Electrode ink, method for producing same, and method for producing electrode

Abstract

The present disclosure relates to a method for producing an electrode ink for an enzyme battery, the electrode ink containing an enzyme, a water-insoluble mediator, and a porous conductive substance, and the method comprising: a step 1 for preparing a first mixture containing a liquid in which the mediator is dissolved in a nonaqueous solvent, and the porous conductive substance; a step 2 for implementing a dispersion treatment on the first mixture at 60°C or lower under reduced pressure to volatilize and remove the nonaqueous solvent from the first mixture and obtain a second mixture; and a step 3 for adding and mixing the enzyme, an aqueous medium, and a binder with the second mixture to obtain the electrode ink.

Description

Electrode ink and manufacturing method thereof, and electrode manufacturing method

[0001] The present disclosure relates to an electrode ink for an enzyme battery, a method for manufacturing the same, and a method for manufacturing an electrode using the electrode ink.

[0002] Research and development is underway on biofuel cells, which use enzymes as electrode catalysts to generate electricity using biomass resources such as sugar, alcohol, and organic waste liquids as fuel. Biofuel cells that use enzymes are also called enzyme cells, and generally generate electricity by oxidizing and decomposing fuel at the negative electrode (anode) using oxidizing enzymes to extract electrons, and then reducing oxygen at the positive electrode (cathode) using reductase enzymes to produce water.

[0003] Electrodes for such enzyme batteries are generally manufactured by preparing a composition (electrode slurry) in which a conductive material such as carbon powder is dispersed in a binder prepared by dissolving a resin in an organic solvent, and then applying the composition to a substrate or a conductive layer (substrate, etc.). Then, a mediator is dropped onto the obtained electrode, and then an enzyme is dropped onto the electrode to support the mediator, thereby manufacturing an electrode (enzyme electrode) (see, for example, Patent Documents 1 and 2).

[0004] International Publication No. 2018 / 062419 Japanese Patent Application Laid-Open No. 2021-96991

[0005] In the above-described electrode manufacturing method, an electrode slurry containing a conductive material, a mediator, and an enzyme are added stepwise to a substrate or the like, which requires many steps, makes handling of the manufacturing raw materials complicated, and is likely to increase the workload.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide an electrode ink and a method for manufacturing the same, as well as a method for manufacturing an electrode, that can simplify the manufacturing process of electrodes for enzyme batteries, reduce the workload in manufacturing the electrodes, and enable the development of good electrode characteristics.

[0007] The present disclosure is based on the discovery that an electrode ink containing an enzyme produced under specified conditions can simplify the electrode production process and also exhibit good electrode characteristics.

[0008] The present disclosure provides the following means: [1] A method for producing an electrode ink for an enzyme battery, comprising an enzyme, a water-insoluble mediator, and a porous conductive material, the method comprising: Step 1: preparing a first mixture containing a liquid in which the mediator is dissolved in a non-aqueous solvent, and the porous conductive material; Step 2: subjecting the first mixture to a dispersion treatment under reduced pressure at 60°C or less to volatilize and remove the non-aqueous solvent from the first mixture to obtain a second mixture; and Step 3: adding and mixing the enzyme, an aqueous medium, and a binder to the second mixture to obtain the electrode ink. [2] A method for producing an electrode ink according to [1], wherein in Step 3, the second mixture and at least a portion of the aqueous medium are mixed, the pH is adjusted to 4 or higher, and then the enzyme is added and mixed. [3] A method for producing an electrode ink according to either [1] or [2], wherein in Step 3, a water-soluble polymer is further added and mixed. [4] The method for producing an electrode ink according to [3], wherein in step 3, the water-soluble polymer is added and mixed to the second mixture, and then the enzyme and the aqueous medium are added and mixed.

[0009] [5] An electrode ink for an enzyme battery, comprising an enzyme, a water-insoluble mediator, and a porous conductive material, wherein the enzyme is ubiquitously present within the pores of the porous conductive material. [6] A method for manufacturing an electrode, comprising the steps of applying the electrode ink manufactured by the manufacturing method of any one of [1] to [4] to a substrate or a conductive layer, and drying the applied electrode ink.

[0010] According to the present disclosure, an electrode ink and a method for manufacturing the same, as well as a method for manufacturing an electrode, are provided that can simplify the manufacturing process of electrodes for enzyme batteries, reduce the workload in manufacturing the electrodes, and exhibit good electrode characteristics.

[0011] FIG. 1 is a diagram showing an outline of the arrangement of each electrode in chronoamperometry measurement in an example.

[0012] The definitions and meanings of terms and notations used in this specification are as follows. The notation "X to Y" (X and Y are numbers) refers to a numerical range with X as the lower limit and Y as the upper limit. In a numerical range (e.g., a range of content, etc.), the lower and upper limits described in stages may be independently combined. The lower and upper limits of a numerical range may be replaced with numerical values ​​described in the Examples. For example, when a structural unit constituting a polymer is a polymer having a structural unit derived from an ethylenically unsaturated monomer, the chemical structure of the structural unit other than the portion corresponding to the ethylenically unsaturated bond of the ethylenically unsaturated monomer is the same as the chemical structure of the structural portion other than the ethylenically unsaturated bond of the ethylenically unsaturated monomer from which the structural unit is derived. For example, a polymer having a structural unit derived from styrene has a phenyl group, which is the structural portion of styrene. "(Meth)acrylic" is a general term for acrylic and methacrylic. Similarly, "(meth)acrylate" is a general term for acrylate and methacrylate, and "(meth)acryloyl" is a general term for acryloyl and methacryloyl. The nonvolatile content is the residue remaining after drying the object, excluding liquid media such as non-aqueous solvents and aqueous media. The particle median diameter D50 is the 50% cumulative particle diameter on a volume basis determined from a particle size distribution curve measured by dynamic light scattering (DLS). The glass transition temperature is the peak-top temperature of the temperature derivative curve of differential scanning calorimetry (DSC). Specifically, it is measured by the method described in the examples.

[0013] [Method for Producing Electrode Ink] The method for producing an electrode ink of the present disclosure is a method for producing an electrode ink for an enzyme battery, which contains an enzyme, a water-insoluble mediator, and a porous conductive material, and includes the following steps: Step 1: preparing a first mixture containing a liquid in which the mediator is dissolved in a non-aqueous solvent, and the porous conductive material; Step 2: subjecting the first mixture to a dispersion treatment under reduced pressure at 60°C or less to volatilize and remove the non-aqueous solvent from the first mixture, thereby obtaining a second mixture; and Step 3: adding and mixing the enzyme, an aqueous medium, and a binder to the second mixture, thereby obtaining the electrode ink.

[0014] The manufacturing method disclosed herein is a method for manufacturing an electrode ink for an enzyme battery, the electrode ink including an enzyme, a water-insoluble mediator, and a porous conductive material. According to the manufacturing method disclosed herein, an electrode ink capable of exhibiting good electrode characteristics can be obtained. By manufacturing an electrode using the electrode ink, the manufacturing process for an enzyme battery electrode can be simplified compared to a process in which each component is sequentially applied to a substrate or conductive layer (hereinafter also referred to as a substrate, etc.), and the workload involved in manufacturing the electrode can be reduced.

[0015] The total content of the enzyme, mediator, and porous conductive material in the electrode ink is preferably 1 to 50% by mass, more preferably 2 to 30% by mass, and even more preferably 3 to 20% by mass, from the viewpoints of ease of handling the electrode ink and ease of obtaining sufficient electrode performance.

[0016] (Enzyme battery) An enzyme battery is a battery in which an enzyme is contained in at least one of the anode and cathode, and generates electricity by using biomass resources such as sugar, alcohol, and organic waste liquid as fuel, and utilizing electrons and ions generated at the anode and an oxygen reduction reaction at the cathode. The electrode ink produced by the production method of the present disclosure is used to produce the anode or cathode of such an enzyme battery, or both electrodes containing the enzyme.

[0017] The fuel for an enzyme battery is not particularly limited as long as it is an organic substance that can be decomposed by enzymes, and a wide range of organic substances can be used, including monosaccharides such as D-glucose, polysaccharides such as starch, alcohols such as ethanol, and organic acids. Of these, glucose, lactic acid, fructose, and the like are preferred from the standpoints of output stability and ease of handling. Furthermore, an electrolyte solution containing a dissolved electrolyte such as a phosphate or sodium salt, a solid polymer electrolyte, or the like may be used as an ion conductor that conducts ions between the anode and cathode along with the fuel.

[0018] Enzyme batteries can also be used in living organisms, such as in biosensors. For example, by attaching an enzyme battery to an adherend such as skin, clothing, or a diaper, the amount of substances in bodily fluids such as sweat, urine, blood, tears, and saliva supplied from the adherend can be detected as electricity, and fluctuations in this amount can be measured, allowing for use in wearable devices such as those for health management and measurement and management of exercise volume.

[0019] (Enzyme) The enzyme in the present disclosure is not particularly limited as long as it is an enzyme (oxidoreductase) that can donate and receive electrons through a reaction. The enzyme is appropriately selected depending on the fuel, cost, type of device, etc. of the enzyme battery. The oxidoreductase is preferably an enzyme that can promote various oxidation-reduction reactions in vivo, such as metabolism.

[0020] When the electrode ink of the manufacturing method of the present disclosure is used for the anode (anode ink), an enzyme that promotes the oxidation of fuel in an enzyme battery is preferably used. The enzyme may be used alone or in combination of two or more. Examples of enzymes for the anode include oxidases, which catalyze the oxidation of sugars and organic acids, and dehydrogenases, which catalyze dehydrogenation. Specific examples include glucose oxidase and glucose dehydrogenase, which are relatively inexpensive and highly stable and can use glucose contained in human blood, urine, etc. as fuel; lactate oxidase and lactate dehydrogenase, which can use lactic acid in sweat and blood as fuel; and fructose oxidase and fructose dehydrogenase, which can use fructose as fuel.

[0021] When the electrode ink of the manufacturing method of the present disclosure is used for a cathode (cathode ink), an enzyme that promotes oxygen reduction is preferably used. The enzyme may be used alone or in combination of two or more. Examples of the enzyme for the cathode include bilirubin oxidase, laccase, ascorbic acid oxidase, and tyrosinase.

[0022] The content of the enzyme in the electrode ink is preferably 1.0 to 200 parts by mass, more preferably 5.0 to 100 parts by mass, even more preferably 10 to 80 parts by mass, and still more preferably 30 to 40 parts by mass, relative to 100 parts by mass of the porous conductive material, from the viewpoint of ensuring that the enzyme is sufficiently supported by the porous conductive material and making it easier to obtain good electrode performance.

[0023] (Mediator) The mediator is a redox compound that mediates the transfer of electrons between the electrode and the enzyme, and is selected appropriately depending on the type of fuel, enzyme, etc. In the manufacturing method of the electrode ink of the present disclosure, a water-insoluble mediator is used, and the mediator is dissolved in a non-aqueous solvent. In the present disclosure, a compound is defined as "water-insoluble" if its solubility in 100 g of water (25°C) is less than 10 mg.

[0024] Examples of water-insoluble mediators include organic sulfur compounds such as tetrathiafulvalene, quinone compounds such as 1,2-naphthoquinone and 1,4-naphthoquinone, ferrocene, polymers modified with these compounds, polymers modified with osmium complexes, etc. The mediators may be used alone or in combination of two or more.

[0025] From the viewpoint of ensuring that the enzyme is sufficiently supported on the porous conductive material and making it easier to obtain good electrode performance, the content of the mediator in the electrode ink is preferably 1.0 to 40 parts by mass, more preferably 2.0 to 30 parts by mass, even more preferably 3.0 to 20 parts by mass, and even more preferably 5.0 to 12 parts by mass, relative to 100 parts by mass of the porous conductive material. The content of the mediator in the electrode ink is preferably 0.10 to 100 parts by mass, more preferably 1.0 to 80 parts by mass, even more preferably 5.0 to 60 parts by mass, even more preferably 10 to 50 parts by mass, and even more preferably 15 to 30 parts by mass, relative to 100 parts by mass of the enzyme.

[0026] (Porous conductive material) The porous conductive material increases the electronic conductivity at the electrode and facilitates the promotion of the redox reaction, and has a large number of pores into which the enzyme and mediator can enter. Examples of the conductive material include carbon and metal. The conductive material may be used alone or in combination of two or more. Of these, carbon is preferred. The porous conductive material may be used in combination with a conductive material other than the porous conductive material.

[0027] As the porous conductive material, porous carbon is preferred because it is easy to support the enzyme and mediator in the pores. Examples of porous carbon include mesoporous carbon, and specific examples include Ketjen black, carbon nanotubes, graphene, and mesoporous carbon produced by a template method such as MgO-templated carbon. Among these, MgO-templated carbon is preferred from the viewpoint of good enzyme support.

[0028] The porous conductive material preferably has a BET specific surface area of ​​100 to 700 m from the viewpoint of supporting a larger amount of enzyme on the porous conductive material. ２ / g, more preferably 200 to 600 m ２ / g, more preferably 300 to 500m ２ / g.

[0029] From the viewpoint of supporting a larger amount of enzyme on the porous conductive material, the total pore volume of the porous conductive material is preferably 0.50 to 3.0 mL / g, more preferably 0.70 to 2.0 mL / g, and even more preferably 0.80 to 1.5 mL / g. The BET specific surface area and the total pore volume are determined from a nitrogen adsorption isotherm at 77 K.

[0030] From the viewpoint of more efficiently supporting the enzyme, the porous conductive material preferably has a micropore volume of 0.030 to 0.40 mL / g, more preferably 0.080 to 0.30 mL / g, and even more preferably 0.12 to 0.20 mL / g. The micropore volume can be determined by extrapolating a straight line derived by the least squares method from a plot of the region corresponding to mesopores in a nitrogen adsorption isotherm at 77 K to a relative pressure of 0.

[0031] From the viewpoint of binding a sufficient amount of porous conductive material to the substrate or the like, the content of the porous conductive material in the electrode ink is preferably 40 to 85 parts by mass, more preferably 45 to 80 parts by mass, and even more preferably 50 to 80 parts by mass, per 100 parts by mass of the non-volatile content of the electrode ink.

[0032] (Step 1) In step 1, a first mixture is prepared containing a liquid in which a mediator is dissolved in a non-aqueous solvent and a porous conductive material. The non-aqueous solvent here refers to an organic solvent capable of dissolving the mediator. The non-aqueous solvent is used to enable the water-insoluble mediator to be used as a solution, from the viewpoint of promoting penetration of the mediator into the pores of the porous conductive material. The non-aqueous solvent is preferably one that is easy to volatilize and remove in a subsequent step, and preferably has a boiling point at 1 atmosphere (0.10 MPa) of 150°C or less, more preferably 110°C or less, and even more preferably 90°C or less.

[0033] The non-aqueous solvent is appropriately selected depending on the type of compound used as the mediator. For example, when 1,2-naphthoquinone is used as the mediator in the anode ink, acetonitrile, for example, can be used as the non-aqueous solvent.

[0034] The amount of the non-aqueous solvent used to dissolve the mediator is not particularly limited as long as it is an amount that can dissolve the mediator. The amount of the non-aqueous solvent used is preferably 200 to 2500 parts by mass, more preferably 300 to 1500 parts by mass, and even more preferably 500 to 1200 parts by mass per 100 parts by mass of the porous carbon powder, taking into consideration that the non-aqueous solvent is sufficiently compatible with the porous conductive material and the workload for volatilization and removal in a subsequent step.

[0035] The first mixture is prepared, for example, by adding a powder of the porous conductive material to a liquid in which the mediator is dissolved in a non-aqueous solvent. The method for preparing the first mixture is not particularly limited, but it is preferable to mix or knead the first mixture using, for example, a planetary kneader to thoroughly disperse the porous conductive material in the first mixture.

[0036] The mixing or kneading is preferably carried out at a temperature at which the non-aqueous solvent does not volatilize and is not significantly reduced, and is preferably a temperature lower than the temperature in the subsequent dispersion treatment in Step 2. The temperature during mixing or kneading is preferably less than 30° C., more preferably 25° C. or lower. The mediator is used by dissolving it in a non-aqueous solvent, but water may be contained in the first mixture.

[0037] (Step 2) In step 2, the first mixture obtained in step 1 is subjected to a dispersion treatment under reduced pressure at 60°C or less to volatilize and remove the non-aqueous solvent from the first mixture, thereby obtaining a second mixture. It is believed that this step allows the mediator to be supported on the surface of the porous conductive material with little distribution bias.

[0038] The second mixture is obtained by removing the non-aqueous solvent from the first mixture, and the mediator is supported on the porous conductive material. In order to maintain sufficient activity of the enzyme in the electrode ink, it is preferable to remove as much of the non-aqueous solvent as possible, but it is not necessary to remove it completely, and some of it may remain.

[0039] The temperature of the dispersion treatment in step 2 is set to 60° C. or lower, preferably 50° C. or lower, and more preferably 40° C. or lower, from the viewpoint of maintaining the stability of the enzyme to be added later. Heating may be performed to maintain the desired temperature.

[0040] The pressure during the reduced pressure in the dispersion treatment is preferably 0.0300 MPa or less, more preferably 0.0100 MPa or less, and even more preferably 0.0050 MPa or less, in order to volatilize the non-aqueous solvent as much as possible, and so-called vacuum drying is preferred.

[0041] The dispersion treatment referred to here is an operation of applying at least one of shear force and impact to the first mixture to disperse each component in the mixture. The dispersion treatment is preferably carried out so as to thoroughly knead or mix the first mixture in order to efficiently volatilize the nonaqueous solvent, and can be carried out using, for example, a kneader, a stirring device equipped with blades, an ultrasonic irradiator, or the like. The same kneader, etc. used in the method for mixing the first mixture may be used.

[0042] (Step 3) In step 3, the enzyme, aqueous medium, and binder are added to and mixed with the second mixture obtained in step 2 to obtain an electrode ink. In step 3, the electrode ink is obtained as a mixture of the porous conductive material carrying the enzyme and mediator, the aqueous medium, and the binder.

[0043] In step 3, from the viewpoint of ensuring that the enzyme is well supported on the porous conductive material, it is preferable to add an enzyme solution prepared by dissolving the enzyme in an aqueous medium to the second mixture and mix them, and then add an aqueous emulsion of the binder and mix them in. The concentration of the enzyme solution is preferably 0.10 to 50% by mass, more preferably 1.0 to 30% by mass, even more preferably 3.0 to 20% by mass, and even more preferably 5.0 to 10% by mass.

[0044] The mixing in step 3 is an operation of dispersing or dissolving in a mixed system the components contained in the second mixture and the components to be added to the second mixture in step 3. The mixing in step 3 may be performed by the same operation method as the dispersion treatment in step 2 or by a different operation method, and may be performed at atmospheric pressure (0.10 MPa) or at a temperature lower than the temperature of the dispersion treatment in step 2.

[0045] (Aqueous Medium) In the present disclosure, the aqueous medium refers to water, a liquid compatible with water, or a mixture thereof. Examples of liquids compatible with water include methanol, ethanol, isopropyl alcohol, N-methylpyrrolidone, and 1,3-butylene glycol. From the viewpoint of reducing environmental impact, the aqueous medium preferably contains water. The aqueous medium may be a mixture of water and a liquid compatible with water, as long as the variation of each component in the electrode ink is sufficiently suppressed.

[0046] The water content in the aqueous medium is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass, in order to ensure that the enzyme is sufficiently supported on the porous conductive material and to prevent the enzyme from being deactivated.

[0047] (Binder) The binder serves to favorably bind the porous conductive material to the substrate or the like while maintaining the dispersibility of particles of each component in the electrode ink. Examples of binders include acrylic resin, styrene-acrylic resin, polyurethane resin, polyester resin, phenolic resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, formaldehyde resin, silicone resin, fluororesin, and synthetic rubber such as styrene-butadiene rubber (SBR). Modified products, mixtures, or copolymers of these resins may also be used. One type of binder may be used alone, or two or more types may be used in combination.

[0048] The content of the binder in the electrode ink is preferably 10 to 100 parts by mass, more preferably 20 to 80 parts by mass, and even more preferably 30 to 70 parts by mass, in terms of non-volatile content, relative to 100 parts by mass of the porous conductive material, from the viewpoints of good dispersibility of each component in the electrode ink and good binding of the porous conductive material to the substrate or the like.

[0049] The binder can be used in the form of an aqueous emulsion dispersed in an aqueous medium. The aqueous emulsion is not particularly limited, but examples thereof include (meth)acrylic emulsions, styrene-(meth)acrylic emulsions, nitrile emulsions, urethane emulsions, and diene emulsions (such as SBR emulsions).

[0050] As the binder, 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) ​​can be suitably used. The polymer (A) may have other structural units in addition to the first structural unit, the second structural unit, and the third structural unit. To obtain good electrode performance, the total of the first structural unit, the second structural unit, and the third structural unit is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, even more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass, of all structural units constituting the polymer (A).

[0051] The polymer (A) is preferably present as an aqueous emulsion in a dispersed state in an aqueous medium. The suitable particle diameter of the particles dispersed in the aqueous emulsion varies depending on the form, particle size, etc. of the porous conductive material. In order to function well as a binder, the particles of the polymer (A) in the aqueous emulsion preferably have a median diameter D50 of 0.050 to 1.0 μm, more preferably 0.080 to 0.80 μm, and even more preferably 0.10 to 0.40 μm.

[0052] Furthermore, from the viewpoints of dispersibility of the porous conductive material, binding ability to a substrate or the like, and good flexibility of the electrode, the polymer (A) preferably has a glass transition temperature of −30 to 100° C., more preferably −20 to 90° C., and even more preferably −10 to 80° C.

[0053] <First Structural Unit> In order to obtain a polymer (A) that functions well as a binder, 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 60.0 to 98.0 mass%, more preferably 75.0 to 97.0 mass%, and even more preferably 90.0 to 96.0 mass%.

[0054] The nonionic ethylenically unsaturated monomer (a1) from which the first structural unit is derived has one ethylenically unsaturated bond per molecule and has neither an anionic functional group nor a cationic functional group. The nonionic ethylenically unsaturated monomer (a1) may be used alone or in combination of two or more. The nonionic ethylenically unsaturated monomer (a1) is preferably at least one selected from the group consisting of aromatic ethylenically unsaturated compounds, (meth)acrylic acid alkyl esters, and polar group-containing ethylenically unsaturated carboxylic acid esters, and preferably contains all of these.

[0055] The aromatic ethylenically unsaturated compound contributes to good binding properties of the porous conductive material to the substrate, etc. Examples of aromatic ethylenically unsaturated compounds include styrene, tert-butylstyrene, α-methylstyrene, p-methylstyrene, 1,1-diphenylethylene, and benzyl (meth)acrylate. The aromatic ethylenically unsaturated compounds may be used alone or in combination of two or more. Of these, aromatic vinyl compounds are preferred, and styrene is more preferred.

[0056] The proportion of the aromatic ethylenically unsaturated compound in the nonionic ethylenically unsaturated monomer (a1) is preferably 25 to 70 mass %, more preferably 35 to 65 mass %, and even more preferably 45 to 60 mass %, from the viewpoints of dispersibility of the porous conductive material and binding ability to a substrate or the like.

[0057] The (meth)acrylic acid alkyl ester contributes to the ease of synthesis and durability of the polymer (A). Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. The (meth)acrylic acid alkyl ester may be used alone or in combination of two or more. Among these, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, with 2-ethylhexyl acrylate being more preferred. In terms of good electrode flexibility and the like, the (meth)acrylic acid alkyl ester preferably has 2 to 9 carbon atoms in the alkyl group bonded to the (meth)acryloyloxy group, more preferably 4 to 9 carbon atoms, and even more preferably has an alkyl group having 4 to 9 carbon atoms bonded to the acryloyloxy group.

[0058] The proportion of the (meth)acrylic acid alkyl ester in the nonionic ethylenically unsaturated monomer (a1) is preferably 20.0 to 70.0 mass%, more preferably 30.0 to 60.0 mass%, and even more preferably 40.0 to 50.0 mass%, from the viewpoints of the flexibility of the electrode, the dispersibility of the porous conductive material, and the binding property to the substrate, etc.

[0059] The polar group-containing ethylenically unsaturated carboxylic acid ester contributes to good polymerizability during synthesis of the polymer (A) and mechanical stability of the electrode. Examples of the polar group of the polar group-containing ethylenically unsaturated carboxylic acid ester include a hydroxy group and a cyano group. Examples of the polar group-containing ethylenically unsaturated carboxylic acid ester include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl acrylate, and (meth)acrylonitrile. The polar group-containing ethylenically unsaturated carboxylic acid ester may be used alone or in combination of two or more. Of these, 2-hydroxyethyl (meth)acrylate is preferred, and 2-hydroxyethyl methacrylate is more preferred.

[0060] The proportion of the polar group-containing ethylenically unsaturated carboxylic acid ester in the nonionic ethylenically unsaturated monomer (a1) is preferably 0.5 to 20.0 mass%, more preferably 1.0 to 15.0 mass%, and even more preferably 2.0 to 10.0 mass%, from the viewpoints of good polymerizability during synthesis of the polymer (A), dispersibility of the porous conductive material, adhesion to a substrate, and swelling resistance of the electrode during use of the enzyme battery.

[0061] <Second Structural Unit> In order to obtain a polymer (A) that functions well as a binder, 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 20.0 mass%, more preferably 3.0 to 15.0 mass%, and even more preferably 4.5 to 10.0 mass%.

[0062] The anionic ethylenically unsaturated monomer (a2) from which the second structural unit is derived has one ethylenically unsaturated bond per molecule and an anionic functional group. The anionic ethylenically unsaturated monomer (a2) may be used alone or in combination of two or more. Examples of the anionic functional group include a carboxy group, a sulfo group, and a phosphate group. The anionic functional group may form a salt. The anionic ethylenically unsaturated monomer (a2) is preferably at least one selected from the group consisting of ethylenically unsaturated carboxylic acids and salts thereof, and ethylenically unsaturated sulfonic acids and salts thereof, and more preferably includes all of these.

[0063] Examples of ethylenically unsaturated carboxylic acids and salts thereof include 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 salts thereof. The ethylenically unsaturated carboxylic acids and salts thereof may be used alone or in combination of two or more. Of these, (meth)acrylic acid and itaconic acid are preferred.

[0064] The proportion of the ethylenically unsaturated carboxylic acid and its salt in the anionic ethylenically unsaturated monomer (a2) is preferably 70.0 to 99.0 mass%, more preferably 80.0 to 98.0 mass%, and even more preferably 85.0 to 95.0 mass%, from the viewpoints of good polymerizability during synthesis of the polymer (A), dispersibility of the porous conductive material, and binding ability to a substrate or the like.

[0065] Examples of ethylenically unsaturated sulfonic acids and salts thereof include parastyrenesulfonic acid and salts thereof. The ethylenically unsaturated sulfonic acids may be used alone or in combination of two or more. Among these, sodium parastyrenesulfonate is preferred.

[0066] The proportion of the ethylenically unsaturated sulfonic acid and its salt in the anionic ethylenically unsaturated monomer (a2) is preferably 1.0 to 30.0 mass%, more preferably 2.0 to 20.0 mass%, and even more preferably 3.0 to 15.0 mass%, from the viewpoints of good polymerizability during synthesis of the polymer (A), dispersibility of the porous conductive material, and binding ability to a substrate or the like.

[0067] <Third structural unit> The content of the third 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 0.010 to 5.0 mass%, more preferably 0.020 to 2.0 mass%, even more preferably 0.030 to 1.5 mass%, and still more preferably 0.030 to 0.10 mass%, from the viewpoint of the swelling resistance of the electrode when the enzyme battery is used.

[0068] The crosslinking agent (a3) ​​from which the third structural unit is derived has two or more ethylenically unsaturated bonds per molecule. The crosslinking agent (a3) ​​may be used alone, or two or more types may be used in combination. The two or more ethylenically unsaturated bonds of the crosslinking agent (a3) ​​can form a crosslinked structure by, for example, an addition reaction between the two or more ethylenically unsaturated bonds and the ethylenically unsaturated bonds of other synthesis raw material compounds of the polymer (A). In other words, the polymer (A) is a crosslinked polymer. Examples of the crosslinking agent (a3) ​​include divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, and trimethylolpropane tri(meth)acrylate. Of these, divinylbenzene is preferred.

[0069] <Synthesis Method> The polymer (A) can be produced by polymerizing synthetic raw materials including a nonionic ethylenically unsaturated monomer (a1), an anionic ethylenically unsaturated monomer (a2), and a crosslinking agent (a3). The polymerization method is not particularly limited, and, for example, emulsion polymerization is preferred. Emulsion polymerization is carried out in an aqueous medium in the presence of a polymerization initiator, with the addition of a surfactant and other additives as necessary. The synthetic raw materials may be charged all at once or may be fed successively by dropwise addition, and the reaction is typically carried out at 30 to 90°C with stirring.

[0070] From the viewpoint of the stability of the polymer (A) in the reaction system, it is preferable to add a basic substance during or after the polymerization reaction as necessary to neutralize and adjust the pH. Preferred examples of the basic substance include ammonia, triethylamine, ethanolamine, morpholine, 2-amino-2-methyl-1-propanol, lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide. The basic substance may be used alone or in combination of two or more.

[0071] The aqueous medium used in synthesizing the polymer (A) may be the same as the aqueous medium used in producing the electrode ink, and may be the same as or different from the aqueous medium. From the viewpoints of dispersion stability of the synthetic raw materials and the polymer, reduction of environmental load, etc., water is preferred. A mixture of water and a liquid compatible with water may also be used within a range that does not impair dispersion stability.

[0072] The amount of the aqueous medium used is adjusted as appropriate depending on the dispersibility of the synthetic raw materials in the aqueous medium, the viscosity of the reaction system, etc. From the viewpoint of appropriate progress of the polymerization reaction, the amount of the aqueous medium used is preferably 50 to 300 parts by mass, more preferably 80 to 250 parts by mass, and even more preferably 100 to 200 parts by mass per 100 parts by mass of the total of the nonionic ethylenically unsaturated monomer (a1), the anionic ethylenically unsaturated monomer (a2), and the crosslinking agent (a3).

[0073] The polymerization initiator is not particularly limited, but a radical polymerization initiator can be used, and examples thereof include peroxides such as ammonium persulfate, potassium persulfate, hydrogen peroxide, and tert-butyl hydroperoxide. The polymerization initiator may be used alone or in combination of two or more. Redox polymerization may also be performed using these polymerization initiators in combination with a reducing agent such as sodium bisulfite, Rongalit, or ascorbic acid.

[0074] From the viewpoint of the dispersion stability of the synthesis raw materials and the resulting polymer (A) in an aqueous medium, the surfactant is preferably at least one selected from the group consisting of nonionic surfactants and anionic surfactants. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. The nonionic surfactants may be used alone or in combination of two or more. Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, and fatty acid salts. The anionic surfactants may be used alone or in combination of two or more.

[0075] As the anionic surfactant, a reactive surfactant having an ethylenically unsaturated bond is also suitably used. Examples of the reactive surfactant include compounds represented by the following formulas (1) to (4). The reactive surfactant may be used alone or in combination of two or more. Among these, the compound represented by formula (4) is preferred, and sodium alkylaryl sulfosuccinate is more preferred.

[0076] In formula (1), R １ is an alkyl group, and p is an integer from 10 to 40. １ is preferably an alkyl group having 10 to 40 carbon atoms, more preferably a straight chain alkyl group having 10 to 40 carbon atoms.

[0077] In formula (2), R ２ is an alkyl group, and q is an integer from 10 to 12. ２ is preferably an alkyl group having 10 to 40 carbon atoms, more preferably a straight chain alkyl group having 10 to 40 carbon atoms.

[0078] In formula (3), R ３ is an alkyl group, and M １ is NH ４ Or Na. ３ is preferably an alkyl group having 10 to 40 carbon atoms, more preferably a straight chain alkyl group having 10 to 40 carbon atoms.

[0079] In formula (4), R ４ is an alkyl group, and M ２ is NH ４ Or Na. ４ is preferably an alkyl group having 10 to 40 carbon atoms, more preferably a straight chain alkyl group having 10 to 40 carbon atoms.

[0080] The reactive surfactant not only exhibits an emulsifying effect on the reaction system in emulsion polymerization, but also has copolymerizability with the nonionic ethylenically unsaturated monomer (a1), the anionic ethylenically unsaturated monomer (a2), and the crosslinking agent (a3), but is not considered to be a structural unit constituting the polymer (A) in the present disclosure.

[0081] The amount of surfactant added is preferably 0.05 to 1.2 parts by mass, more preferably 0.1 to 1.0 part by mass, and even more preferably 0.15 to 0.5 parts by mass, relative to 100 parts by mass of the total of the nonionic ethylenically unsaturated monomer (a1), the anionic ethylenically unsaturated monomer (a2), and the crosslinking agent (a3), from the viewpoints of stable progress of the polymerization reaction, dispersion stability of the synthetic raw materials and the produced polymer (A) in the aqueous medium, and adhesion of the porous conductive material to a substrate or the like.

[0082] Other additives may be added as optional components within the range that allows the polymer (A) to function well as a binder. Examples of other additives include chain transfer agents such as thiol, thiol glycolic acid and its esters, and 3-mercaptopropionic acid and its esters.

[0083] (pH Adjustment) In step 3, from the viewpoint of suppressing deactivation of the enzyme and obtaining good electrode performance, it is preferable to mix the second mixture and at least a part of the aqueous medium, adjust the pH to 4 or more, and then add and mix the enzyme. The pH is more preferably 5 to 9, and even more preferably 6 to 8. The pH adjustment can be performed by adding a basic substance similar to the pH adjustment during the synthesis of the polymer (A) described above.

[0084] (Water-soluble polymer) In step 3, from the viewpoint of controlling the hydrophilicity of the electrode ink, it is preferable to further add and mix a water-soluble polymer. The water-soluble polymer may be added after or before the enzyme and the aqueous medium are added to the second mixture. From the viewpoint of good dispersibility of the porous conductive material in the electrode ink, it is preferable to add and mix the water-soluble polymer and then add and mix the enzyme and the aqueous medium.

[0085] Examples of water-soluble polymers include water-soluble cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, polystyrene sulfonic acid, polyacrylic acid, and their ammonium salts and alkali metal salts. The water-soluble polymers may be used alone or in combination of two or more. Examples of water-soluble cellulose derivatives include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and salts thereof. Of these, carboxymethyl cellulose and its salts are preferred.

[0086] When a water-soluble polymer is contained in the electrode ink, the content of the water-soluble polymer is preferably 1 to 50 parts by mass, more preferably 5 to 40 parts by mass, and even more preferably 10 to 30 parts by mass relative to 100 parts by mass of the porous conductive material, from the viewpoint of obtaining good dispersibility without interfering with the binding ability of the porous conductive material to the substrate or the like.

[0087] (Other Components) The electrode ink may contain other components in addition to the enzyme, water-insoluble mediator, and porous conductive material, as well as binder, aqueous medium, and additive for pH adjustment, i.e., the various components described above, as long as the electrode performance is not impaired. Examples of other components include surfactants, etc., from the viewpoint of dispersion stability of the porous conductive material, etc.

[0088] [Electrode Ink] The electrode ink of the present disclosure is an electrode ink for an enzyme battery, which contains an enzyme, a water-insoluble mediator, and a porous conductive material, and the enzyme is ubiquitously present in the pores of the porous conductive material. Such an electrode ink can be suitably produced by the production method of the present disclosure described above.

[0089] The term "ubiquitous distribution" as used herein means that the enzyme penetrates into the pores of the porous conductive material and there is little variation in the distribution of the enzyme among the pores. In other words, in the electrode ink of the present disclosure, the enzyme is ubiquitously present within the pores of the porous conductive material, and therefore the enzyme is distributed evenly throughout the entire porous conductive material.

[0090] The electrode ink of the present disclosure is believed to exhibit better electrode characteristics than an electrode ink in which the enzyme is not fully incorporated into the pores, due to the ubiquitous presence of the enzyme within the pores of the porous conductive material. The ubiquitous presence of the enzyme within the pores of the porous conductive material can be confirmed by detecting nitrogen atoms (N) derived from the enzyme in the emission spectrum measured by soft X-ray emission spectroscopy (SXES) for each pore. The presence of nitrogen atoms (N) derived from the enzyme within the pores can be confirmed, specifically, by the method described in the Examples below.

[0091] [Electrode Manufacturing Method] The electrode manufacturing method of the present disclosure includes the steps of applying the electrode ink manufactured by the manufacturing method of the present disclosure described above to a substrate or a conductive layer, and drying the applied electrode ink. By applying the electrode ink containing a porous conductive material, a mediator, and an enzyme to a substrate or the like, the manufacturing process of an enzyme battery electrode can be simplified and the workload for manufacturing the electrode can be reduced compared to when the porous conductive material, the mediator, and the enzyme are each applied to or supported on a substrate or the like in separate steps.

[0092] Examples of substrates onto which the electrode ink is applied include woven fabric, nonwoven fabric, paper, and resin film. The substrate is preferably porous and has good compatibility with the electrode ink. From the viewpoint of consideration of the environmental impact when disposing of the electrode, for example, paper is preferred, and further, from the viewpoint of durability, for example, oil-resistant and waterproof paper is more preferred.

[0093] The electrode ink may be applied to a conductive layer formed on a substrate. The conductive layer may be made of, for example, metal particles, metal foil, or a carbon material, and is preferably a substrate coated with a carbon paste.

[0094] The method for applying the electrode ink is not particularly limited. Examples of application methods include screen printing, reverse roll printing, direct roll printing, and doctor blade printing. Among these, screen printing is preferred because it allows for simple and efficient pattern formation. Note that even when forming a conductive layer by applying a carbon paste to a substrate, the same method as the method for applying the electrode ink to a substrate can be used, and screen printing is preferred.

[0095] The method for drying the electrode ink applied to a substrate or the like is not particularly limited as long as the aqueous medium is sufficiently removed. Examples of drying methods include air drying, heat drying, hot air (50°C or higher), low-temperature air (less than 50°C), reduced pressure, vacuum, and (far) infrared radiation. These drying conditions may be combined.

[0096] The electrode manufacturing method of the present disclosure may be applied to the manufacture of either an anode or a cathode, and may be applied to the manufacture of either the anode or the cathode in an enzyme battery, or may be applied to the manufacture of both.

[0097] The electrode performance can be evaluated, for example, by measuring the current response characteristics by chronoamperometry, and specifically, can be measured and evaluated by the method shown in the Examples.

[0098] Hereinafter, embodiments of the present disclosure will be described in detail based on examples. The present disclosure is not limited to the following examples, and various modifications are possible within the scope of the present disclosure.

[0099] [Production of Polymer (A)] The methods for measuring various physical properties in the following synthesis examples are as follows. <Glass transition temperature> Differential scanning calorimetry (DSC) was measured using a differential scanning calorimeter (EXSTAR DSC7020, manufactured by Hitachi High-Tech Science Corporation; heating rate 10°C / min, nitrogen gas atmosphere), and the peak top temperature of the DSC temperature derivative curve was taken as the glass transition temperature. <Median diameter D50> The median diameter D50 (volume basis) was determined from a particle size distribution curve measured by dynamic light scattering (DLS).

[0100] (Synthesis Example 1) A reaction vessel equipped with a condenser, thermometer, stirrer, and dropping funnel was charged with 60 parts by weight of ion-exchanged water and heated to 75 ° C. Into this reaction vessel, in the formulation shown in Table 1, a total of 100 parts by weight of nonionic ethylenically unsaturated monomer (a1), anionic ethylenically unsaturated monomer (a2), and crosslinker (a3), 0.20 parts by weight of Eleminol JS-20 (excluding solvent), 0.20 parts by weight of Hitenol 08E, and a mixed solution containing 80 parts by weight of ion-exchanged water were added dropwise over 3 hours and stirred and mixed. At the same time, a solution of 0.40 parts by weight of potassium persulfate dissolved in 10 parts by weight of ion-exchanged water was added dropwise over 3 hours, stirred and mixed, and polymerized. Two hours after the end of the dropwise addition, the reaction product was neutralized with 0.90 parts by weight of ammonia water with a concentration of 25% by weight to obtain a polymer (A1) dispersion with a concentration of 40% by weight.

[0101]

[0102] Details of the surfactants in Table 1 are as follows: Eleminol JS-20: sodium alkylaryl sulfosuccinate; manufactured by Sanyo Chemical Industries, Ltd., anionic reactive surfactant, non-volatile content 38.5% by mass Hitenol 08E: polyoxyethylene oleyl cetyl ether ammonium sulfate; manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., anionic surfactant

[0103] The polymer (A1) had a glass transition temperature of 15° C. and a median diameter D50 of 0.26 μm.

[0104] [Production of Electrode Ink] The raw materials used in the production of the electrode ink are as follows: Porous carbon powder: Knobel MJ(3)100-00, manufactured by Toyo Tanso Co., Ltd., BET specific surface area 390 m ２ / g, total pore volume 0.91 mL / g, micropore volume 0.15 mL / g, mesopore diameter 75 nm, bulk density 0.06 g / mL, porous conductive material 1,2-naphthoquinone: manufactured by Kanto Chemical Co., Ltd., mediator acetonitrile: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., non-aqueous solvent CMC: sodium carboxymethylcellulose; Sunrose MAC 500LC, manufactured by Nippon Paper Industries Co., Ltd., water-soluble polymer GDH: glucose dehydrogenase; manufactured by Amano Enzyme Inc., enzyme binder (emulsion): dispersion of polymer (A1) produced in Synthesis Example 1 (non-volatile content 40% by mass)

[0105] Example 1 0.19 g of 1,2-naphthoquinone was dissolved in 25.60 g of acetonitrile and charged into a mixing vessel, to which 2.70 g of porous carbon powder was added, and the mixture was mixed in a planetary centrifugal mixer (Hibismix 2P-03, manufactured by Primix Corporation; hereinafter, the same mixer will be used) for 60 minutes. －１ The pressure in the mixing vessel was reduced to 0.0030 MPa, and the first mixture was kneaded at a set temperature of 30° C. for 60 minutes. －１ The mixture was kneaded (dispersed) at 40°C for 30 minutes, and the acetonitrile was removed by evaporation to obtain a second mixture. After the pressure in the mixing vessel was returned to normal pressure, 10.00 g of water, 0.03 g of 25% by mass ammonia water, and 19.00 g of 2% by mass CMC solution were added to the second mixture, and the mixture was kneaded for 60 minutes. －１After confirming that the pH of the resulting kneaded mixture was within the range of 6 to 8, an enzyme solution prepared by dissolving 0.94 g of GDH in 12.00 g of water was added, and the mixture was kneaded for 40 minutes. －１ The mixture was kneaded for 15 minutes, and then 3.35 g of a binder (emulsion) was added, followed by kneading for 40 minutes. －１ The ink composition is shown in Table 2, Composition 1.

[0106] Example 2 An anode ink was obtained in the same manner as in Example 1, except that the enzyme solution was changed to one in which 0.47 g of GDH was dissolved in 6.00 g of water. The formulation of the ink is shown in Formulation 2 in Table 2.

[0107] Comparative Example 1 An anode ink was obtained in the same manner as in Example 2, except that the operation of reducing the pressure inside the mixing vessel was not performed. The ink formulation was Formulation 2 in Table 2, but acetonitrile remained in the ink (non-volatile component concentration 7.5% by mass).

[0108]

[0109] [Manufacture of Electrode] Using each of the anode inks manufactured in the above Examples and Comparative Examples, an anode was manufactured by the following procedure. ２ A carbon paste (JELCON CH-8, manufactured by Jujo Chemical Co., Ltd.) was screen-printed on one surface of the substrate, and dried at 120°C for 20 minutes to form a conductive layer on the substrate. The conductive layer had a basis weight of 2.0 mg / cm. ２ The conductive layer had a length of 25 mm and a width of 5.0 mm. The area from one end of the conductive layer to 20 mm in the longitudinal direction was the electrode portion, and the remaining 5 mm was the lead portion. The anode ink was screen-printed on the electrode portion of the conductive layer, and the process of drying at 40°C for 30 minutes was repeated five times to obtain a coating weight of 3.0 mg / cm. ２ An ink coating layer having a length of 20 mm and a width of 5.0 mm was formed to prepare an anode.

[0110] [SXES Spectroscopic Measurement] Cross-sectional samples were prepared for the anodes manufactured using the anode inks of Example 1 and Comparative Example 1, and the distribution state of the enzyme in the pores of the porous carbon powder was confirmed by SXES spectroscopy. Details of the SXES spectroscopy measurement method (preparation of cross-sectional samples, measurement device, and measurement conditions) are described below.

[0111] (Preparation of Cross-Sectional Sample) The ink-coated surface of the anode was attached to one surface of a 150 μm-thick silicon wafer using conductive double-sided tape. Next, a cross-sectional sample was prepared by irradiating the silicon wafer from its surface with an argon ion beam using a cross-sectional sample preparation device (IB-19510CP, manufactured by JEOL Ltd.; cooling temperature: −60° C., ion acceleration voltage: 6 kV).

[0112] (Measurement equipment and measurement conditions) Field emission scanning electron microscope (FE-SEM): "JSM-7800FPRIME", manufactured by JEOL Ltd. Soft X-ray emission spectrometer: "Super Spectrometer SS-94040SXSER", manufactured by JEOL Ltd. Measurement conditions: acceleration voltage 5 kV, irradiation current 50 nA, irradiation distance 10 mm, exposure time 15 to 30 seconds, number of accumulations 10, diffraction grating "JS300N"

[0113] When the anode ink of Example 1 was used, nitrogen atoms (N) derived from the enzyme were detected in all SXES spectra measured in four randomly selected pores of the porous carbon powder. Furthermore, mapping of the nitrogen atoms (N) in the SXES spectra also confirmed that the nitrogen atoms (N) were distributed evenly throughout the porous carbon powder. This suggests that the enzyme is ubiquitously present in the pores of the porous carbon powder.

[0114] When the anode ink of Comparative Example 1 was used, no nitrogen atoms (N) derived from the enzyme were detected in any of the SXES spectra measured in four randomly selected pores of the porous carbon powder.

[0115] For comparison, an electrode was prepared using an electrode ink prepared by omitting the enzyme from the components of Formulation 2. An enzyme solution prepared by dissolving GDH in 10 mmol / L phosphate buffer (pH 7.0) was then dripped onto the electrode surface to impregnate the electrode, producing an anode. SXES spectroscopy was also performed on this anode. In the SXES spectrum measured in four randomly selected pores of the porous carbon powder, nitrogen atoms (N) derived from the enzyme were detected in only two locations.

[0116] [Chronoamperometry Measurement] Chronoamperometry measurement was performed on the anode produced as described above as follows. An overview of the arrangement of each electrode in chronoamperometry measurement is shown in Figure 1. Within 24 hours of production, the anode was immersed in a 0.1 mol / L potassium phosphate buffer solution 1 containing D(+)-glucose at a concentration of 0.1 mol / L to serve as the working electrode 2, Pt (PT-351481, manufactured by Nilaco Corporation, 1.0 mm diameter platinum wire) to serve as the reference electrode 3, and Ag-AgCl (RE-T7A, manufactured by EC Frontier Co., Ltd.) to serve as the reference electrode 4. The control electrode 3 and reference electrode 4 were immersed in the buffer solution 1, and after 1 minute, a voltage of 0.5 V was applied between the working electrode and the reference electrode for 300 seconds using a potentiostat 5 (SP-150, manufactured by Bio-Logic), and chronoamperometry measurement was performed at 25°C. Table 3 shows the measured current density (applied voltage 0.5 V, after 300 seconds).

[0117]

[0118] The current density (applied voltage 0.5 V, after 300 seconds) is preferably 0.5 mA / cm from the viewpoint of good electrode performance. ２ More preferably, 0.7 mA / cm ２ More preferably, 1.0 mA / cm ２ It can be said that by using the electrode ink obtained by the manufacturing method of the present disclosure (Examples 1 and 2), an enzyme electrode with a larger current response can be manufactured using a simplified process.

[0119] 1 Buffer solution 2 Working electrode 3 Control electrode 4 Reference electrode 5 Potentiostat

Claims

1. A method for producing an electrode ink for an enzyme battery, which contains an enzyme, a water-insoluble mediator, and a porous conductive material, comprising: step 1 of preparing a first mixture containing a liquid in which the mediator is dissolved in a non-aqueous solvent, and the porous conductive material; step 2 of subjecting the first mixture to a dispersion treatment under reduced pressure at 60°C or less to volatilize and remove the non-aqueous solvent from the first mixture, thereby obtaining a second mixture; and step 3 of adding and mixing the enzyme, an aqueous medium, and a binder to the second mixture, thereby obtaining the electrode ink.

2. The method for producing an electrode ink according to claim 1, wherein in step 3, the second mixture and at least a portion of the aqueous medium are mixed, the pH is adjusted to 4 or higher, and then the enzyme is added and mixed.

3. The method for producing an electrode ink according to claim 1, wherein in step 3, a water-soluble polymer is further added and mixed.

4. The method for producing an electrode ink according to claim 3, wherein in step 3, the water-soluble polymer is added to and mixed with the second mixture, and then the enzyme and the aqueous medium are added and mixed.

5. An electrode ink for an enzyme battery comprising an enzyme, a water-insoluble mediator and a porous conductive material, wherein the enzyme is ubiquitously present within the pores of the porous conductive material.

6. A method for manufacturing an electrode, comprising the steps of applying the electrode ink manufactured by the manufacturing method according to any one of claims 1 to 4 to a substrate or a conductive layer, and drying the applied electrode ink.

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