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

Abstract

This carbon material for a catalyst carrier of a solid polymer fuel cell comprises a porous activated carbon black satisfying the following requirements (A) and (B).　(A) The BET specific surface area SBET obtained by a BET analysis of a nitrogen gas adsorption isotherm is 400-1200 m2 / g.　(B) In a mercury porosimetry, when the difference between the mercury absorption amount (mL / g) at 10 MPa mercury insertion pressure and the mercury absorption amount (mL / g) at 100 MPa mercury insertion pressure after applying pressure to the porous activated carbon black at a pressure of 100 MPa with a mold and said difference before applying pressure to the porous activated carbon black at a pressure of 100 MPa with a mold are represented by ΔVfin and ΔVini, respectively, the ratio ΔVfin / ΔVini is 0.75-0.95.

Description

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

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

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

[0003] A fuel gas such as hydrogen is introduced into the separator on the anode side. After diffusing the fuel into the gas diffusion layer on the anode side, it is introduced into the anode. The anode contains a catalyst component, a catalyst carrier that supports a fuel cell catalyst, and an electrolyte material with proton conductivity. Hereinafter, the catalyst component that promotes the power generation reaction (oxidation reaction or reduction reaction described below) in the fuel cell will also be referred to as the "fuel cell catalyst." The catalyst carrier is often made of a porous carbon material. An oxidation reaction of the fuel gas occurs on the fuel cell catalyst, generating protons and electrons. For example, when the fuel gas becomes hydrogen gas, the following oxidation reaction occurs: H ２ →2H ＋ +2e － (E ０ = 0 V)

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

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

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

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

[0008] For example, Patent Document 1 proposes "a membrane electrode assembly including a polymer electrolyte membrane and a pair of electrode catalyst layers sandwiching the polymer electrolyte membrane, wherein at least one of the pair of electrode catalyst layers contains catalyst-supported particles, a polymer electrolyte, and a fibrous material having an average fiber diameter of 10 nm or more and 300 nm or less, wherein the mass of the fibrous material is 0.02 to 1.0 times the mass of the support in the catalyst-supported particles, and the mass of the polymer electrolyte is 0.4 to 1.0 times the mass of the support in the catalyst-supported particles."

[0009] Patent Document 2 proposes a "carbon material for use as a catalyst support for a polymer electrolyte fuel cell, which has a three-dimensionally branched dendritic structure, the branch diameter of which is 81 nm or less, and which simultaneously satisfies the following (A) and (B)." (A) BET specific surface area S obtained by BET analysis of a nitrogen gas adsorption isotherm ＢＥＴ 400 to 1500m ２ / g. (B) Mercury pressure P measured by mercury porosimetry Ｈｇ (kPa) and mercury absorption V Ｈｇ In this relationship, the mercury pressure P Ｈｇ Common logarithm LogP Ｈｇ The amount of mercury absorbed V measured when the value of Ｈｇ The increase in ΔV Ｈｇ：４．３－４．８ is 0.82 to 1.50 cc / g.

[0010] Patent Document 3 proposes "a method for producing a catalyst ink to be applied to both sides of an electrolyte membrane of a fuel cell, comprising: (1) a step of pulverizing, using a jet mill, catalyst-supported particles having activated carbon black and a catalyst supported on the carbon black; (2) a step of stirring a suspension solution obtained by mixing the pulverized catalyst-supported particles, an electrolyte, and a solvent for suspending the catalyst-supported particles and the electrolyte; and (3) a step of dispersing the suspension solution using an ultrasonic homogenizer, wherein in step (3), the catalyst-supported particles are dispersed so that, in a frequency distribution of particle sizes of the catalyst-supported particles in the catalyst ink as measured by a laser diffraction particle size distribution measurement method, a first peak is present in a particle size range of 1 micrometer or less, and no peak having a height equal to or greater than 1 / 4 of the height of the first peak is present in a particle size range exceeding 1 micrometer."

[0011] Patent Document 4 proposes "a carbon material for a catalyst carrier used in a catalyst carrier of a polymer electrolyte fuel cell, which has a three-dimensionally branched dendritic structure, and is characterized by simultaneously satisfying the following (1) and (2)." (1) In particle size distribution measurement using a laser diffraction / scattering particle size distribution analyzer, the DL / DH ratio is 1.5 or greater, where DL is the cumulative distribution [%] of particles with a particle diameter of 1 μm or less based on the volume diameter, and DH is the cumulative distribution [%] of particles with a particle diameter of more than 1 μm. (2) The mode diameter of pores in the range of 20 nm to 200 nm in diameter measured by mercury porosimetry is 40 nm to 70 nm.

[0012] Patent Document 1: JP 2023-022654 A Patent Document 2: WO 2018 / 182047 A Patent Document 3: Japanese Patent No. 5790537 Patent Document 4: JP 2022-156985 A

[0013] The ability of polymer electrolyte fuel cells (hereinafter referred to as "PEFC") to achieve both power generation characteristics and durability is an important characteristic for the widespread use of fuel cell vehicles (hereinafter referred to as "FCV"), and is an essential issue that must be resolved, particularly for commercial vehicles, where market growth is expected in the future.

[0014] In general, the power generation characteristics of PEFCs are governed by two factors: the contribution of the metal catalyst (e.g., platinum nanoparticles) to the reaction (hereinafter also referred to as "catalyst utilization") and the diffusivity of oxidizing gases. The pore structure of the carbon support (porous carbon material) correlates with catalyst utilization, while the three-dimensional structure of the carbon support (e.g., dendritic structure) correlates with gas diffusivity. A desirable pore structure is one in which only pores of sufficient size are selectively present to accommodate metal catalysts (e.g., platinum nanoparticles) of several nanometers in size. Mesoporous carbon is generally considered to be a suitable support. While the pore size suitable for gas diffusion is unclear, the pore size of the catalyst layer for nucleic acids, estimated from various currently used carbon supports, is around several tens to hundreds of nanometers. The pores in the catalyst layer are realized by the three-dimensional structure (e.g., dendritic structure) of the carbon support. The pore structure is preferably one in which only pores of a size sufficient to accommodate catalytic metals of several nanometers are selectively present, and mesoporous carbon materials are generally considered to be suitable carbon supports.

[0015] However, the carbon supports (porous carbon materials) of the prior art, including those disclosed in Patent Documents 1 to 5, still have room for improvement in terms of preventing a decrease in power generation characteristics (particularly, high-load characteristics). Specifically, the decrease in power generation characteristics (particularly, high-load characteristics) is caused by the collapse of the three-dimensional structure of the carbon support when a mechanical load such as pulverization is applied during preparation of an ink for forming a catalyst layer, and there is room for improvement. There is a demand for this improvement to be achieved using carbon black, which is an inexpensive and useful carbon support (porous carbon material).

[0016] Therefore, an object of the present disclosure is to provide a carbon material for a catalyst support of a polymer electrolyte fuel cell, which exhibits reduced power generation characteristics (particularly, high load characteristics), a catalyst layer for a polymer electrolyte fuel cell using the same, and a fuel cell.

[0017] The means for solving the problems include the following aspects: <1> A carbon material for a catalyst support of a polymer electrolyte fuel cell, comprising a porous activated carbon black that satisfies the following requirements (A) and (B): (A) a BET specific surface area S determined by BET analysis of a nitrogen gas adsorption isotherm; ＢＥＴ 400 to 1200m ２ (B) In the mercury porosimetry method, the difference between the mercury absorption amount (mL / g) at a mercury insertion pressure of 10 MPa and the mercury absorption amount (mL / g) at a mercury insertion pressure of 100 MPa after the porous activated carbon black was pressed at a pressure of 100 MPa using a mold and before the porous activated carbon black was pressed at a pressure of 100 MPa using a mold was defined as ΔV ｆｉｎ , ΔV ｉｎｉ When this is the case, the ratio ΔV ｆｉｎ / ΔV ｉｎｉ <2> The carbon material for a catalyst support of a polymer electrolyte fuel cell according to <1>, further satisfying at least one of the following requirements (C) and (D): (C) the ΔV ｉｎｉ (D) In ​​the Raman spectrum obtained by Raman spectroscopy, the peak density is 1300 to 1360 cm －１ The intensity of the D band of Ｄ, 1560-1620cm －１ The G band intensity of Ｇ When the intensity ratio I Ｄ / I Ｇ is 1.40 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 a polymer electrolyte fuel cell according to <1> or <2>. <4> A fuel cell, comprising the catalyst layer for a polymer electrolyte fuel cell according to <3>. <5> The fuel cell according to <4>, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on a cathode side.

[0018] According to the present disclosure, there are provided a carbon material for a catalyst carrier of a polymer electrolyte fuel cell, which exhibits a deterioration in power generation characteristics (particularly, high-load characteristics), a catalyst layer for a polymer electrolyte fuel cell using the same, and a fuel cell.

[0019] FIG. 1 is a schematic diagram showing an example of the general configuration of a fuel cell according to the present disclosure.

[0020] An example of the present disclosure will be described. In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when "greater than" or "less than" is added to the numerical values ​​before and after "to", the numerical range means a range that does not include these numerical values ​​as the lower or upper limit. In this disclosure, the term "process" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. In this disclosure, a "proton-conductive electrolyte material" used in a catalyst layer of a fuel cell is also referred to as an "ionomer."

[0021] <Carbon material for catalyst support of polymer electrolyte fuel cell> The carbon material for catalyst support of polymer electrolyte fuel cell of the present disclosure is made of porous activated carbon black that satisfies the requirements (A) and (B) described below. Here, porous activated carbon black is carbon black that has been made porous by activation. Note that porous activated carbon black is also referred to as "porous carbon black."

[0022] The carbon material for a catalyst support according to the present disclosure is a carbon material whose power generation characteristics (particularly, high load characteristics) deteriorate. The carbon material according to the present disclosure was discovered based on the following findings.

[0023] In general, the power generation characteristics of a fuel cell depend heavily on the overvoltage of the cathode reaction. The following three factors are thought to be the main causes of overvoltage at the cathode: (1) The magnitude of the ohmic resistance of the catalyst layer, which is the combination of two resistances: electron conduction resistance and proton conduction resistance; (2) The diffusion resistance of oxidizing gases within the catalyst layer; and (3) The electrochemical resistance on the catalyst metal surface, i.e., the resistance in the chemical reaction involving electron transfer (i.e., the resistance in the catalytic reaction).

[0024] In order to improve "(2) the diffusion resistance of oxidizing gases within the catalyst layer," one of the above major causes, the inventors investigated ways to increase the mechanical strength of the three-dimensional structure (i.e., dendritic structure) derived from the aggregate structure of porous carbon black. As a result, they discovered the following:

[0025] During processes such as the production of ink for forming a catalyst layer, porous carbon black is subjected to mechanical stresses, such as stirring, to improve dispersion. It is preferable that this mechanical stress does not destroy the three-dimensional (dendritic) structure, but rather disaggregates the carbon black into the smallest aggregates. Disaggregation results in the formation of voids (i.e., pores) within the catalyst layer, which are derived from the uniform three-dimensional (dendritic) structure. As a result, the diffusion resistance of oxidizing gases is reduced, improving power generation characteristics (particularly high-load performance). On the other hand, if the three-dimensional (dendritic) structure is destroyed by mechanical stress, fine powder is generated in the ink, and the voids within the catalyst layer derived from the three-dimensional (dendritic) structure are blocked by the fine powder. In other words, it becomes difficult to form pores within the catalyst layer. This increases the diffusion resistance of oxidizing gases, resulting in reduced power generation characteristics (particularly high-load performance).

[0026] In other words, the mechanical strength of porous carbon black contributes to improving power generation characteristics (especially high load characteristics).

[0027] Here, mercury porosimetry has conventionally been used to quantify the development of the three-dimensional structure (dendritic structure) of porous carbon black and to quantify the voids in the catalyst layer. The mercury absorption pressure (MPa) in mercury porosimetry varies depending on the three-dimensional structure (dendritic structure) of porous carbon black (for example, the thickness of the branches of the dendritic structure (corresponding to the primary particle diameter of carbon black) and the size of the dendritic structure (corresponding to the aggregate diameter). In other words, the size of the voids formed by the three-dimensional structure (dendritic structure) is reflected in the amount of mercury absorbed (mL / g). Therefore, mercury porosimetry is suitable for quantifying the three-dimensional structure (dendritic structure) of porous carbon black. Considering the minimum branch thickness required to increase the mechanical strength of the three-dimensional structure (dendritic structure) of porous carbon black, mercury absorption begins at an insertion pressure of 10 MPa or more. On the other hand, considering that the primary particle diameter of carbon black, which corresponds to the branch thickness, is practically limited to 80 nm, the upper limit of the mercury insertion pressure is 100 MPa. Therefore, the difference ΔV in the amount of mercury absorbed (mL / g) at insertion pressures of 10 MPa and 100 MPa, measured using mercury porosimetry, is suitable as a quantitative indicator of the three-dimensional structure (dendritic structure) of porous carbon black.

[0028] Therefore, the inventors conducted the following experiment. In order to simulate the mechanical load acting on the porous carbon black during the ink preparation process for forming the catalyst layer, the ΔV of the porous carbon black was measured before and after the ink preparation process using a planetary ball mill. Meanwhile, the porous carbon black was mechanically destroyed by pressing it with a mold, and the ΔV before and after was measured. Then, by investigating the correlation between the two, the mechanical strength of the three-dimensional structure (dendritic structure) of the porous carbon black, which shows little deterioration in power generation characteristics (especially high-load characteristics) in any ink process, was quantified as the ratio of ΔV before and after pressing with a mold. As a result of this investigation, the amount of mercury absorption VΔ before pressing with a mold was calculated. ｉｎｉ , the amount of mercury absorbed after pressing in the mold ΔV ｆｉｎ and the ratio ΔV ｆｉｎ / ΔV ｉｎｉIt was shown that this is the best indicator of mechanical strength in the ink manufacturing process of porous carbon black.

[0029] Meanwhile, the present inventors have investigated a method for producing porous carbon black having a large BET specific surface area and a three-dimensional structure (dendritic structure) with high mechanical strength, and have obtained the following findings.

[0030] By activating raw carbon black to make it porous and then heat-treating it to increase its crystallinity, porous carbon black suitable for catalyst supports can be obtained that has high power generation characteristics (especially high load characteristics) and durability. To improve the mechanical strength of such porous carbon black, the following guidelines are required: (1) Activation to prevent a decrease in mechanical strength, (2) Increasing the heat treatment temperature, and (3) Using raw carbon black with a large diameter.

[0031] Of the above guidelines, "(1) Activation that suppresses a decrease in mechanical strength" is important. If the surface of the raw carbon black is selectively oxidized and consumed prior to activation, rather than directly activating the raw carbon black, oxidation of the raw carbon black surface can be suppressed during subsequent activation. This allows for the formation of internally developed pores in the raw carbon black while suppressing surface oxidation during activation. Porous carbon black obtained by suppressing surface oxidation and developing internal pores has improved mechanical strength despite its high BET specific surface area. Treatments suitable for selectively oxidizing the surface of raw carbon black (pre-activation treatment) are low-temperature oxidation treatment using ozone at a temperature between room temperature (25°C) and 70°C, or oxidation treatment using air at a temperature between 300°C and 500°C.

[0032] Furthermore, "(2) Increasing the heat treatment temperature" ensures the pore volume necessary to achieve excellent power generation characteristics (especially high-load characteristics). However, increasing the heat treatment temperature causes the pores to collapse. Therefore, in order to ensure the target BET specific surface area of ​​the resulting porous carbon black, it is necessary to optimize the activation conditions, along with "(3) Using large-diameter raw carbon black," which is easily activated.

[0033] From the above findings, it has been found that the carbon material for a catalyst support according to the present disclosure is a carbon material whose power generation characteristics (particularly, high load characteristics) deteriorate.

[0034] The requirements (A) and (B) will be explained below. From the viewpoint of further suppressing a deterioration in power generation characteristics (particularly, high-load characteristics), it is preferable that the carbon material for a catalyst support of the present disclosure satisfies at least one of the requirements (C) and (D) in addition to the requirements (A) and (B).

[0035] (Requirement (A)) (A) BET specific surface area S obtained by BET analysis of nitrogen gas adsorption isotherm ＢＥＴ 400 to 1200m ２ / g.

[0036] BET specific surface area S of porous carbon black ＢＥＴ is the most suitable characteristic for quantitatively expressing the degree of pore development as a catalyst support. ＢＥＴ is 400m ２ / g or less, the amount of carbon required to support the catalytic metal increases, the thickness of the catalyst layer increases, and the gas diffusion resistance increases, resulting in a deterioration in power generation characteristics (especially high load characteristics). ＢＥＴ is 1200m ２ If the average particle size exceeds 1 / g, the requirement (B) described below cannot be satisfied. In other words, because the three-dimensional structure (dendritic structure) of the porous carbon black has low mechanical strength, the three-dimensional structure (dendritic structure) is destroyed during the preparation of the ink for forming the catalyst layer, resulting in the inclusion of fine particles in the ink. As a result, the fine particles clog the pores of the catalyst layer. This increases gas diffusion resistance and reduces power generation characteristics (particularly high-load characteristics).

[0037] The lower limit of the BET specific surface area of ​​porous carbon black is 450 m ２ / g or more is preferable, and 500m ２ The upper limit of the BET specific surface area of ​​the porous carbon black is 1150 m ２ / g or less is preferable, and 1100m ２ / g or less is more preferable.

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

[0039] (Requirement (B)) (B) In the mercury porosimetry method, the difference between the mercury absorption amount (mL / g) at a mercury insertion pressure of 10 MPa and the mercury absorption amount (mL / g) at a mercury insertion pressure of 100 MPa after the porous carbon black is pressed at a pressure of 100 MPa using a mold and before the porous carbon black is pressed at a pressure of 100 MPa using a mold is defined as ΔV ｆｉｎ , ΔV ｉｎｉ When this is the case, the ratio ΔV ｆｉｎ / ΔV ｉｎｉ is 0.75 or more and 0.95 or less. Here, the difference between the mercury absorption amount (mL / g) when the mercury insertion pressure is 10 MPa and the mercury absorption amount (mL / g) when the mercury insertion pressure is 100 MPa is "mercury absorption amount when the mercury insertion pressure is 100 MPa" - "mercury absorption amount when the mercury insertion pressure is 10 MPa."

[0040] Ratio ΔV of porous carbon black ｆｉｎ / ΔV ｉｎｉ is an index that utilizes the fracture behavior caused by die pressing, and is an index that indicates that the porous carbon black is less likely to be fractured during the production of ink for forming a catalyst layer, etc. ｆｉｎ / ΔV ｉｎｉ If the ratio ΔV of the porous carbon black is less than 0.75, the mechanical strength of the three-dimensional structure (dendritic structure) of the porous carbon black is low. Therefore, during ink production, the porous carbon black is destroyed, and fine particles are mixed into the ink. As a result, the fine particles clog the pores of the catalyst layer. This increases gas diffusion resistance and reduces power generation characteristics (especially high load characteristics). On the other hand, the ratio ΔV of the porous carbon black ｆｉｎ / ΔV ｉｎｉ The upper limit (0.95) of the ratio ΔV ｆｉｎ / ΔV ｉｎｉ This is the upper limit in the substantial sense, at which there are no materials that exhibit a value of 0.95 or more.

[0041] Ratio ΔV of porous carbon black ｆｉｎ / ΔV ｉｎｉThe lower limit of the ratio ΔV of the porous carbon black is preferably 0.76 or more, and more preferably 0.77 or more. ｆｉｎ / ΔV ｉｎｉ The upper limit of is preferably 0.94 or less, more preferably 0.93 or less.

[0042] The ratio ΔV of porous carbon black ｆｉｎ and ΔV ｉｎｉ is a value measured by the method described in the Examples below.

[0043] (Requirement (C)) (C) The difference ΔV between the amount of mercury absorbed (mL / g) when the mercury is inserted at a pressure of 10 MPa before the porous carbon black is pressed at a pressure of 100 MPa using a mold and the amount of mercury absorbed (mL / g) when the mercury is inserted at a pressure of 100 MPa ｉｎｉ is 0.80 mL or more and 1.50 mL / g.

[0044] ΔV of porous carbon black ｉｎｉ is an index that quantitatively indicates the degree of development of the three-dimensional structure (dendritic structure) of the porous carbon black, and is an index that is strongly correlated with the volume of the voids in the catalyst layer. ｉｎｉ If the ΔV of the porous carbon black is less than 0.80 mL / g, the pore volume of the voids formed in the catalyst layer is small, the gas diffusion resistance increases, and the power generation performance (particularly the high load characteristics) decreases. ｉｎｉ If the average particle size exceeds 1.50 mL / g, the porous carbon black surface is significantly rough, failing to meet requirement (B). The three-dimensional structure (dendritic structure) of the porous carbon black has low mechanical strength, which causes the porous carbon black to break during ink production, resulting in the inclusion of fine particles in the ink. As a result, the fine particles clog the pores in the catalyst layer. This increases gas diffusion resistance, degrading power generation characteristics (particularly high-load characteristics).

[0045] ΔV of porous carbon black ｉｎｉ The lower limit of ΔV of the porous carbon black is preferably 0.82 mL / g or more, and more preferably 0.84 mL / g or more. ｉｎｉ The upper limit is preferably 1.45 mL / g or less, more preferably 1.40 mL / g or less.

[0046] In addition, ΔV of porous carbon black ｉｎｉ is a value measured by the method described in the Examples below.

[0047] (Requirement (D)) (D) In ​​the Raman spectrum obtained by Raman spectroscopy, －１ The intensity of the D band of Ｄ , 1560-1620cm －１ The G band intensity of Ｇ When the intensity ratio I Ｄ / I Ｇ is 1.40 or more and 2.20 or less.

[0048] Intensity ratio I of porous carbon black Ｄ / I Ｇ is an index showing the crystallinity of porous carbon black. Ｄ / I Ｇ If the intensity ratio I of the porous carbon black is less than 1.4, the crystallinity of the porous carbon black is too high, making it difficult to maintain the surface area of ​​the pores required for power generation. This increases the amount of carbon required to support the catalytic metal, and the thickness of the catalyst layer increases. As a result, gas diffusion resistance increases, leading to a deterioration in power generation characteristics (especially high-load characteristics). Ｄ / I Ｇ If the value exceeds 2.2, the crystallinity of the porous carbon black is too low and the minimum durability is not achieved.

[0049] Intensity ratio I of porous carbon black Ｄ / I Ｇ The lower limit of the intensity ratio I of the porous carbon black is preferably 1.45 or more, and more preferably 1.50 or more. Ｄ / I Ｇ The upper limit of is preferably 2.15 or less, more preferably 2.10 or less.

[0050] In addition, the intensity ratio I Ｄ / I Ｇ is a value measured by the method described in the Examples below.

[0051] <Method for producing carbon material for catalyst support of polymer electrolyte fuel cell> Hereinafter, an example of a method for producing a carbon material for catalyst support of a polymer electrolyte fuel cell according to the present disclosure (hereinafter also referred to as a "method for producing a carbon material") will be described.

[0052] The method for producing a carbon material according to the present disclosure is, for example, a method including the following three steps: By the method for producing a carbon material according to the present disclosure, a carbon material satisfying requirements (A) and (B), preferably a carbon material satisfying requirements (A) and (B) as well as at least one of requirements (C) and (D) (i.e., porous activated carbon black) can be obtained.

[0053] Oxidation treatment step: An oxidation treatment step in which the surface of raw carbon black is selectively oxidized using ozone or oxygen. Activation treatment step: An activation treatment step in which the raw carbon black oxidized in the oxidation treatment step (hereinafter referred to as oxidized raw carbon) is made porous by activation. Heat treatment step: A heat treatment step in which the oxidized raw carbon black (hereinafter referred to as porous raw carbon) made porous in the activation treatment step is heat-treated. Ozone treatment step: An ozone treatment step in which the porous raw carbon black heat-treated in the heat treatment step (hereinafter referred to as heat-treated porous raw carbon black) is oxidized using ozone.

[0054] Each step will be described in detail below. First, the raw material carbon black used will be described.

[0055] (Raw Carbon Black) As the raw carbon black, carbon black that satisfies the three specific structures described below, namely, primary particle size, three-dimensional structure (aggregate structure formed by linked primary particles), and granulation state, can be suitably used.

[0056] Primary Particle Diameter The size of the voids in the catalyst layer is determined by the three-dimensional structure and primary particle diameter of the raw carbon black. That is, because the three-dimensional structure is formed by a series of primary particles, the primary particle diameter x the number of beads = void size. If the three-dimensional structure is developed and the primary particle diameter is 20 nm or greater, gas diffusion in the catalyst layer becomes rate-limiting and the power generation performance does not deteriorate. That is, the preferred range of primary particle diameter is 20 nm to 80 nm. Since it becomes difficult to develop a three-dimensional structure when the primary particle diameter exceeds 80 nm, 80 nm is the practical limit for manufacturing. Pore formation by activation is presumed to occur from the outside to the inside, and since the surface area is continuously exposed to oxidation treatment, combustion loss is significant. Assuming this, the larger the primary particle diameter, the more likely it is that small pores are formed internally, but relatively large pores are formed near the surface. In fact, activation treatment of raw carbon black with a large primary particle diameter results in weaker pore development, even with increased mass reduction, compared to smaller particle diameters. That is, the larger the primary particle size, the more difficult it is to increase the BET surface area. On the other hand, although the mechanism is not entirely clear, raw carbon black with a larger primary particle size has higher resistance to oxidative attenuation than raw carbon black with a smaller primary particle size, assuming the same crystallinity as measured by Raman or X-ray diffraction. In other words, the larger the primary particle size, the more important durability becomes. In particular, raw carbon black with a primary particle size exceeding 40 nm is effective in improving durability. Raw carbon black with a primary particle size of 50 nm or more is effective in significantly improving durability, and raw carbon black with a primary particle size exceeding 60 nm is effective in significantly improving durability.

[0057] The primary particle diameter of raw carbon black is one of the basic physical properties, and the primary particle diameter values ​​in the carbon black manufacturer's catalog are referenced. However, if the carbon black manufacturer's catalog value cannot be referenced, the arithmetic mean value of the primary particle diameter is calculated from images of primary particles measured with an electron microscope, as recommended by the Carbon Black Association, i.e., the method described in the Carbon Black Yearbook. More specifically, "i. Electron microscope photography method," "ii. Particle size measurement," and "iii. Particle size calculation method," page 176 of the Carbon Black Handbook (edited by the Carbon Black Association, first edition 1971), were referenced. To obtain a statistical average, the sizes of at least 100 primary particles are measured, and the arithmetic mean is determined as the primary particle diameter. The arithmetic mean diameter is calculated using the following formula: d = Σn ｉ di / Σn ｉ , where n ｉ is the particle diameter d ｉ is the number of.

[0058] Three-dimensional structure: Porous carbon black with a well-developed three-dimensional structure (dendritic structure) is preferred as a structure suitable for a catalyst support in a fuel cell. When a catalyst layer is formed with this three-dimensional structure, the catalyst layer becomes highly porous with voids, and the diffusion rate of oxidizing gas increases. Examples of physical properties that reflect the three-dimensional structure include DBP oil absorption, BET specific surface area, and mercury intrusion distribution measured by mercury porosimetry.

[0059] DBP oil absorption is an industrial index of the typical colloidal physical properties of carbon black, and is the value listed in the catalog. The physical property specifications in this disclosure also use the value listed in the physical property table of the carbon black manufacturer. A specific DBP oil absorption value is preferably 80 mL / 100 g or more, more preferably 100 mL / 100 g, and even more preferably 120 mL / 100 g. Since the specific gravity of raw carbon black is approximately 1.8 g / mL, if the DBP oil absorption is considered to correspond to the voids in the catalyst layer, a DBP oil absorption of 80 mL / 100 g corresponds to voids 1.4 times or more the volume of the raw carbon black. If the DBP oil absorption is less than 80 mL / 100 g, the development of the three-dimensional structure is too small, resulting in a decrease in high-load performance. On the other hand, the upper limit of DBP oil absorption is 180 mL / 100 g, which is the theoretical upper limit in manufacturing. The DBP oil absorption indicates the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black, and is a value defined in ASTM (American Standard Test Method) D2414-6TT.

[0060] The BET specific surface area is the most basic physical property of porous carbon black. The BET specific surface area of ​​the raw carbon black affects the activation in the first activation treatment step. The specific BET specific surface area is preferably 20 to 200 m ２ / g, more preferably 25 to 180 m ２ The BET specific surface area is a value measured by the method described in the Examples section below.

[0061] The evaluation of the three-dimensional structure by mercury porosimetry is performed by converting the hydrostatic pressure applied to mercury into pore diameters when assuming a cylindrical shape using the surface tension of mercury against the raw carbon black, and then obtaining the distribution of the integrated values ​​of the pore volumes larger than the pore diameters on the horizontal axis and the vertical axis, respectively. Raw carbon black with a three-dimensional structure absorbs mercury in proportion to the pore volume at a relative injection pressure corresponding to the pore size created by the three-dimensional structure, so the three-dimensional structure can be quantitatively evaluated from the pore size distribution of the amount of mercury absorbed. Specifically, the increment in the amount of mercury absorbed when the mercury injection pressure is increased from 10 MPa (corresponding to pores of approximately 10 nm) to 100 MPa (corresponding to pores of approximately 100 nm) is preferably 0.5 to 1.5 mL / g, taking into account the DBP oil absorption appropriate for the pores in the catalyst layer described above. If the increment in the amount of mercury is less than 0.5 mL / g, the development of the three-dimensional structure is too small, resulting in a decrease in high-load performance. On the other hand, the increase in the amount of mercury of 1.5 mL / g is the upper limit in principle in terms of production.

[0062] (Oxidation Treatment Step) The oxidation treatment step is a step of selectively oxidizing the surface of raw carbon black with ozone or oxygen. That is, the oxidation treatment step may be either an ozone treatment step in which the surface of raw carbon black is selectively oxidized with ozone, or an oxygen treatment step in which the surface of raw carbon black is selectively oxidized with oxygen.

[0063] -Ozone treatment process- Ozone (O ３Ozone has an oxidizing power second only to fluorine and can therefore be applied to the oxidation treatment of raw carbon black. The blackness of raw carbon black can be increased by adjusting the amount of oxygen-containing functional groups, so it is industrially used in the production of color carbon black. By utilizing the strong oxidizing power of ozone, the surface of raw carbon black can be selectively oxidized. Specifically, selective oxidation of the raw carbon black surface before activating it to make it porous significantly promotes pore development through activation, although the mechanism is not entirely clear. This improves both the branch strength of the three-dimensional structure (dendritic structure) of the resulting porous carbon black and pore development. It is speculated that selective oxidation of the raw carbon black surface burns and burns off a thin skin of about a few nanometers thick, forming pores in the raw carbon black that allow the introduction of activation gas. Alternatively, it is speculated that activation facilitates the formation of pores in the oxidized raw carbon black that allow the introduction of activation gas.

[0064] Thus, ozone treatment plays a role in developing the pores formed in the activated porous raw carbon black. That is, ozone treatment increases the pore volume and the surface area of ​​the pores, while simultaneously forming only the pores favorable for a catalyst support. In addition, ozone treatment also plays a role in preventing the occurrence of surface roughness and thinning of the branches of the three-dimensional (dendritic) structure of the porous carbon black in downstream processes, which are unsuitable for power generation characteristics (particularly high-load characteristics). Roughening of the porous carbon black surface due to combustion and thinning of the branches of the three-dimensional (dendritic) structure lead to a decrease in the mechanical strength of the three-dimensional (dendritic) structure. Therefore, ozone treatment can provide porous carbon black that satisfies requirements (A) and (B) (preferably, requirement (C) in addition to requirements (A) and (B)).

[0065] For ozone treatment, any device capable of generating ozone at a rate of 10 mg / hour or more may be used, and there are no limitations on the ozone generation mechanism or device structure. To increase the ozone generation rate, pure oxygen is usually used as the input gas. This is because, when air is input, the content of oxygen, which is the ozone raw material, is low, and the amount of ozone generated decreases accordingly. Because ozone is unstable and self-decomposes over time, it is preferable to contact the raw carbon black with an ozone-containing gas in a steady state. To increase the reaction rate, the ozone gas and raw carbon black may be contacted in a heated state.

[0066] The ozone treatment temperature is room temperature (25°C) to 70°C. Since the rate of ozone self-decomposition increases with increasing ozone treatment temperature, 70°C is the practical upper limit for oxidizing raw carbon black. The ozone treatment time is preferably 1 to 9 hours, under conditions such that the time required for the oxidation consumption rate of the raw carbon black to reach 3.0% is on the order of several hours. Ozone treatment times shorter than 1 hour are inappropriate because they generate too much heat and make it difficult for the entire raw carbon black powder to react uniformly. Ozone treatment times longer than 9 hours result in significant combustion of the raw carbon black surface. This surface combustion causes surface roughening of the porous carbon black and thinning of the branches of its three-dimensional (dendritic) structure, resulting in a decrease in the mechanical strength of the three-dimensional (dendritic) structure.

[0067] As is the case with oxygen treatment, ozone treatment of raw carbon black is a highly exothermic reaction, so the heat generated by the reaction must be diffused to the outside without being stored. This requires some ingenuity in actual treatment. For example, it is effective to increase the flow rate of ozone gas to release the heat generated by the gas, or to reduce the height at which the raw carbon black is piled up to shorten the heat diffusion path.

[0068] -Oxygen Treatment Step- In the oxygen treatment step, oxygen is brought into contact with the raw carbon black in a high temperature range, thereby achieving the same effect as in the ozone treatment step. In other words, the oxygen treatment step plays the same role as the ozone treatment. By carrying out the oxygen treatment step, porous carbon black that satisfies requirements (A) and (B) (preferably, in addition to requirements (A) and (B), at least one of requirements (C) and (D)) can be obtained.

[0069] In the oxygen treatment step, oxidation by oxygen generates a large amount of heat, so it is necessary to suppress ignition due to heat accumulation. The oxygen concentration of the oxidizing gas is preferably high, but it is at least 70% by volume or less, and preferably 50% by volume or less. The oxygen treatment temperature is also preferably high, but if it is too high, CO ２ The energy required for the formation of the carbon black decreases. Therefore, the oxygen treatment temperature is 500°C or lower, preferably 450°C or lower. On the other hand, the oxygen treatment temperature is preferably 300°C or higher. Temperatures below 300°C result in a slow reaction rate, making them impractical and unsuitable for the purpose of selectively oxidizing the surface of the raw carbon black. The oxygen treatment time is not particularly limited, but is preferably 2 to 15 hours. If the oxygen treatment time is less than 2 hours, oxidation is insufficient, and the pores formed in the activated porous raw carbon black do not develop. If the oxygen treatment time exceeds 15 hours, the surface of the raw carbon black will be significantly burned. This surface combustion causes surface roughness of the porous carbon black and thinning of the branches of the three-dimensional structure (dendritic structure), resulting in a decrease in the mechanical strength of the three-dimensional structure (dendritic structure). However, if the treatment temperature is 450°C or higher and 500°C or lower, the oxygen treatment time is preferably 2 to 9 hours.

[0070] Here, from the viewpoint of improving the efficiency of the oxidation treatment, devices suitable for the oxygen treatment step include, for example, a rotary kiln or a fluidized bed in which gas is forcibly brought into contact with the raw carbon black. Rotary kilns and fluidized beds allow fresh oxidation gas and raw carbon black to come into contact efficiently and uniformly, thereby achieving oxygen treatment in a short period of time. However, while fluidized beds have a high gas utilization rate and can complete oxygen treatment in a short period of time, they generate a large amount of heat per unit time and unit volume, so it is important to design the device so that it can easily remove heat. For example, by increasing the floor area and limiting the vertical load of raw carbon black, the oxidation gas itself can act as a heat removal medium for the reaction heat.

[0071] (Activation Treatment Step) The activation treatment step is a step of activating the oxidized raw carbon black oxidized in the oxidation treatment step to make it porous. The mechanism of activation of raw carbon black is considered to be as follows. Raw carbon black is heated in a gas atmosphere containing water vapor (H ２ O), or CO ２ By exposing the raw carbon black to an activation gas such as HCl and maintaining it at 800°C to 1100°C, the carbon atoms that make up the raw carbon black are removed as CO. This reaction optimizes the reaction rate, selectively oxidizing and consuming the peripheral (edge) portions of the easily combustible condensed polycyclic aromatic rings of the several nanometer-sized crystallites that make up the raw carbon black. As a result, gaps form between the crystallites, and the consumption of the crystallites continues inward. This results in the formation of porous carbon black. This is the process by which carbon black is made porous through activation.

[0072] Increasing the activation temperature increases the reaction rate, accelerating combustion near the surface that comes into contact with a high concentration of activation gas, while the concentration of activation gas diffusing inside becomes even lower, slowing down internal combustion. To develop pores inside without changing the surface condition, the reaction rate must be controlled appropriately. ２ Oxygen is the most suitable activation gas because it can control the reaction rate over a wide range of temperatures. The reasons why oxygen activation is not industrially applicable are as follows: ２The oxidation reaction of raw carbon black with oxygen is an endothermic reaction, and the reaction will not proceed unless heat is applied. This reaction can be controlled by the amount of heat supplied, making it easy to scale up. On the other hand, the oxidation reaction of raw carbon black with oxygen is an exothermic reaction, and if the heat generated is greater than the heat removed, the temperature at the reaction site rises monotonically, making the reaction difficult to control. This phenomenon accelerates with scale up, so oxidation with oxygen is not suitable for mass production, and it is preferable to use water vapor or CO ２ As an activation gas, activation using

[0073] As long as a manufacturing process in which this activation reaction proceeds can be realized, there are no restrictions on the activation device. To efficiently promote activation, it is desirable to increase the concentration of activation gas on the surface of the raw carbon black pellets. To achieve this, it is desirable to reduce the thickness of the boundary film of oxidizing gas formed near the surface of the raw carbon black pellets, and it is effective to increase the relative velocity of the activation gas with respect to the raw carbon black pellets. A rotary kiln or fluidized bed, which are generally used in industrial production, is preferred because it can increase the uniformity of the activation gas within the furnace. Because it can increase the relative velocity of the activation gas with respect to the raw carbon black pellets, a fluidized bed is an excellent device in terms of gas utilization rate and reaction rate, and is particularly preferred.

[0074] The specific activation conditions are to control the temperature depending on the reaction strength of the activation gas. The activation gas is water vapor or CO ２ When water vapor is used as the activation gas, the preferred temperature is 750 to 900°C, and CO ２ When the activation gas is used, the preferred temperature is 800 to 950°C. ２ / g), the mass loss rate of the porous raw carbon black due to activation is, for example, 60% to 80% by mass. The treatment time required to reach such a mass loss rate is, for example, 5 to 100 hours, preferably 10 to 80 hours, and more preferably 20 to 80 hours. Under activation conditions under which the time required to reach a mass loss rate of 50% by mass is shorter than 5 hours, the BET surface area is smaller than, for example, when the time required to reach the same mass loss rate is 20 hours. This difference in BET surface area occurs because, if the reaction rate is too high, the surface combustion of the oxidized raw carbon black is relatively large compared to the internal combustion for forming internal pores, and part of the mass loss is consumed in surface combustion, preventing the BET specific surface area from increasing. Furthermore, large irregularities of 10 nm or more are generated due to surface combustion (pores formed when depressions at the bonding points of primary particles develop due to surface combustion). That is, to suppress surface combustion, it is preferable to lower the activation temperature and lengthen the activation time. On the other hand, activation for a long time, such as when the time required for the mass reduction rate to reach 50 mass% exceeds 100 hours, is not preferable because the activation rate is too slow, causing surface combustion to prevail over internal combustion and inhibiting the development of pores.

[0075] It is also preferable to activate under conditions where the activation gas pressure is increased. Because the activation gas concentration is high, the rate of the oxidation reaction increases almost in proportion to the concentration, and the activation time can be shortened without changing the pore development, i.e., the BET surface area, or the rate of surface combustion. The activation time can be shortened in proportion to the pressure within a pressure range of up to several atmospheres. At pressures of 6 atmospheres or higher, the effect of the actual pressure increase is difficult to see, so a pressure of 6 atmospheres or less is preferable. The activation time when activating under pressurized conditions is, for example, 3 to 50 hours, preferably 5 to 30 hours, and more preferably 5 to 20 hours. The lower and upper limits of the activation time are determined to avoid the same phenomenon as when activating under normal pressure.

[0076] The activation treatment step described above forms pores inside the raw carbon black, allowing the production of porous carbon black that satisfies requirement (A). During the heat treatment step to increase the crystallinity, the texture and crystalline structure of the porous raw carbon black undergo changes toward a more stable graphite structure, causing the pores, which could be considered defects, to collapse. Therefore, the pore structure of the porous raw carbon black obtained in the activation treatment step must be more developed than the final desired pore structure, so that a desirable pore structure is maintained even after the pores are collapsed in the heat treatment step. In other words, in order to satisfy requirement (A) after the activation treatment step, the BET surface area of ​​the porous raw carbon black obtained in the activation treatment step must be at least 400 m, the lower limit of requirement (A). ２ / g or more, and ２ / g is more preferable, and 800m ２ / g or more is more preferable.

[0077] (Heat Treatment Step) The heat treatment step is a step in which the porous raw carbon black obtained in the activation treatment step is heat-treated. The catalyst support is exposed to a noble potential of 1 V or more in the operating environment of the fuel cell. Because the ionomer has sulfonic acid groups, the catalyst support coated with the ionomer is placed in a noble potential of 1 V or more and in a strongly acidic environment. When porous carbon black is used in such an environment, thermodynamic stability cannot be expected, so the general countermeasure is to increase its crystallinity as much as possible to rapidly avoid oxidative consumption.

[0078] To enhance the crystallinity of porous carbon black, it is common to heat treat it in an inert gas atmosphere or a reducing atmosphere. In the heat treatment step, for example, the porous raw carbon black obtained in the activation treatment step is subjected to a heat treatment step (i.e., graphitization step) at 1400°C to 1800°C under an inert gas atmosphere at normal pressure (i.e., 1 atmosphere) for 10 minutes to 10 hours.

[0079] In the heat treatment step, graphitization of the porous raw carbon black can increase the crystallinity of the porous raw carbon black. More specifically, by subjecting the porous raw carbon black having a BET specific surface area that has been activated under the above-mentioned strong activation conditions to a heat treatment under the above-mentioned conditions, the crystallinity of the porous raw carbon black can be increased while maintaining the pores. This makes it possible to produce porous carbon black that satisfies requirement (D) in addition to requirements (A) and (B).

[0080] The heat treatment step is not particularly limited as long as it can heat the porous raw carbon black under the above conditions. Examples of the heating method include resistance heating, microwave heating, high-frequency heating, and furnace-type heating methods. The furnace type is not limited, and may be a graphitization furnace, batch furnace, tunnel furnace, or the like, as long as it can achieve atmospheric pressure and an inert gas atmosphere.

[0081] Through the above steps, the carbon material for a catalyst support of the present disclosure is obtained.

[0082] In the carbon material for a catalyst support according to the present disclosure, after the heat treatment step, an activation treatment may be carried out again to restore pores collapsed by heat. However, since activation is accompanied by a decrease in the strength of the porous structure, it is important to keep the treatment amount low. Specifically, the mass loss rate due to activation after the heat treatment is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0083] <Catalyst Layer for Polymer Electrolyte Fuel Cell and Polymer Electrolyte Fuel Cell> A catalyst layer for a polymer electrolyte fuel cell according to the present disclosure will now be described, along with a polymer electrolyte fuel cell. The carbon material according to the present disclosure can be applied to, for example, catalyst layers 150 and 160 provided in a polymer electrolyte fuel cell 100 shown in FIG. 1. FIG. 1 is a schematic diagram showing an example of the overall configuration of a fuel cell according to the present disclosure. The polymer electrolyte fuel cell 100 shown in FIG. 1 includes separators 110 and 120, gas diffusion layers 130 and 140, catalyst layers 150 and 160, and an electrolyte membrane 170.

[0084] The separator 110 is an anode-side separator that introduces a reducing gas such as hydrogen into the gas diffusion layer 130. The separator 120 is a cathode-side separator that introduces an oxidizing gas such as oxygen gas or air into the gas diffusion condensation phase. The types of the separators 110 and 120 are not particularly limited, and may be any separator used in conventional fuel cells (e.g., solid polymer fuel cells).

[0085] The gas diffusion layer 130 is an anode-side gas diffusion layer that diffuses the reducing gas supplied from the separator 110 and then supplies the gas to the catalyst layer 150. The gas diffusion layer 140 is a cathode-side gas diffusion layer that diffuses the oxidizing gas supplied from the separator 120 and then supplies the gas to the catalyst layer 160. The type of gas diffusion layers 130 and 140 is not particularly limited, and they may be any gas diffusion layer used in conventional fuel cells (e.g., polymer electrolyte fuel cells). Examples of the gas diffusion layers 130 and 140 include porous carbon materials (carbon cloth, carbon paper, etc.) and porous metal materials (metal mesh, metal wool, etc.). A preferred example of the gas diffusion layers 130 and 140 is a gas diffusion layer with a two-layer structure. Specifically, the gas diffusion layers 130 and 140 have a two-layer structure in which the layer on the separator 110 or 120 side is a gas diffusion fiber layer mainly composed of a fibrous carbon material, and the layer on the catalyst layer 150 or 160 side is a micropore layer mainly composed of carbon black.

[0086] The catalyst layer 150 is a so-called anode. In the catalyst layer 150, an oxidation reaction of the reducing gas occurs, producing protons and electrons. For example, when the reducing gas becomes hydrogen gas, the following oxidation reaction occurs: H ２ →2H ＋ +2e － (E ０ = 0 V)

[0087] Protons produced by the oxidation reaction pass through the catalyst layer 150 and electrolyte membrane 170 to reach the catalyst layer 160. Electrons produced by the oxidation reaction pass through the catalyst layer 150, gas diffusion layer 130, and separator 110 to reach the external circuit. The electrons perform work (generate electricity) in the external circuit and then enter the separator 120. The electrons then pass through the separator 120 and gas diffusion layer 140 to reach the catalyst layer 160.

[0088] There are no particular limitations on the configuration of the catalyst layer 150 that serves as the anode. The configuration of the catalyst layer 150 may be the same as that of a conventional anode, the same as that of the catalyst layer 160, or a configuration that is more hydrophilic than the catalyst layer 160.

[0089] The catalyst layer 160 is a so-called cathode. Within the catalyst layer 160, a reduction reaction of the oxidizing gas occurs, producing water. For example, when the oxidizing gas becomes oxygen gas or air, the following reduction reaction occurs. The water produced by the oxidation reaction is discharged to the outside of the polymer electrolyte fuel cell 100 together with the unreacted oxidizing gas. ２ +4H ＋ +4e － →2H ２ O (E ０ = 1.23 V)

[0090] In this way, the energy difference (potential difference) between the oxidation reaction and the reduction reaction is utilized to generate electricity in the polymer electrolyte fuel cell 100. In other words, the electrons generated in the oxidation reaction perform work in an external circuit.

[0091] The catalyst layer 160 contains the carbon material for a catalyst support of the present disclosure. That is, the catalyst layer 160 contains the carbon material for a catalyst support of the present disclosure, an electrolyte material (ionomer), and a catalyst component (platinum, etc.). This can improve the power generation characteristics (particularly high-load characteristics) in the catalyst layer 160. This can also improve the power generation characteristics (particularly high-load characteristics) of the polymer electrolyte fuel cell 100.

[0092] The catalyst loading rate in the catalyst layer 160 is not particularly limited, but is preferably 30% by mass or more and less than 80% by mass. A catalyst loading rate within this range further improves power generation characteristics (particularly high-load characteristics). Here, the catalyst loading rate is expressed as the mass % of the catalyst component relative to the total mass of the catalyst-loaded particles (particles in which the catalyst component is loaded on a carbon material for catalyst support). If the catalyst loading rate is less than 30% by mass, it may be necessary to thicken the catalyst layer 160 to make the polymer electrolyte fuel cell 100 practical. On the other hand, if the catalyst loading rate is 80% by mass or more, catalyst aggregation is likely to occur. Furthermore, if the catalyst layer 160 becomes too thin, flooding may occur.

[0093] The mass ratio I / C of the mass I of the electrolyte material in the catalyst layer 160 to the mass C of the catalyst support carbon material is not particularly limited, but is preferably greater than 0.5 and less than 5.0. In this case, both the pore network and the electrolyte material network can be achieved, resulting in improved power generation characteristics (particularly high-load characteristics). On the other hand, if the mass ratio I / C is 0.5 or less, the electrolyte material network tends to be weak and the proton conduction resistance tends to increase. If the mass ratio I / C is 5.0 or more, the pore network may be disrupted by the electrolyte material. In either case, the power generation characteristics (particularly high-load characteristics) may be reduced.

[0094] Furthermore, the thickness of the catalyst layer 160 is not particularly limited, and is preferably more than 5 μm and less than 20 μm. In this case, the oxidizing gas is more likely to diffuse within the catalyst layer 160, and flooding is less likely to occur. If the thickness of the catalyst layer 160 is 5 μm or less, flooding is more likely to occur. If the thickness of the catalyst layer 160 is 20 μm or more, the oxidizing gas is less likely to diffuse within the catalyst layer 160, and the catalytic components near the electrolyte membrane 170 become less effective. In other words, there is a possibility that the catalyst utilization rate will decrease.

[0095] The electrolyte membrane 170 is composed of a proton-conducting electrolyte material. The electrolyte membrane 170 introduces protons generated in the oxidation reaction to the catalyst layer 160 (cathode). The type of electrolyte material is not particularly limited, and any electrolyte material used in conventional fuel cells, such as solid polymer fuel cells, may be used. An example of a suitable electrolyte material is an electrolyte resin. Examples of electrolyte resins include polymers with phosphate groups, sulfonic acid groups, etc. Specific examples include perfluorosulfonic acid polymers and polymers with benzenesulfonic acid, etc. Of course, other types of electrolyte materials may also be used. Examples of such electrolyte materials include inorganic and inorganic-organic hybrid electrolyte materials. The solid polymer fuel cell 100 may be a fuel cell that operates within a temperature range from room temperature (25°C) to 150°C.

[0096] <Method for manufacturing a polymer electrolyte fuel cell> The method for manufacturing the polymer electrolyte fuel cell 100 is not particularly limited, and may be the same as a conventional manufacturing method. However, the catalyst carrier uses the carbon material for a catalyst carrier of the present disclosure. Of the catalyst layers 150 and 160, it is preferable to use the carbon material for a catalyst carrier of the present disclosure for the catalyst carrier of at least the catalyst layer 160 that serves as the cathode. Of course, the carbon material for a catalyst carrier of the present disclosure may also be used for the catalyst carrier of both the catalyst layer 150 that serves as the anode and the catalyst layer 160 that serves as the cathode.

[0097] Examples of the carbon material for a catalyst support according to the present disclosure will be described below. First, the method for measuring each parameter will be described.

[0098] <Method for measuring each parameter> (Measurement of nitrogen adsorption / desorption isotherm (BET specific surface area)) Approximately 30 mg of sample was weighed and vacuum dried at 120°C for 2 hours. Next, the sample was set in an automatic specific surface area measuring device (Microtrackbell, BELSORP MAX), and the nitrogen adsorption / desorption isotherm was measured at a measurement temperature of liquid nitrogen temperature (approximately 77K) using nitrogen gas as the adsorbate. The BET specific surface area was calculated by the relative pressure P / P ratio in the nitrogen adsorption isotherm. ０The BET value was calculated by BET analysis in the range of 0.05 to 0.15. The BET value was calculated using the calculation software attached to the device.

[0099] (ΔV measured by mercury porosimetry ｆｉｎ and ΔV ｉｎｉ Measurement of mercury absorption (mL / g)) 0.3 to 1.0 g of sample was weighed out and lightly compressed to form a block to prepare a measurement sample. The measurement sample was loaded into the sample container of a measurement device (Shimadzu Corporation, Autopore IV9520), and mercury was injected under conditions of an initial introduction pressure of 5 kPa and a maximum injection pressure of 400 MPa. The mercury absorption (mL / g) was measured when the mercury injection pressure values ​​were 10 MPa and 100 MPa. The difference in the measured values ​​was then referred to as "the difference ΔV between the mercury absorption (mL / g) at a mercury insertion pressure of 10 MPa before the porous activated carbon black was pressurized with a mold at a pressure of 100 MPa and the mercury absorption (mL / g) at a mercury insertion pressure of 100 MPa." ｉｎｉ (mL / g)".

[0100] On the other hand, a sample was packed into a cylindrical mold with a diameter of 10 mm to a height of about 5 mm, pressurized at 100 MPa and held for 1 minute, then the pressure was released and the sample was removed from the mold and crushed in a mortar. The crushed sample was then packed into the mold again in the same manner as above and pressed at 100 MPa for 1 minute to obtain a measurement sample. The mercury absorption (mL / g) at mercury insertion pressures of 10 MPa and 100 MPa was measured in the same manner as above, except that the obtained measurement sample was used. The difference in the measured values ​​was then referred to as "the difference ΔV between the mercury absorption (mL / g) at a mercury insertion pressure of 10 MPa and the mercury absorption (mL / g) at a mercury insertion pressure of 100 MPa after the porous activated carbon black was pressurized in the mold at a pressure of 100 MPa." ｆｉｎ (mL / g)".

[0101] (Raman spectroscopy intensity ratio I Ｄ / I Ｇ Approximately 3 mg of a sample was weighed and taken, and the Raman spectrum was measured using a laser Raman spectrophotometer (manufactured by JASCO Corporation, NRS-3100 model). From the Raman spectrum obtained under the following measurement conditions, a band in the range of 1300 to 1360 cm called the D band was observed. －１and a peak in the range of 1560-1620 cm called the G band. －１ cm －１ The peaks in the range of 1000 to 10000 were extracted, and the intensities (areas) of these two peaks were analyzed using the spectrum analysis software attached to the instrument to determine the D band intensity I. Ｄ and the G-band intensity I Ｇ From these values, the intensity ratio I Ｄ / I Ｇ Measurement conditions: Excitation laser: 532 nm, laser power: 10 mW (sample irradiation power: 1.1 mW), microscope arrangement: backscattering, objective lens: ×100 magnification, spot diameter: 1 μm, exposure time: 30 sec, observed wave number: 2000 cm －１ ~300cm －１ , Number of times accumulated: 6 times.

[0102] <Experimental Example> (Raw Carbon Black) As raw carbon black, Niteron #200 and Niteron #SH manufactured by Nippon Steel Carbon Corporation, and Toka Black #4500 and GFY manufactured by Tokai Carbon Co., Ltd. were prepared, and these raw carbon blacks were subjected to the oxidation treatment, activation treatment step, and heat treatment step described below.

[0103] On the other hand, as raw carbon black, Ketjenblack EC300J and EC600JD manufactured by Lion Corporation were prepared. Since these raw carbon blacks were porous, only the heat treatment step described below was performed.

[0104] Table 1 below shows the primary particle size (arithmetic mean particle size), DBP oil absorption, and BET specific surface area values ​​for each of the raw carbon black materials cited from Carbon Black Yearbook No. 72 (2022), compiled by the Carbon Black Association, and posted on the Ketjen Black product website.

[0105]

[0106] (Oxidation Treatment Step) According to Table 2, an ozone treatment step (in the table, "O") was performed as an oxidation treatment. ３ " in the table), or oxygen treatment process ("O ２ ") was conducted.

[0107] -Ozone Treatment Process- Pure oxygen was used as the input gas to a research-grade ozone generator manufactured by Kotohira Kogyo Co., Ltd. The ozone gas generation principle of this device is a so-called discharge method, where the ozone concentration is adjusted by the voltage and current between the electrodes and the gas flow rate. That is, a mixture of ozone and oxygen was the output gas from the generator. The electrode voltage was fixed, while the input oxygen gas flow rate was variable, at 2 L / min. The larger the surface area of ​​raw carbon black, the more easily it is oxidized by ozone. Furthermore, the more crystallinity is enhanced by heat treatment, the less susceptible it is to oxidation. Because the ozone oxidation of raw carbon black is an exothermic reaction, a large reaction volume can trap heat and cause localized temperature increases, resulting in ignition. Therefore, in this experiment, the output gas from the ozone generator was mixed with argon gas to dilute the ozone to a level where the carbon would not ignite due to the reaction heat, resulting in the oxidizing gas. The amount of gas sent to the reaction tube was also controlled. The reaction volume of the ozone treatment was adjusted by the contact time with the output gas or by placing the reaction tube in an electric furnace and heating it.

[0108] The specific reactor used was a vertical quartz reaction tube with an outer diameter of 35 mm, with a filter made of fused quartz beads attached to the inside of the tube as a dispersion plate. Fine-fiber quartz wool was laid on top of the dispersion plate as needed, and the raw carbon black was placed on top of that. Oxidizing gas was then passed from bottom to top, with the flow rate increased to a level sufficient to prevent powder from scattering outside the system and adjusted to the flow rate shown in Table 2 to minimize reaction unevenness. The reaction volume was determined by mass change. At the beginning of the reaction, the mass increased by up to 0.5% due to the addition of oxygen functional groups, and then transitioned to a mass loss. The pore structure after ozone oxidation was investigated using nitrogen gas adsorption isotherms. The isotherms before and after treatment nearly overlapped, confirming that the surface had burned off and that the pore size distribution due to internal combustion or other factors had not changed due to ozone oxidation. Table 2 lists the treatment temperature (controlled by the temperature of the electric furnace) and treatment time, which are control factors of the ozone treatment process.

[0109] -Oxygen Treatment Step- A quartz tube with an outer diameter of 50 mm, inside which a quartz filter (pore size 40-50 μm) was fused as a dispersion plate, was used as the reaction tube. Quartz wool was packed into the reaction tube to a height of approximately 1 cm, and raw carbon black in a granulated state was placed on top of it. Approximately 20-25 g of quartz wool was charged, and dry air or a mixture of dry air and argon gas was flowed as an oxidizing gas from the bottom to the top of the reaction tube at the flow rate shown in Table 2. The oxygen treatment temperature was selected while taking care to avoid ignition due to heat accumulation caused by the exothermic reaction. Since the combustion rate varies depending on the type of raw carbon black, it is important to carefully select the conditions for each carbon black. Table 2 lists the control factors of the oxygen treatment step: the treatment temperature (controlled by the temperature of the electric furnace) and the treatment time.

[0110] (Activation Treatment Step) A reaction tube was prepared by fusing a quartz filter as a dispersion plate inside a quartz tube with an outer diameter of 35 mm, placing quartz wool on the dispersion plate to a height of about 1 cm, and then placing 5 to 15 g of the oxidation raw material carbon black on top of that, and then setting the reaction tube in a vertical electric furnace normally used at 1100°C. Before heating, argon gas was flowed from the bottom to the top of the reaction tube to replace the inside of the reaction tube with argon gas, and then the temperature was raised at a rate of 10°C / min, and the reaction tube was heated to 850 to 950°C. After the predetermined temperature was reached, CO was added. ２ The gas was switched to argon gas. The flow rate was adjusted so that the linear velocity was 1 to 2 cm / sec at the furnace temperature. After treatment for a predetermined time, the reaction tube was removed from the furnace, and the gas was simultaneously switched to argon gas and allowed to cool. After confirming that the temperature had cooled to near room temperature, the porous raw material carbon black was removed and its mass was measured, and the mass reduction rate of the yield relative to the charged mass (charged mass / recovered mass) was calculated. The activation temperature and activation time were adjusted as shown in Table 2 as activation treatment conditions so that the mass reduction rate was in the range of 55 to 80% by mass.

[0111] (Heat Treatment Step) A so-called graphitization furnace was used as the heating furnace, which uses graphite material as a heating element. The porous raw carbon black obtained in the activation treatment step was placed in a graphite crucible with a volume of approximately 100 cc. After the pressure was reduced to a vacuum and replaced with argon gas, the temperature was raised at 10°C per minute with an argon flow rate sufficient to replace the furnace volume within several tens of minutes. After holding at the specified temperature for a certain period of time, the material was allowed to cool to near room temperature and then removed. The holding time at the heat treatment temperature was variable, and the conditions are shown in Table 2.

[0112] Through the above steps, a carbon material for a catalyst support (porous activated carbon black) was obtained for each example.

[0113] <Preparation of Membrane Electrode Assembly (MEA)> (Preparation of Catalyst) The carbon material for catalyst support (porous activated carbon black) of each example was added to an ethanol / water mixed solvent and dispersed by processing with an ultrasonic homogenizer for 2 minutes. A predetermined amount of a nitric acid solution of dinitrodiammine platinum complex was added thereto, and the platinum loading was adjusted to 40 mass %, and the mixture was stirred in an oil bath for 15 hours while maintaining a temperature several degrees lower than the boiling point. After processing, the mixture was filtered, dispersed again in distilled water, filtered again, and vacuum dried at 90°C for 5 hours to obtain a catalyst.

[0114] (Preparation of ink) An ionomer solution manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was diluted with ethanol to adjust the solid content concentration to 10% by mass, and then added dropwise to an ethanol solution in which a catalyst had been previously dispersed. Dispersion was further promoted using an ultrasonic homogenizer, and the mixture was stirred with 1 mm diameter glass beads for 10 to 15 hours. In this way, an ink for forming a catalyst layer was obtained.

[0115] <MEA Fabrication> The ink was uniformly applied to a Teflon (registered trademark) sheet using a sprayer and dried in an air circulating dryer at 60°C to prepare a decal with a catalyst layer formed thereon. Electrodes of a predetermined size of 36 mm were cut out from the decal. Two identical sheets were used as the positive and negative electrodes, and the positive and negative electrodes were placed on both sides of a Nafion membrane and heat-sealed. In this way, an MEA was obtained.

[0116] <Battery Evaluation> (Evaluation of power generation characteristics (high load characteristics)) Each MEA produced using the catalyst carrier carbon material (porous activated carbon black) of each example was assembled into a cell, which was then set in a fuel cell measuring device, and the performance of the fuel cell was evaluated according to the following procedure.

[0117] The reaction gases were supplied at a back pressure of 0.04 MPa, with air supplied to the cathode side and pure hydrogen supplied to the anode side, with the pressure adjusted by a back pressure valve installed downstream of the cell so that the utilization rates were 25% and 70%, respectively. The cell temperature was set to 80°C, and the reaction gases supplied were both bubbled with distilled water kept at 80°C in a humidifier, and humidified gas at 80°C was supplied to the cell at 80°C to evaluate power generation.

[0118] Under these conditions, the reactive gas was supplied to the cell, and the load was gradually increased. The output current density of the cell was measured after the output voltage was maintained at 0.3 V for 1 hour, and the cell was evaluated according to the following pass / fail ranking criteria. The results are shown in Table 2. [Pass Rank] A: The current density after the output voltage was maintained at 0.3 V for 1 hour was 1200 mA / cm ２ B: The current density after holding the output voltage at 0.3 V for 1 hour is 1100 mA / cm or more. ２ C: The current density after holding the output voltage at 0.3 V for 1 hour is 1100 mA / cm or more. ２ Something that is less than.

[0119] Details of the experimental example are shown in Table 2. In Table 2, "gas type / gas type: mL / min / mL / min" means the flow rate of each of the two gas types.

[0120]

[0121]

[0122]

[0123]

[0124] The above results show that the carbon material for catalyst carriers (porous activated carbon black) of this example is superior in power generation characteristics (particularly high-load characteristics) compared to the carbon material for catalyst carriers of the comparative examples. Also, the reference examples show that Ketjenblack EC300J and EC600JD manufactured by Lion Corporation do not provide sufficient power generation characteristics (particularly high-load characteristics).

[0125] Furthermore, when raw carbon black with a large particle size is used, it is generally not suitable for activation, and pores do not develop, resulting in a small BET surface area. However, by applying the manufacturing method of the present disclosure, it is possible to obtain a carbon material for a catalyst support (porous activated carbon black) that has excellent power generation characteristics (particularly, high-load characteristics) regardless of the particle size of the raw carbon black, as long as the physical property specifications of the present disclosure are met. That is, all of the examples using raw carbon black with a primary particle size of 29 nm to 72 nm showed excellent power generation characteristics (particularly, high-load characteristics). From these results, it is clear that when raw carbon black with a primary particle size of 20 nm to 80 nm is used, a carbon material for a catalyst support (porous activated carbon black) with excellent power generation characteristics (particularly, high-load characteristics) can be obtained.

[0126] The symbols are explained as follows: 100: polymer electrolyte fuel cell 110, 120: separator 130, 140: gas diffusion layer 150, 160: catalyst layer 170: electrolyte membrane

[0127] The disclosure of Japanese Patent Application No. 2023-108953 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A carbon material for a catalyst support in a polymer electrolyte fuel cell, comprising a porous activated carbon black that satisfies the following requirements (A) and (B): (A) a BET specific surface area S determined by BET analysis of a nitrogen gas adsorption isotherm ＢＥＴ 400 to 1200m ２ (B) In the mercury porosimetry method, the difference between the mercury absorption amount (mL / g) at a mercury insertion pressure of 10 MPa and the mercury absorption amount (mL / g) at a mercury insertion pressure of 100 MPa after the porous activated carbon black was pressed at a pressure of 100 MPa using a mold and before the porous activated carbon black was pressed at a pressure of 100 MPa using a mold was defined as ΔV ｆｉｎ , ΔV ｉｎｉ Then, the ratio ΔV ｆｉｎ / ΔV ｉｎｉ is not less than 0.75 and not more than 0.

95.

2. The carbon material for a catalyst support of a polymer electrolyte fuel cell according to claim 1, further satisfying at least one of the following requirements (C) and (D): (C) the ΔV ｉｎｉ (D) In ​​the Raman spectrum obtained by Raman spectroscopy, －１ The intensity of the D band of I Ｄ , 1560-1620cm －１ The G band intensity of I Ｇ Then, the intensity ratio I Ｄ / I Ｇ is 1.40 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 a polymer electrolyte fuel cell according to claim 1 or 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 catalyst layer on the cathode side.

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