Cathode electrode

Abstract

To provide a cathode electrode that can be used in fuel cells.SOLUTION: A cathode electrode combining reductase and amorphous carbon, a fuel cell including the same, and a method of power generation are provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a cathode electrode. [Background technology]

[0002] In conventional enzyme fuel cells, bilirubin oxidase (BOD) electrodes were known as cathode electrodes (e.g., Non-Patent Document 1). In this system, BOD on the surface of the cathode electrode accepts electrons while reducing oxygen in the air to water. However, BOD is not widely available as an industrial enzyme and is relatively expensive compared to other enzymes. Another known type of battery uses platinum (Pt) as the cathode electrode, but platinum material is expensive.

[0003] Another known cathode electrode for enzyme fuel cells uses glucose oxidase (GOD) and peroxidase (POD) (see, for example, Non-Patent Document 2). In this system, glucose, the fuel, is oxidized to gluconolactone by GOD, producing hydrogen peroxide. Then, POD accepts electrons and reduces the hydrogen peroxide to water. This system uses two types of enzymes, but both are readily available as industrial enzymes and therefore can be constructed using only inexpensive enzymes. It also has the advantage of being able to produce a battery using the same fuel as the anode electrode, making it easy to use in glucose fuel cells.

[0004] However, in a reported example of a battery using a cathode electrode combining GOD and POD, for example, the open-circuit voltage of the battery disclosed in Non-Patent Document 2 was 0.45V. Since the redox potential of the mediator at the anode electrode of this battery is approximately -0.05V (vs. Ag / AgCl) and the oxidation initiation potential upon glucose addition is approximately -0.1V (vs. Ag / AgCl), the cathode electrode potential is around 0.35~0.4V, which is not necessarily sufficient performance. In the cyclic voltammogram of the cathode electrode, the current density at +0.2V (vs. Ag / AgCl) upon glucose addition is approximately -100μA / cm². 2 inYes, it was. Graphite was used as the carbon material.

[0005] As an example of a reported peroxidase electrode, Non-Patent Document 3 describes that a reduction current can be obtained from around -0.2V using a POD electrode (Figure 5 in the same document). Another example is Non-Patent Document 4, which discloses a glucose sensor using POD and GOD by combining Ketjenbrak EC300J and a glassy carbon rotating electrode.

[0006] There was a need for an enzyme electrode for cathodes that could produce greater output without requiring expensive enzymes.

[0007] This specification references numerous documents, including patent applications and manufacturers' manuals. While the disclosure of these documents is not considered relevant to the patentability of the present invention, all referenced documents are incorporated herein by reference, as is indicated specifically and individually where each document is incorporated by reference. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Biosens Bioelectron. 2012 May 15; 35(1): 140-146 [Non-Patent Document 2] Electroanalysis 2013, 25, No. 12, 2677-2683 [Non-Patent Document 3] Anal Biochem 2002, 307, 110-116 [Non-Patent Document 4] Analytical Sciences July 2017, Vol. 33, 839-844 [Overview of the project] [Problems that the invention aims to solve]

[0009] The objective of this disclosure is to provide a cathode electrode usable in enzyme fuel cells that can at least partially solve the problems of conventional cathode electrodes. [Means for solving the problem]

[0010] As a result of diligent research to solve the aforementioned problems, the present inventors fabricated an enzyme fuel cell using a cathode electrode combining glucose oxidase (GOD), peroxidase (POD), and amorphous carbon, and surprisingly found that a battery with an output current several times higher than that of previously reported examples was obtained. The present invention was completed, incorporating this as one embodiment.

[0011] This disclosure includes the following embodiments. [1] A cathode electrode combining a reductase and amorphous carbon. [2] The electrode according to Embodiment 1, wherein the oxidase is further immobilized. [3] The electrode according to Embodiment 2, wherein the oxidase produces hydrogen peroxide as a reaction product. [4] The electrode according to any one of Embodiments 1 to 3, wherein the reductase is catalase or peroxidase. [5] The electrode according to any one of Embodiments 2 to 4, wherein the oxidase is glucose oxidase or lactate oxidase. [6] The electrode according to any one of embodiments 1 to 5, wherein the amorphous carbon is conductive carbon black. [7] The electrode according to Embodiment 6, wherein the conductive carbon black is produced by a thermal decomposition method or an incomplete combustion method. [8] A battery having a cathode electrode and an anode electrode according to any of Embodiments 1 to 7. [9] The battery according to Embodiment 8, having an anode electrode on which an enzyme is immobilized.

[10] A fuel cell having a cathode electrode, an anode electrode, a fuel tank, and an electrolyte according to any one of embodiments 1 to 7.

[11] A method of generating power using a battery as described in any of Embodiments 8 to 10.

[0012] This specification incorporates the disclosure of Japanese Patent Application No. 2020-103348, which is the basis of the priority of this application.

Advantages of the Invention

[0013] According to the present disclosure, a cathode electrode with good output performance is provided. Further, a fuel cell provided with this cathode electrode is provided.

Modes for Carrying Out the Invention

[0014] Regarding the cathode electrode In one embodiment, the present disclosure provides a cathode electrode. In one embodiment, the cathode electrode can be a cathode electrode that combines (includes) a reductase and amorphous carbon. In one embodiment, the amorphous carbon can be carbon black, activated carbon, carbon fiber, or mesoporous carbon. In one embodiment, the cathode electrode can be a cathode electrode that combines (includes) a reductase and conductive carbon black. In one embodiment, the reductase can be an enzyme capable of reducing hydrogen peroxide. Examples of enzymes capable of reducing hydrogen peroxide include, but are not limited to, peroxidase and catalase.

[0015] In one embodiment, the cathode electrode may have glucose oxidase (GOD), peroxidase (POD), and amorphous carbon, preferably conductive carbon black. The solid carbon materials are roughly classified into nanocarbons such as carbon nanotubes and fullerenes, three-dimensional crystals such as diamond and graphite, (conductive) carbon black and activated carbon, carbon fibers, and amorphous carbon (also called amorphous carbon or amorphous carbon) such as mesoporous carbon. In the present specification, the term amorphous carbon is used in a general sense. That is, amorphous carbon means carbon having no clear crystal structure. Conductive carbon black is generally a carbon black material that can impart conductivity to an object with a small addition amount. In one embodiment, the conductive carbon black is Ketjen black. Examples of Ketjen black that can be used for the cathode electrode of the present disclosure include Lionite EC200L, Ketjen black EC300J, Lionite CB, Ketjen black EC600JD, and pulverized products thereof, such as Carbon ECP200L, Carbon ECP, and Carbon ECP600JD, but are not limited thereto. Ketjen black is available from Ketjen Black International Company or Lion Specialty Chemicals Co., Ltd. In another embodiment, the conductive carbon black is acetylene black. In another embodiment, the conductive carbon black is Denka black (registered trademark). Activated carbon is obtained by activating carbon at a high temperature using water vapor or the like as a raw material and increasing the adsorption performance by 5 to 10 times compared to carbon by increasing the micropores. There are roughly two types of activation treatments: gas activation method and chemical activation method. Mesoporous carbon is carbon having regularly sized pores on the nanometer scale.

[0016] In one embodiment, carbon black can be produced by pyrolysis or incomplete combustion. Regarding the production method of conductive carbon black, an example is reported in "Current Status of Conductive Carbon Black," Journal of the Japan Society of Printing Science and Technology, Vol. 44, No. 3. The entire contents of these documents are incorporated herein by reference. Examples of pyrolysis methods include the thermal black method and the acetylene black method. Examples of incomplete combustion methods include the oil furnace method using aromatic oils and the gas furnace method using natural gas. In another embodiment, carbon black produced by pyrolysis or incomplete combustion can be secondarily treated with nitric acid, nitrogen dioxide, ozone, etc., to actively increase acidic functional groups (oxidation treatment) and modify / alter the particle surface. In yet another embodiment, instead of oxidation treatment, the particle surface can be modified by contact with water vapor or carbon dioxide at a high temperature of 900°C or higher to remove crystallites and form pores (also called gasification treatment). Ketjenblack is a representative carbon black that undergoes activation treatment. In another embodiment, the particle surface can be modified by treating it at a high temperature of 2000°C to 3000°C in an inert atmosphere to eliminate surface functional groups and promote the growth of crystals within the particles, thereby changing the particle shape from spherical to polyhedral (also called graphitization treatment). In this specification, conductive carbon black may be simply referred to as carbon black.

[0017] Ketjenblack EC300J is a granular conductive carbon black with a particle size of 2-4 mm and a bulk density of 130 g / L. Furthermore, Ketjenblack EC300J has a DBP oil absorption capacity (ml / 100g) of 365, a primary particle size (nm) of 40, and a BET specific surface area (m²). 2The carbon black has the following physical properties: a density ( / g) of 800, porosity (%) of 60, volatile content (%) of 0.5, ash content (%) of 0.1, and median diameter (Dmed, nm) of 125. DBP oil absorption is the amount of dibutyl phthalate (DBP) absorbed. Carbon black particles fuse together to form aggregates that are linked together in a grape-like manner, which is called the structure. The size of the structure, like the particle size, affects the blackness and dispersibility of carbon black. Generally, as the structure increases, dispersion improves but blackness decreases. Also, carbon black with a large structure exhibits excellent conductivity. The structure can be indirectly evaluated by the DBP absorption amount. BET specific surface area is the specific surface area measured by the BET method (gas adsorption method). Volatile content refers to the amount of volatile matter, i.e., the weight loss, when carbon black is placed in a crucible and heated at 950°C for 7 minutes. This is due to the detachment of surface functional groups of carbon black as CO, H2O, CO2, etc. Bulk density is the mass per unit volume exhibited by carbon black filled under certain conditions in a container of a certain volume.

[0018] In another embodiment, carbon black can be produced by the acetylene process. For example, Denka Black® is a type of carbon black produced by the thermal decomposition of acetylene. Therefore, Denka Black® can be considered a type of acetylene black. Denka Black® has particles linked together in a chain-like structure and is highly graphitized. Denka Black® is of high purity, with remarkably low levels of undecomposed or functionally occurring hydrogen, and contains almost no oxygen-containing functional groups. Denka Black® is available in powder, pressed, and granular forms depending on its shape. The powder is a light powder as it is produced in the decomposition furnace. The pressed product is the powder that has been pressed to increase its bulk density. The granular product is a granular material with high bulk density. Denka Black® is commercially available in grades such as FX-35, HS-100, 50% pressed, and 100% pressed (Denka Co., Ltd.).

[0019] Carbon black #3230B (manufactured by Mitsubishi Chemical Corporation) has a particle size of 23 nm, a nitrogen adsorption specific surface area of ​​220, a DBP absorption amount of 140 for granular material, a volatile content of 1.4%, a pH value of 6.4, and an ash content of 0.2. The particle size referred to here is the arithmetic mean diameter obtained by observing carbon black particles with an electron microscope. The nitrogen adsorption specific surface area referred to here is the specific surface area calculated from the nitrogen adsorption amount using the S-BET formula in accordance with JIS K6217. The DBP absorption amount referred to here is the amount of DBP absorbed by 100 g of carbon black in accordance with JIS K6221. The volatile content referred to here is the amount of volatile matter, i.e., the weight loss, when carbon black is heated at 950°C for 7 minutes. The pH value referred to here is the value obtained by measuring a mixture of carbon black and distilled water with a glass electrode pH meter. Furthermore, the ash content referred to here is the residue remaining after carbon black is ashed at 750°C, in accordance with JIS K6218. Carbon black #3230B (manufactured by Mitsubishi Chemical Corporation) is produced by introducing fuel and air into a reaction chamber lined with bricks that can withstand temperatures up to approximately 2,000°C, completely burning it to create a high-temperature atmosphere of over 1,400°C, and then continuously spraying liquid raw material oil into it for thermal decomposition.

[0020] The physical properties and manufacturing methods of each carbon black are described in the product catalog. Furthermore, the physical properties of carbon black can be determined as appropriate by conventional methods, official methods, JIS standards, international standards, etc. In this specification, unless otherwise specified, the particle size of carbon black refers to the arithmetic mean diameter obtained by observing carbon black particles with an electron microscope. In this specification, unless otherwise specified, the nitrogen adsorption specific surface area of ​​carbon black refers to the specific surface area calculated from the nitrogen adsorption amount using the S-BET formula, in accordance with JIS K6217. In this specification, unless otherwise specified, the DBP absorption amount of carbon black refers to the DBP absorbed by 100g of carbon black, in accordance with JIS K6221. In this specification, unless otherwise specified, the volatile content of carbon black refers to the volatile content (weight loss) when carbon black is heated at 950°C for 7 minutes. In this specification, unless otherwise specified, the pH value of carbon black refers to the value measured using a glass electrode pH meter for a mixture of carbon black and distilled water. In this specification, unless otherwise specified, the ash content of carbon black refers to the residue after ashing of carbon black at 750°C in accordance with JIS K6218. Carbon ECP200L, Carbon ECP, and Carbon ECP600JD are powdered conductive carbon blacks that can pass through a 75 μm filter, i.e., a 75 μm filter, and have a bulk density of 30 (g / L). Therefore, in one embodiment, the conductive carbon black usable for the cathode electrode of this disclosure is granular conductive carbon black with a particle size of 2-4 mm and a bulk density of 130 (g / L). In another embodiment, the conductive carbon black usable for the cathode electrode of this disclosure has a DBP oil absorption rate (ml / 100g) of 365, a primary particle size (nm) of 40, and a BET specific surface area (m²). 2This conductive carbon black has the following physical properties: a density ( / g) of 800, a porosity (%) of 60, a volatile content (%) of 0.5, an ash content (%) of 0.1, and a median diameter (Dmed, nm) of 125. In one embodiment, the conductive carbon black usable for the cathode electrode of this disclosure is a powdered conductive carbon black with a particle size of less than 75 μm (75 μm pass) and a bulk density of 30 (g / L). In one embodiment, the conductive carbon black may be Denka Black (registered trademark). In one embodiment, the conductive carbon black may be Denka Black FX-35. In one embodiment, the conductive carbon black is 100% pressed Denka Black. In one embodiment, the conductive carbon black is 50% pressed Denka Black. In one embodiment, the conductive carbon black is Denka Black HS-100. In one embodiment, the conductive carbon black is Carbon Black #3230B (manufactured by Mitsubishi Chemical Corporation).

[0021] In this specification, unless otherwise specified, the basic particle size refers to the diameter of the microspherical portion constituting the aggregate (primary aggregate), which is considered the primary particle, measured using a circular approximation. The basic particle size is also called the primary particle size, and it can be measured from electron microscope images using an image analysis device. Alternatively, the primary particle size can be measured by approximating the diameter of individual projected particles using electron microscope images. For example, an automated particle size analyzer manufactured by Zeiss can be used. In this specification, unless otherwise specified, the average particle size of the primary particle size refers to the arithmetic mean particle size of the primary particle size. For example, carbon black nanoparticles can be measured using the IG-1000 Plus (Shimadzu Corporation). The particle size distribution of carbon black nanoparticles after ultrasonic dispersion treatment can be measured using the IG-1000 Plus. In this specification, unless otherwise specified, when simply referring to particle size for carbon black, it refers to the particle size of the aggregate. The particle size of the aggregate can be measured with a particle size analyzer. In this specification, unless otherwise specified, the particle size of nanoparticles is defined as the primary particle size measured by IG-1000 Plus (Shimadzu Corporation), and the particle size of aggregates is defined as the particle size measured by Horiba, Ltd.'s Partica LA-960V2.

[0022] In one embodiment, carbon nanotubes are excluded from the conductive carbon black used in the electrodes of this disclosure. This does not prevent the presence or contamination of trace amounts of carbon nanotubes in the conductive carbon black used in the electrodes of this disclosure. In other words, in one embodiment, the exclusion of carbon nanotubes from the conductive carbon black used in the electrodes of this disclosure means that the main component of the conductive carbon black used in the electrodes of this disclosure is conductive carbon black and not carbon nanotubes. The main component here means 90% or more by weight, for example, 95% or more.

[0023] Commercially available products can be used as activated carbon, carbon fiber, or mesoporous carbon.

[0024] As the reductase, any enzyme capable of reducing hydrogen peroxide can be used. Examples of enzymes capable of reducing hydrogen peroxide include peroxidase (POD, EC 1.11.1.7) and catalase (EC 1.11.1.6). As the peroxidase (POD), any known peroxidase can be used. Examples of peroxidases include those derived from horseradish, rice, and soybeans. Commercially available products include PEO-131 (manufactured by Toyobo), PEO-301 (manufactured by Toyobo), PEO-302 (manufactured by Toyobo), etc. As the catalase, any known catalase can be used. Examples of catalases include those derived from Aspergillus niger and bovine liver, but are not limited to these. In some embodiments, the peroxidase or catalase can be immobilized on the electrode material. Methods of immobilization include using an immobilizing agent or crosslinking reagent, encapsulating in a polymer matrix, coating with a dialysis membrane, and using photocrosslinkable polymers, conductive polymers, or redox polymers. The immobilization can be performed by immobilizing in the polymer or by adsorption onto an electrode, or by using a combination of these methods. Glutaraldehyde is an example of an immobilizing agent. When using glutaraldehyde, the peroxidase is immobilized on an electrode (e.g., a carbon electrode) with glutaraldehyde, and then the glutaraldehyde is blocked by treatment with a reagent containing an amine group. The amount of peroxidase to be immobilized can be determined as appropriate, and can be an amount that can generate the current necessary for fuel cell power generation.

[0025] In one embodiment, an oxidase may be immobilized on the cathode electrode. In one embodiment, the oxidase may produce hydrogen peroxide as a reaction product. In one embodiment, a known oxidase can be used as the oxidase. Examples of oxidases include glucose oxidase, lactate oxidase, amino acid oxidase, sarcosine oxidase, etc. Any known glucose oxidase can be used as the glucose oxidase (GOD). In one embodiment, the glucose oxidase can be immobilized on the electrode material. In another embodiment, the glucose oxidase is not immobilized on the electrode material. The immobilization method and immobilizing agent may be the same as in the case of peroxidase described above. In one embodiment, the glucose oxidase may be an Aspergillus-derived GOD, for example, an Aspergillus niger-derived GOD. In another embodiment, the glucose oxidase may include, but is not limited to, Toyobo's GOD (catalog number GLO-201, derived from Aspergillus sp.), Fujifilm Wako Pure Chemical Industries' GOD (Wako Pure Chemical Industries catalog number 074-02401, derived from Aspergillus niger), Sigma-Aldrich GOD type VII (derived from Aspergillus niger), and Sigma-Aldrich GOD type XS (derived from Aspergillus niger). Any known lactate oxidase (EC 1.1.3.2) can be used, such as, but is not limited to, those derived from Lactococcus lactis, Aerococcus viridans, and Enterococcus sp. The amino acid oxidase (EC 1.4.3.2) may be derived from microorganisms or snakes, such as those from the Viperidae, Viperinae, and Elapidae families, but is not limited to these.Examples of sarcosine oxidase (EC 1.5.3.1) (also called sarcosine oxidase) include those derived from the genera Corynebacterium, Bacillus, Cylindrocarbon, Pseudomonas, and Arthrobacter, as well as their modified counterparts (Japanese Patent Publication Nos. 2005-176828, 2005-168487, and 2000-175685). Commercially available oxidases can also be used. In this specification, "derived from" in relation to genes and enzymes includes not only the wild type of a particular organism, but also mutants and variants derived from the wild type, and even mutants obtained by modifying the wild type. Artificially synthesized sequences are also included in the derived from which the sequence is derived if the sequence matches that of the wild type. The same applies to artificially synthesized sequences that are highly similar to the wild type. High similarity here means that when comparing the two sequences, there is only a difference of one or a few amino acids, such as substitution, deletion, or addition. The term "several" here refers to a maximum of 15, 14, ... 3, or 2 items.

[0026] Method for manufacturing a cathode electrode In one embodiment, the disclosure provides a method for manufacturing a cathode electrode. This method includes the steps of: dispersing a carbon material (e.g., Ketjenbrak) in a suitable solvent such as methanol, coating an electrode (e.g., a carbon electrode or a carbon printed electrode) with the dispersed material, and drying it; coating the electrode with a peroxidase and an enzyme immobilizer (e.g., glutaraldehyde) and drying it; and optionally, stirring and washing the electrode in water (e.g., pure or ultrapure water). The manufactured cathode electrode can be incorporated into a fuel cell.

[0027] In one embodiment, the present disclosure provides a battery having the above-described cathode electrode. In one embodiment, in the battery of the present disclosure, peroxidase is immobilized on the cathode electrode, and the cathode electrode is treated with a carbon material that imparts conductivity. Glucose oxidase is also present on the cathode electrode side. The glucose oxidase may be immobilized on the electrode or may be present in a solution. In one embodiment, a method for generating power using the battery of the present disclosure is provided.

[0028] In one embodiment, the disclosure provides a fuel cell. In one embodiment, the fuel cell of the disclosure comprises the cathode electrode, anode electrode, fuel tank, and electrolyte described above. The fuel cell of the disclosure may optionally have a load resistor between the anode and cathode and may include wiring for such a resistor. In one embodiment, the load resistor is part of the fuel cell of the disclosure. In one embodiment, the load resistor is not part of the fuel cell of the disclosure, and the fuel cell of the disclosure is configured to be connected to an appropriate load resistor.

[0029] Regarding the anode electrode In some embodiments, the anode electrode may be a carbon electrode or a metal electrode. For example, electrodes made of conductive carbonaceous materials such as carbon black, graphite, or activated carbon, or electrodes made of metals such as gold or platinum can be used. Specifically, examples include carbon paper, glassy carbon, and HOPG (highly oriented pyrolysis graphite). The anode may also be configured to be in contact with an oxidoreductase, such as glucose oxidase or glucose dehydrogenase. In some embodiments, the oxidoreductase used in the anode of the fuel cell of this disclosure constitutes a part of the anode. For example, the oxidoreductase may be in close proximity to or in contact with the anode, immobilized, or adsorbed. The fuel tank contains a compound that serves as a substrate for the oxidoreductase immobilized on the electrode. For example, if glucose oxidase or glucose dehydrogenase is immobilized on the electrode, the fuel may be glucose. For example, if fructose oxidase or fructose dehydrogenase is immobilized on the electrode, the fuel may be fructose. For example, if a combination of invertase and glucose dehydrogenase or glucose oxidase is immobilized on the electrode, the fuel may be sucrose. For example, if a combination of amylase and glucose dehydrogenase or glucose oxidase is immobilized on the electrodes, the fuel may be starch. In one embodiment, the fuel cell of this disclosure may have an ion exchange membrane separating the anode and cathode. The ion exchange membrane may have pores ranging from 1 nm to 20 nm.

[0030] In one embodiment, the oxidoreductase used in the anode electrode may be flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (GDH). Flavin adenine dinucleotide-dependent glucose dehydrogenase may be referred to as FAD-GDH in this specification. Examples of FAD-GDH include those derived from the genera Aspergillus, Botryotinia, Mucor, Absidia, Actinomucor, and Circinella.

[0031] Examples of microorganisms belonging to the genus Mucor include Mucor prainii, Mucor javanicus, Mucor circinelloides f. circinelloides, Mucor guilliermondii, Mucor hiemalis, Mucor hiemalis f. silvaticus, Mucor subtilissimus, Mucor RD056860, and Mucor dimorphosporus. Examples of microorganisms belonging to the genus Absidia include Absidia cylindrospora and Absidia hyalospora. An example of a microorganism belonging to the genus Actinomucor is Actinomucor elegans. Examples of Circinella microorganisms include Circinella minor, Circinella mucoroides, Circinella muscae, Circinella rigida, Circinella simplex, Circinella umbellata, Circinella RD055423, and Circinella RD055422. Note that the RD strains are stocked strains of the NBRC (National Biotechnology Center, National Institute of Technology and Evaluation). FAD-GDH derived from these strains and their variants can be used.

[0032] In another embodiment, the oxidoreductase used in the anode electrode may be fructose dehydrogenase (EC 1.1.99.11). Fructose dehydrogenase is also called D-fructose dehydrogenase or fructose-5-dehydrogenase. Fructose dehydrogenase catalyzes the reduction of D-fructose to 5-dehydro-D-fructose. Examples of fructose dehydrogenase include, but are not limited to, those derived from Gluconobacter industrius. Commercially available fructose dehydrogenase derived from Gluconobacter industrius, or equivalents thereof, can be used.

[0033] In one embodiment, a mediator having the property of adsorbing to the electrode may be used on the anode electrode side of the battery. The mediator (also called an artificial electron mediator, artificial electron acceptor, or electron mediator) is not particularly limited as long as it can accept electrons from the oxidoreductase used in the anode electrode. Examples of mediators include quinones, phenazines, viologens, cytochromes, phenoxazines, phenothiazines, ferricyanides, such as potassium ferricyanide, ferredoxins, ferrocene, osmium complexes and their derivatives, and examples of phenazine compounds include, but are not limited to, PMS and methoxyPMS. Examples of mediators having the property of adsorbing to electrodes include those described in International Publication No. 2019 / 198359 (PCT / JP2019 / 007373), Japanese Patent Publication No. 2019-186122 (Japanese Patent No. 6484741), or Japanese Patent Publication No. 2019-180335 (Japanese Patent No. 6484742), and include, but are not limited to, N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), N,N'-diphenyl-p-phenylenediamine (DPPD), and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD).

[0034] In the electrode, the enzyme may be positioned at any location. In one embodiment, it may be positioned on the surface of the electrode that is in contact with the fuel or oxygen. To increase the surface area of ​​the electrode in contact with the fuel or oxygen and improve power generation efficiency, for example, an electrode with pores may be formed and the enzyme may be placed inside the pores. From the viewpoint of forming an electrode with pores, particulate materials can be used as the conductive material, for example, particulate materials with pores can be used.

[0035] In a power generation device, electrodes may be positioned in any location. In one embodiment, electrode material can be applied to a substrate by screen printing or the like. This is preferable from the viewpoint of making the power generation device thinner. In this case, the anode and cathode may be formed on the same substrate, or the anode and cathode may be formed on different substrates.

[0036] The substrate may have lead portions for electrically connecting electrodes. These lead portions may be formed using commonly used conductive materials. The lead portions may have through holes in the portion in contact with the cathode. This allows for an increase in the supply of oxygen to the cathode.

[0037] The material of the substrate forming the electrodes may be a natural material or a synthetic material, and is not particularly limited. The substrate may be, for example, paper or cloth made from a natural material, but is not limited to these. In certain embodiments, a water-repellent substrate may be used, or a substrate made of a material that does not absorb liquid may be used. This prevents short circuits between the anode and cathode from occurring due to the liquid supplied to the power generation device. A spacer may also be provided between the anode and cathode. This also prevents short circuits between the anode and cathode.

[0038] The shape of the electrodes, for example, the shape of the electrodes in a power generation device, can be anything and is not particularly limited. The shape can be, for example, a pattern in which multiple anodes or cathodes are connected. This can improve power generation efficiency.

[0039] (Other components) A power generation device may, in some cases, have other components besides fuel and electrodes. Examples include, but are not limited to, protective materials for protecting the power generation device from the outside air, adhesives for fixing the power generation device to a substrate, hydrogels, etc.

[0040] In certain embodiments, the power generation device may further include means for measuring the concentration of a substance in a liquid supplied using the electricity generated by the power generation, means for wirelessly transmitting the data obtained by the measurement, and so on.

[0041] In one embodiment, a method for generating electricity using a fuel cell of the present disclosure is provided. The method for generating electricity of the present disclosure includes the step of supplying fuel to the anode. When fuel is supplied to the anode, the substrate is oxidized, and the electrons generated at the same time are transferred to the anode electrode, and an electric current is generated when the electrons reach the cathode electrode through wiring (external circuitry) from the anode electrode.

[0042] Protons (H) generated in the above process + The protons move through the electrolyte solution to the cathode electrode. At the cathode electrode, the protons that have moved from the anode through the electrolyte solution, the electrons that have moved from the anode side via an external circuit, and an oxidizing agent such as oxygen or hydrogen peroxide (cathode substrate) react to produce water. This reaction can be used to generate electricity.

[0043] In some embodiments, a known electron transfer mediator may be used depending on the type of enzyme used in the anode. In some embodiments, the fuel used in the fuel tank may be selected depending on the type of enzyme. Examples of fuels include, but are not limited to, sugars, alcohols, aldehydes, amino acids, amines, lactic acid, and uric acid. There may be one or more types of fuel. For example, if glucose dehydrogenase is used, the fuel tank may contain glucose. Or, if fructose dehydrogenase is used, the fuel tank may contain fructose. Or, if lactate oxidase is used, the fuel tank may contain lactic acid.

[0044] In one embodiment, an oxygen-selective film (e.g., a dimethylpolysiloxane film) can be placed around the cathode electrode to avoid the influence of impurities (such as ascorbic acid or uric acid) that interfere with the electrode reaction at the cathode.

[0045] In one embodiment, the cathode electrode of the Disclosure can be used in a battery. In another embodiment, the cathode electrode of the Disclosure can be used in a fuel cell. In yet another embodiment, the cathode electrode of the Disclosure can be used for power generation. These are illustrative examples, and the applications of the cathode electrode of the Disclosure are not limited to these.

[0046] The present invention is further illustrated by the following examples. However, the technical scope of the present invention is not limited in any way by these examples. [Examples]

[0047] [Example 1] (Preparation of carbon black solution) Denka Black FX-35 (manufactured by Denka Co., Ltd.) was suspended in a 50% ethanol solution to a concentration of 20 mg / ml and treated with an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., US-150E, output 30%) for at least 3 minutes.

[0048] (Electrode fabrication) 0.5 cm The above carbon black suspension was applied to 20 μl on each side of a corner carbon cloth and dried at 60°C for at least 1 hour. Subsequently, 20 μl of a 5 mg / ml peroxidase (POD, Toyobo Co., Ltd.) and a 5% glutaraldehyde solution were applied and dried at room temperature for 2 hours to prepare the electrodes.

[0049] (Electrochemical measurement) The above electrode was used as the working electrode and wired to an ALS electrochemical analyzer 814D (BAS Corporation), and immersed in 10 ml of 100 mM potassium phosphate buffer (pH 7.0). A silver-silver chloride electrode (BAS Corporation) was used as the reference electrode and a platinum electrode (BAS Corporation) as the counter electrode. Cyclic voltammetry (CV) measurements were performed by sweeping the voltage in the range of +200 mV to +700 mV (vs. Ag / AgCl) while stirring the solution at 400 rpm. The sweep rate was 20 mV / sec. Subsequently, hydrogen peroxide solution was added to a final concentration of 1 mM, and CV measurements were performed in the same manner. Comparing the cyclic voltammograms before and after the addition of hydrogen peroxide solution, a higher reduction current was observed after the addition of hydrogen peroxide solution compared to before, at potentials below approximately +570 mV (vs. Ag / AgCl). At +200mV (vs. Ag / AgCl), the current after adding hydrogen peroxide solution increased to 331 μA / cm² compared to before adding the hydrogen peroxide solution. 2 A high reduction current was observed.

[0050] [Example 2] (Preparation of carbon black solution) Denka Black 100% pressed product (manufactured by Denka Co., Ltd.) was suspended in a 50% ethanol solution to a concentration of 70 mg / ml and treated with an ultrasonic homogenizer for at least 3 minutes.

[0051] (Electrode fabrication) 0.5 cm The above carbon black suspension was applied to 20 μl on each side of a corner carbon cloth and dried at 60°C for at least 1 hour. Subsequently, 20 μl of POD with a final concentration of 5 mg / ml and a 5% glutaraldehyde solution were applied and dried at room temperature for 2 hours to prepare the electrodes.

[0052] (Electrochemical measurement) Using the above electrode as the working electrode, CV measurements were performed in the same manner as in Example 1. Comparing the cyclic voltammograms before and after the addition of hydrogen peroxide solution, a higher reduction current was observed after the addition of hydrogen peroxide solution compared to before, at potentials below approximately +570 mV (vs. Ag / AgCl). At +200 mV (vs. Ag / AgCl), the reduction current was 326 μA / cm² after the addition of hydrogen peroxide solution compared to before the addition of hydrogen peroxide solution. 2 A high reduction current was observed.

[0053] [Example 3] (Preparation of carbon black solution) Carbon black #3230B (manufactured by Mitsubishi Chemical Corporation) was suspended in a 50% ethanol solution to a concentration of 70 mg / ml and treated with an ultrasonic homogenizer for at least 3 minutes.

[0054] (Electrode fabrication) 20 μl of the above carbon black suspension was applied to each side of a 0.5 mm square carbon cloth and dried at 60°C for at least 1 hour. Subsequently, 20 μl of POD with a final concentration of 5 mg / ml and a 5% glutaraldehyde solution were applied and dried at room temperature for 2 hours to prepare the electrodes.

[0055] (Electrochemical measurement) Using the above electrode as the working electrode, CV measurements were performed in the same manner as in Example 1. Comparing the cyclic voltammograms before and after the addition of hydrogen peroxide solution, a higher reduction current was observed after the addition of hydrogen peroxide solution compared to before, at potentials below approximately +490 mV (vs. Ag / AgCl). At +200 mV (vs. Ag / AgCl), the reduction current was 361 μA / cm² after the addition of hydrogen peroxide solution compared to before the addition of hydrogen peroxide solution. 2 A high reduction current was observed.

[0056] [Example 4] (Preparation of carbon black solution) Ketjenbrak ECP600JD (manufactured by Lion Specialty Chemicals) was suspended in a 50% ethanol solution at a concentration of 7 mg / ml and treated with an ultrasonic homogenizer for at least 3 minutes.

[0057] (Electrode fabrication) 20 μl of the above carbon black suspension was applied to each side of a 0.5 mm square carbon cloth and dried at 60°C for at least 1 hour. Subsequently, 20 μl of POD with a final concentration of 5 mg / ml and a 5% glutaraldehyde solution were applied and dried at room temperature for 2 hours to prepare the electrodes.

[0058] (Electrochemical measurement) Using the above electrode as the working electrode, CV measurements were performed in the same manner as in Example 1. Comparing the cyclic voltammograms before and after the addition of hydrogen peroxide solution, a higher reduction current was observed after the addition of hydrogen peroxide solution compared to before, at potentials below approximately +560 mV (vs. Ag / AgCl). At +200 mV (vs. Ag / AgCl), the reduction current was 733 μA / cm² after the addition of hydrogen peroxide solution compared to before the addition of hydrogen peroxide solution. 2 The reduction current was high.

[0059] [Example 5] (Preparation of carbon black solution) Ketjenbrak ECP200L (manufactured by Lion Specialty Chemicals) was suspended in a 50% ethanol solution at a concentration of 20 mg / ml.

[0060] (Fabrication of cathode electrodes) 20 μl of the above carbon black suspension was applied to each side of a 0.5 mm square carbon cloth and dried at 60°C for at least 1 hour. Subsequently, 20 μl each of glucose oxidase (Sigma-Ace) at a final concentration of 5 mg / ml, POD at a final concentration of 5 mg / ml, and a 5% glutaraldehyde solution were applied and dried at room temperature for 2 hours to prepare the electrodes.

[0061] (Electrochemical measurement) Using the above electrode as the working electrode, CV measurement was performed in the same manner as in Example 1. However, instead of the hydrogen peroxide solution, a glucose solution with a final concentration of 10 mM was added as the substrate. As a result of comparing the cyclic voltammograms before and after the addition of glucose, a higher reduction current was observed after the addition of the glucose solution compared to before the addition at a potential of about +640 mV (vs. Ag / AgCl) or lower.

[0062] (Fabrication of Anode Electrode) Single-walled carbon nanotubes were immobilized on a 0.5 mm square carbon cloth, and N-isopropyl-N'-phenyl-1,4-phenylenediamine (IPPD, manufactured by Tokyo Chemical Industry Co., Ltd., product code P0327) was adsorbed and fixed. Subsequently, 20 μl of 20 mg / ml glucose dehydrogenase (GDH, manufactured by Kikkoman Biochemifa Co., Ltd.) was applied and dried, and the above carbon cloth was exposed to 25% glutaraldehyde vapor for 30 minutes to crosslink and fix GDH, thereby obtaining an anode electrode.

[0063] (Evaluation of Battery) The above cathode electrode, anode electrode, variable resistor, and potentiostat were connected, and open-circuit potential measurement was performed. The solution was the same as that used for the evaluation of the cathode electrode, and a glucose solution was added to a final concentration of 10 mM. As a result, the open-circuit voltage was +0.66 V, and a current density of 0.15 mA / cm 2 was obtained when connected to 10 kΩ.

[0064] [Example 6] A 0.5 mm square carbon cloth coated with Ketjenblack ECP600JD prepared in Example 4 was applied with 20 μl of a 5 mg / ml catalase derived from bovine liver (manufactured by Tokyo Chemical Industry Co., Ltd.) and a 5% glutaraldehyde solution, and dried at room temperature for 2 hours to fabricate an electrode.

[0065] (Electrochemical Measurement) Using the above electrode as the working electrode, CV measurements were performed in the same manner as in Example 1. Comparing the cyclic voltammograms before and after the addition of hydrogen peroxide solution, a higher reduction current was observed with hydrogen peroxide solution added compared to without hydrogen peroxide solution at potentials below approximately +600 mV (vs. Ag / AgCl). At +200 mV (vs. Ag / AgCl), the reduction current was 200 μA / cm with hydrogen peroxide solution added compared to without hydrogen peroxide solution. 2 That was the only high reduction current.

[0066] [Example 7] Electrodes were prepared by coating a 0.5 mm square carbon cloth with Ketjenblack ECP600JD prepared in Example 4, then coating it with 20 μl of lactate oxidase (Toyobo Co., Ltd.) at a final concentration of 5 mg / ml, POD at a final concentration of 5 mg / ml, and a 5% glutaraldehyde solution, and drying it at room temperature for 2 hours.

[0067] (Electrochemical measurement) Using the above electrode as the working electrode, CV measurements were performed in the same manner as in Example 1. However, instead of hydrogen peroxide solution, a sodium L-lactate solution was added as the substrate to a final concentration of 10 mM. Comparing the cyclic voltammograms before and after the addition of sodium L-lactate solution, a higher reduction current was observed with sodium L-lactate solution added compared to without sodium L-lactate solution at potentials below approximately +650 mV (vs. Ag / AgCl). At +200 mV (vs. Ag / AgCl), the current was 140 μA / cm with sodium L-lactate solution added compared to without sodium L-lactate solution. 2 That was the only high reduction current.

[0068] [Comparative Example] Cathode electrodes were fabricated using a multi-walled carbon nanotube dispersion solution instead of a carbon black suspension. 20 μl of the multi-walled carbon nanotube dispersion solution was applied to each side of a 0.5 mm square carbon cloth and dried at 60°C for at least 1 hour. Subsequently, 20 μl of POD with a final concentration of 5 mg / ml and a 5% glutaraldehyde solution were applied, and the electrodes were fabricated by drying at room temperature for 2 hours.

[0069] (Electrochemical measurement) Using the above electrode as the working electrode, CV measurements were performed in the same manner as in Example 1. Comparing the cyclic voltammograms before and after the addition of hydrogen peroxide solution, no difference in reduction current was observed in the range of +200mV to +700mV (vs. Ag / AgCl).

[0070] Non-patent document 3 describes a biofuel cell using GOD for the anode and cathode, and POD for the cathode. The open-circuit voltage of the battery in Non-patent document 3 is +0.45V, and the current is approximately 0.02mA / cm when connected to approximately 10kΩ. 2 The current density was approximately [value missing]. The redox potential of the mediator used in the anode electrode of this battery was approximately -0.05V. Generally, the lower the redox potential of the anode electrode, the greater the difference between it and the redox potential of the cathode electrode, resulting in a higher open-circuit voltage and thus higher battery performance. Therefore, compared to the battery disclosed in Non-Patent Document 3, the battery of this disclosure obtained the above output despite using an anode electrode with an IPPD fixed to it that has a redox potential of +0.1V, which is a disadvantage. In other words, the cathode electrode of this disclosure is of better performance than conventional ones. Furthermore, it is thought that an even greater output can be obtained if the cathode electrode of this disclosure is combined with an anode electrode with a mediator fixed to it that has a redox potential of -0.05V. [Industrial applicability]

[0071] The cathode electrode of this disclosure can be used in batteries, such as fuel cells, and can also be used for power generation.

Claims

1. A battery having a cathode electrode and an anode electrode made of a reductase and amorphous carbon, wherein both the cathode electrode and the anode electrode are electrodes that are not rotating electrodes, and the reductase is catalase or peroxidase.

2. The battery according to claim 1, wherein an oxidase is further immobilized on the cathode electrode.

3. The battery according to claim 2, wherein the oxidase produces hydrogen peroxide as a reaction product.

4. The battery according to claim 2 or 3, wherein the oxidase is glucose oxidase or lactate oxidase.

5. The battery according to any one of claims 1 to 4, wherein the amorphous carbon is conductive carbon black.

6. The battery according to claim 5, wherein the conductive carbon black is manufactured by a thermal decomposition method or an incomplete combustion method.

7. The battery according to claim 1, having an anode electrode on which an enzyme is immobilized.

8. A fuel cell in which the battery is a fuel cell, and further comprises a cathode electrode and an anode electrode in the battery according to any one of claims 1 to 6, and a fuel tank and an electrolyte.

9. A method for generating power using a battery according to any one of claims 1 to 8.