Power generation method and power generation element using humidity fluctuations

Abstract

To provide a power generation method and a power generation element, capable of obtaining electromotive force by utilizing humidity fluctuations in an environment and having excellent operational stability.SOLUTION: An aqueous solution of a deliquescent ionic compound is separated by an ion-permeable membrane and electrodes are inserted on both sides thereof; one is shielded from the outside air and sealed and the other is connected to the outside air; a humidity change in the outside air causes ion concentration differences across the ion-permeable membrane, derived from the ionic compound in the aqueous solution; and the electromotive force is generated between the electrodes.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power generation method and a power generation element that utilizes humidity fluctuations in the environment to generate electromotive force, and more particularly to a power generation method and a power generation element that utilizes humidity fluctuations using a deliquescent material. [Background technology]

[0002] With the spread of IoT technology, a huge number of small sensors and electronic devices are being installed everywhere. It is not realistic to wire these small sensors with a power source or to install large batteries that need to be replaced. Therefore, there is a demand for using microbatteries as primary cells that can provide stable operation over a long period of time.

[0003] For example, Patent Document 1 discloses a microbattery using an ionic liquid gel electrolyte that can be directly integrated on the same substrate as the device that supplies power. The structure uses an ionic liquid electrolyte that swells into a polymer at room temperature to form a non-aqueous gel, replacing the conventional alkaline and acidic liquid electrolytes (and separators) of zinc-metal oxide batteries. Such cells are said to be able to stably obtain about 1.5 V and 5 mAh of power per cell.

[0004] Meanwhile, many power generation methods have been proposed for converting energy present in the environment, such as vibrations and electromagnetic waves, into electric power, including photoelectric conversion elements such as solar cells (solar panels) and thermoelectric elements that convert heat into electricity. These are also called environmental power generation or energy harvesting. Power generation devices that utilize such power generation methods are also considered for use as driving sources for the above-mentioned IoT sensors and the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-49833 A Summary of the Invention [Problem to be solved by the invention]

[0006] With regard to energy harvesting, for example, just as the operation of solar cells is easily affected by weather, some environmental energy sources can have problems such as a lack of stability, as battery operation is greatly affected by environmental changes, leading to intermittent operation, etc. On the other hand, if changes in humidity in the air can be converted into electromotive force, it will undergo a certain degree of change continuously throughout the day, and it is thought that a certain degree of stability as a primary battery can be obtained.

[0007] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a power generation method and a power generation element that can generate electromotive force by utilizing humidity fluctuations in the environment and have excellent operational stability. [Means for solving the problem]

[0008] The power generation method according to the present invention is a method for generating electromotive force by utilizing humidity fluctuations in the environment, in which an aqueous solution of a deliquescent ionic compound is separated by an ion-permeable membrane, and electrodes are inserted on both sides of the membrane, one of which is sealed and isolated from the outside air, while the other is connected to the outside air, and a difference in ion concentration originating from the ionic compound in the aqueous solution is generated across the ion-permeable membrane by the humidity changes in the outside air. The ions are moved toward an equilibrium that eliminates the concentration difference of the ions, and an electromotive force corresponding to the concentration difference of the ions is generated, and the ionic compound is a halide. be.

[0009] The power generating element according to the present invention is an element that generates electromotive force by utilizing humidity fluctuations in the environment, and includes an ion-permeable membrane that separates an aqueous solution of an ionic compound having deliquescent properties, and electrodes inserted into the aqueous solution on both sides of the membrane, one of the aqueous solutions separated by the ion-permeable membrane is sealed off from outside air, and the other is connected to outside air, so that a difference in ion concentration originating from the ionic compound in the aqueous solution is generated across the ion-permeable membrane by humidity changes in the outside air. The ions are moved toward an equilibrium that eliminates the concentration difference of the ions, and an electromotive force corresponding to the concentration difference of the ions is generated, and the ionic compound is a halide. be.

[0010] In the above-mentioned invention, electromotive force is obtained by utilizing humidity fluctuations in the environment, which have large diurnal variations, and the operation stability is excellent. Moreover, since humidity fluctuations occur anywhere in the environment, the device is not dependent on the installation location and is also convenient. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view of a power generating element according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of a power generating element according to the present invention. [Diagram 3] FIG. 4 is a cross-sectional view of another power generating element according to the present invention. [Figure 4] FIG. 11 is a cross-sectional view of still another power generating element according to the present invention. [Diagram 5] FIG. 11 is a cross-sectional view of still another power generating element according to the present invention. [Figure 6] FIG. 11 is a cross-sectional view of still another power generating element according to the present invention. [Figure 7] 1 is a graph showing the open circuit voltage when a humidity change is applied to a power generating element according to the present invention. [Figure 8] 1 is a graph showing the open circuit voltage when a humidity change is applied to a power generating element according to the present invention. [Figure 9] (a) A graph of the voltage and current when a load is connected to the power generating element, and (b) a graph of the output calculated from the obtained voltage and current. [Figure 10] FIG. 2 is a cross-sectional view of two power generating elements according to the present invention connected in series. [Figure 11] 1 is a graph showing the open circuit voltage when a humidity change is applied to a power generating element according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Example 1] Hereinafter, a power generating element according to one embodiment of the present invention will be described with reference to FIG.

[0013] As shown in FIG. 1, the power generating element 10 includes a closed tank 1 and an open tank 2, which respectively contain an aqueous solution 9a and an aqueous solution 9b. The closed tank 1 and the open tank 2 are separated from each other by an ion-permeable membrane 3. An electrode 4a and an electrode 4b are inserted into the closed tank 1 and the open tank 2, respectively, so as to be in contact with the aqueous solutions 9a and 9b. The closed tank 1 is sealed and isolated from the outside air, while the open tank 2 is in communication with the outside air, connecting the contained aqueous solutions to the outside air. The electrodes 4a and 4b are connected to wiring or the like for extracting the electromotive force generated between them to the outside.

[0014] The aqueous solutions 9a and 9b are aqueous solutions of ionic compounds having deliquescent properties. Therefore, by connecting the open tank 2 to the outside air, the ion concentration of the aqueous solution 9b is changed by absorbing or discharging moisture due to changes in humidity in the outside air. In addition, as the ionic compound having deliquescent properties, for example, halides such as chlorides and bromides can be suitably used. Note that the open tank 2 only needs to be able to exchange moisture with the outside, so a lid made of a membrane or the like that is permeable to water vapor but not permeable to the aqueous solution 9b may be provided. The aqueous solution 9b in the open tank 2 can be prevented from flowing out to the outside, making it easier to handle the power generation element 10.

[0015] Here, a plate 11 having a recess for forming a closed chamber 1 and a plate 12 having an ion permeable membrane 3 and a hole for forming an open chamber 2 are stacked in order, and the outer periphery of the ion permeable membrane 3 is fixed to the plates 11 and 12 while sealing the space between the plates 11 and 12 with a gasket 14, thereby forming a cell for obtaining a power generating element 10.

[0016] Next, a power generation method using the power generation element 10 will be described with reference to Fig. 2. Here, a case will be described in which a lithium chloride aqueous solution is used as the aqueous solutions 9a and 9b, a silver-silver chloride electrode is used as the electrodes 4a and 4b, and a cation exchange membrane is used as the ion permeable membrane 3.

[0017] When the humidity of the air outside the power generating element 10 is low, the aqueous solution 9b in the open tank 2 evaporates water, increasing the concentration of the solute lithium chloride. On the other hand, in the closed tank 1, there is no change in the concentration of the aqueous solution because no water flows in or out. As a result, the aqueous solution 9b in the open tank 2 becomes more concentrated than the aqueous solution 9a in the closed tank 1. At this time, the cations in the aqueous solution 9b, Li + The concentration of Li is also higher than that of the aqueous solution 9a. + This ion concentration difference is the driving force for Li + permeates through the ion permeable membrane 3 toward the aqueous solution 9 a in the closed vessel 1 .

[0018] In the open tank 2, the anion Cl in the aqueous solution 9b is - is a cation Li + In order to obtain equilibrium, it reacts with the silver at the electrode 4b to generate silver chloride and electrons, as shown in the following chemical reaction formula (Formula 1). Ag+Cl - →AgCl+e - (Formula 1)

[0019] On the other hand, in closed tank 1, Cl - Li + In order to obtain equilibrium, the silver chloride at electrode 4a is decomposed into silver and Cl using electrons as shown in the following chemical reaction formula (Formula 2). - Generate. AgCl+e - →Ag+Cl - (Formula 2)

[0020] In this case, the electrons obtained by (Equation 1) flow through the circuit 13 from the electrode 4b of the open cell 2 to the electrode 4a of the closed cell 1. In other words, a current flows from the electrode 4a to the electrode 4b. That is, an electromotive force can be generated between the electrodes 4a and 4b.

[0021] On the other hand, when the humidity of the air outside the power generating element 10 is high, the aqueous solution 9b in the open tank 2 absorbs moisture due to its deliquescent nature, lowering the concentration of the solute lithium chloride. On the other hand, in the closed tank 1, there is no change in the concentration of the aqueous solution 9a because no moisture enters or leaves. As a result, the aqueous solution 9b in the open tank 2 becomes more diluted than the aqueous solution 9a in the closed tank 1. At this time, the cations in the aqueous solution 9b, Li + The concentration of Li is also lower than that of aqueous solution 9a. + permeates through the ion permeable membrane 3 toward the aqueous solution 9 b in the open tank 2 .

[0022] Then, the reaction of (Equation 1) occurs in the closed vessel 1, and the reaction of (Equation 2) occurs in the open vessel 2. In other words, the reaction proceeds in the opposite direction to the above, and a reverse electromotive force can be obtained.

[0023] In this way, according to the power generating element 10, a concentration difference is generated between the closed tank 1 and the open tank 2 by the humidity fluctuation in the outside air, and an electromotive force can be generated between the electrodes. In particular, when the humidity in the outside air is high and when it is low, the direction of the chemical reaction can be reversed to generate an electromotive force. Since an electromotive force can be obtained by repeating such a reversible reaction, excellent operational stability can be achieved by utilizing the humidity fluctuation in the environment, which has large diurnal fluctuations. Moreover, since the humidity fluctuation occurs anywhere in the environment, it is not dependent on the installation location of the power generating element 10, and is also excellent in convenience. In addition, since no reactant is lost from the power generating element 10, an electromotive force can be obtained by a reaction that is theoretically completely reversible.

[0024] In addition, when a chloride is used as the ionic compound dissolved in the aqueous solution as in (Formula 1) and (Formula 2), the above-mentioned reversible reaction can be obtained by also including a chloride in the electrode. In other words, the ionic compound used in the aqueous solution and the electrode material are a combination containing a compound with the same ion.

[0025] In addition, it is preferable that the power generating element has a small internal resistance, for example, 10 ohms or less. By using the above-mentioned combination of an aqueous lithium chloride solution and silver-silver chloride electrodes, the internal resistance can be reduced to about several ohms.

[0026] [Example 2] Next, a vertical power generating element according to another embodiment will be described with reference to FIG.

[0027] As shown in FIG. 3, the power generating element 10a is similar to the power generating element 10 described above in that a plate 11 having a recess for forming a closed tank 1 and a plate 12 having a hole for forming an ion-permeable membrane 3 and an open tank 2 are stacked on each other, and the outer periphery of the ion-permeable membrane 3 is fixed to the plate 11 and the plate 12 while sealing the gap between the plate 11 and the plate 12 with a packing 14. Here, the plate 12 forming the open tank 2 is provided with a wall 12b so as to cover a part of the lower side of the opening of the hole, and the aqueous solution 9b contained therein can be held in the open tank 2 even in a vertical type. The electrode 4b is integrally provided on the plate-shaped main surface of the porous body 5b that can permeate and hold the aqueous solution 9b. The porous body 5b extends from the lower end to the upper end in the open tank 2, and can permeate and hold the aqueous solution 9b up to the upper end. Therefore, the electrode 4b can reliably contact the aqueous solution 9b on the porous body 5b. Similarly, in the closed vessel 1, the electrode 4a is provided integrally on the main surface of the porous body 5a, ensuring that the electrode 4a is in contact with the liquid. Here, filter paper is used as the porous body 5b, and the electrode is formed and integrated by printing on the filter paper.

[0028] According to the power generating element 10a, even in a vertical arrangement, the electrodes 9a and 9b can be reliably brought into contact with the porous bodies 5a and 5b, and an electromotive force can be generated. This allows a relatively high degree of freedom in the arrangement of the power generating element 10a, even if the aqueous solution 9b flowing downward due to gravity is held in the open tank 2.

[0029] [Example 3] As yet another embodiment, a three-chamber power generating element will be described with reference to FIGS.

[0030] As shown in FIG. 4, the power generating element 10b has two open tanks 2b and 2c arranged to sandwich the sealed tank 1, and an anion exchange membrane 3b and a cation exchange membrane 3c are arranged between the sealed tank 1 and each of them as ion permeable membranes. That is, the sealed tank 1 is formed by a hole provided in the plate body 11', and the open tanks 2b and 2c are formed by holes provided in two plates 12 arranged to sandwich the plate body 11' via the anion exchange membrane 3b and the cation exchange membrane 3c. In the open tank 2a and the open tank 2b, plate-shaped porous bodies 5b and 5c are arranged to extend from the lower end to the upper end, respectively, and the aqueous solution 9b and the aqueous solution 9b are permeated. The porous bodies 5b and 5c integrally form the electrodes 4b and 4c, respectively, and ensure the contact of the electrodes 4b and 4c with the liquid.

[0031] 5 and 6, a power generation method using the power generation element 10b will be described. Here, a case will be described in which lithium chloride aqueous solutions are used as the aqueous solutions 9a, 9b, and 9c, and silver-silver chloride electrodes are used as the electrodes 4b and 4c.

[0032] As shown in FIG. 5, when the humidity of the air outside the power generating element 10b is low, the aqueous solutions 9b and 9c in the open tanks 2b and 2c evaporate water, increasing the concentration of the solute lithium chloride. On the other hand, in the closed tank 1, there is no change in the concentration of the aqueous solutions because there is no flow of water. As a result, the aqueous solutions 9b and 9c in the open tanks 2b and 2c become more concentrated than the aqueous solution 9a in the closed tank 1. At this time, the cations in the aqueous solutions 9b and 9c, Li + and the anion Cl - The concentration of Li is also higher than that of the aqueous solution 9a, and the Li + and Cl - This difference in ion concentration is the driving force for the Cl - permeates through the anion exchange membrane 3b from the open vessel 2b toward the aqueous solution 9a in the closed vessel 1, and Li + permeates through the cation exchange membrane 3c from the open tank 2c toward the aqueous solution 9a in the closed tank 1.

[0033] In the open tank 2b, the cation Li in the aqueous solution 9b is + is an anion Cl - In order to obtain equilibrium, the silver chloride in electrode 4b is decomposed to silver and Cl, as shown in the above chemical reaction formula (Formula 2). - Generate.

[0034] On the other hand, in the open tank 2c, the anion Cl in the aqueous solution 9c - is a cation Li + In order to obtain equilibrium, the silver reacts with the silver at the electrode 4c to generate silver chloride and electrons, as shown in the above chemical reaction formula (Formula 1).

[0035] In this case, the electrons obtained by (Equation 1) flow through the circuit 13 from the electrode 4c in the open chamber 2c to the electrode 4b in the open chamber 2b. In other words, a current flows from the electrode 4b to the electrode 4c. That is, an electromotive force can be generated between the electrodes 4b and 4c.

[0036] On the other hand, as shown in FIG. 6, when the humidity of the air outside the power generating element 10b is high, the aqueous solutions 9b and 9c in the open tanks 2b and 2c absorb moisture due to their deliquescent nature, lowering the concentration of the solute lithium chloride. On the other hand, in the closed tank 1, there is no change in the concentration of the aqueous solution 9a because there is no flow of moisture. As a result, the aqueous solutions 9b and 9c in the open tanks 2b and 2c become more diluted than the aqueous solution 9a in the closed tank 1. At this time, the cations in the aqueous solutions 9b and 9c, Li + and the anion Cl - The concentration of Cl is also lower than that of the aqueous solution 9a. - permeates through the anion exchange membrane 3b toward the aqueous solution 9b in the open chamber 2b, and Li + permeates through the cation exchange membrane 3c toward the aqueous solution 9c in the open tank 2c.

[0037] Then, the reaction of (Formula 1) occurs in the open vessel 2b, and the reaction of (Formula 2) occurs in the open vessel 2c. In other words, the reaction proceeds in the opposite direction to the above, and a reverse electromotive force can be obtained.

[0038] In this way, even with the three-chamber power generating element 10b, a difference in concentration of ions derived from ionic compounds in the aqueous solution between the closed tank 1 and the open tanks 2b and 2 can be generated by fluctuations in humidity in the outside air, and an electromotive force can be generated between the electrodes 4b and 4c. In addition, the direction of the chemical reaction can be reversed when the humidity in the outside air is high and when it is low, to generate an electromotive force.

[0039] [Manufacturing test] The power generating element as described above was actually manufactured, and the performance thereof was examined. The results will be described with reference to FIGS.

[0040] Here, two-chamber type power generation elements such as the power generation element 10 and the power generation element 10a and three-chamber type power generation elements such as the power generation element 10b were manufactured, and tests were performed with different combinations of the aqueous solution and the ion-permeable membrane. A lithium chloride aqueous solution or a calcium chloride aqueous solution was used as the aqueous solution. The lithium chloride aqueous solution was adjusted to a concentration of 20%, and 0.75 mL of the aqueous solution was placed in each of the closed tank and the open tank. The calcium chloride aqueous solution was adjusted to a concentration of 30%, and 0.75 mL of the aqueous solution was placed in each of the closed tank and the open tank. In the two-chamber type power generation element, Neocepta CSE (registered trademark, manufactured by Astom Co., Ltd.) or Nafion117 (registered trademark, manufactured by Sigma-Aldrich Co., Ltd.) was used as the cation exchange membrane. In the three-chamber type power generation element, the same cation exchange membrane as above was used, and Neocepta ASE (registered trademark, manufactured by Astom Co., Ltd.) was used as the anion exchange membrane. In addition, a silver-silver chloride electrode was used as the electrode. The electrode was prepared by printing silver paste in a mesh shape on filter paper and then anodizing it in a lithium chloride aqueous solution.

[0041] Figures 7 and 8 show the results of measuring the open circuit voltage when the obtained power generation element was subjected to a humidity change. The power generation element was placed in a thermo-hygrostat and maintained at 25°C, and the humidity was changed by alternating between 30% and 90% every 4 hours. As a result, the highest voltage was obtained with a two-chamber power generation element using a lithium chloride aqueous solution and Neocepta CSE as the cation exchange membrane. The voltage was about 26 to 28 mV at a humidity of 30%, and about -18 to -19 mV at a humidity of 90%. Even when a calcium chloride aqueous solution was used, the two-chamber power generation element using Neocepta CSE was able to obtain the highest voltage.

[0042] Figure 9 shows the results of measuring the output when a load was connected while a voltage of 28 mV was being obtained from the two-chamber power generating element using a lithium chloride aqueous solution and Neocepta CSE. The short-circuit current was 4.6 mA (Figure 9(a)). According to the output calculated from the current and voltage, the maximum value was obtained when the load was 5 Ω, and was 34 μW (Figure 9(b)).

[0043] As shown in Fig. 10, two vertical power generating elements 10a were arranged back to back and connected in series to produce a power generating element. That is, the electrode 4b in the open tank 2 of one power generating element 10a-1 (on the right side of the figure) was connected to GND, and the electrode 4a in the closed tank 1 was connected to the electrode 4b in the open tank 2 of the other power generating element 10a-2 (on the left side of the figure). Wiring was then performed so that the voltage of the electrode 4a in the closed tank 1 of the power generating element 10a-2 could be measured. A lithium chloride aqueous solution was used as the aqueous solution, and Neocepta CSE was used as the cation exchange membrane 3.

[0044] Figure 11 shows the results of measuring the open-circuit voltage when changing the humidity of the power generation element obtained. The power generation element was placed in a thermo-hygrostat and maintained at 25°C, and the humidity was changed by alternating between 30% and 90% every four hours. As a result, it was confirmed that a voltage about twice that obtainable from a single power generation element was obtained.

[0045] While the present invention has been described with reference to exemplary embodiments thereof, it is not intended to be limiting, and those skilled in the art will be able to make various alternative embodiments and modifications without departing from the spirit of the invention or the scope of the appended claims. [Explanation of symbols]

[0046] 1 Closed tank 2 Open tank 3. Ion-permeable membrane 4a, 4b electrode 9a, 9b Aqueous solution 10 Power generation element

Claims

1. A power generation method for generating electromotive force by utilizing humidity fluctuations in the environment, comprising the steps of: an aqueous solution of a deliquescent ionic compound is separated by an ion-permeable membrane, and electrodes are inserted on either side of the membrane, one of the electrodes being sealed off from the outside air and the other connected to the outside air, and a concentration difference is generated across the ion-permeable membrane due to a change in humidity in the outside air, The ions are moved toward an equilibrium that eliminates the concentration difference of the ions, and an electromotive force is generated according to the concentration difference of the ions; The method for generating electricity using humidity fluctuations, wherein the ionic compound is a halide.

2. The method of generating electricity according to claim 1 , wherein the ion permeable membrane is a cation exchange membrane.

3. The power generation method described in claim 1 or 2, wherein the electrode is a silver-silver halide electrode.

4. 4. The method of claim 3, wherein the halide is a lithium halide.

5. The power generating method according to claim 1 , wherein the aqueous solution is permeated and held in a porous body.

6. A power generating element that generates electromotive force by utilizing humidity fluctuations in the environment, The apparatus has an ion-permeable membrane that separates an aqueous solution of a deliquescent ionic compound, and electrodes inserted into the aqueous solution on both sides of the membrane, one side of the aqueous solution separated by the ion-permeable membrane is sealed off from outside air, and the other side is connected to the outside air, so that a concentration difference of ions derived from the ionic compound in the aqueous solution is generated across the ion-permeable membrane by a humidity change in the outside air; The ions are moved toward an equilibrium that eliminates the concentration difference of the ions, and an electromotive force is generated according to the concentration difference of the ions; The ionic compound is a halide, and the power generating element utilizes humidity fluctuations.

7. The power generating element according to claim 6 , wherein the ion permeable membrane is a cation exchange membrane.

8. The power generating element described in claim 6 or 7, wherein the electrode is a silver-silver halide electrode.

9. The power generating element according to claim 8 , wherein the halide is a lithium halide.

10. The power generating element according to claim 6 , wherein the aqueous solution is permeated and held in a porous body.

11. The power generating element according to claim 6 , wherein the internal resistance is 10 ohms or less.

Images