JP7563145B2 - Porous carbon and its manufacturing method - Google Patents

Description

The present invention relates to porous carbon and its manufacturing method.

Porous carbon has a high surface area and a regular, uniform pore structure, and is highly resistant to heat, chemicals, and corrosion, so it is widely used in a wide range of applications, from general industry to semiconductors and aerospace, as a gas adsorbent, water treatment agent, catalyst, etc. Research is also being conducted on its use as an electrode for electricity storage devices such as capacitors and fuel cells, and it is used as a power source for small portable electronic devices such as digital cameras and mobile phones.

In addition, in recent years, there are growing expectations for applications in bioelectrical power generation devices that use organic matter such as sugars, alcohols, and organic acids as fuel and utilize the electrical energy contained in electrons generated by microbial or enzymatic reactions, and the manufacturing methods, structures, and uses of porous carbon are becoming more diverse.

For example, for adsorption purposes, porous carbon with uniform pore size and high specific surface area is desired. Furthermore, for use as a power generation device such as biopower generation, porous carbon with high electrical conductivity and pore structure controlled at the nanometer order suitable for reaction is desired.

Methods for producing porous carbon include chemical activation, which uses raw materials such as charcoal, coconut shell ash, coal, rayon, and phenolic resin, and adds chemicals such as zinc chloride and phosphoric acid before heating in an activation gas atmosphere to carbonize the material, and gas activation, which uses water vapor, air, combustion gas, etc., on the carbonized raw materials.

Patent Document 1 describes a method for producing activated carbon by chemical activation of solidified carbon material using an alkali metal hydroxide. While this activation method can produce porous carbon with a high specific surface area, it has problems such as a decrease in the crystallinity of the carbon due to activation and difficulty in controlling the pore size.

Patent Document 2 describes a manufacturing method that uses porous zeolite as a template, injects an organic substance into the zeolite, carbonizes it, and then removes the template. By using porous zeolite as the template agent, it is possible to precisely control the pores to reflect the particle size and shape of the template agent. However, hydrofluoric acid or hydrochloric acid is used to remove the template agent, which causes problems such as a decrease in electrical conductivity due to the acid and safety concerns.

Patent Document 3 describes a method for producing porous carbon by heat treating granulated particles composed of a carbon material and a binder resin at a temperature equal to or higher than the decomposition temperature of the binder resin. The particle size is constant and the specific surface area can be easily adjusted, but there is a problem in that the conductivity decreases due to uneven distribution of the carbon material.

JP 2014-34475 A JP 2003-206112 A JP 2016-141592 A

The problem that the present invention aims to solve is to provide porous carbon with controlled pore size and excellent electrical conductivity, and a method for producing porous carbon that allows easy control of the pore size to a uniform size.

The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.
That is, the present invention provides a porous carbon having mesopores and macropores,
The present invention relates to a porous carbon characterized in that the pore volume is between 0.5 cm ³ /g and 5 cm ³ /g and the volume resistivity is less than 1.0×10 ⁻¹ Ω·cm.

The present invention also relates to the porous carbon, which is characterized in that the peak pore diameter is 30 nm or more.

The present invention also relates to the porous carbon, which is a sintered body of granulated particles containing at least a conductive carbon material (A) and a dispersed resin (B).

The present invention also relates to the porous carbon, characterized in that the conductive carbon material (A) contains at least one conductive carbon material selected from the group consisting of carbon black, graphite, fibrous carbon, and graphene.

The present invention also relates to the porous carbon, characterized in that the conductive carbon material (A) contains carbon black having an average primary particle size of 1 to 100 nm and a volume average particle size (D50) of 0.2 to 3 μm.

The present invention also relates to a method for producing the porous carbon, which comprises a first step of preparing a slurry by mixing and dispersing a conductive carbon material (A) and a dispersion resin (B) in a liquid medium (C), a second step of removing the liquid medium (C) from the slurry to prepare granulated particles, and a third step of firing the granulated particles at a temperature equal to or higher than the decomposition temperature of the dispersion resin (B) to prepare porous carbon.

The present invention also relates to a method for producing the porous carbon, in which the conductive carbon material (A) is 50 to 95 mass % and the dispersion resin (B) is 5 to 50 mass % of the 100 mass % solid content of the slurry.

The present invention makes it possible to provide porous carbon with controlled pore size and excellent electrical conductivity, as well as a method for producing porous carbon with easily uniform pore size control.

<Porous carbon>
The porous carbon in the present invention is a carbon material having a basic skeleton of a hexagonal carbon network surface in which carbon atoms are covalently bonded in a hexagonal network shape, and has numerous pores in the solid structure. The IUPAC classifies pores in solids into three classes based on the size of the pore diameter: mesopores with a pore diameter of 2 nm to 50 nm, macropores with a pore diameter of more than 50 nm, and micropores with a pore diameter of less than 2 nm. The porous carbon referred to here is porous carbon having mesopores and macropores among the above three classes of pores.

The pore volume of the porous carbon in the present invention is 0.5 cm ³ /g to 5 cm ³ /g. The volume resistivity is less than 1.0×10 ⁻¹ Ω·cm. When the pore volume is within the above range, the reaction field in which the reaction of the adsorbent or the like occurs can be increased, and when the volume resistivity is within the above range, the electrons required for the oxidation-reduction reaction in the electrode can be supplied to the reaction field, which tends to lead to an increase in current. Thus, since the conductivity is high when the pore volume is relatively large, the porous carbon can be used in electricity storage devices such as fuel cells and capacitors, and power generation devices such as biopower generation.

The pore volume is preferably 0.5 to 4.0 cm ³ /g, more preferably 0.8 to 3.5 cm ³ /g. The volume resistivity is preferably less than 7.5×10 ⁻² Ω·cm, more preferably less than 5.0×10 ⁻² Ω·cm.

In the present invention, the pore volume refers to the total pore volume per unit mass of the sample, and can be determined by the nitrogen adsorption method. In the nitrogen adsorption method, the adsorption and desorption isotherms are measured by adsorbing and desorbing nitrogen as an adsorbed molecule on the adsorbent, and the measured data is analyzed to calculate the specific surface area, pore volume, and pore diameter. The specific surface area is determined by the BET method, and the pore volume and pore diameter are determined by the BJH method, which is a widely used pore distribution analysis method. The BJH method allows the pore distribution of 2 to 300 nm to be plotted, and the presence of mesopores and macropores can be confirmed. The pore diameter is determined by calculating the peak pore diameter from the obtained pore distribution.

The volume resistivity in this invention refers to the volume resistance per unit volume, and can be determined by the four-terminal method. It can be determined by passing a constant current A (A) through a cross-sectional area W x t and measuring the potential difference V (V) between electrodes separated by a distance L. The volume resistivity referred to here can be measured using a powder resistivity measurement system (MCP-PD51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and a resistivity meter (Loresta-GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.); specifically, the porous carbon is placed in the cell of the powder resistivity measurement system, and the volume resistivity is measured when a load of 4 kN is applied.

The porous carbon in the present invention preferably has a peak pore diameter of 30 nm or more as determined by the above-mentioned nitrogen adsorption method and BJH analysis. A pore diameter of 30 nm or more allows selective adsorption and separation of adsorbed substances such as enzymes, microorganisms, and viruses, and can be effectively used in power generation devices, sensors, decontamination, resource recovery, etc. Furthermore, a pore diameter of 50 nm or more is even more preferable.

The porous carbon in the present invention is preferably a sintered body of granulated particles consisting of at least a conductive carbon material (A) and a dispersed resin (B).

<Conductive Carbon Material (A)>
In the present invention, the conductive carbon material (A) can be an inorganic carbon material. For example, carbon black (furnace black, acetylene black, ketjen black, medium thermal carbon black), graphite, fibrous carbon (carbon nanotube, carbon nanofiber, carbon fiber), carbon nanohorn, graphene, and fullerene can be used alone or in combination of two or more. From the viewpoint of conductivity and availability, carbon black, graphite, fibrous carbon, and graphene are preferred, and it is more preferred to use two or more of carbon black, graphite, fibrous carbon, and graphene in combination.

Commercially available inorganic carbon materials include, for example:
Acetylene black manufactured by Denka Company, such as Denka Black, Denka Black HS-100, and FX-35;
Ketjenblack manufactured by Lion Specialty Chemicals, such as Ketjenblack EC-300J, EC-600JD, and Lionite EC-200L;
Furnace blacks manufactured by Tokai Carbon Co., Ltd., such as Toka Black #4300, #4400, #4500, and #5500; furnace blacks manufactured by Degussa Corporation, such as Printex L;
Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULT
RA, Conductex SC ULTRA, 975 ULTRA, PUER BLACK 100, 115, and 205, and other furnace blacks manufactured by Colombian;
Furnace blacks manufactured by Mitsubishi Chemical Corporation, such as #2350, #2400B, #2600B, #3050B, #3030B, #3230B, #3350B, #3400B, and #5400B;
Cabot furnace blacks such as MONARCH 1400, 1300, 900, Vulcan XC-72R, and BlackPearls 2000;
TIMCAL furnace blacks such as Ensaco 250G, Ensaco 260G, Ensaco 350G, and Super P-Li;
Graphite manufactured by Showa Denko K.K., such as SCMG-AH, SCMG-AR, SCMG-AR-H, SCMG-AF, SCMG-AFC, UF-G10, and UF-G30;
Graphite manufactured by Nippon Graphite Industries Co., Ltd., such as CPB, UCP, AP, P#1, PAG-5, HAG-10W, ACP, ACB-150, SP-10, SP-20, J-SP, GR-15, UP-5N, UP-15N, CGC-20, CGB-20, J-SP-α, UP-5-α, SP-5030-α, and EXP-SM;
Graphite manufactured by Fuji Graphite Industries Co., Ltd., such as UF-2, BF-3A, BF-5A, BF-8A, BF-10A, BF-20A, CNG-44N, BSP-5A, BSP-20A, A-0, FAG-1C, JSG-25, JSG-75, WF-10, WF-20, and WF-30;
graphite manufactured by Ito Graphite Industries Co., Ltd., such as Z-5F, CNP-7, CNP-15, CNP-35, Z+80, Z-25, Z-50, X-10, X-20, SRP7, SRP10, CP2000M, EC1500, SG-BH8, and SG-BH;
Carbon nanotubes manufactured by Showa Denko K.K., such as VGCF, VGCF-H, and VGCF-X;
Carbon nanotubes manufactured by Meijo Nano Carbon Co., Ltd.;
Carbon nanotubes manufactured by Zeon Corporation;
Examples of graphene nanoplatelets manufactured by XGSciences include, but are not limited to, xGnP-C-300, xGnP-C-500, xGnP-C-750, xGnP-M-5, xGnP-M-15, xGnP-M-25, xGnP-H-5, xGnP-H-15, and xGnP-H-25.

In addition, the smaller the primary particle diameter of the carbon black used in the present invention, the more particles there are per unit mass, and the more contact points there are between the carbon black particles, which is advantageous for lowering the volume resistivity of the porous carbon. Specifically, from the standpoint of electrical conductivity and ease of availability, the average primary particle diameter is preferably 1 to 100 nm, more preferably 10 to 80 nm, and even more preferably 20 to 70 nm. However, the average primary particle diameter referred to here is the average particle diameter of the spherical particles that form the aggregates (primary agglomerates) measured using an electron microscope or the like.

The carbon black used in the present invention forms agglomerates (secondary aggregates) formed by aggregation of aggregates (primary aggregates). When the size of the secondary aggregates is larger than a certain size, it becomes easier to form a conductive network, which is advantageous for reducing the volume resistance. Forming secondary aggregates is preferable because it makes it easier to obtain porous carbon having a predetermined pore size. In the present invention, the secondary aggregates are represented by a volume average particle size, and specifically, the volume average particle size (D50) is preferably 0.2 to 3 μm, more preferably 0.2 to 2 μm, and even more preferably 0.2 to 1 μm.
The volume average particle diameter (D50) referred to here is a particle diameter (D50) at 50% when the volume ratios of particles are integrated from the finest particle diameter in a volume particle size distribution, and is measured by a general particle size distribution meter, for example, a laser scattering type particle size distribution meter.

<Dispersion Resin (B)>
The dispersing resin is not particularly limited, but examples thereof include nonionic dispersants, anionic dispersants, cationic dispersants, amphoteric dispersants, etc. These are, for example, in the form of a polymer having at least one functional group selected from the group consisting of an anionic functional group, a cationic functional group, and a nonionic functional group, or a neutralized product of the polymer, and can be used more preferably when an aqueous solvent is used as the solvent.

The weight average molecular weight of the dispersion resin is preferably 5,000 or more, and more preferably 30,000 or more. The upper limit is preferably 1,500,000 or less, and more preferably 800,000 or less. The above range is preferable because it provides excellent dispersibility of the conductive carbon material (A).

(Nonionic dispersant)
Nonionic resins include resins that do not have ionic functional groups. Specific examples of nonionic resins include vinylpyrrolidone resins such as polyvinyl acetal, polyvinyl butyral, polyvinyl alcohol, polyalkylene glycol modified acrylic resins, polyalkylene oxides, polyvinyl ethers, polyvinyl caprolactam, polyvinylpyrrolidone, vinyl acetate-vinylpyrrolidone copolymers, vinylpyrrolidone-methacrylic acid amide-vinylimidazole copolymers, and alkylated vinylpyrrolidone-1-butene copolymers, lignin, pectin, gelatin, xanthan gum, welan gum, succinoglycan, cellulose resins (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, etc.), chitins, chitosans, and starch, but are not particularly limited thereto.
Among these, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone are preferable.

(Anionic Dispersant)
The anionic dispersant is not particularly limited, but examples thereof include polyvinylidene fluoride resins having acidic functional groups, polyvinyl resins having acidic functional groups, polyester resins having acidic functional groups, and other commercially available resins having acidic functional groups, etc. Examples of the acidic functional groups include carboxyl groups, sulfonic acid groups, and phosphoric acid groups.
The acid value of the anionic dispersant is preferably in the range of 100 mgKOH/g or more and 600 mgKOH/g or less, and more preferably in the range of 300 mgKOH/g or more and 600 mgKOH/g or less.

Examples of the anionic dispersant having a carboxyl group include dispersing resins obtained by copolymerizing an ethylenically unsaturated monomer having a carboxyl group and, if necessary, other monomers.
The ethylenically unsaturated monomer having a carboxyl group is not particularly limited as long as it is a monomer having a carboxyl group, but methacrylic acid and acrylic acid are particularly preferred.
Examples of the copolymerizable monomer include ethylenically unsaturated monomers having an aromatic ring, such as styrene, α-methylstyrene or benzyl (meth)acrylate, alkyl (meth)acrylates, and alkylene glycol (meth)acrylates.

The anionic dispersant having sulfonic acid is not particularly limited as long as it is a resin having sulfonic acid, but for example, a formalin condensation product of aromatic sulfonic acid can be used. The formalin condensation product of aromatic sulfonic acid is, for example, a product obtained by condensing benzenesulfonic acid, alkylbenzenesulfonic acid, or naphthalenesulfonic acid (or their alkali metal salts) with formalin.

(Cationic Dispersant)
The cationic dispersant preferably has at least one of an aliphatic amine and an aromatic amine as a cationic moiety, and the amine value is preferably in the range of 110 mgKOH/g or more and less than 1000 mgKOH/g, and more preferably in the range of 250 mgKOH/g or more and less than 1000 mgKOH/g.

The cationic dispersant having an aliphatic amine or aromatic amine is not particularly limited as long as it is a resin having an aliphatic amine or aromatic amine, but for example, it is obtained by polymerizing or condensing a monomer having an aliphatic amino group or an aromatic amino group, and preferably by polymerizing an ethylenically unsaturated monomer having an aliphatic amino group or an aromatic amino group and other monomers as necessary.

Examples of the ethylenically unsaturated monomer having an aliphatic amino group or an aromatic amino group include those having an aliphatic amino group such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methylethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, and allylamine, and those having an aromatic amino group such as aminostyrene, dimethylaminostyrene, and diethylaminostyrene.
Examples of the copolymerizable monomer include ethylenically unsaturated monomers having an aromatic ring, such as styrene, α-methylstyrene or benzyl (meth)acrylate, alkyl (meth)acrylates, and alkylene glycol (meth)acrylates.

(Amphoteric dispersant)
The amphoteric dispersant is preferably a copolymer or a neutralized product of the copolymer, the copolymer essentially consisting of an ethylenically unsaturated monomer having an aromatic ring, an ethylenically unsaturated monomer having a carboxyl group, and an ethylenically unsaturated monomer having an amino group. The monomers may be the same as those exemplified for the anionic dispersant or cationic dispersant.

<Liquid medium (C)>
The liquid medium (C) used in the present invention can be used without any particular limitation. If necessary, for example, to improve dispersibility, a mixture of multiple solvents may be used. Examples of the solvent include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, nitriles, and water. Among them, water and alcohol-based solvents having 4 or less carbon atoms are preferred.

<Method of manufacturing porous carbon>

In the present invention, the porous carbon is produced by a first step of preparing a slurry by mixing and dispersing a conductive carbon material (A) and a dispersion resin (B) in a liquid medium (C), and a second step of removing the liquid medium (C) from the slurry to prepare granulated particles. More preferably, the porous carbon is produced by a first step of preparing a slurry by mixing and dispersing a conductive carbon material (A) and a dispersion resin (B) in a liquid medium (C), a second step of removing the liquid medium (C) from the slurry to prepare granulated particles, and a third step of firing the granulated particles at a temperature equal to or higher than the decomposition temperature of the dispersion resin (B) to prepare porous carbon.

In the present invention, the porous carbon is preferably produced by the second step immediately after the first step of preparing a slurry in which the conductive carbon material (A) and the dispersion resin (B) are mixed and dispersed in the liquid medium (C). "Immediately after" refers to the time during which the conductive carbon material (A) is maintained in a dispersed state, and specifically, this can be confirmed by the volume average particle size (D50) described above. According to this step, the secondary particles are larger than a certain size, which makes it easier to form a conductive network and is advantageous for reducing the volume resistance. In addition, by controlling the secondary aggregates of carbon black, porous carbon having a predetermined pore size can be easily produced.

In the first step of the present invention, it is preferable to completely or partially dissolve the dispersion resin (B) in the liquid medium (C), and add, mix, and disperse the conductive carbon material (A) in the solution. This is because the conductive carbon material (A) can be dispersed close to the primary particles while the dispersion resin (B) is adsorbed and coated on the conductive carbon material (A) to disperse it in the solvent. In addition, in the first step, it is more preferable to completely or partially dissolve the dispersion resin (B) in the liquid medium (C) after baking the conductive carbon material (A) at a high temperature of 1800° C. or more, and then add, mix, and disperse the conductive carbon material (A) in the solution.
In terms of electrical conductivity, the content of the conductive carbon material (A) in 100% by mass of the slurry solid content is preferably 50 to 95% by mass, more preferably 50 to 90% by mass, and even more preferably 65 to 85% by mass.
The content of the dispersion resin (B) in the slurry solid content of 100% by mass is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 35% by mass, from the viewpoints of electrical conductivity and dispersion stability.

As the apparatus used in obtaining the slurry of the conductive carbon material in the first step of the present invention, a dispersing machine normally used for dispersing pigments can be used. For example, mixers such as Disper, Homomixer, Planetary Mixer, homogenizers (M Technique's "Clearmix", Primix, etc.), paint conditioners (Red Devil), ball mills, sand mills (Shinmaru Enterprises' "Dynomill", etc.), attritors, pearl mills (Eirich's "DCP Mill", etc.), media-type dispersing machines such as Coball Mills, wet jet mills (Genus PY, Sugino Machine's "Starburst", Nanomizer, etc.), M Technique's "Clear SS-5", Nara Machine's "MICROS", and other media-less dispersing machines, roll mills, etc., are listed, but are not limited to these. In addition, these dispersing machines may be used alone or in combination of two or more types. Furthermore, it is preferable to use a disperser that has been treated to prevent metal contamination from the disperser.

For example, when using a media-type disperser, it is preferable to use a disperser with an agitator and vessel made of ceramic or resin, or a disperser in which the surface of a metal agitator and vessel has been treated with tungsten carbide spraying or resin coating. As the media, it is preferable to use ceramic beads such as glass beads, zirconia beads, and alumina beads. Also, when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersing device may be used, or multiple types of devices may be used in combination.

In the first step, a carbonizing agent that becomes a carbon material may be further included. The carbonizing agent may be a resin or sugar with a large molecular weight that becomes a carbon material when fired in an inert atmosphere. The carbonizing agent can control the pore size and pore volume of the porous carbon, for example, by coating the surface of the primary particles of the conductive carbon material (A) to block the micropores or filling the gaps between the primary particles. When a carbonizing agent is used, it is preferable to set the firing temperature to 2000°C or higher in the third step described below, since this facilitates graphitization of the carbonizing agent and does not inhibit the conductivity of the porous carbon.

In the second step, the liquid medium (C) is removed from the slurry produced in the first step to produce granulated particles. The method for removing the liquid medium (C) is not particularly limited, but can be selected from, for example, spray drying, stirring drying, and static drying. Among these, a spray dryer is preferably used because it can granulate the particles into spherical shapes that are easy to pack.

In the third step, the granulated particles produced in the second step are fired at a temperature equal to or higher than the decomposition temperature of the dispersion resin (B) to produce porous carbon. By firing at a temperature equal to or higher than the decomposition temperature of the dispersion resin (B), the organic matter is carbonized, which does not adversely affect the electrical conductivity. It is preferable to perform firing in an inert atmosphere, and examples of the inert atmosphere include an atmosphere filled with nitrogen or argon, or a vacuum atmosphere.

In the third step, the granulated particles produced in the second step are preferably fired at a temperature of 1800°C or higher to produce porous carbon. The crystallinity of the conductive carbon material (A) is improved while maintaining the pore size and pore volume of the porous carbon, resulting in good conductivity. The optimal firing temperature varies depending on the type of conductive carbon material (A), but it is more preferable to set the firing temperature at 2000°C or higher, at which graphitization begins to progress.

The porous carbon of the present invention can selectively adsorb and desorb adsorbents such as enzymes, microorganisms, viruses, and gases, and can be effectively used in water purification, soil reform, chromatography, gas occlusion and release, protein uptake, decontamination, and resource recovery. In addition, because it has excellent electrical conductivity, it can be used as a conductive material for electrodes in electricity storage devices such as fuel cells and capacitors, power generation devices such as biopower generation, and sensors. In particular, in enzyme power generation devices, the porous carbon of the present invention can be suitably used as a conductive material for device electrodes.

[Enzyme power generation device]
The enzyme power generation device includes an anode that contains an oxidoreductase and oxidizes fuel, a cathode where oxygen reduction occurs, and, if necessary, a separator that electrically separates the anode and cathode, and, if necessary, further includes an ion conductor for transmitting ions from the anode to the cathode.

Specific examples of enzyme power generation devices include enzyme fuel cells and organic matter sensors. Enzyme fuel cells use organic matter such as sugars and alcohols as fuel, generate electricity through the above-mentioned reactions including an oxidation reaction at the negative electrode and a reduction reaction at the positive electrode, and output electricity. Organic matter sensors can detect the presence or amount of a substance to be sensed by detecting the presence or absence of power generation or the amount of power generation. Enzyme power generation devices can function as both a power source and a sensor, and can be used as a sensor with a power source function.

The fuel or sensing target substance is not particularly limited as long as it is an organic substance that can be decomposed by oxidoreductase, and examples of such substances include monosaccharides such as glucose (preferably natural D-glucose) and fructose; polysaccharides such as starch; alcohols such as ethanol; and organic acids such as lactic acid. Among these, one or more organic substances selected from the group consisting of glucose, fructose, and lactic acid are preferred. The fuel may be supplied from the outside, or may be built into the enzyme power generation device, for example by being supported on a separator or the like.

The porous carbon of the present invention can be used as a paste for forming electrodes for enzyme power generation devices. The electrode paste contains porous carbon, a solvent, and a binder, and may further contain other components such as a dispersant as necessary. The ratio of each component is not particularly limited and can be designed as appropriate.

The solvent used in the electrode paste is not particularly limited, and any known solvent may be used, including alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, nitriles, and water. Of these, water and alcohol-based solvents having 4 or less carbon atoms are preferred.

The binder used in the electrode paste is used to bind other electrode constituent materials such as porous carbon, and a known binder resin is used which has little effect of dispersing the other electrode constituent materials in a solvent.
Examples of the binder include acrylic resins, polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, formaldehyde resins, silicone resins, synthetic rubbers such as styrene-butadiene rubber and fluororubber, conductive resins such as polyaniline and polyacetylene, fluorine-containing compounds such as polyvinylidene fluoride (PVdF), polyvinyl fluoride, perfluorocarbon, and tetrafluoroethylene, modified products thereof, etc. These binders can be used alone or in combination of two or more.

When an aqueous liquid medium is used as the solvent, an aqueous emulsion may be used as the binder. The aqueous emulsion is a dispersion in which the binder resin is not dissolved in water but is dispersed in the form of fine particles.
The aqueous emulsion is not particularly limited, and examples thereof include (meth)acrylic emulsions; nitrile emulsions; urethane emulsions; diene emulsions containing diene rubbers such as SBR (styrene butadiene rubber); and fluorine-based emulsions containing fluorine-containing polymers such as PVdF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene).

The dispersant used in the electrode paste as needed is not particularly limited, and examples thereof include the dispersion resins exemplified for the porous carbon. In addition, the electrode paste may contain other components such as oxidoreductases and catalysts as needed, and conventionally known dispersants can be used.

<Porous carbon>
Example 1A
14 parts by mass of carbon black (Lionite EC-200L, manufactured by Lion Specialty Chemicals) as a conductive carbon material, 60 parts by mass (6 parts by mass as solid content) of a 10% aqueous solution of polyvinylpyrrolidone (PVP K-30, manufactured by Wako Co., Ltd.) as a dispersion resin, and 126 parts by mass of ion-exchanged water were collected, mixed in a mixer, and dispersed for 30 minutes using a sand mill to obtain a slurry. Next, the slurry was spray-granulated at 125°C using a spray dryer Mini Spray Dryer B-290 manufactured by Nippon Buchi Co., Ltd. to obtain granulated particles of the conductive carbon material. The obtained powder was then heated and fired at 500°C for 1 hour in a nitrogen atmosphere to obtain porous carbon (1).

The materials used in the examples and comparative examples were evaluated as follows.
(Average primary particle size of conductive carbon material)
Using a transmission electron microscope (JEM-1010 manufactured by JEOL Datum Co., Ltd.), the carbon material particles were photographed at an acceleration voltage of 100 kV. The diameters of 100 spherical particles forming an aggregate (primary agglomerate) were measured and averaged to obtain the diameter.
(Volume average particle size of conductive carbon material)
The slurry in which the conductive carbon material and the dispersion resin were mechanically dispersed was diluted with water 100 to 1000 times depending on the solid content, and the diluted slurry was injected into a cell of a Microtrac (MT3300EXII manufactured by Nikkiso Co., Ltd.) until an appropriate concentration was reached by sampling loading. After inputting the refractive index conditions of the dispersion medium according to the sample, measurements were performed, and D50 was taken as the average particle size.
(Decomposition temperature of dispersion resin)
The dispersed resin was measured by simultaneous differential thermal and thermogravimetric analysis (TG-DTA) using a thermal analyzer (Hitachi High-Tech Science EXSTAR6000). The weight was measured in the range of 35 to 500° C. under a nitrogen flow, and the thermal decomposition temperature of the dispersed resin was calculated.
(Specific surface area, pore volume, pore diameter of porous carbon)
The porous carbon was heat-treated at 150°C for 4 hours under nitrogen flow, and the weight was measured. Then, the adsorption/desorption isotherm was measured at an adsorption temperature of 77K using a nitrogen adsorption measuring device (Microtrackbell BELSORP-mini). From the obtained adsorption/desorption isotherm, the specific surface area was calculated using the BET method. In addition, the presence of mesopores and macropores was confirmed for the porous carbon of the examples using the BJH method, and the pore volume and pore diameter were calculated.
(Volume Resistivity of Porous Carbon)
The porous carbon was placed in a cell of a powder resistivity measurement system (MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd.), and the volume resistivity under a load of 4 kN was measured using a resistivity meter (Loresta GP <MCP-T610>).

(Examples 2A to 13A, 15A, and 16A)
Porous carbons of the examples (2) to (13), (15), and (16) were obtained in the same manner as in Example 1A, except that the solid content ratio, the conductive carbon material (A), the dispersion resin (B), and the liquid medium (C) were changed as shown in Table 1. Note that, for Example 6A, after the granulated particles of the conductive carbon material were obtained by spray granulation, heating and sintering were not performed.

The materials used in the examples and comparative examples are shown below.
(Conductive Carbon Material (A))
Lionite EC-200L (manufactured by Lion Specialty Chemicals, primary particle size 40 nm, hereinafter abbreviated as "EC200L")
Ketjenblack EC-300J (manufactured by Lion Specialty Chemicals, primary particle diameter 38 nm, hereinafter abbreviated as "EC300J")
Denka Black HS-100 (manufactured by Denka Company, primary particle size 45 nm, hereinafter abbreviated as "HS100")
Toka Black #5500 (manufactured by Tokai Carbon Co., Ltd., primary particle size 25 nm, hereinafter abbreviated as "#5500")
Graphene nanoplatelet xGnP-M-5 (manufactured by XGscience, hereinafter abbreviated as "GNP-M")
Graphite SP-270 (manufactured by Nippon Graphite Co., Ltd., hereinafter abbreviated as "SP-270")
(Dispersion Resin (B))
Polyvinylpyrrolidone K-30 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., decomposition temperature 390°C, hereinafter abbreviated as "PVP")
CMC Daicel #1240 (manufactured by Daicel Chemical Industries, Ltd., decomposition temperature 260°C, hereinafter abbreviated as "CMC")
Kuraray Poval PVA 235 (manufactured by Kuraray Co., Ltd., decomposition temperature 280°C, hereinafter abbreviated as "PVA")
Polyacrylic acid, average molecular weight 5000 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., decomposition temperature 190°C, hereinafter abbreviated as "PAA")
(Liquid medium (C))
- Ion-exchanged water (hereinafter referred to as "water")
Isopropyl alcohol / ethanol (mixture of 9/1 by weight) (hereinafter referred to as "IPA / EtOH")

(Example 14A)
14 parts by mass of carbon black (Lionite EC-200L, manufactured by Lion Specialty Chemicals) as a conductive carbon material and 200 parts by mass (6 parts by mass as solids) of a 3% aqueous solution of carboxymethylcellulose (CMC Daicel #1240, manufactured by Daicel Chemical Industries, Ltd.) as a dispersing resin were collected, mixed in a mixer, and dispersed for 30 minutes using a sand mill to obtain a slurry. Next, the slurry was spray-granulated at 125°C using a spray dryer Mini Spray Dryer B-290 manufactured by Nippon Buchi Co., Ltd. to obtain granulated particles of the conductive carbon material. The obtained powder was then heated and fired at 500°C for 1 hour under a nitrogen atmosphere to obtain porous carbon (14).

(Examples 17A to 20A)
Porous carbons (17) to (20) of the respective examples were obtained in the same manner as in Example 1A, except that the dispersion time in the sand mill was extended to change the volume average particle diameter of the conductive carbon material (A) shown in Table 1.

(Examples 21A to 23A)
Porous carbons (21) to (23) of the respective examples were obtained in the same manner as in Example 18A, except that the heating and sintering temperature of the granulated particle powder was changed as shown in Table 1.

(Example 24A)
Carbon black (Lionite EC-200L, manufactured by Lion Specialty Chemicals) as a conductive carbon material was heated and baked at 2000° C. for 1 hour under a nitrogen atmosphere. Then, 14 parts by mass of the baked carbon black, 60 parts by mass (6 parts by mass as solid content) of a 10% aqueous solution of polyvinylpyrrolidone (PVP K-30, manufactured by Wako Co., Ltd.) as a dispersion resin, and 126 parts by mass of ion-exchanged water were collected, mixed in a mixer, and dispersed for 30 minutes using a sand mill to obtain a slurry. Next, the slurry was spray-granulated at 125° C. using a spray dryer Mini Spray Dryer B-290 manufactured by Nippon Buchi Co., Ltd. to obtain granulated particles of a conductive carbon material. Then, the obtained powder was heated and baked at 500° C. for 1 hour under a nitrogen atmosphere to obtain porous carbon (24).

(Comparative Example 1A)
The conductive carbon material was carbon black (Lionite EC200L, manufactured by Lion Specialty Chemicals) in an amount of 14 parts by mass, and the dispersion resin was polyvinylpyrrolidone (PVP K-30, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in an amount of 60 parts by mass (60 parts by mass in terms of solid content) in a 10% aqueous solution.
The mixture was mixed in a mixer and dispersed for 30 minutes using a sand mill to obtain a slurry. The slurry was then spray-granulated at 125°C using a spray dryer, Mini Spray Dryer B-290, manufactured by Nippon Buchi Co., Ltd., to obtain granulated particles of the conductive carbon material, which was used as porous carbon (25).
(Comparative Example 2A)
Porous carbon (26) was obtained in the same manner as in Example 1A, except that the heating and sintering temperature in a nitrogen atmosphere was changed to 200°C.
(Comparative Example 3A)
A porous carbon (27) was obtained in the same manner as in Example 1A, except that the dispersing resin was changed to a styrene-butadiene emulsion (TRD2001 (aqueous dispersion with a solid content of 48%), manufactured by JSR Corporation, hereinafter abbreviated as "SBR").

<Electrode slurry for enzyme power generation device>
Example 1B
4.8 parts of the porous carbon (1) of Example 1A, 49.2 parts of water as a solvent, and 40 parts of an aqueous carboxymethyl cellulose solution (2% solids content) as a thickener were mixed in a mixer, and then dispersed in a sand mill. After that, 6 parts (50% solids content) of an emulsion-type acrylic resin dispersion solution (W-168 manufactured by Toyochem Co., Ltd.) was added as a binder and mixed in a mixer to obtain an electrode slurry (1) for an enzyme power generating device.

(Examples 12B, 17B to 20B, 22B, Comparative Examples 1B to 3B)
Using the porous carbons (12), (17) to (20), (22), and (25) to (27), electrode slurries for enzyme power generating devices (12), (17) to (20), (22), and (25) to (27) were obtained in the same manner as in Example 1B.

(Comparative Example 4B)
An electrode slurry (28) for an enzyme power generating device was obtained in the same manner as in Example 1B, except that Ketjen Black EC-600JD (manufactured by Lion Specialty Chemical Co.) was used as a conductive carbon material instead of porous carbon.

<Electrodes for enzyme power generation devices>
(Examples 1C, 12C, 17C to 20C, 22C, Comparative Examples 1C to 4C) The electrode slurries for enzyme power generation devices (1), (12), (17) to (20), (22), (25) to (28) were applied using a doctor blade onto a carbon paper base material made of carbon fiber manufactured by Toray Industries, Inc. as a conductive support so that the basis weight of the carbon-based material for enzyme power generation devices after drying was 2 mg/ ^cm2 , and the resulting material was dried at 95°C for 60 minutes in an air atmosphere to produce electrodes for enzyme power generation devices (1), (12), (17) to (20), (22), (25) to (28).

<Preparation of anode for enzyme power generation device>
(Examples 1D, 12D, 17D to 20D, 22D, Comparative Examples 1D to 4D)
A methanol solution of tetrathiafulvalene and an aqueous glucose oxidase (GOD) solution were dropped as mediators onto the enzymatic power generation device electrodes (1), (12), (17) to (20), (22), and (25) to (28) of Examples 1C, 12C, 17C to 20C, and 22D, and Comparative Examples 1C to 4C, respectively, and the electrodes were naturally dried to prepare enzymatic power generation device negative electrodes (1), (12), (17) to (20), (22), and (25) to (28).

<Preparation of positive electrode for enzyme power generation device>
Example 17E
An aqueous bilirubin oxidase (BOD) solution was dropped onto the enzyme power generating device electrode (17) of Example 17C, and the electrode was allowed to dry naturally to prepare an enzyme power generating device positive electrode (17).

(Comparative Example 4E)
An aqueous bilirubin oxidase (BOD) solution was dropped onto the electrode (28) containing the conductive carbon material of Comparative Example 4C, and the electrode was naturally dried to prepare a positive electrode (28) for an enzyme power generating device.

<Evaluation of cycle stability of the negative electrode for enzyme power generating devices against glucose>
The enzymatic power generation device negative electrodes (1), (12), (17)-(20), (22), (25)-(28) were placed in an electrolyte (ion conductor) of 0.1 M phosphate buffer (pH 7.0) with the working electrode, a platinum coil electrode as the counter electrode, and a silver-silver-silver chloride electrode (Ag/AgCl) as the reference electrode. Then, using a potentio-galvanostat, cyclic voltammetry (CV) measurements were performed at pH 7, room temperature, and in a potential range of -0.2 to 0.5 V to investigate the cycle characteristics (10 cycles) for glucose as the fuel (sensing object).
The maximum current (mA/ ^cm2 ) was compared from the oxidation current curves before and after the cycles obtained from the CV measurement. The maximum current value in the first cycle was taken as the initial value, and the maximum current retention rate was calculated from the ratio of the maximum current value in the 10th cycle to the initial value, and was evaluated as an index of cycle stability.

The results of evaluation based on the following criteria are shown in Table 2.

(Initial maximum current value)
⊚: The initial maximum current value is greater than the maximum current value of the non-porous carbon Comparative Example 4D (particularly good).
◯: The initial maximum current value is equivalent to the maximum current value of the non-porous carbon Comparative Example 4D (Good).
×: The initial maximum current value is smaller than the maximum current value of the non-porous carbon Comparative Example 4D (poor).
(Cycle Stability Evaluation)
◎: Maximum current retention rate before and after cycling (10 cycles) 80% or more (very good)
◯: Maximum current maintenance rate before and after cycling (10 cycles) 65% or more and less than 80% (particularly good) ◯△: Maximum current maintenance rate before and after cycling (10 cycles) 50% or more and less than 65% (good)
×: Maximum current maintenance rate before and after cycling (10 cycles) less than 50% (defective)

<Evaluation of cycle stability of the positive electrode for enzyme power generating devices against glucose>
The enzyme power generating device positive electrodes (17) and (28) were used instead of the enzyme power generating device negative electrodes (1), (12), (17) to (20), (22), and (25) to (28), oxygen bubbling was performed for 30 minutes before the CV measurement, and the potential range was changed to 0.8 to −0.8 V. The initial maximum current value was based on Comparative Example 4E.

As shown in Table 1, it was confirmed that the examples were porous carbons having both a high pore volume and a low volume resistivity, as compared with Comparative Examples 1A to 3A.
On the other hand, the unsintered Comparative Example 1A, the Comparative Example 2A which was sintered at a temperature below the decomposition temperature of the dispersing resin, and the Comparative Example 3A which did not use a dispersing resin had porous carbon with high volume resistivity and low conductivity.
In Comparative Example 1A and Comparative Example 2A, a large amount of dispersed resin with a lower conductivity than the carbon material remained, and therefore, in Comparative Example 3A, the dispersion of the binder resin and the carbon material was not uniform, which is considered to have caused the local conductive path formation to collapse and increased the volume resistance. Furthermore, in Comparative Example 1A and Comparative Example 2A, the pore volume was low and the porosity was insufficient. This is considered to be due to the fact that a large amount of dispersed resin remained between the carbon particles, which reduced the porosity between the carbon particles.
In contrast, it is believed that Examples 1A to 24A exhibited low volume resistivity due to the good dispersion state of the conductive carbon material and the dispersion resin.

As shown in Table 2, it was confirmed that the use of an electrode formed from the porous carbon of the present invention in an enzyme power generating device exhibited excellent current value and cycle stability. This is believed to be because the compatibility of porosity and conductivity allows efficient and stable transfer of electrons in the enzymatic reaction of the carbon, thereby suppressing the deterioration of the unstable enzyme even in repeated reactions.

Claims (7)

A porous carbon having mesopores and macropores,
A porous carbon for use in an electrode of an enzyme power generating device , characterized in that the carbon has a pore volume of 0.5 cm ³ /g to 5 cm ³ /g, a volume resistivity of less than 1.0×10 ⁻¹ Ω·cm , and a peak pore diameter of 30 nm or more . The porous carbon for an electrode of an enzyme power generating device according to claim 1 , characterized in that the porous carbon is a sintered body of granulated particles containing at least a conductive carbon material (A) and a dispersed resin (B). The porous carbon for use in an electrode of an enzyme power generating device as described in claim 2 , characterized in that the conductive carbon material (A) contains at least one conductive carbon material selected from the group consisting of carbon black, graphite, fibrous carbon and graphene. The porous carbon for use in an enzyme power generating device electrode according to claim 2 or 3, characterized in that the conductive carbon material (A) contains carbon black having an average primary particle diameter of 1 to 100 nm and a volume average particle diameter (D50) of 0.2 to 3 μm. 5. A paste for an enzyme power generating device electrode, comprising the porous carbon for an enzyme power generating device electrode according to claim 1, a solvent, and a binder. 5. A method for producing porous carbon for an electrode of an enzyme power generating device according to claims 1 to 4, comprising: a first step of preparing a slurry in which a conductive carbon material (A) and a dispersion resin (B) are mixed and dispersed in a liquid medium (C); a second step of removing the liquid medium (C) from the slurry to prepare granulated particles; and a third step of firing the granulated particles at a temperature equal to or higher than the decomposition temperature of the dispersion resin ( B) to prepare porous carbon. The method for producing porous carbon for an enzyme power generating device electrode, as described in claim 6, wherein the conductive carbon material (A) is 50 to 95 mass% and the dispersion resin (B) is 5 to 50 mass% of 100 mass% of the solid content of the slurry.