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

Technical Field

[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.

Background Art

[0002] A polymer electrolyte fuel cell, which is a type of fuel cell, includes a pair of catalyst layers disposed on both sides of a polymer electrolyte membrane, a gas diffusion layer disposed outside each catalyst layer, and a separator disposed outside each gas diffusion layer. Among the pair of catalyst layers, one catalyst layer serves as the anode of the polymer electrolyte fuel cell, and the other catalyst layer serves as the cathode of the polymer electrolyte fuel cell. In a normal polymer electrolyte fuel cell, a plurality of unit cells having the above-described components are stacked to obtain a desired output.

[0003] A fuel gas such as hydrogen is introduced into the separator on the anode side. The gas diffusion layer on the anode side diffuses the fuel and then introduces it into the anode. The anode includes a catalyst component, a catalyst support that supports the fuel cell catalyst, and an electrolyte material having proton conductivity. Hereinafter, the catalyst component that promotes the power generation reaction (oxidation reaction or reduction reaction described later) in the fuel cell is also referred to as the "fuel cell catalyst". The catalyst support is often composed of a porous carbon material. On the fuel cell catalyst, an oxidation reaction of the fuel gas occurs, generating protons and electrons. For example, when the fuel gas is hydrogen gas, the following oxidation reaction occurs. H2→2H + +2e - (E0=0V)

[0004] The protons generated by this oxidation reaction are introduced into the cathode through the electrolyte material (ionomer) in the anode and the polymer electrolyte membrane. Also, the electrons are introduced into the external circuit through the catalyst support, the gas diffusion layer, and the separator. These electrons do work in the external circuit and are then introduced into the separator on the cathode side. Then, these electrons are introduced into the cathode through the separator on the cathode side and the gas diffusion layer on the cathode side.

[0005] The solid polymer electrolyte membrane is composed of an electrolyte material having proton conductivity. The solid polymer electrolyte membrane introduces the 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 to the cathode. The cathode includes a fuel cell catalyst, a catalyst carrier supporting the fuel cell catalyst, and an electrolyte material having proton conductivity. The catalyst carrier is often composed of a porous carbon material. On the fuel cell catalyst, a reduction reaction of the oxidizing gas occurs and water is generated. For example, when the oxidizing gas is oxygen gas or air, the following reduction reaction occurs. O2+4H + +4e - →2H2O (E0=1.23V)

[0006] The water generated in the reduction reaction is discharged to the outside of the fuel cell together with the unreacted oxidizing gas. Thus, in the solid polymer fuel cell, power is generated by utilizing the free energy difference (potential difference) generated along with the oxidation reaction of the fuel gas. In other words, the free energy generated in the oxidation reaction is converted into the work done by electrons in the external circuit.

[0007] By the way, regarding the porous carbon material (hereinafter also referred to as "carbon carrier") applied to the catalyst carrier of the solid polymer fuel cell, studies have been conducted and various proposals have been made.

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

[0009] Patent Document 2 proposes "a carbonaceous material for a catalyst carrier of a solid polymer fuel cell, which is a porous carbon material and simultaneously satisfies the following (1), (2), (3), and (4).". (1) In the differential thermogravimetric curve (DTG) obtained by thermogravimetric analysis when the temperature is raised at 10 °C / min in an air atmosphere, the intensity (I 750 ) at 750 °C and the peak intensity (I peak ) near 690 °C, the intensity ratio (I 750 / I peak ) is 0.10 or less. (2) The BET specific surface area determined by BET analysis of the nitrogen gas adsorption isotherm is 400 to 1500 m 2 / g. (3) The cumulative pore volume V 2-10 of the pore size of 2 to 10 nm determined by the analysis using the Dollimore-Heal method of the nitrogen gas adsorption isotherm is 0.4 to 1.5 mL / g. (4) In the nitrogen gas adsorption isotherm, the nitrogen gas adsorption amount V macro at a relative pressure of 0.95 to 0.99 is 300 to 1200 cc(STP) / g.

[0010] Patent Document 3 discloses "a carbon-based support for a fuel cell catalyst, wherein the carbon-based support is a solid type support, and the carbon-based support has an external surface area of 100 to 450 m 2 / g, a mesopore volume of 0.25 to 0.65 cm 3 / g, and a micropore volume of 0.01 to 0.05 cm 3A base carrier having a micropore volume of / g (each of the outer surface area, the mesopore volume, and the micropore volume is the arithmetic mean of the measured values obtained using a BET (Brunauer-Emmett-Teller) analyzer (Micromeritics, ASAP-2020) from 5 randomly selected samples).」 has been proposed.

[0011] Patent Document 4 discloses, "The cumulative pore volume V of pores having a pore diameter of 2 nm or more and 4 nm or less in diameter 2-4 and the cumulative pore volume V of pores having a pore diameter of more than 4 nm and 20 nm or less in diameter 4-20 The ratio V 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, a carbon carrier for a catalyst.」 has been proposed.

[0012] Patent Document 5 discloses, "An electrode catalyst carrier containing a porous composite oxide doped with at least one of P, As, Sb, Bi, V, Nb, Ta, F, and Cl as a doping agent, wherein the porous composite oxide contains silica, the volume resistivity of the carrier is 10,000 Ω·cm or less, 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. An electrode catalyst carrier characterized by this.」 has been proposed.

[0013] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2022-156985 Patent Document 2: International Publication No. 2020 / 066010 Patent Document 3: International Publication No. 2022 / 085963 Patent Document 4: Japanese Unexamined Patent Application Publication No. 2019-89021 Patent Document 5: Japanese Unexamined Patent Application Publication No. 2017-162572

Summary of the Invention

Problems to be Solved by the Invention

[0014] The compatibility between the power generation characteristics and durability of a polymer electrolyte fuel cell (hereinafter also referred to as "PEFC") is an important characteristic for the popularization of fuel cell vehicles (hereinafter also referred to as "FCV"), and in particular, it is an essential issue to be solved for commercial vehicles for which market growth is expected in the future.

[0015] Generally, one of the main causes of the durability degradation of PEFC is the deterioration of the catalyst, and the oxidation consumption of the carbon support and the dissolution of platinum nanoparticles are the factors. Both of these two factors are caused by the potential fluctuations of the electrode, especially the potential fluctuations including the high potential region exceeding 1V. The solution to platinum dissolution is to increase the particle size to gain time until dissolution. The solution to the oxidation consumption of the carbon support is to increase the crystallinity (that is, increase the in-plane size of the crystallites and increase the stacking thickness) in order to suppress the consumption due to the oxidation of the carbon support, thereby reducing the area of the edges of the carbon network plane that is the starting point of oxidation consumption and slowing down the oxidation rate.

[0016] The power generation characteristics are mainly governed by two factors: the contribution ratio of the metal catalyst (such as platinum nanoparticles) to the reaction (hereinafter also referred to as "catalyst utilization rate") and the diffusibility of the oxidizing gas. The pore structure of the carbon support (porous carbon material) correlates with the catalyst utilization rate, and the three-dimensional structure of the carbon support (such as dendritic structure) correlates with the gas diffusibility. Although the pores suitable for gas diffusion are not clear, it is inferred from various carbon supports currently applied that the pore diameter of the voids in the catalyst layer for nucleic acids is about several tens to 100 nm. The voids in the catalyst layer are realized by the three-dimensional structure of the carbon support (specifically, the aggregate structure of carbon black, etc.). For the pore structure, it is desirable that only pores of a size sufficient for metal catalysts (such as platinum nanoparticles) of several nm to exist in the pores are selectively present. Generally, mesoporous carbon is regarded as suitable for the support.

[0017] However, in the prior art including Patent Documents 1 to 5, there is still room for improvement in the compatibility between power generation characteristics (especially low load characteristics) and durability.

[0018] In Patent Documents 1 and 2, the pore structure peculiar to the material is suitable for the catalyst support and exhibits excellent power generation characteristics. However, there is room for improvement in order to satisfy the durability (oxidation resistance and consumption resistance) for heavy-duty vehicle (HDV) applications such as long-distance trucks. In Patent Document 3, mesoporous-dominated pores are formed in acetylene black, and the durability is extremely excellent, and the power generation characteristics are excellent in an operating environment with high humidity. However, there is room for improvement in the low-load characteristics, which is one of the important characteristics in practical use. In Patent Document 4, it is presumed that ketjen black is used as a raw material, the durability is enhanced by heat treatment, the water repellency is increased by heating, and an oxygen-containing functional group is imparted to prevent the decrease in the moisture retention of the catalyst layer, thereby achieving both durability and power generation characteristics. However, the decrease in pore volume due to heat treatment leads to a decrease in power generation characteristics, and there is room for improvement in achieving both (especially low-load characteristics) and high durability. In Patent Document 5, a catalyst support of an oxide having a pore structure is shown. However, even if the conductivity of the oxide itself is sufficient, the contact resistance between the oxides is high, and a decrease in power generation characteristics including low-load characteristics such as a large ohmic resistance of the catalyst layer occurs.

[0019] As described above, in the prior art, there is still room for improvement in achieving both power generation characteristics (especially low-load characteristics) and durability. In addition, it is desired to realize such improvement with inexpensive and useful carbon black among carbon supports (porous carbon materials).

[0020] Therefore, an object of the present disclosure is to provide a carbon material for a catalyst support of a polymer electrolyte fuel cell excellent in durability together with power generation characteristics (especially low-load characteristics), a catalyst layer for a polymer electrolyte fuel cell using the same, and a fuel cell. Another object of the present disclosure is to provide oxygen-treated carbon black and activated carbon black suitable for obtaining a carbon material for a catalyst support of a polymer electrolyte fuel cell excellent in durability together with power generation characteristics (especially low-load characteristics).

Means for Solving the Problems

[0021] The means for solving the problems include the following aspects. <1> Oxygen-treated carbon black that satisfies the following requirement (A). (A) When 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> Furthermore, the oxygen-treated carbon black according to <1> that satisfies the following requirement (B). (B) When 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. <3> Activated carbon black that simultaneously satisfies the following requirements (C), (D), and (E). (C) The BET specific surface area (m 2 / g) calculated by nitrogen gas adsorption isotherm measurement is 700 or more and 1500 or less. (D) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, when the integrated value of the pore volume with a pore diameter of 2 nm or more and less than 6 nm is Σ 2-6 then Σ 2-6 is 0.22 or more and less than 1.00. (E) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, when the integrated value of the pore volume with a pore diameter of 2 nm or more and less than 6 nm is Σ 2-6 and the integrated value of the pore volume with a 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. <4> A carbon material for a catalyst support of a polymer electrolyte fuel cell, which is composed of porous activated carbon black and simultaneously satisfies the following requirements (F), (G), (H), and (I). (F) The BET specific surface area (m 2 / g) measured by nitrogen gas adsorption is 400 or more and 1200 or less. (G) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, when the integrated value of the pore volume with a pore diameter of 2 nm or more and less than 6 nm is Σ 2-6 , Σ 2-6 is 0.20 or more and less than 0.70. (H) In the mesopore distribution obtained by analyzing the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, when the integrated value of the pore volume with a pore diameter of 2 nm or more and less than 6 nm is Σ 2-6 , the integrated value of the pore volume with a pore diameter of 6 nm or more and less than 10 nm is Σ 6-10 , then Σ 6-10 / Σ 2-6 is 0.120 or more and 0.500 or less. (I) In the Raman spectrum obtained by Raman spectroscopy measurement, when the intensity of the D band at 1300 - 1360 cm -1 is I D , and the intensity of the G band at 1560 - 1620 cm -1 is I G , then 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 the 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 cathode-side catalyst layer.

Advantages of the Invention

[0022] According to the present disclosure, there are provided a carbon material for a catalyst carrier of a polymer electrolyte fuel cell excellent in durability, a catalyst layer for a polymer electrolyte fuel cell using the same, and a fuel cell, together with power generation characteristics (particularly, low load characteristics). According to the present disclosure, there are provided oxygen-treated carbon black and activated carbon black suitable for obtaining a carbon material for a catalyst carrier of a polymer electrolyte fuel cell excellent in durability, together with power generation characteristics (particularly, low load characteristics).

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0024] An example of the present disclosure will be described. In the present disclosure, a numerical range represented by “~” means a range including the numerical values described before and after “~” as the lower limit value and the upper limit value. Further, a numerical range in the case where “exceeding” or “less than” is attached to the numerical values described before and after “~” means a range not including these numerical values as the lower limit value or the upper limit value. In the present disclosure, the term “step” includes not only an independent step but also a step included in this term even if it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved. In the present disclosure, the “electrolyte material having proton conductivity” used in the catalyst layer of the fuel cell is also referred to as “ionomer”.

[0025] <Carbon black treated with oxygen, activated carbon black, carbon material for catalyst support of polymer electrolyte fuel cell> The oxygen-treated carbon black of the present disclosure satisfies requirement (A) described below. It is preferable that the oxygen-treated carbon black of the present disclosure satisfies requirement (B) described below. The activated carbon black of the present disclosure simultaneously satisfies requirements (C), (D), and (E) described below. The carbon material for catalyst support of polymer electrolyte fuel cell of the present disclosure is composed of porous activated carbon black that simultaneously satisfies 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 material carbon black to oxygen treatment. The activated carbon black of the present disclosure is carbon black that has been subjected to first activation on the oxygen-treated carbon black of the present disclosure and has been made porous. The carbon material for catalyst support (porous activated carbon black) of the present disclosure is carbon material (porous carbon black) obtained by subjecting the activated carbon black of the present disclosure to heat treatment and second activation to enhance crystallinity. That is, 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. Further, the activated carbon black of the present disclosure corresponds to an intermediate for producing the carbon material for catalyst support (porous activated carbon black) of the present disclosure.

[0027] The carbon material for catalyst support (porous activated carbon black) of the present disclosure is a carbon material that is excellent in durability as well as power generation characteristics (particularly, low load characteristics). And the oxygen-treated carbon black and activated carbon black of the present disclosure are carbon black suitable for obtaining a carbon material (that is, porous activated carbon black) that is excellent in durability as well as power generation characteristics (particularly, low load characteristics). The carbon material for catalyst support, oxygen-treated carbon black, and activated carbon black of the present disclosure were found based on the following findings.

[0028] Generally, the power generation characteristics of a fuel cell largely depend on the overvoltage of the cathode reaction. The overvoltage at the cathode electrode is considered to be mainly caused by the following three factors. (1) The synthesis of two resistances, namely, the electron conduction resistance and the proton conduction resistance, depending on the magnitude of the ohmic resistance of the catalyst layer (2) The diffusion resistance of the oxidizing gas in the catalyst layer (3) The resistance in the electrochemical reaction, that is, the chemical reaction involving electron transfer, on the surface of the catalyst metal (i.e., the resistance of the catalytic reaction)

[0029] Among the above main causes, reducing “(3) the resistance of the catalytic reaction”, especially the factor that dominates the utilization rate of the catalyst metal, depends on whether the catalyst metal in the pores of the porous activated carbon black is in contact with the ionomer, and the ease of the ionomer to penetrate into the pores of the porous activated carbon black. Therefore, the inventors studied the pore size distribution of gas adsorption in pores suitable for supporting the catalyst metal and at the same time suitable for the penetration of the ionomer, regarding the factor of “(3) the resistance of the catalytic reaction”. As a result, the following findings were obtained.

[0030] (A) In the porous activated carbon black as the carbon material for the catalyst support, the optimal pore size for the penetration of the ionomer and the support of the catalyst metal can be quantitatively evaluated by the pore size distribution of nitrogen gas adsorption, which selectively forms only the pore size distribution of that pore size. Specifically, as the pore structure in which the catalyst metal is supported in the pores and the ionomer easily penetrates into the pores, it is important that the pore volume with a pore size of 2 nm or more and less than 6 nm is large, and the pore volume with a pore size of 6 nm or more and 10 nm or less is as small as possible. (B) By subjecting the raw material carbon black to oxygen treatment, oxygen-treated carbon black that satisfies requirement (A) can be obtained. Here, the oxygen treatment is a treatment that forms pores in the raw material carbon black and at the same time imparts a large number of oxygen-containing functional groups in the pores by oxidizing the raw material carbon black at a low temperature. In the oxygen-treated carbon black, the pores with oxygen-containing functional groups serve to introduce activation gases such as water vapor or CO2 into the interior of the oxygen-treated carbon black during the first activation. At the same time, it is speculated that the oxygen-containing functional groups form a surface structure that facilitates the progress of activation. As a result, activated carbon black that is porous and satisfies requirements (C) to (E) can be obtained. (C) The pore structure of the activated carbon black produced in (A) and (B) above is heat-treated in an inert atmosphere to enhance durability. However, in the process, it causes a side effect of pore collapse. If used as a catalyst support as it is, the power generation characteristics (especially low-load characteristics) deteriorate mainly due to the small pore volume and small BET specific surface area. By performing a second activation with an activation gas such as water vapor or CO2 again after the heat treatment, a pore structure close to that before the heat treatment is formed while suppressing surface roughness. As a result, porous activated carbon black that satisfies requirements (F) to (I) can be obtained.

[0031] From the above findings, it has been found that the carbon material for a catalyst support of the present disclosure is a carbon material excellent in durability as well as power generation characteristics (especially low-load characteristics). In addition, it has been found that the oxygen-treated carbon black and the activated carbon black of the present disclosure are carbon blacks suitable for obtaining a carbon material (that is, porous activated carbon black) excellent in durability as well as power generation characteristics (especially low-load characteristics).

[0032] Hereinafter, the details of the oxygen-treated carbon black, the activated carbon black, and the carbon material for a catalyst support (that is, porous activated carbon black) of the present disclosure will be described.

[0033] [Oxygen-Treated Carbon Black] Commercially available raw material carbon black is considered to have no pores, but in reality, even with the same particle size, the surface area measured by nitrogen gas adsorption is different. Also, it is recognized that the smaller the particle size, the larger the surface area tends to be. From the perspective of the first activation, when selecting the raw material carbon black, for the pore volume formed after the first activation to be large and the BET specific surface area to also be large, among carbon blacks with the same particle size, it is the raw material carbon black with a large BET specific surface area. On the other hand, for the development of the pore structure by the first activation, it is preferable that the oxygen content of the oxygen-treated carbon black, which is the object of the first activation, is higher. This phenomenon is presumably considered because the sites that burn out to become CO2 during activation correlate with the sites containing a large amount of oxygen. That is, it is inferred that the crystallite sites with oxygen-containing functional groups become the starting points for selective oxidation during activation. As a treatment for imparting oxygen-containing functional groups (that is, a treatment that simultaneously increases the oxygen content and the BET specific surface area), oxygen treatment with air is performed on the raw material carbon black. Specifically, the raw material carbon black is heat-treated under the flow of an oxidizing gas containing oxygen as an oxidizing agent (for example, an oxidizing gas diluted with air and an inert gas).

[0034] The oxidized carbon black obtained by such oxygen treatment suitable for such an object satisfies requirement (A), and preferably satisfies requirements (A) and (B).

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

[0036] During the oxygen treatment of the raw material carbon black with the oxidizing gas, pores are formed in the raw material carbon black and the BET specific surface area increases. At the same time, various functional groups containing oxygen are introduced on the surface of the pores. It is inferred that the types of functional groups added vary depending on the temperature of the oxygen treatment. For example, the carboxyl group has the lowest thermal stability. Specifically, in an oxygen treatment with an oxygen treatment temperature of 350 °C or higher, the abundance decreases. When the oxygen treatment temperature exceeds 500 °C, the abundances of the hydroxyl group and the lactone group also decrease sharply. And oxygen-containing functional groups such as cyclic ether type and quinone type become stable functional groups in the high temperature range where the oxygen treatment temperature is 500 °C or higher.

[0037] When the oxygen-treated carbon black after oxygen treatment is subjected to a first activation at a temperature of 800 °C or higher in an activation gas atmosphere of, for example, water vapor or CO2, many oxygen-containing functional groups are desorbed as CO2 gas. Thereby, it is presumed that the carbon atoms on the pore surface with oxygen-containing functional groups are removed, and the pores are widened by one carbon atom. Further, it is presumed that when the oxygen-containing functional groups are desorbed, the aromatic ring is broken, and the reaction of the first activation proceeds more easily.

[0038] Regardless of the type of oxygen-containing functional group, the above action occurs, and the oxygen content of the oxygen-treated carbon black can be quantitatively defined according to the pore development by 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 preferable range of the oxygen content is a function of the BET specific surface area. When the lower limit of the oxygen-treated carbon black is S BET / 100 mass% or more, pore development with a specific pore diameter in the first activation is brought about. 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 of the oxygen content of the oxygen-treated carbon black corresponding to 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 mass% or less.

[0040] When the oxygen content of the oxygen-treated carbon black is S BETWhen it is less than 100% by mass, the amount of oxygen-containing functional groups in the oxygen-treated carbon black is too small, and no contribution to the development of pores with a specific pore diameter by the first activation is recognized. As a result, the power generation characteristics (especially the low-load characteristics) are not improved. When 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 large, resulting in non-uniformity in the coating of the porous activated carbon black with the ionomer. As a result, the amount of ionomer entering the pores decreases, the catalyst utilization rate decreases, and ultimately the power generation characteristics (especially the low-load characteristics) deteriorate.

[0041] The lower limit of the oxygen content of the oxygen-treated carbon black is preferably S BET / 90% by mass or more, and more preferably S BET / 80% by mass or more. The upper limit of the oxygen content of the oxygen-treated carbon black is preferably 7.50% by mass or less, and 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 below.

[0043] (Requirement (B)) (B) When 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] The BET specific surface area S of the oxygen-treated carbon black BET (m2 / g), assuming that the density of the oxygen-treated carbon black is constant, for example, commercially available furnace black can be approximately expressed by the formula: S BET = 2400 / DF (where DF is the primary particle diameter (nm) of the carbon black of the furnace black). The BET specific surface area of the oxygen-treated carbon black is obtained by adding the BET specific surface area of the pores introduced by the oxygen treatment to the BET specific surface area of the raw material carbon black. And the added BET specific surface area is also inversely proportional to the primary particle size.

[0045] Therefore, the lower limit of the BET surface area S of the oxygen-treated carbon black for bringing about a minimum effect on the pore development of a specific pore diameter in the first activation is BET 5500 / Dm 2 / g or more is preferable. The upper limit of the BET surface area S of the oxygen-treated carbon black is BET 500 m 2 / g or less is preferable. For the BET surface area S of the carbon black subjected to the chemical treatment BET If it exceeds 500 m 2 / g, the surface roughness of the oxygen-treated carbon black is too large, resulting in non-uniformity in the coating of the porous activated carbon black of the ionomer. As a result, the amount of the ionomer that penetrates into the pores decreases, the catalyst utilization rate decreases, and finally the power generation characteristics (especially the low load characteristics) deteriorate.

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

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

[0048] The primary particle size is a value measured by the method described in the examples below. The primary particle size of the oxygen-treated carbon black is equivalent to that 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 the porous activated carbon black suitable for the catalyst support is as follows: (1) there are many sites for supporting the catalyst metal (the BET covering area is large), (2) the pore volume of pores with a pore diameter of 2 nm or more and less than 6 nm, which is suitable for accommodating the size of the catalyst metal of 2 to 5 nm, is large, and (3) only pores with the required pore diameter exist, and the pore volume of pores with a small pore diameter of 6 nm or more and 10 nm or less, which corresponds to surface roughness leading to a decrease in power generation characteristics (especially low-load characteristics), is relatively small compared to the pore volume of pores with a pore diameter of 2 nm or more and less than 6 nm. These are important.

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

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

[0052] When the BET specific surface area of the activated carbon black is less than 700 m 2 / g, the BET surface area after heat treatment of the activated carbon black becomes too small. Therefore, a sufficient BET surface area without surface roughness cannot be obtained by the second activation. As a result, the power generation characteristics (especially low-load characteristics) deteriorate. When the BET specific surface area of the activated carbon black exceeds 1500 m 2 / g, the thickness of the carbon wall forming the pores becomes several carbon layers. Therefore, even if heat treatment is performed on the activated carbon black to aim for high crystallization, the durability cannot be enhanced because the thickness of the carbon layer stack is thin.

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

[0054] The BET specific surface area is a value measured by the method described in the examples 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 with a pore diameter (i.e., pore diameter) of 2 nm or more and less than 6 nm is Σ 2-6 When set as 2-6 is 0.22 or more and less than 1.00.

[0056] The integrated value Σ 2-6 of the pore volume of the activated carbon black is less than 0.22. In this case, the integrated value Σ 2-6 of the pore volume of the porous activated carbon black obtained by heat-treating and second-activating the activated carbon black also becomes small. As a result, the amount of the catalytic metal supported per unit mass of the porous activated carbon black decreases, and the amount of carbon increases to keep the amount of the catalytic metal constant. And an increase in the thickness of the corresponding catalyst layer occurs. The increase in the thickness of the catalyst layer inhibits gas diffusion in the catalyst layer, leading to a decrease in power generation characteristics (especially low-load characteristics). The integrated value Σ 2-6 of the pore volume of the activated carbon black is 1.00 or more. In this case, the thickness of the carbon wall forming the pores becomes very thin. Therefore, even if high crystallization is aimed for by heat-treating the activated carbon black, since the thickness of the carbon layer stacking is thin, the durability cannot be enhanced.

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

[0058] Note that the integrated value Σ of the pore volume in the mesopore distribution 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 the nitrogen gas adsorption isotherm using the BJH (Barrett Joyner Halenda) method, let the integrated value of the pore volume with a pore diameter (i.e., pore diameter) of 2 nm or more and less than 6 nm be Σ 2-6 , and the integrated value of the pore volume with a pore diameter (i.e., pore diameter) of 6 nm or more and less than 10 nm be Σ 6-10 . Then, when Σ 6-10 / Σ 2-6 is 0.100 or more and 0.490 or less.

[0060] The lower limit of the ratio Σ 6-10 / Σ 2-6 of the activated carbon black indicates the limit value that can be substantially reached including prediction, even if the introduction of micropores of the activated carbon black is excessive and the first activation with an activation gas such as steam or CO2 is carefully carried out. Therefore, the lower limit of the ratio Σ 6-10 / Σ 2-6 of the activated carbon black is 0.100, and the closer it is to the lower limit, the more the power generation characteristics (especially low load characteristics) are improved. When the ratio Σ 6-10 / Σ 2-6 of the activated carbon black exceeds 0.490, the surface roughness of the activated carbon black is too large, 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, the catalyst utilization rate decreases, and ultimately the power generation characteristics (especially low load characteristics) deteriorate.

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

[0062] 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 support (porous activated carbon black)] The pore structure of the porous activated carbon black suitable as a catalyst support is common to the pore structure of the activated carbon black as an intermediate. However, the porous activated carbon black requires a more developed pore structure in order to increase the crystallinity (i.e., durability) by heat treatment and second activation of the activated carbon black and obtain a pore structure having a certain pore volume.

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

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

[0066] When the BET specific surface area of the porous activated carbon black is less than 400 m 2 / g, it becomes impossible to support as many catalyst metals as possible inside the particles, which is an advantage of the porous activated carbon black. As a result, the number of porous activated carbon blacks required to support the same number of catalyst metals increases. That is, the catalyst layer becomes thicker. As a result, the diffusion distance of the oxidizing gas in the catalyst layer becomes longer, leading to a decrease in low-load characteristics. When the BET specific surface area of the porous activated carbon black is 1200 m 2When it exceeds / g, the thickness of the carbon wall forming the pore structure becomes thin. Specifically, the average number of stacked layers of the carbon network surface becomes 3 or less, the mechanical strength is weak, and when the carbon wall is oxidized and consumed by the nano-sized catalytic metal, the number of stacked layers becomes thin and the amount of carbon consumed is small, but structural destruction is likely to occur. The deterioration of the power generation characteristics associated with durability is accelerated.

[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 500 m 2 / g or more is more preferable. 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 1100 m 2 / g or less is more preferable.

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

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

[0070] When the integrated value Σ 2-6 of the pore volume of the porous activated carbon black is less than 0.20, the pore volume of the porous activated carbon black becomes small. As a result, the amount of the catalytic metal supported per unit mass of the porous activated carbon black decreases, and the amount of carbon increases to keep the amount of the catalytic metal constant. And an increase in the thickness of the corresponding catalyst layer occurs. The increase in the thickness of the catalyst layer inhibits gas diffusion in the catalyst layer, leading to a decrease in power generation characteristics (especially low load characteristics). The integrated value Σ 2-6When it is 0.70 or more, the thickness of the carbon wall forming the pores becomes extremely thin. Therefore, the durability cannot be enhanced.

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

[0072] Note that the integrated value Σ of the pore volume in the mesopore distribution 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 the nitrogen gas adsorption isotherm by the BJH (Barrett Joyner Halenda) method, let the integrated value of the pore volume with a pore diameter of 2 nm or more and less than 6 nm be Σ 2-6 , and the integrated value of the pore volume with a pore diameter of 6 nm or more and less than 10 nm be Σ6 -10 , then when Σ 6-10 / Σ 2-6 is 0.120 or more and 0.500 or less.

[0074] Ratio Σ of the porous activated carbon black 6-10 / Σ 2-6 The lower limit value of is that even if the introduction of micropores of the porous activated carbon black is excessive and the second activation with an activation gas such as water vapor or CO2 is carefully advanced, including prediction, it shows the limit value that can be substantially reached. Therefore, the ratio Σ of the porous activated carbon black 6-10 / Σ 2-6 The lower limit value of is 0.120, and the closer it is to the lower limit value, the more the power generation characteristics (especially the low load characteristics) are improved. Ratio Σ of the porous activated carbon black 6-10 / Σ 2-6When it exceeds 0.500, the surface roughness of the porous activated carbon black is too large, resulting in non-uniformity in the coating of the porous activated carbon black with the ionomer. As a result, the amount of ionomer entering the pores decreases, the catalyst utilization rate decreases, and ultimately the power generation characteristics (especially the low load characteristics) deteriorate.

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

[0076] Note that 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 spectroscopic measurement, the intensity of the D band at 1300 to 1360 cm -1 is I D , and the intensity of the G band at 1560 to 1620 cm -1 is I G . When taking them, I D / I G is 1.20 or more and 2.20 or less.

[0078] The durability of the porous activated carbon black as a catalyst carrier, that is, when maintained at a high potential exceeding 1 V, (1) the oxidative consumption of the edge portion of the porous activated carbon black, and (2) the local oxidative consumption at the site where the catalytic metal is in contact in the state where the nano-sized catalytic metal is supported. Durability against these two oxidative consumptions is required. The measure for enhancing this durability is to improve the crystallinity of the porous activated carbon black. By improving the crystallinity, the oxidation resistance of the porous activated carbon black is improved due to both an increase in the size of the carbon network plane and an increase in the number of stacked layers.

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

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

[0081] Strength 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] Note that the strength 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 support of solid polymer fuel cell (porous activated carbon black)> Hereinafter, an example of a method for producing oxygen-treated carbon black, activated carbon black, and a carbon material for catalyst support of a solid polymer fuel cell (porous activated carbon black) will be described.

[0084] The method for producing the carbon material for catalyst support (porous activated carbon black) of the present disclosure has the following four steps. Oxygen treatment step: An oxygen treatment step of subjecting raw material carbon black to oxygen treatment to obtain oxygen-treated carbon black First activation step: A first activation step of subjecting the oxygen-treated carbon black to first activation to obtain activated carbon black Heat treatment step: A heat treatment step of subjecting the activated carbon black to heat treatment to obtain heat-treated activated carbon black Second activation step: A second activation step of subjecting the heat-treated activated carbon black to second activation to obtain porous activated carbon black

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

[0086] The method for manufacturing the activated carbon black of the present disclosure includes the above oxygen treatment step and the above first activation step. In the method for manufacturing the activated carbon black of the present disclosure, by going through the above steps, activated carbon black satisfying requirements (C) to (E) can be obtained.

[0087] The method for manufacturing the oxygen-treated carbon black of the present disclosure includes the above oxygen treatment step. In the method for manufacturing the oxygen-treated carbon black of the present disclosure, by going through the above steps, oxygen-treated carbon black satisfying requirement (A) (preferably requirements (A) to (B)) can be obtained.

[0088] Details of each step will be described below. First, the raw material carbon black to be used will be described.

[0089] (Raw material carbon black) As the raw material carbon black, carbon black satisfying two structures of a predetermined primary particle diameter and a three-dimensional structure (an aggregate structure in which primary particles are strung together) described later can be preferably applied.

[0090] -Primary particle diameter- The size of the voids in the catalyst layer is determined from the three-dimensional structure and the primary particle diameter of the raw material carbon black. That is, since primary particles are connected to form a three-dimensional structure, primary particle diameter × number of beads = void size. If the three-dimensional structure is developed and the primary particle diameter is 20 nm or more, gas diffusion in the catalyst layer will not be rate-determining and the power generation characteristics will not deteriorate. That is, the preferable range of the primary particle diameter is 2 0 nm or more and 80 nm or less. If the primary particle diameter exceeds 80 nm, it becomes difficult to develop a three-dimensional structure, so 80 nm is a practical manufacturing limit. Pore formation by the first activation is presumed to form pores from the outside to the inside. Since the surface vicinity continues to be exposed to oxygen treatment, the loss due to combustion is large. Assuming so, the larger the primary particle size, the smaller the pore diameter pores are formed inside, but the pores in the vicinity of the surface tend to have a relatively large pore diameter. Actually, the activation of raw material carbon black with a large primary particle size shows less pore development compared to that with a small particle size even when the mass reduction progresses. 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 necessarily clear, if the crystallinity by Raman or X-ray diffraction is the same, the raw material carbon black with a larger primary particle size has higher oxidation consumption resistance than the raw material carbon black with a smaller primary particle size. That is, the durability becomes higher as the primary particle size becomes larger. In particular, raw material carbon black with a primary particle size exceeding 40 nm has an effect on improving durability. Raw material carbon black with a particle size of 50 nm or more has a significant effect on improving durability, and raw material carbon black with a particle size exceeding 60 nm has a remarkable durability improvement effect.

[0091] The primary particle size of the raw material carbon black is one of the basic physical properties, and the primary particle size in the catalog value of the carbon black manufacturer is referred to. However, when the catalog value of the carbon black manufacturer cannot be referred to, the method recommended by the Carbon Black Association, that is, the arithmetic mean value of the primary particle size is calculated from the image of the primary particles measured by an electron microscope, which is the method described in the Carbon Black Yearbook. More specifically, refer to page 176 of the Carbon Black Handbook (edited by the Carbon Black Association, first edition in 1971), "i. Electron Microscopy Photography Method", "ii. Measurement of Particle Size", and "iii. Calculation Method of Particle Size". In order to take a statistical average, at least 100 primary particle sizes are measured, and the arithmetic mean is determined as the primary particle size. The arithmetic mean diameter is calculated by the following formula. d = Σn i di / Σn i , where n i is the number of particles with a particle size d i is.

[0092] -Three-dimensional structure- As a structure suitable for the catalyst support of a fuel cell, porous activated carbon black with a developed three-dimensional structure is preferable. When a catalyst layer is formed by the three-dimensional structure, a highly porous catalyst layer with voids is formed, and the diffusion rate of the oxidizing gas increases. Physical property values reflecting the three-dimensional structure can be applied to, for example, the DBP oil absorption amount, the BET specific surface area, and the mercury intrusion amount distribution by the mercury porosimetry method.

[0093] The DBP oil absorption amount is an industrial index of typical colloidal physical properties of carbon black, which is a so-called catalog-listed value. Also in the physical property regulations in the present disclosure, the value listed in the physical property table of the carbon black manufacturer is used. Specific numerical values of the DBP oil absorption amount are preferably 80 mL / 100 g or more, more preferably 100 mL / 100 g, and still more preferably 120 mL / 100 g. Since the specific gravity of the raw material carbon black is approximately 1.8 g / mL, considering that the DBP oil absorption amount corresponds to the voids in the catalyst layer, a DBP oil absorption amount of 80 mL / 100 g corresponds to voids that are 1.4 times or more the volume of the raw material carbon black. If the DBP oil absorption amount is less than 80 mL / 100 g, the development of the three-dimensional structure is too small, resulting in a decrease in low-load characteristics. On the other hand, the upper limit of the DBP oil absorption amount is 180 mL / 100 g, which is the theoretical upper limit in manufacturing. Note that the DBP oil absorption amount indicates the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black, and is a value defined by ASTM (American Standard Test Method) D2414-6TT.

[0094] The BET specific surface area is the most basic physical property value of carbon black. The BET specific surface area of the raw material carbon black affects the activation in the first activation treatment step. Specific BET specific surface areas are preferably 20 - 200 m 2 / g, and more preferably 25 - 180 m 2 / g. The BET specific surface area is a value measured by the method described in the examples below.

[0095] The evaluation of the three-dimensional structure by the mercury porosimetry method is carried out by converting the hydrostatic pressure applied to mercury into pore diameter when assuming a cylinder using the surface tension of mercury with respect to the raw material carbon black, and obtaining the distribution of the integrated value of the volume of pores larger than that pore diameter with the pore diameter on the horizontal axis and the vertical axis. In the raw material carbon black having a three-dimensional structure, mercury absorption proportional to the pore volume occurs at the intrusion relative pressure corresponding to the void size brought about by the three-dimensional structure, so the three-dimensional structure can be quantitatively evaluated from the pore size distribution of the mercury absorption amount. Specifically, considering the DBP absorption oil amount suitable for the voids of the above-mentioned catalyst layer, the increment of the mercury amount absorbed when the mercury intrusion pressure rises from 10 MPa (corresponding to pores of about 10 nm) to 100 MPa (corresponding to pores of about 100 nm) is preferably 0.5 to 1.5 mL / g. If the increment of the mercury amount is less than 0.5 mL / g, the development of the three-dimensional structure is too small, resulting in a decrease in low-load characteristics. On the other hand, an increment of the mercury amount of 1.5 mL / g is the theoretical upper limit in terms of manufacturing.

[0096] (Oxygen treatment step) The oxygen treatment step is the pre-stage for the first activation, and micropores are introduced into the raw material carbon black by the 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. Specifically, the role of the oxygen treatment step is to obtain oxygen-treated carbon black in which the BET specific surface area and the pore volume of the pores, which are factors for improving the power generation characteristics, are increased by the first activation, and pores that cause surface roughness, which is the cause of the power generation characteristics deterioration, do not develop. The pores that are factors for improving the 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, which is the cause of the power generation characteristics deterioration, are pores with a pore diameter of 6 nm or more and 10 nm or less.

[0097] In order to exhibit the function of pore development by the first activation, which is the oxygen treatment, the required characteristics of the oxygen-treated carbon black are the oxygen content (preferably the oxygen content and the BET specific surface area). And by the oxygen treatment, the oxygen content (preferably the oxygen content and the BET specific surface area) can be increased.

[0098] Here, both the oxygen treatment and the first activation have the function of pore formation (that is, porosity). However, the oxygen treatment temperature of the oxygen treatment is lower than the activation temperature of the first activation. Since the oxygen treatment is a low-temperature reaction, oxygen-containing functional groups constantly exist on the surface of the raw material carbon black during the oxidation reaction. As a result, a large number of oxygen-containing functional groups exist on the pore surface of the oxygen-treated carbon black. That is, the oxygen content of the oxygen-treated carbon black increases almost proportionally to the BET specific surface area. The oxygen-containing functional groups are considered to have an effect of promoting activation in the first activation. By the first activation, the oxygen-containing functional groups are desorbed as CO and CO2. When desorbing, since it breaks the aromatic ring, it has the effect of making the next oxidation reaction likely to occur. Thereby, by the first activation, the BET surface area and the pore volume of the pores, which are factors for improving the power generation characteristics, are increased, and oxygen-treated carbon black is obtained in which pores that cause surface roughness and lead to a decrease in power generation characteristics do not develop.

[0099] Under the conditions of the oxygen treatment in which the oxygen content (preferably the oxygen content and the BET specific surface area) can be controlled the upper limit of the oxygen treatment temperature is restricted, and it is preferably 500 °C or lower, more preferably 450 °C or lower. When the oxygen treatment temperature exceeds 500 °C, the oxidizing power becomes too high, so the surface combustion of the raw material carbon black becomes remarkable, and pores with a large pore diameter are likely to be formed on the surface. As a result, it becomes difficult to satisfy requirement (E) and requirement (H). At the same time, when the oxygen concentration is high, the surface of the carbon black burns and pore formation does not proceed, so there is an upper limit of the oxygen concentration corresponding to the temperature. Specifically, the optimum range of the oxidation treatment temperature corresponding to the oxygen concentration is 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 25% by volume or more and less than 50% by volume, which is about the level of air, the oxygen treatment temperature is preferably 300°C to 400°C. If the oxygen concentration is 10% by volume or more and less than 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 is preferably set to a temperature at which the time required for the oxygen treatment exceeds 100 hours. From the perspective of increasing the oxygen content, in the oxygen treatment of raw carbon black, the factor of the oxygen treatment temperature is dominant. That is, even if the BET specific surface area increases as the oxygen treatment temperature increases, there is a tendency for the oxygen content to decrease. This is presumably because as the oxygen treatment temperature increases, the types of oxygen-containing functional groups that can exist stably are limited, and the amount of oxygen-containing functional groups present is restricted. Specifically, when the oxygen treatment temperature exceeds 500°C, the oxygen content drops to 0.5% by mass or less. 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 depends greatly on the oxygen concentration and the oxygen treatment temperature. However, if the oxygen concentration and the oxygen treatment temperature are within the above ranges, 1 to 40 hours can be exemplified. The upper limit of the oxygen treatment time is, for example, 100 hours. When the oxygen treatment time exceeds 100 hours, the proportion of surface combustion of the raw carbon black increases, and it becomes difficult to realize a pore structure that satisfies requirement (E) and requirement (H).

[0101] From the perspective of oxygen addition, oxygen treatment with ozone can also be applied. However, since pores are not formed in the oxygen treatment with ozone, it is preferable to perform ozone treatment on the raw carbon black after oxygen treatment in an oxidizing gas containing ozone under conditions of 100°C or less after the oxygen treatment.

[0102] Since the oxygen treatment of raw carbon black using these oxygen or ozone as oxidation gases is an exothermic reaction, it is necessary to pay attention to suppressing thermal runaway due to the accumulation of reaction heat. As an apparatus suitable for the oxygen treatment, for example, a rotary kiln or a fluidized bed in which the gas is forcibly brought into contact with the raw carbon black can be applied. In the rotary kiln and the fluidized bed, fresh oxidation gas and raw carbon black come into contact with each other, and a uniform oxygen treatment can be realized in a short time. However, since the fluidized bed has a high gas utilization rate, the oxygen treatment can be completed in a short time. However, since the heat generation amount per unit time and per unit volume is large, a device design that can easily remove heat is important. For example, by increasing the floor area and restricting the loading amount of the raw carbon black in the height direction, the oxidation gas itself can act as a heat removal medium for the reaction heat.

[0103] As the action of the oxygen treatment, as the mass reduction rate increases, the proportion of surface combustion increases. For example, it is not possible to produce porous activated carbon black having a BET specific surface area exceeding 500 m 2 / g. That is, the pore structure by the oxygen treatment is only a pre-treatment, and the finishing treatment of the pore structure is carried out by the first activation with steam or CO2 after the oxygen treatment.

[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 as follows. The oxygen-treated carbon black is brought into contact with an activating gas such as steam (H2O) or CO2 and maintained at 800 °C to 1100 °C, whereby the carbon atoms constituting the oxygen-treated carbon black are removed as CO. By optimizing the reaction rate of this reaction, the peripheral part (edge part) of the condensable polycyclic aromatic hydrocarbons that are easy to burn in the crystallites of several nanometers in size forming the oxygen-treated carbon black is selectively oxidized and consumed. As a result, gaps are formed between the crystallites, and further, the consumption of the crystallites continues toward the inside. Thereby, a porous carbon black is formed. This is the process of making the carbon black porous by the activation operation.

[0105] When the activation treatment temperature is increased, the reaction rate increases, the combustion near the surface in contact with the high-concentration activating gas is accelerated, and the concentration of the activating gas diffusing into the interior becomes even lower, so that the internal combustion is decelerated. In order to develop pores inside without changing the surface state, it is necessary to control the reaction rate appropriately. Steam and CO2 are optimal activating gases from the viewpoint that the reaction rate can be controlled over a wide range by temperature. The reason why the application of activation by oxygen has not been industrialized is as follows. The oxidation reaction of oxygen-treated carbon black by steam and CO2 is an endothermic reaction, and the reaction does not proceed without supplying heat. From the viewpoint that it can be controlled by the amount of heat supplied, it is easy to scale up. On the other hand, the oxidation reaction of oxygen-treated carbon black by oxygen is an exothermic reaction, and if the heat generation is more than the heat removal, the temperature of the reaction site rises monotonously and the reaction is difficult to control. Since this phenomenon is accelerated with scale-up, oxidation by oxygen is not suitable for mass production, and activation using steam or CO2 as the activating gas is suitable.

[0106] If a manufacturing process that allows such an activation reaction to proceed is realized, there are no restrictions on the activation device. To promote activation efficiently, it is advisable to increase the concentration of the activation gas on the surface of the oxygen-treated carbon black pellets. To achieve this, it is often beneficial to reduce the thickness of the boundary layer of the 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 with respect to the pellets of the oxygen-treated carbon black. Generally, a rotary kiln or a fluidized bed used in industrial production is preferable as it can enhance the uniformity of the activation gas in the furnace. Since the relative velocity of the activation gas with respect to the oxygen-treated carbon black pellets can be increased, the fluidized bed is an excellent device in terms of gas utilization efficiency and reaction rate, and is particularly suitable.

[0107] The specific conditions for the first activation involve controlling the temperature according to the reaction intensity of the activation gas. The activation gas is preferably steam or CO2. When steam is used as the activation gas, the preferred activation treatment temperature is 750°C to 900°C, and when CO2 is used as the activation gas, the preferred activation treatment temperature is 800°C to 950°C. To obtain activated carbon black that meets requirements (C) to (E), the mass reduction rate of the carbon black treated with oxygen 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 reduction rate is, for example, 5 to 100 hours, preferably 10 to 80 hours, more preferably 20 to 80 hours. Under activation conditions where the time required for the mass reduction rate to reach 50% by mass is shorter than 5 hours, for example, compared to the case where the time required for the same mass reduction rate is 20 hours, the BET specific surface area is smaller, and the integrated value Σ of the pore volume with a pore diameter of more than 2 nm and less than 6 nm 2-6 is smaller, or the ratio of the integrated value of the pore volume Σ 6-10 / Σ 2-6 becomes larger. 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 internal pore formation, and a part of the mass reduction is consumed in surface combustion, resulting in no increase in the BET specific surface area. Also, surface combustion This is because the pore volume of pores with a pore diameter of 6 nm or more and less than 10 nm increases. That is, in order to suppress surface combustion, it is preferable to lower the activation temperature and increase the activation time. In the case of activation for a long time such that the time required for the mass reduction rate to reach 50% by mass exceeds 100 hours, since the reaction rate is too slow, surface combustion becomes dominant over internal combustion, and the development of pores with a pore diameter of 2 nm or more and less than 6 nm is suppressed, which is not preferable. Note that in the activation treatment with a high activation treatment temperature and a long activation treatment time (for example, activation with an activation treatment temperature of 980 °C or higher and an activation treatment time of 110 hours or longer), for the above reasons, activated carbon black satisfying requirement (E) and requirement (H) cannot be obtained.

[0108] It is also preferable to perform activation while increasing the activation gas pressure. Since the activation gas concentration is high, the rate of the oxidation reaction increases almost proportionally to the concentration, and the activation time can be shortened without changing the pore development, that is, the BET specific surface area and the pore size distribution, and without changing the ratio of surface combustion. In the pressure range up to several atmospheres, the activation time can be shortened in proportion to the pressure. At a pressure of 6 atmospheres or more, the effect of increasing the pressure is hardly visible, and a pressure of 6 atmospheres or less is preferable. The activation time in the case of activation under pressure is, for example, 3 to 50 hours, preferably 5 to 30 hours, and more preferably 5 to 20 hours. In order to avoid the same phenomenon as in the case of normal pressure, the lower limit and the upper limit of the activation time are determined.

[0109] By the above first activation step, pores with a pore diameter of 6 nm or more and less than 10 nm develop inside the oxygen-treated carbon black, and activated carbon black satisfying requirements (C) to (E) can be manufactured. In the process of enhancing crystallinity in the heat treatment step, the porous activated carbon black changes in its tissue structure and crystal structure toward a more stable graphite structure. Therefore, the pores, which can be regarded as defects, change in the direction of being crushed. Accordingly, the pore structure of the activated carbon black obtained in the first activation step needs to create a structure that is more developed than the finally desired pore structure so as to maintain a preferable pore structure even when the pores are crushed in 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 carrier is exposed to a noble potential of 1 V or higher in the operating environment of the fuel cell. Since the ionomer has a sulfonic acid group, the catalyst carrier coated with the ionomer is placed in a noble potential of 1 V or higher and a strongly acidic environment. When applying porous activated carbon black to such an environment, thermodynamic stability cannot be expected, so as a general countermeasure, it is common to increase its crystallinity as much as possible to avoid oxidative consumption in terms of speed.

[0111] To increase the crystallinity of the porous activated carbon black, it is a common method to perform heat treatment 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., a graphitization treatment step) at 1400°C to 1900°C for 10 minutes to 10 hours under normal pressure (i.e., 1 atmosphere) in an inert gas atmosphere. If the temperature exceeds 1900°C, the crushing of pores due to heat treatment is significant, so in practice, 1900°C or lower is preferable.

[0112] In the heat treatment step, the crystallinity of the activated carbon black can be increased by graphitization of the activated carbon black. More specifically, by subjecting the activated carbon black obtained by performing the first activation under the above strong activation conditions to heat treatment under the above conditions, the crystallinity of the activated carbon black can be increased while maintaining the pores without crushing them. Thereby, in addition to requirements (F) to (H), it is possible to produce a porous activated carbon black that satisfies requirement (I).

[0113] The heat treatment step may be any step that can heat the activated carbon black under the above conditions and is not particularly limited. Examples of the heating method include resistance heating, microwave heating, high-frequency heating, and furnace-type heating methods. For the furnace type, there is no limitation as long as a graphitization furnace, a batch furnace, a tunnel furnace, etc. can achieve normal pressure and an inert gas atmosphere.

[0114] (Second activation step) In the second activation step, the heat-treated activated carbon black obtained by heat treatment is subjected to a second activation. As the activation gas, steam or CO2 is preferable. By the second activation, crystallites that have been miniaturized or burned out due to oxidative consumption during the first activation come into contact with each other by thermal fluctuations, and a chemical bond is formed at the contact point, forming a tissue structure in which the crystallites are continuous.

[0115] During the second activation process, the primary particle size generally shrinks, and the shape also changes from spherical to an irregular shape. Along with the deformation, the gaps between the crystallites become smaller, and the pore volume and BET specific surface area become smaller. The second activation is a treatment for expanding the reduced voids or reopening the blocked pores. If the heat-treated activated carbon black is used as a catalyst support without performing the second activation, the power generation characteristics (especially the low-load characteristics) are significantly inferior compared to the porous activated carbon black after the second activation. This is presumably because the ionomer hardly penetrates into the pores due to the reduced pore diameter, resulting in a decrease in the catalyst utilization rate and a decrease in the power generation characteristics. Since the purpose of the second activation is to expand the voids and reopen the blocked pores, the combustion of carbon by the second activation is preferably minimized. From this perspective, the mass reduction rate by the second activation 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 several hours (for example, 1 hour or more and 5 hours or less) at 800°C to 950°C. More specifically, when the heat treatment temperature exceeds 1800 °C and is 1900 °C or lower, and the activation temperature of the second activation exceeds 900 °C and is 950 °C or lower, the activation time is preferably 1.5 hours or more and 5.0 hours or less. When the heat treatment temperature is high, the crystallinity increases and the progress of activation in the second activation slows down. Therefore, there is a tendency to increase the activation temperature of the second activation. However, when the activation temperature of the second activation exceeds 900 °C and is 950 °C or lower, oxidation consumption of the carbon surface is likely to occur. Therefore, the activation time is lengthened to reduce the ratio of surface oxidation consumption as much as possible. Therefore, as the minimum activation time, 1.5 hours or more and 5.0 hours or less is preferable. On the other hand, when the heat treatment temperature is 1800 °C or lower, the above considerations are not necessary.

[0116] <Catalyst Layer for Solid Polymer Fuel Cell and Solid Polymer Fuel Cell> A solid polymer fuel cell will be described together with the catalyst layer for a solid polymer fuel cell of the present disclosure. The carbon material of the present disclosure is applicable to, for example, the catalyst layers 150 and 160 provided in the solid polymer fuel cell 100 shown in FIG. 1. FIG. 1 is a schematic diagram showing an example of the schematic configuration of the fuel cell of the present disclosure. The solid polymer 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 and introduces a reducing gas such as hydrogen into the gas diffusion layer 130. The separator 120 is a cathode-side separator and introduces an oxidizing gas such as oxygen gas or air into the gas diffusion agglomerate phase. The types of the separators 110 and 120 are not particularly limited, and any separator used in a conventional fuel cell (for example, a solid polymer fuel cell) may be used.

[0118] The gas diffusion layer 130 is the gas diffusion layer on the anode side. After diffusing the reducing gas supplied from the separator 110, it is supplied to the catalyst layer 150. The gas diffusion layer 140 is the gas diffusion layer on the cathode side. After diffusing the oxidizing gas supplied from the separator 120, it is supplied to the catalyst layer 160. The types of the gas diffusion layers 130 and 140 are not particularly limited, and any gas diffusion layer used in a conventional fuel cell (for example, a polymer electrolyte fuel cell) may be used. Examples of the gas diffusion layers 130 and 140 include porous carbon materials (carbon cloth, carbon paper, etc.), porous metal materials (metal mesh, metal wool, etc.). Note that preferred examples of the gas diffusion layers 130 and 140 include a gas diffusion layer having a two-layer structure. Specifically, in the gas diffusion layers 130 and 140, the layers on the separator 110 and 120 sides become gas diffusion fiber layers mainly composed of fibrous carbon materials, and the layers on the catalyst layers 150 and 160 sides become micropore layers mainly composed of carbon black, and a two-layer structure gas diffusion layer can be mentioned. A two-layer structured gas diffusion layer can be mentioned in which the layer on the separator 110 and 120 sides becomes a gas diffusion fiber layer mainly composed of fibrous carbon materials, and the layer on the catalyst layers 150 and 160 sides becomes 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, generating protons and electrons. For example, when the reducing gas is hydrogen gas, the following oxidation reaction occurs. H2→2H + +2e - (E0=0V)

[0120] The protons generated by the oxidation reaction reach the catalyst layer 160 through the catalyst layer 150 and the electrolyte membrane 170. The electrons generated by the oxidation reaction reach the external circuit through the catalyst layer 150, the gas diffusion layer 130, and the separator 110. The electrons perform work (generate electricity) in the external circuit and then are introduced into the separator 120. Thereafter, the electrons reach the catalyst layer 160 through the separator 120 and the gas diffusion layer 140.

[0121] The configuration of the catalyst layer 150 serving as the anode is not particularly limited. The configuration of the catalyst layer 150 may be the same as that of a conventional anode, may be the same as that of the catalyst layer 160, or may have a higher hydrophilicity than the catalyst layer 160.

[0122] The catalyst layer 160 is a so-called cathode. In the catalyst layer 160, a reduction reaction of an oxidizing gas occurs and water is generated. For example, when the oxidizing gas is oxygen gas or air, the following reduction reaction occurs. The water generated in the oxidation reaction is discharged to the outside of the polymer electrolyte fuel cell 100 together with the unreacted oxidizing gas. O2+4H + +4e - →2H2O (E0=1.23V)

[0123] Thus, in the polymer electrolyte fuel cell 100, power is generated by utilizing the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, the electrons generated in the oxidation reaction perform work in the external circuit.

[0124] The catalyst layer 160 contains the carbon material for catalyst support of the present disclosure. That is, the catalyst layer 160 contains the carbon material for catalyst support of the present disclosure, an electrolyte material (ionomer), and a catalyst component (such as platinum). Thereby, the power generation characteristics (particularly low load characteristics) and durability within the catalyst layer 160 can be enhanced. And the power generation characteristics (particularly low load characteristics) and durability of the polymer electrolyte fuel cell 100 can be enhanced.

[0125] Note that the catalyst loading ratio in the catalyst layer 160 is not particularly limited, and it is preferably 30% by mass or more and less than 80% by mass. When the catalyst loading ratio is within this range, the power generation characteristics (especially the low load characteristics) and durability are further improved. Here, the catalyst loading ratio is represented by the mass percentage of the catalyst component with respect to the total mass of the catalyst-supported particles (particles obtained by supporting the catalyst component on the carbon material for the catalyst carrier). When the catalyst loading ratio is less than 30% by mass, it may be necessary to increase the thickness of the catalyst layer 160 in order for the polymer electrolyte fuel cell 100 to withstand practical use. On the other hand, when the catalyst loading ratio is 80% by mass or more, catalyst aggregation is likely to occur. In addition, the catalyst layer 160 may become too thin, resulting in the possibility of flooding.

[0126] The mass ratio I / C of the mass I of the electrolyte material to the mass C of the carbon material for the catalyst carrier in the catalyst layer 160 is not particularly limited, and it is preferably more than 0.5 and less than 5.0. In this case, the pore network and the electrolyte material network can coexist, and the power generation characteristics (especially the low load characteristics) and durability are improved. On the other hand, when the mass ratio I / C is 0.5 or less, the electrolyte material network becomes weak, and the proton conduction resistance tends to increase. When the mass ratio I / C is 5.0 or more, the pore network may be divided by the electrolyte material. In any case , the power generation characteristics (especially the low load characteristics) and durability may decrease.

[0127] Also, the thickness of the catalyst layer 160 is not particularly limited, and it is preferably more than 5 μm and less than 20 μm. In this case, the oxidizing gas diffuses easily in the catalyst layer 160, and flooding is less likely to occur. When the thickness of the catalyst layer 160 is 5 μm or less, flooding is likely to occur. When the thickness of the catalyst layer 160 is 20 μm or more, the oxidizing gas diffuses hardly in the catalyst layer 160, and the catalyst component near the electrolyte membrane 170 is less likely to function. That is, the catalyst utilization rate may decrease.

[0128] The electrolyte membrane 170 is composed of an electrolyte material having proton conductivity. The electrolyte membrane 170 introduces the protons generated in the above oxidation reaction into the catalyst layer 160 (cathode). Here, the type of the electrolyte material is not particularly limited, and any electrolyte material used in a conventional fuel cell, for example, a polymer electrolyte fuel cell, may be used. Examples of suitable electrolyte materials include electrolyte resins. Examples of electrolyte resins include polymers into which a phosphoric acid group, a sulfonic acid group, etc. are introduced. Specifically, for example, perfluorosulfonic acid polymers, polymers into which benzenesulfonic acid, etc. are introduced, etc. may be mentioned. Of course, the electrolyte material may be other types of electrolyte materials. Examples of such electrolyte materials include inorganic-based, inorganic-organic hybrid-based electrolyte materials, etc. Note that the polymer electrolyte fuel cell 100 may be a fuel cell that operates within a range of normal 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 any manufacturing method similar to the conventional one may be used. However, the carbon material for the catalyst carrier of the present disclosure is used for the catalyst carrier. Among the catalyst layers 150 and 160, it is preferable to use the carbon material for the catalyst carrier of the present disclosure for at least the catalyst carrier in the catalyst layer 160 that serves as the cathode. Of course, the carbon material for the catalyst carrier of the present disclosure may be used for the catalyst carriers of both catalyst layers in the catalyst layer 150 that serves as the anode and the catalyst layer 160 that serves as the cathode.

Examples

[0130] Examples of the carbon material for the catalyst carrier of the present disclosure will be described. First, the measurement methods for each parameter will be described.

[0131] <Measurement methods for each parameter> (Measurement of oxygen content) A few milligrams of the sample were weighed and elemental analysis was performed using an elemental analyzer (fully automatic organic trace element analyzer "PerkinElmer 2400 II CHNS / O" (Imidium Co., Ltd.)). Then, the mass percentages of C, H, and N in the sample were analyzed, and the difference between the total mass percentage of C, H, and N and 100% was calculated as the mass percentage of O, which was taken as the oxygen content (mass percentage).

[0132] (Measurement of nitrogen adsorption - desorption isotherm (BET specific surface area)) Approximately 30 mg of the sample was weighed and dried under vacuum at 120 °C for 2 hours. Subsequently, the sample was set in an automatic specific surface area measuring device (BELSORP MAX manufactured by MicrotracBEL Corp.), and the nitrogen adsorption - desorption isotherm was measured at a measurement temperature of liquid nitrogen temperature (about 77 K) using nitrogen gas as the adsorbate. The BET specific surface area was calculated by performing BET analysis in the range of relative pressure P / P0 of 0.05 - 0.15 in the nitrogen adsorption isotherm. The BET value was calculated using the calculation software attached to the device. value was calculated.

[0133] (Primary particle size) The primary particle size of the oxidized carbon black was measured as follows. Refer to page 176 of "Carbon Black Handbook" (edited by the Carbon Black Association, first edition in 1971), "i. Electron microscope photography method", "ii. Measurement of particle size", and "iii. Particle size calculation method". To take the statistical average, the sizes of at least 100 primary particles were measured, and the arithmetic average was determined as the primary particle size D of the oxidized carbon black. The arithmetic average diameter is calculated by the following formula. D = Σnidi / Σni, where ni is the number of particles with particle size di.

[0134] (Pore size distribution of mesopores) The pore size distribution of mesopores was analyzed by the BJH method. Using the calculation software of the HK method attached to the device, the pore size distribution of mesopores was calculated, and the integrated value Σd of the pore volume with pore diameter (diameter) of 2 nm, 6 nm, and 10 nm or less <2 、Σd <6 、Σd <10, was calculated (see Figure 1). Then, Σ d<6 -Σ d<2 was calculated, and the integrated value Σ 2-6 of the pore volume with a pore diameter of 2 nm or more and less than 6 nm was adopted (see Figure 2). Further, Σd <10 -Σ d<6 was calculated, and the value was divided by Σ d<6nm -Σ d<2nm to obtain the ratio Σ 2-6 of the integrated value Σ 6-10 of the pore volume with a pore diameter of 2 nm or more and less than 6 nm to the integrated value Σ 6-10 / Σ 2-6 of the pore volume with a pore diameter of 6 nm or more and less than 10 nm, which was adopted (see Figure 2).

[0135] (Measurement of the intensity ratio I D / I G by Raman spectroscopy)) Approximately 3 mg of the sample was weighed, and a Raman spectrum was measured using a laser Raman spectrophotometer (manufactured by JASCO Corporation, model NRS - 3100). From the Raman spectrum obtained under the following measurement conditions, peaks in the range of 1300 - 1360 cm -1 called the D band and peaks in the range of 1560 - 1620 cm -1 called the G band were extracted, and the intensities of these two peaks were analyzed using the spectrum analysis software attached to the apparatus to calculate the intensity I D of the D band and the intensity I G of the G band. Since the area of the Raman peak reflects the amount of carbon material belonging to each band, the area of each peak (each band) at the time of peak separation by the analysis software was adopted as the intensity. From these values, the intensity ratio I D / I G was calculated. - Measurement conditions - Excitation laser: 532 nm, laser power: 10 mW (sample irradiation power: 1.1 mW), microscope configuration: Backscattering, objective lens: ×100 magnification, spot diameter: 1 μm, exposure time: 30 sec, observation wavenumber: 2000 cm -1 ~300 cm -1 , integration times: 6 times.

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

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

[0138] Table 1 below shows the values of the primary particle diameter (arithmetic mean particle diameter), DBP oil absorption, and BET specific surface area of the raw carbon blacks respectively cited from the Carbon Black Yearbook No. 72 (2022), edited by the Carbon Black Association, and the product homepage of Ketjenblack.

[0139]

Table 1

[0140] <Oxygen treatment process> A reaction tube was used, which was a quartz tube with an outer diameter of 50 mmφ in which a quartz filter (pore diameter 40 to 50 μm) was fused as a dispersion plate. Quartz wool was packed to a height of about 1 cm, and the raw carbon black in granulated form was placed on it. The charge was generally 20 to 25 g, and dry air or dry air mixed with argon gas was flowed as an oxidizing gas from the bottom to the top of the reaction tube at a linear velocity in the range of 1.0 to 3.0 cm / second. The oxygen treatment temperature was selected while paying attention not to ignite due to heat accumulation from the exothermic reaction. Since the combustion rate varies depending on the type of raw carbon black, the conditions were carefully selected for each raw carbon black. Specifically, the raw carbon blacks shown in Table 1 were subjected to oxygen treatment at the oxygen concentration, oxygen treatment temperature, and mass reduction rate shown in Table 1. However, in the case of #200 which is easy to burn, in order to suppress ignition by reducing the calorific value, an oxidizing gas obtained by mixing oxygen and argon gas to the oxygen concentration shown in Table 1 was used, and the linear velocity was suppressed to 0.5 to 1.0 cm / second or less to subject the raw material carbon black to oxygen treatment. Also, in the case of #SH and GFY with large particle diameters and slow combustion rates, an oxidizing gas obtained by mixing oxygen and argon gas to the oxygen concentration shown in Table 1 was flowed at a linear velocity of 1.0 to 2.0 cm / second to subject the raw material carbon black to oxygen treatment. Also, in the case of #4500, since it has an intermediate combustion rate between the two, an oxidizing gas obtained by mixing oxygen and argon gas to the oxygen concentration shown in Table 1 was flowed at a linear velocity of 0.7 to 1.5 cm / second to subject the raw material carbon black to oxygen treatment. Here, the primary particle diameter D of the obtained oxygen-treated carbon black was equivalent to that of the raw material carbon black.

[0141] Note that EC300J, EC600JD, and XE2B are already porous carbon blacks, and the pore structure indices are listed as reference examples and compared with the experimental examples after the first activation. Also, EC200L was slightly activated and had a low BET surface area, which was similar to the BET surface area of the oxygen-treated carbon black of the present disclosure. The pore structure indices were listed as reference examples and compared with the experimental examples after oxygen treatment.

[0142] <First activation step> A quartz filter was fused as a dispersion plate inside a quartz tube with an outer diameter of 35 mmφ to form a reaction tube. Quartz wool was placed on the dispersion plate to a height of about 1 cm, and 5 g to 15 g of oxygen-treated carbon black was placed on top of it. The reaction tube was set in a vertical electric furnace at a normal operating temperature of 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. Heating was carried out up to 850 - 950°C, and after reaching the predetermined temperature, the gas was switched to CO2 gas. The flow rate was adjusted so that the linear velocity was 1 - 2 cm / sec under the condition of the furnace temperature. After treatment for a predetermined time, the reaction tube was taken out of the furnace and simultaneously switched to argon gas for cooling. After confirming cooling near room temperature (25°C), the carbon black was taken out and the quality was measured, and the mass reduction rate of the yield with respect to the charged mass (charged mass / recovered mass) was calculated. The conditions of 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 - 80 mass%.

[0143] <Heat treatment process> A so-called heat treatment furnace using a graphite material for the heating element was used. The first activated activated carbon black was placed in a graphite crucible with a volume of about 100 cc. After depressurizing and vacuum replacing with argon gas, the temperature was raised at a rate of 10°C per minute with an argon flow rate such that the furnace volume could be replaced in several tens of minutes. After holding at a predetermined temperature for a certain period of time, it was cooled and taken out after cooling to near room temperature. The holding time of the treatment temperature was made variable. The conditions are shown in Table 2.

[0144] <Second activation process> The basic treatment process was the same as that of the first activation, with the activation time set to 1 - 5 hours to reduce the mass reduction rate. The following shows the specific treatment process. A quartz filter was fused as a dispersion plate inside a quartz tube with an outer diameter of 35 mmφ to serve as a reaction tube. Quartz wool was placed on the dispersion plate to a height of about 1 cm, and 2 g to 5 g of heat-treated heat-treatment activated carbon black was put on top. The reaction tube was set in a vertical electric furnace at a normal operating temperature of 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 started to be raised at a rate of 10°C / min. It was heated to 820 - 950°C, and after reaching the predetermined temperature, it was switched to CO2 gas. The flow rate was adjusted so that the linear velocity was 1 - 2 cm / sec under the state of the furnace temperature. After being treated for a predetermined time, the reaction tube was taken out of the furnace and simultaneously switched to argon gas for cooling. After confirming cooling near room temperature, the carbon black was taken out and weighed, and the mass reduction rate of the yield relative to the charged mass (charged weight / recovered weight) was calculated. The conditions of 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 - 20 mass%.

[0145] Through the above steps, carbon materials (porous activated carbon black) for catalyst carriers of each example were obtained.

[0146] <Fabrication of Membrane Electrode Assembly (MEA)> (Fabrication of Catalyst) The carbon material for catalyst carrier (porous activated carbon black) of each example was added to an ethanol / water mixed solvent and treated with an ultrasonic homogenizer for 2 minutes to disperse it. A predetermined amount of a nitric acid solution of dinitrodiammine platinum complex was added thereto, adjusted so that the platinum loading rate became 40 mass%, maintained at a temperature several degrees lower than the boiling point, and stirred in an oil bath for 15 hours. After the treatment, it was filtered, dispersed again in distilled water, re-filtered, and treated by vacuum drying at 90°C for 5 hours to obtain a catalyst.

[0147] (Fabrication of Ink) The ionomer solution manufactured by FUJIFILM Wako Pure Chemical Corporation was diluted with ethanol to adjust the solid content concentration to 10% by mass, and then dropped into an ethanol solution in which a catalyst had been previously dispersed. The dispersion was further advanced using an ultrasonic homogenizer and stirred with 1 mmφ glass beads for 10 to 15 hours. In this way, ink for forming a catalyst layer was obtained.

[0148] <Fabrication of MEA> The above ink was uniformly applied onto a Teflon (registered trademark) sheet using a sprayer and dried with a 60°C air circulation dryer to prepare a decal on which a catalyst layer was formed. Electrodes of a predetermined 36 mm size were cut out from the decal. Two identical cut sheets were used as the positive electrode and the negative electrode, and the positive electrode and the negative electrode were combined 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)) Regarding the MEAs fabricated using the carbon material (porous activated carbon black) for the catalyst support of each example, they were each incorporated into a cell, set in a fuel cell measurement device, and the performance evaluation of the fuel cell was conducted according to the following procedure.

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

[0151] Under the condition of supplying the oxidizing gas to the cell with such settings, the load was gradually increased, and the output voltage of the cell after holding the current density at 100 mA / cm 2 for 1 hour was measured, and the evaluation was conducted according to the criteria of the following pass rank and fail rank. The results are shown in Table 2. 〔Pass Rank〕 A: When the current density is 100 mA / cm 2Those in which the cell voltage after 1 hour has elapsed is 0.875 V or more. B: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is 0.872 V or more. C: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is 0.870 V or more. 〔Failed rank〕 D: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is less than 0.870 V.

[0152] (Evaluation of durability) In the above cell, with the anode left as it is and argon gas with the same humidification conditions as above flowing through the cathode, an operation of maintaining the cell voltage at 1.0 V for 4 seconds and an operation of maintaining the cell voltage at 1.3 V for 4 seconds are repeated (the repeated operation of rectangular-wave voltage fluctuation), and one cycle is defined as this repeated operation of rectangular-wave voltage fluctuation. After performing 4000 cycles of this repeated operation of rectangular-wave voltage fluctuation, the durability was investigated in the same manner as the evaluation of the above power generation characteristics. The evaluation was conducted based on the following pass and fail rank criteria. The results are shown in Table 2. 〔Pass rank〕 A: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is 0.820 V or more. B: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is 0.815 or more. C: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is 0.810 V or more. 〔Failed rank〕 D: The current density is 100 mA / cm 2 Those in which the cell voltage after 1 hour has elapsed is less than 0.810 V.

[0153]

Table 2-1

[0154]

Table 2-2

[0155]

Table 2-3

[0156]

Table 2-4

[0157] From the above results, it can be seen that the carbon material for catalyst carriers (porous activated carbon black) corresponding to this example is excellent in durability as well as power generation characteristics (especially low load characteristics) compared to the carbon material for catalyst carriers corresponding to the comparative example. In addition, it can be seen that the oxygen-treated carbon black and the activated carbon black corresponding to this example are suitable for producing the carbon material for catalyst carriers (porous activated carbon black) corresponding to this example, which is excellent in durability as well as power generation characteristics (especially low load characteristics). Also, from the reference examples, it can be seen that in the case of Ketjenblack EC300J, EC600JD, EC200L manufactured by Lion Corporation and Printex XE2B manufactured by Orion Corporation, sufficient power generation characteristics (especially low load characteristics) cannot be obtained together with durability.

[0158] Generally, when applying raw material carbon black with a particle size exceeding 40 nm, the pores become finer during the activation treatment. The pores are not well-developed and it is difficult for the BET surface area to increase. However, by performing oxygen treatment, it is possible to form pores that can be applied to a catalyst support even with raw carbon black having a primary particle diameter of 72 nm, and it was confirmed that a carbon material for a catalyst support (porous activated carbon black) with excellent power generation characteristics (especially low load characteristics) can be obtained. Also, even when applying raw carbon black with a primary particle diameter of 29 nm, it was confirmed that a carbon material for a catalyst support (porous activated carbon black) with excellent power generation characteristics (especially low load characteristics) can be obtained by performing optimal oxygen treatment, activation treatment, heat treatment, and secondary activation treatment. From these, it was confirmed that when applying raw carbon black with a primary particle diameter of 20 nm or more and 80 nm or less, a carbon material for a catalyst support (porous activated carbon black) with excellent power generation characteristics (especially low load characteristics) can be obtained.

[0159] The explanations of the symbols are as follows. 100 Polymer electrolyte fuel cell 110, 120 Separator 130, 140 Gas diffusion layer 150, 160 Catalyst layer 170 Electrolyte membrane

[0160] Note that 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 in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. Activated carbon black that simultaneously satisfies the following requirements (C), (D), and (E). (C) The BET specific surface area (m ２ / g) calculated by nitrogen gas adsorption isotherm measurement is 700 or more and 1500 or less. (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 with a pore diameter of 2 nm or more and less than 6 nm is Σ ２－６ When it is defined as Σ ２－６ is 0.22 or more and less than 1.

00. (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 with a pore diameter of 2 nm or more and less than 6 nm is Σ ２－６ , and the integrated value of the pore volume with a pore diameter of 6 nm or more and less than 10 nm is Σ ６－１０ . When this is the case, Σ ６－１０ / Σ ２－６ is 0.100 or more and 0.490 or less.

2. A carbon material for a catalyst support of a polymer electrolyte fuel cell, comprising porous activated carbon black that simultaneously satisfies the following requirements (F), (G), (H), and (I). The BET specific surface area (m ２ / g) by nitrogen gas adsorption measurement is 400 or more and 1200 or less. (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 with a pore diameter of 2 nm or more and less than 6 nm is Σ ２－６ When it is defined as ２－６ Σ is 0.20 or more and less than 0.

70. 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 with a pore diameter of 2 nm or more and less than 6 nm is Σ ２－６ , and the integrated value of the pore volume with a pore diameter of 6 nm or more and less than 10 nm is Σ ６－１０ . When this is the case, Σ ６－１０ / Σ ２－６ is 0.120 or more and 0.500 or less. In the Raman spectrum obtained by Raman spectroscopic measurement, the intensity of the D band at 1300 to 1360 cm －１ is I Ｄ , and the intensity of the G band at 1560 to 1620 cm －１ is I Ｇ . When this is the case, I Ｄ / I Ｇ is 1.20 or more and 2.20 or less.

3. A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst support of the polymer electrolyte fuel cell according to Claim 2.

4. A fuel cell, comprising the catalyst layer for a polymer electrolyte fuel cell according to Claim 3.

5. The fuel cell according to Claim 4, wherein the catalyst layer for the polymer electrolyte fuel cell is a cathode-side catalyst layer.

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