Catalyst layer and method for manufacturing the same

Abstract

The present invention provides a catalyst layer capable of improving the power generation performance of a fuel cell. The catalyst layer is characterized by comprising catalyst-supported carbon and an ionomer, wherein the catalyst-supported carbon has at least two aggregate particle size peaks, namely, an aggregate particle size peak of less than 1 μm and an aggregate particle size peak of 1 μm or greater, in a particle size distribution obtained by laser diffraction and scattering. The catalyst layer, when the thickness of the catalyst layer is divided into three equal parts, comprises a first region on the gas diffusion layer side, a second region in the center, and a third region on the electrolyte membrane side. The porosity V of the first region is 100%. G The porosity V of the third region is M The mass ratio I / C of the ionomer to the catalyst-supporting carbon in the third region is higher by 5% or more, and the mass ratio I / C of the ionomer to the catalyst-supporting carbon in the third region is higher by 0.10 or more than the I / C in the second region.

Description

Technical Field

[0001] The present invention relates to a catalyst layer and a method for producing the same. Background Art

[0002] A fuel cell (FC) consists of a single cell (sometimes referred to as a cell) or a stack of multiple cells (hereafter simply referred to as a stack). It is a power generation device that generates electricity through the electrochemical reaction of a fuel gas such as hydrogen and an oxidant gas such as oxygen. It should be noted that the fuel gas and oxidant gas supplied to a fuel cell are often a mixture of gases that do not contribute to oxidation or reduction. In particular, the oxidant gas is often air containing oxygen.

[0003] In the following, fuel gas and oxidant gas may be simply referred to as "reactant gas" or "gas" without particular distinction. In addition, a single cell and a fuel cell stack composed of stacked cells may be referred to as a fuel cell.

[0004] A single cell of the fuel cell generally includes a membrane electrode assembly (MEA: Membrane Electrode Assembly).

[0005] A membrane electrode assembly (MEA) has a structure in which a catalyst layer and a gas diffusion layer (GDL, sometimes referred to as a diffusion layer) are sequentially formed on both sides of a solid polymer electrolyte membrane (hereinafter referred to as an "electrolyte membrane" or "membrane"). Therefore, the MEA is sometimes referred to as a membrane electrode gas diffusion layer assembly (MEGA).

[0006] The cell, as needed, includes two separators sandwiching the membrane electrode gas diffusion layer assembly. The separators typically have grooves formed on the surface in contact with the gas diffusion layer, serving as channels for the reactant gases. The separators are electron-conductive and function as current collectors for the generated electricity.

[0007] In a fuel cell's fuel electrode (anode), hydrogen (H2) supplied as fuel gas from the gas flow path and gas diffusion layer is protonated by the catalytic action of the catalyst layer and then moves through the electrolyte membrane to the oxidant electrode (cathode). Simultaneously, electrons generated perform work in an external circuit and then move to the cathode. Oxygen (O2), supplied as oxidant gas to the cathode, reacts with the protons and electrons in the cathode's catalyst layer to produce water. The generated water imparts appropriate humidity to the electrolyte membrane, and excess water passes through the gas diffusion layer and is discharged from the system.

[0008] Various studies have been conducted on fuel cells for use in fuel cell vehicles (hereinafter sometimes referred to as vehicles).

[0009] For example, Patent Document 1 discloses a solid electrolyte fuel cell in which a cathode layer is formed on one side of a solid electrolyte layer and an anode layer is formed on the other side of the solid electrolyte layer.

[0010] Patent Document 2 discloses a fuel cell having a catalyst electrode that has a high efficiency of platinum catalyst utilization and is easy to manufacture.

[0011] Patent Document 3 discloses a solid electrolyte fuel cell in which the power generation efficiency is improved by improving the performance of the current collector.

[0012] Patent Document 4 discloses a method for forming a catalyst layer for a polymer electrolyte fuel cell having a fine structure with excellent ion conductivity, gas permeability, and electron conductivity.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-273144

[0016] Patent Document 2: Japanese Patent Application Laid-Open No. 2007-265734

[0017] Patent Document 3: Japanese Patent Application Laid-Open No. 2002-358980

[0018] Patent Document 4: Japanese Patent Application Laid-Open No. 2003-173785 Summary of the Invention

[0019] Improving fuel cell power generation performance requires simultaneously satisfying the requirements for oxygen diffusion, proton conduction pathway formation, and water drainage during the cathode reaction. Creating a large number of voids to improve gas diffusion and drainage creates a conflicting issue: proton conduction pathways are obstructed, leading to reduced power generation performance. Conversely, reducing voids or excessively increasing the amount of ionomer to maintain proton conductivity impairs gas diffusion and drainage, failing to improve power generation performance.

[0020] In Patent Document 1, a catalyst layer with low porosity is placed on the electrolyte membrane side, and a catalyst layer with high porosity is placed on the gas diffusion layer side. This configuration is preferred for improving power generation performance. However, forming two cathode catalyst layers with different porosities complicates the process. Furthermore, since these catalyst layers are formed separately, separation at their interface is likely to occur during fuel cell power generation, potentially reducing fuel cell power generation performance.

[0021] The present invention has been made in view of the above-mentioned actual situation, and its main object is to provide a catalyst layer capable of improving the power generation performance of a fuel cell.

[0022] The catalyst layer of the present invention is a catalyst layer for a fuel cell, characterized in that:

[0023] The fuel cell comprises an electrolyte membrane, the catalyst layer, and a gas diffusion layer in this order.

[0024] The catalyst layer comprises catalyst-supported carbon and ionomer,

[0025] The catalyst-supported carbon has at least two agglomerate particle size peaks, namely, a peak of agglomerate particle size of less than 1 μm and a peak of agglomerate particle size of 1 μm or more, in a particle size distribution obtained by laser diffraction and scattering.

[0026] The catalyst layer has a first region on the gas diffusion layer side, a second region in the center, and a third region on the electrolyte membrane side when the thickness of the catalyst layer is divided into three equal parts.

[0027] The porosity V of the first region is G The porosity V of the third region is M More than 5% higher,

[0028] The mass ratio (I / C) of the ionomer to the catalyst-supporting carbon in the third region is higher than the I / C in the second region by 0.10 or more.

[0029] In the catalyst layer of the present invention, the porosity V of the first region is G can be more than 40% and less than 44%, and

[0030] The porosity V of the third region is M can be 34% or more and less than 40%, and

[0031] The porosity V of the first region is G The porosity V of the third region can be M 8% to 10% higher.

[0032] In the catalyst layer of the present invention, the I / C of the third region may be greater than 0.90 and less than 1.30, and

[0033] The I / C of the second region may be greater than 0.90 and less than 1.00, and

[0034] A mass ratio (I / C) of the ionomer to the catalyst-supporting carbon in the third region may be higher than the I / C in the second region by 0.15 to 0.35.

[0035] The fuel cell of the present invention includes the above-mentioned catalyst layer.

[0036] The method for producing a catalyst layer of the present invention is a method for producing a catalyst layer for a fuel cell, characterized in that:

[0037] The fuel cell comprises an electrolyte membrane, the catalyst layer, and a gas diffusion layer in this order.

[0038] The method for manufacturing the catalyst layer comprises the following steps:

[0039] a step of preparing a composite material for a catalyst layer containing catalyst-supported carbon and an ionomer,

[0040] The catalyst layer composite material is mixed with a solvent to prepare a catalyst ink.

[0041] a step of applying the catalyst ink to a transfer sheet, and

[0042] a drying step of drying the catalyst ink in a drying time of less than 1 minute to remove the solvent and form a catalyst layer;

[0043] The catalyst-supported carbon has at least two agglomerate particle size peaks, namely, a peak of agglomerate particle size of less than 1 μm and a peak of agglomerate particle size of 1 μm or greater, in a particle size distribution obtained by a laser diffraction / scattering method.

[0044] In the method for producing a catalyst layer of the present invention, the solid content in the catalyst ink may be 5% by mass to 15% by mass.

[0045] In the method for producing a catalyst layer of the present invention, in the drying step, the drying time of the catalyst ink may be 3 seconds or longer and less than 1 minute.

[0046] In the method for producing a catalyst layer of the present invention, in the drying step, the wind speed during drying of the catalyst ink may be 10 m / s to 30 m / s.

[0047] In the method for producing a catalyst layer of the present invention, in the drying step, the temperature at which the catalyst ink is dried may be 100°C to 130°C.

[0048] According to the catalyst layer of the present invention, the power generation performance of a fuel cell can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram schematically showing an example of the method for producing the catalyst layer of the present invention.

[0050] Figure 2 This is a schematic diagram showing an example of a conventional method for producing a catalyst layer.

[0051] Figure 3 This is a graph showing the particle size distribution of the catalyst-supporting carbon support particles prepared in Example 1, obtained by a laser diffraction / scattering method.

[0052] Figure 4 This is a graph showing the particle size distribution of the catalyst-supporting carbon support particles prepared in Comparative Example 1, obtained by a laser diffraction / scattering method.

[0053] Figure 5 TEM images of cross sections of the first region on the gas diffusion layer side, the second region in the center, and the third region on the electrolyte membrane side of the catalyst layer of Example 1.

[0054] Figure 6 This is a fluorescence microscope image of a cross section of the catalyst layer of Example 1.

[0055] Figure 7 This is a graph showing the relationship between the fluorescence intensity and thickness of the catalyst layer in Example 1.

[0056] Figure 8 This is a fluorescence microscope image of a cross section of the catalyst layer of Comparative Example 1.

[0057] Figure 9 This is a graph showing the relationship between the fluorescence intensity and thickness of the catalyst layer in Comparative Example 1. DETAILED DESCRIPTION

[0058] 1. Catalyst layer

[0059] The catalyst layer of the present invention is a catalyst layer for a fuel cell, characterized in that:

[0060] The fuel cell comprises an electrolyte membrane, the catalyst layer, and a gas diffusion layer in this order.

[0061] The catalyst layer comprises catalyst-supported carbon and ionomer,

[0062] The catalyst-supported carbon has at least two agglomerate particle size peaks, namely, a peak of agglomerate particle size of less than 1 μm and a peak of agglomerate particle size of 1 μm or more, in a particle size distribution obtained by laser diffraction and scattering.

[0063] The catalyst layer has a first region on the gas diffusion layer side, a second region in the center, and a third region on the electrolyte membrane side when the thickness of the catalyst layer is divided into three equal parts.

[0064] The porosity V of the first region is G The porosity V of the third region is M More than 5% higher,

[0065] The mass ratio (I / C) of the ionomer to the catalyst-supporting carbon in the third region is higher than the I / C in the second region by 0.10 or more.

[0066] Figure 1This is a schematic diagram schematically showing an example of the method for producing the catalyst layer of the present invention.

[0067] Figure 2 This is a schematic diagram showing an example of a conventional method for producing a catalyst layer.

[0068] like Figure 2 As shown, in the existing method for manufacturing a catalyst layer, a catalyst ink containing catalyst-supported carbon having one agglomerate particle size peak is used, and the solvent in the catalyst ink is dried for a drying time of more than 1 minute, so that the porosity and ionomer ratio remain unchanged on the electrolyte membrane side and the diffusion layer side of the catalyst layer.

[0069] The catalyst layer of the present invention has an integrated structure with a low porosity on the electrolyte membrane side and a high porosity on the gas diffusion layer side. Specifically, the manufacturing method is controlled so that the composition of the catalyst-supporting carbon and ionomer components is tilted in the thickness direction of the catalyst layer.

[0070] like Figure 1 As shown, according to the present invention, by applying a catalyst ink containing catalyst-supported carbon exhibiting two or more aggregate particle size peaks to a transfer sheet, rapidly drying the solvent in less than one minute, and then transferring the ink to the electrolyte membrane, the voids in the catalyst layer's thickness direction can be increased on the diffusion layer side, and the ionomer content can be gradually increased on the electrolyte membrane side. By applying this catalyst layer to a fuel cell membrane electrode assembly, proton resistance can be reduced without increasing gas diffusion resistance, thereby improving fuel cell power generation performance over a wide temperature range.

[0071] The catalyst layer of the present invention is used in a fuel cell. The catalyst layer of the present invention may be a cathode catalyst layer or an anode catalyst layer. That is, the catalyst layer of the present invention may be at least one selected from a cathode catalyst layer and an anode catalyst layer. Both the cathode catalyst layer and the anode catalyst layer may be the catalyst layer of the present invention. From the perspective of further improving the power generation performance of the fuel cell, the catalyst layer of the present invention may be at least the cathode catalyst layer.

[0072] When the thickness of the catalyst layer is divided into three equal parts, the catalyst layer comprises a first region on the gas diffusion layer side, a second region in the center, and a third region on the electrolyte membrane side. Specifically, when the catalyst layer is divided into three equal parts perpendicular to the thickness direction, the catalyst layer may comprise a first region on the gas diffusion layer side, a second region in the center, and a third region on the electrolyte membrane side.

[0073] The thickness of the catalyst layer is not particularly limited and may be 3 μm to 1000 μm.

[0074] The porosity V of the first region on the gas diffusion layer sideG The porosity V of the third region on the electrolyte membrane side can be M That is, the porosity difference ΔV (=V G -V M )≥5%. Thus, the gas diffusion capacity of the catalyst layer is guaranteed. When ΔV is too large, the gap on the electrolyte membrane side is insufficient, and the drainage and gas diffusion properties are reduced. Therefore, the porosity V of the first region is G The porosity V of the third region M 8% to 10% higher. That is, 10% ≥ ΔV ≥ 8% is also acceptable.

[0075] The porosity V of the first region on the gas diffusion layer side G It may be more than 40% and less than 44%.

[0076] The porosity V of the third region on the electrolyte membrane side M It may be 34% or more and less than 40%.

[0077] The void ratio V of the second region in the central part C As long as the porosity V of the third region on the electrolyte membrane side is M higher than the porosity V of the first region on the gas diffusion layer side. G There is no particular limitation on low.

[0078] The mass ratio (I / C) of the ionomer to the catalyst-supported carbon in the third region on the electrolyte membrane side may be higher than the I / C in the second region in the center by 0.10 or more. 第三区域 -I / C 第二区域 ) ≥ 0.10. This ensures the proton conductivity of the catalyst layer. If ΔI / C is too large, the GDL side will be insufficient for ionomer, reducing proton conductivity. Therefore, the I / C of the third region on the electrolyte membrane side can be 0.15 to 0.35 higher than the I / C of the second region in the center. In other words, 0.35 ≥ ΔI / C ≥ 0.15 is sufficient.

[0079] The I / C of the third region on the electrolyte membrane side may be greater than 0.90 and less than or equal to 1.30.

[0080] The I / C of the second region in the central portion may be lower than the I / C of the third region on the electrolyte membrane side by 0.10 or more, and may be higher than 0.90 and lower than 1.00.

[0081] The I / C of the first region on the gas diffusion layer side is not particularly limited as long as it is smaller than the I / C of the second region in the central portion, and may be 0.50 or more and less than 1.00.

[0082] The catalyst layer includes catalyst-supported carbon and ionomer.

[0083] The catalyst-supported carbon has at least two agglomerate particle size peaks, namely, a peak for agglomerate particle size of less than 1 μm and a peak for agglomerate particle size of 1 μm or greater, in a particle size distribution obtained by a laser diffraction and scattering method (light scattering method). It suffices to have one peak for agglomerate particle size of less than 1 μm and one peak for agglomerate particle size of 1 μm or greater; it may have two or more peaks for agglomerate particle size of less than 1 μm, or it may have two or more peaks for agglomerate particle size of 1 μm or greater.

[0084] As the catalyst, for example, platinum (Pt) and alloys of Pt and other metals (for example, a Pt alloy obtained by mixing cobalt, nickel, etc.) can be used.

[0085] The ionomer may have proton conductivity or may be a fluorine-based resin. For example, a perfluorosulfonic acid resin such as Nafion (registered trademark) may be used as the fluorine-based resin. For example, a perfluorosulfonic acid resin such as Nafion (registered trademark) may be used as the ionomer.

[0086] The carbon used as the support (carbon support) may be, for example, a generally commercially available carbon material. Examples of the carbon material include Ketjen Black (trade name: manufactured by Gepanzer Black International), Vulcan (trade name: manufactured by Cabot Corporation), NORIT (trade name: manufactured by Norit Corporation), Black Pearls (trade name: manufactured by Cabot Corporation), acetylene black (trade name: manufactured by Chevron Corporation), carbon nanotubes, carbon nanohorns, carbon nanowalls, carbon nanofibers, and carbon alloys.

[0087] The carbon support may be in the form of granular carbon support particles.

[0088] The average particle size of the carbon support particles is not particularly limited and may be 10 nm to 10 μm.

[0089] The average particle size of the particles in the present invention is calculated by conventional methods. An example of a method for calculating the average particle size of particles is as follows. First, in a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image at an appropriate magnification (e.g., 50,000 to 1,000,000 times), for a certain particle, calculate the particle size when the particle is regarded as a sphere. The particle size calculation using such TEM observation or SEM observation is performed on 200 to 300 particles of the same type, and the average of these particles is taken as the average particle size.

[0090] 2. Method for manufacturing catalyst layer

[0091] The method for producing a catalyst layer of the present invention is a method for producing a catalyst layer for a fuel cell, characterized in that:

[0092] The fuel cell comprises an electrolyte membrane, the catalyst layer, and a gas diffusion layer in this order.

[0093] The method for manufacturing the catalyst layer comprises the following steps:

[0094] a step of preparing a composite material for a catalyst layer containing catalyst-supported carbon and an ionomer;

[0095] The catalyst layer is mixed with a composite material and a solvent to prepare a catalyst ink;

[0096] The step of applying the catalyst ink to a transfer sheet;

[0097] A drying step of drying the catalyst ink to remove the solvent in a drying time of less than 1 minute to form a catalyst layer;

[0098] The catalyst-supported carbon has at least two aggregate particle size peaks, namely, an aggregate particle size peak of less than 1 μm and an aggregate particle size peak of 1 μm or greater, in a particle size distribution obtained by a laser diffraction / scattering method.

[0099] The method for producing a catalyst layer of the present invention comprises (1) a preparation step, (2) a preparation step, (3) a coating step, and (4) a drying step.

[0100] (1) Preparation process

[0101] The preparation step is a step of preparing a composite material for a catalyst layer containing catalyst-supporting carbon and an ionomer.

[0102] The composite material for the catalyst layer contains catalyst-supporting carbon and an ionomer.

[0103] Examples of the catalyst-supporting carbon and ionomer include the same ones as exemplified in the above-mentioned "1. Catalyst layer".

[0104] (2) Preparation process

[0105] The preparation step is a step of mixing the composite material for a catalyst layer and a solvent to prepare a catalyst ink.

[0106] The solvent is not particularly limited and may be appropriately selected depending on the ionomer used. Examples of the solvent include water, methanol, ethanol, propanol, propylene glycol, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, and N,N-diethylacetamide. A mixture of two or more solvents may be used.

[0107] The mixing method is not particularly limited, and examples thereof include a homogenizer, a ball mill, a shear mixer, and a roll mill. From the viewpoint of improving dispersibility, a ball mill can be used.

[0108] The ball mill is not particularly limited, and examples thereof include a planetary ball mill.

[0109] The material of the ball is not particularly limited, and materials such as zirconia and alumina can be used.

[0110] The diameter of the ball is not particularly limited and may be 0.5 to 2 mm.

[0111] The base rotation speed of the ball mill is not particularly limited and may be 300 to 500 rpm.

[0112] The rotation time of the ball mill is not particularly limited and may be 3 hours or longer, 6 hours or longer, or 100 hours or shorter.

[0113] In the present invention, the ball mill is a conventionally known device that rotates balls and materials in a container, and is a concept that includes a bead mill.

[0114] The content of the ionomer in the catalyst ink can be appropriately set according to the amount of the catalyst-supported carbon. The mass ratio of the catalyst-supported carbon to the ionomer can be catalyst-supported carbon:ionomer = 1:0.5 to 1:1.3.

[0115] The amount of solids in the catalyst ink is not particularly limited and can be 5% by mass or more, 7% by mass or more, 15% by mass or less, 11% by mass or less, or 9% by mass or less. By setting the solids content in the catalyst ink within the above range, it is easier to adjust the tilt ΔI / C within the specified range. Furthermore, by setting the solids content in the catalyst ink within the above range, it is possible to suppress the movement of the solids during the drying process.

[0116] (3) Coating process

[0117] The coating step is a step of coating the catalyst ink on the transfer sheet.

[0118] The catalyst ink coating method is not particularly limited and conventionally known methods may be used. Examples of catalyst ink coating methods include doctor blade coating, metal mask printing, electrostatic coating, dip coating, spray coating, roller coating, gravure coating, and screen printing.

[0119] As the transfer sheet, a self-supporting transfer sheet can be appropriately selected and used. For example, metal foils such as Cu and Al, and resins such as polytetrafluoroethylene (PTFE) can be used.

[0120] (4) Drying process

[0121] The drying step is a step of drying the catalyst ink in a drying time of less than 1 minute to remove the solvent and form a catalyst layer.

[0122] During the drying process, the catalyst ink can be dried for a time of 3 seconds or longer and less than 1 minute. High-speed drying of a single catalyst layer in less than 1 minute allows for efficient accumulation of solids on the catalyst ink coating surface. High-speed drying facilitates the segregation of aggregates and fine carbon (agglomerated) particles toward the ink surface due to capillary forces between carbon (agglomerated) particles.

[0123] In the drying step, the wind speed during drying of the catalyst ink may be 10 m / s to 30 m / s.

[0124] In the drying step, the catalyst ink may be dried at a temperature of 100°C to 130°C.

[0125] By transferring and bonding the catalyst layer on the obtained transfer sheet to the electrolyte membrane and bonding the gas diffusion layer on the side opposite to the electrolyte membrane, a catalyst layer can be made in which the porosity of the catalyst layer on the gas diffusion layer side is large and the concentration of the ionomer on the electrolyte membrane side becomes higher, thereby causing the concentration of the ionomer to be inclined.

[0126] 3. Fuel Cells

[0127] The fuel cell of the present invention includes the catalyst layer of the present invention. The fuel cell comprises at least an electrolyte membrane, a catalyst layer, and a gas diffusion layer in this order. The catalyst layer referred to herein is either a cathode catalyst layer or an anode catalyst layer. The gas diffusion layer referred to herein is the cathode-side gas diffusion layer when the catalyst layer is a cathode catalyst layer, and is the anode-side gas diffusion layer when the catalyst layer is an anode catalyst layer.

[0128] A fuel cell generally has single cells.

[0129] A fuel cell may have only one unit cell, or may be a fuel cell stack which is a stack of a plurality of unit cells.

[0130] The number of stacked cells is not particularly limited, and may be, for example, 2 to several hundred, 2 to 300, or 2 to 200.

[0131] The fuel cell stack may include end plates at both ends in the stacking direction of the single cells.

[0132] The fuel cell may include a membrane electrode gas diffusion layer assembly. The fuel cell may include a first separator and a second separator sandwiching the membrane electrode gas diffusion layer assembly.

[0133] The membrane electrode gas diffusion layer assembly includes a first gas diffusion layer, a first catalyst layer, an electrolyte membrane, a second catalyst layer, and a second gas diffusion layer in this order.

[0134] Specifically, the membrane electrode gas diffusion layer assembly includes 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.

[0135] The first catalyst layer and the second catalyst layer, one of which is a cathode catalyst layer and the other of which is an anode catalyst layer. The catalyst layer included in the fuel cell of the present invention may be a cathode catalyst layer or an anode catalyst layer. Both the cathode catalyst layer and the anode catalyst layer may be catalyst layers included in the fuel cell of the present invention. From the perspective of further improving the power generation performance of the fuel cell, the catalyst layer included in the fuel cell of the present invention may be at least the cathode catalyst layer.

[0136] The cathode (oxidant electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer.

[0137] The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer.

[0138] The first catalyst layer and the second catalyst layer are collectively referred to as catalyst layers. The cathode catalyst layer and the anode catalyst layer are collectively referred to as catalyst layers.

[0139] One of the first gas diffusion layer and the second gas diffusion layer is a cathode-side gas diffusion layer, and the other is an anode-side gas diffusion layer.

[0140] The first gas diffusion layer is a cathode-side gas diffusion layer when the first catalyst layer is a cathode catalyst layer, and is an anode-side gas diffusion layer when the first catalyst layer is an anode catalyst layer.

[0141] The second gas diffusion layer is a cathode-side gas diffusion layer when the second catalyst layer is a cathode catalyst layer, and is an anode-side gas diffusion layer when the second catalyst layer is an anode catalyst layer.

[0142] The first gas diffusion layer and the second gas diffusion layer are collectively referred to as gas diffusion layers or diffusion layers. The cathode side gas diffusion layer and the anode side gas diffusion layer are collectively referred to as gas diffusion layers or diffusion layers.

[0143] The gas diffusion layer may be a gas-permeable conductive member or the like.

[0144] Examples of the conductive member include carbon porous bodies such as carbon cloth and carbon paper, and metal porous bodies such as metal mesh and foamed metal.

[0145] The fuel cell may have a microporous layer (MPL) between the catalyst layer and the gas diffusion layer. The microporous layer may include a mixture of a hydrophobic resin such as PTFE and a conductive material such as carbon black.

[0146] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as a film of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. Examples of the electrolyte membrane include Nafion membranes (manufactured by DuPont).

[0147] One of the first separator and the second separator is a cathode-side separator, and the other is an anode-side separator.

[0148] The first separator is a cathode-side separator when the first catalyst layer is a cathode catalyst layer, and is an anode-side separator when the first catalyst layer is an anode catalyst layer.

[0149] The second separator is a cathode-side separator when the second catalyst layer is a cathode catalyst layer, and is an anode-side separator when the second catalyst layer is an anode catalyst layer.

[0150] The first separator and the second separator are collectively referred to as separators. The anode-side separator and the cathode-side separator are collectively referred to as separators.

[0151] The membrane electrode gas diffusion layer assembly is sandwiched between the first separator and the second separator.

[0152] The separator may have supply holes and discharge holes for allowing the reaction gas and the coolant to flow in the stacking direction of the cells. As the coolant, a mixed solution of ethylene glycol and water may be used, for example, to prevent freezing at low temperatures.

[0153] Examples of the supply holes include fuel gas supply holes, oxidant gas supply holes, and refrigerant supply holes.

[0154] Examples of the discharge holes include a fuel gas discharge hole, an oxidant gas discharge hole, and a refrigerant discharge hole.

[0155] The isolation member may have more than one fuel gas supply hole, may have more than one oxidant gas supply hole, may have more than one refrigerant supply hole, may have more than one fuel gas exhaust hole, may have more than one oxidant gas exhaust hole, and may have more than one refrigerant exhaust hole.

[0156] The separator may have a reaction gas flow path on the surface in contact with the gas diffusion layer. In addition, the separator may have a coolant flow path on the surface opposite to the surface in contact with the gas diffusion layer for maintaining a constant temperature of the fuel cell.

[0157] When the separator is an anode side separator, it may have one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more refrigerant supply holes, one or more fuel gas discharge holes, one or more oxidant gas discharge holes, and one or more refrigerant discharge holes. The anode side separator may have a fuel gas flow path on the surface in contact with the anode side gas diffusion layer, for allowing the fuel gas to flow from the fuel gas supply hole to the fuel gas discharge hole, and may have a refrigerant flow path on the surface opposite to the surface in contact with the anode side gas diffusion layer, for allowing the refrigerant to flow from the refrigerant supply hole to the refrigerant discharge hole.

[0158] When the separator is a cathode side separator, it can have one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more refrigerant supply holes, one or more fuel gas discharge holes, one or more oxidant gas discharge holes, and one or more refrigerant discharge holes. The cathode side separator can have an oxidant gas flow path on the surface in contact with the cathode side gas diffusion layer, allowing the oxidant gas to flow from the oxidant gas supply hole to the oxidant gas discharge hole, and can have a refrigerant flow path on the surface opposite to the surface in contact with the cathode side gas diffusion layer, allowing the refrigerant to flow from the refrigerant supply hole to the refrigerant discharge hole.

[0159] The separator may be an airtight conductive member, etc. Examples of the conductive member include dense carbon made airtight by compressing carbon, and a press-formed metal (e.g., iron, aluminum, stainless steel, etc.) plate. Furthermore, the separator may have a current collecting function.

[0160] The fuel cell stack may include a manifold such as an inlet manifold through which the supply holes communicate and an outlet manifold through which the exhaust holes communicate.

[0161] Examples of the inlet manifold include an anode inlet manifold, a cathode inlet manifold, and a refrigerant inlet manifold.

[0162] Examples of the outlet manifold include an anode outlet manifold, a cathode outlet manifold, and a refrigerant outlet manifold.

[0163] In the present invention, fuel gas and oxidant gas are collectively referred to as reactant gases. The reactant gas supplied to the anode is fuel gas, and the reactant gas supplied to the cathode is oxidant gas. Fuel gas is a gas primarily containing hydrogen, but may also be hydrogen. Oxidant gas may be oxygen, air, dry air, or the like.

[0164] Example

[0165] (Example 1)

[0166] [Preparation process]

[0167] A composite material for a catalyst layer containing catalyst-supporting carbon support particles and an ionomer is prepared.

[0168] Figure 3 This is a graph showing the particle size distribution of the catalyst-supporting carbon support particles prepared in Example 1, obtained by a laser diffraction / scattering method.

[0169] like Figure 3 As shown, as the catalyst-supporting carbon support particles, carbon support particles having two types of aggregate particle size peaks, namely, peaks of less than 1 μm and peaks of 1 μm or more, are used.

[0170] As the ionomer, a perfluorocarbon sulfonic acid resin dispersion (trade name: Nafion, manufactured by DuPont) was used.

[0171] [Preparation process]

[0172] The composite material for the catalyst layer was added to a solvent containing water and alcohol, and the mixture was stirred and mixed to prepare a catalyst ink having a solid content of 9% by mass.

[0173] [Coating process]

[0174] Prepare a PTFE sheet for transfer and apply catalyst ink to the PTFE sheet.

[0175] [Drying process]

[0176] Hot air at a speed of 10 m / s and a temperature of 100° C. was blown toward the catalyst ink for 0.3 minutes (18 seconds) to dry the solvent at high speed, thereby obtaining a catalyst layer.

[0177] (Example 2)

[0178] In the drying step, a catalyst layer was obtained by the same method as in Example 1 except that hot air at a speed of 20 m / s and a temperature of 130° C. was blown toward the catalyst ink for 0.2 minutes (12 seconds) to dry the solvent at high speed.

[0179] (Example 3)

[0180] In the drying step, a catalyst layer was obtained by the same method as in Example 1 except that hot air at a speed of 30 m / s and a temperature of 130° C. was blown to the catalyst ink for 0.05 minutes (3 seconds) to dry the solvent at high speed.

[0181] (Comparative Example 1)

[0182] Figure 4 This is a graph showing the particle size distribution of the catalyst-supporting carbon support particles prepared in Comparative Example 1, obtained by a laser diffraction / scattering method.

[0183] like Figure 4As shown, in the preparation step, carbon support particles having one type of aggregate particle size peak are used as catalyst-supporting carbon support particles.

[0184] In the drying step, a catalyst layer was obtained by the same method as in Example 1 except that hot air at a speed of 0.1 m / s and a temperature of 100° C. was blown to the catalyst ink for 2 minutes to dry the solvent.

[0185] (Comparative Example 2)

[0186] In the drying step, a catalyst layer was obtained by the same method as in Example 1 except that hot air at a speed of 0.1 m / s and a temperature of 130° C. was blown toward the catalyst ink for 1 minute to dry the solvent.

[0187] (Comparative Example 3)

[0188] In the drying step, a catalyst layer was obtained in the same manner as in Comparative Example 1 except that hot air at a speed of 20 m / s and a temperature of 130° C. was blown toward the catalyst ink for 0.2 minutes (12 seconds) to dry the solvent at high speed.

[0189] For each catalyst layer obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the porosity V of the first region on the gas diffusion layer side when the thickness of each catalyst layer is divided into three equal parts was measured by observing the TEM image of the catalyst layer cross section. G , the porosity V of the third region on the electrolyte membrane side M , their porosity difference ΔV(=V G -V M ).

[0190] For each catalyst layer obtained in Examples 1 to 3 and Comparative Examples 1 to 3, fluorescence microscopic images of the catalyst layer cross section were observed to measure the I / C of the third region on the electrolyte membrane side, the I / C of the second region in the center, and the inclination ΔI / C (=I / C 第三区域 -I / C 第二区域 ).

[0191] The proton resistance and gas diffusion resistance were measured for each catalyst layer obtained in Examples 1 to 3 and Comparative Examples 1 to 3. The results are shown in Table 1.

[0192] [Table 1]

[0193]

[0194] Figure 5 TEM images of the cross sections of the first region on the gas diffusion layer side, the second region in the center, and the third region on the electrolyte membrane side of the catalyst layer of Example 1. Figure 5As shown in Table 1, in the catalyst layer of Example 1, the porosity of the first region on the gas diffusion layer side is higher than that of the third region on the electrolyte membrane side.

[0195] Figure 6 This is a fluorescence microscope image of a cross section of the catalyst layer of Example 1.

[0196] Figure 7 : is a graph showing the relationship between the fluorescence intensity and thickness of the catalyst layer of Example 1. The fluorescence intensity is proportional to the amount of ionomer. Figure 6 、 Figure 7 As shown in Table 1, in the catalyst layer of Example 1, the third region on the electrolyte membrane side has a higher I / C than the second region in the center.

[0197] Figure 8 This is a fluorescence microscope image of a cross section of the catalyst layer of Comparative Example 1.

[0198] Figure 9 : is a graph showing the relationship between the fluorescence intensity and thickness of the catalyst layer of Comparative Example 1. Figure 8 、 Figure 9 As shown in Table 1, it can be seen that in the catalyst layer of Comparative Example 1, the I / C of the third region on the electrolyte membrane side and the second region in the center portion are the same.

[0199] As shown in Table 1, in each catalyst layer of Comparative Examples 1 to 3, the first region on the gas diffusion layer side and the third region on the electrolyte membrane side have the same porosity, and the third region on the electrolyte membrane side and the second region in the center have the same I / C.

[0200] As shown in Table 1, in each catalyst layer of Examples 1 to 3, the porosity of the first region on the gas diffusion layer side is higher than that of the third region on the electrolyte membrane side, and the I / C of the third region on the electrolyte membrane side is higher than that of the second region in the center.

[0201] As shown in Table 1, it can be seen that the proton resistance of each catalyst layer of Examples 1 to 3 is lower than that of each catalyst layer of Comparative Examples 1 and 2, and the gas diffusion resistance is about the same.

[0202] From the results of Comparative Example 2, it is understood that in order to reduce proton resistance, the drying time needs to be less than 1 minute.

[0203] As shown in Table 1, it can be seen that Comparative Example 3 has lower proton resistance but higher gas diffusion resistance than the catalyst layers of Comparative Examples 1 and 2.

[0204] The results of Comparative Example 3 show that the catalyst-supported carbon having only one agglomerate particle size peak cannot achieve the effect of reducing the gas diffusion resistance even when subjected to high-speed drying with a drying time of less than 1 minute.

Claims

1. A catalyst layer, characterized in that: It is the catalyst layer for fuel cells. The fuel cell comprises an electrolyte membrane, the catalyst layer, and a gas diffusion layer in this order. The catalyst layer comprises catalyst-supported carbon and ionomer, The catalyst-supported carbon has at least two agglomerate particle size peaks, namely, an agglomerate particle size peak of less than 1 μm and an agglomerate particle size peak of 1 μm or more, in a particle size distribution obtained by a laser diffraction / scattering method. The catalyst layer has a first region on the gas diffusion layer side, a second region in the center, and a third region on the electrolyte membrane side when the thickness of the catalyst layer is divided into three equal parts. The porosity V of the first region G is 43% or more and 44% or less, The porosity V of the third region M is 34% or more and 35% or less, The porosity V of the second region C The porosity V of the third region is M Higher than the porosity V of the first region G Low, The mass ratio I / C of the ionomer to the catalyst-supporting carbon in the third region is 1.1 or more and 1.30 or less. The I / C of the second region is 0.95 or more and 1.00 or less.

2. A fuel cell comprising the catalyst layer according to claim 1.

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