Catalyst Layer for Electrolyte Membrane-Electrode Assembly and Fuel Cell Using the Same

Abstract

To provide a highly efficient catalyst layer by suppressing a decrease in catalytic activity due to ionomer poisoning, without impairing hydrogen ion conductivity.SOLUTION: A catalyst layer in the present disclosure includes a conductive mesoporous material with a catalyst supported inside a mesopore, conductive catalyst-unsupported particles that do not support a catalyst, and ionomers covering the mesoporous material and the catalyst-unsupported particles, the catalyst layer being used for an electrolyte membrane-electrode assembly. The hydrophobic properties of the catalyst-unsupported particles are higher than that of the mesoporous material, and the ionomers each include a hydrophilic functional group and a hydrophobic main chain. The ratio of the surface area of the catalyst-unsupported particles covered with the ionomers and the entire surface area of the catalyst-unsupported particles is more than the ratio of the surface area of the mesoporous material covered with the ionomers and the entire surface area of the mesoporous material.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a catalyst layer for an electrolyte membrane - electrode assembly and a fuel cell using the same.

Background Art

[0002] Patent Document 1 discloses a catalyst layer used in an electrolyte membrane - electrode assembly, in which a mesoporous material having a catalyst supported in mesopores is coated with an ionomer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides a catalyst layer that enables a highly efficient catalytic reaction by suppressing a decrease in catalytic activity due to ionomer poisoning without impairing hydrogen ion conductivity.

Means for Solving the Problems

[0005] In the present disclosure, the catalyst layer includes a conductive mesoporous material having a catalyst supported inside mesopores, conductive catalyst - non - supported particles not having a catalyst supported thereon, and an ionomer coating the mesoporous material and the catalyst - non - supported particles, and is used in an electrolyte membrane - electrode assembly.

[0006] The hydrophobicity of the catalyst - non - supported particles is higher than that of the mesoporous material, and the ionomer has a hydrophilic functional group and a hydrophobic main chain.

[0007] The ratio of the surface area of the catalyst non-supported particles coated with the ionomer to the total surface area of the catalyst non-supported particles is greater than the ratio of the surface area of the mesoporous material coated with the ionomer to the total surface area of the mesoporous material, which is characteristic.

[0008] In addition, the method for manufacturing a catalyst layer in the present disclosure is a method for manufacturing a catalyst layer used in an electrolyte membrane-electrode assembly, and includes a first step, a second step, and a third step.

[0009] The first step is a step of mixing and dispersing an ionomer having a hydrophilic functional group and a hydrophobic main chain, conductive catalyst non-supported particles not carrying a catalyst, and a hydrophilic solvent to prepare a first ink.

[0010] The second step is a step of adding and mixing a conductive mesoporous material having a lower hydrophobicity than the catalyst non-supported particles and carrying a catalyst inside the mesopores to the first ink to prepare a second ink.

[0011] The third step is a step of applying and drying the second ink.

Advantages of the Invention

[0012] The catalyst layer of the present disclosure can suppress a decrease in catalyst activity due to ionomer poisoning without impairing hydrogen ion conductivity, and thus can provide an electrolyte membrane-electrode assembly equipped with a catalyst layer enabling a highly efficient catalytic reaction.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0014] (Findings underlying the present disclosure, etc.) When the inventors arrived at the present disclosure, in the technology of forming a triple-phase interface in a catalyst of a fuel cell, it has been considered that bringing a catalyst into contact with an ionomer leads to performance improvement from the viewpoint of hydrogen ion supply. However, in recent years, it has been found that the catalyst is poisoned by the ionomer due to the contact between the ionomer and the catalyst, rather deteriorating the performance.

[0015] Therefore, in the industry, as an issue of suppressing the poisoning of the catalyst by the ionomer, it has been common to perform a product design in which the catalyst is encapsulated in a carbon carrier having a large amount of mesopores such as a mesoporous material so as not to bring the ionomer into contact with the catalyst.

[0016] However, there has been a problem that the catalyst also exists outside the mesoporous material, and since some ionomers may penetrate into the mesopores, using a mesoporous material encapsulating the catalyst in the mesopores is not sufficient as a means for suppressing the poisoning of the catalyst by the ionomer.

[0017] Under such circumstances, the inventors obtained an idea of adsorbing an ionomer to catalyst non-supported particles to reduce the adsorption amount of the ionomer to the mesoporous material.

[0018] Then, hinting at the fact that the hydrophilic group of the ionomer is oriented outward by changing the polarity in the catalyst ink, the inventors found that in order to realize the idea, there is a problem of controlling the polarity of the solvent and the particles in the catalyst ink for forming a catalyst layer to enhance the adsorption force between the catalyst non-supported particles and the ionomer rather than the adsorption force between the ionomer and the mesoporous material. To solve the problem, the inventors arrived at constituting the subject matter of the present disclosure.

[0019] Therefore, the present disclosure provides a catalyst layer that enables a highly efficient catalytic reaction, which can reduce the amount of ionomer coating the mesoporous material so that the ionomer preferentially coats the catalyst-free particles, suppress the decrease in catalytic activity due to ionomer poisoning, and not impair the hydrogen ion conductivity.

[0020] Hereinafter, embodiments will be described in detail with reference to the drawings. However, a more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions 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.

[0021] Note that 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.

[0022] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to FIGS. 1 to 3.

[0023] [1-1. Configuration] (Fuel Cell) FIG. 1 shows a configuration example of a fuel cell, which is a basic unit of a fuel cell. The fuel cell 10 shown in FIG. 1 is a polymer electrolyte fuel cell that generates electricity by reacting hydrogen supplied to the anode with oxygen supplied to the cathode.

[0024] As shown in FIG. 1, the fuel cell 10 has an electrolyte membrane - electrode assembly 5 between an anode separator 6a and a cathode separator 6c.

[0025] The anode separator 6a has a flow path on the surface in contact with the anode 2a of the electrolyte membrane - electrode assembly 5 for flowing hydrogen supplied to the fuel cell 10 to the anode 2a of the electrolyte membrane - electrode assembly 5.

[0026] ​The cathode separator 6c has a flow path on the surface in contact with the cathode 2c of the electrolyte membrane - electrode assembly 5 for flowing oxygen supplied to the fuel cell 10 to the cathode 2c of the electrolyte membrane - electrode assembly 5.

[0027] When the fuel cell 10 has a stack structure, the adjacent anode separator 6a and cathode separator 6c electrically connect between adjacent cells.

[0028] (Electrolyte membrane - electrode assembly) As shown in FIG. 1, the electrolyte membrane - electrode assembly 5 includes an electrolyte membrane 1, an anode (fuel electrode) 2a including an anode catalyst layer 3a and an anode gas diffusion layer 4a, and a cathode (air electrode) 2c including a cathode catalyst layer 3c and a cathode gas diffusion layer 4c, and both sides of the electrolyte membrane 1 are sandwiched by the anode 2a and the cathode 2c.

[0029] (Electrolyte membrane) The electrolyte membrane 1 conducts ions (hydrogen ions) between the anode 2a and the cathode 2c, and it is necessary to have both hydrogen ion conductivity and gas barrier properties. In the present embodiment, a perfluorosulfonic acid resin membrane is used as the electrolyte membrane 1. This perfluorosulfonic acid resin membrane is preferable because it has high hydrogen ion conductivity and exists stably even in the power generation environment of the fuel cell.

[0030] (Gas diffusion layer) The anode gas diffusion layer 4a and the cathode gas diffusion layer 4c are layers having both a current collecting function, gas permeability, and water repellency. The anode gas diffusion layer 4a and the cathode gas diffusion layer 4c may have a structure including two layers of a base material and a coating layer.

[0031] The base material may be a material excellent in conductivity, gas and liquid permeability. In the present embodiment, carbon paper is used as the base material.

[0032] The coating layer is interposed between the base material, the anode catalyst layer 3a, and the cathode catalyst layer 3c, and is a layer for reducing their contact resistance and improving the liquid permeability (drainage property).

[0033] In the present embodiment, as the coating layer, one formed mainly of a conductive material such as carbon black and a water-repellent resin such as polytetrafluoroethylene (PTFE) was used.

[0034] (Catalyst layer) The anode catalyst layer 3a and the cathode catalyst layer 3c are layers that accelerate the rate of the electrochemical reaction of the anode 2a and the cathode 2c.

[0035] The anode catalyst layer 3a includes a catalyst support material, a catalyst, and an ionomer (hydrogen ion conductive resin), and the catalyst is configured to be supported at least on the catalyst support material.

[0036] Also, as shown in FIG. 2, the cathode catalyst layer 3c includes a mesoporous material 12 as a catalyst support material, a catalyst 14, catalyst non-supported particles 11, and an ionomer 13, and the catalyst 14 is supported at least inside the mesoporous material 12.

[0037] In the cathode catalyst layer 3c, the ratio of the surface area of the mesoporous material 12 covered by the ionomer 13 to the surface area of the mesoporous material 12 is smaller than the ratio of the surface area of the catalyst non-supported particles 11 covered by the ionomer 13 to the surface area of the catalyst non-supported particles 11.

[0038] (Catalyst) The catalyst is not particularly limited as long as it has a catalytic action on hydrogen or oxygen. However, in the present embodiment, from the viewpoints of improving the catalytic activity, the poisoning resistance against carbon monoxide, etc., and the heat resistance, etc., platinum, a mixture or alloy containing platinum was used as the catalyst.

[0039] In this embodiment, the platinum content was set to 30 to 90 atomic %, and the content of other metals was set to 10 to 70 atomic %. The average particle diameter of the catalyst is not particularly limited, but from the viewpoints of catalyst utilization efficiency and improvement of the supportability on the carbon carrier, it is preferably 1 to 30 nm. A particle diameter that can enter the mesopores (smaller than the diameter of the mesopore inlet) is preferred.

[0040] (Catalyst support material) In this embodiment, carbon black was used as the catalyst support material used in the anode catalyst layer 3a and the mesoporous material 12 used in the cathode catalyst layer 3c. As the catalyst support material, it is preferably a conductive material having pores inside, and porous carbon is suitable for this.

[0041] Examples of the porous carbon include carbon blacks such as Ketjenblack (registered trademark), acetylene black, and Vulcan (registered trademark), and carbon having a structure in which a plurality of graphene sheets are laminated to form mesopores.

[0042] The carbon black as the mesoporous material 12 used in the cathode catalyst layer 3c of this embodiment is configured to have an average particle diameter of 500 nm. Before supporting the catalyst metal particles, the mode radius of the mesopores is 10 nm, and the pore volume of the mesopores is 2.0 cm 3 / g.

[0043] (Catalyst non-supported particles) In this embodiment, Ketjenblack was used as the catalyst non-supported particles 11, but it is not particularly limited as long as it is hydrophobic and conductive particles. The hydrophobicity of the catalyst non-supported particles 11 is higher than that of the mesoporous material 12 supporting the catalyst.

[0044] For example, when a catalyst is supported on carbon black, the hydrophilic catalyst metal is supported on the water-repellent carbon black, so its hydrophobicity decreases, and the carbon black not supporting the catalyst has higher hydrophobicity than the carbon black supporting the catalyst.

[0045] The particle diameter of the non-supported catalyst particles 11 is not particularly limited, but the mode diameter of the non-supported catalyst particles 11 is preferably 0.22 times or less of the mode diameter of the mesoporous material 12.

[0046] The diameter of the sphere that fits into the interparticle gap when spheres of a certain size are packed in a hexagonal close-packed manner is 0.2247 times the diameter of the original sphere.

[0047] Therefore, by making the mode diameter of the non-supported catalyst particles 11 0. 22 times or less of the mode diameter of the mesoporous material 12, the mesoporous materials 12 come close to each other, and the non-supported catalyst particles 11 are arranged around the mesoporous material 12 so as to fill the gap formed between the mesoporous materials 12, increasing the conductive contacts between the particles.

[0048] Also, usually, an electrode catalyst layer containing carbon particles with an average particle diameter of 10 to 100 nm can obtain high drainage performance by capillary force. Therefore, the mode diameter of the non-supported catalyst particles 11 is preferably 10 nm or more and 0.22 times or less of the mode diameter of the mesoporous material 12.

[0049] (Ionomer) In this embodiment, a perfluorosulfonic acid polymer was used as the ionomer 13. As the ionomer 13 that can be used for the anode catalyst layer 3a and the cathode catalyst layer 3c, a polymer having a hydrophilic functional group and a hydrophobic main chain is preferable. Examples thereof include ion-exchange polymers such as fluorine-based polymers having acidic functional groups and hydrocarbon-based polymers having acidic functional groups.

[0050] The ionomer 13 has an acidic functional group with a polymer having a repeating structure as the main chain.

[0051] The acidic functional group is not particularly limited as long as it is a functional group showing acidity. Examples thereof include a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group. Among them, from the viewpoint of hydrogen ion (H + ) conductivity, a sulfonic acid group is preferable.

[0052] As a mechanism of hydrogen ion conduction by the ionomer 13, a hydrophilic core is formed by an acidic functional group, and a network of clusters in which water molecules are localized in the core is formed, and a model in which hydrogen ions move through this hydrophilic network has been proposed.

[0053] Examples of the fluorine-based polymer having an acidic functional group include perfluorosulfonic acid polymers.

[0054] The perfluorosulfonic acid polymer has a polytetrafluoroethylene (PTFE) unit and a perfluorosulfonic acid unit, and the sulfonic acid is hydrophilic and the main chain made of polytetrafluoroethylene is hydrophobic.

[0055] As the perfluorosulfonic acid polymer, commercially available products can also be used. Examples of commercially available products that can be used include Nafion (registered trademark) of DuPont, Aquivion (registered trademark) of Solvay, Flemion (registered trademark) of Asahi Glass Co., Ltd., and Aciplex (registered trademark) of Asahi Kasei Corporation.

[0056] (Method for manufacturing the catalyst layer) The catalyst layer according to the embodiment of the present disclosure was created by the following steps. FIG. 3 is a flowchart schematically showing a method for manufacturing the catalyst layer of the cathode.

[0057] (First step of the method for manufacturing the catalyst layer) In the first step, the ionomer 13 is adsorbed onto the catalyst non-supported particles 11 in a hydrophilic solvent. First, the solvent ratio of the hydrophilic solvent is determined. Water 16, ethanol 17, and an ionomer solution 15 dispersed in water and ethanol are mixed so that the composition is 85% water, 15% ethanol, and 3 wt% ionomer, and the catalyst non-supported particles 11 are added and dispersed. As the dispersion method, a ball mill, a wet atomization device, ultrasonic waves, or the like can be used.

[0058] In order to select the solvent ratio of water 16 and ethanol 17 as the hydrophilic solvent, the particle size distribution of the ionomer 13 dispersed in a certain solvent ratio is measured by an ultrasonic particle size distribution analyzer. When the proportion of water 16 is gradually decreased from 50%, it is preferable to select the solvent ratio that results in a mode diameter smaller than the mode diameter of the ionomer 13 when the proportion of water is 50%. When the proportion of water is gradually decreased from 50%, it is preferable to select the solvent ratio that results in a mode diameter smaller than the mode diameter of the ionomer 13 when the proportion of water is 50%.

[0059] The perfluorosulfonic acid polymer used for the ionomer 13 in the present embodiment has a hydrophilic and acidic sulfonic acid group (functional group) and a hydrophobic main chain.

[0060] When the ionomer 13 is placed in a hydrophilic solvent, the hydrophobic main chain generates a repulsive force with water and aggregates, taking a form with the hydrophilic sulfonic acid group (side chain) facing outward. As a result, the peak particle size of the particle size distribution of the ionomer 13 becomes smaller. By selecting the solvent ratio that causes a decrease in the peak particle size of the particle size distribution due to this shape change, it is possible to create an ink internal environment in which the repulsive force between the hydrophobic main chain of the ionomer 13 and water is large.

[0061] Water 16, ethanol 17, and the ionomer solution 15 are added so as to have this ratio of the hydrophilic solvent, and further the catalyst non-supported particles 11 are added and dispersed (S01). Then, the catalyst non-supported particles 11 with a large hydrophobicity generate a repulsive force with water and become relatively more likely to adsorb to the hydrophobic main chain of the ionomer 13.

[0062] Then, the hydrophobic main chain of the ionomer 13 adsorbs around the catalyst non-supported particles 11, taking a shape with the hydrophilic sulfonic acid group (side chain) of the ionomer 13 facing outward, and aggregates of ketjen black and the ionomer 13 are dispersed in the hydrophilic solvent.

[0063] (Second step of the method for manufacturing the catalyst layer) In the second step, the mesoporous material 12 supporting the catalyst 14 inside the mesopores is added to the mixed dispersion (first ink) prepared in the first step and mixed and dispersed (S02).

[0064] The dispersion method can use a ball mill, a wet atomization device, or ultrasonic waves. The mesoporous material 12 supporting the catalyst 14 inside the mesopores has weaker hydrophobicity than the catalyst-free particles 11 due to the support of the catalyst 14.

[0065] Therefore, the repulsion between the solvent and the mesoporous material 12 in the hydrophilic solvent is weaker than the repulsion between the solvent and the catalyst-free particles 11, and the attraction between the hydrophobic main chain of the ionomer 13 and the catalyst-free particles 11 is stronger than that with the mesoporous material 12. Without the adsorption between the already formed catalyst-free particles 11 and the hydrophobic main chain of the ionomer 13 being released, the mesoporous material 12 is dispersed.

[0066] (The third step of the method for manufacturing the catalyst layer) In the third step, the catalyst layer is formed (S04) by applying (S03) and drying the second ink prepared in the second step. At this time, the second ink may be directly applied to the electrolyte membrane 1, or may be applied and dried on a substrate and then transferred to the electrolyte membrane 1. As a result, a cathode catalyst layer 3c is obtained in which the catalyst-free particles 11 are mainly coated with the ionomer 13 and the area where the outside of the mesoporous material 12 is coated with the ionomer 13 is reduced.

[0067] [1-2. Operation] In the fuel cell 10 configured as described above, its operation and action will be described below.

[0068] Based on FIGS. 1 and 2, the operation method and action of the fuel cell 10 will be described. The operation method of the fuel cell 10 is to set (maintain) the temperature of the fuel cell 10 at 60°C, supply hydrogen with a dew point of 60°C to the flow path of the anode separator 6a at a flow rate of 100 cc / min, and supply air with a dew point of 60°C to the cathode separator 6c at a flow rate of 300 cc / min, and then apply a voltage between the anode 2a and the cathode 2c so that a current of 10 A flows from the anode 2a through the electrolyte membrane 1 to the cathode 2c. That is, it is to apply a voltage between the anode 2a and the cathode 2c.

[0069] Next, the movement of substances and electrochemical reactions within the operating electrochemical device will be described. The hydrogen supplied to the flow path of the anode separator 6a passes through the anode gas diffusion layer 4a and reaches the catalyst 14 of the anode catalyst layer 3a.

[0070] In the anode catalyst layer 3a, an oxidation reaction occurs in which hydrogen dissociates into hydrogen ions (H + ) and electrons, as shown in (Chemical Formula 1). The hydrogen ions (H + ) pass through the ionomer 13 in the anode catalyst layer 3a, through the electrolyte membrane 1, through the ionomer 13 in the cathode catalyst layer 3c, through the water in the cathode catalyst layer 3c, and move to the catalyst 14 in the cathode catalyst layer 3c.

[0071]

Chemical Formula

[0072] The electrons separated by the catalyst 14 in the anode catalyst layer 3a pass through the anode catalyst layer 3a, the anode gas diffusion layer 4a, the anode separator 6a, through the electric wire and the electronic load device, through the cathode separator 6c, the cathode gas diffusion layer 4c, the cathode catalyst layer 3c, and reach the catalyst 14 in the cathode catalyst layer 3c.

[0073] The oxygen in the air supplied to the flow path of the cathode separator 6c passes through the cathode gas diffusion layer 4c, through the cathode catalyst layer 3c, and reaches the catalyst 14 in the cathode catalyst layer 3c.

[0074] In the cathode catalyst layer 3c, a reduction reaction occurs in which hydrogen ions (H + ), oxygen (O), and electrons combine to form water, as shown in (Chemical Formula 2).

[0075]

Chemical Formula

[0076] As shown in Fig. 2, in the cathode catalyst layer 3c of the present embodiment, since the ratio of the area of the portion covered with the ionomer 13 with respect to the outer surface of the mesoporous material 12 is small, not only the catalyst 14 supported inside the mesopores of the mesoporous material 12 but also the catalyst 14 supported on the portion exposed on the outer surface of the mesoporous material 12 has a reduced amount of the catalyst 14 directly contacting the ionomer 13. As a result, the amount of poisoning of the catalyst 14 can also be reduced, and the catalytic activity can be improved.

[0077] In addition, the ionomer 13 covering the catalyst-free particles 11 that do not carry a catalyst conducts hydrogen ions (H + ) in the cathode catalyst layer 3c. Up to the catalyst 14 supported on the mesoporous material 12 in contact with the catalyst-free particles 11, hydrogen ion conduction is performed using water generated during power generation or water supplied by humidifying the supply gas as a medium. Therefore, even if the coating amount of the ionomer 13 on the mesoporous material 12 decreases, a decrease in the conductivity of hydrogen ions (H + ) in the catalyst layer can be suppressed.

[0078] [1-3. Effects, etc.] As described above, the cathode catalyst layer 3c of the present embodiment includes a conductive mesoporous material 12 having a catalyst 14 supported inside the mesopores, a conductive catalyst-free particle 11 not carrying a catalyst, and an ionomer 13 covering the mesoporous material 12 and the catalyst-free particle 11, and is used for the electrolyte membrane-electrode assembly 5.

[0079] The hydrophobicity of the catalyst-free particles 11 is higher than that of the mesoporous material 12, and the ionomer 13 has a hydrophilic functional group (side chain) and a hydrophobic main chain.

[0080] And the ratio of the surface area of the catalyst-free particles 11 covered with the ionomer 13 to the total surface area of the catalyst-free particles 11 is larger than the ratio of the surface area of the mesoporous material 12 covered with the ionomer 13 to the total surface area of the mesoporous material 12.

[0081] Thus, in the step of creating the catalyst ink by mixing and dispersing the ionomer 13, the non-supported catalyst particles 11, the mesoporous material 12, and the hydrophilic solvent, in the catalyst ink, the hydrophobic main chain of the ionomer generates a repulsive force with the hydrophilic solvent, so that the hydrophilic functional groups (side chains) of the ionomer face outward in the ink, and the hydrophobic main chain takes a shape that aggregates inward.

[0082] Also, since the hydrophobic non-supported catalyst particles 11 also generate a repulsive force with the hydrophilic solvent, the hydrophobic main chain of the ionomer 13 and the non-supported catalyst particles 11 aggregate, taking a shape with the hydrophilic functional groups (side chains) of the ionomer 13 facing outward. On the other hand, the mesoporous material 12 with the catalyst 14 supported at least inside the mesopores has a lower hydrophobicity than the hydrophobicity of the non-supported catalyst particles 11, so the repulsive force with the hydrophilic solvent is weaker than that of the non-supported catalyst particles 11, and the cohesive force with the hydrophobic main chain of the ionomer 13 is also weakened. Therefore, the ionomer 13 adsorbs more to the non-supported catalyst particles 11 than to the mesoporous material 12.

[0083] When this catalyst ink is applied and dried to create the cathode catalyst layer 3c, a large amount of the ionomer 13 adsorbs to the non-supported catalyst particles 11, and the mesoporous material 12 supporting the catalyst 14 exists around it, and a cathode catalyst layer 3c with a structure in which the non-supported catalyst particles 11 adsorb more of the ionomer 13 than the mesoporous material 12 can be obtained.

[0084] In this way, since the amount of the ionomer 13 covering the outer surface of the mesoporous material 12 is small (the ratio of the area of the portion covered with the ionomer 13 to the outer surface of the mesoporous material 12 is small), not only the catalyst 14 supported inside the mesopores of the mesoporous material 12 but also the amount of poisoning of the catalyst 14 supported on the portion exposed on the outer surface of the mesoporous material 12 can be reduced.

[0085] The ionomer 13 covering the catalyst-free particles 11 that do not carry a catalyst conducts hydrogen ions in the cathode catalyst layer 3c. Since hydrogen ions are conducted through water as a medium from the mesoporous material 12 in contact with the catalyst-free particles 11 to the catalyst 14, a decrease in the amount of the ionomer 13 covering the mesoporous material 12 can be suppressed, thereby suppressing a decrease in the hydrogen ion conductivity of the cathode catalyst layer 3c.

[0086] Therefore, it is possible to suppress a decrease in the catalytic activity due to poisoning of the ionomer 13 without impairing the hydrogen ion conductivity, and a highly efficient cathode catalyst layer 3c can be obtained.

[0087] As in the present embodiment, in the cathode catalyst layer 3c, the mode diameter of the catalyst-free particles 11 is 0.22 times or less of the mode diameter of the mesoporous material 12, the mesoporous materials 12 are close to each other, and the catalyst-free particles 11 are preferably arranged around the mesoporous material 12 so as to fill the gap formed between the mesoporous materials 12.

[0088] If the mode diameter of the catalyst-free particles 11 is 0.22 times or less of the mode diameter of the mesoporous material 12, the mesoporous materials 12 are close to each other, and the catalyst-free particles 11 can enter the gap formed between the mesoporous materials 12.

[0089] And if the mesoporous materials 12 are close to each other and the catalyst-free particles 11 are arranged around the mesoporous material 12 so as to fill the gap formed between the mesoporous materials 12, the conductive contact points between the particles increase, thereby improving the conductivity of the cathode catalyst layer 3c and reducing the resistance overvoltage.

[0090] In addition, the method for manufacturing the cathode catalyst layer 3c used in the electrolyte membrane - electrode assembly 5 of the present embodiment includes a first step (S01) of mixing and dispersing an ionomer 13 having a hydrophilic functional group (side chain) and a hydrophobic main chain, conductive catalyst - non - supported particles 11 not carrying a catalyst, and a hydrophilic solvent to prepare a first ink, a second step (S02) of adding and mixing a conductive mesoporous material 12 having a lower hydrophobicity than the catalyst - non - supported particles 11 and carrying a catalyst 14 inside mesopores to the first ink to prepare a second ink, and a third step (S03, S04) of applying and drying the second ink.

[0091] Thus, in the first step (S01) of mixing and dispersing the ionomer 13, the catalyst - non - supported particles 11, and the hydrophilic solvent to prepare the first ink, since the hydrophobic main chain of the ionomer 13 generates a repulsive force with the hydrophilic solvent, in the hydrophilic solvent, the ionomer takes a form in which the hydrophilic functional group (side chain) faces outward and the hydrophobic main chain aggregates inward.

[0092] Furthermore, when the hydrophobic catalyst - non - supported particles 11 are added and dispersed, since the hydrophobic catalyst - non - supported particles 11 generate a repulsive force with the hydrophilic solvent, the hydrophobic main chain of the ionomer 13 and the catalyst - non - supported particles 11 attract and aggregate, taking a form in which the hydrophilic functional group (side chain) of the ionomer 13 faces outward.

[0093] Next, in the second step (S02) of adding and mixing a conductive mesoporous material 12 having a lower hydrophobicity than the catalyst - non - supported particles 11 and carrying a catalyst 14 inside mesopores to the first ink prepared in the first step to prepare a second ink, since the hydrophobicity of the mesoporous material 12 carrying the catalyst 14 is lower than the hydrophobicity of the catalyst - non - supported particles 11, the adsorption force between the hydrophobic main chain of the ionomer 13 in the hydrophilic solvent and the mesoporous material 12 carrying the catalyst 14 becomes weaker than the adsorption force between the hydrophobic main chain of the ionomer 13 and the catalyst - non - supported particles 11, and the mesoporous material 12 carrying the catalyst 14 is dispersed in the ink without the adsorption between the catalyst - non - supported particles 11 and the ionomer 13 being released.

[0094] In the third step (S03, S04) of applying and drying the second ink produced in the second step, when this ink is applied and dried to form the cathode catalyst layer 3c, a large amount of the ionomer 13 is adsorbed onto the catalyst non-supported particles 11, and a cathode catalyst layer 3c having a structure in which the mesoporous material 12 supporting the catalyst 14 exists around the ionomer 13 is obtained.

[0095] The cathode catalyst layer 3c formed in three steps as described above has more of the ionomer 13 adsorbed onto the catalyst non-supported particles 11, and the coverage rate of the ionomer 13 on the mesoporous material 12 supporting the catalyst is lower than the coverage rate of the ionomer 13 on the catalyst non-supported particles 11. Therefore, the contact between the catalyst 14 and the ionomer 13 is reduced, and a decrease in catalytic activity can be suppressed.

[0096] Also, the hydrogen ions (H + ) necessary for the electrochemical reaction are conducted through the cathode catalyst layer 3c by the ionomer 13 adsorbed in large amounts around the catalyst non-supported particles 11, and are conducted to the catalyst 14 through water, thereby ensuring the hydrogen ion (H + ) conductivity.

[0097] As a result, a cathode catalyst layer 3c having a structure in which more of the ionomer 13 is adsorbed around the catalyst non-supported particles 11 can be obtained by a simple process of ink preparation and coating, and a highly efficient cathode catalyst layer 3c that achieves both an improvement in catalytic activity and a suppression of a decrease in hydrogen ion conductivity can be obtained.

[0098] (Other embodiments) As described above, as an example of the technology disclosed in this submission, Embodiment 1 has been described. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, etc. are made. It is also possible to combine the constituent elements described in Embodiment 1 above to form a new embodiment.

[0099] Therefore, other embodiments will be exemplified below.

[0100] In Embodiment 1, as an example of the electrolyte membrane - electrode assembly 5, the fuel cell 10 in which the catalyst layer of the present disclosure is applied to the cathode catalyst layer 3c was described. However, the catalyst layer of the present disclosure may be applied to the anode catalyst layer 3a.

[0101] If the catalyst layer of the present disclosure is applied to the anode catalyst layer 3a, the amount of the ionomer 13 in direct contact with the catalyst 14 decreases. Therefore, even in the oxidation reaction (Chemical Equation 1) in which hydrogen occurring at the anode 2a dissociates into hydrogen ions and electrons, a decrease in catalytic activity can be suppressed.

[0102] Furthermore, by ensuring hydrogen ion conductivity by the ionomer 13 adsorbed on the catalyst - non - supported particles 11, a decrease in the hydrogen ion conductivity of the anode catalyst layer 3a due to a decrease in the coating amount of the ionomer 13 on the mesoporous material 12 can be suppressed.

[0103] Therefore, without impairing the hydrogen ion conductivity, a decrease in catalytic activity due to ionomer poisoning can be suppressed, and a highly efficient electrolyte membrane - electrode assembly 5 can be provided.

[0104] In Embodiment 1, as an example of the electrolyte membrane 1, a perfluorosulfonic acid resin membrane was described. However, the electrolyte membrane 1 is for conducting ions (hydrogen ions) between the anode 2a and the cathode 2c, and any material having both hydrogen ion conductivity and gas barrier properties may be used.

[0105] Therefore, the electrolyte membrane 1 is not limited to the perfluorosulfonic acid resin membrane. Examples of the electrolyte membrane 1 include an ion - exchangeable fluorine - based resin membrane or an ion - exchangeable hydrocarbon - based resin membrane.

[0106] However, the perfluorosulfonic acid resin membrane used for the electrolyte membrane 1 in Embodiment 1 is preferable because it has high hydrogen ion conductivity and exists stably even in the power generation environment of the fuel cell 10.

[0107] The ion exchange capacity of the ion exchange resin is preferably 0.9 meq / g or more and 2.0 meq / g or less of dry resin. When the ion exchange capacity is 0.9 meq / g or more of dry resin, it is easy to obtain high hydrogen ion conductivity. When the ion exchange capacity is 2.0 meq / g or less of dry resin, swelling of the resin due to water absorption is suppressed, and dimensional changes of the electrolyte membrane 1 are suppressed, which is preferable.

[0108] Also, the film thickness of the electrolyte membrane 1 is preferably 5 μm or more and 50 μm or less. When the film thickness is 5 μm or more, high gas barrier properties can be obtained, and when it is 50 μm or less, high hydrogen ion conductivity can be obtained.

[0109] In Embodiment 1, as an example of the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c, a structure including two layers of carbon paper and a coating layer was used. However, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c may be any layer having a current collecting function, gas permeability, and water repellency.

[0110] Therefore, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c are not limited to a structure including two layers of carbon paper and a coating layer. The base material may be any material having excellent conductivity and gas and liquid permeability. Examples of materials other than carbon paper include porous materials such as carbon fiber cloth and carbon fiber felt.

[0111] The coating layer is a layer interposed between the base material and the anode catalyst layer 3a and the cathode catalyst layer 3c to reduce their contact resistance and improve the liquid permeability (drainage property). For example, it is formed mainly of a conductive material such as carbon black and a water repellent resin such as polytetrafluoroethylene (PTFE).

[0112] In Embodiment 1, as an example of the catalyst 14, platinum, a mixture or alloy containing platinum was used. However, the catalyst 14 is not particularly limited as long as it has a catalytic action on hydrogen gas or oxygen gas.

[0113] For materials of the catalyst 14 other than platinum, mixtures or alloys containing platinum, examples include metals such as ruthenium (Ru), iridium (Ir), rhodium (Rh), palladium (Pd), osmium (Os), tungsten (W), lead (Pb), iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), vanadium (V), molybdenum (Mo), gallium (Ga), and aluminum (Al), mixtures of these metals, alloys, etc.

[0114] However, platinum, mixtures or alloys containing platinum used for the catalyst 14 in Embodiment 1 are preferable as materials for the catalyst 14 from the viewpoints of improving catalytic activity, poisoning resistance against carbon monoxide, etc., and heat resistance.

[0115] When the catalyst is made of an alloy, the composition of the alloy can be such that the platinum content is 30 to 90 atomic % and the content of other metals is 10 to 70 atomic %, although it also depends on the types of metals to be alloyed. The average particle size of the catalyst is not particularly limited, but from the viewpoints of improving catalyst utilization and the supportability on the carbon carrier, it is preferably 1 to 30 nm. A particle size that can enter the interior of the mesopores is preferable.

[0116] In Embodiment 1, carbon black was used as the catalyst support material for the anode catalyst layer 3a and the mesoporous material 12 for the cathode catalyst layer 3c. However, the catalyst support material for the anode catalyst layer 3a and the mesoporous material 12 for the cathode catalyst layer 3c are not limited to carbon black.

[0117] As the catalyst support material for the anode catalyst layer 3a and the mesoporous material 12 for the cathode catalyst layer 3c, conductive porous carbon having pores inside (such as mesoporous carbon) can be used.

[0118] Before supporting the catalyst metal particles, the mesoporous carbon has a mode radius of mesopores of 1 to 25 nm and a pore volume of mesopores of 1.0 to 3.0 cm 3 / g may be sufficient. The pore volume of the mesopores is 1.0 cm 3If it is 3.0 g or more, a large amount of catalytic metal can be supported inside the mesoporous carbon, and 3.0 cm 3 If it is 3.0 g or less, the strength of the mesoporous carbon as a structure increases.

[0119] Further, the mesoporous carbon may be configured such that the average particle size is 200 to 1000 nm. If the average particle size is 200 nm or more, the region where the ionomer 13 penetrates into the mesopores becomes small with respect to the pore volume of the mesopores, so the proportion of the catalytic metal affected by the poisoning by the ionomer 13 becomes small.

[0120] Therefore, it is considered that the catalytic activity can be improved by setting the average particle size of the mesoporous carbon to 200 nm or more. Further, if the average particle size of the mesoporous carbon is 1000 nm or less, the reaction gas is easily supplied to the catalyst 14 supported inside the mesopores of the mesoporous carbon.

[0121] Note that the above-described 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 the equivalent scope thereof.

Industrial Applicability

[0122] The present disclosure can suppress a decrease in catalytic activity due to ionomer poisoning without impairing hydrogen ion conductivity, and thus is applicable to an electrolyte membrane-electrode assembly having a highly efficient catalyst layer. Specifically, it is useful for an electrode catalyst used in an electrolyte membrane-electrode assembly constituting a cell of a fuel cell, a cell of a hydrogen purifier, or a cell of water electrolysis.

Explanation of Reference Numerals

[0123] 1 Electrolyte membrane 2a Anode 2c Cathode 3a Anode catalyst layer 3c Cathode catalyst layer 4a Anode gas diffusion layer 4c Cathode gas diffusion layer 5 Electrolyte membrane - electrode assembly 6a Anode separator 6c Cathode separator 10 Fuel cell 11 Catalyst non - supported particles 12 Mesoporous material 13 Ionomer 14 Catalyst 15 Ionomer solution 16 Water 17 Ethanol

Claims

1. A conductive mesoporous material with a catalyst supported inside its mesopores, conductive catalyst-free particles without a supported catalyst, and an ionomer coating the mesoporous material and the catalyst-free particles, which is a catalyst layer used in an electrolyte membrane-electrode assembly, wherein the hydrophobicity of the catalyst-free particles is higher than that of the mesoporous material, the ionomer comprises a hydrophilic functional group and a hydrophobic main chain, and a catalyst layer characterized in that the ratio of the surface area of the catalyst-free particles coated with the ionomer to the total surface area of the catalyst-free particles is greater than the ratio of the surface area of the mesoporous material coated with the ionomer to the total surface area of the mesoporous material.

2. The mode diameter of the catalyst-free particles is 0.22 times or less the mode diameter of the mesoporous material, the mesoporous materials are in proximity to each other, and the catalyst-free particles are arranged around the mesoporous material so as to fill the gaps formed between the mesoporous materials. The catalyst layer according to Claim 1.

3. An electrolyte membrane, an anode provided on one main surface of the electrolyte membrane, and a cathode provided on the other main surface of the electrolyte membrane, wherein the cathode includes the catalyst layer according to Claim 1 or 2. An electrolyte membrane-electrode assembly.

4. A fuel cell comprising the electrolyte membrane-electrode assembly according to Claim 3.

5. A method for manufacturing a catalyst layer used in an electrolyte membrane-electrode assembly, a first step of mixing and dispersing an ionomer having a hydrophilic functional group and a hydrophobic main chain, conductive catalyst-free particles without a supported catalyst, and a hydrophilic solvent to prepare a first ink, a second step of adding and mixing a conductive mesoporous material having a lower hydrophobicity than the catalyst-free particles and having a catalyst supported inside its mesopores to the first ink to prepare a second ink, and a third step of applying and drying the second ink. A method for manufacturing a catalyst layer.

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