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

Abstract

Provided are: a carbon material which is for a catalyst carrier of a polymer electrolyte fuel cell, and which is composed of a porous activated carbon black and satisfies the following requirements (A)-(C); a catalyst layer for a polymer electrolyte fuel cell using the carbon material; and a fuel cell.　(A) A BET specific surface area SBET is 410 m2 / (g) to 1.000 m2 / (g).　(B) A peak intensity ratio ID / IG of a D-band peak intensity ID to a G-band peak intensity IG is 1.2 to 2.2.　(C) A full width at half maximum ΔG of a G band peak is 72 cm-1 to 83 cm-1.

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] 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. In particular, attention has been paid to improving durability, and studies have been made to enhance crystallinity by heat treatment at 1500 °C or higher to improve oxidation resistance and consumption resistance, that is, to improve durability, and on the other hand, to maintain a developed pore structure to enhance power generation performance.

[0009] For example, Patent Document 1 discloses a porous carbon material for a catalyst carrier of a solid polymer fuel cell that satisfies the following requirements (A), (B), (C), and (D). (A) The specific surface area determined by BET analysis of the nitrogen adsorption isotherm is 450 to 700 m ２ / g, (B) In the nitrogen adsorption-desorption isotherm, the difference in adsorption amount V0.4-0.9 obtained by subtracting the adsorption amount at a relative pressure of 0.4 from the adsorption amount at a relative pressure of 0.9 is 150-450 mL / g, (C) When V0.1-0.4 is the difference in adsorption amount obtained by subtracting the adsorption amount at a relative pressure of 0.1 from the adsorption amount at a relative pressure of 0.4 in the nitrogen adsorption-desorption isotherm, the difference in adsorption amount ΔV0.1-0.4 obtained by subtracting V0.1-0.4 after heat treatment at 2200°C from V0.1-0.4 after heat treatment at 2400°C is 10-30 mL / g, (D) Raman spectroscopy measurement was 1500-1700 cm －１ The half-width of the G-band detected in the range is 35-45 cm. －１ It is disclosed that "it is."

[0010] Patent Document 2 states that "the catalyst support is 300 to 700 m ２ A fuel cell electrode is disclosed, characterized by being a highly crystalline carbon black having a BET specific surface area of ​​1 / g and a crystallite size Lc of 2.0 nm or more. Since commercially available carbon black manufactured by a general furnace method has a crystallite size Lc of less than 2.0 nm, this electrode is made highly crystalline by heat treatment to improve durability.

[0011] Patent Document 3 describes a carbon material for catalyst support in a polymer electrolyte fuel cell that has a three-dimensional dendritic structure and simultaneously satisfies the following conditions (A), (B), and (C): (A) In laser Raman spectroscopy measurements at a wavelength of 532 nm, the D-band intensity (1360 cm) measured at 50 measurement points with a beam diameter of 1 μm. －１ (Nearby) and G-band intensity (1580 cm) －１ The standard deviation Δ(R) of the relative intensity ratio (R value) with neighboring samples is 0.01 to 0.07. (B) BET specific surface area S ＢＥＴ 400-1520m ２ It must be / g. (C) Relative pressure ｐ／ｐ０ Nitrogen gas adsorption amount V between 0.4 and 0.8 Ｎ：０．４－０．８ The disclosure states that the amount is 100 to 300 cc (STP) / g, and also a method for producing such a carbon material for catalyst supports.

[0012] Patent Document 4 describes a catalyst support carbon material that is excellent in both durability and power generation performance under low humidity operating conditions, particularly against repeated load fluctuations such as starting and stopping, and a catalyst for a polymer electrolyte fuel cell prepared using the same, characterized in that it satisfies the following conditions (A), (B), (C), and (D): (A) Oxygen content contained in the catalyst support carbon material ＩＣＰ (B) Amount of oxygen remaining after heat treatment at 1200°C in an inert gas (or vacuum) atmosphere of 0.1 to 3.0 mass% １２００℃ (C) BET specific surface area of ​​0.1 to 1.5 mass% ２ / g(D) Raman spectroscopy spectrum at 1550–1650 cm⁻¹ －１ The half-width ΔG of the G-band detected within this range is 30-70 cm. －１ " has been disclosed.

[0013] Patent Document 5 states that, when used as a carrier for a catalyst for a polymer electrolyte fuel cell, it exhibits excellent power generation performance under high-humidity operating conditions for the polymer electrolyte fuel cell, and is a porous carbon material used as a carrier carbon material for a polymer electrolyte fuel cell, having a hydrogen content in the range of 0.004% by mass or more and 0.010% by mass or less, and a nitrogen adsorption BET specific surface area of ​​600 m². ２ / g or more 1500m ２ It is less than or equal to / g, and is in the D-band, which is 1200-1400 cm⁻¹, obtained from Raman spectroscopy. －１ Peak intensity in the range (I Ｄ ) and the G-band, which is 1500-1700 cm －１ Peak intensity in the range (I Ｇ ) Relative intensity ratio (I Ｄ / I Ｇ A carrier carbon material and a metal catalyst particle-supported carbon material for polymer electrolyte fuel cells are disclosed, characterized in that the ratio is 1.0 or more and 2.0 or less.

[0014] Japanese Patent Publication No. 7277770, Japanese Patent Publication No. 6478677, International Publication No. 2018-182048, International Publication No. 2016 / 133132, International Publication No. 2015-088025

[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 within the carbon black, so low-load characteristics (power generation characteristics at low current density) are required for power generation performance. On the other hand, for applications in long-distance trucks and buses, high durability of the catalyst is required. However, in conventional technology, including all of the above-mentioned literature, the porosity within the carbon black is not sufficient and the crystallinity is not sufficiently high, so further improvements in low-load characteristics and durability are required. In particular, as crystallinity increases, the water repellency of carbon increases, so the problem is less likely to become apparent in high-humidity operation, but improving the significant decrease in low-load characteristics during low-humidity operation is an urgent issue.

[0016] Patent Document 1 discloses a material obtained by heat-treating a porous template carbon made using MgO as a template or porous carbon made from silver acetylide in an inert atmosphere at 2200°C or higher. While the durability is greatly improved due to the improved crystallinity and the large pore volume, resulting in high power generation performance in high-humidity operation, there was room for improvement in power generation performance in low-humidity operation. Patent Document 2 uses highly crystallized carbon black with an Lc of 2.0 nm or more as a support. The increase in water repellency associated with the high crystallization treatment is addressed by introducing oxygen-containing acidic functional groups through oxidation treatment in 1.5N nitric acid at 100°C for 45 hours to make it hydrophilic. However, the decrease in low-load characteristics in low-humidity operation is significant compared to the low-load characteristics in high-humidity operation, indicating room for improvement in low-load characteristics.

[0017] Patent Document 3 describes using porous carbon produced from silver acetylide as a raw material for the porous carbon material, and describes the D-band intensity (1360 cm) in Raman measurement. －１ (Nearby) and G-band intensity (1580 cm) －１ Relative intensity ratio (R value) with neighboring areas, G-band intensity (1580 cm) －１By defining the range of the standard deviation and absolute value of the full width at half maximum (FMAX) ΔG (in the vicinity), the uniformity of porous carbon is enhanced, and high crystallinity is achieved through the R value and the absolute value of ΔG. However, porous carbon produced using silver acetylide as a raw material is a so-called non-graphitizable carbon material, and even with heat treatment at high temperatures exceeding 2000°C, there are limitations to improving its crystallinity. As a result, there is room for improvement in achieving the high durability that is the objective of this invention.

[0018] Patent Document 4 describes how porous carbon can be obtained by activating commercially available carbon black with CO2, and how a specific amount of oxygen-containing functional groups can be selectively added while maintaining a specific surface area and not decreasing even after treatment at 1200°C, and how a ΔG of 30 to 70 cm² can be measured by Raman measurement. －１ This approach aims to achieve both durability through high crystallinity and high hydrophilicity through highly durable oxygen-containing functional groups that are resistant to high temperatures, thereby improving power generation performance during low-humidity operation. However, there is room for improvement in low-load characteristics in operating environments with relative humidity below 40%.

[0019] Patent Document 5 describes how, for porous carbon materials prepared using silver acetylide as a raw material, the improvement of power generation characteristics, particularly under high-humidity operating conditions, is addressed by controlling the physical properties of BET specific surface area and hydrogen content, and how the durability of the porous carbon carrier against oxidative wear is improved, specifically in the 1200-1400 cm⁻¹ range, known as the D-band in Raman measurements. －１ The peak intensity (ID) in the range of 1500-1700 cm² and the G-band, which is called the G-band. －１ Relative intensity ratio of peak intensity (IG) within the range I Ｄ / I Ｇ This was guaranteed. However, there was room for improvement in the power generation characteristics during extremely low-humidity operation, such as when the relative humidity fell below 50%.

[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 durability as well as low load characteristics during low-humidity operation of the fuel cell, 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) BET specific surface area S obtained by analyzing nitrogen adsorption isotherms using the BET method. ＢＥＴ However, 410m ２ / g or more 1000m ２ (B) 1330 cm² obtained by Raman spectroscopy. －１ Nearby D-band peak intensity I Ｄ And, 1580cm －１ Nearby G-band peak intensity I Ｇ Peak intensity ratio I Ｄ / I Ｇ However, it is between 1.2 and 2.2. (C) 1580 cm obtained by Raman spectroscopy －１ The half-width (ΔG) of the nearby G-band peak is 72 cm. －１ 83cm or more －１ The following: <2> A carbon material for catalyst support of a polymer electrolyte fuel cell described in <1>, which further satisfies the following requirement (D). (D) The peak intensity ratio I Ｄ / I Ｇ The ratio of the half-width ΔG of the G-band peak (I Ｄ / I Ｇ ) / △G) is 0.016 or more and 0.026 or less. <3> A catalyst layer for a polymer electrolyte fuel cell containing a carbon material for the catalyst support of the polymer electrolyte fuel cell as described in <1> or <2>. <4> A fuel cell containing the catalyst layer for a polymer electrolyte fuel cell as described in <3>. <5> The fuel cell as described in <4>, 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 support in polymer electrolyte fuel cells that offers excellent durability and low-load characteristics during low-humidity operation of the fuel cell, 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 activated carbon black that satisfies requirements (A), (B), and (C) described later (preferably satisfies requirements (A), (B), (C), and (D) described later). Here, porous activated carbon black is carbon black that has been made porous by, for example, "activation" by contacting carbon black with an oxidizing gas.

[0026] The carbon material for catalyst support disclosed herein is a carbon material that exhibits excellent durability and low-load characteristics during low-humidity operation of fuel cells. The carbon material disclosed herein was discovered through the following findings: firstly, the specific physical properties of the desired porous activated carbon black structure were identified; and secondly, a specific method for manufacturing porous activated carbon black was discovered. The optimal porous activated carbon black structure and the method for manufacturing porous activated carbon black are described below.

[0027] (Optimal structure for porous activated carbon black) Generally, the power generation characteristics of fuel cells depend largely on the overpotential of the cathode reaction. In other words, if the overpotential can be reduced, the power generation characteristics will improve. The following three 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, depending on 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, (2) is resolved by ensuring voids in the catalyst layer that reduce the gas diffusion resistance. By using porous activated carbon black as the support, the aggregate structure formed by the aggregation of primary carbon black particles, i.e., the three-dimensional structure, uniformly forms voids in the catalyst layer corresponding to the primary particle size. Therefore, (2) is resolved by applying porous activated carbon black, which is obtained by activating carbon black having an aggregate structure. Furthermore, the aggregate structure of porous activated carbon black ensures the electronic conductivity of the catalyst support itself, and the large contact area between the porous activated carbon blacks reduces contact resistance. As a result of the high electronic conductivity of the catalyst support itself and the reduced contact resistance between the catalyst supports, the ohmic resistance of the catalyst layer in (1) is improved.

[0029] Reducing the resistance of the catalytic reaction in (3) is particularly important for improving low-load characteristics. Furthermore, to improve low-load characteristics during low-humidity operation, it is necessary to increase the number of catalytic metals contributing to the catalytic reaction, and at the same time, maintain a high humidity state in the ionomers within the pores of porous activated carbon black even during low-humidity operation. To increase the number of catalytic metals that can substantially participate in the catalytic reaction, the ratio of catalytic metals present in the pores to catalytic metals adsorbed on the catalyst support surface should be increased. In other words, the surface area within the pores of porous activated carbon black should be increased to adsorb catalytic metals into the pores. Specifically, the surface area within the pores of porous activated carbon black can be indicated by the surface area calculated by the BET method using nitrogen gas adsorption. The surface area of ​​so-called commercially available non-porous carbon black is 25 to 80 m², assuming a primary particle diameter of 30 to 70 nm. ２ The value is / g, and the specific surface area calculated by the BET method is 410 m². ２ If the concentration is greater than / g, most of the catalyst metal will be adsorbed into the pores of the catalyst support. Even during low-humidity operation, one way to maintain a high moisture level of ionomers in the pores of porous activated carbon black is to improve the structure of crystallites, which are the smallest units that make up carbon black. Crystallites are made up of stacked graphene sheets composed of polycyclic aromatic compounds, and reducing the size of the graphene sheets increases the edge area of ​​the crystallites. A larger edge area leads to an increase in the amount of ionomers that can penetrate, and as a result, even in low-humidity environments, it becomes possible to maintain a state where the ionomers in the pores are less likely to dry out due to the large amount of ionomers.

[0030] On the other hand, improvements in durability are intended to be achieved through two guidelines. The first guideline is to reduce the rate of oxidative wear by increasing the number of stacked crystallites, that is, the thickness in the direction of crystallite stacking. The second guideline is to increase the number of chemical bonds between crystallites by making the graphene sheet smaller during the heat treatment process in the manufacturing method described later. As a result, even as oxidative wear progresses, the crystallites remain strongly chemically bonded to each other, maintaining the morphology of the primary particles of carbon black and suppressing the collapse of pores due to oxidative wear. Consequently, the durability of the catalytic activity is improved.

[0031] In other words, to achieve both improved durability and low-load characteristics during low-humidity operation, porous activated carbon black with a crystallite structure that is not normally achievable, where the graphene sheets are small but the number of layers is large, is effective. The inventors have identified the optimal range of the following physical properties as quantitative physical property indicators for this porous activated carbon black, and have succeeded in manufacturing porous activated carbon black with a special crystallite structure through the special manufacturing process described later.

[0032] Thus, with porous activated carbon black, the inventors aimed to achieve both high durability and high low-load characteristics during low-humidity operation by improving the above physical properties. As a result, the inventors found that by simultaneously satisfying (a) to (c) below, it is possible to achieve both high low-load characteristics during low-humidity operation, and furthermore, in order to further improve the low-load characteristics during low-humidity operation, it is important to simultaneously satisfy (a) to (d) below. (a) Increase the surface area inside the pores (improve low-load characteristics). (b) Increase the thickness in the stacking direction of the crystallites (graphene sheet laminates) that make up porous activated carbon black. (c) Decrease the size of the graphene sheets in the crystallites (graphene sheet laminates) that make up porous activated carbon black. (d) Increase the ratio of the thickness of the crystallites to the size of the graphene sheets.

[0033] Specifically, the inventors, after diligent study, found the following to be the specific physical properties corresponding to the above guidelines: (a) The physical property suitable for (a) is the BET surface area obtained by nitrogen gas adsorption measurement (requirement (A)) (b) The physical property suitable for (b) is the intensity ratio of the G band and D band obtained by Raman spectroscopy I Ｄ / I Ｇ (Requirement (B)) (c) The physical property value suitable for (c) is the full width at half maximum (referred to as ΔG) of the G band obtained by Raman spectroscopy (Requirement (C)) (d) I Ｄ / I Ｇ I divided by triangle G Ｄ / I Ｇ / △G (requirement (D))

[0034] From the above, it was found that the carbon material for catalyst support of this disclosure is a carbon material that exhibits excellent durability as well as low load characteristics during low-humidity operation of fuel cells.

[0035] 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 requirement (D) in addition to requirements (A) to (C).

[0036] (Requirement (A): BET specific surface area S ＢＥＴ (A) BET specific surface area S obtained by analyzing nitrogen adsorption isotherms using the BET method ＢＥＴ However, 410m ２ / g or more 1000m ２ It is less than or equal to / g.

[0037] The BET specific surface area corresponds to the area of ​​the support surface for adsorption of catalyst metal particles. The more pores are developed, the larger the specific surface area. In the case of porous activated carbon black, crystallites are the smallest constituent units, and catalyst metal particles adsorb onto the surface of the crystallites. That is, the specific surface area changes in correlation with requirements (B) and (C). 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.

[0038] BET specific surface area S ＢＥＴ 410m ２ / g or more 1000m ２ / g or less, 500m ２ / g or more 900m ２ Preferably less than or equal to / g. BET specific surface area S ＢＥＴ 410m ２ At concentrations of 1 / g or higher, high-density support of the catalyst metal on porous activated carbon black is achieved, suppressing the decline in power generation performance, especially low-load characteristics. BET specific surface area S ＢＥＴ 1000m ２ If the value is less than / g, excessive pore development is suppressed, and in particular, the peak intensity ratio I, which is the crystallite stacking thickness of requirement (B), is reduced. Ｄ / I ＧIt becomes easy to satisfy the upper limit. Additionally, it becomes easy to satisfy the upper limit of the full width at half maximum ΔG of the G-band peak, which is an index of the size of the graphene sheets constituting the crystallites of requirement (C). As a result, it becomes easy to achieve both power generation performance (particularly low-load performance during low-humidity operation) and durability.

[0039] Note that the BET specific surface area S ＢＥＴ is a value measured by the method described in the examples below.

[0040] (Requirement (B): peak intensity ratio I Ｄ / I Ｇ (corresponding to the thickness of the crystallite)) (B) The peak intensity ratio I －１ of the D-band peak intensity I Ｄ around 1330 cm －１ and the G-band peak intensity I Ｇ around 1580 cm are Ｄ / I Ｇ 1.2 or more and 2.2 or less.

[0041] In the Raman spectrum obtained by Raman spectroscopic measurement of porous activated carbon black, there are a G-band (a band having the center of the peak around 1580 cm －１ ), which is a Raman-active vibration mode of the graphite structure, and a D-band (a band having the center of the peak around 1330 cm －１ ), which reflects the disorder from the graphite structure, specifically, the structure of the edge portion of the crystallite. Based on these two vibration modes (vibration bands) of the crystal lattice, seven vibration modes including their overtones (2D, 2G) and the combined mode (D + G) of the two modes are observed. It is the relative peak intensity, not the absolute value of the peak intensity of each band, that has physical meaning. As a result of intensive studies, as an index that accurately reflects the thickness in the stacking direction of the crystallites, particularly a size of about several nm, the peak intensity ratio I Ｄ / I Ｇ of the G-band and D-band in the Raman spectrum is optimal. Note that the peak intensity I Ｄ corresponds to the volume of the edge, and the peak intensity I [[ID=3,8]] Ｇ corresponds to the volume having the graphite structure, and the peak intensity ratio I Ｄ / I ＧIt is known that this has a strong correlation with the degree of crystal development, particularly with the stacking thickness in the stacking direction.

[0042] And, the peak intensity ratio I Ｄ / I Ｇ The optimal range is 1.2 to 2.2. Peak intensity ratio I Ｄ / I Ｇ However, if the peak intensity ratio is less than 1.2, the crystallite stacking thickness is small, resulting in insufficient resistance to oxidation and wear, and reduced durability. Ｄ / I Ｇ When the peak intensity ratio exceeds 2.2, the thickness of the crystallites becomes too large, making it difficult to form chemical bonds between crystallites. As a result, the morphology of the primary particles is not maintained due to oxidative wear, the pores collapse, and durability decreases. Ｄ / I Ｇ Preferably, the value is between 1.2 and 2.2, and more preferably between 1.5 and 1.9.

[0043] Note that D-band peak intensity I Ｄ and G-band peak intensity I Ｇ This is a value measured by the method described in the examples below. Note that the D-band peak intensity I of the Raman spectrum is Ｄ and G-band peak intensity I Ｇ This refers to the area of ​​each peak (the volume of the edge portion and graphite crystal portion), not the peak top value of each peak. Also, 1330 cm² －１ Nearby D-band peak intensity I Ｄ This refers to 1300-1360 cm －１ This is the D-band peak intensity, at 1580 cm⁻¹. －１ Nearby G-band peak intensity I Ｇ This refers to a height of 1560-1620 cm. －１ This is the G-band peak intensity.

[0044] (Requirement (C): Full width at half maximum of the G-band peak (size of the graphene sheet constituting the crystallite) △G) (C) 1580 cm obtained by Raman spectroscopy －１ The half-width (ΔG) of the nearby G-band peak is 72 cm. －１ 83cm or more －１The following is true: While the intensity of a peak in a Raman spectrum corresponds to the volume of the structure belonging to that band, the shape of the peak, particularly its linewidth (full width at half maximum, denoted as ΔG), is known to have a strong correlation with the crystallite size of the structure belonging to that band. The linewidth of the G band, which is the vibrational mode of a graphite structure or a single-layer graphene sheet, is presumed to be an indicator that reflects the size of the graphene sheet. That is, a larger linewidth ΔG (broader peak) corresponds to a smaller graphene sheet. Conversely, a smaller linewidth ΔG (sharper peak) corresponds to a larger graphene sheet.

[0045] Furthermore, the optimal range for the half-width △G of the G-band peak is 72 cm. －１ 83cm or more －１ The following is true: The half-width (ΔG) of the G-band peak is 72 cm. －１ Below this level, the graphene sheet becomes too large, reducing the edge area and degrading the low-load characteristics during low-humidity operation. The half-width ΔG of the G-band peak is 83 cm. －１ Beyond this point, the graphene sheet becomes too small, resulting in a significant decrease in durability. The half-width (ΔG) of the G-band peak is 75 cm. －１ 80cm or more －１ The following are preferable.

[0046] Here, the porous activated carbon black of this disclosure undergoes a series of special manufacturing processes described later, thereby achieving a crystallite structure that is not normally attainable, specifically, a peak intensity ratio of I Ｄ / I Ｇ The structure has a small width at half maximum (ΔG) of the G-band peak, meaning the thickness in the stacking direction of the graphene sheet is large. On the other hand, the porous activated carbon black of this disclosure achieves a special structure in which the half maximum width ΔG of the G-band peak is large, meaning the size of the graphene sheet is small, and the surface area is controlled to an optimal size for supporting the catalyst metal. As a result, durability and low-load characteristics during low-humidity operation can be improved at a high level.

[0047] The half-width ΔG of the G-band peak is a value measured by the method described in the examples below. Here, 1580 cm－１ The half-width (ΔG) of the nearby G-band peak is 1560–1620 cm. －１ This is the half-width (FWHM) of the G-band peak, △G.

[0048] (Requirement (D): Peak intensity I Ｄ / I Ｇ The ratio of the full width at half maximum (FWHM) of the G-band peak to ΔG (the ratio of the crystallite stacking thickness to the size of the graphene sheet) (I Ｄ / I Ｇ ) / △G) (D) Peak intensity ratio I Ｄ / I Ｇ The ratio of the half-width ΔG of the G-band peak ((I Ｄ / I Ｇ The ratio of () / △G) is between 0.016 and 0.026.

[0049] The porous activated carbon black of this disclosure has a BET surface area that falls within a certain range, while the size of the graphene sheet (ΔG) is small and the layer thickness of the graphene sheet (I Ｄ / I Ｇ ) has a crystallite structure with large ) In addition, the porous activated carbon black of this disclosure has the size of the graphene sheet (ΔG) and the stacking thickness of the graphene sheet (I Ｄ / I Ｇ The relative relationship between the two, that is, the ratio of the two (I Ｄ / I Ｇ By controlling ) / △G, further improvements in power generation performance and high durability become possible.

[0050] And the ratio (I Ｄ / I Ｇ The optimal range for ) / △G is preferably 0.016 to 0.026, and more preferably 0.018 to 0.022. Ｄ / I Ｇ When the ratio (I) / ΔG is 0.016 or greater, the relative thickness of the crystallite stacking increases, thus improving durability. Ｄ / I Ｇ When ) / ΔG is 0.026 or less, the relative size of the graphene sheet becomes smaller, which increases the amount of ionomer that penetrates the pores, improving the low-load characteristics during low-humidity operation.

[0051] <Method for manufacturing carbon material for catalyst support in polymer electrolyte fuel cell> Guidelines for manufacturing 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) in addition to requirement (D)), 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.

[0052] Therefore, as an example of a method for producing a carbon material for catalyst support in a polymer electrolyte fuel cell according to this disclosure, a method having four steps is provided: a pretreatment step, a first activation step, a heat treatment step, and a second activation step. Pretreatment step: The raw material carbon black is oxidized in a gas atmosphere of low-concentration oxygen obtained by diluting air with an inert gas. By using low-concentration oxygen, at a relatively low temperature, and slowing the flow rate of the oxidizing mixed gas, the treatment time is extended, forming fine pores with a diameter of 2 nm or less toward the interior of the carbon black, and forming developed pores while suppressing oxidation of the surface during this process. 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.

[0053] The following describes each step.

[0054] (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 particle size of the raw material carbon black is preferably 30 nm or more and 100 nm or less, and more preferably 40 nm or more and 80 nm or less. If the average primary 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 particle size of the raw material carbon black is preferably 100 nm or less. If the average primary particle size of the raw material carbon black is 30 nm or more, pore development becomes easier and durability is improved.

[0055] 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.

[0056] 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 15 arbitrary 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-Endter 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.

[0057] (Pretreatment process: Oxidation treatment with a mixed gas of oxygen and argon) In the pretreatment process, the raw material carbon black is oxidized under a flowing atmosphere of a mixed gas of oxygen and argon.

[0058] As a result of diligent research into methods to develop pores inside the raw material carbon black while suppressing surface oxidation, we have determined that by lowering the oxygen concentration in the mixed gas, controlling the flow rate and processing temperature, and extending the processing time to allow the oxidation reaction to proceed slowly, we can suppress the oxidation (combustion) of the carbon black surface while introducing a large number of micropores with a diameter of 2 nm or less that extend into the carbon black. By increasing the number of micropores, it becomes possible to uniformly reduce the size of the graphene sheets that make up the crystallites.

[0059] The oxygen concentration (volume %) in the mixed gas of oxygen and argon is, for example, 2% to 15%, more preferably 5% to 12%. If the oxygen concentration is less than 2% by volume, the time required for a weight loss rate of several percent or more due to oxidation is 300 hours or more, which is not practical from the standpoint of industrial production. On the other hand, if the oxygen concentration exceeds 15%, the oxidation rate of the surface is large, and the rate of increase in the volume of micropores relative to the weight loss becomes low.

[0060] The flow rate of the mixed gas of oxygen and argon is preferably 0.2 m / s to 1.5 m / s in linear velocity, and more preferably 0.3 m / s to 1.3 m / s. If the flow rate (linear velocity) is less than 0.2 m / s, the reaction rate is too low, and surface combustion becomes dominant over the formation of micropores of 2 nm or less, making it difficult to satisfy requirements (B) and (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation). Conversely, if it exceeds 1.5 m / s, the oxidizing power becomes too high, leading to increased surface oxidation and combustion, and the formation of mesopores larger than micropores, again making it difficult to satisfy requirements (B) and (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation).

[0061] The heat treatment temperature for the oxidation of carbon black is, for example, 280°C to 400°C, preferably 290°C to 380°C. If the heating temperature is below 280°C, the reaction rate is too low, and surface combustion becomes dominant over the formation of micropores smaller than 2 nm, making it difficult to satisfy requirements (B) and (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation). If the heating temperature exceeds 400°C, the oxidizing power becomes too high, leading to increased surface oxidation and combustion, and the formation of mesopores larger than micropores, again making it difficult to satisfy requirements (B) and (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation).

[0062] The heating time for oxidation treatment is, for example, 20 hours or more and 200 hours or less, preferably 50 hours or more and 150 hours or less. If the heating time is less than 20 hours, the reaction rate is too high, so surface combustion takes precedence over micropore formation, making it difficult to satisfy requirements (B) and (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation). If the heating time exceeds 200 hours, the reaction time is too long, again making it difficult to satisfy requirements (B) and (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation).

[0063] (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 through are formed inside the raw material carbon black 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.

[0064] 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.

[0065] 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 930°C. 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 750°C to 930°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).

[0066] The activation time in the first activation step, like temperature, is an important factor in controlling pore development and requirement (B). The activation time in the first activation step is preferably 10 hours or more and 100 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 and making it difficult to satisfy requirement (B), leading to a decrease in power generation performance (especially low-load characteristics). If the activation time in the first activation step exceeds 100 hours, the reaction rate is too slow, increasing the relative rate of surface oxidation to pore formation, making it difficult to satisfy requirement (B), leading to a decrease in power generation performance (especially low-load characteristics).

[0067] 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.

[0068] (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, 0.5 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).

[0069] 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.

[0070] (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.

[0071] 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.

[0072] 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 900°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. ２ When used as the activating gas, a temperature of 750°C to 900°C is preferred. If the second activation is performed at a temperature lower than the lower limit temperature of 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 of 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 of the second activation step exceeds 900°C, surface oxidation will be promoted, making it difficult to satisfy requirement (B) and resulting in a decrease in power generation performance (especially low-load characteristics).

[0073] The activation time for the second activation step is preferably 0.5 hours or more and 3 hours or less. If the activation time for the second activation step is less than 0.5 hours, the activation will be insufficient and it will be difficult to meet requirement (A), resulting in a decrease in power generation performance (especially low-load characteristics). If the activation time for the second activation step exceeds 3 hours, surface oxidation will be accelerated, making it difficult to meet requirement (B), resulting in a decrease in power generation performance (especially low-load characteristics).

[0074] <Catalyst Layer for Solid Polymer Fuel Cell and Solid Polymer Fuel Cell> A solid polymer fuel cell will be described together with the catalyst layer for solid polymer fuel cells of this disclosure. The carbon material of this disclosure is applicable, for example, to 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 the 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] Examples of the carbon material for catalyst supports of this disclosure will be described. First, the measurement methods for each parameter will be described.

[0089] <Measurement method for each parameter> (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 ＢＥＴ The calculation software included with the device determines the relative pressure P / P in the nitrogen adsorption isotherm. ０ This was calculated by performing a BET analysis within the range of 0.05 to 0.15.

[0090] (D-band peak intensity I measured by Raman spectroscopy) Ｄ G-band peak intensity I Ｇ (Measurement of the full width at half maximum ΔG of the G-band peak) 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 (JASCO Corporation, NRS-7100). From the Raman spectrum obtained under the following measurement conditions, the 1300 cm⁻¹ band, called the D-band, was measured. －１ ~1360cm －１ The peak in the range and the G band, which is 1560-1620 cm. －１ Peaks within the specified range are extracted, and curve fitting is performed using the analysis software included with the device. The D-band peak intensity I is then calculated. Ｄ(Specifically, peak area), G-band peak intensity I Ｇ The peak area (specifically) was calculated. Additionally, the peak width at half the height of the G-band peak was calculated as the full width at half maximum (FMAX) of the G-band peak (ΔG). —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: 880 cm⁻¹ －１ ~3300cm －１ Total number of times: 6.

[0091] <Experimental Example> (Raw Carbon Black) As raw carbon black, we prepared Toka Black #4500 and GFY manufactured by Tokai Carbon Co., Ltd., and #200 and HTC #20 manufactured by Nippon Steel Carbon Co., Ltd. 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 values ​​of the raw carbon blacks, respectively, which were quoted from the Carbon Black Yearbook No. 72 (2022), edited by the Carbon Black Association.

[0092]

[0093] <Pretreatment Process> A reaction tube packed with quartz wool as a dispersion plate was placed vertically inside a quartz reaction tube with an outer diameter of 35 mmφ, and granulated raw material carbon black (raw material carbon black shown in Table 2) was placed on top of the dispersion plate. The initial charge was approximately 10 to 20 g, and a gas mixture of high-purity oxygen and high-purity argon was flowed from the bottom to the top of the reaction tube. The oxygen concentration was adjusted to a range of 1% to 30% by volume fraction. The flow rate was also adjusted so that the flow velocity (linear velocity) of the mixed gas was between 0.05 m / sec and 1.5 m / sec. The reaction tube was placed in an electric furnace, heating was started, and the predetermined temperature was reached in about 20 minutes, after which the reaction was carried out for a predetermined time. The oxygen concentration, flow rate, heating temperature, and heating time are shown in Table 2.

[0094] <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 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.

[0095] <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 / min at an argon flow rate sufficient to replace the furnace volume in several tens of minutes. After holding the mixture 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.

[0096] <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 2.

[0097] Through the above process, carbon materials for catalyst supports (porous activated carbon black) were obtained for each example.

[0098] <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.

[0099] (Ink preparation) An ionomer solution manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was diluted with ethanol to adjust the solid content concentration to 10% by mass. 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.

[0100] <Preparation of MEA> The above ink was uniformly applied to a Teflon® sheet using a sprayer, and dried in an air-circulating dryer at 60°C 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.

[0101] <Battery Evaluation> (Evaluation of power generation characteristics (low load characteristics during low-humidity operation)) 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.

[0102] For the oxidizing gas, air was supplied to the cathode side and pure hydrogen to the anode side, with flow rates adjusted to achieve utilization rates of 40% and 60%, respectively. The pressure was adjusted using a back pressure valve located downstream of the cell, supplying a back pressure of 0.04 MPa. The cell temperature was set to 80°C. The pure hydrogen on the anode side was supplied to the cell by passing it through a humidifier maintained at 80°C, while the air on the cathode side was introduced to the cell by passing it through a humidifier whose temperature was adjusted to achieve a relative humidity of 40% relative to the saturation vapor pressure at the cell temperature of 80°C. Power generation was evaluated under these conditions.

[0103] 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 0.5 hours, 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.

[0104] (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.

[0105]

[0106]

[0107] 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 durability as well as low-load characteristics during low-humidity operation of fuel cells.

[0108] 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

[0109] Furthermore, the disclosure of Japanese Patent Application No. 2024-230854 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 a catalyst carrier of a solid polymer fuel cell, comprising porous activated carbon black, which satisfies the following requirements (A), (B), and (C). (A) The BET specific surface area S Ｇ , Ｄ obtained by analyzing the nitrogen adsorption isotherm by the BET method is ２ 410 m ２ / g or more and 1000 m －１ / g or less. (B) The peak intensity ratio I Ｄ of the D band peak near 1330 cm －１ obtained by Raman spectroscopic measurement to the peak intensity I Ｇ of the G band peak near 1580 cm Ｄ / I Ｇ is 1.2 or more and 2.2 or less. (C) The full width at half maximum ΔG of the G band peak near 1580 cm －１ obtained by Raman spectroscopic measurement is 72 cm －１ or more and 83 cm －１ or less.

2. A carbon material for a catalyst support for a polymer electrolyte fuel cell according to claim 1, further satisfying the following requirement (D): (D) The peak intensity ratio I Ｄ / I Ｇ The ratio of the half-width ΔG of the G-band peak (I Ｄ / I Ｇ The ratio of () / △G) is between 0.016 and 0.

026.

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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