Oxygen-treated carbon black, activated carbon black, carbon material for catalyst carriers of polymer electrolyte fuel cells, catalyst layer for polymer electrolyte fuel cells, and fuel cell

Abstract

Disclosed is a carbon material for catalyst carriers of polymer electrolyte fuel cells, the carbon material being composed of a porous activated carbon black that satisfies the requirements described below. (F) The BET specific surface area (m2 / g) is 400 to 1200. (G) If Σ2-6 is the integrated value of the pore volumes of pores having a pore diameter of not less than 2 nm but less than 6 nm in the mesopore distribution, Σ2-6 is not less than 0.20 but less than 0.70. (H) If Σ2-6 is the integrated value of the pore volumes of pores having a pore diameter of not less than 2 nm but less than 6 nm and Σ6-10 is the integrated value of the pore volumes of pores having a pore diameter of not less than 6 nm but less than 10 nm in the mesopore distribution, Σ6-10 / Σ2-6 is 0.120 to 0.500. (I) If ID is the intensity of the D-band and IG is the intensity of the G-band in the Raman spectrum, ID / IG is 1.20 to 2.20.

Description

Oxygen-treated carbon black, activated carbon black, carbon material for catalyst support in polymer electrolyte fuel cells, catalyst layer for polymer electrolyte fuel cells, and fuel cells

[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 fuel gas such as hydrogen is introduced into the separator on the anode side. After diffusing the fuel into the gas diffusion layer on the anode side, it is introduced into the anode. The anode contains a catalyst component, a catalyst carrier that supports a fuel cell catalyst, and an electrolyte material with proton conductivity. Hereinafter, the catalyst component that promotes the power generation reaction (oxidation reaction or reduction reaction described below) in the fuel cell will also be referred to as the "fuel cell catalyst." The catalyst carrier is often made of a porous carbon material. An oxidation reaction of the fuel gas occurs on the fuel cell catalyst, generating protons and electrons. For example, when the fuel gas becomes hydrogen gas, the following oxidation reaction occurs: H ２ →2H ＋ +2e － (E ０ = 0 V)

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

[0005] The solid polymer electrolyte membrane is made of an electrolyte material with proton conductivity. The solid polymer electrolyte membrane introduces protons generated in the above oxidation reaction to the cathode. 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 fuel cell catalyst, a catalyst support that supports the fuel cell catalyst, and an electrolyte material with proton conductivity. The catalyst support is often made of a porous carbon material. A reduction reaction of the oxidizing gas occurs on the fuel cell catalyst, producing water. For example, when the oxidizing gas becomes oxygen gas or air, the following reduction reaction occurs: O ２ +4H ＋ +4e － →2H ２ O (E ０ = 1.23 V)

[0006] The water produced by the reduction reaction is discharged outside the fuel cell along with the unreacted oxidizing gas. In this way, solid polymer fuel cells generate electricity by utilizing the free energy difference (potential difference) generated by the oxidation reaction of the fuel gas. In other words, the free energy generated by the oxidation reaction is converted into work performed by electrons in an external circuit.

[0007] Meanwhile, porous carbon materials (hereinafter also referred to as "carbon supports") that can be used as catalyst supports for polymer electrolyte fuel cells have been studied and various proposals have been made.

[0008] For example, Patent Document 1 proposes "a carbon material for a catalyst carrier used in a catalyst carrier of a polymer electrolyte fuel cell, which has a three-dimensionally branched dendritic structure, and is characterized by simultaneously satisfying the following (1) and (2)." (1) In particle size distribution measurement using a laser diffraction / scattering particle size distribution analyzer, the DL / DH ratio is 1.5 or greater, where DL is the cumulative distribution [%] of particles with a particle diameter of 1 μm or less based on the volume diameter, and DH is the cumulative distribution [%] of particles with a particle diameter of more than 1 μm. (2) The mode diameter of a pore diameter range of 20 nm to 200 nm measured by mercury porosimetry is 40 nm to 70 nm.

[0009] Patent Document 2 proposes a "porous carbon material for use as a catalyst carrier in a polymer electrolyte fuel cell, which simultaneously satisfies the following (1), (2), (3), and (4)." (1) In a differential thermogravimetric curve (DTG) obtained by thermogravimetric analysis when the temperature is raised at a rate of 10°C / min in an air atmosphere, the strength (I ７５０ ) and the peak intensity around 690 °C (I ｐｅａｋ ) and the intensity ratio (I ７５０ / I ｐｅａｋ (2) The BET specific surface area determined by BET analysis of the nitrogen gas adsorption isotherm is 400 to 1500 m ２ (3) The cumulative pore volume V of pores with diameters of 2 to 10 nm determined by analysis of nitrogen gas adsorption isotherms using the Dollimore-Heal method. 2-10 (4) In the nitrogen gas adsorption isotherm, the nitrogen gas adsorption amount V at a relative pressure of 0.95 to 0.99 is macro is 300 to 1200 cc (STP) / g.

[0010] Patent Document 3 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))."

[0011] Patent Document 4 states that "the cumulative pore volume V of pores having a diameter of 2 nm or more and 4 nm or less ２－４and the cumulative pore volume V of pores having a pore diameter of more than 4 nm and not more than 20 nm. ４－２０ V is the ratio of ２－４ / V ４－２０ is 0.20 or more and 0.55 or less, and the amount of functional groups is 3% or more and 10% or less."

[0012] Patent Document 5 describes an electrode catalyst carrier comprising a porous complex oxide containing tin oxide doped with at least one of P, As, Sb, Bi, V, Nb, Ta, F, and Cl as a dopant, wherein the porous complex oxide contains silica, the volume resistivity of the carrier is 10,000 Ω cm or less, and the BET specific surface area of ​​the carrier is 50 to 300 m. ２ / g, the pore volume of the carrier is 0.2 ml / g or more, and 5% or more of the pore volume of the carrier is occupied by pores having a pore diameter of 10 nm or less."

[0013] Patent Document 1: JP 2022-156985 A Patent Document 2: WO 2020 / 066010 Patent Document 3: WO 2022 / 085963 Patent Document 4: JP 2019-89021 A Patent Document 5: JP 2017-162572 A

[0014] The ability of polymer electrolyte fuel cells (hereinafter referred to as "PEFC") to achieve both power generation characteristics and durability is an important characteristic for the widespread use of fuel cell vehicles (hereinafter referred to as "FCV"), and is an essential issue that must be resolved, particularly for commercial vehicles, where market growth is expected in the future.

[0015] Generally, one of the major causes of reduced durability in PEFCs is catalyst degradation, which is caused by oxidative consumption of the carbon support and dissolution of platinum nanoparticles. Both of these causes are caused by fluctuations in the electrode potential, particularly in the high-potential range exceeding 1 V. A solution to platinum dissolution is to increase the particle size to increase the time until dissolution. A solution to carbon support oxidative consumption is to increase the crystallinity (i.e., increase the in-plane size of the crystallites and the layer thickness) to suppress oxidative consumption of the carbon support, thereby reducing the area of ​​the carbon network plane edges that are the starting point for oxidative consumption and slowing the oxidation rate.

[0016] The power generation characteristics are governed by two main factors: the contribution of the metal catalyst (e.g., platinum nanoparticles) to the reaction (hereinafter also referred to as "catalyst utilization rate") and the diffusibility of oxidizing gases. The pore structure of the carbon support (porous carbon material) correlates with catalyst utilization rate, and the three-dimensional structure of the carbon support (e.g., dendritic structure) correlates with gas diffusivity. The pore size suitable for gas diffusion is not clear, but the pore size of the catalyst layer for nucleic acids, estimated from various currently used carbon supports, is several tens to hundreds of nanometers. The pores in the catalyst layer are realized by the three-dimensional structure of the carbon support (specifically, the aggregate structure of carbon black, etc.). It is desirable for the pore structure to selectively contain only pores large enough to accommodate metal catalysts (e.g., platinum nanoparticles) of several nanometers in size within the pores; mesoporous carbon is generally considered to be a suitable support.

[0017] However, in the prior art including Patent Documents 1 to 5, there is still room for improvement in terms of achieving both power generation characteristics (particularly low load characteristics) and durability.

[0018] In Patent Documents 1 and 2, the pore structure specific to the material is suitable for catalyst supports and exhibits excellent power generation characteristics, but there is room for improvement in meeting the durability (oxidation wear resistance) required for heavy-duty vehicle (HDV) applications such as long-distance trucks. In Patent Document 3, acetylene black is formed with pores primarily composed of mesopores, resulting in excellent durability and excellent power generation characteristics in high-humidity operating environments, but there is room for improvement in low-load characteristics, one of the important practical characteristics. In Patent Document 4, Ketjen black is used as a raw material, and durability is enhanced by heat treatment. It is believed that oxygen-containing functionality is imparted to the material to prevent the water repellency of the catalyst layer from decreasing due to heating, thereby achieving both durability and power generation characteristics. However, the reduction in pore volume caused by heat treatment leads to a decrease in power generation characteristics (particularly low-load characteristics), and there is room for improvement in achieving both high levels of durability (particularly low-load characteristics). Patent Document 5 discloses a catalyst support made of an oxide with a pore structure. Although the conductivity of the oxide itself is sufficient, the contact resistance between the oxides is high, and the ohmic resistance of the catalyst layer is high, resulting in a decrease in power generation characteristics, including low load characteristics.

[0019] As described above, the conventional techniques still have room for improvement in terms of achieving both power generation characteristics (particularly low load characteristics) and durability. In addition, there is a demand for achieving such improvement using carbon black, which is an inexpensive and useful carbon support (porous carbon material).

[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 durability as well as power generation characteristics (particularly, low-load characteristics), a catalyst layer for a polymer electrolyte fuel cell that uses the carbon material, and a fuel cell. Another object of the present disclosure is to provide oxygen-treated carbon black and activated carbon black that are suitable for obtaining a carbon material for a catalyst support of a polymer electrolyte fuel cell that has excellent durability as well as power generation characteristics (particularly, low-load characteristics).

[0021] The means for solving the problems include the following aspects: <1> Oxygen-treated carbon black that satisfies the following requirement (A): (A) A BET specific surface area calculated by nitrogen gas adsorption is S ＢＥＴ (m ２ / g), the oxygen content (mass%) is S ＢＥＴ <2> The oxygen-treated carbon black according to <1>, further satisfying the following requirement (B): (B) a BET specific surface area calculated by nitrogen gas adsorption is S ＢＥＴ (m ２ / g), and the primary particle diameter of the oxygen-treated carbon black is D (nm), S ＢＥＴ (m ２ <3> Activated carbon black that simultaneously satisfies the following requirements (C), (D), and (E): (C) a BET specific surface area (m ) calculated by nitrogen gas adsorption isotherm measurement; ２ (D) In ​​the mesopore distribution obtained by analyzing a nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the volume of pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ When this is the case, Σ ２－６ (E) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the volume of pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ , the integrated value of the pore volume of pores with a diameter of 6 nm or more and less than 10 nm is Σ ６－１０ , then Σ ６－１０ / Σ ２－６ <4> A carbon material for a catalyst support of a polymer electrolyte fuel cell, comprising a porous activated carbon black that simultaneously satisfies the following requirements (F), (G), (H), and (I): (F) a BET specific surface area (m ２ (G) In the mesopore distribution obtained by analyzing a nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the volume of pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ When this is the case, Σ ２－６(H) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the volume of pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ , the integrated value of the pore volume of pores with a diameter of 6 nm or more and less than 10 nm is Σ ６－１０ , then Σ ６－１０ / Σ ２－６ (I) In the Raman spectrum obtained by Raman spectroscopy, －１ The intensity of the D band of Ｄ , 1560-1620cm －１ The G band intensity of Ｇ When I Ｄ / I Ｇ is 1.20 or more and 2.20 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 <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 durability as well as power generation characteristics (particularly low-load characteristics), a catalyst layer for a polymer electrolyte fuel cell that uses the carbon material, and a fuel cell. According to the present disclosure, there are provided an oxygen-treated carbon black and an activated carbon black that are suitable for obtaining a carbon material for a catalyst support of a polymer electrolyte fuel cell that has excellent durability as well as power generation characteristics (particularly low-load characteristics).

[0023] 1 is a schematic diagram showing an example of the general configuration of a fuel cell according to the present disclosure. Fig. 2 is a graph showing the integrated value Σ of the pore volume of mesopores with a pore diameter of 2 nm or more and less than 6 nm in a mesopore distribution obtained by analyzing a nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method. ２－６、 and the integrated value of the pore volume of pores with a diameter of 2 nm or more and less than 6 nm is Σ ２－６ , the integrated value Σ of the pore volume of pores with a diameter of 6 nm or more and less than 10 nm ６－１０ 1 is a graph for explaining the above.

[0024] An example of the present disclosure will be described. In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when "greater than" or "less than" is added to the numerical values ​​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, a "proton-conductive electrolyte material" used in a catalyst layer of a fuel cell is also referred to as an "ionomer."

[0025] <Oxygen-treated carbon black, activated carbon black, and carbon material for catalyst support in polymer electrolyte fuel cells> The oxygen-treated carbon black of the present disclosure satisfies the requirement (A) described below. The oxygen-treated carbon black of the present disclosure preferably satisfies the requirement (B) described below. The activated carbon black of the present disclosure simultaneously satisfies the requirements (C), (D), and (E) described below. The carbon material for catalyst support in polymer electrolyte fuel cells of the present disclosure is made of porous activated carbon black simultaneously satisfying the requirements (F), (G), (H), and (I) described below.

[0026] Here, the oxygen-treated carbon black of the present disclosure is carbon black obtained by subjecting raw carbon black to oxygen treatment. The activated carbon black of the present disclosure is carbon black obtained by subjecting the oxygen-treated carbon black of the present disclosure to a first activation and making it porous. The carbon material for catalyst supports (porous activated carbon black) of the present disclosure is a carbon material (porous carbon black) obtained by subjecting the activated carbon black of the present disclosure to a heat treatment and a second activation to enhance crystallinity. In other words, the oxygen-treated carbon black of the present disclosure corresponds to an intermediate for producing the activated carbon black and porous activated carbon black of the present disclosure. Furthermore, the activated carbon black of the present disclosure corresponds to an intermediate for producing the carbon material for catalyst supports (porous activated carbon black) of the present disclosure.

[0027] The carbon material for catalyst supports (porous activated carbon black) of the present disclosure is a carbon material that has excellent power generation properties (particularly low-load properties) and durability. The oxygen-treated carbon black and activated carbon black of the present disclosure are carbon blacks suitable for obtaining carbon materials (i.e., porous activated carbon black) that have excellent power generation properties (particularly low-load properties) and durability. The carbon material for catalyst supports, oxygen-treated carbon black, and activated carbon black of the present disclosure were discovered based on the following findings.

[0028] In general, the power generation characteristics of a fuel cell depend heavily on the overvoltage of the cathode reaction. The following three factors are thought to be the main causes of overvoltage at the cathode: (1) The magnitude of the ohmic resistance of the catalyst layer, which is a combination of two resistances: electron conduction resistance and proton conduction resistance; (2) The diffusion resistance of oxidizing gases within the catalyst layer; and (3) The electrochemical resistance on the catalyst metal surface, i.e., the resistance in the chemical reaction involving electron transfer (i.e., the resistance in the catalytic reaction).

[0029] Among the above major causes, the factor that governs the reduction of "(3) resistance to catalytic reaction," particularly the utilization rate of the catalytic metal, is whether the catalytic metal in the pores of the porous activated carbon black is in contact with the ionomer, and the ease with which the ionomer penetrates into the pores of the porous activated carbon black. Therefore, the inventors investigated the factors behind "(3) resistance to catalytic reaction" by examining the pore size distribution of gas adsorption in pores that are suitable for supporting the catalytic metal and at the same time, suitable for the penetration of the ionomer. As a result, they obtained the following findings.

[0030] (A) In porous activated carbon black as a carbon material for a catalyst support, the optimal pore size for ionomer penetration and catalytic metal loading can be quantitatively evaluated by the pore size distribution of nitrogen gas adsorption, which selectively forms only those pore sizes. Specifically, for a pore structure in which the catalytic metal is loaded in the pores and the ionomer can easily penetrate into the pores, it is important that the pore volume of pores with a pore size of 2 nm or more but less than 6 nm is large and the pore volume of pores with a pore size of 6 nm or more but 10 nm or less is as small as possible. (B) Oxygen-treated carbon black that satisfies requirement (A) can be obtained by subjecting raw carbon black to oxygen treatment. Here, oxygen treatment refers to a process in which raw carbon black is oxidized at a low temperature to form pores in the raw carbon black and simultaneously impart a large number of oxygen-containing functional groups to the pores. In the oxygen-treated carbon black, the pores with oxygen-containing functional groups are formed by the addition of water vapor or CO during the first activation. ２ It is presumed that the oxygen-containing functional groups serve to introduce activation gases such as CO₂ and CO₂ into the oxygen-treated carbon black, while at the same time forming a surface structure that facilitates activation. This results in a porous activated carbon black that satisfies requirements (C) to (E). (C) The pore structure of the activated carbon black created by steps (A) and (B) above is heat-treated in an inert atmosphere to enhance durability. However, this process has the side effect of collapsing the pores. If the carbon black is used as a catalyst support in this state, power generation characteristics (especially low-load characteristics) will be reduced, mainly due to the small pore volume and small BET specific surface area. After the heat treatment, water vapor or CO₂ is again used. ２ By performing the second activation with an activation gas such as the above, a pore structure close to that before the heat treatment can be formed while suppressing surface roughness, thereby obtaining a porous activated carbon black that satisfies requirements (F) to (I).

[0031] 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 that has excellent durability as well as power generation characteristics (particularly low-load characteristics). Furthermore, it has been found that the oxygen-treated carbon black and activated carbon black according to the present disclosure are carbon blacks suitable for obtaining carbon materials (i.e., porous activated carbon blacks) that have excellent durability as well as power generation characteristics (particularly low-load characteristics).

[0032] The oxygen-treated carbon black, activated carbon black, and carbon material for catalyst supports (i.e., porous activated carbon black) of the present disclosure will be described in detail below.

[0033] [Oxygen-Treated Carbon Black] Commercially available raw carbon black is considered to be pore-free, but in reality, the surface area due to nitrogen gas adsorption varies even for the same particle diameter. Smaller particle diameters tend to result in larger surface areas. When selecting raw carbon black from the perspective of the first activation, raw carbon black with a larger BET specific surface area will have a larger pore volume formed after the first activation and a larger BET specific surface area, given the same particle diameter. On the other hand, for the development of a pore structure through the first activation, it is preferable that the oxygen-treated carbon black, which is the target of the first activation, has a higher oxygen content. This phenomenon is probably due to the CO ２ This is thought to be because the portions that burn off due to oxidation correlate with the portions containing a large amount of oxygen. In other words, it is presumed that the crystallite portions with oxygen-containing functional groups become the starting points for selective oxidation during activation. As a treatment for imparting oxygen-containing functional groups (i.e., a treatment that simultaneously increases the oxygen content and BET specific surface area), the raw carbon black is subjected to oxygen treatment with air. Specifically, the raw carbon black is heat-treated under a flow of oxidizing gas containing oxygen as an oxidizing agent (e.g., oxidizing gas diluted with air and inert gas).

[0034] The oxidation-treated carbon black obtained by oxygen treatment suitable for such a purpose satisfies requirement (A), and preferably satisfies requirements (A) and (B).

[0035] (Requirement (A)) (A) The BET specific surface area calculated by nitrogen gas adsorption is S ＢＥＴ (m ２ / g), the oxygen content (mass%) is ＢＥＴ / 100 or more and 8.00 or less.

[0036] During the oxygen treatment of raw carbon black with an oxidizing gas, pores are formed in the raw carbon black, increasing the BET specific surface area. At the same time, various oxygen-containing functional groups are introduced onto the pore surfaces. It is believed that the type of functional group added varies depending on the temperature of the oxygen treatment. For example, carboxyl groups have the lowest thermal stability, and specifically, their abundance decreases when the oxygen treatment temperature is 350°C or higher. When the oxygen treatment temperature exceeds 500°C, the abundance of hydroxyl groups and lactone groups also decreases dramatically. Furthermore, oxygen-containing functional groups such as cyclic ethers and quinones become stable functional groups at high temperatures, i.e., when the oxygen treatment temperature is 500°C or higher.

[0037] The oxygen-treated carbon black after the oxygen treatment is then treated with, for example, water vapor or CO ２ When the first activation is performed at a temperature of 800°C or higher in an activation gas atmosphere, many oxygen-containing functional groups are converted to CO ２ The oxygen-containing functional group is released as a gas. This is thought to remove the carbon atoms on the surface of the pores to which the oxygen-containing functional group is attached, widening the pores by one carbon atom. Furthermore, when the oxygen-containing functional group is released, the aromatic ring is destroyed, which is thought to facilitate the first activation reaction.

[0038] The above effect occurs regardless of the type of oxygen-containing functional group, and the oxygen content of the oxygen-treated carbon black can be quantitatively determined depending on the development of pores due to the first activation.

[0039] Since the oxygen content of the oxygen-treated carbon black increases in a positive correlation with the BET specific surface area, the preferred range of the oxygen content is a function of the BET specific surface area. ＢＥＴ When the oxygen content is 100% by mass or more, pores of a specific pore size are developed in the first activation. The upper limit of the oxygen-treated carbon black is determined by the BET specific surface area, because excessive oxygen treatment causes surface roughness. Therefore, there is an upper limit to the oxygen content of the oxygen-treated carbon black depending on the upper limit of the BET specific surface area of ​​the oxygen-treated carbon black. Specifically, the upper limit of the oxygen content of the oxygen-treated carbon black is 8.00% by mass or less.

[0040] The oxygen content of the oxygen-treated carbon black is S ＢＥＴ If the oxygen content is less than 100% by mass, the amount of oxygen-containing functional groups in the oxygen-treated carbon black is too small to contribute to the development of pores with a specific pore size through the first activation. As a result, power generation characteristics (particularly low-load characteristics) are not improved. If the oxygen content of the oxygen-treated carbon black exceeds 8.00% by mass, the surface roughness of the oxygen-treated carbon black is too great, resulting in non-uniformity in the coating of the ionomer on the porous activated carbon black. As a result, the amount of ionomer that penetrates into the pores decreases, reducing catalyst utilization and ultimately resulting in a deterioration in power generation characteristics (particularly low-load characteristics).

[0041] The lower limit of the oxygen content of the oxygen-treated carbon black is S ＢＥＴ / 90 mass % or more is preferable, and S ＢＥＴ The upper limit of the oxygen content of the oxygen-treated carbon black is preferably 7.50% by mass or less, more preferably 7.00% by mass or less.

[0042] The BET specific surface area is a value measured by the method described in the Examples section below.

[0043] (Requirement (B)) (B) The BET specific surface area calculated by nitrogen gas adsorption is S ＢＥＴ (m ２ / g), and the primary particle diameter of the oxygen-treated carbon black is D (nm), S ＢＥＴ (m ２ / g) is 5500 / D or more and 500 or less.

[0044] BET specific surface area S of oxygen-treated carbon black ＢＥＴ (m ２ / g) is calculated by assuming that the density of the oxygen-treated carbon black is constant. For example, commercially available furnace black has a density of 1 / 2 g, which is expressed by the formula: ＢＥＴ= 2400 / DF (where DF is the primary particle size (nm) of the carbon black in the furnace black). The BET specific surface area of ​​the oxygen-treated carbon black is the sum of the BET specific surface area of ​​the raw carbon black and the BET specific surface area of ​​the pores introduced by the oxygen treatment. The added BET specific surface area is also inversely proportional to the primary particle size.

[0045] Therefore, in order to have a minimum effect on the development of pores of a specific pore size in the first activation, the BET surface area S ＢＥＴ The lower limit is 5500 / Dm ２ The BET surface area S of the oxygen-treated carbon black is preferably 1 / g or more. ＢＥＴ The upper limit is 500m ２ The BET surface area S of the chemically treated carbon black is preferably 1 / g or less. ＢＥＴ 500m ２ If the surface roughness of the oxygen-treated carbon black exceeds 1 / g, the surface roughness of the oxygen-treated carbon black becomes too large, causing non-uniformity in the coating of the ionomer on the porous activated carbon black, which results in a decrease in the amount of ionomer that penetrates into the pores, lowering the catalyst utilization rate and ultimately resulting in a deterioration in power generation characteristics (especially low load characteristics).

[0046] BET surface area S of oxygen-treated carbon black ＢＥＴ The lower limit is 5600 / Dm ２ / g or more is more preferable, and 5800 / Dm ２ / g or more is more preferable.

[0047] BET surface area S of oxygen-treated carbon black ＢＥＴ The upper limit is 480m ２ / g or less is preferable, and 460m ２ / g or less is more preferable.

[0048] The primary particle diameter is a value measured by the method described in the Examples below. The primary particle diameter of the oxygen-treated carbon black is equivalent to the primary particle diameter of the raw material carbon black, and is preferably 20 nm or more and 80 nm or less.

[0049] [Activated Carbon Black] The pore structure of porous activated carbon black suitable for a catalyst carrier must have the following characteristics: (1) a large number of sites for supporting the catalytic metal (large BET coverage area); (2) a large pore volume with pore diameters of 2 to 5 nm, which is suitable for accommodating the catalytic metal, and (3) only pores with the necessary pore diameters are present, and the pore volume with small pore diameters of 6 to 10 nm, which corresponds to surface roughness that leads to a decrease in power generation characteristics (particularly low load characteristics), is relatively small compared to the pore volume with pore diameters of 2 to 6 nm.

[0050] The activated carbon black of the present disclosure, which is an intermediate for the porous activated carbon black used as a catalyst support and is suitable for such purposes, satisfies the following requirements (C), (D), and (E).

[0051] (Requirement (C)) (C) BET specific surface area (m) calculated by nitrogen gas adsorption isotherm measurement ２ / g) is 700 or more and 1500 or less.

[0052] The BET specific surface area of ​​activated carbon black is 700m ２ If the BET specific surface area of ​​the activated carbon black is less than 1500 m / g, the BET surface area of ​​the activated carbon black after the heat treatment becomes too small. Therefore, a sufficient BET surface area without surface roughness cannot be obtained in the second activation. As a result, the power generation characteristics (especially low load characteristics) deteriorate. ２ If the carbon black has a thickness exceeding 1 / g, the carbon walls forming the pores will have a thickness of several carbon layers. Therefore, even if activated carbon black is heat-treated to increase the crystallinity, the carbon layer thickness is too thin to improve durability.

[0053] The lower limit of the BET specific surface area of ​​activated carbon black is 750 m ２ / g or more is preferable, and 800m ２ The upper limit of the BET specific surface area of ​​the activated carbon black is 1450 m ２ / g or less is preferable, and 1400m ２ / g or less is more preferable.

[0054] The BET specific surface area is a value measured by the method described in the Examples section below.

[0055] (Requirement (D)) (D) In ​​the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of pores having a pore diameter of 2 nm or more and less than 6 nm is calculated as Σ ２－６ When this is the case, Σ ２－６ is equal to or greater than 0.22 and less than 1.00.

[0056] Integrated value of pore volume of activated carbon black Σ ２－６ When the integrated value Σ of the pore volume of the porous activated carbon black obtained by subjecting the activated carbon black to the heat treatment and the second activation is less than 0.22, ２－６ This reduces the amount of catalytic metal carried per unit mass of porous activated carbon black, and the amount of carbon increases to maintain a constant amount of catalytic metal. This in turn increases the thickness of the corresponding catalyst layer. An increase in catalyst layer thickness inhibits gas diffusion within the catalyst layer, resulting in a decrease in power generation characteristics (especially low load characteristics). The integrated value Σ of the pore volume of activated carbon black ２－６ When the ratio is 1.00 or more, the thickness of the carbon walls forming the pores becomes very thin. Therefore, even if high crystallization is attempted by heat treatment of activated carbon black, the carbon layer lamination thickness is too thin to improve durability.

[0057] Integrated value of pore volume of activated carbon black Σ ２－６ The lower limit of the integrated value Σ of the pore volume of the activated carbon black is preferably 0.23 or more, and more preferably 0.24 or more. ２－６ The upper limit of is preferably 0.95 or less, more preferably 0.90 or less.

[0058] The integrated value of the pore volume in the mesopore distribution, Σ ２－６ is a value measured by the method described in the Examples below.

[0059] (Requirement (E)) (E) In the mesopore distribution obtained by analyzing a nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of pores having a pore diameter of 2 nm or more and less than 6 nm is calculated as Σ ２－６ , the integrated value of the pore volume of pores with a pore diameter (i.e., pore diameter) of 6 nm or more and less than 10 nm is Σ ６－１０ , then Σ ６－１０ / Σ ２－６ is 0.100 or more and 0.490 or less.

[0060] Activated carbon black ratio Σ ６－１０ / Σ ２－６ The lower limit of the above is to excessively introduce micropores into the activated carbon black and to prevent the introduction of water vapor or CO ２ Even if the first activation is carefully carried out using an activation gas such as ６－１０ / Σ ２－６ The lower limit of the ratio Σ of activated carbon black is 0.100, and the closer to the lower limit, the more the power generation characteristics (particularly low load characteristics) are improved. ６－１０ / Σ ２－６ If the ratio exceeds 0.490, the surface roughness of the activated carbon black becomes too large, causing non-uniformity in the coating of the ionomer on the porous activated carbon black, resulting in a decrease in the amount of ionomer that penetrates into the pores, lowering the catalyst utilization rate and ultimately resulting in a deterioration in power generation characteristics (especially low load characteristics).

[0061] Activated carbon black ratio Σ ６－１０ / Σ ２－６ The lower limit of the ratio Σ of activated carbon black is preferably 0.110 or more, and more preferably 0.120 or more. ６－１０ / Σ ２－６ The upper limit of is preferably 0.480 or less, more preferably 0.470 or less.

[0062] In addition, the ratio Σ in the mesopore distribution ６－１０ / Σ ２－６ is a value measured by the method described in the Examples below.

[0063] [Carbon material for catalyst carriers (porous activated carbon black)] The pore structure of porous activated carbon black suitable for catalyst carriers is the same as that of activated carbon black, which is an intermediate. However, the pore structure of porous activated carbon black is required to be more developed in order to obtain a pore structure with a certain pore volume after increasing the crystallinity (i.e., durability) through heat treatment and second activation of the activated carbon black.

[0064] Porous activated carbon black suitable for such a purpose as a catalyst support satisfies the following requirements (F), (G), (H) and (I).

[0065] (Requirement (F)) (F) BET specific surface area (m) measured by nitrogen gas adsorption ２ / g) is 400 or more and 1200 or less.

[0066] The BET specific surface area of ​​the porous activated carbon black is 400 m ２ If the BET specific surface area of ​​the porous activated carbon black is less than 1200 m / g, it will be impossible to support as many catalytic metals as possible within the particle, which is an advantage of the porous activated carbon black. As a result, the number of porous activated carbon black particles required to support the same number of catalytic metals will increase. In other words, the catalyst layer will become thicker. As a result, the diffusion distance of the oxidizing gas within the catalyst layer will increase, leading to a deterioration in low load characteristics. ２ If the pore size exceeds 1 / g, the thickness of the carbon wall forming the pore structure becomes thin. Specifically, the average number of layers of the carbon net plane becomes 3 or less, resulting in weak mechanical strength. Furthermore, when the carbon wall is oxidized and consumed by a nano-sized catalytic metal, the number of layers becomes thin, making the structure prone to destruction even though the amount of carbon consumed is small. This accelerates the deterioration of power generation characteristics due to durability.

[0067] The lower limit of the BET specific surface area of ​​the porous activated carbon black is 450 m ２ / g or more is preferable, and 500m ２ The upper limit of the BET specific surface area of ​​the porous activated carbon black is 1150 m ２ / g or less is preferable, and 1100m ２ / g or less is more preferable.

[0068] The BET specific surface area is a value measured by the method described in the Examples section below.

[0069] (Requirement (G)) (G) In the mesopore distribution obtained by analyzing a nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of pores having a pore diameter of 2 nm or more and less than 6 nm is calculated by Σ ２－６ When this is the case, Σ ２－６ is 0.20 or more and less than 0.70.

[0070] Integrated value of pore volume of porous activated carbon black Σ ２－６ When the pore volume of the porous activated carbon black is less than 0.20, the pore volume of the porous activated carbon black becomes smaller. As a result, the amount of catalytic metal supported per unit mass of the porous activated carbon black decreases, and the carbon amount increases to maintain a constant amount of catalytic metal. This results in an increase in the thickness of the corresponding catalyst layer. An increase in the thickness of the catalyst layer inhibits gas diffusion within the catalyst layer, resulting in a deterioration in power generation characteristics (especially low load characteristics). The integrated value Σ of the pore volume of the porous activated carbon black ２－６ If the value is 0.70 or more, the thickness of the carbon walls forming the pores becomes very thin, and therefore durability cannot be improved.

[0071] Integrated value of pore volume of porous activated carbon black Σ ２－６ The lower limit of the integrated value Σ of the pore volume of the porous activated carbon black is preferably 0.22 or more, more preferably 0.23 or more, and even more preferably 0.24 or more. ２－６ The upper limit of is preferably 0.68 or less, more preferably 0.65 or less.

[0072] The integrated value of the pore volume in the mesopore distribution, Σ ２－６ is a value measured by the method described in the Examples below.

[0073] (Requirement (H)) (H) In the mesopore distribution obtained by analyzing a nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６, the integrated value of the pore volume of pores with a diameter of 6 nm or more and less than 10 nm is Σ ６ －１０ , then Σ ６－１０ / Σ ２－６ is 0.120 or more and 0.500 or less.

[0074] Ratio of porous activated carbon black Σ ６－１０ / Σ ２－６ The lower limit of the above is set to be such that the introduction of micropores into the porous activated carbon black is excessive and the amount of water vapor or CO ２ Even if the second activation with an activation gas such as ６－１０ / Σ ２－６ The lower limit of the ratio Σ is 0.120, and the closer it is to the lower limit, the more the power generation characteristics (particularly low load characteristics) improve. ６－１０ / Σ ２－６ If the surface roughness of the porous activated carbon black is too large, the ionomer coating on the porous activated carbon black becomes non-uniform, resulting in a decrease in the amount of ionomer that penetrates into the pores, lowering the catalyst utilization rate and ultimately leading to a deterioration in power generation characteristics (particularly low load characteristics).

[0075] Ratio of porous activated carbon black Σ ６－１０ / Σ ２－６ The lower limit of the ratio Σ of the porous activated carbon black is preferably 0.125 or more, and more preferably 0.130 or more. ６－１０ / Σ ２－６ The upper limit of is preferably 0.380 or less, more preferably 0.370 or less, and even more preferably 0.360 or less.

[0076] In addition, the ratio Σ in the mesopore distribution ６－１０ / Σ ２－６ is a value measured by the method described in the Examples below.

[0077] (Requirement (I)) (I) In the Raman spectrum obtained by Raman spectroscopy, －１ The intensity of the D band of Ｄ , 1560-1620cm －１The G band intensity of Ｇ When I Ｄ / I Ｇ is 1.20 or more and 2.20 or less.

[0078] The durability of porous activated carbon black as a carbon material for catalyst supports must be such that it can withstand two types of oxidative attenuation when held at a high potential exceeding 1 V: (1) oxidative attenuation at the edges of the porous activated carbon black, and (2) localized oxidative attenuation at the site in contact with the nano-sized catalytic metal when the porous activated carbon black is supported. A measure to enhance this durability is to improve the crystallinity of the porous activated carbon black. Improving the crystallinity increases the size of the carbon network surface and the number of layers, thereby improving the resistance of the porous activated carbon black to oxidative attenuation.

[0079] In the Raman spectrum of the porous activated carbon black obtained by Raman spectroscopy, the D band peak (1300 to 1360 cm ) reflecting the size of the edge area of ​​the carbon network plane is observed. －１ ) and the G band peak (1560-1620 cm ) which reflects the size of the carbon network plane and the number of layers. －１ From the spectrum of the two peaks, I and G, it is possible to obtain information about the crystallinity of the porous activated carbon black. That is, it is generally believed that the area of ​​the D band peak and the area of ​​the G band peak correspond to the volume of the amorphous region and the volume of the crystalline region, respectively, contained in the carbon material to be measured. In this specification, the area of ​​the peak in the Raman spectrum is referred to as the intensity. Therefore, the intensity I of the D band Ｄ , the G band intensity is I Ｇ When the intensity ratio is: I Ｄ / I Ｇ The activated carbon black obtained by the first activation is heat-treated in an inert atmosphere at 1400 to 1900°C (also called graphitization treatment), and the intensity ratio I of the D band to the G band of the porous activated carbon black obtained by the second activation is Ｄ / I Ｇ sensitively reflects the change in crystallinity due to heat treatment.

[0080] Therefore, the intensity ratio I of the porous activated carbon black Ｄ / I Ｇ When the intensity ratio I of the porous activated carbon black is 1.20 or more and 2.20 or less, the crystallinity is increased and the durability is improved. Ｄ / I Ｇ If the intensity ratio I of the porous activated carbon black is less than 1.20, the requirements (C) to (H) cannot be maintained, and the power generation characteristics (particularly the low load characteristics) deteriorate. Ｄ / I Ｇ If the crystallinity is greater than 2.20, the degree of crystallinity is too low and no improvement in durability is observed.

[0081] Intensity ratio I of porous activated carbon black Ｄ / I Ｇ is preferably 1.20 or more and 2.10 or less, and more preferably 1.20 or more and 2.00 or less.

[0082] In addition, the intensity ratio I Ｄ / I Ｇ is a value measured by the method described in the Examples below.

[0083] <Method for producing oxygen-treated carbon black, activated carbon black, and carbon material for catalyst supports in polymer electrolyte fuel cells (porous activated carbon black)> Hereinafter, an example of a method for producing oxygen-treated carbon black, activated carbon black, and carbon material for catalyst supports in polymer electrolyte fuel cells (porous activated carbon black) will be described.

[0084] The method for producing a carbon material for a catalyst support (porous activated carbon black) according to the present disclosure comprises the following four steps: Oxygen treatment step: an oxygen treatment step in which raw carbon black is oxygen-treated to obtain oxygen-treated carbon black; First activation step: a first activation step in which the oxygen-treated carbon black is subjected to a first activation to obtain activated carbon black; Heat treatment step: a heat treatment step in which the activated carbon black is heat-treated to obtain heat-treated activated carbon black; Second activation step: a second activation step in which the heat-treated activated carbon black is subjected to a second activation to obtain porous activated carbon black.

[0085] In the method for producing a carbon material for a catalyst support (porous activated carbon black) according to the present disclosure, a carbon material for a catalyst support (porous activated carbon black) that satisfies requirements (F) to (I) can be obtained through the above steps.

[0086] The method for producing activated carbon black according to the present disclosure includes the oxygen treatment step and the first activation step, and by undergoing these steps, activated carbon black that satisfies requirements (C) to (E) can be obtained.

[0087] The method for producing oxygen-treated carbon black according to the present disclosure includes the oxygen treatment step described above. By undergoing the steps described above, oxygen-treated carbon black that satisfies requirement (A) (preferably requirements (A) to (B)) can be obtained.

[0088] Each step will be described in detail below. First, the raw material carbon black used will be described.

[0089] (Raw Carbon Black) As the raw carbon black, carbon black that satisfies the two predetermined structures described below, namely, the primary particle size and the three-dimensional structure (an aggregate structure formed by linked primary particles) can be suitably used.

[0090] Primary Particle Diameter The size of the voids in the catalyst layer is determined by the three-dimensional structure and primary particle diameter of the raw carbon black. That is, because the primary particles are connected to form the three-dimensional structure, the primary particle diameter x the number of strings = void size. If the three-dimensional structure is developed and the primary particle diameter is 20 nm or greater, gas diffusion in the catalyst layer becomes rate-limiting and the power generation performance does not deteriorate. That is, the preferred range of primary particle diameter is 20 nm to 80 nm. Since it becomes difficult to develop the three-dimensional structure when the primary particle diameter exceeds 80 nm, 80 nm is the practical limit for manufacturing. Pore formation by the first activation is presumed to occur from the outside to the inside, and since the surface area is continuously exposed to oxygen treatment, combustion loss is significant. Assuming this, the larger the primary particle diameter, the more likely it is that small pores will be formed internally, but relatively large pores will be formed near the surface. In fact, activation of raw carbon black with a large primary particle diameter results in weaker pore development, even with mass reduction, compared to smaller particle diameters. That is, the larger the primary particle size, the more difficult it is to increase the BET specific surface area. On the other hand, although the mechanism is not entirely clear, raw carbon black with a larger primary particle size has higher resistance to oxidative attenuation than raw carbon black with a smaller primary particle size, assuming the same crystallinity as measured by Raman or X-ray diffraction. In other words, the larger the primary particle size, the more important durability becomes. In particular, raw carbon black with a primary particle size exceeding 40 nm is effective in improving durability. Raw carbon black with a primary particle size of 50 nm or more is effective in significantly improving durability, and raw carbon black with a primary particle size exceeding 60 nm is significantly effective in improving durability.

[0091] The primary particle diameter of raw carbon black is one of the basic physical properties, and the primary particle diameter values ​​in the carbon black manufacturer's catalog are referenced. However, if the carbon black manufacturer's catalog value cannot be referenced, the arithmetic mean value of the primary particle diameter is calculated from images of primary particles measured with an electron microscope, as recommended by the Carbon Black Association, i.e., the method described in the Carbon Black Yearbook. More specifically, "i. Electron microscope photography method," "ii. Particle size measurement," and "iii. Particle size calculation method," page 176 of the Carbon Black Handbook (edited by the Carbon Black Association, first edition 1971), were referenced. To obtain a statistical average, the sizes of at least 100 primary particles are measured, and the arithmetic mean is determined as the primary particle diameter. The arithmetic mean diameter is calculated using the following formula: d = Σn ｉ di / Σn ｉ , where n ｉ is the particle diameter d ｉ is the number of.

[0092] Three-dimensional structure: Porous activated carbon black with a well-developed three-dimensional structure is preferred as a structure suitable for a catalyst support in a fuel cell. When a catalyst layer is formed with this three-dimensional structure, the catalyst layer becomes highly porous with voids, and the diffusion rate of oxidizing gas increases. Examples of physical properties that reflect the three-dimensional structure include DBP oil absorption, BET specific surface area, and mercury intrusion distribution measured by mercury porosimetry.

[0093] DBP oil absorption is an industrial index of the typical colloidal physical properties of carbon black, and is the value listed in the catalog. The physical property specifications in this disclosure also use the value listed in the physical property table of the carbon black manufacturer. A specific DBP oil absorption value is preferably 80 mL / 100 g or more, more preferably 100 mL / 100 g, and even more preferably 120 mL / 100 g. Since the specific gravity of raw carbon black is approximately 1.8 g / mL, if the DBP oil absorption is considered to correspond to the voids in the catalyst layer, a DBP oil absorption of 80 mL / 100 g corresponds to voids 1.4 times or more the volume of the raw carbon black. If the DBP oil absorption is less than 80 mL / 100 g, the development of the three-dimensional structure is too small, resulting in poor low-load performance. On the other hand, the upper limit of DBP oil absorption is 180 mL / 100 g, which is the theoretical upper limit in manufacturing. The DBP oil absorption indicates the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black, and is a value defined in ASTM (American Standard Test Method) D2414-6TT.

[0094] The BET specific surface area is the most basic physical property of carbon black. The BET specific surface area of ​​the raw carbon black affects the activation in the first activation treatment step. The specific BET specific surface area is preferably 20 to 200 m ２ / g, more preferably 25 to 180 m ２ The BET specific surface area is a value measured by the method described in the Examples section below.

[0095] The evaluation of the three-dimensional structure by mercury porosimetry is performed by converting the hydrostatic pressure applied to mercury into pore diameters when assuming a cylindrical shape using the surface tension of mercury against the raw carbon black, and then obtaining the distribution of the integrated values ​​of the pore volumes larger than the pore diameters on the horizontal axis and the vertical axis, respectively. Raw carbon black with a three-dimensional structure absorbs mercury proportional to the pore volume at a relative injection pressure corresponding to the pore size created by the three-dimensional structure, so the three-dimensional structure can be quantitatively evaluated from the pore size distribution of the amount of mercury absorbed. Specifically, the increment in the amount of mercury absorbed when the mercury injection pressure is increased from 10 MPa (corresponding to pores of approximately 10 nm) to 100 MPa (corresponding to pores of approximately 100 nm) is preferably 0.5 to 1.5 mL / g, taking into account the DBP oil absorption appropriate for the pores in the catalyst layer described above. If the increment in the amount of mercury is less than 0.5 mL / g, the development of the three-dimensional structure is too small, resulting in reduced low-load performance. On the other hand, the increase in the amount of mercury of 1.5 mL / g is the upper limit in principle in terms of production.

[0096] (Oxygen Treatment Step) The oxygen treatment step is a step preceding the first activation step, in which micropores are introduced into the raw carbon black by oxygen treatment. The role of the oxygen treatment step is to obtain oxygen-treated carbon black in which pores are developed by the first activation step. Specifically, the role of the oxygen treatment step is to obtain oxygen-treated carbon black in which pores are developed by the first activation step, thereby increasing the BET surface area and pore volume of the pores, which are factors in improving power generation characteristics, and preventing the development of pores that cause surface roughness that deteriorates power generation characteristics. Note that the pores that improve power generation characteristics are pores with a pore diameter of 2 nm or more and less than 6 nm, and the pores that cause surface roughness that deteriorates power generation characteristics are pores with a pore diameter of 6 nm or more and 10 nm or less.

[0097] In order to realize the function of oxygen treatment, i.e., pore development by the first activation, the required property of the oxygen-treated carbon black is the oxygen content (preferably the oxygen content and the BET specific surface area).The oxygen treatment can increase the oxygen content (preferably the oxygen content and the BET specific surface area).

[0098] Here, both the oxygen treatment and the first activation have the function of forming pores (i.e., making the carbon black porous). However, the oxygen treatment temperature in the oxygen treatment is lower than the activation temperature in the first activation. Because the oxygen treatment is a low-temperature reaction, oxygen-containing functional groups are constantly present on the surface of the raw carbon black during the oxidation reaction. As a result, many oxygen-containing functional groups are present on the pore surfaces of the oxygen-treated carbon black. In other words, the oxygen content of the oxygen-treated carbon black increases almost in proportion to the BET specific surface area. It is believed that the oxygen-containing functional groups have the effect of promoting activation in the first activation. By the first activation, the oxygen-containing functional groups are converted into CO and CO. ２ The first activation step increases the BET surface area and pore volume of the pores, which are factors that improve power generation performance, and oxygen-treated carbon black is obtained that does not develop pores that cause surface roughness that deteriorates power generation performance.

[0099] Under oxygen treatment conditions that allow control of the oxygen content (preferably the oxygen content and BET specific surface area), the upper limit of the oxygen treatment temperature is restricted, and is preferably 500°C or lower, more preferably 450°C or lower. If the oxygen treatment temperature exceeds 500°C, the oxidizing power becomes too high, causing significant surface combustion of the raw carbon black, and making it easier for large pores to form on the surface. As a result, it becomes difficult to satisfy requirements (E) and (H). At the same time, if the oxygen concentration is too high, the surface of the carbon black will burn and pore formation will not proceed, so there is an upper limit to the oxygen concentration depending on the temperature. Specifically, the optimal ranges for the oxygen concentration and the corresponding oxidation treatment temperature are as follows: If the oxygen concentration exceeds 50% by volume, the oxygen treatment temperature is preferably 250°C to 350°C. If the oxygen concentration is between 25% and 50% by volume, which is similar to that of air, the oxygen treatment temperature is preferably 300°C to 400°C. If the oxygen concentration is between 10% and 25% by volume, the oxygen treatment temperature is preferably 350°C to 450°C. If the oxygen concentration is less than 10% by volume, the oxygen treatment temperature is preferably 400°C to 500°C. The lower limit of the oxygen treatment temperature should be set at a temperature at which the time required for the oxygen treatment exceeds 100 hours. From the perspective of increasing the oxygen content, the oxygen treatment of raw carbon black is dominated by the oxygen treatment temperature. That is, as the oxygen treatment temperature increases, the oxygen content tends to decrease even if the BET specific surface area increases. This is presumably because, as the oxygen treatment temperature increases, the types of oxygen-containing functional groups that can exist stably and the amount of oxygen-containing functional groups present is limited. Specifically, the oxygen content drops to 0.5 mass % or less when the oxygen treatment temperature exceeds 500° C. Therefore, the upper limit of the oxygen treatment temperature is preferably 500° C. or less, and more preferably 450° C. or less.

[0100] The oxygen treatment time largely depends on the oxygen concentration and the oxygen treatment temperature, but can be, for example, 1 to 40 hours, provided that the oxygen concentration and the oxygen treatment temperature are within the above-mentioned ranges. The upper limit of the oxygen treatment time is, for example, 100 hours. If the oxygen treatment time exceeds 100 hours, the proportion of surface combustion of the raw material carbon black increases, making it difficult to achieve a pore structure that satisfies requirements (E) and (H).

[0101] From the viewpoint of providing oxygen, oxygen treatment using ozone can also be applied. However, since pores are not formed by oxygen treatment using ozone, it is preferable to ozone-treat the raw material carbon black after the oxygen treatment in an oxidizing gas containing ozone at a temperature of 100° C. or less.

[0102] Because oxygen treatment of raw carbon black using oxygen or ozone as the oxidizing gas is an exothermic reaction, careful attention must be paid to preventing thermal runaway due to the accumulation of reaction heat. Suitable equipment for oxygen treatment includes, for example, a rotary kiln or a fluidized bed, which forcibly contacts the gas with the raw carbon black. Rotary kilns and fluidized beds allow fresh oxidizing gas to come into contact with the raw carbon black, achieving uniform oxygen treatment in a short period of time. Fluidized beds, however, have a high gas utilization rate, allowing oxygen treatment to be completed in a short period of time. However, since the amount of heat generated per unit time and unit volume is large, it is important to design the equipment so that heat can be easily removed. For example, by increasing the floor area and limiting the vertical load of raw carbon black, the oxidizing gas itself can act as a heat removal medium for the reaction heat.

[0103] The effect of oxygen treatment is that the rate of surface combustion increases as the mass reduction rate increases. For example, when the BET specific surface area is 500 m ２ In other words, the pore structure formed by oxygen treatment is merely a pre-treatment, and the finishing treatment of the pore structure is carried out by using water vapor or CO after the oxygen treatment. ２ This is the primary activation.

[0104] (First activation step) In the first activation step, the oxygen-treated carbon black is made porous by the first activation. The activation mechanism of the oxygen-treated carbon black is considered to be as follows. The oxygen-treated carbon black is heated in a gas atmosphere containing water vapor (H ２ O), or CO ２By exposing the carbon black to an activation gas such as HCl and maintaining it at 800°C to 1100°C, the carbon atoms that make up the oxygen-treated carbon black are removed as CO. This reaction optimizes the reaction rate, selectively oxidizing and consuming the peripheral portions (edges) of the easily combustible condensed polycyclic aromatic rings in the several nanometer-sized crystallites that make up the oxygen-treated carbon black. As a result, gaps form between the crystallites, and the consumption of the crystallites continues inward, resulting in the formation of porous carbon black. This is the process by which carbon black is made porous through activation.

[0105] Increasing the activation treatment temperature increases the reaction rate, accelerating combustion near the surface that comes into contact with a high concentration of activation gas, while the concentration of activation gas diffusing inside becomes even lower, slowing down internal combustion. Appropriate reaction rate control is required to develop pores inside without changing the surface condition. ２ Oxygen is the most suitable activation gas because it can control the reaction rate over a wide range of temperatures. The reasons why oxygen activation is not industrially applicable are as follows: ２ The oxidation reaction of oxygen-treated carbon black with oxygen is an endothermic reaction, and the reaction does not proceed unless heat is applied. Therefore, it can be controlled by the amount of heat supplied, making it easy to scale up. On the other hand, the oxidation reaction of oxygen-treated carbon black with oxygen is an exothermic reaction, and if the heat generation is greater than the heat removal, the temperature at the reaction site rises monotonically, making the reaction difficult to control. Since this phenomenon accelerates with scale up, oxidation with oxygen is not suitable for mass production, and it is recommended to use water vapor or CO ２ As an activation gas, activation using

[0106] As long as a manufacturing process in which such an activation reaction can proceed can be realized, there are no restrictions on the activation device. To efficiently promote activation, it is desirable to increase the concentration of the activation gas on the surface of the oxygen-treated carbon black pellets. To achieve this, it is desirable to reduce the thickness of the boundary film of oxidizing gas formed near the surface of the oxygen-treated carbon black pellets, and it is effective to increase the relative velocity of the activation gas relative to the oxygen-treated carbon black pellets. A rotary kiln or fluidized bed, which is generally used in industrial production, is preferred because it can increase the uniformity of the activation gas within the furnace. Because it can increase the relative velocity of the activation gas relative to the oxygen-treated carbon black pellets, a fluidized bed is an excellent device in terms of gas utilization rate and reaction rate, and is particularly preferred.

[0107] The specific conditions for the first activation are to control the temperature according to the reaction strength of the activation gas. The activation gas is water vapor or CO ２ When water vapor is used as the activation gas, the preferred activation treatment temperature is 750 to 900°C. ２ When an activation gas containing 200 to 600 carbon black is used as the activation gas, a preferred activation treatment temperature is 800 to 950°C. To obtain activated carbon black that satisfies requirements (C) to (E), the mass loss rate of the carbon black in the oxygen treatment by the first activation is, for example, 50 to 85% by mass, preferably 60 to 80%. The treatment time required to reach such a mass loss rate is, for example, 5 to 100 hours, preferably 10 to 80 hours, and more preferably 20 to 80 hours. Under activation conditions under which the time required to reach a mass loss rate of 50% by mass is shorter than 5 hours, the BET specific surface area is smaller than, for example, when compared to when the time required to reach the same mass loss rate is 20 hours, and the integrated value Σ of the pore volume of pores with diameters of 2 nm or more and less than 6 nm is 0.01. ２－６ is small, or the ratio of the integrated value of the pore volume Σ ６－１０ / Σ ２－６becomes large. If the reaction rate is too high, the surface combustion of the oxygen-treated carbon black is relatively large compared to the internal combustion for forming internal pores, and part of the mass loss is consumed by surface combustion, resulting in a failure to increase the BET specific surface area. This is also because the pore volume of pores with diameters of 6 nm to less than 10 nm due to surface combustion increases. That is, to suppress surface combustion, it is preferable to lower the activation temperature and lengthen the activation time. Activation for a long time, such as when the time required for the mass loss rate to reach 50% by mass exceeds 100 hours, is undesirable because the reaction rate is too slow, causing surface combustion to prevail over internal combustion and suppressing the development of pores with diameters of 2 nm to less than 6 nm. For the reasons mentioned above, activation treatments performed at high activation temperatures and long activation times (e.g., activation at a temperature of 980°C or higher and for a time of 110 hours or longer) do not yield activated carbon black that satisfies requirements (E) and (H).

[0108] It is also preferable to activate under conditions where the activation gas pressure is increased. Because the activation gas concentration is high, the rate of the oxidation reaction increases almost in proportion to the concentration, and the activation time can be shortened without changing pore development, i.e., the BET specific surface area and pore size distribution, or without changing the surface combustion ratio. The activation time can be shortened in proportion to the pressure within a pressure range of up to several atmospheres. At pressures of 6 atmospheres or higher, the effect of the actual pressure increase is difficult to see, so a pressure of 6 atmospheres or less is preferred. The activation time when activated under pressurized conditions is, for example, 3 to 50 hours, preferably 5 to 30 hours, and more preferably 5 to 20 hours. The upper and lower limits of the activation time are determined to avoid the same phenomenon as when activated under normal pressure.

[0109] The above-described first activation step develops pores with diameters of 6 nm or more and less than 10 nm within the oxygen-treated carbon black, enabling the production of activated carbon black that satisfies requirements (C) to (E). During the heat treatment step to increase crystallinity, the texture and crystalline structure of the porous activated carbon black change toward a more stable graphite structure. As a result, the pores, which could be considered defects, change in a direction toward collapse. Therefore, the pore structure of the activated carbon black obtained in the first activation step must be more developed than the final desired pore structure, so that the desired pore structure is maintained even if the pores are collapsed during the heat treatment step.

[0110] (Heat Treatment Step) In the heat treatment step, the activated carbon black obtained in the first activation step is heat-treated. The catalyst support is exposed to a noble potential of 1 V or more in the operating environment of the fuel cell. Because the ionomer has sulfonic acid groups, the catalyst support coated with the ionomer is placed in a noble potential of 1 V or more and in a strongly acidic environment. When using porous activated carbon black in such an environment, thermodynamic stability cannot be expected, so the general approach is to increase its crystallinity as much as possible to rapidly avoid oxidative consumption.

[0111] To enhance the crystallinity of porous activated carbon black, it is common to heat treat it in an inert gas atmosphere or a reducing atmosphere. In the heat treatment step, for example, the activated carbon black obtained in the first activation step is subjected to a heat treatment step (i.e., graphitization step) at 1400°C to 1900°C for 10 minutes to 10 hours under an inert gas atmosphere at normal pressure (i.e., 1 atmosphere). Temperatures above 1900°C cause significant collapse of pores during heat treatment, so in practice, a temperature of 1900°C or less is preferred.

[0112] In the heat treatment step, the crystallinity of the activated carbon black can be increased by graphitizing the activated carbon black. More specifically, by subjecting activated carbon black that has been subjected to the first activation under the above-mentioned strong activation conditions to a heat treatment under the above-mentioned conditions, the crystallinity of the activated carbon black can be increased while maintaining the pores without collapse. This makes it possible to produce porous activated carbon black that satisfies requirement (I) in addition to requirements (F) to (H).

[0113] The heat treatment step is not particularly limited as long as it can heat the activated carbon black under the above conditions. Examples of the heating method include resistance heating, microwave heating, high-frequency heating, and furnace-type heating. The furnace type can be a graphitization furnace, a batch furnace, a tunnel furnace, or the like, and is not limited as long as it can achieve atmospheric pressure and an inert gas atmosphere.

[0114] (Second activation step) In the second activation step, the heat-treated activated carbon black is subjected to a second activation. The activation gas is water vapor or CO ２ In the second activation, the crystallites that have been reduced in size or burned away due to oxidative consumption in the first activation come into contact with each other due to thermal fluctuation, and chemical bonds are formed at the contact points, forming a structure in which the crystallites are linked together.

[0115] During the second activation process, the primary particle size generally shrinks and the shape changes from spherical to amorphous. As this occurs, the intercrystalline gaps become smaller, and the pore volume and BET specific surface area decrease. The second activation is a treatment to expand the reduced pores or reopen blocked pores. When heat-treated activated carbon particles are used as a catalyst support without the second activation process, their power generation characteristics (particularly low-load characteristics) are significantly inferior to those of porous activated carbon black after the second activation process. This is presumably because the reduced pore size makes it difficult for the ionomer to penetrate into the pores, resulting in a decrease in catalyst utilization and a decrease in power generation characteristics. Since the purpose of the second activation process is to expand the pores and reopen blocked pores, it is desirable to minimize the amount of carbon combustion during the second activation process. From this perspective, the mass loss rate during the second activation process is preferably 1 to 15% by mass, more preferably 3 to 12% by mass. The activation temperature and activation time suitable for the second activation are preferably 800°C to 950°C and several hours (e.g., 1 hour to 5 hours). More specifically, when the heat treatment temperature is greater than 1800°C and less than 1900°C, and the activation temperature for the second activation is greater than 900°C and less than 950°C, the activation time is preferably 1.5 hours to 5.0 hours. A high heat treatment temperature increases crystallinity and slows the progress of activation in the second activation. Therefore, there is a tendency to increase the activation temperature for the second activation. However, when the activation temperature for the second activation is greater than 900°C and less than 950°C, oxidation and attenuation of the carbon surface are likely to occur. Therefore, the activation time should be extended to minimize the rate of oxidation and attenuation of the surface. Therefore, the minimum activation time is preferably 1.5 hours to 5.0 hours. On the other hand, when the heat treatment temperature is 1800°C or less, the above considerations are not necessary.

[0116] <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 to, for example, 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.

[0117] 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).

[0118] 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 may 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.

[0119] 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)

[0120] 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.

[0121] 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.

[0122] 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)

[0123] 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.

[0124] 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 power generation characteristics (particularly low-load characteristics) and durability of the catalyst layer 160. This can also improve the power generation characteristics (particularly low-load characteristics) and durability of the polymer electrolyte fuel cell 100.

[0125] The catalyst loading rate in the catalyst layer 160 is not particularly limited, but is preferably 30% by mass or more and less than 80% by mass. A catalyst loading rate within this range further improves power generation characteristics (particularly low-load characteristics) and durability. Here, the catalyst loading rate is expressed as the mass percentage 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 catalyst support). If the catalyst loading rate is less than 30% by mass, it may be necessary to thicken the catalyst layer 160 to ensure practical use of the polymer electrolyte fuel cell 100. 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.

[0126] 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, the pore network and the electrolyte material network can coexist, resulting in improved power generation characteristics (particularly low-load characteristics) and durability. 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 power generation characteristics (particularly low-load characteristics) and durability may be reduced.

[0127] 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.

[0128] 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.

[0129] <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.

[0130] 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.

[0131] <Method of measuring each parameter> (Measurement of oxygen content) A few mg of sample was weighed out and subjected to elemental analysis using an elemental analyzer (fully automatic organic trace elemental analyzer "PerkinElmer 2400 II CHNS / O" (Inmedium Co., Ltd.)). The mass percentages of C, H, and N in the sample were analyzed, and the difference between the mass percentage of the total of C, H, and N and 100% was calculated as the mass percentage of O, which was then taken as the oxygen content (mass%).

[0132] (Measurement of nitrogen adsorption / desorption isotherm (BET specific surface area)) Approximately 30 mg of sample was weighed and vacuum dried at 120°C for 2 hours. Next, the sample was set in an automatic specific surface area measuring device (Microtrackbell, BELSORP MAX), and nitrogen adsorption / desorption isotherm was measured at a measurement temperature of liquid nitrogen temperature (approximately 77K) using nitrogen gas as an adsorbate. The BET specific surface area was calculated by the relative pressure P / P ratio in the nitrogen adsorption isotherm. ０ The BET value was calculated by BET analysis in the range of 0.05 to 0.15. The BET value was calculated using the calculation software attached to the device.

[0133] (Primary Particle Diameter) The primary particle diameter of the oxidation-treated carbon black was measured as follows. Reference was made to page 176 of the Carbon Black Handbook (edited by the Carbon Black Association, first edition published in 1971), sections "i. Electron Microscope Photography," "ii. Measurement of Particle Diameter," and "iii. Calculation Method of Particle Diameter." To calculate a statistical average, the sizes of at least 100 primary particles were measured, and the arithmetic mean was determined as the primary particle diameter D of the oxidation-treated carbon black. The arithmetic mean diameter was calculated using the following formula: D = Σnidi / Σni, where ni is the number of particles with a diameter di.

[0134] (Mesopore diameter distribution) The mesopore diameter distribution was analyzed by the BJH method. The mesopore diameter distribution was calculated using the HK method calculation software attached to the apparatus, and the integrated values ​​Σd of the pore volumes of pores with diameters (diameters) of 2 nm, 6 nm, and 10 nm or less were calculated. ＜２ , Σd ＜６ , Σd ＜１０ , was calculated (see Figure 1). ｄ＜６ -Σ ｄ＜２ Calculate the integrated value Σ of the pore volume of pores with a diameter of 2 nm or more and less than 6 nm ２－６(See Figure 2). Furthermore, Σd ＜１０ -Σ ｄ＜６ Calculate the value of Σ ｄ＜６ｎｍ -Σ ｄ＜２ｎｍ Divide by the integrated value Σ of the pore volume of pores with a diameter of 2 nm or more and less than 6 nm ２－６ and the integrated value Σ of the pore volume of pores with a diameter of 6 nm or more and less than 10 nm ６－１０ Ratio to Σ ６－１０ / Σ ２－６ (See Figure 2).

[0135] (Raman spectroscopy intensity ratio I Ｄ / I Ｇ Approximately 3 mg of the sample was weighed and taken, and the Raman spectrum was measured using a laser Raman spectrophotometer (manufactured by JASCO Corporation, NRS-3100 model). From the Raman spectrum obtained under the following measurement conditions, a band of 1300 to 1360 cm called the D band was observed. －１ and a peak in the range of 1560-1620 cm called the G band. －１ The peaks in the range of 1000 to 10000 were extracted, and the intensities of these two peaks were analyzed using the spectrum analysis software attached to the instrument. Ｄ and the G-band intensity I Ｇ The area of ​​the Raman peak reflects the amount of carbon material belonging to each band, so the area of ​​each peak (each band) when the peaks are separated using analysis software is used as the intensity. From these values, the intensity ratio I Ｄ / I Ｇ Measurement conditions: Excitation laser: 532 nm, laser power: 10 mW (sample irradiation power: 1.1 mW), microscope arrangement: backscattering, objective lens: ×100 magnification, spot diameter: 1 μm, exposure time: 30 sec, observed wave number: 2000 cm －１ ~300cm －１ , Number of times accumulated: 6 times.

[0136] <Experimental Example> (Raw Carbon Black) As raw carbon black, Niteron #200, Niteron #4500, and Niteron #SH manufactured by Nippon Steel Carbon Corporation, and Toka Black #4500 and GFY manufactured by Tokai Carbon Co., Ltd. were prepared, and these raw carbon blacks were subjected to the first activation step, heat treatment step, and second activation step described below.

[0137] On the other hand, as raw carbon black, Ketjenblack EC300J, EC600JD, and EC200L manufactured by Lion Corporation and Printex XE2B manufactured by Orion Co., Ltd. were prepared. These carbon blacks were used as carbon materials for catalyst supports and subjected to the evaluations described below (Reference Examples 1-1 to 1-4).

[0138] Table 1 below shows the primary particle size (arithmetic mean particle size), DBP oil absorption, and BET specific surface area values ​​for each of the raw carbon black materials cited from Carbon Black Yearbook No. 72 (2022), compiled by the Carbon Black Association, and posted on the Ketjen Black product website.

[0139]

[0140] <Oxygen Treatment Step> A quartz tube with an outer diameter of 50 mm and a fused quartz filter (pore size 40-50 μm) used as a dispersion plate was used as a reaction tube. Quartz wool was packed to a height of approximately 1 cm, and raw carbon black in a granulated state was placed on top of it. Approximately 20-25 g of quartz wool was charged, and dry air or a mixture of dry air and argon gas was flowed as an oxidizing gas from the bottom to the top of the reaction tube at a linear velocity of 1.0-3.0 cm / sec. The oxygen treatment temperature was selected carefully to avoid ignition due to heat accumulation caused by the exothermic reaction. Because the combustion rate differs depending on the type of raw carbon black, the conditions were carefully selected for each raw carbon black. Specifically, the raw carbon black shown in Table 1 was oxygen-treated at the oxygen concentration, oxygen treatment temperature, and mass reduction rate shown in Table 1. However, in the case of #200, which is highly flammable, the raw carbon black was oxygen-treated with an oxidizing gas mixture of oxygen and argon gas at a linear velocity of 0.5 to 1.0 cm / sec to achieve the oxygen concentration shown in Table 1, with the aim of reducing the heat generation and suppressing ignition. In the case of #SH and #GFY, which have large particle sizes and slow combustion rates, the raw carbon black was oxygen-treated with an oxidizing gas mixture of oxygen and argon gas at a linear velocity of 1.0 to 2.0 cm / sec to achieve the oxygen concentration shown in Table 1. In the case of #4500, which has an intermediate combustion rate between the two, the raw carbon black was oxygen-treated with an oxidizing gas mixture of oxygen and argon gas at a linear velocity of 0.7 to 1.5 cm / sec to achieve the oxygen concentration shown in Table 1. The primary particle diameter D of the resulting oxygen-treated carbon black was equivalent to the primary particle diameter of the raw carbon black.

[0141] EC300J, EC600JD, and XE2B are carbon blacks that have already been treated to make them porous, and their pore structure indicators are listed as reference examples for comparison with the experimental example after the first activation. EC200L is slightly activated and has a low BET surface area, but its BET surface area is similar to that of the oxygen-treated carbon black of the present disclosure. EC200L's pore structure indicators are listed as reference examples for comparison with the experimental example after the oxygen treatment.

[0142] <First activation step> A reaction tube was prepared by fusing a quartz filter as a dispersion plate inside a quartz tube with an outer diameter of 35 mm, placing quartz wool to a height of about 1 cm on the dispersion plate, and then placing 5 g to 15 g of oxygen-treated carbon black on top of that. The reaction tube was then set in a vertical electric furnace normally used at 1100°C. Before heating, argon gas was flowed from the bottom to the top of the reaction tube to replace the inside of the reaction tube with argon gas, and then the temperature was raised at a rate of 10°C / min. The reaction tube was heated to 850 to 950°C, and once the predetermined temperature was reached, CO was added. ２ The gas was switched to argon gas. The flow rate was adjusted so that the linear velocity was 1 to 2 cm / sec at the furnace temperature. After treatment for a predetermined time, the reaction tube was removed from the furnace, and the gas was simultaneously switched to argon gas and allowed to cool. After confirming that the temperature had cooled to approximately room temperature (25°C), the carbon black was removed and its mass was measured, and the mass reduction rate of the yield relative to the charged mass (charged mass / recovered mass) was calculated. The conditions for the first activation (activation temperature and activation time shown in Table 2) were adjusted so that the mass reduction rate was in the range of 55 to 80 mass%.

[0143] <Heat Treatment Step> A so-called heat treatment furnace using graphite as a heating element was used. The first activated carbon black was placed in a graphite crucible with a volume of approximately 100 cc. After the pressure was reduced and the atmosphere was replaced with argon gas, the temperature was increased at a rate of 10°C per minute with an argon flow rate sufficient to replace the furnace volume in several tens of minutes. After holding at the predetermined temperature for a certain period of time, the material was allowed to cool to near room temperature and then removed. The holding time at the treatment temperature was variable. The conditions are shown in Table 2.

[0144] <Second activation step> The basic treatment steps were the same as in the first activation step, with the activation time being set to 1 to 5 hours to reduce the mass loss rate. The specific treatment steps are described below. A reaction tube was prepared by fusion bonding a quartz filter as a dispersion plate inside a quartz tube with an outer diameter of 35 mm, and quartz wool was placed on the dispersion plate to a height of about 1 cm. 2 to 5 g of heat-treated activated carbon black was then placed on top of the quartz wool, and the reaction tube was then set in a vertical electric furnace normally used at 1100°C. Before heating, argon gas was flowed from the bottom to the top of the reaction tube to replace the inside of the reaction tube with argon gas, and the temperature was then raised at a rate of 10°C / min. The reaction tube was heated to 820 to 950°C, and once the predetermined temperature was reached, CO ２The gas was switched to argon gas. The flow rate was adjusted so that the linear velocity was 1 to 2 cm / sec at the furnace temperature. After treatment for a predetermined time, the reaction tube was removed from the furnace, and the gas was simultaneously switched to argon gas and allowed to cool. After confirming that the temperature had cooled to near room temperature, the carbon black was removed and its mass was measured, and the mass reduction rate of the yield relative to the charged mass (charged weight / recovered weight) was calculated. The conditions for the second activation treatment (activation temperature and activation time shown in Table 2) were adjusted so that the mass reduction rate was in the range of 3 to 20% by mass.

[0145] Through the above steps, a carbon material for a catalyst support (porous activated carbon black) was obtained for each example.

[0146] <Preparation of Membrane Electrode Assembly (MEA)> (Preparation of Catalyst) The carbon material for catalyst support (porous activated carbon black) of each example was added to an ethanol / water mixed solvent and dispersed by processing with an ultrasonic homogenizer for 2 minutes. A predetermined amount of a nitric acid solution of dinitrodiammine platinum complex was added thereto, and the platinum loading was adjusted to 40 mass %, and the mixture was stirred in an oil bath for 15 hours while maintaining a temperature several degrees lower than the boiling point. After processing, the mixture was filtered, dispersed again in distilled water, filtered again, and vacuum dried at 90°C for 5 hours to obtain a catalyst.

[0147] (Preparation of ink) An ionomer solution manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was diluted with ethanol to adjust the solid content concentration to 10% by mass, and then added dropwise to an ethanol solution in which a catalyst had been previously dispersed. Dispersion was further promoted using an ultrasonic homogenizer, and the mixture was stirred with 1 mm diameter glass beads for 10 to 15 hours. In this way, an ink for forming a catalyst layer was obtained.

[0148] <MEA Fabrication> The ink was uniformly applied to a Teflon (registered trademark) sheet using a sprayer and dried in an air circulating dryer at 60°C to prepare a decal with a catalyst layer formed thereon. Electrodes of a predetermined size of 36 mm were cut out from the decal. Two identical sheets were used as the positive and negative electrodes, and the positive and negative electrodes were placed on both sides of a Nafion membrane and heat-sealed. In this way, an MEA was obtained.

[0149] <Battery Evaluation> (Evaluation of power generation characteristics (low load characteristics)) Each MEA produced using the catalyst carrier carbon material (porous activated carbon black) of each example was assembled into a cell, which was then set in a fuel cell measuring device, and the performance of the fuel cell was evaluated according to the following procedure.

[0150] The oxidizing gas was supplied at a back pressure of 0.04 MPa by adjusting the pressure with a back pressure valve installed downstream of the cell, and air was supplied to the cathode side and pure hydrogen to the anode side so that the utilization rates were 40% and 70%, respectively. The cell temperature was set to 80°C, and the oxidizing gas supplied was bubbled with distilled water kept at 80°C in a humidifier at both the cathode and anode, and humidified gas at 80°C was supplied to the cell at 80°C to evaluate power generation.

[0151] Under these conditions, the load was gradually increased while an oxidizing gas was supplied to the cell, and the current density was increased to 100 mA / cm ２ The cell output voltage was measured after holding the cell at 100 mA / cm for 1 hour, and the cell was evaluated according to the following criteria of pass and fail. The results are shown in Table 2. [Pass Rank] A: Current density is 100 mA / cm ２ B: The cell voltage after 1 hour is 0.875 V or more. ２ C: The cell voltage after 1 hour is 0.872 V or more. ２ The cell voltage after 1 hour is 0.870 V or more. [Failure Rank] D: Current density is 100 mA / cm ２ The cell voltage after 1 hour is less than 0.870V.

[0152] (Evaluation of durability) In the above cell, while the anode was left as it was, argon gas was passed through the cathode under the same humidification conditions as above, and the cell voltage was set to 1.0 V and held for 4 seconds, and then set to 1.3 V and held for 4 seconds, repeating this cycle (repeated square-wave voltage fluctuation). After 4,000 cycles of this repetitive square-wave voltage fluctuation, durability was investigated in the same manner as in the evaluation of power generation characteristics described above. Evaluation was performed using the following criteria of pass and fail ranks. The results are shown in Table 2. [Pass rank] A: Current density 100 mA / cm ２ B: The cell voltage after 1 hour is 0.820 V or more at a current density of 100 mA / cm ２ C: The cell voltage after 1 hour is 0.815 or higher. C: The current density is 100 mA / cm ２ The cell voltage after 1 hour is 0.810 V or more. [Failure Rank] D: Current density is 100 mA / cm ２ The cell voltage after 1 hour is less than 0.810V.

[0153]

[0154]

[0155]

[0156]

[0157] The above results show that the carbon material for catalyst carriers (porous activated carbon black) according to this example has excellent power generation characteristics (particularly low-load characteristics) and durability compared to the carbon material for catalyst carriers according to the comparative examples. It is also clear that the oxygen-treated carbon black and activated carbon black according to this example are suitable for producing the carbon material for catalyst carriers (porous activated carbon black) according to this example, which has excellent power generation characteristics (particularly low-load characteristics) and durability. The reference examples also show that Ketjenblack EC300J, EC600JD, and EC200L manufactured by Lion Corporation and Printex XE2B manufactured by Orion Co., Ltd. do not provide sufficient power generation characteristics (particularly low-load characteristics) and durability.

[0158] Generally, when raw carbon black with a particle size exceeding 40 nm is used, pores do not develop during activation treatment, and the BET surface area is not likely to increase. However, oxygen treatment was performed to form pores suitable for use in catalyst supports, even with raw carbon black with a primary particle size of 72 nm, and it was confirmed that a carbon material for catalyst supports (porous activated carbon black) with excellent power generation characteristics (particularly low-load characteristics) can be obtained. Furthermore, even when raw carbon black with a primary particle size of 29 nm is used, optimal oxygen treatment, activation treatment, heat treatment, and second activation treatment can be performed to obtain a carbon material for catalyst supports (porous activated carbon black) with excellent power generation characteristics (particularly low-load characteristics). These results confirm that the use of raw carbon black with a primary particle size of 20 nm to 80 nm can produce a carbon material for catalyst supports (porous activated carbon black) with excellent power generation characteristics (particularly low-load characteristics).

[0159] 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

[0160] The disclosure of Japanese Patent Application No. 2023-108954 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. Oxygen-treated carbon black that satisfies the following requirement (A): (A) The BET specific surface area calculated by nitrogen gas adsorption is S ＢＥＴ (m ２ / g), the oxygen content (mass%) is S ＢＥＴ / 100 or more and 8.00 or less.

2. The oxygen-treated carbon black according to claim 1, further satisfying the following requirement (B): (B) a BET specific surface area calculated by nitrogen gas adsorption is S ＢＥＴ (m ２ / g), the primary particle diameter of the oxygen-treated carbon black is D (nm), ＢＥＴ (m ２ / g) is 5500 / D or more and 500 or less.

3. Activated carbon black that simultaneously satisfies the following requirements (C), (D), and (E): (C) BET specific surface area (m2) calculated by nitrogen gas adsorption isotherm measurement ２ (D) In ​​the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of the pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ Then, Σ ２－６ (E) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of the pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ , the integrated value of the pore volume of the pores having a diameter of 6 nm or more and less than 10 nm is Σ ６－１０ , then,Σ ６－１０ / Σ ２－６ is equal to or greater than 0.100 and equal to or less than 0.

490.

4. A carbon material for a catalyst support in a polymer electrolyte fuel cell, comprising a porous activated carbon black that simultaneously satisfies the following requirements (F), (G), (H), and (I): (F) BET specific surface area (m2) measured by nitrogen gas adsorption measurement ２ (G) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ Then, Σ ２－６ (H) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, the integrated value of the pore volume of the pores having a diameter of 2 nm or more and less than 6 nm is Σ ２－６ , the integrated value of the pore volume of the pores having a diameter of 6 nm or more and less than 10 nm is Σ ６－１０ , then,Σ ６－１０ / Σ ２－６ (I) In the Raman spectrum obtained by Raman spectroscopy, －１ The intensity of the D band of I Ｄ , 1560-1620cm －１ The G band intensity of I Ｇ Then, I Ｄ / I Ｇ is equal to or greater than 1.20 and equal to or less than 2.

20.

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 claim 4.

6. A fuel cell comprising the catalyst layer for a polymer electrolyte fuel cell according to claim 5.

7. The fuel cell according to claim 6, wherein the catalyst layer for the polymer electrolyte fuel cell is a catalyst layer on the cathode side.

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