WO2011025021A1

WO2011025021A1 - Electrode for microbial fuel cell, and microbial fuel cell using same

Info

Publication number: WO2011025021A1
Application number: PCT/JP2010/064764
Authority: WO
Inventors: 橋本和仁; 石井和之; 中村龍平; 渡邉一哉; 趙勇
Original assignee: 独立行政法人科学技術振興機構; 国立大学法人東京大学
Priority date: 2009-08-31
Filing date: 2010-08-31
Publication date: 2011-03-03
Also published as: JPWO2011025021A1

Abstract

Disclosed are: an electrode for a microbial fuel cell, which can generate a high-output electric current in a microbial fuel cell; and a microbial fuel cell equipped with the electrode. Specifically disclosed is an electrode for a microbial fuel cell, which comprises an electrode base and an electrically conductive polymer formed on the whole or a part of the surface of the electrode base and having a nano-wire structure, and which can be used as an anode for a microbial fuel cell. In the electrode, the surface area is significantly increased. Therefore, the affinity between an electron conductive microorganism and the electrode is increased, and consequently the efficiency of the charge transfer from the microorganism to the electrode can be dramatically increased.

Description

Microbial fuel cell electrode and microbial fuel cell using the same

The present invention relates to an electrode used in a microbial fuel cell, more specifically, an electrode comprising an electrode substrate having a nanowire structure on the surface, and a microbial fuel cell using the same.

Microbial fuel cells are attracting attention as a new power generation system that replaces conventional fossil fuels.

A microbial fuel cell is a power generation system that converts chemical energy into electrical energy using the biological activity of microorganisms. Microbial fuel cells have the advantage of being a sustainable power generation system and capable of decomposing organic waste in parallel with power generation because they can use unused biomass such as organic waste liquid, sludge, and food residues as fuel. Have. In addition, if microorganisms having the ability to use pollutants are used, it is possible to purify the environment such as processing of contaminated waste liquid. Furthermore, since the microorganism itself functions as a biocatalyst for extracting electrons from organic substances, it does not require a gas exchange process or the like as in a conventional chemical fuel cell such as a hydrogen fuel cell, and has a very high energy conversion efficiency at low cost. There is also an advantage.

On the other hand, the current microbial fuel cell has a big problem that the output current density is low, and further improvement is required to obtain a practical power generation. In general, the increase in output current density in a microbial fuel cell depends on the efficiency of charge transfer from the microorganism to the electrode. The charge transfer efficiency is affected by the electrode surface area and electrode characteristics.

In order to solve the above problems, for example, an electron mediator (electron carrier) such as HNQ (2-hydroxy-1,4-naphthoquinone) is added to the electrolytic cell to improve the efficiency of electron transfer from the microorganism to the electrode. Attempts have been made to increase the output current density (Non-patent Document 1). However, the electronic mediator itself is generally expensive, and there are many problems that are harmful to the human body. Furthermore, the amount of current generated is insufficient in terms of practicality.

Also, Patent Document 1 discloses a microbial fuel cell in which polyaniline is further applied or dipped on carbon fibers serving as an electrode base using an electron storage type microbial mutant. By using carbon fiber, the surface of the electrode is increased, and polyaniline is coated as an electron mediator so that electrons can be efficiently extracted directly from microorganisms. However, this microbial fuel cell only has a thin film of polyaniline formed on the carbon fiber surface, and there is room for further improvement in improving the electron transfer between the microorganism and the electrode.

JP 2007-32405 A

In view of the above-described problems, the present invention aims to develop and provide an electrode for a microbial fuel cell capable of generating a high output current by further increasing the charge transfer efficiency from the microorganism to the electrode in the microbial fuel cell. And

It is another object of the present invention to provide a high-power microbial fuel cell using the electrode.

As a result of intensive studies to solve the above problems, the present inventors have formed a nanowire structure with a conductive polymer on the surface of the electrode substrate to increase the electrode surface area, thereby improving the efficiency of charge transfer from microorganisms to the electrode. Has been found to be 10 to 100 times stronger than the conventional microbial fuel cell electrode. This invention is based on the said knowledge, ie, provides the following.

(1) An electrode for a microbial fuel cell comprising an electrode substrate and a conductive polymer having a nanowire structure formed on all or part of the surface thereof.

(2) The electrode according to (1), wherein the nanowire structure includes a nanowire network.

(3) The electrode according to (1) or (2), wherein the electrode substrate contains metal or carbon.

(4) The electrode according to any one of (1) to (3), wherein the electrode is a fiber structure aggregate or a porous structure.

(5) The electrode according to any one of (1) to (4), wherein the electrode includes gaps or pores larger than the cell size of the electron-donating microorganism.

(6) The electrode according to (5), wherein the length and / or width of the gap and the diameter of the pores are 6 μm to 20 μm.

(7) The electrode according to (5) or (6), which contains an electron donating microorganism in the gap or pore.

(8) The conductive polymer is a polymer composed of aniline, aminophenol, diaminophenol, pyrrole, thiophene, paraphenylene, fluorene, furan, acetylene or a derivative thereof, or a combination thereof, or a mixture of the above polymers. The electrode according to any one of (1) to (7).

(9) The electrode according to (8), wherein the conductive polymer is polyaniline, aniline / aminophenol copolymer or aniline / diaminophenol copolymer.

(10) A microbial fuel cell using the electrode according to any one of (1) to (9).

(11) A microbial fuel cell comprising an anode and / or a cathode comprising the electrode according to any one of (1) to (9), an electrolyte solution, and an electrolytic cell containing them, The microbial fuel cell, wherein the electrolyte solution in the tank further comprises an electron donating microorganism consisting of a single species or a plurality of species and a nutrient substrate necessary for metabolism of the microorganism.

(12) The microbial fuel cell according to (11), wherein the cathode has a gas permeable air cathode and the electrolytic cell has a single cell structure composed only of an anode cell.

(13) The microbial fuel cell according to any one of (11) to (12), further comprising a redox mediator compound, an electron mediator and / or conductive fine particles in a tank in which the anode or the cathode is installed.

This specification includes the contents described in the specification and / or drawings of Japanese Patent Application No. 2009-200422 which is the basis of the priority of the present application.

According to the microbial fuel cell electrode of the present invention, the surface area of the electrode can be remarkably increased by the nanowire structure. As a result, an electrode capable of generating a high output current density can be provided.

According to the microbial fuel cell of the present invention, the output can be dramatically improved as compared with the conventional microbial fuel cell.

The specific example of the chemical structure of the conductive polymer in this invention. (A) shows the structural unit of polyaniline. (B) is a partial structure constituting an aniline / aminophenol copolymer (in this figure, aminophenol is orthoaminophenol, but may be metaaminophenol), and the aniline / amino of the present invention A phenol copolymer has at least one said structure in the structure which an aniline structural unit (a) superposes | polymerizes. Conversely, at least one aniline structural unit (a) may be included in the structure of the structural unit that is polymerized. (C) constitutes an aniline / diaminophenol copolymer (in this figure the diaminophenol is 2,4-diaminophenol, but may be 2,2-diaminophenol or 2,3-diaminophenol) It is a partial structure, and the aniline / diaminophenol copolymer of the present invention has at least one such structure in the structure in which the aniline structural unit (a) is polymerized. Conversely, at least one aniline structural unit (a) may be included in the structure of the structural unit that is polymerized. Scanning electron micrographs (a, c and e) of the nanowire structure of conductive polymer (in this figure, forming a nanowire network) formed on the surface of ITO supported on a glass plate and their magnification Figures (b, d and f). a and b are polyaniline, c and d are aniline / aminophenol copolymers (aniline: orthoaminophenol = 20: 1), e and f are aniline / diaminophenol copolymers (aniline: 2,4-diaminophenol = 20: 1) is shown respectively. Microbial fuel cell electrode (b) and one of the present invention comprising a carbon felt (a) and a fiber structure assembly in which a polyaniline nanowire structure (in this figure, a nanowire network is formed) is formed on the surface thereof. The scanning electron microscope figure of the electrode structural unit (d) for microbial fuel cells as a fiber structure aggregate | assembly of this invention which formed the nanowire structure of polyaniline on the surface of carbon fiber (c) of this invention. The electrochemical cell used in Example 2. The generated current obtained by the use of each anode in Experiment A of Example 2. (A) shows an ITO electrode, (b) shows an ITO / polyaniline smooth electrode, and (c) shows an ITO / polyaniline nanowire electrode. Generated current obtained by use of each anode in Experiment B of Example 2. (A) is a carbon plate (CP) electrode, (b) is a CP / polyaniline nanowire electrode, (c) is a CP / PAAP nanowire electrode, and (d) is a CP / PADAP nanowire electrode. Current density obtained by use of each anode in Experiment C of Example 2. (A) is an ITO electrode, (b) is an ITO / polyaniline smooth electrode, (c) is an ITO / PAAP smooth electrode, and (d) is an ITO / PADAP smooth electrode. The conceptual diagram which shows an example of the microbial fuel cell of this invention. The polarization curve of the microbial fuel cell by each anode of Example 3. (A) is a carbon felt electrode, (b) is a carbon felt / polyaniline thin layer electrode, and (c) is a carbon felt / polyaniline nanowire electrode. The output of the microbial fuel cell by each anode of Example 3. (A) is a carbon felt electrode, (b) is a carbon felt / polyaniline thin layer electrode, and (c) is a carbon felt / polyaniline nanowire electrode. The cyclic voltammogram of the microbial fuel cell by each anode of Example 3. FIG. (A) is a carbon felt electrode, (b) is a carbon felt / polyaniline thin layer electrode, and (c) is a carbon felt / polyaniline nanowire electrode.

1. Microbial fuel cell electrode 1-1. Configuration of Microbial Fuel Cell Electrode One aspect of the present invention is a microbial fuel cell electrode.

A microbial fuel cell (」MFC) uses an electron-donating microorganism as a biocatalyst to acquire or extract electrons generated by metabolism such as respiration of the microorganism and transmit it to an electrode to generate electricity. Refers to the device.

Here, the “electron-donating microorganism” refers to an electron generated by metabolism directly (for example, by contact between an electron carrier present in a cell membrane and the electrode) or indirectly ( A microorganism that can transmit (for example, via an electron-transmitting intermediary).

“Electron transfer mediator” refers to an electron carrier capable of transporting electrons from a microorganism to an electrode, such as a redox mediator compound, an electron mediator and / or conductive fine particles.

"Redox mediator compound" is mainly produced in an electron-donating microorganism, then released to the outside of the cell, and transports electrons generated by the metabolism of the microorganism by its own redox while reciprocating between the microorganism and the electrode. An electronic shuttle compound that can be used. Examples include phenazine-1-carboxamide, pyocyanin, 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ).

“Electron mediator” refers to an artificially synthesized redox compound having the same function as the redox mediator compound. For example, neutral red, safranine, phenazine etsulfate, thionine, methylene blue, toluidine blue O, phenothiazinone, resorufin, galocyanine, 2-hydroxy-1,4-naphthoquinone, porphyrin.

“Conductive fine particles” are fine particles made of metal or semiconductor that can bind to electron-donating microorganisms and extract the electrons from the microorganisms, and then transfer the electrons to the electrodes. For example, iron oxide, iron sulfide, oxidized Manganese is mentioned.

The type of electron-donating microorganism is not particularly limited as long as it is a microorganism that can transfer electrons to the electrode for a microbial fuel cell of the present invention. Preferred is a microorganism having an extracellular electron transfer capability. “Extracellular electron transfer ability” refers to a series of processes that oxidize and reduce electron carriers to acquire energy necessary for life activity and to transfer generated electrons to cell membranes (for example, membrane-bound type). (Lovley DR; Nat. Rev. Microbiol., 2006, 4, 497-508). If it is a microorganism having such a capability, the electrons held in the electron carrier on the cell membrane can be easily transferred by direct contact between the electron carrier and the electrode, and an intermediate such as a redox mediator compound can be used. Substances are preferred because they can easily extract electrons from microorganisms. Examples of electron-donating microorganisms having extracellular electron transfer ability include catabolic metal reducing bacteria such as the genus Shewanella and the genus Geobacter, the genus Pseudomonas and the genus Rhodoferax. Can be mentioned. Specific examples of bacteria belonging to the genus Shewanella include S. loihica, S. oneidensis, S. putrefaciens, and S. algae. Can be mentioned. Specific examples of bacteria belonging to the genus Geobacter include Geobacter sulfreduscens (G. sulfurreducens) and Geobacter metallireducens (G. metallireducens). Specific examples of bacteria belonging to the genus Pseudomonas include P. aeruginosa. Specific examples of bacteria belonging to the genus Rhodoferax include R. ferrireducens.

Furthermore, an electron donating microorganism capable of producing a redox mediator compound and releasing it to the outside of the cell is particularly preferable in the present invention. This is because the oxidation-reduction mediator compound can exert the effects of the present invention more by performing direct electron transfer with the nanowire structure of the present invention. Examples of the electron-donating microorganism that produces and releases the redox mediator compound include, for example, the genus Chewanella, Pseudomonas, and Rhodoferax.

Electron-transporting microorganisms can be of any wild type or mutant type. For example, a mutant electron-donating microorganism that releases more electrons out of the cell by genetic manipulation and / or a mutant electron-donating microorganism that generates and releases more redox mediator compounds meet the object of the present invention. More preferable.

“Electrode for microbial fuel cell” refers to an electrode used for the microbial fuel cell. In particular, in a microbial fuel cell, electrons from a microorganism to an electrode can be directly contacted between the electrode and an electron-donating microorganism or indirectly through the redox mediator compound, electron mediator, or conductive fine particles. Is caused to occur, whereby a potential is generated.

This electrode normally functions as an anode (cathode, negative electrode or negative electrode) when used in a microbial fuel cell, but can also be used as a cathode (anode, positive electrode or positive electrode). Moreover, the electrode for microbial fuel cells of the present invention can be used not only for microbial fuel cells but also for other applications to which the electrode of the present invention can be applied due to its configuration. This will be described in detail later in “1-2. Other Applications of Microbial Fuel Cell Electrode”.

The electrode for a microbial fuel cell according to the present invention is composed of an electrode substrate and a conductive polymer, and the conductive polymer forms a nanowire structure so that the electrode surface area is significantly increased as compared with a conventional electrode. It is characterized by having. Hereafter, each component in the electrode of this invention and the electrode for microbial fuel cells of this invention of this invention are demonstrated.

1-1-1. Electrode base “Electrode base” refers to a conductor constituting an electrode body. In principle, the electrode substrate has a connection terminal for connecting a lead wire connecting the electrode body and an external circuit.

The conductor may be an electronic conductor, an ionic conductor, or an electron / ion mixed conductor. Examples of the electronic conductor include metal, carbon (including carbon black, graphite, and the like) or a combination thereof. Examples of the metal include titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo), and ruthenium (Ru). ), Rhodium (Rh), palladium (Pd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), indium (In), tin (Sn) ) And the like. Here, the metal may be a single metal, its metal oxide, an alloy composed of a plurality of metals, or a combination thereof. For example, indium tin oxide (ITO: Indium Tin Oxide) is an example of the metal oxide.

In one embodiment, the electrode substrate has a rigidity that can hold the shape of the electrode itself. For example, when an electrode is comprised with a metal or carbon, it becomes possible to hold | maintain a fixed shape as an electrode by making the thickness or thickness into a predetermined magnitude or more. In this case, the electrode substrate itself also serves as an electrode support.

In other embodiments, the electrode substrate does not have to be rigid enough to hold the shape of the electrode. For example, the case where the electrode is powder-like fine particles or the case where the electrode is a very thin thin film such as a coating film is applicable. In this case, the electrode substrate is formed on a support surface made of another material that imparts an electrode shape. This configuration is convenient when the material of the electrode substrate is expensive and / or when it is difficult to have rigidity due to the nature of the material. The material of the “support made of another substance” is not particularly limited as long as it is a rigid insulator and is preferably a water-resistant substance. For example, glass, plastic, synthetic rubber, ceramics, water-resistant paper or plant pieces can be used. Examples of the method for supporting the electrode substrate on the surface of the support include application (including immersion), spraying, sticking, and vapor deposition. These may be performed based on methods known in the art. For example, a method in which carbon powder is mixed with an appropriate adhesive and applied onto the surface of the glass plate can be mentioned. The thickness of the electrode substrate formed on the surface of the support can form a nanowire structure of a conductive polymer, which will be described later, on the surface, and transmits the electrons received from the electron-donating microorganisms to the lead wire connected to the electrode substrate. There is no particular limitation if possible. What is necessary is just to determine suitably according to the magnitude | size of an electrode, the production cost of an electrode, the environment in the tank which throws an electrode, etc. In general, the thicker the electrode substrate, the higher the strength. As an example, when ITO is supported on a glass plate as a support, the ITO only needs to have a thickness of 0.01 to 100 μm.

1-1-2. Conductive polymer “Conductive polymer” is a general term for polymer compounds having electrical conductivity. Examples of the conductive polymer in the present invention include aniline, aminophenol (including orthoaminophenol, metaaminophenol, and paraaminophenol), diaminophenol (2,2-diaminophenol, 2,3-diaminophenol, 2,4- (Including diaminophenol), pyrrole, thiophene, paraphenylene, fluorene, furan, acetylene, or a polymer composed of a single monomer having a derivative thereof as a structural unit. Specifically, for example, polyaniline (PANI: PolyANIline; FIG. 1 (a)), polyaminophenol (including polyorthoaminophenol, polymetaaminophenol, polyparaaminophenol), polydiaminophenol (poly 2,2-diamino) And polymers of phenol, poly 2,3-diaminophenol, poly 2,4-diaminophenol), polypyrrole, polythiophene, polyparaphenylene, polyfluorene, polyfuran, polyacetylene, and derivatives thereof.

The conductive polymer in the present invention may be a copolymer composed of a combination of two or more different monomers and their derivatives. For example, an aniline / aminophenol copolymer composed of aniline and aminophenol (FIG. 1 (b)), an aniline / diaminophenol copolymer composed of aniline and diaminophenol (FIG. 1 (c)), 2,2-diaminophenol and 2,4 -2,2- / 2,4-diaminophenol copolymers composed of diaminophenol and aniline / 1,2,4-triaminobenzene copolymers composed of aniline and 1,2,4-triaminobenzene. In the present invention, polyaniline, aniline / aminophenol copolymer, and aniline / diaminophenol copolymer are preferably used, but are not limited thereto.

In the case of a copolymer, the mixing ratio of each monomer constituting it is not particularly limited. For example, in the case of an aniline / aminophenol copolymer, the ratio of aminophenol: aniline is 1: 1 to 1:30, 1: 1 to 1:25, 1: 1 to 1:20, 1: 1 to 1:15, The ratio may be from 1: 1 to 1:10 or from 1: 1 to 1: 5. In the case of an aniline / diaminophenol copolymer, the ratio of dianiphenol to aniline is 1: 1 to 1:30, 1: 1 to 1:25, 1: 1 to 1:20, 1: 1 to 1:15, It may be 1: 1 to 1:10 or 1: 1 to 1: 5.

Furthermore, although the conductive polymer constituting the electrode of the present invention is usually composed of a single polymer species, it may be composed of a mixture (composite) of a plurality of different conductive polymers. Specifically, for example, a mixture of a conductive polymer composed of a single monomer such as polyaniline and polypyrrole, or a mixture of a conductive polymer composed of a single monomer such as polyaniline and a copolymer such as an aniline / aminophenol copolymer. Is mentioned.

The conductive polymer in the present invention is characterized by having a nanowire structure formed on all or a part of the surface of the electrode substrate.

“Nanowire” is an artificial linear nanostructure composed of various materials such as metals, semiconductors, and polymers. A nanowire structure made of any of the above materials can be used for the electrode for a microbial fuel cell of the present invention. In this specification, a case where a nanowire made of a conductive polymer is used as an example is shown below.

“Nanowire structure” refers to a structure having nanowires as a structural unit. The nanowire structure of the present specification includes a two-dimensional nanowire structure and / or a nanowire network composed of a plurality of independent nanowires extending on the same plane as one form of the structure. As used herein, a “nanowire network” is formed by fusing together individual nanowires that are adjacent to each other on the same plane and / or different planes by growing in contact and / or longitudinal and / or radial directions. A three-dimensional network structure. For example, the structure shown in FIGS. 2, 3b, and 3d is applicable. The nanowire network normally has innumerable pores of about 10 nm to about 1 μm that can be invaded by an electron-transmitting mediator such as a redox mediator compound, although microorganisms cannot invade. By forming such a nanowire structure on the electrode substrate surface, the surface area of the electrode of the present invention can be dramatically increased.

The nanowire structure of the conductive polymer of the present invention can be prepared by a method known in the art (for example, Zhang H., et al., 2008, Mocromol. Rapid Commun., 29: 68-73; Cheng S ., 2006, Electrochem. Commun., 8: 489-494; Zang J., et al, 2008, Macromolecules, 41: 7053-7057, and Debiemme-Chouvy C., 2009, Electrochem. Commun., 11 Wanna) A nanowire structure is generally prepared by immersing the electrode substrate in a solution containing a monomer that is a constituent of a conductive polymer at a predetermined concentration, and then applying an electric current to deposit the electrode substrate on the electrode substrate. it can. A specific production method will be described in the section “1-3. Production of electrode for microbial fuel cell” described later.

1-1-3. Microbial Fuel Cell Electrode The shape of the microbial fuel cell electrode of the present invention is not particularly limited as long as it can function as an electrode. What is necessary is just to determine suitably according to the shape etc. of the microbial fuel cell which uses this electrode. For example, a flat plate shape, a substantially flat plate shape, a column shape, a substantially columnar shape, a spherical shape, a substantially spherical shape, or a combination thereof can be given. Such an electrode shape can be determined by configuring the electrode substrate in the desired shape when the electrode substrate itself has rigidity capable of holding the electrode shape. If the electrode substrate itself does not have sufficient rigidity to hold the electrode shape, it can be determined by configuring the support in a desired shape.

In one embodiment, the electrode of the present invention is a fiber structure aggregate or a porous structure. By forming the electrode as a fiber structure aggregate or a porous structure, a large number of irregularities are formed on the surface of the electrode, so that the surface area of the electrode increases as compared to a flat electrode such as a flat electrode. As a result, the chances of contact with the electron-donating microorganism or the electron-transmitting mediator increase, and the electron transfer rate from these to the electrode is improved, so that electrons generated from the electron-donating microorganism can be efficiently transmitted to the electrode. . In the present specification, the “fiber structure assembly” means that a plurality of thin linear electrode units (for example, electrodes having a structure as shown in FIG. 3d) are assembled to constitute the microbial fuel cell electrode of the present invention as a whole. (For example, an electrode having a structure as shown in FIG. 3b). Examples of the fiber structure aggregate include a carbon fiber aggregate (for example, carbon felt, carbon wool) or a metal fiber aggregate (for example, metal wool) in which a conductive polymer having a nanowire structure is formed entirely or partially on the surface thereof. ), Or a glass fiber aggregate (for example, glass wool), a cellulose fiber aggregate (for example, paper), or a fibrous protein carrying an electrode substrate on which a conductive polymer having a nanowire structure is formed on the entire surface or a part thereof Examples include aggregates (for example, silk felt) or plastic fiber aggregates. Examples of the porous structure include a porous carbon or porous metal in which a conductive polymer having a nanowire structure is formed on the whole or a part of the surface, or a conductive polymer having a nanowire structure on the whole or a part of the surface. Examples thereof include porous ceramics, porous plastics, plant pieces (for example, wood), animal pieces (for example, bones, shells, sponges) and the like that support the electrode substrate formed in the above.

In one embodiment, the electrode having a fibrous structure aggregate or porous structure includes one or more gaps or pores larger than the electron-donating microorganism used. As the electron-donating microorganisms enter the gaps or pores of the electrodes, the chances of contact between the electrodes and the electron-donating microorganisms or electron-transmitting mediators are increased compared to the smooth electrode. This is because the electron transfer rate can be improved and the electron-donating microorganism can be fixed and propagated in the gaps or pores. In general, the size of the electron-donating microorganism used in the electrode for the microbial fuel cell is about 0.5 to 2 μm in diameter for cocci, and about 0.2 to 1 μm in short diameter and about 1 to 2 in long diameter in the case of Neisseria gonorrhoeae. 8 μm. Accordingly, the size of the gaps or pores may be such that these microorganisms can easily enter, for example, the gap may have a length and width of 6 μm to 20 μm, preferably 8 μm to 18 μm. In the case of holes, the diameter may be 6 μm to 20 μm, preferably 8 μm to 18 μm. However, since it is sufficient that the electron-donating microorganism can enter, one or more gaps or pores larger than the above-described size may be provided.

In one embodiment, the electrode for a microbial fuel cell of the present invention may contain an electron donating microorganism in the gap or pore. As described above, a microbial fuel cell generates power using an electron-donating microorganism as a biocatalyst and biomass such as organic wastewater as fuel. Therefore, the microbial fuel cell electrode of the present invention is used by immersing it in the biomass. Usually, various kinds of microorganisms other than electron-donating microorganisms are mixed in such biomass. When a microorganism other than the electron-donating microorganism, that is, a microorganism that does not contribute to electron transfer with the electrode enters the gap or pore and occupies the site, the contact rate between the electron-donating microorganism and the electrode decreases, As a result, the power generation efficiency of the electrode of the present invention may be reduced. Therefore, the electron-donating microorganism is previously included and occupied in the gaps or pores of the electrode of the present invention. This configuration is convenient when it is desired to transfer electrons between a predetermined electron-donating microorganism and an electrode, or when biomass containing many microorganisms other than the electron-donating microorganism is used as a fuel. The electron-donating microorganisms used here are not limited to a single species, and may be a plurality of species as long as they can coexist and do not inhibit the electron transfer between each microorganism and the electrode. The method for including the electron donating microorganism in advance in the gaps or pores of the electrode is not particularly limited. Usually, the electrode of the present invention is placed in a solution such as a culture solution containing only the electron donating microorganism as a microorganism for a predetermined period of time. For example, it may be immersed for 30 minutes to 3 days, 1 hour to 1 day, 6 hours to 12 hours. Such electrodes are preferably kept water or moisturized until use in order to prevent drying or the like, or sealed in the case of anaerobic electron donating microorganisms.

In one embodiment, the electrode of the present invention containing the electron-donating microorganism may be covered with a housing having pores smaller than those of the microorganism. As a result, it is possible to completely eliminate the entry of microorganisms other than electron donating microorganisms from biomass into the gaps or pores during use of the present electrode, and it can be contained in or around the electrode so that the electron donating microorganisms do not diffuse. Therefore, the current can be generated more efficiently. “Beyond microorganisms” means that it is more than microorganisms normally present in biomass, and includes other microorganisms as well as electron-donating microorganisms. In the present specification, the term “pore smaller than the microorganism” means that the microorganism cannot pass through, but the organic substance that can be used as a fuel for the electron-donating microorganism and its degradation product, and the electron transfer carrier such as the electron mediator and conductive fine particles can pass through. A hole. Specifically, for example, it is 0.45 μm or less, preferably 0.2 μm or less. The casing does not necessarily have rigidity as long as the electrode of the present invention and the microorganisms in the biomass can be isolated. The material of the housing is not particularly limited as long as it is water-resistant and has a hole of the above size. For example, cellulose acetate, hydrophilic polyvinylidene fluoride, hydrophilic polyether sulfone and the like used in commercially available filter sterilization filters can be used. The electrode for a microbial fuel cell having such a configuration is particularly effective when it is desired to generate electricity using only a specific electron-donating microorganism by using biomass or the like in which various microorganisms exist as fuel.

The conductive polymer in the electrode for a microbial fuel cell of the present invention is formed so as to cover all or a part of the surface of the electrode substrate, and has a nanowire structure. This structure dramatically reduces the surface area compared to an electrode having a (quasi-) smooth polyaniline thin layer coating (for example, see JP-A-2007-324005), which is known in conventional microbial fuel cells. It can be increased. In general, electrode performance depends on its surface area. Therefore, the electrode of the present invention can obtain a dramatic output value as compared with the conventional microbial fuel cell electrode.

Although the nanowire structure dramatically increases the electrode surface, electron donating microorganisms cannot normally enter the gaps and / or pores formed by the structure. However, in the electrode for a microbial fuel cell of the present invention, which will be described later, it is considered that the above-described electron-transmitting intervening material enters this gap and / or pore and effectively utilizes the increased surface area due to the nanowire structure. Therefore, even if the electron donating microorganisms cannot enter, the electrode of the present invention can efficiently collect electrons.

Furthermore, in the present invention, the electrode surface area is further increased by using the electrode as a fiber structure aggregate or a porous structure.

1-2. Other Applications of Microbial Fuel Cell Electrodes In other embodiments, the microbial fuel cell electrodes of the present invention can be used for applications other than microbial fuel cells.

The electrode for a microbial fuel cell of the present invention increases the direct or indirect electron transfer efficiency with an electron conductive microorganism by dramatically increasing its surface area compared to a conventional electrode by a nanowire structure. As a result, the generated potential is remarkably increased.

Therefore, the electrode of the present invention can be used in the same manner for electrodes in other fields to which the principle can be applied. Examples include microbial solar cell electrodes, microbial electrolysis cells, and biosensors.

The microbial solar cell uses a photosynthetic bacterium such as cyanobacteria and transmits electrons generated when the bacterium performs photosynthesis to an electrode, as described in the aforementioned Japanese Patent Application Laid-Open No. 2007-32405. Thus, the microbial solar cell electrode is used as the electrode.

A microbial electrolysis cell is a device that has the same configuration as a microbial fuel cell and generates hydrogen from protons at a low potential electrode using a current generated by microorganisms from organic matter. The biosensor here refers to a detection device using microorganisms having the same configuration as that of a microbial fuel cell. An example is a BOD sensor.

1-3. Production of Microbial Fuel Cell Electrode The microbial fuel cell electrode of the present invention can be produced using any method known in the art for forming a conductive polymer nanowire structure on a conductive substrate. For example, Zhang H., et al., 2008, Mocromol. Rapid Commun., 29: 68-73; Cheng S., 2006, Electrochem. Commun., 8: 489-494; Zang J., et al, 2008, Macromolecules, 41: 7053-7057, and Debiemme-Chouvy C., 2009, Electrochem. Commun., 11. Hereinafter, a specific method for producing the electrode for a microbial fuel cell of the present invention will be described with an example.

(1) Preparation of electrode substrate When the electrode substrate itself has rigidity to be a support, it is prepared in a size and / or shape as required. For example, when carbon felt is used as an electrode substrate, a commercially available carbon felt having a suitable thickness may be cut into a desired size and shape by matching the shape of the microbial fuel cell. When the electrode substrate is formed on another support, for example, an appropriate support such as a glass fiber is prepared in a size and / or shape as required, and then the electrode is formed on the support. The base carbon or metal may be formed by a technique known in the art, for example, coating, vapor deposition, or the like. Alternatively, a commercially available electrode substrate having such a configuration can be used. Examples thereof include ITO supported on a glass plate.

In particular, when a hydrophobic fiber structure aggregate such as carbon or a porous structure is used for the electrode substrate, it is preferable to perform a hydrophilic treatment under appropriate conditions. “Monomer solution” refers to an electrolytic solution containing a monomer of a conductive polymer formed on an electrode substrate, such as an aniline monomer, a pyrrole monomer, a thiophene monomer, or the like, or a mixture thereof. The “monomer solution solvent” refers to a solvent capable of dissolving the monomer. Examples thereof include sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), perchloric acid (HClO ₄ ), and the like. The concentration of the solvent may be the same or substantially the same as the solvent in the monomer solution. The immersion time may vary depending on the size, shape, etc. of the electrode substrate, but it is usually 1 hour to 2 days, preferably 3 hours to 1 day. After the treatment, it is preferable to sufficiently wash with pure water or the like.

(2) Formation of conductive polymer having nanowire structure The conductive polymer having a nanowire structure can be usually formed by electrolytic reduction at room temperature. That is, it can be formed by using the electrode substrate as a working electrode and immersing it in an electrolytic cell together with a counter electrode, which is an energizing electrode, and applying an appropriate electrolysis voltage to the electrode to cause electrodeposition on the electrode substrate surface. In this method, whether or not the monomer forms a conductive polymer having a nanowire structure is determined by the monomer concentration, the current or potential scan speed applied to the electrode substrate, the number of current or potential scans, and the like. Hereinafter, the method for forming a conductive polymer having a nanowire structure of the present invention will be specifically described in order, but the present invention is not limited to this method.

First, one end of a conducting wire such as a titanium wire is connected to one end of the electrode substrate prepared in the above (1), and this is used as a working electrode. The other end of the conducting wire is connected to the power supply device. The power supply device is preferably one that can make the potential or current applied to the working electrode constant in order to control the current or potential scan speed and the current or potential scan frequency applied to the electrode substrate. For example, a potentiostat or a galvanostat is mentioned. In this example, a case where a power supply device is connected to a potentiostat will be described.

A monomer solution using the working electrode, a counter electrode (for example, platinum or platinum black) connected to the potentiostat, and a reference electrode (for example, a silver-silver chloride electrode (Ag / AgCl) immersed in a saturated KCl solution) as an electrochemical cell Immerse in. The reference electrode is an electrode necessary for measuring or controlling the potential of the working electrode.

The monomer concentration in the monomer solution varies depending on the monomer used and / or the desired nanowire structure to be formed on the electrode substrate, but is generally 0.02 mol / L to 0.8 mol / L, preferably 0.03 mol / L to 0.7. mol / L, more preferably 0.04 mol / L to 0.6 mol / L, still more preferably 0.05 mol / L to 0.5 mol / L. When the concentration is lower than 0.02 mol / L, there is a high possibility that only a thin layer of conductive polymer with a smooth or semi-smooth shape will be formed on the electrode substrate, and conversely when the concentration exceeds 0.8 mol / L. Nanowires are not preferred because they are likely to become thick due to rapid growth, making it difficult to form a desired nanowire structure, particularly a nanowire network.

Next, the working electrode potential is set within the range of −0.1 V to 2.0 V, preferably −0.3 V to 1.6 V, more preferably −0.5 V to 1.3 V with respect to the reference electrode. The scanning speed is in the range of 10 mV / sec to 100 mV / sec, and the number of scans is applied 5 to 20 round trips. The scanning speed means a speed at which the potential is changed. In general, when forming a conductive polymer having the same nanowire structure at different set potentials, the scan speed on the side where the set potential is low is slow, the number of scans is large, and the scan speed on the side where the set potential is high is reversed. What is necessary is just to reduce the number of scans quickly. If the scanning speed is the same, the larger the number of scans, the faster the growth of nanowires, so that a nanowire structure can be formed in a short time. Further, when forming conductive polymers having the same nanowire structure at different monomer concentrations, the higher the monomer concentration, the slower the scan speed and the fewer the number of scans. Therefore, the combination of the monomer concentration, the scan speed, and the number of scans may be appropriately determined in consideration of the conditions for forming a desired nanowire structure within each numerical range.

(3) Cleaning and drying After forming the conductive polymer on the electrode substrate surface, which is the working electrode, remove it from the potentiostat and several times with distilled water, ion-exchanged water or ultrapure water, for example, Wash three or more times to completely remove the monomer solution. Thus, the microbial fuel cell electrode of the present invention is obtained.

2. 2. Microbial fuel cell 2-1. Configuration of Microbial Fuel Cell One aspect of the present invention is a microbial fuel cell using the electrode for a microbial fuel cell according to any one of the present invention. As a specific example, a conceptual diagram of the microbial fuel cell of the present invention shown in FIG. 8 will be used. The microbial fuel cell of the present invention is usually electrically connected to a pair of electrodes (81 and 82), an electrolytic cell (80) containing a diaphragm (83) and an electrolyte solution (84 and 85), and the pair of electrodes. Connected external circuit (eg, data logger) (86). Hereinafter, the configuration will be described. However, the configuration of the microbial fuel cell of the present invention is not limited to the above configuration, and includes any known microbial fuel cell that can use the electrode for the microbial fuel cell of the present invention. Shall be.

2-1-1. Electrode The microbial fuel cell of the present invention includes an anode (fuel electrode) (81) and a cathode (air electrode) (82) as a pair of electrodes.

The electrode for a microbial fuel cell of the present invention is used for the anode. At least one surface of the anode needs to be in direct contact with an electrolyte solution in an anode tank described later. Usually, the anode is used by being immersed in an electrolyte solution of an electrolytic cell.

The cathode is not particularly limited. For example, any material including a conductor such as carbon or metal may be used. The cathode may be an air cathode (air positive electrode) that is open to the atmosphere. In this case, the cathode preferably has gas (especially oxygen) permeability. Examples thereof include carbon paper, carbon cloth, and 4-polytetrafluoroethylene (PTFE) carrying platinum particles. When using an air cathode, it is not necessarily in direct contact with the electrolyte solution in the electrolytic cell.

2-1-2. Diaphragm The diaphragm (83) is configured to separate the pair of electrodes in the electrolytic cell. The material of the diaphragm is not particularly limited as long as it can selectively permeate cations. An example is a proton (H ⁺ ) exchange membrane (PEM). The proton exchange membrane is a proton-conducting ion exchange polymer electrolyte, and examples thereof include perfluorosulfonic acid-based fluorine ion exchange resins or organic / inorganic composite compounds. The perfluorosulfonic acid-based fluorine ion exchange resin is, for example, a polymer unit based on perfluorovinyl ether having a sulfo group (—SO ₃ H) and / or a carboxyl group (—COOH), and tetrafluoroethylene. And a copolymer containing polymer units. A specific example is Nafion (registered trademark: DuPont). The organic / inorganic composite compound is a substance composed of a compound in which a hydrocarbon polymer (for example, mainly polyvinyl alcohol) and an inorganic compound (for example, tungstic acid) are combined. These are known membranes, and since many are commercially available like Nafion, they can also be used.

Also, when the cathode is opened to the atmosphere, the cathode (air cathode) and the diaphragm can be combined and integrated. Such an integrated cathode / diaphragm can be used in a single tank microbial fuel cell.

In the microbial fuel cell of the present invention, the diaphragm (83) is not an essential component. However, considering the practicality of the battery, such as the life of the electrode, it is desirable to have a diaphragm.

2-1-3. Electrolyte Solution The electrolyte solution (84) is a solution containing an electrolyte. The electrolyte used in the microbial fuel cell of the present invention is not particularly limited as long as it is a substance that can be ionized in water. Moreover, it is not restricted to a single kind, The mixture of a some electrolyte can also be used. Specific examples of the electrolyte include K ₂ HPO ₄ / KH ₂ PO ₄ , NaCO 3 / NaHCO 3, and the like.

2-1-4. Electrolytic cell The electrolytic cell constitutes the main body of the microbial fuel cell of the present invention. As the electrolytic cell, there are known a two-cell type separated into an anode cell and a cathode cell by a diaphragm, and a single cell type having a configuration in which an air cathode and a diaphragm are integrated and only an anode cell is formed. Any type of microbial fuel cell of the invention can be used.

In the case of the two-tank type, the anode tank is arranged in the anode tank, and the cathode tank in the cathode tank is arranged in such a manner that all or a part thereof is in direct contact with the electrolyte solution.

The anode tank, which is a fuel tank, contains, in addition to the electrolyte solution, an electron-donating microorganism, its fuel and electron donor, and, if necessary, electron mediators such as an electron mediator and conductive fine particles.

The electron-donating microorganism used in the anode tank may be either a single species or a plurality of species. When using organic wastewater or sludge as a fuel, mixed systems consisting of multiple types of electron-donating microorganisms can use the electron-donating microorganisms that originally live in them without adding electron-donating microorganisms from the outside. Excellent in advantages. For example, Pseudomonas aeruginosa and Geobacter inhabit every part of the natural environment such as soil, fresh water, and seawater. Therefore, if sludge is used as fuel, it can be used without being added from the outside. Further, as described above, Pseudomonas aeruginosa is very useful as the electron-donating microorganism of the present invention because it can produce a redox mediator compound.

On the other hand, the cathode tank which is an air layer is configured to be able to supply air containing oxygen.

Fuel is a nutrient substrate necessary for maintenance and / or growth of electron donating microorganisms. The nutrient substrate is not particularly limited as long as the microorganism can be metabolized by the microorganism. For example, alcohols such as methanol and ethanol, monosaccharides such as glucose, starch, amylose, amylopectin, glycogen, cellulose, maltose, sucrose, useful resources such as polysaccharides such as lactose, and agricultural industrial waste, Unused resources such as organic drainage, human waste, sludge, and food residues, that is, organic waste can be used. The fuel may also contain a substance that can be an electron donor of an electron donating microorganism (for example, lactic acid). Fuel can be added as needed for the maintenance and growth of electron donating microorganisms in the anode cell and / or for the supply of electron donors.

The electron-transmitting intervening material may be added to the electrolytic cell as necessary. As long as at least one of the included electron donating microorganisms can produce / release the redox mediator compound, the electron-transmitting mediator does not necessarily have to be added. On the other hand, when any of the included electron donating microorganisms is a species that cannot produce / release the redox mediator compound, it is essential to add an electron transferable mediator.

<Example 1: Production of electrode for microbial fuel cell>
In this example, the electrode for a microbial fuel cell (hereinafter referred to as “(electrode substrate) of the electrode substrate of the present invention and a conductive polymer (nanowire conductive polymer) having a nanowire structure formed on all or part of its surface”). ITO / conductive polymer nanowire electrode (A) and carbon / conductive polymer nanowire electrode (B) as well as their control electrodes (C) ) Will be described.

A: Production of ITO / conductive polymer nanowire electrode An ITO / conductive polymer nanowire electrode in which the nanowire conductive polymer formed on the surface of ITO, which is the electrode substrate, is composed of polyaniline or a polyaniline copolymer was produced.

(1) Preparation of ITO ITO (Kuramoto Seisakusho) supported on a glass slide was cut into 9 cm ² .

(2) Formation of polyaniline having nanowire structure (nanowire polyaniline) The monomer solution as the electrolytic solution was a 1M sulfuric acid solution containing 0.2M aniline monomer (Wako Pure Chemical Industries).

One end of a titanium wire as a lead wire was connected to one end of ITO prepared in (1), which was used as a working electrode, and the other end of the lead wire was connected to a potentiostat (HZ-5000, Hokuto Denko). Furthermore, a reference electrode (Ag / AgCl electrode immersed in a saturated KCl solution) and a counter electrode (platinum) were connected to the potentiostat. These electrodes were immersed in the monomer solution. Subsequently, the potential of the working electrode is set between −0.3 V and 1.3 V with respect to the reference electrode, and is scanned 10 times back and forth at an electrode scan speed of 50 mV / sec. Nanowire polyaniline was electrodeposited.

FIGS. 2a and 2b show a polyaniline nanowire structure (in this figure, forming a polyaniline network) (a) and an enlarged view (b) thereof on the surface of a plate ITO electrode substrate prepared by this method. It can be seen that the polyaniline nanowires are fused with other adjacent polyaniline nanowires to form a three-dimensional network structure (network) having numerous pores.

The working electrode was removed from the potentiostat, washed three times with distilled water, and then dried to obtain an electrode for a microbial fuel cell (ITO / polyaniline nanowire electrode) comprising ITO / nanowire polyaniline of the present invention.

(3) Formation of a copolymer of aniline and another monomer having a nanowire structure (nanowire polyaniline copolymer) In this example, an aniline / aminophenol copolymer (hereinafter referred to as PAAP) is used as a copolymer of aniline and another monomer (polyaniline copolymer). ) And aniline / diaminophenol copolymer (hereinafter referred to as PADAP) were formed on the smooth surface ITO.

In the monomer solution as the electrolyte, 0.2M aniline monomer (Wako Pure Chemical) and 0.01M orthoaminophenol (Wako Pure Chemical) are used for PAAP, and 0.2M aniline monomer (Wako Pure Chemical) is used for PADAP. And 1M sulfuric acid solution containing 0.01M 2,4-diaminophenol (Wako Pure Chemical Industries, Ltd.), respectively.

As in (2) above, one end of a titanium wire, which is a conductor, is connected to one end of ITO prepared in (1), which is used as a working electrode, and the other end of the conductor is a potentiostat (HZ-5000, Hokuto Denko). ). The active area of the ITO working electrode is 3.14 cm ² . Furthermore, a reference electrode (Ag / AgCl electrode immersed in a saturated KCl solution) and a counter electrode (platinum) were connected to the potentiostat. These electrodes were immersed in the monomer solution. Subsequently, the potential of the working electrode is set between −0.4 V to 1.1 V with respect to the reference electrode, and is scanned 10 times back and forth at an electrode scan speed of 50 mV / sec. Nanowire polyaniline copolymer was electrodeposited.

Figures 2c-f show the nanowire structure of the polyaniline copolymer on the surface of the planar ITO electrode substrate prepared by this method. c and d indicate PAAP, e and f indicate PADAP, and d and f are enlarged views of c and e, respectively. It can be seen that the nanowire structures of PAAP and PADAP shown in these figures are formed by fusing adjacent nanowires to form a three-dimensional network structure (network) having innumerable pores.

After the electrodeposition of the nanowire polyaniline copolymer, the working electrode is removed from the potentiostat, washed with distilled water three times, and then dried. Nanowire electrode or ITO / PADAP nanowire electrode).

B: Fabrication of carbon / conductive polymer nanowire electrode Carbon felt or carbon plate (CP: Carbon Plate) is used as the electrode base, and the nanowire conductive polymer formed on the surface is carbon made of nanowire polyaniline or nanowire polyaniline copolymer. / Conductive polymer nanowire electrodes were prepared.

(1) Preparation of carbon felt Carbon felt (manufactured by Sogo Carbon Co., Ltd., thickness: 3 mm) was cut into 1 cm ² , and then immersed in 1M sulfuric acid as a solvent for the monomer solution at room temperature for 1 day. Thereafter, ultrasonic cleaning with distilled water was performed for 1 day to remove sulfuric acid.

(2) Preparation of carbon plate (hereinafter referred to as “CP”) The carbon plate was cut into 9 cm ² and then immersed in 1M sulfuric acid at room temperature for 1 day. Thereafter, ultrasonic cleaning with distilled water was performed for 1 day to remove sulfuric acid.

(3) Formation of polyaniline having nanowire structure on carbon felt or CP (nanowire polyaniline) The monomer solution as the electrolytic solution was a 1M sulfuric acid solution containing 0.2M aniline monomer (Wako Pure Chemical Industries).

One end of a titanium wire as a conducting wire was connected to one end of the carbon felt or CP prepared in (1), which was used as a working electrode, and the other end of the conducting wire was connected to a potentiostat (HZ-5000, Hokuto Denko). Further, one end of a reference electrode (Ag / AgCl electrode immersed in a saturated KCl solution) and a counter electrode (platinum) was connected to the potentiostat. These electrodes are immersed in the monomer solution, and then the potential of the working electrode is -0.5V to 1.3V with respect to the reference electrode in the case of carbon felt, and with respect to the reference electrode in the case of CP. After each setting between -0.4V and 1.3V, the electrode scan speed is 50mV / sec. The electrodes are scanned 10 times in the case of carbon felt and 15-20 times in the case of CP. Nanowire polyaniline was electrodeposited on the carbon felt or CP surface as a base. FIG. 3 shows a polyaniline nanowire structure (FIG. 3b) on the surface of a carbon felt electrode substrate (FIGS. 3a and c) prepared by this method and an enlarged view (FIG. 3d). It can be seen that adjacent nanowires formed on the same and / or different carbon fiber surfaces are fused to form a complex three-dimensional nanowire structure (nanowire network) together with the carbon felt of the fibrous assembly.

The working electrode after the electrodeposition of nanowire polyaniline was removed from the potentiostat, washed 3 times with distilled water, and dried. This was used as a microbial fuel cell electrode (carbon felt / polyaniline nanowire electrode) comprising the carbon felt / nanowire polyaniline of the present invention.

(4) Formation of copolymer of aniline and other monomer (nanowire polyaniline copolymer) having nanowire structure on CP In this example, PAAP and PADAP were each formed on CP as a polyaniline copolymer.

One end of a titanium wire as a conducting wire was connected to one end of the CP prepared in (2), which was used as a working electrode, and the other end of the conducting wire was connected to a potentiostat (HZ-5000, Hokuto Denko). The active area of the CP working electrode is 3.14 cm ² . Further, one end of a reference electrode (Ag / AgCl electrode immersed in a saturated KCl solution) and a counter electrode (platinum) was connected to the potentiostat. These electrodes are immersed in the monomer solution, and then the potential of the working electrode is set between −0.4 V and 1.3 V with respect to the reference electrode, and then 15 to 20 reciprocations at an electrode scanning speed of 50 mV / sec. The nanowire polyaniline copolymer was electrodeposited on the CP surface as the electrode substrate according to the number of scans.

The working electrode after electrodeposition of the nanowire polyaniline copolymer was removed from the potentiostat, washed three times with distilled water, and then dried. This was used as a microbial fuel cell electrode (CP / PAAP nanowire electrode or CP / PADAP nanowire electrode) comprising the CP / nanowire polyaniline copolymer of the present invention.

C: Preparation of smooth surface thin layer electrode (smooth surface electrode) C-1: Preparation of ITO / polyaniline smooth surface electrode According to the preparation method of A (1) and (2). However, the concentration of the aniline monomer in the step A (2) was set to 1/10, that is, 0.02M.

C-2: Preparation of ITO / PAAP smooth electrode It was according to the preparation method of A (1) and (3). However, the concentrations of aniline monomer and orthoaminophenol in the step A (3) were 1/10, that is, 0.02M and 0.001M, respectively. The number of electrode scans was set to 5.

C-3: Preparation of ITO / PADAP smooth electrode According to the preparation methods of A (1) and (3). However, the concentrations of the aniline monomer and 2,4-diaminophenol in step A (3) were 1/10, that is, 0.02M and 0.001M, respectively. The number of electrode scans was set to 5.

C-4: Preparation of carbon felt / polyaniline smooth electrode According to the preparation method of B (1) and (3). However, the concentration of the aniline monomer in the step B (3) was 1/10, that is, 0.02M.

D: Preparation of control electrode D-1: Preparation of ITO electrode According to the preparation method of A (1).

D-2: Production of carbon felt electrode The same method as in B (1) was used.

D-3: Production of CP electrode The preparation method of B (2) was followed.

<Example 2: Verification of power generation capability in electrode for microbial fuel cell of the present invention>
The power generation capability of the microbial fuel cell electrode of the present invention was verified by an electrochemical cell using a potentiostat system.

1. Electrode The working electrode as the anode was used in the following combinations.

(1) The ITO / polyaniline nanowire electrode and the ITO / polyaniline smooth surface electrode produced in Example 1 and the electrode (ITO electrode) made of only ITO supported on the glass plate were used. Hereinafter, an experiment in which the power generation performance is verified with this combination of electrodes is referred to as “experiment A”.

(2) The CP / PAAP nanowire electrode, the CP / PADAP nanowire electrode, the CP / polyaniline nanowire electrode, and the electrode composed only of CP (CP electrode) prepared in Example 1 were used. Hereinafter, an experiment in which the power generation performance is verified with this combination of electrodes is referred to as “experiment B”.

(3) The ITO / PAAP smooth electrode, ITO / PADAP smooth electrode, ITO / polyaniline smooth electrode, and ITO electrode prepared in Example 1 were used. Hereinafter, an experiment in which the power generation performance is verified with this combination of electrodes is referred to as “experiment C”.

¡Each electrode size is the same. A platinum electrode and an Ag / AgCl (saturated KCl) electrode were used as a counter electrode and a reference electrode, respectively.

2. Electron-donating microorganism In any of Experiments A to C, Shewanella loihica PV-4 strain (American type culture collection: ATCC No. BAA-1088; 2008 edition) was used as the electron-donating microorganism.

S. loihica PV-4 was inoculated in advance into 10 ml of 20 g / L Marine Broth 2216 medium (MB medium: Wako Pure Chemical Industries) and cultured aerobically at 30 ° C. for 1 day. Subsequently, MB medium was replaced with DM medium (Difined Media), and aerobically cultured at 30 ° C. for 2 days was used as a preculture solution. The composition of the DM medium is 2.5 g / L NaHCO ₃ , 0.08 g / L CaCl ₂ · 2H ₂ O, 1.0 g / L NH ₄ Cl, 0.2 g / L MgCl ₂ · 6H ₂ O, 10 g / L NaCl, 7.2 g / L HEPES. In addition, 10 mM sodium lactate (Wako Pure Chemical Industries) is used as an electron donor to S. loihica PV-4, and 0.5 g / L is supplied to supply micronutrients necessary for the growth of S. loihica PV-4 during main culture. Yeast Extract (Wako Pure Chemical Industries) was added. Hereinafter, the DM medium containing sodium lactate is referred to as DM-L medium.

3. Preparation of Electrolyzer FIG. 4 shows a potentiostat system used in this example. A working electrode (41) as an anode was laid on the bottom of the electrolytic cell (40), 5 ml of DM-L medium was placed in the cell, and purged with pure nitrogen for 10 minutes. After placing the counter electrode (42) and the reference electrode (43) in the tank, using a potentiostat (HSV-100, Hokuto Denko) (45), a constant voltage of 0.2 V is applied to the reference electrode (Ag / AgCl electrode). 1 ml of the preculture solution was added to the electrolytic cell to which voltage was applied so that OD ₆₀₀ = about 1.0.

(result)
FIG. 5 shows the results of Experiment A, FIG. 6 shows the results of Experiment B, and FIG. 7 shows the results of Experiment C. These figures show the generated current obtained from S. loihica PV-4 when each anode was used. Hereinafter, the results of Experiments A to C will be described.

Experiment A: First, when an ITO electrode was used as the anode, the current started to increase immediately after the introduction of S. loihica PV-4, and then remained at a constant value of about 1 μA / cm ² (a). This result reflects that S. loihica PV-4 oxidized lactic acid and transferred the generated electrons directly to the anode.

Subsequently, when an ITO / polyaniline smooth electrode was used, a constant value of about 2 to 3 μA / cm ² was obtained (b). This shows that the affinity between S. loihica PV-4 and the ITO electrode was increased by coating ITO with a smooth film of polyaniline, and the efficiency of charge transfer from S. loihica PV-4 to the electrode was improved. ing.

On the other hand, when the ITO / polyaniline nanowire electrode, which is an electrode for a microbial fuel cell of the present invention, is used, S. loihica PV-4 is introduced (indicated by the arrow in “PV-4 addition” in FIG. 5). After half a day, a very large current reaching 45 μA / cm ² was obtained (c). Thereafter, the current decreased with the depletion of lactic acid, but after removing 1 ml of the supernatant in the electrolytic cell, 1 ml of DM-L medium containing 50 mM lactic acid was added (see “Addition of DM-L medium” in FIG. 5). It recovered immediately and reached a high value again. The current by this electrode reached a maximum value of 100 μA / cm ² two days after the introduction of S. loihica PV-4. This is 100 times that of the ITO electrode and 30-50 times that of the ITO / polyaniline smooth surface electrode.

From the above results, the microbial fuel cell electrode of the present invention is a microbial fuel cell electrode compared to conventional biofuel cell electrodes because of its high affinity with electron-donating microorganisms and high electron recovery efficiency. It became clear that it has very good power generation capacity.

Experiment B: First, when a CP electrode was used as the anode, the current started to increase immediately after addition of S. loihica PV-4 (indicated by the arrow in “PV-4 addition” in FIG. 6), and then about 20 μA It remained at a constant value of / cm ² (a). This result reflects that S. loihica PV-4 oxidizes lactic acid and transfers the generated electrons directly to the anode, similar to the ITO electrode of Experiment A.

On the other hand, in the CP / polyaniline nanowire electrode, CP / PAAP nanowire electrode, or CP / PADAP nanowire electrode that are the electrodes for the microbial fuel cell of the present invention, a rapid increase in current is observed after the introduction of S. loihica PV-4 Then, the point at which the current decreases with the depletion of lactic acid, DM-L medium was additionally added (indicated by three arrows each within the “DM-L medium addition” range of FIG. 6). The overall power generation pattern, such as recovery and high current, was obtained, which was similar to the ITO / polyaniline nanowire electrode in Experiment A. However, with the CP / polyaniline nanowire electrode, a current of about 200 μA / cm ² was obtained about half a day after the introduction of S. loihica PV-4 (FIG. 6 b), generating more power than the ITO / polyaniline nanowire electrode in Experiment A It turns out that the efficiency is high. Also, CP / PAAP nanowire electrode using copolymer (Fig. 6c) and CP / PADAP nanowire electrode (Fig. 6d), after recovery by addition of DM-L medium, CP / PAAP nanowire electrode is about the same as CP / polyaniline nanowire electrode. With 1.3 to 2 times the CP / PADAP nanowire electrode, a current about 2 to 3 times higher than that of the CP / polyaniline nanowire electrode was obtained. This ranges from about 30 times the CP electrode (CP / PAAP nanowire electrode) or about 40 times (CP / PADAP nanowire electrode).

As described above, PAAP and PADAP nanowire electrodes, which are copolymers, have higher power generation efficiency than polyaniline nanowire electrodes, which are polymers of monomolecular compounds (aniline). One reason for this is the difference in specific surface area of each conductive polymer formed on the substrate surface as shown in Table 1, that is, the difference in surface area per electrode weight.

The specific surface area of the conductive polymer nanowires formed on the ITO substrate is 2.5 and 3.8 times greater for the copolymers PAAP and PADAP, respectively, than the single monomer polymer polyaniline (PANI), The current density generated in proportion to the magnitude was also high. Therefore, it has been clarified that the conductive polymer constituting the microbial fuel cell electrode of the present invention is preferably a material having a property of having a larger specific surface area when a nanowire structure is formed on the substrate surface.

From the above results, the electrode for the microbial fuel cell of the present invention can obtain the same power generation ability even when the ITO or CP base is different, and a polyaniline copolymer (for example, this example) than when polyaniline is used. Thus, it has been clarified that the use of PAAP or PADAP has a larger specific surface area and better power generation capability.

Experiment C: The transition of current generated after addition (0.0 hour) of S. loihica PV-4 (OD ₆₀₀ = 1.0) when each electrode is used as an anode is shown. When any electrode was used, the power generation efficiency was less than 6 μA / cm ^2, which was significantly lower than the electrode having the conductive polymer nanowire structure used in Experiments A and B (FIG. 7). That is, this shows that the output current density of the nanowire electrode of the present invention is higher than that of the conventional smooth surface electrode even when the electrode substrate surface is coated with the same conductive polymer.

On the other hand, when compared with the ITO electrode (a), it was revealed that the electrodes (b to d) having a conductive polymer on the surface had a 3 to 5 times higher output current density than the ITO electrode (a). Furthermore, even with the conductive polymer, the ITO / PADAP smooth electrode (d) was about 1.5 times higher in output current density than the ITO / polyaniline smooth electrode (b). In FIG. 6, the output current density of the CP / PADAP nanowire electrode (d) was higher than that of the CP / polyaniline nanowire electrode (b). This is because the specific surface area of the PADAP nanowire is that of the polyaniline nanowire as described above. Compared to that, PADAP, which is a copolymer rather than polyaniline, which is a polymer of monomolecular compounds, is a microbial fuel cell electrode with higher power generation efficiency, as well as higher properties as a conductive polymer material. Is shown.

<Example 3: Verification of power generation capability in an electrode for a microbial fuel cell of the present invention composed of a fiber structure assembly>
The power generation capability of the electrode for a microbial fuel cell of the present invention composed of a fiber structure aggregate was verified using a microbial fuel cell not containing an electron mediator and conductive fine particles.

1. Electrode As the anode, the carbon felt / polyaniline nanowire electrode and the carbon felt / polyaniline thin layer electrode prepared in Example 1 and an electrode composed of only carbon felt (carbon felt electrode) were used. Each electrode size is the same.

An air cathode was used as the cathode. The air cathode consists of 4-polytetrafluoroethylene (PTFE) carrying 8 mg / cm ² platinum particles (Sigma).

2. Preparation of electron-donating microorganism As the electron-donating microorganism, a microorganism included in paddy soil collected in Kamaishi, Japan was used.

The paddy soil microorganisms were cultured according to the following procedure. For the cultivation, 12 ml of PS medium (NH ₄ CL 10 mM, KH ₂ PO ₄ 1 mM, MgCl ₂ 0.5 mM, CaCl ₂ 0.5 mM, NaHCO ₃ 5 mM, HEPES 10 mM, Yeast extract 0.5 g / L) was used. During the culture, sodium acetate (10 mM) was added as an electron donor. In addition, 0.5 g / L of Yeast exatract was added to supply a small amount of fuel necessary for microorganisms. As a microorganism source, 20 mg (wet weight) of paddy field soil was added to the PS medium. The culture was performed at 30 ° C., and sodium acetate (10 mM) was added again when the current density decreased (when acetic acid was deficient).

3. Preparation of electrolytic cell The electrode cell used in this example is a single cell type electrolytic cell having no diaphragm (83) in the microbial fuel cell of the present invention shown in FIG. In addition, an electrolytic solution to which an electron donating microorganism and a nutrient substrate are added is accommodated in the tank. Specifically, 12 ml of buffer solution containing 200 mM K ₂ HPO ₄ / KH ₂ PO ₄ (pH 6.8) is placed as an electrolyte solution in an electrolytic cell having a capacity of 15 ml, and starch is used as a nutrient substrate. : Peptone: Fish meal mixed with 3: 1: 1 (289 g COD / L, COD = chemical oxygen demand) was added at 0.12 mL per day. Subsequently, the medium was purged with nitrogen for 5 minutes before adding the culture medium. 0.2 ml of soil suspension was added to the electrolytic cell and cultured anaerobically at 30 ° C. Thereafter, a mixed substrate (300 g COD / L) containing starch, peptone and fish extract was added to the electrolyzer at 0.12 ml per day.

Electrical production was monitored by measuring the voltage across the external resistance with a data logger (Graphtech). In addition, a polarization curve was created using a potentiostat (HA-1510, Hokuto Denko) at appropriate times.

(result)
The results are shown in FIGS. 9 and 10 show the polarization curve and output of the microbial fuel cell when each anode is used, respectively. When using the carbon felt electrodes in the anode, the power density of the short-circuit current density and 24μW / cm ² of 107μA / cm ^2, were obtained (Fig. 9a and 10a). In the case of using the carbon felt / polyaniline thin layer electrode on the anode, the power density of the short-circuit current density and 70μW / cm ² of 270μA / cm ^2, were obtained (Figure 9b and 10b). That is, the output increased by a factor of 3 or more by coating the carbon felt surface with a smooth polyaniline. As in Example 2, it is considered that the affinity with the electron donating microorganism was increased by polyaniline. On the other hand, when a carbon felt / polyaniline nanowires electrodes is an electrode for a microbial fuel cell of the present invention, the power density of the short-circuit current density and 230μW / cm ² of 2.5 mA / cm ^2, were obtained (Fig. 9c And 10c). That is, according to the carbon felt / polyaniline nanowire electrode of the present invention, it has been clarified that the current and output are increased by one digit compared with those of the electrode having the conventional configuration.

From the results of Examples 2 and 3, it was found that the three-dimensional nanowire network made of polyaniline formed on ITO and carbon felt becomes an extremely effective electron recovery body in a microbial fuel cell.

The microbial fuel cell of this example is composed of a system closer to the microbial fuel cell used in the practical application stage. For example, the electron-donating microorganism used was included in paddy soil and has not been identified. The soil also includes many other microorganisms that cannot be the electron-donating microorganism of the present invention. In other words, this system does not necessarily add electron-donating microorganisms from the outside, but by using sludge or organic effluents that are used as fuel in actual microbial fuel cells as they are, electron donation that exists universally to them is used. It has been shown that the microorganism fuel cell of the present invention can sufficiently achieve the effects of the present invention by microorganisms.

<Example 4: Cyclic voltammogram of each microbial fuel cell electrode>
The cyclic voltammogram was measured in the microbial fuel cell using each anode in Example 3, and the electron transfer characteristics in the presence of the microbial mixture were examined. The cyclic voltammogram is a measurement of the current flowing in the electrochemical cell by continuously changing the potential of the working electrode with respect to the reference electrode. The redox potential of this reaction system is obtained from the midpoint of the + and-peaks at that time.

(result)
The results are shown in FIG. (A) shows a case where a carbon felt electrode is used for the anode, (b) shows a case where a carbon felt / polyaniline thin layer electrode is used, and (c) shows a case where the carbon felt / polyaniline nanowire electrode of the present invention is used. ing. In this example, since the same microorganism was used, the redox potential was almost the same regardless of the electrode, and only the flowing current was changed. In both cases, a pair of clear redox waves (redox waves) was obtained. The anode or cathode of the peak current density of each electrode, respectively (a) at 0.8 and 0.6 mA / cm ^2, 35 and 32 mA / cm ² met with (b) at 2.7 and 2.8 mA / cm ² and, (c) It was. That is, the current density of the microbial fuel cell electrode of the present invention was increased by about 40 times compared to that of the electrode made of only the conductive carbon fiber. In general, it is known that the charge density of an electrode in a particular reaction is related to the electrode surface area and its properties. Considering this result, it is considered that the electrode for microbial fuel cell of the present invention has a significantly increased electrode surface area due to the nanowire structure of polyaniline, so that the electron recovery efficiency is enhanced and a remarkably high current density is obtained. .

All publications, patents and patent applications cited in this specification shall be incorporated into the present specification as they are.

Claims

An electrode for a microbial fuel cell comprising a conductive polymer having a nanowire structure formed on all or part of the electrode substrate and its surface.
The electrode of claim 1, wherein the nanowire structure comprises a nanowire network.
The electrode according to claim 1 or 2, wherein the electrode substrate contains metal or carbon.
The electrode according to any one of claims 1 to 3, wherein the electrode is a fiber structure aggregate or a porous structure.
The electrode according to any one of claims 1 to 4, wherein the electrode comprises gaps and / or pores larger than the cell size of the electron-donating microorganism.
6. The electrode according to claim 5, wherein the length and / or width of the gap and the diameter of the pores are 6 μm to 20 μm.
The electrode according to claim 5 or 6, comprising an electron donating microorganism in the gap or pore.
The conductive polymer is a polymer composed of aniline, aminophenol, diaminophenol, pyrrole, thiophene, paraphenylene, fluorene, furan, acetylene, or a derivative thereof, or a combination thereof, or a mixture of the polymers. The electrode according to any one of 1 to 7.
The electrode according to claim 8, wherein the conductive polymer is polyaniline, aniline / aminophenol copolymer or aniline / diaminophenol copolymer.
A microbial fuel cell using the electrode according to any one of claims 1 to 9.
An anode and / or a cathode comprising the electrode according to any one of claims 1 to 9,
A microbial fuel cell comprising an electrolyte solution and an electrolytic cell containing them,
In the electrolytic cell, the microbial fuel cell, wherein the electrolyte solution in the electrolytic cell further includes an electron donating microorganism composed of a single species or a plurality of species and a nutrient substrate necessary for metabolism of the microorganism.
The microbial fuel cell according to claim 11, wherein the microbial fuel cell has a single cell structure in which the cathode is an air cathode having gas permeability and the electrolytic cell is composed only of an anode cell.
The microbial fuel cell according to claim 11 or 12, further comprising a redox mediator compound, an electron mediator and / or conductive fine particles in a tank in which the anode or the cathode is installed.