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

Abstract

The present invention provides: a carbon material for a catalyst support of a polymer electrolyte fuel cell, said carbon material being composed of porous activated carbon black and satisfying the following requirements (A) to (D); a catalyst layer using the same; and a fuel cell.　(A) The adsorption amount at a relative pressure of 0.1 is 100 mL / g to 250 mL / g.　(B) The nitrogen adsorption amount for pores having a pore diameter of 2 nm to 6 nm as obtained by subtracting the nitrogen adsorption amount at a relative pressure of 0.218 from the nitrogen adsorption amount at a relative pressure of 0.671 is 50 mL / g to 300 mL / g.　(C) The difference obtained by subtracting the adsorption amount at a relative pressure of 0.8 according to an adsorption isotherm from the adsorption amount at a relative pressure of 0.8 according to a desorption isotherm is 50 mL / g or less.　(D) The line width of a peak appearing near 1580 cm-1 in a Raman spectrum is 70 cm-1 to 84 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. After the oxidizing gas is diffused by the gas diffusion layer on the cathode side, it is introduced 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 perform 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, that is, durability, and on the other hand, to maintain a developed pore structure to enhance power generation performance.<00,00136>

[0009] For example, Patent Document 1 discloses, "In order to provide a solid polymer fuel cell electrode catalyst that can obtain high performance even when the amount of catalyst metal used is small, it includes a carrier made of a conductive material and catalyst particles supported on the surface of the carrier. The carrier has interconnected mesopores and satisfies the relationship of 1.0 ≤ ΔVdes / ΔVads ≤ 1.14. Here, ΔVdes = Vdes(0.49) - Vdes(0.01), ΔVads = Vads(0.49) - Vads(0.01), and Vdes(0.49) is the relative pressure Ｐ／Ｐ０The following is disclosed: = 0.49, adsorption amount in the desorption process of the nitrogen adsorption isotherm in the mesopore region, Vdes(0.01) is relative pressure P / P0 = 0.01, adsorption amount in the desorption process of the nitrogen adsorption isotherm in the micropore region, Vads(0.49) is relative pressure P / P0 = 0.49, adsorption amount in the adsorption process of the nitrogen adsorption isotherm in the mesopore region, Vads(0.01) is relative pressure P / P0 = 0.01, adsorption amount in the adsorption process of the nitrogen adsorption isotherm in the micropore region.

[0010] Patent Document 2 describes a novel and improved carbon template material for fuel cell catalyst support capable of further improving power generation performance, wherein the relative pressure (P / P) at which the hysteresis loop formed by the nitrogen adsorption / desorption isotherm closes. ０ ) c is greater than 0.55 and less than 0.8, (P / P ０ )c+0.1~(P / P ０ The amount of nitrogen desorption dV between intervals c is 65 cm ３ It is greater than / g and has a BET specific surface area of ​​700m². ２ A template carbon material for fuel cell catalyst supports, characterized by having a concentration of more than 1 / g, is disclosed.

[0011] Patent Document 3 describes a novel and improved polymer electrolyte fuel cell catalyst support that further reduces overvoltage at high currents and improves durability, and is made of a carbon material that satisfies the following requirements (A), (B), (C), and (D): (A) Specific surface area of ​​nitrogen adsorption isotherm determined by BET analysis is 450 to 1500 m². ２ / g. (B) The nitrogen adsorption / desorption isotherm is relative pressure P / P ０ = A hysteresis loop is formed within the range of greater than 0.47 to 0.90, and the area of ​​the hysteresis loop is ΔS ０．４７－０．９ (C) The relative pressure P at which the hysteresis loop closes. ｃｌｏｓｅ / P ０ (D) Raman spectroscopy measurements showed 1500–1700 cm⁻¹. －１ The half-width at half maximum (FMAX) of the G-band detected in the range is 45-75 cm. －１ It is disclosed that "it is."

[0012] Patent Document 4 describes a "novel and improved carbon material for a solid polymer fuel cell catalyst support that can achieve both low-load and high-load characteristics, wherein the particle size is 10 to 20 nm and the BET specific surface area is 200 to 700 m²." ２ / g, relative pressure P / P ０ The difference between the nitrogen desorption isotherm value and the nitrogen adsorption isotherm value at 0.5 is 0.10 ml / g or less, the DBP oil absorption is 300 to 520 ml / 100 g, and the half width at half maximum (ΔG) of the G band obtained from the Raman spectroscopy spectrum is 40 to 70 cm. －１ A carbon material for a solid polymer fuel cell catalyst support, characterized by the following, is disclosed.

[0013] Patent Document 5 describes a "novel and improved carbon material for solid polymer fuel cell catalyst support that can further reduce overvoltage at high currents, wherein the relative pressure P / P ０ A carbon material for a polymer electrolyte fuel cell catalyst support is disclosed, wherein, in the range of 0.4 or higher, the nitrogen adsorption / desorption isotherm shows two hysteresis loops having a first hysteresis loop and a second hysteresis loop.

[0014] Japanese Patent Publication No. 2017-091812, Japanese Patent Publication No. 696448, Japanese Patent Publication No. 6956181, Japanese Patent Publication No. 7110842, Japanese Patent Publication No. 2022-66847

[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] For example, Patent Document 1 uses mold carbon (CNovel-MH manufactured by Toyo Tanso Co., Ltd.) with MgO as the mold as the raw material, and after heat treatment at 1700°C, 1900°C, and 2100°C in an inert atmosphere, heat treatment at around 500°C in air (activating oxidation treatment) is performed to obtain porous carbon with high coherence, that is, with no hysteresis at a relative pressure of 0.49 or less. As a result of the present inventor's diligent research, the above mold carbon belongs to the so-called non-graphitizable carbon material, and even after heat treatment at 2100°C, the improvement in crystallinity is small, and it does not meet a high level of durability, leaving room for improvement.

[0017] Patent Document 2 describes the preparation of template carbon using polyvinyl alcohol powder as the carbon source and MgO powder as the template source. In the usual preparation, after carbonization treatment in an inert atmosphere at 600°C to 900°C, MgO is dissolved and removed with a strong acid such as sulfuric acid. However, in Patent Document 2, after the carbonization treatment, a second heat treatment is performed at a temperature higher than the carbonization treatment temperature (1100°C to 1600°C) to perform an activation treatment using MgO as a catalyst, developing interconnected pores and improving power generation performance. A third heat treatment for graphitization (2000°C, in an inert atmosphere) is performed to increase crystallinity, but because the crystallites become finer due to the activation treatment, there is a risk that graphitization at a high temperature of 2000°C may not meet a high level of durability.

[0018] 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) －１ By 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 high durability.

[0019] Patent Document 4 describes using commercially available carbon black as CO ２By activating it, porous carbon is obtained, and after heat treatment at 1800°C for several hours in an inert atmosphere, the pores that collapsed during the heat treatment are re-treated with CO2. ２ The material is restored through activation, supported with Pt particles, and heated in air at 350°C using the Pt particles as a catalyst to increase pore connectivity, thereby achieving a balance between high and low load performance. However, due to the small ΔG value and excessively high crystallinity, there is room for improvement in the low-load characteristics during extremely low-humidification operation, such as when the relative humidity falls below 50%.

[0020] Patent Document 5 describes a porous carbon material prepared using silver acetylide as a raw material. By improving the raw material preparation, the amount of heat generated during explosion is increased, and by pressurizing the material during the first heat treatment (explosion process), the degree of connectivity of the porous carbon after silver removal is increased. Then, by treatment at 1800°C in an inert atmosphere, a highly crystalline, well-developed pore structure with high connectivity is achieved, particularly reducing overvoltage under high load conditions. However, there is room for improvement in the low-load characteristics during extremely low-humidity operation, such as when the relative humidity falls below 50%.

[0021] 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.

[0022] Means for solving the problem include the following embodiments: <1> A carbon material for catalyst support of a polymer electrolyte fuel cell, consisting of porous activated carbon black, that satisfies the following requirements (A), (B), (C), and (D): (A) The amount of adsorption V at a relative pressure of 0.1 in the adsorption isotherm obtained by nitrogen adsorption desorption measurement. ０．１ However, it is between 100 mL / g and 250 mL / g. (B) Nitrogen adsorption amount V for pore diameters between 2 nm and 6 nm obtained by analyzing the adsorption isotherm obtained by the BJH (Barrett-Joyner-Halenda) method, subtracting the nitrogen adsorption amount for pore diameters between 6 nm and 6 nm from the nitrogen adsorption amount for pore diameters between 6 nm and 6 nm with a relative pressure of 0.671. ２－６ｎｍHowever, it is between 50 mL / g and 300 mL / g. (C) Difference ΔV obtained by subtracting the amount of adsorption at a relative pressure of 0.8 of the adsorption isotherm from the amount of adsorption at a relative pressure of 0.8 of the desorption isotherm obtained by nitrogen adsorption and desorption measurement. ０．８ However, it is 50 mL / g or less. (D) 1580 cm⁻¹ appearing in the Raman spectrum obtained by Raman spectroscopy. －１ The line width △G of the nearby peak is 70 cm. －１ 84cm or more －１ The following applies: <2> A carbon material for catalyst support in a polymer electrolyte fuel cell as described in <1>, which further satisfies the following requirement (E). (E) The maximum value of the difference between the amount of desorption and the amount of adsorption at the same relative pressure, in the range of relative pressure 0.45 to 0.55, between the adsorption isotherm and the desorption isotherm obtained by nitrogen adsorption and desorption measurement. ０．４５－０．５５ However, it is 150 mL / g 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 according to <1> or <2>. <4> A fuel cell containing the catalyst layer for a polymer electrolyte fuel cell according to <3>. <5> The fuel cell according to <4>, wherein the catalyst layer for the polymer electrolyte fuel cell is the catalyst layer on the cathode side.

[0023] 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.

[0024] Figure 1 is a schematic diagram showing an example of the general configuration of the fuel cell of this disclosure.

[0025] 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".

[0026] <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 the requirements (A), (B), (C), and (D) described later (preferably requirements (A), (B), (C), and (D), in addition to requirement (E)). 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.

[0027] The carbon material for catalyst support disclosed herein is a carbon material that exhibits excellent durability as well as low-load characteristics when fuel cells are operated under low-humidity conditions. The carbon material disclosed herein was discovered through the following findings: firstly, the optimal structure of the porous activated carbon black was identified as specific physical properties, and secondly, a specific manufacturing method for it was developed. The optimal structure of the porous activated carbon black will be described below.

[0028] (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)

[0029] Of the main causes mentioned above, (2) is solved by securing voids in the catalyst layer that reduce the gas diffusion resistance. By using porous activated carbon black as the catalyst 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. For this reason, (2) is solved 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 low contact resistance between the catalyst supports, the ohmic resistance of the catalyst layer in (1) is improved.

[0030] Reducing the resistance of the catalytic reaction in (3) is particularly important for improving low-load characteristics. Furthermore, there are two ways to improve the low-load characteristics of the fuel cell during low-humidity operation. The first way to improve is to increase the number of catalytic metals that contribute to the reaction. The second way to improve is to maintain a high humidity state in the electrolyte material (ionomer) within the pores of the 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 of the porous activated carbon black to catalytic metals adsorbed on the surface of the porous activated carbon black should be increased. In other words, the volume of the pores in the porous activated carbon black should be increased to allow catalytic metals to be adsorbed within the pores. Specifically, the pore volume of pores with a diameter of 2 to 6 nm, calculated by nitrogen gas adsorption, should be increased. A pore diameter of 2 to 6 nm corresponds to the size (diameter) of the catalytic metal.

[0031] There are two strategies for maintaining a high level of moisture in the electrolyte material (ionomer) within the pores of porous activated carbon black, even during low-humidity operation. The first strategy is to ensure liquid water within the porous carbon even at low relative pressure, and to maintain the moisture state of the electrolyte material (ionomer) within the pores using the vapor pressure of that water. The pore structure for this purpose is to increase the so-called micropore volume. The second strategy is to allow as much electrolyte material (ionomer) as possible to penetrate into the pores. Generally, linear polymers can easily and quickly penetrate into pores. However, fluoropolymers, such as electrolyte material (ionomer), which use fluorine instead of hydrogen, have low flexibility. Also, polymers with a structure in which relatively large side chains are densely attached to the main chain have low flexibility and the presence of side chains. Therefore, it is difficult for electrolyte material (ionomer) to penetrate into the pores. Even at present, controlling the amount of electrolyte material (ionomer) that penetrates is not easy.

[0032] In response to this, two improvement measures are envisioned to increase the amount of electrolyte material (ionomer) that can penetrate. The first improvement measure is to minimize surface irregularities so that the filaments of aggregated electrolyte material (ionomer) are adsorbed onto the surface, reducing the inhibition of penetration into the pores. Converted to pore diameters calculated by nitrogen gas adsorption measurement, pore diameters of 10 to 20 nm are more likely to adsorb the filaments of aggregated electrolyte material (ionomer). Therefore, it is important to minimize irregularities in pore diameters of 10 to 20 nm, and this corresponds to requirement (C). That is, the smaller the difference in adsorption amounts between the desorption and adsorption isotherms at a relative pressure of 0.8 corresponding to a pore with a pore diameter of 10 nm, the less surface roughness there is near the 10 nm diameter. The second improvement measure is to create a pore structure that makes it easier for the electrolyte material (ionomer) that has penetrated into the pores to penetrate deep into the pore structure.

[0033] On the other hand, improving durability lies in the structure of crystallites, the smallest units that make up carbon black. Since the decrease in durability is due to the structural breakdown of porous activated carbon black that occurs with oxidative consumption, it is necessary to make the crystallites less susceptible to oxidation. One way to do this is to increase the size of the crystallites to reduce the surface area that serves as the starting point for oxidative consumption. A physical property that sensitively reflects the structure of the crystallites is the vibrational mode called the G band, which reflects the graphite structure and is obtained by Raman spectroscopy of porous activated carbon black. The linewidth of the G band peak in the Raman spectrum corresponding to this vibration reflects the size of the crystallites.

[0034] In other words, the inventors discovered that the power generation performance at low loads during low-humidity operation could be improved, while at the same time maintaining high durability even in harsh operating environments such as trucks and buses. Furthermore, through a special manufacturing process described later, the inventors succeeded in producing porous activated carbon black with a special crystallite structure.

[0035] Thus, the inventors aimed to achieve both high durability and high low-load characteristics during low-humidity operation in porous activated carbon black by improving the physical properties as described above. As a result, the inventors found that satisfying (a) to (d) below simultaneously can achieve both high low-load characteristics during low-humidity operation, and that satisfying (a) to (e) below simultaneously is important to further improve the low-load characteristics during low-humidity operation. (a) Increase the pore volume of micropores (improves low-load characteristics during low-humidity operation) (b) Increase the volume of pores with a diameter of 2 to 6 nm to increase the amount of catalyst metal particles in the pores (improves low-load characteristics during low-humidity operation) (c) Suppress the adsorption of ionomer aggregates due to surface irregularities (improves low-load characteristics during low-humidity operation) (d) Increase the size of crystallites (enhances crystallinity) (results in high durability) (e) Allow the electrolyte material (ionomer) to penetrate deeper into the pore structure (improves low-load characteristics during low-humidity operation)

[0036] Specifically, after diligent study, the inventors discovered the following specific physical properties corresponding to the above guidelines: (a) The physical property suitable for (a) is the amount of nitrogen adsorbed at a relative pressure of 0.1 obtained by nitrogen gas adsorption measurement (Requirement (A)) (b) The physical property suitable for (b) is the pore volume of 2 to 6 nm in diameter obtained by nitrogen gas adsorption measurement (Requirement (B)) (c) The physical property suitable for (c) is the difference between the amount of adsorption of desorption and adsorption at a relative pressure of 0.8 obtained by nitrogen gas adsorption measurement (Requirement (C)) (d) The physical property suitable for (d) is the full width at half maximum of the G band obtained by Raman spectroscopy measurement (referred to as ΔG) (Requirement (D)) (e) The physical property suitable for (e) is the difference between the amount of adsorption of desorption and adsorption at a relative pressure of 0.45 to 0.55 obtained by nitrogen gas adsorption measurement (Requirement (E))

[0037] Requirements (A), (B), (C), and (D) are described below. Hereinafter, from the viewpoint of improving the low-load characteristics when operated under low-humidity conditions, it is preferable that the carbon material for catalyst support of this disclosure satisfies requirement (E) in addition to requirements (A) to (D).

[0038] (Requirement (A): Nitrogen adsorption amount V at relative pressure 0.1) ０．１ (A) In the adsorption isotherm obtained by nitrogen adsorption and desorption measurement, the amount of adsorption V at a relative pressure of 0.1 ０．１ However, the concentration is between 100 mL / g and 250 mL / g.

[0039] As mentioned above, it is known that the smaller the pore diameter, the better it can retain liquid water within the pores, even at high relative pressures. Analysis of the water vapor adsorption behavior of porous activated carbon black shows that pores with a diameter of 2 nm or less, generally called micropores, are suitable for retaining water in a liquid state. For example, to improve low-load characteristics in low-humidity conditions of 40% relative humidity or less, the ionomer within the pores must be kept moist at a relative humidity of around 40%. Since a relative pressure of 0.1 in nitrogen adsorption measurements corresponds to pores with a diameter of 2 nm or less, the amount of adsorption V at a relative pressure of 0.1 in the adsorption isotherm obtained from nitrogen adsorption and desorption measurements... ０．１ A larger value allows for the retention of a larger amount of liquid water, which is effective in improving low-load characteristics when operating under humidification conditions.

[0040] Adsorption amount V at relative pressure 0.1 ０．１ However, if the amount is less than 100 mL / g, it may not be possible to secure the moisture necessary to keep the electrolyte material (ionomer) moist, which could lead to a decrease in low-load characteristics during low-humidity operation. V at relative pressure 0.1 ０．１ If the value exceeds 250 mL / g, the overall pore volume is increased, and the surface irregularities also become larger. As a result, it becomes difficult to meet requirements (B) and (C). Consequently, there is a risk that the low-load characteristics during low-humidification operation will deteriorate.

[0041] Therefore, the amount of adsorption V at a relative pressure of 0.1 ０．１ The concentration shall be between 100 mL / g and 250 mL / g. Adsorption amount V at relative pressure 0.1 ０．１ The amount of adsorption V at a relative pressure of 0.1 is preferable to be 150 mL / g or more and 250 mL / g or less. ０．１ This is a value measured by the method described in the examples below.

[0042] (Requirement (B): Pore volume V of pores with a pore diameter of 2-6 nm) ２－６ｎｍ (B) Nitrogen adsorption amount V for pore diameters between 2 nm and 6 nm, obtained by analyzing the adsorption isotherms obtained by nitrogen adsorption and desorption measurements using the BJH (Barrett-Joyner-Halenda) method, and subtracting the nitrogen adsorption amount at a relative pressure of 0.218 corresponding to a pore diameter of 2 nm from the nitrogen adsorption amount at a relative pressure of 0.671 corresponding to a pore diameter of 6 nm. ２－６ｎｍ However, the concentration is between 50 mL / g and 300 mL / g.

[0043] The pore volume with a suitable pore diameter for adsorption of the catalytic metal is the amount of nitrogen adsorption V. ２－６ｎｍTherefore, for fuel cell catalyst metals, larger particle sizes are preferred from the viewpoint of durability. On the other hand, smaller particle sizes are preferable from the viewpoint of power generation performance because they reduce the reaction surface area per unit mass. As a balance between these factors, the size of catalyst metals is generally in the range of 2 nm to 6 nm. Consequently, the larger the pore volume with a diameter of 2 to 6 nm, which is suitable for the particle size of the catalyst metal, the more catalyst metal is supported within the pores than adsorbed on the surface, and the more catalyst surface area that can be used as a reaction field becomes substantially larger. Therefore, high power generation performance can be expected, and low load characteristics during low-humidity operation can also be expected.

[0044] Nitrogen adsorption capacity V for pores with a diameter of 2 nm to 6 nm ２－６ｎｍ If the amount is less than 50 mL / g, the number of catalyst metals that can be supported in the pores decreases, which may impair the low-load characteristics during sufficiently low-humidification operation. Nitrogen adsorption amount V for pore diameters of 2 nm to 6 nm ２－６ｎｍ If the concentration exceeds 300 mL / g, the pore volume of pores with a diameter of 10 nm or more also becomes too large. As a result, it becomes difficult to satisfy requirement (C), and aggregates of the electrolyte material (ionomer) adsorb onto the porous activated carbon black surface, which may reduce the low-load characteristics during low-humidity operation.

[0045] Therefore, the amount of nitrogen adsorption V for pores with a diameter of 2 nm to 6 nm ２－６ｎｍ The amount of nitrogen adsorption V for pores with a diameter of 2 nm to 6 nm is 50 mL / g or more and 300 mL / g or less. ２－６ｎｍ Preferably, the amount is between 100 mL / g and 290 mL / g.

[0046] Note that the nitrogen adsorption amount V is for pores with a diameter of 2 nm to 6 nm. ２－６ｎｍ This is a value measured by the method described in the examples below.

[0047] (Requirement (C): Difference △V between the amount of adsorption on the desorption side and the amount of adsorption on the adsorption side at a relative pressure of 0.8) ０．８ (C) The difference ΔV obtained by subtracting the amount of adsorption at a relative pressure of 0.8 on the adsorption isotherm from the amount of adsorption at a relative pressure of 0.8 on the desorption isotherm obtained by nitrogen adsorption and desorption measurement. ０．８ However, it is 50 mL / g or less.

[0048] As mentioned above, the ideal structure for porous activated carbon black is one with minimal surface irregularities. This reduces the inhibition of the aggregated electrolyte material (ionomer) filaments adsorbing to the surface and entering the pores, thereby increasing the amount of electrolyte material (ionomer) present in the pores. As a result, even during low-humidity operation, the high amount of electrolyte material (ionomer) prevents drying, allowing for the maintenance of high low-load characteristics even during prolonged low-humidity operation. The surface irregularities of the porous activated carbon black are quantitatively represented by ΔV. ０．８ It is. △V ０．８ A larger value corresponds to a larger volume of irregularities, △V ０．８ A smaller value corresponds to a smaller volume of irregularities. Therefore, to improve the low-load characteristics during low-humidity operation, ΔV ０．８ It is preferable that it is small.

[0049] △V ０．８ If the concentration exceeds 50 mL / g, the surface irregularities of the porous activated carbon black become too large, leading to increased adsorption of electrolyte material (ionomer) aggregates, which may reduce the low-load characteristics during low-humidity operation. ０．８ The minimum value of is zero, which corresponds to the adsorption isotherm and desorption isotherm coinciding at a relative pressure of 0.8, meaning there are no irregularities of 10-20 nm in size on the porous activated carbon black surface. Therefore, the difference in adsorption amount is ΔV. ０．８ The amount should be 50 mL / g or less. Difference in adsorption amount △V ０．８ The concentration is preferably 30 mL / g or less.

[0050] The adsorption amount at a relative pressure of 0.8 on the desorption isotherm and the adsorption amount at a relative pressure of 0.8 on the adsorption isotherm are values ​​measured by the method described in the examples below.

[0051] (Requirement D: Size of the graphene sheet constituting the crystallite △G) (D) 1580 cm⁻¹ appearing in the Raman spectrum obtained by Raman spectroscopy －１ The line width △G of the nearby peak is 70 cm. －１ 84cm or more －１ The following applies:

[0052] In Raman spectra, the intensity of a peak corresponds to the volume of the structure belonging to that band, while the shape of the peak, particularly its linewidth (half-maximum full width, 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 vibration 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 ΔG (broader peak) corresponds to a smaller graphene sheet. Conversely, a smaller ΔG (sharper peak) corresponds to a larger graphene sheet. By obtaining porous activated carbon black through a special series of manufacturing processes, it is possible to achieve a porous activated carbon black structure that is not normally attainable. This structure achieves high low-load characteristics in low-humidity operation by developing the aforementioned micropore volume and mesopore volume while maintaining low surface roughness, even with a large graphene sheet that satisfies high durability requirements.

[0053] △G is 70cm －１ Below this value, the graphene sheet may become too large, reducing the edge area and potentially degrading the low-load performance during low-humidity operation. △G = 84cm －１ If it exceeds this, the graphene sheet may become too small, potentially leading to a significant decrease in durability. Therefore, △G should be 70 cm. －１ 84cm or more －１ The following applies: △G is 73cm －１ 81cm or more －１ The following are preferable.

[0054] Note that △G is a value measured by the method described in the examples below. 1580 cm －１ The line width △G of the nearby peak is 1560–1620 cm. －１ This is the full width at half maximum of the G-band peak.

[0055] (Requirement (E): The maximum value of the difference between the amount of adsorption on the desorption side and the amount of adsorption on the adsorption side at a relative pressure of 0.45 to 0.55 △V) ０．４５-０．５５(E) In the adsorption and desorption isotherms obtained by nitrogen adsorption and desorption measurements, the maximum value of the difference obtained by subtracting the adsorption amount from the desorption amount at the same relative pressure within the range of relative pressure 0.45 to 0.55 is ΔV. ０．４５－０．５５ However, it is 150 mL / g or less.

[0056] △V ０．８ This is an index for suppressing surface irregularities of porous activated carbon black. On the other hand, ΔV ０．４５-０．５５ This is a physical property introduced to represent the degree of connectivity of the pores in porous activated carbon black. Generally, in nitrogen gas adsorption measurements of porous activated carbon black with a pore structure, the isotherms for adsorption and desorption measurements do not coincide, and the isotherm on the desorption side shows a larger adsorption amount than the isotherm on the adsorption side. In the desorption measurement, the relative pressure is gradually reduced from a saturated humidified state, so it is smaller than the external pressure (relative pressure controlled by the device) by the amount of surface tension of liquid nitrogen, and the smaller the pore diameter, the smaller the radius of curvature, and therefore the larger the surface tension. The pores in porous activated carbon black do not have a uniform diameter or uniform slit width, and pores of various diameters or slit widths are interconnected. The interconnected parts tend to have smaller pore diameters (slit widths). If the three-dimensional connectivity between pores is well-developed (high degree of connectivity), it results in larger pores, i.e., smaller surface tension. As a result, the difference between desorption and adsorption becomes smaller. Thus, the difference between the amount of desorption and adsorption can be considered an indicator of the degree of communication. △V ０．４５-０．５５ This indicates a high degree of connectivity within the pore size of 2-3 nm, which is said to be the pore size through which electrolyte materials (ionomers) can penetrate. ０．４５-０．５５ The smaller the value, the higher the degree of connectivity within 2-3 nm, which serves as an indicator of how easily the electrolyte material (ionomer) can penetrate into the deeper pores.

[0057] △V ０．４５-０．５５ When the concentration is 150 mL / g or less, the amount of electrolyte material (ionomer) that penetrates into the pores increases, which makes it easier to improve the low-load characteristics during low-humidity operation. Therefore, △V ０．４５-０．５５ The concentration is preferably 150 mL / g or less, and more preferably 120 mL / g or less. ０．４５-０．５５ The lower limit is 0.

[0058] Note: △V ０．４５-０．５５ This is a value measured by the method described in the examples below.

[0059] <Method for manufacturing carbon material for catalyst support in solid polymer fuel cells>

[0060] The following describes in detail suitable manufacturing methods and processes for meeting the physical property values ​​within the ranges specified in requirements (A) to (D) and (E).

[0061] <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), (C), and (D) (preferably requirements (A) to (D) in addition to requirement (E)), are to develop pores in the raw material carbon black while suppressing surface roughness, reduce pore collapse due to heat treatment to improve durability, and restore the pores collapsed by heat treatment by activation after heat treatment.

[0062] 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, one example is a manufacturing method having four steps: a pretreatment step, a first activation step, a heat treatment step, and a second activation step. Pretreatment step: Using a mixed gas diluted by mixing air and an inert gas (e.g., argon gas), the raw material carbon black is oxidized under conditions of low oxygen concentration, relatively low temperature, pressurized state, slow flow rate of the mixed gas, and long processing time. This oxidation treatment forms fine pores with a diameter of 2 nm or less into the interior of the raw material carbon black, and develops pores while suppressing surface oxidation 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.

[0063] The following describes each step.

[0064] (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 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 30 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, but it also has the advantage of being highly resistant to oxidation and thus easier to improve durability. For this reason, the average primary particle size of the raw material carbon black is preferably 80 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.

[0065] 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.

[0066] Furthermore, the average primary particle size of the raw carbon black was measured as follows: The raw carbon black was observed at a magnification of 5x and in any 15 fields of view using a transmission electron microscope (TEM) with a resolution of at least 1.5 to 2.0 nm. For each observation image, the approximate circular diameter (i.e., equivalent circle diameter) of the raw carbon black was calculated using commercially available particle size measurement software (Zeiss-Ender Particle Size Analyzer). The arithmetic mean of the equivalent circle diameters of 3500 raw carbon black particles was then taken as the average primary particle size of the raw carbon black. However, if the raw carbon black is a commercially available product, the "primary particle size" listed in the "Carbon Black Yearbook" published by the Carbon Black Association may be used.

[0067] (Pretreatment step: Oxidation treatment with a mixed gas of air and an inert gas (e.g., argon)) In the pretreatment step, a low-concentration oxygen mixed gas is used, which is obtained by diluting air (e.g., pure air gas filled in a commercially available cylinder) as an oxidizing agent with an inert gas (e.g., argon) to reduce its oxidizing power. For example, the air and inert gas are mixed so that the air concentration is 1 / 2 on a volume basis. Then, under a low-concentration oxygen mixed gas atmosphere, the raw material carbon black is oxidized at a relatively low temperature, under a low pressure, with a slow gas flow rate and a long processing time.

[0068] In this way, under pressurized conditions, the oxygen concentration in the mixed gas is kept low, the flow rate of the mixed gas and the processing temperature are controlled, and the processing time is extended to slowly advance the oxidation reaction of the raw material carbon black. This suppresses oxidation (combustion) of the surface of the carbon black while introducing a large number of micropores with a diameter of 2 nm or less that extend into the interior of 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. In this way, oxidation of the surface of the raw material carbon black can be suppressed while simultaneously forming highly interconnected, well-developed internal pores. In other words, it is possible to develop internal pores of the raw material carbon black while suppressing surface oxidation of the raw material carbon black. Then, after the oxidation treatment, by going through the first activation step, the heat treatment step and the second activation step, porous activated carbon black with a highly interconnected pore structure that satisfies requirements (C) and (E) in particular can be obtained.

[0069] The specific oxidation treatment conditions for the raw material carbon black carried out in the pretreatment process are as follows: The pressurized pressure during the oxidation treatment is, for example, 0.2 MPa to 1.0 MPa in gauge pressure (pressure with atmospheric pressure as the reference (pressure 0)). If the pressurized pressure (gauge pressure) is less than 0.2 MPa, the effect of pressurization, i.e., the suppression of oxidation on the surface of the raw material carbon black, is insufficient, leading to uneven distribution of the electrolyte material (ionomer) due to surface oxidation (roughness), and a decrease in power generation performance (especially low-load characteristics during low-humidity operation). If the pressurized pressure (gauge pressure) exceeds 1.0 MPa, the oxygen concentration becomes too high and the reaction rate becomes too high. As a result, the development of micropores inside the raw material carbon black is inhibited, making it difficult to satisfy requirements (A) and (B).

[0070] The oxygen concentration (volume %) in a mixed gas of air and an inert gas (e.g., argon) is, for example, 2% to 15%, more preferably 5% to 12%. For example, the oxygen concentration of a mixed gas obtained by mixing equal volumes of high-purity dry air and argon is approximately 10.5%. If the oxygen concentration is less than 2 volume%, the time required for a weight loss rate of several percent or more due to oxidation will exceed 300 hours, which is impractical from an industrial production standpoint. On the other hand, if the oxygen concentration exceeds 15%, the oxidation rate of the surface is large, and there is a risk that the rate of increase in the volume of micropores relative to the weight loss will be low.

[0071] The flow velocity of the mixed gas of air and an inert gas (e.g., argon) is preferably 0.5 m / s to 2.0 m / s in linear velocity, and more preferably 0.8 m / s to 1.9 m / s. If the flow velocity (linear velocity) is less than 0.5 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 the flow velocity (linear velocity) exceeds 2.0 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).

[0072] The heating temperature for the oxidation treatment is, for example, 300°C to 400°C, preferably 310°C to 380°C. If the heating temperature is below 300°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).

[0073] The heating time for the 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).

[0074] The weight loss rate of raw carbon black due to oxidation treatment is, for example, 30-50%. If the weight loss rate is less than 30%, it becomes difficult to penetrate the interior of the raw carbon black with micropores for the first activation, which is the effect of the pretreatment process. As a result, the surface roughness (surface oxidation) of the porous activated carbon black and the size of the pores near the surface increase with the first activation, making it difficult to meet requirement (C). If the weight loss rate exceeds 50%, the micropores penetrating the raw carbon black develop sufficiently, but surface roughness (surface oxidation) also occurs in parallel, and this surface roughness remains as surface roughness of the porous activated carbon black even after going through the first activation process, the heat treatment process and the second activation process. As a result, the adsorption of the electrolyte material (ionomer) becomes uneven, leading to a decrease in power generation performance (especially low load characteristics during low-humidity operation).

[0075] (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.

[0076] In the first activation step, the gas used as the oxidizing agent is water vapor (H ２ O), or CO２ Oxidizing gases such as the above are preferably used. In the first activation step, for example, the pre-treated carbon black can be made porous by contacting it with an oxidizing gas and maintaining the activation temperature at 750°C to 930°C.

[0077] 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 activation 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 requirements (A) and (B), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation). 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 (C), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation).

[0078] The activation time in the first activation step is an important factor in controlling pore development, similar to temperature. The activation time in the first activation step is preferably 5 hours or more and 50 hours or less, and more preferably 7 hours or more and 40 hours or less. If the activation time in the first activation step is less than 5 hours, the oxidation rate is too fast, resulting in significant surface oxidation and making it difficult to meet requirement (C), which may lead to a decrease in power generation performance (especially low-load characteristics during low-humidity operation). If the activation time in the first activation step exceeds 50 hours, pore formation progresses too much, increasing mesopores and decreasing micropores, making it difficult to meet requirements (A) and (B), which may lead to a decrease in power generation performance (especially low-load characteristics during low-humidity operation).

[0079] 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.

[0080] (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 oxidation resistance and improves durability. Specifically, in order to suppress carbon oxidation, 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 heat treatment time is, for example, 0.5 hours to 10 hours. If the heat treatment temperature is below 1400°C, the crystalline development is not sufficient, making it difficult to meet requirement (D) and resulting in a decrease in durability. If the heat treatment temperature exceeds 1900°C, the pores collapse as crystallinity develops, making it difficult to meet requirements (D), as well as requirements (A) through (C) and (E), resulting in a decrease in durability and power generation performance (especially low-load characteristics during low-humidity operation). If the heat treatment time is less than 0.5 hours, it takes time for the activated carbon black structure to stabilize due to the heat treatment, so the entire activated carbon black does not reach a uniform crystalline structure. As a result, the low crystallinity is the main cause of the decrease in durability. If the heat treatment time exceeds 10 hours, the aggregate particles of the activated carbon black after the first activation process chemically bond with each other to form clumps, increasing the resistance of gas flow within the clumps. Therefore, it becomes difficult to meet requirements (A) through (C) and (E), resulting in a decrease in power generation performance (especially low-load characteristics during low-humidity operation).

[0081] 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.

[0082] (Second Activation Step) In the second activation step, the heat-treated activated carbon black is subjected to a second activation to obtain porous activated carbon black. In the second activation step, the heat-treated activated carbon black that has undergone heat treatment is subjected to a second activation to revive the pores that have been crushed by chemical bonds between crystallites or the like during the heat treatment. Alternatively, the size of the pores reduced by the heat treatment is increased in pore diameter by the second activation.

[0083] In the second activation step, the gas used as the oxidizing agent is preferably steam (H ２ 2O) or an oxidizing gas such as CO ２ .

[0084] In the second activation step, for example, the heat-treated activated carbon black is brought into contact with the oxidizing gas and maintained at an activation temperature of 700°C or higher and 900°C or lower, whereby the heat-treated activated carbon black can be made porous. When steam is used as the activation gas in the second activation step, the activation temperature is preferably 700°C or higher and 850°C or lower, and when CO ２ is used as the activation gas, the activation temperature is preferably 750°C or higher and 900°C or lower. If the activation temperature in the second activation step is less than 750°C, the activation is insufficient and it becomes difficult to satisfy requirement (A), resulting in a decrease in power generation performance (especially low-load characteristics). If the activation temperature in the second activation step exceeds 900°C, surface oxidation is promoted, making it difficult to satisfy requirement (B), and there is a risk of a decrease in power generation performance (especially low-load characteristics).

[0085] The activation time in the second activation step is preferably 0.5 hours or more and 3 hours or less. If the activation time in the second activation step is less than 0.5 hours, the activation is insufficient and it becomes difficult to satisfy requirement (A), and there is a risk of a decrease in power generation performance (especially low-load characteristics). If the activation time in the second activation step exceeds 3 hours, surface oxidation is promoted, making it difficult to satisfy requirement (B), and there is a risk of a decrease in power generation performance (especially low-load characteristics).

[0086] <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.

[0087] 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.

[0088] 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.

[0089] The catalyst layer 150 is a so-called anode. In the catalyst layer 150, an oxidation reaction of a 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 = 0 V)

[0090] The protons generated by the oxidation reaction reach the catalyst layer 160 through the catalyst layer 150 and the electrolyte membrane 170. The electrons generated by the oxidation reaction reach the external circuit through the catalyst layer 150, the gas diffusion layer 130, and the separator 110. The electrons do work (generate electricity) in the external circuit and then are introduced into the separator 120. Thereafter, the electrons reach the catalyst layer 160 through the separator 120 and the gas diffusion layer 140.

[0091] The configuration of the catalyst layer 150 serving as the anode is not particularly limited. The configuration of the catalyst layer 150 may be the same as that of a conventional anode, may be the same as that of the catalyst layer 160, or may be a configuration with higher hydrophilicity than the catalyst layer 160.

[0092] The catalyst layer 160 is a so-called cathode. In the catalyst layer 160, a reduction reaction of an oxidizing gas occurs, generating water. For example, when the oxidizing gas is oxygen gas or air, the following reduction reaction occurs. The water generated by the reduction reaction is discharged to the outside of the solid polymer fuel cell 100 together with the unreacted oxidizing gas. O ２ + 4H ＋ + 4e － → 2H ２ O (E ０ = 1.23 V)

[0093] Thus, in the solid polymer fuel cell 100, electricity 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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., have been introduced. 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.

[0099] <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.

[0100] Examples of the carbon material for catalyst supports of this disclosure will be described. First, the measurement methods for each parameter will be described.

[0101] <Measurement methods for each parameter>

[0102] (Measurement of nitrogen adsorption isotherms and V ０．１ , V ２－６ｎｍ , △V ０．８ , and △V ０．４５－０．５５(Calculation Method) Approximately 30 mg of the carbon material for catalyst support was weighed out and vacuum-dried at 90°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 and desorption isotherms were measured at a liquid nitrogen temperature (approximately 77 K) using nitrogen gas as the adsorbate. The amount of nitrogen adsorbed on the vertical axis of the adsorption isotherm is expressed as the volume of adsorbed nitrogen gas in mL / g under standard conditions (20°C, 0.1 MPa). The amount of nitrogen adsorbed during adsorption and desorption is expressed in this unit as the volume per unit mass, i.e., mL / g. V ０．１ This value was taken from the adsorption isotherm obtained by measurement, specifically the value of nitrogen adsorption at a relative pressure of 0.1. ２－６ｎｍ The relative pressures corresponding to pore diameters of 2 nm (0.218) and 6 nm (0.671) were calculated by performing BJH analysis on the adsorption isotherms using the analysis software included with the device. The nitrogen adsorption amount at each relative pressure was then read, and the difference was calculated by subtracting the adsorption amount at 2 nm from the adsorption amount at 6 nm. ０．８ The difference was calculated by subtracting the amount of nitrogen adsorbed in the adsorption measurement from the amount of nitrogen adsorbed in the desorption measurement at a relative pressure of 0.8. ０．４５－０．５５ Similarly to the above, within the relative pressure range of 0.45 to 0.55, the largest difference was calculated by subtracting the nitrogen adsorption amount of the adsorption isotherm from the nitrogen adsorption amount of the desorption isotherm at the same relative pressure.

[0103] (Measurement of the linewidth ΔG of the G-band peak by Raman spectroscopy) Approximately 3 mg of carbon material for catalyst support was weighed out, and the Raman spectrum was measured using a laser Raman spectrophotometer (NRS-7100, manufactured by JASCO Corporation). From the Raman spectrum obtained under the following measurement conditions, the linewidth ΔG of the G-band, called 1560-1620 cm⁻¹, was measured. －１Peaks within the specified range were extracted, and curve fitting was performed using the analysis software included with the instrument to calculate the full width at half maximum (FMAX) of the G-band peak. The obtained FMAX was then defined as the line width 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.

[0104] <Experimental Example> (Raw Carbon Black) Tokai Carbon's Toka Black #4500 and GFY, and Nippon Steel Carbon's #200IN and #SH were prepared as raw carbon blacks. These raw carbon blacks were subjected to the pretreatment process, the first activation process, the heat treatment process, and the second activation process described below. Table 1 below shows the primary particle diameter (arithmetic mean particle diameter), DBP oil absorption amount, and BET specific surface area of ​​the raw carbon blacks, as referenced from Carbon Black Yearbook No. 72 (2022, edited by the Carbon Black Association).

[0105]

[0106] <Pretreatment Process> A reaction tube packed with quartz wool as a dispersion plate was vertically installed inside a heat-resistant metal reaction tube made of nickel alloy with an outer diameter of 1 inch, 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 15 g, and a mixed gas, consisting of equal amounts of high-purity dry air and argon gas, was flowed from the bottom to the top of the reaction tube. Specifically, the high-purity dry air and argon gas were controlled by mass flow controllers to equalize their flow rates before being combined and mixed to form the mixed gas. To adjust the reaction pressure for the pretreatment of the raw material carbon black, a pressure relief valve and pressure gauge were installed downstream of the reaction tube, and the gas flow rate was controlled under pressurized conditions by adjusting the pressure relief valve. The pressurized pressure was adjusted in the range of 0 MPa (no pressurization) to 1.1 MPa in gauge pressure, and the gas flow rate (linear velocity) of the pure air gas was adjusted in the range of 0.4 to 2.2 m / sec. The gas flow velocity (linear velocity) of pure air was calculated considering the volume increase proportional to temperature as an ideal gas and the inner diameter (internal area) of the reaction tube (shown in Table 2). The reaction tube was placed in an electric furnace, heating was started, and the predetermined temperature was reached in about 20 minutes. The reaction was then carried out for a predetermined time after reaching the predetermined temperature. The heating temperature was adjusted from 290°C to 410°C, and the heating time from 20 hours to 50 hours. The gauge pressure (MPa) under pressurization, gas flow velocity (linear velocity: m / sec), heating temperature, and heating time are shown in Table 2. In addition, the raw material carbon black was removed after pretreatment, its mass in grams was measured, and the weight loss rate relative to the initial amount in grams was calculated (%) and shown in Table 2.

[0107] <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 the pre-treated raw material carbon black was placed on top of that. The reaction tube was then set in a vertical electric furnace. 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 the heating was started at 10°C / min. Once the predetermined temperature was reached, CO 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.

[0108] <Heat Treatment Process> In the heat treatment process, a so-called heat treatment furnace using graphite material as the heating element was used. Activated carbon black, which had undergone initial activation, was placed in a graphite crucible with a volume of approximately 100 cc. After replacing the chamber with argon gas under reduced pressure, the temperature was raised at an argon flow rate of 10°C / min, sufficient to replace the furnace volume in several tens of minutes. The carbon black was then held at a predetermined temperature (heat treatment temperature) for a predetermined time (heat treatment time), after which it was allowed to cool to near room temperature before being removed. The holding time at the heat treatment temperature (heat treatment time) was variable. The conditions are shown in Table 2.

[0109] <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.

[0110] Through the above process, carbon materials for catalyst supports (porous activated carbon black) were obtained for each example.

[0111] <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.

[0112] (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.

[0113] <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.

[0114] <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.

[0115] 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.

[0116] 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 0.865V or higher. B: Current density is 100mA / cm² ２ The cell voltage after 0.5 hours is 0.860V or higher. [Failure Rank] C: Current density is 100mA / cm² ２ The cell voltage after 0.5 hours is less than 0.860V.

[0117] (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.

[0118]

[0119]

[0120] 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.

[0121] 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

[0122] Furthermore, the disclosure of Japanese Patent Application No. 2024-230856 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A carbon material for catalyst support in a polymer electrolyte fuel cell, consisting of porous activated carbon black, that satisfies the following requirements (A), (B), (C), and (D): (A) The amount of adsorption V at a relative pressure of 0.1 in the adsorption isotherm obtained by nitrogen adsorption desorption measurement. ０．１ However, it is between 100 mL / g and 250 mL / g. (B) Nitrogen adsorption amount V for pore diameters between 2 nm and 6 nm obtained by analyzing the adsorption isotherm obtained by the BJH (Barrett-Joyner-Halenda) method, subtracting the nitrogen adsorption amount for pore diameters between 6 nm and 6 nm from the nitrogen adsorption amount for pore diameters between 6 nm and 6 nm with a relative pressure of 0.

671. ２－６ｎｍ However, it is between 50 mL / g and 300 mL / g. (C) Difference ΔV obtained by subtracting the amount of adsorption at a relative pressure of 0.8 of the adsorption isotherm from the amount of adsorption at a relative pressure of 0.8 of the desorption isotherm obtained by nitrogen adsorption and desorption measurement. ０．８ However, it is 50 mL / g or less. (D) 1580 cm⁻¹ appearing in the Raman spectrum obtained by Raman spectroscopy. －１ The line width △G of the nearby peak is 70 cm. －１ 84cm or more －１ The following applies:

2. A carbon material for a catalyst support in a polymer electrolyte fuel cell according to claim 1, further satisfying the following requirement (E): (E) The maximum value of the difference between the amount of desorption and the amount of adsorption at the same relative pressure, in the range of relative pressure 0.45 to 0.55, between the adsorption isotherm and the desorption isotherm obtained by nitrogen adsorption-desorption measurement. ０．４５－０．５５ However, it is 150 mL / g or less.

3. A catalyst layer for a polymer electrolyte fuel cell comprising a carbon material for catalyst support of 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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