JP2015082394A - Electrode for microorganism fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a microorganism fuel battery which has a diaphragm less expensive compared to an ion-exchange membrane, and in which an inter-electrode distance is reduced for reduction in battery internal resistance, and an electric charge transfer density is increased by arranging microorganism to be present on the face of a negative electrode opposed to a positive electrode.SOLUTION: An electrode for a microorganism fuel battery comprises: a diaphragm 4 made of an insulative material having a three-dimensional structure which enables the prevention of contact between electrodes; and pores inside the diaphragm or on at least part of the surface thereof. The pores have an average pore size of 150 μm to 5 cm; and at least part of the pores preferably form through-holes.

Description

  The present invention relates to an electrode for a microbial fuel cell having a diaphragm made of an insulating material having a three-dimensional structure that prevents the electrodes from contacting each other. More specifically, the present invention relates to a microbial fuel cell having a diaphragm separating electrodes, which is made of an insulating material having a porous three-dimensional structure capable of transferring microorganisms and biofilms containing the microorganisms and nutrients thereof. It relates to an electrode.

  As a sustainable energy, a microbial fuel cell that uses biomass to generate electric power is in the spotlight. A microbial fuel cell is a fuel cell in which microorganisms are applied as a reaction catalyst, and is a battery that uses technology that can convert various organic substances that can be metabolized by microorganisms that are used as catalysts. Microbial fuel cells are an excellent system that can recover energy while treating organic waste, but there is a problem that the output power density of microbial fuel cells is low because the power generated by organic matter-decomposing microorganisms is very small. Further improvements are needed to obtain practical power generation.

  In order to solve such a problem, it is conceivable to improve the power generation efficiency by reducing the distance between the electrodes in order to reduce the internal resistance of the battery and also allowing microorganisms to be present on the negative electrode side facing the positive electrode. For example, the electrode structure of the microbial fuel cell developed so far has a structure in which an ion permeable membrane is sandwiched as shown in Patent Document 1 below. This is a method in which each electrode is attached directly or by biting a spacer, but does not have a space where microorganisms and their nutrients can move. In addition, ion exchange membranes represented by Nafion (Dupon) are one of the causes of high cost of microbial fuel cells due to their high price. Non-Patent Document 1 below introduces a microbial fuel cell that does not use a separator such as an ion exchange membrane. If a rigid body such as a graphite rod is used as an electrode, it is easy to install at a distance that does not short-circuit, but when using a flexible material such as carbon felt, it is difficult to make the distance between the electrodes constant and stable power. Is difficult to obtain, and a sufficient distance between the electrodes must be taken so as not to cause a short circuit, which leads to an increase in internal resistance.

JP 2009-93661 A

Jae Kyung Jang et al., Process Biochm. 2004, 39, p. 1007-1012

  In view of the problems associated with the prior art described above, the problem to be solved by the present invention is to reduce the distance between the electrodes in order to reduce the internal resistance of the battery, and to reduce the distance between the electrodes and to allow the presence of microorganisms on the negative electrode surface facing the positive electrode, thereby In addition, it is to provide an electrode for a microbial fuel cell having a diaphragm that is cheaper than an ion exchange membrane.

  As a result of intensive studies and repeated experiments to solve the above-mentioned problems, the present inventors have provided a hole having a hole diameter not embedded in a biofilm derived from a microorganism in the diaphragm so that the microorganism itself can move and the diaphragm can be moved. It has been found that microorganisms can adhere to the electrode surface in contact with each other, and that nutrients necessary for the microorganisms can be sufficiently transferred to increase the ratio of microorganisms per unit volume of the electrode and increase the power generation efficiency. In addition, by providing an insulating structure between the electrodes, the distance between the electrodes can be kept constant, contributing to the stabilization of the output. Furthermore, the material for the diaphragm is not required to be an expensive organic material such as an ion exchange membrane, and any material that does not biodegrade such as a resin can be used. This has been found and the present invention has been completed.

That is, the present invention is as follows:
[1] A diaphragm made of an insulating material having a three-dimensional structure for preventing contact between electrodes, and having a plurality of pores having an average pore diameter of 150 μm or more and 5 cm or less inside or on the surface thereof Microbial fuel cell electrode.

  [2] The microbial fuel cell electrode according to [1], wherein at least some of the plurality of holes are through holes.

  [3] The microbial fuel cell electrode according to [1] or [2], wherein the insulating substance is a substance that does not undergo biodegradation.

  [4] The electrode for a microbial fuel cell according to any one of [1] to [3], wherein the diaphragm has a single layer or a laminated structure.

  In filter paper (average pore diameter of several μm to several tens of μm) and ion exchange membranes (average pore diameter of the order of several nm), which are generally used in microbial fuel cells and used as a comparison target of the present invention, microorganisms enter the inside. Microorganisms could not exist on the electrode surface in contact with the diaphragm. On the other hand, the microbial fuel cell of the present invention has a diaphragm having pores with an average pore diameter of 150 μm or more that are not covered with a biofilm made of microorganisms, so that the microorganism can easily reach the electrode surface in contact with the diaphragm. In addition, it is possible to facilitate the supply of organic substances necessary for the growth of the microorganisms and increase the power generation efficiency.

The hole shown here refers to a through hole and a blocking hole. A through-hole is a hole penetrating from the surface having a hole in the surface toward another surface, and a closed hole is a hole that does not penetrate. As long as the microorganism has a diaphragm structure in which microorganisms can exist on the negative electrode surface facing the positive electrode, any of the through-hole blocking holes may be used.
In the microbial fuel cell electrode, since the positive electrode and the negative electrode are brought into contact with each other due to bending when placed close to each other, a short-circuit prevention diaphragm structure is required at least in the center of the electrode in order to prevent the contact. If the areas of the positive and negative electrodes are different, the size of the diaphragm is determined according to the size of the negative electrode holding the microorganisms, but if the structure can secure the rigidity of the negative electrode itself and a constant distance between the positive and negative electrodes Not so.
Further, the membrane of the microbial fuel cell of the present invention is not subject to biodegradation like filter paper made of cellulose or the like, and expensive materials such as ion exchange membranes are not used. Can be suppressed.
By providing these three features, the microbial fuel cell electrode of the present invention can obtain high output power by using it compared to the conventional microbial fuel cell electrode, and can be manufactured at low cost. It is.

The conceptual diagram which shows an example of the microbial fuel cell using the electrode for microbial fuel cells of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
(Configuration of microbial fuel cell)
With reference to FIG. 1, the specific example using the diaphragm for microbial fuel cells of this invention is demonstrated.
The microbial fuel cell generally comprises a pair of electrodes (a negative electrode (3) and a positive electrode (5)), a diaphragm (4), a reaction tank (1) containing an electrolyte solution (2), and the pair of electrodes and an electric Connected external circuit (eg, data logger, potentiostat, etc.) (6). Hereinafter, embodiments of the present invention will be described based on the above-described configuration, but the configuration of the microbial fuel cell of the present invention is not limited to the one having such a configuration.

[Electrode and diaphragm for microbial fuel cell]
The arrangement of the electrodes and the diaphragm is fixed so that the electrodes are in contact with both sides so as to sandwich the diaphragm. As a method for joining the contact surfaces, in addition to joining with an adhesive, the contact surfaces may be sandwiched with a fixture.
A diaphragm made of an insulating material having a three-dimensional structure that prevents the electrodes from contacting each other has a large number of holes having an average pore diameter of 150 μm or more and 5 cm or less inside or at least a part of the surface thereof, and at least a part of the holes. Can be a through hole. The shape and distribution are not limited as long as the pores have an average pore diameter of 150 μm or more in which microorganisms and biofilms containing them can exist inside the electrode. The average pore diameter of the diaphragm according to the present invention is preferably 200 μm ≦ R (average pore diameter) <2 cm, more preferably 300 μm ≦ R (average pore diameter) <1.5 cm.
Usually, the surface covered with biofilm is covered with the biofilm in the case of holes of about several tens of μm, and the hole itself is buried, and the function as a hole is lost. However, when the average pore diameter is 150 μm or more, the scaffold supporting the biofilm The biofilm itself is not formed and the function as a hole is maintained. The term “surface” with respect to the diaphragm means all surfaces constituting a solid.

  By the way, microorganisms can also adhere to the negative electrode surface facing the positive electrode, and when the biofilm produced by the microorganisms grows, it comes into contact with the positive electrode, resulting in a possibility of short circuit. In order to prevent the contact, a diaphragm having a thickness at least larger than the thickness of the biofilm is required. The thickness of the biofilm depends on the bacterial species, but is usually about 150 μm even if it is thick. Therefore, a thickness of 150 μm or more is necessary at least. More preferably, it is 200 micrometers or more, More preferably, it is 300 micrometers or more. The diaphragm thickness is very related to the internal resistance and is proportional to the square of the distance of the diaphragm (distance between electrodes). Therefore, it is desirable to install so that the distance between electrodes which can prevent the short circuit described above takes a minimum value. If necessary, it is preferable to measure the biofilm thickness of the microorganism used in the preliminary culture in advance and select a diaphragm having a thickness corresponding to the thickness.

Hereinafter, the three-dimensional structure as a diaphragm material having a three-dimensional insulating material having an average pore diameter of 150 μm or more will be described in detail.
An example of the three-dimensional structure is Fusion (registered trademark) of Asahi Kasei Fibers Corporation. Fusion (registered trademark) is composed of an insulating material having a three-dimensional structure with an average pore diameter of 150 μm or more. Usually, Fusion (registered trademark) is thin in order to reduce the distance between the electrodes and reduce the internal resistance, but the thickness can be changed according to the bacterial species, the state of the biofilm, the reaction tank, and the like.

Fusion (registered trademark) as a diaphragm of a cell for a microbial fuel cell of the present invention does not undergo biodegradation unlike filter paper made of cellulose or the like, and is not an expensive material like an ion exchange membrane. The manufacturing cost can be reduced. This Fusion (registered trademark) is a three-dimensional three-dimensional fabric made of a resin material such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, or nylon.
Other materials that are not subject to biodegradation include polypropylene, polycarbonate, polyvinyl chloride, polyester, epoxy resin, melamine resin, phenol resin, polyurethane and other inorganic materials, glass, mica, asbestos, ceramics and other inorganic materials, isoprene rubber, ethylene Rubber-like copolymers such as propylene rubber, urethane rubber, silicone rubber, and other composite materials can be raised, but this is not limited as long as it is an insulating substance that does not undergo biodegradation. Further, even if the substrate is made of a material that undergoes biodegradation, this is not limited as long as the surface is covered with an insulating material that does not undergo biodegradation.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples.
[Production of electrodes for microbial fuel cells]
Fusion (registered trademark) (AKE64606, Asahi Kasei Fibers Co., Ltd.) was used for the diaphragm, and it was molded to a size of 70 mm × 30 mm × 3 mm. Carbon felt of 70 mm x 30 mm x 5 mm for the negative electrode (LFP-205, Tokyo Carbon Industry Co., Ltd.), carbon fiber of the same size as the negative electrode for the positive electrode (30% wet-proofed by E-TEK or similar) A 60% 4-polytetrafluoroethylene (PTFE) solution was applied to one side of the film, and four layers of PTFE layers that had been heated and dried were laminated. On the other side, 20% platinum / carbon powder (Tanaka Kikinzoku Sales Co., Ltd.) ) Was suspended in a 5% Nafion solution (manufactured by Sigma), and an air cathode made of air-dried was used.

[Pore diameter measurement]
In the measurement of the pore diameter of the diaphragm, any surface with a ruler, caliper, etc., as long as it can be visually confirmed, any surface with an optical microscope (SZX16, Olympus Corporation), an electron microscope (S-3000N, Hitachi, Ltd.) A 1cm square was photographed. In addition, when the hole diameter was larger than the field of view, the magnification was reduced and measured appropriately. From the image data, the area of each aperture was calculated by two-dimensional image analysis software (A Image-kun, Asahi Kasei Engineering Co., Ltd.). The diameters when the obtained area was a perfect circle were taken as the respective hole diameters.

From the distribution diagram of the obtained pore diameter and the total area obtained by multiplying the area of the pore diameter by the area of the pore diameter, centering on the hole diameter showing the maximum area value in the range of 150 μm or more, the pore diameter in the range of ± 2 μm before and after that is the average pore diameter. . Since Fusion (registered trademark) (AKE64606, Asahi Kasei Fibers Co., Ltd.) used in the examples can be visually measured, measurement was performed using calipers, and it was confirmed that the average pore diameter was 10.05 mm.
For comparison, filter paper (No. 101, ADVANTEC) (Comparative Example 1) and Nafion (117, Dupont) (Comparative Example 2) were used, and the average pore sizes were 4.8 μm and 54 nm, respectively.

[Reaction tank]
A reaction vessel having an inner diameter of 100 mm × 60 mm × 30 mm was made of acrylic. A through hole of 66 mm × 26 mm was provided on one side of 100 mm × 60 mm, a carbon felt electrode inside the tank at this position, an air cathode on the outside, and a diaphragm so as to be sandwiched between them.

[Power generation microorganisms]
Geobacter sulfurreducens (ATCC deposit No. 51573) was used as a power generation microorganism.

[Preparation of electrolyte solution]
An electrolyte solution having the following composition was prepared with distilled water to a final volume of 1.0 L.
NH ₄ Cl 1.5 g
NaH ₂ PO ₄ 0.6 g
KCl 0.1g
NaHCO ₃ 2.5 g
CH ₃ COONa 0.82g
HOOCHC = CHCOONa 8.0g
To the prepared electrolyte solution, a nutrient substrate at a ratio of starch: peptone: fishmeal of 3: 1: 1 (289 g COD / L, COD = chemical oxygen demand) is added to 1/100 volume of the electrolyte solution, A reaction vessel solution was obtained.

[Output measurement]
A potentiostat (G300, Gamry) and a multiplexer (ECM8, Gamry) were connected between a pair of electrodes, and the generated power was monitored.
The output curve increased with the number of bacteria after the start of culture, and the time when the number of bacteria reached a saturated state after about one week and the output stabilized was taken as the output of the sample. At the time of output measurement, the external resistance was set to 75Ω, and the current value was shown.
The results are shown in Table 1 below.

[Negative electrode findings]
After the experiment, each reaction tank was disassembled and the negative electrode surface in contact with the diaphragm was observed. The presence of microorganisms was confirmed on the diaphragm contact surface of the electrode using Fusion (registered trademark). In 1) and Nafion (Comparative Example 2), microorganisms could not be confirmed on the contact side electrode surface. This is a good output result when the difference in output between Fusion (registered trademark) with microorganisms attached to both sides of the negative electrode and Comparative Examples 1 and 2 without microorganisms attached to the electrode surface on the diaphragm contact surface side was approximately double. It was consistent.

  The electrode for a microbial fuel cell of the present invention has a diaphragm having a through-hole having a size that allows movement of microorganisms, so that microorganisms can adhere to the electrode surface in contact with the diaphragm. Necessary nutrients are sufficiently transferred to increase the ratio of microorganisms per unit volume of the electrode and increase the power generation efficiency. Further, the constituent material of the diaphragm is not required to be an expensive organic material such as an ion exchange membrane, and may be any material such as a resin that is not biodegradable. Therefore, the electrode for microbial fuel cells of the present invention can be suitably used as an electrode for microbial fuel cells.

DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Electrolyte liquid 3 Negative electrode 4 Diaphragm 5 Positive electrode 6 External circuit (potentiostat, data logger, etc.)

Claims (4)

  For a microbial fuel cell comprising a three-dimensional insulating material that prevents electrodes from contacting each other, and having a diaphragm having a plurality of pores having an average pore diameter of 150 μm or more and 5 cm or less inside or at least part of the surface thereof electrode.   The microbial fuel cell electrode according to claim 1, wherein at least some of the plurality of holes are through holes.   The microbial fuel cell electrode according to claim 1 or 2, wherein the insulating substance is a substance that does not undergo biodegradation.   The microbial fuel cell electrode according to any one of claims 1 to 3, wherein the diaphragm has a single layer or a laminated structure.

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