Hydrogen generation apparatus and hydrogen generation method

Abstract

This hydrogen generation apparatus 10 includes: a vessel 13 that receives an inert gas; a plasma generation means 11 that applies energy to the inert gas in the vessel 13 to generate plasma in the vessel 13; and a container 12 that holds water W and receives the plasma fed from the vessel 13. The contact of the plasma with the water W in the container 12 induces water splitting, thereby generating a hydrogen gas. This hydrogen generation method includes: a step in which a plasma generation means 11 applies energy to an inert gas in a vessel 13 to generate plasma; and a step in which the plasma is fed from the vessel 13 into a container 12 holding water W and brought into contact with the water W in the container 12 to induce water splitting, thereby generating a hydrogen gas.

Description

Hydrogen generation device and hydrogen generation method

[0001] The present invention relates to a hydrogen generation device and a hydrogen generation method for generating hydrogen by water decomposition.

[0002] Approximately 50% of the world's hydrogen demand is met by steam reforming of natural gas. However, when hydrogen is produced from natural gas such as methane, carbon dioxide is also produced along with hydrogen, as shown in the following reaction formula: CH ４ +H ２ O → CO + 3H ２ CH ４ +2H ２ O → CO ２ +4H ２ CO + H ２ O → CO ２ +H ２

[0003] Currently, efforts are being made around the world to combat global warming, including reducing emissions of carbon dioxide, a greenhouse gas. One of the goals for curbing climate change caused by global warming is the "1.5 degree target" and "2 degree target" set by COP26. Needless to say, energy conversion through the expanded use of fuels such as hydrogen, which do not emit carbon dioxide, is essential to achieving these targets.

[0004] Furthermore, from the perspective of reducing carbon dioxide emissions, it is important to produce hydrogen using so-called green methods. In this regard, research into water electrolysis, one green method of producing hydrogen, is currently being widely conducted.

[0005] JP 2013-241303 A

[0006] However, water electrolysis has the following problems: 1) The amount of energy required for the water electrolysis process is large (approximately 4.5 to 5 kWh / m ３(It is said that the electrochemical reaction is very rapid.) 2) Because water does not conduct electricity, a highly concentrated electrolyte solution (for example, 25-30% concentration) is generally used. 3) The electrolysis of water, an electrochemical reaction, occurs only in water molecules within a dozen or so angstroms of the electrode surface in the solution, and the reaction volume (= amount of hydrogen produced per unit time) depends on the surface area of ​​the electrode. 4) Platinum and other metals, which are thought to have high catalytic properties for water splitting, are used as electrodes, which increases the equipment costs.

[0007] Furthermore, as a method for obtaining hydrogen through a water decomposition reaction other than water electrolysis, a method that utilizes the thermal energy of a heat medium heated by solar thermal energy is disclosed, for example, in Patent Document 1. This method has the advantage of reducing the environmental load by utilizing natural energy, and also reducing the load of collecting high-temperature solar thermal energy. However, obtaining hydrogen using this method requires a large amount of energy, and improvements are needed in terms of cost.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hydrogen generation device and a hydrogen generation method that are capable of generating hydrogen using a new method of water decomposition.

[0009] A hydrogen generation apparatus according to a first aspect of the present invention that meets the above-mentioned objectives comprises a container for holding an inert gas, plasma generation means for applying energy to the inert gas in the container to generate plasma in the container, and a container for holding water and into which the plasma is introduced from the container, and the water is brought into contact with the plasma in the container to cause water decomposition and generate hydrogen gas.

[0010] A hydrogen generation method according to a second invention that meets the above-mentioned objective includes a step in which a plasma generating means applies energy to an inert gas in a container to generate plasma, and a step in which the plasma is introduced from the container into a container that contains water, and the plasma is brought into contact with the water within the container to cause water decomposition and produce hydrogen gas.

[0011] According to the hydrogen generation device according to the first aspect of the present invention and the hydrogen generation method according to the second aspect of the present invention, hydrogen can be generated by a new method of water decomposition.

[0012] It is a schematic diagram of a hydrogen generation device according to an embodiment of the present invention. It is an explanatory diagram showing the measurement results of the amount of hydrogen generated. It is an explanatory diagram showing the analysis results by electron spin resonance spectroscopy. It is an explanatory diagram showing the measurement results of an emission spectrum. It is an explanatory diagram showing the measurement results of the power required for hydrogen gas generation.

[0013] Next, with reference to the accompanying drawings, specific embodiments of the present invention will be described to facilitate understanding of the present invention. As shown in Fig. 1, a hydrogen generator 10 according to one embodiment of the present invention is an apparatus including a container 13 for containing an inert gas, plasma generating means 11 for applying energy to the inert gas in the container 13 to generate plasma, and a container 12 for containing water. The hydrogen generator 10 will be described in detail below.

[0014] In this embodiment, the plasma generating means 11 has electrodes 14 and 15 fixed to a vessel 13, as shown in Fig. 1. An AC power supply 16 is connected to the electrodes 14 and 15. In this embodiment, the vessel 13 is cylindrical, and a support member 17 to which a rod-shaped electrode 14 (in this embodiment, made of SUS) is attached is fixed to one longitudinal end of the vessel 13. A portion of the electrode 14 is disposed outside the vessel 13, and the majority of the electrode 14 is disposed inside the vessel 13, and the region of the electrode 14 disposed inside the vessel 13 is aligned along the axis of the vessel 13 so as not to come into contact with the vessel 13.

[0015] The strip-shaped electrode 15 made of Au is fixed to the container 13 by a fixing member (not shown) in a state of being in close contact with the outside of the container 13 so as to surround the side surface of the container 13 360 degrees. Therefore, the electrodes 14 and 15 are arranged with a gap between them. It goes without saying that there are no particular limitations on the shape or size of the container 13 and the electrodes 14 and 15. The container 13 is filled with granular dielectric 18, and a large number of dielectrics 18 are arranged between the electrodes 14 and 15. In this embodiment, titanium oxide is used as the dielectric 18, but this is not limiting. For example, alumina, zirconia, or quartz glass may be used instead of titanium oxide.

[0016] An inert gas (argon gas in this embodiment) can be supplied into the container 13. When an AC voltage or an AC current is applied from the AC power supply 16 to the electrodes 14 and 15 while the inert gas is present in the container 13, electrical energy generated by a barrier discharge is imparted to the inert gas in the container 13. As a result, ionization occurs in the inert gas, and the inert gas becomes plasma (i.e., plasma is generated in the container 13), as shown in the following reaction formula:

[0017] Ar+e － →Ar ＊

[0018] The supply of the inert gas to the container 13 may be performed manually or by providing an automatic mechanism.

[0019] A box-shaped container 12 containing water (which may be an aqueous solution) W is disposed near the other end of the container 13 (opposite the one end to which the support member 17 is fixed). The space inside the container 13 (inside the container 13) is connected to the space inside the container 12 (specifically, the region adjacent to the water inside the container 12) by a pipe 19 attached to the other end of the container 13. Therefore, the inert gas that has not become plasma inside the container 13 and the plasma generated inside the container 13 flow into the container 12 via the pipe 19.

[0020] That is, plasma is introduced into the container 12 from the vessel 13. The container 13 may be directly connected to the container 12 without using the pipe 19. The plasma generating means 11 is designed so that the only path through which the inert gas or plasma in the container 13 can flow out of the container 13 is via the pipe 19 (for example, the connection between the container 13 and the pipe 19 is processed so that the inert gas or the like does not leak out to the outside).

[0021] The plasma that has flowed into the container 12 comes into contact with the water W in the container 12, causing decomposition of the water W, and hydrogen (H ２ The water decomposition is expressed by the following reaction formula, in which water molecules are first decomposed into hydrogen radicals and hydroxyl radicals when they come into contact with argon plasma.

[0022] H ２ O + Ar ＊ →・H+・OH+Ar

[0023] Then, as shown in the following reaction formula, hydrogen molecules are produced from hydrogen radicals, and hydrogen peroxide molecules are produced from hydroxyl radicals: H+H→H ２ ・OH+・OH→H ２ O ２

[0024] Therefore, in this embodiment, hydrogen peroxide is generated in addition to hydrogen gas in the container 12 due to the decomposition of the water W caused by contact between the plasma and the water W. Since the hydrogen peroxide immediately dissolves in the water W in the container 12, the water W in the container 12 becomes rich in hydrogen peroxide. ２ In the case of using an aqueous solution, water decomposition occurs due to contact between the plasma and the water (water molecules) contained in the aqueous solution, resulting in the generation of hydrogen gas.

[0025] The inert gas does not have to be argon. For example, the inert gas may be one or more gases selected from the group consisting of argon, helium, neon, krypton, xenon, radon, oganesson, nitrogen, and carbon dioxide. However, it has been confirmed that when nitrogen is used as the inert gas, ammonia is also produced from the water W along with hydrogen gas.

[0026] In contrast, when the inert gas is one or more selected from the group consisting of argon, helium, neon, krypton, xenon, radon, and oganesson (so-called noble gases), the generation of substances other than hydrogen gas and hydrogen peroxide can be suppressed. Therefore, from the viewpoint of efficient generation of hydrogen gas, it is preferable that the inert gas is one or more selected from the group consisting of argon, helium, neon, krypton, xenon, radon, and oganesson.

[0027] In this embodiment, the container 12 is connected to a gas recycling means 21 via a pipe 20. The mixed gas in the container 12 (in this embodiment, a mixed gas containing hydrogen gas, an inert gas, and other gases; hereinafter, simply referred to as "mixed gas") is supplied to the gas recycling means 21 via the pipe 20. The other gases are, for example, air (nitrogen, oxygen, etc.) that was in the container 12 and the container 13 before argon was supplied to the container 13.

[0028] The gas recycling means 21 is designed to be able to separate the mixed gas into hydrogen gas and an inert gas. There are no particular limitations on the gas separation method used by the gas recycling means 21. Examples of gas separation methods that can be used include the PSA method, hollow fiber filter filtration fractionation, and column filtration fractionation. The gas recycling means 21 is provided with three outlets 22, 23, and 24 through which hydrogen gas, inert gas, and other gases, respectively, flow out of the gas recycling means 21.

[0029] A pipe 25 for releasing other gases into the atmosphere is connected to the outlet 24, a pipe 26 for sending the inert gas to the support member 17 is connected to the inert gas outlet 23, and a pipe 27 for sending hydrogen gas to a gas recovery device (not shown) is connected to the hydrogen gas outlet 22. An on-off valve (not shown) is attached to the pipe 25, and this on-off valve is opened only when the other gases are released from the pipe 25 and is normally closed. A space 28 communicating with the pipe 26 is formed in the support member 17, and the inert gas sent to the space 28 from the gas recycling means 21 via the pipe 26 flows from the space 28 into the container 13, and an AC voltage is applied inside the container 13.

[0030] Therefore, the gas recycling means 21 separates the inert gas from the mixed gas containing hydrogen gas and inert gas obtained from the container 12 and supplies it to the plasma generating means 11. By using the gas recycling means 21, the inert gas can be recycled and the amount of inert gas supplied from outside to the hydrogen generator 10 can be reduced. The gas recycling means 21 is not necessarily required, and the gas recycling means 21 may be omitted from the hydrogen generator 10.

[0031] In this embodiment, the inert gas is converted into plasma by barrier discharge, but the discharge method for generating plasma is not limited to barrier discharge. For example, spark discharge, corona discharge, glow discharge, or arc discharge may be used instead of barrier discharge. However, barrier discharge is preferable because it is more efficient than other discharges. Furthermore, the method for converting the inert gas into plasma is not limited to using discharge; for example, radiation such as ultraviolet rays, X-rays, or gamma rays, or microwaves may be used to generate plasma. Therefore, the energy applied to the inert gas to generate plasma is not limited to electrical energy.

[0032] From the explanation so far, the hydrogen generation method using the hydrogen generation device 10 comprises the steps of: using the plasma generation means 11 to apply energy to the inert gas in the container 13 to generate plasma; and introducing the plasma from the container 13 into the container 12 containing water W and bringing the plasma into contact with the water W in the container 12 to cause water decomposition and generate hydrogen gas from the water W. Furthermore, when the gas recycling means 21 is used, the hydrogen generation method further comprises the step of separating the inert gas from the mixed gas containing hydrogen gas and the inert gas obtained from the container 12 and supplying the inert gas to the container 13. Experimental Example

[0033] Next, an experiment conducted to confirm the effects of the present invention will be described. A gas container equipped with a SUS304 electrode and an Au electrode, and a reaction container containing water into which gas and plasma flowed from the gas container via a tube were prepared. After the gas in the gas container and the reaction container were both replaced with argon, a 20 A, 18 kHz, sine wave AC voltage was applied to the two electrodes while supplying argon to the gas container at 3 L / min, generating plasma in the gas container. Hydrogen gas was then generated in the reaction container using the plasma flowing in from the gas container.

[0034] <First Experiment> For 5 minutes after the start of application of voltage to the two electrodes, the gas (approximately 15 L of gas) released from the reaction vessel was collected in a gas bag, and the amount of hydrogen gas contained in the gas in the gas bag was measured by gas chromatography using a GC3210 manufactured by GL Science. The measurement was performed four times under different conditions. The measurement results are shown in Figure 2.

[0035] In FIG. 2, discharger 1_2 cm, discharger 1_4 cm, discharger 2_2 cm, and discharger 2_4 cm indicate that the measurements were performed under the conditions shown below (the same applies to the second and third experiments below).

[0036] Discharger 1_2cm: TiO ２ Yes, 2cm Discharger 1_4cm: TiO ２ Yes, 4cm Discharger 2_2cm: TiO ２ None, 2cm Discharger 2_4cm: TiO ２ None, 4cm

[0037] In addition, "TiO ２ "Yes" indicates that there is TiO in the gas container. ２ This indicates that the beads were filled with "TiO ２ "None" indicates that nothing was filled in the gas container, and "2 cm" and "4 cm" indicate the distance from the gas outlet of the tube to the surface of the water stored in the reaction container.

[0038] <Second Experiment> For each of Discharger 1_2 cm and Discharger 2_2 cm in the first experiment, the water in the reaction vessel after hydrogen gas generation was analyzed for spin species by electron spin resonance spectroscopy using a JES-X310 manufactured by JEOL RESONANCE Co., Ltd. The analysis results are shown in Figure 3. Figure 3 also lists publicly known spin information for H radicals and OH radicals. The results shown in Figure 3 confirmed that the water in both Discharger 1_2 cm and Discharger 2_2 cm contained H radicals and OH radicals, i.e., water decomposition had occurred.

[0039] <Third Experiment> In the discharge vessel 1_2 cm of the first experiment, the emission spectrum inside the reaction vessel was measured using an ultraviolet-visible spectrophotometer (SHIMADZU.UV-2600). The measurement results are shown in Figure 4. In Figure 4, the upper part marked "-OH (OH radical)" shows the measurement results for wavelengths of 300 nm to 320 nm, and the lower part marked "-H (H radical)" shows the measurement results for the emission spectrum for wavelengths of 645 nm to 665 nm. The measurement results shown in Figure 4 confirmed the presence of hydrogen peroxide and hydrogen inside the reaction vessel.

[0040] <Fourth Experiment> In each of the dischargers 1_2 cm and 2_2 cm in the first experiment, the amount of power consumed for applying an AC voltage to the electrodes was measured. The measurement results are shown in the form of a Lissajous figure in FIG. 5. In FIG. 5, ２ "Yes" means the measurement result of discharger 1_2cm, and "TiO ２ "None" refers to the measurement result of discharger 2_2cm. From Figure 5, it can be seen that the power consumption of discharger 1_2cm and discharger 2_2cm was about the same.

[0041] Here, from the first experiment, the amount of hydrogen generated in the discharger 1_2 cm was 68.09 μmol, while the amount of hydrogen generated in the discharger 2_2 cm was 8.51 μmol (see FIG. 2). ２ When beads of TiO ２ It was confirmed that more hydrogen can be generated with a given amount of power consumption than when the beads are not packed.

[0042] Although the present invention has been described above by way of example, it is not limited to the above-described embodiments, and all modifications of conditions that do not depart from the gist of the invention are within the scope of the present invention. For example, the container does not have to be designed to store water (or an aqueous solution, hereinafter the same). The container may have a nozzle through which water is supplied from the outside and a reaction space portion through which plasma is supplied, and the nozzle may spray water in the form of droplets or mist into the reaction space portion to come into contact with the plasma. In this case, the plasma generating means may be disposed outside or inside the reaction space portion.

[0043] The hydrogen generation device and method according to the present invention can realize hydrogen generation by water decomposition using a new method, thereby facilitating the generation of hydrogen usable as fuel, etc.

[0044] 10: Hydrogen generation device, 11: Plasma generation means, 12: Container, 13: Container, 14: Electrode, 15: Electrode, 16: AC power supply, 17: Support member, 18: Dielectric, 19: Tube, 20: Tube, 21: Gas recycling means, 22: Outlet, 23: Outlet, 24: Outlet, 25: Tube, 26: Tube, 27: Tube, 28: Space, W: Water

Claims

1. A hydrogen generation device comprising: a container for containing an inert gas; plasma generation means for applying energy to the inert gas in the container to generate plasma within the container; and a container for containing water and into which the plasma is introduced from the container, wherein the water is brought into contact with the plasma within the container to cause water decomposition and generate hydrogen gas.

2. The hydrogen generation device according to claim 1, further comprising a gas recycling means for separating the inert gas from the mixed gas containing the hydrogen gas and the inert gas obtained from the container and supplying the inert gas to the container.

3. The hydrogen generating apparatus according to claim 1 or 2, wherein the inert gas is one or more selected from the group consisting of argon, helium, neon, krypton, xenon, radon, and oganesson.

4. A method for generating hydrogen, comprising: a step in which plasma generating means applies energy to an inert gas in a container to generate plasma; and a step in which the plasma is introduced from the container into a container containing water, and brought into contact with the water within the container to cause water decomposition and generate hydrogen gas.

5. The method for generating hydrogen according to claim 4, further comprising a step of separating the inert gas from the mixed gas containing the hydrogen gas and the inert gas obtained from the container and supplying the inert gas to the container.

6. The method for generating hydrogen according to claim 4 or 5, wherein the inert gas is one or more selected from the group consisting of helium, neon, argon, krypton, xenon, radon and oganesson.

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