JP2007257983A - Fuel cell and its manufacturing method, negative electrode for fuel cell and its manufacturing method, electronic equipment, electrode reaction utilization device and its manufacturing method, electrode for electrode reaction utilization device and its manufacturing method, high output agent, and mediator diffusion accelerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of generating high output and its manufacturing method. <P>SOLUTION: In the fuel cell having structure facing a negative electrode 1 and a positive electrode 2 through a proton conductor 3, and immobilizing enzyme, coenzyme, and mediator in the negative electrode 1, a high output agent comprising phospholipid such as dimyristoyl phosphatidylcholine (DMPC) or its derivative, or a polymer of them in addition to the enzyme, the coenzyme, and the mediator, or a mediator diffusion accelerator is immobilized to the negative electrode 1. As the mediator, a compound having quinone skeleton, 2-amino-1,4-naphtoquinone (ANQ) for example is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell, a method for producing the same, a negative electrode for a fuel cell, a method for producing the same, an electronic device, an electrode reaction utilizing device, a method for producing the electrode, an electrode for an electrode reaction utilizing device, a method for producing the electrode, a high output agent, and a mediator diffusion promotion. The agent is suitable for application to, for example, a fuel cell in which an enzyme as a catalyst and a mediator that mediates the transfer of electrons are immobilized on a negative electrode, and various devices, apparatuses, or systems using the fuel cell.

The fuel cell has a structure in which a positive electrode (oxidant electrode) and a negative electrode (fuel electrode) face each other with an electrolyte (proton conductor) interposed therebetween. In the conventional fuel cell, the fuel (hydrogen) supplied to the negative electrode is oxidized and separated into electrons and protons (H ⁺ ), the electrons are transferred to the negative electrode, and H ⁺ moves through the electrolyte to the positive electrode. In the positive electrode, this H ⁺ reacts with oxygen supplied from the outside and electrons sent from the negative electrode through the external circuit to generate water (H ₂ O).

  In this way, fuel cells are highly efficient power generators that directly convert the chemical energy of fuel into electrical energy, and the chemical energy of fossil energy such as natural gas, oil, and coal can be used regardless of where and when it is used. Moreover, it can be extracted as electric energy with high conversion efficiency. For this reason, research and development of fuel cells for large-scale power generation has been actively conducted. For example, a fuel cell is mounted on the space shuttle, and it has proven that it can supply water for crew members at the same time as electric power, and that it is a clean power generator.

Furthermore, in recent years, fuel cells having a relatively low operating temperature range from room temperature to about 90 ° C., such as solid polymer fuel cells, have been developed and attracting attention. For this reason, not only large-scale power generation applications but also applications to small systems such as automobile power supplies and portable power supplies such as personal computers and mobile devices are being sought.
Thus, the fuel cell can be used in a wide range of applications from large-scale power generation to small-scale power generation, and has attracted much attention as a highly efficient power generation device. However, in fuel cells, natural gas, petroleum, coal, etc. are usually used as fuel by converting them into hydrogen gas using a reformer, which consumes limited resources and needs to be heated to a high temperature. There are various problems such as the need for an expensive noble metal catalyst such as (Pt). Even when hydrogen gas or methanol is used directly as a fuel, care must be taken when handling it.

Accordingly, attention has been paid to the fact that biological metabolism performed in living organisms is a highly efficient energy conversion mechanism, and proposals have been made to apply this to fuel cells. The biological metabolism here includes respiration, photosynthesis and the like performed in microbial somatic cells. Biological metabolism has the characteristics that the power generation efficiency is extremely high and the reaction proceeds under mild conditions of about room temperature.
For example, respiration takes nutrients such as sugars, fats, and proteins into microorganisms or cells, and these chemical energies are converted to carbon dioxide (glycolytic and tricarboxylic acid (TCA) cycles through a number of enzymatic reaction steps. In the process of generating CO ₂ ), nicotinamide adenine dinucleotide (NAD ⁺ ) is reduced to reduced nicotinamide adenine dinucleotide (NADH) to convert it into redox energy, that is, electric energy, and further, an electron transfer system In this mechanism, the electric energy of NADH is directly converted into electric energy of proton gradient, and oxygen is reduced to generate water. The electrical energy obtained here produces ATP from adenosine diphosphate (ADP) via adenosine triphosphate (ATP) synthase, and this ATP is used for reactions necessary for the growth of microorganisms and cells. Used. Such energy conversion occurs in the cytosol and mitochondria.

In addition, photosynthesis captures light energy and reduces nicotinamide adenine dinucleotide phosphate (NADP ⁺ ) via an electron transfer system to reduce nicotinamide adenine dinucleotide phosphate (NADPH), thereby converting it into electrical energy. In the process of conversion, it is a mechanism that oxidizes water to produce oxygen. This electric energy takes in CO ₂ and is used for carbon fixation reaction, and is used for carbohydrate synthesis.
As a technique for utilizing the above-described biological metabolism for a fuel cell, electric energy generated in a microorganism is taken out of the microorganism through a mediator (also referred to as an electron mediator or an electron acceptor compound), and the electrons are transferred to an electrode. A microbial battery that obtains an electric current has been reported (for example, see Patent Document 1).

However, since microorganisms and cells have many unnecessary reactions in addition to the intended reaction such as conversion from chemical energy to electrical energy, the above-described method consumes electrical energy for unwanted reactions, resulting in sufficient energy conversion efficiency. Is not demonstrated.
Therefore, a fuel cell (biofuel cell) that performs only a desired reaction using an enzyme has been proposed (see, for example, Patent Documents 2, 3, and 4). In this biofuel cell, a fuel is decomposed by an enzyme to be separated into protons and electrons, and those using alcohols such as methanol and ethanol or sugars such as glucose have been developed as fuel.

  In a biosugar-air fuel cell, as a method of immobilizing a mediator and an enzyme on an electrode, 30 μl of tetrathiafulvalene (TTF) saturated solution dissolved in methanol and 20 μl of glucose oxidase (GOD) (3 u / μl) on a glassy carbon electrode. ) And then dropping 5 μl (1 wt%) of polystyrene sulfonic acid (PSS) and 5 μl (1 wt%) of poly-L-lysine (PLL) to form a polyion complex, whereby the mediator and enzyme solution It is disclosed that a membrane that prevents elution is formed, and a biocompatible phospholipid membrane (MPC) is cast by 10 μl (5 wt%) to produce an electrode that is hardly soluble and biocompatible. (Refer nonpatent literature 1.). However, Non-Patent Document 1 does not disclose or suggest that phospholipids increase the output of fuel cells, increase the diffusion coefficient of mediators, and promote the diffusion of mediators.

JP 2000-133297 A JP 2003-282124 A JP 2004-71559 A JP 2005-13210 A [Search January 12, 2006] Internet <URL: http: //www.business-ijp/sentan/jusyou/2004/>

However, in the biofuel cell, a large output is not obtained at present.
Therefore, the problem to be solved by the present invention is to provide a fuel cell capable of increasing output and a method for manufacturing the same.
Another problem to be solved by the present invention is to provide a fuel cell negative electrode suitable for use in the above fuel cell and a method for producing the same.
Another problem to be solved by the present invention is to provide an electronic device using the excellent fuel cell as described above.

Other problems to be solved by the present invention are, more generally, an electrode reaction utilization device capable of increasing output, a manufacturing method thereof, an electrode for an electrode reaction utilization device suitable for use in this electrode reaction utilization device, and The manufacturing method is provided.
Another problem to be solved by the present invention is to provide a high output agent capable of greatly increasing the output of an electrode reaction utilization device such as a fuel cell.
Another problem to be solved by the present invention is to provide a mediator diffusion promoter capable of greatly increasing the diffusion coefficient of the mediator and greatly promoting the diffusion of the mediator.

As a result of intensive studies in order to solve the above-described problems of the prior art, the present inventors have a structure in which a positive electrode and a negative electrode are opposed to each other through a proton conductor, and an enzyme and a mediator are fixed to the negative electrode. In a fuel cell (biofuel cell), the output of the fuel cell can be greatly improved by immobilizing phospholipids such as dimyristoylphosphatidylcholine (DMPC) in addition to the enzyme and mediator on the negative electrode I found a phenomenon that I can do it. That is, it has been found that phospholipid functions as a high output agent. As described above, various studies have been made on the reason why high output can be achieved by immobilizing phospholipids. One of the reasons why a sufficiently large output cannot be obtained in a conventional fuel cell is that an enzyme and a mediator immobilized on the negative electrode. Is not uniformly mixed, and both are separated from each other and are in an agglomerated state. However, by immobilizing phospholipids, the enzyme and mediator can be prevented from separating from each other and agglomerated. It came to the conclusion that it is because it can mix uniformly with a mediator. Furthermore, the cause of the ability to mix the enzyme and mediator uniformly by adding phospholipids was investigated, and a very rare phenomenon in which the diffusion coefficient of the mediator reductant was significantly increased by the addition of phospholipids. discovered. That is, it was found that phospholipid functions as a mediator diffusion promoter. This phospholipid immobilization effect is particularly remarkable when the mediator is a compound having a quinone skeleton.
The above is for the negative electrode of the fuel cell, but the same effect can be obtained by adding phospholipids to any electrode other than the negative electrode of the fuel cell as long as the electrode immobilizes the enzyme and the mediator. Furthermore, although the enzyme is not immobilized, the same effect can be obtained by adding phospholipid even at least an electrode that immobilizes the mediator. In addition, the same effect can be obtained by using a phospholipid derivative or a polymer of phospholipid or a derivative thereof instead of phospholipid.
The high output agent is most generally said to improve the reaction rate at least at the electrode on which the mediator is immobilized, thereby achieving high output. A mediator diffusion promoter, most generally speaking, increases the diffusion coefficient of the mediator at least inside the electrode on which the mediator is immobilized, or maintains or increases the mediator concentration in the vicinity of the electrode. Is.
The present invention has been devised based on the above-mentioned knowledge obtained independently by the present inventors.

That is, in order to solve the above problem, the first invention
A fuel cell having a structure in which a positive electrode and a negative electrode are opposed via a proton conductor, and an enzyme and a mediator are immobilized on the negative electrode,
In addition to the enzyme and the mediator, a high-power agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the negative electrode.

The second invention is
A method for producing a fuel cell, wherein a positive electrode and a negative electrode have a structure facing each other via a proton conductor, and an enzyme and a mediator are immobilized on the negative electrode,
In addition to the enzyme and the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode.

  Here, basically any phospholipid may be used, and either glycerophospholipid or sphingophospholipid may be used. Examples of the glycerophospholipid include, but are not limited to, phosphatidic acid, phosphatidylcholine (lecithin), phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, and diphosphatidylglycerol (cardiolipin). Sphingophospholipids include, but are not limited to, sphingomyelin. The amount of the high-power agent or mediator diffusion accelerator comprising this phospholipid or derivative thereof or a polymer thereof can be appropriately selected according to the amount of immobilized enzyme and mediator, but it is extremely small. However, it is possible to obtain a high output effect or a mediator diffusion promoting effect. In order to prevent the formation of vesicles, it is preferable that the solvent used for immobilizing the high output agent or mediator diffusion accelerator composed of this phospholipid or a derivative thereof or a polymer thereof on the negative electrode is preferably used. Alcohol such as ethanol is used. One or two or more other solvents other than alcohol may be included as necessary.

  Basically, any mediator may be used, but a compound having a quinone skeleton, particularly, a compound having a naphthoquinone skeleton is preferably used. As the compound having a naphthoquinone skeleton, various naphthoquinone derivatives can be used. Specifically, for example, 2-amino-1,4-naphthoquinone (ANQ), 2-amino-3-methyl-1 2, 4-naphthoquinone (AMNQ), 2-methyl-1,4-naphthoquinone (VK3), 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ), and the like are used. As a compound having a quinone skeleton, for example, anthraquinone or a derivative thereof can be used in addition to a compound having a naphthoquinone skeleton. In addition to the compound having a quinone skeleton, the mediator may contain one or more other compounds acting as a mediator, as necessary. As a solvent used when a compound having a quinone skeleton, particularly a compound having a naphthoquinone skeleton, is immobilized on the negative electrode, acetone is preferably used. Thus, by using acetone as a solvent, the solubility of the compound having a quinone skeleton can be increased, and the compound having a quinone skeleton can be efficiently immobilized on the negative electrode. If necessary, the solvent may contain one or two or more other solvents other than acetone.

The enzyme to be immobilized on the negative electrode is selected depending on the fuel used. For example, when a monosaccharide such as glucose is used as the fuel, the enzyme contains an oxidase that promotes and decomposes the oxidation of the monosaccharide. In addition to this, coenzyme oxidase which returns the coenzyme reduced by oxidase to the oxidant is included. By the action of the coenzyme oxidase, electrons are generated when the coenzyme returns to the oxidized form, and the electrons are transferred from the coenzyme oxidase to the electrode via the mediator. For example, glucose dehydrogenase (GDH) as an oxidase, preferably NAD-dependent glucose dehydrogenase, nicotinamide adenine dinucleotide (NAD ⁺ ) as an oxidant of a coenzyme, and NADH such as diaphorase as a coenzyme oxidase Dehydrogenase is used.

  When using polysaccharides (a broadly defined polysaccharide, which refers to all carbohydrates that produce two or more monosaccharides by hydrolysis, including oligosaccharides such as disaccharides, trisaccharides, and tetrasaccharides) as fuel, Preferably, in addition to the above-mentioned oxidase, coenzyme oxidase, coenzyme and mediator, a degradation enzyme that promotes degradation such as hydrolysis of polysaccharides and produces monosaccharides such as glucose is also immobilized. Specific examples of the polysaccharide include starch, amylose, amylopectin, glycogen, cellulose, maltose, sucrose, and lactose. These are a combination of two or more monosaccharides, and any polysaccharide contains glucose as a monosaccharide of the binding unit. Note that amylose and amylopectin are components contained in starch, and starch is a mixture of amylose and amylopectin. When glucoamylase is used as a polysaccharide-degrading enzyme and glucose dehydrogenase is used as an oxidase that degrades monosaccharides, polysaccharides that can be degraded to glucose by glucoamylase, such as starch, amylose, amylopectin, glycogen As long as it contains any one of maltose, it is possible to generate electricity using this as fuel. Glucoamylase is a degrading enzyme that hydrolyzes α-glucan such as starch to produce glucose, and glucose dehydrogenase is an oxidase that oxidizes β-D-glucose to D-glucono-δ-lactone. The decomposing enzyme that decomposes the polysaccharide may also be fixed on the negative electrode, and the polysaccharide that will eventually become the fuel may also be fixed on the negative electrode.

  Further, when starch is used as fuel, it is possible to use a gelatinized fuel obtained by gelatinizing starch. In this case, the gelatinized starch can be brought into contact with the negative electrode on which the enzyme or the like is immobilized, or the enzyme and the like can be immobilized on the negative electrode. In this way, the starch concentration on the negative electrode surface can be kept higher than when starch dissolved in the solution is used, the enzymatic decomposition reaction becomes faster, the output is improved, and the fuel Since it is easier to handle than in the case of a solution, the fuel supply system can be simplified, and the fuel cell does not need to be used upside down, it is very advantageous when used in a mobile device, for example.

In one example, the negative electrode is 2-methyl-1,4-naphthoquinone (VK3) as a mediator, reduced nicotinamide adenine dinucleotide (NADH) as a coenzyme, glucose dehydrogenase and coenzyme oxidase as oxidases Of diaphorase, preferably 1.0 (mol): 0.33-1.0 (mol): (1.8-3.6) × 10 ⁶ (U): (0.85 1.7) immobilized at a ratio of × 10 ⁷ (U). However, U (unit) is an index indicating enzyme activity, and indicates the degree to which 1 μmol of substrate reacts per minute at a certain temperature and pH.

On the other hand, an enzyme may or may not be immobilized on the positive electrode. When an enzyme is immobilized on the positive electrode, this enzyme typically includes an enzyme that reduces oxygen. Examples of the enzyme that reduces oxygen include bilirubin oxidase, laccase, and ascorbate oxidase. In this case, a mediator is preferably immobilized on the positive electrode in addition to the enzyme. As the mediator, for example, potassium hexacyanoferrate is used. The mediator is preferably immobilized at a sufficiently high concentration, for example, 0.64 × 10 ⁻⁶ mol / mm ² or more on average.

  Various materials are used as the immobilization material for immobilizing an enzyme, coenzyme, mediator, phospholipid or derivative thereof or a polymer thereof, or a high output agent or mediator diffusion accelerator, on the negative electrode or the positive electrode. Preferably, a polycation or a salt thereof such as poly-L-lysine (PLL) and a polyanion or a salt thereof such as polyacrylic acid (for example, sodium polyacrylate (PAAcNa)) A polyion complex formed by using an enzyme, an enzyme, a coenzyme, an electron mediator, a high output agent, a mediator diffusion accelerator, or the like can be contained inside the polyion complex.

  As a material of the positive electrode or the negative electrode, a conventionally known material such as a carbon-based material can be used, and a skeleton composed of a porous material and a carbon-based material covering at least a part of the surface of the skeleton are mainly used. It is possible to use a porous conductive material including the material described above. This porous conductive material can be obtained by coating at least a part of the surface of the skeleton made of the porous material with a material mainly composed of a carbon-based material. The porous material constituting the skeleton of the porous conductive material may be basically any material as long as the skeleton can be stably maintained even if the porosity is high. It does not matter whether or not there is sex. As the porous material, a material having high porosity and high conductivity is preferably used. Specifically, as such a porous material having a high porosity and high conductivity, a metal material (metal or alloy), a carbon-based material with a strong skeleton (improved brittleness), or the like is used. Can do. When a metal material is used as the porous material, various options are conceivable because the metal material has different state stability depending on the usage environment such as pH and potential of the solution. For example, nickel, copper, silver, gold A foam metal such as nickel-chromium alloy and stainless steel or a foam alloy is one of the easily available materials. As the porous material, a resin material (for example, a sponge-like material) can be used in addition to the metal material and the carbon-based material. The porosity and pore diameter (minimum pore diameter) of this porous material are in balance with the thickness of the material mainly composed of a carbon-based material that is coated on the surface of the skeleton made of this porous material. Is determined according to the required porosity and pore diameter. The pore diameter of the porous material is generally 10 nm to 1 mm, typically 10 nm to 600 μm. On the other hand, it is necessary to use a material that covers the surface of the skeleton and has conductivity and is stable at an assumed operating potential. Here, a material mainly composed of a carbon-based material is used as such a material. Carbon-based materials generally have a wide potential window, and many are chemically stable. Specifically, the carbon-based material is mainly composed of a carbon-based material, and the carbon-based material is the main component, and the secondary material is selected according to the characteristics required for the porous conductive material. Some materials contain a small amount of material. Specific examples of the latter material include a material whose electrical conductivity has been improved by adding a metal or other highly conductive material to the carbon-based material, or a polytetrafluoroethylene-based material or the like added to the carbon-based material. Thus, it is a material imparted with a function other than conductivity, such as imparting surface water repellency. There are various types of carbon-based materials, but any carbon-based material may be used. In addition to carbon alone, carbon may be added with other elements. The carbon-based material is particularly preferably a fine powder carbon material having high conductivity and a high surface area. Specific examples of the carbon-based material include materials imparted with high conductivity such as KB (Ketjen Black) and functional carbon materials such as carbon nanotubes and fullerenes. As a coating method of the material mainly composed of the carbon-based material, any coating method can be used as long as the surface of the skeleton made of the porous material can be coated by using an appropriate binder as necessary. Also good. The pore diameter of the porous conductive material is selected to a size that allows a solution containing a substrate or the like to easily enter and exit through the pores, and is generally 9 nm to 1 mm, more typically 1 μm to 1 mm, and more generally Specifically, it is 1 to 600 μm. A state in which at least a part of the surface of the skeleton made of a porous material is coated with a material mainly composed of a carbon-based material, or a surface of at least a part of the skeleton made of a porous material is mainly composed of a carbon-based material In the state coated with the material, it is desirable to prevent all the holes from communicating with each other or clogging with a material mainly composed of a carbon-based material.

In the case of using an electrolyte containing a buffer substance as a proton conductor, in order to obtain a sufficient buffer capacity at the time of high output operation and to fully exhibit the ability inherent in the enzyme, It is effective that the concentration of the buffer substance contained in the electrolyte is 0.2M to 2.5M, preferably 0.2M to 2M, more preferably 0.4M to 2M, and even more preferably. 0.8M to 1.2M. Buffer substances, in general, as long as _a pK _a of 6 to 9, may it be used What Specific examples and, dihydrogen phosphate ion (H ₂ PO ₄ ^- ), 2-amino-2-hydroxymethyl-1,3-propanediol (abbreviated to Tris), 2- (N-morpholino) ethanesulfonic acid (MES), cacodylic acid, carbonic acid (H ₂ CO ₃ ), hydrogen citrate Ions, N- (2-acetamido) iminodiacetic acid (ADA), piperazine-N, N′-bis (2-ethanesulfonic acid) (PIPES), N- (2-acetamido) -2-aminoethanesulfonic acid ( ACES), 3- (N-morpholino) propanesulfonic acid (MOPS), N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES), N-2-hydroxyethylpiperazine- '-3-propanesulfonic acid (HEPPS), N- [tris (hydroxymethyl) methyl] glycine (abbreviation tricine), glycylglycine, N, N-bis (2-hydroxyethyl) glycine (abbreviation bicine), etc. . Examples of the substance that generates dihydrogen phosphate ions (H ₂ PO ₄ ⁻ ) include sodium dihydrogen phosphate (NaH ₂ PO ₄ ) and potassium dihydrogen phosphate (KH ₂ PO ₄ ). The pH of the electrolyte containing the buffer substance is preferably around 7, but may generally be any of 1-14.

  This fuel cell can be used for almost anything that requires electric power, and can be of any size. For example, electronic devices, mobile objects (automobiles, motorcycles, aircraft, rockets, spacecrafts, etc.), power devices, construction machinery It can be used for machine tools, power generation systems, cogeneration systems, etc. The output, size, shape, type of fuel, etc. are determined depending on the application. When this fuel cell is used in a power generation system or a cogeneration system, as a fuel, in addition to monosaccharides and polysaccharides themselves, garbage containing polysaccharides may be used.

The third invention is
A negative electrode for a fuel cell in which an enzyme and a mediator are immobilized,
In addition to the enzyme and the mediator, a high-power agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the negative electrode.

The fourth invention is:
A method for producing a negative electrode for a fuel cell in which an enzyme and a mediator are immobilized,
In addition to the enzyme and the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode.
In the third and fourth inventions, what has been described in relation to the first and second inventions is valid as long as it is not contrary to the nature thereof.

The fifth invention is:
In an electronic device using one or more fuel cells,
At least one of the fuel cells is
A fuel cell having a structure in which a positive electrode and a negative electrode are opposed via a proton conductor, and an enzyme and a mediator are immobilized on the negative electrode,
In addition to the enzyme and the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid or a derivative thereof or a polymer thereof is immobilized on the negative electrode.
This electronic device may basically be any type, and includes both portable and stationary types. Specific examples include cell phones, mobile devices, robots, personal computers, and the like. Computers, game devices, in-vehicle devices, home appliances, industrial products, etc.

The sixth invention is:
An electrode reaction utilization device having an electrode on which at least a mediator is immobilized,
In addition to the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the electrode.

The seventh invention
A method for producing an electrode reaction utilization device having an electrode having at least a mediator immobilized thereon,
In addition to the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the electrode.

In the sixth and seventh inventions, in the electrode reaction utilization apparatus, in addition to the enzyme reaction utilization apparatus having the electrode on which the enzyme and the mediator are immobilized, the mediator is immobilized, but the enzyme is not immobilized. Therefore, the thing which does not utilize an enzyme reaction is also included. The enzyme reaction utilization device includes various devices utilizing an enzyme reaction, and specifically includes a fuel cell, a biosensor, a bioreactor, and the like.
In the sixth and seventh inventions, what has been described in relation to the first and second inventions holds true for matters other than those described above, unless they are contrary to the nature thereof.

The eighth invention
An electrode for an electrode reaction utilization device having at least a mediator immobilized thereon,
In addition to the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the electrode.

The ninth invention
A method for producing an electrode for an electrode reaction utilization device in which at least a mediator is immobilized,
In addition to the mediator, a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the electrode.
In the eighth and ninth inventions, what has been described in relation to the first, second, sixth, and seventh inventions holds true for matters other than those described above, unless they are contrary to their properties.

The tenth invention is
A high-power agent characterized by comprising a phospholipid or a derivative thereof or a polymer thereof.
The eleventh invention is
A mediator diffusion promoter characterized by comprising a phospholipid or a derivative thereof or a polymer thereof.
In the tenth and eleventh inventions, what has been described in relation to the first and second inventions is valid as long as the nature is not contrary.

  In the present invention configured as described above, by immobilizing a negative electrode or an electrode with a high-output agent or mediator diffusion accelerator composed of a phospholipid or a derivative thereof or a polymer thereof in addition to an enzyme and a mediator, The diffusion coefficient of the mediator reductant can be greatly increased, the enzyme and the mediator can be prevented from separating and aggregating with each other, the enzyme and the mediator can be mixed uniformly, and consequently High output can be achieved.

According to the present invention, the enzyme immobilized on the negative electrode and the mediator can be mixed uniformly, etc., so that the function of the mediator can be sufficiently exhibited, and more electrons can be supplied to the negative electrode. The output of the fuel cell can be increased. By using a fuel cell capable of increasing the output in this way, a high-performance electronic device, a moving body, a power generation system, a cogeneration system, and the like can be realized.
In addition, since the enzyme immobilized on the electrode and the mediator can be uniformly mixed, it is possible to increase the output of an electrode reaction utilization device such as an enzyme reaction utilization device.
Furthermore, even when the enzyme is not immobilized on the electrode, the output of the electrode reaction utilization apparatus can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a biofuel cell according to a first embodiment of the present invention. In this biofuel cell, glucose is used as the fuel. FIG. 2 schematically shows details of the configuration of the negative electrode of the biofuel cell, an example of an enzyme group immobilized on the negative electrode, and an electron transfer reaction by the enzyme group.
As shown in FIG. 1, this biofuel cell has a structure in which a negative electrode 1 and a positive electrode 2 face each other with a proton conductor 3 interposed therebetween. The negative electrode 1 decomposes glucose supplied as fuel with an enzyme to extract electrons and generate protons (H ⁺ ). The positive electrode 2 generates water from protons transported from the negative electrode 1 through the proton conductor 3, electrons sent from the negative electrode 1 through an external circuit, and oxygen in the air, for example.

The negative electrode 1 is composed of, for example, an electrode 11 (see FIG. 2) made of porous carbon or the like, an enzyme involved in glucose decomposition, and a coenzyme in which a reductant is generated in an oxidation reaction in the glucose decomposition process (for example, , NAD ⁺ ), a coenzyme oxidase (eg, diaphorase) that oxidizes a reduced form of the coenzyme (eg, NADH), and an electron generated from the coenzyme oxidase accompanying the oxidation of the coenzyme. A mediator (for example, ANQ, AMNQ, or VK3) to be passed, and a phospholipid or a derivative thereof (for example, DMPC) or a polymer thereof as a high-power agent or a mediator diffusion promoter, is used as an immobilizing material (not shown) ( For example, a polycation such as poly-L-lysine (PLL) and a polyanion such as sodium polyacrylate (PAAcNa)) Is constructed immobilized by a polyion complex) formed by using.

As an enzyme involved in the degradation of glucose, for example, glucose dehydrogenase (GDH), preferably NAD-dependent glucose dehydrogenase can be used. In the presence of this oxidase, for example, β-D-glucose can be oxidized to D-glucono-δ-lactone.
Furthermore, this D-glucono-δ-lactone can be decomposed into 2-keto-6-phospho-D-gluconate by the presence of two enzymes, gluconokinase and phosphogluconate dehydrogenase (PhGDH). Can do. That is, D-glucono-δ-lactone is converted to D-gluconate by hydrolysis, and D-gluconate is converted to adenosine triphosphate (ATP) and adenosine diphosphate (ADP) in the presence of gluconokinase. And then phosphorylated to 6-phospho-D-gluconate. This 6-phospho-D-gluconate is oxidized to 2-keto-6-phospho-D-gluconate by the action of the oxidase PhGDH.

In addition to the above decomposition process, glucose can also be decomposed to CO ₂ by utilizing sugar metabolism. The decomposition process utilizing sugar metabolism is roughly divided into glucose decomposition and pyruvic acid generation by a glycolysis system and a TCA cycle, which are widely known reaction systems.
The oxidation reaction in the monosaccharide decomposition process is accompanied by a coenzyme reduction reaction. This coenzyme is almost determined by the acting enzyme. In the case of GDH, NAD ⁺ is used as the coenzyme. That is, when β-D-glucose is oxidized to D-glucono-δ-lactone by the action of GDH, NAD ⁺ is reduced to NADH to generate H ⁺ .

The produced NADH is immediately oxidized to NAD ⁺ in the presence of diaphorase (DI), generating two electrons and H ⁺ . Therefore, two electrons and two H ⁺ are generated by one-step oxidation reaction per glucose molecule. In the two-stage oxidation reaction, a total of four electrons and four H ⁺ are generated.
Electrons generated in the above process are transferred from diaphorase to the electrode 11 through the mediator, and H ⁺ is transported to the positive electrode 2 through the proton conductor 3.

The above enzymes, coenzymes and mediators are optimal for the enzyme by using a buffer solution such as a phosphate buffer solution or a Tris buffer solution contained in the proton conductor 3 so that the electrode reaction can be carried out efficiently and constantly. It is preferably maintained at a low pH, for example, around pH 7. As the phosphate buffer, for example, NaH ₂ PO ₄ or KH ₂ PO ₄ is used. Further, the ionic strength (IS) is too large or too small to adversely affect the enzyme activity, but considering the electrochemical response, it should be an appropriate ionic strength, for example, about 0.3. Is preferred. However, pH and ionic strength have optimum values for each enzyme used, and are not limited to the values described above.

In FIG. 2, for example, glucose dehydrogenase (GDH) is an enzyme involved in the degradation of glucose, NAD ⁺ is a coenzyme that produces a reductant in the oxidation reaction in the glucose degradation process, and a reductant of coenzyme. The case where the coenzyme oxidase that oxidizes certain NADH is diaphorase (DI), and the electron mediator that receives electrons generated from the coenzyme oxidase accompanying the oxidation of the coenzyme and passes it to the electrode 11 is VK3.

The positive electrode 2 is made of, for example, carbon powder on which a catalyst is supported or catalyst particles that are not held by carbon. As the catalyst, for example, platinum (Pt) fine particles, or fine particles of transition metal such as iron (Fe), nickel (Ni), cobalt (Co) or ruthenium (Ru) and platinum, or oxide fine particles are used. It is done. For example, the positive electrode 2 is formed in a structure in which a catalyst layer made of a catalyst or a carbon powder containing a catalyst and a gas diffusion layer made of a porous carbon material are laminated in order from the proton conductor 3 side. The positive electrode 2 is not limited to this configuration, and oxygen reductase can also be used as a catalyst. In this case, it is preferably used in combination with a mediator that transfers electrons to and from the electrode.
In the positive electrode 2, in the presence of a catalyst, oxygen in the air is reduced by H ⁺ from the proton conductor 3 and electrons from the negative electrode 1 to generate water.

The proton conductor 3 is for transporting H ⁺ generated in the negative electrode 1 to the positive electrode 2 and is made of a material that does not have electron conductivity and can transport H ⁺ . Specific examples of the proton conductor 3 include a perfluorocarbon sulfonic acid (PFS) resin film, a copolymer film of a trifluorostyrene derivative, a polybenzimidazole film impregnated with phosphoric acid, and an aromatic polyether. Examples thereof include a ketone sulfonic acid film, PSSA-PVA (polystyrene sulfonate polyvinyl alcohol copolymer) and PSSA-EVOH (polystyrene sulfonate ethylene vinyl alcohol copolymer). Among these, those made of an ion exchange resin having a fluorine-containing carbon sulfonic acid group are preferable, and specifically, Nafion (trade name, DuPont, USA) is used.

In the biofuel cell configured as described above, when glucose is supplied to the negative electrode 1, the glucose is decomposed by a degrading enzyme containing an oxidase. Since oxidase is involved in the monosaccharide decomposition process, electrons and H ⁺ can be generated on the negative electrode 1 side, and a current can be generated between the negative electrode 1 and the positive electrode 2.
According to the first embodiment, on the electrode 11 of the negative electrode 1, an enzyme involved in the decomposition of glucose, a coenzyme in which a reductant is generated by an oxidation reaction in the glucose decomposition process, and a reduced form of the coenzyme In addition to the coenzyme oxidase and mediator that oxidize phospholipids, derivatives thereof or polymers thereof as a high-power agent or mediator diffusion promoter, for example, in or near the electrode 11 The mediator is greatly facilitated to diffuse, the above-mentioned enzyme, coenzyme, coenzyme oxidase and mediator can be mixed uniformly, and thus the mediator concentration in the vicinity of the electrode 11 can be maintained or increased, The function of the mediator can be fully exerted, more electrons can be supplied to the electrode 11, and finally the buffer can be supplied. It is possible to significantly higher output of the biofuel cell.

Next, the results of an experiment conducted to evaluate the function of the high output agent or mediator diffusion accelerator in the immobilized electrode of the enzyme / coenzyme / mediator / high output agent or mediator diffusion accelerator used as the negative electrode 1 will be described. To do.
FIG. 3 shows an electrochemical measurement system used for electrochemical measurement at the single electrode of the enzyme / coenzyme / mediator / high output agent or mediator diffusion promoter-immobilized electrode used as the negative electrode 1. As shown in FIG. 3, a measurement solution 22 was placed in a container 21, and a working electrode 23, a counter electrode 24, and a reference electrode 25 were immersed in the measurement solution 22, and an electrochemical measurement device 26 was connected thereto. A buffer solution (0.1 M NaH ₂ PO ₄ —NaOH—NaCl, IS = 0.3, pH 7) was used as the measurement solution 22. The working electrode 23 includes a glassy carbon disk electrode (3 mmφ, 0.071 cm ² ), ANQ as a mediator, diaphorase (DI), NADH, glucose dehydrogenase (GDH), and DMPC as a high output agent or a mediator diffusion accelerator. A polyion complex formed using poly-L-lysine (PLL) and sodium polyacrylate (PAAcNa) was used as an immobilizing material. The counter electrode 24 is Pt wire, and the reference electrode 25 is Ag | AgCl. The measurement was performed under atmospheric pressure, and the measurement temperature was 25 ° C. The amount of the measurement solution 22 was 1 ml, and deoxygenation was performed by sufficiently bubbling by sending Ar gas into the measurement solution 22 by a bubbler 27 before measurement. FIG. 4 shows the structural formula of DMPC.

[Comparative Example 1]
An enzyme / coenzyme / mediator-immobilized electrode in which a high output agent or a mediator diffusion accelerator was not immobilized was prepared as follows.
Solution preparation First, various solutions were prepared as follows. As the buffer solution, the same one as that used as the measurement solution 22 was used.
・ GDH / DI / NADH enzyme ・ Coenzyme buffer solution ((1))
10 mg of diaphorase (DI) (EC 1.6.99.-, manufactured by Amano Enzyme, DH “Amano” 3) was weighed and dissolved in 200 μl of a buffer solution ((1) ′). The buffer solution for dissolving the enzyme is preferably refrigerated at 8 ° C. or less until immediately before, and the enzyme buffer solution is preferably refrigerated at 8 ° C. or less as much as possible.
13.8 mg of glucose dehydrogenase (GDH) (NAD-dependent, EC 1.1.1.47, Amano Enzyme, GDH-2) was weighed and dissolved in 180 μl of a buffer solution. To this, 20 μl of the above solution (1) ′ was added and mixed well to finally make 200 μl of GDH / DI = 4.2 / 20 U / μl solution.
-NADH buffer solution ((2))
64 mg of NADH (manufactured by Sigma-Aldrich, N-8129) was weighed and dissolved in 0.1 ml of a buffer solution (640 μg / μl).
・ PLL aqueous solution ((3))
An appropriate amount of poly-L-lysine hydrobromide (PLL) (manufactured by Sigma-Aldrich, P-2174) was weighed and dissolved in deionized water to 2 wt%.
・ ANQ acetone solution ((4))
10 mg of 2-amino-1,4-naphthoquinone (ANQ) was weighed and dissolved in 964 μl of an acetone solution to give 60 mM.
-PAAcNa aqueous solution ((5))
Sodium polyacrylate (PAAcNa) (manufactured by Sigma-Aldrich, 41,604-5) was weighed in an appropriate amount and prepared by adding deionized water to 0.022 wt%.

Preparation of Immobilized Membrane The various solutions prepared as described above were applied in the following order in the following order on the surface of a glassy carbon disk electrode (manufactured by BAS, 002012, 3 mmφ, 0.071 cm ² ). After being dropped and mixed with the solution, drying was appropriately performed at room temperature or 40 ° C. or lower to prepare an enzyme / coenzyme / electron mediator immobilized electrode.
GDH / DI enzyme buffer solution ((1)): 8 μl
NADH buffer solution (2): 2 μl
PLL aqueous solution ((3)): 10 μl
ANQ acetone solution ((4)): 18.7 μl
PAAcNa aqueous solution ((5)): 12 μl
The enzyme / coenzyme / electron mediator immobilized electrode produced with this composition was named ANQE4.

[Example 1]
An enzyme / coenzyme / mediator / mediator diffusion promoter-immobilized electrode was prepared as follows.
Solution preparation Various solutions were prepared as follows. As the buffer solution, the same one as that used as the measurement solution 22 was used.
DMPC ethanol solution (6)
1 mg of dimyristoylphosphatidylcholine (DMPC) (manufactured by Wako Pure Chemical Industries, 163-12771) was dissolved in 1 ml of ethanol to obtain a 0.1% (w / v) ethanol solution.
GDH / DI enzyme buffer solution ((1)), NADH buffer solution ((2)), PLL aqueous solution ((3)), ANQ acetone solution (4), and PAAcNa aqueous solution ((5)) were the same as in Comparative Example 1. Prepared.

Preparation of Immobilized Membrane The various solutions prepared as described above were applied in the following order in the following order on the surface of a glassy carbon disk electrode (manufactured by BAS, 002012, 3 mmφ, 0.071 cm ² ). Then, the solution was dried at room temperature or 40 ° C. or lower as appropriate to prepare an enzyme / coenzyme / mediator / high output agent or mediator diffusion accelerator-immobilized electrode.
GDH / DI enzyme buffer solution ((1)): 8 μl
NADH buffer solution ((2)): 2 μl
PLL aqueous solution ((3)): 10 μl
ANQ acetone solution ((4)): 18.7 μl
PAAcNa aqueous solution ((5)): 12 μl
DMPC ethanol solution (6): 10 μl
That is, this composition is ANQE4 + DMPC.

The ANQE4 immobilized electrode and the ANQE4 + DMPC immobilized electrode prepared as described above were subjected to chronoamperometry at 0.1 V for 1 hour with respect to the reference electrode Ag | AgCl in the measurement solution 22, and then the potential − Cyclic voltammetry (CV) between 0.6 and +0.6 V was performed twice at a scan speed of 10 mV / s. Measurement was performed by immersing each electrode in a buffer solution containing 400 mM glucose (Solartron Multistat 1480 was used for measurement). The measurement results are shown in FIGS.
From the result of the constant potential measurement of FIG. 5A, Example 1 (ANQE4 + DMPC fixed electrode) is about 2.8 times after 5 minutes (300 seconds) in comparison with Comparative Example 1 (ANQE4 fixed electrode). After 30 minutes (1800 seconds), the ratio is about 1.8 times, and it can be said that the addition of DMPC is effective in increasing the current value. This can also be seen from the fact that the peak value is increased in the cyclic voltammetry of FIG. 5B.

[Example 2]
In order to investigate the cause of the increase in the current value due to the addition of DMPC, an electrode in which DMPC was applied to a glassy carbon disk electrode was prepared, and the diffusion coefficient of the mediator was calculated.
Electrode preparation 10 μl of DMPC ethanol solution (6) was added on the glassy carbon disk electrode surface, left at 40 ° C. for 15 minutes, and dried.
Electrochemical measurement , potential step, chronoamperometry (PSCA)
The DMPC-coated glassy carbon disk electrode is mixed with ANQ, AMNQ or VK3 (Nacalai) in a buffer solution (0.1 M NaH ₂ PO ₄ -NaOH-NaCl, IS = 0.3, pH 7) to a final concentration of 10 mM. (1) -0.4V 5 minutes → 0.4V 3 minutes (2) 0.6V in a state in which Tesque, 36405-84) is dissolved and replaced with Ar gas for 20 minutes to remove oxygen from the system as much as possible. 5 minutes-> -0.4V The constant potential measurement was performed for 3 minutes, and the electric current value was measured.
・ Cyclic voltammetry (CV)
The above DMPC-coated glassy carbon disk electrode is placed in a buffer solution (0.1 M NaH ₂ PO ₄ -NaOH-NaCl, IS = 0.3, pH 7) to a final concentration of 10 mM or 100 mM. ANQ, AMNQ, VK3 Is dissolved, Ar gas is substituted for 20 minutes, and oxygen is eliminated from the system as much as possible. Cyclic voltammetry between -0.6V and 0.6V is scanned at 50, 20, 10, 5mV / s. Two laps were made at speed.

ただし、Ｉ（ｔ）_lim は電流値（Ａ）、Ｆはファラデー定数、Ａは電極面積（ｃｍ² ）、Ｃ^* ₀ はメディエータ濃度（ｍｏｌ／ｃｍ³ ）、Ｄ₀ は拡散係数（ｃｍ／ｓ）、ｔは時間（ｓ）である。
式１より、系内が拡散律速の場合、電流値Ｉ（ｔ）_lim と時間ｔ（ｓ）の平方根の逆数との間には比例関係が成立し、その傾きから拡散係数Ｄ₀ を求めることができる。 [Comparative Example 2]
In Example 2, a glassy carbon disk electrode not coated with DMPC was prepared, and PSCA measurement and CV measurement were similarly performed on each mediator.
The Cottrell equation in PSCA is shown in Equation 1.

Where I (t) _lim is the current value (A), F is the Faraday constant, A is the electrode area (cm ² ), C ^* ₀ is the mediator concentration (mol / cm ³ ), D ₀ is the diffusion coefficient (cm / s) ), T is time (s).
From Equation 1, when the system is diffusion-controlled, a proportional relationship is established between the current value I (t) _lim and the inverse of the square root of time t (s), and the diffusion coefficient D ₀ is obtained from the slope. Can do.

ただし、Ｉ_pcはＣＶより得られた酸化・還元反応それぞれのピーク電流値（Ａ）、ｎは電子数、Ａは電極面積（ｃｍ² ）、Ｃ^* ₀ はメディエータ濃度（ｍｏｌ／ｃｍ³ ）、Ｄ₀ は拡散係数（ｃｍ² ／ｓ）、ｖはスキャン速度（Ｖ／ｓ）である。
式２もＰＳＣＡと同様に拡散律速の場合、ピーク電流値Ｉ_pc（Ａ）とスキャン速度ｖ（Ｖ／ｓ）の平行根との間には比例関係が成立するため、やはりその傾きから拡散係数を求めることができる。式１、２より得られたＡＮＱ、ＡＭＮＱ、ＶＫ３各メディエータの拡散係数の値を表１に示す。また、拡散係数の算出に用いたポテンシャルステップ・クロノアンペロメトリーおよびサイクリック・ボルタノメトリーの測定結果の一例（メディエータがＡＮＱである場合）を図６に示す。 Further, the relational expression of Expression 2 is established between the current value obtained from CV and the scan speed.

However, I _pc is the peak current value (A) of each oxidation / reduction reaction obtained from CV, n is the number of electrons, A is the electrode area (cm ² ), C ^* ₀ is the mediator concentration (mol / cm ³ ), D ₀ is the diffusion coefficient (cm ² / s), and v is the scan speed (V / s).
In the case of Formula 2 as well as PSCA, in the case of diffusion rate limiting, since a proportional relationship is established between the peak current value I _pc (A) and the parallel root of the scan speed v (V / s), the diffusion coefficient is also determined from the slope. Can be requested. Table 1 shows the diffusion coefficient values of the ANQ, AMNQ, and VK3 mediators obtained from Equations 1 and 2. FIG. 6 shows an example of measurement results of potential step chronoamperometry and cyclic voltammetry used for calculating the diffusion coefficient (when the mediator is ANQ).

From the above results, it was found that the diffusion coefficient of the reductant of each mediator was increased by the addition of DMPC. A possible reason for this is that a more hydrophilic mediator reductant is likely to diffuse due to the presence of DMPC on the electrode surface. This is considered to be one of the causes of the current value increase in the electrode obtained in Example 1.
FIG. 7 shows the results of observing the enzyme (GDH, DI) and mediator (ANQ) immobilized on the ANQE4 electrode with a confocal microscope (Olympus Fluoview FV1000 × 100 lens zoom × 1). From FIG. 7, it is observed that the enzyme and the mediator are separated from each other and aggregate, and in particular, the mediator forms a needle-like crystal and is non-uniform.
FIG. 8 shows the results of observing the enzyme (GDH, DI) and mediator (ANQ) immobilized on the ANQE4 + DMPC electrode in the same manner as described above. From FIG. 8, the needle-like crystal composed of the mediator is not observed, and it is observed that the enzyme and the mediator are uniformly mixed with each other. This result confirms that the addition of DMPC facilitates diffusion of the mediator reductant.

Next, a specific structural example of the biofuel cell will be described.
As shown in FIGS. 9A and 9B, this biofuel cell has an enzyme, a coenzyme, a mediator, and a high output agent or a mediator diffusion accelerator on a carbon felt (for example, an area of 0.25 cm ² ). Enzymes and mediators are immobilized on the negative electrode 1 composed of the carbon electrode immobilized with the enzyme / coenzyme / mediator / high-power agent or mediator diffusion accelerator immobilized on the surface and, for example, carbon felt (for example, area 0.25 cm ² ). The positive electrode 2 composed of an enzyme / mediator-immobilized carbon electrode immobilized with a chemical material is opposed to the proton conductor 3 via a proton conductor 3. In this case, Ti current collectors 31 and 32 are placed under the positive electrode 2 and the negative electrode 1, respectively, so that current collection can be performed easily. Reference numerals 33 and 34 denote fixed plates. The fixing plates 33 and 34 are fastened to each other by screws 35, and the positive electrode 2, the negative electrode 1, the proton conductor 3, and the Ti current collectors 33 and 34 are sandwiched between them. One surface (outer surface) of the fixing plate 33 is provided with a circular recess 33a for taking in air, and a plurality of holes 33b penetrating to the other surface are provided on the bottom surface of the recess 33a. These holes 33 b serve as air supply paths to the positive electrode 2. On the other hand, a circular recess 34a for fuel loading is provided on one surface (outer surface) of the fixed plate 34, and a number of holes 34b penetrating to the other surface are provided on the bottom surface of the recess 34a. These holes 34 b serve as fuel supply paths to the negative electrode 1. A spacer 36 is provided on the periphery of the other surface of the fixing plate 34, and when the fixing plates 33 and 34 are fastened to each other with screws 35, the interval between them becomes a predetermined interval. .
As shown in FIG. 9B, a load 37 is connected between the Ti current collectors 31, 32, and power is generated by, for example, putting a glucose solution as a fuel in the recess 34 a of the fixed plate 34.

Next explained is a biofuel cell according to the second embodiment of the invention.
The biofuel cell according to the second embodiment is the same as the biofuel cell according to the first embodiment except that a porous conductive material as shown in FIG. 10 is used as the material of the electrode 11 of the negative electrode 1. It has a configuration.
FIG. 10A schematically shows the structure of the porous conductive material, and FIG. 10B is a cross-sectional view of the skeleton of the porous conductive material. As shown in FIGS. 10A and 10B, this porous conductive material includes a skeleton 41 made of a porous material having a three-dimensional network structure, and a carbon-based material 42 covering the surface of the skeleton 41. This porous conductive material has a three-dimensional network structure in which a large number of holes 43 surrounded by the carbon-based material 42 correspond to a network. In this case, these holes 43 communicate with each other. The form of the carbon-based material 42 is not limited and may be any of a fibrous shape (needle shape) and a granular shape.

As the skeleton 41 made of a porous material, a foam metal or a foam alloy such as nickel foam is used. The porosity of the skeleton 41 is generally 85% or more, more typically 90% or more, and the pore diameter is typically, for example, 10 nm to 1 mm, more typically 10 nm to 600 μm, and more generally 1 to 600 μm, typically 50 to 300 μm, more typically 100 to 250 μm. The carbon material 42 is preferably a highly conductive material such as ketjen black, but a functional carbon material such as carbon nanotube or fullerene may be used.
The porosity of the porous conductive material is generally 80% or more, more typically 90% or more, and the diameter of the hole 43 is typically, for example, 9 nm to 1 mm, more generally 9 nm to It is 600 μm, more generally 1 to 600 μm, typically 30 to 400 μm, more typically 80 to 230 μm.

Next, a method for producing this porous conductive material will be described.
As shown in FIG. 11A, first, a skeleton 41 made of a foam metal or a foam alloy (for example, foam nickel) is prepared.
Next, as shown in FIG. 11B, a carbon-based material 42 is coated on the surface of the skeleton 41 made of the foam metal or foam alloy. As this coating method, a conventionally known method can be used. For example, the carbon-based material 42 is coated by spraying an emulsion containing carbon powder, an appropriate binder, or the like onto the surface of the skeleton 41 by spraying. The coating thickness of the carbon-based material 42 is determined according to the porosity and the pore diameter required for the porous conductive material in consideration of the porosity and the pore diameter of the skeleton 41 made of the foam metal or foam alloy. In this coating, a large number of holes 43 surrounded by the carbon-based material 42 are communicated with each other.
In this way, the target porous conductive material is manufactured.

  According to the second embodiment, the porous conductive material obtained by coating the surface of the skeleton 41 made of foam metal or foam alloy with the carbon-based material 42 has a sufficiently large diameter of the holes 43 and a rough three-dimensional network shape. While having a structure, it has high strength and high conductivity, and a necessary and sufficient surface area can be obtained. Therefore, the electrode 11 is formed using the porous conductive material, and the enzyme / coenzyme / mediator / obtained by immobilizing an enzyme, a coenzyme, a mediator, and a high-power agent or a mediator diffusion promoter on the electrode 11. The negative electrode 1 composed of a high-output agent or a mediator diffusion accelerator-immobilized electrode can cause the enzyme metabolism reaction on the electrode 1 to be performed with high efficiency, or can efficiently perform the enzyme reaction phenomenon occurring in the vicinity of the electrode 11. It can be well understood as an electric signal, and is stable regardless of the use environment, and a high-performance biofuel cell can be realized.

Next explained is a biofuel cell according to the third embodiment of the invention.
In the biofuel cell according to the third embodiment, the proton conductor 3 is composed of an electrolyte layer containing a buffer solution such as a phosphate buffer solution or a Tris buffer solution, and at least the enzyme immobilized on the negative electrode 1 and the positive electrode 2 is used. The surrounding electrolyte layer has a buffer solution of 0.2M to 2.5M, preferably 0.2M to 2M, more preferably 0.4M to 2M, and even more preferably 0.8M to 1.2M. The following concentrations are included. In this way, a high buffer capacity can be obtained, and even at the time of high output operation of the biofuel cell, it can be maintained at an optimum pH for the enzyme, for example, near pH 7, so that the original ability of the enzyme can be fully exhibited. be able to. As the phosphate buffer, for example, NaH ₂ PO ₄ or KH ₂ PO ₄ is used.
Other than the above are the same as in the first embodiment.

  As described above, according to the third embodiment, the concentration of the buffer substance (buffer solution) contained in the electrolyte layer constituting the proton conductor 3 is not less than 0.2M and not more than 2.5M. Therefore, the pH of the electrolyte layer around the enzyme immobilized on the positive electrode 2 and the negative electrode 1 can be maintained near the optimum pH even when the biofuel cell is operated at high power. And the ability of the enzyme can be fully demonstrated. Thereby, a high-performance biofuel cell capable of high output operation can be realized.

Next explained is a biofuel cell according to the fourth embodiment of the invention.
In this biofuel cell, starch, which is a polysaccharide, is used as a fuel. In addition, with the use of starch as fuel, glucoamylase, which is a degrading enzyme that decomposes starch into glucose, is also immobilized on the negative electrode 11.
In this biofuel cell, when starch is supplied as fuel to the negative electrode 1 side, this starch is hydrolyzed into glucose by glucoamylase, and this glucose is further decomposed by glucose dehydrogenase, accompanied by an oxidation reaction in this decomposition process. NAD ⁺ is reduced to produce NADH, which is oxidized by diaphorase and separated into two electrons, NAD ⁺ and H ⁺ . Therefore, two electrons and two H ⁺ are generated by one-step oxidation reaction per molecule of glucose. In the two-stage oxidation reaction, a total of 4 electrons and 4 H ⁺ are generated. The generated electrons are transferred to the electrode 11 a of the negative electrode 1, and H ⁺ moves to the positive electrode 2 through the proton conductor 3. In the positive electrode 2, this H ⁺ reacts with oxygen supplied from the outside and electrons sent from the negative electrode 1 through an external circuit to generate H ₂ O.
Other than the above, the biofuel cell according to the first embodiment is the same.
According to the fourth embodiment, the same advantages as in the first embodiment can be obtained, and the amount of power generation can be increased by using starch as the fuel, compared with the case where glucose is used as the fuel. The advantage that it can be obtained.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
For example, the numerical values, structures, configurations, shapes, materials, and the like given in the above-described embodiments are merely examples, and different numerical values, structures, configurations, shapes, materials, and the like may be used as necessary.

1 is a schematic diagram showing a biofuel cell according to a first embodiment of the present invention. It is a basic diagram which shows typically the detail of a structure of the negative electrode of the biofuel cell by 1st Embodiment of this invention, an example of the enzyme group fix | immobilized by this negative electrode, and the electron transfer reaction by this enzyme group. 1 shows a measurement system used for electrochemical measurement of a single electrode of an enzyme / coenzyme / mediator / high power agent or mediator diffusion promoter immobilized electrode used for a negative electrode in a biofuel cell according to the first embodiment of the present invention. FIG. It is a basic diagram which shows the chemical structure of DMPC which is an example of the high output agent or mediator diffusion promoter immobilized on the negative electrode in the biofuel cell according to the first embodiment of the present invention. Chronoamperometry obtained by electrochemical measurement at a single electrode of an enzyme / coenzyme / mediator / high power agent or mediator diffusion promoter immobilized electrode used as a negative electrode in the biofuel cell according to the first embodiment of the present invention It is a basic diagram which shows the measurement result of this, and the measurement result of cyclic voltammetry. Cyclic volta obtained by electrochemical measurement at a single electrode of an enzyme / coenzyme / mediator / high power agent or mediator diffusion promoter immobilized electrode used as a negative electrode in the biofuel cell according to the first embodiment of the present invention It is a basic diagram which shows the measurement result of Nometry. 6 is a drawing-substituting photograph showing the observation result of the enzyme / coenzyme / mediator immobilized electrode according to Comparative Example 1 using a confocal microscope. FIG. 3 is a drawing-substituting photograph showing the observation result of the enzyme / coenzyme / mediator / high-power agent or mediator diffusion promoter immobilized electrode according to Example 1 using a confocal microscope. 1 is a cross-sectional view and a schematic diagram illustrating a specific configuration example of a biofuel cell according to a first embodiment of the present invention. It is a basic diagram and sectional drawing for demonstrating the structure of the porous electrically conductive material used for the electrode material of a negative electrode in the biofuel cell by the 2nd Embodiment of this invention. It is a basic diagram for demonstrating the manufacturing method of the porous electroconductive material used for the electrode material of a negative electrode in the biofuel cell by the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Negative electrode, 2 ... Positive electrode, 3 ... Proton conductor, 11 ... Electrode, 31, 32 ... Ti current collector, 33, 34 ... Fixing plate, 37 ... Load, 41 ... Skeleton, 42 ... Carbon material, 43 ... Hole

Claims (18)

A fuel cell having a structure in which a positive electrode and a negative electrode are opposed via a proton conductor, and an enzyme and a mediator are immobilized on the negative electrode,
A fuel cell, wherein a high output agent or a mediator diffusion accelerator comprising a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode in addition to the enzyme and the mediator.   2. The fuel cell according to claim 1, wherein the mediator is a compound having a quinone skeleton.   The fuel cell according to claim 1, wherein the enzyme includes an oxidase immobilized on the negative electrode, which promotes and decomposes monosaccharides.   4. The enzyme according to claim 3, wherein the enzyme includes a coenzyme oxidase that returns a coenzyme reduced by oxidation of the monosaccharide to an oxidant and passes electrons to the negative electrode through the mediator. Fuel cell. The fuel cell according to claim 4, wherein the oxidant of the coenzyme is NAD ⁺ and the coenzyme oxidase is NADH dehydrogenase.   4. The fuel cell according to claim 3, wherein the oxidase is glucose dehydrogenase.   2. The enzyme according to claim 1, wherein the enzyme comprises a degrading enzyme immobilized on the negative electrode for promoting the degradation of the polysaccharide to produce a monosaccharide and an oxidase for promoting the oxidation of the produced monosaccharide for decomposing. The fuel cell as described.   8. The fuel cell according to claim 7, wherein the degrading enzyme is glucoamylase and the oxidase is glucose dehydrogenase. A method for producing a fuel cell, wherein a positive electrode and a negative electrode have a structure facing each other via a proton conductor, and an enzyme and a mediator are immobilized on the negative electrode,
A method for producing a fuel cell, wherein a high output agent or a mediator diffusion accelerator comprising a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode in addition to the enzyme and the mediator. A negative electrode for a fuel cell in which an enzyme and a mediator are immobilized,
A negative electrode for a fuel cell, wherein a high output agent or a mediator diffusion accelerator comprising a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode in addition to the enzyme and the mediator. A method for producing a negative electrode for a fuel cell in which an enzyme and a mediator are immobilized,
Production of a negative electrode for a fuel cell, wherein a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode in addition to the enzyme and the mediator Method. In an electronic device using one or more fuel cells,
At least one of the fuel cells is
A fuel cell having a structure in which a positive electrode and a negative electrode are opposed via a proton conductor, and an enzyme and a mediator are immobilized on the negative electrode,
An electronic device, wherein a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof or a polymer thereof is immobilized on the negative electrode in addition to the enzyme and the mediator. An electrode reaction utilization device having an electrode on which at least a mediator is immobilized,
An electrode reaction utilization apparatus, wherein a high output agent or a mediator diffusion accelerator comprising a phospholipid, a derivative thereof or a polymer thereof is immobilized on the electrode in addition to the mediator. A method for producing an electrode reaction utilization device having an electrode having at least a mediator immobilized thereon,
A method for producing an electrode reaction utilization apparatus, wherein a high output agent or a mediator diffusion accelerator comprising a phospholipid, a derivative thereof or a polymer thereof is immobilized on the electrode in addition to the mediator. An electrode for an electrode reaction utilization device having at least a mediator immobilized thereon,
An electrode for an electrode reaction utilization device, wherein a high output agent or a mediator diffusion accelerator composed of a phospholipid, a derivative thereof, or a polymer thereof is immobilized on the electrode in addition to the mediator. A method for producing an electrode for an electrode reaction utilization device in which at least a mediator is immobilized,
A method for producing an electrode for an electrode reaction utilization device, wherein a high output agent or a mediator diffusion accelerator comprising a phospholipid, a derivative thereof or a polymer thereof is immobilized on the electrode in addition to the mediator .   A high-power agent comprising a phospholipid or a derivative thereof or a polymer thereof. A mediator diffusion promoter characterized by comprising a phospholipid or a derivative thereof or a polymer thereof.

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