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

Abstract

To provide a method for producing templated carbon material with high carbon yields and good yields, 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.SOLUTION: The present invention provides a method for producing templated carbon material using a carbon source satisfying the following requirement (A) and a template source satisfying the following requirement (B). The (A) carbon source is an aliphatic hydrocarbon compound that comprises two or more carboxyl groups, wherein, out of the two or more carboxyl groups, at least two carboxyl groups have two or more and four or less carbon atoms interposed therebetween. The (B) template source is at least one selected from oxide, carbonate, sulfate, and hydroxide of magnesium and alkaline-earth metal.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present 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. [Background technology]

[0002] 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.

[0003] Furthermore, since the carbon coating process typically involves heat treatment at temperatures of 600°C to 1500°C, it is also possible to use, as the template source, compounds that chemically change into magnesium oxide or calcium oxide during the heat treatment process (e.g., carbonates, hydroxides, sulfates, etc.).

[0004] 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 material is prepared at a temperature exceeding 1000°C. However, high-temperature treatment that involves the formation of carbides such as calcium carbide or metal acetylides must be avoided. In practice, the heat treatment temperature for carbon coating is limited to around 1800°C.

[0005] 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.

[0006] Templated carbon materials with isotropic interconnected pores are sometimes referred to as interconnected pores in the field of polymer electrolyte fuel cells, and it is believed that the good gas flow (fast diffusion) within the material will improve power generation performance when used as a catalyst support, making them a promising material. 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 several tens of nanometers in size, in contrast to the pores formed by activation methods, which are inevitably distributed widely from micropores to mesopores.

[0007] The thickness of the carbon layer in the template carbon material can be freely controlled by changing the mixture ratio of the template source and the carbon source, so there is a high degree of freedom in the specific surface area per mass.

[0008] Because templated 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 in which they serve as catalyst supports for solid polymer fuel cells, such as those in which Ketjen black is used, and fields in which they are used 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.

[0009] For example, a porous carbon material consisting only of micropores using zeolite as a template can achieve an astonishing surface area of ​​4,000 m by selecting the type of template and optimizing the conditions for carbon coating inside the pores using CVD with propylene gas as the raw material. 2 It has been reported that the solubility of HCl reaches up to / g (Non-Patent Document 1). Because the pore diameter is on the order of a few tenths of a nanometer at the atomic level, the carbon walls that coat the pores are formed as a single atomic layer, and the pore walls contain five-membered rings, seven-membered rings, etc. to maintain 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.

[0010] On the other hand, a method for producing a template carbon material 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 treated at 900°C for 1 hour in a nitrogen atmosphere (Non-Patent Document 2).

[0011] Also known is a method for producing activated carbon, which uses organic acid magnesium having a carbon number of 6 or more as a raw material, heats the raw material to 300°C or higher in an inert atmosphere, and then cools and washes the raw material with acid (Patent Document 1). In this method for producing activated carbon, citric acid and polyvinyl alcohol (PVA) are used as carbon sources.

[0012] Also known is a method for producing activated carbon that includes a step of 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.

[0013] Another known method for producing a porous carbon material involves thermal CVD treatment of alumina nanoparticles (average crystallite size 10 nm, commercially available product) using methane as a carbon source gas (Patent Document 3). In this method for producing a porous carbon material, 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 in which the carbon layer is controlled to two or less 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. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-013394 [Patent Document 2] Patent No. 4955952 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-164889 [Non-patent literature]

[0015] [Non-Patent Document 1] Formation of new type of porous carbon by carbonization in zeolite nanochannels, Chemistry of materials, 2, 609-615(1997) [Non-patent document 2] A review of the controle of pore structure in MgO-templated nanoporous carbons, Carbon, 48, 2690-2707(2010)) Summary of the Invention [Problem to be solved by the invention]

[0016] In the above-mentioned example, 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. Therefore, the thickness of the carbon covering the pores is also 1 nm or less per atomic layer, so a synthesis method using a gas phase method such as CVD (Chemical Vapor Deposition) must be used. In this case, the material is 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 are therefore suitable for industrial materials in terms of 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 that constitutes the template carbon relative to the weight of the resin used as the carbon source is at most just over 10%.

[0017] Generally, activated porous carbon materials, such as activated carbon and Ketjen black, 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 and controlling the strength of carbon materials, and it is desirable for the heat treatment to cause minimal changes in the pore structure. From this perspective, templated carbon materials are preferred.

[0018] Therefore, there is currently a demand for a method for producing template carbon materials with high carbon yield and good production yield.

[0019] Therefore, the object of the present invention is to provide a method for producing a template carbon material with 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. [Means for solving the problem]

[0020] 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> In the carbon source, the aliphatic hydrocarbon compound has 4 to 6 carbon atoms. <1> A method for producing the template carbon material described in 1. <3> In the carbon source, the aliphatic hydrocarbon compound is at least one of succinic acid and a succinic acid derivative. <1> or <2> A method for producing the template carbon material described in 1. <4> In the template source, at least one selected from oxides, carbonates, sulfates, and hydroxides of magnesium and calcium is <1> ~ <3> 1. A method for producing the template carbon material according to any one of claims 1 to 9. <5> The template source is at least one selected from magnesium carbonate and magnesium sulfate. <1> ~ <4> 1. A method for producing the template carbon material according to any one of claims 1 to 9. <6> <1> ~ <5> 1. A method for producing a catalyst, comprising using the carbon material obtained by the method for producing a templated carbon material described in 1. above as a support and supporting a catalyst component on the surface of the support. <7> <6> 2. 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 claim 1. <8> <7> 1. 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 claim 1. <9> The catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on the cathode side. <8> A method for manufacturing the fuel cell according to claim 1. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a method for producing a template carbon material with a high carbon yield and good 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. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram showing a general configuration of a fuel cell according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 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.

[0025] The method for producing a template carbon material of the present invention is a method for producing a template carbon material with a high carbon yield and good production yield. The method for producing a template carbon material of the present invention was discovered based on the following findings.

[0026] 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 unique 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 resins contain oxygen in the monomer structure, typically the formula (-(CH2-CHOH) n -) is a polyvinyl alcohol. 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 behind. 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.

[0027] 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 resin as a carbon source is not necessarily required, and using a low-molecular-weight compound with multiple oxygen-containing functional groups instead of resin can achieve a much higher carbon yield than 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 a template source, due to the mechanism described below.

[0028] 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 the carbon source and heated together with the template source in a non-oxidizing atmosphere, the carbon yield is increased. Furthermore, a high carbon yield is achieved only when, in an aliphatic hydrocarbon compound as a carbon source, 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 escapes in the form of carbon dioxide (CO2) during a thermal process, the carbon in the molecular structure between the two carboxyl groups is fixed.

[0029] For example, in the case of a straight-chain aliphatic hydrocarbon compound such as an alkyl with 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 (adipic acid, for example) show a yield equal to or greater than that of resin, but at any higher number of carbon atoms, the carbon yield drops sharply to less than 10%. Formula (-(CH2-CHOH) nEven when a typical resin material such as polyvinyl alcohol (represented by -) is used as a carbon source, the gaseous compound produced by thermal decomposition always contains oxygen atoms in its structure. It is presumed that the carbon yield is determined by the affinity of these oxygen-containing moieties (tentatively referred to as functional groups) for the template source surface and the strength of their adsorption 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 adsorption power (affinity) for the template source compared to -COOH. Furthermore, the distance between the functional groups is too short, so the reinforcement of the adsorption power for the template source is presumed to be weak. This is presumed to result in a low overall carbon yield. For the template source, it is important to select one that stabilizes as an oxide upon thermal decomposition, specifically limited to oxides, carbonates, sulfates, and hydroxides of magnesium and alkaline earth metals. When these template sources are thermally decomposed in the presence of a carbon source, magnesium and alkaline earth metal oxides such as MgO and CaO are formed. It is presumed that the carbon source's -CO2 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.

[0030] From the above findings, it has been found that the method for producing a template carbon material of the present invention provides a high carbon yield and is a method for producing a template carbon material with good yield.

[0031] The method for producing the template carbon material of the present invention will be described in detail below.

[0032] 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 will be described in detail below.

[0033] (Mixing process) In this step, a carbon source and a template source are mixed together.

[0034] -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.

[0035] 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.

[0036] 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 there are three or more carboxyl groups, at least one pair of two carboxyl groups among the three or more carboxyl groups may be 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.

[0037] In the specific structure, two or more carboxyl groups may form an anhydride, and two or more carboxyl groups may form an alkyl metal salt.

[0038] The aliphatic hydrocarbon compound may be either a saturated aliphatic hydrocarbon compound or an unsaturated aliphatic hydrocarbon compound, as long as it has a specific structure. Furthermore, the aliphatic hydrocarbon compound may be any of a linear, branched, or cyclic compound, as long as it has a specific structure.

[0039] The aliphatic hydrocarbon compound preferably has 4 to 8 carbon atoms, more preferably 4 to 7 carbon atoms, and even more preferably 4 to 6 carbon atoms, from the viewpoint of improving the 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.

[0040] Among aliphatic hydrocarbon compounds, examples of 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), and 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.

[0041] Examples of 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.

[0042] 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.

[0043] 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, 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 double bond -C=C- between carbon atoms, such as fumaric acid and maleic acid. The carbon source may contain a carbon source other than the aliphatic hydrocarbon compound having the specific structure (for example, a conventional polymer compound), provided that the carbon source contains, for example, at least 50% by mass or more, preferably 60% by mass or more, of the aliphatic hydrocarbon compound having the specific structure.

[0044] -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.

[0045] 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.

[0046] Among these, from the viewpoint of improving the 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 more preferably at least one selected from magnesium carbonate and magnesium sulfate.

[0047] -Mixing ratio of carbon source and template source-

[0048] The mixing ratio of the carbon source and the 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 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.

[0049] (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 is 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 or alkaline earth metal oxide). For example, in the case of magnesium sulfate, 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 for inexpensive electric furnaces is 1100°C, but if there are no limitations to the electric furnace, it is possible to heat it up to around 1700°C, for example, when a magnesium-based template source is used.

[0050] (Mold source removal process) 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. This removes 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.

[0051] (Second heating step) In the second heating step, for example, the obtained intermediate body of the template carbon material is held in an inert gas atmosphere at 2000 to 2600° C. for 0.5 to 3.0 hours. This heat treatment increases the crystallinity of the template carbon material and improves its durability (resistance to oxidation and wear) at high temperatures. Furthermore, 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 at 1000°C to 2000°C, or the second heating step itself can be omitted, with the template removal step being the final step.

[0052] Through the above steps, the desired template carbon material (that is, porous carbon material) is obtained.

[0053] The method for producing a templated carbon material of the present invention is applicable to fields in which a carbon material called activated carbon is used (for example, the field of adsorbents for selective adsorption of specific gases and molecules with specific structures in the liquid phase), fields in which Ketjen black is used as a catalyst support for solid polymer fuel cells, and fields in which supercapacitor electrodes are used.

[0054] <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.

[0055] The catalyst production method of the present invention can be applied to the production of electrodes that provide a large reaction surface area and are required to have 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.

[0056] <Method of manufacturing a polymer electrolyte fuel cell> The method for producing a template carbon material of the present invention is applicable 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 Figure 1. The solid polymer fuel cell 100 includes separators 110, 120, gas diffusion layers 130, 140, catalyst layers 150, 160, and an electrolyte membrane 170, for example.

[0057] Separator 110 is an anode-side separator that introduces a fuel 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 the gas diffusion condensation layer. There is no particular restriction on the type of separators 110 and 120, and they may be any separators used in conventional fuel cells, such as solid polymer fuel cells.

[0058] 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 is no particular restriction on the type of gas diffusion layers 130 and 40, as long as they are gas diffusion layers used in conventional fuel cells, such as solid polymer fuel cells. Examples of gas diffusion layers 130 and 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.

[0059] 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. H2→2H + +2e - (E0=0V)

[0060] 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.

[0061] The configuration of the catalyst layer 150 that 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, may be the same as that of the catalyst layer 160, or may be more hydrophilic than the catalyst layer 160.

[0062] 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. O2+4H + +4e - →2H2O (E0=1.23V)

[0063] 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.

[0064] 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 can increase the catalyst utilization rate in the catalyst layer 160. As a result, the catalyst utilization rate of the polymer electrolyte fuel cell 100 can be increased.

[0065] 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. 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 likely to occur. Furthermore, if the catalyst layer 160 becomes too thin, flooding may occur.

[0066] 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 the pore network and the 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 increase. 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 decrease.

[0067] Furthermore, the thickness of the catalyst layer 160 is not particularly limited, but 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 fuel cell catalyst near the electrolyte membrane 170 becomes less effective. In other words, the catalyst utilization rate may decrease.

[0068] The electrolyte membrane 170 is made of an electrolyte material having proton conductivity. 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 limited, and any electrolyte material used in conventional fuel cells, such as solid polymer fuel cells, may be used. A suitable example is an electrolyte material used in solid polymer fuel cells, i.e., an electrolyte resin. Examples of the electrolyte resin include polymers having phosphate groups, sulfonic acid groups, or the like introduced therein (e.g., perfluorosulfonic acid polymers or polymers having benzenesulfonic acid introduced therein). 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 to 150°C. [Example]

[0069] <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 will 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 use in the test to a volume average particle size of 1.0 to 10.0 μm. The mixture was mixed in a mortar for at least several minutes before use. Next, the mixture was fired (first heat treatment) in a gas-flow type 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 / min, and the temperature was raised from room temperature to 900°C at a rate of 20°C / min, held at 900°C for 1 hour, and then allowed to cool until it reached 100°C or below, at which point the mixture was removed to obtain a composite of carbon and the template. 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. This was then dispersed in distilled water and filtered twice more, followed by washing, to remove the template. Next, the washed material 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 (that is, a porous carbon material) was obtained.

[0070] <Evaluation> The obtained template carbon material (that is, the porous carbon material) was evaluated as follows.

[0071] (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, after the first heat treatment described above, the sample was held at 900°C for 1 hour, and then the template was removed by a sulfuric acid solution treatment and a subsequent washing treatment. The template carbon intermediate obtained by further performing a vacuum tube treatment was weighed, and the mass was divided by the mass of the carbon source used as the raw material to calculate the carbon yield in %.

[0072] (Nitrogen adsorption / desorption isotherm measurement) Approximately 30 mg of 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 (MicrotrackBell, BELSORP MAX) 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 in general measurements (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.

[0073] Next, the BET analysis of the nitrogen adsorption isotherm in the relative pressure P / P0 range of 0.05 to 0.15 was performed to determine the BET specific surface area S BET The BET analysis was performed using the analysis software that came with the device.

[0074] (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.

[0075] (1) Preparation of catalysts (platinum-supported carbon materials) for polymer electrolyte fuel cells The resulting template carbon material was dispersed in distilled water, and formaldehyde was added to the dispersion. The dispersion was then placed in a water bath set at 40°C. Once the temperature of the dispersion reached the same temperature as the bath (40°C), an aqueous solution of dinitrodiamine platinum 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, crushed in a mortar, and then heat-treated for 1 hour at 200°C in an argon atmosphere containing 5% hydrogen by volume to produce a platinum catalyst particle-supported carbon material. The amount of platinum carried in this platinum-supported carbon material was adjusted to 40 mass % relative 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).

[0076] (2) Preparation of the 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 a ratio of 1.0 times the mass of the Nafion solids relative to the mass of the platinum catalyst particle-supported carbon material, and 0.5 times the mass of the non-porous carbon. After light stirring, the Pt catalyst was crushed using ultrasound, and ethanol was added so that the total solid concentration of the Pt catalyst and electrolyte resin combined was adjusted to 1.0 mass %, thereby preparing a catalyst layer ink liquid in which the Pt catalyst and electrolyte resin were mixed.

[0077] Ethanol was further added to each catalyst layer ink liquid thus prepared, each having a solids concentration of 1.0% by mass, to prepare a catalyst layer ink liquid 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 (registered trademark) sheet, which was then dried in argon at 120°C for 60 minutes to prepare a catalyst layer.

[0078] (3) Preparation of MEA Using the catalyst layer prepared as above, an MEA (membrane electrode assembly) was prepared 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 way 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.

[0079] Next, a pair of square carbon paper sheets with sides of 2.5 cm were cut out from carbon paper (35BC manufactured by SGL Carbon Co., Ltd.) to form gas diffusion layers. The catalyst layer-electrolyte membrane assembly was sandwiched between these carbon paper sheets so that the anode and cathode catalyst layers were aligned with each other without any misalignment, and the sheets were pressed at 120°C and 50 kg / cm2 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 MEA produced 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.

[0080] (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 materials for catalyst supports 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 reactant 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 reactant gas supplied to both the cathode and anode was 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.

[0081] Under these conditions, the reaction gas was supplied to the cell, and the load was gradually increased until the current density reached 100 mA / cm. 2 The voltage between the cell terminals at this time 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] ◎: 100mA / cm 2 The output voltage is 0.880V or more. ○: 100mA / cm 2The output voltage is 0.870V or more. [Failure rank] ×:100mA / cm 2 The output voltage is 0.850V or more and less than 0.870V.

[0082] [Table 1-1]

[0083] [Table 1-2]

[0084] From the above results, it can be seen that the method for producing template carbon material in the example of the present invention is a method for producing template carbon material with a high carbon yield and good yield, equal to or higher than that of 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.

[0085] 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) [Explanation of symbols]

[0086] 100 Polymer electrolyte fuel cell 110, 120 separator 130, 140 Gas diffusion layer 150, 160 catalyst layer 170 Electrolyte membrane

Claims

1. 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 other than 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.

2. 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. 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. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

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