Electrode for microbial fuel cell

Abstract

According to the present disclosure, provided is an electrode for a microbial fuel cell, the electrode comprising a tube-shaped container. The tip end of the container is sealed by a semipermeable membrane. At least a portion of the interior of the container is filled with an aqueous solvent. A cathode is inserted into the distal end of the container. The cathode is at least partially immersed in the aqueous solvent inside the container.

Description

Electrodes for microbial fuel cells

[0001] The present disclosure relates to electrodes for microbial fuel cells.

[0002] The use of microbial fuel cells (MFCs) has been proposed for the purposes of soil environmental sensing and power generation. In MFCs, electrons are generated by the oxidation of organic matter by a microbial community on the anode under anaerobic conditions and transferred to the anode. The electrons move to the cathode through an electric circuit, and protons generated by the oxidation of organic matter are simultaneously transported to the cathode, resulting in an oxygen reduction reaction. It is known that stable MFC output can be obtained in soil with a high moisture content, such as rice paddies (Non-Patent Document 1).

[0003] One example of conventional MFC technology is a method in which conductive materials that serve as the anode and cathode are buried underground, and electricity is extracted from a titanium wire or the like that connects the anode and cathode (Non-Patent Document 2).

[0004] In soil with low moisture content, the anode and cathode become insulated, hindering proton transfer and making output unstable, which makes stable use of MFCs difficult in soil with low moisture content, such as in upland fields.

[0005] Potential of microbial fuel cells: A challenge to green innovation, Chemistry and Biology, 50(3), p150-152, 2012. Plant microbial fuel cells-based energy harvester system for self-powered IoT applications. Sensors 19(6):1378, 2019.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an electrode for a microbial fuel cell.

[0007] One aspect of the present disclosure is an electrode for a microbial fuel cell, the electrode comprising a tubular container, the tip of the container being sealed by a semipermeable membrane, at least a portion of the interior of the container being filled with an aqueous solvent, a cathode being inserted into the end of the container, and the cathode being at least partially immersed in the aqueous solvent inside the container.

[0008] According to the present disclosure, an electrode for a microbial fuel cell can be provided.

[0009] 1 is a schematic diagram showing a microbial fuel cell system including an electrode 1 for a microbial fuel cell according to an embodiment.

[0010] Non-limiting embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to the examples in the following embodiments.

[0011] 1 is a schematic diagram showing an example of a microbial fuel cell system including an electrode 1 for a microbial fuel cell according to an embodiment. The figure shows the electrode 1 for a microbial fuel cell, a container 2, a tip 21 of the container 2, a semipermeable membrane 3, an end 22 of the container 2 filled with an aqueous solvent 4, a cathode 5, air 6, an end cap 7, an opening 71 in the end cap 7, a tip cap 8, an opening 81 in the tip cap 8, a logger 9 and an anode 10, a conductor 11 electrically connecting the logger 9 and the cathode 5, a conductor 12 electrically connecting the logger 9 and the anode 10, a resistor 13, and soil 14. In this disclosure, the term "tip" in relation to the container 2 refers to the end positioned deeper when inserted into the soil, and the term "end" refers to the end opposite the "tip."

[0012] <Electrode for Microbial Fuel Cell> The electrode 1 for a microbial fuel cell of the present disclosure includes a tubular container 2. In the present disclosure, a cathode 5 is inserted into the container 2 containing an aqueous solvent 4 in which protons can diffuse, making it easier for protons generated around the anode 10 and entering the container through the semipermeable membrane 3 to reach the cathode 5. This stabilizes the output of the microbial fuel cell in soil with a low moisture content.

[0013] The tip 21 of the container 2 is sealed (i.e., hermetically closed) by a semipermeable membrane 3. A semipermeable membrane that allows protons to pass through but does not allow water molecules to pass through can be used as the semipermeable membrane 3. An example of such a semipermeable membrane having selective permeability is a cation exchange membrane that has selective proton permeability. By using such a membrane having selective permeability as the semipermeable membrane 3 to seal the tip 21 of the container 2, it is possible to prevent leakage of the aqueous solvent in the container 2 and to allow protons generated by soil microorganisms around the anode 10 to enter the container 2.

[0014] The material of the container 2 is not limited as long as it is impermeable to water, but it is preferable to use an insulating material. It is also preferable to use a resin that can be formed into a shape including a screw thread at the leading end 21 and the trailing end 22 of the container 2.

[0015] At least a portion of the interior of the container 2 is filled with an aqueous solvent 4. The aqueous solvent 4 is not particularly limited as long as it is a solvent in which protons are soluble, but is preferably water.

[0016] A cathode 5 is inserted into an end portion 22 of the container 2. Protons that have entered the container 2 through the semipermeable membrane 3 reach the cathode 5 by diffusing through the aqueous solvent 4, and react with oxygen and electrons supplied from the cathode 5 to produce water. The oxygen used in this reaction can be oxygen contained in the air 6 or dissolved oxygen in the aqueous solvent 4 (which may be dissolved oxygen derived from the air 6, or dissolved oxygen that is not derived from the air 6 but has been brought in together with the aqueous solvent 4).

[0017] The material of the cathode 5 is not particularly limited as long as it has properties, including conductivity, suitable for use as an electrode in a microbial fuel cell. The cathode 5 may be made of, for example, a metal material, a carbon material, or a combination thereof. The cathode 5 may also contain an oxidation-reduction reaction catalyst known to those skilled in the art. The cathode 5 may, for example, contain a material in which a platinum-based or platinum group-based catalyst is adsorbed onto the surface of carbon. Alternatively, the cathode 5 may contain a material in which an alloy of platinum and cobalt is adsorbed as a catalyst.

[0018] The cathode 5 may have properties suitable for an oxygen electrode known to those skilled in the art of fuel cells. For example, the cathode 5 may be a membrane electrode having an oxygen-permeable layer and, optionally, a catalyst layer. The oxygen-permeable layer may be formed from a polymer or the like that is selectively permeable to oxygen, known to those skilled in the art, and may function to supply oxygen necessary for the redox reaction to the catalyst layer. The catalyst layer functions to promote the redox reaction of the supplied reactants containing oxygen, protons, and electrons. Fuel cell electrodes using such a membrane electrode can be manufactured using materials and methods known to those skilled in the art. When the cathode 5 is inserted into the container 2, the oxygen-permeable layer preferably faces at least a portion of the air 6 in the container 2, and the catalyst layer preferably faces at least a portion of the aqueous solvent 4. In such a reaction using a membrane electrode, the reaction occurs at the three-phase interface between water, air, and the cathode. Therefore, it is preferable that the cathode 5 is at least partially immersed in or in contact with the aqueous solvent 4 inside the container 2 (e.g., the catalyst layer side of the membrane electrode). It is also preferable that at least a portion of the inside of the container 2 is filled with air 6 or a gas containing oxygen, and that the cathode 5 is at least partially in contact with this (e.g., the oxygen-permeable layer side of the membrane electrode).

[0019] The end portion 22 of the container 2 may have an end cap 7. The end cap 7 may be threaded, for example, and may be joined to the end portion 22 having a corresponding thread formed thereon. The end cap 7 has an opening 71 for inserting the cathode 5. After the cathode 5 is inserted, at least a portion of the opening 71 in the end cap 7 may be sealed with a sealant. This sealing may be performed for the cathode 5 as illustrated in FIG. 1 , or for a lead wire connected to the cathode 5 (in this latter case, the upper end of the cathode 5 may be located below the end cap 7). The end cap 7 may be a breathable cap. The end cap 7 may, for example, serve to properly position the cathode 5 within the container 2 and / or to prevent foreign matter, such as soil, from entering the container 2 from the external environment.

[0020] The tip portion 21 of the container 2 may have a tip cap 8. The tip cap 8 may be threaded, for example, and may be joined to the tip portion 21 having a corresponding thread formed thereon. The tip cap 8 has an opening 81 for allowing protons to flow into the container 2 through the semipermeable membrane 3. The semipermeable membrane 3 may be fixed to the tip portion 21 by tightening the tip cap 8, which is a screw cap. The tip cap 8 may play a role in helping the semipermeable membrane 3 to seal the tip portion 21.

[0021] <Microbial fuel cell system> The anode 10 is an electrode electrically connected to the logger 9 and resistor 13 by a conductor 12. It will be understood by those skilled in the art that one of the two poles of the logger is connected to the electrode 1 including the cathode 5, and the other is connected to the anode 10. In other words, the anode 10 is electrically connected to the cathode 5 of the electrode 1 by a conductor 11, sandwiching the logger 9 and resistor 13 between them. The material of the anode 10 is not particularly limited as long as it has properties, including conductivity, for use as an electrode in a microbial fuel cell. For example, an electrode material suitable for a microbial fuel cell can be selected from carbon materials, metal materials, and combinations thereof known to those skilled in the art.

[0022] At least a portion of the anode 10, preferably the entire anode 10, is embedded in the soil 14. More specifically, the anode 10 can be placed 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. As shown in FIG. 1, the anode 10 is preferably embedded approximately horizontally in the soil. The electrode 1 is also embedded or inserted at least partially or entirely in the soil 14 with its tip 21 pointing in the depth direction. As illustrated in FIG. 1, only the end cap 7, not the container 2, may be exposed at the ground surface. Preferably, the cathode 5 and aqueous solvent 4 do not directly contact the soil 14. The anode 10 is preferably embedded deeper than the tip of the electrode 1. When viewed vertically downward from the surface of the soil 14, at least a portion or all of the anode 10 preferably overlaps the position of the semipermeable membrane 3. The anode 10 may also be in partial contact with a portion of the electrode 1, such as the container 2, the semipermeable membrane 3, or the end cap 8. From the viewpoint of stabilizing the output of the microbial fuel cell, it is preferable that the semipermeable membrane 3 and the anode 10 are close to each other, and for example, it is preferable that the distance between the centers of gravity between the semipermeable membrane 3 and the anode 10 is within 20 cm, 10 cm, 5 cm, 1 cm, or 0.5 cm. Alternatively, it is preferable that the closest distance between the semipermeable membrane 3 and the anode 10 is within 20 cm, 10 cm, 5 cm, 1 cm, or 0.5 cm.

[0023] The logger 9 of the microbial fuel cell system of the embodiment includes a voltage measurement unit and / or a current measurement unit. Although Fig. 1 shows an example of an embodiment including a voltage measurement unit, it is also possible to consider an example in which the voltage measurement unit is replaced with a current measurement unit.

[0024] By measuring the voltage generated by the fuel cell, the logger 9 and resistor 13 can be used to monitor the amount of oxidative activity of soil materials (especially soil organic matter) by microorganisms, and the amount of photosynthetic activity that indirectly leads to the accumulation of that organic matter in the soil. Those skilled in the art will understand that the logger 9 may also be configured as a data logger capable of recording the output of the microbial fuel cell over time at any time interval and output range. Those skilled in the art will also understand that in addition to or instead of a voltage measuring unit and resistor 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 the logger. The resistance value of the resistor can be appropriately set to a value suitable for the above measurement by those skilled in the art.

[0025] The microbial fuel cell system of the embodiment can be installed, for example, by digging a hole in the soil 14, placing the anode 10 in the hole, and then inserting the electrode 1 into the hole. Any remaining space in the hole can be filled with soil as needed. At this time, the semipermeable membrane 3 of the electrode 1 is installed so that it is at least partially in contact with the soil 14. The installation may also include connecting the anode 10, the cathode 5 included in the electrode 1, and a voltage measurement unit and / or a current measurement unit via conductors 11 and 12. For example, the anode 10, an external resistor 13, and the cathode 5 may be connected, and the positive and negative terminals of a logger equipped with a voltage measurement unit may be connected to both sides of the resistor 4, or a logger equipped with a current measurement unit may be connected in series to the resistor 13. The output range of the logger may be adjusted depending on the value of the voltage or current generated by the microbial fuel cell.

[0026] <Method for measuring the amount of material oxidation by soil microorganisms>

[0027] In one embodiment, there is provided a method for measuring the amount of substance oxidation by microorganisms in soil, comprising measuring voltage and / or current using the system described in the section <Microbial fuel cell system>. The voltage and / or current is preferably measured over time.

[0028] The amount of substance oxidation measured in the method for measuring the amount of substance oxidation 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. Increased photosynthetic activity of plants can increase the amount of organic substances secreted into the soil. Examples of such substances include root exudates containing proteins, sugars, amino acids, organic acids, flavonoids, etc.

[0029] In an embodiment, measuring the amount of substance oxidation by microorganisms in soil may include simply detecting whether the amount of substance oxidation is higher or lower, or increasing or decreasing, based on the voltage and / or current values ​​measured using the system described in the "Microbial Fuel Cell System" section. In this case, the measured amount of substance oxidation may be expressed in corresponding voltage units and / or current units (or electron mole units), or in any unit correlated with the voltage and / or current values. Alternatively, the method may include converting the measured voltage and / or current values ​​into the amount of substance oxidation expressed in specific units such as mass. Such conversion may be performed, for example, using any model that shows the relationship between the voltage and / or current values ​​and the amount of substance oxidation. Such a model may be, for example, a machine learning model. More specifically, models such as random forests, support vector machines, neural networks, general linear models, regularized linear discriminant analysis, regularized logistic regression, and lasso (least absolute shrinkage and selection operator) regression may be used. Known algorithms used to build machine learning models or other models may be used to build the model. From the constructed models, the model whose output value best matches the actual measured value when the verification data is input to the model 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 previously acquired data on the voltage and / or current and the corresponding amount of substance oxidation (or amount of oxidizable substance) that existed.

[0030] In the embodiment, estimating the amount of a substance to be oxidized in soil from the measured amount of oxidation of that substance may, in its simplest form, involve estimating, based on the measured amount of oxidation of the substance, whether the corresponding amount of a substance oxidizable by microorganisms in the soil is higher or lower, or whether it has increased or decreased. For example, under plant cultivation conditions where organic fertilizers or the like are not applied, an increase or decrease in root-secreted organic matter can be estimated from an increase or decrease in the measured amount of oxidation of the substance. Alternatively, in situations where it is estimated or known that a specific ion, compound, or combination thereof contained in the soil is a major substrate for oxidation by microorganisms, it is also possible to estimate the amount of that ion, compound, or combination thereof present in the soil from the measured amount of oxidation of the substance.

[0031] In the embodiment, estimating the abundance of the substance in the soil from the amount of substance oxidation may be performed using any model that shows the relationship between the amount of substance oxidation and the amount of the substance. 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 can be used. To construct the model, known algorithms used for constructing machine learning models or other models can be used. From the constructed models, a model whose output value best matches the actual measured value when validation data is input into the model can be selected and used as the optimal model. Such a model can be constructed using a method known to those skilled in the art using previously acquired data on the amount of substance oxidation and the amount of the substance in the soil. The amount of the substance can be obtained, for example, using a metabolome analysis method known to those skilled in the art.

[0032] By using the microbial fuel cell electrode, microbial fuel cell system, and method for measuring the amount of material oxidation by soil microorganisms disclosed herein, changes in soil organic matter content can be monitored inexpensively. By using the microbial fuel cell electrode disclosed herein, stable monitoring is possible even in low-moisture soil environments such as farm fields. Furthermore, by using the microbial fuel cell electrode disclosed herein, stable power supply can be achieved even in low-moisture soil environments such as farm fields.

[0033] The present disclosure includes the following embodiments. (Item 1) An electrode for a microbial fuel cell, the electrode comprising a tubular container, a tip of the container sealed by a semipermeable membrane, at least a portion of the interior of the container filled with an aqueous solvent, a cathode inserted into the end of the container, and the cathode at least partially immersed in the aqueous solvent inside the container. (Item 2) The electrode according to Item 1, wherein at least a portion of the interior of the container is filled with air. (Item 3) The electrode according to Item 1 or 2, wherein the semipermeable membrane is permeable to protons but not to water molecules. (Item 4) The electrode according to any of Items 1 to 3, wherein the end portion has an end cap, the end cap having an opening for inserting the cathode. (Item 5) The electrode according to any of Items 1 to 4, wherein the end portion has a tip cap, the tip cap having an opening for allowing protons to flow into the interior of the container through the semipermeable membrane, and the semipermeable membrane is fixed to the end portion by the tip cap. (Item 6) A microbial fuel cell system comprising: (a) a logger including a voltage measurement unit and / or a current measurement unit; (b) an anode electrically connected to (a); and (c) the electrode according to any one of Items 1 to 5 electrically connected to (a). (Item 7) A method for measuring the amount of substance oxidation by microorganisms in soil, comprising measuring the voltage and / or current using the system according to Item 6. (Item 8) The method according to Item 7, further comprising estimating the amount of substance present in the soil from the measured amount of substance oxidation.

Claims

1. An electrode for a microbial fuel cell, the electrode comprising a tubular container, the tip of the container being sealed by a semipermeable membrane, at least a portion of the interior of the container being filled with an aqueous solvent, a cathode being inserted into the distal end of the container, and the cathode being at least partially immersed in the aqueous solvent inside the container.

2. The electrode of claim 1, wherein the interior of said container is at least partially filled with air.

3. The electrode of claim 1, wherein the semipermeable membrane is permeable to protons but impermeable to water molecules.

4. The electrode of claim 1, wherein said end portion has an end cap, said end cap having an opening for inserting said cathode.

5. The electrode of claim 1, wherein the tip has a tip cap, the tip cap having an opening for allowing protons to flow into the interior of the container through the semipermeable membrane, and the semipermeable membrane is fixed to the tip by the tip cap.

6. A microbial fuel cell system comprising: (a) a logger including a voltage measuring unit and / or a current measuring unit; (b) an anode electrically connected to (a); and (c) an electrode according to any one of claims 1 to 5 electrically connected to (a).

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

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

Images