JP7759782B2 - Method for manufacturing template carbon material, method for manufacturing catalyst, method for manufacturing catalyst layer for polymer electrolyte fuel cell, and method for manufacturing fuel cell - Google Patents

Description

This disclosure relates to a method for producing a template carbon material, a method for producing a catalyst, a method for producing a catalyst layer for a polymer electrolyte fuel cell, and a method for producing a fuel cell.

Template carbon materials are carbon materials characterized by the shape in which the shape of the template is inverted by coating the surface of a compound that serves as a template with carbon and then removing the template component.
A method for producing a template carbon material is a process in which a general-purpose resin, such as polyvinyl alcohol, is used as a carbon source, and a compound of an alkaline earth metal, such as magnesium oxide, is used as a template source, and these are thoroughly mixed together. The mixture is then heat-treated at 600°C to 1500°C in a non-oxidizing atmosphere, and the template source is then dissolved and removed with an acid, or in some other way, to carbonize the carbon source and remove the template source.
Magnesium oxide and calcium oxide can be easily dissolved in hydrochloric acid, sulfuric acid, etc., and therefore template carbon materials using these compounds as template sources are often investigated.

In addition, since the carbon coating process typically involves heat treatment at temperatures between 600°C and 1500°C, it is possible to use compounds (e.g., carbonates, hydroxides, sulfates, etc.) that chemically change to magnesium oxide or calcium oxide during the heat treatment process as the template source.

The temperature of the heat treatment for carbon coating is selected depending on the purpose. For example, if a highly amorphous porous carbon material containing a large amount of functional groups is to be prepared, a temperature of 600°C to 900°C is selected. If a highly crystalline porous carbon material is to be obtained, the temperature is higher than 1000°C.
However, it is necessary to avoid high-temperature treatment that involves the formation of carbides such as calcium carbide or metal acetylides. In practice, the heat treatment temperature for carbon coating is limited to about 1800°C.

Templated carbon materials are classified as one type of porous carbon material that corresponds to porous carbon materials (such as activated carbon) produced by a so-called activation method.
The structural feature of templated carbon materials is that, while the pores of activated porous carbon materials grow from the outside toward the inside through oxidative attrition, the pore structure of templated carbon materials is essentially homogeneous within the material, although the outermost surface is affected by the manufacturing method, etc., and the pores are generally isotropically connected. This is a structural feature of templated carbon materials that is particularly in contrast to the pore structure of activated porous carbon materials.

Templated carbon materials with isotropic interconnected pores are sometimes referred to as interconnected pores in the field of polymer electrolyte fuel cells. The good gas flow (fast diffusion) within the material is believed to improve power generation performance when used as a catalyst support, and they are considered to be promising materials.
Furthermore, in principle, templated carbon materials can produce pores that are an inverse copy of the template, making it possible to obtain highly uniform pore structures ranging from micropores to tens of nanometers in size, in contrast to the pores formed by activation methods, which are inevitably distributed widely from micropores to mesopores.

The thickness of the carbon layer in template carbon materials can be freely controlled by changing the mixture ratio of the template source and carbon source, allowing for a high degree of freedom in the specific surface area per mass.

Since template carbon materials are porous carbon materials, they are applicable to fields in which carbon materials known as activated carbons are used (for example, in the field of adsorbents for selective adsorption of specific gases or molecules with specific structures in a liquid phase), fields as catalyst supports for solid polymer fuel cells in which Ketjen black is used, and fields as electrodes for supercapacitors.
One area that seems to be unique to templated carbon materials is their use in taking advantage of the high diffusivity within the material, which is achieved by taking advantage of the interconnected isotropic pores.

For example, it has been reported that a porous carbon material consisting only of micropores using zeolite as a template can achieve an astonishing surface area of 4000 m ² /g by selecting the type of template and optimizing the conditions for coating the inside of the pores with carbon using CVD with propylene gas as the raw material (Non-Patent Document 1).
Since the pore diameter is on the order of a few tenths of a nanometer at the atomic level, the carbon coating wall is formed of a monoatomic layer, and the pore wall contains five-membered rings, seven-membered rings, etc. to maintain the curvature.
Therefore, as mentioned above, the pore volume and pore surface area per mass are large, but on the other hand, the carbon structure with curvature tends to be inferior in mechanical strength and chemical stability compared to aromatic structures.

On the other hand, a method for producing templated carbon materials is also known in which magnesium citrate is heat-treated at 900°C for 1 hour in a nitrogen atmosphere, the resulting MgO powder is mixed with polyvinyl alcohol powder, and then the mixture is heated at 900°C for 1 hour in a nitrogen atmosphere (Non-Patent Document 2).

Another known method for producing activated carbon involves heating organic acid magnesium with a carbon number of 6 or more to 300°C or higher in an inert atmosphere, followed by cooling and acid washing (Patent Document 1). This method uses citric acid and polyvinyl alcohol (PVA) as carbon sources.

Also known is a method for producing activated carbon that includes mixing an organic resin with at least one alkaline earth metal compound selected from the group consisting of alkaline earth metal oxides, hydroxides, carbonates, and organic acid salts, and then heating and firing the mixture in a non-oxidizing atmosphere, in which the pore size of the activated carbon is adjusted depending on the crystallite size of the alkaline earth metal oxide produced after firing and carbonization (Patent Document 2). In this method for producing activated carbon, resin materials such as polyvinyl alcohol (PVA), polyethylene terephthalate (PET), and hydroxypropyl cellulose (HPC) are used as carbon sources.

A method for producing porous carbon materials is also known in which alumina nanoparticles (commercially available, with an average crystallite size of 10 nm) are subjected to thermal CVD treatment using methane as a carbon source gas (Patent Document 3). In this method, experimental conditions such as the heat treatment temperature, gas concentration, and treatment time are thoroughly optimized to obtain alumina nanoparticles coated with a carbon film with two or fewer carbon layers. The alumina is then dissolved in a hydrofluoric acid solution, diluted with distilled water, filtered, dispersed again in distilled water, filtered, and the resulting powder is vacuum-dried to obtain porous carbon.

Japanese Patent Application Laid-Open No. 2008-013394 Patent No. 4955952 JP 2015-164889 A

Formation of new type of porous carbon by carbonization in zeolite nanochannels, Chemistry of materials, 2, 609-615(1997) A review of the controle of pore structure in MgO-templated nanoporous carbons, Carbon, 48, 2690-2707(2010))

In the above-mentioned examples, for example, in the case of carbon materials using zeolite as a template, the zeolite used as the template itself has a molecular sieve function, i.e., the pore diameter is on the order of several angstroms, and therefore the thickness of the carbon covering the pores is also 1 nm or less per atomic layer, so that a synthesis method using a gas phase method such as CVD (Chemical Vapor Deposition) must be used, which makes the material unsuitable for industrial-scale mass production.
On the other hand, the methods for producing template carbon materials using MgO or the like as a template source, as exemplified in Patent Documents 1 to 3, are simple production methods and therefore suitable for industrial materials in terms of the production process and production scale. However, as a result of extensive investigations by the present inventors, there is a problem in that the yield of carbon constituting the template carbon relative to the weight of the resin used as the carbon source is at most just over 10%.

Here, activated porous carbon materials, such as activated carbon and Ketjen Black, generally experience a significant reduction in pore volume and specific surface area when heated in a non-oxidizing atmosphere at temperatures above 1500°C. Heat treatment in a non-oxidizing atmosphere is a common processing method for ensuring the chemical stability of carbon materials and controlling their strength, and it is desirable for heat treatment to result in minimal changes to the pore structure. From this perspective, templated carbon materials are preferred materials.

Therefore, there is currently a demand for a method for producing template carbon materials with high carbon yield and good production yield.

The present invention therefore aims to provide a method for producing a template carbon material with a high carbon yield and good production yield, a method for producing a catalyst using the same, a method for producing a catalyst layer for a polymer electrolyte fuel cell, and a method for producing a fuel cell.

The means for solving the problem include the following aspects.
<1>
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 having a structure that contains two or more carboxyl groups and has at least two but not more than four carbon atoms between at least two of the two or more carboxyl groups.
(B) The template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals.
<2>
The method for producing a template carbon material according to <1>, wherein in the carbon source, the aliphatic hydrocarbon compound has 4 to 6 carbon atoms.
<3>
The method for producing a template carbon material according to <1> or <2>, wherein the aliphatic hydrocarbon compound in the carbon source is at least one of succinic acid and a succinic acid derivative.
＜4＞
The method for producing a template carbon material according to any one of <1> to <3>, wherein the template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and calcium.
<5>
<4> The method for producing a template carbon material according to any one of <1> to <4>, wherein the template source is at least one selected from magnesium carbonate and magnesium sulfate.
＜6＞
A method for producing a catalyst, comprising using the carbon material obtained by the method for producing a templated carbon material according to any one of <1> to <5> as a support, and supporting a catalyst component on the surface of the support.
＜７＞
<6> A method for producing a catalyst layer for a polymer electrolyte fuel cell, using a catalyst obtained by the method for producing a catalyst according to <6>.
＜8＞
<7> A method for producing a fuel cell, which uses a catalyst layer obtained by the method for producing a catalyst layer for a polymer electrolyte fuel cell according to <7>.
＜９＞
The method for producing a fuel cell according to <8>, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on a cathode side.

The present invention provides a method for producing a template carbon material with high carbon yield and good production yield, as well as a method for producing a catalyst, a method for producing a catalyst layer for a polymer electrolyte fuel cell, and a method for producing a fuel cell that utilizes the same.

1 is a schematic diagram showing a general configuration of a fuel cell according to an embodiment of the present invention;

The present invention will be described below.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In numerical ranges described in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages.
In a numerical range, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.
The term "process" includes not only an independent process but also a process 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.

The method for producing a template carbon material of the present invention is a production method 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 having a structure that contains two or more carboxyl groups and has at least two but not more than four carbon atoms between at least two of the two or more carboxyl groups.
(B) The template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals.

The method for producing templated carbon materials of the present invention has a high carbon yield and is a method for producing templated carbon materials with good production yield. The method for producing templated carbon materials of the present invention was discovered based on the following findings.

First, conventional methods for producing template carbon materials typically use ceramics (MgO, CaO, alumina, etc.) as the template source and resin as the carbon source. The gaseous components generated by the thermal decomposition of the resin formed a carbon film on the ceramic surface, which is thought to be a phenomenon specific to the decomposition products of the resin, and this is thought to be the reason why resin was used exclusively as the carbon source. Meanwhile, carbon coating of ceramics by thermal CVD using propylene gas is also well known as a common technique, and these two phenomena led to the idea that the gaseous low-molecular-weight compounds generated by thermal decomposition are essentially important for carbon coating of ceramics.
Many of the resins used contain oxygen in the monomer structure, and a typical example is polyvinyl alcohol, which is represented by the formula (-(CH ₂ -CHOH) _n -).
When these resins are simply heated in a non-oxidizing atmosphere, for example, at temperatures above 600°C, they undergo thermal decomposition, leaving no solid material. However, when they coexist with ceramics such as MgO, CaO, or alumina, the decomposed gaseous compounds are adsorbed onto the ceramic and remain as a carbon film. This phenomenon has previously been considered similar to thermal CVD and therefore unique to radical compounds.

Meanwhile, the present inventors have investigated at the atomic level the mechanism by which the material used as the carbon source is carbonized and deposited on the surface of the template source through the elementary processes, and have obtained the following findings.
First, decomposition of the resin as a carbon source is not necessarily required, and by using a low-molecular-weight compound having multiple oxygen-containing functional groups instead of the resin, it is possible to obtain a much higher carbon yield than with the resin. This is presumably because the carbon yield increases when at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals is used as the template source, due to the mechanism described below.

Oxygen-containing functional groups, particularly carboxyl groups, have a strong affinity for the template source (the template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals). Therefore, when an aliphatic hydrocarbon compound having a molecular structure containing two or more carboxyl groups that have an affinity for the template source is used as a carbon source and heated together with the template source in a non-oxidizing atmosphere, the carbon yield is increased.
Furthermore, in an aliphatic hydrocarbon compound as a carbon source, a high carbon yield is exhibited only when at least two of the two or more carboxyl groups are not adjacent to each other and are separated by 2 to 4 carbon atoms.
Although the elementary process of the carbon fixation reaction of the carbon source at the atomic level is not clear, it is presumed that at least the two carboxyl groups in the molecular structure of the carbon source fix the carbon source to the surface of the template source, and when oxygen is released in the form of carbon dioxide (CO ₂ ) during a thermal process, the carbon in the molecular structure between the two carboxyl groups is fixed.

For example, in the case of a linear aliphatic hydrocarbon compound such as an alkyl having carboxyl groups at both ends, the carbon yield is highest when there are two carbon atoms between the two carboxyl groups (succinic acid), and the carbon yield decreases as the number of carbon atoms increases. Up to four carbon atoms between the two carboxyl groups (e.g., adipic acid) show a yield equal to or greater than that of resin, but with more carbon atoms, the carbon yield drops sharply to less than 10%.
Even when a typical resin material such as polyvinyl alcohol represented by the formula (-(CH ₂ -CHOH) _n -) is used as the carbon source, the gaseous compound produced by thermal decomposition always contains an oxygen atom in its structure. It is presumed that the carbon yield is determined by the strength of the affinity of this oxygen-containing portion (tentatively referred to as a functional group) for the template source surface and the strength of its adsorptive power, which depends on the number of functional groups in the gaseous compound. In the case of polyvinyl alcohol, the functional group is presumed to be -OH, which has a relatively weak adsorptive power (affinity) for the template source compared to -COOH, and also because the distance between the functional groups is too short, it is presumed that the reinforcement of the adsorptive power for the template source is weak. For this reason, it is presumed that the overall carbon yield is low.
It is important to select a template source that stabilizes as an oxide upon thermal decomposition, specifically limited to oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals. It is presumed that, when these template sources are thermally decomposed in the presence of a carbon source, oxides of magnesium and alkaline earth metals such as MgO and CaO are formed. During this process, the _-CO2 of the carbon source is adsorbed onto the outermost surface, partially forming metal carbonates, which firmly immobilize the carbon source on the template surface, thereby increasing the carbon yield.

Based on the above findings, it has been discovered that the method for producing templated carbon materials of the present invention has a high carbon yield and is a method for producing templated carbon materials with a good yield.

The method for producing the template carbon material of the present invention is described in detail below.

The method for producing a template carbon material of the present invention includes, for example, a mixing step of mixing a carbon source and a template source, a first heating step, a template source removal step, and a second heating step. Each step is described in detail below.

(Mixing process)
In this step, a carbon source and a template source are mixed together.

-Carbon source-
The carbon source used 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 (hereinafter also referred to as a "specific structure").
In an aliphatic hydrocarbon compound, two or more carboxyl groups are contained in one molecule.

In the specific structure, the number of carboxyl groups is two or more, but from the perspective of improving carbon yield, two to six is preferred, and two to four is even more preferred.

In the specific structure, the number of carbon atoms interposed between at least two of the two or more carboxyl groups is 2 or more and 4 or less, but from the viewpoint of improving the carbon yield, it is preferably 2 or more and 3 or less.
Here, the number of carbon atoms between two carboxyl groups does not include the carbon atoms of the carboxyl groups, but refers to the number of carbon atoms connected in a straight chain between the two carboxyl groups. In other words, when carbon atoms are connected in a branched chain between two carboxyl groups, the number of carbon atoms between the two carboxyl groups does not include the number of carbon atoms in the branched chain. For example, when an isopropylene group is connected between two carboxyl groups, the number of carbon atoms between the two carboxyl groups is two.
In addition, when the polymer has three or more carboxyl groups, it is sufficient that at least one pair of two carboxyl groups among the three or more carboxyl groups are separated by 2 to 4 carbon atoms.
Furthermore, the hydrocarbon group having 2 to 4 carbon atoms interposed between the two carboxyl groups may be an unsaturated hydrocarbon group or an unsaturated hydrocarbon group.

In the specific structure, two or more carboxyl groups may form an anhydride. Also, two or more carboxyl groups may form an alkyl metal salt.

Aliphatic hydrocarbon compounds may be either saturated or unsaturated aliphatic hydrocarbon compounds, so long as they have a specific structure. Furthermore, aliphatic hydrocarbon compounds may be linear, branched, or cyclic compounds, so long as they have a specific structure.

The number of carbon atoms in the aliphatic hydrocarbon compound is preferably 4 to 8, more preferably 4 to 7, and even more preferably 4 to 6, from the viewpoint of improving carbon yield.
Here, the number of carbon atoms in the aliphatic hydrocarbon compound is the number of carbon atoms including the carbon atoms of the carboxyl group.

Among the aliphatic hydrocarbon compounds, examples of the aliphatic hydrocarbon compounds having two carboxyl groups include succinic acid, 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), acid), glutaconic acid, fumaric acid, maleic acid, malic acid (malic acid), citraconic acid (anhydride), aspartic acid, etc.

Aliphatic hydrocarbon compounds 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.

Aliphatic hydrocarbon compounds 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.

Among these, the aliphatic hydrocarbon compound is preferably at least one selected from succinic acid, glutaric acid, and derivatives thereof, and more preferably at least one selected from succinic acid and succinic acid derivatives.
Here, the succinic acid derivatives include compounds in which succinic acid is substituted with at least one group selected from a carbonyl group, a hydroxyl group, an amino group, a methyl group, and a methylene group, as well as compounds having a carbon-carbon double bond -C=C-, such as fumaric acid and maleic acid.
The carbon source may contain a carbon source (e.g., a conventional polymer compound) other than the aliphatic hydrocarbon compound having the specific structure, provided that the carbon source contains, for example, at least 50% by mass or more, and preferably 60% by mass or more, of the aliphatic hydrocarbon compound having the specific structure.

-Mold source-
The template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals, where alkaline earth metals include calcium, barium, strontium, etc.

Examples of oxides of Mg and alkaline earth metals include magnesium oxide (MgO), calcium oxide, barium oxide, and strontium oxide.
Examples of carbonates of Mg and alkaline earth metals include magnesium carbonate, calcium carbonate, barium carbonate, and strontium carbonate.
Examples of sulfates of Mg and alkaline earth metals include magnesium sulfate, calcium sulfate, barium sulfate, and strontium sulfate.
Examples of hydroxides of Mg and alkaline earth metals include magnesium hydroxide, calcium hydroxide, barium hydroxide, and strontium hydroxide.

Among these, from the viewpoint of improving carbon yield, the template source is preferably at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and calcium, more preferably at least one selected from oxides, carbonates, and sulfates of magnesium, and even more preferably at least one selected from magnesium carbonate and magnesium sulfate.

-Mixing ratio of carbon source and template source-

The mixing ratio of the carbon source and template source (template source/carbon source), which is the molar ratio C/M of the magnesium or alkaline earth metal element in the template source to the 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, a template carbon material (i.e., a porous carbon material) with the desired BET specific surface area and pore distribution can be obtained.

(First heating step)
In the first heating step, for example, a mixture of a carbon source and a template source is heated to 800 to 1100°C at a rate of 5 to 30°C/min in an inert gas atmosphere 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, thereby obtaining a composite of carbon and the template (i.e., an oxide of magnesium or an alkaline earth metal). For example, in the case of magnesium sulfate, in order to decompose it into 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 heat treatment temperature must be set to a temperature equal to or higher than the minimum temperature required to decompose the template source into an 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 the heating temperature is set to 1100°C, which is the upper limit for inexpensive electric furnaces. However, if there are no limitations on the electric furnace, for example, when a magnesium-based template source is used, it is possible to heat it up to about 1700°C.

(Mold source removal step)
In the template source removal step, the composite of carbon and the template (i.e., an oxide of magnesium or an alkaline earth metal) is pickled to dissolve the template in the pickling solution, thereby removing the template from the composite of carbon and the template, thereby obtaining a porous carbon material intermediate.
The acid used for pickling may be any acid as long as it dissolves the template, and a preferred example is sulfuric acid. After pickling, the carbon material is washed with water and dried.

(Second heating step)
In the second heating step, for example, the obtained intermediate template carbon material is maintained at 2000 to 2600° C. for 0.5 to 3.0 hours in an inert gas atmosphere.
This heat treatment increases the crystallinity of the template carbon material and improves its durability (resistance to oxidation and wear) at high temperatures.
When the template carbon of the present invention is applied to an application that does not require high crystallinity, the temperature of the second heating step can be kept between 1000°C and 2000°C, or the second heating step itself can be omitted, with the template removal step being the final step.

Through the above steps, the desired template carbon material (i.e., porous carbon material) is obtained.

The method for producing templated carbon materials of the present invention is applicable to fields in which carbon materials known as activated carbon are used (for example, as adsorbents for selective adsorption of specific gases or molecules with specific structures in the liquid phase), as catalyst supports for polymer electrolyte fuel cells such as those used with Ketjen black, and as electrodes for supercapacitors.

<Catalyst manufacturing method>
The method for producing a templated carbon material of the present invention can be applied to a method for producing a catalyst, which involves supporting a catalyst component on the surface of the carbon material obtained by the method for producing a templated carbon material of the present invention as a support.
A typical catalyst component is a catalyst for polymer electrolyte fuel. Examples of catalyst components include platinum and platinum alloys. Examples of alloy components of platinum alloys include Au, Ag, Cr, Fe, Ti, Mn, Co, Ni, Mo, W, Al, Si, Zn, Sn, Ru, Rh, Pd, Os, and Ir.
Other catalyst components include porous carbon with oxygen-containing functional groups, which can be obtained by oxidizing the template carbon obtained by the present invention. If necessary, the coexistence of nitrogen-containing functional groups in addition to the oxygen-containing functional groups is also effective in improving catalytic activity. The template carbon of the present invention, which has been surface-modified in this way, can be used as a catalyst for oxygen reduction reactions.

The catalyst manufacturing method of the present invention can be applied to the manufacture of electrodes that provide a large reaction surface area and require high chemical and electrochemical stability, such as catalyst layers for polymer electrolyte fuel cells, air electrodes for metal-air batteries such as Li-air batteries, and electrodes for redox flow batteries.

<Method of manufacturing a polymer electrolyte fuel cell>
The method for producing a template carbon material of the present invention can be applied to a method for producing a polymer electrolyte fuel cell (or a catalyst layer thereof).
An example of the solid polymer fuel cell to be manufactured is a solid polymer fuel cell 100 shown in Fig. 1. The solid polymer fuel cell 100 includes separators 110 and 120, gas diffusion layers 130 and 140, catalyst layers 150 and 160, and an electrolyte membrane 170, for example.

Separator 110 is the anode-side separator, and introduces fuel gas such as hydrogen into the gas diffusion layer 130. Separator 120 is the cathode-side separator, and introduces oxidizing gases such as oxygen gas and air into the gas diffusion condensation phase. There is no particular restriction on the type of separators 110 and 120; they can be any separator used in conventional fuel cells, such as solid polymer fuel cells.

The gas diffusion layer 130 is an anode-side gas diffusion layer that diffuses the fuel gas supplied from the separator 110 and then supplies it 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 it to the catalyst layer 160. There are no particular restrictions on the type of gas diffusion layer 130, 40, as long as it is a gas diffusion layer used in conventional fuel cells, such as solid polymer fuel cells. Examples of the gas diffusion layers 130, 40 include porous carbon materials (carbon cloth, carbon paper, etc.), porous metal materials (metal mesh, metal wool, etc.), etc.
A preferred example of the gas diffusion layers 130 and 140 is a two-layer gas diffusion layer in which the layer on the separator side of the gas diffusion layer is a gas diffusion fiber layer mainly composed of a fibrous carbon material, and the layer on the catalyst layer side is a micropore layer mainly composed of carbon black.

The catalyst layer 150 is a so-called anode. An oxidation reaction of the fuel gas occurs in the catalyst layer 150, producing protons and electrons. For example, when the fuel gas becomes hydrogen gas, the following oxidation reaction occurs.
H ₂ →2H ⁺ +2e ^- (E ₀ =0V)

Protons produced by the oxidation reaction pass through catalyst layer 150 and electrolyte membrane 170 to reach catalyst layer 160. Electrons produced by the oxidation reaction pass through catalyst layer 150, gas diffusion layer 130, and separator 110 to reach the external circuit. After performing work in the external circuit, the electrons are introduced into separator 120. The electrons then pass through separator 120 and gas diffusion layer 140 to reach catalyst layer 160.

The configuration of the catalyst layer 150, which serves as the anode, is not particularly limited. That is, 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 even more hydrophilic than the catalyst layer 160.

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.
O ₂ +4H ⁺ +4e ^- →2H ₂ O (E ₀ =1.23V)

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

The catalyst layer 160 contains the template carbon material of the present invention. That is, the catalyst layer 160 contains the template carbon material of the present invention, an electrolyte material, and a fuel cell catalyst. This increases the catalyst utilization rate within the catalyst layer 160. As a result, the catalyst utilization rate of the polymer electrolyte fuel cell 100 can be increased.

The fuel cell 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. Here, the fuel cell catalyst loading rate is preferably the mass % of the fuel cell catalyst relative to the total mass of the catalyst-loaded particles (particles in which the fuel cell catalyst is loaded on a template carbon material). In this case, the catalyst utilization rate is further increased. If the fuel cell catalyst loading rate is less than 30% by mass, it may be necessary to thicken the catalyst layer 160 to make the polymer electrolyte fuel cell 100 practical. On the other hand, if the fuel cell catalyst loading rate is 80% by mass or more, catalyst aggregation is more likely to occur. Furthermore, if the catalyst layer 160 becomes too thin, flooding may occur.

The mass ratio I/C of the mass I (g) of the electrolyte material in the catalyst layer 160 to the mass C (g) of the catalyst support carbon material 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, resulting in a high catalyst utilization rate. 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. In either case, the catalyst utilization rate may be reduced.

In addition, the thickness of the catalyst layer 160 is not particularly limited, but is preferably greater than 5 μm and less than 20 μm. In this case, oxidizing gases are 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 gases are less likely to diffuse within the catalyst layer 160, and the fuel cell catalyst near the electrolyte membrane 170 becomes less effective. In other words, the catalyst utilization rate may decrease.

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, which serves as the cathode. The type of electrolyte material is not particularly important; it can be any electrolyte material used in conventional fuel cells, such as polymer electrolyte fuel cells. A suitable example is an electrolyte material used in polymer electrolyte fuel cells, i.e., an electrolyte resin. Examples of electrolyte resins include polymers with introduced phosphate groups, sulfonic acid groups, etc. (e.g., perfluorosulfonic acid polymers or polymers with introduced benzenesulfonic acid). 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 polymer electrolyte fuel cell 100 may be a fuel cell that operates within a temperature range from room temperature to 150°C.

<Test Examples Alk-1 to Alk-59>
The carbon source and template source were mixed in the types and amounts shown in Table 1. Since particles with as small a particle size as possible form a uniform fired product in the first heating step, the carbon source and template source were pulverized in a mortar, planetary ball mill, or the like before testing to have a volume average particle size of 1.0 to 10.0 μm. The mixture was mixed in a mortar for at least several minutes.
The mixture was then fired (first heat treatment) in a gas-flow horizontal tubular electric furnace while flowing argon gas to obtain a composite of carbon and the template. Specifically, argon was flowed at a linear velocity of 3 cm per minute, and the temperature was raised from room temperature to 900°C at a rate of 20°C per minute. After holding at 900°C for 1 hour, the mixture was allowed to cool and then removed when it reached 100°C or below.
Next, the composite was lightly crushed in a mortar, dispersed in a 20% by mass aqueous solution of sulfuric acid, stirred at 90°C for 40 hours, and then suction filtered through a membrane filter. The composite was then dispersed in distilled water and filtered twice more, followed by washing to remove the template.
Next, the washed product was dried in a hot air dryer at 100° C. to remove moisture, and then vacuum dried at 90° C. for 5 hours to obtain an intermediate for the template carbon material.
Next, in order to enhance the crystallinity of the resulting template carbon material, the intermediate of the template carbon material was subjected to a second heat treatment in an inert gas atmosphere at 1500°C for 1.0 hour, after which the intermediate of the template carbon material was subjected to a graphitization treatment (heat treatment).
Through the above steps, a template carbon material (i.e., a porous carbon material) was obtained.

<Evaluation>
The obtained template carbon material (i.e., porous carbon material) was evaluated as follows.

(Carbon Yield)
The carbon yield in the manufacturing method of the template carbon material of each example was determined as follows.
The mass ratio of the mass of carbon after the template source removal step to the mass of the carbon source used as the raw material was defined as the carbon yield, and was measured by the following method.
That is, the sample after the first heat treatment described above, which was held at 900°C for 1 hour, was treated with a sulfuric acid solution and then washed to remove the template, and further subjected to a vacuum tube treatment to obtain a template carbon intermediate. The mass of the intermediate was measured, and this mass was divided by the mass of the carbon source used as the raw material to calculate the carbon yield expressed as a percentage.

(Measurement of nitrogen adsorption/desorption isotherm)
Approximately 30 mg of a sample was weighed out from the obtained template carbon material and vacuum dried for 2 hours at 120° C. Next, the sample was set in an automatic specific surface area measuring device (BELSORP MAX, manufactured by Microtrackbell Co., Ltd.), and the nitrogen adsorption/desorption isotherm was measured at a measurement temperature of 77 K using nitrogen gas as the adsorbate.
In measuring the nitrogen adsorption/desorption isotherm, the measurement interval of the relative pressure P/ _P0 was set smaller than that in a general measurement (specifically, the measurement interval of P/ _P0 was set to take fixed points in increments of 0.005). In other words, the measurement accuracy of the relative pressure P/ _P0 in the measurement was set to 0.005.

Next, the nitrogen adsorption isotherm was analyzed by BET in the relative pressure P/P ₀ range of 0.05 to 0.15 to calculate the BET specific surface area S _BET . The BET analysis was performed using analysis software provided with the apparatus.

(Catalyst preparation, catalyst layer fabrication, MEA fabrication, fuel cell assembly, and cell performance evaluation)
Using the obtained template carbon material, a catalyst for a polymer electrolyte fuel cell carrying a catalytic metal was prepared as follows: the obtained catalyst was used to prepare a catalyst layer ink liquid, which was then used to form a catalyst layer, which was then used to fabricate a membrane electrode assembly (MEA), which was then incorporated into a fuel cell, and a power generation test was performed using a fuel cell measuring device. The preparation of each component and the cell evaluation through the power generation test are described in detail below.

(1) Preparation of a catalyst (platinum-supported carbon material) for a polymer electrolyte fuel cell. The obtained template carbon material was dispersed in distilled water, and formaldehyde was added to this dispersion. The dispersion was placed in a water bath set at 40°C. After the temperature of the dispersion reached 40°C, the same as the bath temperature, an aqueous solution of dinitrodiamine Pt complex nitric acid was slowly poured into the dispersion while stirring. Stirring was continued for approximately 2 hours, followed by filtration and washing of the resulting solid. The solid thus obtained was vacuum dried at 90°C, pulverized in a mortar, and then heat-treated at 200°C for 1 hour in an argon atmosphere containing 5% by volume of hydrogen to prepare a platinum catalyst particle-supported carbon material.
The amount of platinum carried in this platinum-supporting carbon material was adjusted to 40 mass % with respect to the total mass of the template carbon material and platinum particles, and was confirmed by measurement using inductively coupled plasma atomic emission spectrometry (ICP-AES).

(2) Preparation of Catalyst Layer Using the platinum-supported carbon material (Pt catalyst) prepared as described above, and Nafion (registered trademark: Nafion; a persulfonic acid-based ion exchange resin) manufactured by DuPont as the electrolyte resin, the Pt catalyst and Nafion were mixed under an Ar atmosphere in such a manner that the mass of the Nafion solid content relative to the mass of the platinum catalyst particle-supported carbon material was 1.0 times, and the mass of the Nafion solid content relative to the mass of the non-porous carbon was 0.5 times. After lightly stirring, the Pt catalyst was crushed by ultrasonic waves, and ethanol was further added to adjust the total solid content concentration of the Pt catalyst and the electrolyte resin to 1.0 mass %, thereby preparing a catalyst layer ink liquid in which the Pt catalyst and the electrolyte resin were mixed.

Ethanol was further added to each catalyst layer ink solution thus prepared, each with a solids concentration of 1.0% by mass, to produce a catalyst layer ink solution for spray application with a platinum concentration of 0.5% by mass. The spray conditions were adjusted so that the mass of platinum per unit area of the catalyst layer (hereinafter referred to as "platinum coverage") was 0.2 mg/cm2. The catalyst layer ink for spray application was sprayed onto a Teflon® sheet, which was then dried in argon at 120°C for 60 minutes to produce a catalyst layer.

(3) Fabrication of MEA Using the catalyst layer fabricated as described above, an MEA (membrane electrode assembly) was fabricated by the following method.
A square electrolyte membrane with sides of 6 cm was cut out from a Nafion membrane (NR211 manufactured by DuPont). The anode and cathode catalyst layers coated on Teflon (registered trademark) sheets were each cut into a square with sides of 2.5 cm using a cutter knife.
The electrolyte membrane was sandwiched between the anode and cathode catalyst layers cut out in this manner so that the catalyst layers were in contact with each other, sandwiching the center of the electrolyte membrane, and so that there was no misalignment between them. The mixture was pressed at 120°C and 100 kg/cm for 10 minutes, and then cooled to room temperature. After that, the Teflon sheets were carefully peeled off from both the anode and cathode, thereby preparing a catalyst layer-electrolyte membrane assembly in which the anode and cathode catalyst layers were fixed to the electrolyte membrane.

Next, a pair of square carbon paper sheets each measuring 2.5 cm on a side was cut out from carbon paper (35BC manufactured by SGL Carbon Co., Ltd.) to form a gas diffusion layer. The catalyst layer-electrolyte membrane assembly was sandwiched between these carbon papers so that the anode and cathode catalyst layers were aligned with each other without any misalignment, and the assembly was pressed at 120°C and 50 kg/cm for 10 minutes to prepare an MEA.
The basis weight of each component of the catalytic metal component, carbon material, and electrolyte material in each of the produced MEAs was calculated from the mass of the catalyst layer fixed to the Nafion membrane (electrolyte membrane) obtained from the difference between the mass of the Teflon sheet with the catalyst layer before pressing and the mass of the Teflon sheet peeled off after pressing, and then calculated from the mass ratio of the composition of the catalyst layer.

(4) Evaluation of fuel cell power generation characteristics (evaluation of low current characteristics)
The MEAs prepared in each test example and fabricated using the prepared porous carbon material for catalyst support were each incorporated into a cell, which was then set in a fuel cell measuring device, and the performance of the fuel cell was evaluated according to the following procedure.
The reaction gases were supplied at a back pressure of 0.04 MPa, with air supplied to the cathode side and pure hydrogen supplied to the anode side, with the pressure adjusted by a back pressure valve installed downstream of the cell under atmospheric pressure so that the utilization rates were 40% and 70%, respectively. The cell temperature was set to 80°C, and the reaction gases supplied were both bubbled with distilled water kept at 60°C in a humidifier, and humidified gas at 60°C was supplied to the cell at 80°C to evaluate power generation.

Under these conditions, the reactant gas was supplied to the cell, and the load was gradually increased. The cell terminal voltage at a current density of 100 mA/ ^cm2 was recorded as the output voltage, and the performance of the fuel cell was evaluated using the following pass/fail ranking criteria. The results are shown in Table 1.
[Passing rank]
◎: Output voltage at 100 mA/cm ² is 0.880 V or more.
○: Output voltage at 100 mA/cm ² is 0.870 V or more.
[Failure rank]
×: The output voltage at 100 mA/cm ² is 0.850 V or more and less than 0.870 V.

From the above results, it can be seen that the method for producing template carbon material in the present invention is a method for producing template carbon material with a high carbon yield and good yield, equal to or higher than the comparative example in which a resin material was used as the carbon source.
It is also clear that a catalyst using the template carbon material (that is, the porous carbon material) obtained by the method for producing a template carbon material according to the present invention can provide a battery with high cell performance.

Details of the abbreviations in the table are provided below.
PVA: Polyvinyl alcohol (weight average molecular weight = 10,000)
PEG: polyethylene glycol (weight average molecular weight = 600)
PVC: Polyvinyl chloride (weight average molecular weight = 10,000)
PAA: Polyacrylic acid (weight average molecular weight = 10,000)

100 Solid polymer fuel cell 110, 120 Separator 130, 140 Gas diffusion layer 150, 160 Catalyst layer 170 Electrolyte membrane

Claims (9)

a mixing step of mixing a carbon source and a template source;
a first heating step of heat-treating the mixture of the carbon source and the template source to obtain a composite of carbon and the template;
a template source removal step of removing the template source from the composite of the carbon and the template to obtain an intermediate of the template carbon material;
a second heating step of heat-treating the intermediate of the template carbon material;
and
The method for producing a template carbon material , wherein the carbon source satisfies the following requirement (A) and is a carbon source excluding citric acid , and the template source satisfies the following requirement (B):
(A) The carbon source is an aliphatic hydrocarbon compound having a structure that contains two or more carboxyl groups and has at least two but not more than four carbon atoms between at least two of the two or more carboxyl groups.
(B) The template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals. a mixing step of mixing a carbon source and a template source;
a first heating step of heat-treating the mixture of the carbon source and the template source to obtain a composite of carbon and the template;
a template source removal step of removing the template source from the composite of the carbon and the template to obtain an intermediate of the template carbon material;
a second heating step of heat-treating the intermediate of the template carbon material;
and
A method for producing a template carbon material, wherein the carbon source is a carbon source that satisfies the following requirement (C) , and the template source is a template source that satisfies the following requirement (B) .
(C) The carbon source is an aliphatic hydrocarbon compound having a structure containing two or four carboxyl groups and having at least two of the carboxyl groups separated by two to four carbon atoms, or one or more of aconitic acid, 1,2,3-propanetricarboxylic acid, cyclohexane-1,3,5-tricarboxylic acid, cyclohexane-1,2,4-tricarboxylic acid, and methylcitric acid.
(B) The template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals. 3. The method for producing a template carbon material according to claim 1, wherein the aliphatic hydrocarbon compound in the carbon source has 4 to 6 carbon atoms. 4. The method for producing a template carbon material according to claim 1, wherein the aliphatic hydrocarbon compound in the carbon source is at least one of succinic acid and a succinic acid derivative. The method for producing a template carbon material according to any one of claims 1 to 4 , wherein the template source is at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and calcium. The method for producing a template carbon material according to any one of claims 1 to 5 , wherein the template source is at least one selected from magnesium carbonate and magnesium sulfate. A method for producing a catalyst, comprising dispersing a template carbon material obtained by the method for producing a template carbon material according to any one of claims 1 to 6 in water, adding a reducing agent and a catalyst raw material to the obtained dispersion, and then stirring, filtering, washing, drying, and heat treating the mixture, thereby supporting a catalyst component on the surface of the template carbon material. A method for producing a catalyst layer for a polymer electrolyte fuel cell , comprising applying and drying an ink containing the catalyst obtained by the method for producing a catalyst according to claim 7 and an electrolyte resin to produce a catalyst layer. 10. A method for producing a fuel cell, comprising the steps of: arranging the catalyst layers obtained by the method for producing a catalyst layer for a polymer electrolyte fuel cell according to claim 8 as an anode catalyst layer and a cathode catalyst layer on both sides of a solid polymer electrolyte membrane; and then pressing the resulting mixture.