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 improving a utilization factor of catalyst particles carried by a conductive material.SOLUTION: The catalyst layer for electrochemical devices 100 of the present disclosure includes an electrically conductive porous material 11, catalyst particles 12, and an ionomer 30. When a portion including the first main surface of the catalyst layer 100 is defined as a first portion and a portion including the second main surface is defined as a second portion, at least one selected from the group consisting of the following (i) and (ii) is satisfied. (i) The total length of the contact portions between the porous material 11 and the ionomer 30 per unit area in the first part is larger than the total length of the contact portions between the porous material 11 and the ionomer 30 per unit area in the second part. (ii) The capacitance of the electric double layer formed at the interface between the porous material 11 and the ionomer 30 in the first part is larger than the capacitance of the electric double layer formed at the interface between the porous material 11 and the ionomer 30 in the second part.SELECTED DRAWING: Figure 1

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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-88008 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a catalyst layer for an electrochemical device that is suitable for improving the utilization rate of catalyst particles supported on a conductive material. [Means for solving the problem]

[0005] 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, The present invention includes a conductive porous material having pores, catalyst particles supported on the porous material, and an ionomer, When the portion including the first main surface is defined as the first portion and the portion including the second main surface is defined as the second portion, at least one selected from the group consisting of the following (i) and (ii) is satisfied: (i) In a cross section parallel to the thickness direction of the catalyst layer, the total length of the contact area between the porous material and the ionomer per unit area of ​​the first portion is greater than the total length of the contact area between the porous material and the ionomer per unit area of ​​the second portion. (ii) The capacity of the electric double layer formed at the interface between the porous material and the ionomer in the first portion is larger than the capacity of the electric double layer formed at the interface between the porous material and the ionomer in the second portion.

[0006] 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.

[0007] 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]

[0008] According to the present disclosure, in a catalyst layer for an electrochemical device, the utilization rate of catalyst particles supported on a conductive material can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic cross-sectional view showing an example of a catalyst layer in the first embodiment. [Figure 2A] A schematic cross-sectional view showing an example of an electrode catalyst contained in a catalyst layer together with an ionomer. [Figure 2B] Schematic cross-sectional view showing another example of an electrode catalyst contained in a catalyst layer together with an ionomer. [Figure 3] FIG. 10 is a schematic cross-sectional view showing another example of the catalyst layer according to the first embodiment. [Figure 4A]Schematic cross-sectional view of a membrane electrode assembly in embodiment 2. [Figure 4B] Enlarged view of part of Figure 4A [Figure 5] Schematic cross-sectional view of an electrochemical device according to a second embodiment.

[0010] (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 considered to be the smooth movement of reactants such as cations and cations within the cathode catalyst layer to 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 (for example, Patent Document 1). In the catalyst layer shown in Patent Document 1, catalyst particles are supported inside the pores of a porous conductive material that serves as a catalyst support, in order to prevent the catalyst from being poisoned and deteriorated by the ionomer.

[0011] Under these circumstances, the inventors discovered that simply making the amount of ionomer present on the electrolyte membrane side greater than the amount of ionomer present on the gas diffusion layer side causes oxygen diffusibility to decrease from the gas diffusion layer side toward the electrolyte membrane side, both in the oxygen diffusion path in the cathode catalyst layer and in the pores of the conductive material. This is thought to be because, when the amount of ionomer present on the electrolyte membrane side is simply greater than the amount of ionomer present on the gas diffusion layer side, water produced in the pores of the conductive material is more likely to be retained in the pores of the conductive material as it moves from the gas diffusion layer side toward the electrolyte membrane side.

[0012] Therefore, the inventors focused on the contact area between the conductive material and the ionomer to suppress the decrease in oxygen diffusibility on the electrolyte membrane side of the cathode catalyst layer. If the decrease in oxygen diffusibility on the electrolyte membrane side of the cathode catalyst layer can be suppressed, the utilization rate of the catalyst particles supported on the conductive material can be improved, thereby promoting the electrochemical reaction of the cathode catalyst layer. Based on these findings, the inventors have arrived at the subject matter of the present disclosure.

[0013] The present disclosure provides a catalyst layer for an electrochemical device that is suitable for improving the utilization rate of catalyst particles supported on a conductive material.

[0014] 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.

[0015] 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.

[0016] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to FIGS.

[0017] [1-1.Configuration] FIG. 1 is a schematic cross-sectional view showing an example of a catalyst layer 100 for an electrochemical device in Embodiment 1. 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. 1 is a cross-sectional view of the catalyst layer 100 parallel to the thickness direction T100. The catalyst layer 100 includes an electrode catalyst 10 and an ionomer 30.

[0018] 2A is a schematic cross-sectional view showing an example of the electrode catalyst 10 included in the catalyst layer 100, together with the ionomer 30. FIG. 2B is a schematic cross-sectional view showing another example of the electrode catalyst 10, together with the ionomer 30. The electrode catalyst 10 has a conductive porous material 11 having pores 11p and catalyst particles 12 supported on the porous material 11. An electrochemical reaction is promoted on the surface of the catalyst particles 12.

[0019] A portion of the catalyst layer 100 including the first main surface 101 is defined as a first portion 101p, and a portion of the catalyst layer 100 including the second main surface 102 is defined as a second portion 102p. In this embodiment, the catalyst layer 100 satisfies at least one selected from the group consisting of the following (i) and (ii): (i) In a cross section parallel to the thickness direction T100 of the catalyst layer 100, the total length L1 of the contact area between the porous material 11 and the ionomer 30 per unit area of ​​the first portion 101p is greater than the total length L2 of the contact area between the porous material 11 and the ionomer 30 per unit area of ​​the second portion 102p. (ii) The electric double layer capacitance Cdl1 formed at the interface between the porous material 11 and the ionomer 30 in the first portion 101p is larger than the electric double layer capacitance Cdl2 formed at the interface between the porous material 11 and the ionomer 30 in the second portion 102p.

[0020] With this configuration, when the catalyst layer 100 is used as a cathode catalyst layer of a fuel cell with the first main surface 101 disposed on the cathode gas diffusion layer side and the second main surface 102 disposed on the electrolyte membrane side, retention of produced water inside the pores 11p of the porous material 11 on the electrolyte membrane side is suppressed. This suppresses a decrease in oxygen diffusibility on the electrolyte membrane side, thereby improving the utilization rate of the catalyst particles 12 supported on the porous material 11. Furthermore, blocking of the pores 11p of the porous material 11 by the ionomer 30 is suppressed. This facilitates oxygen access to the pores 11p of the porous material 11. As a result, the electrochemical reaction in the catalyst layer 100 can be promoted.

[0021] Regarding the above requirement (i), the total length L1 of the contact portions between the porous material 11 and the ionomer 30 per unit area of ​​the first portion 101p in a cross section parallel to the thickness direction T100 of the catalyst layer 100 can be determined, for example, from a cross-sectional image parallel to the thickness direction T100 of the catalyst layer 100 obtained using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). The TEM may be a 3D-TEM. The SEM may be a 3D-SEM. However, the cross-sectional image includes any range of the first portion 101p. Similarly, the total length L2 of the contact portions between the porous material 11 and the ionomer 30 per unit area of ​​the second portion 102p in a cross section parallel to the thickness direction T100 of the catalyst layer 100 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. However, the cross-sectional image includes any range of the second portion 102p.

[0022] Regarding the above requirement (i), the ratio of L2 to L1 (L2 / L1) 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 L2 to L1 may be 0.5 or less. The lower limit of the ratio of L2 to L1 is, for example, 0.1 or more. The lower limit of the ratio of L2 to L1 may be 0.2 or more, or 0.3 or more.

[0023] Regarding the above requirement (ii), the electric double layer capacitance Cdl1 formed at the interface between the porous material 11 and the ionomer 30 in the first portion 101p can be determined by measuring the electric double layer capacitance Cdl of the first portion 101p of the catalyst layer 100 under low humidity conditions, for example, a relative humidity of 20%. Similarly, the electric double layer capacitance Cdl2 formed at the interface between the porous material 11 and the ionomer 30 in the second portion 102p can be determined by measuring the electric double layer capacitance Cdl of the second portion 102p of the catalyst layer 100 under low humidity conditions, for example, a relative humidity of 20%. The electric double layer capacitance can be used. When measuring the electric double layer capacitance by electrochemical impedance spectroscopy, for example, an electrochemical measurement system HZ-7000 manufactured by Hokuto Denko Corporation can be used as the measurement device. The measurement conditions shown in Table 1 can be used.

[0024] [Table 1]

[0025] Regarding the above requirement (ii), the ratio of Cdl2 to Cdl1 (Cdl2 / Cdl1) 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 Cdl2 to Cdl1 may be 0.5 or less. The lower limit of the ratio of Cdl2 to Cdl1 is, for example, 0.1 or more. The lower limit of the ratio of Cdl2 to Cdl1 may be 0.2 or more, or 0.3 or more.

[0026] The electric double layer capacitance Cdl is proportional to the area of ​​the electrochemically effective interface. Therefore, when the porous material 11 contained in the first portion 101p and the porous material 11 contained in the second portion 102p are the same material, and the ionomer 30 contained in the first portion 101p and the ionomer 30 contained in the second portion 102p are the same material, the electric double layer capacitance Cdl1 being larger than the electric double layer capacitance Cdl2, i.e., satisfying the above requirement (ii), can be considered to be synonymous with satisfying the above requirement (i).

[0027] 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. The catalyst layer 100 having such a configuration is suitable for improving the utilization rate of the catalyst particles 12 supported on the porous material 11.

[0028] The catalyst layer 100 may satisfy at least one selected from the group consisting of the following (I) and (II). (I) In a cross section parallel to the thickness direction T100 of the catalyst layer 100, the total length L11 of the contact area between the porous material 11 and the ionomer 30 per unit area of ​​the first layer 100a is greater than the total length L12 of the contact area between the porous material 11 and the ionomer 30 per unit area of ​​the second layer 100b. (II) Electric double layer capacitance Cdl formed at the interface between the porous material 11 and the ionomer 30 in the first layer 100a 11 However, the capacitance of the electric double layer Cdl formed at the interface between the porous material 11 and the ionomer 30 in the second layer 100b is 12 is greater than.

[0029] Regarding the above requirement (I), the total length L11 of the contact area between the porous material 11 and the ionomer 30 per unit area of ​​the first layer 100a in a cross section parallel to the thickness direction T100 of the catalyst layer 100 and the total length L12 of the contact area between the porous material 11 and the ionomer 30 per unit area of ​​the second layer 100b can be determined by the same method as described regarding the above requirement (i).

[0030] Regarding the above requirement (II), the capacitance Cdl of the electric double layer formed at the interface between the porous material 11 and the ionomer 30 in the first layer 100a 11 and the capacitance Cdl of the electric double layer formed at the interface between the porous material 11 and the ionomer 30 in the second layer 100b. 12 can be determined by the same method as described above with respect to requirement (ii).

[0031] In the catalyst layer 100, the first layer 100a and the second layer 100b are electrically connected to each other. With this configuration, the above-mentioned effect can be easily obtained. That is, the utilization rate of the catalyst particles 12 supported on the porous material 11 can be easily improved.

[0032] 1, 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 not be another layer between the first layer 100a and the second layer 100b.

[0033] The ratio T1 of the thickness of the first layer 100a to the thickness of the catalyst layer 100 may be approximately the same as the ratio T2 of the thickness of the second layer 100b to the thickness of the catalyst layer 100. This configuration tends to make it easier to achieve the above-mentioned effect. That is, it is easier to improve the utilization rate of the catalyst particles 12 supported on the porous material 11.

[0034] The ratio T1 of the thickness of the first layer 100a to the thickness of the catalyst layer 100 may be 50% or less. With such a structure, the ratio T1 of the thickness of the first layer 100a is large, so that an increase in the oxygen diffusion resistance in the catalyst layer 100 can be suppressed.

[0035] The thickness 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 thickness of the first layer 100a is measured for the multiple cross-sectional images obtained. In the catalyst layer 100 of this embodiment, the boundary between the first layer 100a and the second layer 100b can be recognized by using a TEM or SEM. The average of the measured values ​​is considered to be the thickness of the first layer 100a. The thickness of the second layer 100b can be determined in a similar manner.

[0036] The thickness of the first layer 100a is, for example, not less than 2.5 μm and not more than 20 μm.

[0037] The thickness of the second layer 100b is, for example, not less than 5 μm and not more than 20 μm.

[0038] In a cross section parallel to the thickness direction T100 of the catalyst layer 100, the ratio A23 of the area occupied by the ionomer 30 to the area of ​​the second layer 100b may be equal to or smaller than the ratio A13 of the area occupied by the ionomer 30 to the area of ​​the first layer 100a. That is, A23≦A13 may be satisfied. Such a configuration makes it easier to achieve the above-described effects. That is, it makes it easier to improve the utilization rate of the catalyst particles 12 supported on the porous material 11.

[0039] When A23≦A13 is satisfied, the ratio of A23 to A13 (A23:A13) is, for example, within the range of 50:50 to 20:80.

[0040] In the catalyst layer 100, it can be confirmed that the proportion A23 is the same as or smaller than the proportion A13, for example, by observing a cross-sectional image parallel to the thickness direction T100 of the catalyst layer 100 obtained using a TEM or SEM.

[0041] In the example shown in FIG. 1, A23 and A13 satisfy A23≦A13. However, the relationship between A23 and A13 is not limited to the example shown in FIG. 1. FIG. 3 is a schematic cross-sectional view showing another example of the catalyst layer 100 according to the first embodiment. In the catalyst layer 100A shown in FIG. 3, the ratio A23 of the area occupied by the ionomer 30 to the area of ​​the second layer 100b is larger than the ratio A13 of the area occupied by the ionomer 30 to the area of ​​the first layer 100a. As shown in FIG. 3, in the catalyst layer 100, A23 may be larger than A13. That is, A23>A13 may be satisfied. With this configuration, the diffusibility of oxygen inside the pores 11p of the porous material 11 is improved, thereby further improving the utilization rate of the catalyst particles 12 supported on the porous material 11.

[0042] When A23>A13 is satisfied, the ratio of A23 to A13 (A23:A13) is, for example, within the range of 60:40 to 80:20.

[0043] The ratio W23 of the mass of the ionomer 30 contained in the second layer 100b to the mass of the second layer 100b may be equal to or smaller than the ratio W13 of the mass of the ionomer 30 contained in the first layer 100a to the mass of the first layer 100a. That is, W23≦W13 may be satisfied. Such a configuration makes it easier to achieve the above-described effects. That is, it makes it easier to improve the utilization rate of the catalyst particles 12 supported on the porous material 11.

[0044] When W23≦W13 is satisfied, the ratio of W23 to W13 (W23:W13) is, for example, within the range of 50:50 to 20:80.

[0045] Whether the proportion W23 in the catalyst layer 100 is equal to or smaller than the proportion W13 can be confirmed, for example, by the following method. First, the first layer 100a and the second layer 100b are separated from the catalyst layer 100. Next, the ionomer 30 is removed from each of the first layer 100a and the second layer 100b using a solvent, and the weight change is measured by thermal analysis or the like. The proportions W23 and W13 can be calculated based on the measured values.

[0046] The ratio W23 of the mass of the ionomer 30 contained in the second layer 100b to the mass of the second layer 100b may be greater than the ratio W13 of the mass of the ionomer 30 contained in the first layer 100a to the mass of the first layer 100a. That is, W23 > W13 may be satisfied. With this configuration, the diffusibility of oxygen inside the pores 11p of the porous material 11 is improved, thereby further improving the utilization rate of the catalyst particles 12 supported on the porous material 11.

[0047] When W23>W13 is satisfied, the ratio of W23 to W13 (W23:W13) is, for example, within the range of 60:40 to 80:20.

[0048] (electrode catalyst) 2A and 2B, in the electrode catalyst 10, the pores 11p are open to the surface of the porous material 11. In other words, the surface of the porous material 11 has irregularities. The pores 11p may be interconnected pores or closed pores.

[0049] The catalyst particles 12 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 catalyst particles 12 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. Each of the catalyst particles 12 may contain at least one precious metal selected from the group consisting of platinum, palladium, iridium, ruthenium, and rhodium.

[0050] The platinum content in the catalyst particles 12 may be 30% by weight or more and 90% by weight or less, and the other metal (for example, cobalt) content may be 1% by weight or more and 50% by weight or less.

[0051] The average particle diameter of the catalyst particles 12 is not particularly limited. From the viewpoints of catalyst utilization rate and durability, the average particle diameter of the catalyst particles 12 is preferably 1 nm or more and 30 nm or less. The average particle diameter of the catalyst particles 12 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 diameter of an arbitrary number (for example, 10) of catalyst particles 12 is measured. The average value of the equivalent diameters can be considered as the average particle diameter. The equivalent diameter means the diameter of a circle having the same area.

[0052] In this embodiment, the catalyst particles 12 are noble metal nanoparticles.

[0053] The porous material 11 is a conductive material such as carbon particles, and supports catalyst particles 12. Examples of carbon particles include particles of carbon black such as furnace black and acetylene black. The porous material 11 may contain at least one selected from the group consisting of furnace black, acetylene black, and thermal black. Furnace black includes those using petroleum-based hydrocarbons or coal-based hydrocarbons as raw materials, and gas furnace black using natural gas as raw material.

[0054] For example, porous carbon having an average particle diameter of 200 nm or more can be used as the porous material 11. An example of such porous carbon is Knobel (registered trademark) manufactured by Toyo Tanso Co., Ltd. The upper limit of the average particle diameter of the porous material 11 is, for example, 1000 nm.

[0055] The average particle diameter of the porous material 11 can be determined from a cross-sectional image of the catalyst layer 100 obtained using, for example, a TEM or SEM. In the cross-sectional image, the equivalent diameter of an arbitrary number (for example, 10) of porous materials 11 is measured. The average value of the equivalent diameters can be considered as the average particle diameter of the porous material 11. The equivalent diameter means the diameter of a circle having the same area.

[0056] In the present embodiment, the porous material 11 contained in the second layer 100b may have higher hydrophobicity than the porous material 11 contained in the first layer 100a. With this configuration, the ionomer 30 is more easily adsorbed to the porous material 11 contained in the first layer 100a than to the porous material 11 contained in the second layer 100b. Therefore, at least one selected from the group consisting of (i) and (ii) above is likely to be satisfied. Furthermore, at least one selected from the group consisting of (I) and (II) above is likely to be satisfied.

[0057] In the catalyst layer 100, the porous material 11 contained in the second layer 100b has higher hydrophobicity than the porous material 11 contained in the first layer 100a, which can be confirmed, for example, by comparing the BET specific surface areas determined by a water vapor adsorption method. Specifically, this can be confirmed by the following method. First, the first layer 100a and the second layer 100b are separated from the catalyst layer 100. Next, the porous material 11 is extracted from each of the first layer 100a and the second layer 100b using a solvent. For each of the porous material 11 contained in the first layer 100a and the porous material 11 contained in the second layer 100b, the BET specific surface area is determined by converting the adsorption isotherm data obtained by an adsorption method using water vapor at a temperature of 298 K using the Brunauer-Emmett-Teller (BET) method. When the BET specific surface area Sp2 of the porous material 11 contained in the second layer 100b is larger than the BET specific surface area Sp1 of the porous material 11 contained in the first layer 100a, it can be determined that the porous material 11 contained in the second layer 100b has higher hydrophobicity than the porous material 11 contained in the first layer 100a.

[0058] The ratio (Sp2 / Sp1) of the BET specific surface area Sp2 of the porous material 11 contained in the second layer 100b to the BET specific surface area Sp1 of the porous material 11 contained in the first layer 100a may be in the range of 1.1 to 5.0.

[0059] For example, the hydrophobicity of the porous material 11 can be improved by subjecting the porous material 11 to a hydrophobic treatment before or after supporting the catalyst particles 12. For example, the hydrophobic treatment of the porous material 11 can be performed by heat treating the porous material 11 in a reducing atmosphere before or after supporting the catalyst particles 12.

[0060] The ionomer 30 connects the catalyst particles 12 and the porous material 11 in a proton-conductive state.

[0061] In the electrode catalyst 10, the ionomer 30 may cover a portion of the surface of the porous material 11, or may cover the entire surface of the porous material 11. In the example shown in Fig. 2A, the ionomer 30 covers the entire surface of the porous material 11. In the example shown in Fig. 2B, the ionomer 30 covers a portion of the surface of the porous material 11.

[0062] The electrode catalyst 10 included in the first layer 100a may have a configuration similar to the electrode catalyst 10 shown in FIG. 2A. The electrode catalyst 10 included in the second layer 100b may have a configuration similar to the electrode catalyst 10 shown in FIG. 2B. By doing so, at least one selected from the group consisting of (i) and (ii) above is likely to be satisfied. Furthermore, at least one selected from the group consisting of (I) and (II) above is likely to be satisfied.

[0063] However, the configurations of the electrode catalyst 10 and the ionomer 30 are not limited to the examples shown in FIGS. 2A and 2B.

[0064] The ionomer 30 may be a polymer electrolyte resin having ion conductivity. The ionomer 30 may have sulfonic acid groups. The ionomer 30 may be a perfluorocarbon sulfonic acid-based polymer material having sulfonic acid groups, a hydrocarbon-based polymer material, or the like. The ionomer 30 may be a perfluorosulfonic acid resin. The perfluorosulfonic acid resin exhibits excellent proton conductivity and remains stable even in the power generation environment of an electrochemical device. The ionomer 30 typically includes a perfluorocarbon sulfonic acid-based polymer electrolyte having sulfonic acid groups. When the sulfur element contained in the sulfonic acid groups is adsorbed to the precious metal contained in the catalyst particles 12, catalytic activity is inhibited, resulting in so-called catalyst poisoning.

[0065] The ionomer 30 may be made of the same material as the electrolyte membrane, which will be described later.

[0066] Although not shown, the catalyst layer 100 may further include a fibrous conductive material. An ionomer 30 may be attached to the surface of the fibrous conductive material. With this configuration, for example, in the first layer 100a, the ionomer 30 attached to the surface of the porous material 11 and the ionomer 30 attached to the surface of the fibrous conductive material are likely to bond together. For example, in the second layer 100b, the ionomer 30 attached to the surface of the porous material 11 and the ionomer 30 attached to the surface of the fibrous conductive material are likely to bond together. This can further improve the proton conductivity of the catalyst layer 100.

[0067] Next, we will explain a method for manufacturing the above-mentioned catalyst layer 100. The method for manufacturing the catalyst layer 100 includes, for example, producing the electrode catalyst 10 (step S1), preparing a first catalyst solution and a second catalyst solution (step S2), and producing the first layer 100a and the second layer 100b (step S3).

[0068] In step S1, the electrode catalyst 10 is produced. Specifically, catalyst particles 12 are supported on a porous material 11.

[0069] In step S1, the method for supporting the catalyst particles 12 on the porous material 11 is not particularly limited. For example, the catalyst particles 12 can be supported on the porous material 11 using methods such as impregnation-reduction pyrolysis, chemical reduction, gas-phase reduction, surface-modified colloid-reduction pyrolysis, and nanocapsules. The impregnation-reduction pyrolysis method involves dispersing the porous material in a solution such as HO or CHOH, adding a metal precursor solution such as a platinum precursor, filtering, drying, and then heat-treating the resulting solution. The chemical reduction method involves adding a metal precursor solution to the solution containing the dispersed porous material, boiling it, and then adding a reducing agent. The gas-phase reduction method is also known as the sulfite complex method. This method involves reacting HPtCl with sodium hydrogen sulfite (NaHSO) to prepare a sulfite complex (HPt(SO)CH), which is then oxidized and decomposed with hydrogen peroxide (HO) to produce a colloidal oxide (PtO), which is then reduced with hydrogen bubbles to obtain catalyst particles. The surface-modified colloid-reduction pyrolysis method involves preparing colloidal PtRu using tetraoctyanium monium borate as both a reducing agent and a surface modifier, then preparing colloidal PtRu using trimethylaluminum (Al(CH3)3) as a reducing agent and polyethylene glycol dodecyl ether as a surfactant, and using the resulting PtRu colloid as catalyst particles.

[0070] Before step S1, a hydrophobized porous material 11 may be prepared (step S0). Step S0 may be used to control the degree of adsorption of the ionomer 30 onto the porous material 11 in step S2, which will be described later. For example, step S0 may be used to make the ionomer 30 less likely to be adsorbed onto the hydrophobized porous material 11 than onto the porous material 11 that has not been subjected to the hydrophobization treatment.

[0071] 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. The catalyst solutions contain, for example, water and a solvent. The solvent may be, for example, ethanol.

[0072] For example, a first solution can be obtained by adding an electrode catalyst 10A, which is made by supporting catalyst particles 12 on a porous material 11 that has not been subjected to a hydrophobic treatment, to a solvent. The solvent may contain, for example, ethanol and water. Next, an ionomer 30 is added to the first solution and stirred. This results in a first catalyst solution.

[0073] For example, the second solution can be obtained by adding the electrode catalyst 10B, which is formed by supporting catalyst particles 12 on a hydrophobized porous material 11, to a solvent. Next, the ionomer 30 is added to the second solution and stirred. This results in a second catalyst solution. For example, the amount of ionomer 30 adhering to the porous material 11 in the second catalyst solution is less than the amount of ionomer 30 adhering to the porous material 11 in the first catalyst medium.

[0074] Note that instead of step S0, in step S2, the polarity of the first catalyst solution may be made different from the polarity of the second catalyst solution, for example, by changing the content ratio of water to solvent in the catalyst solution. For example, the polarity of the first catalyst solution may be made different from the polarity of the second catalyst solution by changing the type of solvent. By using such a substep, the amount of ionomer 30 adsorbed to the porous material 11 in the second catalyst solution may be made smaller than the amount of ionomer 30 adsorbed to the porous material 11 in the first catalyst medium.

[0075] In step S3, the first layer 100a and the second layer 100b are fabricated.

[0076] For example, the first layer 100a and the second layer 100b can be produced as follows: A first catalyst solution is applied to one surface of the 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 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. The first layer 100a and the second layer 100b are bonded together to form the catalyst layer 100 between the gas diffusion layer and the electrolyte membrane.

[0077] 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.

[0078] Furthermore, 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.

[0079] 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.

[0080] [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.

[0081] (Embodiment 2) Hereinafter, the second embodiment will be described with reference to FIGS. 5A to 6. FIG.

[0082] [2-1.Configuration] Fig. 4A is a schematic cross-sectional view of a membrane electrode assembly 200 for an electrochemical device in accordance with Embodiment 2. Fig. 4B is a partial enlarged view of portion IVB in Fig. 4A. Fig. 5 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, a cathode separator 302, and a power source 307. The membrane electrode assembly 200 is disposed between the anode separator 301 and the cathode separator 302.

[0083] 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.

[0084] 5, 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.

[0085] 4A, 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.

[0086] 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.

[0087] 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.

[0088] 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. These surfaces are flat. A flat surface of the electrolyte membrane 201 allows for good drainage on the surface of the electrolyte membrane 201. The "flat surface" means a surface that has not been processed to provide irregularities.

[0089] 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.

[0090] The membrane electrode assembly 200 may include the catalyst layer 100 described in the first embodiment as the anode catalyst layer 204 .

[0091] 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.

[0092] 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.

[0093] 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. 4B 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. 4B, 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. This configuration can suppress a decrease in oxygen diffusibility on the electrolyte membrane 201 side of the cathode catalyst layer 206, thereby improving the utilization rate of the catalyst particles 12 supported on the porous material 11. As a result, the electrochemical reaction in the catalyst layer 100 can be promoted. This can improve the power generation performance of an electrochemical device 300 using the membrane electrode assembly 200.

[0094] 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.

[0095] The anode catalyst layer 204 may have the same structure as the cathode catalyst layer 206, or may have a different structure.

[0096] As shown in Fig. 5, 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] [2-2. Operation] The operation and function of the electrochemical device 300 configured as above will be described below with reference to FIG.

[0101] 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 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 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. A current is applied by a power source 307 between the anode catalyst layer 204 to which the hydrogen-containing gas G1 has been supplied and the cathode catalyst layer 206 to which the oxygen-containing gas G3 has been supplied.

[0102] 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 toward the cathode 203 through an external circuit (not shown) 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.

[0103] H2→2H + +2e - (I) 4H + +O2+2e - →2H2O (II)

[0104] In the electrochemical device 300, the retention of produced water inside the pores 11p of the porous material 11 on the electrolyte membrane 201 side of the cathode catalyst layer 206 is suppressed. This suppresses a decrease in oxygen diffusibility on the electrolyte membrane 201 side of the cathode catalyst layer 206, thereby improving the utilization rate of the catalyst particles 12 supported on the porous material 11. As a result, the electrochemical reaction in the cathode catalyst layer 206 is promoted.

[0105] (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.

[0106] 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.

[0107] (Addendum) The above description of the embodiments discloses the following techniques.

[0108] (Technology 1) A catalyst layer having a first major surface and a second major surface, The present invention includes a conductive porous material having pores, catalyst particles supported on the porous material, and an ionomer, 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, at least one selected from the group consisting of the following (i) and (ii) is satisfied: Catalyst layers for electrochemical devices. (i) In a cross section parallel to the thickness direction of the catalyst layer, the total length of the contact area between the porous material and the ionomer per unit area of ​​the first portion is greater than the total length of the contact area between the porous material and the ionomer per unit area of ​​the second portion. (ii) The capacity of the electric double layer formed at the interface between the porous material and the ionomer in the first portion is larger than the capacity of the electric double layer formed at the interface between the porous material and the ionomer in the second portion.

[0109] According to the catalyst layer for electrochemical devices of Technique 1, the utilization rate of catalyst particles supported on the porous material can be improved.

[0110] (Technology 2) The catalyst layer for an electrochemical device according to Technical Problem 1 includes a first layer including the first portion and a second layer including the second portion. A catalyst layer having such a configuration is suitable for improving the utilization rate of catalyst particles supported on a porous material.

[0111] (Technology 3) The catalyst layer for an electrochemical device according to Technical Problem 2, wherein the first layer and the second layer are in electrical contact with each other. Such a configuration makes it easy to improve the utilization rate of catalyst particles supported on the porous material.

[0112] (Technology 4) The catalyst layer for electrochemical devices according to technique 2 or 3, wherein in a cross section parallel to the thickness direction of the catalyst layer, the ratio of the area occupied by the ionomer to the area of ​​the second layer is equal to or smaller than the ratio of the area occupied by the ionomer to the area of ​​the first layer. Such a configuration makes it easy to improve the utilization rate of catalyst particles supported on the porous material.

[0113] (Technology 5) The catalyst layer for an electrochemical device according to any one of techniques 2 to 4, wherein the porous material contained in the second layer has higher hydrophobicity than the porous material contained in the first layer. With this configuration, the ionomer is more easily adsorbed to the porous material contained in the first layer than to the porous material contained in the second layer.

[0114] (Technology 6) 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 5. Membrane electrode assemblies for electrochemical devices.

[0115] According to the membrane electrode assembly for electrochemical devices of Technique 6, it is possible to improve the power generation performance of an electrochemical device using the membrane electrode assembly.

[0116] (Technology 7) The membrane electrode assembly according to claim 6 is provided. Electrochemical devices.

[0117] According to the electrochemical device of Technology 7, a highly efficient electrochemical device with high power generation performance can be realized. [Industrial Applicability]

[0118] The present disclosure is useful for electrochemical devices such as fuel cells, hydrogen purification devices, and water electrolysis devices. [Explanation of symbols]

[0119] 100, 100A 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 Electrocatalyst 11 Porous materials 11p pore 12 Catalyst particles 30 Ionomer 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 307 Power supply

Claims

1. A catalyst layer having a first major surface and a second major surface, The present invention includes a conductive porous material having pores, catalyst particles supported on the porous material, and an ionomer, 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, at least one selected from the group consisting of the following (i) and (ii) is satisfied: Catalyst layers for electrochemical devices. (i) In a cross section parallel to the thickness direction of the catalyst layer, the total length of the contact area between the porous material and the ionomer per unit area of ​​the first portion is greater than the total length of the contact area between the porous material and the ionomer per unit area of ​​the second portion. (ii) The electric double layer capacitance formed at the interface between the porous material and the ionomer in the first portion is larger than the electric double layer capacitance formed at the interface between the porous material and the ionomer in the second portion.

2. a first layer including the first portion and a second layer including the second portion, 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. In a cross section parallel to the thickness direction of the catalyst layer, the ratio of the area occupied by the ionomer to the area of ​​the second layer is equal to or smaller than the ratio of the area occupied by the ionomer to the area of ​​the first layer. The catalyst layer for an electrochemical device according to claim 2 .

5. The porous material contained in the second layer has a higher hydrophobicity than the porous material contained in the first layer. The catalyst layer for an electrochemical device according to claim 2 .

6. 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.

7. A fuel cell comprising the membrane electrode assembly according to claim 6 . Electrochemical devices.

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