Catalyst layer for fuel battery, electrolyte membrane-electrode assembly, and fuel battery
Patent Information
- Application Number
- JP2022175191
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-11-01
- Publication Date
- 2025-05-09
- Estimated Expiration
- 2042-11-01
AI Technical Summary
Existing catalyst layers in fuel cells suffer from catalyst poisoning by ionomers, which reduces hydrogen ion conductivity and catalyst activity, leading to decreased performance.
Incorporating hydrophilic non-catalyst-supported fibers with a higher hydrophilicity than mesoporous materials into the catalyst layer, where the ionomer's sulfo groups preferentially adsorb on these fibers, reducing contact with the catalyst and enhancing hydrogen ion conductivity while suppressing poisoning.
The catalyst layer achieves high hydrogen ion conductivity and maintains catalyst activity, resulting in a fuel cell with improved power generation voltage and efficiency.
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Abstract
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 technology]
[0002] Patent Document 1 discloses a catalyst layer in which a catalyst-supported mesoporous material, in which a catalyst is supported in the mesopores of a mesoporous material, is coated with a proton-conductive ionomer. This catalyst layer includes a mesoporous material, a catalyst supported in the mesopores of the mesoporous material, and a proton-conductive ionomer that enhances the utilization rate of the catalyst by coating the mesoporous material and the catalyst. [Prior art documents] [Patent documents]
[0003] [Patent Document 1] International Publication No. 2014 / 175099 Summary of the Invention [Problem to be solved by the invention]
[0004] The present disclosure provides a highly efficient catalyst layer for a fuel cell by improving hydrogen ion conductivity while suppressing catalyst poisoning by ionomers, an electrolyte membrane-electrode assembly using the catalyst layer as a cathode, and a fuel cell using the electrolyte membrane-electrode assembly. [Means for solving the problem]
[0005] One aspect of a catalyst layer for a fuel cell according to the present disclosure comprises an electrically conductive mesoporous material, a catalyst supported at least inside the mesopores of the mesoporous material, non-catalyst-supported fibers that do not support the catalyst, and a proton-conductive ionomer that coats the mesoporous material and the non-catalyst-supported fibers.
[0006] The non-catalyst-supported fiber is more hydrophilic than the mesoporous material, the ionomer has a hydrophilic portion consisting of a sulfo group, and the ratio of the surface area of the non-catalyst-supported fiber coated with the ionomer to the total surface area of the non-catalyst-supported fiber 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 the present disclosure is characterized by comprising the electrolyte membrane-electrode assembly according to the present disclosure. Effect of the Invention
[0009] The fuel cell catalyst layer disclosed herein utilizes the property of the sulfo group, which is the hydrophilic portion of the ionomer, to preferentially adsorb onto the hydrophilic fiber surface, and by preferentially coating the ionomer onto hydrophilic fibers that do not support a catalyst, the amount of ionomer coated on the mesoporous material is reduced. As a result, the proportion of catalyst coated by the ionomer among the catalyst supported on the mesoporous material is reduced, and poisoning of the catalyst supported on the mesoporous material by the ionomer can be suppressed.
[0010] In addition, the ionomer coated on the hydrophilic catalyst-free fiber connects adjacent mesoporous materials, ensuring hydrogen ion transport paths between adjacent mesoporous materials, and the catalyst layer The hydrogen ion conductivity of the electrolyte can be improved.
[0011] Therefore, hydrogen ion conductivity can be improved while suppressing a decrease in catalytic activity due to catalyst poisoning, and a highly efficient catalyst layer for a fuel cell can be provided.
[0012] In the electrolyte membrane-electrode assembly of the present disclosure, the catalyst-free fibers have higher hydrophilicity than the mesoporous material in the cathode catalyst layer, so that the sulfo groups, which are the hydrophilic parts of the ionomer, are preferentially adsorbed to the catalyst-free fibers. This makes it possible to suppress catalyst poisoning and obtain high hydrogen ion conductivity, and to provide an electrolyte membrane-electrode assembly that generates a high power generation voltage when used in a fuel cell.
[0013] The fuel cell according to the present disclosure includes the electrolyte membrane-electrode assembly according to the present disclosure, and therefore can provide a fuel cell that generates a high generated voltage. [Brief description of the drawings]
[0014] [Figure 1] Schematic cross-sectional view of a fuel cell catalyst layer according to the first embodiment. [Diagram 2] 1 is a schematic cross-sectional view of a fuel cell according to a first embodiment; [Diagram 3] Schematic diagram showing the structure of an ionomer in embodiment 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] (The knowledge and other information that formed the basis of this disclosure) At the time when the inventors arrived at this disclosure, it was believed that the technology of forming a three-phase interface in the catalyst layer of a fuel cell would improve performance by bringing the catalyst into contact with an ionomer from the perspective of hydrogen ion supply. However, in recent years, it has become clear that the sulfur element that constitutes the sulfo group in the ionomer strongly adsorbs to the catalyst, poisoning the catalyst and actually reducing its performance.
[0016] Therefore, in order to address the issue of preventing the poisoning of catalysts by ionomers, it has been common to design products in such a way that the ionomers are not brought into contact with the catalyst by encapsulating the catalyst in a carbon support having large mesopores, such as a mesoporous material.
[0017] However, the catalyst outside the mesopores of the mesoporous material and near the entrances to the mesopores come into contact with the ionomer, and poisoning of the catalyst by the ionomer cannot be sufficiently suppressed. As a result, there were conflicting issues: increasing the amount of ionomer increases catalyst poisoning, while decreasing the amount of ionomer causes the ionomer to become discontinuous within the catalyst layer, resulting in high hydrogen ion resistance in the fuel cell catalyst layer.
[0018] Under these circumstances, in order to solve these conflicting problems, the inventors came up with the idea of improving hydrogen ion conductivity in the catalyst layer by connecting adjacent mesoporous materials with non-catalyst-supported fibers coated with ionomer, and at the same time, reducing the amount of sulfo groups adsorbed to the mesoporous material by having the sulfo groups in the ionomer adsorb to the non-catalyst-supported fibers.
[0019] The inventors then discovered that by utilizing the property of the sulfo group, which is the hydrophilic part of the ionomer, to preferentially adsorb to hydrophilic materials and mixing non-catalyst-supporting fibers, which have higher hydrophilicity than the mesoporous material, into the catalyst layer, it is possible to improve hydrogen ion conductivity while suppressing poisoning of the catalyst in the mesoporous material, which constitutes the subject matter of the present disclosure.
[0020] Therefore, the present disclosure provides a catalyst layer for a fuel cell that combines excellent catalytic activity with high hydrogen ion conductivity.
[0021] Hereinafter, the embodiments will be described in detail with reference to the drawings. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters or duplicate description of substantially the same configuration may be omitted.
[0022] It should be noted 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.
[0023] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to FIGS.
[0024] [1-1. Configuration] (fuel cell) Fig. 2 shows an example of the configuration of a fuel cell 40. The fuel cell 40 shown in Fig. 2 is a solid polymer electrolyte fuel cell that receives a supply of hydrogen gas and oxygen gas and generates power.
[0025] As shown in FIG. 2, the fuel cell 40 has 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 anode separator 24 that abuts against the anode 31 of the electrolyte membrane-electrode assembly 30 has a flow path for allowing hydrogen gas to be supplied to the fuel cell 40 to flow to the anode 31 .
[0027] The surface of the cathode separator 28 that abuts against the cathode 32 of the electrolyte membrane-electrode assembly 30 has a flow path for allowing oxygen gas to be supplied to the fuel cell 40 to flow to the cathode 32 .
[0028] In the case where the fuel cells 40 have a stack structure in which multiple fuel cells 40 are stacked in the thickness direction, the surface of the anode separator 24 opposite the surface on which the flow path is formed is electrically connected to the surface of the cathode separator 28 of the fuel cell 40 adjacent to the anode separator 24 opposite the surface on which the flow path is formed, and the surface of the cathode separator 28 opposite the surface on which the flow path is formed is electrically connected to the surface of the anode separator 24 of the fuel cell 40 adjacent to the cathode separator 28 opposite the surface on which the flow path is formed.
[0029] (Electrolyte membrane-electrode assembly) As shown in FIG. 2, the electrolyte membrane-electrode assembly 30 includes 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, and is configured such that the electrolyte membrane 21 is sandwiched between the anode 31 and the cathode 32 on both sides.
[0030] The anode catalyst layer 22 is disposed on one main surface of the electrolyte membrane 21. The cathode catalyst layer 26 is disposed on the other main surface of the electrolyte membrane 21. The anode gas diffusion layer 23 is disposed on the side of the anode catalyst layer 22 opposite the electrolyte membrane 21. The cathode gas diffusion layer 27 is disposed on the side of the cathode catalyst layer 26 opposite the electrolyte membrane 21.
[0031] An anode separator 24 is disposed on the side of the anode gas diffusion layer 23 opposite to the anode catalyst layer 22 side, and a cathode separator 28 is disposed on the side of the cathode gas diffusion layer 27 opposite to the cathode catalyst layer 26 side.
[0032] (electrolyte membrane) The electrolyte membrane 21 is for conducting hydrogen ions between the anode 31 and the cathode 32, and is required to have both hydrogen ion conductivity and gas barrier properties. In this embodiment, a perfluorosulfonic acid resin membrane is used as the material for the electrolyte membrane 21. This membrane is preferable because it has high hydrogen ion conductivity and exists stably even in 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 have a current collecting function, gas permeability, and water repellency. The anode gas diffusion layer 23 and the cathode gas diffusion layer 27 may each include two layers, a substrate and a coating layer.
[0034] The substrate may be made of any material that has excellent electrical conductivity and gas and liquid permeability, and in this embodiment, carbon paper is used as the substrate.
[0035] The coating layer is a layer that 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 and improve liquid permeability (drainage ability).
[0036] The coating layer of the present 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 disposed 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 disposed on the other main surface of the electrolyte membrane 21.
[0038] The anode catalyst layer 22 includes a catalyst support material made of carbon black, a platinum catalyst, and a hydrogen ion conductive ionomer. The catalyst is supported on at least the catalyst support material. At least a portion of the outer surface of the catalyst support material supporting the catalyst is covered with the ionomer.
[0039] 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 includes an electrically 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. The hydrophilic catalyst-unsupported fibers 1 are more hydrophilic than the mesoporous material 2. The ionomer 3 has a hydrophilic portion consisting of a sulfo group 4, as shown in FIG. 3.
[0041] In addition, in the catalyst layer 6, the ratio of the surface area of the hydrophilic catalyst-unsupported fibers 1 coated with the ionomer 3 to the total surface area of the hydrophilic catalyst-unsupported fibers 1 is larger than the ratio of the surface area of the mesoporous material 2 coated with the ionomer 3 to the total surface area of the mesoporous material 2. In other words, the coverage of the hydrophilic catalyst-unsupported fibers 1 with the ionomer 3 is higher than the coverage of the mesoporous material 2 with the ionomer 3.
[0042] In the mesoporous material 2 of the present embodiment, the mesoporous material 2 may gather together to form aggregates.
[0043] (catalyst) The material of catalyst 5 is not particularly limited as long as it has a catalytic action 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), resistance to poisoning by carbon monoxide and the like, heat resistance, etc., the material of catalyst 5 is preferably platinum or an alloy containing platinum. Catalyst 5 preferably contains 30 to 90 atomic % platinum and 10 to 70 atomic % of metals other than platinum.
[0044] The average diameter of catalyst 5 is not particularly limited, but from the viewpoints of catalyst utilization rate and durability, the average diameter of catalyst 5 is preferably 1 to 30 nm. Moreover, the average diameter of catalyst 5 is preferably a particle size that can enter the mesopores of 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, with the platinum content being 70 atomic % and the cobalt content being 30 atomic %.
[0046] (Mesoporous materials) In this embodiment, as the mesoporous material 2 used in the catalyst layer 6, hydrophobic mesoporous carbon having mesopores communicating from the surface to the inside of the material was used.
[0047] The mesoporous carbon is configured to have an average diameter of 200 nm or more. When 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 of the material to the inside, and the catalyst 5 with a particle diameter of 20 nm or less can be supported in the mesopores.
[0048] The mesoporous material 2 used in the catalyst layer 6 of this embodiment has an average mesopore radius of 10 nm and a mesopore volume of 2.0 cm before the catalyst 5 is supported in the mesopores. 3 / g. The mesoporous material 2 is configured so that the average diameter is 600 nm.
[0049] (Ionomer) The ionomer 3 of the cathode catalyst layer (catalyst layer 6) transmits the 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 .
[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 preferable because it has high hydrogen ion conductivity among ion conductive resins and exists stably even in the power generation environment of the fuel cell 40.
[0051] Figure 3 shows the structural formula of ionomer 3. It is composed of a main chain skeleton made of carbon and fluorine and perfluoro side chains with sulfo groups 4. The sulfo groups 4 are hydrophilic and play a role in conducting hydrogen ions. In addition, the sulfur element contained in the sulfo groups 4 strongly adsorbs to platinum, causing catalyst poisoning.
[0052] (Hydrophilic catalyst-free fiber) The material of the hydrophilic catalyst-unsupported fiber 1 is not particularly limited as long as it is a fiber having a higher hydrophilicity than the mesoporous material 2 and does not support a catalyst. In this embodiment, as the hydrophilic catalyst-unsupported fiber 1, VGCF (registered trademark) (product name: VGCF (registered trademark)-H) manufactured by Showa Denko, which is a carbon nanotube synthesized by a CVD method, is used from the viewpoints of electrical conductivity and low impurity content.
[0053] The method for hydrophilically treating the non-catalyst-supported fiber that has not been hydrophilically treated is not particularly limited as long as it is a method that can impart hydrophilic functional groups such as hydroxyl groups and carboxyl groups to the non-catalyst-supported fiber that has not been hydrophilically treated. In the present embodiment, a plasma treatment method is used as the method for hydrophilically treating the non-catalyst-supported fiber that has not been hydrophilically treated from the viewpoints of mass productivity and uniformity.
[0054] The plasma treatment in this embodiment was carried out by putting 10 g of VGCF (registered trademark) into a treatment vessel, at an output of 10 kV, for 30 minutes in an Ar gas atmosphere.
[0055] When the functional groups present in the plasma-treated VGCF (registered trademark) were measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS), the results showed that the number of hydroxyl and carboxyl groups had increased compared to before the treatment. It was confirmed that the plasma treatment had produced hydrophilic catalyst-free fiber 1 with high hydrophilicity.
[0056] From the viewpoint of improving hydrogen ion conductivity in the catalyst layer 6, the length of the hydrophilic catalyst-unsupported fibers 1 is preferably longer than twice the average diameter of the mesoporous material 2. In this embodiment, the hydrophilic catalyst-unsupported fibers 1 used had an average length of 6 μm, while the mesoporous material 2 had an average diameter of 600 nm.
[0057] Furthermore, if the hydrophilic catalyst-unsupported fiber 1 is conductive, the contact points between the mesoporous material 2 and the hydrophilic catalyst-unsupported fiber 1 become conductive contacts, thereby increasing the number of conductive contacts in the catalyst layer 6 and improving the conductivity within the catalyst layer 6.
[0058] (Method of manufacturing catalyst layer) The catalyst layer 6 in this embodiment was produced by the following steps.
[0059] (First step of the method for producing the catalyst layer) In the first step, an ionomer 3 is adsorbed onto hydrophilic catalyst-free fibers 1 in a catalyst ink.
[0060] The mesoporous material 2 carrying the catalyst 5 was placed in a mixed solvent containing ethanol and water in a ratio of ethanol:water=1:1.
[0061] Furthermore, hydrophilic catalyst-unsupported fibers 1 (hydrophilically treated VGCF (registered trademark)) were added so that the weight ratio of the hydrophilic catalyst-unsupported fibers 1 to the total weight of the mesoporous material 2 was 0.3.
[0062] Furthermore, ionomer 3 (Flemion (registered trademark), manufactured by AGC Corporation) was added so that the weight ratio of ionomer 3 to the total weight of mesoporous material 2 was 1.4, and a catalyst ink with a solid content concentration of 7% was mixed.
[0063] The mixed catalyst ink was dispersed in the catalyst-supported carrier at 100 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) After that, the catalyst ink was stirred for 20 minutes using a variable-rotation mixer (Mazerustar, manufactured by Kurabo Industries, Ltd.).
[0064] During the process of dispersing and diffusing the catalyst ink, the sulfo group 4, which is the hydrophilic part of the ionomer 3 in the catalyst ink, is preferentially adsorbed onto the surface of the hydrophilic catalyst-unsupported fiber 1, which has higher hydrophilicity than the mesoporous material 2. Therefore, in the catalyst ink, the ionomer 3 is preferentially coated on the outer surface of the hydrophilic catalyst-unsupported fiber 1.
[0065] (Second step of the method for producing the catalyst layer) In the second step, the catalyst ink prepared in the first step was applied and dried to form a catalyst layer 6. At this time, the electrolyte membrane 21 was placed in a coater heated to a plate temperature of 70° C., and the catalyst ink was directly applied to the main surface of the electrolyte membrane 21 by a die coating method. The catalyst ink on the main surface of the electrolyte membrane 21 was then dried to form the catalyst layer 6.
[0066] During the application and drying process, the ink solvent is evaporated and removed, and a state is formed in which the ionomer 3 dispersed in the catalyst ink covers the outer surface of the hydrophilic catalyst-free fiber 1 in a larger amount than the mesoporous material 2.
[0067] Through the above steps, a catalyst layer 6 can be obtained in which the ratio of the surface area of the hydrophilic catalyst-unsupported fiber 1 coated with 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 with 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 to the hydrophilic catalyst-unsupported fiber 1 is higher than the coverage rate of the ionomer 3 to the mesoporous material 2).
[0068] [1-2. Operation] The operation and function of the fuel cell 40 constructed as above will now be described.
[0069] The operation method and action of the fuel cell 40 will be described with reference to FIGS.
[0070] The fuel cell 40 was operated by maintaining the temperature of the fuel cell 40 at a 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 by an external circuit.
[0071] Next, a description will be given of the transfer of materials and electrochemical reactions in the fuel cell 40 during operation. 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 the anode 31, hydrogen gas is converted into hydrogen ions (H + ) and electrons. Then, hydrogen gas dissociates into hydrogen ions (H + ) passes through the ionomer 3 in the anode catalyst layer 22, then passes through the electrolyte membrane 21, and migrates to the cathode catalyst layer .
[0073] [ka]
[0074] Furthermore, electrons dissociated from hydrogen gas in the anode catalyst layer 22 are transmitted to an 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, and 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 + ) combines with electrons and oxygen (O) to produce water in a reduction reaction.
[0077] [ka]
[0078] As shown in FIG. 1, the catalyst layer 6 used in the cathode catalyst layer 26 of this embodiment is composed of hydrophilic catalyst-unsupported fiber 1 coated with ionomer 3, the ionomer 3, and mesoporous material 2 supporting catalyst 5, which are present in a dispersed or aggregated state.
[0079] At this time, since the hydrophilic catalyst-unsupported fiber 1 has a higher hydrophilicity than the mesoporous material 2 supporting the catalyst 5, the sulfo group 4, which is the hydrophilic portion of the ionomer 3, is preferentially adsorbed onto the hydrophilic catalyst-unsupported fiber 1.
[0080] This prevents the catalyst 5 present outside the mesoporous material 2 from coming into contact with the sulfo groups 4 in the ionomer 3, thereby preventing the sulfur elements in the sulfo groups 4 from strongly adsorbing to the catalyst 5 (catalyst poisoning).
[0081] In addition, since the hydrophilic catalyst-unsupported fiber 1 is highly hydrophilic, the ionomer 3 containing the sulfo group 4, which is a hydrophilic portion, is easily adsorbed, and the entire circumference of the hydrophilic catalyst-unsupported fiber 1 becomes a hydrogen ion transport path. As a result, the hydrophilic catalyst-unsupported fiber 1, which has high hydrogen ion conductivity due to being coated with the ionomer 3, connects adjacent mesoporous materials 2, thereby ensuring a hydrogen ion transport path between adjacent mesoporous materials 2, and therefore the hydrogen ion conductivity in the catalyst layer 6 can be improved.
[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-free fibers 1 not supporting the catalyst 5, and a hydrogen ion conductive ionomer 3 coating the mesoporous material 2 and the hydrophilic catalyst-free fibers 1.
[0083] Here, the hydrophilic catalyst-unsupported fiber 1 is more hydrophilic than the mesoporous material 2, the ionomer 3 has a hydrophilic portion consisting of a sulfo group 4, and the sulfo group 4, which is the hydrophilic portion of the ionomer 3, is preferentially adsorbed onto the hydrophilic catalyst-unsupported fiber 1. Therefore, the ratio of the surface area of the hydrophilic catalyst-unsupported fiber 1 coated with 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 with the ionomer 3 to the total surface area of the mesoporous material 2.
[0084] The catalyst layer 6 used in the cathode catalyst layer 26 of the fuel cell 40 of this embodiment can reduce the amount of ionomer 3 coated on the mesoporous material 2 by preferentially coating the ionomer 3 on the hydrophilic catalyst-non-supporting fiber 1, and can prevent the catalyst 5 present outside the mesoporous material 2 from coming into contact with the sulfo groups 4 in the ionomer 3, thereby preventing the sulfur elements in the sulfo groups 4 from strongly adsorbing to the catalyst 5 (catalyst poisoning).
[0085] In addition, since the hydrophilic catalyst-unsupported fiber 1 is highly hydrophilic, the ionomer 3 containing the sulfo group 4, which is a hydrophilic portion, is easily adsorbed, and the entire circumference of the hydrophilic catalyst-unsupported fiber 1 becomes a transport path for hydrogen ions.
[0086] As a result, a hydrophilic catalytic non-catalyst having high hydrogen ion conductivity due to the coating of the ionomer 3 is obtained. The support fiber 1 connects adjacent mesoporous materials 2 to each other, thereby ensuring hydrogen ion transport paths between adjacent mesoporous materials 2, thereby improving the hydrogen ion conductivity in the catalyst layer 6. As a result, a fuel cell catalyst layer that generates a high power generation voltage can be obtained.
[0087] In the catalyst layer 6 used in the cathode catalyst layer 26 of the fuel cell 40 of this embodiment, the length of the hydrophilic catalyst-non-supporting fibers 1 may be longer than twice the average particle size of the mesoporous material 2 .
[0088] As a result, the mesoporous materials 2 separated by intervals of approximately the average particle size of the mesoporous materials 2 can be connected by the hydrophilic catalyst-unsupported fibers 1 having high hydrogen ion conductivity due to the coating of the ionomer 3, improving the hydrogen ion conductivity in the catalyst layer 6. As a result, the hydrogen ion conductivity can be further improved, and a catalyst layer 6 that enables a more efficient catalytic reaction can be obtained.
[0089] Like the catalyst layer 6 of this embodiment, the hydrophilic catalyst-non-supporting fiber 1 may be conductive.
[0090] As a result, the contact points between the mesoporous material 2 and the hydrophilic catalyst-non-supporting fibers 1 become conductive contacts, increasing the number of conductive contacts 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] When 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, the hydrogen ions necessary for the catalytic reaction are transmitted to every corner of the catalyst layer 6. Furthermore, when 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 less than 1.8, clogging of the catalyst layer 6 with water due to an excessive amount of ionomer 3 can be suppressed.
[0093] Therefore, when 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 generates 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, and the cathode 32 (cathode catalyst layer 26) may include the catalyst layer 6 of the present embodiment.
[0095] As a result, in the cathode catalyst layer 26 in the electrolyte membrane-electrode assembly 30, the hydrophilic catalyst-non-supporting fibers 1 have higher hydrophilicity than the mesoporous material 2, so that the sulfo groups 4, which are the hydrophilic parts of the ionomer 3, are preferentially adsorbed to the hydrophilic catalyst-non-supporting fibers 1. This makes it possible to suppress catalyst poisoning and obtain high hydrogen ion conductivity, and when used in a fuel cell 40, it is possible to obtain an electrolyte membrane-electrode assembly 30 that exhibits a high power generation voltage.
[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 generated voltage.
[0097] (Other embodiments) As described above, the first embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and may be modified, added, omitted, or the like. The present invention can also be applied to other embodiments. Furthermore, the components described in the first embodiment can be combined to form new embodiments.
[0098] Therefore, other embodiments will be exemplified below.
[0099] In the first embodiment, the cathode catalyst layer 26 has been described as an example of the catalyst layer 6. The catalyst layer 6 may be any catalyst layer designed to allow the catalytic reaction to proceed quickly. Therefore, the catalyst layer 6 is not limited to the cathode catalyst layer 26. If the catalyst layer 6 is used as the anode catalyst layer 22, it is possible to suppress the poisoning of the catalyst 5 by the ionomer and to achieve high hydrogen ion conductivity at the same time, so that the hydrogen oxidation reaction can proceed quickly and a high power generation voltage can be achieved.
[0100] In embodiment 1, VGCF (registered trademark) manufactured by Showa Denko is used as an example of hydrophilic catalyst-unsupported fiber 1, but this is not limited thereto. The hydrophilic catalyst-unsupported fiber 1 can be selected from, for example, PAN-based carbon fiber, pitch-based carbon fiber, carbon nanotube, etc., from the standpoint of electrical conductivity and low impurity content.
[0101] In the first embodiment, plasma treatment is used as an example of hydrophilic treatment for catalyst-free fibers. The method for hydrophilic treatment of catalyst-free fibers may be any treatment that can impart hydrophilic functional groups such as hydroxyl groups and carboxyl groups to catalyst-free fibers. Therefore, the hydrophilic treatment for catalyst-free fibers can be selected from strong acid treatment, heat treatment, fluorine gas treatment, etc.
[0102] The average diameter of the VGCF (registered trademark)-H used for the hydrophilic catalyst-unsupported fiber 1 in the first embodiment was 150 nm. The average diameter of the hydrophilic catalyst-unsupported fiber 1 may be any diameter that allows the ionomer 3 to be easily adsorbed and ensures electrical 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 the first embodiment, the weight ratio of the hydrophilic catalyst-non-supporting 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-non-supporting fibers 1 included in the catalyst layer 6 to the total weight of the mesoporous material 2 included in the catalyst layer 6 may be any weight ratio that can improve hydrogen ion conductivity without making the catalyst layer 6 too thick. Therefore, the weight ratio of the hydrophilic catalyst-non-supporting fibers 1 included in the catalyst layer 6 to the total weight of the mesoporous material 2 included in the catalyst layer 6 can be selected from the range of 0.05 to 0.5.
[0105] It should be noted that the above-described embodiments are intended to illustrate the technology of the present disclosure, and various modifications, substitutions, additions, omissions, and the like can be made within the scope of the claims or their equivalents. [Industrial Applicability]
[0106] The present disclosure is applicable to highly efficient catalyst layers because it is possible to suppress catalyst poisoning by ionomers while also achieving high hydrogen ion conductivity. Specifically, the present disclosure is applicable to catalyst layers constituting fuel cells, hydrogen purifiers, or water electrolysis devices. [Explanation of symbols]
[0107] 1 Hydrophilic catalyst-free 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 Anode 32 Cathode 40 Fuel Cell
Claims
1. The present invention relates to a catalyst-supporting fiber, and a catalyst-supporting fiber comprising: an electrically conductive mesoporous material; a catalyst supported at least inside the mesopores of the mesoporous material; a catalyst-supporting fiber that does not support the catalyst; and a proton-conductive ionomer that coats the mesoporous material and the catalyst-supporting fiber; the catalyst-unsupported fibers are more hydrophilic than the mesoporous material; The ionomer has a hydrophilic portion formed of a sulfo group, A catalyst layer for a fuel cell, characterized in that the ratio of the surface area of the catalyst-free fiber coated with the ionomer to the total surface area of the catalyst-free fiber 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 catalyst layer for a fuel cell according to claim 1 , wherein the length of the catalyst-unsupporting fibers is more 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-free fibers are electrically conductive.
4. 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; 4. An electrolyte membrane-electrode assembly, wherein the cathode comprises the fuel cell catalyst layer according to claim 1.
5. A fuel cell comprising the electrolyte membrane-electrode assembly according to claim 4.