Carbon material for catalyst carrier of solid polymer fuel cell, catalyst layer for solid polymer fuel cell, and fuel cell

Abstract

Provided are: a carbon material for a catalyst carrier of a solid polymer fuel cell having excellent low load characteristics; a catalyst layer for a solid polymer fuel cell using the same; and a fuel cell.　The carbon material for a catalyst carrier of a solid polymer fuel cell comprises porous carbon black that satisfies requirements (A) to (C). (A) The BET specific surface area is 350 m2 / g or more. (B) The outer specific surface area is 10 m2 / g to 200 m2 / g. (C) The volume of pores with pore diameters of 2 nm or less is 0.025 mL / g or more.

Description

Carbon material for catalyst support of polymer electrolyte fuel cell, catalyst layer for polymer electrolyte fuel cell, and fuel cell

[0001] The present disclosure relates to a carbon material for a catalyst support of a polymer electrolyte fuel cell, a catalyst layer for a polymer electrolyte fuel cell, and a fuel cell.

[0002] A polymer electrolyte fuel cell, a type of fuel cell, comprises a pair of catalyst layers disposed on both sides of a solid polymer electrolyte membrane, gas diffusion layers disposed on the outer side of each catalyst layer, and separators disposed on the outer side of each gas diffusion layer. One of the pair of catalyst layers serves as the anode of the polymer electrolyte fuel cell, and the other serves as the cathode of the polymer electrolyte fuel cell. In a typical polymer electrolyte fuel cell, multiple unit cells each having the above components are stacked to obtain the desired output.

[0003] A reducing gas such as hydrogen is introduced into the separator on the anode side. The reducing gas is diffused into the gas diffusion layer on the anode side and then introduced into the anode. The anode contains a catalyst component, a catalyst carrier that supports the catalyst component, and an electrolyte material (ionomer) that has proton conductivity. The catalyst carrier is often made of a carbon material. An oxidation reaction of the reducing gas occurs on the catalyst component, producing protons and electrons. For example, when the reducing gas becomes hydrogen gas, the following oxidation reaction occurs: H ２ →2H ＋ +2e － (E ０ = 0 V)

[0004] Protons produced by this oxidation reaction pass through the electrolyte material in the anode and the solid polymer electrolyte membrane and are introduced into the cathode. Electrons pass through the catalyst support, gas diffusion layer, and separator to be introduced into the external circuit. After performing work (generating electricity) in the external circuit, these electrons are introduced into the cathode-side separator. These electrons then pass through the cathode-side separator and cathode-side gas diffusion layer to be introduced into the cathode.

[0005] The solid polymer electrolyte membrane is made of a proton-conductive electrolyte material and introduces the protons generated in the oxidation reaction to the cathode.

[0006] An oxidizing gas such as oxygen gas or air is introduced into the separator on the cathode side. The gas diffusion layer on the cathode side diffuses the oxidizing gas and then introduces it into the cathode. The cathode includes a catalyst component, a catalyst carrier that supports the catalyst component, and an electrolyte material (ionomer) having proton conductivity. The catalyst carrier is often composed of a carbon material. On the catalyst component, a reduction reaction of the oxidizing gas occurs and water is generated. For example, when the oxidizing gas is oxygen gas or air, the following reduction reaction occurs. O ２ +4H ＋ +4e － →2H ２ O (E ０ =1.23V)

[0007] The water generated by the reduction reaction is discharged to the outside of the fuel cell together with the unreacted oxidizing gas. Thus, in a solid polymer fuel cell, power is generated by utilizing the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, the electrons generated by the oxidation reaction perform work in the external circuit.

[0008] By the way, from the viewpoint of the power generation performance of fuel cells, it has been proposed to use porous carbon black for the catalyst carrier.

[0009] For example, Patent Document 1 discloses "an electrode catalyst layer for a fuel cell, which includes a catalyst, a porous carrier that supports the catalyst, and a polymer electrolyte, wherein the average particle diameter of the porous carrier is 20 to 100 nm, and the pore volume of pores having a pore diameter of 4 to 20 nm in the porous carrier is 0.23 to 0.78 cm ３ / g, and the mode diameter of the pore distribution of the porous carrier is 4 to 20 nm."

[0010] Patent Document 2 discloses "a method for producing high-surface-area graphitized carbon, which includes a step of oxidizing a starting carbon material and a step of graphitizing the starting carbon material in order to produce high-surface-area graphitized carbon having a surface area at least 100 m ２ / g larger than the surface area of the starting carbon material, wherein the oxidation is performed before the graphitization, and high-surface-area carbon is generated by the oxidation, and the average pore volume of the high-surface-area graphitized carbon is at least 1.32 cc / g."

[0011] In Patent Document 3, "the specific surface area measured by the BET method is 200 to 500 m 2 / g, a crystalline layer thickness Lc measured by X-ray diffraction of 20 to 30 Å, an average primary particle diameter of 15 to 25 nm, and a volatile content of 0.10 to 1.00%."

[0012] Patent Document 4 describes a carbon material for a catalyst carrier capable of supporting a catalyst component for a polymer electrolyte fuel cell, which has a half-width of the G band measured by Raman spectroscopy of 30 cm －１ Super 65cm －１ The BET specific surface area S evaluated by the BET method is less than ＢＥＴ (m ２ / g) is 700m ２ / g over 3000m ２ / g, and the total specific surface area S ｔｏｔａｌ and external specific surface area S ｏｕｔ Ratio to S ｏｕｔ / S ｔｏｔａｌ is greater than 0.3, and the external specific surface area S evaluated by t-plot analysis ｏｕｔ is 300m ２ / g or more.

[0013] Patent Document 5 describes a carbon-based support for a fuel cell catalyst, which is a solid-type support, and has a thickness of 100 to 450 m. ２ / g external surface area, 0.25-0.65 cm ３ / g mesopore volume, and 0.01 to 0.05 cm ３ / g (each of the external surface area, mesopore volume, and micropore volume is the arithmetic mean of measurements obtained from five randomly taken samples using a Brunauer-Emmett-Teller (BET) analyzer (Micromeritics, ASAP-2020))."

[0014] Japanese Patent Publication No. 2013-109856 Japanese Patent No. 5650542 Japanese Patent No. 6563945 Japanese Patent No. 6814339 Japanese Patent No. 7416938

[0015] When porous carbon black is used as a carbon material for a catalyst support in a polymer electrolyte fuel cell, a large amount of catalytic metal can be supported inside the carbon black, and therefore low-load characteristics (power generation characteristics at low current) are required as power generation performance. However, in the prior art, including the above-mentioned documents, the interior of the carbon black is not sufficiently porous, and therefore further improvement in low-load characteristics is required.

[0016] For example, in Patent Document 2, a carbon black starting material having a first BET nitrogen surface area is contacted with an oxidant in a fluidized bed under conditions effective to produce a carbon black product having a second BET nitrogen surface area greater than the first BET nitrogen surface area. This causes the oxidant and carbon black to react in the fluidized bed, resulting in porosity. However, the reaction in the fluidized bed only improves uniform contact between the oxidant and the carbon black, and may not achieve the effect of exposing edge surfaces, which serve as activation initiation points, deeper into the carbon black, as described in this disclosure. Consequently, the carbon black may not be sufficiently porous. Therefore, there is room for improvement in low-load characteristics.

[0017] In Patent Document 3, an activation treatment is carried out after the heat treatment. However, since the heat-treated highly crystalline carbon wall is activated, the activation effect is low and the carbon may not be sufficiently porous. Therefore, the catalytic metal particles are not sufficiently supported inside the carbon, and there is room for improvement in low-load characteristics.

[0018] In Patent Document 4, activation is performed by hollowing out the carbon to increase the hydrophilicity of the carbon support. As a result, the carbon support is characterized by a relatively large external specific surface area. However, in such a carbon support with a large external specific surface area, it is believed that not only the interior of the carbon but also the exterior surface is largely activated. As the activation of the exterior surface progresses, openings leading to the interior of the carbon expand on the exterior surface of the carbon. Therefore, when this is used as a catalyst support for a fuel cell, there is a risk that the proton-conducting electrolyte material (ionomer) will excessively penetrate into the interior of the carbon, poisoning the catalyst metal particles and resulting in a deterioration of low-load characteristics.

[0019] In Patent Document 5, acetylene black is air-activated at a temperature of 20% by weight less than the thermal decomposition temperature ±40°C. This selectively increases mesopores, resulting in an external specific surface area of ​​100 to 450 m. ２ / g, mesopore volume is 0.25 to 0.65 cm ３ / g, micropore volume of 0.01 to 0.05 cm ３ / g of porous carbon has been achieved. However, while micropores are not thought to contribute to catalytic activity, it is believed that moisture adsorbed within the micropores contributes to maintaining moisture within the fuel cell catalyst layer. Proton transport within the fuel cell catalyst layer is achieved by a proton-conductive electrolyte material (ionomer), and the propagation speed increases as the humidity within the catalyst layer increases. Furthermore, proton transport occurs even on carbon surfaces not coated with ionomer due to condensed water, and the formation of proton transport pathways is promoted at higher humidity levels. Therefore, without sufficient micropore volume, the humidity required for proton transport cannot be maintained, raising concerns about a decline in low-load characteristics.

[0020] Therefore, an object of the present disclosure is to provide a carbon material for a catalyst support of a polymer electrolyte fuel cell that has excellent low-load characteristics, a catalyst layer for a polymer electrolyte fuel cell that uses the same, and a fuel cell.

[0021] The means for solving the problems include the following aspects: <1> A carbon material for a catalyst support of a polymer electrolyte fuel cell, which is made of porous carbon black and satisfies the following requirements (A), (B), and (C): (A) a BET specific surface area of ​​350 m ２(B) The external specific surface area determined by analysis using the t-plot method is 10 m ２ / g or more 200m ２ (C) The volume of pores having a diameter of 2 nm or less, as determined by analyzing a nitrogen adsorption isotherm using the Dollimore-Heal (DH) method, is 0.050 mL / g or more. ２ / g or more 800m ２ <3> A carbon material for a catalyst support of a polymer electrolyte fuel cell, comprising porous carbon black, which satisfies the following requirements (A1), (B1), and (C1): (A1) a BET specific surface area of ​​350 m ２ / g or more 600m ２ (B1) The external specific surface area determined by analysis using the t-plot method is 10 m ２ / g or more 100m ２ / g or less. (C1) The pore volume of pores with a diameter of 2 nm or less, as determined by analyzing a nitrogen adsorption isotherm using the Dollimore-Heal (DH) method, is 0.025 mL / g or more and less than 0.050 mL / g. <4> The carbon material for a catalyst support of a polymer electrolyte fuel cell according to any one of <1> to <3>, further satisfying the following requirement (D): (D) In ​​an XRD (X-ray diffraction) spectrum obtained by XRD measurement, Lc(002) obtained by analyzing peaks between a diffraction angle 2θ of 20° to 26.5° is 1.7 nm or more and 4.0 nm or less. <5> A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst support of a polymer electrolyte fuel cell according to any one of <1> to <4>. <6> A fuel cell comprising the catalyst layer for a polymer electrolyte fuel cell according to <5>. <7> The fuel cell according to <6>, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on the cathode side.

[0022] According to the present disclosure, there are provided a carbon material for a catalyst support of a polymer electrolyte fuel cell that has excellent low-load characteristics, a catalyst layer for a polymer electrolyte fuel cell that uses the same, and a fuel cell.

[0023] FIG. 1 is a schematic diagram showing an example of the general configuration of a fuel cell according to the present disclosure.

[0024] In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Furthermore, when "greater than" or "less than" is added to the numerical values ​​written before and after "to", the numerical range means a range that does not include these numerical values ​​as the lower or upper limit. In this disclosure, the term "process" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. In this disclosure, the "electrolyte material having proton conductivity" used in the catalyst layer of a fuel cell is also referred to as an "ionomer."

[0025] <Carbon material for catalyst support of polymer electrolyte fuel cell> The carbon material for catalyst support of polymer electrolyte fuel cell of the present disclosure is made of porous carbon black that satisfies the requirements (A), (B), and (C) described below. Here, the porous carbon black is carbon black that has been made porous by, for example, "activation" in which an oxidizing gas is brought into contact with the carbon black.

[0026] The carbon material for a catalyst support according to the present disclosure is a carbon material having excellent low load characteristics. The carbon material according to the present disclosure was discovered based on the following findings.

[0027] In recent years, with the growing interest in carbon neutrality, ２ Demand for fuel cells is increasing in the field of large-scale commercial mobility vehicles (hereinafter referred to as "HDVs") with high emissions. The performance requirements for fuel cells are increasing year by year as HDVs become more widespread. These include further improvements in low-current power generation performance (low-load characteristics), which directly impacts fuel economy, and high durability of catalyst carriers. In addition to these performance requirements, further cost reductions in the materials used are also an important requirement for the future widespread use of HDVs.

[0028] When porous carbon materials with internal mesopores, such as dendritic carbon materials obtained by the autolysis reaction of silver acetylide, Ketjen Black, and Knobel, are used as carbon materials for catalyst supports, the catalyst supported in the internal mesopores is protected from poisoning by ionomers, resulting in improved activity and low-load characteristics. However, because these porous carbon materials are expensive, using porous carbon black, which is made porous by activating carbon black, an inexpensive raw material, is effective in reducing costs. On the other hand, when considering fuel cell stacks used in fuel cell vehicles, low-load characteristics increase with the number of unit cells in the stack, but improving the low-load performance per unit cell allows for a reduction in the number of cell stacks. As a result, the amount of precious metals, such as platinum, used as catalytic metals can be reduced, leading to significant cost savings. Therefore, further improvements in the low-load characteristics of porous carbon black are needed.

[0029] Therefore, the inventors have investigated how to improve the low load characteristics of carbon black by making it porous, and have obtained the following findings.

[0030] As the BET specific surface area increases, the external specific surface area determined by analysis using the t-plot method also increases, resulting in a deterioration of low-load characteristics. When the BET specific surface area of ​​porous carbon black is large, numerous pores are formed on the surface. This allows a larger amount of catalyst component to be supported within the pores. One method for obtaining porous carbon black is known as the "activation method," in which carbon black is made porous by contacting it with an oxidizing gas. In this activation method, as the porosity increases, the surface is depleted (the external specific surface area of ​​the carbon increases), and large openings are thought to form on the surface of the porous carbon black. As a result, the ionomer penetrates excessively into the carbon through these openings, resulting in ionomer poisoning of the catalyst particles and a deterioration of low-load characteristics.

[0031] In contrast, the porous carbon black of the present disclosure has a large BET specific surface area while suppressing an increase in the external specific surface area. As a result, the carbon black has many pores capable of supporting a catalyst inside, and the formation of large openings on the external surface is suppressed. This not only improves low-load characteristics by increasing porosity, but also suppresses a decrease in low-load characteristics due to excessive penetration of ionomer through the openings.

[0032] Here, the role of pores (micropores) of the carrier carbon with a diameter of 2 nm or less in the development of low-load characteristics will be explained. In the catalyst layer of a fuel cell, oxygen gas and protons (H ＋ ) generates electrical energy through a reaction that produces water. The protons required for the reaction are transported by the ionomer, and the higher the humidity in the catalyst layer, the higher the proton conduction rate. It is also believed that even when there is no ionomer near the catalyst metal, protons are conducted through the condensed water on the catalyst support surface. For these reasons, maintaining a high humidity level within the catalyst layer is necessary for efficient proton transport and, ultimately, for improved low-load characteristics. The larger the volume of the micropores, which are more likely to retain adsorbed moisture, the more they contribute to moisture retention.

[0033] The presence of many micropores with a pore size of 2 nm or less facilitates water adsorption, which improves the moisture retention within the catalyst layer, leading to efficient proton conduction and improved low-load characteristics.

[0034] From the above findings, it has been found that the carbon material for a catalyst support according to the present disclosure is a carbon material with excellent low load characteristics.

[0035] The requirements (A), (B), and (C) will be explained below. From the viewpoint of further improving durability in addition to the low load characteristics, it is preferable that the carbon material for a catalyst support of the present disclosure satisfies the requirement (D) in addition to the requirements (A), (B), and (C).

[0036] (Requirement (A)) (A) BET specific surface area is 350 m ２ / g or more. When the BET specific surface area of ​​the porous carbon black is large, many pores are formed on the surface of the porous carbon black, allowing a larger amount of catalytic metal to be supported in the pores. ２ If the BET specific surface area of ​​the porous carbon black is less than 350 m / g, the particle size of the catalyst metal increases and the catalyst metal particles tend to aggregate when the catalyst metal loading rate is increased. As a result, it becomes difficult to obtain high low-load characteristics. ２ However, from the viewpoint of suppressing deterioration in durability, the BET specific surface area of ​​the porous carbon black is set to 1000 m ２ / g or less is preferred.

[0037] The BET specific surface area of ​​the porous carbon black is preferably 600 m ２ / g or more 800m ２ / g or less. The BET specific surface area of ​​the porous carbon black is 600 m ２ / g or more 800m ２ When the BET specific surface area is 600 m / g or less, durability and better low load characteristics can be obtained. ２ When the BET specific surface area is 800 m / g or more, a larger amount of catalytic metal can be supported in the pores of the porous carbon black. ２ / g or less, the skeleton of the porous carbon black is prevented from becoming brittle, and as a result, deterioration of low-load characteristics due to destruction of the catalyst layer can be prevented.

[0038] The BET specific surface area is a value measured by the method described in the Examples section below.

[0039] (Requirement (B)) (B) The external specific surface area determined by analysis using the t-plot method is 10 m ２ / g or more 200m ２ / g or less. The external specific surface area of ​​the porous carbon black is 10 m ２ / g or more, 200m ２ When the external specific surface area of ​​the porous carbon black is 10 m / g or less, the ionomer is uniformly coated on the surface of the porous carbon black, and the deterioration of the low load characteristics is suppressed.２ When the external specific surface area of ​​the porous carbon black is less than 200 m / g, the carbon black is often not porous enough to be supported in the pores, and sufficient power generation performance may not be obtained. ２ When the external specific surface area of ​​the porous carbon black exceeds 10 m / g, it is considered that not only the inside but also the surface of the porous carbon black is depleted, and large openings are generated on the external surface of the porous carbon black. As a result, the ionomer penetrates excessively into the carbon through the openings, which leads to ionomer poisoning of the catalyst metal and a decrease in low load characteristics. Therefore, the external specific surface area of ​​the porous carbon black is 10 m / g or less. ２ / g or more, 200m ２ The external specific surface area of ​​the porous carbon black is preferably 10 m ２ / g or more 100m ２ / g or less. The external specific surface area of ​​many commercially available raw carbon blacks is 10 m ２ / g or more, and activation further increases the external specific surface area.

[0040] The external specific surface area is a value measured by the method described in the Examples below.

[0041] (Requirement (C)) (C) The pore volume of pores with a diameter of 2 nm or less, as determined by analyzing a nitrogen adsorption isotherm using the Dollimore-Heal (DH) method, is 0.050 mL / g or more. When the pore volume of pores with a diameter of 2 nm or less in the porous carbon black is 0.050 mL or more, sufficient micropores (amount of adsorbed water) are present to maintain high humidity in the catalytic layer. As a result, proton transport in the catalytic layer is efficient, and low-load characteristics are improved. Conversely, when the pore volume of pores with a diameter of 2 nm or less in the porous carbon black is less than 0.050 mL, the micropores (amount of adsorbed water) are insufficient to maintain high humidity in the catalytic layer. As a result, the humidity in the catalytic layer decreases, and the proton transport capacity in the catalytic layer decreases, resulting in a deterioration in low-load characteristics. However, from the viewpoint of oxygen gas inhibition by condensed water in the pores inside the carbon (oxygen gas in the fuel cell reaction cannot reach the surface of the catalytic metal particles), the pore volume of pores with a diameter of 2 nm or less in the porous carbon black is preferably 0.25 mL / g or less. The volume of pores with a diameter of 2 nm or less in the porous carbon black is preferably 0.050 mL / g or more.

[0042] However, for porous carbon black, the BET specific surface area is 350 m ２ / g or more 600m ２ / g or less, and the external specific surface area is 10 m ２ / g or more 100m ２ / g or less, good low-load characteristics can be obtained even if the pore volume of pores with diameters of 2 nm or less is 0.025 mL / g or more and less than 0.050 mL / g. In other words, the carbon material for a catalyst support of the present disclosure may be a carbon material for a catalyst support made of porous carbon black that satisfies the following requirements (A1), (B1), and (C1): (A1) A BET specific surface area of ​​350 m ２ / g or more 600m ２ (B1) The external specific surface area determined by analysis using the t-plot method is 10 m ２ / g or more 100m ２ (C1) The volume of pores with a diameter of 2 nm or less, as determined by analyzing a nitrogen adsorption isotherm using the Dollimore-Heal (DH) method, is 0.025 mL / g or more and less than 0.050 mL / g.

[0043] The volume of pores with a diameter of 2 nm or less is a value measured by the method described in the Examples below.

[0044] (Requirement (D)) (D) In ​​an XRD spectrum obtained by XRD (X-ray diffraction) measurement, the Lc(002) obtained by analyzing the peaks between diffraction angles 2θ = 20° and 26.5° is 1.7 nm or more and 4.0 nm or less. When the Lc(002) of the porous carbon black is 1.7 nm or more, the strength of the outer shell of the carbon black primary particles is increased, and crushing of the catalyst layer during fuel cell operation can be suppressed, thereby improving durability. When the Lc(002) of the porous carbon black is 4.0 nm or less, a decrease in the BET specific surface area of ​​the porous carbon black is suppressed, and low-load characteristics are improved. Therefore, it is preferable that the Lc(002) of the porous carbon black is 1.7 nm or more and 4.0 nm or less, since it is possible to achieve both durability and low-load characteristics. The Lc(002) of the porous carbon black is preferably 1.8 nm or more and 2.5 nm or less.

[0045] It should be noted that Lc(002) is a value measured by the method described in the Examples below.

[0046] <Method for producing carbon material for catalyst support of polymer electrolyte fuel cell> Hereinafter, an example of a method for producing a carbon material for catalyst support of a polymer electrolyte fuel cell according to the present disclosure (hereinafter also referred to as a "method for producing a carbon material") will be described.

[0047] The method for producing a carbon material according to the present disclosure is, for example, a method for treating raw material carbon black in the order of a "nitric acid treatment step," a "first activation step," a "heat treatment step," and a "second activation step." The method for producing a carbon material according to the present disclosure can provide a carbon material (i.e., porous carbon black) that satisfies requirements (A) to (C) (preferably requirements (A) to (D)). Furthermore, the method for producing a carbon material according to the present disclosure can provide a carbon material (i.e., porous carbon black) that satisfies requirements (A1) to (C1) (preferably requirements (A1) to (C1) and requirement (D)).

[0048] The method for producing a carbon material according to the present disclosure was discovered based on the following findings: The inventors investigated a production method that reduces the external specific surface area even when the porosity of carbon black is increased by activation, and discovered the following.

[0049] To make carbon black porous uniformly, it is important to bring as many carbon crystal edge faces into contact with the oxidizing agent during activation. ２ Carbon is removed by oxidation by contacting carbon black with an oxidizing agent such as water vapor at high temperatures. ２ For example, CO ２ In carbon with low crystallinity, the activation reaction proceeds at temperatures above 800°C. However, the reaction usually proceeds on the edge faces of the carbon crystal, with almost no reaction occurring on the basal faces. In other words, carbon with low crystallinity has many edge faces, making the activation reaction more likely to proceed.

[0050] It is known that carbon black typically has more low-crystalline regions toward the interior and higher crystallinity toward the outer surface. The porous carbon black targeted by the present invention aims to create a site for supporting catalytic metals within the carbon black by removing the low-crystalline carbon from within the carbon black. However, in the highly crystalline regions near the outer surface of the carbon black, low-crystalline carbon exists between the carbon crystallites, preventing the low-crystalline carbon within the carbon black from being exposed. If the low-crystalline carbon within the carbon black cannot be quickly exposed, activation of the interior of the carbon black will be slow, and activation near the outer surface will take precedence, resulting in the formation of large openings on the carbon black surface. Therefore, in the present invention, carbon black is treated with nitric acid before the activation reaction, which removes the low-crystalline carbon connecting the crystallites near the outer surface and exposes the low-crystalline regions within the carbon black. Therefore, even when the carbon black is made porous through activation, the increase in external surface area, as in the past, is suppressed.

[0051] From the above findings, the method for producing the carbon material of the present disclosure has been found.

[0052] The method for producing the carbon material of the present disclosure will be described in detail below.

[0053] (Raw Carbon Black) Examples of raw carbon black include furnace black, which is produced by continuously pyrolyzing a gaseous or liquid raw material in a reactor; channel black, which is produced by burning a raw material gas and applying the flame to the bottom surface of a channel steel to rapidly cool and precipitate; thermal black, which is produced by periodically repeating combustion and pyrolysis of a gas as a raw material; and acetylene black, which is produced from acetylene gas as a raw material. Furnace black is preferred as the raw carbon black from the viewpoints of ease of generating internal pores upon activation and a primary particle size suitable for use as a catalyst support for solid polymer fuel cells. These carbon blacks can be used alone or in combination of two or more types, but from the viewpoint of uniformly progressing activation, it is preferable to use them alone.

[0054] (Nitric Acid Treatment Step) In the nitric acid treatment step, the raw carbon black is treated with nitric acid. Specifically, in the nitric acid treatment step, for example, the raw carbon black is heated in an aqueous nitric acid solution to remove low-crystalline carbon that connects the crystallites of the raw carbon black, thereby exposing edge surfaces that serve as activation starting points deeper into the raw carbon black.

[0055] Low-crystalline carbon, which connects the crystallites of raw carbon black, is thought to be present in a small amount relative to the weight of the raw carbon black. The amount of nitric acid charged in the nitric acid treatment step may be set within a range that allows for its removal. Specifically, the amount of nitric acid charged is preferably 1 / 1 or more in terms of the mass ratio of raw carbon black to nitric acid in the nitric acid aqueous solution (raw carbon black / nitric acid in the nitric acid aqueous solution). There is no particular upper limit to the amount of nitric acid charged, but adding an excess amount of nitric acid will result in unused nitric acid remaining. Therefore, from an economical point of view, the amount of nitric acid charged is preferably 1 / 100 or less in terms of the mass ratio of raw carbon black to nitric acid in the nitric acid aqueous solution (raw carbon black / nitric acid in the nitric acid aqueous solution).

[0056] The nitric acid concentration of the nitric acid aqueous solution is preferably 1% by mass or more and 67% by weight or less. By setting the nitric acid concentration to 1% by weight or more, it is possible to efficiently remove low-crystalline carbon. By setting the nitric acid concentration to 67% by weight or less, it is possible to prevent the outer surface of the raw carbon black from being worn away due to oxidation of high-crystalline portions. Furthermore, the temperature of the nitric acid treatment step is preferably 20°C or more and 90°C or less. By setting the temperature to 20°C or more, it is possible to efficiently remove low-crystalline carbon. By setting the temperature to 90°C or less, it is possible to prevent the outer surface of the raw carbon black from being worn away due to oxidation of high-crystalline portions.

[0057] In the first activation step, the starting carbon black that has been treated with nitric acid is activated. In the first activation step, the activation temperature (maximum temperature) varies depending on the type of activation gas used. For example, in the case of carbon dioxide, it is preferable to adjust the temperature to 800°C or higher and 1100°C or lower, and to achieve a mass loss of 50% by mass or higher and 80% by mass or lower (the mass of the carbon black charged in the first activation step being 100% by mass).

[0058] (Heat Treatment Step) In the heat treatment step performed after the first activation step, heat treatment is performed in an inert atmosphere to grow the crystallites that constitute the raw carbon black that has undergone the first activation step, thereby imparting the durability required for fuel cells. By performing the heat treatment step, the Lc(002) of the porous carbon black can be maintained high, thereby improving durability.

[0059] In the heat treatment step, the raw carbon black that has undergone the first activation step is heat-treated in a vacuum or in an inert gas (nitrogen, argon, etc.) atmosphere at a temperature of 1300°C to 1900°C (preferably 1500°C to 1700°C). Heat treatment at 1300°C or higher develops highly aromatic carbon crystals that form the skeleton of the porous carbon black, and the pore walls become sufficiently thick, resulting in porous carbon black with a large Lc(002). Heat treatment at 1900°C or lower suppresses a decrease in the BET specific surface area and the volume of pores with a diameter of 2 nm or less, which would be caused by excessive crystallization of the carbon.

[0060] (Second activation step) In the second activation step, activation is carried out to reopen the pores of the heat-treated carbon black intermediate that were closed in the heat treatment step. This increases the BET specific surface area and the volume of pores with a pore diameter of 2 nm or less that were reduced in the heat treatment step. Without the second activation step, it is difficult to obtain a sufficient BET specific surface area and volume of pores with a pore diameter of 2 nm or less.

[0061] In the second activation step, the activation temperature (maximum temperature) varies depending on the type of activation gas used. For example, in the case of carbon dioxide, it is preferable to adjust the temperature to 800°C or higher and 1100°C or lower, and the weight loss due to activation to 2% by mass or higher and 30% by mass or lower (the mass of carbon black charged in the second activation step being taken as 100% by mass).

[0062] Then, by undergoing the nitric acid treatment step, the first activation step, the heat treatment step, and the second activation step, porous carbon black is obtained that has sufficient space inside the porous carbon black for supporting the catalytic metal and has small openings on the surface, satisfying requirements (A) to (C) (preferably requirements (A) to (D)). Also, porous carbon black is obtained that satisfies requirements (A1) to (C1) (preferably requirements (A1) to (C1) and requirement (D)).

[0063] (Activation Modes in the First Activation Step and the Second Activation Step) The type of activation gas used in the first activation step and the second activation step is not particularly limited as long as it contains a gas capable of oxidizing and consuming the carbon constituting the raw carbon black through a reaction. Examples of gases capable of oxidizing and consuming the carbon constituting the raw carbon black through a reaction include air, oxygen, ozone, water vapor, carbon dioxide, nitrogen dioxide, nitric oxide, and nitrous oxide. The activation gas may be a mixture of these gases. Alternatively, the activation gas may be a gas diluted with an inert gas such as nitrogen, argon, or helium. Furthermore, the activation gas may be an exhaust gas or industrial gas containing these gases. Preferably, the activation gas is water vapor or carbon dioxide, or a gas containing these. The type of gas used in the first activation step and the second activation step may be different.

[0064] As the activation device for the first activation step and the second activation step, various types of devices such as a rotary kiln, a fluidized bed furnace, a fixed bed furnace, a moving bed furnace, etc. can be used, and either a continuous furnace in which raw materials are continuously charged and products are discharged, or a batch furnace in which they are discharged intermittently, can be used. As the activation device, a rotary kiln and a fixed bed furnace are preferred because they allow easy switching of the gas introduction direction. Furthermore, from the viewpoint of uniformity of the activation degree, a batch furnace is preferred because a continuous furnace in which raw materials are continuously charged causes a distribution of the activation degree.

[0065] <Catalyst Layer for Polymer Electrolyte Fuel Cell and Polymer Electrolyte Fuel Cell> A catalyst layer for a polymer electrolyte fuel cell according to the present disclosure will now be described, along with a polymer electrolyte fuel cell. The carbon material according to the present disclosure can be applied, for example, to catalyst layers 150 and 160 provided in a polymer electrolyte fuel cell 100 shown in FIG. 1. FIG. 1 is a schematic diagram showing an example of the overall configuration of a fuel cell according to the present disclosure. The polymer electrolyte fuel cell 100 shown in FIG. 1 includes separators 110 and 120, gas diffusion layers 130 and 140, catalyst layers 150 and 160, and an electrolyte membrane 170.

[0066] The separator 110 is an anode-side separator that introduces a reducing gas such as hydrogen into the gas diffusion layer 130. The separator 120 is a cathode-side separator that introduces an oxidizing gas such as oxygen gas or air into the gas diffusion condensation phase. The types of the separators 110 and 120 are not particularly limited, and may be any separator used in conventional fuel cells (e.g., solid polymer fuel cells).

[0067] The gas diffusion layer 130 is an anode-side gas diffusion layer that diffuses the reducing gas supplied from the separator 110 and then supplies the gas to the catalyst layer 150. The gas diffusion layer 140 is a cathode-side gas diffusion layer that diffuses the oxidizing gas supplied from the separator 120 and then supplies the gas to the catalyst layer 160. The type of gas diffusion layers 130 and 140 is not particularly limited, and they may be any gas diffusion layer used in conventional fuel cells (e.g., polymer electrolyte fuel cells). Examples of the gas diffusion layers 130 and 140 include porous carbon materials (carbon cloth, carbon paper, etc.) and porous metal materials (metal mesh, metal wool, etc.). A preferred example of the gas diffusion layers 130 and 140 is a gas diffusion layer with a two-layer structure. Specifically, the gas diffusion layers 130 and 140 have a two-layer structure in which the layer on the separator 110 or 120 side is a gas diffusion fiber layer mainly composed of a fibrous carbon material, and the layer on the catalyst layer 150 or 160 side is a micropore layer mainly composed of carbon black.

[0068] The catalyst layer 150 is a so-called anode. In the catalyst layer 150, an oxidation reaction of the reducing gas occurs, producing protons and electrons. For example, when the reducing gas becomes hydrogen gas, the following oxidation reaction occurs: H ２ →2H ＋ +2e － (E ０ = 0 V)

[0069] Protons produced by the oxidation reaction pass through the catalyst layer 150 and electrolyte membrane 170 to reach the catalyst layer 160. Electrons produced by the oxidation reaction pass through the catalyst layer 150, gas diffusion layer 130, and separator 110 to reach the external circuit. The electrons perform work (generate electricity) in the external circuit and then enter the separator 120. The electrons then pass through the separator 120 and gas diffusion layer 140 to reach the catalyst layer 160.

[0070] There are no particular limitations on the configuration of the catalyst layer 150 that serves as the anode. The configuration of the catalyst layer 150 may be the same as that of a conventional anode, the same as that of the catalyst layer 160, or a configuration that is more hydrophilic than the catalyst layer 160.

[0071] The catalyst layer 160 is a so-called cathode. Within the catalyst layer 160, a reduction reaction of the oxidizing gas occurs, producing water. For example, when the oxidizing gas becomes oxygen gas or air, the following reduction reaction occurs. The water produced by the oxidation reaction is discharged to the outside of the polymer electrolyte fuel cell 100 together with the unreacted oxidizing gas. ２ +4H ＋ +4e － →2H ２ O (E ０ = 1.23 V)

[0072] In this way, the energy difference (potential difference) between the oxidation reaction and the reduction reaction is utilized to generate electricity in the polymer electrolyte fuel cell 100. In other words, the electrons generated in the oxidation reaction perform work in an external circuit.

[0073] The catalyst layer 160 contains the carbon material for a catalyst support of the present disclosure. That is, the catalyst layer 160 contains the carbon material for a catalyst support of the present disclosure, an electrolyte material (ionomer), and a catalyst component (platinum, etc.). This can improve the low-load characteristics within the catalyst layer 160. This can also improve the low-load characteristics of the polymer electrolyte fuel cell 100.

[0074] The catalyst loading rate in the catalyst layer 160 is not particularly limited, and is preferably 30% by mass or more and less than 80% by mass. A catalyst loading rate within this range further enhances low-load characteristics. Here, the catalyst loading rate is expressed as the mass % of the catalyst component relative to the total mass of the catalyst-loaded particles (particles in which the catalyst component is loaded on a carbon material for a catalyst carrier). If the catalyst loading rate is less than 30% by mass, it may be necessary to thicken the catalyst layer 160 to ensure that the polymer electrolyte fuel cell 100 is practically usable. On the other hand, if the catalyst loading rate is 80% by mass or more, catalyst aggregation is likely to occur. Furthermore, if the catalyst layer 160 becomes too thin, flooding may occur.

[0075] The mass ratio I / C of the mass I of the electrolyte material in the catalyst layer 160 to the mass C of the catalyst support carbon material is not particularly limited, but is preferably greater than 0.5 and less than 5.0. In this case, both the pore network and the electrolyte material network can be achieved, resulting in improved low-load characteristics. On the other hand, if the mass ratio I / C is 0.5 or less, the electrolyte material network tends to be weak and the proton conduction resistance tends to increase. If the mass ratio I / C is 5.0 or more, the pore network may be disrupted by the electrolyte material. In either case, the low-load characteristics may be degraded.

[0076] Furthermore, the thickness of the catalyst layer 160 is not particularly limited, and is preferably more than 5 μm and less than 20 μm. In this case, the oxidizing gas is more likely to diffuse within the catalyst layer 160, and flooding is less likely to occur. If the thickness of the catalyst layer 160 is 5 μm or less, flooding is more likely to occur. If the thickness of the catalyst layer 160 is 20 μm or more, the oxidizing gas is less likely to diffuse within the catalyst layer 160, and the catalytic components near the electrolyte membrane 170 become less effective. In other words, there is a possibility that the catalyst utilization rate will decrease.

[0077] The electrolyte membrane 170 is composed of a proton-conducting electrolyte material. The electrolyte membrane 170 introduces protons generated in the oxidation reaction to the catalyst layer 160 (cathode). The type of electrolyte material is not particularly limited, and any electrolyte material used in conventional fuel cells, such as solid polymer fuel cells, may be used. An example of a suitable electrolyte material is an electrolyte resin. Examples of electrolyte resins include polymers with phosphate groups, sulfonic acid groups, etc. Specific examples include perfluorosulfonic acid polymers and polymers with benzenesulfonic acid, etc. Of course, other types of electrolyte materials may also be used. Examples of such electrolyte materials include inorganic and inorganic-organic hybrid electrolyte materials. The solid polymer fuel cell 100 may be a fuel cell that operates within a temperature range from room temperature (25°C) to 150°C.

[0078] <Method for manufacturing a polymer electrolyte fuel cell> The method for manufacturing the polymer electrolyte fuel cell 100 is not particularly limited, and may be the same as a conventional manufacturing method. However, the catalyst carrier uses the carbon material for a catalyst carrier of the present disclosure. Of the catalyst layers 150 and 160, it is preferable to use the carbon material for a catalyst carrier of the present disclosure for the catalyst carrier of at least the catalyst layer 160 that serves as the cathode. Of course, the carbon material for a catalyst carrier of the present disclosure may also be used for the catalyst carrier of both the catalyst layer 150 that serves as the anode and the catalyst layer 160 that serves as the cathode.

[0079] Experimental examples of the carbon material for a catalyst support according to the present disclosure will be described below. First, the method for measuring each parameter will be described.

[0080] <Method of measuring each parameter> (Measurement of nitrogen adsorption / desorption isotherm (BET specific surface area, pore volume with pore diameter of 2 nm or less)) Approximately 30 mg of a sample of the carbon material for catalyst support was weighed and vacuum dried at 200°C for 2 hours, and then nitrogen adsorption / desorption isotherm was measured using an automatic specific surface area measuring device (AUTOSORB iQ manufactured by Anton Paar Japan) with nitrogen gas as the adsorbate. The BET specific surface area was measured at a relative pressure P / P ０ The pore volume of pores with a diameter of 2 nm or less was calculated by analyzing the nitrogen adsorption / desorption isotherm by the DH method using the software attached to the apparatus.

[0081] (Measurement of external specific surface area) Approximately 30 mg of a sample of the carbon material for catalyst support was weighed and vacuum-dried at 200°C for 2 hours. Next, the sample was placed in an automatic specific surface area measuring device (MicrotrackBell, BELSORP MAX), and nitrogen adsorption / desorption isotherms were measured at a measurement temperature of liquid nitrogen temperature (approximately 77 K) using nitrogen gas as the adsorbate. For the external specific surface area, the nitrogen adsorption / desorption isotherms were analyzed by the t-plot method using the software provided with the device. Using BEL-GCB (Graphitized Carbon) provided with the software as a standard substance, the external specific surface area was calculated from the slope of the line in the range of adsorption thickness t = 2 to 3 nm.

[0082] (Measurement of Lc(002)) Approximately 3 mg of a sample of the carbon material for a catalyst support was weighed and placed on a silicon anti-reflection plate. This silicon anti-reflection plate was set in an X-ray diffractometer (RINT-TTRIII manufactured by Rigaku Corporation). Next, an XRD spectrum was measured using this apparatus under the following conditions: room temperature, a scan step of 0.02°, an angle sweep rate of 1° / min, and a Cu-Kα radiation source. The background of the obtained XRD spectrum was removed and smoothed in the 2θ range of 10° to 40°. For the XRD spectrum in the 2θ range of 10° to 40°, Lc(002) was calculated using the Scherrer formula (Lc=Kλ / βcosθ) for the waveform after background removal and smoothing.

[0083] <Examples and Comparative Examples: Preparation of Carbon Material for Catalyst Support> (Example 1) (1) Nitric Acid Treatment Step 10 g of raw carbon black (Nitelon #10 manufactured by Nippon Steel Carbon) and 500 mL of a 10% by mass aqueous solution of nitric acid (product name "10% nitric acid", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a 1-L recovery flask and heated at 80°C for 1 hour in an oil bath while stirring. After heating, the raw carbon black was filtered, washed with distilled water, and dried under reduced pressure at 90°C for 5 hours. (2) First Activation Step 5 g of the raw carbon black after the nitric acid treatment step was loaded into a 1-inch diameter tubular reactor, and a CO flow rate of 400 Nml / min was applied using a mass flow controller installed upstream of the tubular reactor. ２ In this state, the temperature of the tubular reactor was increased to 850°C at a rate of 20°C / min, and the temperature was maintained at 850°C for 30 hours. After that, the flow gas was changed to N ２ The temperature was switched to 0°C, the temperature was lowered, and a first activation sample was recovered. (3) Heat Treatment Step The entire amount of the recovered first activation sample was loaded into a heating crucible, and the temperature was raised at 15°C / min in a heating furnace under Ar flow, and a heat treatment step was carried out at 1350°C for 1 hour, and a heat-treated sample was recovered. (4) Second Activation Step The entire amount of the heat-treated sample was loaded again into a tubular reactor with a diameter of 1 inch, and CO2 gas was circulated at 400 Nml / min using a mass flow controller set upstream of the tubular reactor. In this state, the tubular reactor was heated to 850°C at 20°C / min, and held at 850°C for 2 hours, after which the circulating gas was changed to N2. ２ The temperature was lowered.

[0084] The second activated sample obtained by these operations was collected as the carbon material for a catalyst support of Example 1.

[0085] Example 2 A carbon material for a catalyst support was obtained in the same manner as in Example 1, except that the maximum temperature in the first activation step was 850°C, the holding time was 40 hours, and the holding temperature in the heat treatment step was 1600°C.

[0086] Example 3 A carbon material for a catalyst support was obtained in the same manner as in Example 2, except that the maximum temperature in the first activation step was 900° C. and the holding time was 15 hours.

[0087] Example 4 A carbon material for a catalyst support was obtained in the same manner as in Example 2, except that the maximum temperature in the first activation step was 900° C., the holding time was 15 hours, and the holding time in the second step was 6 hours.

[0088] Example 5 A carbon material for a catalyst support was obtained in the same manner as in Example 2, except that the holding time at the maximum temperature in the second activation step was set to 4 hours.

[0089] Example 6 A carbon material for a catalyst support was obtained in the same manner as in Example 2, except that the holding time at the maximum temperature in the first activation step was 45 hours and the holding time in the second activation step was 4 hours.

[0090] Example 7: A carbon material for a catalyst carrier was obtained using Niteron #SH manufactured by Nippon Steel Carbon as the raw material carbon black, the maximum temperature in the first activation step was 900°C, the holding time was 15 hours, the holding temperature in the heat treatment step was 1700°C, and the holding time in the second activation step was 4 hours. The other conditions were the same as in Example 1.

[0091] Example 8 The maximum temperature in the first activation step was 850°C, the holding time was 30 hours, the holding temperature in the heat treatment step was 1400°C, and the holding time in the second activation step was 2 hours. The other conditions were the same as in Example 7, and a carbon material for a catalyst support was obtained.

[0092] Example 9 A carbon material for a catalyst support was obtained under the same conditions as in Example 7, except that the maximum temperature in the first activation step was 850°C, the holding time was 45 hours, the holding temperature in the heat treatment step was 1600°C, and the holding time in the second activation step was 2 hours.

[0093] Example 10 The maximum temperature in the first activation step was 850°C, the holding time was 45 hours, the holding temperature in the heat treatment step was 1600°C, and the holding time in the second activation step was 4 hours. The other conditions were the same as in Example 7, and a carbon material for a catalyst support was obtained.

[0094] Example 11 A carbon material for a catalyst support was obtained under the same conditions as in Example 1, except that the holding time at the maximum temperature in the first activation step was set to 5 hours and the heat treatment step and the second activation step were not performed.

[0095] Example 12 A carbon material for a catalyst carrier was obtained under the same conditions as in Example 2, except that Niteron #200 manufactured by Nippon Steel Carbon was used as the raw carbon black.

[0096] Example 13 A carbon material for a catalyst support was obtained under the same conditions as in Example 8, except that the holding time at the maximum temperature in the first activation step was set to 25 hours and the heat treatment step and the second activation step were not performed.

[0097] Example 14 A carbon material for a catalyst support was obtained under the same conditions as in Example 9, except that the holding time at the maximum temperature in the first activation step was 50 hours and the heat treatment temperature was 1800°C.

[0098] Comparative Example 1 A carbon material for a catalyst support was obtained under the same conditions as in Example 2 except that the nitric acid treatment step was not performed, the maximum temperature in the first activation step was 900°C, the holding time was 15 hours, and the holding time in the second activation step was 4 hours.

[0099] Comparative Example 2 A carbon material for a catalyst support was obtained under the same conditions as in Example 2, except that the nitric acid treatment step was not performed, the retention time in the first activation step was 50 hours, and the retention time in the second activation step was 4 hours.

[0100] Comparative Example 3 A carbon material for a catalyst support was obtained in the same manner as in Example 2, except that the nitric acid treatment step was not carried out.

[0101] Comparative Example 4 A carbon material for a catalyst support was obtained in the same manner as in Example 2, except that the nitric acid treatment step was not carried out and the retention time in the first activation step was set to 35 hours.

[0102] Comparative Example 5 A carbon material for a catalyst support was obtained in the same manner as in Example 1, except that the nitric acid treatment step was not carried out and the retention time in the first activation step was set to 25 hours.

[0103] Comparative Example 6 A carbon material for a catalyst support was obtained under the same conditions as in Example 2, except that the nitric acid treatment step was not performed, the retention time in the first activation step was 50 hours, and the retention time in the second activation step was 4 hours.

[0104] Comparative Example 7 Ketjen Black EC300J manufactured by Lion Specialty Chemicals Co., Ltd., which was not subjected to any additional treatment, was used as the carbon material for a catalyst support in Comparative Example 7.

[0105] (Comparative Examples 8 and 9) 2 g of Ketjen Black EC300J (manufactured by Lion Specialty Chemicals Co., Ltd.) as raw material carbon black was subjected to a heat treatment step in a heat treatment furnace under a flow of Ar at 1400°C for 1 hour to obtain a carbon material for a catalyst support of Comparative Example 8. Similarly, a heat treatment step was performed at 1600°C for 1 hour to obtain a carbon material for a catalyst support of Comparative Example 9.

[0106] (Comparative Examples 10, 11, and 12) 2 g of Ketjen Black EC600JD manufactured by Lion Specialty Chemicals Co., Ltd. was used as raw material carbon black and was subjected to a heat treatment step at 1400°C for 1 hour in a heat treatment furnace under a flow of Ar, thereby obtaining a carbon material for a catalyst support of Comparative Example 10. Similarly, heat treatment steps were also performed at 1600°C and 1800°C for 1 hour, respectively, to obtain carbon materials for a catalyst support of Comparative Examples 11 and 12.

[0107] <Preparation of catalyst, preparation of catalyst layer, fabrication of MEA, assembly of fuel cell, and evaluation of cell performance (power generation performance, durability)> Next, using each of the porous carbon blacks prepared as described above, a catalyst for a polymer electrolyte fuel cell carrying a catalyst metal was prepared as follows. A catalyst layer ink liquid was prepared using the obtained catalyst, and then a catalyst layer was formed using this catalyst layer ink liquid. Furthermore, a membrane electrode assembly (MEA) was fabricated using the formed catalyst layer. This fabricated MEA was incorporated into a fuel cell, and a power generation test was performed using a fuel cell measuring device. The preparation of each component and the cell evaluation through the power generation test are described in detail below.

[0108] (1) Preparation of catalyst (platinum-supported carbon material) for polymer electrolyte fuel cell The catalyst support carbon material of each example was dispersed in distilled water, formaldehyde was added to this dispersion, and the dispersion was placed in a water bath set at 40°C. After the temperature of the dispersion reached 40°C, the same as the bath temperature, an aqueous solution of dinitrodiamine Pt complex nitric acid was slowly poured into the dispersion under stirring. Stirring was continued for about 2 hours, followed by filtration and washing of the resulting solid. The solid thus obtained was vacuum dried at 90°C, pulverized in a mortar, and then heat-treated at 200°C for 1 hour in an argon atmosphere containing 5% by volume of hydrogen to produce a platinum-supported carbon material. The amount of platinum carried on this platinum-supporting carbon material was adjusted to 35 mass % with respect to the total mass of the catalyst carrier carbon material and platinum particles, and was confirmed by measurement using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0109] (2) Preparation of Catalyst Layer Using the platinum-supported carbon material (Pt catalyst) prepared as described above and a 5 mass % Nafion solution (DE2020CS, registered trademark: Nafion, manufactured by DuPont) as the electrolyte resin, the Pt catalyst and Nafion were mixed under an Ar atmosphere in a ratio of 1.0 times the mass of the Nafion solid content relative to the mass of the porous carbon black (the mass of only the porous carbon black in the Pt catalyst excluding the Pt content), and after light stirring, the Pt catalyst was crushed by ultrasonic waves. Ethanol was further added to adjust the total solid content concentration of the Pt catalyst and the electrolyte resin to 0.5 mass %, thereby preparing a catalyst layer ink liquid in which the Pt catalyst and the electrolyte resin were mixed.

[0110] Using the catalyst layer ink liquid thus prepared, a platinum catalyst layer was prepared so that the mass per unit area of ​​the platinum catalyst layer (hereinafter referred to as "platinum coverage") was 0.2 mg / cm ２ The catalyst layer ink was sprayed onto a Teflon (registered trademark) sheet, and then dried in argon at 120° C. for 60 minutes to prepare a catalyst layer.

[0111] (3) Fabrication of MEA Using the catalyst layers fabricated as described above, an MEA (membrane electrode assembly) was fabricated by the following method. A square electrolyte membrane with sides of 6 cm was cut out from a Nafion membrane (NR211 manufactured by DuPont). The anode and cathode catalyst layers coated on Teflon (registered trademark) sheets were each cut out into a square with sides of 2.5 cm using a utility knife. The electrolyte membrane was sandwiched between the anode and cathode catalyst layers cut out in this way so that the catalyst layers were in contact with each other across the center of the electrolyte membrane and were not misaligned with each other. The MEA was then heated at 120°C and 100 kg / cm. ２ After cooling to room temperature, the Teflon (registered trademark) sheets were carefully peeled off from both the anode and cathode to prepare a catalyst layer-electrolyte membrane assembly in which the anode and cathode catalyst layers were fixed to the electrolyte membrane.

[0112] Next, a pair of square carbon paper sheets, each 2.5 cm on a side, was cut out from carbon paper (39BC manufactured by SGL Carbon Co., Ltd.) to form a gas diffusion layer. The catalyst layer-electrolyte membrane assembly was sandwiched between these carbon paper sheets so that the anode and cathode catalyst layers were aligned with each other without any misalignment. The assembly was then heated at 120°C and 50 kg / cm ２ The membrane was pressed for 10 minutes at 100°C to prepare an MEA. The basis weight of each of the catalytic metal component, carbon material, and electrolyte material in each prepared MEA was calculated from the mass of the catalyst layer fixed to the Nafion membrane (electrolyte membrane) obtained by calculating the mass of the catalyst layer from the difference between the mass of the Teflon (registered trademark) sheet with the catalyst layer before pressing and the mass of the Teflon (registered trademark) sheet peeled off after pressing, and the mass ratio of the catalyst layer composition.

[0113] (4) Fuel Cell Assembly and Initial Power Generation Performance Evaluation The MEAs fabricated using the porous carbon materials according to each Example and Comparative Example were assembled into cells and set in a fuel cell measuring device. The initial power generation performance of the fuel cells was evaluated according to the following procedure. Air was supplied to the cathode side and pure hydrogen was supplied to the anode side. The pressure was adjusted using a back-pressure valve installed downstream of the cell to achieve utilization rates of 40% and 70%, respectively, so that the back-pressure gauge pressure was 0.1 MPaG. The cell temperature was set to 80°C, and the air and pure hydrogen supplied to the fuel cell were humidified by passing them through distilled water kept at 80°C in a humidifier (i.e., bubbling). This set the relative humidity of the anode and cathode to approximately 100%. Under these conditions, with the reactant gas supplied to the cell, the current density was gradually increased 20 times until the cell terminal voltage reached 0.3 V. Thereafter, the current density was increased to 0.2 A / cm. ２ The cell terminal voltage was recorded when the cell was held at this temperature for 15 minutes, and the low load performance was evaluated using the following criteria: pass rank A or B, and fail rank C. The results are shown in Table 1-2. [Pass rank] A: Current density 0.2 A / cm ２ B: The voltage between the cell terminals is 0.83 V or more at a current density of 0.2 A / cm ２ The voltage between the cell terminals is 0.81 V or more. [Failure rank] C: Not meeting the pass rank B.

[0114] (5) Evaluation of Durability After the above-described evaluation of the initial power generation performance, a durability test was conducted under the following conditions. First, the cell temperature was 80°C, the relative humidity was 100%, the cell back pressure was set to 0.0 MPaG, and the cathode gas was switched to argon gas. Next, the cell voltage was set to 0.6 V and held for 4 seconds, and then the cell voltage was set to 1.2 V and held for 4 seconds, which constituted one cycle. This rectangular wave voltage fluctuation operation was repeated 1000 times. Thereafter, the anode and cathode gas utilization rates were set to 40% and 70%, respectively, the cell back pressure gauge pressure was 0.1 MPaG, the cell temperature was 80°C, and the relative humidity was 100%, and the current density was set to 0.2 A / cm. ２ The cell terminal voltage was recorded when the cell was fixed at 1000 cycles and held for 15 minutes, and durability was evaluated according to the following criteria. The results are shown in Table 2. [Pass Rank] A: Current density of 0.2 A / cm after 1000 cycles ２ B: The cell terminal voltage at 1000 cycles is 89% or more of the voltage at the time of initial power generation performance evaluation. ２ The cell terminal voltage at this stage is 85% or more of that at the time of the initial power generation performance evaluation. [Failure Rank] C: Not meeting the pass rank.

[0115]

[0116]

[0117] From the above results, it can be seen that the carbon material for a catalyst carrier of the example (i.e., porous carbon black) has excellent low load characteristics.

[0118] The symbols are explained as follows: 100: polymer electrolyte fuel cell 110, 120: separator 130, 140: gas diffusion layer 150, 160: catalyst layer 170: electrolyte membrane

[0119] The disclosure of Japanese Patent Application No. 2024-105663 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A carbon material for a catalyst support in a polymer electrolyte fuel cell, comprising porous carbon black, that satisfies the following requirements (A), (B), and (C): (A) a BET specific surface area of ​​350 m ２ (B) The external specific surface area determined by analysis using the t-plot method is 10 m ２ / g or more 200m ２ (C) The volume of pores with a diameter of 2 nm or less, as determined by analyzing a nitrogen adsorption isotherm using the Dollimore-Heal (DH) method, is 0.050 mL / g or more.

2. The BET specific surface area is 600 m ２ / g or more 800m ２ 2. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1, wherein the carbon material has a molecular weight of 1 / g or less.

3. A carbon material for a catalyst support of a polymer electrolyte fuel cell, comprising porous carbon black, which satisfies the following requirements (A1), (B1), and (C1): (A1) a BET specific surface area of ​​350 m ２ / g or more 600m ２ (B1) The external specific surface area determined by analysis using the t-plot method is 10 m ２ / g or more 100m ２ (C1) The volume of pores with a diameter of 2 nm or less, as determined by analyzing a nitrogen adsorption isotherm using the Dollimore-Heal (DH) method, is 0.025 mL / g or more and less than 0.050 mL / g.

4. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1, further satisfying the following requirement (D): (D) In ​​an XRD (X-ray diffraction) spectrum obtained by XRD measurement, Lc(002) obtained by analyzing the peaks between the diffraction angles 2θ = 20° and 26.5° is 1.7 nm or more and 4.0 nm or less.

5. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 3, further satisfying the following requirement (D): (D) In ​​an XRD (X-ray diffraction) spectrum obtained by XRD measurement, Lc(002) obtained by analyzing the peaks between the diffraction angles 2θ = 20° and 26.5° is 1.7 nm or more and 4.0 nm or less.

6. A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst support of a polymer electrolyte fuel cell according to any one of claims 1 to 5.

7. A fuel cell comprising the catalyst layer for a polymer electrolyte fuel cell according to claim 6.

8. The fuel cell according to claim 7, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on the cathode side.

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