Catalyst layer for electrochemical device, membrane electrode assembly for electrochemical device, and electrochemical device

Abstract

To provide a catalyst layer for an electrochemical device suitable for smoothly moving a reactant necessary for power generation reaction.SOLUTION: A catalyst layer 100 for electrochemical devices according to the present disclosure includes a first electrode catalyst 10 having first conductive particles 11 and first catalyst particles 12, a second electrode catalyst 20 having second conductive particles 21 and second catalyst particles 22, conductive fibers 30, and an ionomer 40. The mode diameter of the first conductive particles 11 is larger than the mode diameter of the second conductive particles 21. The first electrode catalyst 10 is preferentially disposed in the first portion including the first main surface of the catalyst layer 100, and the second electrode catalyst 20 is preferentially disposed in the second portion including the second main surface. In a cross section parallel to the thickness direction of the catalyst layer 100, the area occupied by the conductive fibers 30 per unit area of the second portion is larger than the area occupied by the conductive fibers 30 per unit area of the first portion.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to a catalyst layer for an electrochemical device, a membrane electrode assembly for an electrochemical device, and an electrochemical device. [Background technology]

[0002] Patent Document 1 describes that in an electrode catalyst layer formed by stacking catalyst supports coated with a polymer electrolyte (ionomer) having selective permeability for hydrogen ions, the amount of polymer electrolyte coating the catalyst supports is changed along the stacking direction of the catalyst supports, thereby making the gaps between the catalyst supports larger on the electrode side than on the solid polymer electrolyte membrane side.

[0003] Patent Document 2 describes that at least one of the cathode catalyst layer and the anode catalyst layer has a structure in which a plurality of catalyst layers with different pore structures are stacked, such that the pore structure of the catalyst layer on the electrolyte membrane side is larger than the pore structure of the catalyst layer on the gas diffusion layer side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-88008 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-186798 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a catalyst layer for an electrochemical device that is suitable for smoothly transporting reactants required for a power generation reaction. [Means for solving the problem]

[0006] The catalyst layer for an electrochemical device according to the present disclosure comprises: A catalyst layer having a first major surface and a second major surface, a first electrode catalyst, a second electrode catalyst, conductive fibers, and an ionomer; the first electrode catalyst has first conductive particles and first catalyst particles supported on the first conductive particles; the second electrode catalyst has second conductive particles and second catalyst particles supported on the second conductive particles, the mode particle diameter of the first conductive particles is larger than the mode particle diameter of the second conductive particles; When a portion including the first main surface is defined as a first portion and a portion including the second main surface is defined as a second portion, the first electrode catalyst is preferentially disposed in the first portion, and the second electrode catalyst is preferentially disposed in the second portion; In a cross section parallel to the thickness direction of the catalyst layer, the area occupied by the conductive fibers per unit area of ​​the second portion is larger than the area occupied by the conductive fibers per unit area of ​​the first portion.

[0007] In another aspect, the membrane electrode assembly for electrochemical devices according to the present disclosure comprises: an anode; a cathode; an electrolyte membrane disposed between the anode and the cathode; Equipped with The cathode includes the catalyst layer for an electrochemical device of the present disclosure.

[0008] In yet another aspect, the electrochemical device according to the present disclosure comprises: The electrochemical device includes the membrane electrode assembly of the present disclosure. [Effects of the Invention]

[0009] According to the present disclosure, in a catalyst layer for an electrochemical device, reactants necessary for a power generation reaction can be smoothly transported. [Brief explanation of the drawings]

[0010] [Figure 1A] Schematic cross-sectional view showing an example of a catalyst layer in the first embodiment. [Figure 1B] Enlarged view of part of Figure 1A [Figure 2] Schematic cross-sectional view showing an example of a first electrode catalyst included in a catalyst layer together with an ionomer. [Figure 3] A schematic cross-sectional view showing an example of a second electrode catalyst included in a catalyst layer together with an ionomer. [Figure 4] Schematic cross-sectional view showing an example of conductive fibers contained in a catalyst layer [Figure 5A] Schematic cross-sectional view of a membrane electrode assembly in embodiment 2. [Figure 5B] Enlarged view of part of Figure 5A [Figure 6] Schematic cross-sectional view of an electrochemical device according to a second embodiment.

[0011] (Findings that formed the basis of this disclosure) To improve the power generation efficiency of electrochemical devices such as fuel cells, the development of technology to accelerate the electrochemical reaction in the cathode catalyst layer is being considered. In order to accelerate the electrochemical reaction in the cathode catalyst layer, it is necessary to increase the amount of oxygen and protons (H + One of the problems is how smoothly reactants such as cations and cations can move through the cathode catalyst layer and reach the catalyst. To solve this problem, for example, a catalyst layer has been proposed in which the amount of ionomer present on the electrolyte membrane side is greater than the amount of ionomer present on the gas diffusion layer side (Patent Document 1). Another catalyst layer has been proposed in which the pore structure on the electrolyte membrane side is larger than the pore structure on the gas diffusion layer side (Patent Document 2). However, with the catalyst layer proposed in Patent Document 1, increasing the current value can cause the pores in the catalyst layer on the electrolyte membrane side to become clogged with generated water, inhibiting oxygen movement. With the catalyst layer proposed in Patent Document 2, increasing the current fluctuation range can cause the pores to become clogged with generated water, inhibiting oxygen movement.

[0012] Under these circumstances, the inventors discovered that increasing the pore size of the catalyst layer from the electrolyte membrane side toward the gas diffusion layer side, which is the drainage direction, is desirable to prevent oxygen transport from being hindered even when the current value or current fluctuation range is increased. A larger pore size in the catalyst layer on the gas diffusion layer side reduces the likelihood of the pores being clogged with generated water, thereby reducing the inhibition of oxygen transport. On the other hand, the amount of generated water retained within the catalyst layer on the electrolyte membrane side is smaller than that on the gas diffusion layer side. Therefore, to increase the total surface area of ​​the conductive member supporting the catalyst particles and thereby increase the current value, it is advantageous to use a conductive member with a small particle size. However, because the ionomer responsible for proton conduction is distributed along the surface of the conductive member, the smaller the particle size of the conductive member, the longer the proton conduction path. Therefore, the inventors discovered that adding more long conductive members on the electrolyte membrane side than on the gas diffusion layer side optimizes the proton conduction path through the ionomer.

[0013] Based on these findings, the present inventors have come to form the subject of the present disclosure.

[0014] The present disclosure provides a catalyst layer for an electrochemical device that is suitable for smoothly transporting reactants required for a power generation reaction.

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

[0016] The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0017] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to FIGS. 1A to 4. FIG.

[0018] [1-1.Configuration] FIG. 1A is a schematic cross-sectional view showing an example of a catalyst layer 100 for an electrochemical device in the first embodiment. The catalyst layer 100 has a first main surface 101 and a second main surface 102 opposite to the first main surface 101. In this specification, the term "main surface" refers to the surface of the catalyst layer 100 having the largest area. The direction from the first main surface 101 toward the second main surface 102 is defined as the thickness direction T100 of the catalyst layer 100. FIG. 1A is a cross-sectional view of the catalyst layer 100 parallel to the thickness direction T100. The catalyst layer 100 includes a first electrode catalyst 10, a second electrode catalyst 20, conductive fibers 30, and an ionomer 40. The ionomer 40 is omitted in FIG. 1A. Pores 50 are formed between the first electrode catalysts 10 and between the second electrode catalysts 20.

[0019] FIG. 2 is a schematic cross-sectional view showing an example of a first electrode catalyst 10 included in the catalyst layer 100, together with an ionomer 40. FIG. 3 is a schematic cross-sectional view showing an example of a second electrode catalyst 20 included in the catalyst layer 100, together with the ionomer 40. The first electrode catalyst 10 has first conductive particles 11 and first catalyst particles 12 supported on the first conductive particles 11. An electrochemical reaction is promoted on the surface of the first catalyst particles 12. The second electrode catalyst 20 has second conductive particles 21 and second catalyst particles 22 supported on the second conductive particles 21. An electrochemical reaction is promoted on the surface of the second catalyst particles 22. In this embodiment, the mode particle diameter M1 of the first conductive particles 11 is larger than the mode particle diameter M2 of the second conductive particles 21.

[0020] A portion including the first main surface 101 is defined as a first portion 101p, and a portion including the second main surface 102 is defined as a second portion 102p. As shown in FIG. 1A , in this embodiment, the first electrode catalyst 10 is preferentially disposed in the first portion 101p, and the second electrode catalyst 20 is preferentially disposed in the second portion 102p. In a cross section parallel to the thickness direction T100 of the catalyst layer 100, an area A23 occupied by the conductive fibers 30 per unit area of ​​the second portion 102p is larger than an area A13 occupied by the conductive fibers 30 per unit area of ​​the first portion 101p. In this specification, "a cross section parallel to the thickness direction T100 of the catalyst layer 100" is synonymous with "a cross section having a normal perpendicular to the thickness direction T100 of the catalyst layer 100."

[0021] According to this configuration, when the catalyst layer 100 is used as a cathode catalyst layer of a fuel cell so that the first main surface 101 faces the cathode gas diffusion layer and the second main surface 102 faces the electrolyte membrane, the following effects can be achieved. Because the mode particle diameter M1 of the first conductive particles 11 is larger than the mode particle diameter M2 of the second conductive particles 21, the pores 50 in the first portion 101p tend to have larger pore diameters than the pores 50 in the second portion 102p. This reduces blockage of the pores 50 by generated water in the first portion 101p, thereby promoting oxygen transfer. Meanwhile, because the second electrode catalyst 20 is preferentially disposed in the second portion 102p, the combined surface area of ​​the first conductive particles 11 and the second conductive particles 21 is larger than that of the first portion 101p, thereby reducing a decrease in the current value. Furthermore, since the area A23 occupied by the conductive fibers 30 per unit area of ​​the second portion 102p is larger than the area A13 occupied by the conductive fibers 30 per unit area of ​​the first portion 101p, the proton conduction path in the second portion 102p can be optimized. Therefore, according to the catalyst layer 100 of this embodiment, the reactants necessary for the power generation reaction can be smoothly transported. As a result, the electrochemical reaction in the catalyst layer 100 can be promoted.

[0022] As described above, in this embodiment, the mode particle diameter M1 of the first conductive particles 11 is larger than the mode particle diameter M2 of the second conductive particles 21. The mode particle diameter M1 of the first conductive particles 11 can be determined, for example, from a cross-sectional image of the first portion 101p of the catalyst layer 100 obtained using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). First, the equivalent diameters of any number (at least 50) of first conductive particles 11 are determined from the cross-sectional image of the first portion 101p to obtain a frequency distribution (histogram) of the equivalent diameters. Note that each section in the histogram has the same width of 10 nm. The median value of the section with the highest frequency among the sections in the histogram is defined as the mode particle diameter M1 of the first conductive particles 11. Note that the equivalent diameter means the diameter of a circle having the same area. Similarly, the mode particle diameter M2 of the second conductive particles 21 can be determined, for example, from a cross-sectional image of the second portion 102p of the catalyst layer 100 obtained using a TEM or SEM. First, the equivalent diameters of a given number (at least 50) of second conductive particles 21 are determined from the cross-sectional image of the second portion 102p, and a frequency distribution (histogram) of the equivalent diameters is obtained. Each section in the histogram has the same width of 10 nm. The median value of the section with the highest frequency among the sections in the histogram is taken as the mode particle diameter M2 of the second conductive particles 21. If the number of first conductive particles 11 contained in the cross-sectional image of the first portion 101p is small (for example, less than 50), making it difficult to obtain a histogram, the average value of the determined equivalent diameters of the first conductive particles 11 may be used as the mode particle diameter M1. The same applies to the second conductive particles 21.

[0023] The most frequent particle size of the first conductive particles 11 and second conductive particles 21 as raw material powder can be determined from the particle size distribution obtained by measurement based on a laser diffraction / scattering method.

[0024] The ratio of M2 to M1 (M2 / M1) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less. The lower limit of the ratio of M2 to M1 is, for example, 0.1 or more. The lower limit of the ratio of M2 to M1 may be 0.2 or more.

[0025] The mode particle diameter M1 of the first conductive particles 11 is, for example, not less than 40 nm and not more than 1200 nm.

[0026] The mode particle diameter M2 of the second conductive particles 21 is, for example, not less than 20 nm and not more than 1000 nm.

[0027] As described above, in this embodiment, the first electrode catalyst 10 is preferentially disposed in the first portion 101p, and the second electrode catalyst 20 is preferentially disposed in the second portion 102p. In this embodiment, "the first electrode catalyst 10 is preferentially disposed in the first portion 101p" means that, in a cross section parallel to the thickness direction T100 of the catalyst layer 100, the area A11 occupied by the first electrode catalyst 10 per unit area of ​​the first portion 101p is larger than the area A12 occupied by the second electrode catalyst 20 per unit area of ​​the first portion 101p. "The second electrode catalyst 20 is preferentially disposed in the second portion 102p" means that, in a cross section parallel to the thickness direction T100 of the catalyst layer 100, the area A22 occupied by the second electrode catalyst 20 per unit area of ​​the second portion 102p is larger than the area A21 occupied by the first electrode catalyst 10 per unit area of ​​the second portion 102p.

[0028] The area A11 occupied by the first electrode catalyst 10 and the area A12 occupied by the second electrode catalyst 20 per unit area of ​​the first portion 101p can be determined, for example, from a cross-sectional image of the first portion 101p of the catalyst layer 100 obtained using a TEM or SEM. Similarly, the area A22 occupied by the second electrode catalyst 20 and the area A21 occupied by the first electrode catalyst 10 per unit area of ​​the second portion 102p can be determined, for example, from a cross-sectional image of the second portion 102p of the catalyst layer 100 obtained using a TEM or SEM. However, the cross-sectional image of the first portion 101p always includes the first main surface 101, and the cross-sectional image of the second portion 102p always includes the second main surface 102, and the areas of the objects to be measured in both cross-sectional images are the same.

[0029] The ratio of A12 to A11 (A12 / A11) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less. The lower limit of the ratio of A12 to A11 may be, for example, 0.05 or more, and A12 may be 0.

[0030] The ratio of A21 to A22 (A21 / A22) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less. The lower limit of the ratio of A21 to A22 may be, for example, 0.05 or more, and A21 may be 0.

[0031] As described above, in the present embodiment, in a cross section parallel to the thickness direction T100 of the catalyst layer 100, the area A23 occupied by the conductive fibers 30 per unit area of ​​the second portion 102p is larger than the area A13 occupied by the conductive fibers 30 per unit area of ​​the first portion 101p. The area A23 occupied by the conductive fibers 30 per unit area of ​​the second portion 102p can be determined, for example, from a cross-sectional image of the second portion 102p of the catalyst layer 100 obtained using a TEM or SEM. Similarly, the area A13 occupied by the conductive fibers 30 per unit area of ​​the first portion 101p can be determined, for example, from a cross-sectional image of the first portion 101p of the catalyst layer 100 obtained using a TEM or SEM. However, the cross-sectional image of the first portion 101p always includes the first main surface 101, and the cross-sectional image of the second portion 102p always includes the second main surface 102, and the areas of the objects to be measured in both cross-sectional images are the same.

[0032] The ratio of A13 to A23 (A13 / A23) may be 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. The upper limit of the ratio of A13 to A23 may be 0.5 or less. The lower limit of the ratio of A13 to A23 is, for example, 0.01 or more. The lower limit of the ratio of A13 to A23 may be 0.05 or more, and A13 may be 0.

[0033] In this embodiment, the catalyst layer 100 includes a first layer 100a including a first portion 101p and a second layer 100b including a second portion 102p.

[0034] 1B is a partial enlarged view of portion IB in FIG. 1A. As shown in FIGS. 1A and 1B, in the catalyst layer 100 of this embodiment, the boundary line between the first layer 100a and the second layer 100b may not be clear. In this case, as shown in FIG. 1B, in a cross section of the catalyst layer 100 parallel to the thickness direction T100, among straight lines perpendicular to the thickness direction T100, the total length across the first electrode catalyst 10 is longer than the total length across the second electrode catalyst 20, and the straight line closest to point 11p that defines the minimum height of the surface profile of the first electrode catalyst 10 is defined as the boundary line L100 between the first layer 100a and the second layer 100b in the cross-sectional image.

[0035] In a cross section parallel to the thickness direction T100 of the catalyst layer 100, the ratio B11 of the area occupied by the first electrode catalyst 10 to the area of ​​the first layer 100a may be greater than the ratio B12 of the area occupied by the second electrode catalyst 20 to the area of ​​the first layer 100a. The ratio B22 of the area occupied by the second electrode catalyst 20 to the area of ​​the second layer 100b may be greater than the ratio B21 of the area occupied by the first electrode catalyst 10 to the area of ​​the second layer 100b. A catalyst layer 100 having such a configuration is suitable for smooth movement of reactants necessary for the power generation reaction.

[0036] The ratio B11 of the area occupied by the first electrode catalyst 10 to the area of ​​the first layer 100a and the ratio B12 of the area occupied by the second electrode catalyst 20 to the area of ​​the first layer 100a can be determined, for example, from a cross-sectional image of the first layer 100a of the catalyst layer 100 obtained using a TEM or SEM. Similarly, the ratio B22 of the area occupied by the second electrode catalyst 20 to the area of ​​the second layer 100b and the ratio B21 of the area occupied by the first electrode catalyst 10 to the area of ​​the second layer 100b can be determined, for example, from a cross-sectional image of the second layer 100b obtained using a TEM or SEM.

[0037] The ratio of B12 to B11 (B12 / B11) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less. The lower limit of the ratio of B12 to B11 is, for example, 0.01 or more. The lower limit of the ratio of B12 to B11 may be 0.05 or more.

[0038] The ratio of B21 to B22 (B21 / B22) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, or even 0.5 or less. The lower limit of the ratio of B21 to B22 is, for example, 0.01 or more. The lower limit of the ratio of B21 to B22 may be 0.05 or more.

[0039] The first layer 100a may contain only the first electrode catalyst 10. That is, B11:B12 may be 100:0. The second layer 100b may contain only the second electrode catalyst 20. That is, B22:B21 may be 100:0.

[0040] In a cross section parallel to the thickness direction T100 of the catalyst layer 100, the ratio B23 of the area occupied by the conductive fibers 30 to the area of ​​the second layer 100b may be greater than the ratio B13 of the area occupied by the conductive fibers 30 to the area of ​​the first layer 100a. A catalyst layer 100 having such a configuration is suitable for smooth movement of reactants necessary for the power generation reaction.

[0041] The ratio B23 of the area occupied by the conductive fibers 30 to the area of ​​the second layer 100b can be determined, for example, from a cross-sectional image of the second layer 100b of the catalyst layer 100 obtained using a TEM or SEM. Similarly, the ratio B13 of the area occupied by the conductive fibers 30 to the area of ​​the first layer 100a can be determined, for example, from a cross-sectional image of the first layer 100a obtained using a TEM or SEM.

[0042] The ratio of B13 to B23 (B13 / B23) may be 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. The upper limit of the ratio of B13 to B23 may be 0.5 or less. The lower limit of the ratio of B13 to B23 is, for example, 0.01 or more. The lower limit of the ratio of B13 to B23 may be 0.05 or more, or 0.1 or more.

[0043] The first layer 100a may not contain the conductive fibers 30, and only the second layer 100b may contain the conductive fibers 30. In other words, B13:B23 may be 0:100.

[0044] In the catalyst layer 100, the first layer 100a and the second layer 100b are in electrical contact with each other. This configuration makes it easier to achieve the above-mentioned effect, namely, to facilitate smooth transfer of reactants necessary for the power generation reaction.

[0045] 1A, the first layer 100a and the second layer 100b are continuous in the thickness direction T100. In this manner, the first layer 100a and the second layer 100b may be continuous. That is, there may be no other layer between the first layer 100a and the second layer 100b.

[0046] The ratio T11 of the thickness T1 of the first layer 100a to the thickness of the catalyst layer 100 may be the same as or different from the ratio T12 of the thickness T2 of the second layer 100b to the thickness of the catalyst layer 100. For example, the ratio of the thickness T1 of the first layer 100a to the thickness of the catalyst layer 100 may be smaller than the ratio of the thickness T2 of the second layer 100b to the thickness of the catalyst layer 100.

[0047] The ratio of T11 to T12 (T11 / T12) may be 2 or less, 1.7 or less, 1.5 or less, 1.2 or less, 1 or less, 0.9 or less, or even 0.8 or less. The upper limit of the ratio of T11 to T12 may be 0.7 or less. The lower limit of the ratio of T11 to T12 is, for example, 0.5 or more.

[0048] The thickness T1 of the first layer 100a can be measured, for example, by the following method. First, a sample is prepared by exposing a cross section of the catalyst layer 100 parallel to the thickness direction T100. A TEM or SEM is used to obtain multiple (e.g., 10) cross-sectional images of the sample. The boundary line L100 is defined for the multiple cross-sectional images obtained as described above. The distance in the thickness direction T100 from the boundary line L100 to the first main surface 101 is measured, and this is defined as the thickness T1 of the first layer 100a. The distance in the thickness direction T100 from the boundary line L100 to the second main surface 102 is measured, and this is defined as the thickness T2 of the second layer 100b.

[0049] The thickness T1 of the first layer 100a is, for example, not less than 3 μm and not more than 30 μm.

[0050] The thickness T2 of the second layer 100b is, for example, not less than 2 μm and not more than 20 μm.

[0051] (electrode catalyst) As shown in FIG. 2, the first conductive particles 11 are a conductive porous material having pores 11p. In the first electrode catalyst 10, the pores 11p open to the surface of the first conductive particles 11. In other words, the surface of the first conductive particles 11 has irregularities. As shown in FIG. 3, the second conductive particles 21 are a conductive porous material having pores 21p. In the second electrode catalyst 20, the pores 21p open to the surface of the second conductive particles 21. In other words, the surface of the second conductive particles 21 has irregularities. The pores 11p and pores 21p may each be interconnected pores or independent pores.

[0052] The first catalyst particles 12 and the second catalyst particles 22 are not particularly limited as long as they are metal particles that have the ability to reduce an oxygen-containing gas. From the viewpoint of improving the catalytic activity and heat resistance of the catalyst layer 100, the material of the first catalyst particles 12 and the second catalyst particles 22 may be particles containing a precious metal such as platinum or a platinum alloy. Examples of platinum alloys include alloys of platinum with at least one selected from the group consisting of cobalt, nickel, ruthenium, and palladium. The first catalyst particles 12 and the second catalyst particles 22 may each contain at least one precious metal selected from the group consisting of platinum, palladium, iridium, ruthenium, and rhodium.

[0053] The platinum content in the first catalyst particles 12 and the second catalyst particles 22 may be 30 atomic % or more and 90 atomic % or less, and the other metal (for example, cobalt) content may be 10 atomic % or more and 70 atomic % or less.

[0054] The average particle diameters of the first catalyst particles 12 and the second catalyst particles 22 are not particularly limited. From the viewpoint of catalyst utilization rate and durability, it is desirable that the average particle diameters of the first catalyst particles 12 and the second catalyst particles 22 are each 1 nm or more and 30 nm or less. The average particle diameter can be calculated, for example, from a cross-sectional image of the catalyst layer 100 obtained using a TEM or SEM. In the cross-sectional image, the equivalent diameters of an arbitrary number (e.g., 10) of catalyst particles are measured. The average value of the equivalent diameters can be considered to be the average particle diameter.

[0055] In this embodiment, the first catalyst particles 12 and the second catalyst particles 22 are precious metal nanoparticles having the same composition. That is, common precious metal nanoparticles can be used for the first catalyst particles 12 and the second catalyst particles 22. This contributes to reducing the cost of the catalyst layer 100. However, the composition of the first catalyst particles 12 may be different from the composition of the second catalyst particles 22. The average particle diameter of the first catalyst particles 12 may be different from the average particle diameter of the second catalyst particles 22.

[0056] The first conductive particles 11 are made of a conductive material such as carbon particles and support first catalyst particles 12. The second conductive particles 21 are made of a conductive material such as carbon particles and support second catalyst particles 22. Examples of carbon particles include carbon black particles such as furnace black and acetylene black. The first conductive particles 11 and the second conductive particles 21 may each contain at least one selected from the group consisting of furnace black, acetylene black, and thermal black. Furnace black includes those made from petroleum-based hydrocarbons or coal-based hydrocarbons, and gas furnace black made from natural gas.

[0057] The first conductive particles 11 and the second conductive particles 21 can be formed from the same material. That is, the same material can be used as the material for the first conductive particles 11 and the second conductive particles 21. This contributes to reducing the cost of the catalyst layer 100. However, the structure of the first conductive particles 11 may be different from the structure of the second conductive particles 21. The composition of the first conductive particles 11 may be different from the composition of the second conductive particles 21.

[0058] 4 is a schematic cross-sectional view showing an example of the conductive fibers 30 contained in the catalyst layer 100. The conductive fibers 30 may be a fibrous carbon material. Examples of the fibrous carbon material include carbon nanofibers, carbon nanotubes, electrospun carbon fibers, vapor-grown carbon fibers, polyacrylonitrile-based carbon fibers, and pitch-based carbon fibers. The conductive fibers 30 may contain at least one selected from the group consisting of carbon nanofibers and carbon nanotubes.

[0059] In this embodiment, the shape of the conductive fibers 30 contained in the first layer 100a may be the same as or different from the shape of the conductive fibers 30 contained in the second layer 100b. The composition of the conductive fibers 30 contained in the first layer 100a may be the same as or different from the composition of the conductive fibers 30 contained in the second layer 100b. For example, carbon nanotubes may be used as the conductive fibers 30 contained in the first layer 100a, and vapor-grown carbon fibers may be used as the conductive fibers 30 contained in the second layer 100b.

[0060] The most frequent length M31 of the conductive fibers 30 in the short direction is, for example, 6 nm or more and 2000 nm or less, and the most frequent length M32 of the conductive fibers 30 in the long direction is, for example, 0.1 μm or more and 25 μm or less.

[0061] The most frequent length M31 in the lateral direction of the conductive fibers 30 can be determined, for example, from a cross-sectional image parallel to the thickness direction T100 of the catalyst layer 100 obtained using a TEM or SEM. First, the lengths L31 in the lateral direction of an arbitrary number (at least 50) of conductive fibers 30 are measured from the cross-sectional image to obtain a frequency distribution (histogram) of the lengths L31. Each section in the histogram has the same width of 1 nm. The median value of the section with the highest frequency among the sections in the histogram is defined as the most frequent length M31 in the lateral direction of the conductive fibers 30. Similarly, the most frequent length M32 in the longitudinal direction of the conductive fibers 30 can be determined, for example, from a cross-sectional image parallel to the thickness direction T100 of the catalyst layer 100 obtained using a TEM or SEM. First, the lengths L32 in the longitudinal direction of an arbitrary number (at least 50) of conductive fibers 30 are measured from the cross-sectional image to obtain a frequency distribution (histogram) of the lengths L32. However, each section in the histogram has the same width of 0.1 μm. The median value of the section with the highest frequency among the sections in the histogram is taken as the most frequent length M32 of the conductive fibers 30 in the longitudinal direction. Note that if the number of conductive fibers 30 included in the cross-sectional image is small (for example, less than 50) and it is difficult to obtain a histogram, the average value of the lengths L31 in the lateral direction of the conductive fibers 30 may be used as the most frequent length M31 in the lateral direction. The same applies to the most frequent length M32 of the conductive fibers 30 in the longitudinal direction.

[0062] In the present embodiment, the ratio (M32 / M31) of the most frequent length M32 of the conductive fibers 30 in the longitudinal direction to the most frequent length M31 of the conductive fibers 30 in the lateral direction may be 30 or more. The ratio (M2 / M31) of the most frequent particle diameter M2 of the second conductive particles 21 to the most frequent length M31 of the conductive fibers 30 in the lateral direction may be 5 or more. This configuration can increase the relative bulkiness of the conductive fibers 30 contained in the second layer 100b. As a result, it is possible to increase the ratio of the volume occupied by the pores 50 to the volume of the catalyst layer 100, i.e., the porosity, while suppressing an increase in the proton conduction resistance.

[0063] The lower limit of the ratio (M32 / M31) of the conductive fibers 30 may be 4 or more, 8 or more, 20 or more, or even 100 or more. The upper limit of the ratio (M32 / M31) of the conductive fibers 30 is, for example, 4000 or less.

[0064] The lower limit of the ratio (M2 / M31) of the mode particle diameter M2 of the second conductive particles 21 to the mode length M31 of the conductive fibers 30 in the short direction may be 3 or more, 6 or more, or even 10 or more. The upper limit of the ratio of the mode particle diameter M2 of the second conductive particles 21 to the mode length M31 of the conductive fibers 30 in the short direction is, for example, 80 or less.

[0065] When the first layer 100a and the second layer 100b contain conductive fibers 30, the most frequent length M31a in the short direction of the conductive fibers 30 contained in the first layer 100a may be greater than the most frequent length M31b in the short direction of the conductive fibers 30 contained in the second layer 100b. That is, M31a > M31b may be satisfied. This configuration makes it easier to optimize the proton conduction pathways in the second layer 100b.

[0066] However, the magnitude relationship between M31a and M31b is not limited to the above example. The most frequent length M31a in the short direction of the conductive fibers 30 contained in the first layer 100a may be equal to or less than the most frequent length M31b in the short direction of the conductive fibers 30 contained in the second layer 100b. That is, M31a≦M31b may be satisfied.

[0067] When the first layer 100a and the second layer 100b contain the conductive fibers 30, the ratio (M32b / M31b) of the most frequent length M32b in the longitudinal direction to the most frequent length M31b in the lateral direction of the conductive fibers 30 contained in the second layer 100b may be larger than the ratio (M32a / M31a) of the most frequent length M32a in the longitudinal direction to the most frequent length M31a in the lateral direction of the conductive fibers 30 contained in the first layer 100a. With this configuration, the pores 50 in the first layer 100a are easily maintained.

[0068] The ratio of M32a / M31a to M32b / M31b ((M32a / M31a) / (M32b / M31b)) may be 0.9 or less, 0.8 or less, 0.7 or less, or even 0.6 or less. The upper limit of the ratio of M32a / M31a to M32b / M31b may be 0.5 or less. The lower limit of the ratio of M32a / M31a to M32b / M31b is, for example, 0.1 or more.

[0069] When the first layer 100a and the second layer 100b contain conductive fibers 30, the ratio (M32a / M31a) of the conductive fibers 30 contained in the first layer 100a may be less than 60 and may be equal to or less than the ratio (M32b / M31b) of the conductive fibers 30 contained in the second layer 100b. This configuration makes it easy to obtain a catalyst layer 100 in which the porosity of the first layer 100a is appropriately adjusted. By using such a catalyst layer 100, a fuel cell can be obtained in which deterioration in efficiency, current characteristics, etc. is suppressed.

[0070] When the first layer 100a and the second layer 100b contain conductive fibers 30, the ratio W13 of the total mass of the conductive fibers 30 contained in the first layer 100a to the total mass of the first conductive particles 11 contained in the first layer 100a may be smaller than the ratio W23 of the total mass of the conductive fibers 30 contained in the second layer 100b to the total mass of the second conductive particles 21 contained in the second layer 100b. In other words, W23 > W13 may be satisfied. This configuration makes it easier to obtain a catalyst layer 100 in which the porosity of the first layer 100a is appropriately adjusted.

[0071] Whether W23 > W13 is satisfied in the catalyst layer 100 can be confirmed, for example, by the following method. After forming the catalyst layer 100 so that the first layer 100a is exposed, the exposed surface is sputtered with a particle beam while measuring the component ratio along the thickness direction T100. Specifically, for example, the first electrode catalyst 10 is selectively excited with an electron beam, and the element ratio of the first conductive particles 11 to the first catalyst particles 12 is obtained from the characteristic X-ray intensity. When the element of the conductive fiber 30 is different from the element of the first conductive particles, the first layer 100a is excited, and the component ratios are obtained from the characteristic X-ray intensity, so W13 can be calculated. When the element of the conductive fiber 30 is the same as the element of the first conductive particles 11, the element ratio of the first catalyst particles 12 to the first conductive particles 11 of the first electrode catalyst 10 is obtained. Therefore, the amount of the first conductive particles 11, which is the same element as the conductive fiber 30, is calculated from the amount of the first catalyst particles 12, and W13 can be calculated based on this. Even when the ionomer 40 contains the same element, W13 can be calculated by adding the components of the ionomer 40 based on the elemental ratio specific to the ionomer 40. It is desirable to supplement the results by combining not only characteristic X-rays but also the results of separation based on the mass of decomposition fragments. Similarly, for the second layer 100b, the catalyst layer 100 is shaped so that the second layer 100b is exposed. Then, W23 can be calculated by obtaining the elemental ratios of the second electrode catalyst 20, the second conductive particles 21, the second catalyst particles 22, the conductive fibers 30, and the ionomer 40 from the exposed surface. By comparing the W13 and W23 calculated in this way, it can be confirmed that W23 > W13 is satisfied. However, the above confirmation method is merely an example, and it is also possible to confirm that W23 > W13 is satisfied based on W13 and W23 calculated by other methods.

[0072] The ratio of W13 to W23 (W13 / W23) may be 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. The upper limit of the ratio of W13 to W23 may be 0.5 or less. The lower limit of the ratio of W13 to W23 is, for example, 0.01 or more. The lower limit of the ratio of W13 to W23 may be 0.05 or more, or 0.1 or more.

[0073] The ionomer 40 adheres to the first conductive particles 11 and enables proton conduction to the first catalyst particles 12. The ionomer 40 adheres to the second conductive particles 21 and enables proton conduction to the second catalyst particles 22.

[0074] In the example shown in FIG. 2 , the ionomer 40 covers the entire surfaces of the first conductive particles 11 in the first electrode catalyst 10. In the example shown in FIG. 3 , the ionomer 40 covers the entire surfaces of the second conductive particles 21 in the second electrode catalyst 20. However, the configurations of the first electrode catalyst 10, the second electrode catalyst 20, and the ionomer 40 are not limited to the examples shown in FIGS. 2 and 3 . In the first electrode catalyst 10, the ionomer 40 may cover a portion of the surface of the first conductive particles 11. That is, the surface of the first conductive particles 11 may have an exposed portion that is not covered by the ionomer 40. In the second electrode catalyst 20, the ionomer 40 may cover a portion of the surface of the second conductive particles 21. That is, the surface of the second conductive particles 21 may have an exposed portion that is not covered by the ionomer 40. Such a configuration can improve electronic conductivity between the conductive particles.

[0075] As the ionomer 40, a polymer electrolyte resin having ion conductivity can be used. The ionomer 40 may have sulfonic acid groups. As the ionomer 40, a perfluorocarbon sulfonic acid-based polymer material having sulfonic acid groups, a hydrocarbon-based polymer material, or the like can be used. As the ionomer 40, a perfluorosulfonic acid resin can be used. The perfluorosulfonic acid resin exhibits excellent proton conductivity and is stable even in the power generation environment of an electrochemical device. The ionomer 40 typically includes a perfluorocarbon sulfonic acid-based polymer electrolyte having sulfonic acid groups.

[0076] The ionomer 40 may be made of the same material as the electrolyte membrane, which will be described later.

[0077] The ratio of the total mass of the ionomer 40 contained in the first layer 100a to the total surface area of ​​the first conductive particles 11 contained in the first layer 100a is defined as R1, and the ratio of the total mass of the ionomer 40 contained in the second layer 100b to the total surface area of ​​the second conductive particles 21 contained in the second layer 100b and the total surface area of ​​the conductive fibers 30 is defined as R2. In this case, the catalyst layer 100 may satisfy the following formula (1): |R1-R2|≦0.2 (1)

[0078] In a catalyst layer 100 that satisfies formula (1), the second layer 100b, which has a large content of second conductive particles 21, is prevented from having an excessive content of ionomer 40. This prevents the oxygen migration path in the second layer 100b from becoming too narrow. Furthermore, when the ionomer 40 contains a perfluorocarbon sulfonic acid-based polymer electrolyte having sulfonic acid groups, the sulfur element contained in the sulfonic acid groups adsorbs to the precious metal contained in the first catalyst particles 12 and the second catalyst particles 22, inhibiting catalytic activity, or so-called catalyst poisoning, occurs. However, when formula (1) is satisfied, the occurrence of catalyst poisoning is suppressed.

[0079] The total surface area of ​​the first conductive particles 11 contained in the first layer 100a, the total surface area of ​​the second conductive particles 21 contained in the second layer 100b, and the total surface area of ​​the conductive fibers 30 contained in the second layer 100b can be determined, for example, by the following method. The cross section of the first layer 100a is observed using an SEM, and the surface area of ​​each of the first conductive particles 11 and the conductive fibers 30 is determined from the shape distribution of each of the first conductive particles 11 and the conductive fibers 30 contained in the cross-sectional image. Similarly, the cross section of the second layer 100b is observed using an SEM, and the surface area of ​​each of the second conductive particles 21 and the conductive fibers 30 is determined from the shape distribution of each of the second conductive particles 21 and the conductive fibers 30 contained in the cross-sectional image. Measurement of the shape distribution is not limited to SEM; laser microscopes, TEMs, etc. can also be used as long as they can measure the minor and major axes of the conductive particles. TEM may also be used to obtain the fine shape of the conductive particle surface and obtain more detailed surface areas. It is best to use the same method to measure the surface areas of the first conductive particles 11 and the second conductive particles 21.

[0080] R1 and R2 may satisfy |R1-R2|≦0.15, may satisfy |R1-R2|≦0.1, or may further satisfy |R1-R2|≦0.05.

[0081] The mode particle diameter M1 of the first conductive particles 11, the mode particle diameter M2 of the second conductive particles 21, the thickness T1 of the first layer 100a, and the thickness T2 of the second layer 100b may satisfy the following formula (2). M1≧M2×T2 / T1 (2)

[0082] In the catalyst layer 100 that satisfies formula (2), the pore size is ensured to such an extent that the pores 50 are not easily blocked by the generated water in the first layer 100a, which has a large content of the first conductive particles 11. This promotes the transfer of oxygen to the second layer 100b.

[0083] The methods for determining the mode particle diameter M1 of the first conductive particles 11, the mode particle diameter M2 of the second conductive particles 21, the thickness T1 of the first layer 100a, and the thickness T2 of the second layer 100b are as described above.

[0084] Next, we will explain a method for manufacturing the above-mentioned catalyst layer 100. The method for manufacturing the catalyst layer 100 includes producing the first electrode catalyst 10 and the second electrode catalyst 20 (step S1), preparing the first catalyst solution and the second catalyst solution (step S2), and producing the catalyst layer 100 having the first layer 100a and the second layer 100b (step S3).

[0085] In step S1, the first electrode catalyst 10 and the second electrode catalyst 20 are produced. Specifically, first catalyst particles 12 are supported on first conductive particles 11. Second catalyst particles 22 are supported on second conductive particles 21. The average particle diameter of the first conductive particles 11 as raw material powder is larger than the average particle diameter of the second conductive particles 21 as raw material powder.

[0086] In step S1, there is no particular limitation on the method for supporting the first catalyst particles 12 on the first conductive particles 11. For example, the first catalyst particles 12 can be supported on the first conductive particles 11 using known methods such as an impregnation-reduction pyrolysis method, a chemical reduction method, a gas-phase reduction method, a surface-modified colloid-reduction pyrolysis method, or a nanocapsule method.

[0087] In step S1, there is no particular limitation on the method for supporting the second catalyst particles 22 on the second conductive particles 21. The second catalyst particles 22 can be supported on the second conductive particles 21 using the same method as that described for the first conductive particles 11.

[0088] In step S2, a first catalyst solution and a second catalyst solution are prepared. The first catalyst solution is a catalyst solution for forming the first layer 100a. The second catalyst solution is a catalyst solution for forming the second layer 100b.

[0089] First, a first solution is obtained by adding the first electrode catalyst 10 to a solvent. The solvent contains, for example, ethanol and water. Next, an ionomer 40 is added to the first solution and stirred. This results in a first catalyst solution. A second solution is prepared by adding the second electrode catalyst 20 and conductive fibers 30 to the solvent. Next, the ionomer 40 is added to the second solution and stirred. This results in a second catalyst solution.

[0090] In step S3, a catalyst layer 100 having a first layer 100a and a second layer 100b is fabricated.

[0091] For example, a catalyst layer 100 having a first layer 100a and a second layer 100b can be produced as follows: A first catalyst solution is applied to one surface of a gas diffusion layer to form a first coating film. The first coating film is dried to remove the solvent, thereby obtaining the first layer 100a. A second catalyst solution is applied to one surface of an electrolyte membrane to form a second coating film. The second coating film is dried to remove the solvent, thereby obtaining the second layer 100b. The first layer 100a and the second layer 100b are bonded together, thereby forming the catalyst layer 100 between the gas diffusion layer and the electrolyte membrane.

[0092] In the above method, a transfer sheet may be used instead of the gas diffusion layer and the electrolyte membrane. The catalyst layer 100 may be formed by bonding the first layer 100a and the second layer 100b formed on the transfer sheet together.

[0093] For example, the first layer 100a and the second layer 100b can be produced as follows: A second catalyst solution is applied to one surface of the electrolyte membrane to form a second coating film. The second coating film is dried to remove the solvent, thereby obtaining the second layer 100b. A first catalyst solution is applied to the surface of the second layer 100b opposite the electrolyte membrane to form a first coating film. The first coating film is dried to remove the solvent, thereby obtaining the first layer 100a. In this manner, the catalyst layer 100 can be formed on one surface of the electrolyte membrane. Note that, as long as the first layer 100a and the second layer 100b are laminated after the first coating film has dried, it is also possible to apply the first catalyst solution even when the second coating film is not completely dry.

[0094] In the above method, a transfer sheet may be used instead of the electrolyte membrane. The catalyst layer 100 may be formed by forming the first layer 100a on the surface of the second layer 100b formed on the transfer sheet.

[0095] [1-2. Operation] The operation and function of the catalyst layer 100 configured as above will be explained in connection with the electrochemical device 300 according to the second embodiment, which will be described later.

[0096] (Embodiment 2) Hereinafter, the second embodiment will be described with reference to FIGS. 5A to 6. FIG.

[0097] [2-1.Configuration] Fig. 5A is a schematic cross-sectional view of a membrane electrode assembly 200 for an electrochemical device in accordance with Embodiment 2. Fig. 5B is a partial enlarged view of portion VB in Fig. 5A. Fig. 6 is a schematic cross-sectional view of an electrochemical device 300 in accordance with Embodiment 2. The electrochemical device 300 includes the membrane electrode assembly 200, an anode separator 301, and a cathode separator 302. The membrane electrode assembly 200 is disposed between the anode separator 301 and the cathode separator 302.

[0098] In this embodiment, the electrochemical device 300 may be used in a fuel cell, thereby providing a highly efficient fuel cell with high power generation performance.

[0099] 6, the electrochemical device 300 is a polymer electrolyte fuel cell (PEFC) that generates electricity by receiving a supply of a hydrogen-containing gas G1 as an anode gas and an oxygen-containing gas G3 as a cathode gas. The electrochemical device 300 may be used as other electrochemical devices, such as a hydrogen purification device that purifies hydrogen or a water electrolysis device that electrolyzes water, in addition to a fuel cell.

[0100] 5A, the membrane electrode assembly 200 has an anode 202, an electrolyte membrane 201, and a cathode 203. The electrolyte membrane 201 is disposed between the anode 202 and the cathode 203. The anode 202 is bonded to one surface of the electrolyte membrane 201. The cathode 203 is bonded to the other surface of the electrolyte membrane 201.

[0101] The anode 202 has an anode catalyst layer 204 and an anode gas diffusion layer 205. The anode catalyst layer 204 is disposed between the electrolyte membrane 201 and the anode gas diffusion layer 205. The cathode 203 has a cathode catalyst layer 206 and a cathode gas diffusion layer 207. The cathode catalyst layer 206 is disposed between the electrolyte membrane 201 and the cathode gas diffusion layer 207.

[0102] The electrolyte membrane 201 conducts protons between the anode catalyst layer 204 and the cathode catalyst layer 206. The electrolyte membrane 201 is made of a polymer material that has proton conductivity and gas barrier properties. Typically, the electrolyte membrane 201 is a perfluorocarbon sulfonic acid-based or hydrocarbon-based polymer electrolyte membrane having sulfonic acid groups. The electrolyte membrane 201 may also be a perfluorosulfonic acid-based polymer electrolyte membrane. A perfluorosulfonic acid-based polymer electrolyte membrane exhibits excellent proton conductivity and is stable even in the power generation environment of the electrochemical device 300.

[0103] The electrolyte membrane 201 has a surface in contact with the anode catalyst layer 204 and a surface in contact with the cathode catalyst layer 206. In order to improve drainage on the surface of the electrolyte membrane 201, the surface of the electrolyte membrane 201 may be flat. A "flat surface" means a surface that has not been processed to provide irregularities.

[0104] The anode catalyst layer 204 has the function of promoting the electrochemical reaction that dissociates hydrogen into protons. The anode catalyst layer 204 includes a conductive material and catalyst particles supported on the conductive material. The anode catalyst layer 204 may include a coating layer made of an electrolyte resin that covers at least a portion of the surface of the conductive material.

[0105] The membrane electrode assembly 200 may include the catalyst layer 100 described in the first embodiment as the anode catalyst layer 204 .

[0106] The anode gas diffusion layer 205 has a function of supplying the hydrogen-containing gas G1 to the anode catalyst layer 204 and a function of receiving electrons from the anode catalyst layer 204. The anode gas diffusion layer 205 is made of a material that is gas permeable, water repellent, and conductive. The anode gas diffusion layer 205 has, as its main material, for example, a conductive porous body. An example of the porous body is a carbon fiber aggregate such as carbon paper.

[0107] The cathode catalyst layer 206 has a function of promoting an electrochemical reaction that produces water from protons and oxygen. The cathode catalyst layer 206 includes a conductive material and catalyst particles supported on the conductive material.

[0108] In this embodiment, the cathode 203 includes the catalyst layer 100 described in the first embodiment. That is, the membrane electrode assembly 200 includes the catalyst layer 100 described in the first embodiment as the cathode catalyst layer 206. FIG. 5B shows an example in which the membrane electrode assembly 200 includes the catalyst layer 100 as the cathode catalyst layer 206. As shown in FIG. 5B, the first main surface 101 of the cathode catalyst layer 206 is in contact with the cathode gas diffusion layer 207. The second main surface 102 of the cathode catalyst layer 206 is in contact with the electrolyte membrane 201. The ionomer 40 is omitted in FIG. 5B. This configuration allows smooth transfer of oxygen and protons required for the power generation reaction in the cathode catalyst layer 206. As a result, the electrochemical reaction in the cathode catalyst layer 206 can be accelerated. This improves the power generation performance of an electrochemical device 300 using the membrane electrode assembly 200.

[0109] The cathode gas diffusion layer 207 has the function of supplying an oxygen-containing gas to the cathode catalyst layer 206 and the function of transferring electrons to the cathode catalyst layer 206. The cathode gas diffusion layer 207 is made of a gas-permeable, water-repellent, and conductive material. The cathode gas diffusion layer 207 has, as its main material, for example, a conductive porous body. An example of the porous body is a carbon fiber aggregate such as carbon paper.

[0110] The anode catalyst layer 204 may have the same structure as the cathode catalyst layer 206, or may have a different structure.

[0111] As shown in Fig. 6, the anode separator 301 has an anode gas inlet 303, an anode gas outlet 304, and an anode gas flow channel 301g. The anode gas flow channel 301g is a groove-shaped gas flow channel that guides a hydrogen-containing gas G1 to the anode 202. The anode gas inlet 303 is provided at the upstream end of the anode gas flow channel 301g. The anode gas outlet 304 is provided at the downstream end of the anode gas flow channel 301g. The hydrogen-containing gas G1 is introduced into the anode gas flow channel 301g from the outside through the anode gas inlet 303. Unreacted hydrogen-containing gas G2 is discharged from the anode gas flow channel 301g to the outside through the anode gas outlet 304.

[0112] The cathode separator 302 has a cathode gas inlet 305, a cathode gas outlet 306, and a cathode gas flow channel 302g. The cathode gas flow channel 302g is a groove-shaped gas flow channel that guides an oxygen-containing gas G3 to the cathode 203. The cathode gas inlet 305 is provided at the upstream end of the cathode gas flow channel 302g. The cathode gas outlet 306 is provided at the downstream end of the cathode gas flow channel 302g. The oxygen-containing gas G3 is introduced into the cathode gas flow channel 302g from the outside through the cathode gas inlet 305. The unreacted oxygen-containing gas G4 is discharged from the cathode gas flow channel 302g to the outside through the cathode gas outlet 306.

[0113] The shapes of the anode gas flow channel 301g and the cathode gas flow channel 302g are not particularly limited. The anode gas flow channel 301g and the cathode gas flow channel 302g may each have a serpentine shape. A serpentine shape is a shape of a flow channel in which one or more flow channels meander within a plane. When the anode gas flow channel 301g and the cathode gas flow channel 302g have the above-mentioned shapes, gas can be supplied to the entire catalyst layers 204, 206 at a constant flow rate. This makes it easier for the gas to reach all of the catalyst particles.

[0114] The anode separator 301 and the cathode separator 302 are made of a conductive material. The anode separator 301 and the cathode separator 302 may each be made of a conductive material such as carbon or metal. To prevent corrosion, the anode separator 301 and the cathode separator 302 may be provided with a corrosion-resistant coating such as a resin or plating.

[0115] [2-2. Operation] The operation and function of the electrochemical device 300 configured as above will be described below with reference to FIG.

[0116] A hydrogen-containing gas G1 is supplied from the anode gas inlet 303 to the anode gas flow channel 301g of the anode separator 301. The hydrogen-containing gas G1 is a humidified gas containing hydrogen. The humidified gas containing hydrogen may be, for example, humidified hydrogen gas. As a result, the hydrogen-containing gas G1 is supplied to the anode catalyst layer 204 via the anode gas diffusion layer 205. An oxygen-containing gas G3 is supplied from the cathode gas inlet 305 to the cathode gas flow channel 302g of the cathode separator 302. The oxygen-containing gas G3 is a humidified gas containing oxygen. The humidified gas containing oxygen may be, for example, humidified air. As a result, the oxygen-containing gas G3 is supplied to the cathode catalyst layer 206 via the cathode gas diffusion layer 207. It is possible to draw a current between the anode catalyst layer 204 to which the hydrogen-containing gas G1 is supplied and the cathode catalyst layer 206 to which the oxygen-containing gas G3 is supplied.

[0117] In the anode catalyst layer 204 to which the hydrogen-containing gas G1 is supplied, hydrogen (H2) is converted into protons (H + ) and electrons (e -) occurs. The protons pass through the electrolyte membrane 201 and move to the cathode catalyst layer 206. The electrons dissociated in the anode catalyst layer 204 move from the anode 202 to the cathode 203 through an external circuit 401 equipped with a load 402, and reach the cathode catalyst layer 206. In the cathode catalyst layer 206, a reduction reaction occurs in which water (H2O) is produced by an electrochemical reaction of protons, oxygen (O2), and electrons, as expressed by the following formula (II). The protons used in this reduction reaction are protons that are dissociated by the oxidation reaction in the anode catalyst layer 204 shown in the following formula (I), pass through the electrolyte membrane 201, and move to the cathode catalyst layer 206.

[0118] H2→2H + +2e - (I) 4H + +O2+4e - →2H2O (II)

[0119] In the electrochemical device 300, oxygen and protons required for the power generation reaction can be smoothly transferred in the cathode catalyst layer 206. As a result, the electrochemical reaction in the cathode catalyst layer 206 can be accelerated.

[0120] (Other embodiments) As described above, Embodiments 1 and 2 have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these and can be applied to embodiments with modifications, additions, omissions, etc. Furthermore, it is also possible to combine the components described in the above embodiments and modifications to create new embodiments.

[0121] It should be noted that the above-described embodiments are intended to illustrate the technology of the present disclosure, and various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0122] (Addendum) The above description of the embodiments discloses the following techniques.

[0123] (Technology 1) A catalyst layer having a first major surface and a second major surface, a first electrode catalyst, a second electrode catalyst, conductive fibers, and an ionomer; the first electrode catalyst has first conductive particles and first catalyst particles supported on the first conductive particles; the second electrode catalyst has second conductive particles and second catalyst particles supported on the second conductive particles, the mode particle diameter of the first conductive particles is larger than the mode particle diameter of the second conductive particles; When a portion including the first main surface is defined as a first portion and a portion including the second main surface is defined as a second portion, the first electrode catalyst is preferentially disposed in the first portion, and the second electrode catalyst is preferentially disposed in the second portion; In a cross section parallel to the thickness direction of the catalyst layer, the area occupied by the conductive fibers per unit area of ​​the second portion is larger than the area occupied by the conductive fibers per unit area of ​​the first portion. Catalyst layers for electrochemical devices.

[0124] The catalyst layer for electrochemical devices of Technique 1 allows the reactants necessary for the power generation reaction to move smoothly.

[0125] (Technology 2) The catalyst layer for electrochemical devices according to Technology 1, wherein the catalyst layer comprises a first layer including the first portion and a second layer including the second portion, and in a cross section parallel to the thickness direction of the catalyst layer, the ratio of the area occupied by the first electrode catalyst to the area of ​​the first layer is larger than the ratio of the area occupied by the second electrode catalyst to the area of ​​the first layer, and the ratio of the area occupied by the second electrode catalyst to the area of ​​the second layer is larger than the ratio of the area occupied by the first electrode catalyst to the area of ​​the second layer. A catalyst layer having such a configuration is suitable for smooth transport of reactants required for a power generation reaction.

[0126] (Technology 3) The catalyst layer for electrochemical devices according to Technical Problem 2, wherein the first layer and the second layer are in electrical contact with each other. Such a configuration facilitates smooth transfer of reactants required for the power generation reaction.

[0127] (Technology 4) The catalyst layer for an electrochemical device according to any one of techniques 1 to 3, wherein a ratio of a most frequent length in the longitudinal direction of the conductive fibers to a most frequent length in the lateral direction of the conductive fibers is 30 or more, and a ratio of a most frequent particle diameter of the second conductive particles to a most frequent length in the lateral direction of the conductive fibers is 5 or more. With this configuration, it is possible to increase the porosity while suppressing an increase in proton conduction resistance.

[0128] (Technology 5) The catalyst layer for an electrochemical device according to any one of techniques 2 to 4, wherein |R1-R2|≦0.2 is satisfied, where R1 is the ratio of the total mass of the ionomer contained in the first layer to the total surface area of ​​the first conductive particles contained in the first layer, and R2 is the ratio of the total mass of the ionomer contained in the second layer to the combined surface area of ​​the total surface area of ​​the second conductive particles and the total surface area of ​​the conductive fibers. With this configuration, the oxygen transfer path in the second layer is prevented from becoming too narrow.

[0129] (Technology 6) The catalyst layer for an electrochemical device according to any one of techniques 2 to 5, wherein M1 ≧ M2 × T2 / T1 is satisfied, where M1 is a mode particle diameter of the first conductive particles, M2 is a mode particle diameter of the second conductive particles, T1 is a thickness of the first layer, and T2 is a thickness of the second layer. With this configuration, oxygen transfer to the second layer is promoted.

[0130] (Technology 7) an anode; a cathode; an electrolyte membrane disposed between the anode and the cathode; Equipped with The cathode comprises the catalyst layer for an electrochemical device according to any one of techniques 1 to 6. Membrane electrode assemblies for electrochemical devices.

[0131] According to the membrane electrode assembly for electrochemical devices of Technique 7, it is possible to improve the power generation performance of an electrochemical device using the membrane electrode assembly.

[0132] (Technology 8) The membrane electrode assembly according to technique 7 is provided. Electrochemical devices.

[0133] According to the electrochemical device of Technology 8, a highly efficient electrochemical device with high power generation performance can be realized. [Industrial Applicability]

[0134] The present disclosure is useful for electrochemical devices such as fuel cells, hydrogen purification devices, and water electrolysis devices. [Explanation of symbols]

[0135] 100 Catalyst layer for electrochemical devices 101 first principal surface 102 Second main surface 101p Part 1 102p Part 2 100a First layer 100b Second layer 10 First electrode catalyst 11 First conductive particle 11p pore 12 First catalyst particle 20 Second electrode catalyst 21 Second conductive particle 21p pore 22 Second catalyst particle 30 Conductive Fiber 40 Ionomer 50 vacancies T100 thickness direction 200 Membrane electrode assembly 201 Electrolyte membrane 202 Anode 203 Cathode 204 Anode catalyst layer 205 Anode gas diffusion layer 206 Cathode catalyst layer 207 Cathode gas diffusion layer 300 Electrochemical Devices 301 Anode separator 301g Anode gas flow path 302 Cathode separator 302g Cathode gas flow path 303 Anode gas inlet 304 Anode gas outlet 305 Cathode gas inlet 306 Cathode gas outlet 401 External circuit 402 Load

Claims

1. A catalyst layer having a first major surface and a second major surface, a first electrocatalyst, a second electrocatalyst, conductive fibers, and an ionomer; the first electrode catalyst has first conductive particles and first catalyst particles supported on the first conductive particles; the second electrode catalyst has second conductive particles and second catalyst particles supported on the second conductive particles, the mode particle diameter of the first conductive particles is larger than the mode particle diameter of the second conductive particles; When a portion including the first main surface is defined as a first portion and a portion including the second main surface is defined as a second portion, the first electrode catalyst is preferentially disposed in the first portion, and the second electrode catalyst is preferentially disposed in the second portion; In a cross section parallel to the thickness direction of the catalyst layer, the area occupied by the conductive fibers per unit area of ​​the second portion is larger than the area occupied by the conductive fibers per unit area of ​​the first portion. Catalyst layers for electrochemical devices.

2. the catalyst layer comprises a first layer including the first portion and a second layer including the second portion; In a cross section parallel to the thickness direction of the catalyst layer, a ratio of an area occupied by the first electrode catalyst to an area of ​​the first layer is larger than a ratio of an area occupied by the second electrode catalyst to an area of ​​the first layer; a ratio of an area occupied by the second electrode catalyst to an area of ​​the second layer is larger than a ratio of an area occupied by the first electrode catalyst to an area of ​​the second layer; The catalyst layer for an electrochemical device according to claim 1 .

3. The first layer and the second layer are in electrical contact with each other. The catalyst layer for an electrochemical device according to claim 2 .

4. The ratio of the most frequent length of the conductive fibers in the longitudinal direction to the most frequent length of the conductive fibers in the lateral direction is 30 or more, a ratio of the most frequent particle diameter of the second conductive particles to the most frequent length in the short direction of the conductive fibers is 5 or more; The catalyst layer for an electrochemical device according to claim 1 .

5. When the ratio of the total mass of the ionomer contained in the first layer to the total surface area of ​​the first conductive particles contained in the first layer is defined as R1, and the ratio of the total mass of the ionomer contained in the second layer to the total surface area of ​​the second conductive particles and the total surface area of ​​the conductive fibers contained in the second layer is defined as R2, |R1-R2|≦0.2 is satisfied. The catalyst layer for an electrochemical device according to claim 2 .

6. When the mode particle diameter of the first conductive particles is defined as M1, the mode particle diameter of the second conductive particles is defined as M2, the thickness of the first layer is defined as T1, and the thickness of the second layer is defined as T2, M1≧M2×T2 / T1, The catalyst layer for an electrochemical device according to claim 2 .

7. an anode; a cathode; an electrolyte membrane disposed between the anode and the cathode; Equipped with The cathode comprises the catalyst layer for an electrochemical device according to claim 1 . Membrane electrode assemblies for electrochemical devices.

8. A fuel cell comprising the membrane electrode assembly according to claim 7 . Electrochemical devices.

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