Porous carbon material and method for producing same, catalyst for fuel cell, and fuel cell

Abstract

The present invention pertains to a porous carbon material that has, in a pore diameter distribution thereof which is determined by analyzing a nitrogen adsorption isotherm by a Barrett-Joyner-Halenda (BJH) method and in which dV / d(logD) is used as the vertical axis and the pore diameter D is used as the horizontal axis, a first peak in a pore diameter range of 2-6 nm, said first peak being the maximum value of dV / d(logD) in a pore diameter region of not more than 10 nm, and has a second peak in a pore diameter range of 20-150 nm, said second peak being the maximum value of dV / d(logD) in a pore diameter region of more than 10 nm. The pore volume VD2-6 of pores having a diameter of 2-6 nm is not less than 0.50 cm3 / g. The present invention also pertains to a method for producing the porous carbon material, a catalyst for fuel cells, and a fuel cell.

Description

Porous carbon material and its manufacturing method, catalyst for fuel cell, and fuel cell

[0001] The present disclosure relates to a porous carbon material and a method for producing the same, a catalyst for a fuel cell, and a fuel cell.

[0002] A polymer electrolyte fuel cell, a type of fuel cell, comprises a pair of catalyst layers disposed on both sides of a solid polymer electrolyte membrane, gas diffusion layers disposed on the outer side of each catalyst layer, and separators disposed on the outer side of each gas diffusion layer. One of the pair of catalyst layers serves as the anode of the polymer electrolyte fuel cell, and the other serves as the cathode of the polymer electrolyte fuel cell. In a typical polymer electrolyte fuel cell, multiple unit cells each having the above components are stacked to obtain the desired output.

[0003] Porous carbon materials are known as catalyst supports used in fuel cell catalysts, and various proposals have been made.

[0004] For example, Patent Document 1 discloses the following: "A method for producing a template carbon material using, as raw materials, a carbon source that satisfies the following requirement (A) and a template source that satisfies the following requirement (B): (A) the carbon source is an aliphatic hydrocarbon compound that contains two or more carboxyl groups and has a structure in which at least two of the two or more carboxyl groups are separated by 2 to 4 carbon atoms; and (B) the template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals."

[0005] For example, Patent Document 2 discloses "a porous carbon material characterized in that the total pore volume, which is the sum of the micropore volume and the mesopore volume, is 1 ml / g or more, and the ratio of the mesopore volume to the total pore volume is 50% or more and 80% or less."

[0006] For example, Patent Document 3 describes a porous carbon material carrier for a polymer electrolyte fuel cell, characterized in that the pore volume and pore area determined by the BJH analysis method from the nitrogen adsorption isotherm during the adsorption process satisfy the following conditions: ＡThe pore area S of the pores is 1 ml / g or more and 5 ml / g or less, and the pore area S of the pores is 2 nm or more and 50 nm or less. ２－５０ is 300m ２ / g or more 1500m ２ / g or less, and the pore volume V Ａ (ml / g), the pore volume V of pores with a radius of 5 nm or more and 25 nm or less ５－２５ (ml / g) ratio (V ５－２５ / V Ａ ) is 0.4 or more and 0.7 or less, and the pore volume V ２－５ (ml / g) ratio (V ２－５ / V Ａ ) is 0.2 or more and 0.5 or less."

[0007] For example, Patent Document 4 discloses a carbon porous body, in which, in a nitrogen adsorption / desorption isotherm at a temperature of 77 K, a derivative curve of the nitrogen adsorption amount with respect to the relative pressure of the desorption isotherm includes a first peak apex in the relative pressure P / P range of 0.5 to 0.95 and a second peak apex at a relative pressure P / P higher than the first peak apex, and the carbon porous body has a first mesopore diameter region corresponding to the peak including the first peak apex, and a second mesopore diameter region larger than the first mesopore diameter region corresponding to the peak including the second peak apex.

[0008] For example, Patent Document 5 discloses "a porous conductive carbon material including graphene stacks (2) and having first and second pores (6, 8) within first and second different pore size ranges, respectively, wherein the first pores (6) are three-dimensionally irregularly shaped and interconnected to form migration paths through the carbon material and have sizes within the first pore size range of 10 μm to 100 nm, the second pores (8) are defined between adjacent graphene stacks (2), are three-dimensionally irregularly shaped and interconnected, and communicate directly or indirectly with the first pores via other second pores, and have sizes within the second pore size range of 3 nm or more and less than 100 nm, and the graphene stacks defining the second pores form wall material between the first pores (6)."

[0009] JP 2023-84551 A Japanese Patent No. 6071261 A International Publication No. 2016 / 152447 Japanese Patent No. 2018-30767 A Japanese Patent No. 5191483 A

[0010] When porous carbon materials are used as catalyst supports for fuel cell catalysts, including those in Prior Art 1 to 5, the challenge is to achieve both high levels of performance under low current conditions (low-load performance) and high current conditions (high-load performance). Porous carbon materials have fine pores of a few nanometers in size, which can confine catalytic metals (e.g., Pt particles) within the pores. This improves the utilization efficiency of the catalytic metal, thereby improving low-load performance. On the other hand, porous carbon materials with only fine pores of a few nanometers in size have low diffusivity of oxygen gas required for the reaction, resulting in insufficient high-load performance. Enlarging the pore diameter of a porous carbon material is expected to improve high-load performance by improving gas diffusivity, but coating the catalytic metal with a proton-conducting electrolyte material (e.g., ionomer) reduces activity and leads to a decrease in low-load performance. Thus, there is a current demand for porous carbon materials that can achieve both high levels of low-load performance and high-load performance.

[0011] Therefore, an object of the present disclosure is to provide a porous carbon material that can achieve both low-load performance and high-load performance in a fuel cell at a high level, a method for producing the same, a fuel cell catalyst, and a fuel cell.

[0012] The means for solving the problems include the following aspects: <1> In a pore size distribution obtained by analyzing a nitrogen adsorption isotherm by the BJH (Barrett-Joyner-Halenda) method, with the vertical axis representing dV / d (log D) and the horizontal axis representing pore diameter D, a first peak representing the maximum value of dV / d (log D) in the region where the pore diameter is 10 nm or less is in the pore diameter range of 2 to 6 nm, and a second peak representing the maximum value of dV / d (log D) in the region where the pore diameter is more than 10 nm is in the pore diameter range of 20 to 150 nm, and a pore volume VD of the pore diameters of 2 to 6 nm is ２－６ is 0.50 cm ３ / g or more. <2> The porous carbon material according to <1>, wherein the porous carbon material is a porous carbon material other than carbon black. <3> The porous carbon material according to <1> or <2>, wherein the porous carbon material is a template carbon material. <4> The porous carbon material according to any one of <1> to <3>, wherein in a pore size distribution obtained by analyzing a nitrogen adsorption isotherm by the BJH (Barrett-Joyner-Halenda) method, with the vertical axis representing dV / d (log D) and the horizontal axis representing pore diameter D, the peak value of a first peak, which is the maximum value of dV / d (log D) in a region where the pore diameter is 10 nm or less, is 1.2 or more. <5> The porous carbon material according to any one of <1> to <4>, wherein the second peak is in a pore diameter range of 20 to 100 nm. <6> The pore volume VD of pores with a diameter of 20 to 100 nm, which is obtained by analyzing a nitrogen adsorption isotherm using the BJH (Barrett-Joyner-Halenda) method. ２０－１００ is 0.30 cm ３ <7> The porous carbon material according to any one of <1> to <5>, wherein the pore volume VD ２－６ and the pore volume VD of the pore diameter of 20 to 100 nm ２０－１００ Ratio of VD ２－６ / VD ２０－１００is 0.5 to 2.0. <8> The porous carbon material according to any one of <1> to <7>, wherein the second peak is in a pore diameter range of 20 to 70 nm. <9> The porous carbon material according to any one of <1> to <8>, wherein one particle has pores with a pore diameter of 2 to 6 nm and pores with a pore diameter of 10 to 50 nm. <10> A fuel cell catalyst comprising the porous carbon material according to any one of <1> to <9> as a catalyst support. <11> A fuel cell comprising the fuel cell catalyst according to <10>. <12> A method for producing a porous carbon material, using as starting materials a carbon source containing succinic acid and a template source containing an aliphatic carboxylate of magnesium, comprising: a first step of heating the starting materials under an inert gas atmosphere to obtain a template-containing carbide; and a second step of removing the template from the template-containing carbide. <13> A method for producing a porous carbon material, comprising: a first step of heating a carbon source containing succinic acid and an aliphatic hydrocarbon compound satisfying requirement (A) and a template source containing an inorganic substance satisfying requirement (B) below as starting materials in an inert gas atmosphere to obtain a carbide containing a template; and a second step of removing the template from the carbide containing a template. (A) An aliphatic hydrocarbon compound other than succinic acid, which contains two or more carboxyl groups and has a structure in which at least two of the two or more carboxyl groups are separated by 2 to 4 carbon atoms. (B) At least one inorganic substance selected from oxides, carbonates, sulfates, and hydroxides of magnesium. <14> A method for producing a porous carbon material according to <12> or <13>, which comprises a third step of graphitizing the carbide from which the template has been removed at a temperature of 1600 to 2400°C.

[0013] According to the present disclosure, it is possible to provide a porous carbon material that can achieve both low load performance and high load performance in a fuel cell at a high level, a method for producing the same, a fuel cell catalyst, and a fuel cell.

[0014] 1A is a secondary electron image of the porous carbon material at a magnification of 25,000 times using a scanning transmission electron microscope, FIG. 1B is a secondary electron image of the porous carbon material at a magnification of 250,000 times using a scanning transmission electron microscope, and FIG. 1C is a bright-field transmission electron image of the porous carbon material at a magnification of 1,000,000 times using a scanning transmission electron microscope. It is a schematic diagram showing an example of the general configuration of a fuel cell according to the present disclosure. It is a pore size distribution, with the vertical axis representing dV / d (log D) and the horizontal axis representing the pore diameter D, obtained by analyzing the nitrogen adsorption isotherms of the pore morphologies of the porous carbon materials in Example 1, Example 5, and Comparative Example 1 and Comparative Example 3 using the BJH (Barrett-Joyner-Halenda) method.

[0015] An example of the present disclosure will be described below. In this disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when "greater than" or "less than" is added to the numerical values ​​before and after "to", the numerical range means a range that does not include these numerical values ​​as the lower or upper limit. In numerical ranges described in stages, the upper or lower limit stated in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. In numerical ranges, the upper or lower limit stated in a certain numerical range may be replaced with a value shown in the examples. The term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. A "combination of preferred embodiments" is a more preferred embodiment.

[0016] <Porous Carbon Material> The porous carbon material of the present disclosure has a pore size distribution, obtained by analyzing a nitrogen adsorption isotherm by the BJH (Barrett-Joyner-Halenda) method, with the vertical axis representing dV / d (log D) and the horizontal axis representing pore diameter D. In the distribution, a first peak, which is the maximum value of dV / d (log D) in the region where the pore diameter is 10 nm or less, is in the pore diameter range of 2 to 6 nm, and a second peak, which is the maximum value of dV / d (log D) in the region where the pore diameter is more than 10 nm, is in the pore diameter range of 20 to 150 nm. ２－６ is 0.50 cm ３ / g or more.

[0017] The porous carbon material of the present disclosure, due to the above-described configuration, can achieve both low-load performance and high-load performance in a fuel cell at a high level. The porous carbon material of the present disclosure was discovered based on the following findings.

[0018] The inventors conducted extensive research into porous carbon materials that achieve both high levels of low-load and high-load performance in fuel cells. As a result, the inventors discovered that: (1) in the pore size distribution, pore diameters of 10 nm or less have a significant impact on low-load performance, and in particular, pores with diameters in the range of 2 to 6 nm serve as catalytic metal support sites, sufficiently confine the catalytic metal, and achieve high catalytic metal utilization efficiency; (2) pore diameters of more than 10 nm have a significant impact on high-load performance, and in particular, pores with diameters in the range of 20 to 150 nm serve as oxygen gas diffusion paths, enhancing oxygen gas diffusivity; and (3) the presence of both of these pores can achieve both improved catalytic metal utilization efficiency and improved oxygen diffusivity. Furthermore, as described below, the inventors discovered that in a method for producing a porous carbon material by a template method, by selecting starting materials (i.e., a carbon source and a template source), a porous carbon material having both the above-mentioned fine pores and the above-mentioned coarse pores can be obtained.

[0019] Based on the above findings, the porous carbon material of the present disclosure has been found, which is capable of achieving both low load performance and high load performance in a fuel cell at a high level.

[0020] The porous carbon material of the present disclosure will be described in detail below.

[0021] (Pore Size Distribution Characteristics) In the porous carbon material of the present disclosure, in a pore size distribution obtained by analyzing a nitrogen adsorption isotherm by the BJH method, with the vertical axis representing dV / d (log D) and the horizontal axis representing pore diameter D, a first peak, which is the maximum value of dV / d (log D) in the region where the pore diameter is 10 nm or less, is present in a pore diameter range of 2 to 6 nm, and a second peak, which is the maximum value of dV / d (log D) in the region where the pore diameter is more than 10 nm, is present in a pore diameter range of 20 to 150 nm (preferably 20 to 100 nm, more preferably 20 to 70 nm).

[0022] If the first peak is located within a pore diameter range of less than 2 nm, the number of catalytic metal support sites will be reduced, resulting in poor low-load performance, whereas if the first peak is located within a pore diameter range of more than 6 nm, the catalytic metal will be covered by the electrolyte material, resulting in poor catalytic activity and poor low-load performance.

[0023] If the second peak is in the range of pore diameters less than 20 nm, the number of oxygen gas diffusion paths will be reduced, resulting in a decrease in oxygen gas diffusibility, and therefore a decrease in high-load performance. If the second peak is in the range of pore diameters greater than 150 nm, the pore distribution will be non-uniform, resulting in a decrease in oxygen gas diffusibility, and therefore a decrease in high-load performance. In addition, the mechanical strength of the porous carbon material will also decrease.

[0024] Therefore, by having a first peak in the pore diameter range of 2 to 6 nm and a second peak in the pore diameter range of 20 to 150 nm in the pore size distribution, it is possible to achieve both low-load performance and high-load performance at a high level. In particular, when the second peak is in the pore diameter range of 20 to 100 nm (preferably 20 to 70 nm), oxygen gas diffusibility increases, and high-load performance is likely to improve. This is because the pore distribution becomes more uniform.

[0025] (Peak value PD of the first peak １ｓｔIn the pore size distribution obtained by analyzing the nitrogen adsorption isotherm using the BJH (Barrett-Joyner-Halenda) method, with the vertical axis representing dV / d (log D) and the horizontal axis representing the pore diameter D, the peak value PD of the first peak is the maximum value of dV / d (log D) in the region where the pore diameter is 10 nm or less. １ｓｔ is preferably 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more. １ｓｔ When the value of the first peak is 1.2 or more, the distribution of the metal catalyst (e.g., Pt) supported on the porous carbon material is less likely to vary. As a result, the decrease in low-load performance is suppressed, and it becomes easier to achieve both low-load performance and high-load performance at a high level. However, although there is no particular upper limit to the peak value of the first peak, from the viewpoint of improving oxidation and wear resistance, it is preferably 4.0 or less, and more preferably 3.0 or less.

[0026] (pore volume VD ２－６ In the pore size distribution obtained by analyzing the nitrogen adsorption isotherm using the BJH method, the vertical axis is dV / d (log D) and the horizontal axis is the pore diameter D, and the pore volume VD of pores with a diameter of 2 to 6 nm is ２－６ is 0.50 cm ３ / g or more, and ３ / g or more is preferable, and 0.55 cm ３ / g or more is more preferable. ２－６ is 0.50 cm ３ If the pore volume VD is less than 1 / g, the number of catalytic metal supporting sites will be reduced, and the low load characteristics will be reduced. ２－６ However, from the viewpoint of oxidation and wear resistance, the pore volume VD ２－６ is 2.00 cm ３ / g or less is preferable, and 1.50 cm ３ / g or less is more preferable.

[0027] (pore volume VD ２０－１００ ) The pore volume VD of pores with diameters of 20 to 100 nm is determined by analyzing the nitrogen adsorption isotherm using the BJH method. ２０－１００ is 0.30 cm ３ / g or more is preferable, and 0.40 cm ３ / g or more is more preferable, and 0.45 cm３ / g or more is more preferable.

[0028] Pore ​​volume VD ２０－１００ is 0.50 cm ３ / g or more, the number of oxygen gas diffusion paths increases, oxygen gas diffusibility increases, and high load performance is easily improved. ２０－１００ However, from the viewpoint of preventing the catalyst layer from becoming thick, the pore volume VD ２０－１００ is 1.5 cm ３ / g or less is preferable, and 1.20 cm ３ / g or less is more preferable, and 1.00 cm ３ / g or less is more preferable.

[0029] (pore volume VD ２－６ / pore volume VD ２０－１００ In the pore size distribution obtained by analyzing the nitrogen adsorption isotherm using the BJH method, the vertical axis is dV / d (log D) and the horizontal axis is the pore diameter D, and the pore volume VD of pores with a diameter of 2 to 6 nm is ２－６ and the pore volume VD of pores with a diameter of 20 to 100 nm ２０－１００ Ratio of VD ２－６ / VD ２０－１００ is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.6 to 1.3. ２－６ / VD ２０－１００ When the ratio VD is within the above range, it is easy to secure a well-balanced catalyst metal support site and an oxygen gas diffusion path. As a result, it is easy to achieve both a high level of low load performance and a high level of high load performance. ２－６ / VD ２０－１００ is preferably in the above range.

[0030] <Measurement of pore size distribution and pore volume of porous carbon material> Pore size distribution and pore volume VD of porous carbon material ２－６ and pore volume VD ２０－１００The measurement method is as follows: The pore size distribution of the porous carbon material is measured using a nitrogen adsorption measurement device (Microtrac BEL "BELSORP MAX"). Specifically, the procedure is as follows: 20 to 50 mg of porous carbon material is weighed and placed in a dedicated standard sample tube, and then a dedicated standard glass rod is placed in the sample tube. This sample tube is attached to a pretreatment device (BEL PREP-vac II) and vacuum-dried at 90°C for at least one hour. The sample tube is then attached to the measurement device and the nitrogen gas adsorption isotherm is measured. The nitrogen gas adsorption measurement is performed at a measurement temperature of 77 K and within a relative pressure range of 0 to 0.995. The obtained nitrogen adsorption isotherm is analyzed using the BJH method using the software (BEL Master ver. 6.3.2.1) provided with the nitrogen adsorption measurement device to obtain the pore size distribution (BJH plot). The standard isotherm of carbon black is used for the analysis. The pore size distribution is a BJH plot on the adsorption side. The pore size distribution (BJH plot) uses a log differential pore volume distribution with the vertical axis representing the log differential pore volume dV / d (log D) and the horizontal axis representing the pore diameter D. Here, the log differential pore volume distribution dV / d (log D) is the value obtained by dividing the differential pore volume dV by the logarithmic difference value d (log D) of the pore diameter.

[0031] In the obtained pore size distribution (BJH plot), if a first peak, which is the maximum value of dV / d(logD) in the region where the pore diameter is 10 nm or less, exists in the pore diameter range of 2 to 6 nm, and if a second peak, which is the maximum value of dV / d(logD) in the region where the pore diameter is more than 10 nm, exists in the pore diameter range of 20 to 150 nm, it is determined that the necessary conditions of the present invention are satisfied (see FIG. 3). It is determined that the second peak exists in the pore diameter range of 20 to 100 nm, more preferably, and that the second peak exists in the pore diameter range of 20 to 70 nm, even more preferably. In other words, the requirements of the present disclosure are determined to be met when the first peak, which is the maximum value of dV / d(logD) in the region where the pore diameter is 10 nm or less, exists in the range of 2 nm to 6 nm, but not in the range of less than 2 nm or in the range of more than 6 nm to 10 nm, and the second peak, which is the maximum value of dV / d(logD) in the region where the pore diameter is greater than 10 nm, exists in the range of 20 nm to 150 nm, but not in the range of more than 10 nm to less than 20 nm or in the range of more than 150 nm. It is determined to be more preferable if the second peak, which is the maximum value of dV / d(logD) in the region where the pore diameter is greater than 10 nm, exists in the range of 20 nm to 100 nm, but not in the range of more than 10 nm to less than 20 nm or in the range of more than 100 nm. It is determined that it is more preferable if the second peak, which is the maximum value of dV / d(logD) in the region where the pore diameter is greater than 10 nm, exists in the range of 20 nm to 70 nm, rather than in the range of greater than 10 nm to less than 20 nm or greater than 70 nm.

[0032] In addition, from the obtained pore size distribution (BJH plot), the pore volume VD of pores with a diameter of 2 to 6 nm was ２－６ and the pore volume VD of pores with a diameter of 20 to 100 nm. ２０－１００ Specifically, each pore volume is calculated as follows. First, within the range of pore diameters for which the pore volume is to be calculated, a plot of cumulative pore volume is calculated under conditions where five or more points can be obtained by the BJH method. The pore volume VD of pores with diameters of 2 to 6 nm is calculated. ２－６is calculated from the difference between the cumulative pore volume of pores with a diameter of 2 nm or more and the cumulative pore volume of pores with a diameter of more than 6 nm. Similarly, the pore volume VD of pores with a diameter of 20 to 100 nm ２０－１００ is determined from the difference between the cumulative pore volume of pores with a diameter of 20 nm or more and the cumulative pore volume of pores with a diameter of more than 100 nm.

[0033] Then, from the obtained pore size distribution (BJH plot), the peak value PD of the first peak １ｓｔ Read.

[0034] In the pore size distribution (BJH plot) obtained by the BJH method, the plot of cumulative pore volume is discrete, and the range of pore diameters to be calculated may differ from the plot points of cumulative pore volume. In such cases, a linear function passing through two adjacent points is calculated, and the cumulative pore volume in the range of pore diameters to be calculated is approximately determined from the linear function.

[0035] (Pore Morphology) The porous carbon material of the present disclosure preferably has pores with a pore diameter of 2 to 6 nm and pores with a pore diameter of 10 to 50 nm per particle (see FIG. 1). The pores with a pore diameter of 2 to 6 nm serve as support sites for the catalytic metal, and the pores with a pore diameter of 10 to 50 nm serve as oxygen gas diffusion paths. Therefore, by having pores with a pore diameter of 2 to 6 nm and pores with a pore diameter of 10 to 50 nm per particle, it becomes easier to achieve both high levels of low-load performance and high-load performance.

[0036] (Determination of Presence or Absence of Pores with a Pore Diameter of 2 to 6 nm and Pores with a Pore Diameter of 10 to 50 nm) Whether or not the porous carbon material of the present disclosure has pores with a pore diameter of 2 to 6 nm and pores with a pore diameter of 10 to 50 nm in one particle is determined as follows.

[0037] First, the porous carbon material is observed using a scanning transmission electron microscope (SU9000 manufactured by Hitachi High-Tech) (hereinafter referred to as STEM). Specifically, the porous carbon material is dispersed on a microgrid for STEM observation (#10-1016 Microgrid NH-15 manufactured by STEM), and excess porous carbon material is removed with an air blower. The porous carbon material dispersed on the microgrid is then observed using the STEM. Here, the acceleration voltage is 30 kV, the emission current is 10 μA, and the working distance is −100 to 0 μm.

[0038] From the observation area of ​​the secondary electron image, one particle of porous carbon material is selected, the maximum magnification of which is 25,000 times or less, at which the entire particle can be observed (see FIG. 1(A)). The presence or absence of pores with a pore diameter of 10 to 50 nm is confirmed from the secondary electron image (see FIG. 1(B)), which is enlarged to 250,000 times so that one particle of porous carbon material occupies at least one-third of the area on the screen. If five or more pores with a pore diameter of 10 to 50 nm are confirmed in one particle of porous carbon material within the observation area, the particle is determined to have pores with a pore diameter of 10 to 50 nm.

[0039] Thereafter, the presence or absence of pores with diameters of 2 to 6 nm is confirmed from a bright-field transmission electron image (see FIG. 1(C)) magnified to 1,000,000 times to ensure that a region of 1 / 5 to 4 / 5 of the screen is occupied by a single particle of porous carbon material. When five or more pores with diameters of 2 to 6 nm surrounded by carbon walls are confirmed in a region within 10 nm from the edge of a particle of porous carbon material, it is determined that pores with diameters of 2 to 6 nm are present.

[0040] The above operation is performed on five randomly selected particles of a porous carbon material, and the presence or absence of pores with a pore diameter of 10 to 50 nm and pores with a pore diameter of 2 to 6 nm is confirmed. When it is determined that four or more particles of a porous carbon material "contain pores with a pore diameter of 2 to 6 nm," it is determined that "each particle of the porous carbon material has pores with a pore diameter of 2 to 6 nm." When it is determined that four or more particles of a porous carbon material "contain pores with a pore diameter of 10 to 50 nm," it is determined that "each particle of the porous carbon material has pores with a pore diameter of 10 to 50 nm." When it is determined that four or more particles of a porous carbon material "contain pores with a pore diameter of 2 to 6 nm" and "contain pores with a pore diameter of 10 to 50 nm," it is determined that "each particle of the porous carbon material has pores with a pore diameter of 2 to 6 nm and pores with a pore diameter of 10 to 50 nm."

[0041] (Types of porous carbon materials) Examples of the porous carbon materials of the present disclosure include template carbon materials, activated carbon, carbon black, etc. Among these, from the viewpoint of facilitating the attainment of the above-mentioned pore characteristics, the porous carbon materials of the present disclosure are preferably porous carbon materials other than carbon black, and template carbon materials are particularly preferred.

[0042] In particular, when carbon black is used, if the peak value of the first peak is adjusted to fall within the above range, the first peak will not be located in the pore diameter range of 2 to 6 nm. This is presumably due to the following reasons: When carbon black is used as a raw material, a porous carbon material can be obtained by performing an activation treatment. Specifically, carbon black is activated using an oxidizing gas to obtain a porous carbon material. Increasing the activation amount increases the pore volume of the carbon black. However, since the activation treatment also has the effect of expanding the pores, increasing the activation amount also increases the pore diameter. In particular, in activation treatment, activation proceeds from the particle surface, which is easily accessible to the gas. Therefore, increasing the activation amount to increase the pore volume preferentially activates the particle surface, which is more easily activated, resulting in an expansion of the pore diameter. Therefore, when carbon black is used as a raw material, if the activation amount is increased so that the peak value of the first peak falls within the above range, the pore diameter will expand, and the first peak will not be located in the pore diameter range of 2 to 6 nm.

[0043] Furthermore, carbon black has a small primary particle size, and a large proportion of the supported catalytic metal (e.g., Pt) is supported on the surface. As a result, the catalytic metal (e.g., Pt) on the carbon black surface is coated with the electrolyte material, resulting in a decrease in low-load performance. In contrast, templated carbon materials are porous carbon materials with a larger primary particle size than carbon black, and a smaller proportion of the supported catalytic metal (e.g., Pt) is supported on the surface. In addition, in activated carbon black, the electrolyte material may block the surface pores, inhibiting oxygen transport to platinum particles within the carbon black particles. In contrast, templated carbon particles generally have interconnected pores. Therefore, even if some pores are blocked by the electrolyte material, oxygen can be transported to platinum particles inside the templated carbon through other pores exposed on the surface. As a result, the catalytic metal (e.g., Pt) on the surface of the templated carbon material is less likely to be coated with the electrolyte material, and low-load performance is less likely to be reduced. Therefore, templated carbon materials are more likely to achieve both high levels of low-load performance and high-load performance compared to carbon black.

[0044] Here, the term "templated carbon material" refers to a porous carbon material obtained by forming a composite of carbon and a template (a substance other than carbon) from a mixture of a carbon source and a template source, and then removing the template. When observed with a scanning electron microscope (SEM), the templated carbon material has a structure in which irregularities on the order of several nanometers caused by pores are exposed on the surface of the carbon particles. When observed with a transmission electron microscope (TEM), the templated carbon material has a structure in which graphene on the order of several nanometers is randomly oriented. Thus, the templated carbon material is a porous carbon material having an irregularity on the order of several nanometers caused by pores exposed on the surface of the carbon particles, and a structure in which graphene on the order of several nanometers is randomly oriented. Note that the templated carbon material is a templated carbon material that does not have a dendritic structure, unlike porous carbon materials such as Escarbon ("ESCARBON MCND" by Nippon Steel Chemical & Material Co., Ltd.).

[0045] <Method for Producing Porous Carbon Material> Hereinafter, an example of a method for obtaining the porous carbon material of the present disclosure will be described.

[0046] A first aspect of the method for producing a porous carbon material according to the present disclosure includes a first step of using a carbon source containing succinic acid and a template source containing an aliphatic carboxylate of magnesium as starting materials, and heating the starting materials under an inert gas atmosphere to obtain a carbide containing the template; and a second step of removing the template from the carbide containing the template.

[0047] A second aspect of the method for producing a porous carbon material according to the present disclosure is a method for producing a porous carbon material, comprising: a first step of heating starting materials, including a carbon source containing succinic acid and an aliphatic hydrocarbon compound satisfying requirement (A), and a template source containing an inorganic substance satisfying requirement (B), in an inert gas atmosphere to obtain a carbide containing the template; and a second step of removing the template from the carbide containing the template. (A) An aliphatic hydrocarbon compound, excluding succinic acid, containing two or more carboxyl groups and having a structure in which at least two but not more than four carbon atoms are separated between at least two of the two or more carboxyl groups (hereinafter also referred to as a "specific structure"). (B) At least one inorganic substance selected from oxide, carbonate, sulfate, and hydroxide of magnesium.

[0048] In both the first and second aspects of the method for producing a porous carbon material of the present disclosure (hereinafter also simply referred to as the "method for producing a porous carbon material of the present disclosure"), the carbon source and template source as starting materials are selected as described above, thereby making it possible to obtain the porous carbon material of the present disclosure (particularly, the pore size distribution characteristics and the pore volume VD ２－６ A porous carbon material satisfying the above requirement can be obtained.

[0049] The method for producing a porous carbon material according to the present disclosure preferably includes a third step of graphitizing the carbide from which the template has been removed at a temperature of 1600 to 2400° C. The third step (i.e., graphitization) increases the crystallinity of the porous carbon material and improves its durability (oxidative wear resistance) at high potentials.

[0050] The method for producing the porous carbon material of the present disclosure will be described in detail below. (First Step) In the first step, a carbon source and a template source are used as starting materials, and the starting materials are heated in an inert gas atmosphere to obtain a carbide containing the template.

[0051] Here, in a first aspect, a carbon source containing succinic acid and a template source containing an aliphatic carboxylate of magnesium are applied. In the first aspect, the proportion of succinic acid in the carbon source is, for example, 90 mass % or more (preferably 95 mass % or more, more preferably 100 mass %). The proportion of the aliphatic carboxylate of magnesium in the template source is, for example, 90 mass % or more (preferably 95 mass % or more, more preferably 100 mass %). In the first aspect, by selecting the carbon source and the template source as described above in the above quantitative ratio, the porous carbon material of the present disclosure (particularly, the pore size distribution characteristics and the pore volume VD ２－６ This makes it easier to obtain a porous carbon material that satisfies the above requirements.

[0052] On the other hand, in the second aspect, a carbon source containing succinic acid and an aliphatic hydrocarbon compound satisfying requirement (A) and a template source containing an inorganic substance satisfying requirement (B) are applied. In particular, when either succinic acid or an aliphatic hydrocarbon compound satisfying requirement (A) is used alone as the carbon source, the porous carbon material of the present disclosure (particularly a porous carbon material satisfying the pore size distribution characteristics and pore volume VD2-6) cannot be obtained. Therefore, in the second aspect, succinic acid and an aliphatic hydrocarbon compound satisfying requirement (A) are used in combination as the carbon source. In the second aspect, the proportion of succinic acid and the aliphatic hydrocarbon compound satisfying requirement (A) in the carbon source is, for example, 90 mass% or more (preferably 95 mass% or more, more preferably 100 mass%). The mass ratio of succinic acid to the aliphatic hydrocarbon compound satisfying requirement (A) (succinic acid:aliphatic hydrocarbon compound satisfying requirement (A)) is preferably 5:1 to 1:5, more preferably 4:1 to 1:4, and even more preferably 2:1 to 1:2. In the second aspect, by selecting the carbon source and template source in the above-mentioned ratio, it is possible to obtain the porous carbon material of the present disclosure (particularly, the pore size distribution characteristics and the pore volume VD ２－６ This makes it easier to obtain a porous carbon material that satisfies the above requirements.

[0053] - Carbon Source - Succinic Acid - Either non-anhydrous or anhydrous succinic acid may be used.

[0054] Aliphatic hydrocarbon compounds satisfying requirement (A) are those having the above-described specific structure, excluding succinic acid. In the aliphatic hydrocarbon compounds satisfying requirement (A), two or more carboxyl groups are contained in one molecule.

[0055] In the specific structure, the number of carboxyl groups is two or more, but from the viewpoint of improving the carbon yield, it is preferably two to six, and more preferably two to four.

[0056] In the specific structure, the number of carbon atoms intervening between at least two of the two or more carboxyl groups is preferably 2 to 4, more preferably 2 to 3. Here, the number of carbon atoms intervening between the two carboxyl groups does not include the carbon atoms of the carboxyl groups, but refers to the number of carbon atoms connected in a linear chain between the two carboxyl groups. In other words, when carbon atoms are connected in a branched chain between the two carboxyl groups, the number of carbon atoms intervening between the two carboxyl groups does not include the number of carbon atoms in the branched chain. For example, when an isopropylene group is intervening between two carboxyl groups, the number of carbon atoms intervening between the two carboxyl groups is 2. Furthermore, when there are three or more carboxyl groups, at least one pair of two carboxyl groups among the three or more carboxyl groups should have 2 to 4 carbon atoms intervening between them. Furthermore, the hydrocarbon group having 2 to 4 carbon atoms intervening between the two carboxyl groups may be an unsaturated hydrocarbon group or a saturated hydrocarbon group.

[0057] In the specific structure, two or more carboxyl groups may form an anhydride, and two or more carboxyl groups may form an alkali metal salt.

[0058] The aliphatic hydrocarbon compound satisfying requirement (A) may be either a saturated aliphatic hydrocarbon compound or an unsaturated aliphatic hydrocarbon compound, so long as it has a specific structure, except for succinic acid. Furthermore, the aliphatic hydrocarbon compound may be any of linear, branched, and cyclic compounds, so long as it has a specific structure, except for succinic acid.

[0059] The number of carbon atoms in the aliphatic hydrocarbon compound satisfying requirement (A) is preferably 4 to 8, more preferably 4 to 7, and even more preferably 4 to 6. Here, the number of carbon atoms in the aliphatic hydrocarbon compound satisfying requirement (A) is the number of carbon atoms including the carbon atoms of the carboxyl group.

[0060] Among the aliphatic hydrocarbon compounds satisfying requirement (A), examples of the aliphatic hydrocarbon compounds having two carboxyl groups include glutaric acid, adipic acid, malic acid, 2-oxoglutaric acid, (1R,3S)-(+)-camphoric acid, (1S,3R)-(-)-camphoric acid, acetylenedicarboxylic acid, adamantanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, tetrahydrofuran-2,5-dicarboxylic acid, 2-butene-1,4-dicarboxylic acid, 1,2-cyclobutanedicarboxylic acid, 1,2-cyclopropanedicarboxylic acid (anhydride), 1,3-propanedicarboxylic acid (glutaric acid), L-glutamic acid, tartaric acid, itaconic acid, 3,3-dimethylglutaric acid (anhydride), (+)-camphoric acid (mercaptosuccinic acid), pentenedioic acid (Pent-2-ene-1,5-dioic acid), and the like. acid), glutaconic acid, fumaric acid, maleic acid, malic acid, citraconic acid (anhydride), aspartic acid, etc.

[0061] Examples of the aliphatic hydrocarbon compound having three carboxyl groups include citric acid, cis-aconitic acid, trans-aconitic acid, 1,2,3-propanetricarboxylic acid (tricaryl acid), 1,1,2-propanetricarboxylic acid, propanetricarboxylic acid, 1α,3α,5α-trimethylcyclohexane-1,3,5-tricarboxylic acid, 1,3,5-pentanetricarboxylic acid, cyclohexane-1,3,5-tricarboxylic acid, (1α,2α,4α)-1,2,4-cyclohexanetricarboxylic acid, 1,3,5-pentanetricarboxylic acid, 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid), and 2-methylcitric acid.

[0062] Examples of the aliphatic hydrocarbon compound having four or more carboxyl groups include mesobutane-1,2,3,4-tetracarboxylic acid and its anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic acid and its anhydride, 1,2,3,4-cyclobutanetetracarboxylic acid and its anhydride, cyclopropane-1,1,2,2-tetracarboxylic acid and its anhydride, 1,2,3,4-cyclopentanetetracarboxylic acid and its anhydride, adamantane-1,3,5,7-tetracarboxylic acid, and (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid.

[0063] Among these, the aliphatic hydrocarbon compound satisfying requirement (A) is preferably malic acid or citric acid.

[0064] -Template Source- --Aliphatic Carboxylate of Magnesium-- Examples of the aliphatic carboxylate of magnesium include magnesium aliphatic carboxylates having 1 to 8 carbon atoms (preferably 2 to 6). Here, the number of carbon atoms in the aliphatic carboxylate includes the number of carbon atoms in the carboxyl group.

[0065] Specific examples of magnesium aliphatic carboxylates include magnesium citrate, magnesium formate, magnesium acetate, magnesium succinate, magnesium malate, and magnesium propionate. Among these, magnesium citrate is preferred as the magnesium aliphatic carboxylate. The magnesium aliphatic carboxylate may be a hydrate of the magnesium aliphatic carboxylate.

[0066] --Inorganic substance satisfying requirement (B)-- The inorganic substance satisfying requirement (B) is at least one inorganic substance selected from oxide, carbonate, sulfate, and hydroxide of magnesium. Specifically, the inorganic substance satisfying requirement (B) is at least one inorganic substance selected from magnesium oxide, magnesium carbonate, magnesium sulfate, magnesium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide, etc. Note that magnesium hydroxide carbonate (basic magnesium carbonate) is also an example of an inorganic substance satisfying requirement (B). Among these, magnesium hydroxide carbonate or magnesium oxide is preferred as the inorganic substance satisfying requirement (B).

[0067] -Mixing ratio of carbon source and template source-

[0068] The mixing ratio of the carbon source and the template source (template source / carbon source), expressed as the molar ratio C / M of magnesium in the template source to carbon C in the carbon source, is preferably 0.1 to 10.0, more preferably 0.2 to 5.0. By controlling the mixing ratio, the porous carbon material (particularly the pore size distribution characteristics and pore volume VD ２－６ This makes it easier to obtain a porous carbon material that satisfies the above requirements.

[0069] -Conditions for the First Step- In the first step, the starting material is heated, for example, in an inert gas atmosphere at a rate of 5 to 30°C / min up to 800 to 1100°C and maintained at that temperature for 10 to 200 minutes. This heat treatment thermally decomposes and oxidizes the template source in parallel with the carbonization of the carbon source, yielding a composite of carbon and the template (i.e., magnesium oxide). For example, in the case of magnesium sulfate, to decompose it to magnesium oxide, it is recommended to heat it to 800°C or higher, preferably 900°C or higher, and more preferably 950°C or higher. Thus, the heating temperature must be set to a temperature equal to or higher than the minimum temperature required to decompose the template source to its oxide. There is no particular upper limit to the heating temperature, as long as it is equal to or lower than the temperature at which metal carbide is formed. Typically, the upper limit of 1100°C is set, which is the upper limit for inexpensive electric furnaces. However, if there are no limitations on the electric furnace, it is possible to heat it to, for example, around 1700°C.

[0070] (Second Step) In the second step, the mold is removed from the carbide containing the mold. In the second step, for example, the carbide containing the mold is pickled to dissolve the mold in the pickling solution. This removes the mold from the carbide containing the mold. The acid used for pickling may be any acid as long as it dissolves the mold, and a preferred example is sulfuric acid. After pickling, the carbide is washed with water and dried.

[0071] (Third Step) In the third step, the carbide from which the template has been removed is graphitized at a temperature of 1600 to 2400°C. In the third step, the carbide from which the template has been removed is graphitized under conditions such as holding the carbide in an inert gas atmosphere at a temperature of 1600 to 2400°C for 0.5 to 3.0 hours. The graphitization treatment increases the crystallinity of the porous carbon material and improves its durability at high temperatures (oxidation wear resistance).

[0072] When the porous carbon material of the present disclosure is applied to an application that does not require enhanced crystallinity, the third step may be omitted and the second step may be the final step.

[0073] Through the above steps, the desired porous carbon material of the present disclosure can be obtained.

[0074] (Applications) The porous carbon material and the method for producing the same according to the present disclosure are applicable to fields in which a carbon material called activated carbon is used (for example, the field of adsorbents for selectively adsorbing specific gases and molecules having a characteristic structure in a liquid phase), the field of catalyst supports for fuel cells (particularly solid polymer fuel cells) in which Ketjen black is used, the field of electrodes for supercapacitors, and the field of lithium ion batteries (particularly lithium-sulfur batteries and lithium-air batteries).

[0075] <Fuel Cell Catalyst and Fuel Cell> The fuel cell catalyst of the present disclosure includes the porous carbon material of the present disclosure as a catalyst support, and the fuel cell of the present disclosure includes the fuel cell catalyst of the present disclosure.

[0076] The fuel cell will be described below together with the fuel cell catalyst of the present disclosure. Fig. 2 is a schematic diagram showing an example of the general configuration of the fuel cell of the present disclosure. The porous carbon material of the present disclosure can be applied to, for example, catalyst layers 150 and 160 provided in the polymer electrolyte fuel cell 100 shown in Fig. 2.

[0077] The polymer electrolyte fuel cell 100 shown in FIG. 2 includes separators 110 and 120 , gas diffusion layers 130 and 140 , catalyst layers 150 and 160 , and an electrolyte membrane 170 .

[0078] Separator 110 is an anode-side separator that introduces a reducing gas such as hydrogen into gas diffusion layer 130. Separator 120 is a cathode-side separator that introduces an oxidizing gas such as oxygen gas or air into gas diffusion layer 140. There are no particular limitations on the type of separators 110 and 120, and they may be any separators that are used in conventional fuel cells (e.g., solid polymer fuel cells).

[0079] The gas diffusion layer 130 is an anode-side gas diffusion layer that diffuses the reducing gas supplied from the separator 110 and then supplies the gas to the catalyst layer 150. The gas diffusion layer 140 is a cathode-side gas diffusion layer that diffuses the oxidizing gas supplied from the separator 120 and then supplies the gas to the catalyst layer 160. The type of gas diffusion layers 130 and 140 is not particularly limited, and they may be any gas diffusion layer used in conventional fuel cells (e.g., polymer electrolyte fuel cells). Examples of the 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 the gas diffusion layers 130 and 140 is a gas diffusion layer with a two-layer structure. Specifically, the gas diffusion layers 130 and 140 have a two-layer structure in which the layer on the separator 110 or 120 side is a gas diffusion fiber layer mainly composed of a fibrous carbon material, and the layer on the catalyst layer 150 or 160 side is a micropore layer mainly composed of carbon black.

[0080] The catalyst layer 150 is a so-called anode. In the catalyst layer 150, an oxidation reaction of the reducing gas occurs, producing protons and electrons. For example, when the reducing gas becomes hydrogen gas, the following oxidation reaction occurs: H ２ →2H ＋ +2e － (E ０ = 0 V)

[0081] Protons produced by the oxidation reaction pass through the catalyst layer 150 and electrolyte membrane 170 to reach the catalyst layer 160. Electrons produced by the oxidation reaction pass through the catalyst layer 150, gas diffusion layer 130, and separator 110 to reach the external circuit. The electrons perform work (generate electricity) in the external circuit and then enter the separator 120. The electrons then pass through the separator 120 and gas diffusion layer 140 to reach the catalyst layer 160.

[0082] There are no particular limitations on the configuration of the catalyst layer 150 that serves as the anode. 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 a configuration that is more hydrophilic than the catalyst layer 160.

[0083] The catalyst layer 160 is a so-called cathode. Within the catalyst layer 160, a reduction reaction of the oxidizing gas occurs, producing water. For example, when the oxidizing gas becomes oxygen gas or air, the following reduction reaction occurs. The water produced by the oxidation reaction is discharged to the outside of the polymer electrolyte fuel cell 100 together with the unreacted oxidizing gas. ２ +4H ＋ +4e － →2H ２ O (E ０ = 1.23 V)

[0084] In this way, the energy difference (potential difference) between the oxidation reaction and the reduction reaction is utilized to generate electricity in the polymer electrolyte fuel cell 100. In other words, the electrons generated in the oxidation reaction perform work in an external circuit.

[0085] The catalyst layer 160 contains the catalyst support carbon material of the present disclosure. That is, the catalyst layer 160 contains the porous carbon material of the present disclosure, an electrolyte material (ionomer), and a catalyst component (platinum, etc.).

[0086] 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. A catalyst loading rate within this range further enhances durability and low-load characteristics. Here, the catalyst loading rate is expressed as the mass percentage of catalyst metal relative to the total mass of catalyst-loaded particles (particles in which catalyst metal is loaded on a porous 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 to ensure practical use of the polymer electrolyte fuel cell 100. On the other hand, if the catalyst loading rate is 80% by mass or more, catalyst aggregation is likely to occur. Furthermore, if the catalyst layer 160 becomes too thin, flooding may occur.

[0087] The mass ratio I / C of the mass I of the electrolyte material in the catalyst layer 160 to the mass C of the porous carbon material for the catalyst support is not particularly limited, but is preferably greater than 0.5 and less than 5.0. In this case, both a pore network and an electrolyte material network can be achieved. On the other hand, if the mass ratio I / C is 0.5 or less, the electrolyte material network tends to be weak and the proton conduction resistance tends to be high. If the mass ratio I / C is 5.0 or more, the pore network may be disrupted by the electrolyte material.

[0088] Furthermore, the thickness of the catalyst layer 160 is not particularly limited, and is preferably more than 5 μm and less than 20 μm. In this case, oxidizing gas is more likely to diffuse within 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 gas is less likely to diffuse within the catalyst layer 160, and the catalytic metal near the electrolyte membrane 170 becomes less effective. In other words, there is a possibility that the catalyst utilization rate will decrease.

[0089] The electrolyte membrane 170 is composed of a proton-conducting electrolyte material. The electrolyte membrane 170 introduces protons generated in the oxidation reaction to the catalyst layer 160 (cathode). The type of electrolyte material is not particularly limited, and any electrolyte material used in conventional fuel cells, such as solid polymer fuel cells, may be used. An example of a suitable electrolyte material is an electrolyte resin. Examples of electrolyte resins include polymers with phosphate groups, sulfonic acid groups, etc. Specific examples include perfluorosulfonic acid polymers and polymers with benzenesulfonic acid, etc. Of course, other types of electrolyte materials may also be used. Examples of such electrolyte materials include inorganic and inorganic-organic hybrid electrolyte materials. The solid polymer fuel cell 100 may be a fuel cell that operates within a temperature range from room temperature (25°C) to 150°C.

[0090] <Method of manufacturing fuel cell> The method of manufacturing the fuel cell 100 is not particularly limited, and may be the same as conventional manufacturing methods. However, the porous carbon material of the present disclosure is used for the catalyst support. Of the catalyst layers 150 and 160, it is preferable to use the porous carbon material of the present disclosure for the catalyst support of at least the catalyst layer 160 that serves as the cathode. Of course, the porous carbon material of the present disclosure may also be used for the catalyst supports of both the catalyst layer 150 that serves as the anode and the catalyst layer 160 that serves as the cathode.

[0091] Examples of the present disclosure are described below. However, the present disclosure is not limited to the examples. Example 1 A porous carbon material was synthesized by the "template method" as follows. First, trimagnesium dicitrate nonahydrate (manufactured by Tokyo Chemical Industry Co., Ltd.) as a template source and succinic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a carbon source were mixed in a mortar at a mass ratio of 7:3 to obtain a starting material. Next, the starting material was heated and fired at 900°C for 1 hour in a tubular furnace under Ar flow to obtain a powder (carbide containing a template) in which carbon grew on the surface of the template (magnesium oxide). The temperature increase rate was 20°C / min. Next, the powder was dispersed in sulfuric acid with a concentration of 20 mass% and stirred in an oil bath at 90°C for 40 hours or more. This dissolved and removed the template (magnesium oxide) from the powder. The powder was then collected by suction filtration and vacuum dried at 90°C for 24 hours or more to obtain carbon powder (carbide from which the template had been removed). The carbon powder was graphitized at 2000°C for 1 hour in an Ar atmosphere. Through the above steps, a porous carbon material was obtained.

[0092] Example 2 A porous carbon material was obtained in the same manner as in Example 1, except that the temperature rise rate during heating and firing in a tubular furnace under an Ar flow was set to 10° C. / min.

[0093] Example 3 A porous carbon material was obtained in the same manner as in Example 1, except that the temperature rise rate during heating and firing in a tubular furnace under an Ar flow was set to 5° C. / min.

[0094] Example 4 A porous carbon material was obtained in the same manner as in Example 1, except that the mass ratio of trimagnesium dicitrate nonahydrate as the template source to succinic acid as the carbon source was 4:6.

[0095] Example 5 A porous carbon material was obtained in the same manner as in Example 3, except that basic magnesium carbonate (FUJIFILM Wako Pure Chemical Industries, Ltd.) as a template source, malic acid (FUJIFILM Wako Pure Chemical Industries, Ltd.) as a carbon source, and succinic acid as a carbon source were mixed in a mass ratio of 4:3:3, and the resulting mixture was used as a starting material.

[0096] Comparative Example 1 A commercially available porous carbon material ("Cnovel-MH" manufactured by Toyo Tanso Co., Ltd.) was prepared and graphitized at 2000°C for 1 hour in an Ar atmosphere to obtain a porous carbon material of Comparative Example 1.

[0097] Comparative Example 2 A commercially available porous carbon material (Ketjenblack EC300J manufactured by Lion Corporation) was used as the porous carbon material of Comparative Example 2.

[0098] Comparative Example 3 A porous carbon material was obtained in the same manner as in Example 1, except that basic magnesium carbonate as a template source and malic acid as a carbon source were mixed at a mass ratio of 8:2, and the resulting mixture was used as a starting material.

[0099] Comparative Example 4 A porous carbon material was obtained in the same manner as in Example 1, except that basic magnesium carbonate as a template source and succinic acid as a carbon source were mixed at a mass ratio of 8:2, and the resulting mixture was used as a starting material.

[0100] <Confirmation of whether or not particles of one porous carbon material have "pores with a pore diameter of 2 to 6 nm" and "pores with a pore diameter of 10 to 50 nm"> For each porous carbon material example, it was confirmed by the method described above whether or not particles of one porous carbon material have "pores with a pore diameter of 2 to 6 nm" and "pores with a pore diameter of 10 to 50 nm". When particles of one porous carbon material have "pores with a pore diameter of 2 to 6 nm" and "pores with a pore diameter of 10 to 50 nm", they are each indicated as "Y" in Table 1. On the other hand, when particles of one porous carbon material do not have "pores with a pore diameter of 2 to 6 nm" and "pores with a pore diameter of 10 to 50 nm", they are each indicated as "N" in Table 1.

[0101] <Measurement of pore size distribution and pore volume of porous carbon material> The pore size distribution (pore diameters of the first peak and the second peak, and the peak value of the first peak) and the pore volume VD of the porous carbon material of each example were measured. ２－６ and pore volume VD ２０－１００ The pore size distributions were measured according to the method described above. The pore size distributions measured in Examples 1 and 5, and Comparative Examples 1 and 3 are shown in FIG.

[0102] <Fabrication of fuel cell / power generation performance evaluation test> Using the porous carbon material of each example as a catalyst support, a fuel cell was fabricated as follows, and a power generation performance evaluation test was carried out.

[0103] (Preparation of Catalyst-Supported Carbon Materials) A carbon material dispersion was prepared by dispersing each porous carbon material in distilled water. Formaldehyde was then added to the carbon material dispersion, and the mixture was placed in a water bath set at 40°C. The temperature of the carbon material dispersion was then allowed to reach 40°C, the same temperature as the bath. Then, while stirring the carbon material dispersion, the dinitrodiamine platinum complex nitric acid aqueous solution was slowly poured into the carbon material dispersion. After stirring for approximately two hours, the carbon material dispersion was filtered, and the resulting solid was washed. The resulting solid was vacuum dried at 90°C and then pulverized in a mortar. The solid was then heat-treated at 200°C for one hour in an argon atmosphere containing 5% hydrogen by volume. This resulted in the preparation of a catalyst-supported carbon material in which platinum was supported on a porous carbon material. The platinum loading in the catalyst-supported carbon material was 40% by mass relative to the total mass of the porous carbon material and platinum.

[0104] (Preparation of Catalyst Layer) A Nafion solution containing dissolved Nafion (manufactured by DuPont, registered trademark: Nafion, a persulfonic acid-based ion exchange resin) as the electrolyte resin was prepared. Next, a catalyst-supported carbon material and the Nafion solution were mixed under an argon atmosphere. The mixed solution was then gently stirred, and the catalyst-supported carbon material in the mixed solution was crushed using ultrasound. Ethanol was then further added to the mixed solution to adjust the total solids concentration of the catalyst-supported carbon material and the electrolyte resin to 1.0 mass% relative to the total mass of the mixture. This resulted in the preparation of a coating ink containing a catalyst-supported carbon material and an electrolyte resin. Further ethanol was then added to the coating ink to adjust the catalyst concentration (concentration of the fuel cell catalyst) in the coating ink to 1.0 mass% relative to the total mass of the coating ink. Next, the mass per unit area of ​​the catalyst layer (hereinafter referred to as "catalyst coverage") to 0.2 mg / cm ２The spray conditions were adjusted so that the ink was sprayed onto a Teflon sheet. A drying treatment was then carried out at 120°C for 60 minutes under an argon atmosphere to produce a catalyst layer. Two identical catalyst layers were produced, one serving as the cathode and the other as the anode.

[0105] (Preparation of Membrane Electrode Assembly (MEA)) An electrolyte membrane was cut out from a Nafion membrane ("NR211" manufactured by DuPont) in the shape of a square with a side of 6 cm. Furthermore, each of the anode and cathode catalyst layers coated on a Teflon (registered trademark) sheet was cut out into a square with a side of 2.5 cm using a cutter knife. The electrolyte membrane was sandwiched between the anode and cathode catalyst layers cut out in this way so that the catalyst layers were in contact with each other with the center of the electrolyte membrane sandwiched between them and there was no misalignment between them. The MEA was then heated at 120°C and 100 kg / cm. ２ The laminate was pressed at 100°C for 10 minutes. The resulting laminate was then cooled to room temperature (25°C). The Teflon (registered trademark) sheets were then carefully peeled off from the anode and cathode catalyst layers. Through these steps, the anode and cathode catalyst layers were fixed to the electrolyte membrane.

[0106] Next, two square carbon paper pieces with sides of 2.5 cm each were cut out from carbon paper (35BC manufactured by SGL Carbon Co., Ltd.) that would become the gas diffusion layer. Next, these carbon papers were stacked on the anode and cathode catalyst layers without misalignment to produce a laminate. Next, the obtained laminate was heated at 120°C and 50 kg / cm ２ The mixture was pressed at 100° C. for 10 minutes to prepare an MEA.

[0107] The mass of the catalyst layer fixed to the Nafion membrane was calculated from the difference between the weight of the Teflon® sheet with the catalyst layer before pressing and the mass of the Teflon® sheet peeled off after pressing, and the catalyst basis weight, catalyst support carbon material basis weight, and electrolyte resin basis weight were calculated from the mass ratio of the catalyst layer composition. By this method, the catalyst basis weight was determined to be 0.2 mg / cm ２ It was confirmed that this is the case.

[0108] (Power Generation Performance Evaluation Test) The fabricated MEAs were each incorporated into a cell, and the power generation performance of the fuel cell was evaluated using a fuel cell measurement device. Air was supplied to the cathode and pure hydrogen to the anode under atmospheric pressure so that the utilization rates were 40% and 70%, respectively. The cell temperature was set to 80°C. In addition, the air and pure hydrogen supplied to the fuel cell were humidified by passing them through distilled water kept at 65°C in a humidifier (i.e., bubbling). In other words, these gases were made to contain water vapor equivalent to the reformed hydrogen. The humidified gas was then supplied to the cell. After supplying the gas to the cell under these conditions, the current value was measured at 5 mA / cm every second. ２ The current is increased by 100mA / cm ２ The cell terminal voltage at 0.3 V was defined as low load performance, and the current value when the terminal voltage dropped to 0.3 V was defined as high load performance, and a power generation performance evaluation test of the fuel cell was carried out.

[0109] The results of the fuel cell power generation performance evaluation test are shown in Table 1. Here, the MEAs were fabricated by changing the mass ratio of the electrolyte resin solid content to the catalyst-supported carbon material in increments of 0.1 within a range of 0.8 to 2.0 times in the preparation of the catalyst layer. The results of the fuel cell power generation performance evaluation test shown in Table 1 indicate the value at the level at which the highest high-load performance was obtained among the test results of MEAs fabricated by changing the mass ratio of the electrolyte resin solid content in the preparation of the catalyst layer, at levels at which low-load performance of 0.875 V or more was obtained. For test examples in which low-load performance of 0.875 V or more was not obtained, the value at the level at which the highest low-load performance was obtained is shown.

[0110]

[0111] From the above results, it can be seen that the porous carbon materials of the present examples can achieve both low-load performance and high-load performance in fuel cells at a high level compared to the porous carbon materials of the comparative examples. In particular, Examples 1 to 5 have a first peak and a second peak in the pore size distribution, a pore volume larger than a predetermined value, and pore morphologies of 2 to 6 nm pores and 10 to 50 nm pores, so it can be seen that both low-load performance and high-load performance can be achieved at a high level. Comparative Examples 1 and 3 have a high level of low-load performance, but VD ２０－１００In Comparative Examples 2 and 4, the high load performance was high, but the VD ２－６ Since is small, it can be seen that the low load performance is at a low level.

[0112] The symbols are explained as follows: 100: polymer electrolyte fuel cell 110, 120: separator 130, 140: gas diffusion layer 150, 160: catalyst layer 170: electrolyte membrane

[0113] The disclosure of Japanese Patent Application No. 2024-147916 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 was specifically and individually indicated to be incorporated by reference.

Claims

1. In a pore size distribution obtained by analyzing a nitrogen adsorption isotherm using the BJH (Barrett-Joyner-Halenda) method, with the vertical axis representing dV / d (log D) and the horizontal axis representing pore diameter D, a first peak representing the maximum value of dV / d (log D) in the region where the pore diameter is 10 nm or less is in the pore diameter range of 2 to 6 nm, and a second peak representing the maximum value of dV / d (log D) in the region where the pore diameter is more than 10 nm is in the pore diameter range of 20 to 150 nm, and a pore volume VD of pore diameters of 2 to 6 nm is ２－６ is 0.50 cm ３ / g or more.

2. The porous carbon material according to claim 1, wherein the porous carbon material is a porous carbon material other than carbon black.

3. The porous carbon material according to claim 1, wherein the porous carbon material is a template carbon material.

4. The porous carbon material according to claim 1, wherein in a pore size distribution obtained by analyzing a nitrogen adsorption isotherm using the BJH (Barrett-Joyner-Halenda) method, with the vertical axis representing dV / d (log D) and the horizontal axis representing pore diameter D, the peak value of a first peak, which is the maximum value of dV / d (log D) in a region where the pore diameter is 10 nm or less, is 1.2 or more.

5. The porous carbon material according to claim 4, wherein the second peak is present in the pore diameter range of 20 to 100 nm.

6. The pore volume VD of pores with diameters of 20 to 100 nm, determined by analyzing the nitrogen adsorption isotherm using the BJH (Barrett-Joyner-Halenda) method. ２０－１００ is 0.30 cm ３ The porous carbon material according to claim 5, wherein the molecular weight is 1 / g or more.

7. The pore volume VD of the pore diameter of 2 to 6 nm ２－６ and the pore volume VD of the pore diameter of 20 to 100 nm ２０－１００ Ratio of VD ２－６ / VD ２０－１００ The porous carbon material according to claim 6, wherein is 0.5 to 2.

0.

8. The porous carbon material according to claim 4, wherein the second peak is present in the pore diameter range of 20 to 70 nm.

9. The porous carbon material according to claim 4, wherein each particle has pores with a pore diameter of 2 to 6 nm and pores with a pore diameter of 10 to 50 nm.

10. A catalyst for a fuel cell, comprising the porous carbon material according to any one of claims 1 to 9 as a catalyst support.

11. A fuel cell comprising the fuel cell catalyst according to claim 10.

12. A method for producing a porous carbon material, comprising: a first step of using as starting materials a carbon source containing succinic acid and a template source containing an aliphatic carboxylate of magnesium, heating the starting materials in an inert gas atmosphere to obtain a carbide containing a template; and a second step of removing the template from the carbide containing the template.

13. A method for producing a porous carbon material, comprising: a first step of heating a carbon source containing succinic acid and an aliphatic hydrocarbon compound satisfying requirement (A) and a template source containing an inorganic substance satisfying requirement (B) below as starting materials in an inert gas atmosphere to obtain a carbide containing a template; and a second step of removing the template from the carbide containing a template. (A) An aliphatic hydrocarbon compound, excluding succinic acid, containing two or more carboxyl groups and having a structure in which at least two of the two or more carboxyl groups are separated by 2 to 4 carbon atoms. (B) At least one inorganic substance selected from oxide, carbonate, sulfate, and hydroxide of magnesium.

14. A method for producing a porous carbon material according to claim 12 or 13, further comprising a third step of graphitizing the carbide from which the template has been removed at a temperature of 1600 to 2400°C.

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