JP2008034122A - Biological fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological fuel cell superior in diffusion performance of a base material in an electrolytic solution and capable of taking out a large current. <P>SOLUTION: The biological fuel cell has a half-cell structure which comprises a conductive substrate connected to the outside circuit, an oxidation reduction enzyme capable of electron transmission between the conductive substrate, and an electrolytic solution containing a base material of the oxidation reduction enzyme at least at one of the anode side and cathode side. At least one of the half-cell structure is provided with a base material diffusion mechanism to promote diffusion of the base material to the direction of the conductive substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biofuel cell.

Enzymes are used in analysis for measuring the abundance of various substances due to their high substrate specificity, such as enzyme sensors. As an enzyme sensor using an enzyme, for example, there is a sensor that measures a current generated by an oxidation-reduction reaction between a target substance (substrate) to be analyzed and an enzyme, and quantifies the target substance. Specifically, there is a glucose sensor that utilizes the fact that an electric current generated with an oxidation-reduction reaction between an enzyme that oxidizes glucose and glucose is proportional to the glucose concentration.
Furthermore, recently, it is also expected as a new catalyst for fuel cells that replaces metal catalysts such as platinum, and research and development of biofuel cells that take the substrate of oxidoreductase as fuel and extract electrons by the oxidation reaction of the substrate has been promoted. ing.

For example, Patent Document 1 discloses, in a fuel cell that extracts electrons by an oxidation reaction of glucose, glucose dehydrogenase, nicotinamide adenine diureotide, diaphorase, and an electrochemical mediator serving as an electron transfer medium between the diaphorase and an electrode. A fuel cell characterized in that it contains at least is described.
Further, Patent Document 2 is a battery having an enzyme, a substrate (fuel), and an electrode, in which electron transfer between them is used for power generation, in which the cathode and a specific mediator are immobilized. A biofuel cell is described which is characterized by comprising:

JP 2003-282124 A JP 2005-79001 A

  On the anode side of a biofuel cell containing a fuel oxidation type oxidoreductase, electrons extracted from the fuel (substrate) by the oxidoreductase are directly from the oxidoreductase, or another oxidoreductase or other electrons. It is transmitted to the anode electrode via a transmission mediator (electron mediator) or the like. On the other hand, on the cathode side of a biofuel cell containing an oxidant-reducing type oxidoreductase, electrons that have moved from the anode electrode to the cathode electrode through an external circuit directly to the oxidoreductase that reduces the oxidant (substrate). Alternatively, it is transmitted to an oxidoreductase that reduces the oxidant via another oxidoreductase or other electron transfer mediator, and further transmitted from the oxidoreductase to the oxidant.

  The oxidoreductase is dispersed in the electrolyte together with the substrate (fuel or oxidant), or is immobilized on the electrode surface made of a conductor (fuel oxidation type oxidoreductase is immobilized on the anode electrode surface or the cathode. There is also an oxidant reducing type oxidoreductase immobilized on the electrode surface). Regardless of the dispersion type or the fixed type, the fuel oxidation type redox enzyme present near the anode electrode or the oxidant reduction type redox enzyme present near the cathode electrode is excellent in electron transfer between the electrode and the fuel. The oxidation reaction or the reduction reaction of the oxidizing agent proceeds smoothly.

Accordingly, the oxidation-reduction reaction of the substrate by the oxidoreductase (fuel oxidation reaction or oxidant reduction reaction) proceeds actively in the vicinity of the electrode, and the fuel concentration decreases in the vicinity of the anode electrode where the fuel is consumed. In the vicinity of the consumed cathode electrode, the oxidant concentration decreases. At this time, if the fuel or the oxidant is not smoothly diffused in the vicinity of the electrode, the oxidoreductase existing in the vicinity of the electrode and capable of smooth electron transfer with the electrode does not work effectively.
However, in the conventional biofuel cell such as the biofuel cell described in Patent Document 1 and Patent Document 2, the diffusivity in the electrolyte of the substrate of the oxidoreductase, which is a fuel or an oxidant, is low, and this is an electrode reaction. The oxidation reaction of the fuel and the reduction reaction of the oxidant did not proceed efficiently and a large generated current could not be obtained.

  The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a biofuel cell that is excellent in diffusibility of a substrate in an electrolytic solution and can take out a high current.

  The biofuel cell of the present invention comprises a conductive substrate connected to an external circuit on at least one of the anode side and the cathode side, an oxidoreductase capable of transferring electrons between the conductive substrate, A biofuel cell having a half-cell structure including an electrolyte containing the oxidoreductase substrate, wherein the at least one half-cell structure diffuses the substrate in the direction of the conductive substrate. It is characterized by having a substrate diffusion mechanism to promote.

  In a biofuel cell that extracts current by oxidation and / or reduction of a substrate dispersed or dissolved in an electrolyte, the substrate oxidation reaction by the oxidoreductase present in the vicinity of the electrode is promoted by promoting the diffusion of the substrate in the vicinity of the electrode. Alternatively, since the reduction reaction proceeds smoothly, high power generation performance can be obtained.

  A specific example of the substrate diffusion mechanism is an ultrasonic transducer. By oscillating the electrolyte with an ultrasonic vibrator, diffusion of the substrate in the electrolyte is promoted, and the substrate is consumed and supplied to the oxidoreductase in the vicinity of the electrode where the substrate is consumed and the substrate concentration is reduced. Is done. As a result, since the progress of the oxidation reaction or reduction reaction of the substrate, which is an electrode reaction, is promoted, a biofuel cell exhibiting excellent battery characteristics capable of taking out a large current can be obtained.

  From the viewpoint of smooth electron transfer between the conductive substrate and the oxidoreductase, the half-cell structure includes an electron mediator that mediates electron transfer between the conductive substrate and the oxidoreductase. It is preferable to include.

  From the viewpoint of the obtained battery characteristics, the biofuel cell of the present invention has at least the half-cell structure on the anode side, and the conductivity of the fuel in which the half-cell structure is a substrate for the anode-side oxidoreductase. It is preferable to provide a substrate diffusion mechanism that promotes diffusion to the substrate. At this time, examples of the fuel include at least one selected from hydrocarbon compounds such as alcohols, aldehydes, saccharides, and ketones, and specifically, at least one selected from ethanol, methanol, and glucose. Species are preferably used.

  The biofuel cell of the present invention exhibits excellent power generation characteristics due to the substrate diffusion promoting effect, and can obtain a high power generation current.

  The biofuel cell of the present invention comprises a conductive substrate connected to an external circuit on at least one of the anode side and the cathode side, an oxidoreductase capable of transferring electrons between the conductive substrate, A biofuel cell having a half-cell structure including an electrolyte containing the oxidoreductase substrate, wherein the at least one half-cell structure diffuses the substrate in the direction of the conductive substrate. It is characterized by having a substrate diffusion mechanism to promote.

Here, an embodiment of the biofuel cell of the present invention will be described with reference to FIG.
First, an oxidoreductase such as GDH (glucose dehydrogenase) oxidizes a substrate such as glucose as a fuel and receives electrons. Next, the oxidoreductase that has received the electrons usually delivers the electrons to an electron mediator that mediates electron transfer between the oxidoreductase and the electrode, and the electrons are transferred to the conductive substrate (anode electrode) by the electron mediator. Is passed. And an electric current generate | occur | produces when an electron reaches | attains a cathode electrode through an external circuit from the electroconductive base material which is an anode electrode. Protons (H ⁺ ) generated in the above process move to the cathode electrode in the electrolyte solution without the proton conducting membrane or the proton conducting membrane. In the cathode electrode, protons that have moved through the electrolyte solution, electrons that have moved from the anode side through the external circuit, and an oxidizing agent (cathode side substrate) such as oxygen or hydrogen peroxide react with each other. Water is produced.

  As described above, in a biofuel cell having an anode-side half-cell structure in which an electric current is extracted by oxidation of fuel by an oxidoreductase, the oxidation reaction of the fuel effective for power generation proceeds in the vicinity of the conductive substrate that is the anode electrode. To do. That is, on the anode side, the fuel is oxidized to receive electrons (reduced oxidoreductase) → the electrons are transferred to an electrode or an electron mediator or the like (oxidized oxidoreductase) → The fuel is oxidized again to receive electrons. It is the oxidoreductase present in the vicinity of the anode electrode that is the partner to which the electron is transferred that can efficiently repeat the cycle of (reduced oxidoreductase). If the oxidoreductase that oxidizes the fuel and receives the electrons cannot smoothly deliver the electrons to the electrodes, the oxidation reaction of the fuel will not be effective for power generation.

  Further, in a biofuel cell having a cathode-side half-cell structure that takes out current by reducing the oxidant with an oxidoreductase, the reduction reaction of the oxidant effective for power generation proceeds in the vicinity of the conductive substrate that is the cathode electrode. . That is, on the cathode side, electrons are received from an electrode or an electron mediator (reduced oxidoreductase) → the electrons are transferred to an oxidizing agent (oxidized oxidoreductase) → an electron is again received from the electrode or electron mediator ( It is the oxidoreductase present in the vicinity of the cathode electrode that is the partner that receives the electrons that can efficiently repeat the cycle of reductive oxidoreductase). If the oxidoreductase cannot smoothly receive electrons from the electrode, the reduction reaction of the oxidant does not proceed and a large current cannot be taken out.

  As described above, the oxidation reaction or reduction reaction of the fuel or oxidant, which is a substrate of the oxidoreductase, proceeds actively in the vicinity of the electrode, and the substrate in the electrolyte solution is intensively consumed in the vicinity of the electrode, Its concentration decreases. When the contact probability between the oxidoreductase existing in the vicinity of the electrode and the substrate decreases due to the occurrence of the substrate shortage state in the vicinity of the electrode, the oxidation reaction or reduction reaction of the substrate does not proceed smoothly. As a result, the fuel cell cannot maintain a sufficient power generation amount.

  Therefore, in the present invention, the substrate diffusion mechanism facilitates diffusion in the direction of the conductive substrate that is the substrate electrode, so that the concentration of the substrate in the vicinity of the electrode can be maintained at a high level, and is present in the vicinity of the electrode. This makes it possible to increase the contact probability between the oxidoreductase functioning effectively for power generation and the substrate. By increasing the probability of contact between the oxidoreductase and the substrate in the vicinity of the electrode, a biofuel cell can be provided in which the oxidation or reduction reaction of the substrate proceeds smoothly in the vicinity of the electrode and exhibits excellent power generation performance.

  In the present invention, the substrate diffusion mechanism refers to a substrate in the vicinity of an electrode made of a conductive substrate that promotes diffusion of the substrate in the electrolyte toward the conductive substrate that is an electrode (anode electrode or cathode electrode). There is no particular limitation as long as the concentration can be maintained at a high level. For example, in addition to those that promote the spontaneous movement of fuel according to the concentration gradient in the electrolyte, those that increase the movement of the substrate by external force are also included.

  Specifically, the movement of the substrate is increased by external force. Specifically, it causes convection in the electrolyte and promotes diffusion of the substrate that is the solute of the electrolyte by convection. And those that promote the diffusion of the substrate in the electrolyte.

  Examples of the method for causing convection of the electrolytic solution include a method of stirring the electrolytic solution in which the substrate is dispersed. The method for stirring the electrolytic solution is not particularly limited. Moreover, as a method of applying vibration to the electrolytic solution, there is an excitation by an ultrasonic vibrator.

  As the substrate diffusion mechanism, excitation to the electrolyte solution with an ultrasonic vibrator is preferable from the viewpoint of ease of incorporation into a biofuel cell, ease of design, and the like.

  Even in a battery configuration in which a substrate or an electrolyte containing the substrate is distributed, depending on the distribution speed of the substrate or the electrolyte containing the substrate, a sufficient substrate diffusion effect by the substrate diffusion mechanism as described above can be obtained. Therefore, the biofuel cell of the present invention may be applied to a form capable of supplying a substrate other than a closed system in which the substrate is not supplied.

  It does not specifically limit as an electroconductive base material which comprises an electrode, A general thing can be used. For example, those made of conductive carbon such as graphite, carbon black and activated carbon, and those made of metal such as gold and titanium can be used.

The biofuel cell of the present invention may have a form of a half cell structure on the anode side and a substrate diffusion mechanism that promotes the diffusion of fuel to the conductive base material that is the anode electrode. It may have a battery structure and a substrate diffusion mechanism that promotes diffusion of an oxidant to a conductive substrate that is a cathode electrode, or may have the half-cell structure on the anode side and the cathode side, A form provided with a substrate diffusion mechanism for promoting the diffusion of fuel to the side electrode and a substrate diffusion mechanism for promoting the diffusion of the oxidant to the cathode electrode may be employed.
Because of the high power generation performance obtained, the biofuel cell of the present invention has the half-cell structure at least on the anode side, and includes a substrate diffusion mechanism that promotes the diffusion of fuel to the conductive substrate that is the anode electrode. It is preferable.

Hereinafter, as one embodiment of the biofuel cell of the present invention, a biofuel cell having the half-cell structure on the anode side and provided with a substrate diffusion mechanism that promotes the diffusion of fuel to the conductive substrate that is the anode electrode is provided. The explanation is centered.
As a fuel, a general thing can be utilized widely, For example, hydrogen etc. other than the hydrocarbon type compound which consists of alcohols, aldehydes, saccharides, and ketones are mentioned. Among them, at least one selected from hydrocarbon compounds composed of alcohols, aldehydes, saccharides, and ketones is preferable from the viewpoint of ease of handling and the like. Specific examples include alcohols such as methanol, ethanol, propanol and glycerin; aldehydes such as formaldehyde and acetaldehyde; saccharides such as glucose, fructose and sorbose; ketones and the like. In addition, metabolic intermediate products such as fats, proteins, and sugars, and mixtures thereof can be used.

  Among these, when glucose or the like having a large molecular weight and low spontaneous diffusivity due to a concentration gradient or the like is used as a fuel, the effect obtained by the present invention is particularly high. In addition, ethanol, methanol, and glucose are preferably used from the viewpoints of easy availability and ease of handling.

  The oxidoreductase that oxidizes the substrate as the fuel is not particularly limited, and may be appropriately selected depending on the fuel to be used. For example, dehydrogenase or oxidase can be used. Specific examples include glucose dehydrogenase (GDH), alcohol dehydrogenase (ADH), aldehyde dehydrogenase, glucose oxidase (GOD), alcohol oxidase (AOD), and aldehyde oxidase. GDH, ADH, GOD, and AOD are preferably used from the viewpoints of fuel availability and management, and safety. Only one kind of enzyme may be used alone, or two or more kinds of enzymes may be used in combination.

The oxidoreductase may be dispersed in the electrolytic solution together with the substrate or may be fixed on the surface of the conductive substrate as long as it can contact the substrate to oxidize or reduce the substrate. It does not specifically limit as a method to fix to the surface of an electroconductive base material, It can carry out according to a general method. For example, polyethylene glycol diglycidyl (PEGDE) or glutaraldehyde having a reactive group capable of covalently bonding oxidoreductases or oxidoreductases and conductive substrates or oxidoreductases and carriers on conductive substrates. Make oxidoreductase conductive by solidifying ionic polymers such as polyvinyl imidazole, polyallylamine, polyamino acid, polypyrrole, polyacrylic acid, polyvinyl alcohol, etc. that use a crosslinking reagent or have electrostatic interaction with the enzyme. A method of immobilizing on the surface is mentioned.
In general, the enzyme is preferably immobilized on the electrode surface from the viewpoint of smooth electron transfer with the conductive substrate.

  The half-cell structure may contain an electron mediator that mediates electron transfer between the oxidoreductase and the conductive substrate. In general, due to the molecular structure of oxidoreductase, it is often difficult to efficiently transfer electrons between the oxidoreductase and the conductive substrate. Therefore, by using an electron mediator that mediates electron transfer between the oxidoreductase and the electrode, the electron transfer between the enzyme and the conductive substrate can be smoothly advanced.

  The electron mediator may be appropriately selected from commonly used substances according to the oxidoreductase used. Examples thereof include metal complexes having a metal element such as Os, Fe, Ru, Co, Cu, Ni, V, Mo, Cr, Mn, Pt, and W as a central metal; heterocyclic compounds such as viologen, and the like.

  Similarly to the oxidoreductase, the electron mediator is preferably immobilized on a conductive substrate from the viewpoint of smooth electron transfer. As an immobilization method, a general method can be applied, and for example, the oxidoreductase immobilization method described above can be used.

  In the biofuel cell of the present invention, electron transfer between an oxidoreductase that oxidizes or reduces a substrate that is a fuel or an oxidant and a conductive substrate is directly performed between the oxidoreductase and the conductive substrate. It may be carried out, may be carried out via an electron mediator as described above, or may be carried out via another oxidoreductase.

  The electrolyte solution in which the fuel or oxidant as the substrate is dispersed or dissolved is used in the tris buffer solution, phosphate buffer solution, morpholinopropane sulfonic acid so that the oxidation reaction or reduction reaction that is an electrode reaction proceeds efficiently and constantly. It is preferably maintained at an optimum pH, for example, around pH 7, by a buffer solution such as (MOPS). Moreover, in order to make an electrode reaction advance efficiently and stably, it is preferable to maintain at about 20-30 degreeC, for example.

  As the cathode paired with the anode having the half-cell structure as described above, for example, an electrode catalyst generally used in a fuel cell such as platinum or a platinum alloy which is an effective catalyst for a reduction reaction of an oxidant is used. Using a cathode made of a carbonaceous material such as graphite, carbon black, activated carbon, or a conductor made of gold, titanium or the like, or a conductor made of an electrode catalyst such as platinum or a platinum alloy. The agent can be supplied to the electrode catalyst.

Alternatively, the cathode paired with the anode having the half-cell structure as described above may have a form having the half-cell structure with or without the oxidant diffusion mechanism. Examples of the oxidoreductase that reduces the oxidant include known ones such as laccase and bilirubin oxidase. When an oxidoreductase is used as a catalyst for reducing the oxidant, a known electron mediator may be used as necessary.
Examples of the oxidizing agent include oxygen and hydrogen peroxide.
In order to avoid the influence of impurities that hinder the electrode reaction at the cathode, an oxygen selective membrane such as dimethylpolysiloxane may be disposed around the cathode electrode.

[Preparation of substrate oxidation enzyme electrode]
First, a composite of poly (1-vinylimidazole) and Os (4,4′-dimethyl-2,2′-bipyridine) ₂ Cl (hereinafter, referred to as “poly (1-vinylimidazole)”) was used on the surface of carbon paper (Φ10 mm). 8 μl of a 15 mg / ml aqueous solution of PVI-Os. Subsequently, 8 μl of 5 mg / mL phosphate buffer solution of glucose dehydrogenase (GDH) was dropped. Next, 8 μl of a 3 mg / ml aqueous solution of polyethylene glycol diglycidyl ether (PEGDE) was dropped.
This was left to stand overnight at room temperature and dried, and GDH as an enzyme and PVI-Os as a mediator were fixed on the surface of the carbon sheet by binding GDH to the polyvinylimidazole chain of PVI-Os via PEGDE. .
As shown in FIG. 3, the carbon paper in which the oxidoreductase and the electron mediator are fixed as described above is fixed to the tip of a member having a carbon core connected to an external circuit with a nylon net and an O-ring, A substrate oxidized enzyme electrode (sample electrode) was used.

[Power generation test]
(Example)
Using the sample electrode, a power generation test (three-electrode electrochemical evaluation, see FIG. 4) was performed while vibrating the electrolyte solution with an ultrasonic vibrator under the following conditions. The results are shown in FIG. In addition, Ag / AgCl ₂ was used as a reference electrode, and a Pt wire was used as a counter electrode.

<Test conditions>
・ Temperature: Room temperature (about 27 ℃)
Electrolyte solution: aqueous solution (pH 7.0) containing MOPS 30 mM, CaCl ₂ 3 mM, KCl 100 mM, and glucose 0.1 M

(Comparative example)
In the examples, a power generation test was conducted in the same manner except that the electrolyte was not vibrated with an ultrasonic vibrator. The results are shown in FIG.

<Result>
As shown in FIG. 2, the example in which the electrolyte is vibrated by an ultrasonic vibrator and the diffusion of glucose as a fuel to the electrode is promoted is a comparison in which the substrate diffusion mechanism that promotes the diffusion of glucose is not used. Compared to the example, an improvement in current density in the high potential range was confirmed. This is because, in the comparative example, the diffusibility of glucose was poor, and the glucose supply to the GDH fixed on the electrode surface was insufficient. This is because glucose was diffused to the electrode due to the excitation of, and a sufficient amount of glucose was always supplied to the GDH fixed to the electrode surface.

It is a conceptual diagram which shows one example of the biofuel cell provided with the enzyme electrode of this invention. It is a graph which shows the evaluation result in an Example. It is a figure which shows the preparation methods of the enzyme electrode in an Example. It is a figure which shows the evaluation system of the electric power generation test (three-electrode-type electrochemical evaluation) in an Example.

Claims (6)

At least one of the anode side and the cathode side contains a conductive substrate connected to an external circuit, an oxidoreductase capable of transferring electrons between the conductive substrate, and a substrate of the oxidoreductase A biofuel cell having a half-cell structure comprising:
The biofuel cell, wherein the at least one half-cell structure includes a substrate diffusion mechanism that promotes diffusion of the substrate in the direction of the conductive substrate.   The biofuel cell according to claim 1, wherein the substrate diffusion mechanism is excitation of the electrolyte solution by an ultrasonic vibrator.   The biofuel cell according to claim 1 or 2, wherein the half-cell structure includes an electron mediator that mediates electron transfer between the conductive substrate and the oxidoreductase.   The said half-cell structure is provided with the substrate diffusion mechanism which accelerates | stimulates the spreading | diffusion to the said electroconductive base material of the fuel which is a substrate of an anode side oxidoreductase, and has the said half-cell structure on the anode side. The biofuel cell according to any one of the above.   The biofuel cell according to claim 4, wherein the fuel is at least one selected from hydrocarbon-based compounds consisting of alcohols, aldehydes, sugars and ketones.   The biofuel cell according to claim 5, wherein the fuel is at least one selected from ethanol, methanol, and glucose.

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