Platinum- or platinum alloy-supporting carbon catalyst and method for producing same, membrane electrode assembly for solid polymer fuel cell using platinum- or platinum alloy-supporting carbon catalyst, and solid polymer fuel cell

Abstract

[Problem] To provide a highly active and highly durable platinum- or platinum alloy-supporting carbon catalyst for solid polymer fuel cells. [Solution] A platinum- or platinum alloy-supporting carbon catalyst in which platinum particles or platinum alloy particles are supported on mesoporous carbon, the platinum- or platinum alloy-supporting carbon catalyst being characterized in that: the platinum or platinum alloy support ratio in the catalyst is 30-70% on a weight basis per the total weight of the catalyst; the total weight of platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon is 60-90% with respect to the total weight of the platinum particles or platinum alloy particles; the average particle diameter D1 of the platinum particles or platinum alloy particles supported in the pores of the mesoporous carbon is the same as or larger than the average particle diameter D2 of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon; and the average particle diameter D1 and the average particle diameter D2 are each independently 2-8 nm.

Description

Platinum or platinum alloy supported carbon catalyst and its manufacturing method, membrane electrode assembly for polymer electrolyte fuel cell using platinum or platinum alloy supported carbon catalyst, and polymer electrolyte fuel cell

[0001] The present invention relates to a highly active and highly durable platinum or platinum alloy supported carbon catalyst for polymer electrolyte fuel cells, in which platinum particles or platinum alloy particles are supported inside and outside the pores of a carrier.

[0002] In recent years, decarbonization and carbon neutrality have been promoted as measures to address energy and environmental issues, and the use of hydrogen as a clean energy alternative to chemical fuels has been attracting attention. Fuel cells, which generate electricity through a chemical reaction between hydrogen and oxygen, do not emit carbon dioxide, a greenhouse gas, and are therefore expected to be a new power generation system that contributes to carbon neutrality. Among these fuel cells, polymer electrolyte fuel cells (PEFCs) use a solid polymer ion-conducting membrane as the electrolyte layer. Their operating temperature is low, ranging from room temperature to 100°C, and they can be miniaturized, so their practical use as power sources for electric vehicles and stationary power sources is being promoted.

[0003] A polymer electrolyte fuel cell has a cell stack structure in which multiple single cells, each consisting of a membrane electrode assembly (MEA) sandwiched between separators, are stacked. The MEA has a structure in which an electrolyte layer is sandwiched between two electrode catalyst layers made of an electrode catalyst and an electrolyte polymer (ionomer).

[0004] In the MEA, the following electrochemical reactions take place to generate electricity. First, hydrogen supplied as fuel is oxidized by an electrode catalyst at the fuel electrode (anode) side electrode catalyst layer, generating protons and electrons. Next, the generated protons pass through an electrolyte layer made of an ion-conductive electrolyte, while the electrons pass through an external circuit to reach the oxygen electrode (cathode) side electrode catalyst layer. The protons and electrons that reach the cathode side electrode catalyst layer react with oxygen supplied to the cathode side to generate water. The electrons generated at the anode side are used as electrical energy as they travel to the cathode side electrode via the external circuit.

[0005] Conventional electrode catalysts are platinum or platinum alloy-supported carbon catalysts, which are made by supporting nanoparticles of platinum (Pt) or platinum alloys on a highly electron-conductive carbon black support. High-specific-surface-area carbon is used in the platinum or platinum alloy-supported carbon catalysts to support platinum particles or platinum alloy particles in a highly dispersed state without agglomeration. This increases the electrode reaction area on the surface of the platinum particles or platinum alloy particles, enabling sufficient activity with a small amount of platinum or platinum alloy supported.

[0006] In order to popularize fuel cell vehicles (FCVs) toward achieving carbon neutrality, there is a need to develop cathode catalysts for polymer electrolyte fuel cells (PEFCs) that are highly efficient and capable of operating at high loads.

[0007] Cited Document 1 discloses a platinum-supported carbon catalyst supported on solid-structure carbon such as furnace black or acetylene black, which has a dense interior.

[0008] Cited Document 2 discloses an electrode catalyst in which platinum particles are supported within the pores of a porous hollow carbon support such as Ketjenblack. It mentions that by supporting platinum particles within the pores, adsorption of ionomer onto the platinum particle surface can be suppressed, and a decrease in the effective reaction surface area of ​​the platinum particles can be prevented.

[0009] JP 2007-112660 A JP 2013-109856 A

[0010] For example, platinum-supported carbon catalysts supported on solid-structure carbon, such as furnace black or acetylene black, have excellent mass transport properties because the platinum particles are supported on the surface of the support, and the reaction easily progresses when the reactant gas comes into contact with the platinum particles. However, because the platinum particles are on the surface of the support, there are problems such as reduced activity due to ionomer poisoning and catalyst deterioration due to platinum particle aggregation (sintering).

[0011] On the other hand, platinum-supported carbon catalysts, which use porous carbon such as Ketjenblack as a support and have platinum particles supported within the pores, are also widely used. Because the platinum particles are supported within the pores of the support, ionomer poisoning is reduced and a decrease in catalytic activity is suppressed. However, while platinum particles supported within the pores have high activity, there is a problem in that access of protons and reactant gases is limited.

[0012] Therefore, there is a need for a method for loading platinum particles or platinum alloy particles inside and outside the pores of a carrier at any ratio. Furthermore, if platinum particles or platinum alloy particles can be loaded inside and outside the pores of a carrier at any ratio, it will be possible to provide catalytically active components with different functions by selectively loading them inside and outside the pores, thereby adjusting performance.

[0013] An object of the present invention is to provide a platinum or platinum alloy supported carbon catalyst that has high initial activity and excellent durability by selectively supporting platinum particles or platinum alloy particles inside and outside the pores of a carbon support.

[0014] The inventors have discovered that by adopting a two-stage loading process, which involves a step of loading platinum particles or platinum alloy particles inside the pores of a carbon support by impregnation, and a step of loading platinum particles outside the pores of the carbon support by liquid-phase reduction, it is possible to control the loading amount and particle size of the platinum particles or platinum alloy particles loaded inside and outside the pores.

[0015] That is, the present invention provides a platinum or platinum alloy-supported carbon catalyst in which platinum particles or platinum alloy particles are supported on mesoporous carbon, wherein the platinum or platinum alloy loading in the catalyst is 30% to 70% by weight of the total weight of the catalyst, the total weight of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon being 60 to 90% of the total weight of the platinum particles or platinum alloy particles, the average particle size D1 of the platinum particles or platinum alloy particles supported inside the pores of the mesoporous carbon is the same as or larger than the average particle size D2 of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon, and the average particle size D1 and the average particle size D2 are independently 2 nm to 8 nm.

[0016] In the above configuration, the average particle diameter D1 may be 2.5 nm or more and 8 nm or less, the average particle diameter D2 may be 2.3 nm or more and 7.3 nm or less, and D1 / D2 may be 1.0 to 2.1.

[0017] The present invention also relates to a manufacturing method for a platinum-supported carbon catalyst, comprising: an intrapore supporting step of supporting platinum within the pores of the mesoporous carbon support, the intrapore supporting step comprising: impregnating a mesoporous carbon support with an aqueous solution containing a platinum compound; drying the mesoporous carbon support impregnated with the aqueous solution containing the platinum compound obtained in the aforementioned step under reduced pressure; and heat-treating the mesoporous carbon support dried under reduced pressure obtained in the drying step in a reducing atmosphere; and an extrapore supporting step of supporting platinum particles outside the pores of the mesoporous carbon support, the extrapore supporting step comprising: suspending the mesoporous carbon support with platinum supported within the pores after the intrapore supporting step in an aqueous solution; and mixing the suspension with a liquid containing the aqueous solution containing the platinum compound and a reducing agent to reduce the platinum compound.

[0018] the intrapore supporting step comprises the steps of: adding and mixing an aqueous solution of dinitrodiamine platinum nitric acid to a mesoporous carbon support to obtain a platinum-supported carbon slurry; drying the obtained slurry at a predetermined temperature under reduced pressure to obtain a dry solid; heat treating the slurry in a reducing atmosphere to reduce dinitrodiamine platinum; and firing the slurry in an inert gas atmosphere (firing temperature T1) to grow platinum particles; and the extrapore supporting step comprises the steps of suspending the mesoporous carbon support with platinum supported in the pores after the intrapore supporting step in an aqueous nitric acid solution, and heating and stirring the suspension, the aqueous solution of dinitrodiamine platinum nitric acid, and a liquid containing L-ascorbic acid at 80°C to 100°C for 30 minutes to 5 hours to support the platinum particles outside the pores of the carbon support; and a step of filtering out the platinum-supported carbon in which the platinum particles are supported outside the pores of the carbon support in the step, washing the carbon, drying the carbon, and then firing the carbon in an inert gas atmosphere (firing temperature T2) to grow the platinum particles.

[0019] The above manufacturing method may include the steps of: adding an aqueous solution containing a compound of a metal to be alloyed with the platinum to the platinum-supported carbon catalyst and mixing them to obtain a slurry; heating and drying the obtained slurry under reduced pressure to obtain a dried product; and an alloying step of performing a pre-treatment firing of the dried product in a reducing atmosphere, followed by firing in an inert gas atmosphere to perform an alloying treatment.

[0020] In the above manufacturing method, the average particle diameters D1 and D2 of the platinum particles may be controlled by setting the firing temperature T1 and the firing temperature T2 to predetermined temperatures, respectively.

[0021] According to the present invention, by selectively supporting platinum particles or platinum alloy particles inside and outside the pores of a carbon support, it is possible to provide a platinum or platinum alloy-supported carbon catalyst that has high initial activity and excellent durability.

[0022] First, the manufacturing method of the present invention will be explained.

[0023] The production method of the present invention is a method for producing a platinum-supported carbon catalyst, comprising: an intrapore supporting step of supporting platinum within the pores of the mesoporous carbon support, the intrapore supporting step comprising: impregnating a mesoporous carbon support with an aqueous solution containing a platinum compound; drying the mesoporous carbon support impregnated with the aqueous solution containing the platinum compound obtained in the aforementioned step under reduced pressure; and heat-treating the mesoporous carbon support dried under reduced pressure obtained in the drying step in a reducing atmosphere; and an extrapore supporting step of supporting platinum particles outside the pores of the mesoporous carbon support, the extrapore supporting step comprising: suspending the mesoporous carbon support with platinum supported within its pores after the intrapore supporting step in an aqueous solution; and mixing the suspension with a liquid containing the aqueous solution containing the platinum compound and a reducing agent to reduce the platinum compound.

[0024] Furthermore, in the manufacturing method of the present invention, the intrapore supporting step includes a step of adding and mixing an aqueous solution of dinitrodiamine platinum nitric acid to a mesoporous carbon support to obtain a platinum-supported carbon slurry, a step of drying the obtained slurry at a predetermined temperature under reduced pressure to obtain a solid, a step of heat treating the slurry in a reducing atmosphere to reduce dinitrodiamine platinum, and a step of firing in an inert gas atmosphere (firing temperature T1) to grow platinum particles; and the extrapore supporting step includes a step of suspending the mesoporous carbon support with platinum supported in the pores after the intrapore supporting step in an aqueous nitric acid solution, and heating and stirring the suspension, the aqueous solution of dinitrodiamine platinum nitric acid, and a liquid containing L-ascorbic acid at 80°C to 100°C for 30 minutes to 5 hours to support the platinum particles outside the pores of the carbon support; and a step of filtering out the platinum-supported carbon in which the platinum particles are supported outside the pores of the carbon support in the step, washing the carbon, drying the carbon, and then firing the carbon in an inert gas atmosphere (firing temperature T2) to grow the platinum particles.

[0025] When a catalytically active component (e.g., platinum) is supplied in the form of a solution and supported on a support, this is called impregnation, and the catalytically active component (e.g., platinum) is likely to be supported in the pores of the support. The production method of the present invention employs a two-stage supporting process in which the catalytically active component (e.g., platinum) is supported in the pores of the support by impregnation, and then the catalytically active component (e.g., platinum) is supported outside the pores of the support by liquid-phase reduction.

[0026] As the platinum-containing aqueous solution, a dinitrodiamine platinum nitric acid aqueous solution, a chloroplatinic acid aqueous solution, or the like can be used.

[0027] Mesoporous carbon is used as the support. Mesoporous carbon is a carbon material with nanometer-order pores. Mesoporous carbon with various pore volumes and specific surface areas can be used for the platinum or platinum alloy-supported carbon catalyst of the present invention.

[0028] In the outside-pore supporting step, L-ascorbic acid, citric acid, etc. can be used as the reducing agent. In the outside-pore supporting step, an alcoholic solvent may be added to the nitric acid aqueous solution as the dispersion solvent. Ethanol, 2-propanol, etc. can be used as the alcoholic solvent.

[0029] The inert gas may be nitrogen, argon, or the like.

[0030] Hereinafter, the platinum particles or platinum alloy particles supported within the pores of the carrier will be referred to as first platinum particles or platinum alloy particles, and the platinum particles or platinum alloy particles supported outside the pores of the carrier will be referred to as second platinum particles or platinum alloy particles.

[0031] The process for supporting platinum in the pores of a mesoporous carbon support is, for example, as follows: A dinitrodiamine platinum nitric acid aqueous solution is added to and mixed with the mesoporous carbon support to form a platinum-supported carbon slurry, which is then dried under reduced pressure at a predetermined temperature to obtain a dried product. The resulting dried product is heat-treated in a reducing atmosphere to reduce the dinitrodiamine platinum, and then calcined in an inert gas (e.g., nitrogen) atmosphere (calcination temperature T1) to grow platinum particles, thereby preparing carbon with first platinum particles supported within the pores.

[0032] The outside-pore supporting step is, for example, as follows: The carbon carrying the first platinum particles within the pores is suspended in an aqueous nitric acid solution, and the suspension is mixed with an aqueous dinitrodiamine platinum nitric acid solution, ethanol, and L-ascorbic acid. Next, this mixture is heated and stirred at 80°C to 100°C for 30 minutes to 5 hours. For example, this mixture is heated at 90°C for 1 hour using a reflux reactor to reduce the dinitrodiamine platinum in the liquid phase, thereby supporting the platinum particles outside the pores of the carbon support. The platinum-supported carbon carrying the second platinum particles outside the pores of the carbon support is filtered out, washed, dried, and then calcined in an inert gas atmosphere (calcination temperature T2) to grow the platinum particles, thereby preparing a platinum-supported carbon catalyst in which platinum particles are selectively supported inside and outside the pores of the carbon support.

[0033] After the above-mentioned filtration, washing, and drying, but before calcination in an inert gas atmosphere (calcination temperature T2), any remaining residue of the reducing agent (L-ascorbic acid) that was not completely removed by washing may be thermally decomposed and removed by heat treatment in an oxygen-free atmosphere, such as a 4.0% hydrogen / nitrogen atmosphere.

[0034] The manufacturing method of the present invention may also include the steps of: adding an aqueous solution containing a compound of a metal to be alloyed with the platinum to the platinum-supported carbon catalyst and mixing them to obtain a slurry; heating and drying the obtained slurry under reduced pressure to obtain a dried product; and an alloying step of performing a pretreatment firing of the dried product in a reducing atmosphere, followed by firing in an inert gas atmosphere to perform an alloying treatment.

[0035] For example, a cobalt nitrate solution prepared by dissolving cobalt (II) nitrate hexahydrate in water is added to the platinum-supported carbon catalyst prepared by the above method, and the mixture is mixed using a kneader to obtain a slurry. The resulting slurry is dried using a vacuum dryer, for example, at 80°C to 250°C under reduced pressure for 1 to 15 hours to obtain a dried product. This dried product is reduced in an atmosphere furnace in a hydrogen / nitrogen mixed atmosphere at 200°C to 600°C for 1 to 5 hours, and then calcined in an inert gas flow at 700°C to 900°C for 0.5 to 5 hours to perform an alloying treatment. The excess cobalt is then removed by acid washing. The product is then filtered, washed, and dried to obtain a platinum-cobalt-supported carbon catalyst.

[0036] In addition, the manufacturing method of the present invention may control the average particle diameter D1 of the platinum particles and the average particle diameter D2 of the platinum particles by setting the firing temperature T1 and the firing temperature T2 to predetermined temperatures, respectively.

[0037] The firing temperature T1 and the firing temperature T2 can be set, for example, to 500° C. to 1000° C. By firing at 500° C. to 1000° C., platinum particles can be formed to a predetermined size.

[0038] Next, the catalyst of the present invention is a platinum or platinum alloy-supported carbon catalyst in which platinum particles or platinum alloy particles are supported on mesoporous carbon, wherein the platinum or platinum alloy loading in the catalyst is 30% to 70% by weight of the total weight of the catalyst, the total weight of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon is 60 to 90% of the total weight of the platinum particles or platinum alloy particles, the average particle size D1 of the platinum particles or platinum alloy particles supported inside the pores of the mesoporous carbon is the same as or larger than the average particle size D2 of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon, and the average particle size D1 and the average particle size D2 are independently 2 nm to 8 nm.

[0039] The platinum or platinum alloy loading rate in the platinum or platinum alloy-supported carbon catalyst can be determined, for example, by using aqua regia to dissolve the metal components contained in the platinum particles or platinum alloy particles from the platinum or platinum alloy-supported carbon catalyst, and then quantifying the metal ions in the solution using an inductively coupled plasma (ICP) optical emission spectrometer.

[0040] The platinum or platinum alloy loading rate in the platinum or platinum alloy-supported carbon catalyst is 30% to 70% by weight based on the total weight of the catalyst. By ensuring that the loading density of platinum particles or platinum alloy particles is within this range, the thickness of the electrode catalyst layer can be controlled to be suitable for proton transfer, gas diffusion, and drainage of generated water during the formation of the electrode catalyst layer.

[0041] The platinum or platinum alloy loading ratio in the platinum or platinum alloy supported carbon catalyst is preferably 35% to 60% by weight based on the total weight of the catalyst, and more preferably 40% to 55% by weight based on the total weight of the catalyst.

[0042] The total weight of platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon relative to the total weight of platinum particles or platinum alloy particles supported on the mesoporous carbon (i.e., the total weight of platinum particles or platinum alloy particles supported inside and outside the pores of the mesoporous carbon) is 60 to 90%. Supporting platinum particles or platinum alloy particles inside the pores of the carbon support reduces the contact area with the ionomer, thereby reducing poisoning of the platinum particles or platinum alloy particles by the sulfonic acid groups of the ionomer and expected to result in high initial activity. However, from the perspective of mass transport properties such as protons and reactant gases, the ratio of the particles supported inside the pores to the particles supported outside the pores must be appropriately adjusted, and the total weight of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon relative to the total weight of the platinum particles or platinum alloy particles supported on the mesoporous carbon is set to 60 to 90%.

[0043] The total weight of platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon is preferably 80% or less, and more preferably 70% or less, of the total weight of platinum particles or platinum alloy particles supported on the mesoporous carbon.

[0044] The catalyst of the present invention may also be configured such that the platinum particles or platinum alloy particles have an average particle size D1 of 2.5 nm or more and 8 nm or less, the platinum particles or platinum alloy particles have an average particle size D2 of 2.3 nm or more and 7.3 nm or less, and D1 / D2 is 1.0 to 2.1.

[0045] In a fuel cell operating environment accompanied by potential fluctuations, small platinum particles preferentially dissolve and are redeposited on the surfaces of larger platinum particles, resulting in coarsening of the platinum particles and degradation of the catalytically active component. To prevent platinum particles or platinum alloy particles supported within the pores, which are resistant to ionomer poisoning and exhibit high activity, from eluting from the pores to the outside, it is preferable that the average particle size D1 be greater than or equal to the average particle size D2. Here, the average particle size D1 is the average particle size of the platinum particles or platinum alloy particles supported within the pores of the mesoporous carbon, and the average particle size D2 is the average particle size of the platinum particles or platinum alloy particles supported outside the pores.

[0046] It is more preferable that the average particle size D1 of the platinum particles or platinum alloy particles (platinum particles or platinum alloy particles inside the pores) is larger than the average particle size D2 of the platinum particles or platinum alloy particles (platinum particles or platinum alloy particles outside the pores).

[0047] D1 / D2 can be set to 1.0 to 2.1, and preferably 1.1 to 1.8.

[0048] By having the average particle size of the platinum particles or platinum alloy particles within the above range, both initial activity and durability can be achieved. If the average particle size of the platinum particles or platinum alloy particles is smaller than the above range, the active surface area will be large and initial activity will be improved, but coarsening due to dissolution and redeposition of the platinum particles or platinum alloy particles will be more likely to occur, resulting in a decrease in durability. On the other hand, if the average particle size of the platinum particles or platinum alloy particles is larger than the above range, coarsening due to dissolution and redeposition and migration and aggregation of the platinum particles or platinum alloy particles will be less likely to occur, but the initial activity will be reduced due to the low active surface area of ​​the platinum particles or platinum alloy particles.

[0049] By selectively supporting platinum particles or platinum alloy particles supported inside the pores, which suppress ionomer poisoning and exhibit high activity, and platinum particles or platinum alloy particles supported outside the pores, which have excellent mass transport properties, performance can be adjusted to exhibit high initial activity. Furthermore, by making the average particle size of the platinum particles or platinum alloy particles supported inside the pores larger than that of the platinum particles or platinum alloy particles supported outside the pores, deterioration due to elution of the platinum particles or platinum alloy particles under operating conditions is suppressed, thereby improving durability.

[0050] The catalytically active component contained in the platinum or platinum alloy supported carbon catalyst of the present invention is platinum (Pt) or a platinum alloy. In the platinum alloy, one or more additional metals forming the platinum alloy can include titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), yttrium (Y), zirconium (Zr), molybdenum (Mo), lanthanum (La), cerium (Ce), gadolinium (Gd), hafnium (Hf), tantalum (Ta), ruthenium (Ru), iridium (Ir), palladium (Pd), osmium (Os), and rhodium (Rh). When the platinum alloy particles contained in the fuel cell electrode catalyst of the present invention contain the above catalytic metal, an electrode catalyst with high activity and high durability can be obtained.

[0051] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0052] (Example 1) 1. Preparation of carbon with platinum supported in pores (step of supporting first platinum particles in pores) ３ / g mesoporous carbon was used. 128.0 g of dinitrodiamine platinum nitric acid aqueous solution containing 8.3 wt% platinum was added to 31.8 g of mesoporous carbon support and mixed for 30 minutes using a kneader to obtain a platinum-supported carbon slurry. The resulting slurry was dried under reduced pressure at 200 ° C for 12 hours using a vacuum dryer to obtain a dried product. The dried product was then heat-treated in an atmospheric furnace at 200 ° C for 2 hours under a 4.0% hydrogen / nitrogen flow to reduce the dinitrodiamine platinum. The mixture was then calcined for 1 hour at a calcination temperature T1 (medium) of 600 ° C under a nitrogen flow to grow platinum particles, and carbon with 25 wt% of the first platinum particles supported in the pores was obtained.

[0053] 2. Preparation of pore- and external-platinum-supported carbon catalyst (external pore second platinum particle support step) 10.0 g of 25 wt% intrapore first platinum particle-supported carbon was suspended in 150 g of 0.1 M nitric acid, to which 48.1 g of dinitrodiamine platinum nitric acid aqueous solution containing 8.3 wt% platinum, 4.0 g of ethanol, and 7.5 g of L-ascorbic acid were added to form a mixture. This mixture was heated at 90 ° C. for 1 hour using a reflux reactor to reduce dinitrodiamine platinum in the liquid phase, and platinum particles were supported outside the carbon support pores. Next, the mixture was allowed to cool to room temperature, and the platinum-supported carbon in the mixture was filtered out, then washed, and dried at 60 ° C. for 12 hours. After drying, the mixture was heat-treated in an atmospheric furnace at 200 ° C. under a 4.0% hydrogen / nitrogen flow for 2 hours, and the attached reducing agent (L-ascorbic acid) residue was thermally decomposed. Next, the catalyst was calcined for 1 hour at a calcination temperature T2 (outside) of 600°C under a nitrogen flow, allowing platinum particles to grow outside the pores. As a result, a carbon catalyst was obtained in which 47 wt% of the first and second platinum particles were supported inside and outside the pores. The total weight of the second platinum particles supported outside the pores of the mesoporous carbon was 63% of the total weight of the first and second platinum particles supported on the mesoporous carbon.

[0054] Example 2 A platinum-supported carbon catalyst was obtained in the same manner as in Example 1, except that the nitrogen calcination temperature T1 (medium) in the step of supporting the first platinum particles in the pores was changed from 600°C to 700°C.

[0055] Example 3 A platinum-supported carbon catalyst was obtained in the same manner as in Example 1, except that the nitrogen calcination temperature T1 (medium) in the step of supporting the first platinum particles in the pores was changed from 600°C to 900°C.

[0056] Example 4 A platinum-supported carbon catalyst was obtained in the same manner as in Example 1, except that the nitrogen calcination temperature T1 (medium) in the step of supporting the first platinum particles in the pores was changed from 600°C to 1000°C.

[0057] (Example 5) The carrier used had a pore volume of 4.5 cm ３ A platinum-supported carbon catalyst was obtained in the same manner as in Example 1, except that the platinum-supported carbon was changed to mesoporous carbon having a molecular weight of 1.001 / g.

[0058] Example 6: To 5.02 g of the intra- and extra-pore platinum-supported carbon catalyst of Example 1, a cobalt nitrate aqueous solution prepared by dissolving 2.48 g of cobalt(II) nitrate hexahydrate in 5.18 g of water was added, and the mixture was mixed for 30 minutes using a kneader to obtain a slurry. The resulting slurry was dried under reduced pressure at 200 °C for 12 hours using a vacuum dryer to obtain a dried product. This dried product was reduced in an atmospheric furnace at 200 °C for 2 hours under a 4.0% hydrogen / nitrogen flow, and then calcined at 800 °C for 1 hour under a nitrogen flow to perform an alloying treatment. Subsequently, to remove excess cobalt by acid washing, 80 g of 1 M nitric acid was added, and the mixture was heated at 90 °C for 1 hour. After cooling to room temperature, the black powder was filtered, washed, and dried at 80 °C for 12 hours to obtain 5.28 g of platinum-cobalt-supported carbon catalyst.

[0059] (Comparative Example 1) Pore volume 3.5 cm ３ 54.2 g of dinitrodiamine platinum nitric acid aqueous solution containing 8.3 wt% platinum was added to 10.0 g of mesoporous carbon support (10.0 g / g) and mixed for 30 minutes using a kneader to obtain a platinum-supported carbon slurry. The resulting slurry was dried under reduced pressure at 200 ° C for 12 hours using a vacuum dryer to obtain a dried product. The dried product was then heat-treated in an atmospheric furnace at 200 ° C for 2 hours under a 4.0% hydrogen / nitrogen flow to reduce the dinitrodiamine platinum. The mixture was then baked at 200 ° C for 2 hours under a nitrogen flow to grow platinum particles. This resulted in carbon supporting 31 wt% of the first platinum particles in the pores. To 12.0 g of this carbon with 31 wt % of the first platinum particles supported in the pores, 43.6 g of an aqueous solution of dinitrodiamine platinum nitrate containing 8.3 wt % of platinum was added again using the same procedure, and the mixture was kneaded, dried, subjected to a reduction heat treatment, and fired to obtain a carbon catalyst with 47 wt % of the first platinum particles supported in the pores.

[0060] (Comparative Example 2) Pore volume 3.5 cm ３10.0 g of mesoporous carbon support (wt%) was suspended in 400 g of 0.1 M nitric acid, to which 106.6 g of dinitrodiamine platinum nitric acid aqueous solution containing 8.3 wt% platinum, 10.3 g of ethanol, and 16.0 g of L-ascorbic acid were added to form a mixture. This mixture was heated at 90 ° C for 1 hour using a reflux reactor to reduce the dinitrodiamine platinum in the liquid phase, resulting in platinum particles being supported outside the pores of the carbon support. Next, the mixture was allowed to cool to room temperature, and the platinum-supported carbon in the mixture was filtered out, washed, and dried at 60 ° C for 12 hours. After drying, the mixture was heat-treated in an atmospheric furnace at 200 ° C for 2 hours under a 4.0% hydrogen / nitrogen flow to thermally decompose the remaining reducing agent (L-ascorbic acid). Next, the mixture was calcined at 200 ° C for 2 hours under a nitrogen flow to grow platinum particles supported outside the pores. As a result, a carbon catalyst was obtained in which 47 wt % of the second platinum particles were supported outside the pores.

[0061] The platinum or platinum alloy supported carbon catalysts of the Examples and Comparative Examples were evaluated for the following physical properties. The results are shown in Table 1.

[0062] [Measurement of particle size distribution of platinum particles or platinum alloy particles in platinum or platinum alloy supported carbon catalyst] The particle size distribution of platinum particles or platinum alloy particles was measured using CuKα radiation as a radiation source and a small angle scattering measurement device (Nano-Viewer manufactured by Rigaku) ​​under the following measurement conditions.

[0063] Small angle X-ray scattering measurement (SAXS) Measurement conditions: Tube: CuKα ray Output: 40 kV-30 mA Slits: 1st slit 0.4 mm, 2nd slit 0.2 mm, 3rd slit 0.45 mm Measurement method: Transmission method Detector: HyPix-3000 Camera length: 680 mm Exposure time: 15 minutes Temperature: Room temperature

[0064] [Measurement of Metal Specific Surface Area of ​​Platinum Particles or Platinum Alloy Particles in Platinum or Platinum Alloy-Supported Carbon Catalyst] The metal specific surface area of ​​the platinum particles or platinum alloy particles was measured using a metal dispersion measurement device (Microtrac-Bell BELMETAL3) by a pulse method using carbon monoxide gas. The metal specific surface area of ​​the catalyst particles was determined from the amount of carbon monoxide adsorption.

[0065] [Measurement of BET specific surface area of ​​carbon support of platinum or platinum alloy supported carbon catalyst] BET specific surface area (m ２ / g), an automatic specific surface area / pore distribution measuring device (BELSORP-mini2 manufactured by Microtrac-Bell) was used to obtain a nitrogen adsorption isotherm by a gas adsorption method using nitrogen gas, and the specific surface area was determined by a multipoint method based on the BET method.

[0066]

[0067] In Example 1, the firing temperatures T1 (middle) and T2 (outside) were both 600°C, and the average particle size D1 of the first platinum particles inside the pores and the average particle size D2 of the second platinum particles outside the pores were 3.5 nm, which were approximately the same size.

[0068] In Examples 2 to 4, the firing temperature T1 (middle) was higher than T2 (outside), and the average particle size D1 of the first platinum particles inside the pores was 3.8 to 7.1 nm, while the average particle size D2 of the second platinum particles outside the pores was 3.4 to 3.5 nm, with the average particle size D1 of the first platinum particles inside the pores being larger.

[0069] In Example 5, mesoporous carbon having a different pore volume from that of Examples 1 to 4 was used. As in Example 1, by treating at firing temperatures T1 (middle) and T2 (outer) of 600°C, the average particle size D1 of the first platinum particles inside the pores and the average particle size D2 of the second platinum particles outside the pores were 3.1 nm, which were approximately the same size.

[0070] In Example 6, the platinum-cobalt supported carbon was adjusted so that the average particle size D1 of the first catalyst particles inside the pores and the average particle size D2 of the second catalyst particles outside the pores were 4.4 nm, which were approximately the same size.

[0071] In Comparative Example 1, the platinum-supported carbon catalyst was prepared by repeating the intrapore supporting step by the impregnation method twice. The average particle size D1 of the first platinum particles in the pores was 3.9 nm.

[0072] In Comparative Example 2, a platinum-supported carbon catalyst was prepared by an outside-pore supporting step using a liquid-phase reduction method. The average particle size D2 of the second platinum particles outside the pores was 3.8 nm.

[0073] The metal specific surface area of ​​the examples and comparative examples is 57 to 100 m ２ g－１ The BET specific surface area of ​​the examples and comparative examples was 290 to 630 m ２ g －１ It was.

[0074] For the platinum or platinum alloy supported carbon catalysts of the Examples and Comparative Examples, membrane electrode assemblies for evaluation of single cells of polymer electrolyte fuel cells were fabricated by the following method.

[0075] 1. Electrode Preparation 0.8 g of the platinum or platinum alloy-supported carbon catalyst of each Example and Comparative Example, 4.16 g of pure water, 1.60 g of ionomer (Nafion DE2020CS manufactured by Chemours), 2.43 mL of 2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 1.88 mL of 1-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.72 mL of propylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed and dispersed in a planetary ball mill for 1 hour, and then degassed in a mixer for 5 minutes to prepare a cathode catalyst slurry. This electrode catalyst slurry was applied to one side of a PTFE sheet (Naflon (registered trademark) sheet manufactured by Nichias Corporation, thickness 200 μm) using a doctor blade and dried at 120 ° C. for 60 minutes under vacuum to form a cathode catalyst layer on the PTFE sheet.

[0076] For the anode catalyst layer, FC-I2 (IFPC40-II manufactured by Ishifuku Metal Industries), which is a reference catalyst of the Catalysis Society of Japan's Fuel Cell Related Catalyst Research Group, was used.

[0077] 2. Preparation of MEA Two previously prepared PTFE sheets with electrode catalyst layers formed thereon were stacked with the electrode catalyst layer-forming sides facing inward, sandwiching a solid polymer electrolyte membrane (Nafion NR-211 manufactured by Chemours, 200 mm x 200 mm square), and hot-pressed at 130°C for 10 minutes at a pressure of 1.5 K / N using a precision heating and pressing device (CYPM manufactured by Sintokogyo). After cooling, the PTFE sheets were peeled off to obtain an assembly in which the electrode catalyst layer was transferred to the solid polymer electrolyte membrane. The transfer rate of the electrode catalyst layer from the PTFE sheet to the solid polymer electrolyte was 100%, and the platinum weight per cm2 of the electrode catalyst layer area on one side of the solid polymer electrolyte membrane was 0.30 mg.

[0078] Next, the previously prepared assembly was sandwiched between two gas diffusion layers (GDL 28BC manufactured by SGL, 100 mm × 100 mm square), and a sealing material (Naflon (registered trademark) sheet manufactured by Nichias Corporation, laminated with a thickness of 150 μm and a thickness of 80 μm) was placed on the outer periphery of the electrode catalyst layer and the gas diffusion layer, to form an MEA.

[0079] Thereafter, a gold-plated current collector with gas flow channels was placed on the fabricated MEA, and the MEA was clamped between stainless steel end plates and clamped to a predetermined surface pressure to obtain a single cell of a polymer electrolyte fuel cell.

[0080] The MEAs using the platinum or platinum alloy supported carbon catalysts of each of the Examples and Comparative Examples were evaluated for power generation as follows. The results are shown in Table 2.

[0081] [Measurement of initial activity of MEA using platinum or platinum alloy supported carbon catalyst] Based on the "NEDO PEFC Cell Evaluation and Analysis Protocol, March 2022 Edition" of the New Energy and Industrial Technology Development Organization (NEDO), I-V measurements were performed using a fuel cell power generation evaluation device (manufactured by Chino) and an electronic load device (PLZ164WA manufactured by Kikusui Electronics Co., Ltd.), and the mass activity was calculated from the current density at 0.85 V and the amount of platinum supported, to determine the initial activity.

[0082] [Measurement of durability of MEA using platinum or platinum alloy-supported carbon catalyst] Based on the potential cycle (load response) test method described in the "NEDO PEFC Cell Evaluation and Analysis Protocol, March 2022 Edition" of the New Energy and Industrial Technology Development Organization (NEDO), a load response simulated potential cycle test that accelerates the deterioration of platinum particles or platinum alloy particles of a platinum or platinum alloy-supported carbon catalyst was carried out using a fuel cell power generation evaluation device (manufactured by Chino) and a potentiogalvanostat (PGSTAT128N manufactured by Metrohm), and the mass activity after the durability test was calculated from the current density at 0.85 V and the amount of platinum supported after 30,000 cycles, to evaluate durability.

[0083] At initial activity, 800 Ag －１ Above: ◎, 300Ag －１ Over 800Ag －１ The activity after durability test was evaluated as 0.－１ Above: ◎, 100Ag －１ More than 300Ag －１ Less than 0.01g －１ Less than this was evaluated as x.

[0084]

[0085] Examples 1 to 6 are platinum or platinum alloy-supported carbon catalysts in which the total weight of the second platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon is adjusted to 60 to 90% of the total weight of the first and second platinum particles or platinum alloy particles supported inside and outside the pores of the mesoporous carbon, and the average particle size D1 of the platinum particles or platinum alloy particles supported inside the pores of the mesoporous carbon is the same as or larger than the average particle size D2 of the platinum particles or platinum alloy particles supported outside the pores, and the initial mass activity is 300 Ag －１ and mass activity after 30,000 cycles is 100Ag －１ The above results indicate that the catalyst had good initial activity and durability.

[0086] Comparative Example 1 is a platinum-supported carbon catalyst prepared by repeating only the intrapore supporting step twice, and the initial mass activity was 498 Ag －１ While the initial activity was good, the mass activity after 30,000 cycles was 52Ag －１ The durability was also low.

[0087] Comparative Example 2 is a platinum-supported carbon catalyst prepared only by the liquid phase reduction method, which is an external support step, and the initial mass activity was 371 Ag －１ While the initial activity was good, the mass activity after 30,000 cycles was 47Ag －１ The durability was also low.

Claims

1. A platinum or platinum alloy supported carbon catalyst in which platinum particles or platinum alloy particles are supported on mesoporous carbon, characterized in that the platinum or platinum alloy support rate in the catalyst is 30% or more and 70% or less by weight of the total weight of the catalyst, the total weight of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon is 60 to 90% of the total weight of the platinum particles or platinum alloy particles, an average particle size D1 of the platinum particles or platinum alloy particles supported within the pores of the mesoporous carbon is the same as or larger than an average particle size D2 of the platinum particles or platinum alloy particles supported outside the pores of the mesoporous carbon, and the average particle size D1 and the average particle size D2 are independently 2 nm or more and 8 nm or less.

2. The platinum or platinum alloy supported carbon catalyst according to claim 1, characterized in that the average particle diameter D1 is 2.5 nm or more and 8 nm or less, the average particle diameter D2 is 2.3 nm or more and 7.3 nm or less, and D1 / D2 is 1.0 to 2.

1.

3. A method for producing a platinum-supported carbon catalyst, comprising: an intrapore supporting step of supporting platinum within the pores of the mesoporous carbon support, the intrapore supporting step comprising: impregnating a mesoporous carbon support with an aqueous solution containing a platinum compound; drying the mesoporous carbon support impregnated with the aqueous solution containing the platinum compound obtained in the intrapore supporting step under reduced pressure; and heat-treating the mesoporous carbon support dried under reduced pressure obtained in the drying step in a reducing atmosphere; and an extrapore supporting step of supporting platinum particles outside the pores of the mesoporous carbon support, the extrapore supporting step comprising: suspending the mesoporous carbon support with platinum supported within the pores after the intrapore supporting step in an aqueous solution; and mixing the suspension with a solution containing the aqueous solution containing the platinum compound and a liquid containing a reducing agent to reduce the platinum compound.

4. The intrapore supporting step includes a step of adding and mixing an aqueous solution of dinitrodiamine platinum nitric acid to a mesoporous carbon support to obtain a platinum-supported carbon slurry, a step of drying the obtained slurry at a predetermined temperature under reduced pressure to obtain a solid product, a step of heat treating the slurry in a reducing atmosphere to reduce dinitrodiamine platinum, and a step of baking in an inert gas atmosphere (baking temperature T1) to grow platinum particles. The extrapore supporting step includes a step of suspending the mesoporous carbon support with platinum supported in the pores after the intrapore supporting step in an aqueous nitric acid solution, and heating and stirring the suspension, the aqueous solution of dinitrodiamine platinum nitric acid, and a liquid containing L-ascorbic acid at 80°C to 100°C for 30 minutes to 5 hours to support the platinum particles outside the pores of the carbon support. a step of filtering out the platinum-supported carbon having platinum particles supported outside the pores of the carbon support in the step, washing the carbon, drying the carbon, and then calcining the carbon in an inert gas atmosphere (calcination temperature T2) to grow platinum particles.

5. A method for producing a platinum alloy-supported carbon catalyst according to claim 3 or 4, comprising the steps of: adding an aqueous solution containing a compound of a metal to be alloyed with the platinum to the platinum-supported carbon catalyst and mixing to obtain a slurry; heating and drying the obtained slurry under reduced pressure to obtain a dry product; and an alloying step of performing an alloying treatment on the dry product by pre-treating the product in a reducing atmosphere and then firing the product in an inert gas atmosphere.

6. A method for producing a platinum or platinum alloy supported carbon catalyst as described in claim 3 or 4, characterized in that the average particle diameter D1 of the platinum particles and the average particle diameter D2 of the platinum particles are controlled by setting the calcination temperature T1 and the calcination temperature T2 to predetermined temperatures, respectively.

7. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising an electrode containing the platinum or platinum alloy supported carbon catalyst according to claim 1.

8. A polymer electrolyte fuel cell comprising the platinum or platinum alloy supported carbon catalyst according to claim 1 contained in an electrode of a membrane electrode assembly.

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