Carbon material for catalyst support 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

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. Of 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, a catalyst component that promotes a power generation reaction (oxidation reaction or reduction reaction described later) in the fuel cell is also referred to as a "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. The electrons are introduced into the external circuit through the catalyst support, the gas diffusion layer, and the separator. After performing work in the external circuit, these electrons are 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 that supports 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 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 includes 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, the mass of the fibrous material is 0.02 times or more and 1.0 times or less the mass of the carrier in the catalyst-supported particles, and the mass of the polymer electrolyte is 0.4 times or more and 1.0 times or less the mass of the carrier in the catalyst-supported particles."

[0009] Patent Document 2 proposes "a carbon material for a catalyst support of a polymer electrolyte fuel cell, which is a porous carbon material having a three-dimensionally branched three-dimensional dendritic structure, with a branch diameter of 81 nm or less, and simultaneously satisfying the following (A) and (B).". (A) The BET specific surface area S obtained by BET analysis of the nitrogen gas adsorption isotherm BET is 400 to 1500 m 2 / g. (B) The mercury pressure P measured by the mercury porosimetry method Hg (kPa) and the mercury absorption amount V Hg in the relationship between them, the common logarithm LogP of the mercury pressure P Hg when increasing from 4.3 to 4.8, the increase amount ΔV of the mercury absorption amount V Hg measured Hg is 0.82 to 1.50 cc / g. Hg:4.3-4.8

[0010] Patent Document 3 proposes "a method for producing a catalyst ink applied to both sides of an electrolyte membrane of a fuel cell, comprising: (1) a step of pulverizing catalyst-supported particles having activated carbon black and a catalyst supported on the carbon black using a jet mill; (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 the step (3), in the frequency distribution of the particle size of the catalyst-supported particles in the catalyst ink measured by the laser diffraction particle size distribution measurement method, there is a first peak in the region where the particle size is 1 micrometer or less, and there is no peak having a height of 1 / 4 or more of the height of the first peak in the region where the particle size is more than 1 micrometer, and the dispersion treatment is performed."

[0011] Patent Document 4 proposes "a carbon material for a catalyst support used for a catalyst support of a polymer electrolyte fuel cell, which has a three-dimensionally branched three-dimensional dendritic structure, and is characterized by simultaneously satisfying the following (1) and (2).".​ In the measurement of the particle size distribution using a laser diffraction / scattering type particle size distribution meter, when the integrated distribution [%] of particles with a particle diameter of 1 μm or less based on the volume diameter is defined as DL and the integrated distribution [%] of particles with a particle diameter exceeding 1 μm is defined as DH, DL / DH is 1.5 or more. (2) The mode diameter in the range of 20 nm to 200 nm of the pore diameter measured by the mercury porosimetry method is 40 nm to 70 nm.

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2023-022654 Patent Document 2: International Publication No. 2018 / 182047 Patent Document 3: Patent No. 5790537 Patent Document 4: Japanese Patent Application Laid-Open No. 2022-156985

Summary of the Invention

Problems to be Solved by the Invention

[0013] 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"). In particular, it is an essential issue to be solved for commercial vehicles, for which market growth is expected in the future.

[0014] Generally, the power generation characteristics of PEFC are mainly determined 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 a dendritic structure) correlates with the gas diffusibility. Regarding the pore structure, it is desirable that only pores of a size sufficient for metal catalysts (such as platinum nanoparticles) with a diameter of several nm to be present in the pores are selectively present. Generally, mesoporous carbon is regarded as suitable for the support. Although the pores suitable for gas diffusion are not clear, they are estimated to be the pore diameters of the voids in the catalyst layer for nucleic acids currently applied from various carbon supports, which are in the range of several tens to 100 nm. The voids in the catalyst layer are realized by the three-dimensional structure (such as a dendritic structure) of the carbon support. The pore structure preferably has only pores of a size sufficient for a catalytic metal of several nm to be present in the pores, and generally, a mesoporous carbon material is regarded as suitable for a carbon carrier.

[0015] However, including Patent Documents 1 to 5, the carbon carriers (porous carbon materials) of the prior art still have room for improvement in suppressing the deterioration of power generation characteristics (particularly, high-load characteristics). Specifically, the deterioration of power generation characteristics (particularly, high-load characteristics) may be caused by the collapse of the three-dimensional structure of the carbon carrier when mechanical loads such as pulverization are applied during the preparation of the ink for forming the catalyst layer, etc., and there is room for improvement. And it is desired to achieve such improvement with inexpensive and useful carbon black among carbon carriers (porous carbon materials).

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

Means for Solving the Problems

[0017] The means for solving the problems include the following aspects. <1> A carbon material for a catalyst carrier of a polymer electrolyte fuel cell comprising porous activated carbon black satisfying the following requirements (A) and (B). (A) The BET specific surface area S obtained by BET analysis of the nitrogen gas adsorption isotherm BET is 400 to 1200 m 2 / g. (B) In the mercury porosimetry method, after pressurizing the porous activated carbon black with a mold at a pressure of 100 MPa and before pressurizing the porous activated carbon black with a mold at a pressure of 100 MPa, 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 is defined as ΔV fin and ΔV ini respectively. When the specific ΔV fin / ΔV ini is 0.75 or more and 0.95 or less. <2> Furthermore, a carbon material for a catalyst carrier of a polymer electrolyte fuel cell according to <1>, which satisfies at least one of the following requirements (C) and (D). (C) The ΔV ini is 0.80 mL or more and 1.50 mL / g or less. (D) In the Raman spectrum obtained by Raman spectroscopic measurement, in the range of 1300 to 1360 cm -1 for the intensity of the D band, I D and in the range of 1560 to 1620 cm -1 for the intensity of the G band, I G when set as such, 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 including the carbon material for a catalyst carrier of a polymer electrolyte fuel cell according to <1> or <2>. <4> A fuel cell including 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 cathode-side catalyst layer.

Advantages of the Invention

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

Brief Description of the Drawings

[0019]

Figure 1

Modes for Carrying Out the Invention

[0020] 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, when a numerical value before and after "~" is attached with "more than" or "less than", the numerical range 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 in which the intended purpose of the step is achieved even if it cannot be clearly distinguished from other steps. In the present disclosure, the "electrolyte material having proton conductivity" used in the catalyst layer of a fuel cell is also referred to as "ionomer".

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

[0022] The carbon material for catalyst support of the present disclosure is a carbon material in which power generation characteristics (particularly, high load characteristics) deteriorate. The carbon material of the present disclosure was found based on the following findings.

[0023] Generally, the power generation characteristics of a fuel cell greatly 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 magnitude of the ohmic resistance of the catalyst layer, which is the combination of two resistances: electron conduction resistance and proton conduction resistance (2) Diffusion resistance of the oxidizing gas in the catalyst layer (3) Resistance in the electrochemical reaction on the catalyst metal surface, that is, the resistance in the chemical reaction involving electron transfer (i.e., the resistance of the catalyst reaction)

[0024] In order to improve, among the above main causes, "(2) Diffusion resistance of oxidizing gas in the catalyst layer", the inventors considered increasing the mechanical strength of the three-dimensional structure (i.e., dendritic structure) derived from the aggregate structure in porous carbon black. As a result, the following findings were obtained.

[0025] In the ink manufacturing process for forming the catalyst layer, stirring or the like is performed for the purpose of improving the dispersion of porous carbon black, so that a mechanical load is applied to the porous carbon black. It is preferable that the three-dimensional structure (dendritic structure) is not destroyed by this mechanical load, but only the aggregation is loosened and crushed into the smallest unit aggregates. By crushing, voids (i.e., pores) derived from a uniform three-dimensional structure (dendritic structure) are formed in the catalyst layer. As a result, the diffusion resistance of the oxidizing gas is reduced, and the power generation characteristics (especially high load characteristics) are improved. On the other hand, if the three-dimensional structure (dendritic structure) is destroyed by the mechanical load, fine powder is generated in the ink, and the voids derived from the three-dimensional structure (dendritic structure) in the catalyst layer are blocked by the fine powder. That is, it becomes difficult to form pores in the catalyst layer. Therefore, the diffusion resistance of the oxidizing gas increases, and the power generation characteristics (especially high load characteristics) deteriorate.

[0026] That is, the mechanical strength of the porous carbon black contributes to the improvement of the power generation characteristics (especially high load characteristics).

[0027] Here, the mercury porosimetry method has been conventionally used for quantifying the development of the three-dimensional structure (dendritic structure) of porous carbon black and the quantification of voids in the catalyst layer. Due to the difference in the three-dimensional structure (dendritic structure) of porous carbon black (for example, depending on 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)), the pressure (MPa) of mercury absorption in the mercury porosimetry method changes. That is, the size of the voids formed by the three-dimensional structure (dendritic structure) is reflected in the mercury absorption amount (mL / g). Therefore, the mercury porosimetry method is suitable for quantifying the three-dimensional structure (dendritic structure) of porous carbon black. In view of the minimum required branch thickness to enhance the mechanical strength of the three-dimensional structure (dendritic structure) of porous carbon black, mercury absorption starts at an insertion pressure of 10 MPa or higher. On the other hand, considering that the primary particle diameter of carbon black corresponding to the branch thickness has a practical upper limit of 80 nm, the upper limit of the mercury insertion pressure is 100 MPa. Therefore, the difference ΔV in mercury absorption (mL / g) at insertion pressures of 10 MPa and 100 MPa using the mercury porosimetry method is suitable as a quantitative index for the three-dimensional structure (dendritic structure) of porous carbon black.

[0028] Therefore, the inventors conducted the following experiment. For the purpose of simulating the mechanical load acting on porous carbon black during the ink formation process for catalyst layer formation, ΔV of porous carbon black before and after the ink manufacturing process using a planetary ball mill was measured. On the other hand, porous carbon black was mechanically destroyed by pressing with a mold, and ΔV before and after that was measured. Then, from the investigation of the correlation between the two, the mechanical strength of the three-dimensional structure (dendritic structure) of porous carbon black, which shows a small decrease in power generation characteristics (especially high load characteristics) in any ink process, was quantified by the ratio of ΔV before and after pressing with a mold. As a result of such an investigation, the mercury absorption amount VΔ before pressing with a mold ini and the mercury absorption amount ΔV after pressing with a mold fin are defined as ΔV fin / ΔV ini It was shown that is optimal as an index of the mechanical strength in the ink manufacturing process of porous carbon black.

[0029] On the other hand, the inventors studied a method for producing porous carbon black having a large BET specific surface area and high mechanical strength of the three-dimensional structure (dendritic structure). As a result, the following findings were obtained.

[0030] By making the raw material carbon black porous by activation and heat-treating it to enhance crystallinity, porous carbon black suitable for a catalyst support with high power generation characteristics (especially high load characteristics) and durability can be obtained. For improving the mechanical strength of such porous carbon black, the following guidelines are necessary. (1) Activation to suppress the decrease in mechanical strength (2) Increase the heat treatment temperature (3) Use of raw material carbon black with a large diameter

[0031] Among the above guidelines, “(1) Activation to suppress the decrease in mechanical strength” is important. Rather than directly activating the raw material carbon black, if the surface of the raw material carbon black is selectively oxidized and consumed before activation, the oxidation of the surface of the raw material carbon black can be suppressed in the subsequent activation. Thereby, while suppressing the oxidation of the surface of the raw material carbon black in activation, pores developed inside the raw material carbon black can be formed. The porous carbon black obtained by suppressing surface oxidation and developing pores inside has improved mechanical strength despite having a high BET specific surface area. And the treatment suitable for selective oxidation of the surface of the raw material carbon black (pretreatment for activation) is a low-temperature oxidation treatment at room temperature (25°C) or higher and 70°C or lower with ozone, or an oxidation treatment at 300°C or higher and 500°C or lower with air.

[0032] Also, by “(2) Increase the heat treatment temperature”, the pore volume necessary for exhibiting excellent power generation characteristics (especially high load characteristics) is ensured. However, when the heat treatment temperature is increased, the pores are crushed. Therefore, it is necessary to optimize the activation conditions together with the use of “(3) Raw material carbon black with a large diameter” which is easily activated so as to ensure the target BET specific surface area of the obtained porous carbon black.

[0033] From the above findings, it has been found that the carbon material for a catalyst carrier of the present disclosure becomes a carbon material with a decrease in power generation characteristics (especially high load characteristics).

[0034] Hereinafter, requirements (A) and (B) will be described. Here, from the viewpoint of further suppressing the deterioration of power generation characteristics (particularly high-load characteristics), in addition to requirements (A) and (B), the carbon material for a catalyst carrier of the present disclosure preferably satisfies at least one of requirement (C) and requirement (D).

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

[0036] The BET specific surface area S of the porous carbon black BET is the most suitable property for quantitatively representing the degree of pore development as a catalyst carrier. The BET specific surface area S of the porous carbon black BET is 400 m 2 / g or less, the amount of carbon required to support the catalyst metal increases, the thickness of the catalyst layer increases, and the gas diffusion resistance increases. As a result, the power generation characteristics (particularly high-load characteristics) deteriorate. On the other hand, when the BET specific surface area S of the porous carbon black BET exceeds 1200 m 2 / g, requirement (B) described below cannot be satisfied. That is, since the mechanical strength of the three-dimensional structure (dendritic structure) of the porous carbon black is low, during the preparation of the ink for forming the catalyst layer, the three-dimensional structure (dendritic structure) is destroyed, and fine particles are mixed in the ink. As a result, the fine powder blocks the voids of the catalyst layer. Thereby, the gas diffusion resistance increases and the power generation characteristics (particularly high-load characteristics) deteriorate.

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

[0038] Incidentally, the BET specific surface area is a value measured by the method described in the examples below.

[0039] (Requirement (B)) (B) In the mercury porosimetry method, after pressurizing the porous carbon black with a mold at a pressure of 100 MPa and before pressurizing the porous carbon black with a mold at a pressure of 100 MPa, 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 is defined as ΔV fin , ΔV ini respectively. When the specific ΔV fin / ΔV ini is 0.75 or more and 0.95 or less. Here, 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 is "mercury absorption amount at a mercury insertion pressure of 100 MPa" - "mercury absorption amount at a mercury insertion pressure of 10 MPa".

[0040] The specific ΔV fin / ΔV ini of the porous carbon black is an index using the fracture behavior by mold pressing, and is an index indicating that the porous carbon black is difficult to break during the production of the ink for forming the catalyst layer or the like. The specific ΔV fin / ΔV ini If it is less than 0.75, the mechanical strength of the three-dimensional structure (dendritic structure) of the porous carbon black is low. Therefore, during the production of the ink, the porous carbon black breaks, and fine particles are mixed in the ink. As a result, the fine powder blocks the voids of the catalyst layer. Thereby, the gas diffusion resistance increases and the power generation characteristics (especially high load characteristics) deteriorate. On the other hand, the upper limit value (0.95) of the specific ΔV fin / ΔV ini is the upper limit value in a substantial sense that there is no material showing a large value where the specific ΔV fin / ΔV ini is 0.95 or more.

[0041] Specific ΔV of porous carbon black fin / ΔV ini The lower limit value is preferably 0.76 or more, more preferably 0.77 or more. Specific ΔV of porous carbon black fin / ΔV ini The upper limit value is preferably 0.94 or less, more preferably 0.93 or less.

[0042] Incidentally, the specific ΔV of the porous carbon black fin and ΔV ini are values measured by the method described in the examples below.

[0043] (Requirement (C)) (C) The difference ΔV 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 before pressurizing the porous carbon black at a pressure of 100 MPa with a mold ini is 0.80 mL or more and 1.50 mL / g.

[0044] ΔV of porous carbon black ini is an index quantitatively indicating the degree of development of the three-dimensional structure (dendritic structure) of the porous carbon black, and is an index strongly correlated with the volume of voids in the catalyst layer. ΔV of porous carbon black ini If it 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 (especially the high load characteristics) deteriorates. ΔV of porous carbon black ini If it exceeds 1.50 mL / g, it corresponds to a large roughness on the surface of the porous carbon black, so requirement (B) cannot be satisfied. The mechanical strength of the three-dimensional structure (dendritic structure) of the porous carbon black is low, and during ink production, the porous carbon black is broken, and fine particles are mixed in the ink. As a result, the fine powder blocks the voids of the catalyst layer. Thereby, the gas diffusion resistance increases and the power generation characteristics (especially the high load characteristics) deteriorate.

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

[0046] Incidentally, the ΔV of the 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 spectroscopic measurement, in the range of 1300 to 1360 cm -1 the intensity of the D band is I D , and in the range of 1560 to 1620 cm -1 the intensity of the G band is I G When, the intensity ratio I D / I G is 1.40 or more and 2.20 or less.

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

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

[0050] Note that the strength 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 carrier of solid polymer fuel cell> Hereinafter, an example of a method for producing a carbon material for a catalyst carrier of a solid polymer fuel cell of the present disclosure (hereinafter, also referred to as "method for producing a carbon material") will be described.

[0052] The method for producing a carbon material of the present disclosure is, for example, a method having the following three steps. By the method for producing a carbon material of the present disclosure, a carbon material satisfying requirement (A) and requirement (B), preferably a carbon material satisfying at least one of requirement (C) and requirement (D) in addition to requirement (A) and requirement (B) (that is, porous activated carbon black) can be obtained.

[0053] Oxidation treatment step: An oxidation treatment step of selectively oxidizing the surface of the raw material carbon black with ozone or oxygen Activation treatment step: An activation treatment step of making the raw material carbon black oxidized in the oxidation treatment step (hereinafter, oxidized raw material carbon) porous by activation. Heat treatment step: A heat treatment step of heat-treating the porous oxidized raw material carbon black (hereinafter, porous raw material carbon black) in the activation treatment step Ozone treatment step: An ozone treatment step of oxidizing the heat-treated porous raw material carbon black (hereinafter, heat-treated porous raw material carbon black) with ozone

[0054] Hereinafter, the details of each step will be described. First, the raw material carbon black to be used will be described.

[0055] (Raw carbon black) As the raw carbon black, carbon black that satisfies the following three structures, namely, a predetermined primary particle diameter, a three-dimensional structure (an aggregate structure in which primary particles are strung together), and a granulated state, can be preferably applied.

[0056] -Primary particle diameter- The size of the voids in the catalyst layer is determined by the three-dimensional structure and the primary particle diameter of the raw carbon black. That is, since primary particles are connected to form a three-dimensional structure, the primary particle diameter × the number of beads = the 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 become rate-determining and the power generation characteristics will not deteriorate. That is, the preferable range of the primary particle diameter is 20 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. It is presumed that pore formation by activation forms pores from the outside to the inside. Since the surface vicinity is continuously exposed to the oxidation treatment, the loss due to combustion is large. Assuming this, the larger the primary particle diameter, 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. In fact, the activation treatment of raw carbon black with a large primary particle diameter has a weaker pore development compared to that with a small particle diameter even when the mass reduction progresses. That is, the larger the primary particle diameter, the more difficult it is to increase the BET 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 carbon black with a larger primary particle diameter has higher oxidation consumption resistance than the raw carbon black with a smaller primary particle diameter. That is, the durability becomes better as the primary particle diameter increases. In particular, raw carbon black with a primary particle diameter exceeding 40 nm has an effect on improving durability. Raw carbon black with a primary particle diameter of 50 nm or more has a significant effect on improving durability, and raw carbon black with a primary particle diameter exceeding 60 nm has a remarkable durability improvement effect.

[0057] Note that 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 pages 176, "i. Electron Microscopy Photography Method", "ii. Particle Size Measurement", and "iii. Particle Size Calculation Method" of the Carbon Black Handbook (edited by the Carbon Black Association, first edition in 1971). In order to take a statistical average, at least 100 primary particle sizes are measured, and the arithmetic average is determined as the primary particle size. The arithmetic average diameter is calculated by the following formula. d = Σn i di / Σn i , where n i is the number of particles with diameter d i .

[0058] -Three-dimensional Structure- As a structure suitable for the catalyst carrier of the fuel cell, porous carbon black with a developed three-dimensional structure (dendritic structure) is preferred. 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 are applicable, for example, to the DBP oil absorption amount, BET specific surface area, and mercury intrusion amount distribution by the mercury porosimetry method.

[0059] The DBP oil absorption amount is an industrial index of the 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 carbon black is approximately 1.8 g / mL, considering the DBP oil absorption equivalent to the voids in the catalyst layer, a DBP oil absorption of 80 mL / 100 g corresponds to voids more than 1.4 times 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 characteristics. On the other hand, the upper limit of the DBP oil absorption is 180 mL / 100 g, which is the theoretical upper limit in manufacturing. Note that the DBP oil absorption indicates the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black and is the value defined in ASTM (American Standard Test Method) D2414-6TT.

[0060] The BET specific surface area is the most basic physical property value 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 - 200 m 2 / g, more preferably 25 - 180 m 2 / g. Note that the BET specific surface area is the value measured by the method described in the examples below.

[0061] The evaluation of the three-dimensional structure by the mercury porosimetry method is carried out by converting the hydrostatic pressure applied to mercury into the pore diameter when assuming a cylinder using the surface tension of mercury with respect to the raw carbon black, and obtaining the distribution of the integral value of the volume of pores larger than that pore diameter with the pore diameter on the horizontal axis. The raw carbon black with a three-dimensional structure causes the absorption of mercury proportional to the void volume at the intrusion relative pressure corresponding to the void size brought about by the three-dimensional structure. Therefore, the three-dimensional structure can be quantitatively evaluated from the pore diameter distribution of the mercury absorption amount. Specifically, considering the DBP absorption amount suitable for the voids of the catalyst layer described above, when the mercury intrusion pressure increases from 10 MPa (corresponding to pores of about 10 nm) to 100 MPa (corresponding to pores of about 100 nm), the increment of the mercury amount absorbed 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 high-load characteristics. On the other hand, 1.5 mL / g of the increment of the mercury amount is the theoretical upper limit in terms of manufacturing.

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

[0063] -Ozone treatment step- Since ozone (O3) has an oxidizing power second only to fluorine, it can be applied to the oxidation treatment of the raw material carbon black. In the raw material carbon black, the blackness can be increased by the amount of oxygen-containing functional groups, so it is industrially used in the production of carbon black for color. By taking advantage of the strong oxidizing power of ozone, the surface of the raw material carbon black can be selectively oxidized. That is, before the raw material carbon black is made porous by activation, by selectively oxidizing the surface of the raw material carbon black, although the mechanism is not necessarily clear, the pore development by activation is significantly promoted. Thereby, both the improvement of the branch strength of the three-dimensional structure (dendritic structure) of the obtained porous carbon black and the pore development can be achieved. It is presumed that selective oxidation of the surface of the raw material carbon black burns and burns off a thin skin of about several nanometers on the surface, and pores for introducing activation gas for activation into the interior are formed in the raw material carbon black. Or, it is inferred that in activation, the pores for introducing activation gas into the interior are made in a state where they are easily formed in the oxidized raw material carbon black.

[0064] Thus, the ozone treatment plays a role in developing pores formed in the activated porous raw material carbon black. That is, the ozone treatment increases the pore volume and the surface area of the pores, and at the same time, plays a role in forming only the preferable pores as a catalyst carrier. In addition, the ozone treatment also plays a role in preventing the surface roughness and the thinning of the branches of the three-dimensional structure (dendritic structure) of the porous carbon black, which are inappropriate for the power generation characteristics (especially high load characteristics) in the subsequent process. The roughness due to the combustion on the surface of the porous carbon black and the thinning of the branches of the three-dimensional structure (dendritic structure) lead to a decrease in the mechanical strength of the three-dimensional structure (dendritic structure). Therefore, by performing the ozone treatment, porous carbon black that satisfies requirement (A) and requirement (B) (preferably, in addition to requirement (A) and requirement (B), requirement (C)) can be obtained.

[0065] For the ozone treatment, an apparatus with an ozone generation amount of 10 mg / h or more may be used, and there is no limitation on the ozone generation mechanism or the apparatus structure. Usually, pure oxygen is used as the input gas to increase the ozone generation rate. That is, when air is input, the oxygen content as the ozone raw material is low, and accordingly, the ozone generation amount decreases. Since ozone is unstable and self-decomposes over time, it is preferable to contact the raw material carbon black with a gas containing ozone in a state where the gas is constantly flowing. To increase the reaction rate, the ozone gas and the raw material carbon black may be contacted in a heated state.

[0066] The ozone treatment temperature shall be from room temperature (25°C) to 70°C. When the ozone treatment temperature increases, the self-decomposition rate of ozone also increases. Therefore, 70°C is the substantial upper limit for oxidizing the raw material carbon black. The ozone treatment time is preferably 1 to 9 hours under the condition that the oxidation consumption rate of the raw material carbon black reaches 3.0% in the order of several hours. If the ozone treatment time is shorter than 1 hour, the calorific value is high, and it is inappropriate because it is difficult for the entire raw material carbon black powder to react uniformly. When the ozone treatment time exceeds 9 hours, the combustion on the surface of the raw material carbon black becomes significant. As a result, surface roughness of the porous carbon black and thinning of the branches of the three-dimensional structure (dendritic structure) occur due to the surface combustion, leading to a decrease in the mechanical strength of the three-dimensional structure (dendritic structure).

[0067] Incidentally, although it is also common to oxygen treatment, since the ozone treatment of the raw material carbon black is a strong exothermic reaction, it is necessary to diffuse the heat accompanying the reaction to the outside without storing it. A device for this purpose is necessary in actual treatment. For example, increasing the flow rate of ozone gas to let the heat escape with the gas, or reducing the height at which the raw material carbon black to be treated is piled up to shorten the heat diffusion path, etc. are effective.

[0068] - Oxygen treatment process - In the oxygen treatment process, by bringing oxygen into contact with the raw material carbon black in a high temperature range, the same effect as the ozone treatment process can be obtained. That is, the oxygen treatment process is a process that plays the same role as the ozone treatment. By performing the oxygen treatment process, porous carbon black that satisfies requirement (A) and requirement (B) (preferably in addition to requirement (A) and requirement (B), at least one of requirement (C) and requirement (D)) can be obtained.

[0069] In the oxygen treatment process, since the oxidation by oxygen has a large heat generation amount, it is necessary to suppress ignition due to heat storage. The oxygen concentration of the oxidation gas is preferably higher, but at least 70% by volume or less, preferably 50% by volume or less is preferable. The oxygen treatment temperature is also preferably higher, but if it is too high, the energy for CO2 generation decreases. Therefore, the oxygen treatment temperature is 500 °C or lower, and 450 °C or lower is preferable. On the other hand, the acid The oxygen treatment temperature is preferably 300 °C or higher. If it is lower than 300 °C, the reaction rate is slow, not practical, and not suitable for the purpose of selective oxidation of the surface of the raw material 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, the oxidation is insufficient, and the pores formed in the activated porous raw material carbon black will not develop. If the oxygen treatment time exceeds 15 hours, the combustion on the surface of the raw material carbon black becomes significant. As a result, surface roughness of the porous carbon black and thinning of the branches of the three-dimensional structure (dendritic structure) due to surface combustion occur, leading to a decrease in the mechanical strength of the three-dimensional structure (dendritic structure). However, when 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, as an apparatus suitable for the oxygen treatment step, for example, a rotary kiln or a fluidized bed in which gas is forcibly brought into contact with the raw material carbon black can be applied. In the rotary kiln and the fluidized bed, fresh oxidation gas and the raw material carbon black can efficiently and homogeneously come into contact, and the 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, it is important to design an apparatus that can easily remove heat. For example, by increasing the floor area and restricting the loading amount of the raw material carbon black in the height direction, 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 making the oxidized raw material carbon oxidized in the oxidation treatment step porous by activation. The activation mechanism of the raw material carbon black is considered as follows. The raw carbon black is brought into contact with an activating gas such as water vapor (H2O) or CO2 and maintained at 800°C to 1100°C, whereby the carbon atoms constituting the raw carbon black are removed as CO. By optimizing the reaction rate of this reaction, the peripheral part (edge part) of the condensed polycyclic aromatic hydrocarbons that are easy to burn in the crystallites of several nm size forming the raw carbon black is selectively oxidized and consumed. As a result, gaps are generated 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.

[0072] When the activation temperature is increased, the reaction rate increases, the combustion near the surface in contact with the high-concentration activating gas is accelerated, the concentration of the activating gas diffusing into the inside becomes even lower, and the internal combustion is decelerated. To develop pores inside without changing the surface state, appropriate control of the reaction rate is performed. Water vapor 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 the raw carbon black by water vapor 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 the raw carbon black by oxygen is an exothermic reaction, and if the heat generation is more than the heat extraction, the temperature of the reaction site rises monotonously and the reaction is difficult to control. Since this phenomenon is accelerated by scaling up, oxidation by oxygen is not suitable for mass production, and activation using water vapor or CO2 as the activating gas is suitable.

[0073] If a manufacturing process that allows such an activation reaction to proceed is realized, there are no restrictions on the activation device. To efficiently promote activation, it is advisable to increase the concentration of the activation gas on the surface of the raw material 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 raw material carbon black pellets, and it is effective to increase the relative velocity of the activation gas with respect to the carbon black pellets of the raw material. 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 raw material 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.

[0074] Specific activation conditions 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, a temperature of 750°C to 900°C is preferable, and when CO2 is used as the activation gas, a temperature of 800°C to 950°C is preferable. Requirement (A) (BET surface area 800 - 1400 m 2 / g) To obtain porous carbon black that meets this requirement, the mass reduction rate of the porous raw material carbon black due to activation is, for example, 60% to 80% by mass. The processing time required to reach such a mass reduction rate is, for example, 5 hours to 100 hours, preferably 10 to 80 hours, and 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, there is a difference in that the BET surface area is smaller. This difference in BET surface area is because when the reaction rate is too high, the surface combustion of the oxidized raw material 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, it is because large irregularities of 10 nm or more (pores formed by the development of the depressions at the joints of primary particles due to surface combustion) are generated by surface combustion. That is, to suppress surface combustion, it is preferable to lower the activation temperature and increase the activation time. On the other hand, in the case of a long-time activation where the time required for the mass reduction rate to reach 50% by mass exceeds 100 hours, since the activation rate is too slow, surface combustion becomes dominant over internal combustion, the development of pores is suppressed, which is not preferable.

[0075] Also, it is 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, i.e., without changing the BET surface area 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 pressures 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, more preferably 5 to 20 hours. In order to avoid the same phenomenon as in the case of normal pressure, the lower and upper limits of the activation time are determined.

[0076] Through the above activation treatment process, pores are formed inside the raw material carbon black, and porous carbon black satisfying requirement (A) can be produced. In addition, in the process of increasing the crystallinity in the heat treatment process, since the porous raw material carbon black that has been made porous changes in its tissue structure and crystal structure toward a more stable graphite structure, the pores, which can be regarded as defects, change in the direction of being crushed. Therefore, the pore structure of the porous raw material carbon black obtained in the activation treatment process needs to form a structure more developed than the finally desired pore structure so as to maintain a preferable pore structure even if the pores are crushed in the heat treatment process. That is, in order to satisfy requirement (A) in the state after the activation treatment process, the BET surface area of the porous raw material carbon black obtained in the activation treatment process is preferably at least 400 m 2 / g or more, more preferably 600 m 2 / g, and even more preferably 800 m 2 / g or more.

[0077] (Heat treatment process) The heat treatment step is a heat treatment step for heat-treating the porous raw material carbon black obtained in the activation treatment step. 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 strong acidic environment. When applying porous carbon black to such an environment, thermodynamic stability cannot be expected. Therefore, as a general countermeasure, it is common to increase its crystallinity as much as possible to avoid oxidative consumption in terms of speed.

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

[0079] In the heat treatment step, the crystallinity of the porous raw material carbon black can be increased by graphitization of the porous raw material carbon black. More specifically, by subjecting the porous raw material carbon black having a BET specific surface area, which has been activated under the above strong activation conditions, to heat treatment under the above conditions, the crystallinity of the porous raw material carbon black can be increased while maintaining the pores without being crushed. Thereby, in addition to requirement (A) and requirement (B), it is possible to produce porous carbon black that satisfies requirement (D).

[0080] The heat treatment step is not particularly limited as long as it is a step capable of heating the porous raw material carbon black under the above conditions. Examples of the heating method include resistance heating, microwave heating, high-frequency heating, and furnace-type heating methods. Regarding 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.

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

[0082] In the carbon material for the catalyst carrier of the present disclosure, after the heat treatment step, an activation treatment may be performed again for the purpose of reviving the pores crushed by heat. However, since activation is accompanied by a decrease in the strength of the porous branches, it is important to keep the treatment amount low. Specifically, the mass reduction rate due to activation after 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 Solid Polymer Fuel Cell and Solid Polymer Fuel Cell> The solid polymer fuel cell will be described together with the catalyst layer for the 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.

[0084] 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 as long as they are separators used in conventional fuel cells (for example, solid polymer fuel cells).

[0085] 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.). In addition, a preferable example of the gas diffusion layers 130 and 140 is 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, which is a two-layer structure gas diffusion layer.

[0086] 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)

[0087] 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 do 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.

[0088] 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, or may be the same as that of the catalyst layer 160, or may have a more hydrophilic configuration than the catalyst layer 160.

[0089] 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)

[0090] 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.

[0091] 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 (especially high load characteristics) in the catalyst layer 160 can be enhanced. And the power generation characteristics (especially high load characteristics) of the polymer electrolyte fuel cell 100 can be enhanced.

[0092] Note that the catalyst loading rate 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 rate is within this range, the power generation characteristics (especially high load characteristics) become even higher. Here, the catalyst loading rate is represented by the mass% 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 catalyst support). When the catalyst loading rate 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 rate is 80% by mass or more, catalyst aggregation is likely to occur. Also, there is a possibility that the catalyst layer 160 becomes too thin and flooding occurs.

[0093] The mass ratio I / C of the mass I of the electrolyte material to the mass C of the carbon material for the catalyst support in the catalyst layer 160 is not particularly limited, and 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 high load characteristics) are improved. On the other hand, when the mass ratio I / C is 0.5 or less, the electrolyte material network becomes poor, and the proton conduction resistance tends to increase. When 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 (especially high load characteristics) may deteriorate.

[0094] Also, 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 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 components near the electrolyte membrane 170 are less likely to function. That is, the catalyst utilization rate may decrease.

[0095] 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 the electrolyte resin 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. are included. Of course, the electrolyte material may be other types of electrolyte materials. Examples of such electrolyte materials include inorganic, inorganic-organic hybrid, etc. electrolyte materials. Note that the polymer electrolyte fuel cell 100 may be a fuel cell that operates in the range of normal temperature (25 °C) to 150 °C.

[0096] <Method for manufacturing a polymer electrolyte fuel cell> The manufacturing method of the solid polymer fuel cell 100 is not particularly limited, and any conventional manufacturing method 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

[0097] 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.

[0098] <Measurement Methods for Each Parameter> (Measurement of Nitrogen Adsorption-Desorption Isotherm (BET Specific Surface Area)) Approximately 30 mg of the sample was weighed and vacuum-dried at 120°C for 2 hours. Then, the sample was set in an automatic specific surface area measurement device (manufactured by MicrotracBEL Corp., BELSORP MAX), and the nitrogen adsorption-desorption isotherm was measured at a measurement temperature of liquid nitrogen temperature (about 77K) 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 to 0.15 in the nitrogen adsorption isotherm. The BET value was calculated using the calculation software attached to the device.

[0099] (Measurement of ΔV fin and ΔV ini by Mercury Porosimetry) 0.3 to 1.0 g of the sample was weighed, lightly consolidated, and formed into a lump to prepare a measurement sample. The measurement sample was loaded into the sample container of a measurement device (AutoPore IV 9520 manufactured by Shimadzu Corporation), and mercury was injected under the conditions of an initial introduction pressure of 5 kPa and a maximum injection pressure of 400 MPa. The mercury absorption amounts (mL / g) were measured when the mercury injection pressure values were 10 MPa and 100 MPa. Then, the difference between the measured values was defined as "the difference ΔV ini (mL / g) 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 before pressurizing the porous activated carbon black at 100 MPa with a mold

[0100] On the other hand, the sample was packed into a cylindrical mold with a diameter of 10 mm to a height of about 5 mm, pressurized at 100 MPa, held for 1 minute, the pressure was removed, the sample was taken out of the mold, and pulverized in a mortar. Then, the pulverized sample was packed into the mold again in the same manner as above, pressed at 100 MPa for 1 minute, and a measurement sample was obtained. Except for using the obtained measurement sample, in the same manner as above, the mercury absorption amounts (mL / g) were measured when the mercury injection pressure values were 10 MPa and 100 MPa. Then, the difference between the measured values was defined as "the difference ΔV fin (mL / g) 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 pressurizing the porous activated carbon black at 100 MPa with a mold

[0101] (Measurement of the intensity ratio I D / I G by Raman spectroscopy Approximately 3 mg of the sample was weighed and measured using a laser Raman spectrometer (NRS-3100 type manufactured by JASCO Corporation) to obtain a Raman spectrum. From the Raman spectrum obtained under the following measurement conditions, peaks in the range of 1300 - 1360 cm -1 referred to as the D band and peaks in the range of 1560 - 1620 cm -1 cm -1 referred to as the G band were extracted, and the intensities (peak areas) of these two peaks were analyzed using the spectral analysis software attached to the device to obtain the intensity I Dand the intensity I of the G band G was calculated. 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), microscopy configuration: Backscattering, objective lens: ×100 magnification, spot diameter: 1 μm, exposure time: 30 sec, observation wavenumber: 2000 cm -1 ~300 cm -1 , number of integrations: 6 times.

[0102] <Experimental example> (Raw carbon black) As raw carbon blacks, Niton #200, Niton #SH manufactured by Nippon Steel Carbon Co., Ltd., Tokablack #4500, GFY manufactured by Tokai Carbon Co., Ltd. were prepared, and these raw carbon blacks were subjected to an oxidation treatment, an activation treatment process, and a heat treatment process described later.

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

[0104] Table 1 below shows the values of the primary particle diameter (arithmetic mean particle diameter), DBP oil absorption amount, and BET specific surface area of the raw carbon blacks respectively cited from Carbon Black Yearbook No. 72 (2022), edited by the Carbon Black Association, and the product homepage of Ketjenblack.

[0105]

Table 1

[0106] (Oxidation treatment process) According to Table 2, as the oxidation treatment, either an ozone treatment process (an example of the column denoted as "O3" in the table) or an oxygen treatment process (an example of the column denoted as "O2" in the table) was carried out.

[0107] - Ozone treatment process - Pure oxygen was used as the input gas in a research ozone generator manufactured by Kotohira Kogyo Co., Ltd. The principle of ozone gas generation in this device is the so-called discharge type, and the ozone concentration is adjusted by the voltage between the electrodes, the current amount, and the gas flow rate of the gas to be circulated. That is, a mixed gas of ozone and oxygen becomes the output gas from the generator. The electrode voltage is fixed for the device and the flow rate of the input oxygen gas is variable, and the flow rate was set to 2 L / min. The raw carbon black is more easily oxidized by ozone as the surface area is larger, and is less easily oxidized as the crystallinity is increased by heat treatment. Since the ozone oxidation of the raw carbon black is an exothermic reaction, if the reaction amount is large, heat accumulates and the temperature locally rises and catches fire. Therefore, in the experiment, the output gas from the ozone generator was mixed with argon gas to dilute the ozone to make an oxidation gas so that the carbon would not catch fire due to the reaction heat. Also, the amount of gas sent to the reaction tube was controlled. The reaction amount of the ozone treatment was adjusted by the contact time with the output gas or by setting the reaction tube in the electric furnace and heating it.

[0108] In a specific reaction apparatus, a vertical quartz reaction tube with an outer diameter of 35 mmφ was used, and a filter formed by fusing quartz beads inside the tube was fused as a dispersion plate. If necessary, quartz wool with a fine fiber diameter was spread on the dispersion plate, and the raw carbon black was placed on it. The oxidation gas was flowed from the bottom to the top, and the flow rate was increased to such an extent that the powder did not scatter outside the system, and it was adjusted to the flow rate shown in Table 2 so that the reaction unevenness was reduced. The reaction amount was judged by the mass change. In the initial stage of the reaction, the mass increase due to the imparting of oxygen functional groups increased up to a maximum of 0.5%, and then shifted to a mass decrease. The pore structure after ozone oxidation was investigated by a nitrogen gas adsorption isotherm. As a result, it was confirmed that the isotherms almost overlapped before and after the treatment, that is, the surface was burned off and the pore size distribution due to combustion inside the pores did not change due to ozone oxidation. Table 2 shows the treatment temperature (controlled by the temperature of the electric furnace), which is a control factor in the ozone treatment process, and the treatment time.

[0109] - Oxygen treatment process - A tube with a quartz filter (pore diameter 40 - 50 μm) fused as a dispersion plate inside a quartz tube with an outer diameter of 50 mmφ was used as the reaction tube. The reaction tube was filled with quartz wool to a height of about 1 cm, and on top of that, raw material carbon black in a granulated state was put in. The charge was generally 20 - 25 g, and from the bottom to the top of the reaction tube, dry air or a gas mixture of dry air and argon gas was flowed as the oxidation gas at the flow rates shown in Table 2. 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 material carbon black, it is important to carefully select the conditions for each carbon black. Table 2 shows the treatment temperature (controlled by the temperature of the electric furnace), which is a control factor in the oxygen treatment process, and the treatment time.

[0110] (Activation treatment process) A quartz tube with a quartz filter fused as a dispersion plate inside a quartz tube with an outer diameter of 35 mmφ was used as the reaction tube. Quartz wool was put on the dispersion plate to a height of about 1 cm, and 5 g - 15 g of oxidized raw material carbon black was put on top of that. 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 10°C / min. It was heated to 850 - 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 condition of the furnace temperature. After treating for a predetermined time, the reaction tube was taken out of the furnace and at the same time switched to argon gas and allowed to cool. After confirming cooling near room temperature, the porous raw material carbon black was taken out and weighed, and the mass reduction rate of the yield with respect to the charged mass (charged mass / recovered mass) was calculated. The activation temperature and activation time were adjusted as shown in Table 2 as the activation treatment conditions so that the mass reduction rate was in the range of 55 - 80 mass%.

[0111] (Heat treatment process) A so-called graphitization furnace that uses a graphite material as a heating element was used as the heating furnace. Porous raw material carbon black obtained in the activation treatment step was placed in a graphite crucible with a volume of about 100 cc, and after being depressurized and vacuum replaced with argon gas, the temperature was raised at a rate of 10 °C per minute at 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 allowed to cool and taken out after cooling to near room temperature. The holding time of the heat treatment temperature was made variable, and the conditions are shown in Table 2.

[0112] Through the above steps, carbon materials (porous activated carbon black) for catalyst carriers of each example were obtained.

[0113] <Fabrication of Membrane Electrode Assembly (MEA)> (Fabrication of Catalyst) The carbon material (porous activated carbon black) for the catalyst carrier 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% by 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, refiltered, and treated by vacuum drying at 90 °C for 5 hours to obtain a catalyst.

[0114] (Fabrication of Ink) An 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 the catalyst had been previously dispersed. The dispersion was further advanced with 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.

[0115] <Fabrication of MEA> On a Teflon (registered trademark) sheet, the above ink was uniformly applied with a sprayer and dried with a 60°C air circulation dryer to prepare a decal with a catalyst layer formed thereon. Electrodes of a predetermined 36 mm size were cut out from the decal. Two identical sheets thus cut out 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 thermally fused together. In this way, an MEA was obtained.

[0116] <Battery Evaluation> (Evaluation of Power Generation Characteristics (High Load Characteristics)) Regarding the MEAs prepared using the carbon materials (porous activated carbon black) for the catalyst carrier of each example, each was incorporated into a cell, set in a fuel cell measurement device, and the performance evaluation of the fuel cell was carried out according to the following procedure.

[0117] Regarding the reaction gases, 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 25% and 70% respectively, and the gases were supplied at a back pressure of 0.04 MPa. Also, the cell temperature was set to 80°C, and regarding the reaction gases 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.

[0118] Under the condition of supplying reaction gases to the cell under such settings, the load was gradually increased, and the output current density of the cell was measured after the output voltage was maintained at 0.3 V for 1 hour, and the evaluation was carried out according to the following pass rank and fail rank criteria. The results are shown in Table 2. 〔Pass Rank〕 A: The current density after the output voltage is maintained at 0.3 V for 1 hour is 1200 mA / cm 2 or more. B: The current density after the output voltage is maintained at 0.3 V for 1 hour is 1100 mA / cm 2 or more. 〔Fail Rank〕 C: The current density after the output voltage is maintained at 0.3 V for 1 hour is less than 1100 mA / cm 2

[0119] ​Table 2 shows the details of the experimental examples. In Table 2, "Gas species / Gas species: mL / min / mL / min" means the flow rate of each of the two gas species.

[0120]

Table 2-1

[0121]

Table 2-2

[0122]

Table 2-3

[0123]

Table 2-4

[0124] From the above results, it can be seen that the carbon material for catalyst support (porous activated carbon black) corresponding to this example is superior in power generation characteristics (especially high load characteristics) compared to the carbon material for catalyst support corresponding to the comparative example. Also, from the reference examples, it can be seen that sufficient power generation characteristics (especially high load characteristics) cannot be obtained with Ketjenblack EC300J and EC600JD manufactured by Lion Corporation.

[0125] Also, when applying raw carbon black with a large particle size, generally it is not suitable for activation, pores do not develop, and it is common that the BET surface area does not increase. However, by applying the manufacturing method of the present disclosure, regardless of the particle size of the raw carbon black, a carbon material for a catalyst support (porous activated carbon black) that satisfies the excellent power generation characteristics (particularly, high load characteristics) of the present disclosure can be obtained if the physical property regulations of the present disclosure are satisfied. That is, all the examples applying 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, it can be understood that when applying raw carbon black with a primary particle size 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 (particularly, high load characteristics) can be obtained.

[0126] The description of the symbols is as follows. 100 Polymer electrolyte fuel cell 110, 120 Separator 130, 140 Gas diffusion layer 150, 160 Catalyst layer 170 Electrolyte membrane

[0127] Note that 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 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. 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) BET specific surface area S obtained by BET analysis of nitrogen gas adsorption isotherm ＢＥＴ 400 to 1200m ２ / g. (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) Said ΔV ｉｎｉ is 0.80 mL or more and 1.50 mL / g or less. (D) In ​​the Raman spectrum obtained by Raman spectroscopy, 1300 to 1360 cm －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. 5. The fuel cell according to claim 4, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on a cathode side.

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