Catalyst carrier carbon material for solid polymer electrolyte fuel cell, catalyst layer for solid polymer electrolyte fuel cell, and fuel cell

Abstract

This catalyst carrier carbon material for a solid polymer electrolyte fuel cell comprises porous activated carbon black satisfying the following requirements (A) to (C).　(A) The pore volume VA20 of pores having a pore diameter of 20 nm or less is 0.45-0.80 mL / g.　(B) The pore volume VA1.5 of pores having a pore diameter of 1.5 nm or less is 0.005-0.045 mL / g.　(C) The pore volume VD5-6 of pores having a diameter of 5-6 nm is 0.004-0.035 mL / g.

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, if 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] The solid polymer electrolyte membrane is composed of an electrolyte material that has 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 by 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 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 do work in the external circuit.

[0008] By the way, from the viewpoint 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, comprising 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, and the pore volume of pores having 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 high surface area graphitized carbon, including a step of oxidizing a starting carbon material and a step of graphitizing the starting carbon material to produce high surface area graphitized carbon having a surface area at least 100 m ２ / 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 high surface area 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-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.

[0013] Patent Document 5 states that "the volume of the first pore having a diameter of 0.5 nm or more and 2.0 nm or less is 0.20 (cm³)." ３ The volume of the second pore, which has a diameter greater than 2.0 nm and less than or equal to 4.0 nm, is 0.20 (cm³) or greater. ３ A carbon support having a weight of 1 / g or more is disclosed.

[0014] Patent Document 6 states that "the cumulative pore volume of a diameter of 2 nm or less is 0.09 cc / g or less, and the BET specific surface area is 900 m²." ２ A carbonaceous material exceeding 1 / g has been disclosed.

[0015] Japanese Patent Publication No. 2013-109856, Japanese Patent Publication No. 5650542, Japanese Patent Publication No. 6563945, Japanese Patent Publication No. 7416938, Japanese Patent Publication No. 7130311, Japanese Patent Publication No. 6956851

[0016] Incidentally, when porous carbon black is used as the carbon material for the catalyst support in polymer electrolyte fuel cells, a large amount of catalyst metal can be supported inside the porous carbon black, which can improve low-load characteristics (power generation performance on the low-current side). On the other hand, when porous carbon black with increased carbon thickness due to activation is applied as a catalyst support in order to further improve power generation performance, there is a problem that the low-load characteristics of the fuel cell deteriorate, especially during low-humidity operation. However, conventional technology, including all of the above-mentioned literature, is still insufficient in improving the low-load characteristics of fuel cells during both high-humidity and low-humidity operation, and further improvement is needed.

[0017] For example, Patent Document 1 provides an example of a catalyst support obtained by heat-treating commercially available porous carbon black. However, porous carbon black obtained by heat treatment as the final step may have blockages in the openings that allow movement between the inside and outside of the carbon black particles, making it difficult to utilize the pores inside the carbon black as a support site for the metal catalyst and thus making it difficult to obtain sufficient power generation performance.

[0018] 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, while the reaction in the fluidized bed improves uniform contact between the oxidizing agent and carbon black and increases the surface area of ​​the carbon black, allowing for the support of more metal catalysts, the porosity of the carbon black interior may not be sufficient, leaving room for improvement in the low-load characteristics during low-humidity operation of the fuel cell.

[0019] In Patent Document 3, an activation treatment is performed on carbon black after heat treatment. Because the activation is performed on the heat-treated, highly crystalline carbon walls, the activation within the carbon black may not progress easily, and porosity may not be sufficiently achieved. As a result, the support of the catalyst metal within the carbon black may not be sufficient, and there is room for improvement in the low-load characteristics during low-humidity operation of the fuel cell.

[0020] Patent Document 4 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 porous carbon 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 an electrolyte material (ionomer) that has proton conductivity, and generally, the proton conduction resistance of the electrolyte material (ionomer) tends to decrease as the humidity within the catalyst layer increases. Furthermore, proton transport may occur on the carbon black surface that is not coated with the electrolyte material (ionomer) due to condensed water, so it is thought that the formation of proton transport pathways is promoted at higher humidity levels. Therefore, if there is not enough micropore volume, the humidity necessary for proton transport will not be maintained, and there are concerns that the low-load characteristics of the fuel cell during low-humidity operation will deteriorate.

[0021] In Patent Document 5, the first pore of the carbon support is described as a site for nucleation of the metal catalyst and growth of catalyst particles. On the other hand, pores with a diameter of 0.5 nm or more and 2.0 nm or less also have the function of adsorbing water, so the 0.20 cm described in Patent Document 5 ３ If the volume exceeds 1g, the catalyst layer may become excessively hydrophilic, preventing water from being discharged from the catalyst layer and potentially reducing the diffusion of oxygen gas within the catalyst layer (decreasing catalytic activity). Therefore, there are concerns about a decrease in the low-load characteristics of the fuel cell during high-humidity operation.

[0022] The material proposed in Patent Document 6 exhibits high performance in both high-humidity and low-humidity operation. However, there are concerns that the manufacturing cost will be high because the carbon production method is a special method that goes through silver acetylide.

[0023] Therefore, the object of this disclosure is to provide a carbon material for catalyst support in a polymer electrolyte fuel cell that exhibits excellent low-load characteristics in both high-humidity and low-humidity operation of the fuel cell, a catalyst layer for a polymer electrolyte fuel cell utilizing the same, and a fuel cell.

[0024] 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) Pore volume V of pores with a pore diameter of 20 nm or less, determined by analysis using the DH (Dollimore-Heal) method for nitrogen adsorption isotherms. Ａ２０ (B) The pore volume V of pores with a diameter of 1.5 nm or less, determined by analysis using the DH (Dollimore-Heal) method for nitrogen adsorption isotherms. Ａ１．５ (C) The pore volume V of a pore diameter of 5-6 nm is determined by analysis using the DH (Dollimore-Heal) method for nitrogen desorption isotherms. Ｄ５～６ <1> The carbon material for catalyst support of a polymer electrolyte fuel cell described in <1> is 0.004 mL / g or more and 0.035 mL / g or less. <2> A carbon material for catalyst support of a polymer electrolyte fuel cell described in <1> that further satisfies the following requirement (D): (D) In ​​the XRD spectrum obtained by XRD (X-ray diffraction) measurement, the Lc(002) obtained by analyzing the peak between the diffraction angle 2θ = 20° to 26.5° is 1.6 nm or more and 4.0 nm or less. <3> A catalyst layer for a polymer electrolyte fuel cell containing the carbon material for catalyst support of a polymer electrolyte fuel cell described in <1> or <2>. <4> A fuel cell containing the catalyst layer for a polymer electrolyte fuel cell described in <3>. <5> The fuel cell described in <4>, wherein the catalyst layer for a polymer electrolyte fuel cell is the catalyst layer on the cathode side.

[0025] This disclosure provides a carbon material for catalyst support in a polymer electrolyte fuel cell that exhibits excellent low-load characteristics in both high-humidity and low-humidity operation of the fuel cell, a catalyst layer for a polymer electrolyte fuel cell utilizing the same, and a fuel cell.

[0026] Figure 1 is a schematic diagram showing an example of the general configuration of the fuel cell of this disclosure.

[0027] 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".

[0028] <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 activated carbon black that satisfies requirements (A), (B), and (C) described later. Here, porous activated carbon black is carbon black that has been made porous by activation. Porous activated carbon black is also referred to as "porous carbon black".

[0029] The carbon material for catalyst support disclosed herein is a carbon material that exhibits excellent low-load characteristics in both high-humidity and low-humidity operation of fuel cells. The carbon material disclosed herein was discovered through the following findings.

[0030] In recent years, due to the growing interest in carbon neutrality, CO ２ The demand for fuel cell technology is increasing in the field of large commercial mobility vehicles (hereinafter also referred to as "HDVs"), which have high emissions. HDVs require higher durability than passenger cars, so catalyst supports need to be even more durable during power generation, while at the same time, since HDVs are mainly used in commercial vehicles, the materials also need to be inexpensive.

[0031] When using dendritic carbon materials obtained by the autodecomposition reaction of silver acetylide, or porous carbon materials with internal mesopores such as Knobel, as carbon materials for catalyst supports, the catalyst supported in the internal mesopores is protected from poisoning by the electrolyte material (ionomer), thus improving its activity and enhancing its low-load characteristics. However, since these porous carbon materials are expensive, using porous activated carbon black, which is made porous by activating carbon black, an inexpensive raw material, is effective in reducing costs. Therefore, further improvements are needed in the power generation characteristics of porous activated carbon black (especially its low-load characteristics during both high-humidity and low-humidity operation of fuel cells).

[0032] Therefore, the inventors investigated how to improve the low-load characteristics of carbon black by making it porous, both during high-humidity and low-humidity operation of fuel cells, and obtained the following findings, although these are estimates.

[0033] In porous activated carbon black used as a catalyst support, pores with a diameter of 20 nm or less function as spaces for supporting the catalyst metal. Pore volume V of pores with a diameter of 20 nm or less Ａ２０ As this increases, more of the catalyst metal can be supported inside the porous activated carbon black. In addition, the pore volume V corresponds to the volume of pores that have openings through which matter can move between the inside and outside of the porous activated carbon black. Ｄ５～６ Increasing this factor facilitates the discharge of reaction-generated water from the inside to the outside of the porous activated carbon black, thereby suppressing inhibition of oxygen gas diffusion. As a result, low-load characteristics can be improved in both high-humidity and low-humidity operation.

[0034] On the other hand, in the catalyst layer of a fuel cell, protons generated at the anode are carried by proton conduction through the electrolyte material (ionomer) in the cathode catalyst layer. However, during low-humidity operation of the fuel cell, that is, when the catalyst layer becomes a low-humidity environment, the proton conduction resistance of the electrolyte material (ionomer) increases, reducing the low-load characteristics. In contrast, if porous activated carbon black contains minute pores including micropores (pores of 2 nm or less), these minute pores can adsorb moisture, thus exhibiting a function of moisturizing the catalyst layer of the fuel cell. Therefore, V corresponds to the volume of the minute pores containing micropores (pores of 2 nm or less). Ａ１．５ Increasing this factor helps maintain the humidity of the catalyst layer even in low-humidity environments, suppressing the increase in the proton conduction resistance of the electrolyte material (ionomer), thereby preventing a decrease in the low-load characteristics of the fuel cell during low-humidity operation.

[0035] Based on the above findings, it has been found that the carbon material for catalyst support of this disclosure is a carbon material that exhibits excellent low-load characteristics in both high-humidity and low-humidity operation of fuel cells.

[0036] Requirements (A), (B), and (C) are described below. Furthermore, from the viewpoint of improving durability as well as low-load characteristics during both high-humidity and low-humidity operation of the fuel cell, it is preferable that the carbon material for catalyst support of this disclosure satisfies requirement (D) in addition to requirements (A), (B), and (C).

[0037] (Requirement (A)) (A) For nitrogen adsorption isotherms, the pore volume V of pores with a diameter of 20 nm or less, determined by analysis using the DH (Dollimore-Heal) method. Ａ２０ The concentration is between 0.45 mL / g and 0.80 mL / g.

[0038] The pore volume V increases due to the activation of the raw material carbon black. Ａ２０ It is thought that the majority of it exists inside the porous activated carbon black. And the pore volume V inside the porous activated carbon black Ａ２０ This functions as a space for supporting the catalyst metal. Pore volume V Ａ２０When the porosity (V) becomes large, such as 0.45 mL / g or more, it is thought that a larger proportion of the catalyst metal is supported on the internal surface of the porous activated carbon black rather than the external surface. Therefore, the low-load characteristics of the fuel cell are improved in both high-humidity and low-humidity operation. Ａ２０ If the concentration is less than 0.45 mL / g, the proportion of catalyst metal supported on the outer surface of the porous activated carbon black increases, and there is a concern that the catalyst metal supported on this outer surface will be poisoned by the electrolyte material (ionomer) acting as a proton-conducting resin, leading to a decrease in the activity of the catalyst metal. Therefore, the low-load characteristics of the fuel cell are likely to deteriorate in both high-humidity and low-humidity operation. Ａ２０ If the concentration exceeds 0.80 mL / g, the void space inside the porous activated carbon black becomes excessively large. As a result, V, which will be discussed later, Ｄ５～６ The size tends to become too large, making it easier for the electrolyte material (ionomer) to penetrate excessively into the porous activated carbon black. As a result, the low-load characteristics tend to deteriorate in both high-humidity and low-humidity operation.

[0039] Therefore, the pore volume V of porous activated carbon black Ａ２０ The above range applies. Pore volume V of porous activated carbon black. Ａ２０ The amount is preferably 0.50 mL / g or more and 0.70 mL / g or less, and more preferably 0.55 mL / g or more and 0.65 mL / g or less.

[0040] Note that the pore volume V Ａ２０ This is a value measured by the method described in the examples below.

[0041] (Requirement (B)) (B) For nitrogen adsorption isotherms, the pore volume V of pores with a diameter of 1.5 nm or less, determined by analysis using the DH (Dollimore-Heal) method. Ａ１．５ The concentration is between 0.005 mL / g and 0.045 mL / g.

[0042] In the DH method, in the region of nitrogen adsorption isotherms where the relative pressure p / p0 with respect to saturated vapor pressure is 0.1 or less (corresponding to a pore diameter of approximately 2 nm or less), a large error occurs in the calculation of pore diameter, making it impossible to discuss with accurate pore diameters. However, the pore volume analyzed in such a low relative pressure region is considered to correspond to the pore volume of minute pores, including micropores. Using Quadra Win (manufactured by Anton Paar), nitrogen adsorption isotherms were analyzed using the DH method, and values ​​for pore volumes of 1.5 nm or less were derived as V. Ａ１．５ This is defined as: V Ａ１．５ However, when the pore volume (V) becomes large enough to reach 0.005 mL / g or more, the porous activated carbon black adsorbs sufficient moisture through its micropores, including micro-pores, even in low-humidity environments. Therefore, even in low-humidity environments, it achieves sufficient water adsorption to keep the catalyst layer moist. Consequently, the low-load characteristics during low-humidity operation are less likely to deteriorate. Pore volume V of porous activated carbon black Ａ１．５ If the pore volume V of porous activated carbon black is less than 0.005 mL / g, the amount of water adsorbed by porous activated carbon black decreases in low-humidity environments, and the low-load characteristics during low-humidity operation deteriorate. Ａ１．５ If the concentration exceeds 0.045 mL / g, the porous activated carbon black tends to adsorb excessive moisture. This can lead to inhibition of oxygen gas diffusion due to condensed water within the porous activated carbon black, making it easier for oxygen gas in the fuel cell reaction to fail to reach the catalyst metal surface. Consequently, the low-load characteristics tend to deteriorate in both high-humidity and low-humidity operation.

[0043] Therefore, the pore volume V of porous activated carbon black Ａ１．５ The above range applies. Pore volume V of porous activated carbon black. Ａ１．５ The concentration is preferably 0.010 mL / g or more and 0.035 mL / g or less, and more preferably 0.015 mL / g or more and 0.030 mL / g or less.

[0044] Note that the pore volume V Ａ１．５ This is a value measured by the method described in the examples below.

[0045] (Requirement (C)) (C) Pore volume V of pores with a diameter of 5-6 nm, obtained by analysis using the DH (Dollimore-Heal) method for nitrogen desorption isotherms. Ｄ５～６ The concentration is between 0.004 mL / g and 0.035 mL / g.

[0046] Pore ​​volume V can be determined from nitrogen desorption isotherms by analysis using the DH method. Ｄ５～６ This is thought to include the volume of pores, which have openings through which matter can move between the inside and outside of the porous activated carbon black. Pore volume V Ｄ５～６ When the pore volume V of porous activated carbon black increases to 0.004 mL / g or higher, reaction-generated water is more easily discharged from the inside to the outside of the porous activated carbon black, thereby suppressing inhibition of oxygen gas diffusion. Therefore, the low-load characteristics are improved in both high-humidity and low-humidity operation. Ｄ５～６ If the pore volume V is less than 0.004 mL / g, the volume of pores that allow substances to move between the inside and outside of the porous activated carbon black decreases, making it difficult to discharge reaction-generated water and increasing the likelihood of inhibited oxygen gas diffusion. Therefore, the low-load characteristics tend to deteriorate in both high-humidity and low-humidity operation. Ｄ５～６ If the value exceeds 0.035 mL / g, the volume of pores, which have openings through which substances can move between the inside and outside of the porous activated carbon black, becomes excessively large, making it easier for ionomers to penetrate excessively into the porous activated carbon black. As a result, the low-load characteristics tend to deteriorate in both high-humidity and low-humidity operation.

[0047] Therefore, the pore volume V of porous activated carbon black Ｄ５～６ The above range applies. Pore volume V of porous activated carbon black. Ｄ５～６ The concentration is preferably 0.005 mL / g or more and 0.025 mL / g or less, and more preferably 0.006 mL / g or more and 0.015 mL / g or less.

[0048] Note that the pore volume V Ｄ５～６ This is a value measured by the method described in the examples below.

[0049] (Requirement (D)) (D) In ​​the XRD spectrum obtained by XRD (X-ray diffraction) measurement, the Lc(002) obtained by analyzing the peak between diffraction angles 2θ = 20° and 26.5° is 1.6 nm or more and 4.0 nm or less.

[0050] When the Lc(002) of porous activated carbon black is 1.6 nm or more, the strength of the outer shell of the porous activated carbon black primary particles increases, which suppresses collapse of the catalyst layer during fuel cell operation, thus improving durability. When the Lc(002) of porous activated carbon black is 4.0 nm or less, the pore volume V of the porous activated carbon black Ａ２０ This makes it easier to control the Lc(002) of the porous activated carbon black within a desirable range, and improves low-load characteristics. Therefore, it is preferable that the Lc(002) of the porous activated carbon black be between 1.6 nm and 4.0 nm, as this makes it possible to achieve both durability and low-load characteristics. Preferably, the Lc(002) of the porous activated carbon black is between 1.8 nm and 2.5 nm.

[0051] Lc(002) is a value measured by the method described in the embodiments below.

[0052] <Method for manufacturing carbon material for catalyst support in polymer electrolyte fuel cell> An example of the method for manufacturing carbon material for catalyst support in polymer electrolyte fuel cell (hereinafter also referred to as the "method for manufacturing carbon material") described herein will be explained below.

[0053] The method for producing the carbon material of this disclosure is, for example, a method of treating raw material carbon black in the order of "nitric acid treatment step," "first activation step," "heat treatment step," and "second activation step." The method for producing the carbon material of this disclosure yields a carbon material (i.e., porous activated carbon black) that satisfies requirements (A) to (C) (preferably requirements (A) to (D)).

[0054] The method for producing the carbon material described herein was discovered through the following findings. The inventors investigated activation methods that increase both the pore volume and the volume of micropores, including micropores, within the raw material carbon black, and obtained the following findings.

[0055] To uniformly increase the porous structure of the raw material carbon black, it is important to bring more carbon crystal edge surfaces into contact with the oxidizing agent during activation. In activation, oxygen and CO2 are used. ２ By bringing an oxidizing agent, such as water vapor, into contact with the raw material carbon black at high temperatures, carbon is oxidized and removed. ２ Taking CO as an example, ２ The activation reaction proceeds at temperatures above 800°C. However, the reaction usually proceeds at the carbon crystal edge planes, with little to no reaction occurring at the basal planes.

[0056] Raw material carbon black is composed of stacked crystallites forming particulate matter. It is known that the interior of the raw material carbon black has more low crystallinity (i.e., smaller crystallite size), while the outer surface has higher crystallinity (larger crystallite size). Therefore, in the activation reaction of raw material carbon black with an oxidizing gas, the highly crystalline outer surface is difficult to remove, and the thinning due to activation proceeds mainly in the interior of the raw material carbon black. At this time, the oxidizing gas penetrates into the interior of the raw material carbon black by utilizing the gaps that exist between the crystallites on the outer surface. However, it is presumed that these gaps are not uniformly present across the entire outer surface of the raw material carbon black, but are limited to a part of the surface. As a result, under conventional activation conditions, thinning tends to proceed locally from the gaps present in a part of the surface of the raw material carbon black, and there was a tendency for large pores to be created as the activation progressed.

[0057] Therefore, before activating the raw material carbon black with an oxidizing gas, a step is added in which the raw material carbon black is treated at high temperature with high-concentration nitric acid. By performing high-concentration nitric acid treatment, some of the crystals on the outer surface of the raw material carbon black are decomposed, and a new oxidizing gas flow path can be formed from the outer surface to the interior of the raw material carbon black. If the activation reaction is performed after high-concentration nitric acid treatment, the activation reaction can proceed more uniformly, and it is thought that the formation of large pores caused by localized activation reactions that occurred under conventional activation conditions can be suppressed.

[0058] Therefore, by activating raw carbon black treated with high-concentration nitric acid, porous activated carbon black that satisfies requirements (A) to (C) can be obtained. In particular, pore volume V Ａ１．５ A porous activated carbon black with a remarkably high volume of micropores (including micropores) is obtained (i.e., a porous activated carbon black that satisfies requirement (B)).

[0059] Based on the above findings, a method for manufacturing the carbon material described herein was discovered.

[0060] The details of the method for manufacturing the carbon material described herein are described below.

[0061] (Raw material carbon black) Examples of raw material carbon black include furnace black, which is produced by continuously thermally decomposing gaseous or liquid raw materials in a reaction furnace; channel black, which is produced by burning raw material gas and rapidly cooling it by applying the flame to the bottom surface of channel steel to precipitate it; thermal black, which is produced by periodically repeating combustion and thermal decomposition using gas as a raw material; and acetylene black, which is produced using acetylene gas as a raw material. From the viewpoint of ease of generating internal pores in the particles through activation and a primary particle size suitable as a catalyst support for solid polymer fuel cells, furnace black is preferred as the raw material carbon black. These carbon blacks can be used alone or in combination of two or more, but from the viewpoint of uniformly proceeding with activation, it is preferable to use them alone.

[0062] (Nitric Acid Treatment Process) In the nitric acid treatment process, the raw material carbon black is treated with nitric acid. Specifically, in the nitric acid treatment process, for example, by heating the raw material carbon black in a highly concentrated aqueous nitric acid solution, some of the crystallites on the outer surface of the raw material carbon black decompose, and new oxidizing gas flow pathways are formed from the outer surface to the interior of the raw material carbon black.

[0063] The nitric acid concentration in the aqueous nitric acid solution is preferably 60% by mass or more and 68% by mass or less. By setting the nitric acid concentration to 60% by mass or more, the decomposition reaction of the carbon black outer surface crystallites can be efficiently promoted. As a result, the pore volume V can be increased by the first and second activation steps performed later. Ａ１．５ and pore volume VＤ５～６ The volume can be increased. By keeping the nitric acid concentration below 68% by mass, the localized decomposition of the raw material carbon black due to the rapid oxidation reaction can be suppressed. As a result, the pore volume V can be increased by the first and second activation steps performed later. Ａ１．５ and pore volume V Ｄ５～６ This prevents an excessive increase in volume.

[0064] The temperature for the nitric acid treatment process is preferably between 90°C and 120°C. A temperature of 90°C or higher allows for efficient decomposition of the carbon black outer surface crystallites. While there is no specific upper temperature limit, it is preferable to keep the temperature below 120°C, as exceeding the boiling point will hinder the oxidation reaction.

[0065] In the nitric acid treatment process, it is sufficient for a portion of the surface crystals of the raw material carbon black to decompose, so the mass ratio of raw material carbon black to nitric acid in the nitric acid aqueous solution (raw material carbon black / nitric acid in nitric acid aqueous solution) should be 1 / 50 or more. Furthermore, there is no particular upper limit on the amount of nitric acid charged, but if an excess of nitric acid is added, unused nitric acid will remain. Therefore, from an economic standpoint, it is preferable that the amount of nitric acid charged be 1 / 20 or less in terms of the mass ratio of raw material carbon black to nitric acid in the nitric acid aqueous solution (raw material carbon black / nitric acid in nitric acid aqueous solution).

[0066] (First Activation Process) In the first activation process, the raw carbon black that has been treated with nitric acid is activated. In the first activation process, the activation temperature (maximum temperature) depends on the type of activation gas used, but for example, in the case of carbon dioxide, it is preferable to adjust it to be between 800°C and 1100°C, and to have a mass loss due to activation of 50% by mass and 80% by mass (assuming the mass of the carbon black used in the first activation is 100% by mass).

[0067] (Heat Treatment Process) In the heat treatment process performed after the first activation process, the crystallites constituting the raw material carbon black that has undergone the first activation process are grown by performing heat treatment in an inert atmosphere, thereby providing the durability required for fuel cells. Durability can be ensured by maintaining a large Lc(002) of the porous carbon black through the heat treatment process.

[0068] In the heat treatment process, the raw material carbon black that has undergone the first activation process is heat-treated in a vacuum or in an inert gas (nitrogen, argon, etc.) atmosphere at a temperature of 1300°C to 1900°C (preferably 1500 to 1700°C). Heat treatment at 1300°C or higher develops highly aromatic carbon crystals that form the framework of the porous carbon black, and the pore walls become sufficiently thick, resulting in porous carbon black with a large Lc(002). Heat treatment at 1900°C or lower leads to excessive crystallization of carbon, resulting in a pore volume V Ａ１．５ The decline is suppressed.

[0069] (Second Activation Process) In the second activation process, the pores of the heat-treated carbon black intermediate that were blocked by the heat treatment process are re-opened. This restores the pore volume V which was reduced by the heat treatment process. Ａ２０ and pore volume V Ａ１．５ This increases the volume. If the second activation step is not performed, the pore volume V will not be sufficient. Ａ２０ and pore volume V Ａ１．５ It is difficult to obtain the required volume.

[0070] In the second activation step, the activation temperature (maximum temperature) depends on the type of activation gas used, but for example, in the case of carbon dioxide, it is preferable to adjust it to be between 800°C and 1100°C, and to have a mass loss due to activation of 2% by mass and 30% by mass (assuming the mass of carbon black charged in the second activation step is 100% by mass).

[0071] (Activation methods for the first and second activation steps) The type of activation gas used in the first and second activation steps is not particularly limited as long as it contains a gas that can oxidize and consume the carbon constituting the raw material carbon black through a reaction. Examples of gases that can oxidize and consume the carbon constituting the raw material carbon black through a reaction include air, oxygen, ozone, water vapor, carbon dioxide, nitrogen dioxide, nitric oxide, and dinitrogen monoxide. These gases may be mixed to form the activation gas. Alternatively, the gas may be diluted with an inert gas such as nitrogen, argon, or helium. Furthermore, exhaust gas or industrial gas containing these gases may also be used. Preferably, the activation gas is water vapor, carbon dioxide, or a gas containing these. The types of gas used in the first and second activation steps may be changed.

[0072] Various types of activation devices can be applied to the first and second activation processes, including rotary kilns, fluidized bed furnaces, fixed bed furnaces, and moving bed furnaces. Both continuous furnaces, which continuously feed raw materials and remove products, and batch furnaces, which intermittently feed raw materials and remove products, can be used. Rotary kilns and fixed bed furnaces are preferred as activation devices because they allow for easy switching of the gas introduction direction. Furthermore, from the viewpoint of uniformity of activation, batch furnaces are preferred because continuous furnaces, which continuously feed raw materials, result in an uneven distribution of activation.

[0073] Then, by going through the nitric acid treatment step, the first activation step, the heat treatment step, and the second activation step, porous carbon black that satisfies requirements (A) to (C) (preferably requirements (A) to (D)) is obtained.

[0074] <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.

[0075] 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.

[0076] 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.

[0077] 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)

[0078] 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. After performing work (generating electricity) in the external circuit, the electrons are introduced into the separator 120. Subsequently, the electrons reach the catalyst layer 160 through the separator 120 and the gas diffusion layer 140.

[0079] The configuration of the catalyst layer 150, which serves as the anode, is not particularly limited. The configuration of the catalyst layer 150 may be the same as that of a conventional anode, the same as that of the catalyst layer 160, or it may be a configuration that is even more hydrophilic than that of the catalyst layer 160.

[0080] The catalyst layer 160 is the so-called cathode. Within the catalyst layer 160, a reduction reaction of the oxidizing gas occurs, producing water. For example, when the oxidizing gas is oxygen or air, the following reduction reaction occurs. The water generated by the reduction reaction, along with the unreacted oxidizing gas, is discharged to the outside of the polymer electrolyte fuel cell 100. ２ +4H ＋ +4e － →2H ２ O (E ０ (= 1.23V)

[0081] Thus, the polymer electrolyte fuel cell 100 generates electricity by utilizing the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, the electrons produced in the oxidation reaction perform work in the external circuit.

[0082] The catalyst layer 160 contains the carbon material for catalyst support of this disclosure. Specifically, the catalyst layer 160 contains the carbon material for catalyst support of this disclosure, an electrolyte material (ionomer), and a catalyst component (platinum, etc.). This enhances the low-load characteristics within the catalyst layer 160. As a result, the low-load characteristics of the polymer electrolyte fuel cell 100 can be improved.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] <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.

[0088] This document describes experimental examples of carbon materials for catalyst supports according to this disclosure. First, the measurement methods for each parameter will be explained.

[0089] <Measurement Method for Each Parameter> Approximately 30 mg of carbon material for catalyst support was weighed and vacuum-dried at 200°C for 2 hours. Then, using an automated specific surface area analyzer (AUTOSORB iQ, manufactured by Anton Paar Japan), nitrogen adsorption and desorption isotherms were measured using nitrogen gas as the adsorbate. The obtained nitrogen adsorption isotherms were analyzed using the DH method with the software attached to the instrument to determine the pore volume V of pores with a diameter of 20 nm or less. Ａ２０ The following was determined. By similar analysis, the pore volume V of pores with a diameter of 1.5 nm or less was found. Ａ１．５The obtained nitrogen desorption isotherms were analyzed using the DH method with the software attached to the instrument to determine the pore volume V of pores with a diameter of 5 nm to 6 nm. Ｄ５～６ They sought it.

[0090] (Measurement of Lc(002)) Approximately 3 mg of the carbon material for the catalyst support was weighed out and placed on a silicon anti-reflector plate. This silicon anti-reflector plate was set in an X-ray diffractometer (RINT-TTRIIII manufactured by Rigaku Corporation). Next, the XRD spectrum was measured using this apparatus under the following conditions: room temperature, scanning step of 0.02°, angular sweep speed of 1° / min, and Cu-Kα as the radiation source. Background removal and smoothing were performed on the obtained XRD spectrum in the range of 2θ from 10° to 40°. For the XRD spectrum in the range of 2θ from 10° to 40°, Lc(002) was determined using Scherrer's equation (Lc = Kλ / βcosθ) for the waveform after background removal and smoothing.

[0091] <Examples and Comparative Examples: Preparation of Carbon Materials for Catalyst Supports> (Example 1) (1) Nitrate Treatment Process: 10 g of Niteron #10 manufactured by Nippon Steel Carbon as raw material carbon black, and 500 mL of a 67% by mass aqueous solution of nitric acid (product name "Nitric Acid (67%)", manufactured by Tokyo Chemical Industry Co., Ltd.) were placed in a 1 L round-bottom flask and heated in an oil bath at 95°C for 1 hour while stirring. After heating, the carbon black was filtered, washed with distilled water, and dried under reduced pressure at 90°C for 5 hours. (2) First Activation Process: 5 g of carbon black after the nitric acid treatment process was packed into a 1-inch diameter tubular reactor, and 400 N ml / min. of CO was added using a mass flow controller set upstream of the tubular reactor. ２ The gas was circulated. In this state, the tubular reactor was heated to 850°C at a rate of 20°C / min., held at 850°C for 40 hours, and then the circulating gas was changed to N ２The process was switched to cooling, and the first activated sample was collected. (3) Heat treatment process The entire amount of the collected first activated sample was filled into a heating crucible, and the heating process was carried out in a heating furnace under Ar flow at 15°C / min., and then at 1300°C for 1 hour, and the heat-treated sample was collected. (4) Second activation process The entire amount of the heat-treated sample was again filled into a tubular reactor with a diameter of 1 inch, and 400 N ml / min. of CO was added using a mass flow controller set upstream of the tubular reactor. ２ The gas was circulated. In this state, the tubular reactor was heated to 850°C at a rate of 20°C / min., held at 850°C for 5 hours, and then the circulating gas was changed to N ２ Switched to the cold air setting and lowered the temperature.

[0092] The second activated sample obtained through these operations was recovered as the carbon material for the catalyst support in Example 1.

[0093] (Example 2) Except that the raw material carbon black was Niteron #200 manufactured by Nippon Steel Carbon, the holding time at 850°C in the first activation step was set to 45 hours, and the holding temperature in the heat treatment step was set to 1400°C, a carbon material for catalyst support was obtained in the same manner as in Example 1.

[0094] (Example 3) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the holding time in the first activation step was 45 hours and the holding temperature in the heat treatment step was 1500°C.

[0095] (Example 4) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the holding time in the first activation step was 35 hours, the holding temperature in the heat treatment step was 1450°C, and the holding time in the second activation step was 2 hours.

[0096] (Example 5) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the holding temperature in the heat treatment process was set to 1500°C.

[0097] (Example 6) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the holding temperature in the heat treatment process was set to 1450°C.

[0098] (Example 7) As the raw material carbon black, Nippon Steel Carbon's Nitelon #SH was used. The maximum temperature of the first activation step was set to 900°C and the holding time to 15 hours. The holding temperature of the heat treatment step was set to 1600°C and the holding time of the second activation step to 8 hours. All other conditions were the same as in Example 1 to obtain a carbon material for catalyst support.

[0099] (Example 8) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the holding temperature in the heat treatment step was 1400°C.

[0100] (Example 9) A carbon material for the catalyst support was obtained in the same manner as in Example 8, except that the holding time in the first activation step was set to 46 hours.

[0101] (Example 10) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the time for the nitric acid treatment step was 2 hours, the time for the first activation step was 35 hours, and the time for the second activation step was 8 hours.

[0102] (Example 11) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the time for the nitric acid treatment step was 5 hours, the time for the first activation step was 30 hours, and the time for the second activation step was 8 hours.

[0103] (Example 12) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the holding temperature in the heat treatment process was set to 1600°C.

[0104] (Comparative Example 1) The nitric acid treatment step was omitted, and the holding time in the first activation step was set to 50 hours. Under all other conditions, the carbon material for the catalyst support was obtained in the same manner as in Example 3.

[0105] (Comparative Example 2) A carbon material for catalyst support was obtained in the same manner as in Example 2, except that a 70% aqueous nitric acid solution (product name "Nitric Acid 1.42", manufactured by Kanto Chemical Co., Ltd.) was used in the nitric acid treatment step and the holding time in the first activation step was set to 40 hours.

[0106] (Comparative Example 3) A carbon material for a catalyst support was obtained in the same manner as in Example 1, except that the nitric acid treatment step was omitted, the holding time in the first activation step was set to 39 hours, and the holding temperature in the heat treatment step was set to 1300°C.

[0107] (Comparative Example 4) A carbon material for a catalyst support was obtained in the same manner as in Example 1, except that the nitric acid treatment step was omitted, the holding time in the first activation step was set to 45 hours, and the heat treatment step and the second activation step were omitted.

[0108] (Comparative Example 5) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that the nitric acid treatment step was omitted, the holding temperature in the heat treatment step was set to 1400°C, and the holding time in the second activation step was set to 2 hours.

[0109] (Comparative Example 6) Ketjenblack EC300J from Lion Specialty Chemicals, Inc., without any additional processing, was used as the carbon material for the catalyst support in Comparative Example 6.

[0110] (Comparative Example 7) As a raw material, 5 g of Ketjenblack EC300J from Lion Specialty Chemicals Co., Ltd. was subjected to a heat treatment process in a heat treatment furnace at 1400°C for 1 hour under Ar flow to obtain the carbon material for catalyst support of Comparative Example 7.

[0111] (Comparative Example 8) Similar to Comparative Example 7, 5g of EC300J was heat-treated at 1400°C, the entire sample was packed into a tubular reactor with a diameter of 1 inch, and 400 N ml / min. of CO2 was added using a mass flow controller set up upstream of the tubular reactor. ２ The gas was circulated. In this state, the tubular reactor was heated to 850°C at a rate of 20°C / min., held at 850°C for 5 hours, and then the circulating gas was changed to N ２ The temperature was then lowered. The second activated sample obtained from these operations was recovered as the carbon material for the catalyst support in Comparative Example 8.

[0112] (Comparative Example 9) A carbon material for catalyst support was obtained in the same manner as in Example 1, except that a 10% by mass aqueous solution of nitric acid (product name "10% Nitric Acid", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the aqueous nitric acid solution in the nitric acid treatment step, and the time of the second activation step was set to 2 hours.

[0113] <Preparation of catalyst, preparation of catalyst layer, fabrication of MEA, assembly of fuel cell, and evaluation of battery performance (power generation performance, durability)> Next, using the porous carbon black prepared as described above, a catalyst for a polymer electrolyte fuel cell with a supporting catalyst metal was prepared as follows. A catalyst layer ink solution was then prepared using the obtained catalyst, and a catalyst layer was formed using this catalyst layer ink solution. A membrane electrode assembly (MEA) was then fabricated using the formed catalyst layer. This fabricated MEA was incorporated into a fuel cell cell, and a power generation test was performed using a fuel cell measurement device. The preparation of each component and the cell evaluation based on the power generation test will be described in detail below.

[0114] (1) Preparation of catalyst for polymer electrolyte fuel cell (platinum-supported carbon material) The carbon material for the catalyst support of each example was dispersed in distilled water, formaldehyde was added to this dispersion, and the mixture was placed in a water bath set to 40°C. After the temperature of the dispersion reached the same temperature as the bath (40°C), an aqueous solution of dinitrodiamine Pt complex nitric acid was slowly poured into the dispersion under stirring. After stirring was continued for about 2 hours, the mixture was filtered and the resulting solid was washed. The resulting solid was vacuum-dried at 90°C, then pulverized in a mortar, and then heat-treated at 200°C for 1 hour in an argon atmosphere containing 5% by volume of hydrogen to produce a platinum-supported carbon material. The amount of platinum supported in this platinum-supported carbon material was adjusted to 35% by mass relative to the total mass of the catalyst support carbon material and platinum particles, and this was confirmed by measurement using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0115] (2) Preparation of the catalyst layer Using the platinum-supported carbon material (Pt catalyst) prepared as described above, and using a 5% by mass Nafion solution (DuPont DE2020CS, registered trademark: Nafion) as the electrolyte resin, the Pt catalyst and Nafion were mixed under an Ar atmosphere in a ratio of 1.0 times the mass of the porous carbon black (the mass of porous carbon black only, excluding the Pt component of the Pt catalyst). After light stirring, the Pt catalyst was broken down with ultrasound, and ethanol was added to adjust the total solid content concentration of the Pt catalyst and electrolyte resin to 0.5% by mass, thereby preparing a catalyst layer ink solution in which the Pt catalyst and electrolyte resin were mixed.

[0116] Using the catalyst layer ink solution prepared in this manner, the mass of platinum per unit area of ​​the catalyst layer (hereinafter referred to as "platinum basis weight") is 0.2 mg / cm². ２ The spray conditions were adjusted accordingly, and the catalyst layer ink was sprayed onto a Teflon® sheet. After that, a drying treatment was performed in argon at 120°C for 60 minutes to produce the catalyst layer.

[0117] (3) Preparation of MEA Using the catalyst layers prepared as described above, a MEA (membrane electrode complex) was prepared by the following method. A square electrolyte membrane with sides of 6 cm was cut from a Nafion membrane (Dupont NR211). In addition, the anode and cathode catalyst layers coated on the Teflon® sheet were each cut into squares with sides of 2.5 cm using a utility knife. The electrolyte membrane was sandwiched between the anode and cathode catalyst layers cut in this way, so that each catalyst layer was in contact with the center of the electrolyte membrane and there was no displacement between them, and the temperature was set at 120°C and 100 kg / cm². ２ After pressing for 10 minutes and then cooling to room temperature, the Teflon® sheets were carefully peeled off from both the anode and cathode to prepare a catalyst layer-electrolyte membrane assembly in which the respective catalyst layers of the anode and cathode were fixed to the electrolyte membrane.

[0118] Next, as the gas diffusion layer, a pair of square carbon papers with a side length of 2.5 cm were cut out from carbon paper (39BC manufactured by SGL Carbon), and the catalyst layer-electrolyte membrane assembly was sandwiched between these carbon papers so that the anode and cathode catalyst layers were aligned and there was no deviation, and pressed at 120 °C and 50 kg / cm ２ for 10 minutes to produce a MEA. Regarding the areal amounts of the catalyst metal component, carbon material, and electrolyte material in each produced MEA, the mass of the catalyst layer fixed to the Nafion membrane (electrolyte membrane) was determined from the difference between the mass of the Teflon (registered trademark) sheet with the catalyst layer before pressing and the mass of the Teflon (registered trademark) sheet peeled off after pressing, and calculated from the mass ratio of the composition of the catalyst layer.

[0119] (4) Assembly of fuel cell and evaluation of initial power generation performance (high humidity condition) For each MEA produced using each porous carbon material according to each example and comparative example, it was incorporated into a cell and set in a fuel cell measurement device, and the initial power generation performance of the fuel cell was evaluated according to the following procedure. Air was supplied to the cathode side, and pure hydrogen was supplied to the anode side. The pressure was adjusted with back pressure valves provided downstream of the cell so that the utilization rates were 40% and 70% respectively, and the gauge pressure of the back pressure was 0.1 MPaG for each. The cell temperature was set to 80 °C, and the air and pure hydrogen supplied to the fuel cell were passed through distilled water kept at 80 °C in a humidifier (i.e., bubbling was performed) to humidify them. As a result, the relative humidity of the anode and cathode was set to about 100%. Under the condition of supplying the reaction gas to the cell with such settings, the operation of gradually increasing the current density until the voltage between the cell terminals reached 0.3 V was repeated 20 times. Then, the voltage between the cell terminals when the current density was fixed at 0.2 A / cm ２ and held for 15 minutes was recorded, and the low load performance evaluation was performed according to the following pass ranks A and B and fail rank C criteria. The results are shown in Table 2. [Pass rank] A: The voltage between the cell terminals at a current density of 0.2 A / cm ２ is 0.83 V or higher. B: The voltage between the cell terminals at a current density of 0.2 A / cm ２ is 0.81 V or higher. [Fail rank] C: Those that do not meet pass rank B.

[0120] (Low humidification condition) Next, the pressure was adjusted with a back pressure valve provided downstream of the cell so that the gauge pressure of the back pressure became 0.05 MPaG respectively. Also, the cell temperature was 80°C, and the air and pure hydrogen supplied to the fuel cell were each passed through distilled water kept warm in a humidifier (i.e., bubbling was performed), and the relative humidity of the anode and cathode was set to about 50%. Under the condition of supplying the reaction gas to the cell with such settings, the operation of gradually increasing the current density until the voltage between the cell terminals became 0.3 V was repeated 20 times. Then, when the current density was fixed at 0.2 A / cm ２ and held for 15 minutes, the voltage between the cell terminals was recorded, and the low-load performance evaluation was performed according to the following passing ranks A and B and failing rank C. The results are shown in Table 2. [Passing rank] A: The voltage between the cell terminals at a current density of 0.2 A / cm ２ is 0.80 V or more. B: The voltage between the cell terminals at a current density of 0.2 A / cm ２ is 0.78 V or more. [Failing rank] C: Those that do not meet the passing rank B.

[0121] (5) Evaluation of durability After the above initial power generation performance evaluation, a durability test was conducted under the following conditions. First, the cell temperature was 80°C, the relative humidity was 100%, the cell back pressure was set to 0.0 MPaG, and the cathode gas was switched to argon gas. Next, an operation of holding the cell voltage at 0.6 V for 4 seconds and then holding the cell voltage at 1.2 V for 4 seconds was defined as one cycle, and this repetitive operation of rectangular-wave voltage fluctuation was performed 1000 cycles. Then, the gas utilization rates of the anode and cathode were set to 40% and 70% respectively, the gauge pressure of the cell back pressure was 0.1 MPaG respectively, the cell temperature was 80°C, and the relative humidity was 100% respectively. When the current density was fixed at 0.2 A / cm ２ and held for 15 minutes, the voltage between the cell terminals was recorded, and the durability evaluation was performed with those meeting the following passing ranks being A and B and those not meeting being C. The results are shown in Table 2. [Passing rank] A: The voltage between the cell terminals at a current density of 0.2 A / cm ２ after 1000 cycles is 89% or more compared to that at the initial power generation performance evaluation. B: The voltage between the cell terminals at a current density of 0.2 A / cm２ The voltage between the cell terminals is 85% or higher compared to the initial power generation performance evaluation. [Failure Rank] C: Does not meet the passing rank B.

[0122]

[0123]

[0124] From the above results, it can be seen that the carbon material for catalyst support in this embodiment (i.e., porous activated carbon black) exhibits excellent low-load characteristics in both high-humidity and low-humidity operation of the fuel cell.

[0125] The symbols are explained as follows: 100 Solid polymer fuel cell 110, 120 Separator 130, 140 Gas diffusion layer 150, 160 Catalyst layer 170 Electrolyte membrane

[0126] Furthermore, the disclosure of Japanese Patent Application No. 2024-230855 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 as being 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) Pore volume V of pores with a diameter of 20 nm or less, determined by analysis using the DH (Dollimore-Heal) method for nitrogen adsorption isotherms. Ａ２０ (B) The pore volume V of pores with a diameter of 1.5 nm or less, determined by analysis using the DH (Dollimore-Heal) method for nitrogen adsorption isotherms. Ａ１．５ (C) The pore volume V of a pore diameter of 5-6 nm is determined by analysis using the DH (Dollimore-Heal) method for nitrogen desorption isotherms. Ｄ５～６ The concentration is between 0.004 mL / g and 0.035 mL / g.

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) In ​​the XRD spectrum obtained by XRD (X-ray diffraction) measurement, the Lc(002) obtained by analyzing the peak between diffraction angles 2θ = 20° to 26.5° is 1.6 nm or more and 4.0 nm or less.

3. A catalyst layer for a polymer electrolyte fuel cell, comprising a carbon material for catalyst support in a polymer electrolyte fuel cell according to claim 1 or claim 2.

4. A fuel cell comprising a catalyst layer for a polymer electrolyte fuel cell as described in claim 3.

5. The fuel cell according to claim 4, wherein the catalyst layer for the polymer electrolyte fuel cell is the catalyst layer on the cathode side.

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