Electrode catalyst and catalyst layer

Abstract

To provide an electrode catalyst exhibiting high low-potential stability and high catalytic activity, and a catalyst layer including the same.SOLUTION: An electrode catalyst includes a support, and catalyst particles supported on the surface of the support. The support consists of Nb-doped tin oxide based particles having a structure in which porous primary particles are fused in a bead-like manner (bead-like structure), and the catalyst particles consist of Pt-based particles. The electrode catalyst preferably has a catalyst particle loading of 4.5 mgcat / m2support or more. The catalyst layer includes such an electrode catalyst and an ionomer.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst and a catalyst layer, and more particularly to an electrode catalyst using porous tin oxide particles doped with Nb as a catalyst support, and a catalyst layer comprising such an electrode catalyst. [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. A gas diffusion layer is usually disposed on the outside of the catalyst layer. Furthermore, a current collector (separator) with gas flow channels is disposed on the outside of the gas diffusion layer. A PEFC typically comprises a structure (fuel cell stack) in which multiple unit 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 catalytic metal particles such as platinum are supported on the surface of a support, and a catalyst layer ionomer. Traditionally, carbon materials such as carbon black and acetylene black have been used primarily as catalyst supports. In particular, carbon supports with mesopores have been attracting attention in recent years (Non-Patent Document 1). It has been found that the use of porous carbon particles with appropriately controlled particle size and pore size as a support can simultaneously reduce catalyst poisoning caused by the sulfonic acid groups of the ionomer and reduce the Knudsen diffusion resistance within the support pores, thereby achieving cell performance that balances low-load and high-load performance (Patent Document 1).

[0004] However, it is known that carbon supports oxidize and corrode when exposed to high potentials, causing the catalytic metal particles supported on the support to fall off, resulting in a decline in electrode performance. To achieve both initial cell performance and durability, it is necessary to fabricate porous supports using materials that are stable at high potentials instead of carbon. Therefore, the use of conductive metal oxides, which are stable at high potentials, as support materials has been proposed as an alternative to carbon.

[0005] For example, Patent Document 2 discloses a porous semiconductor having a beaded structure in which primary particles made of an aggregate of crystallites made of an oxide semiconductor are connected, and the specific surface area is 60 m 2 / g or more of porous oxide semiconductor particles are disclosed. The document describes that when such porous oxide semiconductor particles are used as a catalyst support for a polymer electrolyte fuel cell, the detachment of catalytic metal microparticles due to oxidative corrosion of the support is suppressed, mass transfer within the catalyst layer is promoted, and a decrease in activity due to catalyst poisoning is suppressed.

[0006] Patent Document 3 states: (a) Specific surface area is 93 to 179 m 2 An electrode catalyst comprising a support (Sb-SnO support) made of Sb-doped SnO having a ratio of 1000 to 10000 / g and Pt particles supported on the support surface; and (b) A catalyst layer comprising such an electrode catalyst and an ionomer. has been disclosed. The document describes that optimizing the microstructure and composition of the Sb-SnO2 support makes it possible to achieve both high ORR mass activity and high durability.

[0007] Non-Patent Document 2 discloses an oxygen reduction catalyst in which Pt is supported on a support made of Sb-doped SnO2 (ATO). The document describes that when such an oxygen reduction catalyst is exposed to a potential of 0.3 V or less, Sb is eluted from the ATO.

[0008] Non-Patent Document 3 discloses a catalyst support for a polymer electrolyte fuel cell made of Nb-doped SnO2 aerogel or Sb-doped SnO2 aerogel. In addition, the document also describes the electrical conductivity σ of the entire aerogel, which was determined by measuring the DC resistance and electrochemical impedance of the aerogel. global and the bulk conductivity σ excluding the resistance of the particle interface bulk We are looking for...

[0009] The same document states: (A) Sb-doped SnO aerogel is globaland σ bulk are almost equal (i.e., there is almost no resistance at the particle interface), and (B) Nb-doped SnO aerogel is σ global is σ bulk (i.e., the resistance of the particle interface exists) is stated.

[0010] Non-Patent Document 4 discloses a catalyst for a polymer electrolyte fuel cell in which Pt is supported on a solid support made of Nb-doped SnO2. The same document states the following regarding the origin of resistance at particle interfaces: Oxygen and water are reduced by electrons supplied from the surface of the SnO2 particles, Oxygen species (O 2- , O - , O2 - ) and hydroxide (OH - ) is chemically adsorbed on the surface of SnO2 particles, At this time, an electron depletion layer is formed near the interface of the SnO2 particles. It is explained as follows:

[0011] PEFCs that use Sb-SnO2 supports (especially porous Sb-SnO2 supports with a beaded structure) as the cathode catalyst support exhibit superior power generation performance in low-humidity environments compared to PEFCs that use carbon supports as the cathode catalyst support. However, it is known that Sb elutes from Sb-SnO2 when the Sb-SnO2 support is exposed to a potential of 0.3 V or less (Non-Patent Document 2).

[0012] When a PEFC is operated under conditions where the air electrode catalyst is exposed to such low potentials, Sb elution from the Sb-SnO2 support can reduce the conductivity of the Sb-SnO2 support. Furthermore, the eluted Sb can adsorb onto the Pt surface or replace protons in the acid groups of the electrolyte membrane. This can adversely affect cell performance. Therefore, from the perspective of stability at low potentials below 0.3 V, tin oxide supports doped with dopants, which are stable at low potentials, are considered preferable to Sb-SnO2 supports.

[0013] Nb-doped SnO2 supports (Nb-SnO2 supports) have higher low-potential stability than Sb-SnO2 supports. However, Nb-SnO2 supports have the problem of having electrical conductivity that is about two orders of magnitude lower than Sb-SnO2 supports. Low support conductivity increases the electronic resistance within the catalyst layer, resulting in large IR losses. It is also expected that the supply of electrons to the supported catalyst particles will be hindered, inhibiting catalytic activity. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Patent Publication No. 2021-084852 [Patent Document 2] Japanese Patent Publication No. 2022-077821 [Patent Document 3] Japanese Patent Publication No. 2023-139622 [Non-patent literature]

[0015] [Non-Patent Document 1] S. Ott et al., Nature Mater., 2019, 19, 77 [Non-patent document 2] D. Jalalpoor et al., J. Electrochem. Soc., 2021, 168, 024502 [Non-patent document 3] G. Ozouf et al., J. Mater. Sci., 2016, 51, 5305 [Non-patent document 4] K. Kakinuma et al., ACS Appl. Mater. Interfaces, 2019, 11, 34957 Summary of the Invention [Problem to be solved by the invention]

[0016] The problem to be solved by the present invention is to provide an electrode catalyst that has high low potential stability and exhibits high catalytic activity. Another problem to be solved by the present invention is to provide a catalyst layer including such an electrode catalyst. [Means for solving the problem]

[0017] In order to solve the above problems, the electrode catalyst according to the present invention comprises: A carrier; Catalyst particles supported on the surface of the support; Equipped with the support is made of Nb-doped tin oxide particles having a structure in which porous primary particles are fused together in a beaded shape (a beaded structure); The catalyst particles are made of Pt-based particles. The electrode catalyst has a catalyst particle carrying amount of 4.5 mg. cat / m 2 support More than this is preferred. Here, the "amount of catalyst particles supported" refers to the value obtained by dividing the mass of the catalyst particles supported on the support by the surface area of ​​the support.

[0018] The catalyst layer according to the present invention comprises: an electrode catalyst according to the present invention; Ionomer and It is equipped with: [Effects of the Invention]

[0019] Nb-SnO2 supports have higher low-potential stability than Sb-SnO2 supports. However, Nb-SnO2 supports have lower conductivity than Sb-SnO2 supports. This is thought to be because an electron-deficient layer is less likely to form on the surface of Sb-SnO2 supports, whereas an electron-deficient layer is more likely to form on the surface of Nb-SnO2 supports. In contrast, when an appropriate amount of Pt-based particles is supported on a Nb-SnO2 support, an electrocatalyst exhibiting high catalytic activity is obtained. This is thought to be because the electrons supplied from the Pt-based particles to the Nb-SnO2 support reduce or eliminate the electron-deficient layer at the interface between the Pt-based particles and the Nb-SnO2 support, thereby reducing the interfacial resistance. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an SEM image (backscattered electron image) of Pt / Nb—SnO 2 (Example 1). [Figure 2] 1 shows IV curves at 80% RH and 60° C. for the cells obtained in Examples 1 to 4. [Figure 3] 1 shows the ORR mass activity at 0.84 V (80% RH, 60° C.) of the cells obtained in Examples 1 to 4. [Figure 4] 1 shows IV curves at 80% RH and 60° C. for the cells obtained in Example 1 and Comparative Examples 1 and 2. [Figure 5] 1 shows IV curves at 30% RH and 82° C. of the cells obtained in Example 1 and Comparative Examples 1 and 2.

[0021] [Figure 6] 1 shows the ORR mass activity at 0.84 V (80% RH, 60° C., or 30% RH, 82° C.) of the cells obtained in Example 1 and Comparative Examples 1 and 2. [Figure 7] 1 shows IV curves at 80% RH and 60° C. before and after holding a low potential (0.1 V, 2 hours) of the cells obtained in Example 1 and Comparative Example 1. [Figure 8] 1 shows the ORR mass activity at 0.84 V (80% RH, 60° C.) before and after holding a low potential (0.1 V, 2 hours) for the cells obtained in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0022] [Configuration 1] A carrier; Catalyst particles supported on the surface of the support; Equipped with the support is made of Nb-doped tin oxide particles having a structure in which porous primary particles are fused together in a beaded shape (a beaded structure); The catalyst particles are made of Pt-based particles. Electrocatalyst.

[0023] [Configuration 2] The amount of catalyst particles supported is 4.5 mg cat / m 2 support The electrode catalyst according to the above aspect 1. Here, the "amount of catalyst particles supported" refers to the value obtained by dividing the mass of the catalyst particles supported on the support by the surface area of ​​the support.

[0024] [Configuration 3] The tin oxide particles have a specific surface area of ​​30 m 2 3. The electrode catalyst according to claim 1, wherein the average molecular weight of the electrode catalyst is 1.0 or more.

[0025] [Configuration 4] 4. The electrode catalyst according to any one of configurations 1 to 3, wherein the tin oxide particles have pores with a pore diameter of 2 nm or more and 20 nm or less.

[0026] [Configuration 5] The conductivity of the powder compact is 1×10 -3 5. The electrocatalyst of any one of configurations 1 to 4, wherein the electrocatalyst has a specific surface area of ​​1000 nm or greater.

[0027] [Configuration 6] 6. The electrode catalyst according to any one of configurations 1 to 5, wherein the tin oxide-based particles are doped with Nb in an amount of 2.0 at % or more and 15.0 at % or less.

[0028] [Configuration 7] 7. The electrode catalyst according to any one of configurations 1 to 6, wherein the Pt-based particles have an average particle size of 5 nm or less.

[0029] [Configuration 8] The electrocatalyst according to any one of configurations 1 to 7, Ionomer and A catalyst layer comprising:

[0030] [Configuration 9] 9. The catalyst layer according to configuration 8, wherein the ratio (=I / S) of the mass (I) of the ionomer to the mass (S) of the tin oxide particles is 0.13 or more and 0.39 or less.

[0031] [Configuration 10] Mass activity under highly humidified conditions is 150A / g Pt The catalyst layer according to the above-mentioned configuration 8 or 9. The "mass activity under highly humidified conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the catalyst layer as the air electrode and power is generated under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

[0032] [Configuration 11] Mass activity of 300A / g under low humidity conditions Pt The catalyst layer according to any one of the above aspects 8 to 10. The "mass activity under low humidification conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the catalyst layer as the air electrode and power is generated under the following conditions: cell temperature: 82°C, gas humidity (both electrodes): 30% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

[0033] [Configuration 12] 12. The catalyst layer according to any one of aspects 8 to 11, wherein the activity retention rate represented by the following formula (1) is 20% or more. Activity retention rate = (mass activity after low potential holding test / initial mass activity) × 100 ... (1) however, The "mass activity after a low-potential holding test" refers to the mass activity under high humidity conditions after a polymer electrolyte fuel cell using the catalyst layer as an air electrode is produced and a low-potential holding test is carried out under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, cathode gas: N2, anode gas: H2, cell voltage: 0.1 V, and holding time: 2 hours; The "initial mass activity" refers to the mass activity under high humidity conditions before the low potential holding test is performed, The "mass activity under high humidity conditions" refers to the mass activity of the oxygen reduction reaction when power is generated using the polymer electrolyte fuel cell under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

[0034] An embodiment of the present invention will be described in detail below. [1. Electrocatalyst] The electrode catalyst according to the present invention comprises: A carrier; Catalyst particles supported on the surface of the support; It is equipped with:

[0035] 1.1. Carrier In the present invention, the support is made of Nb-doped tin oxide particles having a structure in which porous primary particles are fused together in a beaded shape (a beaded structure). In the present invention, the term "primary particles" refers to porous particles consisting of an aggregate of crystallites made of tin oxide doped with pentavalent niobium (hereinafter also referred to as "Nb-SnO2"). The term "porous" means that mesopores exist between the crystallites. "Mesopores" generally refer to pores with a diameter of 2 to 50 nm, but in the present invention, the term "mesopores" also includes pores with a diameter of less than 2 nm (so-called "micropores").

[0036] [1.1.1. Primary particles] [A. Nb-SnO2] The crystallites that make up the primary particles are made of Nb—SnO2, which has high durability in a fuel cell environment (especially in a low potential environment), making it suitable as an oxide semiconductor for making up the crystallites.

[0037] [B. Nb doping amount] The "Nb doping amount" refers to the average Nb concentration in the whole particle as measured by inductively coupled plasma (ICP) emission spectroscopy.

[0038] Generally, the higher the Nb doping amount, the higher the conductivity of the tin oxide particles. To obtain high conductivity, the Nb doping amount is preferably 2.0 at% or more. The Nb doping amount is more preferably 3.0 at% or more, 4.0 at% or more, or 5.0 at% or more. On the other hand, if the Nb doping amount is excessive, carrier mobility may decrease and electrical conductivity may decrease. Therefore, the Nb doping amount is preferably 15.0 at% or less. The Nb doping amount is more preferably 12.5 at% or less, or even 10.0 at% or less.

[0039] [C. Average primary particle size] The term "average primary particle size" refers to the average value of the maximum dimension (=diameter) of the primary particles. The average primary particle size can be measured by observation with a scanning electron microscope (SEM).

[0040] Generally, if the average primary particle size is too small, it becomes difficult to support catalyst particles. Therefore, the average primary particle size is preferably 0.05 μm or more. The average primary particle size is more preferably 0.06 μm or more, or 0.07 μm or more. On the other hand, when the tin oxide-based particles according to the present invention are used as a catalyst support to produce a catalyst layer for a fuel cell, if the average primary particle diameter is too large, the thickness of the catalyst layer increases, which may increase the ionic resistance and electronic resistance in the catalyst layer. Therefore, the average primary particle diameter is preferably 2.0 μm or less. The average primary particle diameter is more preferably 1.0 μm or less, or even 0.5 μm or less.

[0041] [D. Average crystallite diameter] The term "average crystallite size" refers to the average value of the maximum dimension (=diameter) of the crystallites. The average crystallite size can be determined from the line width of the X-ray diffraction peak and Scherrer's formula.

[0042] If the average crystallite diameter is too small, the pore size will be too small. Therefore, the average crystallite diameter is preferably 2 nm or more, more preferably 3 nm or more, or even 4 nm or more. On the other hand, if the average crystallite size is too large, the pore size will be too large. Therefore, the average crystallite size is preferably 40 nm or less. The average crystallite size is more preferably 20 nm or less, or 10 nm or less.

[0043] [E. Primary particle shape] In the present invention, the shape of the primary particles is not particularly limited. When porous tin oxide particles are produced using the method described below, the primary particles are usually not perfectly spherical but have an irregular shape with an aspect ratio of about 1.1 to 3.

[0044] [1.1.2. Secondary particles] The tin oxide based particles according to the present invention are secondary particles having a beaded structure. Here, the term "beaded structure" refers to a structure in which primary particles are connected in a beaded pattern. In secondary particles with a beaded structure, the primary particles are loosely connected to each other, so there are relatively large voids between the primary particles. Furthermore, since the primary particles are made up of an aggregate of fine crystallites, there are relatively small voids (mesopores) inside the primary particles.

[0045] As described below, the tin oxide-based particles according to the present invention are produced using mesoporous carbon as a template. Furthermore, mesoporous carbon is produced using mesoporous silica as a template. Mesoporous silica is typically synthesized by condensation polymerization of a silica source in a reaction solution containing a silica source, a surfactant, and a catalyst.

[0046] In this case, by limiting the concentrations of the surfactant and the silica source in the reaction solution to specific ranges, mesoporous silica having a beaded structure and having specific ranges of average primary particle size, pore size, pore volume, tap density, etc. can be obtained. When mesoporous silica with such a beaded structure is used as the first template, mesoporous carbon with a beaded structure can be obtained.Furthermore, when mesoporous carbon with a beaded structure is used as the second template, tin oxide particles with a beaded structure can be obtained.

[0047] 1.1.3. Carrier characteristics [A. Overall conductivity (σ support-total )] Overall conductivity (σ support-total )" means, (a) Tin oxide particles are molded using two stainless steel disks and a plastic jig with a cylindrical hole. (b) Apply a pressure of 2.4 MPa to the obtained powder compact, and measure the voltage while passing a constant current. This refers to the conductivity obtained by

[0048] When tin oxide particles made of Nb-SnO2 are produced using porous carbon as a template, Nb tends to be unevenly distributed on the particle surface. When Nb is unevenly distributed on the particle surface, some of the unevenly distributed Nb does not replace Sn in the SnO2 crystal lattice, and instead becomes NbO x Such unevenly distributed Nb layers reduce the overall conductivity (σ support-total ) can be reduced.

[0049] When tin oxide particles are produced using the method described below, the production conditions can be optimized to achieve a σ support-total is 1.0×10 -4 By further optimizing the manufacturing conditions, tin oxide particles with a σ of 0.05 / cm or more can be obtained. support-total is 2.0 x 10 -4 S / cm or more, or 4.0 x 10 -4 S / cm or more. In addition, when the manufacturing conditions are optimized, σ support-total It is possible to produce tin oxide particles with a specific resistance of 1.0 S / cm.

[0050] [B. Internal conductivity (σ support-bulk )] Internal conductivity (σ support-bulk )" means, (a) Tin oxide particles are molded using two stainless steel disks and a plastic jig with a cylindrical hole. (b) Electrochemical impedance measurements (holding voltage: 0.2 V, amplitude: 0.1 V, frequency: 10 Hz to 5 MHz) were performed on the obtained powder compact under a pressure of 2.4 MPa. (c) Determine the intercept of the obtained Nyquist plot with the real axis on the high frequency side. This refers to the conductivity obtained by

[0051] As mentioned above, a layer of unevenly distributed Nb is likely to form on the surface of tin oxide particles. On the other hand, Nb is not unevenly distributed inside the particles, and the SnO2 is doped with an appropriate amount of Nb. Therefore, the internal conductivity (σ support-bulk ) is usually expressed as the overall conductivity (σ support-total ) becomes larger.

[0052] When tin oxide particles are produced using the method described below, the production conditions can be optimized to achieve a σ support-bulk is 1.0×10 -3 By further optimizing the manufacturing conditions, tin oxide particles with a σ of 0.05 / cm or more can be obtained. support-bulk is 2.0 x 10 -3 S / cm or more, or 3.0 x 10 -3 S / cm or more. In addition, when the manufacturing conditions are optimized, σ support-bulk It is possible to produce tin oxide particles with a specific resistance of 1.0 S / cm.

[0053] [C. Specific surface area] The "specific surface area" refers to a value calculated from a nitrogen adsorption isotherm by the BET method. When the tin oxide-based particles according to the present invention are used as a catalyst support for a PEFC, if the specific surface area of ​​the tin oxide-based particles is too small, the active species of the catalyst cannot be supported in a fine and highly dispersed state, and the effective area of ​​the catalyst becomes small. Therefore, the larger the specific surface area of ​​the tin oxide-based particles, the better.

[0054] The tin oxide particles of the present invention have a beaded structure and mesopores within the primary particles, resulting in a larger specific surface area than conventional materials. When the manufacturing conditions are optimized, the specific surface area can be increased to 30 m 2 / g or more. If the manufacturing conditions are further optimized, the specific surface area will be 50m 2 / g or more, 60m 2 / g or more, 70m 2 / g or more, or 80m 2 / g or more. Using the method described below, the specific surface area is 200m 2 Even tin oxide particles with a particle size of about 1 / g can be synthesized.

[0055] [D. Pore diameter] The "pore size" refers to the average diameter of the mesopores contained in the primary particles, and does not include the size of the voids between the primary particles. The pore diameter can be obtained by analyzing the adsorption side data of the nitrogen adsorption isotherm of the tin oxide particles using the BJH method and determining the pore diameter at which the pore volume is maximum (the most frequent peak value or mode pore diameter).

[0056] The primary particles are aggregates of fine crystallites and therefore have mesopores inside. When the tin oxide-based particles according to the present invention are used as catalyst supports for PEFCs, supporting catalyst particles in the mesopores can suppress catalyst poisoning by the catalyst layer ionomer. In general, if the pore diameter of the primary particles is too small, it becomes difficult to supply reaction gases or protons to the catalyst particles supported in the pores, or it becomes difficult to discharge water produced by the reaction. Therefore, the pore diameter is preferably 2 nm or more. The pore diameter is more preferably 3 nm or more, 4 nm or more, or 5 nm or more. On the other hand, if the pore diameter is too large, the catalyst layer ionomer tends to penetrate into the pores, which can easily cause catalyst poisoning. Therefore, the pore diameter is preferably 20 nm or less. The pore diameter is more preferably 15 nm or less, 10 nm or less, or 7 nm or less.

[0057] [E. Pore Volume] The "pore volume" refers to the volume of mesopores contained in the primary particles, and does not include the volume of voids between the primary particles. The pore volume can be obtained by analyzing the adsorption data of the nitrogen adsorption isotherm of the tin oxide particles by the BJH method and calculating the value of P / P0 = 0.03 to 0.99.

[0058] When the tin oxide-based particles according to the present invention are used as a catalyst support for PEFCs, if the pore volume is too small, the proportion of catalyst particles supported in the pores will be small. Therefore, the pore volume is preferably 0.1 mL / g or more. The pore volume is more preferably 0.15 mL / g or more, or 0.2 mL / g or more. On the other hand, if the pore volume is too large, the proportion of pore walls made of Nb-SnO2 decreases, which may result in a decrease in electronic conductivity. Furthermore, the amount of ionomer penetration increases, which may result in a decrease in activity due to catalyst poisoning. Therefore, the pore volume is preferably 1.0 mL / g or less. The pore volume is more preferably 0.7 mL / g or less, or even 0.5 mL / g or less.

[0059] [F. Tap Density] "Tap density" refers to a value measured in accordance with JIS Z 2512. When the tin oxide-based particles according to the present invention are used in a catalyst layer of a PEFC, if the tap density of the tin oxide-based particles is too small, the thickness of the resulting catalyst layer becomes too large, resulting in a decrease in proton conductivity. 3 The tap density is preferably 0.01 g / cm or more. 3 or more, or 0.05g / cm 3 That's all. On the other hand, if the tap density is too high, when a catalyst layer is produced using this, it may be difficult to ensure voids in the catalyst layer that are sufficient to suppress flooding. Therefore, the tap density is set to 1.0 g / cm. 3 The tap density is preferably 0.75 g / cm or less. 3 The following is the result.

[0060] 1.2. Catalyst particles Catalyst particles are supported on the surface of the support.

[0061] [1.2.1. Composition] In the present invention, the catalyst particles are made of Pt-based particles. (a) Pt particles, (b) Particles made of an alloy of Pt and one or more precious metal elements other than Pt (Au, Ag, Pd, Rh, Ir, Ru, Os), (c) Particles made of an alloy of Pt and one or more base metal elements (e.g., Fe, Co, Ni, Cr, V, Ti, etc.), or (d) Particles consisting of an alloy of Pt, one or more precious metal elements other than Pt, and one or more base metal elements. This refers to...

[0062] Examples of Pt alloys include Pt--Fe alloys, Pt--Co alloys, Pt--Ni alloys, Pt--Pd alloys, Pt--Cr alloys, Pt--V alloys, Pt--Ti alloys, Pt--Ru alloys, and Pt--Ir alloys.

[0063] When Pt-based particles contain metal elements other than Pt, if the Pt content is too low, catalytic activity may decrease. Therefore, the amount of Pt contained in the Pt-based particles is preferably 30 at% or more. The amount of Pt is more preferably 40 at% or more, 50 at% or more, or 60 at% or more.

[0064] 1.2.2. Loading amount "Catalyst particle loading (mg cat / m 2 support)" refers to the value obtained by dividing the mass of catalyst particles supported on the carrier by the surface area of ​​the carrier.

[0065] It is believed that an electron-deficient layer is easily formed on the surface of the Nb-SnO2 support, which reduces the activity of the electrode catalyst. In contrast, catalyst particles supported on the surface of the Nb-SnO2 support are thought to not only catalyze the hydrogen oxidation reaction or oxygen reduction reaction, but also supply electrons to the electron-deficient layer, thereby reducing or eliminating the electron-deficient layer. Therefore, in general, the activity of the electrode catalyst improves as the amount of catalyst particles supported increases. To achieve this effect, the amount of catalyst particles supported should be 4.5 mg. cat / m 2 support The amount of support is more preferably 5.0 mg or more. cat / m 2 support Over 5.5mg cat / m 2 support Over 6.0mg cat / m 2 support Over 6.5mg cat / m 2 support or more, or 6.75 mg cat / m 2 support That's all. On the other hand, if the loading amount is excessive, the catalyst particles may aggregate, making it difficult to load the catalyst particles on the carrier in a highly dispersed state. cat / m 2 support The following is preferred:

[0066] [1.3. Characteristics of Electrocatalysts - Electrical Conductivity of Compacted Powder] Conductivity of the green compact (σ Pt-supported )" means, (a) The electrode catalyst was molded using two stainless steel disks and a plastic jig with a cylindrical hole. (b) Apply a pressure of 2.4 MPa to the obtained powder compact, and measure the voltage while passing a constant current. This refers to the conductivity obtained by

[0067] By optimizing the composition of the support and the amount of catalyst particles loaded, high σ Pt-supported By optimizing the manufacturing conditions, an electrocatalyst having σ Pt-supported is 1.0 x 10 -4 S / cm or more. By further optimizing the manufacturing conditions, Pt-supported is 5.0 x 10 -4 S / cm or more, 1.0×10 -3 S / cm or more, 1.5×10 -3 S / cm or more, or 2.0 x 10 -3 S / cm or more. In addition, when the manufacturing conditions are optimized, σ Pt-supported It is possible to produce an electrode catalyst with a conductivity of 1.0 S / cm.

[0068] [2. Catalyst layer] The catalyst layer according to the present invention comprises: an electrode catalyst according to the present invention; Ionomer and It is equipped with:

[0069] [2.1. Electrocatalyst] The details of the electrode catalyst are as described above, and therefore will not be described here.

[0070] [2.2. Ionomer] [2.2.1. Materials] In the present invention, the type of ionomer is not particularly limited. Examples of ionomers include perfluorocarbon sulfonic acid polymers and high-oxygen-permeable ionomers. The ionomer may consist of any one of these, or may be a combination of two or more of these.

[0071] "Perfluorocarbon sulfonic acid polymer" refers to a fluorine-containing ion exchange resin containing repeating units based on a sulfonyl fluoride vinyl ether monomer. Examples of perfluorocarbon sulfonic acid polymers include Nafion (registered trademark), Flemion (registered trademark), Aquivion (registered trademark), and Aciplex (registered trademark).

[0072] A "highly oxygen-permeable ionomer" refers to a polymer compound that contains an acid group and a cyclic structure within its molecular structure. Highly oxygen-permeable ionomers have a high oxygen permeability coefficient due to the cyclic structure within their molecular structure. Therefore, when used as an ionomer, the oxygen transfer resistance at the interface with the catalyst becomes relatively small. In other words, the "highly oxygen-permeable ionomer" refers to an ionomer having an oxygen permeability coefficient higher than that of perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark).

[0073] Examples of highly oxygen-permeable ionomers include: (a) an electrolyte polymer containing a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having a perfluorosulfonic acid group in a side chain; (b) an electrolyte polymer containing a perfluorocarbon unit having an aliphatic ring structure and an acid group unit having a perfluoroimide in the side chain; (c) an electrolyte polymer containing a unit in which perfluorosulfonic acid is directly bonded to a perfluorocarbon having an aliphatic ring structure; (See References 1-4). [Reference 1] Japanese Patent Application Laid-Open No. 2003-036856 [Reference 2] International Publication No. 2012 / 088166 [Reference 3] JP 2013-216811 A [Reference 4] JP 2006-152249 A

[0074] [2.2.2. Ionomer content (I / S)] "I / S" refers to the ratio of the mass of the ionomer (I) to the mass of the tin oxide-based particles (S).

[0075] Generally, the larger the I / S ratio, the higher the proton conductivity of the catalyst layer. To achieve this effect, the I / S ratio is preferably 0.13 or more. The I / S ratio is more preferably 0.15 or more, or even 0.20 or more. On the other hand, if I / S is too large, the amount of voids in the catalyst layer decreases, which may result in a decrease in the gas diffusion properties of the catalyst layer. Therefore, I / S is preferably 0.39 or less. I / S is more preferably 0.35 or less, or even 0.30 or less.

[0076] [2.3. Characteristics] [2.3.1. Mass activity under highly humidified conditions] The "mass activity under highly humidified conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the catalyst layer as the air electrode and power is generated under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V. "Mass activity" refers to the value obtained by dividing the current density under certain conditions by the mass of Pt contained in the catalyst particles per unit area of ​​the air electrode.

[0077] In the catalyst layer according to the present invention, when the composition of the electrode catalyst and the catalyst layer is optimized, the mass activity under highly humidified conditions is 150 A / g. Pt By further optimizing the composition of the electrode catalyst and catalyst layer, the mass activity under highly humidified conditions can be increased to 200 A / g. Pt More than 250A / g Pt or more than 300A / g Pt That's all. Furthermore, by optimizing the composition of the electrode catalyst and catalyst layer, the mass activity under highly humidified conditions was increased to 400 A / g. Pt It is possible to manufacture a catalyst layer having the above structure.

[0078] 2.3.2. Mass activity under low humidity conditions The "mass activity under low humidification conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is fabricated using the catalyst layer as the air electrode and power is generated under the following conditions: cell temperature: 82°C, gas humidity (both electrodes): 30% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

[0079] In the catalyst layer according to the present invention, when the composition of the electrode catalyst and the catalyst layer is optimized, the mass activity under low humidification conditions is high. When the composition of the electrode catalyst and the catalyst layer is optimized, the mass activity under low humidification conditions is 300 A / g Pt By further optimizing the composition of the electrode catalyst and catalyst layer, the mass activity under low humidification conditions is 400 A / g. Pt , more than 500A / g Pt or more, or 600A / g Pt That's all. Furthermore, by optimizing the composition of the electrode catalyst and catalyst layer, the mass activity under low humidification conditions was increased to 800 A / g. Pt It is possible to manufacture a catalyst layer having such a structure.

[0080] [2.3.3. Activity maintenance rate] The "activity retention rate" refers to the value expressed by the following formula (1). Activity retention rate = (mass activity after low potential holding test / initial mass activity) × 100 ... (1)

[0081] however, The "mass activity after a low-potential holding test" refers to the mass activity under high humidity conditions after a polymer electrolyte fuel cell using the catalyst layer as an air electrode is produced and a low-potential holding test is carried out under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, cathode gas: N2, anode gas: H2, cell voltage: 0.1 V, and holding time: 2 hours; The "initial mass activity" refers to the mass activity under high humidity conditions before the low potential holding test is performed, The "mass activity under high humidity conditions" refers to the mass activity of the oxygen reduction reaction when power is generated using the polymer electrolyte fuel cell under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

[0082] In the catalyst layer according to the present invention, optimizing the composition of the electrode catalyst and catalyst layer results in a high activity retention rate. By optimizing the composition of the electrode catalyst and catalyst layer, the activity retention rate can be 20% or more. By further optimizing the composition of the electrode catalyst and catalyst layer, the activity retention rate can be 30% or more, 50% or more, 70% or more, or 90% or more.

[0083] [3. Manufacturing method of mesoporous silica (first template)] In order to produce the tin oxide particles according to the present invention, it is first necessary to produce mesoporous silica (first template) having a beaded structure. (a) preparing precursor particles by condensation polymerization of the silica source in a reaction solution containing the silica source, a surfactant, and a catalyst; (b) separating the precursor particles from the reaction solution and drying them; (c) If necessary, the dried precursor particles are subjected to a diameter expansion treatment; (d) calcining the precursor particles This is obtained by:

[0084] [3.1. Polycondensation process] First, in a reaction solution containing a silica source, a surfactant, and a catalyst, the silica source is polycondensed to obtain precursor particles (polycondensation step).

[0085] 3.1.1. Silica Source In the present invention, the type of silica source is not particularly limited. Examples of the silica source include: (a) tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane, and tetraethyleneglycoxysilane; (b) trialkoxysilanes such as 3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane; As the silica source, any one of these may be used alone, or two or more of them may be used in combination.

[0086] 3.1.2. Surfactants When a silica source is polycondensed in a reaction solution, adding a surfactant to the reaction solution causes the surfactant to form micelles in the reaction solution. Because hydrophilic groups are clustered around the micelles, the silica source is adsorbed to the surface of the micelles. Furthermore, the micelles with the adsorbed silica source self-assemble in the reaction solution, causing the silica source to polycondense. As a result, mesopores resulting from the micelles are formed inside the primary particles. The size of the mesopores can be controlled (1 to 50 nm) primarily by the molecular length of the surfactant.

[0087] In the present invention, an alkyl quaternary ammonium salt is used as the surfactant. The alkyl quaternary ammonium salt refers to a compound represented by the following formula (a): CH3-(CH2) n -N + (R1)(R2)(R3)X - (a)

[0088] 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 or different. To facilitate aggregation of alkyl quaternary ammonium salts (micelle formation), 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. In formula (a), X represents a halogen atom. The type of halogen atom is not particularly limited, but X is preferably Cl or Br in view of availability.

[0089] In formula (a), n represents an integer of 7 to 21. Generally, as n decreases, a spherical mesoporous material with a smaller central pore diameter is obtained. On the other hand, as n increases, the central pore diameter increases, but if n is too large, the hydrophobic interaction of the alkyl quaternary ammonium salt becomes excessive. As a result, a layered compound is produced, and a mesoporous material cannot be obtained. n is preferably 9 to 17, and more preferably 13 to 17.

[0090] Among those represented by formula (a), alkyltrimethylammonium halides are preferred, such as hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, nonyltrimethylammonium halide, decyltrimethylammonium halide, undecyltrimethylammonium halide, and dodecyltrimethylammonium halide. Among these, alkyltrimethylammonium bromide or alkyltrimethylammonium chloride is particularly preferred.

[0091] 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, the type of alkyl quaternary ammonium salt significantly 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.

[0092] 3.1.3. Catalyst When polycondensing a silica source, a catalyst is usually added to the reaction solution. When synthesizing particulate mesoporous silica, the catalyst may be an alkali such as sodium hydroxide or aqueous ammonia, or an acid such as hydrochloric acid.

[0093] 3.1.4. Solvent The solvent used may be water, an organic solvent such as alcohol, or a mixed solvent of water and an organic solvent. Alcohol is (1) Monohydric alcohols such as methanol, ethanol, and propanol, (2) Dihydric alcohols such as ethylene glycol, (3) Trihydric alcohols such as glycerin, Either is fine. When a mixed solvent of water and an organic solvent is used, the content of the organic solvent in the mixed solvent can be selected arbitrarily depending on the purpose. Generally, adding an appropriate amount of organic solvent to the solvent makes it easier to control the particle size and particle size distribution.

[0094] 3.1.5. Composition of reaction solution The composition of the reaction solution affects the external shape and pore structure of the synthesized mesoporous silica. In particular, the concentrations of the surfactant and silica source in the reaction solution have a significant effect on the average primary particle size, pore size, pore volume, and tap density of the mesoporous silica particles.

[0095] [A. Surfactant concentration] If the surfactant concentration is too low, the particle precipitation rate will be slow and a structure in which primary particles are linked together will not be obtained. Therefore, the surfactant concentration must be 0.03 mol / L or more. The surfactant concentration is preferably 0.035 mol / L or more, more preferably 0.04 mol / L or more.

[0096] On the other hand, if the surfactant concentration is too high, the particle precipitation rate becomes too fast, and the primary particle size easily exceeds 300 nm. Therefore, the surfactant concentration must be 1.0 mol / L or less. The surfactant concentration is preferably 0.95 mol / L or less, and more preferably 0.90 mol / L or less.

[0097] B. Silica Source Concentration If the silica source concentration is too low, the particle precipitation rate will be slow, and a structure in which primary particles are connected will not be obtained. Alternatively, the surfactant may be excessive, making it impossible to obtain uniform mesopores. Therefore, the silica source concentration must be 0.05 mol / L or higher. The silica source concentration is preferably 0.06 mol / L or higher, and more preferably 0.07 mol / L or higher.

[0098] On the other hand, if the concentration of the silica source 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 concentration of the silica source must be 1.0 mol / L or less. The concentration of the silica source is preferably 0.95 mol / L or less, and more preferably 0.9 mol / L or less.

[0099] C. Catalyst Concentration In the present invention, the catalyst concentration is not particularly limited. Generally, if the catalyst concentration is too low, the particle precipitation rate will be slow. On the other hand, if the catalyst concentration is too high, the particle precipitation rate will be fast. It is preferable to select the optimum catalyst concentration depending on the type of silica source, the type of surfactant, the target physical property values, etc.

[0100] 3.1.6 Reaction conditions A silica source is added to a solvent containing a predetermined amount of surfactant, and hydrolysis and polycondensation are carried out, whereby precursor particles containing silica and surfactant are obtained, with the surfactant acting as a template. The optimum reaction conditions are selected depending on the type of silica source, the particle size of the precursor particles, etc. In general, the reaction temperature is preferably −20 to 100° C. The reaction temperature is more preferably 0 to 90° C., and even more preferably 10 to 80° C.

[0101] [3.2. Drying process] Next, the precursor particles are separated from the reaction solution and dried (drying step). Drying is carried out to remove the solvent remaining in the precursor particles. The drying conditions are not particularly limited as long as the solvent can be removed.

[0102] [3.3. Diameter expansion process] Next, if necessary, the dried precursor particles may be subjected to a diameter expansion treatment (diameter expansion step). The "diameter expansion treatment" refers to a treatment for expanding the diameter of mesopores in the primary particles. Specifically, the diameter-enlarging treatment is carried out by subjecting the synthesized precursor particles (from which the surfactant has not been removed) to a hydrothermal treatment in a solution containing a diameter-enlarging agent, which can enlarge the pore size of the precursor particles.

[0103] Examples of the diameter expanding agent 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; etc.

[0104] The reason why the pore size increases upon hydrothermal treatment in the presence of hydrocarbons is thought to be that rearrangement of silica occurs when the diameter-expanding agent is introduced from the solvent into the pores of the more hydrophobic precursor particles. Furthermore, the pore size increases when hydrothermal treatment is performed in the presence of an acid such as hydrochloric acid. This is thought to be due to the dissolution and reprecipitation of silica inside the primary particles. When the manufacturing conditions are optimized, radial pores are formed inside the silica. When this is subjected to hydrothermal treatment in the presence of an acid, silica dissolution and reprecipitation occurs, converting the radial pores into interconnected pores.

[0105] The conditions for the diameter-enlarging treatment are not particularly limited as long as the desired pore diameter is obtained. Usually, it is preferable to add about 0.05 mol / L to 10 mol / L of a diameter-enlarging agent to the reaction solution and perform hydrothermal treatment at 60 to 150°C.

[0106] [3.4. Firing process] Next, after carrying out a diameter expansion treatment as necessary, the precursor particles are calcined (calcination step), thereby obtaining mesoporous silica particles having a beaded structure. Calcination is carried out to dehydrate and crystallize the precursor particles with residual OH groups and to thermally decompose the surfactant remaining in the mesopores. The calcination conditions are not particularly limited as long as they allow for dehydration, crystallization, and thermal decomposition of the surfactant. Calcination is usually carried out by heating in air at 400°C to 700°C for 1 to 10 hours.

[0107] [4. Manufacturing method of mesoporous carbon (second mold)] Next, mesoporous silica having a beaded structure is used as a template to produce mesoporous carbon having a beaded structure (second template). (a) preparing mesoporous silica as a first template; (b) depositing carbon in the mesopores of the mesoporous silica to prepare a silica / carbon composite; (c) removing silica from the composite. This is obtained by: In order to promote graphitization of the obtained mesoporous carbon, the mesoporous carbon may be heat-treated at a temperature higher than 1500° C. after removing the silica.

[0108] [4.1. First mold preparation process] First, mesoporous silica to be used as the first template is prepared (first template preparation step). Details of the method for producing mesoporous silica are as described above, and therefore will not be described again.

[0109] [4.2. Carbon deposition process] Next, carbon is deposited in the mesopores of the mesoporous silica to produce a silica / carbon composite (carbon deposition step). Specifically, carbon deposition in mesopores is achieved by: (a) introducing a carbon precursor into the mesopores; (b) Polymerizing and carbonizing the carbon precursor within the mesopores This is done by:

[0110] 4.2.1. Introduction of carbon precursors The term "carbon precursor" refers to a material capable of producing carbon by thermal decomposition. Specific examples of such carbon precursors include: (1) A polymer precursor that is liquid at room temperature and is thermally polymerizable (e.g., furfuryl alcohol, aniline, etc.), (2) A mixture of an aqueous solution of carbohydrates and an acid (for example, a mixture of monosaccharides such as sucrose, xylose, glucose, or a mixture of disaccharides or polysaccharides with an acid such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid), (3) A mixture of two-component curing polymer precursors (e.g., phenol and formalin), etc. Among these, polymer precursors can be impregnated into mesopores without dilution with a solvent, allowing a relatively large amount of carbon to be produced in the mesopores with a relatively small number of impregnation cycles. Furthermore, they have the advantage of not requiring a polymerization initiator and being easy to handle.

[0111] When a liquid or solution carbon precursor is used, the larger the amount of liquid or solution adsorbed per one time, the better, and it is preferable that the amount be such that the entire mesopores are filled with the liquid or solution. When a mixture of an aqueous solution of a carbohydrate and an acid is used as the carbon precursor, the amount of acid is preferably the minimum amount that can polymerize the organic material. Furthermore, when a mixture of two-component curing polymer precursors is used as the carbon precursor, the optimum ratio is selected depending on the type of polymer precursor.

[0112] 4.2.2. Polymerization and carbonization of carbon precursors The polymerized carbon precursor is then carbonized within the mesopores. 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, vacuum, etc.). Specifically, the heating temperature is preferably 500°C or higher and 1200°C or lower. If the heating temperature is lower than 500°C, the carbon precursor will not be sufficiently carbonized. On the other hand, if the heating temperature exceeds 1200°C, silica and carbon will react, which is not preferable. The optimal heating time is selected depending on the heating temperature.

[0113] The amount of carbon generated in the mesopores should be at least the amount that allows the carbon particles to maintain their shape when the mesoporous silica is removed. Therefore, if the amount of carbon generated in one filling, polymerization, and carbonization process is relatively small, it is preferable to repeat these processes multiple times. In this case, the conditions for each repeated process may be the same or different. Furthermore, when each of the steps of filling, polymerization, and carbonization is repeated multiple times, each carbonization step may be performed at a relatively low temperature, and after the final carbonization step is completed, another carbonization step may be performed at a higher temperature. If the final carbonization step is performed at a higher temperature than the previous carbonization steps, the carbon introduced into the pores in multiple steps is more likely to be integrated.

[0114] [4.3. First mold removal step] Next, the mesoporous silica serving as the first template is removed from the composite (first template removal step), thereby obtaining mesoporous carbon (second template) having a beaded structure. Specific methods for removing mesoporous silica include: (1) A method of heating the complex in an alkaline aqueous solution such as sodium hydroxide, (2) Etching the composite with an aqueous hydrofluoric acid solution; etc.

[0115] [4.4. Graphitization process] Next, if necessary, the mesoporous carbon is heat-treated at a temperature higher than 1500°C (graphitization step). When carbonizing a carbon source within the mesopores of mesoporous silica, the heat treatment temperature must be low to suppress the reaction between silica and carbon. As a result, the degree of graphitization of the carbon after carbonization is low. To achieve a high degree of graphitization, it is preferable to heat-treat the mesoporous carbon at a high temperature after removing the first template.

[0116] If the heat treatment temperature is too low, graphitization will be insufficient. Therefore, the heat treatment temperature is preferably higher than 1500° C. The heat treatment temperature is preferably 1700° C. or higher, and more preferably 1800° C. or higher. On the other hand, if the heat treatment temperature is made higher than necessary, there is no difference in the effect and it is of no practical benefit. Therefore, the heat treatment temperature is preferably 2300°C or less. The heat treatment temperature is preferably 2200°C or less.

[0117] [5. Manufacturing method of tin oxide particles] The method for producing tin oxide-based particles according to the present invention comprises the steps of: A first step of preparing mesoporous carbon having a beaded structure; a second step of precipitating Nb-SnO2 in the mesopores of the mesoporous carbon to obtain a Nb-SnO2 / carbon composite; The third step is to remove carbon from the Nb-SnO2 / carbon composite. It is equipped with:

[0118] [5.1. 1st step] First, mesoporous carbon having a beaded structure is prepared (Step 1). Details of the method for producing mesoporous carbon are as described above, and therefore will not be described here.

[0119] [5.2. 2nd process] Next, Nb-SnO2 is precipitated in the mesopores of the mesoporous carbon (second step), thereby obtaining a Nb-SnO2 / carbon composite. Specifically, Nb-SnO2 is precipitated in the mesopores by introducing a Sn source and a Nb source (hereinafter collectively referred to as "precursors") into the mesopores and converting the precursors into Nb-SnO2.

[0120] [5.2.1. Method for introducing precursors into pores] The method for introducing the precursor into the pores is as follows: (a) A method in which mesoporous carbon is dispersed in a large amount of aqueous solution containing a Sn source and a Nb source, and the Sn source and the Nb source are precipitated in the pores (precipitation method); (b) A method of filling the pores of mesoporous carbon with a solution containing a Sn source and a Nb source in an amount equivalent to the pore volume (filling method). etc. In the present invention, either method may be used.

[0121] 5.2.2. Precursors The precursors for producing Nb-SnO2 are: (a) Contains Sn or Nb; (b) is liquid at room temperature or soluble in a solvent at room temperature; and (c) It is possible to form oxides by thermal decomposition or hydrolysis. Compounds are preferred.

[0122] Examples of Sn sources include: (a) Chlorides such as SnCl4 and SnCl2, (b) Alkoxides such as Sn(OC2H5)2 and Sn(OC(CH3)3)4; (c) acetylacetonate salts such as tin acetylacetonate (Sn(CH3COCHCOCH3)2); (d) acetates such as Sn(CH3COO)2 etc.

[0123] Examples of Nb sources include: (a) Chlorides such as NbCl5, (b) Alkoxides such as Nb(OC2H5)5 and Nb(OC4H9)5; (c) acetylacetonate salts such as niobium acetylacetonate (Nb(CH3COCHCOCH3)5); (d) acetates such as Nb(CH3COO)3 etc.

[0124] The solvent for dissolving the precursor is not particularly limited as long as it can dissolve the precursor and allow the solution to fill the pores of the mesoporous carbon. Examples of the solvent include ethanol, methanol, 1-propanol, 2-propanol, acetonitrile, acetone, N,N-dimethylformamide, and dimethyl sulfoxide. The concentration of the Sn or Nb source in the solution is not particularly limited as long as the solution can be filled into the pores of the mesoporous carbon. To deposit a required amount of Nb-SnO in the pores with fewer filling times, the higher the concentration of the Sn or Nb source in the solution, the better.

[0125] 5.2.3. Conversion of precursors to oxides After filling the pores of mesoporous carbon with a solution containing the precursor, the mesoporous carbon is heated to a predetermined temperature, whereby the precursor undergoes thermal decomposition or hydrolysis to form Nb-SnO2 in the pores. The heating conditions are not particularly limited as long as they allow the formation of Nb-SnO2 in the pores.

[0126] Generally, the higher the heating temperature, the easier it is to form Nb-SnO2. On the other hand, if the heating temperature is too high, the crystallite size and pore size will become large, which may make it difficult to obtain Nb-SnO2 with mesopores. Therefore, the heating temperature is preferably 300°C to 800°C. If a sufficient amount of Nb—SnO cannot be formed in the pores by one filling of the precursor and conversion to the oxide, the filling alone may be repeated multiple times, or the filling and conversion may be repeated multiple times.

[0127] [5.3. Third step] Next, carbon is removed from the Nb—SnO 2 / carbon composite (third step), thereby obtaining the tin oxide-based particles according to the present invention. The method for removing carbon is not particularly limited, and various methods can be used. Examples of the carbon removal method include: (1) A method of heating the Nb-SnO2 / carbon composite in an oxidizing atmosphere, (2) oxygen plasma etching of the composite; etc.

[0128] The removal conditions such as heating temperature and heating time may be any conditions that at least allow carbon to be completely removed without causing coarsening of Nb-SnO2 crystallites.

[0129] [6. Effect] Nb-SnO2 supports have higher low-potential stability than Sb-SnO2 supports. However, Nb-SnO2 supports have lower conductivity than Sb-SnO2 supports. This is thought to be because an electron-deficient layer is less likely to form on the surface of Sb-SnO2 supports, whereas an electron-deficient layer is more likely to form on the surface of Nb-SnO2 supports. In contrast, when an appropriate amount of Pt-based particles is supported on a Nb-SnO2 support, an electrocatalyst exhibiting high catalytic activity is obtained. This is thought to be because the electrons supplied from the Pt-based particles to the Nb-SnO2 support reduce or eliminate the electron-deficient layer at the interface between the Pt-based particles and the Nb-SnO2 support, thereby reducing the interfacial resistance. [Example]

[0130] (Examples 1 to 4, Comparative Examples 1 and 2) 1. Sample Preparation 1.1. Preparation of beaded starburst silica To a mixed solvent of 4.6 g of methanol (MeOH) and 4.6 g of ethylene glycol (EG), 56.3 g of 30 mass% aqueous cetyltrimethylammonium chloride solution was added and stirred at room temperature. 8.8 g of 1 M NaOH was added and heated to 50°C. Hereinafter, this solution will be referred to as "first solution." 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, hereinafter referred to as the "second solution."

[0131] 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 an additional 4 hours or more. Filtration and redispersion in purified water were repeated twice, and then the mixture was dried at 45°C. The dried powder was then calcined in air at 550°C for 6 hours to obtain connected starburst mesoporous silica with radial pores (hereinafter referred to as "connected starburst silica (CSS)").

[0132] 1.2. Preparation of beaded starburst carbon 0.5 g 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 penetrate into the pores of the CSS. This was then heat-treated at 150°C for 24 hours to polymerize the FA. This was then heat-treated in a nitrogen atmosphere for 6 hours at 500°C to further carbonize the FA. This process was repeated twice, and then further heat-treated in a nitrogen atmosphere for 6 hours at 900°C to obtain a CSS / carbon composite.

[0133] This composite was immersed in a 12% HF solution for 4 hours to dissolve the silica component. After dissolution, it was repeatedly filtered and washed, and then dried at 45°C to obtain a connected starburst carbon (hereinafter referred to as "connected starburst carbon (CSC)") with radial pores. The resulting porous material had a BET specific surface area of ​​2122 m. 2 / g, pore volume: 1.3 mL / g, pore diameter: 2.2 nm.

[0134] 1.3. Preparation of Electrocatalysts 1.3.1. Example 1 [A. Preparation of bead-like mesoporous Nb-SnO2 particles (precipitation method)] A mixture was obtained by mixing 250 mL of purified water, 4 mL of concentrated hydrochloric acid (35 mass%, Fujifilm Wako Pure Chemical Industries, Ltd.), 5.0 g of SnCl2 (Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.074 g of NbCl5 (Fujifilm Wako Pure Chemical Industries, Ltd.). 0.1 g of CSC was added to this mixture and dispersed. After stirring this dispersion in air at room temperature for 4 hours, it was filtered and redispersed in purified water twice. The mixture was then dried at 45°C to obtain a beaded mesoporous Nb-SnO2 / carbon composite. This beaded Nb-SnO2 / carbon composite was treated in an air atmosphere at 300°C for 24 hours, and then further treated in an air atmosphere at 700°C for 3 hours to obtain beaded mesoporous Nb-SnO2 particles.

[0135] [B. Pt Support (ALD)] Next, Pt particles were supported on the surface of a support consisting of beaded mesoporous Nb-SnO2 particles using atomic layer deposition (ALD). MeCpPtMe3 (methylcyclopentadienyltrimethylplatinum, manufactured by Tri Chemical Laboratory Co., Ltd.) was used as the Pt precursor. A test tube containing 100 mg of the support was heated to 150°C, and the Pt precursor container was heated to 60°C using a mantle heater. The following ALD cycle (1-4) was repeated 27 times to obtain Pt / Nb-SnO2. The Pt support ratio (the ratio of the mass of Pt to the total mass of the electrode catalyst) was 26.1 mass%.

[0136] 1.Pt precursor supply: MeCpPtMe3 / Ar, 50ccm, 20min 2. Purge: Ar, 200ccm, 5min 3. Pt precursor reduction: H2, 100 ccm, 5 min 4. Purge: Ar, 200ccm, 5min

[0137] 1.3.2. Example 2 [A. Preparation of beaded mesoporous Nb-SnO2 particles (filling method)] A precursor solution was obtained by dissolving 40 mg of NbCl5 and 0.8 g of SnCl2·2H2O (Fujifilm Wako Pure Chemical Industries, Ltd.) in 0.3 mL of ethanol. 0.2 mL of this precursor solution was added to 219 mg of CSC and the mixture was shaken. The CSC filled with the precursor solution was vacuum dried at 80°C for 4 hours, after which 0.08 mL of the precursor solution was added to the CSC and the mixture was shaken. This was then treated in an air atmosphere at 700°C for 3 hours to obtain beaded mesoporous Nb-SnO2 particles.

[0138] [B. Pt Support (ALD)] Pt particles were supported on the surface of a support made of beaded mesoporous Nb-SnO particles by the ALD method in the same manner as in Example 1. However, the ALD cycle was repeated 25 times. The Pt support rate was 17.9 mass%.

[0139] 1.3.3. Example 3 [A. Preparation of beaded mesoporous Nb-SnO2 particles (filling method)] In the same manner as in Example 2, beaded mesoporous Nb-SnO2 particles were obtained.

[0140] [B. Pt loading (colloidal method)] Next, Pt particles were supported on the surface of a support consisting of beaded mesoporous Nb-SnO2 particles using a colloidal method. First, 6 mL of a 0.4 M NaOH / ethylene glycol (EG) solution was mixed with 6 mL of a 0.04 mM HPtCl6 (Fujifilm Wako Pure Chemical Industries, Ltd.) / EG solution to obtain a mixed solution. This mixed solution was heated at 160 °C for 3 hours while stirring in a microwave synthesizer (Monowave 400, Anton Paar) to obtain a Pt nanoparticle colloidal solution.

[0141] Next, 107 mg of carrier was added to 8 mL of Pt nanoparticle colloidal solution and stirred overnight at room temperature. Next, 0.2 mL of 1 M HNO3 was added to the solution, and the solution was stirred at room temperature for 1 hour. This process was repeated twice. 0.5 mL of 1 M HNO3 was then added to the solution, and the solution was stirred at room temperature for 1 hour. After that, filtration and redispersion in purified water were repeated twice. Finally, the solution was dried in vacuum at 80°C to obtain Pt / Nb-SnO2. The Pt loading was 17.5 mass%.

[0142] 1.3.4. Example 4 [A. Preparation of bead-like mesoporous Nb-SnO2 particles (precipitation method)] Beaded mesoporous Nb-SnO2 particles were obtained in the same manner as in Example 1. However, NbCl5 (manufactured by Stream Chemical Co.) was used as the Nb source.

[0143] [B. Pt loading (colloidal method)] Next, Pt particles were supported on the surface of a support made of beaded mesoporous Nb-SnO2 particles by the colloidal method in the same manner as in Example 3. However, the amount of support added to 8 mL of Pt nanoparticle colloidal solution was 126 mg. The Pt support rate was 20 mass%.

[0144] 1.3.5. Comparative Example 1 [A. Preparation of beaded mesoporous Sb-SnO2 particles (precipitation method)] 0.12 g of SbCl3 (Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 4 mL of concentrated hydrochloric acid (35 mass%, Fujifilm Wako Pure Chemical Industries, Ltd.), and 36 mL of purified water was added for dilution. 5.0 g of SnCl2 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added and dissolved in this solution. 0.1 g of CSC was added to this solution and dispersed, followed by stirring in air at room temperature for 2 hours. 200 mL of purified water was then added, followed by stirring in air for an additional 4 hours. Subsequently, filtration and redispersion in purified water were repeated twice, and the mixture was dried at 45°C to obtain a beaded Sb-SnO2 / carbon composite. This beaded Sb-SnO2 / carbon composite was treated in an air atmosphere at 320°C for 24 hours, and then further treated in an air atmosphere at 400°C for 3 hours to obtain beaded mesoporous Sb-SnO2 particles.

[0145] [B. Pt loading (colloidal method)] Next, Pt particles were supported on the surface of the support made of beaded mesoporous Sb—SnO 2 particles by a colloidal method in the same manner as in Example 4. The Pt support rate was 20 mass %.

[0146] 1.3.6. Comparative Example 2 A commercially available Pt / C catalyst (TEC10V30E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used in the test as is.

[0147] 1.4. Fabrication of fuel cell The specified amounts of electrode catalyst, purified water, ethanol, propylene glycol, and ionomer dispersion (21.2 mass%, D2020) were weighed and mixed. The amount of ionomer was adjusted to an I / S ratio of 0.26. This mixture was subjected to alternating shaking and ultrasonic dispersion three times to obtain a catalyst ink. The resulting catalyst ink was applied to a polytetrafluoroethylene (PTFE) sheet using an applicator (gap height: 4 mil) and dried to obtain a cathode catalyst layer sheet. Pt / cm 2 It was decided.

[0148] An anode catalyst layer sheet was produced in the same manner as the cathode catalyst layer sheet, except that 30 mass% Pt / Ketjen (registered trademark) was used as the electrode catalyst. The platinum content was 0.05 mg. Pt / cm 2 , I / S is set to 1.0 The cathode catalyst layer sheet and the anode catalyst layer sheet were each cut into 1 cm squares, and the cut catalyst layers were transferred to a Nafion (registered trademark) membrane (NR211) by hot pressing to prepare an MEA. The hot pressing conditions were 120°C and 0.89 kN / cm. 2, and 5 minutes.

[0149] 2. Test Method [2.1. N2 adsorption measurement] The N2 adsorption isotherm of the obtained beaded mesoporous Nb-SnO2 particles was measured. From the obtained N2 adsorption isotherm, the pore size distribution was calculated using the BJH method, and the mode pore size (the most frequent value of the pore size) was taken as the pore size of the sample. In addition, the specific surface area was calculated from the N2 adsorption isotherm using the BET method.

[0150] 2.2. Conductivity A compact of beaded mesoporous Nb-SnO2 particles was prepared. A direct current was applied to the compact while applying a pressure of 2.4 MPa. The voltage value was measured to determine the overall electrical conductivity of the particles. support-total asked for. In addition, electrochemical impedance measurements (holding voltage: 0.2 V, amplitude: 0.1 V, frequency: 10 Hz to 5 MHz) were performed on the same powder compact while applying a pressure of 2.4 MPa. The conductivity inside the particle (conductivity excluding the resistance of the particle interface) σ was calculated from the intercept value of the real axis on the high frequency side of the obtained Nyquist plot. support-bulk asked for. Furthermore, the DC resistance of the compacted Pt / Nb-SnO2 particles after Pt loading was also measured, and the conductivity of the entire electrode catalyst, σ Pt-supported I asked.

[0151] [2.3. Pt loading rate] The Pt loading rate of Pt / Nb-SnO2 was measured using ICP analysis.

[0152] [2.4. Fuel Cell Evaluation] [2.4.1. Power generation performance evaluation] A voltage sweep was performed under the following conditions to measure the IV curve: The anodic scan of the third cycle was used as the IV curve data. Cell temperature / relative humidity (both poles): 60°C / 80%RH or 82°C / 30%RH Cathode gas: Air, 1000mL / min, back pressure 14.4kPa-G Anode gas: H2, 500mL / min, back pressure 14.4kPa-G Voltage sweep: Sweep from open circuit voltage to 0.1 V at 20 mV / s for 3 cycles

[0153] The current density at 0.84 V on the IV curve (a value after correcting for the cell resistance measured with a 100 kHz high-frequency resistance meter) was converted to a value per Pt mass, and this was defined as the ORR (oxygen reduction reaction) mass activity at 0.84 V.

[0154] 2.4.2. Low-potential holding test A test (low potential holding test) was conducted under the following conditions, in which the cell voltage was held at 0.2 V for 2 hours. Cell temperature / relative humidity (both poles): 60℃ / 80%RH Cathode gas: Air, 1000mL / min, back pressure 14.4kPa-G Anode gas: 10% H2 / N2, 500 mL / min, back pressure 14.4 kPa-G IV measurements were taken before and after the low potential holding test.

[0155] [3. Results] [3.1. Pore size, BET specific surface area, Pt loading rate, and Pt loading amount per support surface area] Table 1 shows the carrier pore size, BET specific surface area, Pt loading rate, and Pt loading amount per carrier surface area of ​​the electrode catalysts obtained in Examples 1 to 4. Example 1 had the highest Pt loading amount per carrier surface area.

[0156] [Table 1]

[0157] 3.2. Conductivity Table 2 shows the electrical conductivity (σ support-total ), the conductivity inside the carrier particles (σ support-bulk ), and the conductivity after Pt loading (σ Pt-supported ) are shown. The beaded mesoporous Nb-SnO2 particles obtained in all examples had a high conductivity (σsupport-total ) is the conductivity inside the carrier particle (σ support-bulk ), which indicates that the electrical conductivity at the interface of the beaded mesoporous Nb-SnO2 particles is lower than that inside the particles, i.e., the electronic resistance at the particle interface is high.

[0158] [Table 2]

[0159] According to Non-Patent Document 4, the reason why the resistance at the interface of SnO2 particles increases is that oxygen and water are reduced by electrons supplied from the surface of the SnO2 particles, and oxygen species (O2 - , O - , O 2- ) and hydroxide (OH - ) chemically adsorbed onto the surface of the SnO2 particles, forming an electron-deficient layer near the interface of the SnO2 particles. Comparing the amount of Pt supported per surface area of ​​the support, Example 1 was 6.93 mg Pt / m 2 support The highest value was obtained. Figure 1 shows an SEM image (backscattered electron image) of Pt / Nb-SnO2 (Example 1). Figure 1 shows that Pt is supported at a high density.

[0160] Conductivity after Pt loading (σ Pt-supported ) is 2.9 × 10 in Example 1 -3 S / cm, the highest among the examples, and the conductivity inside the carrier particles (σ support-bulk ) is 3.3 × 10 -3 The values ​​were very close to 1.5 S / cm. This suggests that the high density of Pt supported on the support surface reduces the electronic resistance at the particle interface. The reason for this may be that the electron-deficient layer on the support particle surface disappears as electrons are supplied from the supported Pt particles to the Nb-SnO2 particle surface.

[0161] On the other hand, in Examples 2 to 4, the amount of Pt supported per carrier surface area was lower than that in Example 1. In addition, the electrical conductivity (σ Pt-supported ) is also lower than that of Example 1, and is 1 × 10 -3 This indicates that the electron-deficient layer on the support surface disappears due to the electronic interaction between the supported Pt particles and the surface of the Nb-SnO2 particles, and the σ Pt-supported The value of is 1×10 -3 It is clear that in order to exceed S / cm, the Pt loading density on the support surface must be above a certain level.

[0162] [3.3. Mass activity] Figure 2 shows the IV curves at 80% RH and 60°C for the cells obtained in Examples 1 to 4. In the cell voltage range of 0.4 V or higher, Example 1 had the highest current density and exhibited excellent performance. Figure 3 shows the ORR mass activity (MA) at 0.84 V (80% RH, 60°C) calculated from the IV curves in Figure 2. The MA for Examples 2 to 4 was 50 A / g Pt In contrast, the MA of Example 1 is 339 A / g Pt This is because σ pt-supported When the value of is low, it indicates that the oxygen reduction reaction is inhibited by the electronic resistance at the particle interface.

[0163] Fig. 4 shows IV curves at 80% RH and 60°C for the cells obtained in Example 1 and Comparative Examples 1 and 2. Fig. 5 shows IV curves at 30% RH and 82°C for the cells obtained in Example 1 and Comparative Examples 1 and 2. Fig. 6 shows the ORR mass activity (MA) at 0.84 V determined from the IV curves in Figs. 4 and 5. The MA of the Pt / Sb-SnO2 catalyst of Comparative Example 1 was 299 A / g under highly humidified conditions. Pt , 496A / g under low humidity conditions Pt In contrast, the MA of the Pt / Nb-SnO2 catalyst of Example 1 was 339 A / g under highly humidified conditions. Pt , 729A / g under low humidity conditions Pt and under all conditions, the MA was higher than that of Comparative Example 1. Moreover, the MA under highly humidified conditions in Example 1 was higher than that of Comparative Example 2 (495 A / gPt ), the MA under low humidity conditions in Example 1 was higher than that of Comparative Example 2 (290 A / g Pt ) was more than twice as high.

[0164] [3.4. Activity maintenance rate] 7 shows the IV curves at 80% RH and 60°C before and after holding a low potential (0.1 V, 2 h) for the cells obtained in Example 1 and Comparative Example 1. Comparative Example 1 showed a significant decrease in IV performance after the low potential holding test. In contrast, Example 1 showed almost no difference in IV performance before and after the test. Fig. 8 shows the ORR mass activity (MA) at 0.84 V determined from the IV curve in Fig. 7. In Comparative Example 1, the MA decreased to 1 / 5 or less after the low-potential holding test. In contrast, in Example 1, the MA did not decrease at all after the low-potential holding test.

[0165] In Comparative Example 1, beaded mesoporous Sb-SnO2 particles were used as the support, but it is known that Sb doped in SnO2 dissolves at potentials below 0.3 V. Therefore, in Comparative Example 1, it is thought that the dissolved Sb ions were adsorbed onto the Pt catalyst surface, inhibiting the catalytic action, resulting in a decrease in MA. On the other hand, in Example 1, beaded mesoporous Nb-SnO2 particles were used as the support, and the Nb doped in SnO2 was stable even at low potentials, which is thought to be why there was no decline in catalytic activity or power generation performance in Example 1.

[0166] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0167] The electrode catalyst according to the present invention can be used as a catalyst for the air electrode or the fuel electrode of a polymer electrolyte fuel cell.

Claims

1. A carrier; Catalyst particles supported on the surface of the support; Equipped with the support is made of Nb-doped tin oxide particles having a structure in which porous primary particles are fused together in a beaded shape (a beaded structure); The catalyst particles are made of Pt-based particles. Electrocatalyst.

2. The amount of catalyst particles carried is 4.5 m cat / m 2 support The electrode catalyst according to claim 1, wherein the above-mentioned Here, the "amount of catalyst particles supported" refers to the value obtained by dividing the mass of the catalyst particles supported on the support by the surface area of ​​the support.

3. The tin oxide particles have a specific surface area of ​​30 m 2 2. The electrode catalyst according to claim 1, wherein the SiO2 content is 1 / g or more.

4. The conductivity of the powder compact is 1 x 10 -3 2. The electrode catalyst according to claim 1, wherein the electrocatalyst has a specific surface area of ​​1000 nm or more.

5. 2. The electrode catalyst according to claim 1, wherein the tin oxide-based particles are doped with Nb in an amount of 2.0 at % or more and 15.0 at % or less.

6. The electrode catalyst according to claim 1; Ionomer and A catalyst layer comprising:

7. 7. The catalyst layer according to claim 6, wherein the ratio (=I / S) of the mass (I) of the ionomer to the mass (S) of the tin oxide-based particles is 0.13 or more and 0.39 or less.

8. Mass activity under highly humidified conditions is 150 A / g Pt The catalyst layer according to claim 6, wherein the catalyst layer is as described above. Here, the "mass activity under highly humidified conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is produced using the catalyst layer as an air electrode and power is generated under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

9. Mass activity under low humidity conditions is 300 A / g Pt The catalyst layer according to claim 6, wherein the catalyst layer is as described above. Here, the "mass activity under low humidification conditions" refers to the mass activity of the oxygen reduction reaction when a polymer electrolyte fuel cell is produced using the catalyst layer as an air electrode and power is generated under the following conditions: cell temperature: 82°C, gas humidity (both electrodes): 30% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

10. 7. The catalyst layer according to claim 6, wherein the activity retention rate represented by the following formula (1) is 20% or more. Activity retention rate = (mass activity after low potential holding test / initial mass activity) × 100 (1) however, The "mass activity after low potential holding test" refers to a test in which a polymer electrolyte fuel cell was produced using the catalyst layer as the air electrode, and the cell temperature was 60°C, the gas humidity (both electrodes) was 80% RH, and the cathode gas was N 2 , anode gas: H 2 , cell voltage: 0.1 V, after conducting a low potential holding test under the condition of holding for 2 hours, under high humidity conditions, The "initial mass activity" refers to the mass activity under high humidity conditions before the low potential holding test is performed, The "mass activity under high humidity conditions" refers to the mass activity of the oxygen reduction reaction when power is generated using the polymer electrolyte fuel cell under the following conditions: cell temperature: 60°C, gas humidity (both electrodes): 80% RH, oxygen partial pressure in the cathode gas: 21 kPa, and cell voltage: 0.84 V.

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