WO2020153359A1

WO2020153359A1 - Thermoelectric conversion device

Info

Publication number: WO2020153359A1
Application number: PCT/JP2020/001961
Authority: WO
Inventors: バントアンヴェン; 崇人小野
Original assignee: 国立大学法人東北大学
Priority date: 2019-01-22
Filing date: 2020-01-21
Publication date: 2020-07-30
Also published as: JP7313616B2; JP2020120474A

Abstract

[Problem] To provide a thermoelectric conversion device that has a relatively excellent conversion efficiency using a nano-sized through holes. [Solution] According to the present invention, a filmmembrane body 11 has a plurality of nano-sized through-holes 11a provided to pass through the thickness thereof. A pair of electrolytic tanks 13a, 13b accommodate therein an electrolytic solutions 13c and are provided so as to communicate with each other via the plurality of through-holes 11a while sandwiching the filmmembrane body 11 is sandwiched therebetween. A pair of electrodes 14a, 14b are provided to the respective electrolytic tanks 13a, 13b. A temperature adjusting means 15 is provided so as to be capable of heating or cooling at least one electrolytic tank so that a temperature difference is generated in between the electrolytic solutions 13c accommodated in each of the respective electrolytic tanks 13a, 13b. When the temperature adjusting means 15 generates the temperature difference in between the electrolytic solutions 13c accommodated in each of the respective electrolytic tanks 13a, 13b, an electromotive force is generated between the electrodes 14a, 14b.

Description

Thermoelectric converter

The present invention relates to a thermoelectric conversion device.

Conventionally, thermoelectric converters have been developed and used that can obtain electric energy by utilizing exhaust heat from factories, geothermal heat, solar heat, combustion heat of fossil fuels, and temperature gradient of seawater. Examples of the thermoelectric conversion device include a device using a thermoelectric element, a device using a hydrogen storage alloy, and a device using a reaction gas (see, for example, Patent Document 1 or 2).

In recent years, nano-sized pores (hereinafter also referred to as nanochannels) have been used for various purposes. The nanochannel has a large scale effect when the pore diameter is close to the Debye length, so that when the surface of the nanochannel comes into contact with the electrolyte solution, an electric double layer is formed along the pore wall of the nanochannel. It The thickness of the electric double layer depends on the Debye length, and the Debye length decreases as the ion concentration of the electrolyte solution increases. Utilizing such behavior of nanochannels in the liquid phase, molecular filtration, ion transport, power generators, etc. have been developed (for example, see Non-Patent Documents 1 to 3). Further, the nanochannel can be formed by anodization, nanoimprint, ion milling, electron beam lithography (EBlithography), deep etching (Deep-RIE), MacEtch (metal-assisted chemical etching), etc. (for example, ,

Non-Patent Documents

2, 4 or 5).

JP 2004-63656 A Japanese Patent Laid-Open No. 2007-282849

The conventional thermoelectric conversion devices as described in Patent Documents 1 and 2 may not have sufficient conversion efficiency depending on the usage conditions due to the performance and characteristics of materials such as thermoelectric elements, hydrogen storage alloys, and reaction gases. There was a problem that there is. Further, there is no thermoelectric conversion device having excellent conversion efficiency that uses nanochannels.

The present invention has been made in view of such problems, and an object thereof is to provide a thermoelectric conversion device having relatively excellent conversion efficiency by utilizing nano-sized through holes.

In order to achieve the above object, the thermoelectric conversion device according to the present invention, a membrane having a plurality of nano-sized through holes provided penetrating the thickness, and contains an electrolyte solution inside, the membrane, A pair of electrolytic cells provided so as to communicate with each other through the plurality of through-holes with the body sandwiched therebetween, a pair of electrodes provided in each electrolytic cell, and the electrolyte solution stored in each electrolytic cell with a temperature. In order to generate a difference, at least one of the electrolytic cells has a temperature adjusting means capable of heating or cooling, and in the electrolyte solution contained in each electrolytic cell, a temperature difference is generated by the temperature adjusting means. It is characterized in that an electromotive force is generated between the electrodes when the electrodes are turned on.

The thermoelectric conversion device according to the present invention is configured to operate according to the following principle. That is, as shown in FIG. 1, let us consider a system in which a pair of electrolyzers containing an electrolyte solution therein communicate with each other through nano-sized pores (nanochannels). Here, as an example, the electrolyte solution is a potassium chloride (KCl) aqueous solution, and the nanochannel is a through hole formed by penetrating alumina (Al ₂ O ₃ ).

As shown in FIG. 1( a ), when there is no temperature difference between the electrolytic cells, K ⁺ ions are arranged in layers along the pore walls of the nanochannel to form an electric double layer. This narrows the passage in the nanochannel, making it difficult for ions to pass through. When the pore diameter of the nanochannel is within a predetermined diameter range, neither K ⁺ ion nor Cl ⁻ ion can pass through due to the formed electric double layer.

Next, as shown in FIG. 1(b), when a temperature difference is applied between the electrolyzers, the electric double layer becomes thin and the passages in the nanochannel widen. In FIG. 1(b), the electric double layer has a constant thickness, but in reality, the electric double layer on the side of the electrolytic cell with the higher temperature (HOT SIDE) is on the side of the electrolytic cell with the lower temperature It becomes thinner than (COLD SIDE). As a result, a heat osmosis phenomenon mainly occurs, and as shown in FIG. 1(c), from the lower temperature electrolytic cell side (COLD SIDE) to the higher temperature electrolytic cell side (HOT SIDE). , K ⁺ ions move. As a result, an electromotive force is generated between the pair of electrodes provided in each electrolytic cell.

As described above, the thermoelectric conversion device according to the present invention can convert the temperature difference into electric energy by utilizing the nano-sized through holes according to the principle shown in FIG. Further, the thermoelectric conversion device according to the present invention has relatively excellent conversion efficiency. The thermoelectric converter according to the present invention utilizes, for example, exhaust heat of a factory or the like, geothermal heat, solar heat, heat of combustion of fossil fuel, heat such as temperature gradient of seawater, or a temperature difference, and a pair of electrolyzers by a temperature adjusting means. By giving a temperature difference between the tanks, electromotive force can be generated between the electrodes to obtain electric energy.

The thermoelectric conversion device according to the present invention is configured such that, when there is no temperature difference in the electrolyte solution housed in each electrolytic cell, the electric double layer prevents ions in the electrolyte solution from passing through the plurality of through holes. May be. In this case, by giving a temperature difference to each electrolytic cell to move the ions and then eliminating the temperature difference in each electrolytic cell, it is possible to store +ion or −ion in each electrolytic cell. You can take action. Further, the thermoelectric conversion device according to the present invention, the electrolyte solution stored in each electrolytic cell, after causing a temperature difference in the temperature adjusting means, by eliminating the temperature difference, at least one of the electrolysis The tank may be configured to be capable of storing electricity by storing +ions or −ions. Also in this case, operation like a capacitor can be performed.

In the thermoelectric conversion device according to the present invention, it is preferable that the membrane body and the electrolyte solution are configured to be able to form an electric double layer along the hole walls of the plurality of through holes. Further, the plurality of through holes preferably have a diameter of 1 nm to 100 nm so that the flow of ions can be controlled by the electric double layer. Further, it is preferable that the plurality of through holes are provided in the film body at a high density. The film body is preferably made of silicon, oxide, nitride, metal or metallic glass. When the film body is made of metal or metallic glass, the internal resistance can be suppressed. The electrolyte solution may contain any electrolyte such as potassium chloride or sodium chloride.

According to the present invention, it is possible to provide a thermoelectric conversion device having relatively excellent conversion efficiency by utilizing nano-sized through holes.

The operation principle of the thermoelectric conversion device according to the present invention is shown (a) there is no temperature difference between the electrolytic cells and an electric double layer is formed, and (b) a temperature difference is given between the electrolytic cells to generate electricity. FIG. 6 is a cross-sectional view showing a state in which the double layer is thinned, (c) a state in which K ⁺ ions move and an electromotive force is generated. It is a front view which shows the thermoelectric conversion device of embodiment of this invention. In the thermoelectric conversion device shown in FIG. 2, (a) the cross section of the membrane and the support, (b) the surface of the membrane, (c) the cross section of the membrane, and (d) the cross section near the boundary between the membrane and the support. It is a micrograph. Fig. 2 is a graph showing changes in temperature and output voltage of each electrolyzer (Hotchamber, Coldchamber) when one of the electrolyzers of the thermoelectric converter shown in Fig. 2 is heated and then naturally radiated. is there. Fig. 2 shows the relationship between the load resistance and the absolute value of output voltage (Absolute output voltage) and output power (Output power) when a temperature difference is applied to each electrolyzer in the thermoelectric converter. It is a graph shown. Fig. 2 shows the relationship between the temperature difference of each electrolyzer and the absolute value of output voltage and power density when changing the temperature difference of each electrolyzer in the thermoelectric converter. It is a graph shown. 3 is a graph showing the relationship between the electrolyte concentration (Electrolyte concentration) and the absolute value of the output voltage when a temperature difference is applied to each electrolytic cell of the thermoelectric conversion device shown in FIG. 2. It is a graph which shows the change of output voltage (Output voltage) when one electrolyzer of the thermoelectric conversion device shown in FIG. 2 is heated, and the temperature difference of each electrolyzer is eliminated. It is a graph which shows the relationship of the elapsed time after the temperature difference of each electrolysis cell in FIG. 8 disappears, and a potential difference (Absolute output voltage) of the thermoelectric converter shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
2 to 9 show a thermoelectric conversion device according to an embodiment of the present invention.
As shown in FIG. 2, the thermoelectric conversion device 10 includes a film body 11, a support 12, a pair of

electrolytic cells

13a and 13b, a pair of

electrodes

14a and 14b, and a temperature adjusting unit 15.

The film body 11 has a plurality of nano-sized through holes 11 a that are provided so as to penetrate through the thickness. In a specific example shown in FIG. 2, the film body 11 is made of an anodized aluminum oxide (AAO; anodized aluminum oxide) film, has a thickness of about 3 μm, and each through hole 11 a has a diameter of about 10 nm. Is. The film body 11 is not limited to the one made of aluminum oxide, but may be made of another oxide, silicon, nitride, metal or metallic glass.

The support 12 is composed of a silicon (Si) substrate 12a and a SiO ₂ film 12b formed on one surface of the silicon substrate 12a. The support 12 is provided with the film body 11 on the surface of the SiO ₂ film 12b opposite to the silicon substrate 12a. The support 12 has a communication hole 12c that penetrates from the surface of the silicon substrate 12a opposite to the film body 11 to the film body 11 and communicates with the plurality of through holes 11a of the film body 11. In the specific example shown in FIG. 2, the silicon substrate 12a is a silicon wafer having a thickness of 300 μm and a size of 2×2 cm ² . The SiO ₂ film 12b has a thickness of 300 nm.

The film body 11 and the support body 12 shown in FIG. 2 are manufactured as follows. That is, first, the SiO ₂ film 12b is formed on the surface of the silicon substrate 12a by the plasma CVD method, and the aluminum film is further formed thereon by sputtering. Next, according to Non-Patent Document 2, an aluminum oxide (AAO) film body 11 having a plurality of through holes 11a is formed on the aluminum film by using an anodic oxidation method. Next, the silicon substrate 12a and the SiO ₂ film 12b are etched by deep reactive ion etching (deep RIE) to form a communication hole 12c.

FIGS. 3(a) to 3(d) show micrographs of the cross-sections of the membrane 11 and the support 12 actually manufactured. As shown in FIG. 3B, it can be confirmed that a plurality of pores having a diameter of about 10 nm are densely present on the surface of the film body 11. Further, as shown in FIGS. 3C and 3D, it can be confirmed that a plurality of holes having a width of about 10 nm extend in the film body 11 along the film thickness direction. From FIG. 3, it can be confirmed that a plurality of through holes 11a having a diameter of about 10 nm are formed in the film body 11 at a high density.

The pair of

electrolytic cells

13a and 13b are provided so as to communicate with each other through the plurality of through holes 11a and the communication holes 12c with the membrane body 11 and the support body 12 interposed therebetween. Each of the

electrolytic cells

13a and 13b contains an electrolyte solution 13c therein. In a specific example shown in FIG. 2, each

electrolytic cell

13a, 13b is composed of a hole formed in a separate Teflon (registered trademark) plate material. The

electrolytic baths

13a and 13b are formed by arranging the plate members so that the opening sides of the holes face each other so as to sandwich the film body 11 and the support body 12 therebetween. Further, the electrolyte solution 13c is made of a potassium chloride (KCl) solution. The electrolyte solution 13c is not limited to potassium chloride and may include any electrolyte such as sodium chloride.

A pair of

electrodes

14a, 14b are provided in each

electrolytic cell

13a, 13b. In a specific example shown in FIG. 2, the

electrodes

14a and 14b are made of silver (Ag), and are attached to the

electrolysis tanks

13a and 13b (holes of the plate material) on the opposite side of the film body 11. The temperature adjusting means 15 is provided so that one of the electrolytic baths 13a can be heated so as to generate a temperature difference between the electrolyte solutions 13c stored in the

electrolytic baths

13a and 13b. In a specific example shown in FIG. 2, the temperature adjusting means 15 has a Peltier element, and the Peltier element is brought into contact with the outer wall of one of the electrolytic baths 13a to heat the electrolyte solution 13c in the electrolytic bath 13a. It is configured as follows.

The thermoelectric conversion device 10 according to the embodiment of the present invention can operate according to the principle shown in FIG. The following experiment was conducted in order to investigate this.

Using the thermoelectric conversion device 10 shown in FIG. 2, an experiment was conducted in which a temperature difference was provided between the

electrolytic cells

13a and 13b and the electric energy obtained thereby was measured. In the experiment, as shown in FIG. 2, the load resistance 21 and the data logger 22 were connected in parallel between the

electrodes

14a and 14b, and the output voltage between the

electrodes

14a and 14b was measured. In addition, during the experiment, the temperature of each

electrolytic cell

13a, 13b was measured with a thermocouple.

First, the electrolyte solution 13c in one of the electrolytic cells 13a is heated by a Peltier element, then the Peltier element is removed to stop the heating, and the temperature change and the output voltage of the

electrolytic cells

13a and 13b when the heat is naturally radiated ( Output voltage) was measured. At the time of measurement, the load resistance 21 was 47 kΩ and the concentration of the electrolyte (KCl) was 10 ⁻⁴ M. The measurement result is shown in FIG.

As shown in FIG. 4, before heating, the electric double layer narrows the passage of each through hole 11a so that ions do not pass therethrough, so that the output voltage is 0 mV. When heated, the absolute value of the output voltage increases as the temperature difference between the electrolytic cell 13a (Hot chamber) and the electrolytic cell 13b (Cold chamber) increases. This is because the passage of each through hole 11a expands as the temperature difference increases, and K ⁺ ions move from the electrolytic cell 13b (Cold chamber) to the electrolytic cell 13a (Hot chamber) mainly due to the heat permeation phenomenon. It is considered that electromotive force is generated between the

electrodes

14a and 14b. During heating, the temperature of the electrolytic cell 13b (Cold chamber) is gradually increased due to heat diffusion from the electrolytic cell 13a (Hot chamber) to the electrolytic cell 13b (Cold chamber).

After heating for about 15 minutes (900 seconds), the temperature of the electrolytic cell 13a (Hot chamber) became constant, and the absolute value of the output voltage reached the maximum value of 23 mV. At this time, the temperature difference between the electrolytic bath 13a (Hot chamber) and the electrolytic bath 13b (Cold chamber) is about 17°C. Also at this time, the temperature of the electrolytic cell 13b (Cold chamber) is gradually increasing. Then, when the heating is stopped, the temperatures of the electrolytic cell 13a (Hot chamber) and the electrolytic cell 13b (Cold chamber) decrease, and as the temperature difference between them decreases, the absolute value of the output voltage also decreases. It finally became 0 mV. This is because the passage of each through hole 11a becomes narrower as the temperature difference becomes smaller, and the amount of movement of K ⁺ ions due to the thermal osmosis phenomenon decreases, but the discharge by the load resistor 21 continues during that period. Conceivable.

Next, the load voltage 21 was changed variously, the same experiment was conducted, and the output voltage was measured. The concentration of the electrolyte (KCl) at the time of measurement was set to 10 ⁻⁴ M. FIG. 5 shows the relationship between the load resistance 21 and the absolute value of the output voltage (Absolute output voltage) when the temperature difference between the

electrolytic cells

13a and 13b is 17°C. FIG. 5 also shows the output power [=(output voltage) ² /load resistance]. As shown in FIG. 5, it was confirmed that when the load resistance 21 was 47 kΩ, the maximum voltage was 23 mV and the maximum output was 12.2 nW.

FIG. 6 shows the relationship between the temperature difference (Temperature difference) between the

electrolytic cells

13a and 13b and the absolute value of the output voltage when the load resistance 21 is 47 kΩ. FIG. 6 also shows the power density [=output power/effective area of the film body 11]. As shown in FIG. 6, it was confirmed that the output voltage and the power density increased as the temperature difference between the

electrolytic cells

13a and 13b increased. For example, when the temperature difference is 30° C., an output voltage of 50 mV and a power density of 255 μW/cm ² are obtained.

Next, the same experiment was conducted by changing the concentration of the electrolyte (KCl) variously, and the output voltage was measured. The load resistance 21 at the time of measurement was set to 47 kΩ. FIG. 7 shows the relationship between the electrolyte concentration and the absolute value of the output voltage when the temperature difference between the

electrolytic cells

13a and 13b is 17°C. As shown in FIG. 7, it was confirmed that the output voltage decreased as the electrolyte concentration increased. It is considered that this is because the electric double layer becomes thinner as the concentration of the electrolyte becomes higher, and the K ⁺ ions that have moved due to the thermal osmosis phenomenon easily flow back.

From the above results, it can be said that the thermoelectric conversion device 10 can convert the temperature difference into electric energy by using the nano-sized through holes 11a. Therefore, the thermoelectric conversion device 10 uses, for example, exhaust heat of a factory or the like, geothermal heat, solar heat, heat of combustion of fossil fuels, heat such as a temperature gradient of seawater, or a temperature difference, and a pair of temperature adjusting means 15 is used. By giving a temperature difference between the

electrolytic cells

13a and 13b, an electromotive force can be generated between the

electrodes

14a and 14b to obtain electric energy.

The thermoelectric conversion device 10 is configured such that ions in the electrolyte solution 13c cannot pass through the plurality of through holes 11a due to the electric double layer when there is no temperature difference between the electrolyte solutions 13c stored in the

electrolytic baths

13a and 13b. May be. In this case, a temperature difference is applied to each of the

electrolytic cells

13a and 13b to move the ions, and then the temperature difference between the

electrolytic cells

13a and 13b is eliminated, so that + ions or − ions are respectively supplied to the

electrolytic cells

13a and 13b. It can be stored and behave like a capacitor.
The following experiment was conducted in order to investigate this.

Measurement of the output voltage (potential difference) between the

electrodes

14a and 14b when the temperature difference is eliminated by applying the temperature difference between the

electrolytic cells

13a and 13b using the thermoelectric conversion device 10 shown in FIG. I went. In the experiment, after heating for about 23 minutes (1380 seconds) to give a maximum temperature difference of 17° C. between the

electrolysis cells

13a and 13b, the

electrolysis cells

13a and 13b are set to the same temperature to make the temperature difference. Lost. The concentration of the electrolyte (KCl) was set to 10 ⁻⁴ M, and the output was opened without the load resistor 21 being attached. The measurement result of the output voltage (Output voltage) at this time is shown in FIG.

As shown in FIG. 8, a potential difference of about 180 mV is generated between the

electrolytic cells

13a and 13b due to heating, and after the temperature difference disappears, the potential difference (absolute value of output voltage) gradually decreases due to spontaneous discharge. It was confirmed to go. Fig. 9 shows the relationship between the elapsed time after the temperature difference disappears and the potential difference (Absolute output voltage). As shown in FIG. 9, it was confirmed that the potential difference rapidly decreased with the passage of time when the temperature difference disappeared, but the reduction rate of the potential difference gradually decreased after several hours. .. It was also confirmed that a potential difference of 60% or more remained after 2 days (48 hours). From the above results, it can be said that the thermoelectric conversion device 10 can operate like a capacitor.

10 Thermoelectric Converter 11 Film Body 11a Through Hole 12 Support 12a Silicon Substrate 12b SiO ₂ Film

12c Communication Hole

13a,

13b Electrolyzer

14a, 14b Electrode 15 Temperature Adjusting Means
21 load resistance 22 data logger

Claims

A film body having a plurality of nano-sized through holes provided through the thickness,
A pair of electrolytic baths that contain an electrolyte solution inside, and that are provided so as to communicate with each other through the plurality of through holes with the membrane body interposed therebetween;
A pair of electrodes provided in each electrolytic cell,
In order to generate a temperature difference in the electrolyte solution housed in each electrolytic cell, at least one of the electrolytic cell has a temperature adjusting means capable of heating or cooling,
A thermoelectric conversion device, wherein an electromotive force is generated between the electrodes when a temperature difference is generated in the electrolytic solution stored in each electrolytic cell by the temperature adjusting means.
The thermoelectric conversion device according to claim 1, wherein the membrane body and the electrolyte solution are configured to be able to form an electric double layer along the hole walls of the plurality of through holes.
When there is no temperature difference in the electrolyte solution stored in each electrolytic cell, the electric double layer is configured so that ions in the electrolyte solution cannot pass through the plurality of through holes. The thermoelectric conversion device according to 2.
After generating a temperature difference in the electrolyte solution stored in each electrolytic cell by the temperature adjusting means, by eliminating the temperature difference, at least one of the electrolytic cells stores +ions or −ions. The thermoelectric conversion device according to any one of claims 1 to 3, wherein the thermoelectric conversion device is configured to be capable of storing electricity.
The thermoelectric conversion device according to any one of claims 1 to 4, wherein the film body is made of silicon, oxide, nitride, metal, or metallic glass.
The thermoelectric conversion device according to any one of claims 1 to 5, wherein the electrolyte solution contains potassium chloride or sodium chloride.
The thermoelectric conversion device according to any one of claims 1 to 6, wherein the plurality of through holes have a diameter of 1 nm to 100 nm.