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

Abstract

The present invention addresses the problem of providing a carbon-supported platinum or platinum alloy catalyst for a solid polymer fuel cell, said catalyst having high activity and high durability. [Solution] A carbon-supported platinum or platinum alloy catalyst in which platinum particles or platinum alloy particles are supported on mesoporous carbon, the carbon-supported platinum or platinum alloy catalyst being characterized in that: the load rate of platinum or platinum alloy in the catalyst is 30-70% by weight of the total weight of the catalyst; relative to the total weight of the platinum particles or the platinum alloy particles, the total weight of the platinum particles or the platinum alloy particles loaded outside the pores of the mesoporous carbon is 60-90%; 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 greater 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 nm or more and 8 nm or less.

Description

Technical Field

[0001] This invention relates to a highly active and durable solid polymer fuel cell catalyst with carbon-supported platinum or platinum alloy particles loaded inside and outside the fine pores of a carrier. Background Technology

[0002] In recent years, decarbonization and carbon neutrality have been proposed as countermeasures to energy and environmental issues. As a clean energy source to replace chemical fuels, hydrogen utilization has received considerable attention. Fuel cells, which generate electricity through the chemical reaction of hydrogen and oxygen, are expected to become a new type of power generation system that contributes to carbon neutrality because they do not emit carbon dioxide, a greenhouse gas. Among them, the solid polymer fuel cell (PEFC), a type of fuel cell, uses a solid polymer ion-conducting membrane in its electrolyte layer. Its operating temperature is as low as room temperature to 100°C, enabling miniaturization of the device. Therefore, its practical application as a power source for electric vehicles and stationary power sources is progressing.

[0003] Solid polymer fuel cells have a stack structure consisting of multiple single cells stacked together, each holding a membrane electrode assembly (MEA) between separators. The MEA has a structure consisting of two electrode catalyst layers (electrode catalyst and electrolyte polymer, ionomer) sandwiching an electrolyte layer.

[0004] In the MEA, the following electrochemical reactions generate electricity. First, hydrogen, supplied as fuel, is oxidized by the electrode catalyst in the fuel electrode (anode) side catalyst layer, becoming protons and electrons. Next, the generated protons travel through an electrolyte layer composed of an ionicly conductive electrolyte, while the electrons travel through an external circuit, respectively, to the oxygen electrode (cathode) side catalyst layer. The protons and electrons reaching the cathode side catalyst layer react with oxygen supplied to the cathode side to produce water. Electrons generated in the anode side electrode move to the cathode side electrode via the external circuit and are used as electrical energy.

[0005] In existing electrode catalysts, carbon-supported platinum or platinum alloy catalysts are used, in which platinum (Pt) or platinum alloy nanoparticles are supported on a carbon black carrier with high electron conductivity. In these carbon-supported platinum or platinum alloy catalysts, carbon with a high specific surface area is used to highly disperse the platinum or platinum alloy particles and prevent aggregation, thereby increasing the electrode reaction area on the surface of the platinum or platinum alloy particles, allowing for sufficient activity with a small amount of platinum or platinum alloy loading.

[0006] The proliferation of fuel cell vehicles (FCVs) aimed at achieving carbon neutrality necessitates the development of efficient and high-load-capable cathode catalysts for solid polymer fuel cells (PEFCs).

[0007] In cited reference 1, there is a carbon-supported platinum catalyst, which is supported on solid carbon structures that are blocked inside particles such as furnace black or acetylene black.

[0008] Reference 2 discloses an electrode catalyst in which platinum particles are loaded into the pores of a porous hollow carbon support such as Ketjen black. It mentions that by loading platinum particles into the pores, the adsorption of ionomers on the surface of the platinum particles is suppressed, thus preventing a decrease in the effective reaction surface area of ​​the platinum particles.

[0009] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2007-112660; Patent Document 2: Japanese Patent Application Publication No. 2013-109856. Summary of the Invention

[0010] The problem that the invention aims to solve For example, carbon-supported platinum catalysts with solid carbon structures blocked inside particles such as furnace black or acetylene black have excellent mass transport characteristics because platinum particles are loaded on the surface of the support. The reaction gas can easily contact the platinum particles and react. However, because the platinum particles are located on the surface of the support, there are problems such as decreased activity due to ionomer poisoning or catalyst deterioration due to platinum particle aggregation (sintering).

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

[0012] Therefore, a method is needed to load platinum particles or platinum alloy particles in any ratio both inside and outside the pores of a support. Furthermore, if platinum particles or platinum alloy particles can be loaded in any ratio both inside and outside the pores of the support, then by selectively loading them inside and outside the pores, catalytically active components with different functions can be supplied, and the performance can be adjusted.

[0013] The purpose of this invention is to provide a carbon-supported platinum or platinum alloy catalyst with high initial activity and excellent durability by selectively loading platinum particles or platinum alloy particles inside and outside the pores of a carbon support.

[0014] Methods for solving problems The inventors have discovered that by employing two loading steps—one of loading platinum particles or platinum alloy particles into the pores of a carbon support via impregnation and the other of loading them onto the outside of the pores via liquid-phase reduction—the loading amount and particle size of the platinum particles or platinum alloy particles loaded into and outside the pores can be controlled.

[0015] That is, the present invention is a carbon-supported platinum or platinum alloy catalyst, which is a carbon-supported platinum or platinum alloy catalyst on mesoporous carbon with platinum particles or platinum alloy particles supported on it, characterized in that: The platinum or platinum alloy loading in the catalyst is, on a weight basis, more than 30% and less than 70% of the total weight of the catalyst. The total weight of the platinum particles or platinum alloy particles loaded on the micropores of the mesoporous carbon is 60% to 90% relative to the total weight of the platinum particles or platinum alloy particles. The average particle size D1 of the platinum particles or platinum alloy particles loaded 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 loaded outside the pores of the mesoporous carbon. The average particle size D1 and the average particle size D2 are each independently greater than 2 nm and less than 8 nm.

[0016] In the above configuration, the average particle size D1 can be set to be 2.5 nm or more and 8 nm or less. The average particle size D2 is greater than 2.3 nm and less than 7.3 nm. D1 / D2 is 1.0 to 2.1.

[0017] Furthermore, the manufacturing method of the present invention relates to a method for manufacturing a carbon-supported platinum catalyst, which includes an intrapore loading step of loading platinum within the pores of the mesoporous carbon support and an extrapore loading step of loading platinum particles outside the pores of the mesoporous carbon support, wherein... The loading process within the fine pores includes: The process of impregnating a platinum-containing aqueous solution into a mesoporous carbon support. The process of vacuum drying the mesoporous carbon support impregnated with an aqueous solution containing a platinum compound obtained in the above steps, and The process of heat-treating the mesoporous carbon support obtained in the vacuum drying process in a reducing atmosphere. The fine-hole external loading process includes: The process of suspending the platinum-loaded mesoporous carbon support in an aqueous solution after the micropore loading process, and... The process of mixing the suspension with an aqueous solution containing a platinum compound and a liquid containing a reducing agent to reduce the platinum compound.

[0018] It can be set as follows: The loading process inside the fine hole includes: The process of adding an aqueous solution of dinitrosodiammineplatinum nitric acid to a mesoporous carbon support and mixing it to obtain a carbon-supported platinum slurry. The process of drying the resulting slurry under reduced pressure and at a specified temperature to form dry solids. The process of heat treatment in a reducing atmosphere to reduce dinitrosodiamineplatinum, and The process of calcining in an inert gas atmosphere (calcination temperature T1) to grow platinum particles; The fine-hole external loading process includes: The mesoporous carbon support loaded with platinum in the micropores after the micropore loading process is suspended in an aqueous nitric acid solution. The process involves heating and stirring the suspension with a dinitrosodiamineplatinic acid aqueous solution and a liquid containing L-ascorbic acid at 80°C–100°C for 30 minutes–5 hours to load platinum particles onto the pores of the carbon support. The process involves filtering out platinum-loaded carbon with platinum particles loaded onto the pores of the carbon support through the aforementioned process, followed by washing, drying, and then firing in an inert gas atmosphere (firing temperature T2) to allow the platinum particles to grow.

[0019] The manufacturing method described above may include: The step of adding an aqueous solution containing a metal that should form an alloy with the platinum to the carbon-supported platinum catalyst and mixing it to obtain a slurry. The process of heating and drying the resulting slurry under reduced pressure to form dry solids, and The dry solid is pretreated and fired in a reducing atmosphere, and then fired in an inert gas atmosphere for alloying.

[0020] In the above manufacturing method, it can be set as follows: by setting the firing temperature T1 and the firing temperature T2 to a specified temperature, the average particle size D1 and the average particle size D2 of the platinum particles can be controlled.

[0021] Invention Effects According to the present invention, by selectively loading platinum particles or platinum alloy particles inside and outside the pores of a carbon support, a carbon-supported platinum or platinum alloy catalyst with high initial activity and excellent durability can be provided. Detailed Implementation

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

[0023] The manufacturing method of the present invention is a method for manufacturing a carbon-supported platinum catalyst, comprising: an intrapore loading step of loading platinum within the pores of the mesoporous carbon support, and an extrapore loading step of loading platinum particles outside the pores of the mesoporous carbon support, wherein... The loading process within the fine pores includes: The process of impregnating a platinum-containing aqueous solution into a mesoporous carbon support. The process of vacuum drying the mesoporous carbon support impregnated with an aqueous solution containing a platinum compound obtained in the above steps, and The process of heat-treating the mesoporous carbon support obtained in the vacuum drying process in a reducing atmosphere. The fine-hole external loading process includes: The process of suspending the platinum-loaded mesoporous carbon support in an aqueous solution after the micropore loading process, and... The process of mixing the suspension with an aqueous solution containing a platinum compound and a liquid containing a reducing agent to reduce the platinum compound.

[0024] Furthermore, the manufacturing method of the present invention can be configured as follows: In the above manufacturing method, The loading process within the fine pores includes: The process of adding and mixing dinitrosodiammineplatinum nitric acid aqueous solution to a mesoporous carbon support to obtain a carbon-supported platinum slurry. The process of drying the obtained slurry under reduced pressure and at a specified temperature to form a dry solid. The process of heat treatment in a reducing atmosphere to reduce dinitrosodiamineplatinum, and The process of calcining in an inert gas atmosphere (calcination temperature T1) to grow platinum particles; The fine-hole external loading process includes: The mesoporous carbon support loaded with platinum in the micropores after the micropore loading process is suspended in an aqueous nitric acid solution. The process involves heating and stirring the suspension with a dinitrosodiamineplatinic acid aqueous solution and a liquid containing L-ascorbic acid at 80°C–100°C for 30 minutes–5 hours to load platinum particles onto the pores of the carbon support. The process involves filtering out platinum-loaded carbon with platinum particles loaded onto the pores of the carbon support through the aforementioned process, followed by washing, drying, and then firing in an inert gas atmosphere (firing temperature T2) to allow the platinum particles to grow.

[0025] When the catalytically active ingredient (e.g., platinum) is supplied in solution and loaded onto a support, this process is called impregnation (immersion). The catalytically active ingredient (e.g., platinum) is readily loaded into the pores of the support. In the manufacturing method of the present invention, after loading the catalytically active ingredient (e.g., platinum) into the pores of the support using the impregnation method, the catalytically active ingredient (e.g., platinum) is loaded onto the outside of the pores of the support using a liquid-phase reduction method. The manufacturing method of the present invention employs these two loading steps.

[0026] As a platinum-containing aqueous solution, dinitrosodiaminoplatinum nitric acid aqueous solution, chloroplatinic acid aqueous solution, etc. can be used.

[0027] The support used is mesoporous carbon. Mesoporous carbon is a carbon material with nanoscale pores. The carbon-supported platinum or platinum alloy catalyst of the present invention can use mesoporous carbon with various pore volumes and specific surface areas.

[0028] In the micropore external loading process, L-ascorbic acid, citric acid, etc., can be used as reducing agents. In the micropore external loading process, an alcohol solvent can be added to the nitric acid aqueous solution as a dispersion solvent. Ethanol, 2-propanol, etc., can be used as alcohol solvents.

[0029] Inert gases such as nitrogen and argon can be used.

[0030] Subsequently, the platinum particles or platinum alloy particles loaded within the pores of the carrier are referred to as the first platinum particles or platinum alloy particles, while the platinum particles or platinum alloy particles loaded outside the pores of the carrier are referred to as the second platinum particles or platinum alloy particles.

[0031] The process of loading platinum into the pores of a mesoporous carbon support is as follows: A dinitrosodiamineplatinum nitric acid aqueous solution is added to the mesoporous carbon support and mixed to prepare a carbon-loaded platinum slurry. This slurry is then dried under reduced pressure at a specified temperature to form a dry solid. The resulting dry solid is heat-treated in a reducing atmosphere to reduce the dinitrosodiamineplatinum, and then calcined in an inert gas atmosphere (e.g., nitrogen) (calcination temperature T1) to allow platinum particles to grow, thereby modulating the first platinum particles loaded with carbon within the pores.

[0032] The process of loading platinum particles onto the carbon support is as follows: The first platinum particle-loaded carbon within the micropores is suspended in an aqueous nitric acid solution. Dinitrosodiammineplatinum aqueous nitric acid solution, ethanol, and L-ascorbic acid are added to the suspension and mixed. Next, the mixture is heated and stirred at 80°C to 100°C for 30 minutes to 5 hours. For example, the mixture is heated at 90°C for 1 hour using a reflux reactor to perform liquid-phase reduction of dinitrosodiammineplatinum, thereby loading the platinum particles onto the micropores of the carbon support.

[0033] The carbon-supported platinum catalyst, in which a second platinum particle is loaded on the outside of the pores of the carbon support, is filtered out, washed, dried, and then calcined in an inert gas atmosphere (calcination temperature T2) to allow the platinum particles to grow, thereby modulating a carbon-supported platinum catalyst in which platinum particles are selectively loaded inside and outside the pores of the carbon support.

[0034] After the aforementioned filtration, washing, and drying, and before firing in an inert gas atmosphere (firing temperature T2), residues of the reducing agent (L-ascorbic acid) that cannot be completely removed by washing can be removed by thermal decomposition through heat treatment in an oxygen-free atmosphere. An example of an oxygen-free atmosphere is 4.0% hydrogen / nitrogen.

[0035] In addition, the manufacturing method of the present invention may include: a step of adding an aqueous solution containing a compound of a metal to be alloyed with the platinum to the carbon-supported platinum catalyst and mixing to obtain a slurry; a step of heating and drying the obtained slurry under reduced pressure to form a dry solid; and an alloying step of pretreating and firing the dry solid in a reducing atmosphere and then firing it in an inert gas atmosphere to perform alloying treatment.

[0036] For example, for the carbon-supported platinum catalyst prepared by the above method, an aqueous solution of cobalt nitrate obtained by dissolving cobalt(II) hexahydrate in water is added, and the mixture is stirred in a mixer to obtain a slurry. The resulting slurry is dried in a vacuum dryer, for example, under reduced pressure at 80°C to 250°C for 1 to 15 hours to form a dry solid. The dry solid is then reduced in an atmosphere furnace at 200°C to 600°C for 1 to 5 hours in a hydrogen / nitrogen mixed atmosphere, and then calcined at 700°C to 900°C for 0.5 to 5 hours under an inert gas flow for alloying treatment. Afterward, excess cobalt is removed by acid washing. Then, the catalyst is filtered, washed, and dried to obtain the carbon-supported platinum-cobalt catalyst.

[0037] In addition, the manufacturing method of the present invention can be configured to control the average particle size D1 and average particle size D2 of platinum particles by setting the firing temperature T1 and the firing temperature T2 to a specified temperature.

[0038] The firing temperatures T1 and T2 can be set, for example, to 500°C to 1000°C. By firing at 500°C to 1000°C, the platinum particles can reach a predetermined size.

[0039] Next, the catalyst of this invention is a carbon-supported platinum or platinum alloy catalyst. It is a carbon-supported platinum or platinum alloy catalyst with platinum particles or platinum alloy particles supported on mesoporous carbon, characterized in that: The platinum or platinum alloy loading in the catalyst is, on a weight basis, more than 30% and less than 70% of the total weight of the catalyst. The total weight of the platinum particles or platinum alloy particles loaded on the micropores of the mesoporous carbon is 60-90% relative to the total weight of the platinum particles or platinum alloy particles. The average particle size D1 of the platinum particles or platinum alloy particles loaded 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 loaded outside the pores of the mesoporous carbon. The average particle size D1 and the average particle size D2 are each independently greater than 2 nm and less than 8 nm.

[0040] The loading rate of platinum or platinum alloy in a carbon-supported platinum or platinum alloy catalyst can be determined, for example, by dissolving the metal components contained in the platinum particles or platinum alloy particles from the carbon-supported platinum or platinum alloy catalyst with aqua regia, and then quantitatively determining the metal ions in the solution using an inductively coupled plasma (ICP) emission spectrometer.

[0041] The platinum or platinum alloy loading rate in the carbon-supported platinum or platinum alloy catalyst is 30% to 70% of the total weight of the catalyst, on a weight basis. By keeping the loading density of platinum particles or platinum alloy particles within this range, the electrode catalyst layer thickness can be controlled to be suitable for proton migration, gas diffusion, and drainage of generated water during electrode catalyst layer formation.

[0042] The platinum or platinum alloy loading rate in the carbon-supported platinum or platinum alloy catalyst is preferably 35% or more and 60% or less by weight of the total catalyst. More preferably, the loading rate is 40% or more and 55% or less by weight of the total catalyst.

[0043] The total weight of platinum particles or platinum alloy particles loaded outside the pores of the mesoporous carbon is 60-90% relative to the total weight of the platinum particles or platinum alloy particles loaded on the mesoporous carbon (i.e., the total weight of platinum particles or platinum alloy particles loaded inside and outside the pores of the mesoporous carbon). By loading the platinum particles or platinum alloy particles inside the pores of the carbon support, the contact area with the ionomer can be reduced, thereby reducing the poisoning of the platinum particles or platinum alloy particles caused by the sulfonic acid groups of the ionomer, and high initial activity can be expected. However, from the viewpoint of mass transport characteristics such as protons and reactant gases, it is necessary to appropriately adjust the loading ratio inside and outside the pores, and the total weight of platinum particles or platinum alloy particles loaded outside the pores of the mesoporous carbon is set to 60-90% relative to the total weight of the platinum particles or platinum alloy particles loaded on the mesoporous carbon.

[0044] The total weight of platinum particles or platinum alloy particles loaded outside the pores of the mesoporous carbon is preferably 80% or less, relative to the total weight of the platinum particles or platinum alloy particles loaded on the mesoporous carbon. More preferably, it is 70% or less.

[0045] In addition, the catalyst of the present invention may be configured as follows: The average particle size D1 of platinum particles or platinum alloy particles is greater than 2.5 nm and less than 8 nm. The average particle size D2 of platinum particles or platinum alloy particles is greater than 2.3 nm and less than 7.3 nm. D1 / D2 is 1.0 to 2.1.

[0046] In fuel cell operating environments with potential changes, small-diameter platinum particles preferentially dissolve and re-precipitate on the surface of large-diameter platinum particles, leading to platinum particle coarsening and degradation of catalytically active components. To suppress the dissolution of platinum particles or platinum alloy particles loaded within the micropores, which are less susceptible to ionomer poisoning and exhibit high activity, from the micropores to the outside, it is preferable that the average particle size D1 ≥ the average particle size D2. Here, the average particle size D1 refers to the average particle size of the platinum particles or platinum alloy particles loaded within the micropores of mesoporous carbon, and the average particle size D2 refers to the average particle size of the platinum particles or platinum alloy particles loaded outside the micropores.

[0047] More preferably, the average particle size D1 (platinum particles or platinum alloy particles inside the pores) is greater than the average particle size D2 (platinum particles or platinum alloy particles outside the pores).

[0048] D1 / D2 can be set to 1.0 to 2.1. D1 / D2 is preferably 1.1 to 1.8.

[0049] By ensuring the average particle size of the platinum particles or platinum alloy particles falls within the aforementioned range, a balance between initial activity and durability can be achieved. If the average particle size of the platinum particles or platinum alloy particles is smaller than the aforementioned range, the active surface area increases, potentially improving initial activity; however, coarsening due to the dissolution / re-precipitation of the platinum particles or platinum alloy particles is more likely to occur, leading to decreased durability. On the other hand, when the average particle size of the platinum particles or platinum alloy particles is larger than the aforementioned range, although coarsening due to dissolution / re-precipitation and migration and agglomeration of the platinum particles or platinum alloy particles are less likely to occur, the initial activity decreases due to the low active surface area of ​​the platinum particles or platinum alloy particles.

[0050] High initial activity is achieved by selectively loading platinum particles or platinum alloy particles loaded within micropores that exhibit high activity and suppress ionomer poisoning, and platinum particles or platinum alloy particles loaded outside micropores that have excellent material transport properties. Furthermore, by making the average particle size of the platinum particles or platinum alloy particles loaded within micropores larger than that loaded outside micropores, degradation caused by the dissolution of platinum particles or platinum alloy particles under operating conditions is suppressed, thereby improving durability.

[0051] The catalytically active component in the carbon-supported platinum or platinum alloy catalyst of the present invention is platinum (Pt) or a platinum alloy. Other metals that form platinum alloys 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 in the electrode catalyst for fuel cells of the present invention contain the aforementioned catalyst metals, an electrode catalyst with high activity and high durability can be obtained. Example

[0052] The present invention will now be described in further detail based on embodiments and comparative examples. The present invention is not limited to these embodiments.

[0053] (Example 1) 1. Modulation of platinum-loaded carbon in micropores (first platinum particle loading process in micropores) Mesoporous carbon with a pore volume of 3.5 cm³ / g was used as a support. 128.0 g of a dinitrosodiammineplatinic acid aqueous solution containing 8.3 wt% platinum was added to 31.8 g of the mesoporous carbon support, and the mixture was stirred for 30 minutes using a mixer to obtain a carbon-supported platinum slurry. The resulting slurry was dried in a vacuum dryer at 200°C for 12 hours under reduced pressure to form a dry solid. Subsequently, in an atmosphere furnace with a 4.0% hydrogen / nitrogen flow, the dry solid was heat-treated at 200°C for 2 hours to reduce dinitrosodiammineplatin. Then, under nitrogen flow, the calcination temperature T1 (internal) was set to 600°C, and calcined for 1 hour to allow platinum particles to grow, resulting in carbon with 25 wt% platinum particles loaded in the pores.

[0054] 2. Modulation of platinum-supported carbon catalyst inside and outside the micropores (second platinum particle loading process outside the micropores) 10.0 g of 25 wt% microporous platinum-loaded carbon particles were suspended in 150 g of 0.1 M nitric acid. 48.1 g of a dinitrosodiammineplatinic 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 the dinitrosodiammineplatinic acid in the liquid phase, thereby loading the platinum particles onto the micropores of the carbon support.

[0055] Next, the mixture was cooled to room temperature, the carbon-supported platinum in the mixture was filtered out, and then washed and dried at 60°C for 12 hours.

[0056] After drying, the residue of the attached reducing agent (L-ascorbic acid) is thermally decomposed in an atmosphere furnace at 200°C for 2 hours under a flow of 4.0% hydrogen / nitrogen.

[0057] Next, under nitrogen flow, the firing temperature T2 (external) was set to 600℃ and fired for 1 hour to allow the platinum particles loaded on the micropores to grow.

[0058] The above results yielded a carbon catalyst with 47 wt% of first and second platinum particles loaded inside and outside the mesoporous carbon. The total weight of the second platinum particles loaded outside the mesoporous carbon was 63% relative to the total weight of the first and second platinum particles loaded on the mesoporous carbon.

[0059] (Example 2) Except for changing the nitrogen firing temperature T1 (inner) in the first platinum particle loading process within the micropores from 600°C to 700°C, the carbon-supported platinum catalyst was obtained by operating in the same manner as in Example 1.

[0060] (Example 3) Except for changing the nitrogen firing temperature T1 (inner) in the first platinum particle loading process within the micropores from 600°C to 900°C, the carbon-supported platinum catalyst was obtained by operating in the same manner as in Example 1.

[0061] (Example 4) Except for changing the nitrogen firing temperature T1 (inner) in the first platinum particle loading process within the micropores from 600°C to 1000°C, the carbon-supported platinum catalyst was obtained by operating in the same manner as in Example 1.

[0062] (Example 5) In addition to changing the carrier used to a micropore volume of 4.5 cm³, 3 Apart from mesoporous carbon, the same procedure as in Example 1 was followed to obtain a carbon-supported platinum catalyst.

[0063] (Example 6) A cobalt nitrate aqueous solution obtained by dissolving 2.48 g of cobalt(II) hexahydrate in 5.18 g of water was added to 5.02 g of the fine-pored platinum-supported carbon catalyst from Example 1. The mixture was stirred in a mixer for 30 minutes to obtain a slurry. The resulting slurry was dried in a vacuum dryer at 200°C for 12 hours under reduced pressure to form a dry solid. The dry solid was then reduced in an atmosphere furnace at 200°C for 2 hours under a 4.0% hydrogen / nitrogen flow, followed by calcination at 800°C for 1 hour under a nitrogen flow for alloying treatment. Subsequently, to remove excess cobalt by acid washing, 80 g of 1M nitric acid was added, and the mixture was heated at 90°C for 1 hour. After cooling to room temperature, a black powder was filtered out, washed, and dried at 80°C for 12 hours to obtain 5.28 g of carbon-supported platinum-cobalt catalyst.

[0064] (Comparative Example 1) 54.2 g of a dinitrosodiammineplatinum nitric acid aqueous solution containing 8.3 wt% platinum was added to 10.0 g of mesoporous carbon support with a pore volume of 3.5 cm³ / g. The mixture was stirred in a mixer for 30 minutes to obtain a platinum-loaded carbon slurry. The resulting slurry was dried in a vacuum dryer at 200 °C for 12 hours under reduced pressure to form a dry solid. The dry solid was then heat-treated in an atmosphere furnace at 200 °C for 2 hours under a 4.0% hydrogen / nitrogen flow to reduce dinitrosodiammineplatinum. Subsequently, it was calcined at 200 °C for 2 hours under a nitrogen flow to allow platinum particles to grow. Through these operations, carbon with 31 wt% platinum particles loaded in the pores was obtained. For 12.0g of carbon with 31wt% of the first platinum particles loaded in the fine pores, 43.6g of dinitrosodiammineplatinum nitric acid aqueous solution containing 8.3wt% platinum was added again according to the same procedure, and the mixture was mixed, dried, reduced heat treated and calcined to obtain a carbon catalyst with 47wt% of the first platinum particles loaded in the fine pores.

[0065] (Comparative Example 2) 10.0 g of mesoporous carbon support with a pore volume of 3.5 cm³ / g was suspended in 400 g of 0.1 M nitric acid. 106.6 g of an aqueous solution of dinitrosodiammineplatinic acid 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 dinitrosodiammineplatinic acid in the liquid phase, thereby loading platinum particles onto the pores of the carbon support.

[0066] Next, the mixture was cooled to room temperature, the carbon-supported platinum in the mixture was filtered out, and then washed and dried at 60°C for 12 hours.

[0067] After drying, the residue of the attached reducing agent (L-ascorbic acid) is thermally decomposed in an atmosphere furnace at 200°C for 2 hours under a flow of 4.0% hydrogen / nitrogen.

[0068] Next, the catalyst was calcined at 200°C for 2 hours under nitrogen flow to allow platinum particles supported on the micropores to grow. The above results yielded a carbon catalyst with 47 wt% second platinum particles supported on the micropores.

[0069] The following physical properties were evaluated for each carbon-supported platinum or platinum alloy catalyst in the examples and comparative examples. The results are shown in Table 1.

[0070] [Determination of particle size distribution of platinum particles or platinum alloy particles in carbon-supported platinum or platinum alloy catalysts] The particle size distribution of platinum particles or platinum alloy particles was measured using CuKα rays as the radiation source and a small-angle scattering measurement device (Rigaku Nano-Viewer) under the following measurement conditions.

[0071] Small-angle X-ray scattering (SAXS) measurement conditions Tube: CuKα rays; Output: 40kV-30mA; Slits: First slit 0.4mm, second slit 0.2mm, third slit 0.45mm; Measurement method: Transmission method; Detector: HyPix-3000; Camera length: 680mm; Exposure time: 15 minutes; Temperature: Room temperature.

[0072] [Determination of the metallic specific surface area of ​​platinum particles or platinum alloy particles in carbon-supported platinum or platinum alloy catalysts] The specific surface area of ​​platinum particles or platinum alloy particles was determined using a metal dispersion measuring device (BELMETAL3 manufactured by MicrotracBEL) via a pulse method using carbon monoxide gas. The specific surface area of ​​the catalyst particles was determined based on the amount of carbon monoxide adsorbed.

[0073] [Determination of BET specific surface area of ​​carbon supports for carbon-supported platinum or platinum alloy catalysts] Regarding the specific surface area of ​​BET (m²) 2 / g), using an automated specific surface area and pore size distribution measuring device (BELSORP-mini2 manufactured by MicrotracBEL), nitrogen adsorption isotherms were obtained by using the nitrogen gas adsorption method, and the specific surface area was determined by a multi-point method based on the BET method.

[0074] In Example 1, the firing temperatures T1 (inner) and T2 (outer) were both 600°C. The average particle size D1 of the first platinum particle inside the micropore and the average particle size D2 of the second platinum particle outside the micropore were both 3.5 nm, indicating that they were of similar size.

[0075] In Examples 2 to 4, the processing was carried out at a temperature where the firing temperature T1 (inner) was higher than that T2 (outer). The average particle size D1 of the first platinum particle inside the pore was 3.8 to 7.1 nm, and the average particle size D2 of the second platinum particle outside the pore was 3.4 to 3.5 nm. The average particle size D1 of the first platinum particle inside the pore was larger.

[0076] In Example 5, mesoporous carbon with a pore volume different from that in Examples 1-4 was used. Similar to Example 1, by processing at firing temperatures T1 (inner) and T2 (outer) of 600°C, the average particle size D1 of the first platinum particle inside the pore and the average particle size D2 of the second platinum particle outside the pore were both 3.1 nm, indicating the same size.

[0077] In Example 6, carbon-supported platinum-cobalt was modulated, and the average particle size D1 of the first catalyst particles inside the micropores and the average particle size D2 of the second catalyst particles outside the micropores were both 4.4 nm, indicating that they were of similar size.

[0078] In Comparative Example 1, a carbon-supported platinum catalyst was prepared by repeating the microporous loading process based on the impregnation method twice. The average particle size D1 of the first platinum particles in the micropores was 3.9 nm.

[0079] In Comparative Example 2, a carbon-supported platinum catalyst was prepared via a microporous external loading process based on liquid-phase reduction. The average particle size D2 of the second platinum particles outside the micropores was 3.8 nm.

[0080] The specific surface area of ​​the metals in the examples and comparative examples is 57–100 m². 2 g -1 The BET specific surface area of ​​the examples and comparative examples is 290–630 m². 2 g -1 .

[0081] Regarding the carbon-supported platinum or platinum alloy catalysts of the Examples and Comparative Examples, membrane electrode assemblies for single-cell evaluation of solid polymer fuel cells were prepared by the following method.

[0082] 1. Electrode modulation 0.8 g of carbon-supported platinum or platinum alloy catalysts from 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 and Kogyo Pure Chemicals), 1.88 ml of 1-propanol (manufactured by Fujifilm and Kogyo Pure Chemicals), and 0.72 ml of propylene glycol (manufactured by Fujifilm and Kogyo Pure Chemicals) were mixed and dispersed in a planetary ball mill for 1 hour, and then degassed with a stirrer for 5 minutes to prepare a cathode catalyst slurry. This electrode catalyst slurry was coated onto one side of a PTFE sheet (Naflon sheet manufactured by Nichias, 200 μm thick) using a doctor blade and dried at 120°C under vacuum for 60 minutes, thereby forming a cathode catalyst layer on the PTFE sheet.

[0083] The anode catalyst layer uses the reference catalyst FC-I2 (IFPC40-II manufactured by Shifu Metal Industry) from the Catalysis Society's Fuel Cell Related Catalyst Research Association.

[0084] 2. MEA Creation Two previously fabricated PTFE sheets with electrode catalyst layers were sandwiched between a solid polymer electrolyte membrane (Nafion NR-211, 200mm x 200mm square, manufactured by Chemours) with the electrode catalyst layer forming side facing inwards. The membrane was then hot-pressed at 130°C for 10 minutes using a precision heating and pressurizing device (CYPM manufactured by Shin-Tung Industrial Co., Ltd.) at a pressure of 1.5 K / N. After cooling, only the PTFE sheets were peeled off, resulting in a composite with the electrode catalyst layer transferred to the solid polymer electrolyte membrane. At this point, the transfer rate of the electrode catalyst layer from the PTFE sheets to the solid polymer electrolyte was 100%, and the platinum weight per square centimeter of the single-sided electrode catalyst layer on the solid polymer electrolyte membrane was 0.30 mg.

[0085] Next, the previously fabricated assembly is sandwiched between two gas diffusion layers (GDL 28BC manufactured by SGL Corporation, 100mm×100mm square), and a sealing material (Naflon (registered trademark) sheet manufactured by Nichias Corporation, 150μm thick and 80μm thick laminate) is applied to the outer periphery of the electrode catalyst layer and the gas diffusion layer to form the MEA.

[0086] Subsequently, a gold-plated current collector with a gas flow path was configured on the fabricated MEA, and clamped and fastened with stainless steel end plates to achieve the specified surface pressure, thus obtaining a single cell of a solid polymer fuel cell.

[0087] The following power generation evaluations were conducted on MEAs using carbon-supported platinum or platinum alloy catalysts from the various examples and comparative examples. The results are shown in Table 2.

[0088] [Determination of the initial activity of MEAs using carbon-supported platinum or platinum alloy catalysts] According to the "NEDO PEFC Battery Evaluation and Analysis Procedure March 2022 Edition" issued by the New Energy and Industrial Technology Development Organization (NEDO), IV measurements were performed using a fuel cell power generation evaluation device (manufactured by CHINO) and an electronic load device (PLZ164WA manufactured by Kikusui Electronics Industry Co., Ltd.). The mass activity was calculated from the current density at 0.85V and the platinum loading to determine the initial activity.

[0089] [Durability determination of MEAs using carbon-supported platinum or platinum alloy catalysts] According to the potential cycling (load response) test method described in the "NEDO PEFC Battery Evaluation and Analysis Procedure March 2022 Edition" of the New Energy and Industrial Technology Development Organization (NEDO), a load response simulated potential cycling test was conducted to accelerate the degradation of platinum particles or platinum alloy particles with carbon-supported platinum or platinum alloy catalysts using a fuel cell power generation evaluation device (manufactured by CHINO) and a constant potential-constant current meter (PGSTAT128N manufactured by Metrohm). The mass activity after the durability test was calculated from the current density at 0.85V and the platinum loading after 30,000 cycles, and the durability was evaluated.

[0090] Regarding initial activity, 800Ag -1 The above ratings are ◎ and 300Ag. -1 Above and below 800Ag -1 The rating is 0. Regarding post-durability activity, 300 Ag... -1 The above ratings are ◎ and 100Ag. -1 Above and below 300Ag -1 The rating is 0 or less than 100 Ag. -1 The rating is ×.

[0091] Examples 1-6 are carbon-supported platinum or platinum alloy catalysts in which the total weight of the second platinum or platinum alloy particles loaded outside the pores of the mesoporous carbon is adjusted to 60-90% relative to the total weight of the first and second platinum particles or platinum alloy particles loaded in two steps inside and outside the pores of the mesoporous carbon, and the average particle size D1 of the platinum particles or platinum alloy particles loaded 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 loaded outside the pores, with an initial mass activity of 300 Ag. -1 The above values ​​were observed, and the mass activity after 30,000 cycles was 100 Ag. -1 The above exhibits good initial activity and durability.

[0092] Comparative Example 1 is a carbon-supported platinum catalyst prepared by repeating the micropore loading process only twice, with an initial mass activity of 498 Ag. -1 It exhibits good initial activity, but on the other hand, the mass activity after 30,000 cycles is 52 Ag. -1 The above indicates low durability.

[0093] Comparative Example 2 is a carbon-supported platinum catalyst prepared solely through a microporous external loading process, i.e., liquid-phase reduction, with an initial mass activity of 371 Ag. -1 It exhibits good initial activity, but on the other hand, the mass activity after 30,000 cycles is 47 Ag. -1 The above indicates low durability.

Claims

1. A carbon-supported platinum or platinum alloy catalyst, which is a carbon-supported platinum or platinum alloy catalyst on mesoporous carbon with platinum particles or platinum alloy particles supported on it, characterized in that: The platinum or platinum alloy loading in the catalyst is, on a weight basis, more than 30% and less than 70% of the total weight of the catalyst. The total weight of the platinum particles or platinum alloy particles loaded on the micropores of the mesoporous carbon is 60% to 90% relative to the total weight of the platinum particles or platinum alloy particles. The average particle size D1 of the platinum particles or platinum alloy particles loaded 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 loaded outside the pores of the mesoporous carbon. The average particle size D1 and the average particle size D2 are each independently greater than 2 nm and less than 8 nm.

2. The carbon-supported platinum or platinum alloy catalyst according to claim 1, characterized in that: The average particle size D1 is greater than 2.5 nm and less than 8 nm. The average particle size D2 is greater than 2.3 nm and less than 7.3 nm. D1 / D2 is 1.0 to 2.

1.

3. A method for manufacturing a carbon-supported platinum catalyst, comprising an in-pore loading step of loading platinum within the pores of a mesoporous carbon support and an out-of-pore loading step of loading platinum particles outside the pores of the mesoporous carbon support. in, The loading process within the fine pores includes: The process of impregnating a platinum-containing aqueous solution into a mesoporous carbon support. The process of vacuum drying the mesoporous carbon support impregnated with an aqueous solution containing a platinum compound obtained in the above steps, and The process of heat-treating the mesoporous carbon support obtained in the vacuum drying process in a reducing atmosphere. The fine-hole external loading process includes: The process of suspending the platinum-loaded mesoporous carbon support in an aqueous solution after the micropore loading process, and... The process of mixing the suspension with an aqueous solution containing a platinum compound and a liquid containing a reducing agent to reduce the platinum compound.

4. The method for manufacturing the carbon-supported platinum catalyst according to claim 3, wherein, The loading process within the fine pores includes: The process of adding and mixing dinitrosodiammineplatinum nitric acid aqueous solution to a mesoporous carbon support to obtain a carbon-supported platinum slurry. The process of drying the resulting slurry under reduced pressure and at a specified temperature to form dry solids. The process of heat treatment in a reducing atmosphere to reduce dinitrosodiamineplatinum, and The process of calcining in an inert gas atmosphere (calcination temperature T1) to grow platinum particles; The fine-hole external loading process includes: The mesoporous carbon support loaded with platinum in the micropores after the micropore loading process is suspended in an aqueous nitric acid solution. The process involves heating and stirring the suspension with a dinitrosodiamineplatinic acid aqueous solution and a liquid containing L-ascorbic acid at 80°C–100°C for 30 minutes–5 hours to load platinum particles onto the pores of the carbon support. The process involves filtering out platinum-loaded carbon with platinum particles loaded onto the pores of the carbon support through the aforementioned process, followed by washing, drying, and then firing in an inert gas atmosphere (firing temperature T2) to allow the platinum particles to grow.

5. The method for manufacturing the carbon-supported platinum alloy catalyst according to claim 3 or 4, comprising: The step of adding an aqueous solution containing a metal that should form an alloy with the platinum to the carbon-supported platinum catalyst and mixing it to obtain a slurry. The process of heating and drying the resulting slurry under reduced pressure to form dry solids, and The dry solid is pretreated and fired in a reducing atmosphere, and then fired in an inert gas atmosphere for alloying.

6. The method for manufacturing the carbon-supported platinum or platinum alloy catalyst according to claim 3 or 4, characterized in that: The average particle size D1 and average particle size D2 of platinum particles are controlled by setting the firing temperature T1 and the firing temperature T2 to specified temperatures, respectively.

7. A membrane electrode assembly for a solid polymer fuel cell, characterized in that: The electrode contains the carbon-supported platinum or platinum alloy catalyst as described in claim 1.

8. A solid polymer fuel cell, characterized in that: The electrode of the membrane electrode assembly contains the carbon-supported platinum or platinum alloy catalyst as described in claim 1.

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