JP2013016439A - Enzyme fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an enzyme fuel cell which has higher output in single cell units than ever.SOLUTION: The enzyme fuel cell includes, on at lease one of cathode and anode sides, a tub which holds therein a dispersion element derived from an oxide reduction substance by dispersing it, with an enzyme electrode provided therein in such a manner as to touch the oxide reduction substance directly. Further, the tub is provided with an enzyme support medium in such a manner as to touch the oxide reduction substance directly, the enzyme support medium being derived by solidifying an enzyme which oxidizes or reduces the oxide reduction substance in a direction opposite to the electrode reaction during non-power generation.

Description

  The present invention relates to an enzyme fuel cell, and more particularly to an enzyme fuel cell capable of providing a higher output than before.

  In recent years, interest in fuel cells has increased as one of countermeasures against environmental problems and resource problems. A fuel cell is a device that directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. A fuel cell that extracts energy electrochemically is not subject to the Carnot cycle, unlike thermal power generation, and thus exhibits high energy conversion efficiency. Commonly known types of fuel cells include polymer electrolyte fuel cells (PEFC), alkaline electrolyte fuel cells (AFC), phosphoric acid fuel cells (PAFC), direct methanol fuel cells (DMFC), etc. There is. These fuel cells often use platinum (Pt) as a catalyst. However, platinum is a very expensive material, which is one of the obstacles to the spread of fuel cells.

  On the other hand, enzyme fuel cells are attracting attention as fuel cells that do not use platinum as a catalyst. In an enzyme fuel cell, an oxidoreductase is used in place of a conventional catalyst such as platinum on at least one of an anode electrode and a cathode electrode. In the enzyme fuel cell, high output is an issue for practical use.

  As an attempt to improve an enzyme fuel cell, Patent Document 1 proposes an enzyme fuel cell configured to decompose a fuel stepwise by a plurality of enzymes and to transfer electrons generated by an oxidation reaction to an electrode. Yes. Patent Document 2 proposes to use a plurality of fuel cells connected in series or in parallel. However, the enzyme fuel cell described in Patent Document 1 has a low current density and cannot provide a desired output. Further, the technique described in Patent Document 2 does not increase the output of a single cell.

JP 2004-71559 A JP 2009-48848 A

  Since the output of the enzyme fuel cell depends on the reaction rate and redox potential of the enzyme reaction used, it is known that it is difficult to fundamentally improve the low output of the enzyme fuel cell. An object of this invention is to provide the enzyme fuel cell which has a higher output than the conventional cell unit.

  As a result of examining the problems as described above, the present inventors have found that an enzyme fuel cell having a higher output than before can be obtained by coexisting an enzyme reaction and a redox reaction other than the enzyme reaction in the system. I found it. The gist of the present invention is as follows.

(1) A tank holding a dispersion in which the redox material is dispersed is provided on at least one of the cathode side and the anode side, and an enzyme electrode is provided so as to be in direct contact with the redox material. Is an enzyme fuel cell in which an enzyme support on which an enzyme that oxidizes or reduces the oxidation-reduction substance in a direction opposite to the electrode reaction at the time of power generation is provided in direct contact with the oxidation-reduction substance during non-power generation.
(2) The enzyme fuel cell according to (1), wherein the tank is provided on the cathode side, and an enzyme that oxidizes a redox substance is immobilized on the enzyme support.
(3) The enzyme fuel cell according to (2), wherein the enzyme immobilized on the enzyme support is multi-copper oxidase.
(4) The enzyme fuel cell according to (3), wherein the multi-copper oxidase is selected from bilirubin oxidase, laccase, CueO, and combinations of two or more thereof.
(5) The enzyme fuel cell according to (1), wherein the tank is provided on the anode side electrode, the tank further contains fuel, and an enzyme that reduces a redox substance is immobilized on the enzyme support. .
(6) The enzyme immobilized on the enzyme support is selected from formate dehydrogenase, glucose dehydrogenase, fructose dehydrogenase, alcohol dehydrogenase, aldehyde dehydrogenase, and combinations of two or more thereof. Enzyme fuel cell.
(7) Redox substances are hexacyanoferrate, octacyanotungstate, quinones, 1-methoxy-5-methylphenazinium methyl sulfate, methylene blue, methylene green, ABTS, EDTA (III), NAD (H ), NADP (H), and a combination of two or more thereof. The enzyme fuel cell according to any one of (1) to (6).

  ADVANTAGE OF THE INVENTION According to this invention, the enzyme fuel cell with the high output per unit cell which was not realizable with the conventional enzyme fuel cell can be provided. Thereby, the enzyme fuel cell can be used for applications requiring high current density, and the applications can be further spread.

It is the schematic of one Embodiment of the enzyme fuel cell of this invention. It is the schematic of the structure of the cell for evaluation in the output measurement of the conventional enzyme fuel cell. It is the schematic of the structure of the cell for evaluation in the output measurement of the enzyme fuel cell which has a redox substance tank on the cathode side. It is a graph showing the test result of the oxidation of potassium hexacyanoferrate (II) by an enzyme.

  FIG. 1 is a schematic view of one embodiment of the enzyme fuel cell of the present invention. Hereinafter, the structure of the enzyme fuel cell of the present invention will be described with reference to FIG. 1, but the enzyme fuel cell of the present invention is not limited to this structure.

  The enzyme fuel cell 1 of the present invention is provided with an anode side electrode 12 and a cathode side electrode 13 so as to sandwich a solid polymer electrolyte membrane 11 as in the case of a conventional enzyme fuel cell. Hereinafter, a case where both the anode side electrode 12 and the cathode side electrode 13 are enzyme electrodes on which an oxidoreductase is immobilized will be described. In the enzyme fuel cell of the present invention, the anode side electrode 12 and the cathode side electrode are used. It is sufficient that at least one of 13 is an enzyme electrode. When either electrode is not an enzyme electrode, a conventional electrode catalyst such as platinum can be used instead of the enzyme.

  A current collector 14 is provided on the anode side electrode 12 and the cathode side electrode 13 so as to be in contact with each electrode in order to make the flow of electrons exchanged by an electrode reaction smooth. As the current collector 14, for example, a mesh material made of a metal such as titanium can be used.

  What will be described below are characteristic components in the present invention. The enzyme fuel cell 1 of the present invention has redox material tanks 15 and 16 on the anode side and the cathode side, respectively. The redox material tanks 15 and 16 hold dispersions in which the redox material is dispersed, respectively. The redox material tank 15 on the anode side usually serves as a fuel tank, and a dispersion in which fuel is dispersed together with the redox material is held therein. The anode side electrode 12 and the cathode side electrode 13 are provided so as to be in direct contact with the dispersion held in the redox substance tank 15 or 16, respectively. That is, the anode side electrode 12 and the cathode side electrode 13 are in direct contact with the redox substance contained in the dispersion. In the oxidation-reduction substance tanks 15 and 16, enzyme supports 17 and 18 are respectively provided so as to be in direct contact with the oxidation-reduction substance contained in the dispersion. Enzymes that can oxidize or reduce the redox substance in the opposite direction to the electrode reaction during power generation are immobilized on the enzyme supports 17 and 18.

  At the time of power generation of the enzyme fuel cell 1, in the anode side electrode 12, the reaction for extracting the electrons and protons by oxidizing and decomposing the fuel proceeds as catalyzed by the enzyme immobilized on the electrode, as in the conventional enzyme fuel cell. . In the enzyme fuel cell 1 of the present invention, at the same time, a reaction in which the redox material contained in the redox material tank 15 is oxidized proceeds. In this way, it is considered that the fuel oxidation reaction and the oxidation reaction of the oxidation-reduction substance proceed at the same time, so that the additive effect of both oxidation-reduction potentials can be obtained and high output can be obtained.

  Similarly, at the time of power generation of the enzyme fuel cell 1, the cathode side electrode 13 proceeds with a reaction in which oxygen is reduced and water is catalyzed by the enzyme immobilized on the electrode. In the enzyme fuel cell 1 of the present invention, at the same time, a reaction in which the redox material contained in the redox material tank 16 is reduced proceeds. For example, when the redox material tank 16 contains potassium hexacyanoferrate (III) (potassium ferricyanide) as a redox material, it is reduced to potassium hexacyanoferrate (II) (potassium ferrocyanide). As described above, it is considered that the reduction reaction of oxygen and the reduction reaction of the oxidation-reduction substance proceed at the same time, thereby obtaining an additive effect of both oxidation-reduction potentials and obtaining a high output.

  If the redox material contained in the redox material tanks 15 and 16 is consumed together with the power generation, and if it is completely oxidized or reduced, the output of the enzyme fuel cell 1 is considered to decrease. However, in the enzyme fuel cell 1 of the present invention, the consumed redox material can be regenerated by the enzyme immobilized on the enzyme support 17 or 18 during non-power generation, that is, while power generation is stopped. . For example, when the redox material tank 16 on the cathode side contains potassium hexacyanoferrate (III) as a redox material, it is reduced to potassium hexacyanoferrate (II) along with power generation as described above. However, an enzyme (for example, bilirubin oxidase) having the ability to oxidize potassium hexacyanoferrate (II) is immobilized on the enzyme support 18 provided in the redox substance tank 16, so that it can generate electricity during non-power generation. The resulting potassium hexacyanoferrate (II) is regenerated to hexacyanoferrate (III) oxide.

  This mechanism for regenerating redox substances consumed during power generation during non-power generation can be regarded as similar to a mechanism for charging a secondary battery by applying voltage from the outside during non-power generation. However, in the enzyme fuel cell of the present invention, the regeneration of the redox substance proceeds automatically by an enzyme reaction during non-power generation, and it is not necessary to apply a voltage from the outside.

  In the embodiment shown in FIG. 1, the redox material tank is provided on both the anode side and the cathode side, but the redox material tank may be provided on at least one of the anode side or the cathode side. When the oxidation-reduction substance tank is provided only on the anode side, the oxidation-reduction substance tank 16 and the enzyme support 18 in FIG. 1 do not exist, and the cathode electrode has the same configuration as the cathode electrode of a conventional fuel cell, for example, A structure can be adopted in which the electrode can take in oxygen directly from the atmosphere.

  The redox material tank is preferably provided at least on the cathode side. When the oxidation-reduction substance tank is provided only on the cathode side, the anode-side tank (corresponding to 15 in FIG. 1) does not contain the oxidation-reduction substance, but only the fuel. In that case, the enzyme support 17 may not be present.

  When the anode-side electrode 12 is an enzyme electrode, an enzyme that oxidizes the substrate fuel, such as formate dehydrogenase, glucose dehydrogenase, fructose dehydrogenase, alcohol dehydrogenase, or aldehyde dehydrogenase, or a combination of two or more of these is fixed to the electrode. It has become. In that case, the fuel contained in the oxidation-reduction substance tank 15 and supplied to the anode side electrode 12 is, for example, formic acid or a salt thereof, glucose, fructose, methanol, ethanol, propanol, acetaldehyde, or the like.

  When the cathode-side electrode 13 is an enzyme electrode, the electrode includes an enzyme that reduces oxygen as a substrate, particularly a multi-copper oxidase (for example, bilirubin oxidase, laccase, or CueO (Copper efflux Oxidase), or a combination of two or more thereof. ) Is fixed. As the substrate, oxygen that is taken in from the air or contained in the dispersion held in the redox substance tank 16 is used.

  An enzyme capable of reducing the redox material oxidized by the electrode reaction during power generation is immobilized on the enzyme support 17 provided in the redox material tank 15 on the anode side. Examples of such enzymes include formate dehydrogenase, glucose dehydrogenase, fructose dehydrogenase, alcohol dehydrogenase, or aldehyde dehydrogenase, or combinations of two or more thereof. When the anode side electrode 12 is an enzyme electrode, the enzyme immobilized on the anode side electrode 12 and the enzyme support 17 may be the same or different. If they are the same, there is an advantage that the manufacturing cost can be reduced. On the other hand, in the case of different ones, there is an advantage that it is possible to select an enzyme most suitable for the function required for each.

  An enzyme capable of oxidizing the redox material reduced by the electrode reaction during power generation is immobilized on the enzyme support 18 provided in the redox material tank 16 on the cathode side. Such enzymes include multi-copper oxidase (eg, bilirubin oxidase, laccase, or CueO, or combinations of two or more thereof). When the cathode side electrode 13 is an enzyme electrode, the enzymes immobilized on the cathode side electrode 13 and the enzyme support 18 may be the same or different.

  The redox material tanks 15 and 16 hold a dispersion in which a redox material (and fuel) as a dispersoid is dispersed in a dispersion medium. The form of the dispersion may be any of solution, sol, gel, aerosol, etc. Among them, the form of solution, sol and gel is preferable. As the dispersion medium, for example, water or various buffer solutions such as phosphate buffer solution, MOPS buffer solution, Tris buffer solution, and imidazole buffer solution can be used.

Compounds that can be used as the redox material in the enzyme fuel cell of the present invention include hexacyanoferrate (hexacyanoiron (II) acid and hexacyanoferrate (III) acid salts, particularly potassium salt, etc.), octacyanotungstic acid. Salt, quinones, 1-methoxy-5-methylphenazinium methyl sulfate (1-mPMS), methylene blue, methylene green, ABTS (2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid)), NAD (H) (nicotinamide adenine dinucleotide), NADP (H) (nicotinamide adenine dinucleotide phosphate), EDTA (III) (ethylenediaminetetraacetic acid and trivalent metal ions (for example Fe ³⁺ and Co ³⁺ ) complexes) ), And combinations of two or more thereof.

  The redox material used in the anode-side redox material tank 15 is preferably one having a redox potential of less than 0 V, particularly less than −100 mV, particularly less than −200 mV. Examples of such a redox material include 1-methoxy-5-methylphenazinium methyl sulfate (1-mPMS), methylene blue, methylene green, NAD (H), and NADP (H).

  As the redox material used for the redox material tank 16 on the cathode side, those having a redox potential of 100 mV or higher, particularly 200 mV or higher, particularly 300 mV or higher are preferable. Examples of such a redox substance include hexacyanoferrate (III) salt, ABTS, and EDTA (III).

  The concentration of the redox material in the redox material tanks 15 and 16 is preferably 0.2M or higher, particularly 0.5M or higher, particularly 1.0M or higher.

  The enzyme supports 17 and 18 can be provided at any location in the redox material tanks 15 and 16 as long as they are in direct contact with the redox material. When the anode-side electrode 12 is an enzyme electrode, if the enzyme immobilized on the electrode has sufficient ability to reduce the redox material during non-power generation, the electrode can be used as the enzyme support 17. May be. Similarly, when the cathode-side electrode 13 is an enzyme electrode, if the enzyme immobilized on the electrode has sufficient ability to oxidize the redox material during non-power generation, the electrode is used as the enzyme support 18. You may also use as. However, the enzyme supports 17 and 18 are preferably provided on at least a part of the inner walls of each of the redox substance tanks 15 and 16, for example, on the inner wall facing the electrode as shown in FIG. .

  In the enzyme fuel cell of the present invention, the redox material does not necessarily have to exist in the vicinity of the reaction field of the enzyme immobilized on the electrode, and the redox material does not have to be immobilized on the enzyme electrode. Absent. Rather, for example, a site where the enzyme is not fixed may be provided on the enzyme electrode so that the reaction of the redox substance can easily proceed.

  The dispersions held in the enzyme supports 17 and 18 and the redox substance tanks 15 and 16 may be gradually deteriorated as the enzyme fuel cell 1 is used. In order to cope with such deterioration, the enzyme fuel cell 1 of the present invention has, for example, the enzyme supports 17 and 18 or the oxidation-reduction substance tanks 15 and 16 provided with these enzyme supports as a cartridge type. It is good also as a structure which can be replaced | exchanged easily.

  Since the enzyme fuel cell of the present invention has a higher output than conventional enzyme fuel cells, for example, small power sources for mobile devices such as mobile phones and laptop computers, automobile power sources, household power sources, and for bio-implantable chips such as pacemakers It is advantageous for application to micro power sources.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to these Examples.

1. Measurement of output of conventional enzyme fuel cell (1) Preparation of enzyme electrode for anode 50 mg of Ketjen black (manufactured by Lion), 222 μL of 10% polyvinyl lysine (manufactured by Sigma Aldrich), and 3 mL of N-methylpyrrolidone (Japanese) A slurry was obtained by mixing and sufficiently dispersing. A carbon fiber mat (Torayca mat, manufactured by Toray Industries, Inc.) was processed into a 1 cm ² circle, and the slurry was applied to the surface and dried to prepare a base electrode.

  The components described in Table 1 were mixed to prepare a Candida boidinii-derived formate dehydrogenase (cbFDH) solution. This cbFDH solution was applied to the base electrode and dried to obtain an anode enzyme electrode.

(2) Preparation of cathode enzyme electrode Bilirubin oxidase (BOD, Amano Enzyme) was dissolved in 100 mM sodium phosphate buffer (pH 7.0, Nacalai Tesque) to prepare a 50 mg / mL BOD solution. . A base electrode prepared in the same manner as in (1) was immersed overnight in a 0.5 mL BOD solution to obtain a cathode electrode. The cathode electrode absorbed excess water with a paper waste before being incorporated into the fuel cell for evaluation.

(3) Output measurement of fuel cell The anode enzyme electrode obtained in (1) and the cathode electrode obtained in (2) were incorporated into a fuel cell for evaluation, and the output was measured.

FIG. 2 shows a schematic diagram of the structure of the fuel cell for evaluation. An anode enzyme electrode 22 and a cathode enzyme electrode 23 are provided so as to sandwich the solid polymer electrolyte membrane 21, and these electrodes are in contact with the current collector 24. On the anode side, a fuel tank 27 is provided by silicon 25 and an acrylic plate 26. Fuel having the following composition was supplied to the fuel tank 27.
[Fuel composition]
Sodium phosphate buffer (pH 7.0) 0.83M
Sodium formate 0.68M
NADH 0.25M
NAD 0.50M

Connect an electronic load device (PLZ164WA) manufactured by Kikusui Electronics Co., Ltd. as an external load device in series between the battery electrodes, and measure the output using sequence creation / control software (Wavy for PLZ4W, manufactured by Kikusui Electronics Co., Ltd.). It was. The measurement was performed under room temperature conditions (about 25 ° C.). As a result of the measurement, an output of 0.76 mW / cm ² was obtained.

2. Measurement of the output of an enzyme fuel cell having a redox material tank on the cathode side In the same manner as in (1) and (2) above, an anode enzyme electrode and a cathode enzyme electrode were prepared, and a redox material tank was provided on the cathode side. The output was measured by incorporating the fuel cell into an evaluation fuel cell.

FIG. 3 shows a schematic diagram of the structure of an evaluation fuel cell having a redox material tank on the cathode side. This evaluation fuel cell is the same as that shown in FIG. 2 except that it has a redox material tank 38 provided with silicon 35 and an acrylic plate 36 on the cathode side. The redox material tank 38 was filled with 1M potassium hexacyanoferrate (III) aqueous solution. When the output was measured under the same conditions as in 1 above, an output of 2.2 mW / cm ² was obtained.

3. Oxidation test of potassium hexacyanoferrate (II) by enzyme (1) Preparation of BOD adsorption base material Bilirubin oxidase (BOD, Amano Enzyme ) is added to 100 mM sodium phosphate buffer (pH 7.0, Nacalai Tesque) After dissolution, a 50 mg / mL BOD solution was prepared. The same base electrode as 1 (1) above was prepared, and was immersed in a 0.5 mL BOD solution overnight to adsorb BOD. Excess water was absorbed with a paper waste to obtain a BOD adsorption base material.

(2) Preparation of laccase adsorption substrate Laccase (Lacase Daiwa Y120, manufactured by Daiwa Kasei Co., Ltd.) is dissolved in 100 mM sodium phosphate buffer (pH 7.0, manufactured by Nacalai Tesque) to prepare a 50 mg / mL laccase solution. did. The same base electrode as the above 1 (1) was prepared, and it was immersed in a 0.5 mL laccase solution overnight to adsorb the laccase. Excess moisture was absorbed with a paper waste to obtain a laccase adsorbing substrate.

(3) Oxidation of potassium hexacyanoferrate (II) by enzyme 15 μL of 200 mM potassium hexacyanoferrate (II) and 285 μL of 100 mM sodium phosphate buffer (pH 7.0, manufactured by Nacalai Tesque) were filled. A tank was prepared. The enzyme adsorption base material prepared in the above (1) and (2) and the control base material immersed in a sodium phosphate buffer solution containing no enzyme are placed on the tank, respectively, and hexacyano iron (II) in the tank is placed. The potassium acid solution was in contact with the enzyme adsorption substrate. Due to the enzymatic reaction, potassium hexacyanoferrate (II) was oxidized to potassium hexacyanoferrate (III), and the solution turned yellow. The degree of discoloration was evaluated using a spectrophotometer (Infinite M200, manufactured by Tecan).

  FIG. 4 is a graph showing the absorbance of the solution measured at 420 nm for each of the control substrate, the BOD substrate, and the laccase substrate. The absorbance of the solution did not increase with the control substrate containing no enzyme, whereas the absorbance increased greatly when the BOD substrate and the laccase substrate were used, and the enzyme caused potassium hexacyanoferrate (II) to be converted to hexacyano It was found that it was oxidized to potassium iron (III).

DESCRIPTION OF SYMBOLS 1 Enzyme fuel cell 11 Solid polymer electrolyte membrane 12 Anode side electrode 13 Cathode side electrode 14 Current collector 15, 16 Redox material tank 17, 18 Enzyme support 21 Solid polymer electrolyte membrane 22 Anode enzyme electrode 23 Cathode enzyme Electrode 24 Current collector 25 Silicon 26 Acrylic plate 27 Fuel tank 31 Solid polymer electrolyte membrane 32 Anode enzyme electrode 33 Cathode enzyme electrode 34 Current collector 35 Silicon 36 Acrylic plate 37 Fuel tank 38 Redox material tank

Claims (7)

  There is a tank for holding a dispersion in which the redox material is dispersed on at least one of the cathode side and the anode side, and an enzyme electrode is provided so as to be in direct contact with the redox material, and the tank has no power generation. An enzyme fuel cell in which an enzyme support on which an enzyme that oxidizes or reduces the redox substance in the opposite direction to the electrode reaction during power generation is sometimes in direct contact with the redox substance.   The enzyme fuel cell according to claim 1, wherein the tank is provided on the cathode side, and an enzyme that oxidizes a redox substance is immobilized on the enzyme support.   The enzyme fuel cell according to claim 2, wherein the enzyme immobilized on the enzyme support is multi-copper oxidase.   The enzyme fuel cell according to claim 3, wherein the multi-copper oxidase is selected from bilirubin oxidase, laccase, CueO, and combinations of two or more thereof.   The enzyme fuel cell according to claim 1, wherein the tank is provided on an anode side electrode, the tank further contains a fuel, and an enzyme that reduces a redox substance is immobilized on the enzyme support.   The enzyme fuel cell according to claim 5, wherein the enzyme immobilized on the enzyme support is selected from formate dehydrogenase, glucose dehydrogenase, fructose dehydrogenase, alcohol dehydrogenase, aldehyde dehydrogenase, and combinations of two or more thereof. .   Redox substances are hexacyanoferrate, octacyanotungstate, quinones, 1-methoxy-5-methylphenazinium methyl sulfate, methylene blue, methylene green, ABTS, EDTA (III), NAD (H), NADP The enzyme fuel cell according to any one of claims 1 to 6, which is selected from (H) and a combination of two or more thereof.

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