Electrode binder for biofuel cells

Abstract

Provided is an electrode binder for a biofuel cell, which can produce a biofuel cell exhibiting excellent output characteristics, and which provides an electrode paste that is low in environmental load and has good dispersibility of an electrically conductive material and is suitable for screen printing. The electrode binder for a biofuel cell of the present invention comprises a polymer (A) having a first structural unit derived from a nonionic ethylenically unsaturated monomer (a1), a second structural unit derived from an anionic ethylenically unsaturated monomer (a2), and a third structural unit derived from a crosslinking agent (a3) having two or more ethylenically unsaturated bonds in one molecule.

Description

[0001] This application is a divisional application of the patent application filed on March 27, 2024, with application number 202480001711.2 and invention title "Electrode Adhesive for Biofuel Cells". Technical Field

[0002] This invention relates to electrode binders for biofuel cells. Background Technology

[0003] As a new generation of fuel cells, research and development have been carried out on biofuel cells that use enzymes and microorganisms as electrode catalysts and use biomass resources such as sugars, alcohols, and organic waste liquids as fuel to generate electricity (for example, see Patent Documents 1 and 2).

[0004] Biofuel cells that utilize enzymes typically generate electricity by oxidizing and decomposing fuel at the negative electrode (anode) using oxidases to release electrons, and reducing oxygen to water at the positive electrode (cathode) using reductases.

[0005] As one of the simple and low-cost processes for manufacturing such biofuel cells, a method for patterning electrode materials by screen printing is known. Specifically, this generally involves preparing an electrode slurry (electrode slurry) by dispersing a conductive material such as carbon powder in an electrode binder (electrode binder) obtained by dissolving poly(1,1-difluoroethylene) in an organic solvent such as N-methylpyrrolidone (NMP), screen printing the slurry onto a substrate, and drying it to form an electrode pattern (see, for example, Patent Document 1).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 6994184

[0009] Patent Document 2: Japanese Patent Application Publication No. 2021-140988 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, there are concerns about the potential damage to screen printing equipment caused by the use of NMP as an organic solvent in the electrode binder. In addition, the environmental impact caused by organic solvents has also become a concern.

[0012] Furthermore, it cannot be said that the adhesion of conductive materials is necessarily sufficient for electrode slurries using PVDF. Moreover, the high water repellency of PVDF has led to issues such as insufficient enzyme fixation on the electrode or easy enzyme inactivation, resulting in biofuel cells that do not exhibit sufficient output characteristics.

[0013] The present invention was proposed to solve such a problem, with the aim of providing an electrode binder for biofuel cells that has a low environmental impact, is suitable for screen printing, and can be used to manufacture biofuel cells that exhibit good output characteristics.

[0014] Methods for solving problems

[0015] This invention is based on the discovery that a specified polymer is suitable as an electrode binder when forming electrodes for biofuel cells by screen printing.

[0016] The present invention provides the following means.

[0017] [1] An electrode binder for a biofuel cell, comprising a polymer (A) having a first structural unit derived from a nonionic olefinic unsaturated monomer (a1), a second structural unit derived from an anionic olefinic unsaturated monomer (a2), and a third structural unit derived from a crosslinking agent (a3), wherein the crosslinking agent (a3) ​​has two or more olefinic unsaturated bonds in one molecule.

[0018] [2] The content of polymer (A) in the electrode binder for biofuel cells according to [1] is 50% by mass or more.

[0019] [3] According to the electrode binder for biofuel cells described in [1], the anionic olefinic unsaturated monomer (a2) comprises one or more selected from olefinic unsaturated carboxylic acids and their salts, and olefinic unsaturated sulfonic acids and their salts.

[0020] The effects of the invention

[0021] According to the present invention, an electrode paste with low environmental impact and suitable for screen printing can be provided, and an electrode binder for biofuel cells that can be manufactured to exhibit good output characteristics can be provided. Attached Figure Description

[0022] Figure 1 A schematic cross-sectional view illustrating an example of the configuration of a biofuel cell according to an embodiment of the present invention.

[0023] Figure 2 A schematic cross-sectional view illustrating another example of the configuration of a biofuel cell according to an embodiment of the present invention.

[0024] Figure 3 For illustrative purposes only Figure 1 A schematic cross-sectional view of an example implementation of a biofuel cell. Detailed Implementation

[0025] The following shows the definitions and meanings of the terms and expressions used in this specification.

[0026] Electrode binders for biofuel cells, electrode binder compositions for biofuel cells, and electrode slurries for biofuel cells are also referred to as “electrode binders,” “electrode binder compositions,” and “electrode slurries,” respectively.

[0027] When referred to simply as an "electrode," this refers to the electrode in the state before the enzyme is immobilized, as opposed to an "enzyme electrode" in which the enzyme is immobilized.

[0028] The expression "X~Y" (where X and Y are numerical values) refers to a numerical range with X as the lower limit and Y as the upper limit. Within a numerical range (e.g., a range of content, etc.), the lower and upper limits recorded in stages can be combined independently. The lower and upper limits of the numerical range can be replaced with the numerical values ​​described in the embodiments.

[0029] The content of each structural unit constituting the polymer is determined by the proportion of compounds that are the source of each structural unit and are used as raw materials for the synthesis of the polymer.

[0030] The term "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. Similarly, the term "(meth)acrylate" is a general term for acrylate and methacrylate, and the term "(meth)acryloyl" is a general term for acryloyl and methacryloyl groups.

[0031] The glass transition temperature is the peak temperature of the differential temperature curve of differential scanning calorimetry (DSC). Specifically, it is determined by the method described in the examples.

[0032] The median particle size D50 is the 50% cumulative particle size of the volume baseline for the aqueous dispersion sample, obtained from the particle size distribution curve measured by dynamic light scattering (DLS).

[0033] [Electrode binders for biofuel cells]

[0034] The electrode adhesive of the embodiment of the present invention (hereinafter referred to as this embodiment) comprises a polymer (A) having a first structural unit derived from a nonionic olefinic unsaturated monomer (a1), a second structural unit derived from an anionic olefinic unsaturated monomer (a2), and a third structural unit derived from a crosslinking agent (a3), wherein the crosslinking agent (a3) ​​has two or more olefinic unsaturated bonds in one molecule.

[0035] Electrode binders containing polymers (A) having such a defined structure have low environmental impact and provide electrode pastes with good dispersibility of conductive materials, suitable for screen printing. By using such electrode pastes, biofuel cells with low environmental impact, low cost, and good output characteristics can be manufactured.

[0036] The electrode binder of this embodiment comprises a polymer (A), and may further comprise a water-soluble cellulose derivative (B) and other additives described later.

[0037] To fully realize the effects of the present invention, the content of polymer (A) in the electrode adhesive is preferably 50% by mass or more. More preferably, it is 60% by mass or more, even more preferably 80% by mass or more, and it can also be 100% by mass.

[0038] (Polymer(A))

[0039] The polymer (A) has a first structural unit derived from a nonionic olefinic unsaturated monomer (a1), a second structural unit derived from an anionic olefinic unsaturated monomer (a2), and a third structural unit derived from a crosslinking agent (a3).

[0040] In addition to the first, second, and third structural units, polymer (A) may also have other structural units. To fully realize the effects of the present invention, of the total 100% by mass of all structural units constituting polymer (A), the sum of the first, second, and third structural units is preferably 80-100% by mass, more preferably 85% by mass or more, further preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0041] <Structural Unit 1>

[0042] The first structural unit constituting polymer (A) is derived from a nonionic olefinic unsaturated monomer (a1).

[0043] In order to obtain a polymer (A) that fully exerts the effects of the present invention, the content of the first structural unit in the total amount of the first structural unit, the second structural unit and the third structural unit constituting the polymer (A) is preferably 60 to 98% by mass. More preferably, it is 75% by mass or more, even more preferably 90% by mass or more, and further preferably 97% by mass or less, even more preferably 96% by mass or less.

[0044] The nonionic olefinic unsaturated monomer (a1), which is the source of the first structural unit, has one olefinic unsaturated bond in one molecule and does not have either anionic or cationic functional groups. The nonionic olefinic unsaturated monomer (a1) can be a single type or two or more types.

[0045] As a nonionic olefinic unsaturated monomer (a1), it is suitable to use one or more selected from aromatic olefinic unsaturated compounds, alkyl (meth)acrylates, and olefinic unsaturated carboxylic esters containing polar groups, preferably all of them.

[0046] Aromatic olefin unsaturated compounds contribute to good adhesion of conductive materials, etc.

[0047] Examples of aromatic olefinic unsaturated compounds include styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, 1,1-diphenylethylene, and benzyl (meth)acrylate. One aromatic olefinic unsaturated compound may be used alone, or two or more may be used in combination. Among these, aromatic vinyl compounds are preferred, and styrene is more preferred.

[0048] From the viewpoint of the adhesion of conductive materials and the tightness of the bond to the substrate, the proportion of aromatic olefinic unsaturated compounds in the nonionic olefinic unsaturated monomer (a1) is preferably 25 to 70% by mass. More preferably, it is 35% by mass or more, even more preferably 45% by mass or more, and even more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0049] Alkyl methacrylates contribute to the ease of synthesis and durability of polymer (A).

[0050] Examples of alkyl methacrylates include, for instance, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, and stearyl methacrylate. Alkyl methacrylates can be used alone or in combination with two or more. Among these, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, and 2-ethylhexyl methacrylate are preferred, and 2-ethylhexyl methacrylate is more preferred.

[0051] As an alkyl methacrylate, from the viewpoint of good flexibility of the electrode adhesive, the alkyl group bonded to the (meth)acryloyloxy group preferably has 2 to 9 carbon atoms, more preferably 4 to 9, and even more preferably has an alkyl group with 4 to 9 carbon atoms bonded to the acryloyloxy group.

[0052] From the viewpoints of the flexibility of the electrode adhesive, the adhesion of the conductive material, and the tightness of the substrate, the proportion of (meth)acrylate alkyl ester in the nonionic olefin unsaturated monomer (a1) is preferably 20 to 70% by mass. More preferably, it is 30% by mass or more, even more preferably 40% by mass or more, and further preferably 60% by mass or less, even more preferably 50% by mass or less.

[0053] The presence of polar groups in olefinic unsaturated carboxylic esters contributes to good polymerizability during the synthesis of polymer (A) and mechanical stability of electrode adhesives.

[0054] Examples of polar groups in olefinic unsaturated carboxylic esters containing polar groups include, for example, hydroxyl and cyano groups.

[0055] Examples of olefinic unsaturated carboxylic esters containing polar groups include, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl acrylate, and (meth)acrylonitrile. One type of olefinic unsaturated carboxylic ester containing a polar group may be used alone, or two or more may be used in combination. Among these, 2-hydroxyethyl (meth)acrylate is preferred, and 2-hydroxyethyl methacrylate is more preferred.

[0056] From the viewpoints of good polymerizability during polymer synthesis (A), adhesion of conductive materials, tightness to substrates, and resistance to swelling of electrode adhesives used in batteries, the proportion of olefinic unsaturated carboxylic esters containing polar groups in the nonionic olefinic unsaturated monomer (a1) is preferably 0.50 to 20% by mass. More preferably, it is 1.0% by mass or more, even more preferably 2.0% by mass or more, and even more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0057] <Second Structural Unit>

[0058] The second structural unit constituting polymer (A) is derived from anionic olefinic unsaturated monomer (a2).

[0059] In order to obtain a polymer (A) that fully exerts the effects of the present invention, the content of the second structural unit in the total amount of the first structural unit, the second structural unit and the third structural unit constituting the polymer (A) is preferably 1.5 to 20% by mass, more preferably 3.0% by mass or more, even more preferably 4.5% by mass or more, further preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0060] The anionic olefinic unsaturated monomer (a2), which becomes the source of the second structural unit, has one olefinic unsaturated bond in one molecule and possesses anionic functional groups. The anionic olefinic unsaturated monomer (a2) can be a single type or two or more types combined.

[0061] Examples of anionic functional groups include carboxyl, sulfonyl, and phosphate groups. Anionic functional groups can form salts.

[0062] As an anionic olefinic unsaturated monomer (a2), it is suitable to use one or more selected from olefinic unsaturated carboxylic acids and their salts, and olefinic unsaturated sulfonic acids and their salts, preferably all of them.

[0063] Examples of olefinic unsaturated carboxylic acids and their salts include, for example, unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; half-esters of unsaturated dicarboxylic acids; and their salts. One type of olefinic unsaturated carboxylic acid and its salt may be used alone, or two or more may be used in combination. Among these, (meth)acrylic acid and itaconic acid are preferred.

[0064] From the viewpoints of good polymerizability during the synthesis of polymer (A), adhesion of conductive materials, and tightness to the substrate, the content of olefinic unsaturated carboxylic acids and their salts in the anionic olefinic unsaturated monomer (a2) is preferably 70 to 99% by mass. More preferably, it is 80% by mass or more, even more preferably 85% by mass or more, and further preferably 98% by mass or less, even more preferably 95% by mass or less.

[0065] Examples of olefinic unsaturated sulfonic acids and their salts include, for example, p-styrene sulfonic acid and its salts. Olefinic unsaturated sulfonic acids can be used alone or in combination of two or more. Among these, sodium p-styrene sulfonate is preferred.

[0066] From the viewpoints of good polymerizability during the synthesis of polymer (A), adhesion of conductive materials, and tightness to the substrate, the proportion of olefinic unsaturated sulfonic acid and its salt in the anionic olefinic unsaturated monomer (a2) is preferably 1.0 to 30% by mass. More preferably, it is 2.0% by mass or more, even more preferably 3.0% by mass or more, and even more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0067] <Structural Unit 3>

[0068] The third structural unit that constitutes polymer (A) is derived from crosslinking agent (a3).

[0069] From the viewpoint of the swelling resistance of the electrode adhesive during battery use, the content of the third structural unit in the total amount of the first, second and third structural units constituting polymer (A) is preferably 0.010 to 0.50% by mass, more preferably 0.020% by mass or more, even more preferably 0.030% by mass or more, and even more preferably 0.30% by mass or less, and even more preferably 0.10% by mass or less.

[0070] The crosslinking agent (a3), which becomes the source of the third structural unit, has two or more olefinic unsaturated bonds in one molecule. The crosslinking agent (a3) ​​can be a single type or two or more types used together.

[0071] The crosslinking agent (a3) ​​can form a crosslinked structure by adding two or more olefinic unsaturated bonds to the olefinic unsaturated bonds of other synthetic raw material compounds of polymer (A). That is, polymer (A) is a crosslinked polymer.

[0072] Examples of crosslinking agents (a3) ​​include divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate. Among these, divinylbenzene is preferred.

[0073] <Glass transition temperature>

[0074] From the viewpoints of the adhesion of conductive materials, the tightness of adhesion to the substrate, and the good flexibility of the electrode adhesive, the glass transition temperature of polymer (A) is preferably -30 to 100°C. More preferably, it is -20°C or higher, even more preferably -10°C or higher, and further preferably 90°C or lower, even more preferably 80°C or lower.

[0075] <Particle size>

[0076] Polymer (A) exists as dispersed particles in an electrode binder composition containing an aqueous dispersion medium. The suitable particle size of the dispersed particles varies depending on the morphology of the conductive material, particle size, etc. To fully realize the effects of the present invention, the median particle size D50 of the particles in the aqueous dispersion is preferably 0.10 to 1.0 μm. More preferably, it is 0.15 μm or more, further preferably 0.20 μm or more, and even more preferably 0.80 μm or less, and even more preferably 0.50 μm or less.

[0077] <Synthetic Method>

[0078] Polymer (A) can be manufactured by polymerizing a synthetic starting material comprising a nonionic olefinic unsaturated monomer (a1), an anionic olefinic unsaturated monomer (a2), and a crosslinking agent (a3). The polymerization method is not particularly limited; emulsion polymerization is a suitable example.

[0079] Emulsion polymerization is carried out in an aqueous medium in the presence of a polymerization initiator, with the addition of surfactants and other additives as needed. The raw materials can be added simultaneously or gradually, such as dropwise. Typically, the reaction is carried out at 30–90°C with stirring.

[0080] In addition, from the viewpoint of the stability of polymer (A) in the reaction system, it is preferable to add an alkaline substance for neutralization and pH adjustment as needed during or after the polymerization reaction.

[0081] Preferred alkaline substances include, for example, ammonia, triethylamine, ethanolamine, morpholine, 2-amino-2-methyl-1-propanol, lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide. One alkaline substance may be used alone, or two or more may be used in combination.

[0082] The aqueous medium is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents include methanol, ethanol, isopropanol, N-methylpyrrolidone (NMP), and 1,3-butanediol.

[0083] From the perspectives of dispersion stability of synthetic raw materials and polymers, and reduction of environmental impact, water is the preferred aqueous medium. Within the range that does not impair dispersion stability, a mixture of water and a hydrophilic solvent is also preferred.

[0084] The aqueous medium used in the synthesis of polymer (A) can serve as an aqueous medium constituting the electrode binder composition and remains directly after synthesis.

[0085] The amount of aqueous medium used is adjusted appropriately based on the dispersibility of the synthetic raw materials in the aqueous medium and the viscosity of the reaction system. From the viewpoint of conducting a moderate polymerization reaction, the amount of aqueous medium used is preferably 50 to 300 parts by mass relative to a total of 100 parts by mass of the nonionic olefinic unsaturated monomer (a1), the anionic olefinic unsaturated monomer (a2), and the crosslinking agent (a3). More preferably, it is 80 parts by mass or more, further preferably 100 parts by mass or more, and even more preferably 250 parts by mass or less, and even more preferably 200 parts by mass or less.

[0086] There are no particular limitations on the polymerization initiator; free radical polymerization initiators can be used, such as ammonium persulfate, potassium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, and other peroxides. A single polymerization initiator can be used, or two or more can be used in combination. Furthermore, redox polymerization can also be performed by combining these polymerization initiators with reducing agents such as sodium bisulfite, sodium hydroxide, and ascorbic acid.

[0087] From the perspective of the dispersion stability of the synthetic raw materials and the resulting polymer (A) in an aqueous medium, it is suitable to use one or more surfactants selected from nonionic surfactants and anionic surfactants.

[0088] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene alkylene alkyl ethers, sorbitol fatty acid esters, and polyoxyethylene sorbitol fatty acid esters. Nonionic surfactants can be used alone or in combination of two or more.

[0089] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts.

[0090] As anionic surfactants, reactive surfactants with olefinic unsaturated bonds are also suitable.

[0091] Examples of reactive surfactants include compounds represented by formulas (1) to (4) below. A single reactive surfactant may be used alone, or two or more may be used in combination. Among these, the compound represented by formula (4) is preferred, and sodium alkylallyl sulfosuccinate is more preferred.

[0092]

[0093] In equation (1), R 1 It is an alkyl group, and p is an integer from 10 to 40. R 1 Preferably, it is an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain alkyl group having 10 to 40 carbon atoms.

[0094]

[0095] In equation (2), R 2 It is an alkyl group, and q is an integer from 10 to 12. R 2 Preferably, it is an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain alkyl group having 10 to 40 carbon atoms.

[0096]

[0097] In equation (3), R 3 It is an alkyl group, M 1 It is NH4 or Na. R 3 Preferably, it is an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain alkyl group having 10 to 40 carbon atoms.

[0098]

[0099] In equation (4), R 4 It is an alkyl group, M 2 It is NH4 or Na. R 4 Preferably, it is an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain alkyl group having 10 to 40 carbon atoms.

[0100] In addition, the reactive surfactant plays an emulsifying role in the reaction system during emulsion polymerization and has copolymerization properties with nonionic olefinic unsaturated monomers (a1), anionic olefinic unsaturated monomers (a2), and crosslinking agents (a3), but in this embodiment, it is not considered as a structural unit constituting polymer (A).

[0101] From the perspectives of stable polymerization reaction, dispersion stability of the synthetic raw materials and the resulting polymer (A) in the aqueous medium, and adhesion of the conductive material to the substrate, the amount of surfactant added is preferably 0.050 to 1.2 parts by mass relative to a total of 100 parts by mass of the nonionic olefinic unsaturated monomer (a1), the anionic olefinic unsaturated monomer (a2), and the crosslinking agent (a3). More preferably, it is 0.10 parts by mass or more, even more preferably 0.15 parts by mass or more, and even more preferably 1.0 parts by mass or less, and even more preferably 0.50 parts by mass or less.

[0102] Other additives include chain transfer agents such as thiols, mercaptoacetic acid and its esters, and 3-mercaptopropionic acid and its esters.

[0103] The addition of other additives is arbitrary and can be made within the range of polymers (A) that do not impair the effects of the present invention.

[0104] (Water-soluble cellulose derivative (B))

[0105] The electrode binder in this embodiment preferably also contains a polymer (A), and further contains a water-soluble cellulose derivative (B).

[0106] Water-soluble cellulose derivatives (B) facilitate the dispersion of conductive materials in electrode slurries.

[0107] Examples of water-soluble cellulose derivatives (B) include, for example, celluloses such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, and their salts; polyvinyl alcohol; and polyvinylpyrrolidone. Examples of cellulose salts include, for example, ammonium salts and alkali metal salts. One type of water-soluble cellulose derivative (B) may be used alone, or two or more may be used in combination. Among these, carboxymethylcellulose and its salts are preferred.

[0108] When the electrode binder contains a water-soluble cellulose derivative (B), from the viewpoint of not hindering the function of the polymer (A) and obtaining good dispersibility of the conductive material, its content is preferably 1 to 50% by mass. More preferably, it is 5% by mass or more, even more preferably 10% by mass or more, and further preferably 40% by mass or less, even more preferably 30% by mass or less.

[0109] The total content of polymer (A) and water-soluble cellulose derivative (B) in the electrode adhesive is preferably 80% by mass or more, more preferably 95% by mass or more, and may also be 100% by mass.

[0110] [Electrode binder composition for biofuel cells]

[0111] The electrode adhesive composition of this embodiment includes the electrode adhesive described above and an aqueous medium, wherein polymer (A) is dispersed in the aqueous medium.

[0112] Electrode binder compositions can be prepared by mixing electrode binder and an aqueous medium. The mixing method is not particularly limited.

[0113] As an aqueous medium in the electrode binder composition, an example may be the same substance as the aqueous medium used in the synthesis method of the polymer (A) described above. The aqueous medium used in the synthesis method of polymer (A) may be the same as or different from the substance used in the synthesis method of polymer (A). The aqueous medium used in the synthesis of polymer (A) may include substances that remain directly after synthesis.

[0114] From the viewpoint of improving the dispersion stability of the electrode binder in the electrode binder composition and reducing environmental impact, water is preferred as the aqueous medium. A mixture of water and a hydrophilic solvent is also preferred, provided it does not impair dispersion stability.

[0115] The content of polymer (A) in the electrode adhesive composition can be appropriately adjusted by arbitrarily adding an aqueous medium during the manufacture of the electrode slurry. However, from the viewpoint of easy operation and dispersion stability of polymer (A), it is preferably 10 to 80% by mass, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0116] [Electrode slurry for biofuel cells]

[0117] The electrode paste of this embodiment includes the electrode binder, conductive material, and aqueous medium described above.

[0118] Electrode slurry can be manufactured by mixing electrode binder, conductive material, and aqueous medium. The mixing method is not particularly limited, but to ensure sufficient and homogeneous dispersion of the conductive material, it is preferable to use a rotary mixer or similar equipment for mixing.

[0119] In addition to electrode binders, conductive materials, and aqueous media, the electrode paste may contain other components, to the extent that it does not impair the effects of the present invention. Examples of such other components, from the viewpoint of dispersion stability, include surfactants.

[0120] To fully realize the effects of the present invention, the total content of electrode binder, conductive material, and aqueous medium in the electrode slurry is preferably 50% by mass or more. More preferably, it is 60% by mass or more, even more preferably 80% by mass or more, and it can also be 100% by mass.

[0121] The aqueous medium in the electrode slurry is described in the same way as the aqueous medium in the electrode adhesive composition described above.

[0122] Examples of conductive materials include carbon materials and metallic materials. Examples of carbon materials include graphite, carbon black, and porous carbon. A single conductive material can be used, or two or more can be used in combination. Among these, from the viewpoints of operability and enzyme immobilization, carbon materials are preferred, and porous carbon is more preferred.

[0123] Examples of porous carbon include mesoporous carbon, specifically mesoporous carbons such as Ketjen black, carbon nanotubes, graphene, and MgO-templated carbon produced by template methods. Among these, MgO-templated carbon is suitable from the viewpoint of good enzyme immobilization.

[0124] From the viewpoint of ensuring a sufficient amount of conductive material adheres closely to the substrate, the content of conductive material in the electrode paste is preferably 40 to 85% by mass. More preferably, it is 45% by mass or more, even more preferably 50% by mass or more, and further preferably 80% by mass or less, even more preferably 75% by mass or less.

[0125] The content of electrode binder in the electrode paste is sufficient for the adhesion of the conductive material to the substrate, and is preferably 10 to 200 parts by weight relative to 100 parts by weight of the conductive material. More preferably, it is 20 parts by weight or more, further preferably 30 parts by weight or more, and even more preferably 150 parts by weight or less, further preferably 120 parts by weight or less, and even more preferably 60 parts by weight or less.

[0126] From the perspective of the applicability of electrode paste to screen printing and the reduction of usage, the total content of electrode binder and conductive material in electrode paste is preferably 40 to 80% by mass. More preferably, it is 45% by mass or more, even more preferably 50% by mass or more, and even more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0127] [Electrodes for biofuel cells]

[0128] Preferably, the electrode binder of this embodiment is included in at least one of the anode and cathode of the electrode for the biofuel cell. More preferably, it is included in both the anode and cathode, in which case the electrode binder included in the anode and the electrode binder included in the cathode may have the same composition or different compositions.

[0129] The electrode comprises a conductive material and an electrode binder. The electrode binder of this embodiment is preferred.

[0130] The electrode preferably has at least a conductive material and an electrode adhesive bonded to a substrate. Such an electrode can be manufactured by coating an electrode paste onto a substrate and then drying it. The electrode paste of this embodiment is preferred as the electrode paste.

[0131] Examples of suitable substrates include inorganic materials such as paper, cloth, resin films, metals, and ceramics. To ensure high-density adhesion of the conductive material, a porous substrate is preferred, exhibiting good adhesion to the electrode adhesive. Considering environmental impacts from biofuel cell waste disposal, materials such as Japanese paper are suitable. Furthermore, from a durability perspective, oil- and water-resistant paper is suitable. The electrode paste can be applied to one or both sides of the substrate.

[0132] There are no particular limitations on the coating method for the electrode paste. Examples of coating methods include screen printing, reverse roller coating, direct roller coating, and doctor blade coating. Among these, screen printing is preferred from the perspective of its ability to form patterns easily and efficiently. In the case of screen printing, for example, it is also possible to form lead portions using conductive materials such as carbon paste and electrode patterns with multiple electrodes printed on the substrate.

[0133] The electrode paste coated on the substrate is dried to thoroughly remove the aqueous medium from the electrode paste. The drying method is not particularly limited as long as the aqueous medium is thoroughly removed. Examples of drying methods include those performed under conditions such as hot air, low-temperature air, reduced pressure or vacuum, or (far)infrared irradiation. These drying conditions can be combined.

[0134] [Enzyme Electrode]

[0135] In this embodiment, the enzyme electrode has an enzyme fixed on it.

[0136] In the case of an enzyme electrode at the anode, an enzyme that promotes the oxidation of fuel in a biofuel cell is used. Alternatively, an enzyme that facilitates the oxidation of fuel through hydrolysis or similar methods can also be used.

[0137] Enzymes used as anode enzyme electrodes include, for example, glucose oxidase or a combination of glucose and glucose dehydrogenase when the fuel is glucose; fructose oxidase or a combination of fructose and fructose dehydrogenase when the fuel is fructose; invertase or a combination of glucose and glucose dehydrogenase when the fuel is sucrose; amylase or a combination of amylase and glucose dehydrogenase when the fuel is starch; and lactate oxidase when the fuel is lactic acid.

[0138] In the case of an enzyme electrode used at the cathode, an enzyme that promotes oxygen reduction is suitable.

[0139] Examples of enzymes used as cathode enzyme electrodes include bilirubin oxidase and laccase.

[0140] Enzyme electrodes can be manufactured, for example, by immobilizing an enzyme on an electrode. Alternatively, enzyme electrodes can be manufactured by coating an enzyme-containing electrode slurry, which contains both an enzyme and an electrode slurry, onto a substrate and then drying it.

[0141] There are no particular limitations on the method of immobilizing enzymes on electrodes. For example, it can be done by coating the electrode with an enzyme solution and then drying it. Enzyme coating can be performed, for example, by adding the enzyme solution dropwise or by impregnation. The enzyme can also be coated after the mediator has been coated.

[0142] Mediators are redox compounds that facilitate electron transfer between electrodes and enzymes, and are appropriately selected based on the type of fuel and enzyme. They are used either by being mounted on the electrode or dissolved in the electrolyte.

[0143] When a dielectric is supported on an electrode, it can be added to the electrode slurry and then coated onto the electrode. Alternatively, the dielectric can be coated after the electrode is formed. The dielectric can be supported on either the anode or the cathode, or on both.

[0144] Examples of mediators include organosulfur compounds such as thionine, thionine acetate, tetrathionylfuvalene, and 2,2'-azonobis(3-ethylbenzothiazoline-6-sulfonate); quinone compounds such as hydroquinone, 1,2-naphthoquinone, and 1,4-naphthoquinone; ferrocene; ferricyanides; osmium coordination compounds; and polymers modified with these compounds. A single mediator can be used, or two or more can be used in combination.

[0145] From the viewpoint of fully promoting power generation, the enzyme immobilized on the electrode is preferably at a concentration of 0.001 U / cm relative to the electrode. 2 The above is preferred, and more preferably is 0.01 U / cm 2 The above is further preferred to be 0.1 U / cm 2 The amount of enzyme immobilized on the electrode should preferably be as high as possible, for example, 2000 U / cm.2 The following can be 1000U / cm 2 Below, it can be 500U / cm 2 the following.

[0146] [Biofuel Cells]

[0147] The biofuel cell of this embodiment generates electricity through a redox reaction using an enzyme as a catalyst, with the enzyme immobilized in at least one of the anode and cathode.

[0148] The enzyme-immobilized electrode may be only one of the anode or the cathode, or both. The enzyme electrode of this embodiment described above is preferred as the enzyme-immobilized electrode. The enzyme electrode of this embodiment may be only one of the anode or the cathode, or both.

[0149] When both the anode and cathode are enzyme electrodes of this embodiment, the substrate, electrode adhesive, and conductive material of the enzyme electrode may be the same or different in the anode and cathode, respectively.

[0150] If the cathode is not the enzyme electrode of this embodiment, the cathode may be, for example, a substance containing an oxygen reduction catalyst or the like, such as platinum, which is immobilized instead of an enzyme.

[0151] There are no particular limitations on the fuel used in biofuel cells, as long as it is a substance that is oxidized by enzymes. Examples of fuels include sugars, alcohols, aldehydes, amino acids, amines, lactic acid, and uric acid. Fuel can be a substance that is hydrolyzed and oxidized by enzymes (e.g., starch or cellulose hydrolyzed into glucose). Fuel can be a single type or a combination of two or more types. Among these, sugars are preferred from the viewpoint of output stability and ease of operation. There are no particular limitations on the type of sugar; examples include monosaccharides, disaccharides, oligosaccharides, polysaccharides, and sugar alcohols. Glucose is a suitable example.

[0152] exist Figure 1 The diagram illustrates an example of the structure of the biofuel cell of this embodiment. Figure 1 The biofuel cell 10 shown has an anode 2 and a cathode 3 formed on the same side of a fuel-containing substrate 1.

[0153] In addition, Figure 2 Another example of the structure of the biofuel cell of this embodiment is illustrated schematically. Figure 2 The biofuel cell 20 shown has an anode 2 formed on one side of a substrate 1 containing fuel, and a cathode 3 formed on the other (opposite) side. In this case, the substrate 1 also serves as a separator between the anode 2 and the cathode 3.

[0154] The biofuel cell of this embodiment can generate electricity, for example, by supplying only gum syrup or the like as fuel. Furthermore, as another embodiment, for example, it can generate electricity by pre-containing sugar, which serves as fuel, in a substrate, thereby using water.

[0155] In addition, as another implementation plan, for example, Figure 3 Solutions such as those shown are applied to the skin for use. In Figure 3 In the example, it was used Figure 1 The biofuel cell 10 shown has lead portions 4 formed on both the anode 2 and the cathode 3. The biofuel cell 10 is fixed to the skin 6 by covering the lead portions 4 with a cover sheet 5, bringing the substrate 1 into contact with the skin 6. The biofuel cell 10 can be fixed to the skin 6 by using an adhesive sheet to attach it to the skin 6, or by using adhesive tape or the like.

[0156] exist Figure 3 In the illustrated embodiment, for example, the anode 2 can be an enzyme electrode with lactate oxidase immobilized, and the cathode 3 can be an enzyme electrode with bilirubin oxidase immobilized. In this case, sweat secreted from the skin 6 is absorbed by the substrate 1, and the lactic acid contained in the sweat is used as fuel to generate electricity. The electricity can be extracted to the outside via the lead portion 4.

[0157] As described above, the biofuel cell of this embodiment can also be used as a biosensor when applied to living organisms. For example, by installing the biofuel cell on adherents such as skin, clothing, and diapers, and using the amount of substances in bodily fluids such as sweat, urine, blood, tears, and saliva supplied from the adherent as electricity to detect and measure changes in these substances, it is expected to be used as a wearable device for health management, exercise measurement and management, etc.

[0158] [Example]

[0159] The present invention will now be described in detail based on specific embodiments. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the spirit of the invention.

[0160] [Manufacturing of Polymer (A)]

[0161] The methods for determining the various physical properties in the following synthetic examples are described below.

[0162] <Glass transition temperature>

[0163] Differential scanning calorimetry (DSC) was measured using a differential scanning calorimeter ("EXSTAR DSC7020", manufactured by Hitachi Hitachi Science Co., Ltd.; heating rate 10°C / min, nitrogen atmosphere). The peak temperature of the temperature differential curve of the DSC was set as the glass transition temperature.

[0164] <Median particle size D50>

[0165] The median particle size D50 was determined from the particle size distribution curve obtained by dynamic light scattering (DLS).

[0166] (Synthesis example 1)

[0167] In a reaction vessel equipped with a cooling pipe, thermometer, stirrer, and dropping funnel, 60 parts by mass of ion-exchanged water were added, and the temperature was raised to 75°C. Over 3 hours, a mixture containing 100 parts by mass of the compound shown in Table 1 (comprising nonionic olefinic unsaturated monomer (a1), anionic olefinic unsaturated monomer (a2), and crosslinking agent (a3), 0.20 parts by mass of Elemino JS-20 (excluding solvent), 0.20 parts by mass of High-Temperature No. 08E, and 80 parts by mass of ion-exchanged water) was added dropwise, and the mixture was stirred. Simultaneously, over 3 hours, a substance obtained by dissolving 0.40 parts by mass of potassium persulfate in 10 parts by mass of ion-exchanged water was added dropwise, and the mixture was stirred to induce polymerization.

[0168] Two hours after the addition was completed, the reaction product was neutralized with 0.90 parts by mass of ammonia solution with a concentration of 25% by mass, to obtain a dispersion of polymer (A1) (polymer (A1) content 40% by mass).

[0169] [Table 1]

[0170] In addition, the details of the surfactants in Table 1 are as follows.

[0171] Elemino JS-20: Sodium alkylallyl sulfosuccinate; "Elemino (registered trademark) JS-20", manufactured by Sanyo Chemical Industry Co., Ltd.; anionic reactive surfactant; non-volatile component 38.5% by mass. High-Teno-08E: Polyoxyethylene oil-based cetyl ether ammonium sulfate; "High-Teno-08E (registered trademark)" is manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.; anionic surfactant. The polymer (A1) has a glass transition temperature of 15℃ and a median particle size D50 of 0.26μm.

[0172] [Electrode paste manufacturing]

[0173] The raw materials used in the manufacture of electrode paste are as follows.

[0174] Porous carbon powder: “Knobel (registered trademark) MJ(3)100-00”, manufactured by Toyo Carbon Co., Ltd.; BET specific surface area 390m² 2 / g, total micropore volume 0.91mL / g, micropore capacity 0.15mL / g, mesopore size 75nm, bulk density 0.06g / mL Electrode binder composition (1): A dispersion of polymer (A1) (electrode binder) produced in Synthesis Example 1 (40% by mass of non-volatile components). Electrode adhesive composition (2): "Kreha KF Polymer L#9305", manufactured by Kreha Co., Ltd.; 5% NMP solution of PVDF ("Kreha KF Polymer L#9300": electrode adhesive) Electrode adhesive composition (3): Styrene / butadiene rubber (electrode adhesive) latex (40% by mass of non-volatile components) Electrode binder composition (4): PTFE (electrode binder) aqueous dispersion (60% by mass of non-volatile components) Porous carbon powder, electrode binder composition, and additive medium are mixed according to the components shown in Table 2 and kneaded using a rotary mixer to produce electrode slurries 1 to 9.

[0175] As shown in Table 2, the dispersibility of porous carbon powder in the obtained electrode slurries is good for electrode slurries 1-8 (○) and poor for electrode slurry 9 (×).

[0176] [Manufacturing of biofuel cells]

[0177] Biofuel cells were manufactured using electrode slurries 1 to 9 according to the method described below. Examples using electrode slurries 1 to 6 are provided, while comparative examples using electrode slurries 7 to 9 are provided.

[0178] The following details the materials and raw materials used in the manufacture of biofuel cells.

[0179] Substrate (Japanese paper): Xuan paper treated with water-repellent process; Izumo washi paper. Substrate (oil and water resistant paper): "Oil and water resistant paper (3)", manufactured by Linkec Co., Ltd. Carbon paste: "JELCON CH-8", manufactured by Jujo Micron Co., Ltd. AzBTS: 2,2'-Z-di-bis(3-ethylbenzothiazoline-6-sulfonate ammonium); manufactured by Tokyo Chemical Industry Co., Ltd. TTF: Tetrathionefulvalene GOD: Glucooxidase; manufactured by Fujifilm Wako Pure Medicine Co., Ltd. Phosphate buffer: 1 mol / L phosphate buffer, pH 7.0 BOD: Bilirubin oxidase; manufactured by Amano Engineering Co., Ltd. Triton X-100: Polyethylene glycol-tert-octylphenyl ether; "Triton (registered trademark) X-100"; Rosh Made by Daigannostixx Corporation; Nonionic surfactant Carbon paste was screen-printed onto the substrate and dried at 120°C for 20 minutes to form the lead section. Electrode paste containing 0.04g of AzBTS as a dielectric was then screen-printed onto the lead section in three layers, followed by drying at 45°C for 30 minutes to form 32 electrodes of 20mm × 5mm each. A 15-minute UV ozone wash was then performed. The electrode pattern consisted of four anodes and four cathodes connected in series and four cathodes connected in parallel.

[0180] At the anode portion of the electrode, a saturated methanol solution of TTF is added dropwise as a mediator. Further, 20 μL of a solution (10 U / μL) containing GOD dispersed in phosphate buffer is added dropwise to each anode.

[0181] In the cathode portion, which corresponds to the electrode, 20 μL of liquid (10 U / μL) was added dropwise to each cathode to disperse BOD in a phosphate buffer solution containing 0.01% by mass of Triton X-100.

[0182] Then, the electrode (patterned electrode) is dried under reduced pressure for 1 hour to create an enzyme electrode plate that fixes GOD on the anode and BOD on the cathode.

[0183] In addition, a phosphate buffer solution (1 mL / cm³) containing 0.1 mol / L glucose was dropped onto another substrate. 2 The glucose-containing substrate is dried at 100°C for 30 minutes.

[0184] The glucose-containing substrate was placed on the enzyme electrode of the enzyme electrode plate to create a biofuel cell.

[0185] In addition, enzyme electrode plates using Japanese paper as a substrate were manufactured using electrode slurries 1, 7, and 8. Furthermore, enzyme electrode plates using oil- and water-resistant paper were manufactured using electrode slurries 1 through 6. Electrode slurry 9 was not used in a biofuel cell due to poor dispersibility (Comparative Example 3).

[0186] [Output Characteristic Evaluation]

[0187] The output of each biofuel cell manufactured using the above method was measured by linear sweep voltammetry (measurement conditions: two-electrode method, scan potential, open circuit voltage 0V, scan rate 1mV / s), and the maximum output was determined. Liquid supply during measurement was achieved by adding 1 mol / L phosphate buffer (pH 7.0).

[0188] The measured values ​​of the maximum output are shown in Table 2.

[0189] [Table 2]

[0190] As shown in Table 2, the biofuel cell manufactured using electrode slurry 1 exhibited good output characteristics (Example 1). Furthermore, the biofuel cells manufactured using electrode slurries 2-6 also showed good output characteristics (Examples 2-6). On the other hand, the biofuel cells manufactured using electrode slurries 7 and 8 had poor output characteristics (Comparative Examples 1 and 2).

[0191] Based on the above, the biofuel cell manufactured using an electrode slurry containing an aqueous electrode binder of this embodiment can be said to exhibit good output characteristics.

[0192] Explanation of symbols

[0193] 1. Substrate

[0194] 2 Anode

[0195] 3 Cathode

[0196] 4. Lead wire section

[0197] 5. Covering sheet

[0198] 6. Skin

[0199] 10, 20 Biofuel cells.

Claims

1. Use of polymer (A) in the preparation of electrode binders for biofuel cells, said polymer (A) having a first structural unit derived from a nonionic olefinic unsaturated monomer (a1), a second structural unit derived from an anionic olefinic unsaturated monomer (a2), and a third structural unit derived from a crosslinking agent (a3). The crosslinking agent (a3) ​​has more than two olefinic unsaturated bonds in one molecule. The content of the third structural unit in the total amount of the first, second and third structural units constituting polymer (A) is 0.010 to 0.50 by mass.

2. In the application according to claim 1, the content of polymer (A) in the electrode binder for biofuel cells is 50% by mass or more.

3. The use according to claim 1, wherein the anionic olefinic unsaturated monomer (a2) comprises one or more selected from olefinic unsaturated carboxylic acids and their salts, and olefinic unsaturated sulfonic acids and their salts.

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