JP2017228410A - Electrode and microbial fuel cell - Google Patents

Abstract

An electrode capable of suppressing oxygen consumption by an aerobic microorganism and effectively performing an oxygen reduction reaction, and a microbial fuel cell using the electrode are provided. An electrode (10) includes a conductor layer (1), a porous body layer (2) having a thickness of 1.0 mm to 40 mm provided on one surface of the conductor layer, and a conductor. A water repellent layer (3) provided on the surface (1a) on the porous body layer side and the surface (1b) on the opposite side of the layer. The microbial fuel cell (100) includes a positive electrode (10A) composed of an electrode (10), a negative electrode (20) holding microorganisms, and an electrolytic solution (70), and the porous body layer and the negative electrode are immersed in the electrolytic solution. Thus, at least a part of the water repellent layer is exposed to the gas phase (90). [Selection] Figure 1

Description

  The present invention relates to an electrode and a microbial fuel cell. Specifically, the present invention relates to an electrode capable of purifying waste water and generating electric energy, and a microbial fuel cell using the electrode.

  In recent years, microbial fuel cells that generate electricity using biomass have attracted attention as sustainable energy. A microbial fuel cell is a wastewater treatment apparatus that converts the chemical energy of an organic substance contained in domestic wastewater or factory wastewater into electrical energy and oxidizes and decomposes the organic substance. The microbial fuel cell is characterized by little generation of sludge and low energy consumption. However, since the power generated by microorganisms is very small and the output current density is low, further improvement is necessary.

  As such a microbial fuel cell, the thing of the following patent documents 1 is indicated. The microbial fuel cell is disposed in an electrolytic cell holding an electrolytic solution, an anode disposed inside the electrolytic cell, a tank body of the electrolytic cell, one surface is in contact with air outside the cell, and the other surface is A cathode in contact with the electrolyte. In addition to the electrolytic solution, the electrolytic cell holds microorganisms and a substrate for oxidative degradation by the microorganisms. As the microorganism, anaerobic microorganisms such as Geobacter genus and Shewanella genus are disclosed. The cathode includes an electrode substrate having electron conductivity and gas permeability, and a water-stopping layer containing silicone is formed on one surface of the electrode substrate that comes into contact with air. A catalyst layer supporting a cathode catalyst is formed on the surface. In the microbial fuel cell of Patent Document 1, after microorganisms oxidize and decompose a substrate to generate electrons and protons, electrons supplied from the anode through an external circuit, protons in the electrolytic solution, and the outside of the electrolytic cell The supplied oxygen reacts with the catalyst layer of the cathode.

  Here, in addition to the above-mentioned anaerobic microorganisms, the microbial fuel cell electrolyte often contains aerobic microorganisms that require oxygen for growth. And since an aerobic microorganism makes oxygen essential, it exists in the interface vicinity of the water stop layer and electrode base material with high oxygen concentration.

Japanese Patent Laying-Open No. 2015-46361

  As described above, in the microbial fuel cell of Patent Document 1, since aerobic microorganisms exist near the interface between the water blocking layer and the electrode base material, oxygen is consumed by the aerobic microorganisms near the interface. End up. As a result, oxygen does not sufficiently reach the catalyst layer disposed inside the electrolytic cell rather than the electrode base material, so that the oxygen reduction reaction is not performed and electric energy cannot be stably obtained.

  The present invention has been made in view of such problems of the prior art. An object of the present invention is to provide an electrode capable of suppressing oxygen consumption by aerobic microorganisms and effectively performing an oxygen reduction reaction, and a microbial fuel cell using the electrode.

  In order to solve the above-described problems, an electrode according to the first aspect of the present invention includes a conductor layer and a porous body layer provided on one surface of the conductor layer and having a thickness of 1.0 mm to 40 mm. And a water repellent layer provided on the surface opposite to the surface on the porous body layer side of the conductor layer.

  A microbial fuel cell according to a second aspect of the present invention comprises a positive electrode comprising the above electrode, a negative electrode holding microorganisms, and an electrolytic solution, wherein the porous body layer and the negative electrode are immersed in the electrolytic solution, and the water repellent layer At least a part of is exposed to the gas phase.

  ADVANTAGE OF THE INVENTION According to this invention, the oxygen consumption by aerobic microorganisms can be suppressed and the electrode and microbial fuel cell which can perform an oxygen reductive reaction effectively can be obtained.

It is sectional drawing which shows an example of the electrode which concerns on embodiment of this invention. It is a perspective view which shows the other example of the electrode which concerns on embodiment of this invention. It is sectional drawing for demonstrating the effect | action of the electrode which concerns on embodiment of this invention. It is a perspective view which shows an example of the microbial fuel cell which concerns on embodiment of this invention. It is sectional drawing along the AA line in FIG. It is a disassembled perspective view which shows the fuel cell unit in the said microbial fuel cell. It is sectional drawing which shows the other example of the microbial fuel cell which concerns on embodiment of this invention. It is a perspective view which shows the other example of the electrode which concerns on embodiment of this invention. It is a graph which shows the relationship between the steady output in the microbial fuel cell using the electrode of Examples 1-4 and Comparative Examples 1 and 2, and elapsed days.

  Hereinafter, the electrode according to the present embodiment and the microbial fuel cell will be described in detail. In addition, the dimension ratio of drawing is exaggerated on account of description, and may differ from an actual ratio.

[Electrode of First Embodiment]
As shown in FIG. 1, the electrode according to the present embodiment includes a conductor layer 1, a porous body layer 2 provided on one surface 1 a of the conductor layer 1, and a porous body layer in the conductor layer 1. And a water repellent layer 3 provided on the opposite surface 1b.

(Conductor layer)
The conductor layer 1 in the electrode 10 has conductivity and oxygen permeability. By providing such a conductor layer 1 on the electrode 10, electrons generated by a local battery reaction described later can be conducted between the catalyst and the external circuit 110. That is, as will be described later, the conductor layer 1 carries a catalyst, and the catalyst is an oxygen reduction catalyst. By providing the conductor layer 1 on the electrode 10, electrons move from the external circuit 110 to the catalyst through the conductor layer 1, and the oxygen reduction reaction by oxygen, hydrogen ions, and electrons can be advanced by the catalyst. Become.

  In the electrode 10, in order to ensure stable performance, oxygen efficiently permeates through the water repellent layer 3 and the conductor layer 1 and is supplied to the catalyst, and hydrogen ions efficiently permeate through the conductor layer 1 and the catalyst. Is preferably supplied. Therefore, the conductor layer 1 is preferably a porous body having many pores through which oxygen and hydrogen ions pass from the surface 1b facing the water repellent layer 3 to the surface 1a on the opposite side. The shape of the conductor layer 1 is particularly preferably a three-dimensional mesh. With such a mesh shape, high oxygen permeability and conductivity can be imparted to the conductor layer 1.

  The conductive material constituting the conductor layer 1 is not particularly limited as long as high conductivity can be secured. However, the conductive material is preferably made of at least one conductive metal selected from the group consisting of aluminum, copper, stainless steel, nickel and titanium. Since these conductive metals have high corrosion resistance and conductivity, they can be suitably used as a material constituting the conductor layer 1.

  The conductive material may be a carbon material. As the carbon material, for example, at least one selected from the group consisting of carbon paper, carbon felt, carbon cloth, and graphite sheet can be used. Further, the conductive material may be made of one selected from the group consisting of carbon paper, carbon felt, carbon cloth and graphite sheet, or may be a laminate formed by laminating a plurality of these. Carbon paper and carbon felt, which are carbon fiber nonwoven fabrics, carbon cloth, which is carbon fiber woven fabric, and graphite sheets made of graphite have high corrosion resistance and electrical resistance equivalent to that of metal materials. It becomes possible to achieve both durability and conductivity.

  The above graphite sheet can be obtained as follows. First, natural graphite is chemically treated with an acid to form an insert between the graphite graphene layers. Next, this is rapidly heated at a high temperature to obtain expanded graphite in which the graphene interlayer is pushed and expanded by the gas pressure due to the thermal decomposition of the intercalated insert. Then, the expanded graphite is pressurized and roll-rolled to obtain a graphite sheet. When the graphite sheet thus obtained is used as the conductor layer 1, the graphene layers in the graphite are arranged along the direction YZ perpendicular to the stacking direction X. Therefore, it is possible to increase the conductivity between the conductor layer 1 and the external circuit 110 and further improve the efficiency of the battery reaction.

(catalyst)
It is preferable that a catalyst is supported on the conductor layer 1. The catalyst is preferably an oxygen reduction catalyst. Since the catalyst is an oxygen reduction catalyst, the reaction rate between oxygen and hydrogen ions transferred to the conductor layer 1 by the water repellent layer 3 can be increased, and the reduction reaction efficiency of oxygen can be improved. Liquid processing can be realized.

  The catalyst is preferably supported on the surface of the conductor layer 1. That is, it may be carried on the surface 1a on the porous body layer 2 side of the conductor layer 1 or may be carried on the surface 1b on the water repellent layer 3 side. Further, the catalyst may be supported inside the conductor layer 1. From the viewpoint of promoting the oxygen reduction reaction by oxygen, hydrogen ions and electrons, the conductor layer 1 and the catalyst are preferably electrically connected, and the conductor layer 1 and the catalyst are in contact with each other. preferable.

  The catalyst may be supported on the surface of the conductor layer 1 and inside the pores using a binder. Thereby, it can suppress that a catalyst detach | desorbs from the surface of the conductor layer 1, and the inside of a pore, and an oxygen reduction characteristic falls. Such a binder is not particularly limited as long as particles can be bound to each other. As the binder, for example, at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM) and Nafion is preferably used.

  The oxygen reduction catalyst is preferably a carbon-based material doped with metal atoms. Although it does not specifically limit as a metal atom, Titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium It is preferably an atom of at least one metal selected from the group consisting of platinum, and gold. In this case, the carbon-based material exhibits excellent performance as a catalyst for promoting the oxygen reduction reaction. What is necessary is just to set suitably the quantity of the metal atom which carbonaceous material contains so that carbonaceous material may have the outstanding catalyst performance.

  The carbon-based material is preferably further doped with one or more nonmetallic atoms selected from nitrogen, boron, sulfur and phosphorus. What is necessary is just to set suitably the quantity of the nonmetallic atom doped by the carbonaceous material so that carbonaceous material may have the outstanding catalyst performance.

  The carbon-based material is based on a carbon source material such as graphite and amorphous carbon, for example, and the carbon source material is doped with a metal atom and one or more non-metal atoms selected from nitrogen, boron, sulfur and phosphorus. Can be obtained.

  A combination of a metal atom and a nonmetal atom doped in the carbon-based material is appropriately selected. In particular, it is preferable that the nonmetallic atom contains nitrogen and the metallic atom contains iron. In this case, the carbonaceous material can have a particularly excellent catalytic activity. The nonmetallic atom may be only nitrogen. Further, the metal atom may be only iron.

  The nonmetallic atom may contain nitrogen, and the metallic atom may contain at least one of cobalt and manganese. Also in this case, the carbon-based material can have a particularly excellent catalytic activity. The nonmetallic atom may be only nitrogen. Further, the metal atom may be only cobalt, only manganese, or only cobalt and manganese.

  A carbon-based material configured as an oxygen reduction catalyst can be prepared as follows. First, for example, a mixture containing a nonmetallic compound containing at least one nonmetal selected from the group consisting of nitrogen, boron, sulfur, and phosphorus, a metal compound, and a carbon source material is prepared. And this mixture is heated at the temperature of 800 degreeC or more and 1000 degrees C or less for 45 second or more and less than 600 second. Thereby, the carbonaceous material comprised as an oxygen reduction catalyst can be obtained.

  As the carbon source material, for example, graphite or amorphous carbon can be used as described above. Further, the metal compound is not particularly limited as long as it is a compound containing a metal atom capable of coordinating with a nonmetal atom doped in the carbon source material. Metal compounds include, for example, metal chlorides, nitrates, sulfates, bromides, iodides, fluorides, etc .; inorganic metal salts such as acetates; inorganic metal salt hydrates; and organic metal salts At least one selected from the group consisting of hydrates can be used. For example, when graphite is doped with iron, the metal compound preferably contains iron (III) chloride. Moreover, when graphite is doped with cobalt, the metal compound preferably contains cobalt chloride. When the carbon source material is doped with manganese, the metal compound preferably contains manganese acetate. The amount of the metal compound used is preferably set so that, for example, the ratio of the metal atom in the metal compound to the carbon source material is in the range of 5 to 30% by mass, and the ratio is in the range of 5 to 20% by mass. It is more preferable to set so as to be within.

  As described above, the nonmetallic compound is preferably at least one nonmetallic compound selected from the group consisting of nitrogen, boron, sulfur and phosphorus. Non-metallic compounds include, for example, pentaethylenehexamine, ethylenediamine, tetraethylenepentamine, triethylenetetramine, ethylenediamine, octylboronic acid, 1,2-bis (diethylphosphinoethane), triphenyl phosphite, benzyldisal At least one compound selected from the group consisting of fido can be used. The amount of the nonmetallic compound used is appropriately set according to the amount of the nonmetallic atom doped into the carbon source material. The amount of the nonmetallic compound used is preferably set so that the molar ratio of the metal atom in the metal compound to the nonmetallic atom in the nonmetallic compound is within the range of 1: 1 to 1: 2. : It is more preferable to set it within the range of 1.5 to 1: 1.8.

  A mixture containing a nonmetallic compound, a metal compound, and a carbon source raw material when preparing a carbon-based material configured as an oxygen reduction catalyst is obtained, for example, as follows. First, a carbon source material, a metal compound, and a nonmetal compound are mixed, and if necessary, a solvent such as ethanol is added to adjust the total amount. These are further dispersed by an ultrasonic dispersion method. Subsequently, after heating them at an appropriate temperature (for example, 60 ° C.), the mixture is dried to remove the solvent. Thereby, the mixture containing a nonmetallic compound, a metal compound, and a carbon source raw material is obtained.

  Next, the obtained mixture is heated, for example, under a reducing atmosphere or an inert gas atmosphere. Thereby, a non-metallic atom is doped to a carbon source raw material, and also a metallic atom is doped by the coordinate bond of a non-metallic atom and a metallic atom. The heating temperature is preferably in the range of 800 ° C. to 1000 ° C., and the heating time is preferably in the range of 45 seconds to less than 600 seconds. Since the heating time is short, the carbon-based material is efficiently produced, and the catalytic activity of the carbon-based material is further increased. In the heat treatment, the temperature rising rate of the mixture at the start of heating is preferably 50 ° C./s or more. Such rapid heating further improves the catalytic activity of the carbon-based material.

  Further, the carbon-based material may be further subjected to acid cleaning. For example, the carbon-based material may be dispersed in pure water with a homogenizer for 30 minutes, and then the carbon-based material may be placed in 2M sulfuric acid and stirred at 80 ° C. for 3 hours. In this case, elution of the metal component from the carbon-based material can be suppressed.

  By such a production method, a carbon-based material having a significantly low content of inert metal compounds and metal crystals and high conductivity can be obtained.

(Water repellent layer)
As shown in FIG. 1, the electrode 10 is provided with a water repellent layer 3 on the surface 1 b opposite to the surface 1 a in contact with the porous body layer 2 in the conductor layer 1. Since the water-repellent layer 3 has water repellency, when the electrode 10 is used as a positive electrode of a microbial fuel cell, an electrolyte solution 70 and a gas phase 90 as a liquid phase held in the waste water tank 80 are formed. To separate. And by providing the water repellent layer 3, it can suppress that the electrolyte solution 70 moves to the gaseous-phase 90 side. In addition, "separation" here means physical interruption | blocking.

  The water repellent layer 3 is in contact with the gas phase 90 containing oxygen, and diffuses oxygen in the gas phase 90. The water repellent layer 3 supplies oxygen substantially uniformly to the surface 1 b of the conductor layer 1. Therefore, the water repellent layer 3 is preferably a porous body so that the oxygen can be diffused. In addition, since the water repellent layer 3 has water repellency, it can suppress that the pore of a porous body obstruct | occludes by dew condensation etc., and the diffusibility of oxygen falls. In addition, since the electrolytic solution 70 hardly penetrates into the water repellent layer 3, oxygen can be efficiently circulated from the surface 3 b in contact with the gas phase 90 in the water repellent layer 3 to the surface 3 a facing the conductor layer 1. Is possible.

  The water repellent layer 3 is preferably formed in a sheet shape from a woven fabric or a non-woven fabric. The material constituting the water repellent layer 3 is not particularly limited as long as it has water repellency and can diffuse oxygen in the gas phase 90. Examples of the material constituting the water repellent layer 3 include polyethylene, polypropylene, polybutadiene, nylon, polytetrafluoroethylene (PTFE), ethyl cellulose, poly-4-methylpentene-1, butyl rubber, and polydimethylsiloxane (PDMS). At least one selected from the group can be used. Since these materials are easy to form a porous body and also have high water repellency, they can suppress clogging of pores and improve gas diffusibility. The water repellent layer 3 preferably has a plurality of through holes in the stacking direction X of the water repellent layer 3 and the conductor layer 1.

  The water repellent layer 3 may be subjected to a water repellent treatment using a water repellent as necessary in order to increase water repellency. Specifically, a water repellent such as polytetrafluoroethylene may be attached to the porous body constituting the water repellent layer 3 to improve water repellency.

  In the electrode 10 shown in FIG. 1, in order to efficiently supply oxygen to the surface 1b of the conductor layer 1, the water repellent layer 3 is preferably bonded to the conductor layer 1 via an adhesive. That is, it is preferable that the surface 3a of the water repellent layer 3 is bonded to the surface 1b of the opposing conductor layer 1 via an adhesive. Thereby, the diffused oxygen is directly supplied to the surface 1b of the conductor layer 1, and the oxygen reduction reaction can be performed efficiently. The adhesive is preferably provided on at least a part between the water repellent layer 3 and the conductor layer 1 from the viewpoint of securing the adhesiveness between the water repellent layer 3 and the conductor layer 1. However, from the viewpoint of improving the adhesiveness between the water repellent layer 3 and the conductor layer 1 and supplying oxygen to the conductor layer 1 stably over a long period of time, the adhesive is made of the water repellent layer 3 and the conductor layer. It is more preferable that it is provided on the entire surface between the two.

  The adhesive preferably has oxygen permeability, and includes at least one selected from the group consisting of polymethyl methacrylate, methacrylic acid-styrene copolymer, styrene-butadiene rubber, butyl rubber, nitrile rubber, chloroprene rubber, and silicone. Resin can be used.

(Porous body layer)
As shown in FIG. 1, the electrode 10 according to the present embodiment includes a porous body layer 2 laminated on one surface 1 a of the conductor layer 1. In FIG. 1, the surface 1a of the conductor layer 1 and the surface 2b of the porous body layer 2 are in contact with each other.

  In the electrode 10, the thickness t of the porous body layer 2 is 1.0 mm to 40 mm. That is, the thickness t of the porous body layer 2 along the stacking direction X of the conductor layer 1, the porous body layer 2, and the water repellent layer 3 is 1.0 mm to 40 mm. When the thickness t of the porous body layer 2 is 1.0 mm to 40 mm, aerobic microorganisms contained in the electrolytic solution 70 enter the inside of the porous body layer 2, and the conductor layer 1 and the water repellent layer 3. It is possible to suppress the presence in the vicinity of the interface. The thickness t of the porous body layer 2 is more preferably 1.5 mm to 10 mm. Since the thickness t of the porous body layer 2 is 1.5 mm to 10 mm, the permeability of hydrogen ions is increased while suppressing the intrusion of aerobic microorganisms into the porous body layer 2, and the conductor layer It becomes possible to efficiently reach hydrogen ions to 1.

  The porous body layer 2 has a large number of pores that transmit the electrolytic solution 70 and hydrogen ions. The porous body layer 2 preferably has continuous pores from the surface 2a to the opposite surface 2b. As a result, the electrolytic solution 70 enters the inside of the pores from the surface 2 a, and hydrogen ions can reach the conductor layer 1 through the electrolytic solution 70. The pore diameter of the porous body layer 2 is not particularly limited as long as the electrolyte solution 70 and hydrogen ions can permeate, but is preferably 0.5 μm or more, for example. When the pore diameter of the porous body layer 2 is 0.5 μm or more, it is possible to sufficiently transmit hydrogen ions and increase the power generation efficiency. In addition, although the upper limit of the hole diameter of the pore in the porous body layer 2 is not specifically limited, For example, it can be 1.0 mm. The pore diameter of the porous body layer 2 can be measured by, for example, a mercury intrusion method.

  The porous body layer 2 may be a conductor or an electrical insulator. However, the porous body layer 2 is preferably an electric insulator. Since the porous body layer 2 is an electrical insulator, as will be described later, when the electrode 10 is used for a microbial fuel cell, the ion transfer layer 30 is not required, and therefore, the microbial fuel cell is thinned and the cell structure is improved. Simplification can be achieved.

  Examples of the material constituting the porous body layer 2 include resin materials such as polyethylene and polypropylene, conductive metals such as aluminum, copper, stainless steel, nickel and titanium, and carbon materials such as carbon paper and carbon felt. At least one selected from the group can be used. The porous body layer 2 is preferably formed of a synthetic resin. By comprising a synthetic resin, it is possible to easily ensure electrical insulation.

  As the porous body layer 2, at least one selected from the group consisting of a sheet having a woven fabric structure, a sheet having a nonwoven fabric structure, and a sheet having a continuous foam structure can be used. The porous body layer 2 may be a laminate in which a plurality of sheets are laminated. However, the porous body layer 2 is preferably made of a nonwoven fabric. By using a sheet having such a plurality of pores as the porous body layer 2, hydrogen ions can easily move in the direction of the conductor layer 1, and the rate of the oxygen reduction reaction can be increased.

  Here, the porous body layer 2 is configured as a separate member from the conductor layer 1, and the electrode 10 is formed by joining the sheet of the conductor layer 1 and the sheet of the porous body layer 2. Yes. The surface 1a of the conductor layer 1 and the surface 2b of the porous body layer 2 may be joined by pressure bonding, or may be joined via an adhesive. As the adhesive, an adhesive for joining the conductor layer 1 and the water repellent layer 3 described above can be used.

  The portion of the conductor layer 1 on which the oxygen reduction catalyst is supported is preferably sealed with the porous layer 2. Specifically, as shown in FIG. 2, the porous layer 2 is laminated on one surface 1a of the conductor layer 1, and the water repellent layer 3 is laminated on the other surface 1b of the conductor layer 1. . In FIG. 2, the water repellent layer 3 is provided on the entire surface 1 b of the conductor layer 1, but the porous body layer 2 is not provided on the conductor layer 1. The outer peripheral portion 2 c, the upper surface 2 d, the side surface 2 e, and the bottom surface 2 f of the surface 2 a in the porous body layer 2 are sealed with a sealing material 4. Furthermore, the outer peripheral portion 1 c, the side surface 1 e, and the bottom surface 1 f of the bonding portion of the conductor layer 1 with the porous body layer 2 are also sealed with the sealing material 4. As described above, the portion of the conductor layer 1 on which the oxygen reduction catalyst is supported is sealed by the porous body layer 2 and the sealing material 4, so that the conductive layer 1 is electrically conductive from the side surface 1 e and the bottom surface 1 f. Invasion of aerobic microorganisms into the body layer 1 can be suppressed. As a result, it is possible to prevent aerobic microorganisms from proliferating near the interface between the conductor layer 1 and the water repellent layer 3.

  The sealing material 4 is preferably made of a material that does not allow at least aerobic microorganisms to pass through. For example, epoxy resin, polymethyl methacrylate, methacrylic acid-styrene copolymer, styrene-butadiene rubber, butyl rubber, nitrile rubber, chloroprene rubber, and A resin containing at least one selected from the group consisting of silicones can be used.

  As described above, in FIG. 2, the porous body layer 2 is not provided on the conductor layer 1, but like the water repellent layer 3, the porous body layer 2 is formed on the surface 1 a of the conductor layer 1. May be provided on the entire surface. However, when the electrode 10 is used in a microbial fuel cell, only the portion of the conductor layer 1 that is immersed in the electrolyte solution 70 needs to be sealed with the porous body layer 2.

  The porous body layer 2 may carry the above-described catalyst. However, since it is preferable that the porous body layer 2 is an electrical insulator, and it is necessary to conduct electrons generated by the local cell reaction between the catalyst and the external circuit 110 as described later, the porous body layer 2 is porous. It is preferable that the material layer 2 does not carry a catalyst.

  The effect | action of the porous body layer 2 in the electrode 10 of this embodiment is demonstrated. When the electrode 10 is used as a positive electrode of a microbial fuel cell, the conductor layer 1 and the porous body layer 2 of the electrode 10 are immersed in the electrolytic solution 70, and at least a part of the surface 3 b of the water repellent layer 3 is in the gas phase 90. Exposed. Since oxygen reaches the conductor layer 1 through the water-repellent layer 3 exposed in the gas phase 90, the aerobic microorganism in the electrolytic solution 70 is a conductor when the porous body layer 2 is not present. It passes through the layer 1 and grows in the vicinity of the interface between the conductor layer 1 and the water repellent layer 3. As a result, oxygen is consumed by aerobic microorganisms in the vicinity of the interface between the conductor layer 1 and the water repellent layer 3, so that oxygen is not sufficiently supplied to the catalyst supported on the conductor layer 1, and the oxygen reduction reaction It becomes difficult to occur.

  On the other hand, when the porous body layer 2 is laminated on the conductor layer 1, the electrolyte 70 contains an organic substance serving as a bait for aerobic microorganisms. Therefore, as shown in FIG. The microbial membrane 11 is formed on the surface 2a exposed in the electrolytic solution 70 in FIG. That is, aerobic microorganisms consume organic substances and propagate, and a microbial membrane 11 formed by aerobic microorganisms gathering on the surface 2a of the porous body layer 2 is formed. The aerobic microorganisms proceed to the gas phase 90 side to which oxygen is supplied. However, the organic substances are consumed by the aerobic microorganisms in the microorganism film 11, and the organic substances entering the porous body layer 2 are reduced. . Furthermore, by increasing the thickness of the porous body layer 2, it becomes difficult for organic substances to move to the conductor layer 1 side, which is preferable on the conductor layer 1 side than the interface between the conductor layer 1 and the porous body layer 2. Aerobic microorganisms cannot grow. As a result, since aerobic microorganisms are not grown near the interface between the conductor layer 1 and the water repellent layer 3, oxygen consumption by the aerobic microorganisms is suppressed, and oxygen is sufficiently supplied to the catalyst supported on the conductor layer 1. It is possible to supply and effectively perform an oxygen reduction reaction.

  Thus, the electrode 10 according to the present embodiment is provided with the conductor layer 1 and the porous body layer 2 provided on one surface 1a of the conductor layer 1 and having a thickness t of 1.0 mm to 40 mm. A water repellent layer 3 provided on the surface 1b on the opposite side to the surface 1a on the porous body layer 2 side of the conductor layer 1 is provided. Furthermore, it is preferable that the oxygen reduction catalyst is supported on the conductor layer 1. With such a configuration, since aerobic microorganisms are not grown near the interface between the conductor layer 1 and the water repellent layer 3, oxygen consumption by the aerobic microorganisms is suppressed. For this reason, the microbial fuel cell using the electrode 10 is prevented from being deteriorated in power generation performance, and can stably produce electric energy.

[Microbial fuel cell]
Next, the microbial fuel cell according to this embodiment will be described. As shown in FIGS. 4 and 5, the microbial fuel cell 100 according to the present embodiment includes a negative electrode 20 that holds microorganisms and a positive electrode 10 </ b> A that includes the electrode 10 described above. The microbial fuel cell 100 further includes an ion moving layer 30 provided between the positive electrode 10A and the negative electrode 20 and having hydrogen ion permeability.

(Negative electrode)
The negative electrode 20 in the present embodiment carries a microbe described later and further has a function of generating hydrogen ions and electrons from at least one of an organic substance and a nitrogen-containing compound in the electrolytic solution 70 by the catalytic action of the microbe. For this reason, the negative electrode 20 of the present embodiment is not particularly limited as long as it has such a function.

  The negative electrode 20 of the present embodiment has a structure in which microorganisms are supported on a conductive sheet having conductivity. As the conductor sheet, it is possible to use at least one selected from the group consisting of a porous conductor sheet, a woven conductor sheet, and a nonwoven conductor sheet. The conductor sheet may be a laminate in which a plurality of sheets are laminated. By using such a sheet having a plurality of pores as the conductor sheet of the negative electrode 20, hydrogen ions generated in the local battery reaction described later easily move toward the ion moving layer 30, and the oxygen reduction reaction The speed can be increased. Further, from the viewpoint of improving ion permeability, the conductor sheet of the negative electrode 20 has a space (void) continuous in the stacking direction X of the positive electrode 10A, the ion moving layer 30, and the negative electrode 20, that is, in the thickness direction. It is preferable.

  The conductor sheet may be a metal plate having a plurality of through holes in the thickness direction. Therefore, as a material constituting the conductor sheet of the negative electrode 20, for example, at least one selected from the group consisting of conductive metals such as aluminum, copper, stainless steel, nickel and titanium, carbon paper, and carbon felt is used. be able to.

  As the conductor sheet of the negative electrode 20, a graphite sheet used in the positive electrode 10A may be used. Moreover, the negative electrode 20 preferably contains graphite, and the graphene layer in the graphite is preferably arranged along a plane in the direction YZ perpendicular to the stacking direction X of the positive electrode 10A, the ion transfer layer 30, and the negative electrode 20. By arranging the graphene layers in this way, the conductivity in the direction YZ perpendicular to the stacking direction X is improved as compared with the conductivity in the stacking direction X. Therefore, the electrons generated by the local battery reaction of the negative electrode 20 can be easily conducted to the external circuit, and the efficiency of the battery reaction can be further improved.

  The microorganism supported on the negative electrode 20 is not particularly limited as long as it is a microorganism that decomposes an organic substance in the electrolyte solution 70 or a compound containing nitrogen. For example, an anaerobic microorganism that does not require oxygen for growth is used. preferable. Anaerobic microorganisms do not require air for oxidizing and decomposing organic substances in the electrolyte solution 70. Therefore, the electric power required for sending air can be significantly reduced. Moreover, since the free energy which microbes acquire is small, it becomes possible to reduce the amount of sludge generation.

  The anaerobic microorganism held in the negative electrode 20 is preferably an electricity producing bacterium having an extracellular electron transfer mechanism, for example. Specifically, examples of the anaerobic microorganism include Geobacter genus bacteria, Shewanella genus bacteria, Aeromonas genus bacteria, Geothrix genus bacteria, and Saccharomyces genus bacteria.

  Anaerobic microorganisms may be held on the negative electrode 20 by stacking and fixing a biofilm containing anaerobic microorganisms on the negative electrode 20. The biofilm generally refers to a three-dimensional structure including a microbial population and an extracellular polymeric substance (EPS) produced by the microbial population. However, the anaerobic microorganisms may be held on the negative electrode 20 without depending on the biofilm. Moreover, the anaerobic microorganisms may be held not only on the surface of the negative electrode 20 but also inside.

(Positive electrode)
The microbial fuel cell 100 of the present embodiment includes a positive electrode 10 </ b> A composed of the electrode 10 described above. And the ion migration layer 30 is provided in the surface 2a side of the porous body layer 2 of 10 A of positive electrodes.

(Ion moving layer)
The microbial fuel cell 100 of this embodiment further includes an ion transfer layer 30 provided between the positive electrode 10A and the negative electrode 20 and having proton permeability. As shown in FIGS. 1 and 2, the negative electrode 20 is separated from the positive electrode 10 </ b> A through the ion moving layer 30. The ion moving layer 30 has a function of transmitting hydrogen ions generated by the negative electrode 20 and moving the hydrogen ions to the positive electrode 10A side.

  As the ion migration layer 30, for example, an ion exchange membrane using an ion exchange resin can be used. As the ion exchange resin, for example, NAFION (registered trademark) manufactured by DuPont, and Flemion (registered trademark) and Selemion (registered trademark) manufactured by Asahi Glass Co., Ltd. can be used.

  Further, a porous membrane having pores through which hydrogen ions can permeate may be used as the ion moving layer 30. That is, the ion moving layer 30 may be a sheet having a space (void) for moving hydrogen ions from the negative electrode 20 to the positive electrode 10A. Therefore, the ion migration layer 30 preferably includes at least one selected from the group consisting of a porous sheet, a woven sheet, and a nonwoven sheet. Moreover, the ion migration layer 30 can use at least one chosen from the group which consists of a glass fiber membrane, a synthetic fiber membrane, and a plastic nonwoven fabric, and the laminated body formed by laminating | stacking these two or more may be used. Since such a porous sheet has a large number of pores inside, hydrogen ions can easily move. The pore diameter of the ion moving layer 30 is not particularly limited as long as hydrogen ions can move from the negative electrode 20 to the positive electrode 10A.

  As described above, the ion moving layer 30 has a function of transmitting the hydrogen ions generated in the negative electrode 20 and moving the hydrogen ions to the positive electrode 10A side. Therefore, for example, if the negative electrode 20 and the positive electrode 10A are close to each other without contact, hydrogen ions can move from the negative electrode 20 to the positive electrode 10A. Therefore, in the microbial fuel cell 100 of this embodiment, the ion moving layer 30 is not an essential component. However, since the provision of the ion moving layer 30 makes it possible to efficiently move hydrogen ions from the negative electrode 20 to the positive electrode 10A, it is preferable to provide the ion moving layer 30 from the viewpoint of improving the output.

  As shown in FIGS. 4 and 5, the microbial fuel cell 100 according to this embodiment includes a plurality of electrode assemblies 40 including a positive electrode 10 </ b> A, a negative electrode 20, and an ion transfer layer 30. In the microbial fuel cell 100, as shown in FIG. 5, the negative electrode 20 is disposed so as to contact one surface 30a of the ion moving layer 30, and the positive electrode is formed on the surface 30b opposite to the surface 30a of the ion moving layer 30. 10A is arranged so as to contact.

  As shown in FIG. 6, the two electrode assemblies 40 are laminated via the cassette base material 50 so that the positive electrodes 10 </ b> A face each other. The cassette base material 50 is a U-shaped frame member along the outer periphery of the surface 10a of the positive electrode 10A, and the upper part is open. That is, the cassette base material 50 is a frame member in which the bottom surfaces of the two first columnar members 51 are connected by the second columnar member 52. And the side surface 53 of the cassette base material 50 is joined with the outer peripheral part of the surface 10a of the positive electrode 10A, and it is suppressed that the electrolyte solution 70 leaks into the inside of the cassette base material 50 from the outer peripheral part of the surface 10a of the positive electrode 10A. it can.

  Then, as shown in FIG. 5, the fuel cell unit 60 formed by laminating the two electrode assemblies 40 and the cassette base material 50 has a waste water tank 80 so that a gas phase 90 communicating with the atmosphere is formed. Placed inside. An electrolyte solution 70 that is a liquid to be treated is held inside the waste water tank 80, and the positive electrode 10 </ b> A, the negative electrode 20, and the ion moving layer 30 are immersed in the electrolytic solution 70.

  As described above, the water repellent layer 3 of the positive electrode 10A has water repellency. Therefore, the electrolytic solution 70 held in the waste water tank 80 is separated from the inside of the cassette base material 50, and the internal space formed by the two electrode assemblies 40 and the cassette base material 50 is the gas phase 90. It has become. As shown in FIG. 5, the positive electrode 10A and the negative electrode 20 are electrically connected to the external circuit 110, respectively.

  Next, the operation of the microbial fuel cell 100 of this embodiment will be described. When the electrode assembly 40 including the electrode 10, the negative electrode 20, and the ion transfer layer 30 is immersed in the electrolytic solution 70, the porous body layer 2 and the negative electrode 20 of the positive electrode 10 </ b> A are immersed in the electrolytic solution 70, and the water repellent layer 3 is exposed to the gas phase 90. At this time, the conductor layer 1 of the positive electrode 10 </ b> A is also immersed in the electrolytic solution 70.

  During operation of the microbial fuel cell 100, the negative electrode 20 is supplied with an electrolyte solution 70 containing at least one of an organic substance and a nitrogen-containing compound, and air is supplied to the positive electrode 10A. At this time, the air is continuously supplied through an opening provided in the upper part of the cassette base material 50.

  In the positive electrode 10 </ b> A, oxygen diffuses into the conductor layer 1 through the water repellent layer 3. In the negative electrode 20, hydrogen ions and electrons are generated from at least one of the organic substance and the nitrogen-containing compound in the electrolytic solution 70 by the catalytic action of microorganisms. The generated hydrogen ions pass through the ion moving layer 30 and move to the positive electrode 10A side. Further, the hydrogen ions pass through the porous body layer 2 in the positive electrode 10 </ b> A and reach the conductor layer 1. Further, the generated electrons move to the external circuit 110 through the conductor sheet of the negative electrode 20, and further move from the external circuit 110 to the conductor layer 1 of the positive electrode 10A. Hydrogen ions and electrons are combined with oxygen by the action of the catalyst in the conductor layer 1 and consumed as water. At this time, the electric energy flowing in the closed circuit is recovered by the external circuit 110.

  Here, in addition to the anaerobic microorganisms described above, the electrolytic solution 70 also includes aerobic microorganisms that require oxygen for growth. Since the positive electrode 10A has the porous body layer 2 laminated on the conductor layer 1, a microbial membrane 11 is formed on the surface 2a of the porous body layer 2 as shown in FIG. The aerobic microorganisms proceed to the gas phase 90 side to which oxygen is supplied. However, the organic substances are consumed by the aerobic microorganisms in the microorganism film 11, and the organic substances entering the porous body layer 2 are reduced. . Furthermore, since the porous body layer 2 has a predetermined thickness, it is difficult for the organic substance to move to the conductor layer 1 side, and the conductor layer 1 is more than the interface between the conductor layer 1 and the porous body layer 2. On the side, aerobic microorganisms cannot grow. As a result, since aerobic microorganisms are not grown near the interface between the conductor layer 1 and the water repellent layer 3, oxygen consumption by the aerobic microorganisms is suppressed, and the oxygen reduction reaction can be performed efficiently.

  As described above, the microbial fuel cell 100 according to the present embodiment includes the positive electrode 10 </ b> A including the electrode 10, the negative electrode 20 holding microorganisms, and the electrolytic solution 70. The porous body layer 2 and the negative electrode 20 are immersed in the electrolytic solution 70, and at least a part of the water repellent layer 3 is exposed to the gas phase 90. Such a configuration makes it difficult for the positive electrode 10A to inhibit oxygen consumption due to aerobic microorganisms, so that the oxygen reduction characteristics of the positive electrode 10A can be improved and electric energy can be stably produced.

  In the positive electrode 10A, when the porous body layer 2 is electrically insulating, the microbial fuel cell 100A does not need to provide the ion transfer layer 30 as shown in FIG. Specifically, the microbial fuel cell 100A includes a plurality of electrode assemblies 40A including a positive electrode 10A and a negative electrode 20. In the microbial fuel cell 100A, one surface 20a of the negative electrode 20 is disposed so as to be in contact with the surface 2a of the porous body layer 2 in the positive electrode 10A. And two electrode assembly 40A is laminated | stacked through the cassette base material 50 so that positive electrode 10A may oppose. The side surface 53 of the cassette base material 50 is joined to the outer peripheral portion of the surface 10a of the positive electrode 10A. Further, the fuel cell unit 60A formed by laminating the two electrode assemblies 40A and the cassette base material 50 is arranged inside the waste water tank 80 so that the gas phase 90 is formed, and the positive electrode 10A and the negative electrode 20 are disposed. Is immersed in the electrolytic solution 70.

  When the porous body layer 2 of the positive electrode 10A is electrically insulative, the conductor layer 1 and the negative electrode 20 of the positive electrode 10A are insulated by the porous body layer 2, so that the ion migration layer 30 is not interposed. The short circuit between the conductor layer 1 and the negative electrode 20 can be prevented. In addition, as described above, the porous body layer 2 can transmit hydrogen ions and can reach the conductor layer 1. Thus, since the porous body layer 2 can perform the same function as the ion moving layer 30, the ion moving layer 30 may not be provided. In FIG. 7, one surface 20a of the negative electrode 20 is disposed so as to be in contact with the surface 2a of the porous body layer 2 in the positive electrode 10A, but between the surface 20a of the negative electrode 20 and the surface 2a of the positive electrode 10A. There may be voids.

  For example, the negative electrode 20 according to the present embodiment may be modified with an electron transfer mediator molecule. Alternatively, the electrolytic solution 70 in the waste water tank 80 may contain electron transfer mediator molecules. Thereby, the electron transfer from an anaerobic microorganism to the negative electrode 20 is accelerated | stimulated, and more efficient liquid processing is realizable.

  Specifically, in the metabolic mechanism by anaerobic microorganisms, electrons are transferred between cells or with the final electron acceptor. When a mediator molecule is introduced into the electrolytic solution 70, the mediator molecule acts as a final electron acceptor of metabolism, and delivers received electrons to the negative electrode 20. As a result, it becomes possible to increase the rate of oxidative decomposition of the organic matter in the electrolytic solution 70. Such an electron transfer mediator molecule is not particularly limited. As the electron transfer mediator molecule, for example, at least one selected from the group consisting of neutral red, anthraquinone-2,6-disulfonic acid (AQDS), thionine, potassium ferricyanide, and methylviologen can be used.

  The fuel cell unit 60 shown in FIG. 6 has a configuration in which two electrode assemblies 40 and a cassette base material 50 are stacked. However, the present embodiment is not limited to this configuration. For example, the electrode assembly 40 may be bonded to only one side surface 53 of the cassette base material 50 and the other side surface may be sealed with a plate member. 4 to 6, the entire upper portion of the cassette base 50 is open. However, the cassette base 50 may be partially opened or closed as long as air can be introduced into the cassette base 50. May be.

  The waste water tank 80 holds the electrolytic solution 70 therein, but may have a configuration in which the electrolytic solution 70 circulates. For example, as shown in FIGS. 4 and 5, the wastewater tank 80 has a wastewater supply port 81 for supplying the electrolyte solution 70 to the wastewater tank 80 and a wastewater tank 80 for discharging the treated electrolyte solution 70 from the wastewater tank 80. The waste water discharge port 82 may be provided. The electrolytic solution 70 is preferably continuously supplied through the waste water supply port 81 and the waste water discharge port 82.

  It is preferable that the inside of the waste water tank 80 is maintained in anaerobic conditions in which, for example, molecular oxygen does not exist or even if molecular oxygen is present, the concentration thereof is extremely small. Thereby, it becomes possible to hold | maintain the electrolyte solution 70 so that it may hardly contact oxygen in the wastewater tank 80. FIG.

[Electrode of Second Embodiment]
Next, the electrode according to the second embodiment will be described in detail based on the drawings. In addition, the same code | symbol is attached | subjected to the same structure as the electrode of 1st embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 8, the electrode 10 </ b> B of this embodiment is provided on the conductor layer 1 and one surface 1 a of the conductor layer 1, and the porous body layer 2 having a thickness t of 1.0 mm to 40 mm. And a water repellent layer 3 provided on the surface 1b opposite to the surface 1a on the porous body layer 2 side of the conductor layer 1. In the electrode 10B, the cassette base material 50 is disposed on the surface 3b of the water repellent layer 3. And the side surface 53 of the cassette base material 50 is joined with the outer peripheral part of the surface 3b of the water repellent layer 3, and it suppresses that the electrolyte solution 70 leaks into the inside of the cassette base material 50 from the outer peripheral part of the surface 3b. ing. In the electrode 10 </ b> B, the water repellent layer 3 is bonded only to one side surface 53 of the cassette base material 50, and the other side surface is sealed with a plate member 54.

  In the electrode shown in FIG. 2, the portion of the conductor layer 1 on which the oxygen reduction catalyst is supported is sealed with the porous body layer 2 and the sealing material 4, and therefore from the side surface 1 e and the bottom surface 1 f of the conductor layer 1. The aerobic microorganisms are prevented from entering the conductor layer 1. On the other hand, the electrode 10B of this embodiment does not use the sealing material 4, and the porous layer 2 covers the portion of the conductor layer 1 on which the oxygen reduction catalyst is supported. That is, not only the surface 1 a of the conductor layer 1 but also the side surfaces and the bottom surface of the conductor layer 1, the water repellent layer 3, and the cassette base material 50 are covered with the porous body layer 2.

  As described above, the conductor layer 1 and the water repellent layer 3 are covered with the box-shaped porous body layer 2 having a space in the interior, so that the conductor can be formed from the surface 1a, the side surface 1e and the bottom surface 1f of the conductor layer 1. It is possible to prevent aerobic microorganisms from entering the inside of the layer 1. As a result, it is possible to prevent aerobic microorganisms from proliferating near the interface between the conductor layer 1 and the water repellent layer 3. Even if the conductor layer 1 and the water repellent layer 3 are covered with the porous body layer 2, since the air is sufficiently supplied to the surface 3 b of the water repellent layer 3 by the cassette base material 50, an oxygen reduction reaction is performed. It becomes possible to carry out efficiently.

  When it is assumed that the electrode 10B is used as a microbial fuel cell, only the portion immersed in the electrolytic solution 70 in the conductor layer 1 needs to be sealed by the porous body layer 2. Therefore, as long as the liquid level of the electrolytic solution 70 is lower than the upper surface 2d of the porous body layer 2, the upper surface 2d of the box-shaped porous body layer 2 may be open. Although it is not necessary to seal the boundary between the upper surface 2d of the porous body layer 2 and the conductor layer 1, the water repellent layer 3, and the cassette base material 50 with a sealing material, the boundary is made of a sealing material. It may be sealed.

  Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[Example 1]
The positive electrode of this example was produced as follows. First, a graphite sheet as a conductor layer and a water repellent sheet as a water repellent layer were joined with a silicone adhesive to produce a laminated sheet composed of graphite sheet / silicone adhesive / water repellent sheet. As the graphite sheet, Carbofit (registered trademark) manufactured by Hitachi Chemical Co., Ltd. was used. As the silicone adhesive, a one-component RTV silicone rubber KE-3475 manufactured by Shin-Etsu Chemical Co., Ltd. was used. As the water repellent sheet, SELPORE (registered trademark) manufactured by Sekisui Chemical Co., Ltd. was used.

A dispersion of the oxygen reduction catalyst was dropped onto the graphite sheet of the laminated sheet and dried. A porous material layer having a thickness of 1.8 mm is formed by laminating 10 non-woven fabrics made of polyethylene and polypropylene having a thickness of 0.18 mm and a density of 15 g / m ² on the portion where the oxygen reduction catalyst is dropped. Formed. As the nonwoven fabric, polyolefin nonwoven fabric # 210 of Pacific Giken Co., Ltd. was used. The periphery of the nonwoven fabric was sealed with an epoxy resin as shown in FIG. Thus, the positive electrode of this example was obtained.

  The oxygen reduction catalyst was prepared as follows. First, 3 g of carbon black, 0.1 M iron (III) chloride aqueous solution, and 0.15 M pentaethylenehexamine ethanol solution were placed in a container to prepare a mixed solution. As carbon black, Ketjen Black ECP600JD manufactured by Lion Specialty Chemicals Co., Ltd. was used. The amount of 0.1M iron (III) chloride aqueous solution used was adjusted so that the ratio of iron atoms to carbon black was 10% by mass. The total amount was adjusted to 9 mL by further adding ethanol to the mixture. And this liquid mixture was ultrasonically disperse | distributed, and it was dried at the temperature of 60 degreeC with the dryer. As a result, a sample containing carbon black, iron (III) chloride, and pentaethylenehexamine was obtained.

  And this sample was packed in the one end part of a quartz tube, and the inside of this quartz tube was substituted by argon subsequently. The quartz tube was pulled out 45 seconds after being placed in a furnace at 900 ° C. When the quartz tube was inserted into the furnace, the quartz tube was inserted into the furnace over 3 seconds to adjust the rate of temperature rise of the sample at the start of heating to 300 ° C./s. Subsequently, the sample was cooled by flowing argon gas through the quartz tube. Thereby, an oxygen reduction catalyst was obtained. The oxygen reduction catalyst dispersion was prepared by mixing 0.35 g of a powdery oxygen reduction catalyst, 0.35 mL of PTFE dispersion, and 2 mL of ion-exchanged water.

  Next, a microbial fuel cell was produced using the positive electrode obtained as described above. First, an electrode assembly was prepared using the positive electrode obtained as described above and a negative electrode made of carbon felt holding anaerobic microorganisms.

  And the microbial fuel cell shown in FIG. 7 was produced using the obtained electrode assembly. The capacity of the waste water tank was 300 cc. Moreover, the electrolyte solution used the model waste liquid whose total organic carbon (TOC) is 800 mg / L, and the liquid temperature of the electrolyte solution was 30 degreeC. Furthermore, the amount of inflow into the wastewater tank was adjusted so that the hydraulic retention time of the electrolyte was 24 hours.

The obtained microbial fuel cell was operated for 40 days, and the change in output characteristics was examined. The evaluation results are shown in FIG. As shown in FIG. 9, it took about one week to start up the microbial fuel cell, and the output gradually improved. The maximum output of the fuel cell of this example was 152 mW / m ² . The maximum output per volume of the fuel cell unit composed of the positive electrode, the negative electrode, and the cassette base material was 317 mW / cm ³ . Further, the thickness of the fuel cell unit excluding the porous body layer was 3 mm. The amount of decrease in output per day after 40 days from the completion of start-up was 1.37 mW / m ² , and good output characteristics were obtained.

[Example 2]
A microbial fuel cell of this example was obtained in the same manner as in Example 1 except that the number of laminated nonwoven fabrics was 20 and a porous layer having a thickness of 3.6 mm was formed.

The obtained microbial fuel cell was operated under the same conditions as in Example 1, and changes in output characteristics were examined. As shown in FIG. 9, the maximum output of the fuel cell of this example was 131 mW / m ² , and the maximum output per volume of the fuel cell unit was 198 mW / cm ³ . The amount of decrease in output per day after 40 days from the completion of start-up was 0.93 mW / m ² , and good output characteristics were obtained.

[Example 3]
A microbial fuel cell of this example was obtained in the same manner as in Example 1 except that the number of laminated nonwoven fabrics was 50 and a porous layer having a thickness of 9.0 mm was formed.

The obtained microbial fuel cell was operated under the same conditions as in Example 1, and changes in output characteristics were examined. As shown in FIG. 9, the maximum output of the fuel cell of this example was 93 mW / m ² , and the maximum output per volume of the fuel cell unit was 77.5 mW / cm ³ . The amount of decrease in output per day after 40 days from the completion of startup was 0.71 mW / m ² , and good output characteristics were obtained.

[Example 4]
A microbial fuel cell of this example was obtained in the same manner as in Example 1 except that the number of laminated nonwoven fabrics was 200 and a porous layer having a thickness of 36 mm was formed.

The obtained microbial fuel cell was operated under the same conditions as in Example 1, and changes in output characteristics were examined. As shown in FIG. 9, the maximum output of the fuel cell of this example was 35 mW / m ² , and the maximum output per volume of the fuel cell unit was 8.97 mW / cm ³ . The amount of decrease in output per day after 40 days from the completion of startup was 0.23 mW / m ² , and good output characteristics were obtained.

[Comparative Example 1]
A microbial fuel cell of this example was obtained in the same manner as in Example 1 except that the number of laminated nonwoven fabrics was one and a porous layer having a thickness of 0.18 mm was formed.

The obtained microbial fuel cell was operated under the same conditions as in Example 1, and changes in output characteristics were examined. As shown in FIG. 9, the maximum output of the fuel cell of this example was 251 mW / m ² and the maximum output per volume of the fuel cell unit was 789 mW / cm ³ . Then, the amount of decrease in output per day after 40 days from the completion of start-up was 7.36 mW / m ² . Therefore, although the maximum output of the microbial fuel cell of this example was high, the amount of output decrease with time increased greatly.

[Comparative Example 2]
A microbial fuel cell of this example was obtained in the same manner as in Example 1 except that the number of laminated nonwoven fabrics was 5, and a porous body layer having a thickness of 0.9 mm was formed.

The obtained microbial fuel cell was operated under the same conditions as in Example 1, and changes in output characteristics were examined. As shown in FIG. 9, the maximum output of the fuel cell of this example was 198 mW / m ² , and the maximum output per volume of the fuel cell unit was 508 mW / cm ³ . Then, the amount of decrease in output per day after 40 days from the completion of startup was 4.57 mW / m ² . Therefore, although the maximum output of the microbial fuel cell of this example was high, the amount of output decrease with time increased greatly.

  From Examples 1 to 4, by providing a porous layer having a thickness of 1.0 mm to 40 mm, a microbial fuel cell that achieves high output without inhibiting the oxygen reduction ability of the positive electrode by aerobic microorganisms It can be seen that In view of the output per volume of the fuel cell unit, if the thickness of the porous body layer exceeds 40 mm, the maximum output per volume gradually approaches zero, so the thickness of the porous body layer Is preferably 40 mm or less. The thickness of the porous body layer is more preferably 1.5 mm to 10 mm from the viewpoint of increasing the output per volume of the fuel cell unit while preventing the aerobic microorganism from inhibiting the oxygen reducing ability of the positive electrode. .

  In general, since the output of a microbial fuel cell decreases as the distance between the positive electrode and the negative electrode increases, conventionally, it has been important to reduce the distance between the positive electrode and the negative electrode. However, contrary to conventional technical common sense, it is understood that if the distance between the positive electrode and the negative electrode is increased to some extent using the porous body layer, the output does not decrease in the long term, and a high output can be maintained. The invention of this embodiment has been completed.

  Although the present embodiment has been described above, the present embodiment is not limited to these, and various modifications can be made within the scope of the gist of the present embodiment. Specifically, in the drawing, the electrode 10 provided with the conductor layer 1, the porous body layer 2, and the water repellent layer 3, the negative electrode 20, and the ion transfer layer 30 are formed in a rectangular shape. However, these shapes are not particularly limited, and can be arbitrarily changed depending on the size of the fuel cell and the desired power generation performance. Further, the area of each layer can be arbitrarily changed as long as a desired function can be exhibited.

DESCRIPTION OF SYMBOLS 1 Conductor layer 2 Porous body layer 3 Water repellent layer 4 Sealing material 10,10B Electrode 10A Positive electrode 20 Negative electrode 30 Ion transfer layer 70 Electrolytic solution 90 Gas phase 100,100A Microbial fuel cell

Claims (7)

A conductor layer;
A porous body layer provided on one surface of the conductor layer and having a thickness of 1.0 mm to 40 mm;
A water repellent layer provided on a surface opposite to the surface on the porous body layer side in the conductor layer;
Electrode.   The electrode according to claim 1, wherein an oxygen reduction catalyst is supported on the conductor layer.   The electrode according to claim 2, wherein a portion of the conductor layer on which the oxygen reduction catalyst is supported is sealed by the porous body layer.   The electrode according to any one of claims 1 to 3, wherein the porous body layer is formed of a synthetic resin.   The electrode according to claim 1, wherein the porous body layer is an electrical insulator. A positive electrode comprising the electrode according to claim 1;
A negative electrode holding microorganisms;
An electrolyte,
With
The microbial fuel cell, wherein the porous body layer and the negative electrode are immersed in the electrolytic solution, and at least a part of the water repellent layer is exposed to the gas phase.   The microbial fuel cell according to claim 6, further comprising an ion transfer layer provided between the positive electrode and the negative electrode and having proton permeability.

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