Electrode for microbial fuel cell, microbial fuel cell, and microbial fuel cell system

Abstract

To solve the problem in which graphite sheets used as negative or positive electrodes exhibit insufficient electrical properties as electrodes.SOLUTION: An electrode for a microbial fuel cell includes non-conductive fibers, a conductive material having conductivity, and a binder for bonding the conductive material to the fibers.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to electrodes for microbial fuel cells, microbial fuel cells, and microbial fuel cell systems. [Background technology]

[0002] Microbial fuel cells that utilize the metabolic capabilities of microorganisms are known. The microbial fuel cell described in Patent Document 1 is composed of a negative electrode, an ion migration layer, and a positive electrode. The negative electrode is composed of a conductive sheet that has electrical conductivity. The conductive sheet uses a metal plate with through holes and a graphite sheet. The positive electrode is composed of a graphite sheet, a filter layer, and a water-repellent layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-117584 Summary of the Invention [Problem to be solved by the invention]

[0004] The graphite sheet used in the negative electrode or positive electrode does not have sufficient electrical properties as an electrode. [Means for solving the problem]

[0005] The electrode for a microbial fuel cell of the present disclosure includes non-conductive fibers, a conductive material having electrical conductivity, and a binder that binds the conductive material to the fibers.

[0006] The microbial fuel cell of the present disclosure is a microbial fuel cell that is in contact with a liquid containing organic matter and electrochemically active bacteria, and includes an anode electrode that includes non-conductive fibers, a conductive material that is conductive, and a binder that binds the conductive material to the fibers, and a cathode electrode that is conductive.

[0007] The microbial fuel cell system of the present disclosure comprises a microbial fuel cell having an anode electrode in contact with a liquid containing organic matter and electrochemically active bacteria, a cathode electrode to which oxygen is supplied, and an ion exchange membrane disposed between the anode electrode and the cathode electrode, and a resistor connected to the anode electrode and the cathode electrode, wherein the anode electrode includes non-conductive fibers, a conductive material having conductivity, and a binder that binds the conductive material to the fibers. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the schematic configuration of a microbial fuel cell system. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of an anode electrode. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of an anode electrode. [Figure 4] FIG. 2 is a diagram showing an example of the configuration of an anode electrode. [Figure 5] FIG. 2 is a diagram showing a schematic configuration of a cathode electrode. [Figure 6] FIG. 2 is a diagram showing an example of the configuration of a cathode electrode. [Figure 7] FIG. 1 shows the configuration of a microbial fuel cell. [Figure 8] FIG. 1 shows the evaluation results of a microbial fuel cell. [Figure 9] FIG. 1 shows the evaluation results of a microbial fuel cell. [Figure 10] FIG. 1 shows the evaluation results of a microbial fuel cell. [Figure 11] FIG. 1 shows the evaluation results of a microbial fuel cell. [Figure 12] FIG. 1 shows the evaluation results of a microbial fuel cell. DETAILED DESCRIPTION OF THE INVENTION

[0009] FIG. 1 shows a schematic configuration of a microbial fuel cell system 100. The microbial fuel cell system 100 uses microorganisms to decompose organic matter contained in a liquid L. The microbial fuel cell system 100 produces energy, useful substances, etc. by electrochemically controlling the metabolism of the microorganisms. The microbial fuel cell system 100 includes a microbial fuel cell 10, a storage container 20, and an external circuit 30. The storage container 20 stores a liquid L containing organic matter and microorganisms.

[0010] The microbial fuel cell 10 converts organic matter, which serves as fuel, into electrical energy using microorganisms. The microbial fuel cell 10 is immersed in a liquid L contained in a container 20. The microbial fuel cell 10 includes an anode electrode 11, an ion exchange membrane 13, a cathode electrode 15, and a shielding member 17.

[0011] The anode electrode 11 collects electrons generated when organic matter in the liquid L is oxidatively decomposed by microorganisms. The electrons collected by the anode electrode 11 move to the cathode electrode 15 via an external circuit 30. The anode electrode 11 comes into contact with the liquid L contained in the container 20. On the anode electrode 11, the microorganisms contained in the liquid L decompose the organic matter to generate electrons and hydrogen ions. The electrons generated by the microorganisms are collected by the anode electrode 11. The anode electrode 11 includes a fibrous body 111, a conductive material 113, and a binding material 115. The detailed configuration of the anode electrode 11 will be described later. The anode electrode 11 corresponds to an example of an electrode for a microbial fuel cell.

[0012] The anode electrode 11 is configured in a hollow cylindrical shape. The anode electrode 11 may be cylindrical or rectangular prism-shaped. The anode electrode 11 may be configured from a single member or a combination of multiple members. The outer peripheral surface of the anode electrode 11 comes into contact with the liquid L and supports the microorganisms in the liquid L.

[0013] The ion exchange membrane 13 allows hydrogen ions generated when the microorganisms decompose organic matter to pass through. The ion exchange membrane 13 has a function of transferring the hydrogen ions from the anode electrode 11 to the cathode electrode 15.

[0014] The ion exchange membrane 13 is disposed on the inner peripheral surface of the anode electrode 11. The ion exchange membrane 13 is configured in a hollow cylindrical shape. The outer peripheral surface of the ion exchange membrane 13 contacts the inner peripheral surface of the anode electrode 11. The inner peripheral surface of the ion exchange membrane 13 contacts the cathode electrode 15. The ion exchange membrane 13 is disposed between the anode electrode 11 and the cathode electrode 15, separating the anode electrode 11 and the cathode electrode 15.

[0015] The ion exchange membrane 13 is made of, for example, an ion exchange resin, such as NAFION manufactured by DuPont Co., Ltd., Flemion manufactured by Asahi Glass Co., Ltd., or Selemion manufactured by Asahi Glass Co., Ltd. NAFION, Flemion, and Selemion are registered trademarks.

[0016] The ion exchange membrane 13 may be composed of a porous membrane having pores through which hydrogen ions pass. The ion exchange membrane 13 may be composed of a porous sheet, a woven sheet, or a nonwoven sheet. The ion exchange membrane 13 is preferably a sheet material containing a non-conductive fiber material, wood powder particles, and an adhesive that bonds the fiber material and the wood powder particles. The fiber material may be the same material as the fiber body 111 contained in the anode electrode 11, or may be a different material. The fiber material is preferably the same material as the fiber body 111. By using the same material as the fiber body 111, the adhesion between the anode electrode 11 and the ion exchange membrane 13 is improved.

[0017] The cathode electrode 15 consumes electrons moving via the external circuit 30 in a reduction reaction of the oxidant. The electrons flow through the external circuit 30 according to the gradient between the potential generated at the anode electrode 11 and the redox potential of the chemical reaction occurring at the cathode electrode 15. The cathode electrode 15 uses oxygen in the air as an oxidant. The oxygen moves within the cathode electrode 15. The oxygen reacts with hydrogen ions moving within the ion exchange membrane 13.

[0018] The cathode electrode 15 is configured in a hollow cylindrical shape. The ion exchange surface 15a, which is the outer peripheral surface of the cathode electrode 15, contacts the inner peripheral surface of the ion exchange membrane 13 directly or via another member. The oxygen permeable surface 15b, which is the inner peripheral surface of the cathode electrode 15, contacts the atmosphere in the atmospheric space AS. The atmospheric space AS is formed on the inner peripheral portion of the cathode electrode 15. The oxygen permeable surface 15b allows oxygen in the atmosphere to permeate into the cathode electrode 15. Oxygen is supplied to the cathode electrode 15. The configuration of the cathode electrode 15 will be described later.

[0019] The shielding member 17 is disposed at one end of the oxygen permeable surface 15b. The shielding member 17 prevents the liquid L from flowing into the atmospheric space AS. The shape of the shielding member 17 is not limited as long as it is configured to prevent the liquid L from flowing into the atmospheric space AS.

[0020] The storage container 20 stores the liquid L. The storage container 20 may be connected to an inflow path and an outflow path. The inflow path is a path for allowing the liquid L to flow into the storage container 20. The outflow path is a path for allowing the liquid L to flow out of the storage container 20. The inflow path and the outflow path are not shown. The microbial fuel cell system 100 shown in FIG. 1 includes a storage container 20, but is not limited to this. The storage container 20 does not have to be provided. When the storage container 20 is not provided, the microbial fuel cell 10 is placed in a lake, a river, etc.

[0021] The liquid L contains organic matter and microorganisms. One example of the liquid L is water collected from lakes, rivers, etc. The liquid L may also be water containing organic mud collected from lakes, etc., or domestic wastewater. The organic matter in the liquid L is consumed as fuel for the microorganisms.

[0022] The microorganisms are electrochemically active bacteria that decompose organic matter in the liquid L. The electrochemically active bacteria include bacteria of the genus Geobacter, Shewanella, Aeromonas, Geothrix, and Saccharomyces. The microorganisms may be contained in the liquid L in advance, or may be added to the liquid L. The microorganisms may be supported on the anode electrode 11 in the form of a biofilm or the like.

[0023] The external circuit 30 is an electric circuit that moves electrons from the anode electrode 11 to the cathode electrode 15. The external circuit 30 is electrically connected to the anode electrode 11 and the cathode electrode 15. The external circuit 30 has a resistor 31. The resistor 31 is connected to the anode electrode 11 and the cathode electrode 15. The resistor 31 may be a variable resistor that switches its resistance value. The resistor 31 adjusts the amount of current flowing through the external circuit 30.

[0024] 1, the anode electrode 11, ion exchange membrane 13, and cathode electrode 15 are integrally configured, but are not limited to this. The anode electrode 11, ion exchange membrane 13, and cathode electrode 15 may be configured separately. The anode electrode 11, ion exchange membrane 13, and cathode electrode 15 are each immersed in liquid L.

[0025] Fig. 2 shows an example of the configuration of the anode electrode 11. Fig. 2 shows a schematic enlarged configuration of a portion of the anode electrode 11. The anode electrode 11 shown in Fig. 2 includes a fibrous body 111, conductive powder 113a which is an example of a conductive material 113, and a binder material 115.

[0026] The fibrous body 111 is made of a non-conductive material. The fibrous body 111 carries conductive powder 113a. When the anode electrode 11 contains the fibrous body 111, the number of pores in the anode electrode 11 increases. The increased number of pores increases the surface area of ​​the anode electrode 11. The increased surface area of ​​the anode electrode 11 increases the number of sites where electron transfer by microorganisms occurs. The fibrous body 111 is, for example, defibrated fiber defibrated by dry fiber technology. Defibrated fiber is cellulose fiber obtained by defibrating waste paper, or plant fiber obtained by defibrating plants such as eucalyptus. The size of the fibrous body 111 is a fiber diameter of 20 μm to 100 μm and a fiber length of 0.5 mm to 100 mm. Multiple fibrous bodies 111 are bonded to each other by a bonding material 115. The fibrous body 111 is preferably an organic material. When the fibrous material 111 is dissolved into the liquid L due to deterioration or the like, the dissolved fibrous material 111 is consumed as fuel for the microorganisms. The fibrous material 111 corresponds to an example of a fiber.

[0027] The conductive powder 113a is conductive. The conductive powder 113a contributes to the conductivity of the anode electrode 11. The conductive powder 113a is bonded to the surface of the fibrous body 111 by a binder 115. Multiple conductive powders 113a are bonded to the fibrous body 111 in contact with each other. The multiple conductive powders 113a are arranged in contact with each other to impart conductivity to the fibrous body 111. The conductive powder 113a is arranged in a single layer or multiple layers on the fibrous body 111. It is preferable that the conductive powder 113a is arranged in multiple layers on the fibrous body 111. By arranging the conductive powder 113a in multiple layers, when the conductive powder 113a on the outermost surface falls off, fresh conductive powder 113a is precipitated on the surface. The precipitation of fresh conductive powder 113a on the surface improves the durability of the microbial fuel cell 10.

[0028] The conductive powder 113a is composed of graphite particles, carbon black particles, etc. The conductive powder 113a is a powder having an average particle size of 0.1 μm to 500 μm on a volume basis. The conductive powder 113a is composed of one or more types of powder. There are no limitations on the material of the conductive powder 113a as long as it has the property of imparting conductivity to the fibrous body 111.

[0029] The content of the conductive powder 113a is preferably 50 mass % or more and 80 mass % or less in terms of the mass ratio of the anode electrode 11. If the content of the conductive powder 113a is less than 50 mass %, the electrical resistance of the anode electrode 11 increases, and the function as an electrode deteriorates. If the content of the conductive powder 113a is more than 80 mass %, the number of pores in the anode electrode 11 decreases.

[0030] The binder material 115 bonds the conductive powder 113a to the fibrous body 111. The binder material 115 bonds the conductive powder 113a to the surface of the fibrous body 111. The binder material 115 bonds the plurality of fibrous bodies 111 to one another. The binder material 115 bonds the plurality of fibrous bodies 111 to one another. The binder material 115 bonds the plurality of conductive powders 113a to one another. The binder material 115 forms the plurality of conductive powders 113a into one or more layers on the fibrous body 111.

[0031] The material of the binding material 115 is not limited as long as it can bind the fibrous body 111 and the conductive powder 113a. The binding material 115 may be a material that is solid or liquid at room temperature. The binding material 115 preferably contains at least one of calcium carbonate, lignin powder, and starch powder. By including at least one of calcium carbonate, lignin powder (average particle size by volume of 26 μm to 70 μm), and starch powder (average particle size by volume of 1 μm to 30 μm), the environmental impact of producing the anode electrode 11 is reduced. In addition, the binding material 115 is configured to have a relatively small bonding force when binding multiple conductive powders 113a. When the conductive powder 113a is configured in multiple layers, the conductive powder 113a in the outermost layer is likely to fall off. When the conductive powder 113a in the outermost layer falls off, fresh conductive powder 113a is exposed. The binding material 115 may be a wax substance produced from resource organisms such as scale insects, etc. The binding material 115 corresponds to an example of a binder.

[0032] The content of the binder 115 is preferably 5% by mass or more and 30% by mass or less relative to the mass of the anode electrode 11. If the content of the binder 115 is less than 5% by mass, the bonding strength of the conductive powder 113a bonded to the fibrous body 111 decreases, making it difficult for the anode electrode 11 to maintain its shape. If the content of the binder 115 is more than 30% by mass, the amount of binder 115 disposed between the multiple conductive powder particles 113a increases, increasing electrical resistance. This degrades the electrical characteristics of the anode electrode 11.

[0033] The anode electrode 11 includes a non-conductive fibrous body 111, a conductive material 113 having electrical conductivity, and a binding material 115 that binds the conductive material 113 to the fibrous body 111. By configuring the anode electrode 11 with the fibrous body 111, the conductive material 113, and the binding material 115, the number of sites where electron transfer by microorganisms occurs increases, and the electrical properties of the anode electrode 11 are improved.

[0034] The binding material 115 preferably includes at least one of calcium carbonate, lignin powder, and starch powder. When the binder material 115 contains at least one of calcium carbonate, lignin powder, and starch powder, the environmental impact when producing the anode electrode 11 is reduced.

[0035] The content of the fibrous body 111 in the anode electrode 11 is the remaining amount excluding the conductive powder 113a and the binding material 115. The anode electrode 11 may contain additives other than the fibrous body 111, the conductive powder 113a, and the binding material 115. When the anode electrode 11 contains additives other than the fibrous body 111, the conductive powder 113a, and the binding material 115, the content of the fibrous body 111 in the anode electrode 11 is the remaining amount excluding the conductive powder 113a, the binding material 115, and the additives.

[0036] The anode electrode 11 is manufactured using a fibrous body 111, conductive powder 113a, and binding material 115. The manufacturer mixes the fibrous body 111 and the binding material 115 in a predetermined mass ratio to produce a mixture. In the mixture, the binding material 115 adheres to the surface of the fibrous body 111. After producing the mixture, the manufacturer adds conductive powder 113a to the mixture and mixes it again. The manufacturer produces an electrode mixture containing the fibrous body 111, conductive powder 113a, and binding material 115. The manufacturer heats and presses the electrode mixture in a predetermined mold to produce a solid product. The pressing pressure is 1 kN / mm 2 More than 20kN / mm 2 The heating temperature is in the range of 80°C or higher and 150°C or lower. The pressure and heating temperature are adjusted appropriately depending on the amounts of conductive powder 113a and binding material 115 added, etc. The manufacturer produces the anode electrode 11 by processing the solid into a desired shape. The anode electrode 11 is a molded body containing pores.

[0037] Fig. 3 shows an example of the configuration of the anode electrode 11. Fig. 3 schematically shows an enlarged portion of the anode electrode 11. The anode electrode 11 shown in Fig. 3 includes a fibrous body 111, conductive powder 113a, a binder material 115, and zero-valent iron particles 117. The anode electrode 11 shown in Fig. 3 has the same configuration as the anode electrode 11 shown in Fig. 2, except that it includes the zero-valent iron particles 117.

[0038] The anode electrode 11 shown in FIG. 3 contains zero-valent iron particles 117. The zero-valent iron particles 117 are conductive. The zero-valent iron particles 117 are iron powder. The zero-valent iron particles 117 are added when the conductive powder 113a is mixed into the mixture of the fibrous body 111 and the binder material 115. The zero-valent iron particles 117 are powder having an average particle size of 0.01 to 100 μm by volume. The amount of the zero-valent iron particles 117 added is 1% by mass or more and 10% by mass or less, relative to the mass of the anode electrode 11. The addition of the zero-valent iron particles 117 reduces the electrical resistance of the anode electrode 11 and improves its electrical characteristics. The zero-valent iron particles 117 correspond to an example of metal particles. The anode electrode 11 shown in FIG. 3 contains, but is not limited to, the zero-valent iron particles 117. The material is not limited as long as it reduces the electrical resistance of the anode electrode 11.

[0039] The anode electrode 11 preferably contains zero-valent iron particles 117 . The anode electrode 11 contains zero-valent iron particles 117, which further reduces the electrical resistance of the anode electrode 11.

[0040] FIG. 4 shows an example of the configuration of the anode electrode 11. FIG. 4 schematically shows an enlarged portion of the anode electrode 11. The anode electrode 11 shown in FIG. 4 includes a fibrous body 111, conductive fibers 113b which are an example of the conductive material 113, and a binder material 115. The anode electrode 11 shown in FIG. 4 has the same configuration as the anode electrode 11 shown in FIG. 2, except that the anode electrode 11 includes conductive fibers 113b instead of the conductive powder 113a. FIG. 4 shows the anode electrode 11 from which the binder material 115 is omitted.

[0041] The conductive fibers 113b are conductive. The conductive fibers 113b contribute to the conductivity of the anode electrode 11. The conductive fibers 113b are bonded to the surface of the fibrous body 111 by a bonding material 115. The plurality of conductive fibers 113b are bonded to the fibrous body 111 in contact with one another. The plurality of conductive fibers 113b are arranged in contact with one another to impart conductivity to the fibrous body 111.

[0042] The conductive fibers 113b are made of carbon fibers. Carbon fibers are produced by cutting PAN (polyacrylonitrile)-based carbon fibers or pitch-based carbon fibers. PAN-based carbon fibers are obtained by carbonizing PAN precursors. Pitch-based carbon fibers are obtained by carbonizing pitch fibers made from coal tar or heavy petroleum. The conductive fibers 113b have an average fiber diameter of 5 μm to 30 μm and an average fiber length of 0.05 mm to 0.1 mm. The fiber diameter and fiber length of the conductive fibers 113b are smaller than those of the fibrous body 111. The conductive fibers 113b may be made of one or more types of carbon fibers. The material of the conductive fibers 113b is not limited as long as it has the property of imparting conductivity to the fibrous body 111.

[0043] The anode electrode 11 is manufactured using a fibrous body 111, conductive fibers 113b, and a binding material 115. The manufacturer mixes the fibrous body 111 and the binding material 115 in a predetermined mass ratio to produce a mixture. In the mixture, the binding material 115 adheres to the surface of the fibrous body 111. After producing the mixture, the manufacturer adds conductive fibers 113b to the mixture and mixes it again. The manufacturer produces an electrode mixture containing the fibrous body 111, conductive fibers 113b, and binding material 115. The manufacturer heats and presses the electrode mixture in a predetermined mold to produce a solid product. The pressing pressure is 1 kN / mm 2 More than 20kN / mm 2 The heating temperature is in the range of 80°C or higher and 150°C or lower. The pressure and heating temperature are adjusted as appropriate depending on the amounts of conductive fibers 113b and binding material 115 added, etc. The manufacturer produces the anode electrode 11 by processing the solid into a desired shape. The anode electrode 11 is a molded body containing pores.

[0044] 4 may include zero-valent iron particles 117. The zero-valent iron particles 117 are added when the conductive fibers 113b are mixed into the mixture of the fibrous body 111 and the binder material 115.

[0045] The anode electrode 11 shown in Fig. 4 includes, but is not limited to, carbon fibers as the conductive fibers 113b. The anode electrode 11 shown in Fig. 4 may also include conductive powder 113a such as graphite particles. The anode electrode 11 preferably includes at least one of the conductive fibers 113b and the conductive powder 113a. The anode electrode 11 contains at least one of the conductive fibers 113b and the conductive powder 113a, thereby reducing the electrical resistance of the anode electrode 11.

[0046] 5 shows a schematic configuration of the cathode electrode 15. The cathode electrode 15 has an ion exchange surface 15a and an oxygen permeable surface 15b. The cathode electrode 15 is provided with a water-repellent layer 18 and a filter layer 19.

[0047] The cathode electrode 15 is electrically conductive and oxygen permeable. The cathode electrode 15 is made of a carbon fiber sheet or the like. The cathode electrode 15 may be made of non-conductive fibers 151, a carbon-based material 153, and an adhesive material 155.

[0048] The ion exchange surface 15a is the surface facing the ion exchange membrane 13. The ion exchange surface 15a contacts the ion exchange membrane 13 directly or via a filter layer 19. Hydrogen ions react with oxygen on or near the ion exchange surface 15a.

[0049] The oxygen permeable surface 15b is a surface that comes into contact with the atmosphere directly or via the water-repellent layer 18. The oxygen permeable surface 15b allows oxygen in the atmosphere to permeate into the cathode electrode 15.

[0050] The water-repellent layer 18 is disposed on the oxygen-permeable surface 15b of the cathode electrode 15. The water-repellent layer 18 is oxygen-permeable and water-repellent. The water-repellent layer 18 allows oxygen in the atmosphere to pass through to the cathode electrode 15. The water-repellent layer 18 prevents the liquid L from adhering to the cathode electrode 15. The water-repellent layer 18 is made of a nonwoven fabric such as polyethylene or polypropylene, a film such as polytetrafluoroethylene (PTFE), a composite material film made by combining polyurethane polymers, beeswax, or the like. By making the water-repellent layer 18 out of beeswax, for example, the environmental impact during the production of the cathode electrode 15 is reduced.

[0051] The cathode electrode 15 preferably includes a water-repellent layer 18 disposed on the oxygen permeable surface 15b, which is different from the ion exchange surface 15a that contacts the ion exchange membrane 13. By providing the water-repellent layer 18, the cathode electrode 15 can prevent the liquid L from adhering thereto and allow oxygen to pass therethrough efficiently.

[0052] The water-repellent layer 18 is preferably made of beeswax. By forming the water-repellent layer 18 from beeswax, it is possible to reduce the environmental impact while maintaining water repellency and oxygen permeability.

[0053] The filter layer 19 is disposed on the ion exchange surface 15a of the cathode electrode 15. The filter layer 19 is disposed between the ion exchange membrane 13 and the cathode electrode 15. The filter layer 19 prevents microorganisms from entering the cathode electrode 15. The filter layer 19 may or may not be disposed on the ion exchange surface 15a of the cathode electrode 15. The filter layer 19 is disposed as appropriate.

[0054] Fig. 6 shows an example of the configuration of the cathode electrode 15. Fig. 6 schematically shows an enlarged configuration of a portion of the cathode electrode 15. Fig. 6 shows the cathode electrode 15 composed of non-conductive fibers 151, a carbon-based material 153, and an adhesive material 155. The cathode electrode 15 may include materials other than the non-conductive fibers 151, the carbon-based material 153, and the adhesive material 155. The cathode electrode 15 corresponds to an example of an electrode for a microbial fuel cell.

[0055] The non-conductive fibers 151 are made of a non-conductive material. The non-conductive fibers 151 support a carbon-based material 153. When the cathode electrode 15 includes the non-conductive fibers 151, the number of pores in the cathode electrode 15 increases. The increase in the number of pores increases the surface area of ​​the cathode electrode 15. As the surface area of ​​the cathode electrode 15 increases, the number of sites where an oxidation-reduction reaction using oxygen occurs increases. As an example, the non-conductive fibers 151 are defibrated fibers defibrated using dry fiber technology. The size of the non-conductive fibers 151 is a fiber diameter of 5 μm to 100 μm and a fiber length of 10 μm to 1000 μm. The multiple non-conductive fibers 151 are bonded to each other by an adhesive material 155. The non-conductive fibers 151 may be made of the same material as the fibrous body 111 or a different material. It is preferable that the non-conductive fibers 151 be made of the same material as the fibrous body 111. The non-conductive fiber 151 can be made of the same material as the fibrous body 111. The non-conductive fiber 151 corresponds to an example of a fiber and a fiber base material.

[0056] The carbon-based material 153 is conductive. The carbon-based material 153 contributes to the conductivity of the cathode electrode 15. The carbon-based material 153 is fixed to the surface of the non-conductive fiber 151 by the fixing material 155. The plurality of carbon-based materials 153 are fixed to the non-conductive fiber 151 in contact with each other. The plurality of carbon-based materials 153 are arranged in contact with each other to impart conductivity to the non-conductive fiber 151. The carbon-based material 153 is arranged in a single layer or multiple layers on the non-conductive fiber 151. It is preferable that the carbon-based material 153 is arranged in multiple layers on the non-conductive fiber 151.

[0057] The carbon-based material 153 is made of carbon powder such as graphite particles, carbon black particles, etc. The carbon-based material 153 is a powder having an average particle size of 0.1 μm to 100 μm on a volume basis. The carbon-based material 153 is made of one or more types of carbon powder. There are no limitations on the material of the carbon-based material 153 as long as it has the property of imparting conductivity to the non-conductive fiber 151. The carbon-based material 153 corresponds to an example of a conductive material and a conductivity-imparting material.

[0058] The carbon-based material 153 may be made of carbon fiber. The carbon fiber is produced by cutting PAN-based carbon fiber or pitch-based carbon fiber. The carbon fiber has an average fiber diameter of 5 μm to 30 μm and an average fiber length of 0.05 mm to 0.1 mm. The fiber diameter and fiber length of the carbon-based material 153 are smaller than those of the non-conductive fiber 151. The carbon-based material 153 may be made of one or more types of carbon fiber. The carbon-based material 153 may be made of a mixture of carbon powder and carbon fiber.

[0059] The carbon-based material 153 may be the same material as the conductive powder 113a or a different material. The carbon-based material 153 may be the same material as the conductive fibers 113b or a different material. The carbon-based material 153 is preferably the same material as the conductive powder 113a or the conductive fibers 113b. By using the carbon-based material 153 as the same material as the conductive powder 113a or the conductive fibers 113b, the anode electrode 11 and the cathode electrode 15 can have the same base material configuration.

[0060] The content of carbon-based material 153 is preferably 50 mass % or more and 80 mass % or less in terms of the mass ratio of cathode electrode 15. If the content of carbon-based material 153 is less than 50 mass %, the electrical resistance of cathode electrode 15 increases, and its function as an electrode deteriorates. If the content of carbon-based material 153 is more than 80 mass %, the number of pores in cathode electrode 15 decreases, and oxygen permeability decreases.

[0061] The adhesive material 155 adhesively bonds the carbon-based material 153 to the non-conductive fiber 151. The adhesive material 155 adhesively bonds the carbon-based material 153 to the surface of the non-conductive fiber 151. The adhesive material 155 adhesively bonds the plurality of non-conductive fibers 151 to one another. The adhesive material 155 adhesively bonds the plurality of non-conductive fibers 151 to one another. The adhesive material 155 adhesively bonds the plurality of carbon-based materials 153 to one another. The adhesive material 155 causes the plurality of carbon-based materials 153 to be formed into one or more layers on the non-conductive fiber 151.

[0062] The adhesive material 155 may be made of any material as long as it can bond the non-conductive fiber 151 and the carbon-based material 153 together. The adhesive material 155 may be a solid material or a liquid material at room temperature. The adhesive material 155 preferably contains at least one of calcium carbonate, lignin powder (average particle size by volume of 26 μm to 70 μm), and starch powder (average particle size by volume of 1 μm to 30 μm). By including at least one of calcium carbonate, lignin powder, and starch powder in the adhesive material 155, the environmental impact of producing the cathode electrode 15 is reduced. The adhesive material 155 may be a wax substance produced from resource-producing organisms such as scale insects. The adhesive material 155 corresponds to an example of a binder and a binder.

[0063] The adhesive material 155 may be the same material as the binding material 115, or may be a different material. The adhesive material 155 is preferably the same material as the binding material 115. When the adhesive material 155 is the same material as the binding material 115, the environmental impact during the production of the cathode electrode 15 is reduced.

[0064] The content of the adhesive material 155 is preferably 5% by mass or more and 30% by mass or less, in terms of the mass ratio of the cathode electrode 15. If the content of the adhesive material 155 is less than 5% by mass, the adhesive strength of the carbon-based material 153 adhered to the non-conductive fiber 151 decreases. It becomes difficult for the cathode electrode 15 to maintain its shape. If the content of the adhesive material 155 is more than 30% by mass, the amount of adhesive material 155 disposed between the multiple carbon-based materials 153 increases, increasing electrical resistance. The electrical characteristics of the cathode electrode 15 deteriorate.

[0065] The cathode electrode 15 preferably includes non-conductive fibers 151, a conductive carbon-based material 153, and an adhesive material 155 that adhesively attaches the carbon-based material 153 to the non-conductive fibers 151. The cathode electrode 15 is made up of the non-conductive fiber 151, the carbon-based material 153, and the adhesive material 155, so that the environmental impact during the production of the cathode electrode 15 is reduced.

[0066] The content of the non-conductive fibers 151 in the cathode electrode 15 is the remaining amount excluding the carbon-based material 153 and the adhesive material 155. The cathode electrode 15 may contain additives other than the non-conductive fibers 151, the carbon-based material 153, and the adhesive material 155. When the cathode electrode 15 contains additives other than the non-conductive fibers 151, the carbon-based material 153, and the adhesive material 155, the content of the non-conductive fibers 151 in the cathode electrode 15 is the remaining amount excluding the carbon-based material 153, the adhesive material 155, and the additives.

[0067] The cathode electrode 15 is made using non-conductive fibers 151, a carbon-based material 153, and an adhesive material 155. The manufacturer mixes the non-conductive fibers 151 and the adhesive material 155 in a predetermined mass ratio to produce a mixture. In the mixture, the adhesive material 155 adheres to the surface of the non-conductive fibers 151. After producing the mixture, the manufacturer adds the carbon-based material 153 to the mixture and mixes it again. The manufacturer produces a cathode electrode mixture including the non-conductive fibers 151, the carbon-based material 153, and the adhesive material 155. The manufacturer heats and presses the cathode electrode mixture in a predetermined mold to produce a solid product. The pressing pressure is 1 kN / mm 2 More than 20kN / mm 2 The heating temperature is in the range of 80°C or higher and 150°C or lower. The pressure and heating temperature are adjusted appropriately depending on the amounts of carbon-based material 153 and adhesive material 155 added, etc. The manufacturer produces cathode electrode 15 by processing the solid into a desired shape. Cathode electrode 15 is a molded body containing pores.

[0068] The microbial fuel cell 10, which comes into contact with a liquid L containing organic matter and microorganisms, comprises an anode electrode 11 including a non-conductive fibrous body 111, a conductive material 113, and a binding material 115 that binds the conductive material 113 to the fibrous body 111, and a conductive cathode electrode 15. The anode electrode 11 is made up of the fibrous body 111, the conductive material 113, and the binding material 115, which increases the number of sites where electron transfer by the microorganisms occurs, thereby improving the performance of the microbial fuel cell 10.

[0069] The microbial fuel cell system 100 comprises a microbial fuel cell 10 having an anode electrode 11 in contact with a liquid L containing organic matter and microorganisms, a cathode electrode 15 to which oxygen is supplied, and an ion exchange membrane 13 disposed between the anode electrode 11 and the cathode electrode 15, and a resistor 31 connected to the anode electrode 11 and the cathode electrode 15. The anode electrode 11 includes a non-conductive fibrous body 111, a conductive material 113 having conductivity, and a binding material 115 that binds the conductive material 113 to the fibrous body 111. The decomposition of organic matter by microorganisms is promoted, and the purification ability of the liquid L by the microbial fuel cell system 100 is improved.

[0070] Example 1 In Example 1, a microbial fuel cell 10 is prepared that includes an anode electrode 11 composed of a fibrous body 111, a conductive material 113, and a binding material 115. The microbial fuel cell 10 prepared in Example 1 is referred to as cell 1.

[0071] The anode electrode 11 is made using a fibrous body 111, a conductive material 113, and a binding material 115. First, a mixture containing the fibrous body 111 and the binding material 115 is made. The fibrous body 111 is made of plant fiber made from eucalyptus, a plant. The binding material 115 is made of scale insect secretions. The scale insect secretions are a waxy substance. The mixing ratio of the plant fiber is 80% by mass, and the mixing ratio of the scale insect secretions is 20% by mass. The plant fiber and the scale insect secretions are mixed using a planetary ball mill to make a mixture.

[0072] After the mixture is created, a conductive material 113 is mixed into the mixture. Chopped carbon fiber fiber, K223HM manufactured by Mitsubishi Chemical Corporation, is used as the conductive material 113. The chopped carbon fiber fiber is an example of carbon fiber. The mixture ratio is 35 mass %, and the mixture ratio of chopped carbon fiber fiber is 65 mass %. The chopped carbon fiber fiber is a short fiber with a fiber diameter of 11 μm and a fiber length of 0.05 mm. The mixture and chopped carbon fiber fiber are mixed using a planetary ball mill to create an anode electrode mixture. The anode electrode mixture is a mixture of 28 mass % plant fiber, 7 mass % scale insect secretions, and 65 mass % chopped carbon fiber.

[0073] After the anode electrode mixture is prepared, it is heated and pressed to form a sheet material. The anode electrode mixture is heated to 120°C by a heater. After being heated, the anode electrode mixture is pressed by a press with a pressure of 5 kN / mm 2 The anode electrode mixture is pressed into an electrode sheet having a thickness of 0.8 mm.

[0074] After being formed, the electrode sheet is processed to a predetermined size. The electrode sheet is processed into rectangular pieces with a width of 20 mm and a length of 30 mm. Multiple rectangular pieces are joined together to form a rectangular prism-shaped anode electrode 11. The formed anode electrode 11 is referred to as electrode material A1.

[0075] An ion exchange resin is used for the ion exchange membrane 13. NAFION manufactured by DuPont is used as the ion exchange resin. A NAFION membrane having a thickness of 0.5 mm is disposed on the inner peripheral surface of the anode electrode 11. The NAFION ion exchange membrane 13 is referred to as an intermediate layer B1.

[0076] Graphite felt manufactured by Nippon Carbon Co., Ltd. is used for the cathode electrode 15. The graphite felt is a carbon-based fiber. The graphite felt is disposed on the inner peripheral surface of the ion exchange membrane 13. A PTFE membrane is disposed on the inner peripheral surface of the graphite felt as a water-repellent layer 18. The PTFE membrane is produced by immersing one surface of the graphite felt in a PTFE solution. The graphite felt cathode electrode 15 is referred to as electrode material C1.

[0077] Battery 1 is made by combining electrode material A1, intermediate layer B1, and electrode material C1. Battery 1 is placed in liquid L. Liquid L is lake water collected from the shore of Lake Suwa. Liquid L contains organic mud and electrochemically active bacteria. The electrochemically active bacteria are Geobacter bacteria.

[0078] Example 2 In Example 2, a microbial fuel cell 10 is prepared that includes an anode electrode 11 composed of a fibrous body 111, a conductive material 113, zero-valent iron particles 117, and a binding material 115. The microbial fuel cell 10 prepared in Example 2 is designated as Cell 2.

[0079] The anode electrode 11 is made using a fibrous body 111, a conductive material 113, zero-valent iron particles 117, and a binding material 115. First, a mixture containing the fibrous body 111 and the binding material 115 is made. The fibrous body 111 is made of plant fiber made from eucalyptus, a plant. The binding material 115 is made of lignin powder, Sanex P321, manufactured by Nippon Paper Industries Co., Ltd. Sanex is a registered trademark. The plant fiber is mixed at a ratio of 75% by mass, and the lignin powder is mixed at a ratio of 25% by mass. The plant fiber and lignin powder are mixed using a planetary ball mill to make a mixture.

[0080] After the mixture is prepared, conductive material 113 and zero-valent iron particles 117 are mixed with the mixture. Graphite particles manufactured by Nishimura Graphite Co., Ltd. are used for the conductive material 113. The graphite particles are an example of carbon powder. The graphite powder is a scaly powder with an average particle size of 500 μm by volume. Iron powder manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. is used for the zero-valent iron particles 117. The iron powder is a powder with an average particle size of 40 μm or less by volume. The mixture is mixed in a ratio of 30% by mass, the graphite powder in a ratio of 65% by mass, and the iron powder in a ratio of 5% by mass. The mixture, graphite particles, and iron powder are mixed in a planetary ball mill to prepare an anode electrode mixture. The anode electrode mixture is a mixture of 22.5% by mass of plant fiber, 7.5% by mass of lignin powder, 65.0% by mass of graphite particles, and 5.0% by mass of iron powder.

[0081] After the anode electrode mixture is prepared, it is heated and pressed to form a sheet material. The anode electrode mixture is heated to 130°C by a heater. After being heated, the anode electrode mixture is pressed to 10 kN / mm 2 The anode electrode mixture is pressed into an electrode sheet having a thickness of 1.0 mm.

[0082] After being formed, the electrode sheet is processed to a predetermined size. The electrode sheet is processed into rectangular pieces with a width of 20 mm and a length of 30 mm. Multiple rectangular pieces are joined together to form a rectangular prism-shaped anode electrode 11. The formed anode electrode 11 is referred to as electrode material A2.

[0083] The battery 2 is made using an electrode material A2. An intermediate layer B1 is used for the ion exchange membrane 13. An electrode material C1 is used for the cathode electrode 15. The battery 2 is made by combining the electrode material A2, the intermediate layer B1, and the electrode material C1. The battery 2 is placed in a liquid L. The liquid L is lake water collected from the shore of Lake Suwa. The liquid L contains organic mud and electrochemically active bacteria. The electrochemically active bacteria are Geobacter bacteria.

[0084] Example 3 In Example 3, a microbial fuel cell 10 is constructed that includes an anode electrode 11 composed of a fibrous body 111, a conductive material 113, and a binding material 115. The microbial fuel cell 10 constructed in Example 3 is designated as Cell 3.

[0085] An electrode material A1 is used for the anode electrode 11. An intermediate layer B1 is used for the ion exchange membrane 13. The cathode electrode 15 is made of non-conductive fibers 151, a carbon-based material 153, and an adhesive material 155. The cathode electrode 15 is provided with a water-repellent layer 18 made of beeswax.

[0086] The cathode electrode 15 is made using non-conductive fibers 151, a carbon-based material 153, and an adhesive material 155. First, a mixture containing the non-conductive fibers 151 and the carbon-based material 153 is made. The non-conductive fibers 151 are made of cellulose fibers made from recycled paper. The adhesive material 155 is made of lignin powder, Sanex P321, manufactured by Nippon Paper Industries Co., Ltd. The mixture ratio of the cellulose fibers is 75% by mass, and the mixture ratio of the lignin powder is 25% by mass. The cellulose fibers and lignin powder are mixed using a planetary ball mill to make a mixture.

[0087] After the mixture is prepared, carbon-based material 153 is mixed into the mixture. Graphite particles manufactured by Nishimura Graphite Co., Ltd. are used as the carbon-based material 153. The graphite particles are an example of carbon powder. The graphite powder is a scaly powder with an average particle size of 500 μm by volume. The mixture is mixed at a ratio of 30 mass % and the graphite powder is mixed at a ratio of 70 mass %. The mixture and the graphite particles are mixed using a planetary ball mill to prepare a cathode electrode mixture. The cathode electrode mixture is a mixture of 22.5 mass % cellulose fiber, 7.5 mass % lignin powder, and 70.0 mass % graphite particles.

[0088] The cathode electrode mixture is heated to 130°C by a heater and then pressed under heat and pressure to form a sheet material. After heating, the cathode electrode mixture is pressed under a pressure of 10 kN / mm 2 The cathode electrode mixture is pressed into a 1.0 mm thick electrode sheet.

[0089] After being formed, the electrode sheet is processed to a predetermined size. The electrode sheet is processed into a rectangular piece with a width of 20 mm and a length of 30 mm. Multiple rectangular pieces are joined together to form a quadrangular prism-shaped cathode electrode 15.

[0090] Beeswax manufactured by Miki Chemical Industry Co., Ltd. is used for the water-repellent layer 18 provided on the cathode electrode 15. The beeswax is applied to the oxygen permeable surface 15b of the cathode electrode 15. The applied beeswax layer functions as the water-repellent layer 18. The cathode electrode 15 provided with the beeswax layer is referred to as electrode material C2.

[0091] The battery 3 is made by combining an electrode material A1, an intermediate layer B1, and an electrode material C2. The battery 3 is placed in a liquid L. The liquid L is lake water collected from the shore of Lake Suwa. The liquid L contains organic mud and electrochemically active bacteria. The electrochemically active bacteria are Geobacter bacteria.

[0092] Comparative Example 1 In Comparative Example 1, a microbial fuel cell 10 is produced, which includes an anode electrode 11 made of carbon fiber, carbon cloth, and a cathode electrode 15 made of graphite felt. The microbial fuel cell 10 produced in Comparative Example 1 is referred to as cell 4.

[0093] Carbon cloth manufactured by Toray Industries, Inc. is used for the anode electrode 11. The thickness of the carbon cloth is 100 μm. The anode electrode 11 using the carbon cloth is represented as electrode material A3.

[0094] The battery 4 is made by combining an electrode material A3, an intermediate layer B1, and an electrode material C1. The battery 4 is placed in a liquid L. The liquid L is lake water collected from the shore of Lake Suwa. The liquid L contains organic mud and electrochemically active bacteria. The electrochemically active bacteria are Geobacter bacteria.

[0095] Figure 7 shows the configuration of each microbial fuel cell 10. Figure 7 shows the configuration of each microbial fuel cell 10, namely, cell 1, cell 2, cell 3, and cell 4. Cell 1, cell 2, and cell 3 are the configurations of the microbial fuel cells 10 prepared in Example 1, Example 2, and Example 3, respectively. Cell 4 is the configuration of the microbial fuel cell 10 prepared in Comparative Example 1.

[0096] Evaluation results Figure 8 shows an example of the evaluation results of the microbial fuel cell 10. Figure 8 shows the change over time in the generated voltage of the microbial fuel cell 10. Figure 8 shows the change over time in the generated voltage of each of cells 1, 2, 3, and 4. The horizontal axis shows the number of days that have passed. The vertical axis shows the generated voltage.

[0097] As shown in Figure 8, the generated voltages of batteries 1, 3, and 4 at the beginning of the measurement are almost the same. As the number of days passes, the generated voltage of battery 4, which is the comparative example, decreases. In batteries 1, 2, and 3, which are the examples, the decrease in generated voltage over the course of days is suppressed. The generated voltage remains constant.

[0098] The voltage generated by Battery 2, which contains zero-valent iron particles 117, is higher than the voltages generated by Battery 1, Battery 3, and Battery 4. In Battery 2, the decrease in the generated voltage over time is suppressed. The inclusion of zero-valent iron particles 117 improves the battery characteristics.

[0099] After a predetermined number of days, the voltage generated by the battery 3 having the water-repellent layer 118 made of beeswax remains higher than the voltage generated by the battery 1 having the water-repellent layer 118 made of PTFE. By using beeswax for the water-repellent layer 118, the battery characteristics are improved.

[0100] Figures 9, 10, 11, and 12 show an example of the evaluation results of the microbial fuel cell 10. Figures 9, 10, 11, and 12 show the polarization analysis results of the microbial fuel cell 10. Figures 9, 10, 11, and 12 show the current-voltage characteristics of the microbial fuel cell 10 and the relationship between current and power. Figures 9, 10, 11, and 12 show the current-voltage characteristics and the relationship between current and power 12 days after the start of evaluation of the microbial fuel cell 10. The current-voltage measurements are performed by changing the resistance value of the resistor 31 connected to the microbial fuel cell 10.

[0101] Figure 9 shows the current-voltage characteristics and the relationship between current and power for battery 1. Figure 10 shows the current-voltage characteristics and the relationship between current and power for battery 2. Figure 11 shows the current-voltage characteristics and the relationship between current and power for battery 3. Figure 12 shows the current-voltage characteristics and the relationship between current and power for battery 4.

[0102] As shown in Figures 9, 10, 11, and 12, the maximum power value, which is the peak value of power, differs depending on the battery. The maximum power values ​​of Battery 1, Battery 2, and Battery 3 are higher than the maximum power value of Battery 4. The characteristics of the microbial fuel cell 10 are improved by using the anode electrode 11, which is composed of a fibrous body 111, a conductive material 113, and a binding material 115.

[0103] The maximum power value of cell 2 is higher than the maximum power values ​​of cells 1 and 3. The addition of zero-valent iron particles 117 to the anode electrode 11 improves the characteristics of the microbial fuel cell 10. Furthermore, the maximum power value of cell 3 is higher than the maximum power value of cell 4. The use of beeswax in the water-repellent layer 18 improves the characteristics of the microbial fuel cell 10. [Explanation of symbols]

[0104] 10...Microbial fuel cell, 11...Anode electrode, 13...Ion exchange membrane, 15...Cathode electrode, 15a...Ion exchange surface, 15b...Oxygen permeable surface, 17...Shielding member, 18...Water-repellent layer, 19...Filter layer, 20...Storage container, 30...External circuit, 31...Resistor, 100...Microbial fuel cell system, 111...Fiber body, 113...Conductive material, 113a...Conductive powder, 113b...Conductive fiber, 115...Binding material, 117...Zerovalent iron particles, 151...Non-conductive fiber, 153...Carbon-based material, 155...Adhesion material, AS...Atmospheric space, L...Liquid.

Claims

1. The method includes the steps of: (a) forming a conductive sheet using a non-conductive fiber; (b) forming a conductive material having electrical conductivity; and (c) forming a binder that binds the conductive material to the fiber. Electrode for microbial fuel cells.

2. The conductive material is at least one of carbon fiber and graphite particles. The electrode for a microbial fuel cell according to claim 1.

3. Contains conductive metal particles, The electrode for a microbial fuel cell according to claim 2.

4. The binder includes at least one of calcium carbonate, lignin powder, and starch powder. The electrode for a microbial fuel cell according to claim 1.

5. 1. A microbial fuel cell in contact with a liquid containing organic matter and electrochemically active bacteria, an anode electrode including non-conductive fibers, a conductive material having electrical conductivity, and a binder that binds the conductive material to the fibers; a conductive cathode electrode; A microbial fuel cell comprising:

6. The cathode electrode includes a non-conductive fiber substrate, a conductive conductivity-imparting material, and a binder that fixes the conductivity-imparting material to the fiber substrate. The microbial fuel cell according to claim 5.

7. The cathode electrode includes a water-repellent layer. The microbial fuel cell according to claim 6.

8. The water-repellent layer is made of beeswax. The microbial fuel cell according to claim 7.

9. The anode electrode contains conductive metal particles. The microbial fuel cell according to claim 5.

10. a non-conductive fiber material, wood flour particles, and an adhesive that bonds the fiber material and the wood flour particles; and an ion exchange membrane that is in contact with the cathode electrode and the anode electrode between the cathode electrode and the anode electrode. The microbial fuel cell according to claim 5.

11. a microbial fuel cell having an anode electrode in contact with a liquid containing organic matter and electrochemically active bacteria, a cathode electrode to which oxygen is supplied, and an ion exchange membrane disposed between the anode electrode and the cathode electrode; a resistor connected to the anode electrode and the cathode electrode, The anode electrode is The method includes the steps of: (a) forming a conductive sheet using a non-conductive fiber; (b) forming a conductive material having electrical conductivity; and (c) forming a binder that binds the conductive material to the fiber. Microbial fuel cell system.

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