Fuel battery

Abstract

To provide a fuel battery capable of indicating a high-power generation performance even under a moisture inclination environment.SOLUTION: A fuel battery comprises a membrane electrode assembly (MEA) in which an anode catalyst layer and a cathode catalyst layer are bonded to both surfaces of an electrolyte film. Here, the cathode catalyst layer comprises: a first electrode catalyst that contains a first carrier having a first pore and a first catalyst particle carried in the first pore; a second electrode catalyst that contains a second carrier having a second pore and a second catalyst particle carried in the second pore; and a catalyst layer ionomer. A first mode diameter of the first pore is smaller than a second mode diameter of the second pore. Then, a content amount of the first electrode catalyst contained in an upstream side region of a cathode passage is larger than that of the first electrode catalyst contained in a downstream region of the cathode passage. Thus, a high-power generation performance can be indicated even under an environment having a moisture inclination.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a fuel cell, and more particularly to a fuel cell that exhibits high power generation performance even in an environment with a humidity gradient. [Background technology]

[0002] A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which electrodes containing catalyst particles are bonded to both sides of an electrolyte membrane. The electrodes generally include a catalyst layer containing catalyst particles. Gas diffusion layers and separators (also called current collectors) having gas flow paths are arranged on both sides of the MEA. A polymer electrolyte fuel cell generally includes a structure (fuel cell stack) in which a plurality of unit cells each consisting of such an MEA, gas diffusion layers, and current collectors are stacked.

[0003] The catalyst layer generally consists of a mixture of an electrode catalyst in which catalyst particles such as platinum or a platinum alloy are supported on the surface of a carrier, and a catalyst layer ionomer. When a fuel (e.g., hydrogen) and an oxidant (e.g., air) are supplied to the anode and cathode of a fuel cell having such a structure, an electrode reaction proceeds and electricity can be obtained.

[0004] However, when air is supplied to a long and narrow cathode flow channel, the concentration (humidity) of water vapor, which is a reaction product, increases toward the downstream side of the cathode flow channel as the electrode reaction proceeds. Therefore, in an electrode with a uniform structure along the gas flow direction, there is a risk of a decrease in power generation performance.

[0005] In order to solve this problem, various proposals have been made in the past. For example, Patent Document 1 states: A first electrode catalyst including catalyst particles (A) whose surfaces are coated with a carbon film; A second electrode catalyst including catalyst particles (B) whose surfaces are not covered with a carbon film; Catalyst layer ionomer Equipped with The content of the first electrode catalyst in the upstream region of the cathode flow channel is greater than the content of the first electrode in the downstream region of the cathode flow channel. A cathode catalyst layer is described.

[0006] The same document states: (1) The upstream region of the cathode flow channel has a relatively low humidity, and the arrangement of the catalyst particles (A) is less affected by the increase in oxygen transfer resistance, and the effect of suppressing catalyst poisoning is greater, resulting in improved power generation performance. (2) The downstream area of ​​the cathode flow channel is relatively humid due to the effect of the generated water, and the arrangement of the catalyst particles (B) mitigates the adverse effects of increased catalyst poisoning, and the effect of reducing oxygen transfer resistance is greater, improving power generation performance. is stated.

[0007] In Patent Document 2, a first catalyst-supporting carbon having first catalyst particles supported on the surface of a first support; a second catalyst-supporting carbon having second catalyst particles supported on the surface of a second support; Catalyst layer ionomer Equipped with The first support is made of a first monodisperse spherical mesoporous carbon having a most frequent pore size of 2.8 nm; The second support is made of a second monodisperse spherical mesoporous carbon with a most frequent pore size of 4.8 nm. A cathode catalyst layer is described.

[0008] The same document states: (1) By supporting catalyst particles on two types of monodispersed spherical mesoporous carbon with different pore sizes and blending the two types of catalyst-supported carbon obtained in a specified ratio, it is possible to achieve both performance in low humidity and high humidity environments. (2) The use of monodisperse spherical mesoporous carbon as the carrier makes it easy to mix the two uniformly. is stated.

[0009] Here, the configuration of Patent Document 1 is considered to have a certain effect in a low humidity environment and a low current density region. However, since the catalyst particles (A) are configured to reduce the contact area with the ionomer, there is a risk that the proton transport path cannot be secured in a low humidity environment and a high current density region, and the power generation performance will not improve. For this reason, further improvement in low humidity environments seems necessary.

[0010] Furthermore, in the configuration of Patent Document 2, either the first catalyst-supporting carbon or the second catalyst-supporting carbon acts in an unfavorable direction in both a high humidity environment and a low humidity environment. For this reason, it seems that further improvements are necessary to more efficiently utilize the first catalyst-supporting carbon and the second catalyst-supporting carbon. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2021-89874 [Patent Document 2] JP 2020-155348 A Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a fuel cell that exhibits high power generation performance even in an environment with a humidity gradient. [Means for solving the problem]

[0013] In order to solve the above problems, the fuel cell according to the present invention has the following configuration. (1) Fuel cells are: a membrane electrode assembly (MEA) in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator provided with an anode flow channel and disposed on the outer side of the anode-side gas diffusion layer; a cathode separator provided with a cathode flow channel and disposed on the outer side of the cathode-side gas diffusion layer; It is equipped with:

[0014] (2) The cathode catalyst layer is a first electrode catalyst including a first support having first pores and first catalyst particles supported in the first pores; a second electrode catalyst including a second support having second pores and second catalyst particles supported in the second pores; Catalyst layer ionomer Equipped with The first mode diameter of the first pores is smaller than the second mode diameter of the second pores.

[0015] (3) The content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel. Effect of the Invention

[0016] [Small pore size] When the pore size of the support is relatively small, the intrusion of the ionomer into the pores can be prevented, thereby suppressing ionomer poisoning of the catalyst particles in the pores, thereby improving power generation performance in the low current density range. Furthermore, even in low humidity environments, water can be adsorbed in the pores through capillary condensation, ensuring proton transport pathways and improving power generation performance. On the other hand, in a high humidity environment, water clogging in the pores due to capillary condensation (so-called flooding phenomenon) is likely to occur, which impedes oxygen transport to the catalyst particle surface and leads to a decrease in power generation performance.

[0017] [Large pore size] When the pore size of the carrier is relatively large, the flooding phenomenon can be suppressed in a high humidity environment, and the deterioration of power generation performance can be suppressed.

[0018] In the cathode flow channel, a humidity gradient occurs, with the upstream region being a low humidity environment and the downstream region being a high humidity environment, due to the influence of water produced during power generation. Here, by placing a large amount of the first electrode catalyst with a small pore size in the upstream region (low humidity environment side) of the cathode flow path and placing a large amount of the second electrode catalyst with a large pore size in the downstream region (high humidity environment side) of the cathode flow path, the first electrode catalyst and the second electrode catalyst can be utilized more efficiently.

[0019] Therefore, the fuel cell of the present invention can exhibit high power generation performance even in an environment with a humidity gradient by making the content of the first electrode catalyst contained in the upstream side of the cathode flow path greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow path. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a graph showing the power generation performance in a low humidity environment (80° C., 30% RH) of a fuel cell having a cathode catalyst layer equipped with an electrode catalyst containing carriers with different pore sizes. [Diagram 2] FIG. 1 is a graph showing the power generation performance in a high humidity environment (60° C., 90% RH) of a fuel cell having a cathode catalyst layer equipped with an electrode catalyst containing carriers with different pore sizes. [Diagram 3] FIG. 1 is a schematic diagram of assumptions used to predict power generation performance. [Figure 4] 1 shows the current density at 0.6 V (IR loss corrected) obtained by simple calculation for the fuel cells of Examples 1 and 2 and Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] [Configuration 1] A fuel cell comprising: (1) Fuel cells are: a membrane electrode assembly (MEA) in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator provided with an anode flow channel and disposed on the outer side of the anode-side gas diffusion layer; a cathode separator provided with a cathode flow channel and disposed on the outer side of the cathode-side gas diffusion layer; It is equipped with: (2) The cathode catalyst layer is a first electrode catalyst including a first support having first pores and first catalyst particles supported in the first pores; a second electrode catalyst including a second support having second pores and second catalyst particles supported in the second pores; Catalyst layer ionomer Equipped with The first mode diameter of the first pores is smaller than the second mode diameter of the second pores. (3) The content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel.

[0022] [Configuration 2] The content of the first electrode catalyst in the upstream region is 90% or more; The content of the first electrode catalyst in the downstream region is less than 10%. 2. The fuel cell according to claim 1.

[0023] [Configuration 3] 3. The fuel cell according to claim 1 or 2, wherein the first support and the second support are each mesoporous carbon.

[0024] [Configuration 4] The first support has a first pore volume of 0.50 cc / g or more and less than 1.30 cc / g; The second support has a second pore volume of 1.30 cc / g or more and 3.70 cc / g or less. The fuel cell according to any one of configurations 1 to 3.

[0025] [Configuration 5] The first mode diameter is equal to or greater than 2.0 nm and less than 5.0 nm, The second mode diameter is 5.0 nm or more and 20.0 nm or less. The fuel cell according to any one of the first to fourth aspects.

[0026] An embodiment of the present invention will be described in detail below. [1. Cathode catalyst layer] The cathode catalyst layer according to the present invention comprises: a first electrode catalyst including a first support having first pores and first catalyst particles supported in the first pores; a second electrode catalyst including a second support having second pores and second catalyst particles supported in the second pores; Catalyst layer ionomer It is equipped with:

[0027] [1.1. First electrode catalyst] The first electrode catalyst includes a first support having first pores and first catalyst particles supported in the first pores, and serves to primarily improve cell performance in low humidity environments. The first catalyst particles may further include first catalyst particles supported outside the first pores, in addition to the first catalyst particles supported inside the first pores.

[0028] [1.1.1. First carrier] In the present invention, the first support has first pores. Furthermore, the first support is not particularly limited as long as it has first pores capable of supporting the first catalyst particles. The first support is preferably mesoporous carbon, and more preferably monodispersed spherical mesoporous carbon. Furthermore, the particle size of monodispersed spherical mesoporous carbon can be easily controlled, making it a suitable material for use as a carrier.

[0029] Here, the term "monodisperse" refers to a degree of monodispersity calculated for a plurality of particles produced under the same conditions being equal to or less than a predetermined value. The degree of monodispersity refers to a value expressed by the following formula: Monodispersity = (Standard deviation of particle size) x 100 / (Average particle size)

[0030] In general, the smaller the variation in particle size of the carrier, the more isotropically the various reactions within the carrier and between carriers proceed. Therefore, the smaller the monodispersity of the first carrier, the better. The monodispersity is preferably 10% or less, and more preferably 5% or less.

[0031] The term "spherical" means that the sphericity calculated for a number of particles produced under the same conditions is equal to or less than a predetermined value. The term "sphericity" means a value expressed by the following formula. Sphericity = Δr max ×100 / r 0 however r 0 is the radius of the smallest circumscribing circle that touches the surface of the particle, r max is the maximum radial distance between the circumscribing circle and each point on the particle surface.

[0032] In general, the closer the shape of the carrier is to a perfect sphere, the more isotropically the various reactions within the carrier and between the carriers proceed. Therefore, the smaller the sphericity of the first carrier, the better. The sphericity is preferably 7% or less, and more preferably 3% or less.

[0033] [1.1.2. First mode diameter] The "first mode diameter" refers to the pore diameter (most frequent peak value) at which the capacity of the first pore is maximum when the adsorption side data of the nitrogen adsorption isotherm of the first support before the first catalyst particles are supported is analyzed by the BJH method. In order to improve the cell performance in a low humidity environment, the first support needs to have relatively small first pores. In general, if the pore diameter of the first support is too large, the water retention in the first pores decreases, and the cell performance in a low humidity environment decreases. In addition, there is a concern about ionomer poisoning of the first catalyst particles. Therefore, the first mode diameter of the first support is preferably less than 5.0 nm. It is preferably 4.5 nm or less, and more preferably 3.5 nm or less.

[0034] On the other hand, if the pore diameter of the first support is too small, it may be difficult to support the first catalyst particles in the first pores. In addition, the Knudsen resistance increases, resulting in high oxygen transfer resistance. Therefore, the first mode diameter of the first support is preferably 2.0 nm or more. It is preferably 2.5 nm or more, and more preferably 3.0 nm or more.

[0035] [1.1.3. First pore volume] In the present invention, the first support has first pores. The volume of the first pores is obtained by integrating the results of pore diameter distribution calculations using the BJH method described above. Generally, if the capacity of the first pore is too large, the ratio of the pore wall becomes small, and the electronic conductivity becomes low. Also, the amount of ionomer penetration increases, and ionomer poisoning is likely to occur. Therefore, the capacity of the first pore is preferably less than 1.30 cc / g. It is preferably 1.25 cc / g or less, and more preferably 1.20 cc / g or less.

[0036] On the other hand, if the capacity of the first pores is too small, the ratio of the first catalyst particles supported in the first pores will be small. Therefore, the first catalyst particles supported outside the first pores will increase, and the first catalyst particles will be more likely to be poisoned by the ionomer. Therefore, the capacity of the first pores is preferably 0.50 cc / g or more. It is preferably 0.80 cc / g or more, and more preferably 0.90 cc / g or more.

[0037] When the first support is monodispersed spherical mesoporous carbon, the first support can be obtained by using monodispersed spherical mesoporous silica as a template, impregnating the pores of the template with a carbon source, carbonizing the carbon source, and removing the template, as described below. By using the method described below, it is possible to obtain a first support having a first mode diameter and a first pore volume within the above-mentioned ranges.

[0038] [1.1.4. Average particle size] The term "average particle diameter of the first support" refers to the median diameter of the first support before the first catalyst particles are supported thereon, as measured by a laser diffraction scattering method. The average particle size of the first carrier is not particularly limited, and an optimal value can be selected depending on the purpose. The average particle size of the first carrier is usually 50 nm to 300 nm.

[0039] [1.1.5. First catalyst particles] In the present invention, the material of the first catalyst particles is not particularly limited. (a) Precious metals (Pt, Au, Ag, Pd, Rh, Ir, Ru, Os), (b) An alloy containing two or more precious metal elements; (c) Alloys containing one or more precious metal elements and one or more base metal elements (e.g., Fe, Co, Ni, Cr, V, Ti, etc.); etc.

[0040] Among these, the first catalyst particles are preferably made of Pt or a Pt alloy, since they have high activity in the electrode reaction of the fuel cell. Examples of Pt alloys include Pt-Fe alloys, Pt-Co alloys, Pt-Ni alloys, Pt-Pd alloys, Pt-Cr alloys, Pt-V alloys, Pt-Ti alloys, Pt-Ru alloys, and Pt-Ir alloys.

[0041] In the present invention, the first catalyst particles can be obtained by impregnating the first pores of the first support with a precursor of the catalyst particles and reducing the precursor in a liquid phase, as described below. In this case, most of the first catalyst particles are supported in the first pores of the first support.

[0042] [1.1.6. Catalyst loading rate] The loading rate of the first catalyst particles on the first support is not particularly limited, and an optimal value can be selected according to the purpose. In general, if the loading rate of the first catalyst particles is too small, the cell performance in a low humidity environment decreases. Therefore, the loading rate of the first catalyst particles is preferably 20 wt% or more. The catalyst loading rate is more preferably 30 wt% or more. On the other hand, even if the loading rate of the first catalyst particles is increased more than necessary, there is no difference in the effect and there is no practical benefit. Therefore, the loading rate of the first catalyst particles is preferably 65 wt% or less. The catalyst loading rate is more preferably 55 wt% or less.

[0043] [1.2. Second electrode catalyst] The second electrode catalyst includes a second support having second pores and second catalyst particles supported in the second pores, and serves to improve cell performance primarily in high humidity environments. The second catalyst particles may further include second catalyst particles supported outside the second pores, in addition to the second catalyst particles supported inside the second pores.

[0044] [1.2.1. Second carrier] In the present invention, the second support has second pores. Here, the second mode diameter of the second pores is larger than the first mode diameter of the first pores, i.e., the first mode diameter of the first pores is smaller than the second mode diameter of the second pores.

[0045] [1.2.2. Second mode diameter] The "second mode diameter" refers to the pore diameter (most frequent peak value) at which the volume of the second pore is maximum when the adsorption side data of the nitrogen adsorption isotherm of the second support before the second catalyst particles are supported is analyzed by the BJH method. In order to improve the battery performance in a high humidity environment, the second support needs to have a relatively large second pore. In general, if the pore diameter of the second support is too small, the flooding phenomenon is likely to occur in a high humidity environment. Therefore, the second mode diameter of the second support is preferably 5.0 nm or more. It is preferably 5.5 nm or more, and more preferably 7.5 nm or more.

[0046] On the other hand, even if the pore diameter of the second support is increased, there is no difference in the effect and there is no practical benefit. Therefore, the second mode diameter of the second support is preferably 20.0 nm or less, more preferably 10.0 nm or less, and even more preferably 8.0 nm or less.

[0047] [1.2.3. Secondary pore volume] In the present invention, the second support has second pores. The volume of the second pores is preferably 1.30 cc / g or more and 3.70 cc / g or less. The volume of the second pores is obtained by integrating the results of the pore diameter distribution calculation by the BJH method described above. Generally, if the volume of the second pores is too large, the thickness of the pore walls of the second support becomes thin, and carbon becomes more susceptible to oxidation. This may result in a decrease in durability (chemical stability). Therefore, the volume of the second pores is preferably 3.70 cc / g or less. Preferably, It is preferably 2.10 cc / g or less, and more preferably 1.80 cc / g or less.

[0048] On the other hand, if the capacity of the second pores is too small, the ratio of the second catalyst particles supported in the second pores will be small. Therefore, the second catalyst particles supported outside the second pores will increase, making ionomer poisoning more likely to occur. Therefore, the capacity of the second pores is preferably 1.30cc / g or more. It is preferably 1.35cc / g or more, and more preferably 1.45cc / g or more.

[0049] When the second support is monodispersed spherical mesoporous carbon, the second support can be obtained by using monodispersed spherical mesoporous silica as a template, impregnating the pores of the template with a carbon source, carbonizing the carbon source, and removing the template, as described below. By using the method described below, a second support having a second mode diameter and a second pore volume within the above-mentioned ranges can be obtained.

[0050] [1.2.4. Average particle size] The "average particle diameter of the second carrier" is not particularly limited, and an optimal value can be selected depending on the purpose. Other points regarding the average particle diameter of the second carrier are the same as those of the first carrier, so the explanation will be omitted.

[0051] [1.2.5. Second catalyst particles] In the present invention, the material of the second catalyst particles is not particularly limited. Details of the composition of the second catalyst particles are similar to those of the first catalyst particles, and therefore a description thereof will be omitted.

[0052] As described later, in the present invention, the second catalyst particles can be obtained by impregnating the second pores of the second support with a precursor of the catalyst particles and reducing the precursor in a liquid phase. In this case, most of the second catalyst particles are supported in the second pores of the second support.

[0053] [1.2.6. Catalyst loading rate] The loading rate of the second catalyst particles on the second support is not particularly limited, and an optimal value can be selected according to the purpose. The details of the loading amount of the second catalyst particles are the same as those of the first catalyst particles, so the explanation is omitted.

[0054] [1.3. Catalyst layer ionomer] The material of the catalyst layer ionomer contained in the cathode catalyst layer is not particularly limited, and an optimum material can be selected depending on the purpose. The content of the catalyst layer ionomer contained in the cathode catalyst layer is not particularly limited, and the optimal content can be selected according to the purpose. For example, when the catalyst particles are supported on a carbon carrier, the ratio (I / C) of the mass (I) of the catalyst layer ionomer to the mass (C) of carbon is preferably 0.3 or more and 2.0 or less.

[0055] [1.4. Content of first electrode catalyst and second electrode catalyst] In the present invention, the content of the first electrode catalyst in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst in the downstream region of the cathode flow channel. The contents of the first electrode catalyst and the second electrode catalyst will be described in detail later.

[0056] [2. Fuel cell] The fuel cell according to the present invention comprises: a membrane electrode assembly (MEA) in which an anode catalyst layer and a cathode catalyst layer are bonded to both sides of an electrolyte membrane; an anode-side gas diffusion layer disposed on the outer side of the anode catalyst layer; a cathode-side gas diffusion layer disposed on the outer side of the cathode catalyst layer; an anode separator provided with an anode flow channel and disposed on the outer side of the anode-side gas diffusion layer; a cathode separator provided with a cathode flow channel and disposed on the outer side of the cathode-side gas diffusion layer; It is equipped with:

[0057] [2.1. Components of a fuel cell] [2.1.1. Electrolyte membrane] In the present invention, the material of the electrolyte membrane is not particularly limited, and an optimum material can be selected depending on the purpose. Examples of the electrolyte material include: (a) perfluorocarbon sulfonic acid polymers such as Nafion®, Flemion®, Aciplex®, and Aquivion®; (b) Hydrocarbon polymers such as sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polyether ether sulfones, sulfonated polysulfides, and sulfonated polyphenylenes; etc.

[0058] [2.1.2. Anode] The anode is bonded to one side of the electrolyte membrane, and includes an anode catalyst layer including an anode catalyst and a catalyst layer ionomer, and an anode-side gas diffusion layer is disposed on the outer side of the anode catalyst layer. In the present invention, the materials of the anode catalyst and the catalyst layer ionomer, and the contents thereof are not particularly limited, and an optimum material can be selected depending on the purpose. The material and structure of the anode-side gas diffusion layer are not particularly limited, and an optimum material and structure can be selected depending on the purpose.

[0059] [2.1.3. Cathode] The cathode is bonded to the other surface of the electrolyte membrane, and includes a cathode catalyst layer including a cathode catalyst and a catalyst layer ionomer, and a cathode-side gas diffusion layer is disposed on the outer side of the cathode catalyst layer. In the present invention, the material of the catalyst layer ionomer and its content are not particularly limited, and an optimum material can be selected depending on the purpose. Furthermore, the material and structure of the cathode side gas diffusion layer are not particularly limited, and an optimum material and structure can be selected depending on the purpose.

[0060] On the other hand, the fuel cell according to the present invention uses, as a cathode catalyst, a first electrode catalyst including a first support having first pores and first catalyst particles supported in the first pores; a second electrode catalyst including a second support having second pores and second catalyst particles supported in the second pores; This is what makes it different from conventional methods. The details of the first electrode catalyst and the second electrode catalyst are as described above, and therefore will not be described here. The content of the cathode catalyst will be described later.

[0061] [2.1.4. Anode separator and cathode separator] An anode separator and a cathode separator are disposed on the outer side of the anode side gas diffusion layer and the outer side of the cathode side gas diffusion layer, respectively. The anode separator has an anode flow path for allowing the fuel gas to flow in a specific direction, and similarly, the cathode separator has a cathode flow path for allowing the oxidant gas to flow in a specific direction.

[0062] The structure of the gas flow channels (anode flow channel and cathode flow channel) is not particularly limited, and an optimal structure can be selected depending on the purpose. For example, the gas flow channel may extend linearly from one end to the other end of the separator. Alternatively, the gas flow channel may be bent or curved within the plane of the separator.

[0063] [2.2. Cathode electrode catalyst content] [2.2.1. Definition] In the present invention, the content of the first electrode catalyst contained in the upstream region of the cathode flow channel is greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow channel. This point differs from the prior art. Here, the "upstream region of the cathode flow channel" refers to the region from the inlet of the cathode flow channel to the midpoint between the inlet and outlet of the cathode flow channel. The "downstream region of the cathode flow channel" refers to the region from the midpoint to the outlet of the cathode flow channel. "Content of the first electrode catalyst" refers to the mass (W 1 ) and the mass of the second electrode catalyst (W 2 ) the mass ratio of the first electrode catalyst to the sum of (= W 1 ×100 / (W 1 +W 2 ))

[0064] The "content of the first electrode catalyst contained in the upstream region" refers to the average content of the first electrode catalyst contained in the upstream region, and does not necessarily mean that the content of the first electrode catalyst contained in the upstream region is uniform regardless of location. For example, the content of the first electrode catalyst may decrease stepwise or continuously from the inlet of the cathode flow channel to the midpoint. Similarly, the "content of the first electrode catalyst contained in the downstream region" refers to the average content of the first electrode catalyst contained in the downstream region, and does not necessarily mean that the content of the first electrode catalyst contained in the downstream region is uniform regardless of location. For example, the content of the first electrode catalyst may decrease stepwise or continuously from the middle point of the cathode flow channel toward the outlet.

[0065] [2.2.2. Content of first electrode catalyst in the upstream region] The first electrode catalyst includes a first support having first pores, and first catalyst particles supported in the first pores. Since the pore diameter of the first pores is relatively small, the ionomer can be prevented from entering the first pores, thereby suppressing ionomer poisoning of the first catalyst particles in the first pores, thereby improving power generation performance in the low current density range. Furthermore, even in a low-humidity environment, the adsorbed water in the first pores can be secured by capillary condensation, which ensures a proton transport path and improves power generation performance.

[0066] Therefore, increasing the content of the first electrode catalyst relatively in the upstream region where humidity is low improves power generation performance. To achieve this effect, the content of the first electrode catalyst in the upstream region is preferably 50% or more. The content is preferably 60% or more, 70% or more, 80% or more, or 90% or more.

[0067] [2.2.3. Content of first electrode catalyst in downstream region] The second electrode catalyst includes a second support having second pores and second catalyst particles supported in the second pores, where a second mode diameter of the second pores is larger than the first mode diameter of the first pores.

[0068] The downstream region of the cathode flow channel generally has high humidity due to the influence of water produced during power generation. Therefore, in the downstream region where humidity is high, the content of the first electrode catalyst is reduced and the content of the second electrode catalyst having the second pores with a relatively large pore diameter is increased, thereby suppressing the adverse effects of the flooding phenomenon. To achieve this effect, the content of the first electrode catalyst in the downstream region is preferably less than 50%. The content is preferably less than 40%, less than 30%, less than 20%, or less than 10%.

[0069] [3. Manufacturing method of monodispersed spherical mesoporous silica (template)] As mentioned above, one example of the carrier is monodispersed spherical mesoporous carbon, and an example of the production method thereof will be described. Monodispersed spherical mesoporous carbon is produced by using monodispersed spherical mesoporous silica as a template. To obtain monodispersed spherical mesoporous carbon with a desired microstructure, it is necessary to use monodispersed spherical mesoporous silica with a corresponding microstructure as a template. By optimizing the synthesis conditions of monodispersed spherical mesoporous silica, it is possible to control the diameter, pore size, pore wall thickness, etc.

[0070] Specifically, the method for producing monodispersed spherical mesoporous silica (template) is as follows: a polymerization step of polycondensing the silica source in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles; a drying step of separating the precursor particles from the reaction solution and drying them; a calcination step of calcining the precursor particles to obtain monodispersed spherical mesoporous silica; It is equipped with: The method for producing monodispersed mesoporous silica spheres may further include a diameter enlarging step of subjecting the dried precursor particles to a diameter enlarging treatment.

[0071] [3.1. Polymerization process] First, in a reaction solution containing a silica source, a surfactant, and a catalyst, the silica source is condensation-polymerized to obtain precursor particles (polymerization step).

[0072] 3.1.1. Silica source In the present invention, the type of silica source is not particularly limited. Examples of the silica source include: (a) tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane, and tetraethyleneglycoxysilane; (b) Trialkoxysilanes such as 3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane. As the silica source, any one of these may be used alone or two or more of them may be used in combination.

[0073] The type of silica source has a large effect on the diameter of the mesoporous silica. For example, tetraethyleneglycoxysilane is more reactive than tetramethoxysilane. In general, the more reactive the silica source, the larger the diameter of the mesoporous silica obtained.

[0074] [3.1.2. Surfactants] When a silica source is polycondensed in a reaction solution, the surfactant forms micelles in the reaction solution. Hydrophilic groups are gathered around the micelles, so the silica source is adsorbed to the surface of the micelles. Furthermore, the micelles to which the silica source is adsorbed self-organize in the reaction solution, and the silica source is polycondensed. As a result, pores due to the micelles are formed inside the primary particles. The size of the pores can be controlled (1 to 50 nm) mainly by the molecular length of the surfactant.

[0075] In the present invention, an alkyl quaternary ammonium salt is used as the surfactant. The alkyl quaternary ammonium salt refers to a compound represented by the following formula: CH 3 -(CH 2 ) n -N + (R 1 )(R 2 )(R 3 )X

[0076] In the formula, R 1 , R 2 , R 3 R each represents an alkyl group having 1 to 3 carbon atoms. 1 , R 2 , and R 3 may be the same or different. In order to facilitate aggregation (formation of micelles) between alkyl quaternary ammonium salts, R 1 , R 2 , and R 3 are preferably all the same. 1 , R 2 , and R3 At least one of them is preferably a methyl group, and it is preferable that all of them are methyl groups. In the formula, X represents a halogen atom. The type of the halogen atom is not particularly limited, but X is preferably Cl or Br in view of availability.

[0077] In the formula, n represents an integer of 7 to 21. In general, the smaller n is, the smaller the mode diameter of the pores of a spherical mesoporous material is. On the other hand, the larger n is, the larger the mode diameter is, but if n is too large, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is produced, and a spherical mesoporous material is not obtained. n is preferably 9 to 17, and more preferably 13 to 17.

[0078] Among those represented by the formula, alkyl trimethyl ammonium halides are preferred. Examples of alkyl trimethyl ammonium halides include hexadecyl trimethyl ammonium halides, octadecyl trimethyl ammonium halides, nonyl trimethyl ammonium halides, decyl trimethyl ammonium halides, undecyl trimethyl ammonium halides, and dodecyl trimethyl ammonium halides. Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

[0079] In the case of synthesizing monodispersed spherical mesoporous silica, one type of alkyl quaternary ammonium salt may be used, or two or more types may be used. However, since the alkyl quaternary ammonium salt serves as a template for forming pores in the primary particles, the type of alkyl quaternary ammonium salt has a large effect on the shape of the pores. In order to synthesize silica particles with more uniform pores, it is preferable to use one type of alkyl quaternary ammonium salt.

[0080] Catalyst When the silica source is polycondensed, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, the catalyst may be an alkali such as sodium hydroxide or aqueous ammonia, or an acid.

[0081] 3.1.4. Solvents The solvent used may be water, an organic solvent such as alcohol, or a mixed solvent of water and an organic solvent. Alcohol is (1) Monohydric alcohols such as methanol, ethanol, and propanol, (2) Dihydric alcohols such as ethylene glycol, (3) Trihydric alcohols such as glycerin, Either is fine. When a mixed solvent of water and an organic solvent is used, the content of the organic solvent in the mixed solvent can be arbitrarily selected depending on the purpose. In general, adding an appropriate amount of an organic solvent to the solvent makes it easier to control the particle size and particle size distribution.

[0082] The type and amount of alcohol contained in the solvent has a large effect on the diameter of mesoporous silica. For example, when the solvent is a mixed solvent of water and methanol, the larger the amount of methanol contained in the mixed solvent, the larger the diameter of the mesoporous silica obtained. Furthermore, for example, when the solvent is a mixed solvent of water, methanol, and ethylene glycol, generally, the greater the amount of ethylene glycol contained in the mixed solvent, the larger the diameter of the mesoporous silica obtained.

[0083] [3.1.5. Composition of reaction solution] The composition of the reaction solution affects the external shape and pore structure of the synthesized mesoporous silica. The concentration of the surfactant and the concentration of the silica source in the reaction solution have a large effect on the diameter, pore size, and specific surface area of ​​the monodispersed spherical mesoporous silica. As described above, the type and amount of alcohol contained in the solvent and the type of silica source have a large effect on the diameter of the mesoporous silica.

[0084] [A. Surfactant concentration] If the concentration of the surfactant is too low, the amount of the surfactant to be the template is insufficient, so that a good porous body cannot be obtained, and the uniformity of the particle size is low. Therefore, the concentration of the surfactant is preferably 0.003 mol / L or more. The concentration of the surfactant is preferably 0.005 mol / L or more, more preferably 0.01 mol / L or more.

[0085] On the other hand, if the concentration of the surfactant is too high, it is not possible to obtain a high proportion of spherical porous bodies, and the uniformity of the particle size is reduced. Therefore, the concentration of the surfactant is preferably 0.03 mol / L or less. The concentration of the surfactant is preferably 0.025 mol / L or less, and more preferably 0.02 mol / L or less.

[0086] [B. Concentration of Silica Source] If the concentration of the silica source is too low, it is not possible to obtain a high proportion of porous bodies having a spherical shape, and the uniformity of the particle size is reduced. Therefore, the concentration of the silica source is preferably 0.005 mol / L or more. The concentration of the silica source is preferably 0.0065 mol / L or more, and more preferably 0.008 mol / L or more.

[0087] On the other hand, if the concentration of the silica source is too high, the amount of the surfactant to be the template is insufficient, so that a good porous body cannot be obtained, and the uniformity of the particle size is low. Therefore, the concentration of the silica source is preferably 0.03 mol / L or less. The concentration of the silica source is preferably 0.025 mol / L or less, more preferably 0.02 mol / L or less.

[0088] [C. Catalyst Concentration] In the present invention, the catalyst concentration is not particularly limited. In general, if the catalyst concentration is too low, the particle precipitation speed becomes slow. On the other hand, if the catalyst concentration is too high, the particle precipitation speed becomes fast. It is preferable to select the optimum catalyst concentration according to the type of silica source, the type of surfactant, the target physical property value, etc.

[0089] [3.1.6 Reaction conditions] A silica source is added to a solvent containing a predetermined amount of a surfactant, and hydrolysis and polycondensation are carried out, whereby precursor particles containing silica and the surfactant are obtained with the surfactant acting as a template. The optimum reaction conditions are selected depending on the type of silica source, the particle size of the precursor particles, etc. In general, the reaction temperature is preferably −20 to 100° C. The reaction temperature is more preferably 0 to 80° C., and further preferably 10 to 40° C.

[0090] [3.2. Drying process] Next, the precursor particles are separated from the reaction solution and dried (drying step). Drying is carried out in order to remove the solvent remaining in the precursor particles. The drying conditions are not particularly limited as long as the solvent can be removed.

[0091] [3.3. Expansion process] Next, if necessary, the dried precursor particles may be subjected to a diameter expansion process (diameter expansion step). The "diameter expansion process" refers to a process for expanding the pore diameter within the particles. In addition, as the pore diameter expands, the thickness of the pore wall also increases. Specifically, the diameter-enlarging treatment is carried out by subjecting the synthesized precursor particles (from which the surfactant has not been removed) to a hydrothermal treatment in a solution containing a diameter-enlarging agent, which can enlarge the pore diameter of the precursor particles and increase the thickness of the pore walls.

[0092] Examples of the diameter expanding agent include: (a) Hydrocarbons such as trimethylbenzene, triethylbenzene, triisopropylbenzene, naphthalene, benzene, cyclohexane, hexane, heptane, octane, nonane, decane, undecane, and dodecane; (b) Hydrochloric acid, sulfuric acid, etc. The reason why the pore size increases by hydrothermal treatment in the presence of a hydrocarbon is believed to be that rearrangement of silica occurs when the diameter-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles. In addition, the pore size increases when hydrothermal treatment is performed in the presence of hydrochloric acid or sulfuric acid, which is believed to be due to the dissolution and reprecipitation of silica inside the particles. When the manufacturing conditions are optimized, radial pores are formed inside the silica. When this is hydrothermal treated in the presence of hydrochloric acid or sulfuric acid, silica dissolves and reprecipitation occurs, and the radial pores are converted into interconnected pores.

[0093] It is preferable to select optimal conditions for the diameter expansion treatment so as to obtain the desired pore diameter, etc. For example, when hydrothermal treatment is performed in the presence of hydrochloric acid, the higher the hydrothermal treatment temperature, the larger the pore diameter, etc. In order to obtain monodispersed spherical carbon porous bodies having a pore diameter of 2.0 to 20 nm, the hydrothermal treatment temperature is preferably 130 to 245°C.

[0094] [3.4. Firing process] Next, after carrying out a diameter expansion treatment as necessary, the precursor particles are calcined (calcination step), whereby monodispersed spherical mesoporous silica is obtained. The calcination is carried out in order to dehydrate and crystallize the precursor particles with residual OH groups, and to thermally decompose the surfactant remaining in the pores. The calcination conditions are not particularly limited as long as the dehydration, crystallization, and thermal decomposition of the surfactant are possible. The calcination is usually carried out by heating in the air at 400°C to 700°C for 1 hour to 10 hours.

[0095] [4. Manufacturing method of monodispersed spherical mesoporous carbon] A method for producing monodisperse spherical mesoporous carbon as an example of the carrier according to the present invention includes the following steps: (a) a first step of preparing monodispersed mesoporous silica spheres as a template; (b) a second step of precipitating carbon in the pores of the monodispersed mesoporous silica spheres to produce a monodispersed mesoporous silica / carbon composite; (c) a third step of removing the silica from the composite; It is equipped with:

[0096] [4.1. First step (preparation of mold)] First, monodispersed mesoporous silica spheres are prepared to serve as a template (first step). The details of the method for producing the monodispersed mesoporous silica spheres are as described above, and therefore will not be described here.

[0097] [4.2. Second step (carbon deposition in pores)] Next, carbon is precipitated in the pores of the monodispersed mesoporous silica spheres to produce a monodispersed mesoporous silica sphere / carbon composite (second step). Specifically, the deposition of carbon in the pores is as follows: (a) introducing a carbon precursor into the pores; (b) Polymerizing and carbonizing the carbon precursor in the pores This is done by:

[0098] [4.2.1. Introduction of carbon precursor] The term "carbon precursor" refers to a material capable of producing carbon by pyrolysis. Specific examples of such carbon precursors include: (1) A polymer precursor that is liquid at room temperature and is thermally polymerizable (e.g., furfuryl alcohol, aniline, etc.), (2) A mixture of an aqueous solution of carbohydrates and an acid (e.g., a mixture of monosaccharides such as sucrose, xylose, glucose, etc., or disaccharides or polysaccharides with an acid such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid), (3) Mixtures of two-component curing polymer precursors (e.g., phenol and formalin, etc.), etc. Among these, the polymer precursor can be impregnated into the pores without diluting with a solvent, so that a relatively large amount of carbon can be produced in the pores with a relatively small number of impregnations. In addition, the polymer precursor has the advantage that a polymerization initiator is not required and it is easy to handle.

[0099] When a liquid or solution carbon precursor is used, the amount of liquid or solution adsorbed per one time is preferably as large as possible, and the amount is preferably such that the entire pores are filled with the liquid or solution. When a mixture of an aqueous solution of a carbohydrate and an acid is used as the carbon precursor, the amount of acid is preferably the minimum amount capable of polymerizing the organic matter. Furthermore, when a mixture of two-liquid curing polymer precursors is used as the carbon precursor, The optimum ratio is selected depending on the type of polymer precursor.

[0100] [4.2.2. Polymerization and carbonization of carbon precursors] The polymerized carbon precursor is then carbonized within the pores. Carbonization of the carbon precursor is carried out by heating the spherical mesoporous body to a predetermined temperature in a non-oxidizing atmosphere (e.g., in an inert atmosphere, in a vacuum, etc.). Specifically, the heating temperature is preferably 500°C or higher and 1200°C or lower. If the heating temperature is lower than 500°C, the carbon precursor is not sufficiently carbonized. On the other hand, if the heating temperature exceeds 1200°C, silica and carbon react with each other, which is not preferable. The optimal heating time is selected depending on the heating temperature.

[0101] The amount of carbon generated in the pores may be equal to or greater than the amount that allows the carbon particles to maintain their shape when the monodispersed spherical mesoporous silica is removed. Therefore, when the amount of carbon generated in one filling, polymerization, and carbonization is relatively small, it is preferable to repeat these steps multiple times. In this case, the conditions for each repeated step may be the same or different. Furthermore, when each of the steps of filling, polymerization, and carbonization is repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization step is completed, another carbonization step may be performed at a higher temperature. If the final carbonization step is performed at a higher temperature than the previous carbonization steps, the carbon introduced into the pores in multiple steps is more likely to be integrated.

[0102] [4.3. Third step (removal of template)] Next, the silica template is removed from the composite (third step), thereby obtaining monodispersed spherical carbon porous bodies. Specific methods for removing silica include: (1) A method of heating the complex in an alkaline aqueous solution such as sodium hydroxide, (2) Etching the composite with an aqueous solution of hydrofluoric acid; etc.

[0103] [5. Manufacturing method of electrode catalyst] An example of a method for producing an electrode catalyst using monodispersed spherical mesoporous carbon is as follows: (a) a first step of preparing monodispersed spherical mesoporous carbon; (b) a second step of dispersing the monodispersed mesoporous carbon spheres and the catalyst precursor in a solvent and reducing them in the liquid phase using a reducing agent; It is equipped with:

[0104] [5.1. First step (preparation of support)] First, monodispersed mesoporous carbon spheres are prepared as the carrier (Step 1). Details of the method for producing monodispersed mesoporous carbon spheres are as described above, and therefore will not be described here.

[0105] [5.2. Second step (liquid phase reduction)] Next, the monodispersed mesoporous carbon spheres and catalyst precursor are dispersed in a solvent and reduced in liquid phase using a reducing agent (second step), thereby obtaining an electrode catalyst in which catalyst particles are supported in the pores of the support made of monodispersed mesoporous carbon spheres.

[0106] It is preferable to select the optimum catalyst precursor depending on the composition of the catalyst particles to be produced, and it is also preferable to select the optimum reducing agent depending on the type of catalyst precursor to be used. Examples of catalyst precursors include Pt compounds such as hexachloroplatinic (IV) acid hexahydrate, dinitrodiammineplatinum (II), hexaammineplatinum (IV) chloride, tetraammineplatinum (II) chloride, and bis(acetylacetonato)platinum (II). The reducing agent includes, for example, ethanol, methanol, formic acid, hydrazine, sodium borohydride, ethylene glycol, and propylene glycol.

[0107] [6. Effect] Using mesoporous carbon with small pores as a support, an electrocatalyst with high water retention can be obtained. Such electrocatalysts perform well in low humidity environments, but perform poorly in high humidity environments. On the other hand, when mesoporous carbon with large pore size is used as the support, an electrode catalyst in which the flooding phenomenon is suppressed can be obtained. Such an electrode catalyst exhibits high performance in a high humidity environment, but its performance is inferior in a low humidity environment.

[0108] In the cathode flow channel, due to the influence of water produced during power generation, there is a humidity gradient, with the upstream region being a low humidity environment and the downstream region being a high humidity environment. Therefore, by placing a large amount of the first electrode catalyst with a small pore diameter in the upstream region of the cathode flow path and a large amount of the second electrode catalyst with a large pore diameter in the downstream region of the cathode flow path, the first electrode catalyst and the second electrode catalyst can be utilized more efficiently.

[0109] Therefore, by making the content of the first electrode catalyst contained in the upstream region of the cathode flow path greater than the content of the first electrode catalyst contained in the downstream region of the cathode flow path, the fuel cell of the present invention can exhibit high power generation performance even in an environment with a humidity gradient. EXAMPLES

[0110] (Reference examples 1~3) [1. Sample preparation] [1.1. Preparation of electrode catalyst α] [1.1.1. Preparation of monodispersed mesoporous silica spheres (template α)] 14.1g of hexadecyltrimethylammonium chloride and 13.7mL of 1N sodium hydroxide solution were added to a mixed solution consisting of 1970g of water and 1216g of methanol. When 14.5g of tetraethoxysilane was added to this mixed solution, the solution became cloudy after a while, and it was confirmed that particles were synthesized. The molar concentration of the surfactant was 0.0125mol / L, and the molar concentration of the silica source was 0.0198mol / L.

[0111] After stirring for 8 hours at room temperature, the mixture was filtered and the residue was redispersed in 1 L of water. After filtering again, the residue was dried in an oven at 45°C. 10 g of the dried sample was dispersed in 300 mL of 2N hydrochloric acid and heated in an autoclave at 130°C for 3 days. After filtering and washing the autoclaved sample, the sample was calcined at 550°C to remove the organic components and obtain monodispersed spherical mesoporous silica (template α).

[0112] [1.1.2. Preparation of monodispersed spherical mesoporous carbon (support α)] 0.5 g of template α was placed in a PFA container (volume 15 mL), and furfuryl alcohol (FA) was added to the pore volume to allow it to penetrate into the pores of template α. This was heat-treated at 150°C for 24 hours to polymerize the FA. This was then heat-treated in a nitrogen atmosphere for 6 hours at 500°C to carbonize the FA. This was repeated twice, and then heat-treated in a nitrogen atmosphere for 6 hours at 900°C to obtain a monodispersed spherical mesoporous silica / carbon composite. This composite was immersed in a 12% HF solution for 12 hours to dissolve the silica component. After dissolution, it was repeatedly filtered and washed, and then dried at 45°C to obtain monodispersed spherical mesoporous carbon (carrier α).

[0113] The nitrogen adsorption isotherm of the support α before supporting the catalyst particles α was measured, and the obtained data on the adsorption side was analyzed by the BJH method to obtain the pore size distribution of the pores α. From this, the mode diameter α of the pore α was 3.1 nm. In addition, the volume of pores α obtained by integrating the results of pore diameter distribution calculations using the BJH method was 1.16 cc / g.

[0114] [1.1.3. Pt catalyst support] The carrier α and Pt precursor were dispersed in an aqueous solvent. Next, Pt was supported on the surface of the carrier α by liquid phase reduction using a reducing agent. The surface of the carrier α includes not only the outer surface of the carrier α but also the inner surface of the pores α. The Pt support rate of the obtained electrode catalyst α was 45 to 51 wt%.

[0115] [1.2. Preparation of electrode catalysts β and γ] Except for changing the temperature of the autoclave treatment, the same procedures were followed as for electrode catalyst α to prepare monodispersed spherical mesoporous silica (templates β and γ), prepare monodispersed spherical mesoporous carbon with large pore size, and support Pt catalyst. The Pt support rate of electrode catalysts β and γ was 45-51 wt%. The electrode catalyst β (support β, pores β, mode diameter β, catalyst particles β) and the electrode catalyst γ (support γ, pores γ, mode diameter γ, catalyst particles γ) have different pore diameters.

[0116] The nitrogen adsorption isotherm of the support β before supporting the catalyst particles β was measured, and the obtained data on the adsorption side was analyzed by the BJH method to obtain the pore size distribution of the pores β. From this, the mode diameter β of the pore β was 7.7 nm. Moreover, the volume of pores β obtained by integrating the results of pore diameter distribution calculations using the BJH method was 1.49 cc / g.

[0117] Similarly, the nitrogen adsorption isotherm of the support γ before supporting the catalyst particles γ was measured, and the obtained data on the adsorption side was analyzed by the BJH method to obtain the pore size distribution of the pores γ. From this, the mode diameter γ of the pore γ was 4.9 nm. Moreover, the volume of pores γ obtained by integrating the results of pore diameter distribution calculations using the BJH method was 1.25 cc / g.

[0118] [1.3. Preparation of cathode catalyst layer] An ink was prepared by dispersing the electrode catalyst α in an ionomer solution (D2020) containing water, ethanol, and Nafion (registered trademark). After degassing using a planetary stirring degassing device, the ink was applied to a polytetrafluoroethylene sheet using an ink coater. After drying, the ink was applied to a 1 cm 2 The cathode catalyst layer (Reference Example 1) was prepared by cutting the sheet into pieces of 0.14 mg / cm2. 2 The mass ratio of ionomer to carbon (I / C ratio) was set to 1.1. Moreover, a cathode catalyst layer (Reference Example 2) was produced in the same manner as in Reference Example 1, except that the electrode catalyst β was used as the cathode catalyst. Furthermore, a cathode catalyst layer (Reference Example 3) was produced in the same manner as in Reference Example 1, except that the electrode catalyst γ was used as the cathode catalyst.

[0119] [1.4. Preparation of anode catalyst layer] For the catalyst, an ink was prepared by dispersing 60 wt% Pt / Vulcan (registered trademark) in an ionomer solution (D2020) containing water, ethanol, and Nafion (registered trademark). After degassing using a planetary stirring degassing device, the ink was applied to a polytetrafluoroethylene sheet using an ink coater. After drying, the ink was applied to a 1 cm 2 The anode catalyst layer was prepared by cutting the anode catalyst layer into pieces of 0.2 mg / cm2. 2 The mass ratio of ionomer to carbon (I / C ratio) was set to 1.0.

[0120] [1.5. Preparation of MEA] The cathode catalyst layer and the anode catalyst layer were thermally transferred onto both sides of an electrolyte membrane (fluoropolymer membrane, 10 μm thick) to prepare a membrane electrode assembly (MEA). The thermal transfer conditions were 120°C, 5 min. of pressureless heating, then 120°C, 50 kgf / cm 2 The pressure was applied at 4.90 MPa for 5 minutes. The electrode area was 1 cm × 1 cm. This MEA was sandwiched between carbon paper diffusion layers with a μ-porous layer (SIGRECET (registered trademark) 22BB, SGL) to form a cell.

[0121] 2. Test Method The above cell was used for break-in operation. Then, the power generation performance was examined in a low humidity environment (cell temperature: 80°C, humidity: 30% RH) and a high humidity environment (cell temperature: 60°C, humidity: 90% RH). The type and flow rate of the gas used was hydrogen / 730nccm on the anode side and air / 1461nccm on the cathode side in the low humidity environment. In the high humidity environment, hydrogen / 750nccm on the anode side and air / 1249nccm on the cathode side. The gas back pressure was 50kPa for both electrodes. In addition, since these flow rates were all far in excess of the reaction consumption amounts, the humidity at the inlet and outlet sides of the cell was almost the same.

[0122] [3. Results] [3.1. Power generation performance in low humidity environments] The power generation performance in a low humidity environment (80°C, 30% RH) of cells using electrode catalyst α (Reference Example 1) and electrode catalyst β (Reference Example 2) is shown in Figure 1. The power generation performance of the cell using electrode catalyst α was significantly higher than that of the cell using electrode catalyst β.

[0123] This can be thought of as follows. The mode diameter α of the pores α is as small as 3.1 nm. Therefore, by preventing the intrusion of the ionomer into the pores α, the ionomer poisoning of the catalyst particles α in the pores α can be suppressed. This improves the power generation performance in the low current density range. Furthermore, even in a low humidity environment, adsorbed water can be secured within the pores α by capillary condensation, which ensures a proton transport path and improves power generation performance.

[0124] [3.2. Power generation performance in high humidity environments] Figure 2 shows the power generation performance in a high humidity environment (60°C, 90% RH) of cells using electrode catalyst α (Reference Example 1) and electrode catalyst β (Reference Example 2). The cell using electrode catalyst α had slightly higher power generation performance at 0.7 V or higher than the cell using electrode catalyst β, but the power generation performance decreased at voltages lower than that. The reason why the power generation performance of the cell using electrode catalyst α is higher at 0.7 V or higher is due to the effect of catalyst particles α in suppressing ionomer poisoning, as in the case of a low humidity environment.

[0125] The mode diameter α of the pores α of the electrode catalyst α is small at 3.1 nm, so in a high-humidity environment, the pores α are prone to clogging with water due to capillary condensation, which slows down the transport of oxygen to the surface of the catalyst particle α and reduces power generation performance. On the other hand, the mode diameter β of the pores β of the electrode catalyst β is as large as 7.7 nm, so that the flooding phenomenon can be suppressed and the decrease in power generation performance can be suppressed. As a result, in the high current density region below 0.7 V, the power generation performance is reversed.

[0126] Although not shown, the power generation performance of the cell using electrode catalyst γ (Reference Example 3) in a low humidity environment (80°C, 30% RH) and a high humidity environment (60°C, 90% RH) was also measured in the same manner as in Reference Examples 1 and 2. The power generation performance of the cell using electrode catalyst γ was not significantly different from that of the cell using electrode catalyst α.

[0127] (Examples 1 and 2, Comparative Examples 1 to 3) In the experiments shown in Figures 1 and 2, a large amount of supply gas is flowing, so the humidity is almost the same on the upstream and downstream sides of the gas flow path. However, in an actual fuel cell, the flow rate of the supply gas is restricted, so even if the humidity of the supply gas is low, the humidity on the downstream side will be high due to water generated during power generation. Therefore, we predicted the power generation performance of a fuel cell that uses different electrode catalysts in the upstream and downstream regions of the cathode flow path.

[0128] Table 1 shows the configuration of the fuel cell for which performance was predicted. Example 1 is a fuel cell in which electrode catalyst α (first electrode catalyst: first mode diameter 3.1 nm: content 100%) is arranged in the upstream region of the cathode flow path, and electrode catalyst β (second electrode catalyst: second mode diameter 7.7 nm: content 100%) is arranged in the downstream region. Example 2 is a fuel cell in which electrode catalyst α (first electrode catalyst: first mode diameter 3.1 nm: content 100%) is arranged in the upstream region of the cathode flow path, and electrode catalyst γ (second electrode catalyst: second mode diameter 4.9 nm: content 100%) is arranged in the downstream region.

[0129] Comparative Example 1 is a fuel cell in which the electrode catalyst α (first electrode catalyst: first mode diameter 3.1 nm: content 100%) is disposed in the upstream region and downstream region of the cathode flow channel. Comparative Example 2 is a fuel cell in which the electrode catalyst β (second electrode catalyst: second mode diameter 7.7 nm: content 100%) is disposed in the upstream region and downstream region of the cathode flow channel. Comparative Example 3 is Example 1 of Patent Document 1.

[0130] [Table 1]

[0131] FIG. 3 shows a schematic diagram of the assumptions used to predict the power generation performance. In the case of Examples 1 and 2 and Comparative Example 3, the area ratio of the first electrode catalyst and the second electrode catalyst was set to half and half. In addition, the supply gas was set to low humidity, but the humidity of the gas in the fuel cell gradually increases due to water generated during power generation. In order to simply express this state, it was assumed that the humidity of the upstream region (first half) of the cathode flow path was 30% RH, and the humidity of the downstream region (second half) of the cathode flow path was 90% RH. In Example 1, the power generation performance of the entire cell was calculated using the power generation performance of FIG. 1 in the first half and the power generation performance of FIG. 2 in the second half.

[0132] 4 shows the current density at 0.6 V (corrected for IR loss) obtained by simple calculation for the fuel cells of Examples 1 and 2 and Comparative Examples 1 to 3. The current density is a relative value when Comparative Example 1 is standardized as 1. It is apparent from FIG. 4 that Example 1 has higher power generation performance than Example 2 and Comparative Examples 1 to 3.

[0133] The results of Example 2 and Comparative Example 1 show that there is a certain effect in disposing a second electrode catalyst having a large pore size in the downstream region. In addition, it is found from the results of Example 1 and Example 2 that the second mode diameter of the second electrode catalyst affects the power generation performance. This shows that in a high humidity environment, the effect of suppressing the flooding phenomenon is more effective when the second mode diameter is equal to or larger than a predetermined value. Furthermore, the results of Example 1 and Comparative Example 3 show the importance of ensuring proton transport pathways in the high current density region.

[0134] In this calculation, the area ratio of the first electrode catalyst and the second electrode catalyst was set to half and half in the examples, but the optimal area ratio varies depending on the operating conditions of the cell. For example, in the case of a fuel cell operated under conditions where the humidity of the entire cell is low, it is desirable to increase the area ratio of the first electrode catalyst. On the other hand, in the case of a fuel cell operated under conditions where the humidity of the entire cell is relatively high, it is desirable to decrease the area ratio of the first electrode catalyst.

[0135] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the present invention. [Industrial Applicability]

[0136] The fuel cell according to the present invention can be used as an in-vehicle power source, a small stationary power generator, and the like.

Claims

1. A fuel cell having the following configuration. (1) The fuel cell includes a membrane electrode assembly (MEA) in which an anode catalyst layer and a cathode catalyst layer are joined to both sides of an electrolyte membrane, an anode-side gas diffusion layer disposed outside the anode catalyst layer, a cathode-side gas diffusion layer disposed outside the cathode catalyst layer, an anode separator having an anode flow path disposed outside the anode-side gas diffusion layer, and a cathode separator having a cathode flow path disposed outside the cathode-side gas diffusion layer. It is provided with. (2) The cathode catalyst layer a first electrode catalyst including a first carrier having first pores and first catalyst particles supported in the first pores, a second electrode catalyst including a second carrier having second pores and second catalyst particles supported in the second pores, and a catalyst layer ionomer is provided with, The first mode diameter of the first pores is smaller than the second mode diameter of the second pores. (3) The content of the first electrode catalyst contained in the upstream region of the cathode flow path is larger than the content of the first electrode catalyst contained in the downstream region of the cathode flow path.

2. The content of the first electrode catalyst contained in the upstream region is 90% or more, The content of the first electrode catalyst contained in the downstream region is less than 10%. The fuel cell according to claim 1.

3. The fuel cell according to claim 1, wherein the first carrier and the second carrier are each mesoporous carbon.

4. The first carrier has a capacity of the first pores of 0.50 cc / g or more and less than 1.30 cc / g, The second carrier has a capacity of the second pores of 1.30 cc / g or more and 3.70 cc / g or less. The fuel cell according to claim 1.

5. The first mode diameter is 2.0 nm or more and less than 5.0 nm, The second mode diameter is 5.0 nm or more and 20.0 nm or less. The fuel cell according to claim 1.

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