Membrane electrode assembly, method for manufacturing membrane electrode assembly, and electrochemical device

Abstract

A membrane electrode assembly (113), wherein a cathode catalyst layer (109) contains a catalyst, an electroconductive carrier supporting the catalyst, and an ionomer having proton conductivity. The cathode catalyst layer (109) also has an inner portion for contacting an electrolyte membrane (102) and an outer portion for contacting or facing a cathode gas diffusion layer (110). When the ratio of the mass of the ionomer to the mass of the carrier is defined as the ionomer existence ratio, the ionomer existence ratio in the inner portion is lower than the ionomer existence ratio in the outer portion. In addition, the coating state of the carrier by the ionomer in the inner portion is different from the coating state of the carrier by the ionomer in the outer portion.

Description

Membrane electrode assembly, method for manufacturing membrane electrode assembly, and electrochemical device

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

[0002] For example, Patent Document 1 discloses a fuel cell comprising an electrode catalyst that has excellent performance in both drainage and water retention, i.e., water management, and is capable of realizing non-humidified operation of the fuel cell, and a catalyst layer formed from this electrode catalyst. The electrode catalyst comprises a carbon support that supports the catalyst and a polymer electrolyte, and the carbon support has a water immersion pH of 1 or less.

[0003] JP 2011-14488 A

[0004] In the prior art, it is desirable to suppress the deterioration of the catalyst in the cathode catalyst layer.

[0005] Therefore, the present disclosure provides a membrane electrode assembly that can suppress deterioration of the catalyst in the cathode catalyst layer, a method for manufacturing the membrane electrode assembly, and an electrochemical device.

[0006] A membrane electrode assembly according to one embodiment of the present disclosure includes an anode, a cathode, and a proton-conductive electrolyte membrane disposed between the anode and the cathode. The cathode includes a cathode gas diffusion layer and a cathode catalyst layer located between the cathode gas diffusion layer and the electrolyte membrane. The electrolyte membrane has a surface in contact with the cathode catalyst layer, and the surface in contact with the cathode catalyst layer is flat. The cathode catalyst layer includes a catalyst, a conductive carrier supporting the catalyst, and a proton-conductive ionomer, and has an inner portion in contact with the electrolyte membrane and an outer portion in contact with or facing the cathode gas diffusion layer. When the ionomer abundance ratio is defined as the ratio of the mass of the ionomer to the mass of the carrier, the ionomer abundance ratio in the inner portion is lower than the ionomer abundance ratio in the outer portion. The state of coverage of the carrier with the ionomer in the inner portion is different from the state of coverage of the carrier with the ionomer in the outer portion.

[0007] In another aspect, a method for producing a membrane electrode assembly according to one embodiment of the present disclosure includes a step of forming an inner portion of a cathode catalyst layer on a surface of a proton-conductive electrolyte membrane using a first solution containing a catalyst and a solvent but not an ionomer, and a step of forming an outer portion of a cathode catalyst layer to be located between the inner portion of the cathode catalyst layer and a cathode gas diffusion layer using a second solution containing an ionomer, a catalyst, and a solvent.

[0008] In yet another aspect, an electrochemical device according to one embodiment of the present disclosure includes the membrane electrode assembly of the present disclosure.

[0009] The membrane electrode assembly, the method for producing the membrane electrode assembly, and the electrochemical device according to the present disclosure can suppress deterioration of the catalyst in the cathode catalyst layer.

[0010] FIG. 1 is a schematic cross-sectional view showing the configuration of a polymer electrolyte fuel cell in embodiment 1. FIG. 2 is a partially enlarged cross-sectional view showing the structure of a cathode catalyst layer in embodiment 1. FIG. 3 is a diagram showing a schematic layer structure of a cathode catalyst layer in embodiment 1. FIG. 4 is a partially enlarged cross-sectional view showing the state of a catalyst and a carrier included in an inner portion in embodiment 1. FIG. 5 is a partially enlarged cross-sectional view showing the state of a catalyst and a carrier included in an intermediate portion in embodiment 1. FIG. 6 is a partially enlarged cross-sectional view showing the state of a catalyst and a carrier included in an outer portion in embodiment 1. FIG. 7 is a process chart showing a method for manufacturing a cathode catalyst layer in embodiment 1.

[0011] (Findings, etc. that form the basis of the present disclosure) At the time when the present inventors arrived at the present disclosure, it was recognized that in order for the catalyst to be effectively utilized in the cathode catalyst layer of a fuel cell, it is important that a three-phase interface is formed in the cathode catalyst layer. The three-phase interface is the interface between the carrier, the catalyst, and the ionomer (polymer electrolyte). At the three-phase interface, protons (H + ) and electrons (e - In order to achieve both water retention and drainage, there is also a technique of making the surface of the carrier contained in the cathode catalyst layer hydrophilic, thereby uniformly coating the carrier with ionomer.

[0012] In light of this situation, the present inventors investigated the cause of catalyst deterioration in the cathode catalyst layer. As a result, they discovered that the catalyst is poisoned by ionomers and deteriorates. Specifically, catalysts can be poisoned by functional groups such as sulfonic acid groups, particularly functional groups containing sulfur atoms.

[0013] The present inventors have come to the conclusion that the subject of the present disclosure is to suppress catalyst poisoning by ionomers and thereby suppress catalyst deterioration in the cathode catalyst layer.

[0014] Hereinafter, embodiments will be described in detail with reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of already well-known matters or redundant description of substantially the same configuration may be omitted.

[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 recited in the claims.

[0016] First Embodiment Hereinafter, a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 7. FIG.

[0017] [1-1. Configuration] Fig. 1 is a schematic cross-sectional view showing the configuration of a polymer electrolyte fuel cell 101 in embodiment 1. The polymer electrolyte fuel cell 101 is an example of an electrochemical device according to the present disclosure, and as shown in Fig. 1, includes a membrane electrode assembly 113, an anode separator 106, and a cathode separator 111. The membrane electrode assembly 113 is disposed between the anode separator 106 and the cathode separator 111.

[0018] The membrane electrode assembly 113 can also be used in other electrochemical devices, such as a hydrogen purification device that purifies hydrogen.

[0019] The membrane electrode assembly 113 has an anode 103, an electrolyte membrane 102, and a cathode 108. The anode 103 is bonded to one surface of the electrolyte membrane 102. The cathode 108 is bonded to the other surface of the electrolyte membrane 102. The anode 103 and the cathode 108 correspond to a first electrode and a second electrode, respectively.

[0020] The electrolyte membrane 102 is made of a polymer material having proton conductivity. Typically, the electrolyte membrane 102 is a perfluorocarbon sulfonic acid-based or hydrocarbon-based polymer electrolyte membrane having sulfonic acid groups.

[0021] The electrolyte membrane 102 is disposed between the anode 103 and the cathode 108. The electrolyte membrane 102 has a surface in contact with the anode catalyst layer 104 and a surface in contact with the cathode catalyst layer 109. These surfaces are flat. If the surface of the electrolyte membrane 102 is flat, drainage on the surface of the electrolyte membrane 102 is good. A "flat surface" means a surface that has not been processed to provide irregularities, and includes a surface that is intended to be flat but has slight irregularities due to error or the like.

[0022] The anode 103 has an anode catalyst layer 104 and an anode gas diffusion layer 105. The anode catalyst layer 104 is disposed between the electrolyte membrane 102 and the anode gas diffusion layer 105. The cathode 108 has a cathode catalyst layer 109 and a cathode gas diffusion layer 110. The cathode catalyst layer 109 is disposed between the electrolyte membrane 102 and the cathode gas diffusion layer 110.

[0023] The anode catalyst layer 104 has a function of promoting an electrochemical reaction that dissociates hydrogen into protons. The anode catalyst layer 104 includes a catalyst 302 and an ionomer 304. In detail, the anode catalyst layer 104 includes the catalyst 302, carbon particles (conductive carrier 303) supporting the catalyst 302, and the ionomer 304.

[0024] The anode gas diffusion layer 105 has a function of supplying a hydrogen-containing gas to the anode catalyst layer 104 and a function of receiving electrons from the anode catalyst layer 104. The anode gas diffusion layer 105 is made of a gas-permeable and electrically conductive material. The anode gas diffusion layer 105 has, as its main material, for example, a conductive porous body. An example of the porous body is a carbon fiber aggregate such as carbon paper.

[0025] The cathode catalyst layer 109 has a function of promoting an electrochemical reaction that produces water from protons and oxygen. The cathode catalyst layer 109 includes a catalyst 302 and an ionomer 304. In detail, the cathode catalyst layer 109 includes the catalyst 302, carbon particles (conductive carrier 303) supporting the catalyst 302, and the ionomer 304 having proton conductivity.

[0026] The cathode gas diffusion layer 110 has the function of supplying an oxidant gas to the cathode catalyst layer 109 and the function of transferring electrons to the cathode catalyst layer 109. The cathode gas diffusion layer 110 is made of a gas-permeable and electrically conductive material. The cathode gas diffusion layer 110 has, as its main material, for example, a conductive porous body. An example of the porous body is a carbon fiber aggregate such as carbon paper.

[0027] The anode separator 106 is provided with an anode gas flow path 107, which is a flow path for anode gas. The cathode separator 111 is provided with a cathode gas flow path 112, which is a flow path for cathode gas. The anode separator 106 and the cathode separator 111 are each made of a conductive material such as carbon or metal. The anode separator 106 and the cathode separator 111 may be provided with a corrosion-resistant coating, such as a resin or plating, to prevent corrosion.

[0028] Fig. 2 is a partially enlarged cross-sectional view showing the structure of the cathode catalyst layer 109. As shown in Fig. 2, the cathode catalyst layer 109 has a carrier 303, a catalyst 302, and an ionomer 304 as an electrode catalyst.

[0029] The catalyst 302 may be particles of a precious metal such as platinum or a platinum alloy. An example of a platinum alloy is an alloy of platinum and at least one selected from the group consisting of cobalt, nickel, ruthenium, and palladium.

[0030] The carrier 303 is a conductive material such as carbon particles, and supports particles of the catalyst 302. Examples of carbon particles include particles of carbon black such as ketjen black and acetylene black. The carrier 303 has a plurality of pores 305 opening on its surface. In other words, the surface of the carrier 303 has irregularities. The specific surface area of ​​the carrier 303 is, for example, 1000 m 2 The catalyst 302 particles are present inside the pores 305 of the support 303 or outside the pores 305 of the support 303 .

[0031] The ionomer 304 is a proton-conductive electrolyte, and connects the catalyst 302 and the carrier 303 in a proton-conductive state. Examples of the ionomer 304 include a perfluorocarbon sulfonic acid-based polymer material having a sulfonic acid group, a hydrocarbon-based polymer material, and the like. The ionomer 304 typically includes a perfluorocarbon sulfonic acid-based polymer electrolyte having a sulfonic acid group. The ionomer 304 may be made of the same material as the electrolyte membrane 102.

[0032] The anode catalyst layer 104 has the same structure as the cathode catalyst layer 109. However, the composition of the catalyst 302 in the anode catalyst layer 104 may be different from the composition of the catalyst 302 in the cathode catalyst layer 109.

[0033] The structure of the cathode catalyst layer 109 will be described in more detail.

[0034] FIG. 3 is a diagram schematically illustrating the layer structure of the cathode catalyst layer 109. As shown in FIG. 3, the cathode catalyst layer 109 has an inner portion 19a, an outer portion 19b, and an intermediate portion 19c. The inner portion 19a is a portion that contacts the electrolyte membrane 102. The outer portion 19b is a portion that contacts or faces the cathode gas diffusion layer 110. The intermediate portion 19c is a layer located between the inner portion 19a and the outer portion 19b. The cathode catalyst layer 109 has a surface 19p that contacts the electrolyte membrane 102 and a surface 19q that contacts the cathode gas diffusion layer 110. However, the intermediate portion 19c may be omitted. The cathode catalyst layer 109 does not have to be in direct contact with the cathode gas diffusion layer 110. If each of the inner portion 19a, the intermediate portion 19c, and the outer portion 19b has a thickness that is 1 / 3 of the thickness of the cathode catalyst layer 109, the inner portion 19a and the outer portion 19b are as follows.

[0035] That is, when the ratio of the mass of ionomer 304 to the mass of carrier 303 is defined as the ionomer abundance ratio, the ionomer abundance ratio in inner portion 19 a is lower than the ionomer abundance ratio in outer portion 19 b. The state of coverage of carrier 303 with ionomer 304 in inner portion 19 a is different from the state of coverage of carrier 303 with ionomer 304 in outer portion 19 b. The proportion of catalyst 302 particles that are not in contact with ionomer 304 in inner portion 19 a is higher than the proportion of catalyst 302 particles that are not in contact with ionomer 304 in outer portion 19 b.

[0036] With the above-described configuration, poisoning of the catalyst 302 by functional groups (e.g., sulfonic acid groups) contained in the ionomer 304 can be suppressed in the inner portion 19a that contacts the electrolyte membrane 102. This suppresses dissolution, aggregation, and precipitation of the catalyst 302 within the electrolyte membrane 102, thereby improving the durability of the membrane electrode assembly 113 and the solid polymer fuel cell 101 (an electrochemical device including the membrane electrode assembly 113). Note that, because the poisoned catalyst does not contribute to the electrochemical reaction, the electrochemical reaction is selectively promoted in the unpoisoned catalyst. As a result, dissolution, aggregation, and precipitation within the electrolyte membrane 102 of the catalyst in which the electrochemical reaction is promoted are more likely to proceed.

[0037] The movement of protons in the inner portion 19a can be supplemented by water. Because protons move from the anode 103 to the cathode 108 through the electrolyte membrane 102, the closer to the electrolyte membrane 102 a reaction field between protons and oxygen is more likely to be formed. In other words, the closer to the electrolyte membrane 102, the more abundant the water. Therefore, even if the amount of ionomer 304 in the portion close to the electrolyte membrane 102 is reduced, it is less likely to affect proton conduction, and the performance of the membrane electrode assembly 113 as a whole is maintained.

[0038] The ionomer abundance ratio can be determined, for example, by examining the element distribution in a cross section of the cathode catalyst layer 109. The cross section is a cross section parallel to the thickness direction of the membrane electrode assembly 113. The element distribution can be examined using an electron probe microanalyzer (EPMA) or energy dispersive X-ray spectroscopy (SEM-EDS).

[0039] The inner portion 19a may or may not contain the ionomer 304. The inner portion 19a may contain a polymer material that does not have proton conductivity as a binder instead of or together with the ionomer 304.

[0040] For example, the ionomer abundance ratio in the inner portion 19a is the lowest in the cathode catalyst layer 109. For example, the ionomer abundance ratio in the outer portion 19b is the highest in the cathode catalyst layer 109. With this configuration, the membrane electrode assembly 113 and the polymer electrolyte fuel cell 101 can achieve an efficient reaction between protons and oxygen while suppressing poisoning of the catalyst 302.

[0041] The ionomer abundance ratio in the middle portion 19 c may be between the ionomer abundance ratio in the inner portion 19 a and the ionomer abundance ratio in the outer portion 19 b. With this configuration, the membrane electrode assembly 113 and the solid polymer fuel cell 101 can realize an efficient reaction between protons and oxygen while suppressing poisoning of the catalyst 302.

[0042] FIG. 4 is a partially enlarged cross-sectional view showing the catalyst 302 and carrier 303 included in the inner portion 19a. In the structure of the inner portion 19a shown in FIG. 4, the catalyst 302 and carrier 303 are not coated with the ionomer 304. In this structure, the medium that assists proton migration is water. The ionomer abundance ratio in the inner portion 19a is, for example, less than 0.5 and may be 0.1 or less. In other words, the ionomer abundance ratio at the surface 19p of the cathode catalyst layer 109 that contacts the electrolyte membrane 102 may be less than 0.5 and may be 0.1 or less. The lower limit of the ionomer abundance ratio is not particularly limited and may even be zero. With this configuration, the membrane electrode assembly 113 and the polymer electrolyte fuel cell 101 can further suppress poisoning of the catalyst 302 in the inner portion 19a.

[0043] Fig. 5 is a partially enlarged cross-sectional view showing the catalyst 302 and carrier 303 contained in the intermediate portion 19c. In the structure of the intermediate portion 19c shown in Fig. 5, the carrier 303 is partially coated with an ionomer 304. The catalyst 302 inside the pores 305 of the carrier 303 is not coated with the ionomer 304. In this structure, the medium that assists the transfer of protons is the ionomer 304 and water. The ionomer abundance ratio in the intermediate portion 19c is, for example, in the range of 0.2 to 1.0.

[0044] FIG. 6 is a partially enlarged cross-sectional view showing the catalyst 302 and carrier 303 included in the outer portion 19b. In the structure of the outer portion 19b shown in FIG. 6, the carrier 303 is sufficiently coated with the ionomer 304. The ionomer 304 is present in a sufficient amount inside the pores 305 of the carrier 303 and also coats the catalyst 302 present inside the pores 305. In the outer portion 19b, the ionomer 304 coats the entire surface of the carrier 303. Almost all of the catalyst 302 present inside the pores 305 of the carrier 303 is coated with the ionomer 304. The ionomer abundance ratio in the outer portion 19b is, for example, greater than 1.0. With this configuration, the membrane electrode assembly 113 and the polymer electrolyte fuel cell 101 can ensure the overall proton conductivity of the cathode catalyst layer 109.

[0045] As described above, the inner portion 19a contains particles of the carrier 303 with the entire surface exposed. The outer portion 19b and the intermediate portion 19c contain particles of the carrier 303 with at least a portion of the surface coated with the ionomer 304. With this configuration, the membrane electrode assembly 113 and the polymer electrolyte fuel cell 101 can ensure the proton conductivity of the cathode catalyst layer 109 as a whole while suppressing poisoning of the catalyst 302 in the inner portion 19a.

[0046] The membrane electrode assembly 113 of this embodiment can be manufactured using a single (one type of) ionomer 304. The ion exchange group equivalent of the ionomer 304 contained in the inner portion 19a of the cathode catalyst layer 109 is equal to the ion exchange group equivalent of the ionomer 304 contained in the outer portion 19b of the cathode catalyst layer 109. The "ion exchange group equivalent" is defined as 1 mol (6.02×10 23 The ion-exchange group equivalent is expressed as the mass of the polymer when it has functional groups (e.g., sulfonic acid groups) of 1000 or more. The unit of the ion-exchange group equivalent is "g / mol".

[0047] Next, a method for manufacturing the membrane electrode assembly 113 will be described.

[0048] First, an anode catalyst layer 104 is formed on one surface of an electrolyte membrane 102, and a cathode catalyst layer 109 is formed on the other surface, thereby obtaining a catalyst-coated electrolyte membrane. Next, the catalyst-coated electrolyte membrane is sandwiched between an anode gas diffusion layer 105 and a cathode gas diffusion layer 110, which are then thermocompression-bonded to obtain a membrane electrode assembly 113.

[0049] The anode catalyst layer 104 is produced, for example, by the following method: A solution containing a carrier 303 carrying a catalyst 302, an ionomer 304, and a solvent is applied to the electrolyte membrane 102 to form a coating film, and the coating film is dried to remove the solvent, thereby obtaining the anode catalyst layer 104.

[0050] FIG. 7 is a process diagram showing a method for manufacturing the cathode catalyst layer 109.

[0051] In step S1, the inner portion 19a is formed on the surface of the electrolyte membrane 102. Specifically, the inner portion 19a is formed on the surface of the electrolyte membrane 102 using a first solution that does not contain the ionomer 304, but contains the catalyst 302 and a solvent. More specifically, the inner portion 19a can be formed by applying the first solution to the electrolyte membrane 102 to form a coating film, and then removing the solvent from the coating film. The catalyst 302 is supported on a carrier 303. The first solution may contain a polymer material as a binder.

[0052] In step S2, the intermediate portion 19c is formed on the inner portion 19a. Specifically, the intermediate portion 19c of the cathode catalyst layer 109 is formed using a third solution containing an ionomer 304, a catalyst 302, and a solvent. More specifically, the third solution is applied to the inner portion 19a to form a coating film, and the solvent is removed from the coating film to form the intermediate portion 19c. In step S2, the inner portion 19a and the intermediate portion 19c are integrated.

[0053] In step S3, the outer portion 19b is formed on the intermediate portion 19c. Specifically, the outer portion 19b to be located between the inner portion 19a and the cathode gas diffusion layer 110 is formed using a second solution containing an ionomer 304, a catalyst 302, and a solvent. More specifically, the second solution is applied to the intermediate portion 19c to form a coating film, and the outer portion 19b can be formed by removing the solvent from the coating film. In step S3, the inner portion 19a, the intermediate portion 19c, and the outer portion 19b are integrated to form the cathode catalyst layer 109.

[0054] By carrying out steps S1 to S3, it is possible to easily manufacture a cathode catalyst layer 109 having an appropriate ionomer abundance ratio.

[0055] The concentration (unit: g / liter) of ionomer 304 in the third solution used to produce intermediate portion 19c is lower than the concentration of ionomer 304 in the second solution used to produce outer portion 19b, thereby obtaining the structures of intermediate portion 19c and outer portion 19b described with reference to Figures 5 and 6.

[0056] The first solution used to manufacture the inner portion 19a may contain the ionomer 304. In this case, the concentration of the ionomer 304 in the first solution is lower than the concentration of the ionomer 304 in the second solution and lower than the concentration of the ionomer 304 in the third solution.

[0057] The first, second, and third solutions have the same concentration of catalyst 302. The composition of each solution (the concentration of ionomer 304 in each solution) is appropriately adjusted so that the ionomer abundance ratio in each of inner portion 19 a, outer portion 19 b, and middle portion 19 c falls within the range described above.

[0058] The first, second and third solutions can be prepared by dispersing powder of the carrier 303 carrying the catalyst 302 in an aqueous solution of the ionomer, and further mixing a volatile solvent such as ethanol or isopropanol.

[0059] [1-2. Operation] The operation and function of the polymer electrolyte fuel cell 101 configured as above will be described below with reference to FIG.

[0060] A hydrogen-containing gas is supplied to the anode gas flow channel 107, and an oxidant gas is supplied to the cathode gas flow channel 112. The oxidant gas is typically air. At the anode 103, hydrogen (H) is converted into protons (H + ) and electrons (e - ) The protons move from the anode 103 to the cathode 108 by conduction through the electrolyte membrane 102. The electrons move from the anode 103 to the cathode 108 through an external circuit. At the cathode 108, water (H2O) is produced by an electrochemical reaction of the protons, oxygen (O2), and electrons, as expressed by the following formula (2):

[0061] H2 → 2H + +2e - (1) 4H + + O2 + 2e -→ 2H2O (2) [1-3. Effects, etc.] As described above, in this embodiment, the membrane electrode assembly 113 includes the anode 103, the cathode 108, and the electrolyte membrane 102, which has proton conductivity and is disposed between the anode 103 and the cathode 108. The cathode 108 includes the cathode gas diffusion layer 110 and the cathode catalyst layer 109, which is disposed between the cathode gas diffusion layer 110 and the electrolyte membrane 102. The electrolyte membrane 102 has a surface in contact with the cathode catalyst layer 109, and the surface in contact with the cathode catalyst layer 109 is flat. The cathode catalyst layer 109 includes the catalyst 302, the conductive carrier 303 supporting the catalyst 302, and the ionomer 304, which has proton conductivity. The cathode catalyst layer 109 has an inner portion 19a in contact with the electrolyte membrane 102 and an outer portion 19b in contact with or facing the cathode gas diffusion layer 110. When the ratio of the mass of the ionomer 304 to the mass of the carrier 303 is defined as the ionomer abundance ratio, the ionomer abundance ratio in the inner portion 19a is lower than the ionomer abundance ratio in the outer portion 19b. Furthermore, the state of coverage of the carrier 303 with the ionomer 304 in the inner portion 19a is different from the state of coverage of the carrier 303 with the ionomer 304 in the outer portion 19b. In this manner, the membrane electrode assembly 113 according to this embodiment can suppress poisoning of the catalyst 302 by functional groups (e.g., sulfonic acid groups) contained in the ionomer 304 in the inner portion 19a in contact with the electrolyte membrane 102. That is, the membrane electrode assembly 113 can suppress deterioration of the catalyst 302 in the cathode catalyst layer 109.

[0062] Furthermore, in the present embodiment, the ionomer abundance ratio in the inner portion 19 a may be the lowest in the cathode catalyst layer 109. In this way, the membrane electrode assembly 113 can realize an efficient reaction between protons and oxygen while suppressing poisoning of the catalyst 302.

[0063] In the present embodiment, the cathode catalyst layer 109 may have a surface 19p in contact with the electrolyte membrane 102, and the ionomer abundance ratio on the surface 19p in contact with the electrolyte membrane 102 may be less than 0.5. In this way, the membrane electrode assembly 113 can further suppress poisoning of the catalyst 302 in the inner portion 19a.

[0064] Furthermore, in the present embodiment, the ionomer abundance ratio in the outer portion 19 b may be the highest in the cathode catalyst layer 109. In this way, the membrane electrode assembly 113 can realize an efficient reaction between protons and oxygen while suppressing poisoning of the catalyst 302.

[0065] In the present embodiment, the ionomer 304 may cover the entire surface of the carrier 303 in the outer portion 19b. In this way, the membrane electrode assembly 113 can ensure the proton conductivity of the cathode catalyst layer 109 as a whole.

[0066] In this embodiment, the outer portion 19 b may contain particles of the carrier 303 at least partly coated with the ionomer 304, and the inner portion 19 a may contain particles of the carrier 303 whose entire surface is exposed. In this way, the membrane electrode assembly 113 can ensure the proton conductivity of the cathode catalyst layer 109 as a whole while suppressing poisoning of the catalyst 302 in the inner portion 19 a.

[0067] In this embodiment, the ion exchange group equivalent of the ionomer 304 contained in the inner portion 19 a may be equal to the ion exchange group equivalent of the ionomer 304 contained in the outer portion 19 b. In this way, the membrane electrode assembly 113 can be manufactured using a single (one type of) ionomer 304.

[0068] In this embodiment, the cathode catalyst layer 109 may further include an intermediate portion 19 c located between the inner portion 19 a and the outer portion 19 b. The ionomer abundance ratio in the intermediate portion 19 c may be between the ionomer abundance ratio in the inner portion 19 a and the ionomer abundance ratio in the outer portion 19 b. In this manner, the membrane electrode assembly 113 can achieve an efficient reaction between protons and oxygen while suppressing poisoning of the catalyst 302.

[0069] In this embodiment, the method for producing the membrane electrode assembly 113 includes a step of forming the inner portion 19a of the cathode catalyst layer 109 on the surface of the proton-conductive electrolyte membrane 102 using a first solution containing the catalyst 302 and a solvent but not the ionomer 304. The method for producing the membrane electrode assembly 113 also includes a step of forming the outer portion 19b of the cathode catalyst layer 109, which is to be located between the inner portion 19a of the cathode catalyst layer 109 and the cathode gas diffusion layer 110, using a second solution containing the ionomer 304, the catalyst 302, and a solvent. This method makes it possible to easily produce a cathode catalyst layer 109 having an appropriate ionomer abundance ratio. Furthermore, it is possible to obtain a membrane electrode assembly 113 that can suppress deterioration of the catalyst 302 in the cathode catalyst layer 109.

[0070] In this embodiment, the polymer electrolyte fuel cell (electrochemical device) 101 includes a membrane electrode assembly 113. By using the membrane electrode assembly 113, the polymer electrolyte fuel cell (electrochemical device) 101 can suppress deterioration of the catalyst 302 in the cathode catalyst layer 109, thereby improving durability.

[0071] The membrane electrode assembly according to the present disclosure is useful for electrochemical devices such as fuel cells and hydrogen purification devices.

[0072] 19a Inner portion 19b Outer portion 19c Middle portion 19p Surface in contact with electrolyte membrane 19q Surface in contact with cathode gas diffusion layer 101 Solid polymer fuel cell (electrochemical device) 102 Electrolyte membrane 103 Anode 104 Anode catalyst layer 105 Anode gas diffusion layer 106 Anode separator 107 Anode gas flow channel 108 Cathode 109 Cathode catalyst layer 110 Cathode gas diffusion layer 111 Cathode separator 112 Cathode gas flow channel 113 Membrane electrode assembly 302 Catalyst 303 Support 304 Ionomer 305 Pore

Claims

1. An anode; A cathode; an electrolyte membrane having proton conductivity and disposed between the anode and the cathode; Equipped with the cathode has a cathode gas diffusion layer and a cathode catalyst layer located between the cathode gas diffusion layer and the electrolyte membrane, the electrolyte membrane has a surface in contact with the cathode catalyst layer, the surface in contact with the cathode catalyst layer being a flat surface; the cathode catalyst layer includes a catalyst, a conductive carrier supporting the catalyst, and an ionomer having proton conductivity, and has an inner portion in contact with the electrolyte membrane and an outer portion in contact with or facing the cathode gas diffusion layer; when the ratio of the mass of the ionomer to the mass of the carrier is defined as an ionomer abundance ratio, the ionomer abundance ratio in the inner portion is lower than the ionomer abundance ratio in the outer portion, A state of coverage of the carrier with the ionomer in the inner portion is different from a state of coverage of the carrier with the ionomer in the outer portion. Membrane electrode assembly.

2. the ionomer abundance ratio in the inner portion is the lowest among the cathode catalyst layers; The membrane electrode assembly according to claim 1 .

3. the cathode catalyst layer has a surface in contact with the electrolyte membrane, The ionomer abundance ratio on the surface in contact with the electrolyte membrane is less than 0.

5. The membrane electrode assembly according to claim 1 .

4. The ionomer abundance ratio in the outer portion is the highest in the cathode catalyst layer. The membrane electrode assembly according to claim 1 .

5. In the outer portion, the ionomer covers the entire surface of the carrier. The membrane electrode assembly according to claim 4.

6. In the outer portion, there are particles of the carrier having at least a portion of a surface thereof coated with the ionomer; In the inner portion, there are particles of the carrier with all of their surfaces exposed. The membrane electrode assembly according to claim 1 .

7. the ion exchange group equivalent of the ionomer contained in the inner portion is equal to the ion exchange group equivalent of the ionomer contained in the outer portion; The membrane electrode assembly according to claim 6.

8. the cathode catalyst layer further has an intermediate portion located between the inner portion and the outer portion, the ionomer abundance ratio in the intermediate portion is between the ionomer abundance ratio in the inner portion and the ionomer abundance ratio in the outer portion; The membrane electrode assembly according to claim 1 .

9. forming an inner portion of a cathode catalyst layer on a surface of an electrolyte membrane having proton conductivity using a first solution that does not contain an ionomer and contains a catalyst and a solvent; forming an outer portion of the cathode catalyst layer to be located between the inner portion of the cathode catalyst layer and a cathode gas diffusion layer using a second solution including the ionomer, the catalyst, and a solvent; A method for producing a membrane electrode assembly, comprising the steps of:

10. An electrochemical device comprising the membrane electrode assembly according to claim 1.