Electrode for microbial fuel cell and microbial fuel cell system having the same

Abstract

To provide an electrode for a microbial fuel cell, and a microbial fuel cell system having the electrode.SOLUTION: The electrode for a microbial fuel cell is in the shape of a tube. The inside of the electrode is connected to the air. There is also provided a microbial fuel cell system including; (a) a voltage measuring unit and / or a current measuring unit; (b) an anode electrically connected to (a); and the electrode as a cathod electrically connected to (a).SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Understanding the growth status of plants in crop production is an important issue from the viewpoint of appropriate cultivation management and yield estimation. Photosynthetic activity is closely related to plant growth and has been considered one of the indices for evaluating the growth status.

[0003] Methods and devices for evaluating photosynthetic activity are known (Non-Patent Documents 1 and 2). However, evaluation of photosynthetic activity requires expensive devices and has low measurement efficiency, making it difficult to widely apply photosynthetic activity evaluation in crop production sites.

[0004] Plants synthesize organic matter through photosynthesis, and secrete a significant portion of it (typically several percent to several tens of percent of the photosynthetically assimilated carbon) from their roots into the soil. It is believed that the amount of organic matter secreted from the roots changes depending on the increase or decrease in photosynthetic activity. Therefore, it is believed that it is possible to understand the growth status of plants by monitoring the changes in the amount of soil organic matter that accompany changes in photosynthetic activity.

[0005] One method for monitoring changes in soil organic matter is the use of microbial fuel cells. In microbial fuel cells, electrons are generated by the oxidation of organic matter by a microbial community on an anode under anaerobic conditions, and the electrons are transferred to the anode. At the same time that the electrons move to the cathode through an electric circuit, protons generated by the oxidation of organic matter are transported to the cathode, causing an oxygen reduction reaction at the cathode. Because the output of a microbial fuel cell is highly dependent on the amount of organic matter present in the system, it is possible to evaluate the amount of organic matter in the environment based on changes in the output.

[0006] When using a microbial fuel cell to evaluate the growth of plants grown in field soil, the cathode must be placed so that it is in contact with both the soil and the air. This is because the cathode must receive protons from the soil and use those protons to reduce oxygen (supplied from the air). To obtain a stable output from the microbial fuel cell, it is necessary to minimize fluctuations in the interface between the three phases consisting of the soil, air, and cathode. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Meiwafosis Co., Ltd., LI-6400XT Plant Comprehensive Analysis System, http: / / www.meiwafosis.com / brochures / pdf / LI-6400XT%20Portable%20Photosynthesis%20System.pdf [Non-Patent Document 2] Robert P. Koester, Brittany M. Nohl, Brian W. Diers, Elizabeth A. Ainsworth, “Has photosynthetic capacity increased with 80 years of soybean breeding? An examination of historical soybean cultivars”, Plant, Cell & Environment (2016), 39,1058-1067. Summary of the Invention [Problem to be solved by the invention]

[0008] In conventional microbial fuel cells, a plate-shaped cathode is placed parallel to the soil surface, so that the bottom surface of the cathode comes into contact with the soil surface, where air also coexists, providing a soil-air-cathode three-phase interface.

[0009] However, the inventors recognized that such a conventional method of using a plate-shaped cathode has a problem that the unevenness of the soil surface, including aggregates and gravel, tends to cause poor contact or unstable contact between the cathode and the soil. In addition, it was also recognized that since the surface of soil in fields and the like is prone to dryness and moisture scarcity, in a conventional microbial fuel cell in which the soil surface is the site of oxygen reduction reaction, proton transport to the cathode is difficult to occur, making it difficult to detect output. Due to the above problems, a microbial fuel cell using a conventional plate-shaped cathode may be prevented from maintaining a stable output in soil such as fields.

[0010] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an electrode for a microbial fuel cell and a microbial fuel cell system including the same. [Means for solving the problem]

[0011] One aspect of the present disclosure is an electrode for a microbial fuel cell, the electrode being tubular in shape and the interior of the electrode being in communication with the atmosphere at least at one of its two ends.

[0012] Another aspect of the present disclosure is a microbial fuel cell system comprising: (a) a voltage measuring unit and / or a current measuring unit; (b) an anode electrically connected to (a); and (c) the above-mentioned electrode, which is a cathode, electrically connected to (a). Effect of the Invention

[0013] According to the present disclosure, it is possible to provide an electrode for a microbial fuel cell and a microbial fuel cell system including the same. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing an electrode for a microbial fuel cell according to an embodiment. [Diagram 2]FIG. 1 is a schematic diagram showing a microbial fuel cell system according to an embodiment. In the figure, H+ represents protons generated by oxidation of soil organic matter by microorganisms on the anode 2 and used in an oxygen reduction reaction at the electrode 1. O2 represents oxygen supplied from the atmosphere. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, non-limiting embodiments of the present disclosure will be described with reference to the drawings.

[0016] <Electrodes for microbial fuel cells>

[0017] 1 is a perspective view showing an example of an electrode for a microbial fuel cell according to an embodiment, in which an electrode 1, both ends 11, and the inside 12 of the electrode are shown.

[0018] The electrode 1 for a microbial fuel cell in the embodiment has a tube shape. Therefore, there is a space inside 12 of the electrode. The tube shape is preferably cylindrical, but is not necessarily limited thereto, and the cross section of the tube may be circular, elliptical, rectangular, polygonal, irregular, etc. The tube is usually longer than its thickness, but the reverse may also be true. The tube-shaped electrode 1 may have a porous region in part or all of the tube that prevents soil from entering the tube but allows air to pass through.

[0019] The tube-shaped electrode 1 can be easily inserted into the soil of a field or the like and installed. Unlike conventional electrodes that provide a soil-air-cathode three-phase interface by essentially "placing" a plate-shaped cathode electrode on the soil surface, the electrode 1 of this embodiment is inserted into the soil while maintaining communication with the air, and is physically fixed while being pressed by the surrounding soil, thereby stabilizing the three-phase interface. In addition to such close contact with the soil, the tip of the electrode 1 of this embodiment that is inserted into the soil is present inside the soil, where moisture is more easily retained than on the soil surface, so that the receipt of protons can also be stabilized.

[0020] The inside 12 of the electrode is in communication with the atmosphere at least at one of the ends 11. That is, at that end, the inside of the tube is not blocked by a foreign object that completely prevents the passage of air, for example. This allows oxygen to move through the cavity, so that the site of the oxygen reduction reaction can be the ground, which has a high moisture content and is stable. Therefore, the output of the microbial fuel cell can be stabilized even in a soil environment such as a field. The electrode 1 is preferably open at both ends, and in use, one of the ends 11 is open upward while communicating with the atmosphere, and the other is embedded in the soil 5.

[0021] The material of the electrode 1 is not particularly limited as long as it has properties for use as an electrode of a microbial fuel cell, including electrical conductivity. The electrode 1 may be composed of, for example, a metal material, a carbon material, or a combination thereof. The electrode 1 may contain an oxidation-reduction reaction catalyst known to those skilled in the art. The electrode 1 may, for example, contain a material in which a platinum-based catalyst is adsorbed on the surface of carbon. Alternatively, it may contain a material in which an alloy of platinum and cobalt is adsorbed as a catalyst. The electrode 1 is preferably one having a strength that promotes penetration into soil. The metal material of the electrode can usually provide that strength by itself. The electrode 1 may also contain a support substrate that imparts to the electrode 1 the strength to promote penetration into soil, in addition to the material for the electrode function.

[0022] The electrode 1 may have characteristics suitable for an oxygen electrode as known to those skilled in the art of fuel cells. For example, the electrode 1 may be a membrane electrode having an oxygen permeable layer and, optionally, a catalyst layer. The oxygen permeable layer may be formed of a polymer or the like that is selectively permeable to oxygen, as known to those skilled in the art, and may provide the catalyst layer with the function of supplying oxygen necessary for the redox reaction. The catalyst layer has the function of promoting the redox reaction by the reactants containing the supplied oxygen, protons, and electrons. An electrode for a fuel cell using such a membrane electrode may be manufactured using materials and methods known to those skilled in the art. When the electrode 1 is in use, the oxygen permeable layer is preferably at least partially facing the interior 12 of the electrode, and the catalyst layer is preferably at least partially facing the soil 5.

[0023] At electrode 1, an oxygen reduction reaction may take place using the electrons supplied to the electrode. The reaction occurring at electrode 1 may further involve protons, which may be generated by an oxidation reaction by microorganisms on anode 2. For example, at electrode 1, water is produced by the reaction of oxygen, electrons, and protons.

[0024] The electrode 1 is preferably a cathode. The electrode 1 as a cathode receives electrons from the anode 2 through a conductive wire, and these electrons are used in the oxygen reduction reaction at the electrode 1.

[0025] <Microbial fuel cell system>

[0026] In one embodiment, a microbial fuel cell system is provided, comprising: (a) a voltage measuring unit and / or a current measuring unit, an anode electrically connected to (a); and (c) the above-mentioned electrode electrically connected to (a).

[0027] Fig. 2 is a schematic diagram showing an example of a microbial fuel cell system of an embodiment. In addition to the electrode 1 (cathode) and both ends 11 and the inside 12 thereof shown in Fig. 1, the diagram shows the tip 13 of the electrode 1, the end 14 of the electrode 1, the soil-free region 15, the anode 2, the voltage measuring section 3, the resistor 4, the soil 5, and the conductor 6. In this disclosure, the "tip" of the tubular electrode 1 refers to the end that is inserted into the soil, and the "end" refers to the end opposite to the "tip".

[0028] The anode 2 is an electrode electrically connected to the voltage measuring unit 3 and the resistor 4 by a conductor 6. It will be understood by those skilled in the art that one of the two poles of the voltage measuring unit is connected to the electrode 1 as a cathode, and the other is connected to the anode 2. In other words, the anode 2 is further electrically connected to the electrode 1 by the conductor 6, sandwiching the voltage measuring unit 3 and the resistor 4. The material of the anode 2 is not particularly limited as long as it has properties for use as an electrode in a microbial fuel cell, including electrical conductivity, and can be, for example, an electrode material suitable for a microbial fuel cell selected from carbon materials, metal materials, and combinations thereof known to those skilled in the art.

[0029] At least a portion of the anode 2, preferably the entire anode 2, is embedded in the soil 5. More specifically, the anode 2 can be installed so that at least a portion of it is in contact with a soil layer containing sufficient moisture for organic matter decomposition by anaerobic microorganisms to occur. As shown in Fig. 2, the anode 2 is preferably embedded approximately horizontally in the soil. The embedded position of the anode 2 is preferably deeper than the tip position of the cathode electrode 1.

[0030] The microbial fuel cell system of the embodiment includes a voltage measuring unit 3 and / or a current measuring unit. Fig. 2 shows an example of an embodiment including a voltage measuring unit 3, but it is also possible to consider an example in which the voltage measuring unit is replaced with a current measuring unit.

[0031] The voltage measuring unit 3 and resistor 4 are for monitoring the amount of oxidation activity of soil materials (particularly soil organic matter) by microorganisms, and the amount of photosynthetic activity that indirectly leads to the accumulation of the organic matter in the soil, by measuring the voltage generated by the fuel cell. It will be understood by those skilled in the art that the voltage measuring unit 3 may further be configured as part of a data logger that can record the output of the microbial fuel cell over time at any time interval and output range. It will also be understood by those skilled in the art that in addition to or instead of the voltage measuring unit 3 and resistor 4 connected in parallel, a current measuring unit and resistor connected in series can be used as a measuring device, for example, as a measuring device that forms part of a logger. The resistance value of the resistor 4 can be appropriately set to a value suitable for the above measurement by those skilled in the art.

[0032] The tip 13 of the electrode 1 is embedded in the soil 5. This means that the tip 13 is inserted deeper than the top surface (ground surface) of the soil. In FIG. 2, a partial enlargement including the tip 13 of the electrode 1 and the soil area around it is shown in the frame on the left side. Also, the end 14 of the electrode 1 is exposed above ground to communicate the inside 12 of the electrode with the atmosphere. By installing the electrode 1 against the soil 5 in this way, the inside 12 of the electrode can include a soil-free area 15 that allows the atmosphere to reach from the end to the tip of the tubular electrode. The presence of the soil-free area 15 does not necessarily mean that soil is completely prevented from entering the inside 12 of the electrode. It should be noted that although there is a possibility that microorganisms may adhere to the surface of the electrode 1, as has been demonstrated in the conventional single-tank microbial fuel cell, the microbial fuel cell can function even under such a possibility. The electrode 1, which has a high oxygen concentration and is typically embedded shallower than the anode 2, may have a different amount, type, or function of microorganisms attached thereto, even if they do adhere thereto, from the anode.

[0033] The microbial fuel cell system of the embodiment can be installed by a method including, for example, inserting a rod having the same diameter as the electrode 1 into the soil 5, then removing the rod to form a hole in the soil 5, and inserting the electrode 1 into the hole. At this time, the electrode 1 as a cathode is installed so as to be in close contact with the soil 5 and not in contact with the anode 2. The installation may also include connecting the anode 2, the electrode 1, and a voltage measuring unit and / or a current measuring unit through a conductor 6. For example, the anode 2-external resistor 4-electrode 1 may be connected, and the positive and negative terminals of a logger equipped with a voltage measuring unit may be connected to both sides of the resistor 4, or a logger equipped with a current measuring unit may be connected in series to the resistor 4. The output range of the logger may be adjusted according to the value of the voltage or current generated from the microbial fuel cell.

[0034] <Method for measuring the amount of substances oxidized by soil microorganisms>

[0035] In one embodiment, a method for measuring the amount of substance oxidation by soil microorganisms is provided, comprising measuring voltage and / or current using the system described in the <Microbial fuel cell system> section. The voltage and / or current is preferably measured over time.

[0036] The amount of oxidation of a substance measured in the method for measuring the amount of oxidation of a substance by soil microorganisms according to the embodiment is not particularly limited as long as it is the amount of oxidation of a substance contained in soil and oxidized by soil microorganisms. The substance is typically an organic substance. The amount of organic substance secreted into the soil may increase with an increase in the photosynthetic activity of plants. Examples of such substances include root secretions containing proteins, sugars, amino acids, organic acids, flavonoids, etc.

[0037] In the embodiment, measuring the amount of substance oxidation by microorganisms in soil may include simply detecting whether the amount of substance oxidation is greater or less, or increased or decreased, based on the voltage and / or current values ​​measured using the system described in the <Microbial fuel cell system> section. In this case, the amount of substance oxidation measured may be an amount expressed in corresponding voltage units and / or current units (or electron mole units), or an amount in any unit correlated with the voltage value and / or current value. Alternatively, it may include converting the measured voltage and / or current value into the amount of substance oxidation expressed in a specific unit such as mass. Such conversion may be performed, for example, using any model that shows the relationship between the voltage and / or current value and the amount of substance oxidation. Such a model may be, for example, a machine learning model. More specifically, models such as random forest, support vector machine, neural network, general linear model, regularized linear discriminant analysis, regularized logistic regression, and Lasso (least absolute shrinkage and selection operator) regression may be used. To build the model, a known algorithm used for building a machine learning model or other models may be used. Among the constructed models, a model in which the value output by inputting the verification data into the model most closely matches the measured value can be selected and used as the optimum model. Such a model can be constructed by a method known to those skilled in the art using the previously acquired data on the voltage and / or current and the corresponding amount of substance oxidation (or amount of oxidizable substance) that existed.

[0038] In the embodiment, estimating the amount of the oxidized substance in the soil from the measured amount of oxidation of the substance may, in the simplest form, include estimating whether the amount of the substance that can be oxidized by microorganisms in the soil is greater or less, or increased or decreased, based on the measured amount of oxidation of the substance. For example, under a plant cultivation condition in which organic fertilizers or the like are not applied, an increase or decrease in the organic substance secreted from the roots can be estimated from an increase or decrease in the measured amount of oxidation of the substance. Alternatively, in a situation in which it is estimated or known that a specific ion, compound, or combination thereof contained in the soil is the main substrate for oxidation by microorganisms, it is also possible to estimate the amount of the ion, compound, or combination thereof in the soil from the measured amount of oxidation of the substance.

[0039] In the embodiment, the estimation of the amount of the substance present in the soil from the amount of oxidation of the substance may be performed using any model that indicates the relationship between the amount of oxidation of the substance and the amount of the substance present. Such a model may be, for example, a machine learning model. More specifically, a model such as a random forest, a support vector machine, a neural network, a general linear model, a regularized linear discriminant analysis, a regularized logistic regression, or a Lasso (least absolute shrinkage and selection operator) regression may be used. In constructing the model, a known algorithm used for constructing a machine learning model or other models may be used. From the constructed models, a model in which the value output by inputting the verification data into the model is most compatible with the actual measured value is selected and used as the optimal model. Such a model is constructed by a method known to those skilled in the art using the amount of oxidation of the substance previously obtained and data on the amount of the substance present in the soil. The data on the amount of the substance present can be obtained, for example, by using a method of metabolome analysis known to those skilled in the art.

[0040] By using the electrodes for microbial fuel cells, the microbial fuel cell system, and the method for measuring the amount of material oxidized by soil microorganisms of the present disclosure, it is possible to inexpensively monitor changes in the amount of soil organic matter. By using the tubular electrodes of the present disclosure, stable monitoring can be performed even in soil environments such as fields.

[0041] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention.

[0042] <Additional Notes> The present disclosure includes the following embodiments. (Appendix 1) An electrode for a microbial fuel cell, comprising: the electrode is tubular; The inside of the electrode is in communication with the atmosphere at least at one of both ends. electrode. (Appendix 2) 2. The electrode of claim 1, wherein the tubular shape is cylindrical. (Appendix 3) 3. The electrode of claim 1 or 2, wherein the electrode is a cathode. (Appendix 4) (a) a voltage measuring unit and / or a current measuring unit; (b) an anode electrically connected to (a); (c) the electrode according to any one of appendices 1 to 3 electrically connected to (a); A microbial fuel cell system comprising: (Appendix 5) 5. The system of claim 4, wherein at least a portion of the anode and at least a tip of the tubular electrode are embedded in soil, and an interior of the electrode includes a soil-free region that allows air to reach from the distal end of the tubular electrode to the tip. (Appendix 6) A method for measuring an amount of substance oxidation by microorganisms in soil, comprising measuring voltage and / or current using the system described in appendix 4 or 5. (Appendix 7) 7. The method of claim 6, further comprising estimating the amount of the substance present in the soil from the measured amount of oxidation of the substance. [Explanation of symbols]

[0043] 1. Microbial fuel cell electrode (cathode) 2 Anode 3. Voltage measurement section 4 resistor 5. Soil 6 conductors 15 Soil-free area

Claims

1. An electrode for a microbial fuel cell, comprising: the electrode is tubular; The inside of the electrode is in communication with the atmosphere at least at one of both ends. electrode.

2. The electrode of claim 1 , wherein the tubular shape is cylindrical.

3. The electrode of claim 1 or 2, wherein the electrode is a cathode.

4. (a) a voltage measuring unit and / or a current measuring unit; (b) an anode electrically connected to (a); (c) the electrode according to claim 3 electrically connected to (a); A microbial fuel cell system comprising:

5. 5. The system of claim 4, wherein at least a portion of the anode and at least a tip of the tubular electrode are embedded in soil, and the interior of the electrode includes a soil-free region that allows air to reach from the distal end of the tubular electrode to the tip.

6. A method for measuring an amount of substance oxidation by microorganisms in soil, comprising measuring a voltage and / or a current by using the system according to claim 5.

7. The method of claim 6 , further comprising estimating the amount of the substance present in the soil from the measured amount of oxidation of the substance.

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