JP2012142250A - Microbial fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient microbial fuel cell which has small time degradation of power generation efficiency and small internal electrical resistance.SOLUTION: In a microbial fuel cell, a substrate tank 12 where a substrate to be decomposed by an anaerobic microorganism is stored and a reaction tank 14 to store a medium for the anaerobic microorganism are separated by a negative electrode 16, and the anaerobic microorganism which releases electron by decomposing the substrate is supported at a reaction tank side of the negative electrode 16. Also, a positive electrode 18 having gas permeability is provided in a different region of the reaction tank 14 from the negative electrode 16. The anaerobic microorganism decomposes the substrate transmitting the negative electrode 16 from the substrate tank 12 to a side of the reaction tank 14 and releases the electron to the negative electrode 16. The electron moves from the negative electrode 16 to the positive electrode 18 through an external circuit. A hydrogen ion generated through decomposition of the substrate moves to the positive electrode 18 in the medium. In the positive electrode 18, the electron is transferred to the hydrogen ion and oxygen transmitting through the positive electrode 18 is reduced with hydrogen to generate water.

Description

  The present invention relates to improvements in microbial fuel cells.

  In recent years, a microbial fuel cell utilizing the property (extracellular electron transfer ability) of emitting electrons to an electrode (conductor) when a microorganism decomposes a substrate such as an organic substance has been proposed. Here, the extracellular electron transfer ability refers to the ability to acquire energy necessary for life activity by a series of flows using metal ions or oxides thereof as electron acceptors and reducing them.

As an example of such a microbial fuel cell, for example, the following Patent Document 1 includes a pair of electrodes, an external circuit that electrically connects the electrodes, and a diaphragm that separates the pair of electrodes. A configuration in which an organic substance as a fuel for supplying nutrients to a cultured culture solution and microorganisms is injected is disclosed. The diaphragm is a membrane configured to selectively transmit protons (H ⁺ ) such as a cation exchange membrane.

  Non-Patent Document 1 below discloses a configuration of a microbial fuel cell in which a diaphragm is omitted from the configuration of Patent Document 1 and an anode and a cathode are arranged in one tank. According to this configuration, ion mobility can be improved.

JP 2010-218690 A

Electricity generation using anair-cathode single chamber microbial fuel cell in the presence and absence of aproton-exchange membrane.Liu, H., Logan, B.E. (2004) .Environmental Science & Technology, 38,4040-4046

  However, in the microbial fuel cell described in Patent Document 1, since the cathode and the anode are separated by a diaphragm, when electrons (current) flow between these electrodes via an external circuit, this is the opposite. Ion migration occurs through the diaphragm, but the resistance when protons permeate the diaphragm increases the hydrogen ion concentration on the cathode side and lowers the pH on the cathode side. For this reason, since the activity of microorganisms falls, there existed a problem that the electric power generation capability of a microbial fuel cell fell with progress of operation time.

  Further, in the microbial fuel cell in which the diaphragm described in Non-Patent Document 1 is omitted, the problem of pH fluctuation as in Patent Document 1 can be solved, but the organic matter as fuel is oxidized and consumed near the anode, There has been a problem that the efficiency of the fuel cell is lowered. Furthermore, there is a problem that the ionic strength in the tank in which the anode and the cathode are arranged is likely to be lowered and the internal resistance is increased.

  An object of the present invention is to provide a microbial fuel cell in which power generation capacity is less deteriorated with time, high efficiency, and low internal resistance.

  In order to achieve the above object, one embodiment of the present invention is a microbial fuel cell, in which a substrate tank that contains a substrate that is decomposed by anaerobic microorganisms, and a reaction tank that contains a medium for the anaerobic microorganisms. And a cathode in which anaerobic microorganisms that decompose the substrate and release electrons by separating the substrate and the reaction vessel are supported on the reaction vessel side, and a region of the reaction vessel that is different from the cathode And an anode having permeability of oxygen-containing gas.

  In the microbial fuel cell, the substrate and oxygen are preferably supplied from different directions.

  In the microbial fuel cell, a permeation rate control layer for controlling the permeation rate of the substrate may be provided on the substrate tank side of the cathode.

  In the microbial fuel cell, an aerobic microorganism may be supported on the anode.

  According to the present invention, it is possible to provide a microbial fuel cell in which power generation capacity is less deteriorated with time, is highly efficient, and has low internal resistance.

It is a figure which shows the structural example of the microbial fuel cell concerning embodiment. It is a figure which shows the measurement result of the voltage value of the microbial fuel cell concerning an Example, an electric current density, and an electric power density.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIG. 1 shows a cross-sectional view of a configuration example of a microbial fuel cell according to the present embodiment. In FIG. 1, the microbial fuel cell 10 includes a substrate tank 12, a reaction tank 14, a cathode 16, an anode 18, and a transmission rate control layer 20.

  The substrate tank 12 contains a substrate that is decomposed by anaerobic microorganisms. This substrate passes through the cathode 16 and is supplied to the reaction vessel 14. As the substrate, any organic or inorganic substance can be used as long as it can be decomposed by microorganisms. Further, it may be liquid or gaseous as long as it can pass through the cathode 16. Examples of the organic substance include ethanol, glucose, and methane, and examples of the inorganic substance include hydrogen and the like.

  The reaction tank 14 is separated from the substrate tank 12 by a cathode 16, and contains a medium for anaerobic microorganisms. The medium is not limited as long as it is a substance that enables the activity of microorganisms and can transmit ions, and examples thereof include the following.

Examples of the liquid medium include an aqueous solution of a mixture containing all or part of the following substances. The concentration is indicated in mg / l in parentheses. NH ₄ Cl (200), MgSO ₄ .7H ₂ O (200), CaCl ₂ .2H ₂ O (150), FeSO ₄ .7H ₂ O (10), NaCl (2925), KH ₂ PO ₄ (461), Na ₂ HPO ₄ (939), AlK (SO ₄ ) ₂ · 12H ₂ O (0.2), H ₃ BO ₃ (0.02), CoCl ₂ · 6H ₂ O (0.3), CuSO ₄ · 5H ₂ O (0.3), MnCl ₂ .5H ₂ O (0.5), NiSO ₄ .6H ₂ O (0.2), ZnCl ₂ (0.2), Na ₂ MoO ₄ .2H ₂ O (0 .1), Na ₂ SeO ₃ (0.1), NaWO ₄ .2H ₂ O (0.05).

  Examples of the semi-solid (gel-like) medium include those obtained by adding agar or the like to the above liquid medium. Seawater can also be used as the liquid medium.

  The cathode 16 has conductivity, and transmits the substrate from the substrate tank 12 to the reaction tank 14 while separating the substrate tank 12 and the reaction tank 14. In this case, in order to adjust the permeation rate of the substrate, it is preferable that holes of an appropriate size are formed in the cathode 16. By adjusting the permeation rate of the substrate, anaerobic microorganisms described later can be appropriately cultured, and the anaerobic microorganism layer can be prevented from peeling off from the cathode 16. The permeation rate of the substrate may be adjusted by a permeation rate control layer 20 described later. Examples of the material of the cathode 16 include carbon fibers (nonwoven fabrics, woven fabrics), graphite thin films, particulate carbon, stainless steel, and other metal nets. An anaerobic microorganism 22 that decomposes the substrate is supported in a layered manner on the surface of the cathode 16 on the reaction tank 14 side. By the anaerobic microorganism 22, for example, an organic substance as a substrate is decomposed to generate hydrogen ions, and electrons are transferred to the cathode 16. The anaerobic microorganism 22 is not particularly limited as long as it decomposes the substrate and emits electrons. For example, Shewanella having the ability to emit electrons outside the body via cytochrome localized in the cell membrane. Examples include microorganisms such as genus Shewanella and genus Geobacter such as loihica and Shewanella oneidensis, and mixed microbial flora containing them.

  The anode 18 is provided in a region of the reaction vessel 14 different from the cathode 16 and is a gas permeable electrode having gas permeability. Here, the region different from the cathode 16 differs when, for example, the microbial fuel cell 10 has a cylindrical shape, the cathode 16 and the anode 18 are provided at both ends thereof, and the microbial fuel cell 10 has a rectangular parallelepiped shape. Examples include, but are not limited to, providing a cathode 16 and an anode 18 on a surface (for example, an opposing surface). For example, it is preferable to dispose the cathode 16 and the anode 18 so that the transmission direction (supply direction) of the substrate of the cathode 16 and the gas transmission direction of the anode 18 are different.

  Further, in the present embodiment, the anode 18 is configured such that air or air with an increased oxygen concentration passes through the reaction tank 14. The oxygen in the air that has passed through the anode 18 reacts with hydrogen ions that have received electrons from the anode 18 and is reduced to water. Examples of the material of the anode 18 include a watertight thin film (woven fabric or the like) carbon, a woven fabric or paper or thin film coated with nanocarbon particles on the surface in contact with water, or a woven fabric coated with a metal catalyst on the surface in contact with water. Examples thereof include cloth, paper, thin film, and woven cloth, paper, thin film, or the like in which a metal net or the like is attached to a portion in contact with gas. Further, an aerobic microorganism may be supported on the surface of the anode 18 on the reaction tank 14 side. This is because the aerobic microorganism (aerobic microorganism 24) serves as a catalyst for anodic reduction of oxygen and improves the efficiency of oxygen reduction. Examples of such aerobic microorganism 24 include Sphingobacterium, Acinetobacterium sp., Acinetobacter sp.

  The transmission rate control layer 20 is provided on the substrate tank 12 side of the cathode 16 and adjusts the transmission rate of the substrate that passes through the cathode 16. The permeation speed control layer 20 may be in contact with the surface of the cathode 16 or may be disposed at an appropriate interval from the cathode 16. Examples of the material of the permeation speed control layer 20 include a network film such as silicon, nylon, and polyethylene. The thickness of the permeation rate control layer 20 is about 1 mm in the case of a gaseous substrate and about 0.5 mm in the case of a liquid substrate, for example.

  In FIG. 1, the length from the end of the substrate tank 12 opposite to the cathode 16 to the transmission rate control layer 20 is L1, and the length from the anode 18 to the transmission rate control layer 20 is L2. These lengths L1 and L2 will be described in Examples.

  Next, the operation of the microbial fuel cell 10 shown in FIG. 1 will be described. The culture medium is accommodated in the reaction tank 14, and the anaerobic microorganism 22 is cultured on the surface of the cathode 16 on the reaction tank 14 side. In this state, a liquid or gaseous substrate is transmitted from the substrate tank 12 through the cathode 16 to the reaction tank 14 side. In this case, the transmission rate of the substrate may be controlled by the transmission rate control layer 20. Further, air is transmitted from the anode 18 to the reaction tank 14 side.

  The substrate that has passed through the cathode 16 is decomposed by the anaerobic microorganisms 22 supported on the surface of the cathode 16 on the reaction tank 14 side. At this time, the anaerobic microorganism 22 emits electrons to the cathode 16. Electrons emitted to the cathode 16 travel through an external circuit shown as a load 26 and reach the anode 18.

  On the other hand, hydrogen ions generated when the substrate is decomposed by the anaerobic microorganisms 22 move in the medium in the direction of the anode 18 at the cathode 16. The hydrogen ions that have reached the anode 18 receive electrons from the anode 18 and react with oxygen in the air that has passed through the anode 18 to reduce the oxygen to water. At this time, the aerobic microorganism 24 described above may be used as a catalyst for the reduction reaction.

  With the above operation, electrons generated at the cathode 16 flow to the anode 18 through the load 26, so that a current can flow from the microbial fuel cell 10 to the external circuit.

  In this embodiment, since the diaphragm which separates the cathode 16 and the anode 18 can be made unnecessary, the fall of pH by the side of the cathode 16 can be avoided, and the waste of the substrate in the anode 18 can be avoided. Furthermore, the substrate can always be supplied to the anaerobic microorganism 22 through the cathode 16. Therefore, it is possible to realize a microbial fuel cell with little deterioration with time in power generation capacity, high efficiency and low internal resistance.

  Hereinafter, specific examples of the present invention will be described as examples. However, the present invention is not limited to the examples described below.

In order to form the microbial fuel cell 10 having the configuration shown in FIG. 1, the permeation rate control layer 20 is sandwiched between two cylindrical containers having an inner diameter D = 20 mm and a length of 30 mm, and L1 = L2 = 30 mm in FIG. It was. Further, a cathode 16 is arranged in the vicinity of the reaction rate 14 side of the permeation rate control layer 20 to separate the substrate vessel 12 and the reaction vessel 14, and an anode 18 is arranged at the end of the reaction vessel 14 facing the cathode 16. . The area of the cathode 16 and the anode 18 is 3.14 cm ² . Of the cylindrical containers, at least the side that is to be the substrate tank 12 is a bottomed cylindrical container, and the bottom part is arranged to be the side opposite to the permeation rate control layer 20.

The reaction vessel 14, as _{medium, AlK (SO 4) 2 ·} 12H 2 O (0.2), H 3 BO 3 (0.02), CoCl 2 · 6H 2 O (0.3), CuSO 4 5H ₂ O (0.3), MnCl ₂ .5H ₂ O (0.5), NiSO ₄ .6H ₂ O (0.2), ZnCl ₂ (0.2), Na ₂ MoO ₄ .2H ₂ O (0.1), Na ₂ SeO ₃ (0.1), NaWO ₄ · 2H ₂ O (0.05), NaOH (0.4) and 36% HCl aqueous solution 0.86 ml / l (in parentheses) (Numerical value is a concentration of mg / l unit) and a small amount of nutrients was added. In addition, the water used for the aqueous solution is normal tap water. When tap water is not used, an extremely small amount of metal ions is added as appropriate. An anaerobic microorganism 22 was cultured on the surface of the cathode 16 opposite to the transmission rate control layer 20. As the anaerobic microorganism 22, one collected from sewage in Tokyo was used. The substrate tank 12 was filled with 0.5% by mass of ethyl alcohol as a substrate.

  As the cathode 16, a composite electrode in which a 5 mm thick carbon fiber felt (carbon felt, 5.0 mm thick type 50CF-15, manufactured by Trusco Nakayama Co., Ltd.) was attached to a stainless steel mesh was used. The anode 18 is made of carbon fiber paper (AV Carb P75T manufactured by Ballard Material Products (BMP)) coated with 70% carbon nanoparticles (Black Pearls 2000 manufactured by Cabot) and 30% PTFE. did. Further, a silicone film having a thickness of 0.5 mm was used for the permeation rate control layer 20.

Using the microbial fuel cell 10 formed as described above, 0.5% by mass of ethyl alcohol as a substrate was applied to the permeation rate control layer 20 (silicone film) at 38 +/− 8 × 10 ⁻⁶ m / hour. Permeation was performed at a permeation rate. In addition, air was allowed to permeate into the reaction vessel 14 through the anode 18, but the permeation rate was not satisfactory.

It was made to operate for 46 days in this state, and the voltage value (battery electromotive force: V) and current density (mA / cm ² ) across the resistor as the load 26 were measured. The current density is a value obtained by dividing the value of the current flowing through the load 26 by the area of the electrode (3.14 cm ² ). The measurement of the voltage value and the current value was performed by NI USB-6008 data acquisition device manufactured by National Instruments. In addition, although it was continuously operated until 100 days passed, it was possible to maintain the above operation state.

2A and 2B show the measurement results. FIG. 2A shows the voltage value, current density, and power density when the resistance value of the load 26 is kept constant at 1000Ω (value obtained by dividing the power consumed by the load 26 by the area of the electrode: μW / cm ² ). The relationship is shown. FIG. 2B shows the relationship between the voltage value and the current density when the resistance value of the load 26 is changed.

  As shown in FIGS. 2 (a) and 2 (b), the microbial fuel cell 10 of this example generates an electromotive force having no practical problem on the 46th day of continuous operation, and the deterioration with time is small. Recognize. Moreover, the used substrate is 0.5 mass% ethyl alcohol, and it turns out that power generation efficiency is high. Furthermore, the internal resistance of the microbial fuel cell of this example was calculated as 872Ω, which was a low value.

  10 microbial fuel cell, 12 substrate tank, 14 reaction tank, 16 cathode, 18 anode, 20 permeation rate control layer, 22 anaerobic microorganism, 24 aerobic microorganism, 26 load.

Claims (4)

A substrate tank containing a substrate to be decomposed by anaerobic microorganisms;
A reaction vessel containing the anaerobic microorganism medium;
Separating the substrate tank and the reaction tank, a cathode on which the anaerobic microorganisms that decompose the substrate and release electrons are supported on the reaction tank side;
An anode provided in a region different from the cathode of the reaction vessel and having permeability of an oxygen-containing gas;
A microbial fuel cell comprising:   The microbial fuel cell according to claim 1, wherein the substrate and oxygen are supplied from different directions.   The microbial fuel cell according to claim 1 or 2, wherein a permeation rate control layer for controlling a permeation rate of the substrate is provided on the substrate tank side of the cathode.   The microbial fuel cell according to any one of claims 1 to 3, wherein an aerobic microorganism is supported on the anode.

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