Catalyst layer for electrolyte membrane-electrode assembly, electrolyte membrane-electrode assembly, and fuel cell using the same

Abstract

To provide a polymer electrolyte-electrode assembly body catalyst layer, capable of performing a high performance catalyst reaction which achieves both of a high proton conductivity and a high gas diffusion property.SOLUTION: A polymer electrolyte-electrode assembly body catalyst layer of the present disclosure, includes: a conductive catalyst carrier material; a catalyst carried by at least the conductive catalyst carrier material; a hydrophilic nature inorganic material of which a mode diameter is smaller than that of the conductive catalyst carrier material; and an ionomer that almost uniformly coats the hydrophilic nature inorganic material. A ratio of an outer front surface area of a part coated with the ionomer in the hydrophilic nature inorganic material and a whole outer surface area of the hydrophilic nature inorganic material is larger than a ratio of an outer surface area of a part coated with the ionomer in the conductive catalyst carrier material and a whole outer surface area of the conductive catalyst carrier material. Thus, an ionomer path with a high continuation is formed as a proton conductive path without blocking a gap as a gas diffusion path, and can provide the polymer electrolyte-electrode assembly body catalyst layer which can perform a catalyst reaction at high efficiency.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a catalyst layer in which a mesoporous material having a catalyst supported in the mesopores is coated with an ionomer. This catalyst layer includes a mesoporous material, a catalyst supported in the mesopores of the mesoporous material, non-catalyst-supported carbon, and an ionomer that coats the mesoporous material, the catalyst, and the non-catalyst-supported carbon. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-181838 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a catalyst layer for an electrolyte membrane-electrode assembly that combines high proton conductivity with excellent gas diffusivity, thereby providing highly efficient power generation performance when used in an electrolyte membrane-electrode assembly of a fuel cell. [Means for solving the problem]

[0005] The catalyst layer for an electrolyte membrane-electrode assembly in the present disclosure includes a conductive catalyst support material, a catalyst supported on at least the conductive catalyst support material, a hydrophilic inorganic material having a mode diameter smaller than that of the conductive catalyst support material, and an ionomer that coats the hydrophilic inorganic material substantially uniformly.

[0006] The ratio of the outer surface area of ​​the portion of the hydrophilic inorganic material that is coated with the ionomer to the total outer surface area of ​​the hydrophilic inorganic material is larger than the ratio of the outer surface area of ​​the portion of the conductive catalyst support material that is coated with the ionomer to the total outer surface area of ​​the conductive catalyst support material. [Effects of the Invention]

[0007] The catalyst layer for an electrolyte membrane-electrode assembly according to the present disclosure can improve proton conductivity and gas diffusivity by forming highly continuous ionomer paths without blocking gaps, and therefore can improve power generation efficiency when used in an electrolyte membrane-electrode assembly of a fuel cell. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a cross section of a fuel cell including an electrolyte membrane-electrode assembly according to a first embodiment; [Figure 2] FIG. 1 is an enlarged schematic diagram of a cross section of a part of a catalyst layer for an electrolyte membrane-electrode assembly in the first embodiment. [Figure 3] FIG. 1 is a schematic diagram showing a state in which an ionomer is coated on a hydrophilic inorganic material used in a catalyst layer for an electrolyte membrane-electrode assembly in the first embodiment. [Figure 4] 1 is a flowchart showing a method for manufacturing a catalyst layer for an electrolyte membrane-electrode assembly according to the first embodiment. [Figure 5] Schematic diagram to explain the structure of close-packed spheres [Figure 6] FIG. 1 is a schematic diagram illustrating the positional relationship between the mesoporous material and the ionomer in the catalyst layer for the electrolyte membrane-electrode assembly in the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that formed the basis of this disclosure) At the time the inventors came up with the idea for this disclosure, fuel cells were attracting attention as a key device necessary for realizing a carbon-free society, as they generate electricity by reacting hydrogen and oxygen and produce only water during the power generation process.

[0010] To improve the power generation efficiency of fuel cells, it is important to reduce the loss at the cathode, which has a large voltage loss. + It is necessary to efficiently supply hydrogen (C) and oxygen (O2) into the cathode catalyst layer and ensure that they reach the catalyst, which is the reaction site.

[0011] It is known that in the catalyst layer of the cathode, protons are conducted via an ionomer, which is a proton-exchangeable polymer resin, and oxygen is conducted by diffusion through the gaps in the catalyst layer.

[0012] For this reason, when the amount of ionomer in the cathode catalyst layer is increased, proton conductivity improves, but oxygen diffusivity decreases because the ionomer blocks the gaps in the catalyst layer. Conversely, when the amount of ionomer is decreased, the blockage of the gaps is resolved and oxygen diffusivity improves, but the insufficient amount of ionomer causes a break in the ionomer path, which is the proton conduction pathway, and conductivity decreases. These are contradictory known problems.

[0013] Therefore, in order to solve these conflicting problems, the inventors came up with the idea of ​​a technology that utilizes the properties of ionomers, which have a high affinity with the surface of hydrophilic inorganic materials and which allow them to be easily adsorbed to the surface of hydrophilic inorganic materials, and uses this as the skeleton of the ionomer path to form a continuous ionomer path without blocking the gaps, which has led to the subject matter of the present disclosure.

[0014] Therefore, the present disclosure provides a catalyst layer for an electrolyte membrane-electrode assembly, an electrolyte membrane-electrode assembly, and a fuel cell using the same, which can improve power generation efficiency when used in an electrolyte membrane-electrode assembly of a fuel cell by achieving both high proton conductivity and excellent gas diffusivity.

[0015] Hereinafter, embodiments will be described in detail with reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters or redundant description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art.

[0016] 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.

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

[0018] [1-1.Configuration] (fuel cell) Fig. 1 shows an example of the configuration of a fuel cell 7, which is a basic unit of a fuel cell. The fuel cell 7 shown in Fig. 1 is a solid polymer electrolyte fuel cell that generates electricity by receiving a supply of hydrogen and oxygen.

[0019] As shown in FIG. 1, the fuel cell 7 comprises an anode separator 5a, a cathode separator 5c, and an electrolyte membrane (ELM) disposed between the anode separator 5a and the cathode separator 5c. and a membrane-electrode assembly 6.

[0020] The anode separator 5a has a flow path on the surface thereof that abuts against the anode 2a of the membrane electrode assembly 6, for allowing hydrogen to be supplied to the fuel cell 7 to flow to the anode 2a.

[0021] The cathode separator 5c has a flow path on the surface thereof that abuts against the cathode 2c of the membrane electrode assembly 6, for allowing oxygen to be supplied to the fuel cell 7 to flow to the cathode 2c.

[0022] When a plurality of fuel cell units 7 are stacked in the thickness direction, the surface of the anode separator 5a opposite to the surface on which the flow paths are formed is electrically connected to the surface of the cathode separator 5c of the fuel cell unit 7 adjacent to the anode separator 5a opposite to the surface on which the flow paths are formed, and the surface of the cathode separator 5c opposite to the surface on which the flow paths are formed is electrically connected to the surface of the anode separator 5a of the fuel cell unit 7 adjacent to the cathode separator 5c opposite to the surface on which the flow paths are formed.

[0023] (Electrolyte membrane-electrode assembly) As shown in FIG. 1, the electrolyte membrane-electrode assembly 6 includes an electrolyte membrane 1, an anode 2a including an anode catalyst layer 3a and an anode gas diffusion layer 4a, and a cathode 2c including a cathode catalyst layer 3c and a cathode gas diffusion layer 4c, and is configured such that both sides of the electrolyte membrane 1 are sandwiched between the anode 2a and the cathode 2c.

[0024] The anode catalyst layer 3a is disposed on one main surface of the electrolyte membrane 1. The cathode catalyst layer 3c is disposed on the other main surface of the electrolyte membrane 1. The anode gas diffusion layer 4a is disposed on the side of the anode catalyst layer 3a opposite to the electrolyte membrane 1 side. The cathode gas diffusion layer 4c is disposed on the side of the cathode catalyst layer 3c opposite to the electrolyte membrane 1 side.

[0025] An anode separator 5a is disposed on the anode gas diffusion layer 4a opposite to the anode catalyst layer 3a side, and a cathode separator 5c is disposed on the cathode gas diffusion layer 4c opposite to the cathode catalyst layer 3c side.

[0026] (electrolyte membrane) The electrolyte membrane 1 is for conducting protons between the anode 2a and the cathode 2c, and is required to have both proton conductivity and gas barrier properties. In this embodiment, a perfluorosulfonic acid resin membrane is used as the material for the electrolyte membrane 1. This perfluorosulfonic acid resin membrane is preferable because it has high proton conductivity and remains stable even in the power generation environment of the fuel cell 7.

[0027] (gas diffusion layer) The anode gas diffusion layer 4a and the cathode gas diffusion layer 4c are layers that have current collecting properties, gas permeability, and water repellency. Each of the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c may include two layers: a substrate and a coating layer.

[0028] 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 material.

[0029] The coating layer is interposed between the catalyst layer (anode catalyst layer 3a, cathode catalyst layer 3c) and the substrate to reduce the contact resistance between the catalyst layer and the substrate and improve liquid permeability (drainage).

[0030] The coating layer of this embodiment is made of a conductive material such as carbon black and polytetrafluoroethylene. It is formed mainly from a water-repellent resin such as tetrafluoroethylene (PTFE).

[0031] (catalyst layer) The anode catalyst layer 3a is a layer that promotes the electrochemical reaction of the anode 2a and is disposed on one main surface of the electrolyte membrane 1. The cathode catalyst layer 3c is a layer that promotes the electrochemical reaction of the cathode 2c and is disposed on the other main surface of the electrolyte membrane 1.

[0032] The anode catalyst layer 3a includes a conductive catalyst support material, a catalyst supported on the conductive catalyst support material, and a proton-conductive ionomer covering at least a portion of the outer surface of the conductive catalyst support material supporting the catalyst.

[0033] As shown in FIG. 2, the cathode catalyst layer 3c includes a conductive catalyst support material 10, a catalyst 12 supported on at least the conductive catalyst support material, a hydrophilic inorganic material 11 having a mode diameter smaller than that of the conductive catalyst support material 10, and an ionomer 13 that coats the hydrophilic inorganic material 11 substantially uniformly.

[0034] The ionomer 13 has a string-like shape with a mode length in the longitudinal direction of the ionomer 13 of 100 to 200 nm and a mode length in the lateral direction of the ionomer 13 of 40 to 80 nm.

[0035] As shown in FIG. 3, the ionomer 13 was in a state of covering the hydrophilic inorganic material 11 having a mode diameter of 100 nm with a mode thickness of 100 nm or less.

[0036] The ratio of the outer surface area of ​​the portion of the hydrophilic inorganic material 11 coated with the ionomer 13 to the total outer surface area of ​​the hydrophilic inorganic material 11 was 0.6 or more. The ratio of the outer surface area of ​​the portion of the conductive catalyst support material 10 coated with the ionomer 13 to the total outer surface area of ​​the conductive catalyst support material 10 was 0.6 or less.

[0037] (Conductive catalyst support material) In this embodiment, the conductive catalyst support material 10 of the cathode catalyst layer 3c is a mesoporous material 15 made of mesoporous carbon with a mode diameter of approximately 500 nm, as shown in Figure 6. Before supporting the catalyst 12, the mesoporous material 15 has mesopores 16 with a mode diameter of 10 nm and a pore volume of 2.0 cm3. 3 / g.

[0038] (catalyst) The catalyst 12 used in the cathode catalyst layer 3c of this embodiment is supported on an electrically conductive catalyst support material 10, as shown in Fig. 2. The catalyst 12 used in the cathode catalyst layer 3c of this embodiment is supported at least inside the mesopores 16 of a mesoporous material 15, as shown in Fig. 6.

[0039] In this embodiment, from the viewpoint of improving catalytic activity, resistance to poisoning by carbon monoxide and the like, and heat resistance, an alloy containing platinum and a metal other than platinum was used as the material for catalyst 12 in cathode catalyst layer 3c. Catalyst 12 in cathode catalyst layer 3c preferably contains 30 to 90 atomic % of platinum and 10 to 70 atomic % of metal other than platinum. In this embodiment, the mode diameter of catalyst 12 used in cathode catalyst layer 3c was 5 nm.

[0040] (hydrophilic inorganic material) In this embodiment, Nb—SnO 2 with a mode diameter of approximately 100 nm was used as the hydrophilic inorganic material 11 of the cathode catalyst layer 3c.

[0041] (ionomer) The ionomer 13 in the cathode catalyst layer 3c transfers the protons that have passed through the electrolyte membrane 1 from the anode 2a side to the cathode 2c side to the catalyst 12 in the cathode catalyst layer 3c.

[0042] As shown in FIG. 3, the ionomer 13 of the cathode catalyst layer 3c of this embodiment coats the hydrophilic inorganic material 11 substantially uniformly.

[0043] Ionomer 13 is a proton (H + Although there are no particular restrictions on the material as long as it is a high molecular weight polymer having proton conductivity, in this embodiment, perfluorosulfonic acid resin, the same as the electrolyte material of the electrolyte membrane 1, is used as the ionomer 13. This perfluorosulfonic acid resin is preferable because it has high proton conductivity among ion exchange resins and is stable even in the power generation environment of a fuel cell.

[0044] (Method for manufacturing catalyst layer) In this embodiment, the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 was produced by the following steps.

[0045] FIG. 4 is a flowchart showing a method for manufacturing the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 of this embodiment.

[0046] (First step of the catalyst layer manufacturing method) In the first step, ionomer 13 is adsorbed onto hydrophilic inorganic material 11 in a hydrophobic solvent. First, water, ethanol, and an ionomer solution dispersed in water and ethanol were mixed to form a composition of 68 wt% ethanol, 29 wt% water, and 3 wt% ionomer. Next, hydrophilic inorganic material 11 was added to the mixed solvent and dispersed therein.

[0047] In this case, a ball mill, a wet atomizer, an ultrasonic disperser, etc. can be used as a dispersion method. The sulfonic acid groups of the ionomer 13 strongly interact with and are strongly adsorbed to the hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the hydrophilic inorganic material 11.

[0048] In this case, since the state in which the ionomer 13 is adsorbed onto the surface of the hydrophilic inorganic material 11 is thermodynamically more stable than the state in which the ionomer 13 is dispersed approximately uniformly in the solvent, the ionomer 13 becomes approximately uniformly coated on the surface of the hydrophilic inorganic material 11.

[0049] (Second step of the catalyst layer manufacturing method) In the second step, the conductive catalyst support material 10 carrying the catalyst 12 is added to the mixed dispersion liquid prepared in the first step and mixed and dispersed (S02). In this case, a ball mill, a wet atomizer, or an ultrasonic disperser can be used as the dispersion method.

[0050] In the mixed dispersion liquid prepared in this step, the hydrophilic inorganic material 11 is more hydrophilic than the conductive catalyst support material 10 supporting the catalyst 12. At this time, the adsorptive power of the ionomer 13 to the hydrophilic inorganic material 11 is higher than the adsorptive power to the conductive catalyst support material 10 supporting the catalyst 12, so the ionomer 13 comes to be preferentially coated on the hydrophilic inorganic material 11.

[0051] (Third step of the catalyst layer manufacturing method) In the third step, the ink prepared in the second step is applied (S03) and dried to form a catalyst layer (S04).

[0052] In this case, the application method may be a method of directly applying ink to one side of the electrolyte membrane 1, or a method of once applying ink to a substrate and drying it, and then transferring the dried ink on the substrate to the electrolyte. Alternatively, the method may be a method of transferring the image to the membrane 1.

[0053] As a result, the hydrophilic inorganic material 11 coated with the ionomer 13, the ionomer 13, and the conductive catalyst support material 10 carrying the catalyst 12 are present in a dispersed or aggregated state, and a catalyst layer is obtained in which the proportion of the outer surface area of ​​the portion coated with the ionomer 13 to the total outer surface area of ​​the hydrophilic inorganic material 11 is greater than the proportion of the outer surface area of ​​the portion coated with the ionomer 13 to the total outer surface area of ​​the conductive catalyst support material 10.

[0054] [1-2. Operation] The operation and function of the electrolyte membrane-electrode assembly 6 having the cathode catalyst layer 3c configured as above in the cathode 2c will be described below using as an example a proton exchange fuel cell 7 equipped with the electrolyte membrane-electrode assembly 6 in which the electrolyte membrane 1 is configured from a proton conductive membrane.

[0055] The operation method and action of the fuel cell 7 will be described with reference to FIG.

[0056] The fuel cell 7 was operated by maintaining the temperature of the fuel cell 7 at 60°C, supplying hydrogen with a dew point of 60°C at a flow rate of 100 cc / min to the flow path between the anode separator 5a and the anode 2a, and supplying air with a dew point of 60°C at a flow rate of 300 cc / min to the flow path between the cathode separator 5c and the cathode 2c, and electrically connecting the anode separator 5a and the cathode separator 5c with an external circuit. At this time, a current of 10 A flowed in the external circuit due to the electrochemical reaction in the fuel cell 7.

[0057] Next, we will explain the transfer of substances and electrochemical reactions that occur within the operating fuel cell 7. Hydrogen supplied to the flow path between the anode separator 5a and the anode 2a (anode gas diffusion layer 4a) permeates the anode gas diffusion layer 4a and reaches the catalyst in the anode catalyst layer 3a.

[0058] At this time, in the catalyst in the anode catalyst layer 3a, hydrogen shown in (Chemical Formula 1) is converted into protons (H + ) and electrons.

[0059] [ka]

[0060] The catalyst in the anode catalyst layer 3a reacts with protons (H + ) passes through the ionomer in the anode catalyst layer 3a to reach the electrolyte membrane 1, and then permeates the electrolyte membrane 1 from the anode catalyst layer 3a side to the cathode catalyst layer 3c side. + ) passes through the ionomer 13 or water in the cathode catalyst layer 3c and reaches the catalyst 12 in the cathode catalyst layer 3c.

[0061] Meanwhile, electrons dissociated from hydrogen by the catalyst in the anode catalyst layer 3a pass through the anode catalyst layer 3a, anode gas diffusion layer 4a, anode separator 5a, external circuit, cathode separator 5c, cathode gas diffusion layer 4c, and cathode catalyst layer 3c in this order, and reach the catalyst 12 in the cathode catalyst layer 3c.

[0062] Furthermore, oxygen in the air supplied to the flow path between the cathode separator 5c and the cathode 2c (cathode gas diffusion layer 4c) permeates the cathode gas diffusion layer 4c and reaches the catalyst 12 in the cathode catalyst layer 3c.

[0063] At this time, the catalyst 12 in the cathode catalyst layer 3c converts protons (H + ) A reduction reaction occurs in which oxygen (O) combines with electrons to produce water, and water is produced by this reduction reaction.

[0064] [ka]

[0065] In order to improve the power generation performance of the fuel cell 7, hydrogen must reach the catalyst in the anode catalyst layer 3a, oxygen must reach the catalyst 12 in the cathode catalyst layer 3c, and protons (H + ) must be efficiently transported to the catalyst 12 in the cathode catalyst layer 3c.

[0066] In the case of a proton exchange type fuel cell 7 having an electrolyte membrane-electrode assembly 6 in which the electrolyte membrane 1 is made of a proton-conductive membrane, it is known that voltage loss is particularly large in the cathode catalyst layer 3c, and therefore a structure in which oxygen and protons are efficiently supplied to the catalyst 12 in the cathode catalyst layer 3c is desirable.

[0067] As shown in FIG. 2, in the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 of the present embodiment, the ionomer 13 responsible for proton conduction is arranged so as to cover the hydrophilic inorganic material 11 substantially uniformly, and is connected by van der Waals forces.

[0068] This improves the continuity of the ionomer path, forming a continuous proton supply path to the conductive catalyst support material 10, thereby improving the proton conductivity of the cathode catalyst layer 3c.

[0069] Furthermore, compared to a case where the ionomer 13 is not configured to preferentially coat the hydrophilic inorganic material 11 having a smaller mode diameter than the conductive catalyst support material 10, the amount of ionomer 13 required to obtain sufficient proton conductivity can be reduced, and therefore the ionomer 13 is less likely to block the gaps 14 that serve as oxygen diffusion paths, thereby improving the gas diffusivity of the cathode catalyst layer 3c.

[0070] If the hydrophilic inorganic material 11 used in the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 of the present embodiment is a conductive material, the electron conduction path in the cathode catalyst layer 3c is increased compared to when the hydrophilic inorganic material 11 is not a conductive material, thereby reducing the resistance of the cathode catalyst layer 3c and improving the electrical conductivity.

[0071] Incidentally, when spheres a of radius r are hexagonally close-packed, connecting the centers of four adjacent spheres a results in a regular tetrahedron with a side length of 2r, as shown in Figure 5. Since the distance between the center of gravity of a regular tetrahedron and its vertices is calculated to be approximately 1.22r, the maximum radius of a sphere that can be placed in the gap between four adjacent spheres a of radius r when they are hexagonally close-packed is approximately 0.22r.

[0072] Therefore, when the mode diameter of the hydrophilic inorganic material 11 is 22% or less of the mode diameter of the conductive catalyst support material 10, the hydrophilic inorganic material 11 can be placed in the gaps that occur between the hexagonally close-packed conductive catalyst support materials 10, and the mode diameter of the gaps 14 becomes small.

[0073] When the mode diameter of the gap 14 in the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 becomes small, the mode diameter between the gap 14 in the cathode catalyst layer 3c and the gap in the cathode gas diffusion layer 4c becomes small. The difference becomes greater.

[0074] This increases the water capillary pressure difference between the cathode catalyst layer 3c and the cathode gas diffusion layer 4c, increasing the force that expels water from the gaps 14, which is a factor that inhibits gas diffusion in the cathode catalyst layer 3c, to the cathode gas diffusion layer 4c, thereby improving drainage and gas diffusion in the cathode catalyst layer 3c.

[0075] As shown in Figure 6, when the conductive catalyst support material 10 is a mesoporous material 15 having mesopores 16 therein and the catalyst 12 is supported within the mesopores 16, contact between the catalyst 12 and the ionomer 13 is suppressed.

[0076] Since the mode diameter of ionomer 13 in the shortest direction of ionomer 13 is 50 nm or more, when catalyst 12 is supported in mesopores 16 with a mode diameter of less than 50 nm, ionomer 13 cannot penetrate into mesopores 16, and contact of ionomer 13 with catalyst 12 is suppressed.

[0077] It is known that when the ionomer 13 comes into contact with the catalyst 12, the catalytic activity of the catalyst 12 decreases. However, by preventing the ionomer 13 from coming into contact with the catalyst 12, it is possible to prevent the activity of the catalyst 12 in the cathode catalyst layer 3c from decreasing.

[0078] [1-3. Effects, etc.] As described above, in the present embodiment, the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 includes the conductive catalyst support material 10, the catalyst 12 supported on at least the conductive catalyst support material 10, the hydrophilic inorganic material 11 having a mode diameter smaller than that of the conductive catalyst support material 10, and the ionomer 13 that coats the hydrophilic inorganic material 11 substantially uniformly.

[0079] The ratio of the outer surface area of ​​the portion of the hydrophilic inorganic material 11 that is coated with the ionomer 13 to the total outer surface area of ​​the hydrophilic inorganic material 11 is larger than the ratio of the outer surface area of ​​the portion of the conductive catalyst support material 10 that is coated with the ionomer 13 to the total outer surface area of ​​the conductive catalyst support material 10.

[0080] This allows the cathode catalyst layer 3c to form highly continuous ionomer paths without blocking the gaps 14, thereby improving the proton conductivity and gas diffusibility of the cathode catalyst layer 3c, and thereby providing a cathode catalyst layer 3c for the electrolyte membrane-electrode assembly 6 that enables highly efficient catalytic reactions.

[0081] Furthermore, as in this embodiment, in the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6, the mode diameter of the hydrophilic inorganic material 11 may be 22% or less of the mode diameter of the conductive catalyst support material .

[0082] This not only shortens the length of the ionomer paths formed between the conductive catalyst support materials 10, but also reduces the thickness of the catalyst layer, further improving proton conductivity. Furthermore, the frequency of gas diffusion obstruction due to water in the gaps 14 decreases, further improving the gas diffusion of the cathode catalyst layer 3c. As a result, it is possible to provide a cathode catalyst layer 3c for an electrolyte membrane-electrode assembly 6 that enables a more efficient catalytic reaction.

[0083] Furthermore, as in this embodiment, in the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6, the hydrophilic inorganic material 11 may be a conductive material.

[0084] This increases the number of electron conduction paths in the cathode catalyst layer 3c, improving electrical conductivity. As a result, in addition to the effects of improving proton conductivity and gas diffusivity, electrical conductivity can also be improved, making it possible to provide a cathode catalyst layer 3c for an electrolyte membrane-electrode assembly 6 that enables a more efficient catalytic reaction.

[0085] Furthermore, as in the present embodiment, the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 may be a mesoporous material 15 in which the conductive catalyst support material 10 has mesopores 16 with a mode diameter of 1 to 50 nm and supports the catalyst 12 at least inside the mesopores 16.

[0086] This prevents contact between the ionomer 13, which has a mode diameter of several tens of nanometers, and the catalyst 12 supported in the mesopores 16. As a result, in addition to the effects of improving proton conductivity and gas diffusibility, it is possible to prevent a decrease in catalytic activity due to contact between the ionomer 13 and the catalyst 12, thereby providing a cathode catalyst layer 3c for an electrolyte membrane-electrode assembly 6 that enables a more efficient catalytic reaction.

[0087] In this embodiment, the electrolyte membrane-electrode assembly 6 includes an electrolyte membrane 1, an anode 2a provided on one main surface of the electrolyte membrane 1, and a cathode 2c provided on the other main surface of the electrolyte membrane 1, and the cathode 2c includes the cathode catalyst layer 3c of this embodiment. This makes it possible to provide an electrolyte membrane-electrode assembly 6 that enables a highly efficient catalytic reaction.

[0088] In this embodiment, the fuel cell 7 includes the electrolyte membrane-electrode assembly 6 of this embodiment, which allows the fuel cell 7 to have improved power generation efficiency.

[0089] (Other embodiments) As described above, the first embodiment has been described as an example of the technology disclosed in this question. However, the technology in this disclosure is not limited to this, and can also be applied to embodiments in which modifications, substitutions, additions, etc. are made. Furthermore, it is also possible to combine the components described in the first embodiment above to create a new embodiment.

[0090] Therefore, other embodiments will be exemplified below.

[0091] In the first embodiment, a perfluorosulfonic acid resin membrane is used as the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6. The electrolyte membrane 1 may be any membrane as long as it has both proton conductivity and gas barrier properties. Therefore, the material of the electrolyte membrane 1 is not limited to a perfluorosulfonic acid resin membrane.

[0092] Examples of materials for the electrolyte membrane 1 include an ion-exchange fluorine-based resin membrane and an ion-exchange hydrocarbon-based resin membrane.

[0093] The ion exchange capacity of the ion exchange resin used in the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6 is preferably 0.9 to 2.0 meq / g dry resin.

[0094] If the ion exchange capacity of the ion exchange resin used in the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6 is 0.9 meq / g dry resin or more, high proton conductivity is easily obtained, and if the ion exchange capacity of the ion exchange resin used in the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6 is 2.0 meq / g dry resin or less, swelling of the resin due to water absorption is suppressed, and dimensional changes of the electrolyte membrane 1 are suppressed, which is preferable.

[0095] The thickness of the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6 is preferably 5 μm or more and 50 μm or less. When the thickness of the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6 is 5 μm or more, high gas barrier properties can be obtained, and when the thickness of the electrolyte membrane 1 of the electrolyte membrane-electrode assembly 6 is 50 μm or less, If there is such a material, high proton conductivity can be obtained.

[0096] In the first embodiment, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c of the electrolyte membrane-electrode assembly 6 are configured to include two layers: a carbon paper substrate and a coating layer. The anode gas diffusion layer 4a and the cathode gas diffusion layer 4c may be any layers that combine current collection properties with gas permeability and water repellency. Therefore, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c are not limited to those that include two layers: a carbon paper substrate and a coating layer.

[0097] The substrate used for the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c of the electrolyte membrane-electrode assembly 6 may be any material that has excellent electrical conductivity and gas and liquid permeability, and examples thereof include porous materials such as carbon paper, carbon fiber cloth, and carbon fiber felt.

[0098] The coating layers used for the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c of the electrolyte membrane-electrode assembly 6 are layers interposed between the catalyst layers (anode catalyst layer 3a, cathode catalyst layer 3c) and the substrate to reduce the contact resistance between the catalyst layers and the substrate and improve liquid permeability (drainage).

[0099] The coating layers used for the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c of the electrolyte membrane-electrode assembly 6 are formed mainly from a conductive material such as carbon black and a water-repellent resin such as polytetrafluoroethylene (PTFE).

[0100] In the first embodiment, a mesoporous material 15 is used as the conductive catalyst support material 10 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6, and mesoporous carbon is used as the mesoporous material 15. However, the conductive catalyst support material 10 may be any conductive material that can support the catalyst 12.

[0101] Examples of the conductive catalyst support material 10 for the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 include carbon-based materials such as Ketjen Black (registered trademark), acetylene black, and Vulcan (registered trademark), metal materials such as Au and Ni, metal oxide materials such as titanium, tin, niobium, tantalum, zirconium, aluminum, and silicon, and composite materials thereof.

[0102] The mesoporous material 15 used for the conductive catalyst support material 10 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 has a mode diameter of mesopores 16 of 1 to 50 nm and a pore volume of mesopores 16 of 1.0 to 3.0 cm before the mesoporous material 15 supports the catalyst 12. 3 / g.

[0103] The pore volume of mesopore 16 is 1.0 cm 3 / g or more, a large amount of catalyst 12 can be supported inside mesopores 16 of mesoporous material 15, and the pore volume of mesopores 16 is 3.0 cm 3 If the mesoporous material 15 has a molecular weight of 1 / g or less, the strength of the mesoporous material 15 as a structure is increased.

[0104] The mesoporous material 15 used in the conductive catalyst support material 10 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 may be configured so that the mode diameter of the mesoporous material 15 is 200 to 1000 nm.

[0105] If the mesoporous material 15 has a mode diameter of 200 nm or more, the area where the ionomer 13 penetrates into the mesopores 16 becomes small relative to the pore volume of the mesopores 16. Therefore, it is considered that the catalytic activity can be improved by setting the mode diameter of the mesoporous material 15 used in the conductive catalyst support material 10 of the cathode catalyst layer 3c to 200 nm or more.

[0106] Furthermore, if the mesoporous material 15 has a mode diameter of 1000 nm or less, the reactant gas (oxygen) can be easily supplied to the catalyst 12 supported inside the mesopores 16 of the mesoporous material 15 .

[0107] In the first embodiment, the catalyst 12 in the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 is made of platinum and an alloy containing a metal other than platinum.

[0108] The catalyst 12 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 is made of a material that contains protons (H + The catalyst material for the anode catalyst layer 3a of the electrolyte membrane-electrode assembly 6 is not particularly limited as long as it has a catalytic action to cause a reduction reaction in which hydrogen (H) combines with oxygen (O) and electrons to produce water. + There are no particular limitations as long as the catalyst has a catalytic action to cause an oxidation reaction in which the catalyst dissociates into hydroxyl groups and electrons.

[0109] Examples of the catalyst 12 of the cathode catalyst layer 3c include metals such as platinum (Pt), 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), as well as mixtures and alloys of these metals.

[0110] Among these, platinum and mixtures or alloys containing platinum are preferred as the catalyst 12 of the cathode catalyst layer 3c from the viewpoint of improving catalytic activity, resistance to poisoning by carbon monoxide and the like, and heat resistance.

[0111] When the catalyst 12 of the cathode catalyst layer 3c is made of an alloy, the composition of the alloy may vary depending on the type of alloying metal, but the platinum content may be 30 to 90 atomic % and the other metal content may be 10 to 70 atomic %.

[0112] The mode diameter of the catalyst 12 in the cathode catalyst layer 3c is not particularly limited. However, from the viewpoint of improving the catalyst utilization rate and the supportability in the conductive catalyst support material 10, the mode diameter of the catalyst 12 in the cathode catalyst layer 3c is preferably 1 to 30 nm. When a mesoporous material 15 is used as the conductive catalyst support material 10 of the cathode catalyst layer 3c and the catalyst 12 is supported inside the mesopores 16 of the mesoporous material 15, it is preferable that the mode diameter of the catalyst 12 in the cathode catalyst layer 3c is smaller than the mode diameter of the mesopores 16 of the mesoporous material 15.

[0113] In the first embodiment, Nb—SnO2 is used as the hydrophilic inorganic material 11 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6. The material for the hydrophilic inorganic material 11 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 is not particularly limited as long as it is an inorganic material with high hydrophilicity that is stable in the operating environment of the fuel cell 7.

[0114] Examples of the hydrophilic inorganic material 11 of the cathode catalyst layer 3c of the electrolyte membrane-electrode assembly 6 include metal oxides such as alumina (AlO), titania (TiO), and silica (SiO), as well as mixtures of these materials that have been surface-treated.

[0115] In the first embodiment, the proton exchange type fuel cell 7 was described in which the electrolyte membrane 1 was a proton conductive membrane and the catalyst layer for an electrolyte membrane-electrode assembly of the present disclosure was used for the cathode catalyst layer 3c. In a hydroxide ion exchange type fuel cell that uses a hydroxide ion conductive membrane as the electrolyte membrane, it is preferable to use the catalyst layer for an electrolyte membrane-electrode assembly of the present disclosure as the anode catalyst layer.

[0116] In a fuel cell using a hydroxide ion conductive membrane as the electrolyte membrane, the reaction shown in (Chemical Formula 3) occurs in the anode catalyst layer to which hydrogen is supplied, and the reaction shown in (Chemical Formula 4) occurs in the cathode catalyst layer to which oxygen is supplied.

[0117] [ka]

[0118] [ka]

[0119] In a fuel cell using a hydroxide ion conductive membrane as the electrolyte membrane, water is generated in the anode catalyst layer. Therefore, the anode catalyst layer is required to efficiently drain the generated water, and improving the drainage properties of the anode catalyst layer is necessary to improve performance. By using the catalyst layer for an electrolyte membrane-electrode assembly according to the present disclosure as the anode catalyst layer, the anode catalyst layer has excellent drainage properties and high electrical conductivity, thereby improving the performance of the fuel cell.

[0120] 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, etc. may be made within the scope of the claims or their equivalents. [Industrial Applicability]

[0121] The present disclosure can provide a catalyst layer for an electrolyte membrane-electrode assembly that has excellent drainage properties and high electrical conductivity, and is applicable to catalyst layers in fuel cells. [Explanation of symbols]

[0122] 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 5a Anode separator 5c Cathode separator 6 Electrolyte membrane-electrode assembly 7 Fuel Cell 10. Conductive catalyst support material 11 Hydrophilic inorganic materials 12 Catalyst 13 Ionoma 14 Gap 15 Mesoporous Materials 16 Mesopores

Claims

1. a conductive catalyst support material, at least a catalyst supported on the conductive catalyst support material, a hydrophilic inorganic material having a mode diameter smaller than that of the conductive catalyst support material, and an ionomer that coats the hydrophilic inorganic material substantially uniformly; a ratio of an outer surface area of ​​a portion of the hydrophilic inorganic material that is coated with the ionomer to a total outer surface area of ​​the hydrophilic inorganic material is greater than a ratio of an outer surface area of ​​a portion of the conductive catalyst support material that is coated with the ionomer to a total outer surface area of ​​the conductive catalyst support material.

2. 2. The catalyst layer for an electrolyte membrane-electrode assembly according to claim 1, wherein the mode diameter of said hydrophilic inorganic material is 22% or less of the mode diameter of said conductive catalyst support material.

3. 3. The catalyst layer for an electrolyte membrane-electrode assembly according to claim 1, wherein the hydrophilic inorganic material is a conductive material.

4. 4. The catalyst layer for an electrolyte membrane-electrode assembly according to claim 1, wherein the conductive catalyst support material is a mesoporous material having mesopores with a mode diameter of 1 to 50 nm and supporting the catalyst at least inside the mesopores.

5. 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; An electrolyte membrane-electrode assembly, wherein the cathode comprises the catalyst layer for an electrolyte membrane-electrode assembly according to any one of claims 1 to 4.

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

Images