CATALYST LAYER

Abstract

Catalyst layer for fuel cells, where the catalyst layer comprises a catalyst metal, a support, and a conductive additive; the support carries the catalyst metal; the specific surface area of ​​the carrier 600 m 2 / gC or less; the conductive additive does not support the catalyst metal and has a larger aspect ratio than the support; the aspect ratio of the conductive additive is greater than 10; when a total mass of the catalyst layer is 100 mass%, a percentage of the conductive additive contained in the catalyst layer is more than 2 mass% and less than 20 mass%; the catalyst layer has a void content of 29% to 42%; and the conductive additive is a non-hydrophilic conductive additive.

Description

TECHNICAL FIELD

[0001] This invention relates to a catalyst layer. BACKGROUND

[0002] A fuel cell (FC) is a power generation device that generates electrical energy through an electrochemical reaction between fuel gas (such as hydrogen) and oxidant gas (such as oxygen and air) in a single fuel cell unit or fuel cell stack (hereinafter referred to simply as a "stack") composed of stacked fuel cell units or unit fuel cells (hereinafter referred to as "cells"). Hereinafter, fuel gas and oxidant gas are referred to simply as "reactant gas" or "gas" without any particular distinction.

[0003] In general, fuel cell units or unit fuel cells comprise a membrane electrode assembly (MEA).

[0004] The membrane electrode assembly has a structure such that a catalyst layer and a gas diffusion layer are sequentially formed on both surfaces of a solid polymer electrolyte membrane (hereinafter referred to simply as the "electrolyte membrane"). Accordingly, a membrane electrode assembly may be referred to as a "membrane electrode gas diffusion layer assembly" (MEGA).

[0005] If necessary, each fuel cell unit includes two separators sandwiching the membrane electrode-gas diffusion layer unit. Generally, the separators have a structure such that a groove is formed as a reactant gas flow path on a surface in contact with the gas diffusion layer. The separators also function as a generated current collector.

[0006] In the fuel electrode (anode) of the fuel cell, hydrogen (H2 ) is supplied as a fuel gas from the gas flow path and the gas diffusion layer; the supplied hydrogen is protonated by a catalytic action of the catalyst layer; and the protonated hydrogen reaches or migrates to the oxidant electrode (cathode) through the electrolyte membrane. Electrons are generated at the same time, travel through an external circuit, perform work, and then reach the cathode. Oxygen (O 2 ) is supplied to the cathode as an oxidant gas, and the supplied oxygen reacts with protons and electrons on the cathode, generating water. The generated water releases appropriate moisture to the electrolyte membrane, and excess water permeates or permeates the gas diffusion layer and is discharged to the outside of the system.

[0007] There is considerable research on fuel cells configured to be mounted and used in a fuel cell vehicle (hereinafter referred to simply as “vehicle”).

[0008] For example, Patent Literature 1 discloses a catalytic layer for fuel cells which is blended with conductive carbon fibers having a high aspect ratio or width-to-height ratio (“high-aspect-ratio conductive carbon fibers”).

[0009] Patent Literature 2 discloses carbon-based fibers for fuel cells comprising carbon nanofibers and carbon particles aggregated in the carbon nanofibers.

[0010] Patent Literature 3 discloses an electrode catalyst for fuel cells, wherein a catalyst metal is deposited on a mixture of carbon containing at least one of nitrogen, phosphorus, oxygen, and sulfur on the surface with a carbon fiber on the surface of which a graphite C-plane is exposed or to which a graphite C-plane is inclined, or another carbon fiber on the surface of which the edge of the graphite C-plane is exposed or to which the edge of the graphite C-plane is inclined.

[0011] Furthermore, Patent Literature 4 and Patent Literature 5 disclose catalyst layers for fuel cells of the prior art. Patent Literature 1: JP 2019-172476 A Patent Literature 2: WO 2017 / 135386 A1 Patent Literature 3: JP 2007-061698 A Patent literature 4: US 2003 / 0 091 891 A1 Patentliteratur 5: US 8 007 953 B2

[0012] There is an attempt to use fuel cells as a power source for commercial vehicles such as buses and trucks. These commercial vehicles are required to operate for long distances and for long periods of time, and the carbon support in the catalyst layer of the fuel cells is oxidized and damaged, thereby reducing the energy output of the fuel cells. Although it is effective to use a carbonaceous material having high crystallinity as a means of preventing oxidative damage to the carbon support, the particles of highly crystalline carbon hardly form a higher-order structure, and the specific surface area of ​​the highly crystalline carbon is small. If the catalyst layer is formed from carbon having a small specific surface area, the carbon particles tend to be closely aggregated.to be accumulated, and the carbon hardly forms a higher-order structure. Accordingly, the catalyst layer is densified; gas is not sufficiently distributed across the entire catalyst layer; and the initial power generation performance of the fuel cells decreases.

[0013] To prevent excessive compaction, it is conceivable to add a conductive additive having an aspect ratio equal to or higher than a predetermined aspect ratio to the catalyst layer. If the aspect ratio is too small and the amount of the conductive additive added is too small, the effect of suppressing compaction will not be achieved.

[0014] The conductive carbon fibers of Patent Literature 1 support metallic particles as a catalyst. The surface of the carbon supporting the metallic particles is hydrophilized. In addition to the hydrophilic properties of the metal itself, the carbon surface invariably becomes hydrophilic because a catalytic process usually includes an acid treatment step. When a catalyst layer is formed from such hydrophilic carbon, the gas diffusivity of the catalyst layer is reduced due to a reduction in the drainage properties of the catalyst layer, and the power generation performance of the fuel cells is reduced. SUMMARY

[0015] In view of the above circumstances, an object of the disclosed embodiments is to provide a catalyst layer having a low gas diffusion resistance and a low proton resistance even when a support having a small specific surface area is used.

[0016] The catalyst layer of the disclosed embodiments is a catalyst layer for fuel cells, wherein the catalyst layer comprises a catalyst metal, a support, and a conductive additive; wherein the support carries the catalyst metal; where a specific surface area of ​​the carrier is 600 m 2 / gC or less; wherein the conductive additive does not support the catalyst metal and has a larger aspect ratio than the support; wherein the aspect ratio of the conductive additive is greater than 10; wherein, when a total mass of the catalyst layer is 100 mass%, a percentage of the conductive additive contained in the catalyst layer is more than 2 mass% and less than 20 mass%; wherein the catalyst layer has a void content of 29% to 42%; and wherein the conductive additive is a non-hydrophilic conductive additive.

[0017] The aspect ratio of the conductive additive may be 18 or more and 40 or less.

[0018] When the total mass of the catalyst layer is 100 mass%, the percentage of the conductive additive contained in the catalyst layer may be 7 mass% or more and 15 mass% or less.

[0019] The carrier and the conductive additive can be carbon-containing materials.

[0020] According to the catalyst layer of the disclosed embodiments, even if the support used has a small specific surface area, it is possible to reduce the gas diffusion resistance and suppress an increase in the proton resistance. DETAILED DESCRIPTION

[0021] The catalyst layer of the disclosed embodiments is a catalyst layer for fuel cells, wherein the catalyst layer comprises a catalyst metal, a support, and a conductive additive; wherein the support carries the catalyst metal; wherein a specific surface area of ​​the support is 600 m 2 / gC or less; wherein the conductive additive does not support the catalyst metal and has a larger aspect ratio than the support; wherein the aspect ratio of the conductive additive is greater than 10; wherein, when a total mass of the catalyst layer is 100 mass%, a percentage of the conductive additive contained in the catalyst layer is more than 2 mass% and less than 20 mass%; and wherein the conductive additive is a non-hydrophilicized conductive additive.

[0022] In the disclosed embodiments, the conductive additive having the high aspect ratio and on which the catalyst metal is not supported is mixed with the support having the small specific surface area and on which the catalyst metal is supported, thereby forming the catalyst layer.

[0023] According to the disclosed embodiments, gas diffusion resistance can be reduced by a void-forming effect and a hydrophobic effect. Also, an increase in proton resistance can be suppressed by adjusting the amount of the conductive additive within a predetermined range. Consequently, by using the catalyst layer of the disclosed embodiments in a fuel cell for commercial vehicles that are operated for a long time, the initial power generation performance of the fuel cell can be increased, and the endurance performance of the fuel cell can be enhanced.

[0024] The catalyst layer of the disclosed embodiments comprises the catalyst metal, the support, and the conductive additive. If desired, the catalyst layer may contain a proton-conductive electrolyte, etc.

[0025] The catalyst metal is supported on the support; however, it is not supported on the conductive additive.

[0026] As the catalyst metal, for example, platinum (Pt) or an alloy of Pt and another metal (e.g. a Pt alloy mixed with cobalt, nickel, or similar) can be used.

[0027] The electrolyte can be a fluorine-based resin or similar. For example, a Nafion solution or similar can be used as the fluorine-based resin.

[0028] The support may be a carbonaceous material. For example, the carbonaceous material may be at least one selected from the group consisting of carbon black, such as acetylene black and furnace black, vapor-grown carbon fibers (VGCF), carbon nanotubes, and carbon nanofibers. The support may be carbon black. For example, a hydrophobized carbon material such that its hydrophobicity increases upon heat treatment may be used as the carbonaceous material.

[0029] The carrier carries the catalyst metal.

[0030] The specific surface area (SSA) of the carrier can be 600 m 2 / gC or less, or may be 580 m 2 / gC or less. The specific surface area of ​​the carrier can be 150 m 2 / gC or more. If the specific surface area of ​​the support is 600 m 2 / gC or less, deterioration or damage of the support due to oxidation can be suppressed. If the specific surface area of ​​the support is 150 m 2 / gC or more, the catalyst can be supported more easily. It is believed that the same effects can be obtained when the specific surface area of ​​the support is within a measurement error of 5%.

[0031] The carrier has a smaller aspect ratio than the conductive additive.

[0032] The shape of the support is not particularly limited as long as the aspect ratio condition is met. Examples of the shape of the support include, but are not limited to, a particulate (spherical) shape, a scaly shape, a fibrous shape, and an undefined shape.

[0033] The conductive additive may be a ceramic oxide, a carbonaceous material, a metal material, or the like. From the viewpoint of reducing gas diffusion resistance, the conductive additive may be a carbonaceous material. As the ceramic oxide, examples include, but are not limited to, titanium oxide. The carbonaceous material may be, for example, at least one selected from the group consisting of carbon black such as acetylene black and furnace black, gas-phase grown carbon fibers (VGCF), carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electrical conductivity, the carbonaceous material may be at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers. As the metal material, examples include, but are not limited to, Ni, Cu, Fe, and SUS.

[0034] The conductive additive does not carry the catalyst metal.

[0035] The conductive additive has a larger aspect ratio than the carrier.

[0036] The aspect ratio (AS) of the conductive additive may be more than 10 from the perspective of suppressing gas diffusion resistance. The aspect ratio of the conductive additive may be 18 or more and 40 or less.

[0037] The shape of the conductive additive is not particularly limited as long as it satisfies the above-mentioned aspect ratio. Examples of the shape of the conductive additive include, but are not limited to, a particulate shape, a scaly shape, a fibrous shape, and an undefined shape. The conductive additive may be in a scaly or fibrous shape.

[0038] A non-hydrophilic conductive additive is used as the conductive additive. This means that the conductive additive exhibits hydrophobicity. If the conductive additive is a carbonaceous material, a non-hydrophilic carbonaceous material exhibits hydrophobicity. For example, the carbonaceous material can be a hydrophobized carbonaceous material, so its hydrophobicity is increased by heat treatment.

[0039] In the disclosed embodiments, the catalyst-supporting carrier is kneaded with the conductive additive to form the catalyst layer, and the catalyst metal is not supported and catalyzed on the conductive additive. When the catalyst metal is supported on the conductive additive, the surface of the conductive additive is hydrophobized by an acid treatment, which is generally performed during a catalysis step. Therefore, even if the catalyst layer is a catalyst layer having a desired void ratio, the drainage function of the catalyst layer is reduced, and the effect of reducing gas diffusion resistance is not obtained.

[0040] According to the disclosed embodiments, the void fraction of the catalyst layer is increased by introducing the conductive additive into the catalyst layer. Since the conductive additive exhibits hydrophobicity, water can also effectively drain from the catalyst layer. These effects can increase the gas diffusivity of the catalyst layer.

[0041] When the total mass of the catalyst layer is 100 mass%, the percentage of the conductive additive contained in the catalyst layer may be more than 2 mass% and less than 20 mass%, or may be 7 mass% or more and 15 mass% or less.

[0042] When the percentage of the conductive additive contained in the catalyst layer exceeds 2 mass%, the effect of reducing gas diffusion resistance begins to be seen. When the percentage of the conductive additive contained in the catalyst layer is less than 20 mass%, the increase in proton resistance is suppressed.

[0043] The catalyst layer of the disclosed embodiments is a catalyst layer for fuel cells.

[0044] The fuel cells may be a fuel cell consisting of only one fuel cell unit or unit fuel cell, or may be a fuel cell stack consisting of stacked unit fuel cells or fuel cell units.

[0045] The number of fuel cell units stacked is not particularly limited. For example, two to several hundred fuel cell units can be stacked, or two to 200 fuel cell units can be stacked.

[0046] The fuel cell stack may include an end plate at both ends of the stacking direction of each fuel cell unit.

[0047] Each fuel cell unit comprises at least one membrane electrode unit.

[0048] The membrane electrode assembly comprises an anode-side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode-side gas diffusion layer in this order.

[0049] The cathode comprises a cathode catalyst layer and a cathode side gas diffusion layer.

[0050] The anode comprises an anode catalyst layer and an anode side gas diffusion layer.

[0051] The cathode catalyst layer and the anode catalyst layer are collectively referred to as the “catalyst layer”.

[0052] As the catalyst layer, the catalyst layer of the disclosed embodiments is used.

[0053] The catalyst layer of the disclosed embodiments can be used as the cathode catalyst layer, and it can be used as the anode catalyst layer. The catalyst layer of the disclosed embodiments can be used as at least the cathode catalyst layer. The catalyst layer of the disclosed embodiments can be used as both the cathode catalyst layer and the anode catalyst layer.

[0054] The cathode-side gas diffusion layer and the anode-side gas diffusion layer are collectively referred to as the “gas diffusion layer”.

[0055] The gas diffusion layer can be a gas-permeable, electrically conductive element, or similar.

[0056] As the electrically conductive member, examples include, but are not limited to, a porous carbonaceous material such as carbon cloth and carbon paper, and a porous metal material such as metal mesh and metal foam.

[0057] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include, but are not limited to, hydrocarbon electrolyte membranes and fluorine electrolyte membranes, such as a moisture-containing thin perfluorosulfonic acid membrane. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont).

[0058] If desired, each fuel cell unit may include two separators sandwiching the membrane electrode assembly. One of the two separators is an anode-side separator, and the other is a cathode-side separator. In the disclosed embodiments, the anode-side separator and the cathode-side separator are collectively referred to as the "separator."

[0059] The separator may include supply or inlet holes and discharge or outlet holes for supplying the reactant gas and the coolant in the fuel cell unit stacking direction. For example, a mixed solution of ethylene glycol and water may be used as the coolant to prevent freezing at low temperatures. The reactant gas is a fuel gas or oxidant gas. The fuel gas may be hydrogen or the like. The oxidant gas may be oxygen, air, dry air, or the like.

[0060] As the inlet or supply hole, examples include, but are not limited to, a fuel gas supply hole, an oxidant gas supply hole, and a coolant supply hole.

[0061] As the discharge hole, examples include, but are not limited to, a fuel gas discharge hole, an oxidant gas discharge hole, and a coolant discharge hole.

[0062] The separator may include one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more coolant supply holes, one or more fuel gas outlet holes, one or more oxidant gas outlet holes, and one or more coolant outlet holes.

[0063] The separator may have a reactant gas flow path on a surface in contact with the gas diffusion layer. On the opposite surface of the surface in contact with the gas diffusion layer, the separator may also have a coolant flow path to maintain the temperature of the fuel cell at a constant level.

[0064] If the separator is the anode-side separator, it may have one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more coolant supply holes, one or more fuel gas outlet holes, one or more oxidant gas outlet holes, and one or more coolant outlet holes. On the surface in contact with the anode-side gas diffusion layer, the anode-side separator may have a fuel gas flow path for supplying the fuel gas from the fuel gas supply hole to the fuel gas outlet hole. On the opposite surface to the surface in contact with the anode-side gas diffusion layer, the anode-side separator may have a coolant flow path for supplying the coolant from the coolant supply hole to the coolant outlet hole.

[0065] When the separator is the cathode-side separator, it may have one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more coolant supply holes, one or more fuel gas outlet holes, one or more oxidant gas outlet holes, and one or more coolant outlet holes. On the surface in contact with the cathode-side gas diffusion layer, the cathode-side separator may have an oxidant gas flow path for supplying the oxidant gas from the oxidant gas supply hole to the oxidant gas outlet hole. On the opposite surface to the surface in contact with the cathode-side gas diffusion layer, the cathode-side separator may have a coolant flow path for supplying the coolant from the coolant supply hole to the coolant outlet hole.

[0066] The separator may be a gas-impermeable, electrically conductive element or the like. The electrically conductive element may be, for example, dense carbon, where carbon is compressed to be gas-impermeable, or a press-formed metal (e.g., iron, aluminum, stainless steel, or the like) plate. The separator may have a collecting or collecting function.

[0067] The fuel cell stack may include a manifold, such as an inlet manifold connecting the supply holes and an outlet manifold connecting the outlet holes.

[0068] As the intake manifold, examples include, but are not limited to, an anode intake manifold, a cathode intake manifold, and a coolant intake manifold.

[0069] As the exhaust manifold, examples include, but are not limited to, an anode exhaust manifold, a cathode exhaust manifold, and a coolant exhaust manifold. EXAMPLESExample 1

[0070] A support carrying a catalyst metal (a catalyst-supporting support) and a conductive additive were prepared.

[0071] A carbonaceous material was found which has a specific surface area of ​​580 m 2 / gC than the carrier used.

[0072] Platinum was used as the catalyst metal.

[0073] Carbon fibers, which have an aspect ratio of 18, were used as the conductive additive.

[0074] A catalyst layer was prepared by kneading the catalyst-supporting support and the conductive additive.

[0075] The amount of conductive additive contained in the catalyst layer was set to 10 mass%.

[0076] The void or gap or pore content of the catalyst layer was 30%.

[0077] The gas diffusion resistance of the catalyst layer was measured at a temperature of 60 °C and a relative humidity (RH) of 120%.

[0078] The proton resistance of the catalyst layer was measured at a temperature of 60 °C and a relative humidity of 30%.

[0079] The results are shown in Table 1. Example 2

[0080] The catalyst layer of Example 2 was prepared in the same manner as in Example 1, except that carbon fibers with an aspect ratio of 40 were used as the conductive additive. The void ratio, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0081] The results are shown in Table 1. Example 3

[0082] The catalyst layer of Example 3 was prepared in the same manner as in Example 1, except that the amount of the conductive additive contained in the catalyst layer was 7 mass%. The void fraction, gas diffusion resistance, and proton resistance of the catalyst layer were measured.

[0083] The results are shown in Table 1. Example 4

[0084] The catalyst layer of Example 4 was prepared in the same manner as in Example 1, except that the amount of the conductive additive contained in the catalyst layer was 15 mass%. The void fraction, gas diffusion resistance, and proton resistance of the catalyst layer were measured.

[0085] The results are shown in Table 1. Comparison example 1

[0086] The catalyst layer of Comparative Example 1 was prepared in the same manner as in Example 1, except that carbon particles having an aspect ratio of 1 were used as the conductive additive. The void ratio, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0087] The results are shown in Table 1. Comparison example 2

[0088] The catalyst layer of Comparative Example 2 was prepared in the same manner as in Example 1, except that carbon fibers with an aspect ratio of 10 were used as the conductive additive. The void ratio, gas diffusion resistance, and proton resistance of the catalyst layer were measured.

[0089] The results are shown in Table 1. Comparison example 3

[0090] The catalyst layer of Comparative Example 3 was prepared in the same manner as in Example 1, except that no conductive additive was used. The void fraction, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0091] The results are shown in Table 1. Comparison example 4

[0092] The catalyst layer of Comparative Example 4 was prepared in the same manner as in Example 1, except that the amount of the conductive additive contained in the catalyst layer was 2 mass%. The void fraction, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0093] The results are shown in Table 1. Comparison example 5

[0094] The catalyst layer of Comparative Example 5 was prepared in the same manner as in Example 1, except that the amount of the conductive additive contained in the catalyst layer was 20 mass%. The void fraction, gas diffusion resistance, and proton resistance of the catalyst layer were measured.

[0095] The results are shown in Table 1. Comparison example 6

[0096] The catalyst layer of Comparative Example 6 was prepared in the same manner as in Example 1, except that the content of the conductive additive contained in the catalyst layer was 30 mass%. The void fraction, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0097] The results are shown in Table 1. Comparison example 7

[0098] The catalyst layer of Comparative Example 7 was prepared in the same manner as in Example 1, except that a conductive additive hydrophilized by acid treatment was used. The void fraction, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0099] The results are shown in Table 1. Comparative example 8

[0100] The catalyst layer of Comparative Example 8 was prepared in the same manner as in Example 1, except that a carbonaceous material having a specific surface area of ​​1200 m 2 / gC when the support was used and no conductive additive was used. The void fraction, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0101] The results are shown in Table 1. Comparison example 9

[0102] The catalyst layer of Comparative Example 9 was prepared in the same manner as in Example 1, except that a carbonaceous material having a specific surface area of ​​1200 m 2 / gC when the support was used, and the amount of the conductive additive contained in the catalyst layer was 10 wt%. The void fraction, gas diffusion resistance, and proton resistance of the catalytic layer were measured.

[0103] The results are shown in Table 1. Table 1 carrier Conductive additive Catalyst layer SSA (m 2 / gC) AS (-) Content (wt%) Acid treated or not Void content (%) Gas diffusion resistance [s / m] 60°C 120%RH Proton resistance (Ω cm 2 ) 60°C 30%RH Comparison example 1 580 1 10 No 25 150 0,96 Comparison example 2 10 10 No 24 148 0,98 Example 1 18 10 No 30 132 0,95 Example 2 40 10 No 42 85 0,95 Comparison example 3 - 0 No 24 149 0,97 Comparison example 4 18 2 No 25 148 0,95 Example 3 18 7 No 29 130 1,00 Example 4 18 15 No 34 100 1,00 Comparison example 5 18 20 No 38 98 1,2 Comparison example 6 18 30 No 45 104 1,35 Comparison example 7 18 10 Acid treated 30 142 0,95 Comparative example 8 1200 - 0 No 43 95 0,95 Comparison example 9 18 10 No 45 93 1,1

[0104] In Comparative Example 7, the conductive additive was acid-treated to hydrophilize its surface and used in the catalyst layer. For the catalyst layer, as in Example 1, an increase in the void ratio was confirmed; however, the effect of suppressing gas diffusion resistance was not significant. The reason is assumed to be as follows: because the added conductive additive was hydrophilic, the drainage function in the catalyst layer was insufficient.

[0105] In the catalyst layer of Comparative Example 8, which used the support having a specific surface area of ​​more than 600 m 2 / gC, since the catalyst layer has a distinct higher-order structure, the gas diffusion resistance is low without the introduction of a conductive additive. It is found that the catalyst layer of Comparative Example 9, which was obtained by introducing the hydrophobic conductive additive into the catalyst layer of Comparative Example 8, does not obtain the effect of increasing the void ratio and the effect of reducing the gas diffusion resistance.

[0106] As a result of comparing the catalytic layers of Comparative Examples 1 and 2 with Examples 1 and 2, it is found that with increasing aspect ratio of the conductive additive, the void fraction increases and the gas diffusion resistance decreases. Likewise, it is found that when the aspect ratio of the conductive additive is greater than 10 and less than or equal to 40, an increase in proton resistance can be suppressed.

[0107] As a result of comparing the catalyst layers of Comparative Examples 3 to 6 and Examples 3 and 4, it is found that the void ratio increases as the amount of the conductive additive contained in the catalyst layer increases. It is found that when the amount of the conductive additive contained in the catalyst layer is 20 mass% or more, while the effect of reducing the gas diffusion resistance is maintained, the proton resistance increases. Therefore, it is found that when the content ratio of the conductive additive in the catalyst layer is more than 2 mass% and less than 20 mass%, the balance between the gas diffusion resistance and the proton resistance is excellent.

Claims

[1] Catalyst layer for fuel cells, where the catalyst layer comprises a catalyst metal, a support, and a conductive additive; the support carries the catalyst metal; the specific surface area of ​​the carrier 600 m 2 / gC or less; the conductive additive does not support the catalyst metal and has a larger aspect ratio than the support; the aspect ratio of the conductive additive is greater than 10; when a total mass of the catalyst layer is 100 mass%, a percentage of the conductive additive contained in the catalyst layer is more than 2 mass% and less than 20 mass%; the catalyst layer has a void content of 29% to 42%; and the conductive additive is a non-hydrophilic conductive additive. [2] The catalyst layer according to claim 1, wherein the aspect ratio of the conductive additive is 18 or more and 40 or less. [3] The catalyst layer according to claim 1 or 2, wherein when the total mass of the catalyst layer is 100 mass%, the percentage of the conductive additive contained in the catalyst layer is 7 mass% or more and 15 mass% or less. [4] The catalyst layer according to any one of claims 1 to 3, wherein the support and the conductive additive are carbonaceous materials.