Apparatus for producing hydrogen gas using photocatalyst

Abstract

To prevent leakage of hydrogen from joints or connection parts when a water tank part is formed by joining a plurality of containers with respect to an apparatus for producing hydrogen gas using a photocatalyst.SOLUTION: An apparatus for producing hydrogen gas includes: a water tank part for storing water; a photocatalyst body having a photocatalyst substance generating excitation electrons and positive holes when a photocatalyst body dispersed or arranged in water in the water tank part is irradiated with light, causing a decomposition reaction of water for decomposing water molecules into hydrogen and oxygen, and generating hydrogen gas; and a light source device emitting light radiated to the photocatalyst body and initiating a water decomposition reaction. The water tank part is formed by joining a plurality of containers, and the joints are brought into contact with a liquid phase of water in the water tank part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrogen gas production device, and more particularly to a device that produces hydrogen gas by a water decomposition reaction using a photocatalyst. [Background technology]

[0002] Hydrogen gas, which is expected to be used as a clean next-generation fuel that does not produce carbon dioxide when burned, can be produced by a water decomposition reaction using light energy with a photocatalyst, and various technologies for producing hydrogen gas using a photocatalyst have been proposed. For example, Patent Document 1 proposes a hydrogen gas production device that includes a container for receiving water, a photocatalyst dispersed or disposed in the water within the container, the photocatalyst having a photocatalytic substance that, when irradiated with light, generates excited electrons and holes, causing a water decomposition reaction that decomposes water into hydrogen and oxygen and generates hydrogen gas, a light source that emits light that causes the water decomposition reaction when irradiated onto the photocatalyst, and a housing that supports the light source, the housing being placed in the water within the container, the water being heated by exhaust heat from the light source emitted from the surface of the housing, and the surface of the housing that comes into contact with the water being coated with the photocatalytic substance. Patent Document 2 discloses a method for operating a photocatalytic module that has a co-catalyst-supported water-splitting catalyst that splits water using light, and generates hydrogen and / or oxygen by supplying water to the water-splitting catalyst. When the activity of the photocatalyst decreases, a liquid of a metal-containing compound, which is a precursor of the co-catalyst, is placed in the module, and a photocatalytic co-catalyst is precipitated on the photocatalyst by light irradiation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2023-094488 [Patent Document 2] Patent Publication No. 2023-106958 Summary of the Invention [Problem to be solved by the invention]

[0004] An apparatus for producing hydrogen gas by storing water containing dispersed or disposed photocatalysts in a water tank and irradiating the water with light from a light source such as an LED to induce a water splitting reaction is advantageous in that it can be installed anywhere. Furthermore, in a hydrogen gas production apparatus with such a configuration, the amount of hydrogen gas generated per unit time or per predetermined time (hereinafter simply referred to as the "hydrogen generation amount") varies depending on the intensity of the light irradiated onto the water. Therefore, the amount of hydrogen generated in the apparatus can be adjusted by adjusting the intensity of the irradiated light. Furthermore, since the amount of water in the water tank decreases as hydrogen gas is generated by the water splitting reaction, it is convenient for the hydrogen gas production apparatus to be equipped with a mechanism for continuously supplying water to the water tank (e.g., a water storage tank, piping and a pump for delivering water from the tank to the water tank, etc.) to enable continuous hydrogen gas production (see Figure 1).

[0005] However, since hydrogen gas generated in the above-described hydrogen gas production apparatus has the smallest molecular weight, it is prone to leaking from seams or joints in the container in which hydrogen gas is generated and sealed, or from the distribution path. Regarding this issue, various measures are taken to prevent hydrogen gas leakage at the joints of the piping along the path that transports hydrogen gas from the water tank portion in the apparatus, which stores water and generates hydrogen gas, to the hydrogen gas tank that accumulates or stores hydrogen gas. However, when the water tank portion is formed by joining multiple containers, for example, when the ends of cylindrical members made of quartz glass are joined using adhesive, if the seams or joints of the containers or cylindrical members come into contact with the gas phase of hydrogen gas, hydrogen gas may leak from the seams or joints. Therefore, in the above-described hydrogen gas production apparatus, it is preferable to take measures to ensure that the seams or joints of the water tank portion come into contact with the liquid phase of water, and not with the gas phase of hydrogen gas.

[0006] Thus, the main objective of the present invention is to prevent hydrogen gas from leaking from the seams or joints in a hydrogen gas production device using a photocatalyst when the water tank portion is formed by joining multiple containers together. [Means for solving the problem]

[0007] According to one aspect of the present invention, the above problem is solved by a hydrogen gas production apparatus, a water tank portion for storing water; a photocatalyst dispersed or placed in the water in the water tank section, the photocatalyst having a photocatalytic substance that generates excited electrons and holes when irradiated with light, and causes a water decomposition reaction that decomposes water molecules into hydrogen and oxygen, thereby generating hydrogen gas; a light source device that emits light that is irradiated onto the photocatalyst to induce the water decomposition reaction; Including, This is achieved by an apparatus in which the water tank portion is formed by joining a plurality of containers, and the seams are configured to come into contact with the liquid phase of water in the water tank portion.

[0008] In the above configuration, the "photocatalytic substance" may be a substance that, when irradiated with light, initiates a water decomposition reaction, reducing water to generate hydrogen gas. The "photocatalyst" may be particles of such a photocatalytic substance dispersed in water, or a component formed of the photocatalytic substance itself, or a substrate or matrix to which the photocatalytic substance is immobilized and disposed at any position in the water, or both (hereinafter, the term "photocatalyst" refers to the photocatalytic substance). The "light source device" may typically be any type of device that receives a supply of electric power and emits light that is absorbed by the photocatalytic substance to initiate a water decomposition reaction. The light emission wavelength of the light source device is preferably selected so that the quantum yield of the photocatalyst exceeds a predetermined threshold (which may be selected arbitrarily) so that the light irradiated onto the photocatalyst is efficiently absorbed by the photocatalyst to generate excited electrons and holes. In this regard, the quantum yield of a typical photocatalyst increases rapidly when the wavelength of the irradiated light falls below a certain wavelength. Therefore, the light source may be selected so that its emission wavelength is shorter than the wavelength at which the quantum yield of the photocatalyst increases sharply. Examples of photocatalysts that can be used in the present invention include SrTiO3 (strontium titanate), La2Ti2O7 (lanthanum titanate), Ga2O3 (gallium oxide), GaN (gallium nitride), NaTaO3 (sodium tantalate), and TiO2 (titanium oxide). These photocatalysts may be used with the addition of a co-catalyst, as appropriate. Various light-emitting diodes (LEDs) may be used as the light-emitting element of the light source device. Specifically, LEDs using indium gallium nitride (InGaN), diamond (ultraviolet), gallium nitride (GaN) / aluminum gallium nitride (AlGaN) (ultraviolet, blue), zinc selenide (blue), and zinc oxide (near-ultraviolet, purple, blue) are available.

[0009] In the device of the present invention, as described above, the water tank portion is formed by joining multiple containers, and the seams are configured to come into contact with the liquid phase of water in the water tank portion. With this configuration, the seams of the water tank portion are not exposed to the gaseous phase of hydrogen gas, and leakage of hydrogen gas from the seams of the water tank portion is prevented (hydrogen gas generated in the liquid phase of water quickly moves above the liquid surface, so there is almost no leakage from seams located in the liquid phase). The water tank portion may be formed, for example, by joining multiple cylindrical containers made of quartz glass or hydrogen gas-impermeable resin, with their ends glued together using a dedicated adhesive.

[0010] In the above-described device of the present invention, one embodiment of the configuration for bringing the seams of the multiple containers in the water tank section into contact with the liquid phase of water may include a water level detection means for detecting the liquid level of water in the water tank section and a water supply means for supplying water into the water tank section. The water supply means may be configured to supply water into the water tank section so that the liquid level detected by the water level detection means is above the seam of the water tank section. As the generation of hydrogen gas and oxygen gas progresses due to the decomposition of water molecules by the photocatalyst, the amount of water decreases accordingly, causing the water level in the water tank section to drop. Therefore, in the present invention, as described above, the water supply means may be operated to supply water into the water tank section so that the liquid level is above the seam of the water tank section. The "water level detection means" may be a means for measuring the water level in the water tank section using any method. As already mentioned, the "water supply means" may include a water storage tank for storing water separate from the water tank section, and piping, a pump, and the like for delivering water from the tank to the water tank.

[0011] Furthermore, the above-described device of the present invention may be configured to include a water level detection means for detecting the liquid level of water in the water tank portion, and to cause the light source device to stop emitting light when the liquid level detected by the water level detection means falls below a predetermined height above the seam of the water tank portion. When the light source device stops emitting light, hydrogen gas generation stops, preventing the water level in the water tank portion from dropping any further. This prevents the seam of the water tank portion from coming into contact with the vapor phase of hydrogen gas, thereby preventing hydrogen gas from leaking from the seam of the water tank portion. [Effects of the Invention]

[0012] Thus, in the hydrogen gas production device of the present invention, when the water tank portion is formed by joining multiple containers, the seams or joints are prevented from coming into contact with the hydrogen gas-filled gas phase, thereby preventing hydrogen gas leakage from the seams or joints. The configuration of the present invention is advantageous because it makes it possible to reduce or prevent hydrogen gas leakage as much as possible, even when the water tank portion is formed by joining multiple container parts and is difficult to mold as a single unit due to its large size, etc.

[0013] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of one aspect of a hydrogen gas production device to which this embodiment is applied. [Figure 2] 2(A) is a flowchart showing the process of replenishing water when the water level in the water tank section drops in the hydrogen gas production device of this embodiment. FIG. 2(B) is a flowchart showing the process of stopping the current supply to the hydrogen gas production device when the water level in the water tank section drops in the hydrogen gas production device of this embodiment. [Explanation of symbols]

[0015] 1...hydrogen gas production device, 2...water tank section, 2a...joint (seam), 3...water, 3a...optical medium, 4...light source device, 5...light-emitting element (LED), 6...power source, 7...current controller, 8...current control indicator, 9...produced gas collection pipe, 10...water storage tank, 11...water supply pipe, 12...pump, 14...water level gauge in water tank BEST MODE FOR CARRYING OUT THE INVENTION

[0016] Hydrogen gas production equipment configuration 1, in a hydrogen gas production device 1 to which this embodiment is applied, water 3 containing a photocatalyst is stored in a water tank section 2, which may be of any shape, and excitation light that induces a water decomposition reaction in the photocatalyst 3a in the water 3 is emitted from a light emitting element 5 supported by a light source device 4. As a result, water molecules are decomposed into hydrogen and oxygen in the photocatalyst 3a irradiated with the excitation light, and hydrogen gas H2 and oxygen gas O2 are generated. The generated hydrogen gas H2 and oxygen gas O2 are sent to a hydrogen separator (not shown) through a collection pipe 9, where the oxygen gas O2 and hydrogen gas H2 are separated and may be stored in a storage tank or the like (not shown). In the configuration of this hydrogen gas production device 1, the photocatalyst 3a contained in the water 3 may be formed from any photocatalytic substance that can be used to produce hydrogen gas through a water-splitting reaction using light, as listed in the Summary of the Invention section, and may be particles 3a dispersed in the water, or a member formed from the photocatalytic substance itself, or a substrate or matrix on which the photocatalytic substance is fixed and placed at any position in the water (not shown), or both. The light-emitting element 5 used in the light source device 4 is typically a light-emitting diode as listed in the Summary of the Invention section, and may be any element that emits light that triggers a water-splitting reaction in the photocatalyst 3a used.

[0017] Furthermore, in the case of the hydrogen gas production apparatus 1 to which this embodiment is applied, as shown in the figure, a water storage tank 10 for storing water is provided separately from the water tank portion 2, and the water w stored in the water storage tank 10 is supplied into the water tank portion 2 by a pump 12 through a water supply pipe 11. More specifically, since the amount of water in the water tank portion 2 decreases as the water decomposition reaction progresses, the water level in the water tank portion 2 is monitored by a water level meter 14 of any type, and the amount of water supplied from the water storage tank 10 to the water tank portion 2 may be adjusted by controlling the operation of the pump 12 in the water supply pipe 11 in response to the detection value of the water level meter 14 so that the water level is appropriate. Although not shown, a configuration for returning the water 3 in the water tank portion 2 to the water storage tank 10 may be provided, allowing water to circulate between the water tank portion 2 and the water storage tank 10. Photocatalysts (photocatalyst particles) may also be dispersed in the water w stored in the water storage tank 10, and may be circulated appropriately between the water tank section 2 and the water storage tank 10 together with the water.

[0018] Furthermore, in the hydrogen gas production device 1 of this embodiment, the current controller 7 controls the magnitude of the current supplied from the power source 6 to the light emitting element 5 of the light source device 4, thereby adjusting the amount of light irradiated onto the photocatalyst 3a in the water in the water tank section 2 and making it possible to adjust the amount of hydrogen generated (the greater the amount of light, the greater the amount of hydrogen generated). Control instructions to the current controller 7 may be given from a current control indicator 8 as appropriate.

[0019] In the configuration of the present embodiment, the water tank portion 2 is a container made of quartz glass, a resin material that is impermeable to hydrogen gas, or the like. However, if the device 1 is large and it is difficult to construct the water tank portion 2 from a single container, the water tank portion 2 is constructed by joining multiple container members. In this case, as shown in the figure, a seam 2a is formed between the multiple container members in the water tank portion 2. In this regard, the multiple container members are joined at the seam 2a using an adhesive or the like. If the seam 2a is exposed to the gas phase of hydrogen gas, hydrogen gas may leak from the seam 2a because it has the smallest molecular weight. Therefore, in this embodiment, the seam 2a is configured to be located below the water surface in the water tank portion 2 so that it is in contact with the liquid phase of water. This prevents the seam 2a from coming into contact with the gas phase of hydrogen gas, thereby preventing leakage of hydrogen gas from the seam 2a. When the water level in the water tank portion 2 approaches the joint 2a, one of the measures described below may be taken.

[0020] Operation to keep the joint of the water tank in contact with the liquid phase of the water In this embodiment, in order to maintain the seam 2a in the water tank portion 2 in contact with the liquid phase of water, the following measures may be taken: either positioning the seam 2a below the water surface of the water tank portion 2 or stopping light irradiation.

[0021] In one embodiment, when water is replenished, referring to FIG. 2(A), after hydrogen gas production starts (step 0), the water level hw in the water tank portion 2 is detected by the water level meter 14 (step 1). When the water level hw falls below a predetermined value ho (step 2), a suitably set amount ΔVw of water is supplied from the water storage tank 10 through the water supply pipe 11 by the pump 12 into the water tank portion 2 (step 3). The predetermined value ho may be set to a height that is higher than the height of the joint 2a in the water tank portion 2 and may be set to any suitable height. Hydrogen gas production may continue as is. With this configuration, the joint 2a is always maintained below the water surface in the water tank portion 2.

[0022] 2(A), after the start of hydrogen gas production (step 10), the water level hw in the water tank 2 is detected by the water level meter 14 (step 11), and when the water level hw falls below a predetermined value ho (step 12), the supply of current I to the light source device 4 is stopped (step 13), which stops the water decomposition reaction and prevents the water level in the water tank 2 from dropping any further, so that it is maintained below the water surface in the water tank 2. In this case, to resume hydrogen gas production, water is supplied to the water tank 2 by any method.

[0023] Thus, according to the hydrogen gas production device of the present embodiment, when the water tank portion is formed by joining multiple containers, it is possible to prevent hydrogen gas leakage from the seams or joints. As mentioned in the summary of the invention, various measures are usually taken to prevent hydrogen gas leakage from the seams and joints of the piping in the hydrogen gas transport path from the water tank portion 2 to the storage tank.

[0024] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-exemplified embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. A hydrogen gas production apparatus, a water tank portion for storing water; a photocatalyst dispersed or placed in the water in the water tank section, the photocatalyst having a photocatalytic substance that generates excited electrons and holes when irradiated with light, and causes a water decomposition reaction that decomposes water molecules into hydrogen and oxygen, thereby generating hydrogen gas; a light source device that emits light that is irradiated onto the photocatalyst to induce the water decomposition reaction; Including, The water tank section is formed by joining a plurality of containers, and the seams are configured to come into contact with the liquid phase of water in the water tank section.

2. 2. The device of claim 1, further comprising a water level detection means for detecting the liquid level of water in the water tank section, and a water supply means for supplying water into the water tank section, wherein the water supply means is configured to supply water into the water tank section so that the liquid level detected by the water level detection means is above the seam of the water tank section.

3. The device of claim 1 further comprises a water level detection means for detecting the liquid level of the water in the water tank section, and is configured to stop emitting light from the light source device when the liquid level detected by the water level detection means falls below a predetermined height above the seam of the water tank section.

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