Patent Application
20050123823
The present invention relates to a photobiological fuel cell utilizing a photoelectrochemical reaction and an enzymatic action which in combination perform generation of electricity by the action of a photosensitizer compound which produces an oxidant species and an electron when irradiated with light, an oxidation-reduction mediator which supplies an electron to the oxidant species, and one or more enzymes that oxidize a carbon-containing compound and reduce the oxidation-reduction mediator to return it to its original form. The carbon-containing compound may be one that is cyclically regenerated in a natural biosphere, such as carbohydrate (e.g., sugar, starch), lipid, hydrocarbon, alcohol, aldehyde or organic acid.
A carbon-containing compound which is cyclically regenerated in a natural biosphere such as carbohydrate (e.g., sugar, starch), lipid, hydrocarbon, alcohol, aldehyde or organic acid is produced from carbon dioxide gas and water by photosynthesis. Solar energy, which has been converted to chemical energy and accumulated in the form of carbon-containing compounds, is used as chemical energy in the metabolism of an organism to produce carbon dioxide gas and water. This forms a clean cyclic system. For example, a carbohydrate, which is a general term for saccharides such as monosaccharide, oligosaccharide and polysaccharide as well as saccharide analogues such as cyclic polyvalent alcohols and amino saccharides, is made by a plant or other photosynthetic organism during photosynthesis. A second organism can ingest a carbohydrate from a plant and use it as a food to provide energy. When glucose, which is a typical carbohydrate represented by the chemical formula C6H12O6, is completely oxidized, it releases 24 electrons per molecule, and is converted to carbon dioxide gas. In the body of an animal or other organism, the potential energy of the 24 electrons is utilized as an energy source. A thermodynamic calculation shows that glucose has a potentially useable energy of 2,872 kJ per mol, or 4.43 Wh per g. This energy density exceeds the weight energy density (3.8 Wh/g) of metallic lithium, which is used as a negative electrode for a lithium battery, which is known as a high energy density battery.
There are several methods for utilizing the chemical energy possessed by a carbon-containing compound such as a carbohydrate. One such method comprises direct combustion of a carbon-containing compound in air to give heat energy. Another method uses a carbon-containing compound as a nutrient in fermentation, wherein a microorganism produces fuels such as methane or ethanol. Yet another method produces an energy-rich compound such as ATP through the mediation of enzymes present in an organism.
As one method for utilizing the chemical energy possessed by a carbon-containing compound, there is a biological fuel cell disclosed in U.S. Pat. No. 6,294,281 that uses an enzyme and an oxidation-reduction mediator. Further, U.S. Pat. No. 4,117,202 discloses a photosynthetically driven biological fuel cell, which generates electricity using a photosynthetic cell derived from a living organism (Digitaria sanguinalis) that uses a carbon-containing compound as a nutrient.
The photosynthetically driven biological fuel cell disclosed in U.S. Pat. No. 4,117,202 can utilize chemical energy possessed by a carbon-containing compound as well as light radiation energy such as sunlight. This may be an improvement compared with the process disclosed in U.S. Pat. No. 6,294,281, which can utilize only chemical energy possessed by a carbon-containing compound. However, the photosynthetically-driven biological fuel cell disclosed in U.S. Pat. No. 4,117,202 utilizes a photosynthetic cell originated from a living organism, and thus requires careful control over temperature, solution formulation, and nutrient to allow the living cells to survive. This fuel cell is also disadvantageous in that a culture vessel for living cells must be used, requiring a complicated and large power-generating apparatus. The biological fuel cell disclosed in U.S. Pat. No. 6,294,281 can generate electric power merely by dipping positive and negative electrodes having an enzyme and an oxidation-reduction mediator fixed thereto into an electrolyte containing a carbon-containing compound. Thus, this biological fuel cell is advantageous in that it requires only a simplified power-generating system and can be miniaturized. However, this biological fuel cell cannot utilize light radiation energy.
It is therefore an aim of the invention to provide a photobiological fuel cell which can be miniaturized and utilize light energy in addition to chemical energy possessed by a carbon-containing compound.
The foregoing aim of the present invention will become apparent from the following detailed description and examples.
The invention provides a photobiological fuel cell comprising a positive electrode and a negative electrode provided with an electrolyte interposed between them. Through the action of several intermediary species, the negative electrode receives an electron from a carbon-containing fuel compound, which is therefore oxidized. The carbon-containing fuel compound may be one that is cyclically regenerated in a natural biosphere, such as carbohydrate (e.g., sugar, starch), lipid, hydrocarbon, alcohol, aldehyde or organic acid. This oxidation is accomplished through several mediators. The first of these is a photosensitizer material, attached to the negative electrode, that is converted to an electronically excited state when irradiated with light. The electronically excited state injects an electron into the electrode, from where it flows into an external circuit to do work. Loss of an electron from the photosensitizer material leaves an oxidized photosensitizer, which is in turn reduced back to its original form by an oxidation-reduction mediator. The resulting oxidized form of the oxidation-reduction mediator is reduced back to its original form by one or more enzymes, which obtain the necessary electrons by oxidation of the carbon-containing fuel compound. Thereby, chemical energy possessed by the carbon-containing fuel compound and light energy such as sunlight can be utilized to generate electricity.
The positive electrode may be one that undergoes an oxygen reduction reaction at a higher potential (i.e., more anodic potential) than the oxidation reaction at the negative electrode, or another suitable electrode.
By way of example and to make the description more clear, reference is made to the accompanying drawings in which:
The photobiological fuel cell of the invention includes a positive electrode and a negative electrode provided as constituents with an electrolyte interposed between them. When the negative electrode receives electrons from a carbon-containing fuel compound via a photosensitizer compound which produces an oxidant and electrons when irradiated with light, an oxidation-reduction mediator which supplies electrons to the oxidized photosensitizer molecule, and enzymes that catalyze oxidation of the carbon-containing fuel compound, an electromotive force is generated across the positive electrode and the negative electrode. This makes it possible to utilize chemical energy accumulated in the carbon-containing compound directly as electrical energy in a form biased by light radiation energy.
The photosensitizer compound S, which produces an oxidant S+ and an electron when irradiated with light, is disposed on an oxide semiconductor. This compound may have a single light absorption peak or a plurality of light absorption peaks in a wavelength range of ˜300 nm to ˜1,000 nm. Such a compound may be a metal complex dye, organic dye, or the like. Examples of a metal complex dye are ruthenium complex dyes or platinum complex dyes having biquinoline, bipyridyl, phenanthroline, or thiocyanic acid or derivatives thereof as ligands. Examples of organic dyes which may also contain metal atoms are porphyrin-based dyes having a single porphyrin ring or a plurality of porphyrin rings. The porphyrin rings may be metal free, or contain zinc (Zn), magnesium (Mg), or the like as a central atom. Examples of such a porphyrin-based dye include those represented by the general formulae P1 to P6 below. Examples of organic dyes are 9-phenylxanthene-based dyes, merocyanine-based dyes, polymethine-based dyes, or the like. In particular, the compound P1, 5-(4-carboxyphenyl)-10,15,20-(4-methylphenyl) porphyrin, having the structure shown below has a high light absorption efficiency and also high affinity for the oxide semiconductor so that it cannot be easily eluted with the electrolyte and thus can be kept stable even after a prolonged contact with the electrolyte. Further, since generation of excited electrons from the compound P1 by irradiation with light can occur over a prolonged lifetime, the compound P1 can exhibit high photoelectric conversion efficiency to advantage. The disposition of a compound which produces an oxidant and an electron when irradiated with light on an oxide semiconductor makes it possible to quickly move an excited electron produced by irradiation with light to the oxide semiconductor and makes less likely the recombination of the oxidant and excited electron produced by irradiation with light, thereby keeping the efficiency of reception of electrons from the carbon-containing compound into the external electrical circuit higher.
As the oxide semiconductor, tin dioxide (SnO2), titanium dioxide (TiO2), zinc oxide (ZnO), tungsten oxide (WO3) or composites thereof such as TiO2—WO3 may be used.
Examples of the carbon-containing fuel compound used in this invention, which may be one that is cyclically regenerated in a natural biosphere, include carbohydrates (e.g., sugars, starches), lipids, hydrocarbons, alcohols, aldehydes and organic acids. Such compounds can be produced from carbon dioxide gas and water by photosynthesis and then accumulated. The solar energy stored in these compounds is used as chemical energy via the metabolism of a organism, producing carbon dioxide gas. This forms a clean cyclic system.
Examples of the oxidation-reduction mediator (R) which receives electrons from the carbon-containing fuel compound through the mediation of enzymes and supplies electrons to the oxidant (S+) produced by irradiation with light to regenerate the original photosensitizer compound (S) are a quinone/hydroquinone oxidation-reduction couple, the NAD+/NADH oxidation-reduction couple, the NADP+/NADPH oxidation-reduction couple, the I2/I3− oxidation-reduction couple, and metal proteins having an oxidation-reduction capacity such as ferredoxin and myoglobin.
The enzymes, which catalyze the transfer of electrons from the carbon-containing fuel compound to an oxidized form of the oxidation-reduction mediator R, are not specifically limited. In practice, however, dehydrogenase enzymes may be used singly or in combination depending on the kind of the carbon-containing fuel compound. In the case where the fuel is glucose, an enzyme system containing at least glucose dehydrogenase (GDH) may be used.
In the case where the fuel is D-glucose-6-phosphate, an enzyme system containing at least D-glucose-6-phosphate dehydrogenase (G-6-PDH) or at least G-6-PDH and 6-phosphogluconate dehydrogenase (6-PGDH) may be used.
In the case where the fuel is methyl alcohol, an enzyme system containing at least an alcohol dehydrogenase (ADH), an enzyme system containing at least ADH and an aldehyde dehydrogenase (ALDH), or an enzyme system containing at least ADH, ALDH and a formate dehydrogenase (FDH) may be used.
In the case where the fuel is ethyl alcohol, an enzyme system containing at least an alcohol dehydrogenase (ADH) or an enzyme system containing at least ADH and an aldehyde dehydrogenase (ALDH) may be used. In the case where a plurality of fuels is used, enzymes corresponding to these fuels may be used in admixture.
As the electrolyte to be incorporated into the photobiological fuel cell of the invention there may be used any material regardless of whether it is an organic material, inorganic material, liquid or solid so far as it allows the movement of anions and/or cations from the positive electrode to the negative electrode and/or from the negative electrode to the positive electrode to cause continuous progress of oxidation-reduction reactions at the positive electrode and the negative electrode. An aqueous solution obtained by dissolving a salt such as KCl, NaCl, MgCl2, NH4Cl and Na2HPO4, an alkali such as NH4OH, KOH and NaOH or an acid such as H3PO4 and H2SO4 in water is safe, causes no environmental pollution, and can be easily handled to advantage. Alternatively, a solution of a quaternary ammonium salt such as pyridinium iodide, a lithium salt such as lithium iodide, an imidazolium salt such as imidazolinium iodide, t-butylpyridine or the like in acetonitrile, methoxyacetonitrile or methoxypropionitrile, an ion exchange membrane made of a polymer material such as fluororesin having sulfonic acid groups, amide groups, ammonium groups, pyridinium groups or the like or a polymer electrolyte such as solution of a salt such as LiBF4, LiClO4 and (C4H9)4NBF4 in a polypropylene oxide, polyethylene oxide, acrylonitrile, polyvinylidene fluoride, polyvinyl alcohol or the like may be used.
The reaction at the positive electrode in the photobiological fuel cell of the invention involves a reduction reaction occurring at a higher (or more anodic) potential than that of the electron taken out of the carbon-containing compound via an optically excited active species (S*) of molecule at the negative electrode. Any reduction reaction can be employed so far as the electron thus taken out is electrochemically received by the positive electrode via the external load.
Examples of the reaction at the positive electrode include reduction reactions of water or oxygen, reduction reactions of hydroxide or oxides such as NiOOH, MnOOH, Pb(OH)2, PbO, MnO2, Ag2O, LiCoO2, LiMn2O4 and LiNiO2, reduction reactions of sulfides such as TiS2, MoS2, FeS and Ag2S, reduction reactions of metal halides such as AgI, PbI2 and CuCl2, reduction reactions of halogen such as Br2 and I2, reduction reactions of organic sulfur compounds such as quinone and organic disulfide compounds, and reduction reactions of electrically-conductive polymers such as polyaniline and polythiophene.
In particular, the positive electrode is preferably an oxygen electrode for reducing oxygen. In this arrangement, a gas containing oxygen can be used as the positive active material, eliminating the necessity of retaining a positive active material in the battery and hence making it possible to form a battery having a higher energy density.
Any material capable of reducing oxygen may be used as the oxygen electrode. Examples of such an oxygen-reducing material include activated charcoal, manganese oxide including MnO2, Mn3O4, Mn2O3 and Mn5O8, platinum, palladium, iridium oxide, platinum-ammine complexes, cobalt-phenylenediamine complexes, metal porphyrins (metal: cobalt, manganese, zinc, magnesium, etc.), and perovskite oxides such as La(Ca)CoO3 and La(Sr)MnO3.
The invention will be further described in the following examples.
As a photosensitizer compound which produces an oxidant and an electron when irradiated with light, 5-(4-carboxyphenyl)-10,15,20-(4-methylphenyl)porphyrin (P1) was used as a typical representative of a porphyrin photosensitizer used to prepare a negative electrode.
A light-transmitting glass substrate with a thickness of 1 mm bearing a thin film of electrically conducting indium-tin oxide (ITO) with a surface resistivity of 10-12 Ω/cm2 was used to prepare the negative electrode. A 1% by weight aqueous dispersion of particulate tin dioxide (SnO2) having an average particle diameter of 10 nm was deposited on the ITO film by spraying or otherwise applying layers over a hot plate. The electrode was dried at a temperature of 80° C., and then sintered at a temperature of 400° C. in air for 1 hour to form a film of particulate SnO2. Subsequently, the electrode was dipped into a 1-5 mM solution of photosensitizer P1 (dissolved in dichloromethane, toluene, or hexanes) for typically 1 hour, withdrawn from the solution, washed with clean solvent, and dried with a stream of nitrogen gas. The presence of P1 on the electrode particulate surface was confirmed by its absorption spectrum. In this manner, the negative electrode was prepared.
The negative electrode thus prepared was then used to assemble a power-generating cell 21 having the structure shown in
In the power-generating cell 21, the film of particulate SnO2 on the negative electrode 23 on which the dye P1 is deposited comes in contact with an electrolyte 26. In the electrolyte 26 are disposed a counter electrode 24 which forms a battery in combination with the negative electrode 23 and a reference electrode 25 which gives a reference potential on the basis of which the potential of the negative electrode 23 is measured. Further disposed is an air electrode 27, which forms a battery in combination with the negative electrode 23 instead of the counter electrode 24. The air electrode 27 was prepared by embedding a mixture of Mn2O3 powder, activated charcoal powder, acetylene black powder and polytetrafluoroethylene (PTFE) binder on a nickel screen having a thickness of 0.2 mm. The reference numeral 22 indicates a silicon plug for fixing the counter electrode 24 and the reference electrode 25 to the power-generating cell 21.
A power-generating cell (a) was assembled as described above, using the negative electrode 23, a platinum (Pt) counter electrode (24), and an electrolyte 26, which is a 0.1 M aqueous solution of sodium acetate (NaOAc) containing 2.5 mM hydroquinone (QH2) as an oxidation-reduction mediator (R).
A power-generating cell (b) was assembled as described above, using the negative electrode 23, a platinum (Pt) counter electrode 24 immersed in a saturated aqueous solution of potassium sulfate free of dissolved oxygen and isolated from the electrolyte 26 by an ion-permeable membrane, and electrolyte 26, which is a 0.1 M aqueous solution of sodium acetate (NaOAc) containing 2.5 mM nicotinamide-adenine dinucleotide in the reduced form (NADH) as an oxidation-reduction mediator (R).
A power-generating cell (c) was assembled as described above, using the negative electrode 23, a counter electrode 24, which is a mercury/mercury (I) sulfate electrode separated from electrolyte 26 by an ion permeable membrane, and electrolyte 26, which is an 0.1 M aqueous solution of sodium acetate containing 2.5 mM nicotinamide-adenine dinucleotide in the reduced form (NADH) as an oxidation-reduction mediator (R).
In these cells, the dye deposited on the negative electrode acts as a photosensitizer compound (S) which upon irradiation produces an excited state (S*). In contact with the metal oxide, it injects an electron into the oxide particle, producing an oxidant (S+). The external circuit removes the electron thus produced, where it is then measured as output current of the battery. In cells of type (c), the oxidant (S+) receives an electron from the oxidation-reduction mediator NADH (or in some cases QH2), regenerating S. Thus, in a cell lacking enzymes or carbon-containing fuel compounds, the supply of electrons to the external circuit lasts until NADH (or QH2 when that is used as the oxidation-reduction mediator) is consumed.
An assay (not performed in the cell) was done to test the production of NADH when NAD+ is present and methanol is used as the carbon-containing fuel compound. An aqueous solution of pH 8.0 containing 1 M NaCl, 5 mM oxidized nicotinamide-adenine-dinucleotide (NAD+) and methanol with 0.0 and 0.05 mM reduced nicotinamide-adenine-dinucleotide (NADH) and an alcohol dehydrogenase (ADH), an aldehyde dehydrogenase (ALDH) and a formate dehydrogenase (FDH) as enzymes added thereto. The change of NADH concentration with time during irradiation with light is shown in
In
In these and other experiments, the concentration of NADH in the electrolyte was determined by the intensity of the peak present in the vicinity of 340 nm in the UV absorption spectrum of NADH.
In the present example, tin oxide (SnO2) was used as the oxide semiconductor. The same evaluation was made with particulate TiO2, and could be made with films of particulate metal oxide such as ZnO and TiO2.WO3 instead of SnO2. The same evaluation using SnO2 was also made on the compounds P2, P3, P4, P5 and P6 instead of the compound P1 as a photosensitizer. These compounds also produce an oxidant and an electron when irradiated with light. As a result, these power-generating cells will exhibit operating characteristics similar to that of P1.
A power-generating cell was formed by the same type of negative electrode 23 as used in Example 1, platinum (Pt) as counter electrode 24 and an aqueous buffered solution at pH 8.0 containing NADP+/NADPH as the oxidation-reduction mediator in the electrolyte. D-Glucose-6-phosphate (G-6-P) was used as a carbon-containing fuel compound. D-glucose-6-phosphate dehydrogenase (G-6-PDH) and 6-phosphogluconate dehydrogenase (6-PGDH) were used as an enzyme system.
In this example, the oxide semiconductor was tin oxide (SnO2). Similar evaluations could be made on films of particulate TiO2 or other particulate metal oxides such as ZnO and TiO2.WO3.
A power-generating cell was formed by the same negative electrode 23 as used in Example 1, platinum (Pt) as a counter electrode 24 and a buffered solution at pH 8.0 containing a 0.5 mM NADH and 10 mM NAD+ as an electrolyte. Ethanol (CH3CH2OH) was used as a carbon-containing fuel compound. The nicotinamide-adenine-dinucleotide couple (NADH)/(NAD+) was used as the oxidation-reduction mediator. An alcohol dehydrogenase (ADH) and an aldehyde dehydrogenase (ALDH) were used as an enzyme system.
A power-generating cell was formed by a negative electrode 23, an air electrode 27 and an electrolyte at pH 8 containing ethanol, NADH and ADH as an enzyme system. When irradiated with sunlight, the power-generating cell operated as a photobiological fuel cell having a voltage of about 0.65 V.
In
A power-generating cell was formed by an electrolyte 23, an air electrode 27, and an electrolyte containing NADH, NAD+, ethanol, and ADH and ALDH as an enzyme system. When irradiated with sunlight, the power-generating cell operated as a photobiological fuel cell having a voltage of about 0.65 V.
In the present example, tin oxide (SnO2) was used as the oxide semiconductor. The same evaluation could be made with films of particulate TiO2, or other particulate metal oxides such as ZnO and TiO2.WO3 instead of SnO2. The same evaluation could also be made on the compounds P2, P3, P4, P5 and P6 instead of the compound P1 as a photosensitizer compound, which produces an oxidant and an electron when irradiated with light.
A power-generating cell was formed by the same negative electrode 23 as used in Example 1, platinum (Pt) as a counter electrode 24 and a buffer solution having pH 7.3 containing an NAD+/NADH oxidation-reduction mediator in the electrolyte. D-glucose was used as a carbon-containing compound was used. D-glucose-dehydrogenase (GDH) was used as an enzyme.
Before addition of the enzyme, NADH is consumed and oxidized to NAD+, with the concurrent production of electrons in the external circuit. After addition of the enzyme, NADH is regenerated and the amount apparently consumed drops slightly below the original amount. In other words, NADH releases electrons to form NAD+, which then receives electrons from D-glucose through catalysis by the enzyme to reform NADH. Thus, in the presence of the enzyme, the amount of NADH consumed is kept constant regardless of the number of electrons thus taken out. This state lasts as long as D-glucose is present in the electrolyte.
In the present example, tin oxide (SnO2) was used as the oxide semiconductor. The same evaluation could be made on films of particulate TiO2, and on other particulate metal oxides such as ZnO and TiO2.WO3, instead of SnO2. The same evaluation could also be made on the compounds P2, P3, P4, P5 and P6 instead of the compound P1 as a photosensitizer compound which produces an oxidant and an electron when irradiated with light.
As mentioned above, the invention provides a photobiological fuel cell, which carries out an oxidation reaction involving the electrochemical reception of electrons from a carbon-containing fuel compound by an external electric circuit, via a photosensitizer molecule optically excited at the negative electrode and suitable electron mediators, to generate an electromotive force across the positive electrode and the negative electrode. In accordance with the invention, chemical energy possessed by the carbon-containing compound can be effectively utilized as electrical energy.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made thereto without departing from the spirit and scope thereof.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US02/11831 | 4/16/2002 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 60364879 | Mar 2002 | US |
