Electrode catalyst layer for fuel cells

Abstract

The present invention provides an electrode catalyst layer for fuel cells that exhibits high power generation performance not only in the initial stages but also after long-term operation. [Solution] A fuel cell electrode catalyst layer is provided, having a two-layer structure comprising a first electrode catalyst layer disposed on the surface of an electrolyte membrane and a second electrode catalyst layer disposed on the surface of the first electrode catalyst layer and facing a gas diffusion layer, wherein the mass ratio of ionomer to carbon support in the gas inlet / outlet region of the first electrode catalyst layer is greater than or equal to a predetermined value, the mass ratio of ionomer to carbon support in the gas inlet / outlet region of the second electrode catalyst layer is less than or equal to a predetermined value, and the average value of the mass ratio of ionomer to carbon support in the gas inlet region of the first electrode catalyst layer and the second electrode catalyst layer, and the average value of the mass ratio of ionomer to carbon support in the gas outlet region of the first electrode catalyst layer and the second electrode catalyst layer are within a predetermined range.

Description

[Technical Field]

[0001] This invention relates to an electrode catalyst layer for fuel cells. [Background technology]

[0002] Fuel cells generate electricity by electrochemically reacting hydrogen and oxygen. In principle, the only byproduct of fuel cell power generation is water. Therefore, they are attracting attention as a clean power generation system with virtually no burden on the global environment. A fuel cell is constructed using a membrane electrode assembly (hereinafter also referred to as "MEA") as its basic unit, in which catalyst layers are arranged on both sides of an electrolyte membrane, and a gas diffusion layer is further arranged outside each catalyst layer. The binder for the electrolyte membrane and catalyst layers is usually a polymer electrolyte (hereinafter also referred to as "ionomer") having ion exchange groups. During fuel cell operation, an electromotive force is obtained by supplying a fuel gas containing hydrogen to the catalyst layer on the anode (fuel electrode) side, and an oxidizing gas containing oxygen to the catalyst layer on the cathode (air electrode) side. At the anode, the oxidation reaction of hydrogen proceeds, and at the cathode, the reduction reaction of oxygen proceeds, supplying electromotive force to the external circuit. Various catalyst layers and their manufacturing methods that can be used in fuel cells have been developed.

[0003] For example, Patent Document 1 describes a membrane electrode assembly for a fuel cell in which an anode electrode containing an anode catalyst layer is provided on one side of a solid polymer electrolyte membrane, and a cathode electrode containing a cathode catalyst layer is provided on the other side, wherein the cathode catalyst layer contains catalyst particles and a polymer electrolyte, and the ratio of the mass Wp of the polymer electrolyte to the mass Wcat of the catalyst particles per unit volume (Wp / Wcat) has a thickness-direction distribution of this ratio (Wp / Wcat) that decreases from the side closer to the solid polymer electrolyte membrane to the side further away in a continuous region corresponding to 50% or more of the cathode-side gas flow path length, and the ratio (Wp / Wcat) decreases from the side closer to the solid polymer electrolyte membrane to the side further away in the thickness direction of the cathode catalyst layer The present invention describes a membrane electrode assembly for a fuel cell, characterized in that, by multiplying, a change point a is selected that decreases from a predetermined first value to a second value, and the interface A obtained by connecting each change point a present in the planar direction of the cathode catalyst layer approaches the solid polymer electrolyte membrane or maintains an equidistant distance from the solid polymer electrolyte membrane from the upstream side to the downstream side in the cathode gas flow direction, regardless of which change point a is selected, and the interface A' obtained by connecting at least one change point a' among the change points a in the cathode catalyst layer in the planar direction has a planar distribution of the ratio (Wp / Wcat) such that it approaches the solid polymer electrolyte membrane from the upstream side to the downstream side in the cathode gas flow direction. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-26539 [Overview of the project] [Problems that the invention aims to solve]

[0005] As mentioned above, water is generated during the operation of a fuel cell. In such a water-containing environment, if a carbon support is used in the cathode electrode catalyst layer of a fuel cell, the carbon support is oxidized and shrinks. When the carbon support shrinks in the cathode electrode catalyst layer, the voids in the carbon support necessary for oxygen gas diffusion become blocked, leading to a problem of reduced power generation performance.

[0006] To address these problems, technologies have been proposed, such as using highly crystalline carbon supports that are resistant to oxidation in order to pre-secure the voids required after long-term operation, and using a combination of multiple carbons to maintain the carbon support's framework. However, all of these technologies suffered from the problem of low initial power generation performance.

[0007] Furthermore, from the perspective of securing the voids necessary after long-term operation, it is preferable to use a smaller amount of ionomer, which plays a role in retaining moisture in the electrode catalyst layer. For this reason, reducing the mass ratio of ionomer to carbon support can contribute to improving power generation performance after long-term operation. However, such technologies have the problem of low initial power generation performance, especially during high-temperature operation.

[0008] Therefore, the present invention aims to provide an electrode catalyst layer for fuel cells that has high power generation performance not only in the initial stages but also after long-term operation. [Means for solving the problem]

[0009] The inventors have investigated various means to solve the above problems. The inventors have found that an electrode catalyst layer for a fuel cell having a carbon support bearing a catalyst metal and an ionomer has a two-layer structure comprising a first electrode catalyst layer disposed on the surface of the electrolyte membrane and a second electrode catalyst layer disposed on the surface of the first electrode catalyst layer and facing the gas diffusion layer, and the first electrode catalyst layer and the second electrode catalyst layer are configured to consist of a gas inlet side region and a gas outlet side region, and furthermore the mass ratio of the ionomer to the carbon support in the gas inlet side region of the first electrode catalyst layer and the mass ratio of the ionomer to the carbon support in the gas outlet side region of the first electrode catalyst layer are set to be greater than or equal to a predetermined value, and the gas inlet side region of the second electrode catalyst layer By setting the mass ratio of ionomer to carbon support in the first electrode catalyst layer and the mass ratio of ionomer to carbon support in the gas outlet region of the second electrode catalyst layer to a predetermined value or less, and by setting the average value of the mass ratio of ionomer to carbon support in the gas inlet region of the first electrode catalyst layer and the gas inlet region of the second electrode catalyst layer, and the average value of the mass ratio of ionomer to carbon support in the gas outlet region of the first electrode catalyst layer and the gas outlet region of the second electrode catalyst layer, to values ​​within a predetermined range, it was found that not only is the initial voltage of the resulting fuel cell improved, but the decrease in voltage after durability treatment is also suppressed. Based on the above findings, the inventors completed the present invention.

[0010] In other words, the present invention encompasses the following aspects and embodiments. (Embodiment 1) A fuel cell electrode catalyst layer comprising at least a substrate, a carbon support disposed on the surface of the substrate, a catalyst metal supported on the carbon support, and an ionomer disposed on the surface and in the voids of the support, The electrode catalyst layer for the fuel cell comprises a first electrode catalyst layer m disposed on the surface of the electrolyte membrane, and a second electrode catalyst layer g disposed on the surface of the first electrode catalyst layer m and facing the gas diffusion layer. The first electrode catalyst layer m consists of a gas inflow region ma and a gas outflow region mb. The second electrode catalyst layer g consists of a gas inlet region ga and a gas outlet region gb. The actual porosity is defined as the percentage of the volume of voids without ionomer relative to the total void volume of the carbon support, and the mass ratio of ionomer to carbon support when the actual porosity is 10% is defined as I / C0. If the mass ratio of ionomer to carbon support in region ma on the gas inlet side of the first electrode catalyst layer is I / Cma and the thickness of region ma is Tma, and the mass ratio of ionomer to carbon support in region ga on the gas inlet side of the second electrode catalyst layer is I / Cga and the thickness of region ga is Tga, then I / Cma is in the range of 1.0 to 1.5 times I / C0. I / Cga is in the range of 0.6 to 1.0 times I / C0. If the mass ratio of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is I / Cmb, and the thickness of the gas outlet region mb is Tmb, and the mass ratio of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is I / Cgb, and the thickness of the gas outlet region gb is Tgb, then, I / Cmb is in the range of 1.0 to 1.5 times I / C0. I / Cgb is in the range of 0.6 to 1.0 times I / C0. Let I / Cava be the average mass ratio of ionomer to carbon support in the gas inlet region ma of the first electrode catalyst layer and the gas inlet region ga of the second electrode catalyst layer, and let I / Cavb be the average mass ratio of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer and the gas outlet region gb of the second electrode catalyst layer. I / Cava is defined as I / Cava = I / Cma × Tma / (Tma + Tga) + I / Cga × Tga / (Tma + Tga), and is in the range of 0.75 to 1.1 times I / C0. I / Cavb is defined as I / Cavb = I / Cmb × Tmb / (Tmb + Tgb) + I / Cgb × Tgb / (Tmb + Tgb), and is in the range of 0.65 to 1.0 times I / C0. The aforementioned electrode catalyst layer for fuel cell. (Embodiment 2) The ratio Tga / Tma of the thickness Tga of the gas inlet-side region of the second electrode catalyst layer to the thickness Tma of the gas inlet-side region of the first electrode catalyst layer, and The electrode catalyst layer for a fuel cell according to Embodiment 1, wherein the ratio Tgb / Tmb, which is the thickness Tgb of the gas outlet side region of the second electrode catalyst layer and the thickness Tmb of the gas outlet side region of the first electrode catalyst layer, is in the range of 0.9 to 7. (Embodiment 3) The ratio Tga / Tma of the thickness Tga of the gas inlet-side region of the second electrode catalyst layer to the thickness Tma of the gas inlet-side region of the first electrode catalyst layer is in the range of 0.9 to 1.1, and The electrode catalyst layer for a fuel cell according to Embodiment 2, wherein the ratio Tgb / Tmb, which is the thickness Tgb of the gas outlet side region of the second electrode catalyst layer to the thickness Tmb of the gas outlet side region of the first electrode catalyst layer, is in the range of 2 to 7. (Embodiment 4) When I / C0 is in the range of 1.0 to 1.2, The thickness Tma of the gas inflow side region of the first electrode catalyst layer is in the range of 1.7 to 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is in the range of 5 to 8.3 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is in the range of 1.2 to 1.4. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is in the range of 0.8 to 1. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is in the range of 1.7 to 5 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is in the range of 5 to 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is in the range of 1.2 to 1.4. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is in the range of 0.8 to 1. An electrode catalyst layer for a fuel cell according to any one of Embodiments 1 to 3. (Embodiment 5) When I / C0 is 1.1, (1) The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 5 μm, The thickness Tga of the gas inflow side region of the second electrode catalyst layer is 5 μm, The mass ratio I / Cma of the ionomer to the carbon carrier in the gas inflow side region ma of the first electrode catalyst layer is 1.2, The mass ratio I / Cga of the ionomer to the carbon carrier in the gas inflow side region ga of the second electrode catalyst layer is 0.8, The thickness Tmb of the gas outflow side region mb of the first electrode catalyst layer is 1.7 μm, The thickness Tgb of the gas outflow side region gb of the second electrode catalyst layer is 8.3 μm, The mass ratio I / Cmb of the ionomer to the carbon carrier in the gas outflow side region mb of the first electrode catalyst layer is 1.4, The mass ratio I / Cgb of the ionomer to the carbon carrier in the gas outflow side region gb of the second electrode catalyst layer is 0.8, or (2) The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 1.7 μm, The thickness Tga of the gas inflow side region of the second electrode catalyst layer is 8.3 μm, The mass ratio I / Cma of the ionomer to the carbon carrier in the gas inflow side region ma of the first electrode catalyst layer is 1.4, The mass ratio I / Cga of the ionomer to the carbon carrier in the gas inflow side region ga of the second electrode catalyst layer is 0.8, The thickness Tmb of the gas outflow side region mb of the first electrode catalyst layer is 5 μm, The thickness Tgb of the gas outflow side region gb of the second electrode catalyst layer is 5 μm, The mass ratio I / Cmb of the ionomer to the carbon carrier in the gas outflow side region mb of the first electrode catalyst layer is 1.2, The mass ratio I / Cgb of the ionomer to the carbon carrier in the gas outflow side region gb of the second electrode catalyst layer is 0.8, or (3) The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 5 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.4. In the gas inflow region ga of the second electrode catalyst layer, the mass ratio I / Cga of the ionomer to the carbon support is 1. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 1.7 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.4. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is 1. An electrode catalyst layer for a fuel cell according to any one of Embodiments 1 to 4. [Effects of the Invention]

[0011] The present invention makes it possible to provide an electrode catalyst layer for fuel cells that has high power generation performance not only in the initial stages but also after long-term operation. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing one embodiment of an electrode catalyst layer for a fuel cell according to one aspect of the present invention. [Figure 2] This is a comparison of the initial power generation performance of various membrane electrode assemblies (MEAs) having a two-layer cathode electrode catalyst layer. In the figure, panel A is a graph comparing the initial power generation performance under low humidity conditions, and panel B is a graph comparing the initial power generation performance under high humidity conditions. The horizontal axis represents the average mass ratio of ionomer to carbon support (I / Cav), and the vertical axis represents the voltage at 3 A / cm2 (V@3 A / cm2). [Figure 3]This is a comparison of the initial power generation performance of various MEAs having a two-layer cathode electrode catalyst layer under over-humidification conditions. The horizontal axis represents the average mass ratio of ionomer to carbon support (I / Cav), and the vertical axis represents the voltage at 2.2 A / cm2 (V@2.2 A / cm2). [Modes for carrying out the invention]

[0013] Preferred embodiments of the present invention will be described in detail below.

[0014] One aspect of the present invention relates to an electrode catalyst layer for a fuel cell. The electrode catalyst layer for a fuel cell according to this aspect comprises at least a substrate, a carbon support disposed on the surface of the substrate, a catalyst metal supported on the carbon support, and an ionomer disposed on the surface and in the voids of the support.

[0015] In each embodiment of the present invention, the substrate constituting the catalyst layer for the fuel cell is usually in the form of a film. The substrate may be formed from a material commonly used in the art. Examples of such materials include thermosetting resins and thermoplastic resins, particularly thermoplastic resins such as polytetrafluoroethylene (PTFE), polyethylene, polypropylene, cyclic polyolefin resins, polyphenylene ether resins, polyethylene naphthalate resins (PEN), polyetherimide, polyimide, polyphenylsulfone (PPS), polyethersulfone, polyphenylsulfone, or polysulfone.

[0016] In each embodiment of the present invention, the carbon support constituting the catalyst layer for the fuel cell can be, for example, conductive carbon. The carbon support is preferably carbon black (acetylene black, Ketjen black, and furnace black, etc.), activated carbon, graphite, glassy carbon, graphite, graphene, carbon fiber, carbon nanotube, carbon nitride, carbon sulfide, carbon phosphide, channel black, roller black, disc black, oil furnace black, gas furnace black, lamp black, thermal black, or vulcan carbon, or a mixture of one or more of these. The carbon support is preferably carbon black.

[0017] In each embodiment of the present invention, examples of catalyst metals constituting the fuel cell catalyst layer include platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. The catalyst metal may consist of the metals exemplified above individually or as an alloy of two or more of them. The catalyst metal may also be an oxide, nitride, sulfide, or phosphide of the metals exemplified above. The catalyst metal is preferably platinum, a platinum alloy, or a composite containing platinum, and more preferably platinum. In the case of platinum alloys and platinum-containing composites, examples of metals other than platinum include ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. Platinum alloys and platinum-containing composites may contain two or more of the metals exemplified above.

[0018] In each embodiment of the present invention, the ionomer constituting the catalyst layer for the fuel cell is usually a polymer electrolyte having ion exchange groups. Examples of ion exchange groups contained in the polymer electrolyte include sulfonic acid groups, phosphate groups, and quaternary ammonium cation groups. Examples of polymers constituting the polymer electrolyte include polymers mainly composed of perfluorocarbon, polyether ether ketone, and polybenzimidazole. The ionomer is preferably a perfluorocarbon sulfonic acid polymer.

[0019] Figure 1 shows a cross-sectional view illustrating one embodiment of the electrode catalyst layer for a fuel cell according to this embodiment. As shown in Figure 1, the electrode catalyst layer 100 for a fuel cell according to this embodiment has a first electrode catalyst layer m disposed on the surface of the electrolyte membrane and a second electrode catalyst layer g disposed on the surface of the first electrode catalyst layer m and facing the gas diffusion layer. The first electrode catalyst layer m consists of a gas inlet side region ma and a gas outlet side region mb, and the second electrode catalyst layer g consists of a gas inlet side region ga and a gas outlet side region gb. In Figure 1, the arrow shown below the electrode catalyst layer 100 for a fuel cell according to this embodiment indicates the direction of gas flow.

[0020] In the electrode catalyst layer for fuel cells according to this embodiment, the actual porosity (%) is defined as the percentage of the volume of voids where the ionomer is not present relative to the total void volume of the carbon support. The mass ratio of the ionomer (I) to the carbon support (C) when the actual porosity is 10% is defined as I / C0. I / C0 represents the appropriate mass ratio of the ionomer to the carbon support in an electrode catalyst layer for fuel cells having an appropriate porosity of the carbon support that ensures gas diffusion even under high humidity conditions. I / C0 is preferably in the range of 1.0 to 1.2, more preferably in the range of 1.0 to 1.1, and even more preferably 1.1.

[0021] In the electrode catalyst layer for fuel cell according to this embodiment, If the mass ratio of ionomer to carbon support in region ma on the gas inlet side of the first electrode catalyst layer is I / Cma and the thickness of region ma is Tma, and the mass ratio of ionomer to carbon support in region ga on the gas inlet side of the second electrode catalyst layer is I / Cga and the thickness of region ga is Tga, then I / Cma is in the range of 1.0 to 1.5 times I / C0. I / Cga is in the range of 0.6 to 1.0 times I / C0. If the mass ratio of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is I / Cmb, and the thickness of the gas outlet region mb is Tmb, and the mass ratio of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is I / Cgb, and the thickness of the gas outlet region gb is Tgb, then, I / Cmb is in the range of 1.0 to 1.5 times I / C0. I / Cgb is in the range of 0.6 to 1.0 times I / C0.

[0022] The thickness Tma of the gas inlet region ma of the first electrode catalyst layer is not the same as the thickness Tmb of the gas outlet region mb of the first electrode catalyst layer. Also, the thickness Tga of the gas inlet region ga of the second electrode catalyst layer is not the same as the thickness Tgb of the gas outlet region gb of the second electrode catalyst layer.

[0023] The mass ratio I / Cma of ionomer to carbon support in the gas inlet region ma of the first electrode catalyst layer is not the same as the mass ratio I / Cga of ionomer to carbon support in the gas inlet region ga of the second electrode catalyst layer. Furthermore, the mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is not the same as the mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer.

[0024] I / Cma is preferably in the range of 1.1 to 1.4 times I / C0. I / Cga is preferably in the range of 0.6 to 0.95 times I / C0. I / Cmb is preferably in the range of 1.1 to 1.4 times I / C0. I / Cgb is preferably in the range of 0.6 to 0.95 times I / C0.

[0025] In the electrode catalyst layer for fuel cell according to this embodiment, Let I / Cava be the average mass ratio of ionomer I to carbon support C in the gas inlet region ma of the first electrode catalyst layer and the gas inlet region ga of the second electrode catalyst layer, and let I / Cavb be the average mass ratio of ionomer I to carbon support C in the gas outlet region mb of the first electrode catalyst layer and the gas outlet region gb of the second electrode catalyst layer. I / Cava is defined as I / Cava = I / Cma × Tma / (Tma + Tga) + I / Cga × Tga / (Tma + Tga), and is in the range of 0.75 to 1.1 times I / C0. I / Cavb is defined as I / Cavb = I / Cmb × Tmb / (Tmb + Tgb) + I / Cgb × Tgb / (Tmb + Tgb), and is in the range of 0.65 to 1.0 times I / C0.

[0026] I / Cava is preferably in the range of 0.75 to 0.95 times I / C0. I / Cavb is preferably in the range of 0.65 to 0.85 times I / C0.

[0027] In the electrode catalyst layer for fuel cells according to this embodiment, the ratio Tga / Tma, which is the thickness Tga of the gas inlet-side region of the second electrode catalyst layer to the thickness Tma of the gas inlet-side region of the first electrode catalyst layer, and the ratio Tgb / Tmb, which is the thickness Tgb of the gas outlet-side region of the second electrode catalyst layer to the thickness Tmb of the gas outlet-side region of the first electrode catalyst layer, are both preferably in the range of 0.9 to 7. The ratio Tga / Tma, which is the thickness Tga of the gas inlet-side region of the second electrode catalyst layer to the thickness Tma of the gas inlet-side region of the first electrode catalyst layer, is more preferably in the range of 0.9 to 5.1, and even more preferably in the range of 0.9 to 1.1. The ratio Tgb / Tmb, which is the thickness Tgb of the gas outlet-side region of the second electrode catalyst layer to the thickness Tmb of the gas outlet-side region of the first electrode catalyst layer, is more preferably in the range of 1 to 7, and even more preferably in the range of 2 to 7.

[0028] In the electrode catalyst layer for fuel cell according to this embodiment, When I / C0 is in the range of 1.0 to 1.2, The thickness Tma of the gas inflow side region of the first electrode catalyst layer is in the range of 1.7 to 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is in the range of 5 to 8.3 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is in the range of 1.2 to 1.4. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is in the range of 0.8 to 1. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is in the range of 1.7 to 5 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is in the range of 5 to 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is in the range of 1.2 to 1.4. Preferably, the mass ratio I / Cgb of the ionomer to the carbon support in the gas outlet region gb of the second electrode catalyst layer is in the range of 0.8 to 1.

[0029] In the electrode catalyst layer for fuel cell according to this embodiment, When I / C0 is 1.1, (1) The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 5 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.2. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is 0.8. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 1.7 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.4. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is 0.8, or (2) The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 1.7 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.4. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is 0.8. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 5 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 5 μm. The mass ratio I / Cmb of the ionomer to the carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.2. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is 0.8, or (3) The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 5 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.4. In the gas inflow region ga of the second electrode catalyst layer, the mass ratio I / Cga of the ionomer to the carbon support is 1. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 1.7 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.4. It is preferable that the mass ratio I / Cgb of the ionomer to the carbon support in the gas outlet region gb of the second electrode catalyst layer is 1.

[0030] The fact that the electrode catalyst layer for fuel cells in this embodiment has the mass ratio of ionomer to carbon support exemplified above can be determined, for example, by dissolving and extracting the ionomer from the electrode catalyst layer and measuring the masses of the ionomer and carbon support contained in the extract, respectively.

[0031] The fact that the electrode catalyst layer for the fuel cell in this embodiment has the thickness exemplified above can be determined, for example, by measuring the thickness of each layer at multiple locations using a transmission electron microscope and calculating the average value of these measurements.

[0032] By having the features exemplified above, the electrode catalyst layer for fuel cells of this embodiment can have high power generation performance not only in the initial stages but also after long-term operation when used in the cathode and anode of a fuel cell, particularly in the cathode.

[0033] The high power generation performance of the fuel cell electrode catalyst layer according to this embodiment can be evaluated, for example, by the following procedure. A membrane electrode assembly (MEA) is fabricated using the fuel cell electrode catalyst layer according to this embodiment as the cathode and / or anode. Using this MEA as a single cell, the initial current-voltage characteristics of the MEA are measured under low humidity conditions (e.g., 30%RH) and high humidity conditions (e.g., 80%RH). After performing an endurance test (high potential test) on the MEA, the IV characteristics after the endurance test are measured using the same procedure. For each MEA, a specific current density (e.g., 2 or 3 A / cm²) is measured. 2 ) Initial and endurance treatment voltage (V@2 A / cm 2 Or V@3 A / cm 2 Calculate ).

[0034] The electrode catalyst layer for fuel cells according to this embodiment can be applied to either the cathode or the anode of a fuel cell. Therefore, another embodiment of the present invention relates to a fuel cell comprising the electrode catalyst layer for fuel cells according to one embodiment of the present invention. The fuel cell according to this embodiment comprises the electrode catalyst layer for fuel cells according to one embodiment of the present invention as at least one of the cathode and the anode, preferably as the cathode, and further comprises an ionomer and, if necessary, the anode or cathode. The anode, cathode, and ionomer used in the fuel cell according to this embodiment, other than the electrode catalyst layer for fuel cells according to one embodiment of the present invention, can be appropriately selected from materials commonly used in the art.

[0035] The fuel cell of this embodiment, by applying the fuel cell electrode catalyst of one embodiment of the present invention to at least one of the cathode and anode, not only has high initial performance but can also maintain high performance even after durability treatment. Therefore, by applying the fuel cell of this embodiment to applications such as automobiles, the fuel cell can substantially prevent performance degradation even during long-term use and can stably exhibit high performance.

[0036] Another aspect of the present invention relates to a method for manufacturing an electrode catalyst layer for a fuel cell according to the embodiment of the present invention described above. The method of this embodiment includes an electrode catalyst ink preparation step and an electrode catalyst layer formation step. The method of this embodiment also optionally includes a material preparation step. Each step will be described below.

[0037] [1: Material preparation process] This process includes preparing carbon supports and ionomers bearing catalyst metals to be used in the following processes.

[0038] The carbon support and ionomer bearing the catalyst metal prepared in this process may be any material having the characteristics described above. Each material may be prepared by the manufacturer themselves to have the specified characteristics, or it may be prepared by purchasing commercially available products.

[0039] [2: Electrode Catalyst Ink Preparation Process] This process includes preparing an electrode catalyst ink containing a carbon support bearing a catalyst metal and an ionomer.

[0040] The electrode catalyst ink may contain a solvent in addition to the carbon support and ionomer bearing the catalyst metal. The solvent is not particularly limited, and any liquid can be used. Examples of solvents include water and alcohol, as well as mixtures of one or more of them. Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol (tert-butyl alcohol), diacetone alcohol, ethylene glycol, and propylene glycol.

[0041] In this process, the electrode catalyst ink is usually prepared by mixing a carbon support bearing a catalyst metal, an ionomer, and optionally a solvent. The means of mixing the materials are not particularly limited. Examples of mixing means include ultrasonic homogenizers, jet mills, bead mills, ball mills, high shears, and film mixers. The specific conditions of the mixing means exemplified above (e.g., stirring speed, stirring time, and rotation speed) are not particularly limited and can be set appropriately within any range.

[0042] In this process, it is preferable to mix the carbon support bearing the catalyst metal and the ionomer in a mass ratio such that the mass ratio I / C of the ionomer to the carbon support in the electrode catalyst layer formed in the electrode catalyst layer formation process described below is a predetermined value.

[0043] [3: Electrode catalyst layer formation process] This process includes applying an electrode catalyst ink to a substrate.

[0044] The base material used in this process may be any material having the characteristics described above. Each material may be prepared by the user themselves to have the specified characteristics, or it may be prepared by purchasing a commercially available product.

[0045] In this process, the means for applying the electrode catalyst ink to the substrate are not particularly limited. Examples of application methods include die coating, spin coating, screen printing, doctor blade, squeegee, spray coating, and applicator methods. The specific conditions for the application methods exemplified above are not particularly limited and can be set appropriately within any range.

[0046] This process may include removing the solvent from the electrode catalyst ink after coating. The removal of the solvent is not particularly limited and can be carried out by any means such as heating and drying. The specific conditions for solvent removal (e.g., temperature, pressure, and processing time) are not particularly limited and can be set as appropriate within any range.

[0047] In this process, by applying the electrode catalyst ink having the characteristics described above to a substrate, an electrode catalyst layer with a mass ratio I / C of the ionomer to the carbon carrier being a predetermined value can be formed.

[0048] In this process, the first electrode catalyst layer and the second electrode catalyst layer can be obtained by forming the first electrode catalyst layer on the surface of the substrate according to the procedure described above, and then forming the second electrode catalyst layer on the surface of the first electrode catalyst layer.

[0049] In this process, the first electrode catalyst layer and the second electrode catalyst layer in the region on the gas inflow side, and the first electrode catalyst layer and the second electrode catalyst layer in the region on the gas outflow side can be obtained by separately producing the first electrode catalyst layer and the second electrode catalyst layer in each region.

Example

[0050] Hereinafter, the present invention will be described more specifically using examples. However, the technical scope of the present invention is not limited to these examples.

[0051] <I: Fabrication of Membrane Electrode Assembly (MEA)> [I-1: Fabrication of Electrode Catalyst Layer Having a Two-Layer Structure] A carbon carrier supporting a catalyst metal and an ionomer (swelling ratio: 146%) were prepared. The carbon carrier and the ionomer were dispersed in water and alcohol so that the mass ratio I / C of the ionomer (I) to the carbon carrier (C) became a predetermined value, and an electrode catalyst ink was prepared. An electrode catalyst ink prepared to have an I / C of the first electrode catalyst layer was applied to the surface of a substrate (PTFE) sheet and dried to form a first electrode catalyst layer m with a thickness Tm. Next, an electrode catalyst ink prepared to have an I / C of the second electrode catalyst layer was applied to the surface of the first electrode catalyst layer m and dried to form a second electrode catalyst layer g with a thickness Tg. The total thickness T of the electrode catalyst layer having a two-layer structure (that is, the sum of the thicknesses Tm and Tg) was made constant. As a control electrode catalyst layer, an electrode catalyst layer having a single-layer structure with a thickness T was formed.

[0052] Using a carbon support without a catalytic metal, the total pore volume of the carbon support was measured. From the amount of ionomer present in the pores and the swelling ratio of the ionomer, the volume of the ionomer present in the pores was calculated. By subtracting the volume of the ionomer present in the pores from the pore volume of the carbon support, the actual pore volume of the carbon support was calculated. From the above values, the actual porosity (%) was calculated as the percentage of the volume of pores without ionomer to the total pore volume of the carbon support. Based on the performance evaluation results shown below, when the calculated actual porosity was 10%, the mass ratio I / C of the ionomer to the carbon support was determined as the appropriate mass ratio I / C0.

[0053] [I-2: Fabrication of MEA] Using the above procedure, a cathode electrode catalyst layer and an anode electrode catalyst layer were fabricated. The obtained cathode electrode catalyst layer and anode electrode catalyst layer were transferred and bonded to an electrolyte membrane to fabricate an MEA.

[0054] [I-3: Fabrication of MEAs for Examples and Comparative Examples] Using the above procedure, cathode electrode catalyst layers in the regions of the gas inlet side and outlet side of the cathode were obtained respectively. Using the same procedure, an anode electrode catalyst layer was fabricated. The obtained cathode electrode catalyst layer and anode electrode catalyst layer were transferred and bonded to an electrolyte membrane to fabricate MEAs for examples and comparative examples.

[0055] [II: Performance Evaluation of Fuel Cell] Using the MEA fabricated by the above procedure as a single cell, the initial current-voltage characteristics of the MEA under low humidity conditions (30%RH) and high humidity conditions (80%RH) were measured. Also, after performing a durability treatment (high potential test) on the MEA, the I-V characteristics after the durability treatment were measured by the same procedure. For each MEA, the initial and post-durability treatment voltages (V@2 A / cm 2 ) or V@3 A / cm 2 or V@3 A / cm 2 ) at a specific current density (2 or 3 A / cm

[0056] The results of comparing the initial power generation performance of various MEAs having a cathode electrode catalyst layer with a two-layer structure are shown in Fig. 2. In the figure, Panel A is a graph comparing the initial power generation performance under low humidification conditions, and Panel B is a graph comparing the initial power generation performance under high humidification conditions. The horizontal axis is the average value (I / Cav) of the mass ratio of the ionomer to the carbon carrier, and the vertical axis is the voltage (V@3 A / cm 2 at 3 A / cm 2 ).

[0057] As shown in Fig. 2, in the case of a control MEA having a single-layer electrode catalyst layer with an electrode catalyst layer thickness T of 10 μm, a certain correlation was confirmed between the mass ratio of the ionomer to the carbon carrier and the voltage under low humidification conditions or high humidification conditions. In particular, under high humidification conditions, the MEA with I / C = 1.1 showed the highest voltage (Fig. 2B). The actual void fraction of the carbon carrier in the cathode electrode catalyst layer contained in this MEA was 10%. From this result, it was judged that when the actual void fraction is 10%, it is an appropriate void fraction of the carbon carrier that can ensure gas diffusibility even under high humidity conditions. Therefore, I / C = 1.1 when the actual void fraction is 10% was determined as the appropriate mass ratio I / C0. Here, some MEAs having a two-layer structure showed initial power generation performance equivalent to or better than that of the control MEA at I / C0 even when I / Cav decreased.

[0058] The results of comparing the initial power generation performance of various MEAs having a cathode electrode catalyst layer with a two-layer structure under overhumidification conditions are shown in Fig. 3. The horizontal axis is the average value (I / Cav) of the mass ratio of the ionomer to the carbon carrier, and the vertical axis is the voltage (V@2.2 A / cm 2 at 2.2 A / cm 2 ).

[0059] As shown in Figure 3, in the case of a control MEA with a single-layer electrode catalyst layer with an electrode catalyst layer thickness T of 10 μm, the voltage was substantially constant when the mass ratio of ionomer to carbon support was I / C0 or less, i.e., when the actual porosity in the carbon support was 10% or more. However, when the mass ratio of ionomer to carbon support exceeded I / C0, i.e., when the actual porosity in the carbon support was less than 10%, the voltage dropped sharply. In contrast, some MEAs with a two-layer structure showed equivalent or better initial power generation performance even when I / Cav decreased.

[0060] Based on the power generation performance of the two-layer structure MEA described above, MEAs of Examples 1 to 3 were fabricated, each having a cathode electrode catalyst layer with a different two-layer structure in the gas inlet and outlet regions of the cathode. Furthermore, MEAs of Comparative Examples 1 to 3 were fabricated, each having a cathode electrode catalyst layer with the same single-layer structure in both the gas inlet and outlet regions of the cathode. Table 1 shows the characteristics of the cathode electrode catalyst layers included in MEAs of Examples 1 to 3 and Comparative Examples 1 to 3, and the results of the MEA performance evaluation.

[0061] [Table 1] TIFF2026109167000003.tif55160

[0062] As shown in Table 1, in the case of the comparative example MEA having a cathode electrode catalyst layer with the same single-layer structure in both the gas inlet and outlet regions of the cathode, when the mass ratio of ionomer to carbon support is I / C0 or less, as in Comparative Example 2, the decrease in voltage after durability treatment can be suppressed, but the initial voltage becomes low. Also, when the mass ratio of ionomer to carbon support is I / C0, as in Comparative Example 1, the initial voltage can be maintained at a predetermined value, but the voltage after durability treatment decreases significantly. This result is presumed to be due to the reduction in the actual void volume in the carbon support caused by the deterioration of the carbon support due to the durability treatment. Thus, in the case of the comparative example MEA, it is difficult to achieve both initial and post-durability power generation performance.

[0063] In contrast, as in the MEAs of Examples 1 to 3, the mass ratio I / Cma of ionomer to carbon support in the gas inlet region ma of the first electrode catalyst layer, and the mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer are set to be I / C0 or greater, particularly in the range of 1.0 to 1.5 times I / C0, and the mass ratio I / Cga of ionomer to carbon support in the gas inlet region ga of the second electrode catalyst layer, and the mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer are set to be I / C0 or less, particularly in the range of I / C0. By setting the mass ratio I / Cava of ionomer to carbon support in the gas inlet region ma of the first electrode catalyst layer and the gas inlet region ga of the second electrode catalyst layer to approximately the same as I / C0, particularly in the range of 0.75 to 1.1 times I / C0, and setting the mass ratio I / Cavb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer and the gas outlet region gb of the second electrode catalyst layer to less than or equal to I / C0, particularly in the range of 0.65 to 1.0 times I / C0, not only was the initial voltage improved, but the voltage decrease after the durability treatment was also suppressed. From these results, it became clear that the MEA of the embodiment having the above characteristics can achieve both initial and durability treatment power generation performance.

[0064] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. In addition, it is possible to add, delete, and / or replace some of the configurations in each embodiment with other configurations. [Explanation of symbols]

[0065] 100... Electrode catalyst layer for fuel cell, m... First electrode catalyst layer, g... Second electrode catalyst layer, ma... Gas inlet side region of the first electrode catalyst layer, mb... Gas outlet side region of the first electrode catalyst layer, ga... Gas inlet side region of the second electrode catalyst layer, gb... Gas outlet side region of the second electrode catalyst layer

Claims

1. A fuel cell electrode catalyst layer comprising at least a substrate, a carbon support disposed on the surface of the substrate, a catalyst metal supported on the carbon support, and an ionomer disposed on the surface and in the voids of the support, The electrode catalyst layer for the fuel cell comprises a first electrode catalyst layer m disposed on the surface of the electrolyte membrane, and a second electrode catalyst layer g disposed on the surface of the first electrode catalyst layer m and facing the gas diffusion layer. The first electrode catalyst layer m consists of a gas inflow region ma and a gas outflow region mb. The second electrode catalyst layer g consists of a gas inlet region ga and a gas outlet region gb. The actual porosity is defined as the percentage of the volume of voids without ionomer relative to the total void volume of the carbon support, and the mass ratio of ionomer to carbon support when the actual porosity is 10% is defined as I / C 0 year, If the mass ratio of ionomer to carbon support in region ma on the gas inlet side of the first electrode catalyst layer is I / Cma and the thickness of region ma is Tma, and the mass ratio of ionomer to carbon support in region ga on the gas inlet side of the second electrode catalyst layer is I / Cga and the thickness of region ga is Tga, then I / Cma is I / C 0 It is in the range of 1.0 to 1.5 times, I / Cga is I / C 0 It is in the range of 0.6 to 1.0 times, If the mass ratio of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is I / Cmb, and the thickness of the gas outlet region mb is Tmb, and the mass ratio of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is I / Cgb, and the thickness of the gas outlet region gb is Tgb, then, I / Cmb is I / C 0 It is in the range of 1.0 to 1.5 times, I / Cgb is I / C 0 It is in the range of 0.6 to 1.0 times, Let I / Cava be the average mass ratio of ionomer to carbon support in the gas inlet region ma of the first electrode catalyst layer and the gas inlet region ga of the second electrode catalyst layer, and let I / Cavb be the average mass ratio of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer and the gas outlet region gb of the second electrode catalyst layer. I / Cava is defined as I / Cava = I / Cma × Tma / (Tma + Tga) + I / Cga × Tga / (Tma + Tga), and also I / C 0 It is in the range of 0.75 to 1.1 times, I / Cavb is given by I / Cavb = I / Cmb × Tmb / (Tmb + Tgb) + I / Cgb × Tgb / (Tmb + Tgb), and also I / C 0 It is in the range of 0.65 to 1.0 times, The aforementioned electrode catalyst layer for fuel cell.

2. The ratio Tga / Tma of the thickness Tga of the gas inlet-side region of the second electrode catalyst layer to the thickness Tma of the gas inlet-side region of the first electrode catalyst layer, and The electrode catalyst layer for a fuel cell according to claim 1, wherein the ratio Tgb / Tmb of the thickness Tgb of the gas outlet side region of the second electrode catalyst layer and the thickness Tmb of the gas outlet side region of the first electrode catalyst layer is in the range of 0.9 to 7.

3. The ratio Tga / Tma of the thickness Tga of the gas inlet-side region of the second electrode catalyst layer to the thickness Tma of the gas inlet-side region of the first electrode catalyst layer is in the range of 0.9 to 1.1, and The electrode catalyst layer for a fuel cell according to claim 2, wherein the ratio Tgb / Tmb, which is the thickness Tgb of the gas outlet side region of the second electrode catalyst layer to the thickness Tmb of the gas outlet side region of the first electrode catalyst layer, is in the range of 2 to 7.

4. I C 0 When is in the range of 1.0 to 1.2, The thickness Tma of the gas inflow side region of the first electrode catalyst layer is in the range of 1.7 to 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is in the range of 5 to 8.3 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is in the range of 1.2 to 1.

4. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is in the range of 0.8 to 1. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is in the range of 1.7 to 5 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is in the range of 5 to 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is in the range of 1.2 to 1.

4. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is in the range of 0.8 to 1. The electrode catalyst layer for a fuel cell according to claim 1.

5. I / C 0 When it is 1.1, （1） The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 5 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.

2. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is 0.

8. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 1.7 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.

4. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is 0.8, or （2） The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 1.7 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.

4. The mass ratio I / Cga of the ionomer to the carbon support in the gas inflow region ga of the second electrode catalyst layer is 0.

8. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 5 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 5 μm. The mass ratio I / Cmb of the ionomer to the carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.

2. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is 0.8, or （3） The thickness Tma of the gas inflow side region of the first electrode catalyst layer is 5 μm. The thickness Tga of the gas inflow region of the second electrode catalyst layer is 5 μm. The mass ratio I / Cma of the ionomer to the carbon support in the gas inflow region ma of the first electrode catalyst layer is 1.

4. In the gas inflow region ga of the second electrode catalyst layer, the mass ratio I / Cga of the ionomer to the carbon support is 1. The thickness Tmb of the gas outlet region mb of the first electrode catalyst layer is 1.7 μm. The thickness Tgb of the gas outflow region gb of the second electrode catalyst layer is 8.3 μm. The mass ratio I / Cmb of ionomer to carbon support in the gas outlet region mb of the first electrode catalyst layer is 1.

4. The mass ratio I / Cgb of ionomer to carbon support in the gas outlet region gb of the second electrode catalyst layer is 1. The electrode catalyst layer for a fuel cell according to claim 1.

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