JP2006085911A - Biological fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological fuel cell which directly utilizes the chemical energy of a fuel originally obtained from a living thing as an electric energy. <P>SOLUTION: The biological fuel cell comprises a positive electrode and a negative electrode which are arranged via an electrolyte. A compound which generates a reductant and electrons by a light irradiation at the negative electrode is made to react. Biological cells oxidize an originally biological fuel consisting of carbonic compounds using a metabolic system in order to supply electrons, and are made to act on molecules of the reductant. Thus, an electromotive force is generated between the positive electrode and the negative electrode by performing the oxidization reaction to take out electrons electrochemically from the originally biological fuel consisting of carbonic compounds being recycled in the animate nature to an external electric circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biofuel that generates electricity using a bio-derived fuel composed of a carbon compound circulated and regenerated in the natural biological world such as carbohydrates such as sugar and starch, lipids, hydrocarbons, alcohols, aldehydes, or organic acids. It relates to batteries.

  Biological fuels consisting of carbon compounds circulated and regenerated in the natural biological world such as sugars, starches and other carbohydrates, lipids, hydrocarbons, alcohols, aldehydes, or organic acids are produced from carbon dioxide and water by plant photosynthesis. Solar energy accumulated as biological fuel is used as chemical energy and heat energy by animal food metabolism, and forms a clean circulatory system that returns to carbon dioxide and water.

For example, in addition to saccharides such as monosaccharides, oligosaccharides, and polysaccharides, carbohydrates, which are generic names of cyclic polyalcohols and amino sugars, which are similar to sugars, are synthesized by plants through photosynthesis, and animals ingest them as food. Energy source. When glucose represented by the chemical formula C ₆ H ₁₂ O ₆ , which is a typical carbohydrate, is completely oxidized, 24 electrons are released per molecule of glucose, and carbon dioxide and water are generated. In the animal body, these 24 electrons are used as an energy source. According to thermodynamic calculations, it has an energy of 2872 kJ per mole of glucose and 4.43 Wh per gram. This is an energy density of 3.8 Wh / g or more of the weight energy density of metallic lithium used for the negative electrode of a lithium battery known as a high energy density battery.
US Pat. No. 6,294,281 U.S. Pat. No. 4,117,202 International Publication No. 02/33775 Pamphlet JP 2000-133296 A (particularly paragraph numbers 0030 and 0042)

  However, methods of using chemical energy possessed by bio-derived fuels typified by carbohydrates include methods of using it as thermal energy by direct combustion in air, methods of using it as nutrients in methane fermentation using microorganisms, or animals. There are few examples of using it directly as electrical energy, except for using it as chemical energy such as ATP by the action of oxidase in the body.

  As a method of directly using chemical energy possessed by biological fuel as electric energy, there is a biofuel cell described in Patent Document 1 using an enzyme and a redox mediator. Further, Patent Literature 2 describes a photobacterial biofuel cell that generates electricity using a photosynthetic bacterium that uses a bio-derived fuel as a nutrient.

  The photobacterial biofuel cell of Patent Document 2 can use light energy such as sunlight in addition to chemical energy possessed by biological fuels. However, in order to inhabit photobacteria, temperature, solution composition However, fine control of nutrients is necessary, and there is a difficulty that a power generation apparatus becomes complicated because a culture vessel dedicated to bacteria is necessary.

  In the biofuel cell of Patent Document 1, as long as there are only two electrodes, a positive electrode and a negative electrode, to which an enzyme or redox mediator is fixed, power can be generated simply by immersing them in an electrolyte containing biological fuel. The apparatus has the advantage that it is simple and can be miniaturized. However, when chemical energy of biological fuels is used with high efficiency, for example, when all 24 electrons per glucose molecule are to be used, a plurality of types of redox mediators and particularly negative electrodes with immobilized enzymes are used. It has the disadvantage that it is necessary and the reaction system becomes extremely complicated.

  The present invention provides a biofuel cell that eliminates such difficulties and makes it possible to use the chemical energy of biological fuels simply and with high efficiency.

  The present invention has a positive electrode and a negative electrode provided via an electrolyte, and in the negative electrode, a compound that generates a reductant and an electron by light irradiation, and a biological compound comprising a carbon compound using a substance metabolism system for the reductant molecule By the action of living cells that oxidize derived fuel and supply electrons, an oxidation reaction is performed in which electrons are electrochemically extracted to an external electric circuit from biological fuels made of carbon compounds that are circulated and regenerated in the natural biological world. Thus, the present invention provides a biofuel cell that generates electricity by using chemical energy of a bio-derived fuel made of a carbon compound easily and with high efficiency.

  The positive electrode is preferably a positive electrode in which a reduction reaction of oxygen occurs at a potential nobler than the oxidation reaction in the negative electrode.

  The present invention relates to a compound that generates a reductant and an electron upon irradiation with light in a negative electrode, and a living cell that supplies electrons by oxidizing a biological fuel composed of a carbon compound to the reductant molecule using a substance metabolism system. By the action, an electromotive force is generated between the positive electrode and the negative electrode by performing an oxidation reaction in which electrons are electrochemically extracted to an external electric circuit from a biological fuel composed of carbon compounds that are circulated and regenerated in the natural biological world. A biofuel cell is provided. According to the present invention, the chemical energy of biological fuel can be effectively used as direct electrical energy.

  The present invention will be described in detail below.

  The biofuel cell according to the present invention comprises a positive electrode and a negative electrode provided via an electrolyte, and a compound that generates a reductant and an electron upon irradiation with light in the negative electrode, and a carbon compound using a substance metabolism system for the reductant molecule Oxidation that extracts electrons from biological fuels consisting of carbon compounds that are circulated and regenerated in the natural biological world to the external electrical circuit by the action of living cells that oxidize biological fuels and supply electrons By causing the reaction, an electromotive force is generated between the positive electrode and the negative electrode. This makes it possible to directly use chemical energy stored in biological fuel as electric energy in a form biased by light energy.

In FIG. 1, the schematic diagram of a structure of the photobiofuel cell of this invention is shown. FIG. 1 shows that electrons (e−) possessed by a biological fuel from a biological fuel (Fuel) through a substance metabolism system (Met) of a living cell (Cell) are converted into a reductant ( The state of flowing from the negative electrode to the positive electrode through the external electric circuit (Load) through the compound (S) that generates S ^* ) and electrons is shown.

S irradiated with light generates electrons (e−) biased with light energy having a base potential determined by an energy difference between S ^* and S and S ^* . S ^* receives electrons from Met of a living cell (Cell) and returns to S. Electrons (e−) biased by light energy work in an external circuit, reach the positive electrode, and are used for the reduction reaction with the substance to be reduced (M) at the positive electrode. By doing so, an electromotive force is generated between the positive electrode and the negative electrode, and power generation can be performed.

  Here, the compound S which generates a reductant and an electron upon irradiation with light is preferably a compound which is disposed on an oxide semiconductor and has a single or plural light absorption peaks at a light wavelength of 300 nm to 1000 nm. As such a compound, a metal complex dye, an organic dye, or the like can be used. As the metal complex dye, a ruthenium complex dye or a platinum complex dye having ruthenium (Ru) as a central atom and biquinoline, bipyridyl, phenanthroline, thiothianic acid, or a derivative thereof as a ligand can be used. Includes single or multiple porphyrin rings with or without copper (Cu), zinc (Zn), magnesium (Mg), iron (Fe), etc. at the central atom, having both metal complex dye and organic dye structures Porphyrin pigments can also be used effectively. As organic dyes, 9-phenylxanthene dyes, merocyanine dyes, polymethine dyes and the like can be used effectively.

  These dyes have high light absorption efficiency, high affinity with oxide semiconductors, are not easily dissolved in the electrolyte solution, are stable even when in contact with the electrolyte solution for a long time, and are excited by light irradiation. A long lifetime of electrons is preferable because of high photoelectric conversion efficiency. By disposing a compound that generates a reductant and electrons by light irradiation on the oxide semiconductor, it is possible to quickly move electrons generated by light irradiation to the oxide semiconductor. The probability of recombination with electrons can be reduced, and the efficiency of extracting electrons from biological fuel can be kept higher.

As the oxide semiconductor, tin oxide (SnO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), tungsten oxide (WO ₃ ), or a composite oxide of TiO ₂ and WO ₃ is used.

  Biological fuels composed of carbon compounds that are recycled in the natural biological world are carbohydrates such as sugars and starch, lipids, hydrocarbons, alcohols, aldehydes, or organic acids. Carbon dioxide and water are produced by plant photosynthesis. The solar energy generated from the plant and stored as biological fuel is used as chemical energy and heat energy by animal food metabolism to form a clean circulatory system that returns to carbon dioxide and water.

  Biological cells that oxidize bio-derived fuels made of carbon compounds using the substance metabolism system to reductant molecules generated by light irradiation and supply electrons can be used as long as they have a substance metabolism system. Any biological cell can be used. In particular, microorganisms located at the border between plants and animals in the natural biological world form one independent living body with one or a small number of cells, and the size of each living body is 1/10 micron. From the viewpoint of industrial use, it is possible to provide a power generation cell having a size as small as 10 to several tens of microns and from a large size to a micro size. Microorganisms include bacteria (bacteria), fungi, viruses, protozoa, algae, protozoa that are unicellular organisms having a size of 1 mm or less, multicellular metazoans, and the like. As the bacteria, Bacillus megatherium, Escherichia coli, Rhodopseudomonas spheroids, Nitrosomonas sp., Staphylococcus aureus, or metal ion reducing bacteria such as Rhodoferax ferrireducens, Geobacteraceae, and Shewanellaceae can be preferably used. As the fungi, yeast for brewing (Brewer's Yeast), E. coli, Fibrobacter succinogenes, which is a cellulose-degrading bacterium, and the like are relatively easy to culture and proliferate, and thus can be suitably used. As protozoa, Vorticella microstoma, Epistylis plicatilis, Colpidium campylun, Paramecium caudatum, and the like can be suitably used because they can live near room temperature. As algae, Anabaena variabilis, Anabaena cylindrica, Cyanobacteria (blue-green algae), Chlorella ellipsoidea and the like can be preferably used because they can be cultured and grown in a relatively wide temperature range, for example, 5 to 35 ° C.

  These living cells are preferably used by crushing part or all of the cell membrane. By disrupting the cell membrane, it becomes easy to move the redox mediators derived from organisms such as NAD / NADH and quinone / hydroquinone contained in the substance metabolism system in the cell into and out of the cell. Electrons obtained by oxidizing a biological fuel composed of a carbon compound using a substance metabolism system can smoothly move to reductant molecules generated by light irradiation through these redox mediators. By making the movement of electrons easier, it is possible to provide a larger current output as a biofuel cell. The degree of disruption varies depending on the type of living cell used. The cell membrane can be completely crushed, or can be crushed as long as it does not interfere with vital functions such as the growth of living cells.

  For the disruption of living cells, a mechanical method such as a homogenizer equipped with a stainless steel rotating blade, a homogenizer equipped with an ultrasonic vibrator, a ball mill equipped with a ceramic ball, a photocatalyst such as titanium oxide or a peroxide was used. Any method such as a chemical method, a physical method such as heating, pressurization, reduced pressure, drying, or freezing can be used.

As an electrolyte used in the biofuel cell of the present invention, an anion or / and cation can be transferred from the positive electrode to the negative electrode and / or from the negative electrode to the positive electrode, and the oxidation / reduction reaction at the positive electrode and the negative electrode can be continuously advanced. As long as it can be used, any organic substance, inorganic substance, liquid, or solid can be used. An aqueous solution in which a metal salt such as KCl, NaCl, MgCl ₂ , NH ₄ Cl, or Na ₂ HPO ₄ , an alkali such as NH ₄ OH, KOH, or NaOH, or an acid such as H ₃ PO ₄ or H ₂ SO ₄ is dissolved in water. Is preferable because it is safe, does not cause environmental pollution, and is easy to handle. Further, quaternary ammonium salts such as pyridinium iodide, lithium salts such as lithium iodide, imidazolium salts such as imidazolinium iodide, acetonitrile, methoxyacetonyl, or methoxypropionitrile in which t-butylpyridine is dissolved. An ion exchange membrane made of a solution, a polymer material such as a fluororesin having a sulfonic acid group, an amide group, an ammonium group, a pyridinium group, or a salt such as LiBF ₄ , LiClO ₄ , (C ₄ H ₉ ) ₄ NBF ₄ Polymer electrolytes such as polypropylene oxide, polyethylene oxide, acrylonitrile, polyvinylidene fluoride, polyvinyl alcohol and the like in which is dissolved can be used.

The reaction of the positive electrode of the biofuel cell of the present invention is a reduction reaction that takes place at a potential that is nobler than the potential of electrons extracted from the biological fuel through the active species (S ^* ) of molecules excited by light at the negative electrode. Any reaction can be used as long as this electron undergoes an external load and is electrochemically accepted by the positive electrode.

Examples of the reaction of the positive electrode include water or oxygen reduction reaction, proton reduction reaction, NiOOH, MnOOH, Pb (OH) ₂ , PbO, MnO ₂ , Ag ₂ O, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _{2 and the} like. Hydroxide or oxide reduction reaction, reduction reaction of sulfides such as TiS ₂ , MoS ₂ , FeS, Ag ₂ S, reduction reaction of metal halides such as AgI, PbI ₂ , CuCl ₂ , Br ₂ , I Reduction reaction of halogen such as ₂ ; reduction reaction of organic sulfur compounds such as quinones and organic disulfide compounds; reduction reaction of conductive polymers such as polyaniline and polythiophene can be used.

  In this, it is preferable that a positive electrode is an oxygen electrode which reduces oxygen. In this case, since a gas containing oxygen can be used as the positive electrode active material, it is not necessary to hold the positive electrode active material in the battery, and thus a battery having a high energy density can be configured.

As the oxygen electrode, any substance capable of reducing oxygen can be used. Such materials include active _{carbon, MnO 2, Mn 3 O 4} , Mn 2 O 3, manganese oxides such as Mn ₅ O _8, platinum, palladium, iridium oxide, platinum ammine complexes, cobalt phenylenediamine complexes, metalloporphyrins (Metals: cobalt, manganese, zinc, magnesium, etc.), perovskite oxides such as La (Ca) CoO ₃ and La (Sr) MnO ₃ .

  Furthermore, the positive electrode is preferably a hydrogen electrode that reduces protons or water. In this way, sugars that are circulated and regenerated in the natural biological world, carbohydrates such as starch, lipids, hydrocarbons, alcohols, aldehydes, or organic substances such as organic acids as fuel, and an electromotive force of 0.05V to Although it is about 0.2 V, which is lower than when an oxygen electrode is used for the positive electrode, a battery capable of producing high purity hydrogen gas on-site can be configured.

As the hydrogen electrode, any electrode capable of reducing protons or water can be used. As an electrode for reducing protons or water, platinum group metals such as platinum (Pt), palladium (Pd), iridium (Ir), Pt—Sn (Pt ₃ Sn, etc.), Pt—Ti (Pt ₃ Ti, etc.) , Pt—Ni, Pt—Co, Pt—Ru (Pt ₇₀ Ru ₃₀ etc.), alloys containing platinum group metals such as Pt—Ir, Pt—Pd, iron (Fe), cobalt (Co), nickel (Ni ), Copper (Cu), silver (Ag), and gold (Au), or an electrode provided with a plurality of types at least on the surface portion in contact with the electrolyte can be effectively used.

  These metals or alloys are preferably disposed on the hydrogen electrode while being dispersed and supported on a conductive carrier having a large specific surface area such as carbon black because hydrogen can be generated with high efficiency.

  Further, a hydrogen electrode in which these metals or alloys are deposited and supported in an atomic size by an electrolytic deposition method or the like on a conductive support having a specific crystal plane such as an Au (111) plane or an Au (100) plane is a hydrogen electrode. This is preferable because the overvoltage of the generation reaction is low and the selectivity is high.

  As the hydrogen electrode for reducing protons, one having an enzyme hydrogenase, which is a natural metal protein possessed by orchids and lower algae, such as nickel-iron hydrogenase, can be used.

As the hydrogen electrode for reducing water, in particular, when the electrolyte is alkaline, one having a hydrogen storage alloy can be used effectively. Examples of such hydrogen storage alloys include TiFe, ZrMn ₂ , ZrV ₂ , ZrNi ₂ , CaNi ₅ , LaNi ₅ , MmNi ₅ (Mm = mixture of rare earth elements such as Misch metal, La and Ce), Mg2Ni, Mg2Cu, and the like. Can be used. In particular, a hydrogen equilibrium pressure of about 0.5 to 1 atm is preferable. As such, MmNi _4.3 Mn _0.4 Al _0.3 , MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 , MmNi _3.8 Mn _0.4 Al _0.3 Co _0.5 can be used effectively. These hydrogen storage alloys are mixed with a conductive agent such as carbon black and a binder in the form of a powder of several tens of μm to form a paste, which is then applied to a porous conductive substrate such as foamed nickel and used as a hydrogen electrode. be able to.

Next, for the purpose of promoting the negative electrode reaction, in addition to the biological cells that supply electrons by oxidizing the biological fuel consisting of carbon compounds to the reductant molecules generated by light irradiation using the substance metabolism system, the biological origin Oxidation derived from living organisms that functions to regenerate the original compound (S) by supplying electrons to the reductant (S *) generated by photoirradiation by the action of biologically derived enzyme (Enzyme) from the fuel. The reducing mediator (R) may be used alone or in combination with a biological enzyme (Enzyme). Such biological redox mediators (R) include quinone / hydroquinone redox couple, NAD ⁺ / NADH redox couple, NAD
P ⁺ / NADPH redox couple, iodine / iodate ion redox couple, metal protein having redox ability such as ferredoxin and myoglobin can be used.

  There is no particular limitation on the biological enzyme (Enzyme) that acts when the biological redox mediator (R) receives electrons from the biological fuel, but depending on the type of biological fuel (Fuel), Dehydrogenases corresponding to these are used alone or in combination of several kinds. When Fuel is glucose, an enzyme containing at least glucose dehydrogenase (GDH) is used.

  When the biological fuel (Fuel) is D-glucose-6-phosphate, at least D-glucose-6-phosphate dehydrogenase (G-6-PDH) or at least G-6-PDH and 6-phosphate are used. Enzymes including gluconate dehydrogenase (6-PGDH) are used. When Fuel is methyl alcohol, an enzyme containing at least alcohol dehydrogenase (ADH), an enzyme containing at least ADH and aldehyde dehydrogenase (ALDH), or an enzyme containing at least ADH, ALDH and formate dehydrogenase (FDH) is used. When Fuel is ethyl alcohol, an enzyme containing at least alcohol dehydrogenase (ADH) or an enzyme containing at least ADH and aldehyde dehydrogenase (ALDH) is used. In addition, when a plurality of types of fuel are included, enzymes corresponding to the respective fuels are mixed and used.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
A configuration of a biofuel cell according to an embodiment of the present invention is shown in FIG. The biofuel cell includes a power generation cell (1), a bacterial incubator (2), and a cell wall crusher (3). The power generation cell (1) includes a photocatalyst electrode (11), an air electrode (12), an electrolyte (13), a diaphragm (14), a supply port (15), a discharge port (16), and a light source (17). The The bacteria (10) cultivated in the bacterial incubator (2) is a photocatalyst separated by the diaphragm (14) of the power generation cell (1) as the cell wall disrupted bacteria (10a) after the cell membrane is crushed by the cell membrane crusher (3). It is supplied to the cell on the electrode side (the left cell in FIG. 2). Fuel is supplied from the supply port (15) to the photocatalytic electrode side. Air is supplied to the air electrode side partitioned by the diaphragm (14). Power generation starts by irradiating the photocatalytic electrode (11) with light from the light source (17).

The photocatalytic electrode (11) is a compound having a porphyrin structure, 5- (4-carboxyphenyl) -10,15,20- (4-methylphenyl) porphyrin (P1a) as a compound that generates a reductant and an electron upon irradiation with light. The structure was as shown in Chemical Formula 1). More specifically, a light-transmitting conductive substrate in which an indium tin oxide (ITO) thin film having a surface resistance of 10 ohm / cm ² is formed on a glass substrate having a thickness of 1 mm is prepared, and an average particle size is 10 nm. An acetonitrile solution containing 30% by weight of polyethylene glycol in which 11% by weight of tin oxide (SnO ₂ ) particles was dispersed was applied on the ITO thin film by a dipping method, dried at 80 ° C., and then in air at 400 ° C. for 1 hour. By firing, a SnO ₂ fine particle film having a thickness of about 10 μm was formed. Next, the SnO ₂ fine particle film is immersed in an ethanol solution in which P1a is dissolved in 10 mM for 1 hour and then lifted, and ethanol is dissipated with dry hot air to deposit P1a on the SnO ₂ fine particle thin film, thereby forming the photocatalytic electrode (11). Produced.

  The air electrode (12) was prepared by holding a mixture of Mn2O3 powder, activated carbon powder, acetylene black powder and polytetrafluoroethylene (PTFE) binder on a nickel-plated stainless steel net having a thickness of 0.2 mm.

  As bacteria (10), Brewer's Yeast was used. The cell wall crusher (3) used a homogenizer equipped with a rotary blade having a diameter of 10 mm.

  As the electrolyte (13), a 0.1 M phosphate buffer solution (pH 7.4) was used.

  Glucose was used as a biological fuel. Glucose was supplied to the power generation cell (1) such that the glucose concentration in the electrolyte (13) on the photocatalyst electrode side partitioned by the diaphragm (14) was 200 mM.

  As the diaphragm (14), a Nafion 117 membrane manufactured by DuPont was used.

(Output characteristics of power generation cell)
FIG. 3 shows the output characteristics of the power generation cell (1) obtained when the power generation cell (1) is irradiated with light having a wavelength of 520 nm from the light source (17) made of a xenon lamp. In FIG. 3, curve (a) is an output characteristic obtained when light is irradiated using bacteria with disrupted cell walls. Curve (b) is an output characteristic obtained when light is irradiated using bacteria that do not pass through a cell wall crusher. Curve (c) shows the output characteristics obtained when using bacteria with disrupted cell walls and without light irradiation. In addition, when bacteria having broken cell walls were used and a glassy carbon electrode was used instead of the photocatalyst electrode (11) and no light was irradiated, the output characteristics were almost the same although slightly exceeding the characteristics of the curve (c).

By using bacteria with disrupted cell walls in combination with a photocatalytic electrode, a power generation output (curve (a)) exceeding 1 mW / cm ² per apparent unit area of the photocatalytic electrode can be obtained. When bacteria that do not disrupt the cell wall are combined with the photocatalytic electrode, the power generation output is small (curve (b)), but compared to when the bacteria that disrupt the cell wall are combined with the electrode that does not irradiate light (curve (c)), A much larger power output can be obtained.

In this example, tin oxide (SnO ₂ ) was used as the oxide semiconductor, but the same evaluation was performed using a TiO ₂ , ZnO, TiO ₂ · WO ₃ fine particle film instead of the SnO ₂ fine particle film. As a result, almost the same output characteristics of the power generation cell were obtained. Further, when P2, P3, P4, and P5 shown in Chemical formulas 2 to 5 are used instead of P1a as a compound that generates a reductant and electrons by light irradiation, substantially the same power generation cell characteristics were obtained.

（実施例２）
バクテリアとして醸造用イーストに代えて細胞壁を破砕した大腸菌（E. Coli K12）を用い、生物由来の燃料としてのエチルアルコール（光触媒電極側の電解質中の濃度が１重量％）を用いた以外は、実施例１と同様にして生物燃料電池を構成し、発電セルの出力特性の評価を行った。
バクテリアセル（大腸菌）の量を少ない（電解質の濁度が０．２度）から多い（電解質の濁度が２．０度）の範囲で段階的に変化させた際の発電セルの電圧と出力電流との関係を図４に示す。バクテリアセルの量に従って、発電セルの特に出力電流の大きさが大きく変化し、バクテリアセルが負極の反応に直接関与し、発電セルを動作させていることが分かる。

(Example 2)
Except for using E. Coli K12 (E. Coli K12) with crushed cell walls instead of yeast for brewing as bacteria, and using ethyl alcohol (concentration in the electrolyte on the photocatalytic electrode side is 1% by weight) as a biological fuel, A biofuel cell was constructed in the same manner as in Example 1, and the output characteristics of the power generation cell were evaluated.
Voltage and output of the power generation cell when the amount of bacterial cells (E. coli) is changed stepwise from low (electrolyte turbidity 0.2 degree) to high (electrolyte turbidity 2.0 degree) FIG. 4 shows the relationship with current. It can be seen that the magnitude of the output current of the power generation cell changes greatly according to the amount of the bacterial cell, and the bacterial cell is directly involved in the reaction of the negative electrode to operate the power generation cell.

In this example, tin oxide (SnO ₂ ) was used as the oxide semiconductor, but the same evaluation was performed using a TiO ₂ , ZnO, TiO ₂ · WO ₃ fine particle film instead of the SnO ₂ fine particle film. As a result, almost the same output characteristics of the power generation cell were obtained. Further, when P2, P3, P4, and P5 shown in Chemical formulas 2 to 5 are used instead of P1a as a compound that generates a reductant and electrons by light irradiation, substantially the same power generation cell characteristics were obtained.

(Example 3)
Example except that metal ion-reducing bacteria (Rhodoferax ferrireducens) were used as bacteria instead of brewing yeast, and methyl alcohol (concentration in the electrolyte on the photocatalyst electrode side was 1.5% by weight) was used as the biofuel. A biofuel cell was constructed in the same manner as in Example 1, and the output characteristics of the power generation cell were evaluated. When light irradiation was performed on bacteria whose cell walls were crushed and bacteria that were not crushed, the output characteristics almost the same as the curves (a), (b), and (c) shown in FIG. 3 were obtained when no light was irradiated.

In this example, tin oxide (SnO ₂ ) was used as the oxide semiconductor, but the same evaluation was performed using a TiO ₂ , ZnO, TiO ₂ · WO ₃ fine particle film instead of the SnO ₂ fine particle film. As a result, almost the same output characteristics of the power generation cell were obtained. Further, even when P2, P3, P4, and P5 shown in Chemical Formula 2 to Chemical Formula 5 were used in place of P1a as a compound that generates a reductant and electrons by light irradiation, substantially the same power generation cell characteristics were obtained.

Example 4
Example 1 except that cell-degrading cellulolytic bacteria (Fibrobacter succinogenes) were used as bacteria instead of brewing yeast, and starch (concentration in the electrolyte on the photocatalytic electrode side was 50 mM) was used as the biofuel. A biofuel cell was constructed in the same manner as described above, and the output characteristics of the power generation cell were evaluated. An output characteristic almost similar to that of the curve (a) shown in FIG. 3 was obtained.

In this example, tin oxide (SnO ₂ ) was used as the oxide semiconductor, but the same evaluation was performed using a TiO ₂ , ZnO, TiO ₂ · WO ₃ fine particle film instead of the SnO ₂ fine particle film. As a result, almost the same output characteristics of the power generation cell were obtained. Further, even when P2, P3, P4, and P5 shown in Chemical Formula 2 to Chemical Formula 5 were used in place of P1a as a compound that generates a reductant and electrons by light irradiation, substantially the same power generation cell characteristics were obtained.

(Example 5)
Cellulose-degrading bacteria (Fibrobacter succinogenes) whose cell walls have been crushed are used as bacteria instead of brewing yeast, starch (concentration in the electrolyte on the photocatalyst electrode side is 50 mM) is used as the biofuel, and SnO ₂ is used as the oxide semiconductor. In place of the fine particle film, a TiO ₂ fine particle film is used, and further, a paste in which platinum fine particles having an average diameter of 5 nm as a positive electrode are dispersed and supported on a carbon black carrier at a ratio of 43 wt% with respect to the whole is mixed with a fluororesin. A biofuel cell was constructed in the same manner as in Example 1 except that a hydrogen electrode prepared by coating on a carbon fiber nonwoven fabric was used, and the output characteristics of the power generation cell were evaluated, and the hydrogen gas generation characteristics from the positive electrode Was evaluated.

  The negative electrode was irradiated with light having a wavelength range of 460 to 1100 nm obtained by cutting the ultraviolet region and infrared region of the xenon lamp light source. Simultaneously with the light irradiation, an electromotive force of 0.17 V was generated between the positive electrode and the negative electrode. When the positive electrode and the negative electrode were short-circuited, hydrogen gas bubbles were continuously generated from the positive electrode. The amount of hydrogen gas generated increased in proportion to the time of light irradiation. If the starch of fuel is not added, an electromotive force is temporarily generated and hydrogen gas bubbles are generated, but continuous generation does not occur. You can see that starch works as a fuel. Electrons generated on the negative electrode side due to the oxidation of starch by the action of the photocatalytic electrode and cellulose-degrading bacteria are used for the reduction of water and protons on the positive electrode side to generate hydrogen gas. That is, when the biofuel cell of the present invention is used, not only electric power can be obtained, but also hydrogen gas fuel can be obtained from starch, which is a biofuel material.

In this example, titanium oxide (TiO ₂ ) was used as the oxide semiconductor. However, when similar evaluation was performed using ZnO, TiO ₂ · WO ₃ fine particle film instead of the TiO ₂ fine particle film, almost the same results were obtained. Similar power cell output characteristics were obtained. Further, even when P2, P3, P4, and P5 shown in chemical formulas 2 to 5 are used in place of P1a as a compound that generates a reductant and electrons by light irradiation, almost the same power generation cell characteristics and hydrogen gas generation characteristics were obtained. .

Example 6
Cellulose-degrading bacteria (Fibrobacter succinogenes) whose cell walls have been crushed are used as bacteria instead of brewing yeast, starch (concentration in the electrolyte on the photocatalyst electrode side is 50 mM) is used as the biofuel, and SnO ₂ is used as the oxide semiconductor. Instead of using a TiO ₂ fine particle film instead of the fine particle film, and using a hydrogen electrode prepared by fixing enzyme hydrogenase and methyl viologen extracted from ransow on the gold electrode surface with poly L-lysine as the positive electrode, A biofuel cell was constructed in the same manner as in Example 1, and the output characteristics of the power generation cell and the hydrogen gas generation characteristics from the positive electrode were evaluated.

  The negative electrode was irradiated with light having a wavelength range of 460 to 1100 nm obtained by cutting the ultraviolet region and infrared region of the xenon lamp light source. Simultaneously with the light irradiation, an electromotive force of 0.13 V was generated between the positive electrode and the negative electrode. When the positive electrode and the negative electrode were short-circuited, hydrogen gas bubbles were continuously generated from the positive electrode. The amount of hydrogen gas generated increased in proportion to the time of light irradiation. If starch of fuel is not added, an electromotive force is temporarily generated and hydrogen gas bubbles are generated, but continuous generation does not occur. You can see that starch works as a fuel. Electrons generated on the negative electrode side due to the oxidation of starch by the action of the photocatalyst electrode and cellulose-degrading bacteria are used for proton reduction on the positive electrode side to generate hydrogen gas. That is, when the biofuel cell of the present invention is used, not only electric power can be obtained, but also hydrogen gas fuel can be obtained from starch, which is a biofuel material.

In this example, titanium oxide (TiO ₂ ) was used as the oxide semiconductor. However, when similar evaluation was performed using ZnO, TiO ₂ · WO ₃ fine particle film instead of the TiO ₂ fine particle film, almost the same results were obtained. Similar power cell output characteristics were obtained. Further, even when P2, P3, P4, and P5 shown in chemical formulas 2 to 5 are used in place of P1a as a compound that generates a reductant and electrons by light irradiation, almost the same power generation cell characteristics and hydrogen gas generation characteristics were obtained. .

  According to the present invention, the chemical energy of biological fuel can be effectively used as direct electrical energy. Furthermore, hydrogen, which is a useful fuel material, can be obtained simultaneously with obtaining electric energy.

The power generation principle of a biofuel cell using a living cell (Cell) of the present invention, a compound (S) that generates a reductant (S *) and an electron (e−) by light irradiation, and a biofuel (Fuel) is shown. Pattern diagram The figure which shows the structure of the biofuel cell used for the output characteristic evaluation of the power generation cell in the Example of this invention. The figure which shows the output characteristic of the electric power generation cell in the Example of this invention The figure which shows the output characteristic of the electric power generation cell in the Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power generation cell 2 Bacteria incubator 3 Cell wall crusher 10 Bacteria 10a Cell wall crushing bacteria 11 Photocatalyst electrode (negative electrode)
12 Air electrode (positive electrode)
13 Electrolyte 14 Membrane 15 Supply Port 16 Discharge Port 17 Light Source

Claims (7)

  A positive electrode and a negative electrode provided via an electrolyte, wherein the reaction of the negative electrode is a compound that generates a reductant and an electron upon irradiation with light, and a biological compound comprising a carbon compound using a substance metabolism system for the reductant molecule. A biofuel cell characterized in that it is an oxidation reaction in which electrons are electrochemically extracted from an organism-derived fuel comprising the carbon compound to an external electric circuit via a living cell that oxidizes fuel and supplies electrons.   The biofuel cell according to claim 1, wherein a cell wall of the living cell is partially crushed.   A compound that generates a reductant and an electron upon irradiation with light is disposed on the oxide semiconductor, has a single or a plurality of light absorption peaks between the wavelength of light of 300 nm and 1000 nm, and the electron generated upon irradiation with light is oxidized. 3. The biofuel cell according to claim 1, wherein the biofuel cell is led to an external electric circuit through a physical semiconductor. 4. The biofuel cell according to claim 3, wherein the compound that generates a reductant and an electron upon irradiation with light is a dye (P1) having a porphyrin structure represented by Chemical Formula 1.

  The biofuel cell according to claim 1 or 2, wherein the biological fuel contains at least starch, glucose, methyl alcohol, and ethyl alcohol.   6. The biofuel cell according to claim 1, wherein the positive electrode is an oxygen electrode that reduces oxygen in the air or electrolyte. 6. The biofuel cell according to claim 1, wherein the positive electrode is a hydrogen electrode that reduces protons or water in the electrolyte.

Images