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

Abstract

Disclosed is a carbon material for a catalyst carrier of a polymer electrolyte fuel cell, the carbon material being composed of porous activated carbon black that satisfies requirements (A) to (C).　(A) The volume of pores having a pore diameter of 2 nm to 6 nm inclusive is 0.1 mL / g to 0.7 mL / g inclusive.　(B) The ratio (OSA / SBET) of the outside specific surface area OSA to the BET specific surface area SBET is 0.1 to 0.5 inclusive.　(C) Lc (002) obtained from the line width of the (002) diffraction line is 1.6 nm to 4.0 nm inclusive.

Description

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

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

[0002] A polymer electrolyte fuel cell (MSF) is a type of fuel cell that comprises a pair of catalyst layers arranged on both sides of a polymer electrolyte membrane, a gas diffusion layer located outside each catalyst layer, and a separator located outside each gas diffusion layer. Of the pair of catalyst layers, one becomes the anode of the MSF, and the other becomes the cathode. In a typical MSF, multiple unit cells having the above components are stacked to obtain the desired output.

[0003] A reducing gas, such as hydrogen, is introduced into the separator on the anode side. The gas diffusion layer on the anode side diffuses the reducing gas before introducing it into the anode. The anode contains a catalyst component, a catalyst support carrying the catalyst component, and a proton-conducting electrolyte material (ionomer). The catalyst support is often composed of carbon material. On the catalyst component, 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: H ２ →2H ＋ +2e － (E ０ (= 0V)

[0004] The protons generated in this oxidation reaction are introduced to the cathode through the electrolyte material in the anode and the solid polymer electrolyte membrane. Electrons are introduced to the external circuit through the catalyst support, gas diffusion layer, and separator. These electrons perform work (generate electricity) in the external circuit and are then introduced to the cathode-side separator. Finally, these electrons are introduced to the cathode through the cathode-side separator and the cathode-side gas diffusion layer.

[0005] Solid polymer electrolyte membranes are composed of electrolyte materials that have proton conductivity. The solid polymer electrolyte membrane introduces protons generated by the oxidation reaction described above into its cathode.

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

[0007] The water generated in the reduction reaction is discharged to the outside of the fuel cell together with the unreacted oxidizing gas. Thus, in a solid polymer fuel cell, power generation is performed 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.

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

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

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

[0011] Patent Document 3 states that "the specific surface area measured by the BET method is 200 to 500 m²." 2 A carbon black characterized by having a concentration of 1 / g, a crystal layer thickness Lc measured by X-ray diffraction of 20 to 30 Å, an average primary particle diameter of 15 to 25 nm, and a volatile content of 0.10 to 1.00% is disclosed.

[0012] Patent Document 4 describes a carbon material for a catalyst support capable of carrying catalyst components for polymer electrolyte fuel cells, wherein the G-band full width at half maximum measured by Raman spectroscopy is 30 cm². －１ Over 65cm －１ The BET specific surface area S is less than or equal to the BET method. ＢＥＴ (m ２ ( / g) is 700m ２ / g over 3000m ２ The total specific surface area S is less than / g and is evaluated by t-plot analysis. ｔｏｔａｌ and external specific surface area S ｏｕｔ The ratio S ｏｕｔ / S ｔｏｔａｌ However, it is greater than 0.3, and the external specific surface area S is evaluated by t-plot analysis. ｏｕｔ 300m ２ A carbon material for catalyst supports, characterized by having a concentration of more than 1 / g, is disclosed.

[0013] Patent Document 5 describes a carbon-based support for fuel cell catalysts, wherein the carbon-based support is a solid-type support, and the carbon-based support is 100 to 450 m ２ External surface area per g: 0.25–0.65 cm² ３ Mesopore volume per g, and 0.01–0.05 cm ３ A carbon-based carrier having a micropore volume of 1 / g (where the outer surface area, mesopore volume, and micropore volume are the arithmetic mean of measurements obtained from five randomly selected samples using a BET (Brunauer-Emmett-Teller) analyzer (Micromeritics, ASAP-2020)) is disclosed.

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

[0015] Incidentally, when porous carbon black is used as a carbon material for catalyst support in polymer electrolyte fuel cells, a large amount of catalyst metal can be supported inside the carbon black, so low-load characteristics (power generation characteristics at low currents) are required for power generation performance. However, in conventional technologies, including all of the above-mentioned literature, the porosity inside the carbon black is not sufficient, so further improvement in low-load characteristics is required.

[0016] For example, Patent Document 2 describes a method for producing a carbon black product having a second BET nitrogen surface area larger than the first BET nitrogen surface area, in which a carbon black starting material having the first BET nitrogen surface area is brought into contact with an oxidizing agent in a fluidized bed under conditions effective for this purpose. This reaction between the oxidizing agent and carbon black in the fluidized bed creates porosity. However, the reaction in the fluidized bed may only improve the uniform contact between the oxidizing agent and carbon black. Furthermore, compared to a treatment that pre-introduces pores into the carbon black through which the gaseous oxidizing agent penetrates, sufficiently developed pore formation may not occur, and the effect of exposing the edge surface that serves as the activation starting point deeper into the carbon black may not be achieved, resulting in insufficient porosity within the carbon black. Therefore, there is room for improvement in terms of low-load characteristics.

[0017] In Patent Document 3, an activation treatment is performed after heat treatment. Because the heat-treated, highly crystalline carbon wall is activated, the effect of pore formation within the carbon black due to activation is low, and there is a possibility that the porosity of the carbon interior will not be sufficient. As a result, the support of catalyst metal particles within the carbon is insufficient, and there is room for improvement in low-load characteristics.

[0018] Patent Document 4 describes activation of the support carbon, which involves hollowing out the carbon, in order to increase the hydrophilicity of the support carbon. As a result, the support carbon is characterized by having a relatively large external specific surface area. However, in such a support carbon with a large external specific surface area, it is thought that not only the inside of the carbon but also the external surface is greatly activated. As the activation of the external surface progresses, the openings leading to the inside of the carbon expand on the outer surface of the carbon. Therefore, if this is used as a catalyst support in a fuel cell, there is a risk that the proton-conducting electrolyte material (ionomer) will penetrate excessively into the carbon, poisoning the catalyst metal particles and leading to a decrease in low-load characteristics.

[0019] Patent Document 5 describes acetylene black being activated with air at a thermal decomposition temperature of ±40°C, with a 20% weight reduction. This selectively increases the mesopore size, resulting in an external specific surface area of ​​100 to 450 m². ２ / g, mesopore volume of 0.25-0.65 cm³ ３ / g, micropore volume of 0.01-0.05 cm³ ３ This material achieves a porous carbon structure with a density of 1 / g. However, while micropores are not considered to contribute to catalytic activity, it is thought that the moisture adsorbed within the micropores contributes to maintaining moisture retention within the fuel cell catalyst layer. Proton transport within the fuel cell catalyst layer is carried out by a proton-conducting electrolyte material (ionomer), and its propagation speed increases with higher humidity within the catalyst layer. Furthermore, proton transport also occurs on the carbon surface not coated with ionomer due to condensed water, so higher humidity promotes the formation of proton transport pathways. Therefore, if there is insufficient micropore volume, the humidity necessary for proton transport will not be maintained, raising concerns about a decrease in low-load characteristics.

[0020] Therefore, the objective of this disclosure is to provide a carbon material for catalyst support in polymer electrolyte fuel cells that is excellent in both durability and low-load characteristics, a catalyst layer for polymer electrolyte fuel cells utilizing the same, and a fuel cell.

[0021] The means for solving the problem include the following embodiments: <1> A carbon material for catalyst support in a polymer electrolyte fuel cell, consisting of porous activated carbon black, that satisfies the following requirements (A), (B), and (C): (A) The pore volume of a pore diameter of 2 nm to 6 nm, determined by analyzing the nitrogen adsorption isotherm by the DH (Dollimore-Heal) method, is 0.10 mL / g to 0.70 mL / g. (B) The external specific surface area OSA, determined by analyzing the nitrogen adsorption isotherm by the t-plot method, and the BET specific surface area S, determined by analyzing the nitrogen adsorption isotherm by the BET method. ＢＥＴ Ratio (OSA / S ＢＥＴ ) is 0.1 or more and 0.5 or less. (C) The Lc(002) obtained from the line width of the (002) diffraction line appearing in the spectrum obtained by powder X-ray diffraction is 1.6 nm or more and 4.0 nm or less. <2> A carbon material for catalyst support of a polymer electrolyte fuel cell as described in <1>, which further satisfies the following requirement (D). (D) BET specific surface area S ＢＥＴ However, 350m ２ / g or more 1200m ２ It is less than or equal to / g. <3> A carbon material for catalyst support of a polymer electrolyte fuel cell as described in <1> or <2>, which further satisfies the following requirement (E). (E) 1580 cm² obtained by Raman spectroscopy. －１ The half-width ΔG of the nearby G-band peak is 65 cm. －１ 105cm or more －１ The following: <4> A carbon material for catalyst support of a polymer electrolyte fuel cell described in any one of <1> to <3>, which further satisfies the following requirement (B1). (B1) The ratio (OSA / S ＢＥＴ ) is 0.10 or more and 0.30 or less. <5> A catalyst layer for a polymer electrolyte fuel cell containing a carbon material for catalyst support of a polymer electrolyte fuel cell as described in any one of <1> to <4>. <6> A fuel cell containing the catalyst layer for a polymer electrolyte fuel cell as described in <5>. <7> The fuel cell as described in <6>, wherein the catalyst layer for the polymer electrolyte fuel cell is the catalyst layer on the cathode side.

[0022] This disclosure provides a carbon material for catalyst supports in polymer electrolyte fuel cells that offers excellent durability and low-load characteristics, a catalyst layer for polymer electrolyte fuel cells utilizing the same, and a fuel cell.

[0023] Figure 1 is a schematic diagram showing an example of the general configuration of the fuel cell of this disclosure.

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

[0025] <Carbon material for catalyst support in polymer electrolyte fuel cell> The carbon material for catalyst support in polymer electrolyte fuel cell according to this disclosure consists of porous carbon black that satisfies requirements (A), (B), and (C) described later. Here, porous carbon black is carbon black that has been made porous by, for example, "activation" by contacting it with an oxidizing gas.

[0026] The carbon material for catalyst supports disclosed herein is a carbon material that exhibits excellent durability and low-load characteristics. This carbon material was discovered through the following findings: firstly, the identification of the desired porous carbon black structure as specific physical properties; and secondly, the development of a specific manufacturing method for it. The optimal structure and manufacturing method are described below.

[0027] (Optimal Structure for Porous Carbon Black) Generally, the power generation characteristics of fuel cells depend heavily on the overpotential of the cathode reaction. The following three factors are considered to be the main causes of overpotential at the cathode electrode: (1) The combination of two resistances, electron conduction resistance and proton conduction resistance, due to the magnitude of the ohmic resistance of the catalyst layer; (2) Diffusion resistance of oxidizing gas within the catalyst layer; (3) Electrochemical resistance at the catalyst metal surface, i.e., resistance in chemical reactions involving electron transfer (i.e., resistance of the catalytic reaction).

[0028] Of the main causes mentioned above, reducing "(3) Resistance to catalytic reaction" is particularly important for improving low-load characteristics. To reduce the resistance to catalytic reaction, the number of catalyst metals contributing to the reaction should be increased. Generally, due to various factors, not all supported catalyst metals can participate in the reaction, so increasing the utilization rate is an effective measure. One way to increase the utilization rate is to check whether the catalyst metals in the pores of porous carbon black are in contact with the ionomer. In other words, it is the ease with which the ionomer penetrates into the pores of porous carbon black. Therefore, the inventors have been investigating the factors affecting "the ease with which the ionomer penetrates into the pores of porous carbon black." Specifically, in addition to the pore structure, which has been a focus of attention as a structure for porous carbon black with excellent low-load characteristics, the inventors have been investigating the surface structure obtained by activation (i.e., the roughness of the surface). As a result, they have obtained the following findings. In porous carbon black, significant surface roughness impairs the uniformity of the ionomer coating thickness adsorbed on the surface. As a result, in areas with thicker coatings, the ionomer exhibits increased gas diffusion barrier properties, increasing resistance to the supply of reactive gases into the pores. Surface roughness is an unavoidable phenomenon in the activation process, and increasing both pore volume and surface area will correspondingly increase surface roughness. What is important is not the surface roughness itself, but the value obtained by dividing surface roughness by surface area; that is, having relatively low surface roughness relative to pore development is essentially crucial for improving low-load characteristics.

[0029] Specifically, (a) increase the pore volume with a pore diameter suitable for the size of the catalyst metal particles. (b) suppress the value obtained by dividing the surface roughness of the carbon black due to oxidation during the activation process by the surface area. (c) improve the crystallinity of the porous carbon black to enhance durability, that is, increase the number of layers of carbon network surfaces, which are the constituent units of porous carbon black. With these three configurations, low-load characteristics are improved while maintaining durability. Preferably, (d) increase the surface area per unit weight of the catalyst support, i.e., the specific surface area corresponding to the floor area on which the catalyst metal is adsorbed, in order to increase the loading density of the catalyst metal. This improves low-load characteristics. Even more preferably, (e) increase the size of the carbon network surface. This can improve durability against oxidative wear.

[0030] The specific quantitative indicators representing (a) above are as follows. From the viewpoint of reducing activity and suppressing dissolution under operating conditions, generally, a particle diameter of 2 nm or more is preferred for catalyst metal particles. On the other hand, from the viewpoint of securing a reaction area, a size of 6 nm or less is preferred for catalyst metal. Therefore, it is necessary to increase the pore volume with a pore diameter suitable for the size of the catalyst metal. For quantification, a pore volume of 2 nm to 6 nm with a pore diameter calculated by the DH method of mesopore analysis from nitrogen gas adsorption measurement is suitable (requirement (A)).

[0031] The specific quantitative indicators representing (b) above are as follows: As a quantitative indicator representing surface roughness necessary to suppress surface roughness of carbon black due to oxidation associated with the activation process, the value obtained by dividing the external specific surface area calculated by t-plot analysis from nitrogen gas adsorption measurement by the specific surface area is appropriate (Requirement (B)).

[0032] The specific quantitative indicators representing the above (c) are as follows: The average number of stacked carbon network planes, which are the smallest constituent units of carbon black obtained by X-ray diffraction (i.e., Lc(002) (nm) obtained from the line width of the (002) diffraction line) is appropriate (Requirement (C)).

[0033] A suitable quantitative indicator to represent the above (d) is the BET specific surface area obtained by nitrogen gas adsorption measurement (Requirement (D)).

[0034] A suitable quantitative indicator to represent the above (e) is the full width at half maximum of the G-band peak of the carbon material, measured by Raman spectroscopy, which represents the size of the carbon network, the smallest constituent unit of carbon black (Requirement (E)).

[0035] From the above findings, it has been found that the carbon material for the catalyst support of the polymer electrolyte fuel cell of this disclosure, by consisting of porous carbon black that satisfies the requirements (A), (B), and (C) described later (preferably, in addition to requirements (A) to (C), at least one of requirements (D) and (E)), becomes a carbon material with excellent low-load characteristics while maintaining durability.

[0036] Requirements (A), (B), and (C) are described below. Hereinafter, from the viewpoint of further improving durability and low load characteristics, it is preferable that the carbon material for catalyst support of this disclosure satisfies at least one of requirements (D) and (E) in addition to requirements (A) to (C).

[0037] (Requirement (A): Pore Volume) (A) The pore volume of pores with a diameter of 2 nm or more and 6 nm or less, as determined by analyzing nitrogen adsorption isotherms using the DH (Dollimore-Heal) method, is 0.10 mL / g or more and 0.70 mL / g or less.

[0038] To efficiently utilize catalyst metals adsorbed within the pores of porous carbon black for power generation, it is considered paramount to increase the pore volume with a pore diameter appropriate to the size of the catalyst metal. It is known that if the particle size of the catalyst metal is too small, its dissolution is accelerated, while if the diameter is less than 2 nm, the catalytic activity decreases. Therefore, the lower limit of the pore diameter is estimated to be around 2 nm. On the other hand, if the catalyst metal is too large, its dissolution is suppressed, improving its durability. However, this reduces the reaction area necessary to maintain the crucial activity, thus creating an upper limit for the optimal particle size. From this perspective, the optimal pore diameter is between 2 nm and 6 nm. Furthermore, the pore size distribution obtained by mesopore analysis of nitrogen gas adsorption measurements is suitable as a quantitative indicator of pore volume. Applying the DH analysis method, the difference between the cumulative adsorption volume up to a pore diameter of 6 nm and the cumulative adsorption volume up to a pore diameter of 2 nm is adopted as the pore volume for pore diameters between 2 nm and 6 nm.

[0039] The optimal range for the pore volume of pores with a diameter of 2 nm to 6 nm is 0.10 mL / g to 0.70 mL / g, preferably 0.30 mL / g to 0.70 mL / g. If the pore volume of pores with a diameter of 2 nm to 6 nm is less than 0.10 mL / g, the density of the supported catalyst metal (i.e., the amount supported per unit mass of the catalyst support) is too low, resulting in a decrease in power generation performance, especially low-load performance. If the pore volume of pores with a diameter of 2 nm to 6 nm exceeds 0.70 mL / g, the mechanical strength of the porous carbon black decreases, leading to damage to the support during the catalyst layer formation process and a decrease in power generation performance.

[0040] The pore volume of pores with a diameter of 2 nm to 6 nm is a value measured by the method described in the examples below.

[0041] (Requirement (B): Indicator of surface roughness) (B) External specific surface area OSA obtained by analyzing nitrogen adsorption isotherms using the t-plot method, and BET specific surface area S obtained by analyzing nitrogen adsorption isotherms using the BET method. ＢＥＴ Ratio (OSA / S ＢＥＴ ) is between 0.10 and 0.50.

[0042] The activation process for porous raw carbon black involves porosity formation through the oxidative consumption of carbon (gasification of carbon) by contact between the raw carbon black and a gaseous oxidizing agent. Therefore, the carbon network surface, which is a few nanometers in size and a component of the raw carbon black, is oxidatively consumed both on the surface of the raw carbon black and similarly within the pores. In other words, it is unavoidable in principle that the roughness of the surface of the raw carbon black due to oxidative consumption during the activation process increases as the activation progresses. However, the method for manufacturing the carbon material for catalyst supports described in this disclosure, as described later, makes it possible to change the ratio of surface roughness (oxidative consumption) and internal oxidation (porosity formation) of the porous carbon black. That is, internal oxidation is prioritized to relatively reduce surface roughness.

[0043] The surface roughness index is the external specific surface area (OSA: mL / g), which is obtained by analyzing nitrogen adsorption isotherms using the t-plot method, and the degree of pore development is the BET specific surface area S, which is obtained by analyzing nitrogen adsorption isotherms using the BET method. ＢＥＴ (S ＢＥＴ :m ２ The value obtained by dividing by ( / g) is OSA / S ＢＥＴ However, it is an optimal indicator as it has a strong correlation with power generation performance.

[0044] External specific surface area OSA obtained by analyzing nitrogen adsorption isotherms using the t-plot method, and BET specific surface area S obtained by analyzing nitrogen adsorption isotherms using the BET method. ＢＥＴ Ratio (OSA / S ＢＥＴ The optimal range for the ratio (OSA / S) is 0.10 or more and 0.50 or less, preferably 0.10 or more and 0.30 or less. ＢＥＴ If the ratio (OSA / S) is less than 0.10, the activation is too weak, making it difficult to meet requirement (A). As a result, power generation performance (especially low-load performance) will decrease. ＢＥＴ If the value exceeds 0.50, the surface roughness is too great, increasing the thickness of the ionomer coating adsorbed on the catalyst support surface and increasing the resistance to the diffusion of reaction gas into the pores. As a result, power generation performance (especially low-load performance) decreases.

[0045] Note that the external specific surface area OSA and BET specific surface area S ＢＥＴ This is a value measured by the method described in the examples below.

[0046] (Requirement (C): Crystallinity indicator Lc(002)) (C) The Lc(002) value, determined from the line width of the (002) diffraction line appearing in the spectrum obtained by powder X-ray diffraction, is 1.6 nm or more and 4.0 nm or less.

[0047] To improve durability (specifically, resistance to oxidation and wear), it is necessary to increase the size of the crystallites made up of carbon network planes. There are two main indicators for size: the size of the carbon network plane stacking (number of stacks) and the size of the carbon network plane itself. For the power generation durability of fuel cells, both the size of the carbon network plane stacking and the size of the carbon network plane are important, but the former is more important. The optimal indicator for the size of the carbon network plane stacking is Lc(002) (nm), which is obtained from the line width of the (002) diffraction line in powder X-ray diffraction.

[0048] The optimal range for Lc(002), determined from the linewidth of the (002) diffraction line appearing in the spectrum obtained by powder X-ray diffraction, is 1.6 nm to 4.0 nm, preferably 2.0 nm to 4.0 nm. If Lc(002) is less than 1.6 nm, the number of layers of the carbon network surface is small, the improvement in oxidation resistance is insufficient, and durability decreases. If Lc(002) exceeds 4.0 nm, the activation of the raw material carbon black is insufficient, the pore volume is small, and the heat treatment temperature is too high, leading to pore collapse, thus reducing power generation performance (especially low-load performance).

[0049] (Requirement (D): BET specific surface area S ＢＥＴ ) (D) BET specific surface area S ＢＥＴ However, 350m ２ / g or more 1200m ２ It is less than / g.

[0050] The BET specific surface area corresponds to the area on which the catalyst metal is adsorbed. The two indicators, "pore volume of pores with a pore diameter of 2 nm or more and 6 nm or less" (requirement (A)) and the BET specific surface area, quantitatively define the optimal range between pore size suitable for the size of the catalyst metal and the area on which the catalyst metal is supported. BET specific surface area S ＢＥＴ This is the BET specific surface area (m²) obtained by BET analysis from the measurement results of nitrogen gas adsorption. ２ ( / g) is optimal.

[0051] BET specific surface area S ＢＥＴ 350m ２ / g or more 1200m ２ Preferably less than / g, 450m ２ / g or more 900m ２ A value of less than or equal to / g is more preferable. BET specific surface area S ＢＥＴ 350m ２ At concentrations of 1 / g or higher, high-density support of the catalytic metal on porous carbon black is achieved, suppressing the decline in power generation performance, especially low-load characteristics. BET specific surface area S ＢＥＴ 1200m ２ If the ratio is less than or equal to / g, excessive pore development is suppressed, and the surface roughness index ratio (OSA / S) of requirement (B) is suppressed. ＢＥＴ This makes it easier to satisfy the requirements (C). In addition, it becomes easier to satisfy the lower limit of the crystallinity index Lc(002) of requirement (C). As a result, it becomes easier to achieve both power generation performance (especially low-load performance) and durability.

[0052] Note that the BET specific surface area S ＢＥＴ This is a value measured by the method described in the examples below.

[0053] (Requirement (E): Crystallinity index ΔG) (E) 1580 cm obtained by Raman spectroscopy －１ The half-width ΔG of the nearby G-band peak is 65 cm. －１ 105cm or more －１ The following applies:

[0054] To improve durability (specifically, resistance to oxidation and wear), it is preferable to have a large number of carbon network layers (large Lc(002)) and a large size of the carbon network itself. An appropriate indicator of the size of the carbon network is the full width at half maximum (the line width of the peak at half the peak height) of the G-band peak, which is the vibrational mode of the high-crystal-performance region that appears in the Raman spectroscopic spectrum.

[0055] 1580 cm² obtained by Raman spectroscopy. －１ The half-width ΔG of the nearby G-band peak is 65 cm. －１ 105cm or more －１ The following is preferable: 65 cm －１ 95cm or more －１ The following is preferable: The half-width ΔG of the G-band peak is 65 cm. －１ As a result, excessive crystallinity promotion is suppressed, and the decrease in power generation performance (especially low-load performance) is suppressed. In other words, the decrease in power generation performance (especially low-load performance) due to pore collapse caused by excessive crystallinity promotion is suppressed. The full width at half maximum ΔG of the G-band peak is 105 cm. －１ The following characteristics result in high crystallinity, making it easier to satisfy the durability requirements for fuel cells.

[0056] The full width at half maximum (FWHM) ΔG of the G-band peak is a value measured by the method described in the examples below.

[0057] <Method for producing carbon material for catalyst support in polymer electrolyte fuel cell> Guidelines for producing carbon material for catalyst support in polymer electrolyte fuel cell, consisting of porous activated carbon black according to the present disclosure, that satisfies requirements (A), (B), and (C) (preferably requirements (A) to (C) plus at least one of requirements (D) and (E)), are to develop pores in the raw material carbon black while suppressing surface roughness, reduce pore collapse due to heat treatment to improve durability, and restore the pores collapsed by heat treatment by activation after heat treatment.

[0058] Therefore, as an example of a method for producing a carbon material for a catalyst support in a polymer electrolyte fuel cell according to this disclosure, one example is a manufacturing method having four steps: a pretreatment step, a first activation step, a heat treatment step, and a second activation step. Pretreatment step: The raw material carbon black is subjected to pressurized air oxidation treatment under an air atmosphere. Pressurized air oxidation treatment under these conditions forms fine pores with a diameter of 2 nm or less toward the interior of the carbon black, forming well-developed pores while suppressing surface roughness due to activation. First activation step: The pretreated carbon black is subjected to a first activation to obtain activated carbon black. Heat treatment step: The activated carbon black is heat-treated to obtain heat-treated activated carbon black. Second activation step: The heat-treated activated carbon black is subjected to a second activation to obtain porous activated carbon black.

[0059] The following describes each step.

[0060] (Raw material carbon black) For example, furnace carbon black can be used as the raw material carbon black. Furnace carbon black is suitable as a raw material carbon black because its pores are easily developed by gas activation with carbon dioxide or water vapor. The raw material carbon black is preferably carbon black having an aggregate structure with a well-developed branch structure in order to increase the voids in the catalyst layer of the fuel cell, and specifically carbon black with a DBP oil absorption rate (mL / 100g carbon black) of 100 or more is preferred. The average primary mean particle size of the raw material carbon black is preferably 20 nm or more and 100 nm or less, and more preferably 30 nm or more and 80 nm or less. If the average primary mean particle size of the raw material carbon black is too large, it is difficult to develop internal pores by activation due to surface oxidation, but it also has the advantage of being highly resistant to oxidation and wear, which can easily improve durability. For this reason, the average primary mean particle size of the raw material carbon black is preferably 100 nm or less. If the primary mean particle size of the raw material carbon black is 20 nm or more, pore development becomes easier and durability is improved.

[0061] Here, the DBP oil absorption amount of the raw carbon black indicates the amount of dibutyl phthalate (DBP) absorbed by 100g of raw carbon black, and is a value defined in ASTM (American Standard Test Procedure) D2414-6TT. When two or more types of raw carbon black are used in combination, the DBP oil absorption amount of the raw carbon black shall be the weighted average value based on the raw carbon black content.

[0062] Furthermore, the average primary particle size of the raw carbon black was measured as follows: The raw carbon black was observed at a magnification of 5x and in any 15 fields of view using a transmission electron microscope (TEM) with a resolution of at least 1.5 to 2.0 nm. For each observation image, the approximate circular diameter (i.e., equivalent circle diameter) of the raw carbon black was calculated using commercially available particle size measurement software (Zeiss-Ender Particle Size Analyzer). The arithmetic mean of the equivalent circle diameters of 3500 raw carbon black particles was then taken as the average primary particle size of the raw carbon black. However, if the raw carbon black is a commercially available product, the "primary particle size" listed in the "Carbon Black Yearbook" published by the Carbon Black Association may be used.

[0063] (Pretreatment process: Pressurized air oxidation treatment) In the pretreatment process, the raw material carbon black is subjected to pressurized air oxidation treatment under a pressurized air atmosphere.

[0064] One method for developing pores within the raw material carbon black while suppressing surface oxidation is to increase the concentration of the oxidizing gas, which is the oxidizing agent, by pressurizing. By increasing the concentration of the oxidizing agent, the difference between the oxidizing agent concentration on the surface and the oxidizing agent concentration inside the pores becomes smaller, reducing the difference in the rate of surface oxidation and internal oxidation, and making it possible to control requirement (B) within an optimal range.

[0065] The pressurizing pressure for the pressurized air oxidation treatment is, for example, 0.1 MPa or higher, preferably 0.3 MPa or higher. From the viewpoint of controlling requirement (B) within the optimal range, 0.9 MPa is the practical upper limit of the pressurizing pressure.

[0066] The heating temperature for the pressurized air oxidation treatment is, for example, 300°C to 450°C, preferably 330°C to 400°C. If the heating temperature is below 300°C, the reaction rate is low and the effect of pressurization is diminished, making it difficult to satisfy requirement (B) and resulting in a decrease in power generation performance (especially low-load characteristics). If the heating temperature exceeds 450°C, the oxidizing power increases and it becomes difficult to relatively suppress the oxidation rate of the surface even with pressurization, again making it difficult to satisfy requirement (B) and resulting in a decrease in power generation performance (especially low-load characteristics).

[0067] The heating time for the pressurized air oxidation treatment is, for example, 1 hour to 200 hours, preferably 10 hours to 150 hours. If the heating time is 1 hour or less, the reaction time is too short, making it difficult to satisfy requirement (B) and resulting in a decrease in power generation performance (especially low-load characteristics). If the heating temperature exceeds 200 hours, the reaction time is too long, again making it difficult to satisfy requirement (B) and resulting in a decrease in power generation performance (especially low-load characteristics).

[0068] (First Activation Process: Pore Formation Treatment by Activation) In the first activation process, the pre-treated carbon black is subjected to the first activation to obtain activated carbon black. In the first activation process, the pre-treated carbon black is made porous by the first activation. Because micropores that allow oxidizing gas to pass into the interior of the raw material carbon black are formed by the pre-treatment, it is possible to form internal pores at a relatively faster rate than surface oxidation. In addition, the micropores introduced by the pre-treatment can form pores uniformly inside the raw material carbon black, and it is possible to increase the pore volume by applying pre-treatment compared to when no pre-treatment is applied.

[0069] In the first activation step, the gas used as the oxidizing agent is water vapor (H ２ O), or CO ２ Oxidizing gases such as the above are preferably used. In the first activation step, for example, the pre-treated carbon black can be made porous by contacting it with an oxidizing gas and maintaining the activation temperature at 750°C to 1100°C.

[0070] The activation temperature in the first activation step is preferably 750°C to 900°C when water vapor is used as the activation gas, and CO ２ When used as the activating gas, a temperature of 800°C to 950°C is preferred. If the first activation is performed at a temperature lower than the lower limit of the activation temperature in the first activation step, pore formation will be insufficient, making it difficult to satisfy requirement (A) and resulting in a decrease in power generation performance (especially low-load characteristics). If the activation temperature exceeds the upper limit of the activation temperature in the first activation step, surface oxidation will be significant, making it difficult to satisfy requirement (B) and resulting in a decrease in power generation performance (especially low-load characteristics).

[0071] The activation time in the first activation step is an important factor, as is temperature, for controlling pore development and requirement (B). The activation time in the first activation step is preferably 10 hours or more and 60 hours or less, and more preferably 20 hours or more and 40 hours or less. If the activation time in the first activation step is less than 10 hours, the oxidation rate is too fast, resulting in significant surface oxidation, making it difficult to satisfy requirement (B), which may lead to a decrease in power generation performance (especially low-load characteristics). If the activation time in the first activation step exceeds 60 hours, the reaction rate is too slow, increasing the relative rate of surface oxidation to pore formation, making it difficult to satisfy requirement (B), which may lead to a decrease in power generation performance (especially low-load characteristics).

[0072] There are no particular restrictions on the equipment used in the first activation process. Generally, industrial furnaces can be used for the first activation. For example, fixed-bed furnaces, fluidized bed furnaces, rotary kilns, etc., can be used for the first activation.

[0073] (Heat treatment process: Crystalline development treatment) In the heat treatment process, activated carbon black is heat-treated to obtain heat-treated activated carbon black. The heat treatment process enlarges the carbon network surface and increases the number of layers that make up the activated carbon black obtained in the first activation treatment, thereby increasing the size of the crystallites. Increasing the size of the crystallites increases the resistance to oxidation and wear, thereby increasing durability. Specifically, in order to suppress the oxidation of carbon, the heat treatment process is carried out in a non-oxidizing atmosphere, usually an inert atmosphere such as argon, at a temperature of 1400°C to 1900°C (preferably 1500°C to 1800°C). The effect of the heat treatment time is hardly noticeable, so there is no limit, but the practical heat treatment time is, for example, about 1 to 10 hours. If the heat treatment temperature is below 1400°C, the crystalline development is not sufficient, making it difficult to meet requirement (C) and resulting in a decrease in durability. When the heat treatment temperature exceeds 1900°C, the pores collapse as crystallinity develops, making it difficult to meet requirement A and resulting in a decrease in power generation performance (especially low-load characteristics).

[0074] The heat treatment process is not particularly limited as long as it is a process that can heat the activated carbon black under the above conditions. Examples of heating methods include resistance heating, microwave heating, high-frequency heating, and furnace heating methods. As for the furnace type, there are no restrictions as long as atmospheric pressure and an inert gas atmosphere can be achieved, such as graphitization furnaces, batch furnaces, and tunnel furnaces.

[0075] (Second Activation Process) In the second activation process, the heat-treated activated carbon black is subjected to a second activation to obtain porous activated carbon black. In the second activation process, the heat-treated activated carbon black is subjected to a second activation to restore the pores that have been crushed by chemical bonding between crystallites during the heat treatment. Alternatively, the pore diameter that has been reduced by the heat treatment is increased by the second activation.

[0076] In the second activation step, the gas used as the oxidizing agent is water vapor (H ２ O), or CO ２ Oxidizing gases such as the above are preferably used.

[0077] In the second activation step, for example, the heat-treated activated carbon black can be made porous by contacting it with an oxidizing gas and maintaining the activation temperature at 750°C to 1100°C. The activation temperature in the second activation step is preferably 800°C to 900°C when water vapor is used as the activation gas, and CO ２ When used as the activating gas, a temperature of 850°C to 950°C is preferred. If the first activation is performed at a temperature lower than the lower limit of the activation temperature in the first activation step, pore formation will be insufficient, making it difficult to satisfy requirement (A) and resulting in a decrease in power generation performance (especially low-load characteristics). If the activation temperature in the second activation step is below 750°C, the activation will be insufficient, making it difficult to satisfy requirement (A) and resulting in a decrease in power generation performance (especially low-load characteristics). If the activation temperature in the second activation step exceeds 1100°C, surface oxidation will be promoted, making it difficult to satisfy requirement (B) and potentially resulting in a decrease in power generation performance (especially low-load characteristics).

[0078] The activation time for the second activation step is preferably 0.5 hours or more and 10 hours or less. If the activation time for the second activation step is less than 0.5 hours, the activation will be insufficient, making it difficult to meet requirement (A), which may lead to a decrease in power generation performance (especially low-load characteristics). If the activation time for the second activation step exceeds 10 hours, surface oxidation will be accelerated, making it difficult to meet requirement (B), which will lead to a decrease in power generation performance (especially low-load characteristics).

[0079] <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 solid polymer fuel cells of this disclosure. The carbon material of this disclosure is applicable, for example, to the catalyst layers 150 and 160 provided in the solid polymer fuel cell 100 shown in Figure 1. Figure 1 is a schematic diagram showing an example of the general configuration of the fuel cell of this disclosure. The solid polymer fuel cell 100 shown in Figure 1 comprises separators 110 and 120, gas diffusion layers 130 and 140, catalyst layers 150 and 160, and an electrolyte membrane 170.

[0080] Separator 110 is the anode-side separator and introduces a reducing gas such as hydrogen into the gas diffusion layer 130. Separator 120 is the cathode-side separator and introduces an oxidizing gas such as oxygen or air into the gas diffusion layer 140. The types of separators 110 and 120 are not particularly limited and any separator used in conventional fuel cells (for example, polymer electrolyte fuel cells) may be used.

[0081] The gas diffusion layer 130 is the anode-side gas diffusion layer, which diffuses the reducing gas supplied from the separator 110 before supplying it to the catalyst layer 150. The gas diffusion layer 140 is the cathode-side gas diffusion layer, which diffuses the oxidizing gas supplied from the separator 120 before supplying it to the catalyst layer 160. The types of gas diffusion layers 130 and 140 are not particularly limited and can be any gas diffusion layer used in conventional fuel cells (e.g., polymer electrolyte fuel cells). Examples of 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 gas diffusion layers 130 and 140 is a two-layer gas diffusion layer. Specifically, the gas diffusion layers 130 and 140 have a two-layer structure in which the layer on the separator 110 and 120 side is a gas diffusion fiber layer mainly composed of fibrous carbon material, and the layer on the catalyst layer 150 and 160 side is a micropore layer mainly composed of carbon black.

[0082] The catalyst layer 150 is the so-called anode. Within 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: H ２ →2H ＋ +2e － (E ０ (= 0V)

[0083] Protons generated by the oxidation reaction reach the catalyst layer 160 through the catalyst layer 150 and the electrolyte membrane 170. Electrons generated by the oxidation reaction reach the external circuit through the catalyst layer 150, the gas diffusion layer 130, and the separator 110. The electrons perform work (generate electricity) in the external circuit and then are introduced into the separator 120. Thereafter, the electrons reach the catalyst layer 160 through the separator 120 and the gas diffusion layer 140.

[0084] The configuration of the catalyst layer 150 serving as the anode is not particularly limited. The configuration of the catalyst layer 150 may be the same as that of a conventional anode, may be the same as that of the catalyst layer 160, or may be a configuration having higher hydrophilicity than the catalyst layer 160.

[0085] 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 by the oxidation reaction is discharged to the outside of the solid polymer fuel cell 100 together with the unreacted oxidizing gas. O ２ +4H ＋ +4e － →2H ２ O (E ０ =1.23V)

[0086] Thus, in the solid polymer 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 by the oxidation reaction perform work in the external circuit.

[0087] The catalyst layer 160 contains the carbon material for catalyst carrier of the present disclosure. That is, the catalyst layer 160 contains the carbon material for catalyst carrier of the present disclosure, an electrolyte material (ionomer), and a catalyst component (such as platinum). Thereby, the low-load characteristics in the catalyst layer 160 can be enhanced. And the low-load characteristics of the solid polymer fuel cell 100 can be enhanced.

[0088] 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. When the catalyst loading rate is within this range, the low-load characteristics are further enhanced. Here, the catalyst loading rate is expressed as the mass percentage of the catalyst component relative to the total mass of catalyst-supported particles (particles on which the catalyst component is supported 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 in order to make the polymer electrolyte fuel cell 100 suitable for practical use. On the other hand, if the catalyst loading rate is 80% by mass or more, catalyst aggregation is more likely to occur. Also, if the catalyst layer 160 becomes too thin, there is a possibility of flooding occurring.

[0089] The mass ratio I / C of the electrolyte material mass I to the carbon material mass C for the catalyst support in the catalyst layer 160 is not particularly limited, but is preferably greater than 0.5 and less than 5.0. In this case, the pore network and the electrolyte material network can coexist, and the low-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 fragmented by the electrolyte material. In either case, the low-load characteristics may decrease.

[0090] Furthermore, the thickness of the catalyst layer 160 is not particularly limited, but it is preferably greater than 5 μm and less than 20 μm. In this case, oxidizing gases diffuse easily into 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, oxidizing gases diffuse less easily into the catalyst layer 160, and the catalytic components near the electrolyte membrane 170 become less effective. In other words, the catalyst utilization rate may decrease.

[0091] The electrolyte membrane 170 is composed of an electrolyte material having proton conductivity. The electrolyte membrane 170 introduces the protons generated in the oxidation reaction into the catalyst layer 160 (cathode). Here, the type of electrolyte material is not particularly limited, and any electrolyte material used in conventional fuel cells, such as polymer electrolyte fuel cells, may be used. Examples of suitable electrolyte materials include electrolyte resins. Examples of electrolyte resins include polymers into which phosphate groups, sulfonic acid groups, etc. Specifically, examples include perfluorosulfonic acid polymers and polymers into which benzenesulfonic acid, etc., have been introduced. Of course, the electrolyte material may be of other types. Examples of such electrolyte materials include inorganic electrolyte materials and inorganic-organic hybrid electrolyte materials. The polymer electrolyte fuel cell 100 may be a fuel cell that operates in the range of room temperature (25°C) to 150°C.

[0092] <Method for Manufacturing a Polymer Electrolyte Fuel Cell> The method for manufacturing the polymer electrolyte fuel cell 100 is not particularly limited, and any conventional manufacturing method is acceptable. However, the catalyst support carbon material for catalyst support of this disclosure is used. Of the catalyst layers 150 and 160, it is preferable to use the catalyst support carbon material for catalyst support of this disclosure for at least the catalyst support in the catalyst layer 160 which becomes the cathode. Of course, the catalyst support carbon material for catalyst support of this disclosure may also be used for the catalyst support in both the catalyst layer 150 which becomes the anode and the catalyst layer 160 which becomes the cathode.

[0093] Examples of the carbon material for catalyst supports of this disclosure will be described. First, the measurement methods for each parameter will be described.

[0094] <Measurement methods for each parameter>

[0095] (Nitrogen adsorption isotherm (BET specific surface area S) ＢＥＴ (Measurement of specific surface area) Approximately 30 mg of carbon material for catalyst support was weighed out and vacuum-dried at 120°C for 2 hours. Then, the sample was placed in an automatic specific surface area analyzer (Microtrac Bell, BELSORP MAX), and nitrogen adsorption / desorption isotherms were measured at a measurement temperature of liquid nitrogen temperature (approximately 77 K) using nitrogen gas as the adsorbate. BET specific surface area S ＢＥＴUsing the calculation software attached to the apparatus, in the nitrogen adsorption isotherm, BET analysis was performed in the range where the relative pressure P / P ０ is 0.05 to 0.15, and it was calculated.

[0096] (Measurement of nitrogen adsorption isotherm (pore volume ΣV of pores with a pore diameter of 2 nm or more and 6 nm or less)) The pore volume ΣV of pores with a pore diameter of 2 nm or more and 6 nm or less ２－６ was calculated by analyzing the nitrogen adsorption / desorption isotherm obtained above by the DH method using the software attached to the apparatus. ２－６ (Measurement of nitrogen adsorption isotherm (external specific surface area OSA)) The external specific surface area OSA was analyzed by the t-plot method using the software BELMaster attached to the apparatus for the nitrogen adsorption / desorption isotherm obtained above. Using NGCB (non-graphitized carbon black) attached to the software as a reference substance, the external specific surface area was calculated from the slope of the straight line in the range where the adsorption thickness t = 1.0 to 1.6 nm.

[0097] (Measurement of Lc(002) by X-ray diffraction of carbon powder) A sample of the carbon material for the catalyst support is weighed about 3 mg and placed on a silicon non-reflecting plate. This silicon non-reflecting plate is set in an X-ray diffractometer (Smart-Lab X-ray diffractometer manufactured by Rigaku Corporation). Then, using the X-ray diffractometer, the X-ray diffraction of the carbon material was measured. For the X-ray source, Cu-Kα rays were used, with an interval of 0.02°, integrated for about 1 minute at each angle, and the diffraction spectrum was measured under the condition of a diffraction angle range of 10° to 90°. Lc(002) was calculated from the obtained diffraction spectrum by the following procedure. For the relatively broad peak near the diffraction angle of 24° corresponding to the (002) diffraction line, a straight line tangent to the peak was used as the background and subtracted from the peak intensity to extract the spectrum of the diffraction peak. From the half-value width (the angular width of the spectrum width at half the height of the peak intensity), Lc(002) was calculated using the Scherrer's formula (Lc = Kλ / βcosθ) generally used for carbon materials.

[0098] (Measurement of Lc(002) by X-ray diffraction of carbon powder) A sample of the carbon material for the catalyst support is weighed about 3 mg and placed on a silicon non-reflecting plate. This silicon non-reflecting plate is set in an X-ray diffractometer (Smart-Lab X-ray diffractometer manufactured by Rigaku Corporation). Then, using the X-ray diffractometer, the X-ray diffraction of the carbon material was measured. For the X-ray source, Cu-Kα rays were used, with an interval of 0.02°, integrated for about 1 minute at each angle, and the diffraction spectrum was measured under the condition of a diffraction angle range of 10° to 90°. Lc(002) was calculated from the obtained diffraction spectrum by the following procedure. For the relatively broad peak near the diffraction angle of 24° corresponding to the (002) diffraction line, a straight line tangent to the peak was used as the background and subtracted from the peak intensity to extract the spectrum of the diffraction peak. From the half-value width (the angular width of the spectrum width at half the height of the peak intensity), Lc(002) was calculated using the Scherrer's formula (Lc = Kλ / βcosθ) generally used for carbon materials.

[0099] (Measurement of the full width at half maximum ΔG of the G-band peak by Raman spectroscopy) Approximately 3 mg of a carbon material sample for catalyst support was weighed out, and the Raman spectrum was measured using a laser Raman spectrophotometer (NRS-3100, manufactured by JASCO Corporation). From the Raman spectrum obtained under the following measurement conditions, the G-band, which is 1560-1620 cm⁻¹, was measured. －１ Peaks within the specified range were extracted, and the full width at half maximum (denoted as ΔG), i.e., the peak width ΔG at half the peak height, was calculated by analyzing the spectrum analysis software attached to the instrument. - Measurement conditions - Excitation laser: 532 nm, Laser power: 10 mW (Sample irradiation power: 1.1 mW), Microscope configuration: Backscattering, Objective lens: ×100x, Spot diameter: 1 μm, Exposure time: 30 sec, Observed wavenumber: 2000 cm⁻¹ －１ ~300cm －１ Total number of times: 6.

[0100] <Experimental Example> (Raw Carbon Black) Tokai Carbon Co., Ltd.'s Toka Black #4500 and GFY were prepared as raw carbon black, and these raw carbon blacks were subjected to the first activation process, heat treatment process, and second activation process described later. Table 1 below shows, for reference, the primary particle diameter (arithmetic mean particle diameter), DBP oil absorption amount, and BET specific surface area of ​​the raw carbon blacks, which were quoted from Carbon Black Yearbook No. 72 (2022), edited by the Carbon Black Association.

[0101]

[0102] <Pretreatment Process> Quartz wool was packed as a dispersion plate into a Ni reaction tube with an outer diameter of 30 mmφ, and granulated raw material carbon black (raw material CB shown in Table 2) was placed on top of it. The initial charge was approximately 10 to 20 g, and dry air was flowed from the bottom to the top of the reaction tube at a flow rate of 300 mL / min. The reaction tube was placed in an electric furnace, and heating was started. The predetermined temperature was reached in about 20 minutes, and immediately after heating, the pressure relief valve was adjusted to the predetermined pressure. The pressurized pressure (gauge pressure), heating temperature, and heating time are shown in Table 2.

[0103] <First Activation Process> A reaction tube was constructed by fusing a quartz filter as a dispersion plate inside a quartz tube with an outer diameter of 35 mm. Quartz wool was placed on top of the dispersion plate to a height of about 1 cm, and then 5 g to 15 g of pre-treated carbon black that had been oxidized with pressurized air was placed on top of that. The reaction tube was then set in a vertical electric furnace with 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 gas inside with argon, and then heating was started at a rate of 10°C / min. Once the predetermined temperature was reached, CO was activated. ２ The system was switched to gas. The flow rate was set to 200 mL / min. The activation temperature and activation time are shown in Table 2.

[0104] <Heat Treatment Process> In the heat treatment process, a so-called heat treatment furnace using graphite material as the heating element was used. The first activated carbon black was placed in a graphite crucible with a volume of approximately 100 cc, and after replacing the chamber with argon gas under reduced pressure, the temperature was raised at 10°C per minute with an argon flow rate sufficient to replace the furnace volume in several tens of minutes. After holding the carbon black at a predetermined temperature (heat treatment temperature) for a predetermined time (heat treatment time), it was allowed to cool to near room temperature and removed. The holding time at the activation temperature (heat treatment time) was variable. The conditions are shown in Table 2.

[0105] <Second Activation Process> The heat-treated carbon black, which had undergone heat treatment in the heat treatment process, was subjected to a second activation in the same manner as in the first activation process. However, the activation temperature and activation time for the second activation were as shown in Table 1.

[0106] Through the above process, carbon materials for catalyst supports (porous activated carbon black) were obtained for each example.

[0107] <Preparation of Membrane Electrode Assembly (MEA)> (Preparation of Catalyst) The carbon material for catalyst support (porous activated carbon black) for each example was added to an ethanol / water mixed solvent and dispersed by ultrasonic homogenizer for 2 minutes. A predetermined amount of nitric acid solution of dinitrodiammineplatinum complex was added to adjust the platinum loading rate to 40% by mass, and the mixture was stirred in an oil bath for 15 hours while maintaining a temperature several degrees below 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 the catalyst.

[0108] (Ink preparation) An ionomer solution manufactured by Fujifilm Wako Pure Chemical Industries was diluted with ethanol to adjust the solid content concentration to 10% by mass. This solution was then added dropwise to an ethanol solution in which the catalyst had been dispersed, and further dispersion was carried out using an ultrasonic homogenizer. The mixture was then stirred with 1 mmφ glass beads for 10 to 15 hours. In this way, an ink for catalyst layer formation was obtained.

[0109] <Preparation of MEA> The above ink was uniformly applied to a Teflon® sheet using a sprayer, and dried in a 60°C air-circulating dryer to prepare a decal with a catalyst layer formed on it. A predetermined 36 mm size electrode was cut out from the decal. Two identical cut-out sheets were used as the positive and negative electrodes, and the positive and negative electrodes were placed on both sides of the Nafion film and heat-fused together. In this way, an MEA was obtained.

[0110] <Battery Evaluation> (Evaluation of power generation characteristics (low-load characteristics)) For each example, the MEA fabricated using the carbon material for catalyst support (porous activated carbon black) was incorporated into a cell, set in a fuel cell measuring device, and the fuel cell performance was evaluated according to the following procedure.

[0111] For the oxidizing gas, air was supplied to the cathode side and pure hydrogen to the anode side, with the pressure adjusted by a back pressure valve located downstream of the cell to achieve utilization rates of 40% and 70%, respectively, resulting in a back pressure of 0.04 MPa. The cell temperature was set to 80°C, and the supplied oxidizing gas was bubbled with distilled water maintained at 80°C in a humidifier at both the cathode and anode. Power generation was evaluated by supplying 80°C humidified gas to an 80°C cell.

[0112] Under these conditions, with an oxidizing gas supplied to the cell, the load was gradually increased, and the current density reached 100 mA / cm². ２ The output voltage of the cell was measured after being held for one hour, and evaluated according to the following criteria for pass and fail ranks. The results are shown in Table 2. [Pass Rank] A: Current density of 100 mA / cm² ２ The cell voltage after 0.5 hours is 0.875V or higher. B: Current density is 100mA / cm² ２The cell voltage after 0.5 hours is 0.870V or higher. [Failure Rank] C: Current density is 100mA / cm² ２ The cell voltage after 0.5 hours is less than 0.870V.

[0113] (Durability Evaluation) In the above cell, with the anode remaining unchanged, argon gas under the same humidification conditions as above was flowed through the cathode. The cell voltage was repeatedly set to 1.0V and held for 4 seconds, then set to 1.3V and held for 4 seconds (repeated rectangular wave voltage fluctuation operation). This repeated rectangular wave voltage fluctuation operation was performed 4000 times, and then the durability was investigated in the same manner as the power generation characteristics evaluation above. The evaluation was performed according to the following criteria for pass rank and fail rank. The results are shown in Table 2. [Pass Rank] A: Current density of 100 mA / cm² ２ The cell voltage after 0.5 hours is 0.820V or higher. B: Current density is 100mA / cm² ２ The cell voltage after 0.5 hours is 0.810V or higher. [Failure Rank] C: Current density is 100mA / cm² ２ The cell voltage after 0.5 hours is less than 0.810V.

[0114]

[0115]

[0116] From the above results, it can be seen that the carbon material for catalyst support in the example (i.e., porous activated carbon black) exhibits excellent low-load characteristics as well as durability.

[0117] The symbols are explained below: 100 Solid polymer fuel cell 110, 120 Separator 130, 140 Gas diffusion layer 150, 160 Catalyst layer 170 Electrolyte membrane

[0118] Furthermore, the disclosure of Japanese Patent Application No. 2024-171035 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 were specifically and individually noted to be incorporated by reference.

Claims

1. A carbon material for catalyst support in polymer electrolyte fuel cells, consisting of porous activated carbon black, that satisfies the following requirements (A), (B), and (C): (A) The pore volume of a pore diameter of 2 nm to 6 nm, determined by analyzing the nitrogen adsorption isotherm using the DH (Dollimore-Heal) method, is 0.10 mL / g to 0.70 mL / g. (B) The external specific surface area OSA, determined by analyzing the nitrogen adsorption isotherm using the t-plot method, and the BET specific surface area S, determined by analyzing the nitrogen adsorption isotherm using the BET method. ＢＥＴ Ratio (OSA / S ＢＥＴ (C) The Lc(002) obtained from the line width of the (002) diffraction line appearing in the spectrum obtained by powder X-ray diffraction is 1.6 nm to 4.0 nm.

2. A carbon material for a catalyst support in a polymer electrolyte fuel cell according to claim 1, further satisfying the following requirement (D): (D) BET specific surface area S ＢＥＴ However, 350m ２ / g or more 1200m ２ It is less than or equal to / g.

3. A carbon material for a catalyst support for a polymer electrolyte fuel cell according to claim 1, further satisfying the following requirement (E): (E) 1580 cm² obtained by Raman spectroscopy. －１ The half-width ΔG of the nearby G-band peak is 65 cm. －１ 105cm or more －１ The following applies:

4. The carbon material for a catalyst carrier of a solid polymer fuel cell according to claim 1, further satisfying the following requirement (B1). (B1) The ratio (OSA / S ＢＥＴ ) is 0.10 or more and 0.30 or less.

5. A catalyst layer for a polymer electrolyte fuel cell comprising a carbon material for catalyst support of a polymer electrolyte fuel cell according to any one of claims 1 to 4.

6. A fuel cell comprising a catalyst layer for a polymer electrolyte fuel cell as described in claim 5.

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

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