Catalyst layer

Abstract

Provided is a catalyst layer in which power generation performance is improved even in a high output power region (high current density region). A cathode catalyst layer (5) and an anode catalyst layer (6) for a membrane-electrode assembly of a solid polymer fuel cell, the cathode catalyst layer (5) and the anode catalyst layer (6) containing catalyst particles (1), an electrically conductive carrier (2), a polymer electrolyte (3), and a fibrous substance (4), the fibrous substance (4) containing at least one of an electron conductor and a proton conductor, the specific surface area of the fibrous substance (4) being in a range of 40 m 2 / g or more and 80 m 2 / g or less.

Description

Technical Field

[0001] This invention relates to the catalyst layer of a solid polymer fuel cell. Background Technology

[0002] In recent years, in order to solve environmental problems such as global warming, there has been a need to develop new energy sources that reduce CO2 emissions. As such an energy source, fuel cells, which do not emit CO2, have attracted much attention.

[0003] A fuel cell uses fuel (e.g., hydrogen) and an oxidant (e.g., oxygen) to oxidize the fuel (hydrogen) and produce harmless water. This fuel cell can convert the chemical energy obtained through water production into electrical energy, and therefore can be used as a power source.

[0004] Fuel cells are classified according to the type of electrolyte used. The main types of fuel cells known include: solid polymer fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, and alkaline electrolyte fuel cells. Phosphoric acid and alkaline electrolyte fuel cells use a substance obtained by impregnating non-woven fabric or other separators with an aqueous solution of phosphoric acid or an alkaline solution as the electrolyte. However, solid polymer and solid oxide fuel cells use solid electrolytes such as polymer membranes or ceramic sheets.

[0005] The suitable operating temperature for fuel cells varies depending on the electrolyte used. For example, the electrolytes for solid oxide fuel cells and molten carbonate fuel cells operate at temperatures ranging from approximately 200°C to 700°C. While these are difficult to miniaturize and reduce in weight, they are suitable for high-power power generation systems. Therefore, they are suitable replacements for small and medium-sized power plants or aging thermal power plants located in isolated islands and remote areas.

[0006] On the other hand, solid polymer fuel cells (PEFC, Polymer Electrolyte (Membrane) Fuel Cell) have the characteristics of low-temperature operation and high output power density, and can be miniaturized and lightweight, so they have been developed as power sources for home and vehicle use.

[0007] Solid polymer fuel cells (PEFCs) have a structure (membrane-electrode junction) formed by sandwiching a polymer electrolyte membrane between a fuel electrode (anode) and an air electrode (cathode). They generate electricity by supplying hydrogen as fuel gas to the fuel electrode side and air containing oxygen gas to the air electrode side, and by the following chemical reaction.

[0008] Anode: H2 → 2H + +2e - ······(Reaction 1)

[0009] Cathode: 1 / 2O2 + 2H+ +2e - →H2O

[0010] ...(Reaction 2)

[0011] The anode and cathode are composed of a stacked structure of a catalyst layer and a gas diffusion layer, respectively.

[0012] Hydrogen gas supplied to the catalyst layer on the anode side reacts chemically with the electrode catalyst to generate protons (hydrogen ions) and electrons (reaction 1). The generated protons move from the polymer electrolyte within the catalyst layer on the anode side through the polymer electrolyte membrane to the cathode. On the other hand, the generated electrons move to the cathode via an external circuit.

[0013] In the catalyst layer on the cathode side, protons, electrons, and oxygen from the air supplied from the outside react to produce water (reaction 2).

[0014] To reduce the cost of solid polymer fuel cells, reducing the amount of platinum used, the most expensive material, has become a challenge. However, reducing the amount of platinum used in the chemical reactions of the fuel cell will lead to a decrease in the output performance and durability of the fuel cell.

[0015] As a technology to address the problem of reducing the amount of platinum used, for example, a technology to improve electronic conductivity by using carbon fibers in a carbon carrier has been disclosed (see Patent Document 1).

[0016] Patent document 1 shows that, instead of the carbon microparticles that have been used in the past, carbon fibers with carbon microparticles fixed on their surface are used as electron conductors to improve conductivity, thereby increasing output power.

[0017] However, as the output power increases, water is generated in the catalyst layer on the cathode side, and it is also necessary to remove this water from the porous catalyst layer. That is, in order to obtain high output power, a mechanism for actively removing the water generated in the catalyst layer on the cathode side is essential. In Patent Document 1, embodiments describe improving the output power in the low current density region, but there is no description of the high current density region.

[0018] Existing technical documents

[0019] Patent documents

[0020] Patent Document 1: Japanese Patent Application Publication No. 2006-172865 Summary of the Invention

[0021] The problem that the invention aims to solve

[0022] The present invention was made in view of the aforementioned actual situation, and its objective is to provide a catalyst layer that improves power generation performance even in the high output power region (high current density region).

[0023] Methods for solving problems

[0024] As a means of solving the above-mentioned problems, one aspect of the present invention relates to a catalyst layer for a membrane-electrode junction in a solid polymer fuel cell. The catalyst layer comprises catalyst particles, a conductive support, a polymer electrolyte, and a fibrous material, wherein the fibrous material comprises at least one of an electron conductor and a proton conductor, and the specific surface area of ​​the fibrous material is 40 m². 2 / g or more 80m 2 Within the range of / g and below.

[0025] Furthermore, for the catalyst layer according to one aspect of the present invention, the peak value Dp of the distribution function dVp / dlogD of the pore volume Vp in the catalyst layer relative to the pore diameter D is preferably in the range of 0.06 μm to 0.10 μm.

[0026] In addition, for the catalyst layer involved in one aspect of the present invention, the full width at half maximum (FWHM) of the peak value Dp of the distribution function dVp / dlogD is preferably in the range of 0.13 μm to 0.18 μm.

[0027] In addition, for the catalyst layer involved in one aspect of the present invention, the average fiber length of the fibrous material is preferably in the range of 3 μm to 50 μm.

[0028] In addition, for the catalyst layer involved in one aspect of the present invention, the average fiber diameter of the fibrous material is preferably in the range of 50 nm to 400 nm.

[0029] Invention Effects

[0030] According to one aspect of the present invention, a catalyst layer can be provided for use in solid polymer fuel cells, exhibiting improved mass mobility and high power generation performance. Specifically, according to one aspect of the present invention, a catalyst layer can be provided that improves power generation performance even in high output power regions (high current density regions) (i.e., maintains power generation performance at the same level as in low current density regions). Attached Figure Description

[0031] [ Figure 1 This is a cross-sectional illustration of the internal structure of a solid polymer fuel cell catalyst layer according to an embodiment of the present invention.

[0032] [ Figure 2[A top view illustration of an example of the layer structure of the film-electrode junction of the present invention.]

[0033] [ Figure 3 [A cross-sectional illustration of the internal structure of the catalyst layer in the examples and comparative examples is provided.] Detailed Implementation

[0034] Reference Figures 1-3 The embodiments of the present invention will be described below. It should be noted that the present invention is not limited to the embodiments described below, and modifications such as design changes can be made based on the knowledge of those skilled in the art, and such modified embodiments are also included within the scope of the present invention.

[0035] <Catalyst Layer>

[0036] The catalyst layer for a solid polymer fuel cell according to embodiments of the present invention will be described.

[0037] The catalyst layer involved in the embodiments of the present invention is a catalyst layer for a membrane-electrode junction in a solid polymer fuel cell.

[0038] The catalyst layer involved in the embodiments of the present invention comprises: catalyst particles, a conductive support, a polymeric electrolyte, and a fibrous material.

[0039] In addition, the fibrous material contains at least one of electron conductors and proton conductors, and the specific surface area of ​​the fibrous material is 40 m². 2 / g or more 80m 2 Within the range of / g and below.

[0040] Furthermore, in embodiments of the present invention, the peak value Dp of the distribution function dVp / dlogD of the pore volume Vp in the catalyst layer relative to the pore diameter D is preferably in the range of 0.06 μm or more and 0.10 μm or less.

[0041] Furthermore, in embodiments of the present invention, the half-width of the peak value Dp of the distribution function dVp / dlogD of the pore volume Vp in the catalyst layer relative to the pore diameter D is preferably in the range of 0.13 μm or more and 0.18 μm or less.

[0042] Furthermore, the average fiber length of the fibrous material contained in the catalyst layer according to the embodiments of the present invention is preferably in the range of 3 μm to 50 μm.

[0043] Furthermore, the average fiber diameter of the fibrous material contained in the catalyst layer according to the embodiments of the present invention is preferably in the range of 50 nm to 400 nm.

[0044] Next, use Figure 1 and Figure 2 The embodiments of the present invention will be described in detail below.

[0045] Figure 1 This is a cross-sectional illustration of the internal structure of the catalyst layer of a solid polymer fuel cell according to one embodiment of the present invention, which is composed of catalyst particles 1, conductive support 2, polymer electrolyte 3, and fibrous material 4.

[0046] Figure 2 This diagram illustrates the layer composition of a membrane-electrode junction according to one embodiment of the present invention, comprising a cathode catalyst layer 5, an anode catalyst layer 6, a polymer electrolyte membrane 7, a gasket material 8, and a gas diffusion layer 9. It should be noted that, for convenience, the cathode catalyst layer 5 and the anode catalyst layer 6 are hereinafter also referred to as "catalyst layers".

[0047] In this embodiment, the thickness of the cathode catalyst layer 5 can be the same as or greater than the thickness of the anode catalyst layer 6. When the thickness of the cathode catalyst layer 5 is greater than that of the anode catalyst layer 6, the thickness of the cathode catalyst layer 5 is preferably in the range of 1.1 to 2 times the thickness of the anode catalyst layer 6, more preferably in the range of 1.3 to 1.7 times the thickness of the anode catalyst layer 6. If the thickness of the cathode catalyst layer 5 is within the above-mentioned range, the reduction in proton conductivity can be reduced while ensuring drainage performance, thereby maintaining high output power performance.

[0048] Next, refer to Figure 1 The composition of the catalyst layer according to the embodiments of the present invention will be described.

[0049] (Catalyst particles)

[0050] In this embodiment, the catalyst particle 1 can be any metal, or alloy thereof, other than platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Furthermore, oxides or composite oxides of the aforementioned substances can also be used as catalyst particles 1. In addition, the average particle size of these catalysts is, for example, 0.1 nm to 1 μm, preferably 0.5 nm to 100 nm, and more preferably 1 nm to 10 nm. If the average particle size of the catalyst particle 1 is within the above-mentioned range, the catalytic reaction proceeds efficiently.

[0051] (Conductive carrier)

[0052] The conductive support 2 supporting these catalyst particles 1 is typically made of carbon particles. The type of carbon particles can be arbitrary, as long as they are microparticles, conductive, and not corroded by the catalyst particles 1; for example, carbon black, graphite, lead black, activated carbon, fullerenes, etc., can be used. Furthermore, to improve the loading capacity of the catalyst particles 1, the conductive support 2 is preferably porous.

[0053] (Polymer electrolyte)

[0054] The polymeric electrolyte 3 used in this embodiment can be any electrolyte with proton conductivity, and can be made of the same material as the polymeric electrolyte membrane 7, such as fluorinated polymeric electrolytes and hydrocarbon polymeric electrolytes. It should be noted that, for example, fluorinated polymeric electrolytes can be materials such as Nafion (registered trademark) manufactured by DuPont.

[0055] (Composition of the catalyst layer)

[0056] The ratio (I / (C+FS)) of the mass C of the conductive support 2 supporting the catalyst particles 1, the mass FS of the fibrous material 4, and the mass I of the polymer electrolyte 3 can be in the range of 0.2 to 1.5. On the other hand, when the ratio (I / (C+FS)) of the above components is less than 0.2, the proton pathway is insufficient, thereby significantly impairing the power generation performance. In addition, when the ratio (I / (C+FS)) of the above components exceeds 1.5, the water permeability of the catalyst layer decreases, thereby significantly impairing the power generation performance of the fuel cell.

[0057] The mass ratio (FS / C) of the fibrous material 4 to the conductive support 2 supported on the catalyst particles 1 can be in the range of 0.05 to 1.20. Preferably, the mass ratio (FS / C) of the conductive support 2 to the fibrous material 4 is in the range of 0.1 to 1.0, which increases the pore volume within the catalyst layer required for material movement, thereby suppressing performance degradation caused by overflow. On the other hand, when the mass ratio (FS / C) of the conductive support 2 to the fibrous material 4 exceeds 1.20, overflow occurs, significantly impairing the power generation performance of the fuel cell. Furthermore, when the mass ratio (FS / C) of the conductive support 2 to the fibrous material 4 is less than 0.05, the pore volume within the catalyst layer required for material movement decreases, significantly impairing the power generation performance of the fuel cell.

[0058] It should be noted that the loading density of catalyst particles 1 relative to the conductive support 2 on which the catalyst particles 1 are loaded is in the range of 15 wt% to 80 wt%, preferably in the range of 20 wt% to 70 wt%. On the other hand, when the loading density of catalyst particles 1 is less than 15 wt%, the number of catalyst particles 1 decreases, thus reducing the overall number of active sites in the catalyst layer and degrading its performance. In addition, when the loading density of catalyst particles 1 exceeds 80 wt%, the catalyst particles 1 agglomerate, promoting the dissolution of catalyst particles 1 generated during power generation, thereby reducing durability.

[0059] (Fibrous material)

[0060] The fibrous material 4 used in this embodiment is not limited to carbon fibers (electron conductors) with electrical conductivity (electron conductivity) such as carbon fibers, carbon nanofibers, and carbon nanotubes. It can also be fibrous materials (proton conductors) with proton conductivity such as sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polysulfides, sulfonated polyphenylene, sulfonated polyimide, and acid-doped polybenzoazoles.

[0061] The average fiber diameter of the fibrous material 4 is preferably in the range of 50 nm to 400 nm. By keeping the average fiber diameter of the fibrous material 4 within the above-mentioned range, the porosity within the catalyst layer can be increased, thereby exhibiting high power generation performance.

[0062] The average fiber length of the fibrous material 4 is preferably in the range of 3 μm to 50 μm. By keeping the average fiber length of the fibrous material 4 within the above-mentioned range, the fibrous material 4 can enhance the skeleton of the catalyst layer, increase the porosity of the catalyst layer, and thus exhibit high power generation performance.

[0063] It should be noted that the average fiber diameter and average fiber length of the fibrous material 4 can be measured / evaluated using a scanning electron microscope or a transmission electron microscope. Specifically, for 100 randomly selected fibrous materials 4, their fiber diameter and fiber length are measured using a scanning electron microscope or a transmission electron microscope, and the values ​​are averaged to determine the average fiber diameter and average fiber length of the fibrous material 4 involved in this embodiment.

[0064] The specific surface area of ​​fibrous material 4 is 10 m². 2 / g or more 100m 2 The specific surface area should be within the range of / g or less. Preferably, the specific surface area is 40m². 2 / g or more 80m 2Within the range of / g or less. If the specific surface area of ​​the fibrous material 4 is within the above-mentioned range, the polymeric electrolyte 3 will not entangle on the fibrous material 4, will not hinder material transport, and will thus inhibit performance degradation. On the other hand, when the specific surface area exceeds 100m², 2 At a specific surface area of ​​ / g, the polymeric electrolyte 3 excessively entangles on the fibrous material 4, resulting in aggregation. The aggregates of polymeric electrolyte 3 and fibrous material 4 fill the pores of the catalyst layer, significantly reducing the pore volume and thus significantly impairing power generation performance. Furthermore, when the specific surface area is less than 10m², 2 At a concentration of / g, the polymeric electrolyte 3 does not entangle with the fibrous material 4. As a result, the overall strength of the catalyst layer is insufficient, making the pores in the catalyst layer easily crushed. Therefore, the pore volume of the catalyst layer is significantly reduced, which significantly impairs power generation performance.

[0065] The peak value Dp of the distribution function dVp / dlogD of the pore volume Vp relative to the pore diameter D in the catalyst layer containing the condensate is preferably in the range of 0.06 μm to 0.10 μm. When the peak value of the distribution function dVp / dlogD of the pore volume Vp relative to the pore diameter D is less than 0.06 μm, although proton conductivity is ensured, water displacement is reduced, thus the output power performance tends to be slightly worse. Furthermore, when the peak value Dp of the distribution function dVp / dlogD of the pore volume Vp relative to the pore diameter D exceeds 0.10 μm, although water displacement is ensured, proton conductivity is reduced, thus the output power performance tends to be slightly worse.

[0066] Furthermore, although the distribution function dVp / dlogD of the pore volume Vp relative to the pore diameter D is unimodal, when the full width at half maximum (FWHM) of the peak value Dp is greater than 0.18 μm or less than 0.13 μm, the distribution of the pore diameter D in the catalyst layer is not within a suitable range. Therefore, the distribution of the pore diameter D in the catalyst layer becomes skewed, and the reactant gas required for power generation cannot be supplied in a sufficient proportion. Thus, the FWHM of the peak value Dp of the distribution function dVp / dlogD of the pore volume Vp relative to the pore diameter D is preferably in the range of 0.13 μm to 0.18 μm.

[0067] It should be noted that the specific surface area of ​​the aforementioned fibrous material 4 can be obtained using BET adsorption, one of the gas adsorption methods. Specifically, the fibrous material 4 is cooled, and then nitrogen gas is blown onto it, causing gas molecules to adsorb onto the surface of the fibrous material 4. The amount of gas adsorbed by the fibrous material 4 can be calculated by applying the BET formula. Furthermore, the specific surface area of ​​the fibrous material 4 can be calculated by multiplying this amount of gas adsorption by the cross-sectional area of ​​a gas molecule.

[0068] The following explains the above-mentioned "orifice diameter D", "orifice volume Vp", or "distribution function dVp / dlogD".

[0069] In this embodiment, pores with a diameter of 3 nm to 5.5 μm within the voids of the catalyst layer are defined as micropores. In the catalyst layer (electrode catalyst layer), the diameter of the micropore, calculated from the micropore volume Vp determined using the mercury indentation method, is the micropore diameter D. It should be noted that the micropore diameter D is defined as the diameter D of the micropore obtained through a cylindrical model obtained by the mercury indentation method. The micropore volume Vp is the total volume of micropores with a specific micropore diameter, determined by the mercury indentation method.

[0070] Here, the distribution of the pore volume Vp is explained. The distribution of the pore volume Vp is represented by the distribution function of the pore volume Vp relative to the pore diameter D (3nm≤D≤5.5μm) (=dVp / dlogD) (Log differential pore volume distribution). This pore volume Vp distribution is obtained by mercury injection method.

[0071] Because mercury has a high surface tension, a predetermined pressure P needs to be applied to allow mercury to penetrate into the pores. The distribution of the pore volume Vp can be determined based on the pressure P applied to allow mercury to penetrate the pores and the amount of mercury forced into the pores. The relationship between the applied pressure P and the pore diameter D that mercury can penetrate under this pressure P is expressed by the following equation (1), known as the Washburn formula. In equation (1), γ is the surface tension of mercury, and θ is the contact angle between mercury and the pore wall. In this embodiment, the surface tension γ is set to 0.48 N / m, and the contact angle θ is set to 130° to calculate the pore diameter D.

[0072] D=-4γcоsθ / P···Equation (1)

[0073] It should be noted that when using the mercury indentation method for actual measurement, the volume of mercury indented is recorded according to the different pressures P. Then, based on the above formula (1), each pressure P is converted into the pore diameter D. In addition, assuming that the volume of the indented mercury is equal to the pore volume Vp, the increase in pore volume Vp when the pore diameter increases from D to D+dD, i.e., the increase in pore volume dV, is plotted relative to the pore diameter D. The peak value of the curve obtained in this way is the peak value Dp of the distribution function dVp / dlogD of the pore volume Vp relative to the pore diameter D.

[0074] In this embodiment, when the value obtained by accumulating the pore volume Vp of pores across the entire range of pore diameter D is taken as the first accumulated volume, and the value obtained by accumulating the pore volume Vp of pores with a pore diameter D of 50 nm or less is taken as the second accumulated volume, the percentage of the second accumulated volume relative to the first accumulated volume is preferably 30% or more and 40% or less. Furthermore, in this embodiment, when the value obtained by accumulating the pore volume Vp of pores with a pore diameter D of 90 nm or more is taken as the third accumulated volume, the percentage of the third accumulated volume relative to the first accumulated volume is preferably 15% or more and 35% or less.

[0075] (solvent)

[0076] There are no particular limitations on the solvent used as the dispersion medium for the ink used to form the catalyst layer, i.e., the catalyst ink. As long as it can dissolve or disperse the polymeric electrolyte 3 into a fine gel in a highly fluid state without corroding the conductive carrier 2, polymeric electrolyte 3, and fibrous material 4 loaded with catalyst particles 1.

[0077] It should be noted that the solvent preferably includes a volatile organic solvent or water. There are no particular limitations on the organic solvent; the following can be used: alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, and pentanol; ketones such as acetone, methyl ethyl ketone, pentanol, methyl isobutyl ketone, heptanol, cyclohexanone, methylcyclohexanone, acetone-based acetone, and diisobutyl ketone; ethers such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, and dibutyl ether; and polar solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, and 1-methoxy-2-propanol. Furthermore, solvents obtained by mixing two or more of these solvents with water can also be used. Additionally, the solvent may contain a dispersant. The mixing / dispersion of the solvent can be achieved using, for example, ball mills, bead mills, planetary mixers, and dissolvers.

[0078] <Membrane-Electrode Junction>

[0079] Next, refer to Figure 2 The fabrication and structure of the membrane-electrode junction are explained.

[0080] (Polymer electrolyte membrane)

[0081] The polymeric electrolyte membrane 7 used in the membrane-electrode junction according to the embodiments of the present invention can be a fluorinated polymeric electrolyte or a hydrocarbon polymeric electrolyte, as long as it has proton conductivity. It should be noted that, for example, Nafion (registered trademark) manufactured by DuPont can be used as a fluorinated polymeric electrolyte. Alternatively, for example, sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetheretherketone, sulfonated polysulfide, sulfonated polyphenylene, etc., can be used as a hydrocarbon polymeric electrolyte membrane. Among these, the fluorinated polymeric electrolyte 7 can appropriately use a material containing perfluorosulfonic acid.

[0082] (Gasket materials, etc.)

[0083] The gasket material 8 or a plastic film with an adhesive layer (not shown) only needs to have heat resistance to the point that it will not melt under heat and pressure. Examples of gasket material 8 include: polyethylene naphthalate, polyethylene terephthalate, polyimide, polyaramid terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylate, and other polymer films. Additionally, heat-resistant fluoropolymers such as ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkyl vinyl ether copolymer, and polytetrafluoroethylene can also be used as gasket material 8. Polyethylene naphthalate is particularly preferred as the base material for gasket material 8, considering gas barrier properties and heat resistance.

[0084] (Adhesive layer)

[0085] The adhesive layer that bonds the gasket material 8 to the polymer electrolyte membrane 7, and the adhesive layer of the plastic film (not shown) with the adhesive layer, can be an acrylic, urethane, silicone, or rubber-based adhesive. When considering the adhesion between the gasket material 8 and the polymer electrolyte membrane 7, and its heat resistance under heat pressure, an acrylic adhesive is preferred. Regarding the adhesion between the gasket material 8 and the adhesive layer of the plastic film, if the adhesion force between the polymer electrolyte membrane 7 and the gasket material 8 is greater than the adhesion force between the gasket material 8 and the plastic film with the adhesive layer, it is easier to impart the gasket material 8 to the membrane-electrode junction; therefore, this is preferable.

[0086] Next, the manufacturing methods for the catalyst layer and the membrane-electrode junction will be described.

[0087] <Manufacturing methods for catalyst layers and membrane-electrode junctions>

[0088] (Dispersion treatment of catalyst ink)

[0089] The catalyst ink involved in this embodiment is an ink used to form a catalyst layer, and is an ink that at least includes catalyst particles 1, conductive carrier 2, polymer electrolyte 3, fibrous material 4, and solvent (dispersion medium).

[0090] The dispersion process during the production of this catalyst ink can be performed using various devices. Examples of dispersion processes include: ball milling, roller milling, shear milling, wet milling, and ultrasonic dispersion. Additionally, homogenizers that utilize centrifugal force for stirring can also be used.

[0091] (Coating treatment of catalyst ink)

[0092] Examples of coating methods for forming catalyst ink on a coating substrate include molding, roller coating, and spraying. However, in this embodiment, the coating method is not limited.

[0093] The substrate for coating, on which the catalyst layer, which is a constituent element of the membrane-electrode junction, is formed, is a polymer electrolyte membrane 7 or a transfer substrate, but in this embodiment, the substrate is not limited to the above.

[0094] When using a transfer method to fabricate the catalyst layer, any material constituting the transfer substrate can form a catalyst layer on its surface and can transfer the catalyst layer to the polymer electrolyte membrane 7. Examples of polymer films that can be used as the transfer substrate include: polyimide, polyethylene terephthalate, polyaramid terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylate, and polyethylene naphthalate. Additionally, heat-resistant fluoropolymers such as ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkyl vinyl ether copolymer, and polytetrafluoroethylene can also be used as the transfer substrate.

[0095] In one embodiment of the membrane-electrode junction, a membrane-electrode junction with excellent power generation performance can be obtained by disposing a catalyst layer on at least one of the anode surface (i.e., the surface on which the anode catalyst layer is to be formed) and the cathode surface (i.e., the surface on which the cathode catalyst layer is to be formed) of the polymer electrolyte membrane 7.

[0096] According to the manufacturing method of the membrane-electrode assembly described above, a membrane-electrode assembly in which the catalyst layer is well bonded to at least one side (preferably both sides) of the polymer electrolyte membrane 7 can be manufactured.

[0097] The present invention will now be described in detail based on embodiments. However, the present invention is not limited to these embodiments.

[0098] [Example]

[0099] (Preparation of catalyst ink)

[0100] The catalyst ink used to form the catalyst layer is composed of a dispersion of a fluorine-based polymeric electrolyte (20% Nafi dispersion DE2020 CS type), platinum-supported carbon (TEC10E50E), fibrous material, 1-propanol, and water. These components are mixed using a ball mill to prepare the catalyst ink for the catalyst layer. The mass ratio of carbon particles to polymeric electrolyte is set to 1:1. The mixture is then dispersed using a planetary ball mill at 300 rpm for 60 minutes. At this point, zirconia balls with a diameter of 5 mm are added to approximately one-third of the volume of the zirconia container. This completes the preparation of the catalyst ink.

[0101] It should be noted that the catalyst ink was prepared in such a manner that the mass of the polymeric electrolyte relative to the mass of the carbon particles was 100% by mass, the mass of the fibrous material relative to the mass of the carbon particles was 100% by mass, the proportion of water in the dispersion medium was 50% by mass, and the solid content in the catalyst ink was 10% by mass.

[0102] (Formation of catalyst layer and fabrication of membrane-electrode junction)

[0103] A membrane-electrode junction was fabricated by forming an anode catalyst layer and a cathode catalyst layer on a polymer electrolyte membrane through molding. At this point, catalyst ink was coated onto the polymer electrolyte membrane, such that the wet film thickness of the catalyst ink on the cathode surface of the polymer electrolyte membrane was 150 μm, and the wet film thickness of the catalyst ink on the anode surface was 100 μm.

[0104] Next, the polymer electrolyte membrane with the coating is placed in an 80-degree warm air oven to dry the coating until it is no longer sticky.

[0105] Thus, the membrane-electrode junctions of the embodiments and comparative examples were obtained.

[0106] (Power Generation Assessment)

[0107] Carbon paper used as a gas diffusion layer is attached by clamping the membrane-electrode assembly prepared in Examples 1-3 and Comparative Examples 1-3 as described later, and then placed inside the power generation evaluation cell.

[0108] Next, using a fuel cell testing device, the battery temperature was set to 80°C, and current and voltage were measured. Hydrogen was used as the fuel gas and air as the oxidant gas, and flow control was performed using a constant utilization rate.

[0109] (Evaluation of dVp / dlogD)

[0110] The distribution of pore volume Vp was determined by mercury infiltration. Specifically, a membrane-electrode junction with only the cathode-side electrode catalyst layer formed on a polymer electrolyte membrane was used, and the pore volume Vp was measured using an automated porosimeter (AutoPore IV9510, manufactured by Micromeritics Instrument Corp.). The measured cell volume was approximately 5 cm³. 3 The pressure of the mercury injection was increased from 3 kPa to 400 MPa. This yielded the mercury injection volume, or pore volume Vp, at each pressure. The injection pressure was converted to the pore diameter D using the Washburn equation, and a curve of the pore volume Vp versus the pore diameter D as a distribution function dVp / dlogD was plotted. It should be noted that in this evaluation, the surface tension γ was set to 0.48 N / m, and the contact angle θ was set to 130°. Then, the pore diameter D corresponding to the peak value of the curve was read as the pore diameter Dp.

[0111] Next, the volumes of all pores with a diameter D of 3 nm to 5.5 μm are accumulated to calculate the first accumulated volume. Additionally, the volumes of pores with a diameter D of 90 nm or more are accumulated to calculate the third accumulated volume. Then, the percentage R(L) of the third accumulated volume relative to the first accumulated volume is calculated by dividing the third accumulated volume by the first accumulated volume and multiplying the result by 100. Furthermore, the volumes of pores with a diameter D of 50 nm or less are accumulated to calculate the second accumulated volume. Then, the percentage R(S) of the second accumulated volume relative to the first accumulated volume is calculated by dividing the second accumulated volume by the first accumulated volume and multiplying the result by 100. Finally, the volume V0 of the electrode catalyst layer used in the determination of the pore volume Vp is calculated by multiplying the area and thickness of the electrode catalyst layer. Then, calculate the percentage V / V0 of the first cumulative volume V relative to the volume V0 of the electrode catalyst layer.

[0112] (Profiling observation using SEM)

[0113] SEM images were performed on the cross-sections of the anode and cathode catalyst layers prepared in Examples 1-15 and Comparative Examples 1-3, as described below. Schematic diagrams of the obtained SEM images are shown below. Figure 3 (a) and (b).

[0114] <Example 1>

[0115] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2A cathode catalyst ink of fibrous material (average fiber length: 10.0 μm, average fiber diameter: 50 nm) was used to fabricate a membrane-electrode junction.

[0116] <Example 2>

[0117] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​55m² 2 A cathode catalyst ink of fibrous material (average fiber length: 7.0 μm, average fiber diameter: 70 nm) was used to fabricate a membrane-electrode junction.

[0118] <Example 3>

[0119] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​80m² 2 A cathode catalyst ink of fibrous material (average fiber length: 5.0 μm, average fiber diameter: 50 nm) was used to fabricate a membrane-electrode junction.

[0120] <Example 4>

[0121] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2 A cathode catalyst ink of fibrous material (average fiber length: 2.5 μm, average fiber diameter: 45 nm) was used to fabricate a membrane-electrode junction.

[0122] <Example 5>

[0123] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2 A cathode catalyst ink of fibrous material (average fiber length: 12 μm, average fiber diameter: 300 nm) was used to fabricate a membrane-electrode junction.

[0124] <Example 6>

[0125] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​80m² 2 A cathode catalyst ink of fibrous material (average fiber length: 2.5 μm, average fiber diameter: 45 nm) was used to fabricate a membrane-electrode junction.

[0126] <Example 7>

[0127] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​80m² 2 / g is a cathode catalyst ink of fibrous material (average fiber length: 12μm, average fiber diameter: 300nm), thereby fabricating a membrane-electrode junction.

[0128] <Example 8>

[0129] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2 A cathode catalyst ink of fibrous material (average fiber length: 3 μm, average fiber diameter: 45 nm) was used to fabricate a membrane-electrode junction.

[0130] <Example 9>

[0131] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2 A cathode catalyst ink of fibrous material (average fiber length: 20 μm, average fiber diameter: 30 nm) was used to fabricate a membrane-electrode junction.

[0132] <Example 10>

[0133] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​80m² 2 A cathode catalyst ink of fibrous material (average fiber length: 3 μm, average fiber diameter: 45 nm) was used to fabricate a membrane-electrode junction.

[0134] <Example 11>

[0135] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​80m² 2 A cathode catalyst ink of fibrous material (average fiber length: 12 μm, average fiber diameter: 300 nm) was used to fabricate a membrane-electrode junction.

[0136] <Example 12>

[0137] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2A cathode catalyst ink of fibrous material (average fiber length: 12 μm, average fiber diameter: 500 nm) was used to fabricate a membrane-electrode junction.

[0138] <Example 13>

[0139] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2 A cathode catalyst ink of fibrous material (average fiber length: 12 μm, average fiber diameter: 400 nm) was used to fabricate a membrane-electrode junction.

[0140] <Example 14>

[0141] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​40m² 2 A cathode catalyst ink of fibrous material (average fiber length: 2.5 μm, average fiber diameter: 50 nm) was used to fabricate a membrane-electrode junction.

[0142] <Example 15>

[0143] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​80m² 2 A cathode catalyst ink of fibrous material (average fiber length: 12 μm, average fiber diameter: 500 nm) was used to fabricate a membrane-electrode junction.

[0144] <Comparative Example 1>

[0145] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​250m². 2 / g of fibrous material was used to make a cathode catalyst ink, thereby creating a membrane-electrode junction.

[0146] <Comparative Example 2>

[0147] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2 The coating method includes a specific surface area of ​​300m² 2 / g of fibrous material was used to make a cathode catalyst ink, thereby creating a membrane-electrode junction.

[0148] <Comparative Example 3>

[0149] By setting the platinum loading of the cathode catalyst layer to 0.3 mg / cm³ 2The coating method includes a specific surface area of ​​800m² 2 / g of fibrous material was used to make a cathode catalyst ink, thereby creating a membrane-electrode junction.

[0150] (Evaluation Results)

[0151] The results of Examples 1-15 and Comparative Examples 1-3 are summarized in Figure 3 And in Table 1. For example... Figure 3 (b) As schematically shown, the fibrous material 4′ of Comparative Examples 1-3 is entangled with the polymeric electrolyte 3, thus narrowing the pores of the catalyst layer. In contrast, as... Figure 3 (a) As schematically shown, the fibrous material 4 of Examples 1 to 15 does not entangle with the polymeric electrolyte 3, thus ensuring a wider pore size than conventional catalyst layers.

[0152] The specific surface area in Examples 1-15 is 40-80 m². 2 / g, and the specific surface area of ​​Comparative Examples 1 to 3 is 250 to 800 m². 2 / g, except that the platinum loading is constant at 0.3 mg / cm³. 2 Other measurement conditions were also the same. That is, at least at this platinum loading, the specific surface area of ​​the catalyst layer in the example was 40–80 m². 2 The output power at / g is 810~850mW / cm 2 The specific surface area of ​​the catalyst layer in the comparative examples is 250–800 m². 2 The output power at / g is 638~724mW / cm 2 It should be noted that if the output power is 800mW / cm 2 Therefore, it can be determined that even in the high output power region (high current density region), the power generation performance is improved (i.e., the power generation performance is maintained at the same level as in the low current density region). It should be noted that the membrane-electrode joints of Comparative Examples 1 to 3 correspond to the membrane-electrode joints involved in the prior art.

[0153] This is believed to be due to the enlargement of pores formed inside the catalyst layer. As a result, although the specific surface area is relatively reduced, it is effective in draining water generated inside the catalyst layer to the outside. It is believed that this can result in high output power.

[0154] [Table 1]

[0155]

[0156] As can be seen from the above results, according to this embodiment, by forming a catalyst layer with wider pores than conventional catalyst layers, the power generation performance of the membrane-electrode junction is improved. Thus, by adding a fibrous material with an appropriate specific surface area to the catalyst layer, the pores of the catalyst layer in this embodiment are larger than those of conventional catalyst layers, making the chemical reaction more active. Simultaneously, the material mobility is also improved, effectively draining water generated in the cathode catalyst layer to the outside, thereby suppressing overflow. As described above, with the catalyst layer according to this embodiment, a catalyst layer capable of achieving high output power and a membrane-electrode junction having this catalyst layer can be provided.

[0157] Industrial applicability

[0158] By employing the membrane-electrode junction described in this embodiment, sufficient drainage and gas diffusion can be achieved, thereby enabling high power generation performance over a long period.

[0159] That is, according to this embodiment, by making the catalyst layer contain a specific surface area of ​​40m² 2 / g or more 80m 2 The fibrous material, weighing less than 1g, can provide electrode catalyst layers, membrane-electrode junctions, and solid polymer fuel cells that exhibit sufficient water permeability and gas diffusion during operation and can maintain high power generation performance over a long period. Therefore, this invention is applicable to stationary cogeneration systems and fuel cell vehicles utilizing solid polymer fuel cells, and has significant industrial value.

[0160] Symbol Explanation

[0161] 1…catalyst particles

[0162] 2…Conductive carrier

[0163] 3…Polymer electrolytes

[0164] 4,4′… fibrous material

[0165] 5…Cathode catalyst layer

[0166] 6…Anode catalyst layer

[0167] 7…Polymer electrolyte membrane

[0168] 8…Gasket Material

[0169] 9…Gas Diffusion Layer

Claims

1. A catalyst layer for a membrane-electrode assembly of a solid polymer type fuel cell, characterized by, the catalyst layer comprising catalyst particles, an electrically conductive carrier, a polymer electrolyte, and a fibrous substance, The fibrous substance contains at least one of an electron conductor and a proton conductor, and the specific surface area of the fibrous substance is in a range of 40 m 2 / g or more and 80 m 2 / g or less. a half-peak width of a peak value Dp of a distribution function dVp / dlogD of a fine pore volume Vp with respect to a fine pore diameter D in the catalyst layer being in a range of 0.13 μm or more and 0.18 μm or less, the peak value Dp of the distribution function dVp / dlogD being in a range of 0.06 μm or more and 0.10 μm or less.

2. The catalyst layer according to claim 1, characterized by, an average fiber length of the fibrous substance being in a range of 3 μm or more and 50 μm or less.

3. The catalyst layer according to claim 1 or 2, characterized by, an average fiber diameter of the fibrous substance being in a range of 50 nm or more and 400 nm or less.

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