To provide a catalyst layer for an electrochemical device, suitable for improving a utilization rate of catalyst particles supported on a conductive material.SOLUTION: A catalyst layer 100 for an electrochemical device of the present disclosure includes: a mesoporous first conductive material 21 having pores 21p; catalyst particles 22 disposed inside the pores 21p of the first conductive material 21; a first ionomer 41 adhered to an internal surfaces 21a of the pores 21p of the first conductive material 21; and a second ionomer 42 having a density smaller than that of the first ionomer 41 and adhered to a surface 21b of the first conductive material 21 at the outside of the pores 21p.SELECTED DRAWING: Figure 2B

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses an electrode catalyst layer of an electrochemical device including a mesoporous material, a catalyst metal supported at least inside the mesoporous material, and an ionomer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a catalyst layer for an electrochemical device suitable for improving the utilization rate of catalyst particles supported on a conductive material.

Means for Solving the Problems

[0005] The catalyst layer for an electrochemical device in the present disclosure is a porous first conductive material having pores, catalyst particles disposed inside the pores of the first conductive material, a first ionomer attached to the inner surface of the pores of the first conductive material, a second ionomer having a density smaller than the density of the first ionomer and attached to the surface of the first conductive material outside the pores, and includes.

[0006] In another aspect, the membrane electrode assembly for an electrochemical device in the present disclosure is An anode, a cathode, an electrolyte membrane disposed between the anode and the cathode, and the cathode includes a catalyst layer for an electrochemical device of the present disclosure.

[0007] In another aspect, an electrochemical device in the present disclosure includes a membrane electrode assembly for an electrochemical device of the present disclosure.

[0008] In still another aspect, a method for manufacturing a catalyst layer for an electrochemical device in the present disclosure includes preparing a first catalyst solution by dispersing a porous first conductive material containing catalyst particles disposed inside pores and a first ionomer in a first solvent, allowing the first catalyst solution to stand, preparing a second catalyst solution by dispersing a second ionomer having a density smaller than the density of the first ionomer in the first catalyst solution after standing, forming a coated film by applying the second catalyst solution to a substrate, and removing a solvent from the coated film. and

Advantages of the Invention

[0009] According to the present disclosure, the utilization rate of catalyst particles supported on a conductive material in a catalyst layer for an electrochemical device can be improved.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

[0011] (Findings and the like on which the present disclosure is based) In order for the catalyst to be effectively utilized in the cathode catalyst layer of an electrochemical device, it is important that a three-phase interface is formed in the cathode catalyst layer. Conventionally, in order to form a three-phase interface in the cathode catalyst layer, it has been recognized that it is effective to uniformly coat a carrier supporting a catalyst with an ionomer from the viewpoints of water retention and drainage. The three-phase interface is the interface of the carrier, the catalyst, and the ionomer. At the three-phase interface, protons (H + ) and electrons (e - ) can move. However, in recent years, it has become clear that the catalyst is poisoned and deteriorated by the ionomer. Specifically, the catalyst may be poisoned by a functional group such as a sulfonic acid group of the ionomer, particularly a functional group containing a sulfur atom. When the inventors of the present invention arrived at the present disclosure, suppressing the contact between the ionomer and the catalyst particles was achieved by supporting the catalyst particles inside the pores of the porous conductive material.

[0012] Under such circumstances, the inventors have obtained the finding that when the ionomer blocks the pores of the porous conductive material, gases such as protons and oxygen are not sufficiently diffused to the catalyst particles located inside the pores of the conductive material. If gases such as protons and oxygen are not sufficiently diffused to the catalyst particles, the catalyst particles located inside the pores of the conductive material cannot be sufficiently utilized. On the other hand, if the amount of the ionomer coating the conductive material is reduced to suppress the blockage of the pores by the ionomer, the ionomer becomes discontinuous in the cathode catalyst layer, and as a result, the proton diffusion resistance of the membrane electrode assembly increases.

[0013] Therefore, the inventors focused on the density of the ionomer. An ionomer with a relatively high density is likely to be disposed inside the pores of the conductive material. The ionomer with a relatively high density disposed inside the pores can promote the diffusion of protons to the catalyst particles located inside the pores. On the other hand, an ionomer with a relatively low density is likely to be disposed on the surface of the conductive material. Since the ionomer with a relatively low density has excellent gas permeability, even if the pores are blocked, the diffusion of gases such as oxygen into the pores is less likely to be inhibited. Based on these findings, the inventors have come to constitute the subject matter of the present disclosure in order to improve the utilization rate of the catalyst particles supported on the conductive material.

[0014] The present disclosure provides a catalyst layer for an electrochemical device suitable for improving the utilization rate of catalyst particles supported on a conductive material.

[0015] 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 already 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.

[0016] The accompanying drawings and the following description are provided for the parties to fully understand the present disclosure and are not intended to limit the subject matter described in the claims thereby.

[0017] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to FIGS. 1 to 3.

[0018] [1-1. Configuration] FIG. 1 is a schematic cross-sectional view of a catalyst layer 100 for an electrochemical device according to Embodiment 1. The catalyst layer 100 can be used in an electrochemical device such as a fuel cell. The catalyst layer 100 includes a porous first conductive material 21, catalyst particles 22, a first ionomer 41, and a second ionomer 42. The first conductive material 21 has a plurality of pores 21p. The catalyst particles 22 are disposed inside the pores 21p of the first conductive material 21. An electrochemical reaction is promoted on the surface of the catalyst particles 22. The second ionomer 42 has a density smaller than that of the first ionomer 41. Hereinafter, for convenience, the first conductive material 21 supporting the catalyst particles 22 may be referred to as a first electrode catalyst 20.

[0019] FIG. 2A is a schematic cross-sectional view showing the first conductive material 21 included in the catalyst layer 100 of FIG. 1 together with the catalyst particles 22, the first ionomer 41, and the second ionomer 42. FIG. 2B is an enlarged view of part A of FIG. 2A. As shown in FIGS. 2A and 2B, in the catalyst layer 100, the first ionomer 41 adheres to the inner surface 21a of the pores 21p of the first conductive material 21, and the second ionomer 42 adheres to the surface 21b of the first conductive material 21 outside the pores 21p. Due to such a structure, as shown in FIG. 2B, protons (H + ) can reach the catalyst particles 22 disposed inside the pores 21p through the first ionomer 41 adhering to the inner surface 21a of the pores 21p. Since the second ionomer 42 has a density smaller than that of the first ionomer 41, it has higher gas permeability than the first ionomer 41. Therefore, as shown in FIG. 2B, even if there is a second ionomer 42 positioned to cover the pores 21p, oxygen (O2) can diffuse to the catalyst particles 22 disposed inside the pores 21p. As a result, the proton conductivity and the gas diffusibility such as oxygen to the catalyst particles 22 disposed inside the pores 21p can be enhanced, and the ratio of the catalyst particles 22 with sufficient supply of gas, protons, and electrons (e - ) can be increased. Therefore, according to the catalyst layer 100, the utilization rate of the catalyst particles 22 supported by the first conductive material 21 can be improved.

[0020] The density of the first ionomer 41 and the density of the second ionomer 42 can be determined, for example, by the following method using a catalyst layer formation process simulator based on the molecular dynamics coarse-graining method. First, the ionomer is placed on the surface of the Pt nanoparticles to obtain a simulation result showing the density of the ionomer in the vicinity of the interface between the Pt nanoparticles and the ionomer. The simulation result shows the relationship between the distance from the surface of the Pt nanoparticles and the density of the ionomer. The average value of the density (g / cm 3 ) of the ionomer in the range where the distance from the surface of the Pt nanoparticles is 7 Å or less can be regarded as the density of the ionomer.

[0021] The density of the first ionomer 41 and the density of the second ionomer 42 can also be determined, for example, by the pycnometer method. Specifically, for example, the volume of the ionomer sample is determined using a He gas replacement type pycnometer. The density of the ionomer can be calculated from the obtained volume and the mass of the ionomer sample measured separately.

[0022] As long as the density of the second ionomer 42 is smaller than the density of the first ionomer 41, the density of the first ionomer 41 and the density of the second ionomer 42 are not particularly limited. The density of the first ionomer 41 can be appropriately set according to the density of the second ionomer 42. Alternatively, the density of the second ionomer 42 can be appropriately set according to the density of the first ionomer 41. The density of the first ionomer 41 may be, for example, in the range of 2.0 g / cm 3 to 3.3 g / cm 3 or less. The density of the second ionomer 42 may be, for example, in the range of 1.3 g / cm 3 to 2.0 g / cm 3 or less.

[0023] As the first ionomer 41 and the second ionomer 42, a polymer electrolyte having ion conductivity such as protons can be used. The first ionomer 41 and the second ionomer 42 connect the catalyst particles 22 and the first conductive material 21 in an ion-conductable state. As the first ionomer 41 and the second ionomer 42, for example, a perfluorocarbon sulfonic acid-based polymer material having a sulfonic acid group, a hydrocarbon-based polymer material, etc. can be used. As the first ionomer 41 and the second ionomer 42, a perfluorosulfonic acid resin may be used. The perfluorosulfonic acid resin exhibits excellent proton conductivity and stably exists even under the power generation environment of a fuel cell. The first ionomer 41 and the second ionomer 42 typically contain a perfluorocarbon sulfonic acid-based polymer electrolyte having a sulfonic acid group.

[0024] The first ionomer 41 may not contain a cyclic structure in the main chain and the side chain. An ionomer without a cyclic structure can reduce the volume of the ionomer and increase the density. Therefore, the first ionomer 41 without a cyclic structure easily penetrates into the pores 21p of the first conductive material 21. As a result, the proton conductivity to the catalyst particles 22 disposed inside the pores 21p can be improved. The cyclic structure may be a 5-membered ring structure or a 6-membered ring structure.

[0025] The first ionomer 41 may have a linear main chain and a linear side chain. The first ionomer 41 having a linear main chain and a linear side chain easily penetrates into the pores 21p of the first conductive material 21. As a result, the proton conductivity to the catalyst particles 22 disposed inside the pores 21p can be improved.

[0026] The first ionomer 41 may be represented by the following formula (1) containing a plurality of types of repeating units.

[0027]

Chemical formula

[0028] In the above formula (1), x and y independently represent numbers greater than 0.

[0029] The above formula (1) may be a random copolymer.

[0030] The molecular structure of the first ionomer 41 may be linear. An ionomer with a linear molecular structure can reduce the volume of the ionomer and increase the density. Therefore, the first ionomer 41 with a linear molecular structure is likely to penetrate into the pores 21p of the first conductive material 21. As a result, the proton conductivity to the catalyst particles 22 disposed inside the pores 21p can be improved.

[0031] The first ionomer 41 may have a molecular structure in which 20 hydrophobic parts and 10 hydrophilic parts are randomly bonded.

[0032] The second ionomer 42 may contain a cyclic structure in at least one selected from the group consisting of the main chain and the side chain. An ionomer containing a cyclic structure can increase the volume of the ionomer and decrease the density. Therefore, the second ionomer 42 containing a cyclic structure in at least one selected from the group consisting of the main chain and the side chain is likely to permeate gases such as oxygen. As a result, the gas diffusibility of gases such as oxygen to the catalyst particles 22 disposed inside the pores 21p can be further improved. The cyclic structure may be a 5-membered ring structure or a 6-membered ring structure.

[0033] The second ionomer 42 may contain a cyclic structure in the main chain. The second ionomer 42 containing a cyclic structure in the main chain is more likely to permeate gases such as oxygen. As a result, the gas diffusibility of gases such as oxygen to the catalyst particles 22 disposed inside the pores 21p can be further improved.

[0034] The second ionomer 42 may include cyclic structures in both the main chain and the side chain. The second ionomer 42 including cyclic structures in both the main chain and the side chain is more permeable to gases such as oxygen. As a result, the gas diffusibility of gases such as oxygen to the catalyst particles 22 disposed inside the pores 21p can be further improved.

[0035] The second ionomer 42 may be represented by the following formula (2) including a plurality of repeating units.

[0036] [Chemical formula]

[0037] In the above formula (2), m and n independently represent numbers greater than 0.

[0038] The molecular structure of the second ionomer 42 may be a curved shape. An ionomer having a curved molecular structure can increase the volume of the ionomer and decrease the density. Therefore, the second ionomer 42 having a curved molecular structure is permeable to gases such as oxygen. As a result, the gas diffusibility of gases such as oxygen to the catalyst particles 22 disposed inside the pores 21p can be further improved.

[0039] The molecular structure of the second ionomer 42 may have a hydrophilic block in which the polymer chain is composed of 20 repeating units of hydrophobic parts and 5 repeating units of hydrophilic parts at both ends, or the polymer chain is composed of 20 repeating units of hydrophobic parts and has a hydrophilic block composed of 10 repeating units of hydrophilic parts at one end.

[0040] From another aspect, the gas permeability of the second ionomer 42 to gases such as oxygen is higher than that of the first ionomer 41 to gases such as oxygen.

[0041] From another aspect, the invasiveness of the second ionomer 42 into the pores 21p is lower than that of the first ionomer 41 into the pores 21p. As used herein, the invasiveness of an ionomer into pores means the ease of invasion of the ionomer into the pores. The invasiveness of an ionomer into pores depends on the density of the ionomer. The greater the density of the ionomer, the more the invasiveness into the pores 21p can be improved.

[0042] The number average molecular weight of the second ionomer 42 may be smaller than the number average molecular weight of the first ionomer 41. In this case, the invasiveness of the first ionomer 41 into the pores 21p can be improved, and the invasiveness of the second ionomer 42 into the pores 21p can be suppressed. However, it is considered that the density of the ionomer has a greater influence on the invasiveness into the pores 21p than the number average molecular weight of the ionomer.

[0043] The number average molecular weight of the first ionomer 41 and the number average molecular weight of the second ionomer 42 can be measured, for example, by gel permeation chromatography (GPC). GPC is a measurement method in which a sample dissolved in a solvent is passed through a column packed with a porous filler, and the size of the molecules is determined from the rate of passage through the column. Also, if the molecular weight of the ionomer is known, it can also be measured by nuclear magnetic resonance (NMR).

[0044] The pores 21p open on the surface of the first conductive material 21. In other words, the surface of the first conductive material 21 has irregularities. The pores 21p may be communicating pores or independent pores.

[0045] As shown in FIG. 2A, catalyst particles 22 may be preferentially arranged inside the pores 21p of the first conductive material 21. In other words, the catalyst particles 22 may be unevenly distributed inside the pores 21p of the first conductive material 21.

[0046] As shown in FIG. 2B, the first ionomer 41 may preferentially adhere to the inner surface 21a of the pores 21p of the first conductive material 21. In other words, the first ionomer 41 may be unevenly distributed on the inner surface 21a of the pores 21p of the first conductive material 21.

[0047] As shown in FIG. 2B, the second ionomer 42 may preferentially adhere to the surface 21b of the first conductive material 21. In other words, the second ionomer 42 may be unevenly distributed on the surface 21b of the first conductive material 21.

[0048] The first conductive material 21 may be a porous conductive particle such as a carbon particle. The first conductive material 21 is typically mesoporous carbon particles. When the first conductive material 21 is mesoporous carbon particles, its average particle size is, for example, from 0.6 μm to 2.0 μm.

[0049] As shown in FIG. 1, the catalyst layer 100 may further include a fibrous second conductive material 31. The second ionomer 42 may adhere to the surface 31b of the second conductive material 31. According to such a structure, the second ionomer 42 attached to the surface 21b of the first conductive material 21 and the second ionomer 42 attached to the surface 31b of the second conductive material 31 are likely to be connected. Therefore, the proton conductivity in the catalyst layer 100 can be further improved.

[0050] The second conductive material 31 may be a fibrous carbon material. Examples of the fibrous carbon material include carbon nanofibers, carbon nanotubes, electrospun carbon fibers, vapor grown carbon fibers, polyacrylonitrile-based carbon fibers, and pitch-based carbon fibers. The second conductive material 31 may include at least one selected from the group consisting of carbon nanofibers and carbon nanotubes.

[0051] From the perspective of improving the catalytic activity and heat resistance, the catalyst particles 22 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 22 may contain at least one noble metal selected from the group consisting of platinum, palladium, iridium, ruthenium, and rhodium.

[0052] The average particle diameter of the catalyst particles 22 is not particularly limited. From the perspectives of catalyst utilization and durability, the average particle diameter of the catalyst particles 22 may be 1 nm or more and 10 nm or less. The average particle diameter is calculated, for example, from a transmission electron microscope (TEM) image of the catalyst particles 22. In the TEM image, the equivalent diameters of any number (for example, 10) of catalyst particles 22 are measured. The average value of the equivalent diameters can be regarded as the average particle diameter of the catalyst particles 22. The equivalent diameter means the diameter of a circle having the same area. The average particle diameters of other materials can also be determined by the same method.

[0053] Next, the method for manufacturing the above-described catalyst layer 100 will be described.

[0054] FIG. 3 is a flowchart showing an example of the method for manufacturing the catalyst layer 100. The method for manufacturing the catalyst layer 100 includes dispersing a porous first conductive material 21 containing catalyst particles 22 disposed inside the pores 21p and a first ionomer 41 in a first solvent to prepare a first catalyst solution (step S1), allowing the first catalyst solution to stand (step S2), dispersing a second ionomer 42 having a density smaller than the density of the first ionomer 41 in the first catalyst solution after standing to prepare a second catalyst solution (step S3), applying the second catalyst solution to a substrate to form a coating film (step S4), and removing the solvent from the coating film (step S5).

[0055] The manufacturing method may include, before step S1, disposing catalyst particles 22 inside the pores 21p of the first conductive material 21 to produce a first electrode catalyst 20 (step S0).

[0056] In step S0, the method for fabricating the first electrode catalyst 20 is not particularly limited. For example, after dispersing the first conductive material 21 in a solvent, a metal precursor solution such as a platinum precursor is added and stirred to prepare a mixed solution, and the obtained mixed solution is filtered and dried, so that the catalyst particles 22 may be disposed inside the pores 21p of the first conductive material 21. By controlling the deposition amount of the catalyst particles 22 with respect to the first conductive material 21, the catalyst particles 22 can be preferentially disposed inside the pores 21p.

[0057] Step S0 may include fabricating the first conductive material 21 having pores 21p. For example, after subjecting the raw material composite to heat treatment and then washing and drying it with dilute sulfuric acid, a porous first conductive material 21 may be fabricated.

[0058] In step S1, the first electrode catalyst 20 and the first ionomer 41 are dispersed in a first solvent to prepare a first catalyst solution. As the first solvent, for example, an aqueous ethanol solution can be used.

[0059] In step S2, the first catalyst solution is allowed to stand. The first ionomer 41 has a relatively large density. Therefore, by allowing the first catalyst solution to stand, the intrusion of the first ionomer 41 into the pores 21p of the first conductive material 21 is promoted. Thereby, the first ionomer 41 can be preferentially attached to the inner surface 21a of the pores 21p of the first conductive material 21.

[0060] The standing time in step S2 is, for example, 1 hour or more and 12 hours or less.

[0061] In step S3, the second ionomer 42 is dispersed in the first catalyst solution after standing to prepare a second catalyst solution. Since the second ionomer 42 has a relatively small density, the second ionomer 42 hardly penetrates into the pores 21p of the first conductive material 21. Thereby, the second ionomer 42 can be preferentially attached to the surface 21b of the first conductive material 21 outside the pores 21p.

[0062] Step S3 may include mixing the first catalyst solution after standing with a third catalyst solution in which the fibrous second conductive material 31 and the second ionomer 42 are dispersed in a second solvent. In the third catalyst solution, the second ionomer 42 adheres to the surface 31b of the second conductive material 31. As the second solvent, for example, an aqueous ethanol solution can be used.

[0063] In step S4, the second catalyst solution is applied to a substrate to form a coating film. The substrate may be the electrolyte membrane 201 described later or a transfer sheet.

[0064] In step S5, the solvent is removed from the coating film. The method for removing the solvent from the coating film is not particularly limited. For example, the solvent may be removed from the coating film by naturally drying the coating film or drying it by heating. Through step S5, the catalyst layer 100 is obtained.

[0065] [1-2. Operation] Regarding the catalyst layer 100 configured as described above, its operation and action will be described below with reference to FIG. 2B.

[0066] FIG. 2B shows an example in which the catalyst layer 100 is used as the cathode catalyst layer of a fuel cell. In FIG. 2B, it is assumed that a hydrogen-containing gas is used as the anode gas and an oxygen-containing gas is used as the cathode gas. Since the first ionomer 41 has a density greater than that of the second ionomer 42, it is likely to penetrate into the pores 21p. Therefore, as shown in FIG. 2B, protons (H +) can be reached. Since the second ionomer 42 has a density lower than that of the first ionomer 41, it has higher gas permeability than the first ionomer 41. Therefore, as shown in FIG. 2B, even if there is a second ionomer 42 positioned to cover the pores 21p, oxygen (O2) can diffuse to the catalyst particles 22 disposed inside the pores 21p. As a result, the proton conductivity and the gas diffusibility such as oxygen to the catalyst particles 22 disposed inside the pores 21p can be enhanced, and the supply of gas, protons, and electrons (e - ) can increase the proportion of the catalyst particles 22 with sufficient supply. Therefore, according to the catalyst layer 100, the utilization rate of the catalyst particles 22 supported on the first conductive material 21 can be improved.

[0067] (Embodiment 2) Hereinafter, Embodiment 2 will be described with reference to FIGS. 4 to 5.

[0068] [2-1. Configuration] FIG. 4 is a schematic cross-sectional view of a membrane electrode assembly 200 for an electrochemical device according to Embodiment 2. FIG. 5 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.

[0069] 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.

[0070] In the example shown in FIG. 5, 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 the fuel cell.

[0071] As shown in FIG. 4, the membrane electrode assembly 200 includes 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.

[0072] The anode 202 includes 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 includes 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.

[0073] The electrolyte membrane 201 conducts protons 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 a sulfonic acid group. 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 stably exists even in the power generation environment of the electrochemical device 300.

[0074] 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 irregularities.

[0075] 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 include a coating layer made of an electrolyte resin that covers at least a part of the surface of the conductive material.

[0076] The membrane electrode assembly 200 may include the catalyst layer 100 described in the first embodiment as the anode catalyst layer 204.

[0077] 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 mainly has, for example, a porous body having conductivity. Examples of the porous body include a carbon fiber aggregate such as carbon paper.

[0078] 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.

[0079] In the present embodiment, the cathode 203 includes the catalyst layer 100 described in the first embodiment. That is, the membrane electrode assembly 200 includes the catalyst layer 100 described in the first embodiment as the cathode catalyst layer 206. According to such a configuration, the discharge of water generated in the pores 21p from the cathode catalyst layer 206 is promoted, so that the clogging of the pores 21p 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.

[0080] 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 delivering 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.

[0081] The anode catalyst layer 204 may have the same structure as that of the cathode catalyst layer 206, or may have a different structure.

[0082] As shown in FIG. 5, 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. Through the anode gas inlet 303, the hydrogen-containing gas G1 is introduced from the outside into the anode gas flow path 301g. Through the anode gas outlet 304, the unreacted hydrogen-containing gas G2 is discharged from the anode gas flow path 301g to the outside.

[0083] 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. Through the cathode gas inlet 305, the oxygen-containing gas G3 is introduced from the outside into the cathode gas flow path 302g. Through the cathode gas outlet 306, the unreacted oxygen-containing gas G4 is discharged from the cathode gas flow path 302g to the outside.

[0084] 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 a 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. Thereby, gas can easily reach all of the catalyst particles.

[0085] 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.

[0086] [2-2. Operation] Regarding the electrochemical device 300 configured as described above, its operation and action will be described below with reference to FIG. 5.

[0087] 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. Thereby, 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. Thereby, 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 supplied with the hydrogen-containing gas G1 and the cathode catalyst layer 206 supplied with the oxygen-containing gas G3.

[0088] In the anode catalyst layer 204 supplied with the hydrogen-containing gas G1, hydrogen (H2) becomes a proton (H + ) and an electron (e -)A dissociation oxidation reaction occurs. 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 towards 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 in 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 reach the cathode catalyst layer 206.

[0089] H2→2H + +2e - (I) 4H + +O2+2e - →2H2O (II)

[0090] (Other Embodiments) As described above, as examples of the technology disclosed in this application, Embodiments 1 to 2 have been described. However, the technology in this disclosure is not limited thereto and can also be applied to embodiments with modifications, additions, omissions, etc. It is also possible to combine the respective components described in the above embodiments and modification examples to form a new embodiment.

[0091] Note that the above embodiments are for exemplifying the technology in this disclosure, and various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or their equivalents.

[0092] (Appendix) From the description of the above embodiments, the following technology is disclosed.

[0093] (Technology 1) A porous first conductive material having pores, Catalyst particles disposed inside the pores of the first conductive material, A first ionomer adhered to the inner surface of the pores of the first conductive material, A second ionomer having a density lower than that of the first ionomer and adhering to the surface of the first conductive material outside the pores, and provided with A catalyst layer for an electrochemical device.

[0094] According to the catalyst layer for an electrochemical device of Technology 1, the utilization rate of the catalyst particles supported on the first conductive material can be improved.

[0095] (Technology 2) The catalyst layer for an electrochemical device according to Technology 1, wherein the first ionomer does not include a cyclic structure and the second ionomer includes a cyclic structure. According to such a configuration, the proton conductivity to the catalyst particles disposed inside the pores can be improved.

[0096] (Technology 3) The catalyst layer for an electrochemical device according to Technology 2, wherein the second ionomer includes a cyclic structure in the main chain. According to such a configuration, the proton conductivity to the catalyst particles disposed inside the pores can be further improved.

[0097] (Technology 4) The catalyst layer for an electrochemical device according to any one of Technologies 1 to 3, wherein the number average molecular weight of the second ionomer is smaller than that of the first ionomer. According to such a configuration, the invasiveness of the first ionomer 41 into the pores 21p can be improved, and the invasiveness of the second ionomer 42 into the pores 21p can be suppressed.

[0098] (Technology 5) The catalyst layer for an electrochemical device according to any one of Technologies 1 to 4, further comprising a fibrous second conductive material, wherein the second ionomer is adhered to at least a part of the surface of the second conductive material. According to such a configuration, the proton conductivity in the catalyst layer can be further improved.

[0099] (Technology 6) An anode, and A cathode, and An electrolyte membrane disposed between the anode and the cathode, comprising, wherein the cathode includes a catalyst layer for an electrochemical device according to any one of Technologies 1 to 5, a membrane electrode assembly for an electrochemical device.

[0100] According to the membrane electrode assembly for an electrochemical device of Technology 6, an electrochemical device with high power generation performance and high efficiency can be obtained.

[0101] (Technology 7) An electrochemical device comprising the membrane electrode assembly according to Technology 6, an electrochemical device.

[0102] According to the electrochemical device of Technology 7, an electrochemical device with high power generation performance and high efficiency can be realized.

[0103] (Technology 8) Dispersing a porous first conductive material containing catalyst particles disposed inside pores and a first ionomer in a first solvent to prepare a first catalyst solution, allowing the first catalyst solution to stand, dispensing a second ionomer having a density smaller than that of the first ionomer into the first catalyst solution after standing to prepare a second catalyst solution, coating the second catalyst solution on a substrate to form a coated film, removing the solvent from the coated film, comprising, a method for manufacturing a catalyst layer for an electrochemical device.

[0104] According to the method for manufacturing a catalyst layer for an electrochemical device of Technology 8, a catalyst layer with improved utilization rate of catalyst particles supported on a conductive material can be manufactured.

[0105] (Technology 9) Preparing the second catalyst solution includes mixing a third catalyst solution in which a fibrous second conductive material and the second ionomer are dispersed in a second solvent with the first catalyst solution after standing. This is the method for manufacturing a catalyst layer for an electrochemical device according to Technique 8. According to such a configuration, a catalyst layer with improved proton conductivity can be manufactured.

Industrial Applicability

[0106] The present disclosure is useful for electrochemical devices such as fuel cells, hydrogen purification devices, and water electrolysis devices.

Explanation of Reference Numerals

[0107] 100 Catalyst layer 20 Electrode catalyst 21 First conductive material 21p Pore 21a Inner surface 21b Surface 22 Catalyst particles 31 Second conductive material 31b Surface 41 First ionomer 42 Second ionomer 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 porous first conductive material having pores, Catalyst particles disposed inside the pores of the first conductive material, A first ionomer attached to the inner surface of the pores of the first conductive material, A second ionomer having a density smaller than that of the first ionomer and attached to the surface of the first conductive material outside the pores, Comprising, A catalyst layer for an electrochemical device.

2. The first ionomer does not include a cyclic structure, The second ionomer includes a cyclic structure, The catalyst layer for an electrochemical device according to Claim 1.

3. The second ionomer includes a cyclic structure in the main chain, The catalyst layer for an electrochemical device according to Claim 2.

4. The number average molecular weight of the second ionomer is smaller than the number average molecular weight of the first ionomer, The catalyst layer for an electrochemical device according to Claim 1.

5. Further comprising a fibrous second conductive material, The second ionomer is attached to at least a part of the surface of the second conductive material, The catalyst layer for an electrochemical device according to Claim 1.

6. 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 5, A membrane electrode assembly for an electrochemical device.

7. Comprising the membrane electrode assembly according to Claim 6, An electrochemical device.

8. Dispersing a porous first conductive material containing catalyst particles disposed inside pores and a first ionomer in a first solvent to prepare a first catalyst solution, Allowing the first catalyst solution to stand, Dispersing a second ionomer having a density smaller than that of the first ionomer in the first catalyst solution after standing to prepare a second catalyst solution, Coating the second catalyst solution on a substrate to form a coated film, Removing the solvent from the coated film, Including, A method for manufacturing a catalyst layer for an electrochemical device.

9. Preparing the second catalyst solution, Includes mixing a third catalyst solution in which a fibrous second conductive material and the second ionomer are dispersed in a second solvent with the first catalyst solution after standing, The method for manufacturing a catalyst layer for an electrochemical device according to Claim 8.

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