Catalyst layer for fuel cells, electrolyte membrane-electrode assembly, and fuel cell

Abstract

To provide a catalyst layer for a fuel battery, with high efficiency by improving a hydrogen ion conductive property while suppressing a catalyst poisoning due to an ionomer.SOLUTION: A catalyst layer for a fuel battery, in the present disclosure, comprises: a conductive mesoporous material; a catalyst carried into an internal part of at least a mesoporous of the mesoporous material; a catalyst non-carrier fiber that does not carry the catalyst; and an ionomer with a hydrogen ion conductive performance for coating the mesoporous material and the catalyst non-carrier fiber. The catalyst non-carrier fiber has a hydrophilic nature higher than that of the mesoporous material, and the ionomer includes a hydrophilic part made of a sulfo group. A ratio of a front surface area of the catalyst non-carrier fiber coated with the ionomer and a whole front surface area of the catalyst non-carrier fiber is larger than a ratio of the front surface area of the mesoporous material coated with the ionomer and the whole front surface of the mesoporous material.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a catalyst layer in which a catalyst-supported mesoporous material having a catalyst supported in mesopores of a mesoporous material is coated with a hydrogen ion-conductive ionomer. This catalyst layer includes a mesoporous material, a catalyst supported in the mesopores of the mesoporous material, and a hydrogen ion-conductive ionomer that coats the mesoporous material and the catalyst to increase the utilization rate of the catalyst.

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 highly efficient catalyst layer for a fuel cell, an electrolyte membrane-electrode assembly using the catalyst layer as a cathode, and a fuel cell using the electrolyte membrane-electrode assembly, by suppressing catalyst poisoning by an ionomer and improving hydrogen ion conductivity.

Means for Solving the Problems

[0005] One aspect of the catalyst layer for a fuel cell according to the present disclosure includes a conductive mesoporous material, a catalyst supported at least inside the mesopores of the mesoporous material, a catalyst-free fiber not supporting the catalyst, and a hydrogen ion-conductive ionomer that coats the mesoporous material and the catalyst-free fiber.

[0006] Furthermore, the catalyst-free fibers have higher hydrophilicity than the mesoporous material, the ionomer has a hydrophilic portion consisting of sulfo groups, and the ratio of the surface area of ​​the catalyst-free fibers coated with the ionomer to the total surface area of ​​the catalyst-free fibers 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.

[0007] One embodiment of the electrolyte membrane-electrode assembly according to the present disclosure comprises 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 a fuel cell catalyst layer according to the present disclosure.

[0008] The fuel cell according to this disclosure is characterized by comprising an electrolyte membrane-electrode assembly according to this disclosure. [Effects of the Invention]

[0009] The fuel cell catalyst layer in this disclosure utilizes the property that the sulfo group, which is the hydrophilic part of the ionomer, preferentially adsorbs onto the hydrophilic fiber surface. By preferentially coating the hydrophilic non-catalyst fibers with the ionomer, the amount of ionomer coating on the mesoporous material is reduced. As a result, the proportion of the catalyst supported on the mesoporous material that is coated with ionomer is reduced, and poisoning of the catalyst supported on the mesoporous material by ionomer can be suppressed.

[0010] Furthermore, the ionomer coated on the hydrophilic catalyst-free fibers connects adjacent mesoporous materials, thereby securing hydrogen ion transport pathways between adjacent mesoporous materials and forming a catalyst layer. This can improve the hydrogen ion conductivity.

[0011] Therefore, it is possible to improve hydrogen ion conductivity while suppressing the decrease in catalytic activity due to catalyst poisoning, thereby providing a highly efficient catalyst layer for fuel cells.

[0012] In the electrolyte membrane-electrode assembly described herein, the catalyst-unsupported fibers have higher hydrophilicity in the catalyst layer of the cathode compared to the mesoporous material. As a result, the sulfo groups, which are the hydrophilic portion of the ionomer, are preferentially adsorbed onto the catalyst-unsupported fibers. Therefore, catalyst poisoning can be suppressed and high hydrogen ion conductivity can be obtained, providing an electrolyte membrane-electrode assembly that exhibits a high power generation voltage when used in a fuel cell.

[0013] The fuel cell in this disclosure comprises the electrolyte membrane-electrode assembly of this disclosure, and therefore can provide a fuel cell that generates a high power output voltage. [Brief explanation of the drawing]

[0014] [Figure 1] Schematic cross-sectional view of the fuel cell catalyst layer in Embodiment 1 [Figure 2] Schematic cross-sectional view of the fuel cell in Embodiment 1 [Figure 3] Schematic diagram showing the structure of the ionomer in Embodiment 1 [Modes for carrying out the invention]

[0015] (Knowledge and other information that formed the basis of this disclosure) At the time the inventors arrived at this disclosure, the technique of forming a three-phase interface in the catalyst layer of a fuel cell was thought to improve performance by bringing the catalyst and ionomer into contact from the perspective of hydrogen ion supply. However, in recent years, it has become clear that the sulfur elements constituting the sulfo groups in the ionomer strongly adsorb to the catalyst, poisoning the catalyst and actually degrading its performance.

[0016] Therefore, in this industry, suppressing catalyst poisoning by ions was a challenge, and it was common practice to design products that prevented contact between the ionomer and the catalyst by encapsulating the catalyst in a carbon support with a large capacity of mesopores, such as a mesoporous material.

[0017] However, the catalysts outside the mesopores of the mesoporous material and near the entrances of the mesopores are in contact with the ionomer, and the poisoning of the catalyst by the ionomer cannot be sufficiently suppressed. As a result, increasing the amount of the ionomer increases the poisoning of the catalyst, while decreasing the amount of the ionomer makes the ionomer discontinuous in the catalyst layer, resulting in the opposite problem that the hydrogen ion resistance of the catalyst layer for fuel cells increases.

[0018] Under such circumstances, in order to solve the opposite problems, the inventors improved the hydrogen ion conductivity in the catalyst layer by connecting adjacent mesoporous materials with catalyst-free fibers coated with an ionomer, and at the same time, obtained the idea of adsorbing the sulfonic acid groups in the ionomer onto the catalyst-free fibers to reduce the amount of sulfonic acid groups adsorbed onto the mesoporous material.

[0019] Then, the inventors utilized the property that the sulfonic acid groups, which are the hydrophilic parts of the ionomer, preferentially adsorb onto hydrophilic materials, and by mixing catalyst-free fibers with higher hydrophilicity than the mesoporous material into the catalyst layer, found that it is possible to suppress the poisoning of the catalyst in the mesoporous material while improving the hydrogen ion conductivity, thus arriving at the subject matter of the present disclosure.

[0020] Therefore, the present disclosure provides a catalyst layer for a fuel cell that achieves both excellent catalytic activity and high hydrogen ion conductivity.

[0021] Hereinafter, embodiments will be described in detail with reference to the drawings. However, detailed descriptions that are not necessary may be omitted. For example, detailed descriptions of well-known matters or duplicate descriptions of substantially the same configurations may be omitted.

[0022] It should be noted that 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.

[0023] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to FIGS. 1 to 3.

[0024] [1-1. Structure] (fuel cell) Figure 2 shows an example configuration of the fuel cell 40. The fuel cell 40 shown in Figure 2 is a solid polymer electrolyte fuel cell that generates electricity by receiving hydrogen gas and oxygen gas.

[0025] As shown in Figure 2, the fuel cell 40 includes an anode separator 24, a cathode separator 28, and an electrolyte membrane-electrode assembly 30 provided between the anode separator 24 and the cathode separator 28.

[0026] The surface of the electrolyte membrane-electrode assembly 30 in the anode separator 24 that is in contact with the anode 31 has a channel for flowing hydrogen gas supplied to the fuel cell 40 to the anode 31.

[0027] The surface of the electrolyte membrane-electrode assembly 30 in the cathode separator 28 that is in contact with the cathode 32 has a channel for flowing oxygen gas supplied to the fuel cell 40 to the cathode 32.

[0028] If the fuel cell 40 is a stack structure in which multiple fuel cells are stacked in the thickness direction, the surface of the anode separator 24 opposite to the surface where the flow path is formed is electrically connected to the surface of the cathode separator 28 of the adjacent fuel cell 40 that is opposite to the surface where the flow path is formed, and the surface of the cathode separator 28 opposite to the surface where the flow path is formed is electrically connected to the surface of the anode separator 24 of the adjacent fuel cell 40 that is opposite to the surface where the flow path is formed.

[0029] (Electrolyte membrane-electrode assembly) As shown in Figure 2, the electrolyte membrane-electrode assembly 30 comprises an electrolyte membrane 21, an anode 31 including an anode catalyst layer 22 and an anode gas diffusion layer 23, and a cathode 32 including a cathode catalyst layer 26 and a cathode gas diffusion layer 27, with the electrolyte membrane 21 sandwiched on both sides by the anode 31 and the cathode 32.

[0030] The anode catalyst layer 22 is located on one main surface of the electrolyte membrane 21. The cathode catalyst layer 26 is located on the other main surface of the electrolyte membrane 21. The anode gas diffusion layer 23 is located on the side of the anode catalyst layer 22 opposite to the electrolyte membrane 21. The cathode gas diffusion layer 27 is located on the side of the cathode catalyst layer 26 opposite to the electrolyte membrane 21.

[0031] An anode separator 24 is positioned on the side of the anode gas diffusion layer 23 opposite to the anode catalyst layer 22, and a cathode separator 28 is positioned on the side of the cathode gas diffusion layer 27 opposite to the cathode catalyst layer 26.

[0032] (electrolyte membrane) The electrolyte membrane 21 facilitates hydrogen ion conduction between the anode 31 and the cathode 32, and therefore needs to possess both hydrogen ion conductivity and gas barrier properties. In this embodiment, a perfluorosulfonic acid resin membrane was used as the material for the electrolyte membrane 21. This membrane is preferred because it has high hydrogen ion conductivity and remains stable even under the power generation environment of the fuel cell 40.

[0033] (Gas diffusion layer) The anode gas diffusion layer 23 and the cathode gas diffusion layer 27 are layers that possess current collection properties, gas permeability, and water repellency, respectively. The anode gas diffusion layer 23 and the cathode gas diffusion layer 27 may each consist of two layers: a substrate and a coating layer.

[0034] The substrate can be any material that has excellent conductivity and permeability to gases and liquids. In this embodiment, carbon paper was used as the substrate material.

[0035] The coating layer is interposed between the catalyst layer (anode catalyst layer 22, cathode catalyst layer 26) and the substrate to reduce the contact resistance between the catalyst layer and the substrate, thereby improving the permeability (drainage) of the liquid.

[0036] The coating layer in this embodiment is formed mainly from a conductive material such as carbon black and a water-repellent resin such as polytetrafluoroethylene (PTFE).

[0037] (catalyst layer) The anode catalyst layer 22 is a layer that promotes the electrochemical reaction of the anode 31 and is located on one main surface of the electrolyte membrane 21. The cathode catalyst layer 26 is a layer that promotes the electrochemical reaction of the cathode 32 and is located on the other main surface of the electrolyte membrane 21.

[0038] The anode catalyst layer 22 contains a catalyst-supporting material made of carbon black, a catalyst made of platinum, and a hydrogen ion-conducting ionomer. The catalyst is supported on at least the catalyst-supporting material. At least a portion of the outer surface of the catalyst-supporting material is covered with the ionomer.

[0039] The cathode catalyst layer 26 is composed of a catalyst layer 6 having the structure shown in Figure 1, and is laminated on the other main surface of the electrolyte membrane 21. The catalyst layer 6 contains hydrophilic catalyst unsupported fibers 1, a mesoporous material 2, an ionomer 3, and a catalyst 5.

[0040] The catalyst layer 6 comprises a conductive mesoporous material 2, a catalyst 5 supported at least inside the mesopores of the mesoporous material 2, hydrophilic catalyst-free fibers 1 that do not support the catalyst 5, and a hydrogen ion-conductive ionomer 3 that covers the mesoporous material 2 and the hydrophilic catalyst-free fibers 1. The hydrophilic catalyst-free fibers 1 are more hydrophilic than the mesoporous material 2. The ionomer 3 has a hydrophilic portion consisting of sulfo groups 4, as shown in Figure 3.

[0041] Furthermore, in the catalyst layer 6, the ratio of the surface area of ​​the hydrophilic catalyst unsupported fibers 1 coated with ionomer 3 to the total surface area of ​​the hydrophilic catalyst unsupported fibers 1 is greater than the ratio of the surface area of ​​the mesoporous material 2 coated with ionomer 3 to the total surface area of ​​the mesoporous material 2. In other words, the coverage rate of ionomer 3 on the hydrophilic catalyst unsupported fibers 1 is higher than the coverage rate of ionomer 3 on the mesoporous material 2.

[0042] In this embodiment, the mesoporous material 2 may aggregate with other mesoporous material 2.

[0043] (catalyst) The material of catalyst 5 is not particularly limited as long as it has catalytic activity for hydrogen gas or oxygen gas, but from the viewpoint of improving catalytic activity (hydrogen oxidation activity for anode catalyst layer 22, and oxygen reduction activity for cathode catalyst layer 26), toxicity resistance to carbon monoxide, heat resistance, etc., the material of catalyst 5 is preferably platinum or an alloy containing platinum. Preferably, catalyst 5 has a platinum content of 30 to 90 atomic percent and a content of a metal other than platinum of 10 to 70 atomic percent.

[0044] The average diameter of catalyst 5 is not particularly limited, but from the viewpoint of catalyst utilization rate and durability, it is preferable that the average diameter of catalyst 5 is 1 to 30 nm. Furthermore, it is preferable that the average diameter of catalyst 5 is such that it fits within the mesopores of the mesoporous material 2.

[0045] In this embodiment, the catalyst 5 for the cathode catalyst layer 26 was an alloy containing platinum and cobalt with an average particle size of 4 nm, having a platinum content of 70 atomic percent and a cobalt content of 30 atomic percent.

[0046] (Mesoporous material) In this embodiment, hydrophobic mesoporous carbon having mesopores that communicate from the material surface to the interior was used as the mesoporous material 2 for the catalyst layer 6.

[0047] The mesoporous carbon is constructed to have an average diameter of 200 nm or more. If the mesoporous carbon has an average diameter of 200 nm or more, mesopores with an average radius of 1 to 25 nm are formed that communicate from the surface to the interior of the material, and catalyst 5 with a particle size of 20 nm or less can be supported within the mesopores.

[0048] The mesoporous material 2 used in the catalyst layer 6 of this embodiment has an average radius of 10 nm for the mesopores and a pore volume of 2.0 cm³ before the catalyst 5 is supported in the mesopores. 3 The value is / g. Furthermore, the average diameter of the mesoporous material 2 is configured to be 600 nm.

[0049] (Ionoma) The ionomer 3 of the cathode catalyst layer 26 (catalyst layer 6) transfers hydrogen ions that have passed through the electrolyte membrane 21 from the anode 31 side to the cathode 32 side to the catalyst 5 in the cathode catalyst layer 26.

[0050] In this embodiment, perfluorosulfonic acid resin, which is a solid polymer material (hydrogen ion conductive resin) of the same quality as the electrolyte membrane 21, is used as the ionomer 3. This perfluorosulfonic acid resin is suitable because it has high hydrogen ion conductivity among ion conductive resins and remains stable even under the power generation environment of the fuel cell 40.

[0051] Figure 3 shows the structural formula of ionoma 3. It consists of a carbon-fluorine main chain skeleton and a perfluoro side chain with sulfo group 4. Sulfo group 4 is hydrophilic and plays a role in conducting hydrogen ions. Furthermore, catalyst poisoning occurs when the sulfur element contained in sulfo group 4 strongly adsorbs to platinum.

[0052] (Hydrophilic catalyst unsupported fiber) The material of the hydrophilic catalyst-free fiber 1 is a fiber with higher hydrophilicity than the mesoporous material 2, and is not particularly limited as long as it does not support a catalyst. In this embodiment, as the hydrophilic catalyst-free fiber 1, VGCF(registered trademark) (product name: VGCF(registered trademark)-H), a carbon nanotube synthesized by the CVD method and manufactured by Showa Denko, was used from the viewpoint of conductivity and low impurity content.

[0053] The method for hydrophilically treating catalyst-unsupported fibers that have not been hydrophilically treated is not particularly limited as long as it can impart hydrophilic functional groups such as hydroxyl groups and carboxyl groups to the catalyst-unsupported fibers that have not been hydrophilically treated. In this embodiment, a plasma treatment method was used as the method for hydrophilically treating the catalyst-unsupported fibers that have not been hydrophilically treated, from the viewpoint of mass production and uniformity.

[0054] In this embodiment, the plasma treatment was performed by placing 10 g of VGCF (registered trademark) into a treatment vessel and using a 10 kV output for 30 minutes under conditions of an Ar gas atmosphere.

[0055] Functional species present in plasma-treated VGCF (registered trademark) were measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the results showed an increase in hydroxyl groups and carboxyl groups compared to before treatment. This confirmed that plasma treatment was able to form hydrophilic catalyst-unsupported fibers 1 with high hydrophilicity.

[0056] From the viewpoint of improving hydrogen ion conductivity within the catalyst layer 6, the length of the hydrophilic catalyst unsupported fiber 1 is preferably longer than twice the average diameter of the mesoporous material 2. In this embodiment, a hydrophilic catalyst unsupported fiber 1 with an average length of 6 μm was used, relative to the average diameter of the mesoporous material 2 of 600 nm.

[0057] Furthermore, if the hydrophilic catalyst unsupported fibers 1 are conductive, the contact points between the mesoporous material 2 and the hydrophilic catalyst unsupported fibers 1 become conductive contact points, thereby increasing the number of conductive contact points in the catalyst layer 6 and improving the conductivity within the catalyst layer 6.

[0058] (Method for manufacturing the catalyst layer) The catalyst layer 6 in this embodiment was fabricated by the following process.

[0059] (First step in the method for manufacturing the catalyst layer) In the first step, the ionomer 3 is adsorbed onto the hydrophilic catalyst-unsupported fiber 1 in the catalyst ink.

[0060] A mesoporous material 2, on which catalyst 5 was supported, was added to a mixed solvent containing ethanol and water in a 1:1 ratio.

[0061] Furthermore, hydrophilic catalyst-free fibers 1 (hydrophilic treated VGCF®) were added such that the weight ratio of hydrophilic catalyst-free fibers 1 to the total weight of mesoporous material 2 was 0.3.

[0062] Furthermore, Ionoma 3 (manufactured by AGC Inc., Flemion®) was added in such a way that the weight ratio of Ionoma 3 to the total weight of the mesoporous material 2 was 1.4, and a catalyst ink with a solid content concentration of 7% was mixed in.

[0063] The mixed catalyst ink was subjected to a wet atomization process (Sugino Machine, Starburst) to disperse the catalyst support at 100 MPa. Subsequently, the catalyst ink was stirred for 20 minutes in a variable-speed mixer (Kurabo, Mazelstar).

[0064] During the dispersion and diffusion processes of the catalyst ink, the sulfo groups 4, which are the hydrophilic portion of ionomer 3 in the catalyst ink, preferentially adsorb onto the surface of the hydrophilic catalyst-unsupported fibers 1, which have higher hydrophilicity than the mesoporous material 2. Therefore, within the catalyst ink, ionomer 3 preferentially coats the outer surface of the hydrophilic catalyst-unsupported fibers 1.

[0065] (Second step in the method for manufacturing the catalyst layer) In the second step, a catalyst layer 6 was formed by applying and drying the catalyst ink prepared in the first step. At this time, the electrolyte film 21 was placed in a coating machine heated to a surface temperature of 70°C, and the catalyst ink was directly applied to the main surface of the electrolyte film 21 by die coating. The catalyst layer 6 was formed by drying the catalyst ink on the main surface of the electrolyte film 21.

[0066] During the coating and drying process, the ink solvent is evaporated and removed, resulting in a state where the ionomer 3 dispersed in the catalyst ink covers the outer surface of the hydrophilic catalyst-unsupported fiber 1 more than the mesoporous material 2.

[0067] Through the above process, a catalyst layer 6 can be obtained in which the ratio of the surface area of ​​the hydrophilic catalyst unsupported fibers 1 coated on the ionomer 3 to the total surface area of ​​the hydrophilic catalyst unsupported fibers 1 is greater than the ratio of the surface area of ​​the mesoporous material 2 coated on the ionomer 3 to the total surface area of ​​the mesoporous material 2 (in other words, a catalyst layer 6 in which the coverage rate of the ionomer 3 on the hydrophilic catalyst unsupported fibers 1 is higher than the coverage rate of the ionomer 3 on the mesoporous material 2).

[0068] [1-2. Operation] The operation and function of the fuel cell 40, configured as described above, will be explained below.

[0069] The operation method and function of the fuel cell 40 will be explained based on Figures 1 and 2.

[0070] The fuel cell 40 was operated by maintaining the temperature of the fuel cell 40 at the set temperature of 60°C, supplying humidified hydrogen gas with a dew point of 60°C at a flow rate of 100 cc / min to the flow path between the anode separator 24 and the anode 31, and supplying humidified air with a dew point of 60°C at a flow rate of 300 cc / min to the flow path between the cathode separator 28 and the cathode 32, and electrically connecting the anode separator 24 and the cathode separator 28 with an external circuit.

[0071] Next, the transfer of matter and electrochemical reactions in the operating fuel cell 40 will be described. Hydrogen gas supplied to the flow path between the anode separator 24 and the anode 31 passes through the anode gas diffusion layer 23 and reaches the anode catalyst layer 22.

[0072] At anode 31, hydrogen gas, as shown in (Chemical Formula 1), is converted into hydrogen ions (H + An oxidation reaction occurs in which hydrogen ions (H) dissociate from hydrogen gas into electrons. + The ionomer 3 in the anode catalyst layer 22 passes through the electrolyte membrane 21 and then moves to the cathode catalyst layer 26.

[0073] [ka]

[0074] Furthermore, electrons dissociated from hydrogen gas in the anode catalyst layer 22 are transmitted to the external circuit via the anode catalyst layer 22, the anode gas diffusion layer 23, and the anode separator 24. Electrons emitted from the external circuit pass through the cathode separator 28 and the cathode gas diffusion layer 27 to reach the cathode catalyst layer 26.

[0075] Furthermore, oxygen gas in the air supplied to the flow path between the cathode separator 28 and the cathode 32 passes through the cathode gas diffusion layer 27 and reaches the cathode catalyst layer 26.

[0076] At the cathode, hydrogen ions (H) are present, as shown in (Chemical Formula 2). + A reduction reaction occurs in which electrons and oxygen (O) combine to produce water.

[0077] [ka]

[0078] As shown in Figure 1, the catalyst layer 6 used in the cathode catalyst layer 26 of this embodiment consists of hydrophilic catalyst-unsupported fibers 1 coated with an ionomer 3, the ionomer 3, and a mesoporous material 2 on which the catalyst 5 is supported, all of which are dispersed or aggregated.

[0079] In this case, since the hydrophilic catalyst-free fiber 1 has higher hydrophilicity than the mesoporous material 2 on which the catalyst 5 is supported, the sulfo group 4, which is the hydrophilic part of the ionomer 3, is preferentially adsorbed onto the hydrophilic catalyst-free fiber 1.

[0080] This suppresses contact between the catalyst 5, which is located outside the mesoporous material 2, and the sulfo group 4 in the ionomer 3, thereby suppressing the strong adsorption of the sulfur element in the sulfo group 4 to the catalyst 5 (catalyst poisoning).

[0081] Furthermore, because the hydrophilic catalyst unsupported fiber 1 is highly hydrophilic, the ionomer 3 containing the hydrophilic sulfo group 4 is easily adsorbed, and the entire circumference of the hydrophilic catalyst unsupported fiber 1 becomes a hydrogen ion transport pathway. As a result, the hydrophilic catalyst unsupported fiber 1, which has high hydrogen ion conductivity due to the coating of the ionomer 3, connects adjacent mesoporous materials 2, thereby securing a hydrogen ion transport pathway between adjacent mesoporous materials 2, and thus improving the hydrogen ion conductivity within the catalyst layer 6.

[0082] [1-3. Effects, etc.] As described above, in this embodiment, the catalyst layer 6 used in the cathode catalyst layer 26 of the fuel cell 40 comprises a conductive mesoporous material 2, a catalyst 5 supported at least inside the mesopores of the mesoporous material 2, hydrophilic catalyst-unsupported fibers 1 that do not support the catalyst 5, and a hydrogen ion-conductive ionomer 3 that covers the mesoporous material 2 and the hydrophilic catalyst-unsupported fibers 1.

[0083] Here, the hydrophilic catalyst unsupported fiber 1 has higher hydrophilicity than the mesoporous material 2, and the ionomer 3 has a hydrophilic portion consisting of sulfo groups 4. Since the sulfo groups 4, which are the hydrophilic portion of the ionomer 3, preferentially adsorb to the hydrophilic catalyst unsupported fiber 1, the ratio of the surface area of ​​the hydrophilic catalyst unsupported fiber 1 coated on the ionomer 3 to the total surface area of ​​the hydrophilic catalyst unsupported fiber 1 is greater than the ratio of the surface area of ​​the mesoporous material 2 coated on the ionomer 3 to the total surface area of ​​the mesoporous material 2.

[0084] In this embodiment, the catalyst layer 6 used in the cathode catalyst layer 26 of the fuel cell 40 preferentially coats the hydrophilic catalyst-unsupported fibers 1 with ionomer 3, thereby reducing the amount of ionomer 3 coating the mesoporous material 2. This suppresses contact between the catalyst 5, which is located outside the mesoporous material 2, and the sulfo groups 4 in the ionomer 3, thus suppressing strong adsorption of sulfur elements in the sulfo groups 4 with the catalyst 5 (catalyst poisoning).

[0085] Furthermore, because the hydrophilic catalyst-free fiber 1 is highly hydrophilic, the ionomer 3 containing the hydrophilic sulfo group 4 is easily adsorbed, and the entire circumference of the hydrophilic catalyst-free fiber 1 becomes a hydrogen ion transport pathway.

[0086] As a result, the coating of ionomer 3 provides a hydrophilic catalyst with high hydrogen ion conductivity. The supporting fibers 1 connect adjacent mesoporous materials 2, thereby securing hydrogen ion transport pathways between them, and thus improving the hydrogen ion conductivity within the catalyst layer 6. As a result, a fuel cell catalyst layer that exhibits a high power generation voltage can be obtained.

[0087] In this embodiment, the catalyst layer 6 used in the cathode catalyst layer 26 of the fuel cell 40 may have hydrophilic catalyst unsupported fibers 1 that are longer than twice the average particle size of the mesoporous material 2.

[0088] This allows the mesoporous materials 2, which are spaced apart at intervals approximately equal to the average particle size of the mesoporous materials 2, to be connected by hydrophilic catalyst-unsupported fibers 1 with high hydrogen ion conductivity through coating with ionomer 3, thereby improving the hydrogen ion conductivity within the catalyst layer 6. As a result, further improvements in hydrogen ion conductivity can be achieved, and a catalyst layer 6 that enables more efficient catalytic reactions can be obtained.

[0089] As in the catalyst layer 6 of this embodiment, the hydrophilic catalyst-unsupported fibers 1 may also be conductive.

[0090] As a result, the contact points between the mesoporous material 2 and the hydrophilic catalyst-unsupported fibers 1 in the catalyst layer 6 become conductive contact points, thereby increasing the number of conductive contact points in the catalyst layer 6 and improving the conductivity of the catalyst layer 6.

[0091] As in this embodiment, the weight ratio of the ionomer 3 contained in the catalyst layer 6 to the total weight of the mesoporous material 2 contained in the catalyst layer 6 may be 0.5 or more and less than 1.8.

[0092] If the weight ratio of ionomer 3 contained in the catalyst layer 6 to the total weight of mesoporous material 2 contained in the catalyst layer 6 is 0.5 or greater, hydrogen ions necessary for the catalytic reaction will be transmitted to every corner of the catalyst layer 6. Furthermore, if the weight ratio of ionomer 3 contained in the catalyst layer 6 to the total weight of mesoporous material 2 contained in the catalyst layer 6 is less than 1.8, water clogging in the catalyst layer 6 due to an excess amount of ionomer 3 can be suppressed.

[0093] Therefore, if the weight ratio of the ionomer 3 contained in the catalyst layer 6 to the total weight of the mesoporous material 2 contained in the catalyst layer 6 is 0.5 or more and less than 1.8, the catalytic reaction is promoted, and a catalyst layer 6 that exhibits a high power generation voltage can be obtained.

[0094] As in this embodiment, the electrolyte membrane-electrode assembly 30 used in the fuel cell 40 comprises an electrolyte membrane 21, an anode 31 provided on one main surface of the electrolyte membrane 21, and a cathode 32 provided on the other main surface of the electrolyte membrane 21, wherein the cathode 32 (cathode catalyst layer 26) may include the catalyst layer 6 of this embodiment.

[0095] As a result, the cathode catalyst layer 26 in the electrolyte membrane-electrode assembly 30 has higher hydrophilicity of the hydrophilic catalyst-unsupported fibers 1 compared to the mesoporous material 2, so the sulfo groups 4, which are the hydrophilic parts of the ionomer 3, are preferentially adsorbed onto the hydrophilic catalyst-unsupported fibers 1. Therefore, catalyst poisoning can be suppressed and high hydrogen ion conductivity can be obtained, and an electrolyte membrane-electrode assembly 30 that exhibits a high power generation voltage when used in a fuel cell 40 can be obtained.

[0096] As in this embodiment, the fuel cell 40 may include the electrolyte membrane-electrode assembly 30 of this embodiment. This makes it possible to obtain a fuel cell 40 that generates a high power output voltage.

[0097] (Other embodiments) As described above, Embodiment 1 has been explained as an example of the technology disclosed in this application. However, the technology in this disclosure is not limited thereto, and modifications, additions, omissions, etc., may be made. This can also be applied to the above embodiment. Furthermore, it is possible to combine the components described in Embodiment 1 to create a new embodiment.

[0098] Therefore, other embodiments are illustrated below.

[0099] In Embodiment 1, a cathode catalyst layer 26 was described as an example of a catalyst layer 6. The catalyst layer 6 only needs to be designed to allow the catalytic reaction to proceed rapidly. Therefore, the catalyst layer 6 is not limited to a cathode catalyst layer 26. If the catalyst layer 6 is used as an anode catalyst layer 22, it is possible to suppress poisoning of the catalyst 5 by ions and achieve both high hydrogen ion conductivity, so that the hydrogen oxidation reaction can proceed rapidly and a high power generation voltage can be achieved.

[0100] In Embodiment 1, VGCF® manufactured by Showa Denko was used as an example of the hydrophilic catalyst unsupported fiber 1. However, the hydrophilic catalyst unsupported fiber 1 can be selected from, for example, PAN-based carbon fiber, pitch-based carbon fiber, carbon nanotubes, etc., from the viewpoint of conductivity and low impurity content.

[0101] In Embodiment 1, plasma treatment was used as an example of hydrophilic treatment for catalyst-free fibers. Any method that can impart hydrophilic functional groups such as hydroxyl groups and carboxyl groups to catalyst-free fibers is acceptable. Therefore, hydrophilic treatment for catalyst-free fibers can be selected from strong acid treatment, heat treatment, fluorine gas treatment, etc.

[0102] In Embodiment 1, the average diameter of VGCF(registered trademark)-H used in the hydrophilic catalyst unsupported fiber 1 was 150 nm. The average diameter of the hydrophilic catalyst unsupported fiber 1 is acceptable as long as it allows for easy adsorption of the ionomer 3 and ensures conductivity. Therefore, the average diameter of the hydrophilic catalyst unsupported fiber 1 can be selected from the range of 20 nm to 500 nm.

[0103] In Embodiment 1, the weight ratio of the hydrophilic catalyst unsupported fibers 1 contained in the catalyst layer 6 to the total weight of the mesoporous material 2 contained in the catalyst layer 6 was 0.3.

[0104] The weight ratio of the hydrophilic catalyst unsupported fibers 1 contained in the catalyst layer 6 to the total weight of the mesoporous material 2 contained in the catalyst layer 6 should be such that the catalyst layer 6 does not become too thick and hydrogen ion conductivity is improved. Therefore, the weight ratio of the hydrophilic catalyst unsupported fibers 1 contained in the catalyst layer 6 to the total weight of the mesoporous material 2 contained in the catalyst layer 6 can be selected from a range of 0.05 to 0.5.

[0105] Since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents. [Industrial applicability]

[0106] This disclosure can achieve both suppression of catalyst poisoning by ions and high hydrogen ion conductivity, making it applicable to highly efficient catalyst layers. Specifically, this disclosure is applicable to catalyst layers constituting fuel cells, hydrogen purifiers, or water electrolysis devices. [Explanation of Symbols]

[0107] 1. Hydrophilic catalyst unsupported fiber 2. Mesoporous materials 3 Ionoma 4. Sulfo group 5 Catalyst 6 Catalyst layer 21 Electrolyte membrane 22 Anode catalyst layer 23 Anode gas diffusion layer 24 Anode Separator 26 Cathode catalyst layer 27 Cathode gas diffusion layer 28 Cathode Separator 30 Electrolyte membrane-electrode assembly 31 Anodes 32 Cathode 40 Fuel Cell

Claims

1. The invention comprises a conductive mesoporous material, a catalyst supported at least inside the mesopores of the mesoporous material, catalyst-free fibers not supported by the catalyst, and a hydrogen ion-conductive ionomer covering the mesoporous material and the catalyst-free fibers. The catalyst-free fibers have higher hydrophilicity than the mesoporous material. The ionomer has a hydrophilic portion consisting of a sulfo group, A catalyst layer for a fuel cell, characterized in that the ratio of the surface area of ​​the catalyst-unsupported fibers coated on the ionomer to the total surface area of ​​the catalyst-unsupported fibers is greater than the ratio of the surface area of ​​the mesoporous material coated on the ionomer to the total surface area of ​​the mesoporous material.

2. The catalyst layer for a fuel cell according to claim 1, wherein the length of the catalyst-unsupported fibers is longer than twice the average particle size of the mesoporous material.

3. The catalyst layer for a fuel cell according to claim 1, wherein the catalyst-unsupported fibers are conductive.

4. The electrolyte membrane comprises an anode provided on one main surface of the electrolyte membrane and a cathode provided on the other main surface of the electrolyte membrane. The cathode is an electrolyte membrane-electrode assembly comprising a fuel cell catalyst layer according to any one of claims 1 or 3.

5. A fuel cell comprising the electrolyte membrane-electrode assembly according to claim 4.

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