Method for producing mesoporous carbon carrier, mesoporous carbon carrier, electrode material, electrode, membrane electrode assembly, and polymer electrolyte fuel cell

Abstract

To provide a method for producing a mesoporous carbon carrier facilitating easy pulverization and enabling production of mesoporous carbon having a small particle size.SOLUTION: A method for producing a mesoporous carbon carrier, comprises the following steps: Step (1): subjecting phenols (A), aldehydes (B), and a surfactant (C) to a polymerization reaction in an aqueous organic solvent in the coexistence of a thermally decomposable polymer (D); Step (2): removing the solvent from the resulting solution to obtain a dried material, and heating the dried material under an inert gas atmosphere to obtain a mesoporous carbon mass; and Step (3): pulverizing the resulting mesoporous carbon mass.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a mesoporous carbon support, and more particularly to a method for producing a mesoporous carbon support suitable for use as a porous carbon support for an electrode material of a polymer electrolyte fuel cell or the like. [Background technology]

[0002] Mesoporous carbon (MC) is a carbon material with meso-sized pores, and has recently attracted attention as an electrode catalyst support for polymer electrolyte fuel cells (PEFCs). A widely known method for producing mesoporous carbon involves mixing a carbon precursor compound with template particles such as magnesium oxide, and then heat-treating the mixture in a nitrogen atmosphere to produce a carbide from which the template particles are eluted to obtain mesoporous carbon (see, for example, Patent Document 1). Another known method for synthesizing mesoporous carbon without using template particles is to obtain mesoporous carbon by heat-treating a self-assembled composition of a surfactant and a carbon precursor in a nitrogen atmosphere to carbonize it (see Patent Document 2 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-208887 [Patent Document 2] WO2008 / 093731 [Non-patent literature]

[0004] [Non-Patent Document 1] ECS Trans., 109(9), 349 (2022) Summary of the Invention [Problem to be solved by the invention]

[0005] When mesoporous carbon is used as an electrode catalyst support for fuel cell electrodes, if the particle size of the mesoporous carbon is large (particle size of about 1 to 2 μm), the inter-particle resistance becomes large, so mesoporous carbon with a small particle size (particle size of about 0.05 to 1 μm) is required. In the mesoporous carbon synthesis method, the carbonized product obtained by heat-treating and carbonizing a carbon precursor is a bulk agglomerate, which must be pulverized to reduce particle size. However, the mesoporous carbon agglomerates obtained by the above-mentioned conventional synthesis method are very hard, and there are limitations to how much they can be pulverized by ball mill pulverization. Furthermore, if the pulverization intensity is increased or the pulverization time is extended to obtain mesoporous carbon with a smaller particle size, the carbon walls that make up the mesopores in the mesoporous carbon are destroyed, which can lead to blockage of the mesopores.

[0006] Under these circumstances, an object of the present invention is to solve the above-mentioned problems in the prior art and to provide a method for producing a mesoporous carbon support that can easily be pulverized to obtain mesoporous carbon with small particle sizes. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the following invention meets the above object, thereby completing the present invention.

[0008] That is, the present invention relates to the following inventions. <1> A method for producing a mesoporous carbon support, comprising the following steps: Step (1): A step of polymerizing a phenol (A), an aldehyde (B), and a surfactant (C) in the presence of a thermally dissipative polymer (D) in a water-containing organic solvent. Step (2): A step of distilling off the solvent from the resulting solution, and then heat-treating the resulting dried product in an inert gas atmosphere to obtain a mesoporous carbon aggregate. Step (3): A step of crushing the obtained mesoporous carbon aggregates <2> In step (1), phenols (A) and aldehydes (B) are prepolymerized in the presence of a surfactant (C), and then mixed with a heat-dissipating polymer (D) to further promote the polymerization reaction. <1> 1. A method for producing the mesoporous carbon support according to claim 1. <3> The phenol (A) is phloroglucinol and the aldehyde (B) is formaldehyde. <1> or <2> 1. A method for producing the mesoporous carbon support according to claim 1. <4> The surfactant (C) is a nonionic surfactant. <1> from <3> 1. A method for producing a mesoporous carbon support according to any one of the preceding claims. <5> The thermally dissipative polymer (D) is a hydrophilic polymer. <1> from <4> 1. A method for producing a mesoporous carbon support according to any one of the preceding claims. <6> The heat-dissipating polymer (D) is polyvinyl alcohol. <1> from <5> 1. A method for producing a mesoporous carbon support according to any one of the preceding claims. <7> <1> from <6> 1. A mesoporous carbon support obtained by the production method according to any one of the above. <8> A porous carbon support and electrode catalyst particles supported on the porous carbon support, At least a portion of the porous carbon support is <7> An electrode material which is the mesoporous carbon support according to claim 1. <9> <8> An electrode comprising the electrode material according to claim 1 and a proton-conducting electrolyte material. <10> A membrane electrode assembly having a solid polymer electrolyte membrane, a cathode bonded to one side of the solid polymer electrolyte membrane, and an anode bonded to the other side of the solid polymer electrolyte membrane, wherein either or both of the anode and the cathode are <9> A membrane electrode assembly, which is the electrode according to claim 1. <11> <10> A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 1. [Effects of the Invention]

[0009] According to the present invention, there is provided a method for producing a mesoporous carbon support that can be easily pulverized to obtain a mesoporous carbon support having a small particle size. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of the procedure for producing the mesoporous carbon support of Example 1. [Figure 2] 1A and 1B are FE-SEM images of mesoporous carbon supports, where (a) is Example 1 and (b) is Comparative Example 1. [Figure 3] 1 shows the results of measuring the pore distribution of mesoporous carbon supports of Example 1 and Comparative Example 1. [Figure 4] 1 shows the IV characteristics and overvoltage characteristics of PEFCs (single cells) using MEAs of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples below and can be practiced with any modifications within the scope of the gist of the present invention. In this specification, the symbol "to" is used as an expression including the numerical value or physical quantity before and after it.

[0012] (Definitions of terms, etc.) In this specification, the term "pore" includes, for example, pores with a diameter of 150 nm or less. In addition, in this specification, the term "micropore" refers to a pore with a diameter of less than 2 nm, the term "mesopore" refers to a pore with a diameter of 2 nm to 50 nm, and the term "macropore" refers to a pore with a diameter of more than 50 nm but not more than 150 nm.

[0013] In this specification, the term "porous carbon support" refers to a porous carbon material that serves as the skeleton (base) of an electrode material, and the term "mesoporous carbon support" refers to a porous carbon support made of mesoporous carbon.

[0014] In this specification, mesoporous carbon may be referred to as "MC", a mesoporous carbon support may be referred to as an "MC support", and a mesoporous carbon aggregate may be referred to as an "MC aggregate".

[0015] In addition, in this specification, the cathode conditions of a polymer electrolyte fuel cell (PEFC) refer to the conditions at the cathode during normal operation of the PEFC, where the temperature is from room temperature to approximately 150°C and a gas containing oxygen such as air is supplied (oxidizing atmosphere), and the anode conditions refer to the conditions at the anode during normal operation of the PEFC, where the temperature is from room temperature to approximately 150°C and a fuel gas containing hydrogen is supplied (reducing atmosphere).

[0016] <1. Method for producing mesoporous carbon support> The present invention relates to a method for producing a mesoporous carbon support, which comprises the following steps: Step (1): A step of polymerizing a phenol (A), an aldehyde (B), and a surfactant (C) in the presence of a thermally dissipative polymer (D) in a water-containing organic solvent. Step (2): A step of distilling off the solvent from the resulting solution, and then heat-treating the resulting dried product in an inert gas atmosphere to obtain a mesoporous carbon aggregate. Step (3): A step of crushing the obtained mesoporous carbon aggregates

[0017] In the following description, the phenols (A), aldehydes (B), surfactants (C), and heat-dissipating polymers (D) may be referred to as component (A), component (B), component (C), and component (D), respectively.

[0018] In the method for producing an MC support of the present invention, a carbon material having mesopores is formed by the reaction of components (A) to (C), and at the same time, an MC aggregate is obtained in which pores larger than the mesopores are formed due to the thermal decomposition and disappearance of component (D). The MC agglomerates are easily crushed starting from the pores derived from the heat-dissipating polymer, component (D), and it is easy to obtain small particle size MC carriers (MC granules) while maintaining the mesopores of the MC during crushing.

[0019] The MC support produced by the production method of the present invention maintains its mesopores without destruction, and can therefore be suitably used as a support for electrode materials (particularly electrode materials for fuel cells). The MC support of the present invention has the following advantages: when electrode catalyst particles such as Pt are supported to prepare an electrode material for a fuel cell, particle growth of the electrode catalyst particles in the pores of the MC support is suppressed, direct contact with Nafion, an ionomer, is reduced, and poisoning of the Pt surface is suppressed (proton conduction is possible just by having Nafion nearby).

[0020] The method for producing the MC carrier of the present invention will be described in detail below.

[0021] <Process (1)> Step (1) is a step of polymerizing a phenol (A), an aldehyde (B), and a surfactant (C) in the presence of a heat-dissipating polymer (D) in a water-containing organic solvent.

[0022] In step (1), carbon precursors, phenols (A) and aldehydes (B), are self-assembled together with a surfactant (C) in an aqueous organic solvent, followed by heat treatment and carbonization to obtain a porous material with mesopores (MC support). In the present invention, by reacting components (A) to (C) in the presence of a heat-dissipating polymer (D), a porous material is formed that contains not only mesopores but also pores larger than the mesopores resulting from component (D).

[0023] Components (A) to (D), the aqueous organic solvent and other components used in the method for producing the MC carrier of the present invention will be described in detail below.

[0024] <Component (A): Phenols> The phenols of component (A) are organic compounds having an OH group on the benzene ring, and examples thereof include monohydric phenols such as phenol, o-cresol, m-cresol, and p-cresol; dihydric phenols such as resorcinol, catechol, hydroquinone, and dihydroxynaphthalene; and trihydric phenols such as phloroglucinol. These phenols can be used alone or in combination of two or more. Among these, phloroglucinol represented by the following formula (1) is preferably used.

[0025] [ka]

[0026] <Component (B): Aldehydes> The aldehydes, which are component (B), are organic compounds having a CO group, such as formaldehyde, acetaldehyde, butylaldehyde, salicylaldehyde, and benzaldehyde, which can be used alone or in combination of two or more. Among these, formaldehyde represented by the following formula (2) is preferably used.

[0027] [ka]

[0028] In the method for producing an MC carrier of the present invention, a combination of carbon precursors (component (A) and component (B)) that is preferably used is phloroglucinol and formaldehyde.

[0029] <Component (C): Surfactant> The surfactant as component (C) is not particularly limited as long as it can promote self-assembly with the phenols (A) and the aldehydes (B), and any of cationic surfactants, anionic surfactants, and nonionic surfactants can be used, with nonionic surfactants being preferred.

[0030] The nonionic surfactant is not limited as long as it does not impair the object of the present invention, and examples thereof include triblock copolymers of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) or polypropylene oxide-polyethylene oxide-polypropylene oxide (PPO-PEO-PPO) with various polymerization ratios and a molecular weight of about 2,000 to about 13,000, as well as polyoxyethylene alkyl ethers having an alkyl group with 12 to 18 carbon atoms, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, sorbitan monopalmitate, sorbitan monolaurate, and sorbitan monostearate. , sorbitan distearate, sorbitan monooleate, sorbitan sesquioleate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, oleic acid monoglyceride, stearic acid monoglyceride, polyoxyethylene laurylamine, polyoxyethylene stearylamine, etc. These may be used alone or in combination of two or more.

[0031] A suitable commercially available non-ionic surfactant is, for example, Pluronic® F-127.

[0032] The proportion of surfactant (C) is appropriately selected within a range that allows the carbon precursors (Components (A) and (B)) to self-assemble and form a sufficient amount of mesopores. The proportion of surfactant (C) varies depending on the types of Components (A) and (B), but is, for example, 0.1 to 60 mass%.

[0033] <Component (D): Heat-dissipating polymer> The thermally dissipative polymer, component (D), is used to form pores larger than mesopores in the MC mass produced through step (2). The method for producing an MC carrier of the present invention is characterized by the use of a heat-dissipating polymer (D). By subjecting the carrier containing the heat-dissipating polymer (D) to the heat treatment step (2), the heat-dissipating polymer disappears, and an MC aggregate having pores (mainly macropores) larger than mesopores can be obtained.

[0034] Although a portion of the thermally dissipative polymer may remain, the remaining component (D) becomes a carbon source that constitutes the MC carrier through further heating and carbonization treatment.

[0035] The thermally dissipative polymer (D) is a polymer that can be dissolved or dispersed in a water-containing organic solvent, has a decomposition temperature lower than the heat treatment temperature for carbonizing the carbon precursors, components (A) and (B), and can be decomposed, gasified, and removed under the heat treatment conditions of step (2), and any polymer can be selected and used as long as it is.

[0036] The molecular weight of the thermally dissipative polymer (D) may be any molecular weight that provides pores (mainly macropores) suitable for pulverizing the MC agglomerates when it is dissipated by heat treatment, for example, a weight-average molecular weight (Mw) of 100,000 or more. There is no upper limit to the molecular weight as long as pores suitable for pulverizing the MC agglomerates are formed, but the upper limit is, for example, 500,000 or less.

[0037] The thermally dissipative polymer may be either a hydrophilic or hydrophobic polymer as long as it is soluble or dispersible in a water-containing organic solvent, but hydrophilic polymers are preferred because they have superior solubility and dispersibility to hydrophobic polymers.

[0038] The hydrophilic polymer is not particularly limited as long as it exhibits the effects of the present invention, and examples thereof include polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyethyleneimine, methylcellulose, etc. These may be used alone or in combination of two or more.

[0039] Among these, polyvinyl alcohol (PVA) is preferably used. Suitable commercially available polyvinyl alcohol agents include, for example, Mowiol (registered trademark) 40-88 (Mw: 205,000, Sigma-Aldrich Inc.).

[0040] The proportion of the heat-dissipating polymer (D) used relative to the carbon precursor (component (A) and component (B)) is not particularly limited as long as the effects of the present invention are achieved, and although it depends on the type of carbon precursor (component (A) and component (B)) used, it is 10% by weight to 70% by weight when the total of component (A) and component (B) is 100% by weight.

[0041] <Water-containing organic solvent> In the method for producing an MC carrier of the present invention, a water-containing organic solvent (a mixed solvent of an organic solvent and water) is used as the solvent.

[0042] The water is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof include distilled water and ion-exchanged water.

[0043] The organic solvent in the water-containing organic solvent may be a hydrophilic organic solvent that is compatible with water and can dissolve components (A) to (D) when mixed with water, and is not particularly limited. Examples include lower alcohols such as methanol, ethanol, n-propanol, and isopropanol; and glycols such as propylene glycol, diethylene glycol, and 1,3-butylene glycol. The organic solvent may be one type, or two or more types may be mixed. Among these, lower alcohols are preferred, and ethanol is more preferred.

[0044] The ratio of water to organic solvent in the aqueous organic solvent is not particularly limited as long as it is within a range that can dissolve components (A) to (D). If the ratio of water is too high, the solubility of the phenols (A) decreases, and if the ratio of organic solvent is too high, the solubility of the aldehydes (B) and the thermally dissipative polymer (D) decreases. Therefore, the ratio of water to organic solvent can be determined depending on the type and concentration of each component and the type of organic solvent. For example, when the organic solvent is ethanol, the proportion of ethanol is, for example, 30 to 70% by weight when the total of all the aqueous organic solvents is 100% by weight.

[0045] <Other ingredients> The solution in step (1) may contain components other than the above components (A) to (D) and the aqueous organic solvent (other components), such as a polymerization catalyst and a reaction accelerator.

[0046] The solution in step (1) may contain a polymerization catalyst to promote the polymerization reaction between the phenol (A) and the aldehyde (B). The polymerization catalyst may be any catalyst that can improve the reactivity of the phenols (A) with the aldehydes (B) and promote the formation of a three-dimensional network structure by polymerization, and either an acidic catalyst or a basic catalyst can be used. As the acidic catalyst, for example, inorganic acids such as hydrochloric acid, sulfuric acid, etc. can be used. As the basic catalyst, for example, sodium hydroxide, sodium carbonate, calcium carbonate, etc. can be used.

[0047] The other components may include a reaction aid, such as triethyl orthoacetate.

[0048] <Reaction conditions> In step (1), the order of addition of components (A) to (D) is not particularly limited as long as the phenols (component (A)), the aldehydes (component (B)), and the surfactant (component (C)) can be polymerized in the presence of a thermally dissipative polymer in an aqueous organic solvent, and the order of addition of components (A) to (D) is not particularly limited as long as there are no particular problems, such as the generation of precipitates. For example, any two or three or more of the constituent components may be blended in advance, and then the remaining components may be mixed, or all of the components may be mixed at once.

[0049] The reaction conditions in step (1) are not particularly limited as long as the polymerization reaction of the carbon precursors (components (A) and (B)) proceeds. The reaction temperature is, for example, 40 to 130°C, and the reaction time is, for example, 3 to 48 hours.

[0050] It is particularly preferred to carry out a prepolymerization reaction of components (A) and (B) in an aqueous organic solvent in the presence of component (C), and then mix the resulting mixture with component (D). A porous material with a high proportion of mesopores can be obtained by prepolymerizing the carbon precursors, components (A) and (B), to partially polymerize them, and then mixing them with component (D). In this case, it is preferable to carry out the prepolymerization reaction of components (A) and (B) at 40 to 60°C, add and mix component (D), and then further proceed with the polymerization reaction at a temperature of 100 to 130°C.

[0051] <Process (2)> Step (2) is a step in which the dried product obtained by distilling off the solvent from the solution obtained in step (1) is heat-treated under an inert gas atmosphere to obtain MC aggregates.

[0052] The method for distilling off the solvent may be any method as long as it does not impair the object of the present invention. Vacuum drying or freeze drying may be used, but a method in which the solvent is evaporated while heating is preferred.

[0053] The resulting dried product is carbonized by heat treatment under an inert gas atmosphere, during which pores (mainly macropores) originating from the thermally dissipative polymer (D) are formed.

[0054] The heat treatment conditions (carbonization conditions) are appropriately determined taking into consideration the types of carbon precursors used, namely, phenols (A), aldehydes (B), surfactants (C) and thermally dissipative polymers (D), as well as the physical properties of the desired MC carrier. As the inert gas, nitrogen, helium, argon, etc. can be used.

[0055] The heat treatment temperature and heat treatment time under an inert gas atmosphere are not particularly limited as long as the desired MC carrier is obtained, but the heat treatment temperature is usually 300 to 1000°C (preferably 350 to 900°C), and the heat treatment time is not particularly limited, but is usually 1 to 20 hours. Alternatively, the heat treatment may be performed at a multiple-stage heat treatment temperature. For example, as in the examples, the heat treatment may be performed at 400°C for 3 hours, then heated to 700°C for 3 hours, and then cooled and heated again to 700°C for 6 hours.

[0056] <Process (3)> Step (3) is a step of pulverizing the MC aggregates obtained in step (2). In step (3), the aggregates are pulverized to obtain the desired MC carrier.

[0057] The obtained MC support can be suitably used as a carbon support for electrode materials in secondary batteries and fuel cells.

[0058] As described above, the MC aggregate obtained in step (2) contains not only mesopores but also pores larger than the mesopores resulting from component (D). Since the pores resulting from component (D) serve as the starting points for milling, even if mechanical milling is performed, destruction of the mesopore portion is avoided or suppressed, and the MC aggregate is milled.

[0059] There are no particular limitations on the pulverization method, but a ball mill is preferably used.

[0060] There is no particular limitation on the degree of pulverization, and it can be appropriately selected depending on the intended use of the MC carrier of the present invention. When the MC support of the present invention is used, for example, as an electrode catalyst support constituting an electrode for a fuel cell, electrical conductivity and gas diffusibility are required within the electrode when the electrode is formed. Therefore, in order to achieve both electrical conductivity and gas diffusibility, a particle size of 0.03 to 2 μm is preferable.

[0061] The size of the MC carrier can be obtained by averaging the sizes of 50 arbitrary MC carriers examined from electron microscope images. If the shape of the MC carrier is not spherical, the length in the direction showing the maximum length is taken as the size of the MC carrier.

[0062] The pulverized MC carrier may be subjected to post-treatment to remove carbon defects on the surface and to improve the connectivity of the pores. For example, as shown in the examples, the post-treatment may involve heat treatment at 800°C or higher in an inert gas atmosphere, followed by cooling to 500°C or lower and heat treatment in air for about 10 minutes.

[0063] The MC carrier obtained by the production method of the present invention has a plurality of pores that form a three-dimensional network structure. "Having a plurality of pores that form a three-dimensional network structure" means that the MC carrier has a plurality of pores on the surface and inside, and adjacent pores are connected to each other, so that the pores are connected three-dimensionally and communicated with each other on the surface, forming open pores.

[0064] The MC support of the present invention contains pores in the mesopore region (2 nm to 50 nm). In particular, as shown in the examples, it is characterized by a higher proportion of pores in the 8 nm to 20 nm range compared to conventional MC supports synthesized without using component (D).

[0065] The MC support of the present invention may contain regions other than mesopores (micropores, macropores).

[0066] <2. Electrode material> The electrode material of the present invention comprises a porous carbon support and electrode catalyst particles supported on the porous carbon support, and at least a part of the porous carbon support is an MC support obtained by the above-described production method of the present invention.

[0067] The electrode material of the present invention is suitable as an electrode material for use in electrodes for polymer electrolyte fuel cells, but can also be used for other purposes.

[0068] The electrode material of the present invention will be described in detail below.

[0069] (porous carbon support) The porous carbon support, which is the skeleton of the electrode material of the present invention, is a porous carbon having a large number of pores. The porous carbon support may consist solely of the MC support of the present invention, or may contain other porous carbon supports in any proportion.

[0070] The size and shape of the electrode material of the present invention depend on those of the porous carbon support, which is its framework material. The size and shape of the porous carbon support are determined so that the electrode material can be in continuous contact with the porous carbon support when the electrode for a fuel cell is formed, and a space large enough to allow smooth diffusion of gases such as hydrogen and oxygen and smooth discharge of water (vapor) within the electrode for a fuel cell can be formed.

[0071] The MC carrier of the present invention is as described above.

[0072] The mesopores in the MC support of the present invention preferably have a three-dimensional network structure, including not only individual pores that are independent of other pores but also interconnected pores in which some or all of the mesopores are interconnected with adjacent mesopores. The presence of interconnected pores promotes the diffusion of substances within the pores of the mesoporous carbon.

[0073] As described above, the MC support of the present invention has a higher proportion of pores of 8 nm to 20 nm compared to conventional MC supports, and even when an electrode catalyst is fixed (supported) on the inner walls of the pores, the diffusion of substances into the pores is not significantly hindered and proceeds smoothly.

[0074] Furthermore, when producing a fuel cell electrode, the electrode material of the present invention is mixed with a proton-conductive electrolyte material (ionomer). However, since the proton-conductive electrolyte material (ionomer) cannot penetrate into small-diameter pores, it is possible to suppress poisoning of the electrode catalyst particles supported via the porous carbon support within the pores of the porous carbon support by the ionomer.

[0075] As other porous carbon supports, carbon materials of any shape and size, such as granular or fibrous, that can be used as electrode materials for fuel cells can be used. Examples of carbon materials include particulate carbon (including chain-linked carbon particles) such as carbon black and activated carbon. Furthermore, mesoporous carbon produced by a method different from that of the present invention may be used as part of the porous carbon support.

[0076] (electrode catalyst particles)

[0077] In the electrode material of the present invention, the electrode catalyst particles are supported inside the pores of the porous carbon support and on the outer surfaces of the pores.

[0078] The electrode catalyst particles may be either a precious metal catalyst or a non-precious metal catalyst as long as they have electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation). Preferably, they are selected from precious metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, and Ag, and alloys containing these precious metals. The term "alloy containing a precious metal" includes both "alloys consisting solely of the above-mentioned precious metals" and "alloys consisting of the above-mentioned precious metals and other metals, containing 10% by mass or more of the above-mentioned precious metals." The "other metals" to be alloyed with the precious metal are not particularly limited, but preferred examples include Co, Ni, and Ta. One or more of these may be used. Furthermore, two or more of the above-mentioned precious metals and alloys containing the precious metals in a phase-separated state may also be used. In the present specification, the above-mentioned precious metals and alloys containing these precious metals may be referred to as "electrocatalyst metals."

[0079] Among the electrode catalyst metals, Pt and alloys containing Pt (Pt alloys) are particularly suitable for use because they have high electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) in the temperature range around 80°C, which is the operating temperature of solid polymer fuel cells. The metal species other than Pt in the Pt alloy is not particularly limited as long as it can form an alloy, but is preferably cobalt (Co).

[0080] The shape of the electrode catalyst particles is not particularly limited, and shapes similar to those of known electrode catalyst particles can be used. Specific shapes include spherical, elliptical, polyhedral, and core-shell structures. Furthermore, the structure of the electrode catalyst particles is not limited to crystalline, and may be amorphous or a mixture of crystalline and amorphous.

[0081] The smaller the size of the electrode catalyst particles, the greater the effective surface area where the electrochemical reaction proceeds, and therefore the higher the electrochemical catalytic activity tends to be. However, if the size is too small, the electrochemical reaction activity decreases. Therefore, the size of the electrode catalyst particles is preferably 0.5 to 4 nm in average particle size.

[0082] The "average particle size of electrode catalyst particles" in the present invention can be obtained by averaging the particle sizes of electrode catalyst particles (20 particles) examined from an electron microscope image. When calculating the average particle size from an electron microscope image, if the shape of the fine particles is other than spherical, the length in the direction showing the maximum length of the particle is taken as the particle size.

[0083] The amount of electrode catalyst particles supported is determined appropriately taking into consideration conditions such as the type of catalyst and the size of the porous carbon support. The amount of electrode catalyst particles supported is, for example, 0.1 to 60 mass % (preferably 30 to 50 mass %) relative to the total weight of the electrode material. Within this range, excellent catalytic activity per unit mass can be achieved, and a desired electrode reaction activity corresponding to the supported amount can be obtained. If the catalyst loading is too low, the electrode performance will be insufficient, and if it is too high, the electrode catalyst particles may aggregate and performance may decrease. The amount of electrode catalyst particles loaded can be determined, for example, by inductively coupled plasma emission spectroscopy (ICP).

[0084] The amount of electrode catalyst particles supported is usually 3 to 40 mass % relative to the porous carbon support. Within this range, excellent catalytic activity per unit mass can be achieved, and desired electrochemical catalytic activity can be obtained according to the supported amount. The amount of electrode catalyst particles carried can be determined by, for example, inductively coupled plasma emission spectrometry (ICP).

[0085] The method for producing the electrode material of the present invention described above is not particularly limited, and a suitable method may be selected as appropriate depending on the types of porous carbon support and electrode catalyst particles that constitute the electrode material of the present invention. A typical example is a method in which a porous carbon support and a solution containing an electrode catalyst precursor are mixed, the solvent is distilled off, and the resulting dried product is heat-treated to produce electrode catalyst particles.

[0086] <3. Electrode> The electrode of the present invention comprises the above-described electrode material of the present invention and a proton-conductive electrolyte material. In the electrode of the present invention, the electrode materials of the present invention are in contact with each other to form a conductive path.

[0087] A fuel cell electrode formed using the electrode material of the present invention will be described below. Specifically, the case where the above-mentioned electrode material is used as an electrode in a polymer electrolyte fuel cell (PEFC) will be described.

[0088] This fuel cell electrode may be composed of only the above-mentioned electrode material, but typically also contains a proton-conductive electrolyte material used in the electrolyte of a fuel cell (hereinafter, sometimes referred to as a "proton-conductive electrolyte material" or simply as an "electrolyte material"). The electrolyte material contained in the fuel cell electrode together with the electrode material may be the same as or different from the electrolyte material used in the fuel cell electrolyte membrane. From the viewpoint of improving adhesion between the fuel cell electrode and the electrolyte membrane, it is preferable to use the same material.

[0089] Proton-conductive electrolyte materials are used in the electrodes and electrolyte membranes of PEFCs. These proton-conductive electrolyte materials are broadly classified into fluorine-based electrolyte materials, which contain fluorine atoms in all or part of the polymer skeleton, and hydrocarbon-based electrolyte materials, which do not contain fluorine atoms in the polymer skeleton. Both of these can be used as electrolyte materials.

[0090] Specific examples of suitable fluorine-based electrolyte materials include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

[0091] Specific examples of suitable hydrocarbon-based electrolyte materials include polymers such as polysulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole sulfonic acid, polybenzimidazole phosphonic acid, and polyimide sulfonic acid, as well as polymers of these having a side chain such as an alkyl group.

[0092] The mass ratio of the electrode material to the electrolyte material mixed with the electrode material can be determined appropriately to provide good proton conductivity within the electrode formed using these materials and to facilitate smooth gas diffusion and water vapor discharge within the electrode. However, if too much electrolyte material is mixed with the electrode material, proton conductivity improves but gas diffusibility decreases. Conversely, if too little electrolyte material is mixed, gas diffusibility improves but proton conductivity decreases. Therefore, the mass ratio of the electrolyte material to the electrode material is preferably in the range of 10 to 50 mass%. If this mass ratio is less than 10 mass%, the continuity of the proton-conducting electrolyte material decreases, making it impossible to ensure sufficient proton conductivity for a fuel cell electrode. Conversely, if it is more than 50 mass%, the continuity of the electrode material decreases, potentially making it impossible to provide sufficient electronic conductivity for a fuel cell electrode. Furthermore, the diffusibility of gases (oxygen, hydrogen, water vapor) within the electrode may decrease.

[0093] The electrode of the present invention may contain components other than the above-mentioned electrode material and proton-conductive electrolyte material, provided that the object of the present invention is not impaired. For example, the electrode material of the present invention may contain a conductive material other than the porous carbon support (hereinafter referred to as "another conductive material"), which may increase the number of conductive paths connecting the electrode materials and improve the conductivity of the electrode as a whole.

[0094] As the other conductive material, known conductive materials used in electrodes for fuel cells can be used.

[0095] Although the electrode containing the electrode material of the present invention has been described as an electrode for a PEFC, the electrode material can also be used as an electrode in various fuel cells other than PEFCs, such as alkaline fuel cells and phosphoric acid fuel cells. The electrode material can also be suitably used as an electrode for a water electrolysis device that uses a polymer electrolyte membrane similar to that of a PEFC. The electrode for a fuel cell comprising the electrode material of the present invention has excellent electrochemical catalytic activity for oxygen reduction and hydrogen oxidation, and can therefore be used as a cathode or an anode. In particular, the electrode has excellent electrochemical catalytic activity for oxygen reduction, and electrochemical oxidative decomposition of the conductive material, which is the carrier, does not occur under the operating conditions of the fuel cell, so the electrode is particularly suitable for use as a cathode.

[0096] <4. Membrane electrode assembly (MEA)> The membrane electrode assembly of the present invention is a membrane electrode assembly having a solid polymer electrolyte membrane, a cathode bonded to one surface of the solid polymer electrolyte membrane, and an anode bonded to the other surface of the solid polymer electrolyte membrane, wherein either or both of the cathode and the anode are the above-described electrodes of the present invention.

[0097] As a preferred embodiment of the present invention, a membrane electrode assembly will be described in which an electrode containing the electrode material of the present invention is used as a cathode.

[0098] The membrane electrode assembly has a structure in which a cathode and an anode are arranged facing a solid polymer electrolyte membrane.

[0099] The cathode is composed of a cathode electrode catalyst layer and a gas diffusion layer. The cathode electrode catalyst layer can be the electrode of the present invention using the electrode material of the present invention described above. The thickness of the cathode electrode catalyst layer is not particularly limited, but is, for example, 1 μm or more and 100 μm or less.

[0100] The gas diffusion layer may be a conventionally known gas diffusion layer. For example, a conductive carbonaceous sheet-like material having a pore size distribution of approximately 100 nm to 90 μm, which has been conventionally used as a gas diffusion layer in PEFCs, may be used. Preferably, carbon paper, carbon cloth, or carbon nonwoven fabric that has been subjected to a water-repellent treatment may be used. Sheet-like materials other than carbonaceous materials, such as stainless steel, may also be used. The thickness of such a gas diffusion layer is not particularly limited, but is typically approximately 50 μm to 1 mm. Furthermore, the gas diffusion layer may have a microporous layer on one side thereof, which is composed of an aggregate of carbon particles with an average particle size of approximately 10 to 100 nm and a water-repellent material.

[0101] The anode is composed of an anode electrode catalyst layer and a gas diffusion layer. In addition to the electrode of the present invention, other known anodes can also be used. For example, an electrode may be formed by coating and drying an electrode material carrying precious metal particles as a catalyst and a dispersion of an electrolyte material for a fuel cell on the surface of a conductive support made of a carbonaceous material such as graphite, carbon black, activated carbon, carbon nanotubes, or glassy carbon, and then forming an electrode catalyst layer on the gas diffusion layer. The gas diffusion layer of the anode can be the same as the gas diffusion layer described for the cathode.

[0102] The solid polymer electrolyte membrane may be any known electrolyte membrane for PEFCs as long as it has proton conductivity and chemical and thermal stability. The thickness of the solid polymer electrolyte membrane is usually about 0.007 to 0.05 mm to reduce electrical resistance.

[0103] Examples of electrolyte materials constituting the solid polymer electrolyte membrane include fluorine-based electrolyte materials and hydrocarbon-based electrolyte materials. Electrolyte membranes formed from fluorine-based electrolyte materials are particularly preferred due to their excellent heat resistance and chemical stability. Specific examples of suitable materials include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

[0104] Although the embodiments of the MEA of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted.

[0105] <5. Polymer electrolyte fuel cell> The polymer electrolyte fuel cell (single cell) of the present invention comprises the membrane electrode assembly of the present invention, and generally has a structure in which the membrane electrode assembly is sandwiched between separators having gas flow paths formed therein.

[0106] In a polymer electrolyte fuel cell, hydrogen is supplied to the anode, and (reaction 1) 2H2 → 4H + +4e - The protons (H + ) is supplied to the cathode through the solid polymer electrolyte membrane, and the generated electrons are supplied to the cathode through an external circuit, resulting in (reaction 2) O2 + 4H + +4e - →2H2O reacts with oxygen to produce water. This electrochemical reaction between the anode and cathode generates a potential difference between the two electrodes. In the polymer electrolyte fuel cell of the present invention, the components other than the membrane electrode assembly of the present invention are the same as those of known polymer electrolyte fuel cells, so detailed description will be omitted. In practice, a fuel cell stack is formed by stacking the polymer electrolyte fuel cells (single cells) of the present invention in a number according to the power generation performance, and is used by assembling other associated devices such as a gas supply device and a cooling device. [Example]

[0107] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0108] 1. Production of MC agglomerates and MC carriers The reagents used are as follows: Phloroglucinol dihydrate (Wako, 162-02052) Resorcinol (Wako, 184-00071) Nonionic surfactant (Pluronic(R) F-127) Formaldehyde (Wako, 064-00406) Triethyl orthoacetate (Wako, 208-08363) Polyvinyl alcohol (PVA) solution (Mowiol® 40-88, Sigma-Aldrich 324590, weight average molecular weight ~ 205,000 g / mol)

[0109] Example 1 At 45°C, 3.01 mL of water, 10.95 mL of ethanol (purity 99.5%), and 0.6 mL of 5 M hydrochloric acid were added and stirred until homogenous, and then 3.19 g of phloroglucinol dihydrate was added as a carbon precursor and stirred until homogenous. To the resulting solution, 3.0 g of a nonionic surfactant (Pluronic F-127) was added and stirred for 15 minutes to dissolve. Then, 1.8 g of formaldehyde and 1.8 mL of triethyl orthoacetate were added and stirred for 15 minutes to perform prepolymerization. The resulting solution was added to 8.25 g of a separately prepared 13 wt% PVA solution (2.6 g of PVA + 17.3 mL of water) and stirred for 15 minutes to dissolve.

[0110] The resulting solution was kept at 110°C for 5 hours under a nitrogen atmosphere to promote the polymerization reaction, and the solvent was distilled off to obtain a dried product. The dried product was heat-treated under the following conditions to obtain the MC aggregate (bulk) of Example 1. <Heat treatment conditions> 1st time: 400℃, 3 hours, 700℃, 3 hours 2nd time: 700℃, 6 hours

[0111] The obtained MC agglomerate of Example 1 was pulverized in a wet ball mill under the following conditions: The MC agglomerate of Example 1 was pulverized into a uniform powder (MC carrier) by ball milling. <Ball mill grinding conditions> Fritsch Pulverisette 7, φ1 mm zirconia balls and φ0.5 mm zirconia balls Primary grinding: 450 rpm, 2 hours Secondary grinding: 800 rpm, 2 hours, 2 times

[0112] The sample after being crushed by the ball mill was subjected to a heat treatment under the following conditions as a post-treatment, thereby obtaining an MC support of Example 1. <Post-processing conditions> 900℃ in nitrogen atmosphere for 3 hours 450℃ in air for 10 minutes

[0113] (Comparative Example 1) At 30°C, 1.65 g of resorcinol as a carbon precursor was added to a solution containing 4.35 g of ultrapure water, 5.75 g of ethanol (purity 99.5%), and 150 μL of 5 M hydrochloric acid, and the mixture was stirred until homogenous. To the resulting solution, 0.945 g of a nonionic surfactant (Pluronic F-127) was added and stirred for 30 minutes to dissolve, after which 1.35 g of formaldehyde and 1.35 mL of triethyl orthoacetate were added and stirred for 24 hours.

[0114] The resulting solution was allowed to stand overnight and then centrifuged, the supernatant was removed, and the resulting residue was heat-treated under the same conditions as in Example 1 to obtain the MC aggregate of Comparative Example 1. The MC aggregate of Comparative Example 1 was ball milled (except for secondary milling three times) and post-treated under the same conditions as in Example 1 to obtain the MC carrier of Comparative Example 1. The MC agglomerates of Comparative Example 1 could not be uniformly pulverized even when the number of times of ball mill pulverization was increased, so the pulverized powder was used as the MC carrier of Comparative Example 1 for the subsequent evaluations.

[0115] 2. Evaluation 2-1. Microstructure observation The microstructures of the MC supports of Example 1 and Comparative Example 1 were observed. Figure 2(a) shows an FE-SEM image of the MC support of Example 1, and Figure 2(b) shows an FE-SEM image of the MC support of Comparative Example 1. A Hitachi High-Tech SU9000 field emission scanning electron microscope (FE-SEM) was used.

[0116] As shown in Figure 2(a), the MC support of Example 1, which was produced by the manufacturing method of the example (with PVA), had a structure consisting of an aggregate of fine carbon particles of about 50 to 100 nm, and pores of about 100 nm were also observed in some places. On the other hand, as shown in FIG. 2(b), the MC obtained from the MC support of Comparative Example 1, which was produced by the conventional production method (without PVA), existed in the form of relatively large plates.

[0117] 2-2. Pore distribution The pore distribution of the MC carriers of Example 1 and Comparative Example 1 was measured using a specific surface area / pore distribution measuring device. The results of evaluation using a device (device name: BELSORP MINI X, manufacturer: Microtrac Bel) are shown in Figure 3. As shown in Figure 3, the MC support of Comparative Example 1 had a sharp pore distribution with a peak near 6 nm, whereas the MC support of Example 1 had a broad pore distribution with a peak near 10 nm. Overall, it was confirmed that the MC support of Example 1 tended to have larger pore diameters than the MC support of Comparative Example 1.

[0118] 2-3. Electrochemical evaluation (single cell, power generation test) (Preparation of electrode materials) First, as a cathode electrode material, Pt was supported on the MC support of Example 1 by the following procedure to prepare the electrode material of Example 1. MC carrier powder (400 mg) and ethanol (49.98 mL) were placed in a three-neck flask and treated with an ultrasonic homogenizer for 1 minute. Ultrapure water (333.25 mL) was then added, and the mixture was stirred with an ultrasonic homogenizer for 10 minutes while being cooled with ice water until homogenized. The flask was then transferred to a stirrer, dinitrodiammineplatinum(II) (4088 mg) was added, the atmosphere inside the flask was replaced with nitrogen, and the mixture was refluxed at 90° C. for 4 hours while stirring under a nitrogen flow. After cooling the flask, the contents were placed in a filter and filtered under reduced pressure to obtain a solid, which was then left to stand for 12 hours to dry temporarily, and then dried for 2 hours at 60°C. The dried product was then heat-treated at 240°C for 4 hours to obtain the target electrode material (45 wt% Pt / MC) of Example 1.

[0119] (Fabrication of electrodes and MEAs) An MEA having a cathode formed using the electrode material of Example 1 was used for electrochemical evaluation. The electrode material used for the anode was 46 wt% Pt / C (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E). In addition, in the formation of the electrodes (anode and cathode), the amount of Pt was 0.15 mg / cm 2 It was prepared so that

[0120] First, the electrode material (46 wt% Pt / C) was dispersed in a specified water / organic solvent containing Nafion solution to prepare the anode formation ink. A PTFE sheet was placed on a bar coater and the catalyst ink was applied using a doctor blade. The coated sheet was then vacuum dried. Next, the electrode material of Example 1 was placed on a bar coater with a PTFE sheet placed on it, and the catalyst ink was applied using a doctor blade. The coated sheet was then vacuum dried. The anode and cathode were then cut into 1 cm squares and hot-pressed with a Nafion membrane sandwiched between them, and a cathode-electrolyte membrane-anode assembly was fabricated using a transfer method. Carbon paper was placed on each of the anode and cathode and pressure-bonded under specified conditions to obtain the MEA of Example 1.

[0121] Furthermore, an electrode material and an MEA of Comparative Example 1 were produced in a manner similar to that of Example 1.

[0122] The evaluation devices used were a fuel cell evaluation device (manufactured by Toyo Corporation, model number: APM-37) and a potentio / galvanostat (manufactured by Biologic, model number: SP-300). Anode supply gas: Supply gas type: 100% H2 Cathode supply gas: Electrode area: 100% O2

[0123] FIG. 4 shows the current-voltage (IV) characteristics and the evaluation results of the overvoltage of the PEFC (single cell) using the MEAs of Example 1 and Comparative Example 1. As shown in FIG. 4, it was confirmed that when the MC carrier of Example 1 was used, the resistance overvoltage (ohmic overvoltage) was significantly reduced compared to when the MC carrier of Comparative Example 1 was used. [Industrial Applicability]

[0124] The mesoporous carbon support according to the present invention can be suitably used as a support for electrode materials (particularly electrode materials for polymer electrolyte fuel cells), and is therefore industrially promising.

Claims

1. A method for producing a mesoporous carbon support, comprising the following steps: Step (1): A step of polymerizing a phenol (A), an aldehyde (B), and a surfactant (C) in the presence of a thermally dissipative polymer (D) in a water-containing organic solvent. Step (2): A step of distilling off the solvent from the resulting solution, and then heat-treating the resulting dried product in an inert gas atmosphere to obtain a mesoporous carbon aggregate. Step (3): A step of pulverizing the obtained mesoporous carbon aggregates

2. 2. The method for producing a mesoporous carbon support according to claim 1, wherein in step (1), the phenols (A) and the aldehydes (B) are prepolymerized in the presence of the surfactant (C), and then mixed with the thermally dissipative polymer (D) to further promote the polymerization reaction.

3. 2. The method for producing a mesoporous carbon support according to claim 1, wherein the phenol (A) is phloroglucinol and the aldehyde (B) is formaldehyde.

4. 2. The method for producing a mesoporous carbon support according to claim 1, wherein the surfactant (C) is a nonionic surfactant.

5. 2. The method for producing a mesoporous carbon support according to claim 1, wherein the thermally dissipative polymer (D) is a hydrophilic polymer.

6. 6. The method for producing a mesoporous carbon support according to claim 5, wherein the thermally dissipative polymer (D) is polyvinyl alcohol.

7. A mesoporous carbon support obtained by the production method according to any one of claims 1 to 6.

8. A porous carbon support and electrode catalyst particles supported on the porous carbon support, An electrode material, wherein at least a part of the porous carbon support is the mesoporous carbon support according to claim 7.

9. An electrode comprising the electrode material of claim 8 and a proton-conducting electrolyte material.

10. 10. A membrane electrode assembly comprising: a solid polymer electrolyte membrane; a cathode bonded to one surface of the solid polymer electrolyte membrane; and an anode bonded to the other surface of the solid polymer electrolyte membrane, wherein either or both of the anode and the cathode are the electrodes according to claim 9.

11. A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 10.

Images