fuel cell electrode catalyst layer

Abstract

To improve power generation performance under a high humidity condition in a fuel cell electrode catalyst layer equipped with an electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles.SOLUTION: A fuel cell electrode catalyst layer includes an electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles, ionomer, and hydrophobic molecules, and the tin oxide-based particles preferably have a structure in which porous primary particles are fused together in a bead-like structure (bead-like structure). The amount of modification of the hydrophobic molecule is preferably 0.2 mass% or more and 8.0 mass% or less. However, the "amount of modification of the hydrophobic molecule" refers to the ratio of the mass of the hydrophobic molecule to the total mass of the electrode catalyst and the hydrophobic molecule.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fuel cell electrode catalyst layer, and more particularly to a fuel cell electrode catalyst layer comprising an electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles. [Background technology]

[0002] A polymer electrolyte fuel cell (PEFC) comprises a membrane electrode assembly (MEA) in which catalyst layers are bonded to both sides of an electrolyte membrane. Typically, a gas diffusion layer is located outside the catalyst layer. Furthermore, a current collector (separator) with a gas channel is located outside the gas diffusion layer. A PEFC typically has a structure (fuel cell stack) in which multiple single cells, each consisting of such an MEA, gas diffusion layer, and current collector, are stacked.

[0003] In PEFCs, the catalyst layer generally consists of a mixture of an electrode catalyst, in which catalyst metal nanoparticles such as platinum are supported on the surface of a support, and a catalyst layer ionomer. Conventionally, carbon materials such as carbon black and acetylene black have been mainly used as catalyst supports. In particular, carbon supports with mesopores have attracted attention in recent years (Non-Patent Document 1). It has been found that by using porous carbon particles with appropriately controlled particle size and pore diameter as a support, it is possible to achieve both a reduction in catalyst poisoning by sulfonic acid groups of the ionomer and a reduction in Knudsen diffusion resistance within the support pores, thereby obtaining cell performance that does not conflict with low-load performance and high-load performance (Patent Document 1).

[0004] However, it is known that carbon supports undergo oxidative corrosion when exposed to high potentials, causing catalyst metal nanoparticles supported on the support to detach and resulting in a decrease in electrode performance. For this reason, it has been proposed to use conductive metal oxides that are stable at high potentials as support materials. For example, Non-Patent Document 2 suggests that porous tin oxide particles (M-SnO2) doped with different elements (M=Nb, Sb, Ta, W, etc.) may be a promising carrier material in terms of high potential stability.

[0005] Patent Document 2 discloses that (a) A powder (electrode catalyst) in which 7 mass% of Pt is supported on a carrier made of SnO2 doped with 4 at% of Nb is prepared, (b) A catalyst ink containing the powder, a solid polymer electrolyte, and graphite carbon black (GCB) is prepared, (c) The catalyst ink is applied to both sides of the electrolyte membrane Thereby, a catalyst layer-coated electrolyte membrane (CCM) is disclosed. The same document describes that when a highly hydrophobic substance such as GCB is added to the catalyst layer, even when a carrier with relatively high hydrophilicity is used as the catalyst carrier, the generated water can be easily discharged from the catalyst layer, and flooding can be suppressed.

[0006] Patent Document 3 discloses that (a) A Pt / SiO2NF electrode is prepared by forming a thin platinum layer on the surface of a non-woven fabric made of SiO2 nanofibers, (b) The Pt / SiO2NF electrode is immersed in a dilute solution containing a fluorine-based polymer and dried Thereby, a fuel cell electrode is disclosed. The same document describes that when a hydrophobic molecule is added to a fuel cell electrode provided with a thin-layer noble metal, the flooding resistance is greatly improved.

[0007] Furthermore, Non-Patent Document 3 discloses a method of introducing a fluorine-based polymer binder into a Pt@C active layer using supercritical CO2 as a solvent. The same document describes that by such a method, an extremely uniform and thin fluorine-based polymer film can be deposited on the surface of the carbon carrier.

[0008] Because the surface of tin oxide particles is hydrophilic, when used as a catalyst support, water tends to accumulate near the Pt under high humidity conditions, easily inhibiting the oxygen reduction reaction. In particular, when Pt is supported within the mesopores of a porous tin oxide support, water is likely to accumulate within the mesopores and cause flooding during high-load operation or under excessively humid conditions.

[0009] On the other hand, Patent Document 2 proposes a method for adding a highly hydrophobic substance to a catalyst layer containing Pt / Nb-SnO2. However, the Nb-SnO2 support used in that document is a solid particle without mesopores, and the highly hydrophobic substance is GCB. Therefore, even if the method described in that document is applied to a catalyst layer equipped with a hydrophilic porous support, it is not possible to make the inside of the pores of the porous support water-repellent.

[0010] Patent Document 3 and Non-Patent Document 3 propose a method for adding hydrophobic molecules to the catalyst layer. However, the support used in these documents is not SnO2 and is a solid support without mesopores. Furthermore, there have been no previous examples of methods proposed for improving the hydrophobicity of the surface and / or within the pores of an electrode catalyst using porous tin oxide as a support, thereby improving power generation performance under high humidity conditions. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2021-084852 [Patent Document 2] International Publication No. 2015 / 151714 [Patent Document 3] Japanese Patent Publication No. 2016-071960 [Non-patent literature]

[0012] [Non-Patent Document 1] S. Ott et al., Nature Mater., 2019, 19, 77 [Non-Patent Document 2] Jalalpoor et al., J. Electrochem. Soc., 2021, 168, 024502 [Non-Patent Document 3] Elmanovich et al., Int. J. Hydrog. Energy, 2013, 38, 10592 [Overview of the project] [Problems that the invention aims to solve]

[0013] The problem that this invention aims to solve is to improve the power generation performance under high humidity conditions in a fuel cell electrode catalyst layer equipped with an electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles. [Means for solving the problem]

[0014] To solve the above problems, the fuel cell electrode catalyst layer according to the present invention is An electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles, Ionoma and, Hydrophobic molecules and It is equipped with. [Effects of the Invention]

[0015] Adding hydrophobic molecules to a catalyst layer comprising an electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles improves power generation performance under high humidity conditions. In particular, when using a dispersion method (a method of preparing the catalyst layer after treating the electrode catalyst with a water-repellent agent) to add hydrophobic molecules to the catalyst layer, optimizing the amount of hydrophobic molecules added yields a catalyst layer that exhibits relatively high oxygen reduction (ORR) activity under high humidity conditions and / or over-humid conditions. This is thought to be because, when using the dispersion method, the surface of the hydrophilic tin oxide particles is directly coated with hydrophobic molecules, thereby increasing the water repellency of the electrode catalyst.

[0016] On the other hand, when using the dip-coating method (a method of treating the electrode catalyst to make it water-repellent after the catalyst layer has been fabricated) to add hydrophobic molecules to the catalyst layer, optimizing the amount of hydrophobic molecules added yields a catalyst layer that exhibits relatively high ORR activity and relatively low catalyst layer resistance under high humidity conditions. This is thought to be because the dip-coating method imparts appropriate water repellency to the electrode catalyst while simultaneously facilitating the securing of electron conduction paths between electrode catalyst particles. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1(A) is a schematic diagram of a catalyst layer fabricated using the dip-coating method. Figure 1(B) is a schematic diagram of a catalyst layer fabricated using the dispersion method. [Figure 2] Figure 2(A) shows the IV curve at 80% RH for cells equipped with the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 2(B) shows the IV curve at 160% RH for cells equipped with the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. [Figure 3] Figure 3(A) shows the IV curve at 80% RH for cells equipped with the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. Figure 3(B) shows the IV curve at 160% RH for cells equipped with the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2.

[0018] [Figure 4] Figure 4(A) shows the ORR mass activity at an IR-corrected voltage of 0.84V for the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 4(B) shows the ORR mass activity at an IR-corrected voltage of 0.84V for the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. [Figure 5] Figure 5(A) shows the ECSA of the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 5(B) shows the ECSA of the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. [Figure 6]This shows the anion adsorption rate at 80% RH for the electrode catalysts obtained in Example 4 and Comparative Example 2.

[0019] [Figure 7] Figure 7(A) shows the catalyst layer resistance of the catalyst layers obtained in Examples 1-3 (dip coating method) and Comparative Example 1. Figure 7(B) shows the catalyst layer resistance of the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. [Figure 8] Figure 8(A) shows the oxygen transport resistance of the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 8(B) shows the oxygen transport resistance of the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. [Figure 9] These are the water vapor adsorption isotherms of the electrode catalysts obtained in Example 4 and Comparative Example 2. [Figure 10] These are EDX spectra obtained from HAADF-STEM images of the cross-sections of the electrode catalysts obtained in Comparative Example 2, Example 4, and Example 6 after FIB processing. [Modes for carrying out the invention]

[0020] One embodiment of the present invention will be described in detail below. [1. Fuel cell electrode catalyst layer] The fuel cell electrode catalyst layer (hereinafter also simply referred to as the "catalyst layer") according to the present invention has the following configuration.

[0021] [Configuration 1] An electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles, Ionoma and, Hydrophobic molecules and A fuel cell electrode catalyst layer equipped with a fuel cell electrode catalyst layer.

[0022] [Configuration 2] The fuel cell electrode catalyst layer according to configuration 1, wherein the tin oxide particles have a structure in which porous primary particles are fused together in a chain-like manner (beaded structure).

[0023] [Configuration 3] The tin oxide particles have a specific surface area of ​​60 m². 2 The fuel cell electrode catalyst layer according to configuration 1 or 2, which is 1 / g or more.

[0024] [Structure 4] The aforementioned tin oxide particles have an electrical conductivity of 1 × 10⁻⁶ in their compacted form. -3 A fuel cell electrode catalyst layer according to any one of configurations 1 to 3, having a density of S / cm or higher.

[0025] [Composition 5] The fuel cell electrode catalyst layer according to any one of configurations 1 to 4, wherein the pore size of the tin oxide particles is 5 nm or more and 8 nm or less.

[0026] [Composition 6] The fuel cell electrode catalyst layer according to any one of configurations 1 to 5, wherein the pore capacity (pre-supported pore capacity) of the tin oxide-based particles is 0.1 cc / g or more and 0.4 cc / g or less.

[0027] [Composition 7] A fuel cell electrode catalyst layer according to any one of configurations 1 to 6, wherein the ratio of the mass (I) of the ionomer to the mass (S) of the tin oxide particles (=I / S) is 0.13 or more and 0.39 or less.

[0028] [Structure 8] The fuel cell electrode catalyst layer according to any one of configurations 1 to 7, wherein the amount of modification of the hydrophobic molecule is 0.2 mass% or more and 8.0 mass% or less.

[0029] [Composition 9] The activity under high humidity conditions was 260 A / g. Pt That is all, and / or, Activity under excessively humid conditions is 100 A / g Pt That's all. A fuel cell electrode catalyst layer as described in any one of configurations 1 to 8.

[0030] [Configuration 10] The activity under high humidity conditions is 100 A / g. Pt That's all. The catalyst layer resistance under high humidity conditions is 0.1 Ωcm. -2 The following is A fuel cell electrode catalyst layer as described in any one of configurations 1 to 8.

[0031] [Composition 11] The fuel cell electrode catalyst layer according to any one of configurations 1 to 10, wherein the tin oxide particles consist of Sb, Nb, Ta, and / or W-doped SnO2.

[0032] [Composition 12] The fuel cell electrode catalyst layer according to any one of configurations 1 to 11, wherein the average particle size of the Pt-based fine particles is 5 nm or less.

[0033] [Composition 13] The fuel cell electrode catalyst layer according to any one of configurations 1 to 12, wherein the hydrophobic molecule is Cytop® (manufactured by AGC, CTL-109A), Teflon® AF (manufactured by Chemours, 1600 or 2400), and / or Hyflon® (manufactured by Solvay, AD60).

[0034] [1.1. Electrocatalyst] Electrode catalysts are Porous tin oxide particles, Pt-based fine particles supported on the surface of porous tin oxide-based particles and It is equipped with.

[0035] [1.1.1. Tin Oxide-Based Particles] [A. Composition] "Tin oxide particles" refers to particles made of SnO2, or particles made of SnO2 containing a dopant. In the present invention, the type of dopant is not particularly limited. Examples of dopants include Nb, Sb, W, Ta, and Al. SnO2 may contain one of these dopants, or it may contain two or more.

[0036] Among these, tin oxide-based particles are preferably SnO₂ doped with Sb, Nb, Ta, and / or W. In particular, the tin oxide-based particles are preferably SnO₂ doped with Sb. SnO₂ doped with Sb has a higher conductivity than SnO₂ containing other dopants, and thus is suitable as a catalyst support for supporting Pt-based fine particles.

[0037] In SnO₂ doped with Sb, the higher the doping amount of Sb, the higher the conductivity. In order to obtain such an effect, the doping amount of Sb is preferably 2.5 at% or more. The doping amount of Sb is more preferably 5.0 at% or more. On the other hand, when the doping amount of Sb becomes excessive, the carrier concentration becomes excessive and the conductivity may decrease. Therefore, the doping amount of Sb is preferably 15.0 at% or less. The doping amount of Sb is more preferably 10.0 at% or less.

[0038] [B. Specific surface area] Generally, the larger the specific surface area of the tin oxide-based particles, the more Pt-based fine particles can be supported in a highly dispersed state, and thus the ORR mass activity is improved. Therefore, the larger the specific surface area of the tin oxide-based particles, the better. In order to obtain a high ORR mass activity, the specific surface area of the tin oxide-based particles is preferably 30 m 2 / g or more. The specific surface area is more preferably 50 m 2 / g or more, 60 m 2 / g or more, 90 m 2 / g or more, or 100 m 2 / g or more.

[0039] [C. Pore diameter] The tin oxide-based particles preferably have pores (hereinafter also referred to as "mesopores") with a pore diameter of 50 nm or less inside. Here, the "mesopore" generally refers to a pore with a diameter of 2 nm or more and 50 nm or less. However, in the present invention, when referring to the "mesopore", unless otherwise specified, in addition to pores with a diameter of 2 nm or more and 50 nm or less, pores with a diameter of less than 2 nm (so-called "micropores") are also included. "Pore diameter" refers to the average diameter of mesopores. The pore size is obtained by analyzing the adsorption-side data of the nitrogen adsorption isotherm of tin oxide particles using the BJH method and determining the pore size (most frequent peak value, or mode pore size) when the pore volume is maximum.

[0040] When tin oxide particles have mesopores, supporting Pt-based fine particles on them increases the proportion of Pt-based fine particles within the mesopores. Therefore, when Pt-based fine particles are supported within the mesopores of tin oxide particles to create an electrode catalyst, and a catalyst layer is fabricated using such an electrode catalyst and an ionomer, poisoning of the Pt-based fine particles by the ionomer and the resulting performance degradation can be suppressed.

[0041] When tin oxide particles have mesopores, the pore size (mesopore size) affects the performance of the electrode catalyst. Generally, if the pore size becomes too small, it becomes difficult to support Pt-based fine particles within the mesopores. As a result, when a catalyst layer is prepared using the electrode catalyst and ionomer according to the present invention, the Pt-based fine particles may be poisoned by the ionomer. Therefore, a pore size of 1 nm or larger is preferable. More preferably, the pore size is 2 nm or larger, and even more preferably, 5 nm or larger.

[0042] On the other hand, if the pore size becomes too large, ions may penetrate into the mesopores, and the Pt-based fine particles supported in the mesopores may be poisoned by the ions. Therefore, a pore size of 20 nm or less is preferable. More preferably, the pore size is 10 nm or less, and even more preferably, 8 nm or less. In particular, when the pore size of the tin oxide particles is set to 5 nm or more and 8 nm or less, high catalytic activity can be obtained when a catalyst layer is fabricated using this as a catalyst support.

[0043] [D. Shape] In the present invention, the shape of the tin oxide particles is not particularly limited, as long as the above-mentioned conditions are met. The tin oxide particles may be isolated particles, or they may be particles having a beaded structure in which porous primary particles are fused together. Here, "beaded structure" refers to a structure in which primary particles are fused together in a chain-like fashion.

[0044] Using the method described later, tin oxide particles with a beaded structure formed by the fusion of porous primary particles can be obtained. In particles with a beaded structure (i.e., secondary particles), the primary particles are loosely connected to each other, resulting in relatively large voids between the primary particles. Therefore, when an electrode catalyst is made using tin oxide particles with a beaded structure, and a catalyst layer is made using this and an ionomer, appropriate voids are formed within the catalyst layer. As a result, the gas diffusion resistance of the catalyst layer decreases. Furthermore, since primary particles consist of aggregates of fine crystallites, there are relatively fine voids (mesopores) inside the primary particles. Therefore, using these as catalyst supports can suppress poisoning of Pt-based nanoparticles by ions.

[0045] The shape of the primary particles is not particularly limited. When tin oxide particles are produced using the method described later, the primary particles are usually not perfectly spherical, but have an irregular shape with an aspect ratio of about 1.1 to 3.

[0046] As described later, the tin oxide particles according to the present invention are manufactured using mesoporous carbon as a template. Mesoporous carbon is manufactured using mesoporous silica as a template. Mesoporous silica is usually synthesized by condensation polymerization of a silica source in a reaction solution containing a silica source, a surfactant, and a catalyst.

[0047] At this time, by limiting the concentrations of the surfactant and the silica source in the reaction solution to a specific range, mesoporous silica is obtained that has a beaded structure and whose specific surface area, pore diameter, etc., are within a specific range. When mesoporous silica with such a beaded structure is used as the first mold, mesoporous carbon with a beaded structure is obtained. Furthermore, when mesoporous carbon with a beaded structure is used as the second mold, tin oxide-based particles with a beaded structure are obtained.

[0048] [E. Average particle size of primary particles] "Average particle size of primary particles" refers to the average of the maximum dimensions of primary particles measured by scanning electron microscopy (SEM) observation. When tin oxide particles are particles having a beaded structure in which porous primary particles are fused together, the average particle size of the primary particles is not particularly limited, and an optimal value can be selected depending on the purpose.

[0049] Generally, if the average particle size of the primary particles becomes too small, it becomes difficult to support the Pt-based fine particles. Therefore, the average particle size of the primary particles is preferably 0.05 μm or larger. More preferably, the average particle size is 0.06 μm or larger, and even more preferably, 0.07 μm or larger. On the other hand, if the average particle size of the primary particles becomes too large, the thickness of the catalyst layer increases, and the ionic resistance and electronic resistance in the catalyst layer increase. Therefore, the average particle size of the primary particles is preferably 2 μm or less. More preferably, the average particle size is 1 μm or less, and even more preferably, 0.5 μm or less.

[0050] [F. Electrical conductivity of compacted powder] "Conductivity of compacted powder" refers to: (a) Using two stainless steel discs and a plastic jig with a cylindrical hole, tin oxide particles are formed. (b) This refers to the value obtained by measuring the voltage while applying a constant current to the compacted powder under a pressure of 2.4 MPa. The conductivity of compacts (i.e., tin oxide particles) depends primarily on the type and amount of dopant. Optimizing the composition of tin oxide particles increases the conductivity of the compact to 1 × 10⁻⁶. -3 The conductivity will be 1 × 10⁻⁶ or higher. When the manufacturing conditions are optimized, the conductivity will be 1 × 10⁻⁶ -2 The result will be S / cm or higher. Using the method described later, even tin oxide-based particles with a compacted conductivity of approximately 10 S / cm can be synthesized.

[0051] [G. Pore Capacity] "Pore volume" refers to the volume of mesopores contained in primary particles, and does not include the volume of voids between primary particles. "Pore capacity of tin oxide particles" refers to the pore capacity of tin oxide particles before they are loaded with Pt-based fine particles or hydrophobic particles (hereinafter also referred to as "pre-loading pore capacity"). Pore ​​capacity is obtained by analyzing the adsorption data of nitrogen adsorption isotherms of tin oxide particles using the BJH method and calculating it as a value of P / P0 = 0.03 to 0.99.

[0052] When the tin oxide particles according to the present invention are used as a catalyst support for PEFCs, if the pore volume becomes too small, the proportion of catalyst particles supported within the pores decreases. Therefore, a pore volume of 0.1 cc / g or more is preferable. Preferably, the pore volume is 0.15 cc / g or more, and more preferably, 0.2 cc / g or more. On the other hand, if the pore volume becomes too large, the proportion of tin oxide particles in the pore walls decreases, resulting in low electronic conductivity. Also, the amount of ionomers entering increases, which may lead to reduced activity due to catalyst poisoning. Therefore, a pore volume of 1.0 cc / g or less is preferable. More preferably, the pore volume is 0.7 cc / g or less, 0.5 cc / g or less, or 0.4 cc / g or less.

[0053] [H. Tap Density] "Tap density" refers to a value measured in accordance with JIS Z 2512. When using the tin oxide particles according to the present invention in the catalyst layer of a PEFC, if the tap density of the tin oxide particles becomes too low, the thickness of the resulting catalyst layer becomes too thick, and the proton conductivity decreases. Therefore, the tap density should be 0.005 g / cm³. 3 The above is preferable. The tap density is preferably 0.01 g / cm³. 3 More preferably, 0.05 g / cm³3 That's all. On the other hand, if the tap density becomes too high, it becomes difficult to secure sufficient voids within the catalyst layer to suppress flooding when the catalyst layer is fabricated using this density. Therefore, the tap density should be 1.0 g / cm³. 3 The following is preferable: The tap density is preferably 0.75 g / cm³. 3 The following applies:

[0054] [I. Preferred form] Among the tin oxide nanoparticles that satisfy the above conditions, in particular, those consisting of Sb-doped SnO2 with a specific surface area of ​​60 m² are preferred. 2 / g or more, preferably 90m 2 It is preferable that the nanoparticles have a density of 1 / g or more and a pore size of 5 nm to 8 nm. When a catalyst layer is prepared using tin oxide nanoparticles that satisfy these conditions as a support, high catalytic activity can be obtained.

[0055] [1.1.2. Pt-based fine particles] [A. Composition] "Pt-based fine particles" refers to fine particles made of Pt or a Pt alloy. The Pt-based fine particles are supported on the surface of tin oxide particles (i.e., the outer surface of the tin oxide particles or the inner surface of the mesopores).

[0056] When Pt-based fine particles consist of a Pt alloy, the composition of the Pt alloy (i.e., the type and content of alloying elements) is not particularly limited, and the optimal composition can be selected according to the purpose. Examples of Pt alloys include: (a) Alloys containing Pt and one or more other precious metal elements (e.g., Pt-Pd alloy, Pt-Ru alloy, Pt-Ir alloy, etc.), (b) Alloys containing Pt and one or more base metal elements (e.g., Fe, Co, Ni, Cr, V, Ti, etc.) (e.g., Pt-Fe alloy, Pt-Co alloy, Pt-Ni alloy, Pt-Cr alloy, Pt-V alloy, Pt-Ti alloy, etc.), These are some examples.

[0057] [B. Average particle size] "Average particle size of Pt-based microparticles" refers to the average value of the maximum dimensions of Pt-based microparticles measured by scanning electron microscopy (SEM). The average particle size of Pt-based microparticles affects the mass activity. Generally, if the average particle size of Pt-based microparticles becomes too large, the mass activity of the Pt-based microparticles decreases. Therefore, the average particle size of Pt-based microparticles is preferably 5 nm or less. More preferably, the average particle size is 4 nm or less. On the other hand, if the average particle size of the Pt-based fine particles becomes too small, the components constituting the fine particles, such as Pt, become more easily eluted. Therefore, the average particle size of the Pt-based fine particles is preferably 1 nm or larger. More preferably, the average particle size is 2 nm or larger.

[0058] [C. Load] The amount of Pt-based fine particles supported is not particularly limited, and the optimal amount can be selected according to the purpose. Generally, if the amount of Pt-based fine particles is too small, the thickness of the catalyst layer required to obtain a predetermined basis weight increases, and the electronic resistance, proton transfer resistance, and / or gas diffusion resistance of the catalyst layer increase. Therefore, a supported amount of Pt-based fine particles of 5 mass% or more is preferable. More preferably, the supported amount is 10 mass% or more, and even more preferably, 15 mass% or more. On the other hand, if the amount of Pt-based fine particles is excessive, the Pt-based fine particles will aggregate on the surface of the support, which will actually decrease the activity of the electrode catalyst. Therefore, the amount of Pt-based fine particles supported is preferably 60 mass% or less. More preferably, the amount is 50 mass% or less, and even more preferably, 40 mass% or less.

[0059] [1.2. Ionoma] [1.2.1. Materials] In the catalyst layer according to the present invention, the ionomer material is not particularly limited. Examples of ionsomers include perfluorocarbon sulfonic acid polymers and highly oxygen-permeable ionsomers. The ionomer may consist of any one of these, or two or more may be used in combination.

[0060] "Perfluorocarbon sulfonic acid polymer" refers to a fluoride-containing ion exchange resin that contains repeating units based on sulfonyl vinyl ether monomer. Examples of perfluorocarbon sulfonic acid polymers include Nafion®, Flemion®, Aquivion®, and Aciplex®.

[0061] A "high oxygen permeable ionomer" refers to a polymer compound that contains acidic groups and cyclic structures within its molecular structure. Because high oxygen permeable ionsomers contain cyclic structures within their molecular structure, they have a high oxygen permeability coefficient. Therefore, when used as an ionomer, the oxygen transport resistance at the interface with the catalyst is relatively low. In other words, a "high oxygen permeability ionomer" refers to an ionomer whose oxygen permeability coefficient is higher than that of perfluorocarbon sulfonate polymers, such as Nafion (registered trademark).

[0062] Examples of high-oxygen-permeability ions include, (a) An electrolyte polymer comprising a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having perfluorosulfonic acid as a side chain, (b) an electrolyte polymer comprising a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having a perfluoroimide as a side chain, (c) An electrolyte polymer containing a unit in which perfluorocarbon having an aliphatic ring structure is directly bonded to perfluorosulfonic acid. These include (see references 1-4). [Reference 1] Japanese Patent Publication No. 2003-036856 [Reference 2] International Publication No. 2012 / 088166 [Reference 3] Japanese Patent Publication No. 2013-216811 [Reference 4] Japanese Patent Publication No. 2006-152249

[0063] [1.2.2. I / S] "I / S" refers to the ratio of the mass of ionomer (I) to the mass of tin oxide particles (S) contained in the catalyst layer. The I / S ratio affects the proton conductivity and / or gas diffusion of the catalyst layer. Generally, if the I / S ratio becomes too low, the proton conductivity of the catalyst layer decreases. Therefore, an I / S ratio of 0.13 or higher is preferred. More preferably, an I / S ratio of 0.20 or higher is preferred. On the other hand, if the I / S ratio becomes too large, the amount of voids in the catalyst layer decreases, and the gas diffusivity of the catalyst layer decreases. Therefore, an I / S ratio of 0.39 or less is preferable. More preferably, an I / S ratio of 0.33 or less is preferable.

[0064] [1.3. Hydrophobic Molecules] [1.3.1. Materials] A "hydrophobic molecule" refers to an organic compound capable of imparting hydrophobicity to an electrode catalyst. Hydrophobic molecules may be high-molecular-weight compounds with a molecular weight of 10,000 or more, or low-molecular-weight compounds with a molecular weight of less than 10,000. The catalyst layer according to the present invention contains hydrophobic molecules. When hydrophobic molecules are present on the outer surface of the electrode catalyst, inside the mesopores of the tin oxide particles, and / or near the electrode catalyst, high mass activity is observed under high humidity conditions or excessive humidity conditions. This is thought to be because the hydrophobic molecules promote the discharge of water.

[0065] In the present invention, the type of hydrophobic molecule is not particularly limited. Amorphous fluorinated polymers are particularly preferred as hydrophobic molecules. Here, "amorphous fluorine-based polymer" refers to an organic polymer composed of F, C, N, H, O, and / or S elements that does not have a region where molecules are regularly arranged (crystalline region).

[0066] Examples of hydrophobic molecules include Cytop® (manufactured by AGC, CTL-109A), Teflon® AF (manufactured by Chemours, 1600 or 2400), and Hyflon® (manufactured by Solvay, AD60). The catalyst layer may contain one of these hydrophobic molecules, or it may contain two or more.

[0067] [1.3.2. Modification State of Hydrophobic Molecules] There are various methods for producing a catalyst layer containing hydrophobic molecules. In the present invention, any of these methods may be used. However, if the method of adding hydrophobic molecules differs, the modified state of the hydrophobic molecules within the catalyst layer may change, and as a result, the performance of the catalyst layer may change.

[0068] For example, a method for producing a catalyst layer containing hydrophobic molecules is: (a) A method of preparing a catalyst layer using a catalyst ink containing an electrode catalyst and an ionomer, impregnating the catalyst layer with a dip coat solution in which hydrophobic molecules are dissolved or dispersed, and removing the solvent (hereinafter also referred to as the "dip coat method"), (b) A method for preparing a catalyst layer using a catalyst ink containing an electrode catalyst / hydrophobic molecule complex and an ionomer, by compounding an electrode catalyst with a hydrophobic molecule (hereinafter also referred to as the "dispersion method"). These are some examples.

[0069] Figure 1(A) shows a schematic diagram of a catalyst layer fabricated using the dip-coating method. When a catalyst layer is fabricated using a catalyst ink containing only an electrode catalyst (Pt / Sb-SnO2) and an ionomer, it is thought that all or part of the surface of the electrode catalyst will be covered with the ionomer. Subsequently, when hydrophobic molecules are introduced into the catalyst layer using the dip-coating method, it is thought that all or part of the surface of the ionomer will be covered with hydrophobic molecules.

[0070] In other words, the catalyst layer fabricated using the dip-coat method is An electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles, An ionomer covering at least a portion of the surface of the electrode catalyst, Hydrophobic molecules that coat at least a portion of the ionomer's surface and It is believed to possess these features.

[0071] Figure 1(B) shows a schematic diagram of a catalyst layer fabricated using a dispersion method. When the electrode catalyst (Pt / Sb-SnO2) and hydrophobic molecules are combined before fabricating the catalyst layer, it is thought that all or part of the surface of the electrode catalyst will be coated with hydrophobic molecules. Subsequently, when a catalyst layer is fabricated using a catalyst ink containing such an electrode catalyst / hydrophobic molecule complex and an ionomer, it is thought that all or part of the surface of the hydrophobic molecules will be coated with the ionomer.

[0072] In other words, the catalyst layer prepared using the dispersion method is An electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles, A hydrophobic molecule that coats at least a portion of the surface of the electrode catalyst, An ionomer that coats at least a portion of the surface of a hydrophobic molecule and It is believed to possess these features. It is believed that the Pt-based fine particles and hydrophobic molecules coat at least a portion of the inner surface of the mesopores of the tin oxide-based particles.

[0073] [1.3.3. Modification amount of hydrophobic molecules] "Modification amount of hydrophobic molecules" refers to the ratio of the mass of hydrophobic molecules to the total mass of the electrode catalyst and hydrophobic molecules.

[0074] The amount of hydrophobic molecule modification affects the oxygen reduction reaction (ORR) mass activity and catalyst layer resistance under high or excessive humidity conditions. Generally, the greater the amount of hydrophobic molecule modification, the higher the ORR mass activity under high or excessive humidity conditions. To obtain such an effect, the amount of hydrophobic molecule modification is preferably 0.2 mass% or more.

[0075] On the other hand, if the amount of hydrophobic molecule modification is excessive, the electron conduction path within the catalyst layer may be interrupted, and the resistance of the catalyst layer may increase. Therefore, the amount of hydrophobic molecule modification is preferably 8.0 mass% or less.

[0076] [1.4. Characteristics] [1.4.1. Activity under high humidity and excessive humidity conditions] "Activity under high humidity conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the fuel cell electrode catalyst layer as the air electrode, and power is generated under the conditions of cell temperature: 60°C, air electrode gas relative humidity: 80%, and cell voltage: 0.86V. "Activity under over-humidified conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the fuel cell electrode catalyst layer as the air electrode, and power is generated under the following conditions: cell temperature: 60°C, air electrode gas relative humidity: 160%, and cell voltage: 0.86V.

[0077] When hydrophobic molecules are added to a catalyst layer comprising an electrode catalyst supported by porous tin oxide particles and an ionomer, the water repellency near the catalyst particles increases. As a result, flooding is suppressed even under high humidity or excessive humidity conditions, and high activity is observed. Optimizing the manufacturing conditions, The activity under high humidity conditions was 260 A / g. Pt That is all, and / or, Activity under excessively humid conditions is 100 A / g Pt That's all. A catalyst layer is obtained. Using dispersion methods makes it easier to obtain catalyst layers with these characteristics.

[0078] [1.4.2. Activity and catalyst layer resistance under high humidity conditions] "Catalyst layer resistance under high humidity conditions" refers to the value obtained by fabricating a polymer electrolyte fuel cell using the fuel cell electrode catalyst layer as the air electrode, and performing impedance measurement by AC impedance method under the following conditions: cell temperature: 60°C, air electrode gas relative humidity: 80%, air electrode gas: N2, fuel electrode gas: H2, cell voltage: 0.4V.

[0079] When adding hydrophobic molecules to a catalyst layer comprising an electrode catalyst supported by porous tin oxide particles and an ionomer, excessive addition of hydrophobic molecules can increase the catalyst layer resistance. This is thought to be because the excess hydrophobic molecules can easily disrupt the electron conduction paths between the electrode catalysts. In particular, when adding hydrophobic molecules using a dispersion method, excessive addition of hydrophobic molecules tends to increase the catalyst layer resistance.

[0080] In contrast, when adding hydrophobic molecules to the catalyst layer, optimizing the method and / or amount of hydrophobic molecules added results in: The activity under high humidity conditions is 100 A / g. Pt That's all. The catalyst layer resistance under high humidity conditions is 0.1 Ωcm. -2 The following is A catalyst layer is obtained. Using the dip-coating method, it is easy to obtain a catalyst layer with these characteristics.

[0081] [1.4.3. Pore volume after loading] "Pore capacity after loading" refers to the pore capacity of the electrode catalyst or the electrode catalyst / hydrophobic molecular complex. The pore volume after loading depends on the pore volume before loading, the amount of Pt-based microparticles loaded, the amount of hydrophobic molecules loaded, and other factors.

[0082] [2. Method for producing mesoporous silica (first mold)] Porous tin oxide particles can be manufactured by various methods. Of these, to manufacture porous tin oxide particles with a beaded structure, it is first necessary to manufacture mesoporous silica (first mold) with a beaded structure. Such mesoporous silica is (a) Precursor particles are produced by condensation polymerization of the silica source in a reaction solution containing a silica source, a surfactant and a catalyst. (b) Separate the precursor particles from the reaction solution and dry them. (c) If necessary, the dried precursor particles are subjected to a diameter-expanding treatment. (d) Calcining the precursor particles It is obtained by doing so.

[0083] [2.1. Polycondensation process] First, the silica source is subjected to condensation polymerization in a reaction solution containing a silica source, a surfactant, and a catalyst to obtain precursor particles (condensation polymerization step).

[0084] [2.1.1. Silica Sources] In the present invention, the type of silica source is not particularly limited. Examples of silica sources 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, These are some examples. Any one of these can be used as the silica source, or a combination of two or more can be used.

[0085] [2.1.2. Surfactants] When a silica source is subjected to condensation polymerization in a reaction solution, the addition of a surfactant to the reaction solution causes the surfactant to form micelles. Because hydrophilic groups are aggregated around the micelles, the silica source is adsorbed onto the surface of the micelles. Furthermore, the micelles with the adsorbed silica source self-assemble in the reaction solution, causing the silica source to undergo condensation polymerization. As a result, mesopores are formed inside the primary particles due to the micelles. The size of the mesopores can be controlled primarily by the molecular length of the surfactant (from 1 to 50 nm).

[0086] In this invention, an alkyl quaternary ammonium salt is used as the surfactant. An alkyl quaternary ammonium salt is a compound represented by the following formula (a). CH3-(CH2) n -N+ (R1)(R2)(R3)X - ...(a)

[0087] (a) In formula (a), R1, R2, and R3 each represent an alkyl group having 1 to 3 carbon atoms. R1, R2, and R3 may be the same as or different from each other. To facilitate aggregation (micelle formation) of alkyl quaternary ammonium salts, it is preferable that R1, R2, and R3 are all the same. Furthermore, it is preferable that at least one of R1, R2, and R3 is a methyl group, and it is preferable that all of them are methyl groups. (a) In formula X, X represents a halogen atom. The type of halogen atom is not particularly limited, but due to their availability, X is preferably Cl or Br.

[0088] (a) In formula n, n represents an integer from 7 to 21. Generally, the smaller n is, the smaller the central pore diameter of the mesopores, resulting in a spherical mesoporous material. On the other hand, the larger n is, the larger the central pore diameter, but if n is too large, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is formed, and a mesoporous material cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

[0089] Among those represented by formula (a), alkyltrimethylammonium halides are preferred. Examples of alkyltrimethylammonium halides include hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, and dodecyltrimethylammonium halide. Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

[0090] When synthesizing 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 acts as a template for forming mesopores within the primary particles, its type greatly affects the shape of the mesopores. To synthesize silica particles with more uniform mesopores, it is preferable to use one type of alkyl quaternary ammonium salt.

[0091] [2.1.3. Catalyst] When condensing a silica source, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, an alkali such as sodium hydroxide or aqueous ammonia may be used as the catalyst, or an acid such as hydrochloric acid may be used.

[0092] [2.1.4. Solvents] The solvent used can be water, organic solvents such as alcohol, or a mixture of water and an organic solvent. Alcohol is (1) Monohydric alcohols such as methanol, ethanol, and propanol, (2) Divalent alcohols such as ethylene glycol, (3) Trivalent alcohols such as glycerin, Either one is fine. When using a mixed solvent of water and an organic solvent, the amount of organic solvent in the mixed solvent can be arbitrarily selected depending on the purpose. Generally, adding an appropriate amount of organic solvent to the solvent makes it easier to control particle size and particle size distribution.

[0093] [2.1.5. Composition of the reaction solution] The composition of the reaction solution affects the external shape and pore structure of the synthesized mesoporous silica. In particular, the concentrations of the surfactant and the silica source in the reaction solution have a significant impact on the average primary particle size, pore size, pore volume, and tap density of the mesoporous silica particles.

[0094] [A. Concentration of surfactant] If the surfactant concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are linked together may not be obtained. Therefore, the surfactant concentration needs to be 0.03 mol / L or higher. Preferably, the surfactant concentration is 0.035 mol / L or higher, and more preferably 0.04 mol / L or higher.

[0095] On the other hand, if the surfactant concentration is too high, the particle precipitation rate may become too fast, and the primary particle size may become excessively large. Therefore, the surfactant concentration needs to be 1.0 mol / L or less. Preferably, the surfactant concentration is 0.95 mol / L or less, and more preferably 0.90 mol / L or less.

[0096] [B. Concentration of silica source] If the silica source concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are linked may not be obtained. Alternatively, there may be an excess of surfactant, and a uniform mesopore may not be obtained. Therefore, the silica source concentration needs to be 0.05 mol / L or higher. Preferably, the silica source concentration is 0.06 mol / L or higher, and more preferably 0.07 mol / L or higher.

[0097] On the other hand, if the silica source concentration is too high, the particle precipitation rate may become too fast, resulting in an excessively large primary particle size. Alternatively, sheet-like particles may be obtained instead of spherical particles. Therefore, the silica source concentration must be 1.0 mol / L or less. Preferably, the silica source concentration is 0.95 mol / L or less, and more preferably 0.9 mol / L or less.

[0098] [C. Catalyst concentration] In this invention, the catalyst concentration is not particularly limited. Generally, if the catalyst concentration is too low, the particle deposition rate will be slow. On the other hand, if the catalyst concentration is too high, the particle deposition rate will be fast. It is preferable to select the optimal catalyst concentration according to the type of silica source, the type of surfactant, the target physical properties, etc.

[0099] [2.1.6 Reaction Conditions] A silica source is added to a solvent containing a predetermined amount of surfactant, and hydrolysis and polycondensation are carried out. This allows the surfactant to function as a template, yielding precursor particles containing silica and the surfactant. The reaction conditions are selected according to the type of silica source, the particle size of the precursor particles, and other factors to ensure optimal conditions. Generally, the reaction temperature is preferably -20 to 100°C. More preferably, the reaction temperature is 0 to 90°C, and even more preferably, 10 to 80°C.

[0100] [2.2. Drying process] Next, the precursor particles are separated from the reaction solution and dried (drying step). Drying is performed to remove any residual solvent within the precursor particles. The drying conditions are not particularly limited, as long as the solvent can be removed.

[0101] [2.3. Diameter expansion process] Next, if necessary, the dried precursor particles may be subjected to a diameter-expanding process (diameter-expanding step). "Diameter-expanding process" refers to a process that enlarges the diameter of the mesopores within the primary particles. Specifically, the pore size expansion process is carried out by hydrothermally treating the synthesized precursor particles (with the surfactant still intact) in a solution containing a pore size expanding agent. This process can enlarge the pore size of the precursor particles.

[0102] Examples of diameter-expanding agents include, (a) hydrocarbons such as trimethylbenzene, triethylbenzene, benzene, cyclohexane, triisopropylbenzene, naphthalene, hexane, heptane, octane, nonane, decane, undecane, and dodecane. (b) Acids such as hydrochloric acid, sulfuric acid, and nitric acid, These are some examples.

[0103] The reason why hydrothermal treatment in the presence of hydrocarbons expands the pore size is thought to be because silica rearrangement occurs when the pore-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles. Furthermore, the expansion of pore size due to hydrothermal treatment in the presence of an acid such as hydrochloric acid is thought to be due to the dissolution and reprecipitation of silica within the primary particles. Optimizing the manufacturing conditions forms radial pores within the silica. When this is subjected to hydrothermal treatment in the presence of an acid, dissolution and reprecipitation of silica occurs, and the radial pores are converted into interconnected pores.

[0104] The conditions for the pore expansion treatment are not particularly limited, as long as the desired pore size can be obtained. Typically, it is preferable to add a pore-expanding agent in a concentration of about 0.05 mol / L to 10 mol / L to the reaction solution and perform hydrothermal treatment at 60 to 150°C.

[0105] [2.4. Firing Process] Next, after performing a diameter-expanding treatment as necessary, the precursor particles are calcined (calcination step). This yields mesoporous silica with a beaded structure. Calcination is performed to dehydrate and crystallize precursor particles containing residual OH groups, and to thermally decompose surfactants remaining in the mesopores. The calcination conditions are not particularly limited, as long as dehydration, crystallization, and thermal decomposition of surfactants are possible. Calcination is usually carried out by heating in air at 400°C to 700°C for 1 to 10 hours.

[0106] [3. Method for producing mesoporous carbon (second mold)] Next, mesoporous carbon (second mold) is manufactured using mesoporous silica as a mold. Such mesoporous carbon is (a) Prepare a mesoporous silica to serve as the first mold, (b) A silica / carbon composite is prepared by precipitating carbon in the mesopores of the mesoporous silica, (c) Remove silica from the composite It is obtained by doing so. Furthermore, in order to promote the graphitization of the obtained mesoporous carbon, the mesoporous carbon may be heat-treated at a temperature higher than 1500°C after the silica has been removed.

[0107] [3.1. First mold preparation process] First, a mesoporous silica, which will serve as the first mold, is prepared (first mold preparation step). The details of the manufacturing method for mesoporous silica are as described above, so the explanation will be omitted.

[0108] [3.2. Carbon Deposition Process] Next, carbon is deposited within the mesopores of mesoporous silica to create a silica / carbon composite (carbon deposition step). The deposition of carbon into mesopores is, specifically, (a) A carbon precursor is introduced into the mesopore, (b) Polymerize and carbonize the carbon precursor within the mesopore. This is done by [means].

[0109] [3.2.1. Introduction of carbon precursors] A "carbon precursor" refers to a substance that can produce carbon through thermal decomposition. Specifically, such carbon precursors include: (1) A polymer precursor that is liquid at room temperature and is thermopolymerizable (e.g., furfuryl alcohol, aniline, etc.), (2) A mixture of an aqueous solution of carbohydrates and an acid (for example, a mixture of monosaccharides such as sucrose, xylose, and glucose, or disaccharides, polysaccharides, and acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid), (3) A mixture of two-component curable polymer precursors (e.g., phenol and formalin), These are some examples. Among these, polymer precursors can be impregnated into mesopores without dilution with a solvent, allowing for the generation of a relatively large amount of carbon within the mesopores with a relatively small number of impregnation steps. Furthermore, they have the advantages of not requiring polymerization initiators and being easy to handle.

[0110] When using a liquid or solution carbon precursor, the amount of liquid or solution adsorbed per step is preferable to be large, and it is desirable that the entire mesopore is filled with the liquid or solution. Furthermore, when using a mixture of an aqueous solution of carbohydrates and an acid as a carbon precursor, it is preferable to use the minimum amount of acid necessary to polymerize the organic material. Furthermore, when using a mixture of two-component curable polymer precursors as the carbon precursor, the optimal ratio should be selected depending on the type of polymer precursor.

[0111] [3.2.2. Polymerization and carbonization of carbon precursors] Next, the polymerized carbon precursor is carbonized within the mesopore. Carbonization of the carbon precursor is carried out by heating mesoporous silica containing the carbon precursor to a predetermined temperature in a non-oxidizing atmosphere (e.g., in an inert atmosphere, in a vacuum, etc.). The heating temperature is preferably between 500°C and 1200°C. If the heating temperature is below 500°C, the carbonization of the carbon precursor will be insufficient. On the other hand, if the heating temperature exceeds 1200°C, the silica and carbon will react, which is undesirable. The heating time should be selected to be optimal according to the heating temperature.

[0112] The amount of carbon generated within the mesopores should be greater than or equal to the amount that allows the carbon particles to maintain their shape after the mesoporous silica is removed. Therefore, if the amount of carbon generated in a single filling, polymerization, and carbonization cycle 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 the filling, polymerization, and carbonization processes are repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization is completed, another carbonization may be performed at a higher temperature. Performing the final carbonization at a higher temperature than the previous carbonization steps makes it easier for the carbon introduced into the pores in multiple stages to integrate.

[0113] [3.3. First Mold Removal Process] Next, the first template, mesoporous silica, is removed from the composite (first template removal step). This yields mesoporous carbon (second template). Specifically, the methods for removing mesoporous silica include: (1) A method of heating the complex in an alkaline aqueous solution such as sodium hydroxide, (2) A method of etching the composite with an aqueous hydrofluoric acid solution. These are some examples.

[0114] [3.4. Graphitization Process] Next, if necessary, the mesoporous carbon is heat-treated at a temperature higher than 1500°C (graphitization process). When carbonizing a carbon source within the mesopores of mesoporous silica, the heat treatment temperature must be kept low in order to suppress the reaction between silica and carbon. Therefore, the degree of graphitization of the carbon after carbonization is low. To obtain a high degree of graphitization, it is preferable to heat-treat the mesoporous carbon at a high temperature after removing the first mold.

[0115] If the heat treatment temperature is too low, graphitization will be insufficient. Therefore, a heat treatment temperature of over 1500°C is preferable. Preferably, the heat treatment temperature is 1700°C or higher, and more preferably, 1800°C or higher. On the other hand, raising the heat treatment temperature unnecessarily does not make a difference in effect and is not beneficial. Therefore, the heat treatment temperature is preferably 2300°C or lower. Preferably, the heat treatment temperature is 2200°C or lower.

[0116] [4. Method for producing tin oxide-based particles] A method for producing porous tin oxide-based particles is: The first step is to prepare the mesoporous carbon, The second step involves precipitating tin oxide or tin oxide containing a dopant (hereinafter collectively referred to as "Sn-containing oxide") in the mesopores of mesoporous carbon to obtain a Sn-containing oxide / carbon composite, The third step involves removing carbon from the Sn-containing oxide / carbon composite. It is equipped with.

[0117] [4.1. 1st step] First, prepare the mesoporous carbon (step 1). Details of the manufacturing method for mesoporous carbon are as described above, so we will omit further explanation.

[0118] [4.2. 2nd step] Next, Sn-containing oxides are deposited in the mesopores of the mesoporous carbon (second step). This yields a Sn-containing oxide / carbon composite. Specifically, the precipitation of Sn-containing oxides into mesopores is carried out by introducing a precursor of Sn-containing oxide into the mesopore and converting the precursor into Sn-containing oxide.

[0119] [4.2.1. Precursors] Specifically, precursors for forming Sn-containing oxides within mesopores include: (1) A compound that contains a metal element constituting a Sn-containing oxide, is soluble in a solvent, and can be oxidized and precipitated by dissolved oxygen in the solvent. (2) Compounds containing metal elements that constitute Sn-containing oxides and capable of forming metal oxides by thermal decomposition or hydrolysis, These are some examples.

[0120] Compounds that can be oxidized and precipitated by dissolved oxygen include: (1) Salts containing divalent Sn, such as SnCl2, (2) Salts containing Nb, Sb, W, Ta, or Al, such as NbCl5, SbCl3, WCl6, TaCl5, AlCl3, These are some examples.

[0121] Compounds that can form metal oxides by thermal decomposition or hydrolysis include: (1) Chlorides such as SnCl4, SnCl2, NbCl5, SbCl3, WCl6, TaCl5, AlCl3, (2) Alkoxides such as tungsten ethoxide (W(OC2H5)6), Sn(OC2H5)2, Sn(OC(CH3)3)4, Nb(OC2H5)5, Ta(OC2H5)5, Sb(OC2H5)3, Al(OC2H5)3, (3) Acetylacetonate salts such as tin acetylacetonate (Sn(CH3COCHCOCH3)2) and Al(CH3COCHCOCH3)3, (4) Acetates such as Sn(CH3COO)2 and Sb(CH3COO)3, These are some examples.

[0122] [4.2.2. Introduction of the precursor into the pores] If the precursor is a liquid, it may be directly adsorbed into the pores of the mesoporous carbon. Alternatively, the precursor may be dissolved in a suitable solvent, and this solution may be adsorbed into the pores of the mesoporous carbon. When dissolving the precursor in a solvent, the type of solvent and the concentration of the precursor are not particularly limited and should be selected according to the purpose.

[0123] [4.2.3. Conversion of Precursors to Oxides] After adsorbing the precursor, the precursor is converted into a Sn-containing oxide. The conversion method is not particularly limited, and the optimal method is selected depending on the type of precursor. For example, when using chloride as a precursor, mesoporous carbon is dispersed in a solution of dissolved chloride and stirred in air. As stirring continues, the chloride is eventually adsorbed into the mesopores of the mesoporous carbon, and the chloride in the mesopores gradually becomes a Sn-containing oxide due to the dissolved oxygen.

[0124] Furthermore, for example, when using an alkoxide as a precursor, the alkoxide or a solution thereof is added to mesoporous carbon, impregnating the mesopores with the alkoxide or its solution. When this is heated to a predetermined temperature, polycondensation of the alkoxide occurs, and a Sn-containing oxide is formed in the mesopores. If a sufficient amount of Sn-containing oxide cannot be formed in the mesopore by a single adsorption of the precursor and conversion to the Sn-containing oxide, the adsorption and conversion may be repeated multiple times.

[0125] [4.3. Third step] Next, carbon is removed from the Sn-containing oxide / carbon composite (third step). This yields tin oxide-based particles according to the present invention. The method for removing carbon is not particularly limited, and various methods can be used. For example, the method for removing carbon is: (1) A method of heating a Sn-containing oxide / carbon composite under an oxidizing atmosphere. (2) Method for oxygen plasma etching of Sn-containing oxide / carbon composite, These are some examples. The removal conditions, such as heating temperature and heating time, are not particularly limited; any conditions that completely remove carbon without coarsening the crystallites of the Sn-containing oxide are acceptable.

[0126] [5. Method for manufacturing fuel cell electrode catalyst layer] The fuel cell electrode catalyst layer according to the present invention can be manufactured by various methods. As mentioned above, methods for manufacturing the catalyst layer include the dip-coating method and the dispersion method.

[0127] When adding hydrophobic molecules to a catalyst layer using the dip-coating method, the concentration of hydrophobic molecules in the dip-coating solution, the solvent used to dissolve or disperse the hydrophobic molecules, etc., are not particularly limited and can be selected to be optimal for the purpose.

[0128] When adding hydrophobic molecules to a catalyst layer using a dispersion method, the method for producing the electrode catalyst / hydrophobic molecule complex is not particularly limited, and the most suitable method can be selected depending on the purpose. For example, the method for producing the complex is as follows: (a) A method in which an electrode catalyst is added to a solution in which hydrophobic molecules are dissolved or dispersed in a solvent under normal pressure and mixed, and the solvent is evaporated. (b) A method of dispersing hydrophobic molecules in supercritical carbon dioxide, adding an electrode catalyst and mixing it, and volatilizing the supercritical carbon dioxide. These are some examples.

[0129] [6. Effect] Adding hydrophobic molecules to a catalyst layer comprising an electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles improves power generation performance under high humidity conditions. In particular, when using a dispersion method (a method of preparing the catalyst layer after treating the electrode catalyst with a water-repellent agent) to add hydrophobic molecules to the catalyst layer, optimizing the amount of hydrophobic molecules added yields a catalyst layer that exhibits relatively high oxygen reduction (ORR) activity under high humidity conditions and / or over-humid conditions. This is thought to be because, when using the dispersion method, the surface of the hydrophilic tin oxide particles is directly coated with hydrophobic molecules, thereby increasing the water repellency of the electrode catalyst.

[0130] On the other hand, when using the dip-coating method (a method of treating the electrode catalyst to make it water-repellent after the catalyst layer has been fabricated) to add hydrophobic molecules to the catalyst layer, optimizing the amount of hydrophobic molecules added yields a catalyst layer that exhibits relatively high ORR activity and relatively low catalyst layer resistance under high humidity conditions. This is thought to be because the dip-coating method imparts appropriate water repellency to the electrode catalyst while simultaneously facilitating the securing of electron conduction paths between electrode catalyst particles.

[0131] For example, in the case of an electrocatalyst (Pt / Sb-SnO2) using Sb-SnO2 as a support and Pt particles as catalyst particles, Pt / Sb-SnO2 modified with hydrophobic molecules exhibits up to 6.1 times the ORR mass activity of unmodified Pt / Sb-SnO2. The effect of modification on improving ORR activity is greater when modified using a dispersion method than when modified using a dip-coat method.

[0132] Because the surface of the Sb-SnO2 support is hydrophilic, water tends to accumulate near the Pt under high humidity conditions. Therefore, it is thought that in catalyst layers using unmodified Pt / Sb-SnO2, the diffusion of oxygen gas is hindered under high humidity conditions, and the oxygen reduction reaction is inhibited. In contrast, modifying the surface of Pt / SnO2 with hydrophobic molecules promotes the removal of water near the Pt. As a result, Pt / Sb-SnO2 modified with hydrophobic molecules is thought to exhibit higher ORR activity compared to unmodified electrocatalysts. [Examples]

[0133] (Examples 1-6, Comparative Examples 1-2) [1. Sample Preparation] [1.1. Preparation of Sb-SnO2 support] [1.1.1. Fabrication of beaded starburst silica] A mixed solvent of methanol (MeOH): 4.6 g and ethylene glycol (EG): 4.6 g was mixed with 56.3 g of 30 mass% cetyltrimethylammonium chloride aqueous solution and stirred at room temperature. 8.8 g of 1 M NaOH was then added and the mixture was heated to 50°C. This solution is hereafter referred to as "Solution 1". Next, 12.3 g of tetraethoxysilane (TEOS) was dissolved in a mixed solvent of 6.5 g of MeOH and 6.5 g of EG. This will be referred to as "solution 2" below.

[0134] The second solution was added to the first solution, which had been heated to 50°C. After the mixture became cloudy, heating was stopped and the mixture was stirred for more than 4 hours. After filtration and redispersion in purified water were repeated twice, the mixture was dried at 45°C. Furthermore, the dried powder was calcined in the air at 550°C for 6 hours to obtain beaded mesoporous silica with radial pores (hereinafter also referred to as "Connected Starburst Silica (CSS)").

[0135] [1.1.2. Fabrication of beaded starburst carbon] 0.5g of CSS was placed in a PFA container, and furfuryl alcohol (FA) was added in an amount equal to the pore volume of the CSS, allowing it to permeate the pores of the CSS. This was then heat-treated at 150°C for 24 hours to polymerize the FA. Furthermore, this was heat-treated at 500°C for 6 hours in a nitrogen atmosphere to promote the carbonization of the FA. After repeating this process twice, the CSS / carbon composite was obtained by further heat-treating at 900°C for 6 hours in a nitrogen atmosphere.

[0136] This composite was immersed in a 12% HF solution for 4 hours to dissolve the silica component. After dissolution, filtration and washing were repeated, and then it was dried at 45°C to obtain beaded mesoporous carbon with radial pores (hereinafter also referred to as "Connected Starburst Carbon (CSC)"). The obtained CSC had a BET specific surface area of ​​2122 m². 2 The values ​​were: 1.3 mL / g, pore volume, and pore diameter: 2.2 nm.

[0137] [1.1.3. Preparation of beaded mesoporous Sb-SnO2] 90.3 mg of SbCl3 (99.9 mass%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), diluted with 108 mL of purified water, and then 15.0 g of SnCl2 (99.9 mass%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added and dissolved. 0.3 g of CSC was added to this solution and dispersed. This dispersion was stirred in air at room temperature for 2 hours, then 600 mL of purified water was added and stirred in air for another 4 hours. Subsequently, filtration and redispersion in purified water were repeated twice, and the mixture was dried at 85°C for 2 hours to obtain a beaded Sb-SnO2 / carbon composite.

[0138] This beaded Sb-SnO2 / carbon composite was treated in an air atmosphere at 320°C for 24 hours to obtain blue beaded mesoporous Sb-SnO2. The Sb doping amount of the obtained beaded mesoporous Sb-SnO2 was 2.5 at%. Furthermore, the mode pore diameter (most frequent value) determined from N2 adsorption measurements was 5.8 nm, and the pore volume (pre-loading pore volume) was 0.218 cc / g.

[0139] [1.2. Fabrication of Electrode Catalysts] Pt nanoparticles were supported on the beaded mesoporous Sb-SnO2 prepared as described above using a colloidal method. First, 16 mL of 0.4 M NaOH / EG solution and 16 mL of 0.04 mM H2PtCl6 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) / EG solution were mixed. This mixture was heated at 160°C for 3 minutes while stirring in a microwave synthesis apparatus (Monowabe 400, manufactured by Anton Paar) to obtain a Pt nanoparticle colloid solution.

[0140] Next, 350 mg of Sb-SnO2 powder was added to 22.4 mL of Pt nanoparticle colloidal solution and stirred overnight at room temperature. Subsequently, 0.2 mL of 1 M HNO3 was added and stirred for 1 hour at room temperature, and this process was repeated twice. Furthermore, 2.8 mL of 1 M HNO3 was added and stirred for 1 hour at room temperature. After that, filtration and redispersion in purified water were repeated twice. Finally, the solid was vacuum-dried at 70°C to obtain Pt / Sb-SnO2 (Pt loading rate: 20 mass%). Table 1 shows the specifications of the Pt / Sb-SnO2 catalyst. Note that "pore capacity" in Table 1 refers to the pore capacity of the electrode catalyst (pore capacity after loading).

[0141] [Table 1]

[0142] [1.3. Fabrication of the catalyst layer (1)] [1.3.1. Comparative Examples 1-2: Catalyst Layers Containing Unmodified Electrocatalysts] To 60 mg of 20 mass% Pt / Sb-SnO2, 100 mg of purified water, 100 mg of ethanol, 8.4 mg of propylene glycol, and 58.9 mg of ionomer dispersion (21.2 mass%, D2020) were added. The catalyst ink was prepared by alternating between shaking (Digital Disruptor Genie, 3000 rpm, 2 min) and ultrasonic dispersion (Bioruptor, 5 min) three times each with the above mixture.

[0143] The obtained catalyst ink was applied to a polytetrafluoroethylene (PTFE) sheet using an applicator (gap height: 4 mils), and vacuum-dried at 80°C for 3 hours to obtain a cathode catalyst layer sheet. Furthermore, a 1 cm square cathode catalyst layer was cut out from the obtained cathode catalyst layer sheet. The platinum basis weight was 0.161 to 0.184 mg / cm². 2 (Examples 1-3, Comparative Example 1), or 0.128-0.139 mg / cm³ 2 (Examples 4-6, Comparative Example 2)

[0144] [1.3.2. Examples 1-3: Water-repellent treatment of electrode catalysts by dip-coating method] A 1 cm square cathode catalyst layer, prepared in the same manner as in Comparative Example 1, was transferred to a glass container. To this container, 1.0 mL of Cytop® solution (AGC Inc., CTL-109AE), diluted to 0.5 mass% with a diluent solvent (AGC Inc., CT-Solv 100E), was added and held for 2 minutes.

[0145] The cathode catalyst layer was removed from the glass container and transferred to another glass container, where it was dried at room temperature for 5 minutes. Then, it was vacuum-dried at 80°C (Example 1), 100°C (Example 2), or 180°C (Example 3) for 1 hour to obtain a water-repellent treated Pt / Sb-SnO2 catalyst layer. The amount of Cytop® modification was 7.7 mass% (Example 1), 4.2 mass% (Example 2), or 7.8 mass% (Example 3). Table 2 shows the specifications of the catalyst layers obtained in Examples 1-3 and Comparative Example 1.

[0146] [Table 2]

[0147] [1.4. Fabrication of the catalyst layer (2)] [1.4.1. Examples 4-6: Water-repellent treatment of electrode catalysts by dispersion method] 32.3 mg of Pt / Sb-SnO2, which had been pre-dried under vacuum at 100°C for 30 minutes, was weighed into a glass container. To this container, 0.2 mL of Cytop® solution (AGC Inc., CTL-109AE), diluted to 0.10 mass% with a diluent solvent (AGC Inc., CT-Solv 100E), was added, and sonication was performed for 2 minutes. Subsequently, the dispersion was dried at room temperature for 5 minutes, and then vacuum-dried at 150°C for 1 hour to obtain a water-repellent treated Pt / Sb-SnO2 catalyst (Example 4). The amount of Cytop® modification was 0.5 mass%.

[0148] 19.4 mg of Pt / Sb-SnO2, which had been pre-dried under vacuum at 100°C for 30 minutes, was weighed into a glass container. To this container, 0.2 mL of Cytop® solution (AGC Inc., CTL-109AE), diluted to 0.12 mass% with a diluent solvent (AGC Inc., CT-Solv 100E), was added, and sonication was performed for 2 minutes. Subsequently, the dispersion was dried at room temperature for 5 minutes, and then vacuum-dried at 150°C for 1 hour to obtain a water-repellent treated Pt / Sb-SnO2 catalyst (Example 5). The amount of Cytop® modification was 1.5 mass%.

[0149] 32.4 mg of Pt / Sb-SnO2, which had been pre-dried under vacuum at 100°C for 30 minutes, was weighed into a glass container. To this container, 0.2 mL of Cytop® solution (AGC Inc., CTL-109AE), diluted to 0.25 mass% with a diluent solvent (AGC Inc., CT-Solv 100E), was added, and sonication was performed for 2 minutes. Subsequently, the dispersion was dried at room temperature for 5 minutes, and then vacuum-dried at 150°C for 1 hour to obtain a water-repellent treated Pt / Sb-SnO2 catalyst (Example 6). The amount of Cytop® modification was 2.4 mass%.

[0150] [1.4.2. Preparation of a catalyst layer containing a water-repellent treated electrode catalyst] A predetermined amount of purified water, ethanol, propylene glycol, and an ionomer dispersion (21.2 mass%, D2020) were added to water-repellent treated Pt / Sb-SnO2. Table 3 shows the amount of each component added. The catalyst ink was prepared by alternating between shaking (Digital Disruptor Genie, 3000 rpm, 2 min) and ultrasonic dispersion (Bioruptor, 5 min) three times each for the above mixture.

[0151] [Table 3]

[0152] The obtained catalyst ink was applied to a PTFE sheet using an applicator (gap height: 4 mils) and vacuum-dried at 80°C for 3 hours to obtain a cathode catalyst layer sheet. Furthermore, a 1 cm square cathode catalyst layer was cut out from the obtained cathode catalyst layer sheet. Table 4 shows the specifications of the catalyst layers obtained in Examples 4 to 6 and Comparative Example 2. Note that "pore capacity" in Table 4 refers to the pore capacity (pore capacity after loading) of the electrode catalyst or the electrode catalyst / hydrophobic molecular complex.

[0153] [Table 4]

[0154] [1.5. Creating the MEA] An anode catalyst layer sheet was prepared using 30 mass% Pt / Ketjen(registered trademark) as the electrode catalyst. The amount of platinum was 0.05 mg. Pt / cm 2 The I / C ratio was 1.0. A 1 cm square anode catalyst layer was cut from the anode catalyst layer sheet. Next, a MEA was fabricated by transferring the cathode catalyst layer and anode catalyst layer onto the Nafion® film using hot pressing. The hot pressing conditions were: temperature: 120°C, pressure: 0.89 kN / cm². 2 The duration was set to 5 minutes.

[0155] [2. Test Method] The MEA prepared above is 1 cm 2 Evaluation was performed using a square cell. Carbon paper with a microporous layer was used as the diffusion layer.

[0156] [2.1. Power Generation Performance Evaluation] The IV curve was measured under the following conditions, and the positive sweep of the third cycle was used as evaluation data. Mass activity was calculated from the current density at 0.84V after IR correction. Cell temperature / relative humidity: 60°C / 80%RH, or 60°C / 160%RH Air electrode gas / flow rate / back pressure: Air / 1L min -1 / 14.4kPa-G Fuel electrode gas / flow rate / back pressure: H2 / 0.5L min -1 / 14.4kPa-G Potential sweep: Sweep from the open-circuit voltage down to 0.1V at 20mV / s.

[0157] [2.2. Cyclic Voltammetry (CV)] The CV was measured under the following conditions, and the data from the third cycle was used. The potential of the air electrode is shown as a value corrected to the RHE standard. From the charge amount of the hydrogen desorption peak of the obtained CV, the conversion factor (210 μC / cm²) was used. 2 Pt The ECSA of Pt was calculated using ). Cell temperature / relative humidity: 60°C / 80%RH, or 60°C / 160%RH Air electrode gas / flow rate / back pressure: N2 / 1L min -1 / 14.4kPa-G Fuel electrode gas / flow rate / back pressure: H2 / 0.5L min -1 / 14.4kPa-G Potential sweep: 1V RHE from 0.1V RHE Sweep the range up to 50 mV / s.

[0158] [2.3. Catalyst layer resistance] Under the following conditions, impedance measurement was performed by the AC impedance method. Using the obtained Nyquist plot, the catalyst layer resistance was estimated from the difference between the intersection of the horizontal axis on the high-frequency side and the intercept of the horizontal axis at the inflection point between the high-frequency side and the low-frequency side. The high-frequency side is the region where the angle with respect to the horizontal axis is 45 degrees. Cell temperature / relative humidity: 60 °C / 80%RH, or 60 °C / 160%RH Air electrode gas / flow rate / back pressure: N2 / 1L min -1 / 14.4 kPa-G Fuel electrode gas / flow rate / back pressure: H2(10%) / 0.5L min -1 / 14.4 kPa-G Potential control: 0.4V RHE held at Frequency: 10 kHz to 1 Hz Amplitude: 0.01V

[0159] [2.4. Oxygen transfer resistance (R other )] While keeping the oxygen partial pressure of the air electrode constant, the limiting current was measured by changing the total pressure in the range of 110 to 150 kPa (80%RH) or 126.2 to 166.2 kPa (160%RH). The measurement conditions are shown below. Cell temperature / relative humidity: 60 °C / 80%RH, or 60 °C / 160%RH Air electrode gas / flow rate / back pressure: Air + N2 / 66 mL min -1 +810 to 1180 mL min -1 / 14.4 kPa-G Fuel electrode gas / flow rate / back pressure: H2 / 0.5L min -1 / 14.4 kPa-G Potential sweep: Sweep from open circuit voltage to 0.1V at 20 mV / s for 3 cycles

[0160] From the measured limiting current value (i lim ), R total was determined by the following equation. R total = C O2 / {i lim / 4F} Where C O2Here, "は" represents oxygen concentration, and "F" represents the Faraday constant. R total was plotted against the total pressure of the air electrode gas, and the oxygen transfer resistance component (R other ) that does not depend on pressure was determined from the intercept of the approximate straight line.

[0161] [2.5. CO Stripping Voltammetry] CO stripping voltammetry was performed under the following conditions. The charge amount Q was calculated from the CO oxidation peak of the obtained CO stripping voltammogram. COstrip Cell temperature / relative humidity: 40 °C / 80% RH Air electrode gas / flow rate / back pressure: N2 / 1 L min -1 / 14.4 kPa-G Fuel electrode gas / flow rate / back pressure: H2(10%) / 0.5 L min -1 / 14.4 kPa-G Potential: 0.3 V during CO adsorption RHE held, then 0.1 V RHE to 1.0 V RHE scanned at 50 mV / s for 2 cycles (held at 1.0 V RHE for 2 min)

[0162] [2.6. Measurement of Anion Adsorption Rate] The anion adsorption rate on Pt was measured by the CO replacement method under the following conditions. Cell temperature / relative humidity: 40 °C / 80% RH Air electrode gas / flow rate / back pressure: N2 / 1 L min -1 / 14.4 kPa-G Fuel electrode gas / flow rate / back pressure: H2(10%) / 0.5 L min -1 / 14.4 kPa-G Potential: 0.35 V (held for 5 min)

[0163] After holding the air electrode potential at 0.35 V for 5 minutes, the air electrode gas was switched from N2 to 5% CO. At that time, the current due to the desorption of anions adsorbed on Pt was measured, and the charge amount Q COdisplacement and the Q obtained by CO stripping voltammetry​COstrip The anion adsorption rate was calculated using the following formula. Anion adsorption rate [%] = Q COdisplacement ×100 / {Q COstrip / 2}

[0164] [2.7. Water vapor adsorption measurement] Water vapor adsorption isotherms were measured using an Autosorb-iQ manufactured by Anton-Paar. The measurements were performed by degassing approximately 30 mg of each sample (Example 4, Comparative Example 2) under vacuum at 130°C for 2 hours, followed by measurement at a water temperature of 25°C.

[0165] [2.8. Nitrogen adsorption measurement] Nitrogen adsorption isotherms were measured using an Autosorb-iQ manufactured by Anton-Paar. The measurements were performed at 77K after vacuum degassing approximately 30 mg of each sample (Examples 4-6, Comparative Example 2) at 130°C for 2 hours. From the adsorption isotherms obtained from the nitrogen adsorption measurements, the specific surface area was determined using the Branauer-Enett-Teller (BET) method, and the pore size distribution was determined using the Barret-Joyner-Halenda (BJH) method.

[0166] [2.9. STEM-EDX] Using an analytical electron microscope (ARM200F, JEOL Ltd.) and an EDX detector (JED-2300T, JEOL Ltd.), the electrode catalysts obtained in Comparative Example 2, Example 4, and Example 6 were observed at an accelerating voltage of 200 kV. Each sample was embedded in resin, and secondary particles were cut by FIB processing for observation. The presence of fluorine was confirmed using EDX spectra from the acquired high-angle scattering annular dark-field scanning electron microscope (HAADF-STEM) images.

[0167] [3. Results] [3.1. IV curve] Figure 2(A) shows the IV curves at 80% RH for cells equipped with the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 2(B) shows the IV curves at 160% RH for cells equipped with the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1.

[0168] As shown in Figure 2(A), the power generation performance at 0.6V or higher at 80%RH was higher for Examples 1 and 2 (dip-coating method) than for Comparative Example 1 (unmodified Pt / Sb-SnO2). On the other hand, at voltages below 0.6V, Examples 1 and 2 had lower limiting current densities than Comparative Example 1. Furthermore, Example 3 had a lower limiting current density than Comparative Example 1 across the entire current range. This is thought to be because the ionomer deteriorated due to an excessively high drying temperature. Furthermore, as shown in Figure 2(B), the power generation performance at 160% RH was higher in Examples 1 and 2 than in Comparative Example 1 across the entire current range.

[0169] Figure 3(A) shows the IV curves at 80% RH for cells equipped with the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. Figure 3(B) shows the IV curves at 160% RH for cells equipped with the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2.

[0170] As shown in Figure 3(A), Examples 4-6 showed a significant improvement in the active range at 80% RH. Under over-humidified conditions, as shown in Figure 3(B), Examples 4-6 showed improved limiting current density compared to Comparative Example 2. In particular, the limiting current density of Example 4 was 0.63 A / cm² higher than that of Comparative Example 2. 2 It showed the largest and highest performance. This is thought to be because directly coating the hydrophilic Sb-SnO2 surface with hydrophobic molecules improved the drainage performance of the catalyst layer and enhanced oxygen transport to Pt.

[0171] [3.2. ORR mass activity and ECSA] Figure 4(A) shows the ORR mass activity at an IR-corrected voltage of 0.84V for the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 4(B) shows the ORR mass activity at an IR-corrected voltage of 0.84V for the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2. Figure 5(A) shows the ECSA of the catalyst layers obtained in Examples 1-3 (dip-coating method) and Comparative Example 1. Figure 5(B) shows the ECSA of the catalyst layers obtained in Examples 4-6 (dispersion method) and Comparative Example 2.

[0172] The ORR mass activities at 80% RH and 160% RH both tended to be higher for the catalyst layers obtained by the dispersion method than for those obtained by the dip-coating method. In particular, the ORR mass activity at 80% RH in Example 4 was 6.1 times that in Comparative Example 2. As shown in Fig. 5(B), since there was no difference in the ECSA between Examples 4 to 6 and that in Comparative Example 2, the improvement in the ORR mass activity in Example 4 is considered to be due to factors other than ECSA.

[0173] [3.3. Anion adsorption rate] Fig. 6 shows the anion adsorption rates at 80% RH of the electrode catalysts obtained in Example 4 and Comparative Example 2. The anion adsorption rate in Example 4 decreased by 2.8% compared to Comparative Example 2. This is presumably because the surface of the electrode catalyst was modified with hydrophobic molecules, suppressing the adsorption of the sulfonic acid groups of the ionomer onto Pt.

[0174] [3.4. Catalyst layer resistance and oxygen transfer resistance] Fig. 7(A) shows the catalyst layer resistances of the catalyst layers obtained in Examples 1 to 3 (dip-coating method) and Comparative Example 1. Fig. 7(B) shows the catalyst layer resistances of the catalyst layers obtained in Examples 4 to 6 (dispersion method) and Comparative Example 2. Fig. 8(A) shows the oxygen transfer resistances of the catalyst layers obtained in Examples 1 to 3 (dip-coating method) and Comparative Example 1. Fig. 8(B) shows the oxygen transfer resistances of the catalyst layers obtained in Examples 4 to 6 (dispersion method) and Comparative Example 2.

[0175] The decrease in the limiting current density at 80% RH of the catalyst layer obtained by the dip-coating method can be explained by an increase in the catalyst layer resistance (Fig. 7(A)) and an increase in the oxygen transfer resistance (Fig. 8(A)). On the other hand, in the case of the catalyst layer obtained by the dispersion method, Example 4, which had a small amount of hydrophobic molecule modification, showed reduced catalyst layer resistance (Figure 7(B)) and oxygen transfer resistance (Figure 8(B)) at 160% RH compared to Comparative Example 2. The oxygen transfer resistance of Example 4 at 160% RH was approximately 30% of that of Comparative Example 2. The improvement in the limiting current density of Example 4 (Figure 3(B)) is thought to be due to the optimal amount of hydrophobic molecule modification.

[0176] [3.5. Water vapor adsorption isotherms] Figure 9 shows the water vapor adsorption isotherms of the electrode catalysts obtained in Example 4 and Comparative Example 2. The hysteresis in the high-pressure region (P / P0 > 0.6) indicates the adsorption of water vapor into the mesopores. In Example 4, this hysteresis was on the high-pressure side compared to Comparative Example 2. This indicates that the mesopores of the Sb-SnO2 support became hydrophobic due to hydrophobic molecular modification. Therefore, the reason why the oxygen transport resistance decreased in Example 4 is thought to be because the retention of water in the mesopores was suppressed.

[0177] [3.6. STEM-EDX] Figure 10 shows the EDX spectra obtained from HAADF-STEM images of the cross-sections of the electrode catalysts obtained in Comparative Example 2, Example 4, and Example 6 after FIB processing. An increase in the F peak was observed with increasing amounts of Cytop® modification. This suggests that, when using the dispersion method, Cytop® coats at least a portion of the inner surface of the Pt / Sb-SnO2 mesopores.

[0178] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0179] The catalyst layer according to the present invention can be used as an air electrode catalyst layer or a fuel electrode catalyst layer in a polymer electrolyte fuel cell.

Claims

1. An electrode catalyst in which Pt-based fine particles are supported on the surface of porous tin oxide-based particles, Ionoma and, Hydrophobic molecules and A fuel cell electrode catalyst layer equipped with a fuel cell electrode catalyst layer.

2. The fuel cell electrode catalyst layer according to claim 1, wherein the tin oxide particles have a structure in which porous primary particles are fused together in a chain-like manner (beaded structure).

3. The tin oxide particles have a specific surface area of ​​60 m². 2 The fuel cell electrode catalyst layer according to claim 1, wherein the amount is 1 / g or more.

4. The aforementioned tin oxide particles have an electrical conductivity of 1 × 10⁻⁶ in their compacted form. -3 The fuel cell electrode catalyst layer according to claim 1, wherein the S / cm is 1 or greater.

5. The fuel cell electrode catalyst layer according to claim 1, wherein the pore size of the tin oxide particles is 5 nm or more and 8 nm or less.

6. The fuel cell electrode catalyst layer according to claim 1, wherein the pore volume (pre-supported pore volume) of the tin oxide-based particles is 0.1 cc / g or more and 0.4 cc / g or less.

7. The fuel cell electrode catalyst layer according to claim 1, wherein the ratio of the mass (I) of the ionomer to the mass (S) of the tin oxide particles (= I / S) is 0.13 or more and 0.39 or less.

8. The fuel cell electrode catalyst layer according to claim 1, wherein the amount of modification of the hydrophobic molecule is 0.2 mass% or more and 8.0 mass% or less. However, the "amount of modification of hydrophobic molecules" refers to the ratio of the mass of the hydrophobic molecules to the total mass of the electrode catalyst and the hydrophobic molecules.

9. The activity under high humidity conditions was 260 A / g. Pt That is all, and / or, The activity under excessively humid conditions is 100 A / g. Pt That's all. A fuel cell electrode catalyst layer according to any one of claims 1 to 8. however, "Activity under high humidity conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the fuel cell electrode catalyst layer as the air electrode, and power is generated under the conditions of cell temperature: 60°C, air electrode gas relative humidity: 80%, and cell voltage: 0.86V. "Activity under over-humidified conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the fuel cell electrode catalyst layer as the air electrode, and power is generated under the following conditions: cell temperature: 60°C, air electrode gas relative humidity: 160%, and cell voltage: 0.86V.

10. The activity under high humidity conditions was 100 A / g. Pt That's all. The catalyst layer resistance under high humidity conditions is 0.1 Ωcm. -2 The following is A fuel cell electrode catalyst layer according to any one of claims 1 to 8. however, "Activity under high humidity conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the fuel cell electrode catalyst layer as the air electrode, and power is generated under the conditions of cell temperature: 60°C, air electrode gas relative humidity: 80%, and cell voltage: 0.86V. "Catalyst layer resistance under high humidity conditions" refers to the following conditions when a polymer electrolyte fuel cell cell is fabricated using the fuel cell electrode catalyst layer as the air electrode, with a cell temperature of 60°C, air electrode gas relative humidity of 80%, and air electrode gas of N2. 2 Fuel electrode gas H 2 The value is obtained by performing impedance measurement using the AC impedance method under the cell voltage of 0.4V.

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