Apparatus for producing hydrogen gas using photocatalyst

Abstract

To provide an apparatus for producing hydrogen gas using photocatalyst in which a parameter for changing a hydrogen production amount is adjusted to make it possible to control a hydrogen production amount.SOLUTION: An apparatus for producing hydrogen gas 1 includes: a water tank part 2 which stores water 3; a photocatalytic body being a photocatalytic body 3a having a photocatalyst substance which is dispersed or arranged in the water inside the water tank part which generates excitation electrons and positive holes when the substance is irradiated with light, and causes decomposition reaction of water of decomposing water molecules into hydrogen and oxygen to generate hydrogen gas; a light source device 4 which emits light that is radiated to the photocatalytic body to initiate decomposition reaction of water; hydrogen generation amount detecting means 16 for detecting a generation amount of hydrogen gas; and hydrogen generation amount adjusting means 50 for adjusting the generation amount of hydrogen gas on the basis of the generation amount of hydrogen gas detected by the hydrogen generation amount detecting means.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, in which, when the activity of the photocatalyst decreases, a liquid of a metal-containing compound that is a co-catalyst precursor is present in the module, and a photocatalytic co-catalyst is deposited on the photocatalyst by light irradiation. Patent Document 3 discloses a photocatalytic water electrolysis device that includes a plurality of photoelectrolysis cells, each of which has a plurality of casings formed by outer walls and a partition wall provided inside, each of which contains an electrolyte solution, and the lower part of the partition wall is formed into a photoelectrolysis electrode membrane assembly having a photocatalytic electrode and a counter electrode formed on both sides of an ion conductive membrane and immersed in the electrolyte, and the photocatalytic electrode and the counter electrode are electrically connected to each other, and the photoelectrolytic electrode membrane assemblies in the plurality of photoelectrolysis cells are electrically connected in series. The publication discloses that the device determines, based on hydrogen amount data, the tilt angle of the photovoltaic water electrolysis cell and the flow rate of the electrolyte supplied to the photovoltaic water electrolysis cell that maximize the energy conversion efficiency when converting sunlight to hydrogen.Patent Document 4 proposes improving the efficiency of hydrogen gas production by using exhaust heat from a light source to heat water in a container that is to be decomposed in a photocatalytic member when irradiated with light, thereby increasing the water temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2023-094488 [Patent Document 2] Patent Publication No. 2023-106958 [Patent Document 3] Patent Publication No. 2008-75097 [Patent Document 3] Patent Publication No. 2022-63186 Summary of the Invention [Problem to be solved by the invention]

[0004] An apparatus for producing hydrogen gas by storing water containing a dispersed or disposed photocatalyst 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, 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 (such as 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. Furthermore, by providing a mechanism for delivering water from the water tank and returning it to the water storage tank, and circulating water between the water tank and the water storage tank, the condition of the water in the water tank can be managed. Furthermore, as described in Patent Documents 1 and 4, since increasing the water temperature increases the amount of hydrogen gas generated, it is advantageous to provide a mechanism for heating the water.

[0005] It is advantageous for a hydrogen gas production device to be able to control the increase or decrease of the amount of hydrogen gas generated per unit time or per predetermined time that may be set appropriately (hereinafter referred to as the "hydrogen generation amount"). The amount of hydrogen generated varies depending on the intensity of light irradiated onto the water, the amount of water circulating between the water tank and the water storage tank, the amount or concentration of photocatalyst in the water, and the water temperature. Therefore, it is advantageous for the hydrogen gas production device to be able to adjust these parameters to increase or decrease the amount of hydrogen generated.

[0006] Thus, a main object of the present invention is to enable the amount of hydrogen produced to be controlled by adjusting parameters that change the amount of hydrogen produced in a hydrogen gas production device using a photocatalyst. [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; a hydrogen generation amount detection means for detecting the amount of hydrogen gas generated; a hydrogen generation amount adjusting means for adjusting the amount of hydrogen gas generated based on the amount of hydrogen gas generated detected by the hydrogen generation amount detecting means; This is achieved by an apparatus comprising:

[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. The "hydrogen generation amount detection means" may be a means for detecting the amount of hydrogen generated by any method, for example, by detecting the pressure inside the water tank, the pressure inside the transport pipe for the generated gas, the hydrogen gas concentration, etc. The "hydrogen generation amount adjustment means" may be a means for adjusting the amount of hydrogen generated by adjusting a setting parameter in a device for increasing or decreasing the amount of hydrogen generated based on the detected amount of hydrogen generated.

[0009] In the device of the present invention, the amount of hydrogen generated is increased or decreased based on the detected amount of hydrogen generated, thereby making it possible to control the amount of hydrogen generated to a desired value.

[0010] Specifically, in one embodiment of the device of the present invention, the hydrogen generation amount adjusting means may be a means for controlling the amount of light emitted from the light source device, and may be configured to adjust the amount of light emitted from the light source device so that the amount of hydrogen generation becomes a desired value. The adjustment of the amount of light emitted from the light source device is achieved by adjusting the power or current supplied to the light source device. As already mentioned, the amount of hydrogen generation increases or decreases as the intensity of the irradiated light increases or decreases, so the amount of hydrogen generation can be adjusted by adjusting the amount of light emitted from the light source device.

[0011] Furthermore, when the hydrogen gas production apparatus is provided with a tank for storing water separate from the water tank and configured to circulate water between the water tank and the tank, the hydrogen generation rate adjustment means may be a means for adjusting the rate of water circulation between the water tank and the tank, and may be configured to adjust the rate of water circulation so that the desired rate of hydrogen generation is achieved. Increasing the rate of water circulation agitates the water in the water tank, increasing the opportunities for the photocatalyst to associate with water molecules and facilitating the separation of hydrogen molecules and oxygen molecules generated on the surface of the photocatalyst, thereby increasing the rate of hydrogen generation (the rate of water circulation can be reduced when the rate of hydrogen generation is desired to be reduced). Water circulation between the water tank and the tank is usually performed using a pump, so the rate of water circulation may be adjusted by, specifically, adjusting the operating speed of the pump.

[0012] In yet another embodiment of the device of the present invention, since the amount of hydrogen generation increases or decreases in response to an increase or decrease in the amount of photocatalyst, the hydrogen generation amount adjusting means may be a means for controlling the amount of photocatalyst dispersed or placed in the water in the water tank. Here, the increase in the amount of photocatalyst may be carried out in any manner. When the photocatalyst is in the form of particles dispersed in water, the amount of photocatalyst particles dispersed in the water in the water tank may be increased. In an embodiment, the photocatalyst particles may be dispersed in water outside the water tank, and the water may be pumped into the water tank. For example, if a mechanism for replenishing water from a water storage tank is provided, a larger amount of photocatalyst particles than usual may be dispersed in the replenishing water, and the water may be supplied to the water tank via a pump or the like. Increasing the amount of photocatalyst in the water in the water tank increases the water decomposition reaction, thereby increasing the amount of hydrogen generation. On the other hand, the amount of photocatalyst can be reduced by using only water or water with a smaller amount of dispersed photocatalyst particles than usual as the replenished water, which makes it possible to reduce the amount of photocatalyst per unit amount of water in the water tank, and also makes it possible to control the amount of hydrogen generated to be reduced.

[0013] Furthermore, as already mentioned, since the amount of hydrogen generated increases as the water temperature in the water tank increases, the hydrogen generation amount adjusting means may be a means for controlling the water temperature in the water tank. If a heater is disposed in the water tank, the tank, or the water supply pipe between the water tank and the tank, the water temperature may be controlled by controlling the operation of the heater.

[0014] In the device of the present invention, the amount of hydrogen generated may be adjusted in any of the above-mentioned ways, and when any of these ways is feasible, the adjustment may be performed in the order of ease of adjustment. Specifically, for example, the adjustment may be performed in the order of irradiated light, water circulation amount, photocatalyst amount, and water temperature. [Effects of the Invention]

[0015] Thus, in the hydrogen gas production device of the present invention, the amount of hydrogen generated is detected and parameters for increasing or decreasing the amount of hydrogen generated are controlled so that the amount of hydrogen generated is the desired or appropriate amount, which is expected to make it possible to adjust the amount of hydrogen generated.

[0016] 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]

[0017] [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] FIG. 2 is a flowchart showing the process of adjusting the amount of irradiated light (current supplied to the light source device), the amount of circulating water (current supplied to the pump), or the temperature of water (current supplied to the heater) in order to adjust the amount of hydrogen generated in the hydrogen gas production device of this embodiment. [Figure 3] FIG. 2 is a flowchart showing the process of adjusting the amount of photocatalyst in water in order to adjust the amount of hydrogen generated in the hydrogen gas production device of this embodiment. [Explanation of symbols]

[0018] 1...hydrogen gas production device, 2...water tank section, 3...water, 3a...optical medium, 4...light source device, 5...light emitting element (LED), 6...power source, 7...current controller, 9...produced gas collection pipe, 10...water storage tank, 11...water supply pipe, 12...pump, 13...water circulation pipe, 15...water circulation controller, 16...pressure gauge, 17...tank water level gauge, 18...photocatalyst supply pipe, 18a...photocatalyst supply controller, 19...pure water supply pipe, 19a...pure water supply controller, 20...tank drain pipe, 20a...filter, 21...tank drain controller, 50...hydrogen generation amount controller (computer device) BEST MODE FOR CARRYING OUT THE INVENTION

[0019] Hydrogen gas production equipment configuration Referring to FIG. 1, in a hydrogen gas production apparatus 1 to which this embodiment is applied, water 3 containing a photocatalyst is stored in a water tank 2, which may be of any shape. A light-emitting element 5 supported by a light source device 4 emits excitation light that induces a water decomposition reaction on the photocatalyst 3a in the water 3. As a result, the water molecules are decomposed into hydrogen and oxygen in the photocatalyst 3a, producing hydrogen gas H2 and oxygen gas O2. 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). A pressure gauge 16 is provided in the collection pipe 9 to detect the pressure of the gas flowing therethrough. The pressure detected by the pressure gauge 16 may be used as an indicator of the amount of hydrogen gas H2 generated.

[0020] In the configuration of the hydrogen gas production device 1 described above, the photocatalyst 3a contained in the water 3 may be formed from any photocatalytic substance that can be used to produce hydrogen gas by a water-splitting reaction using light, as listed in the Summary of the Invention section, and may be particles dispersed in the water, or a member formed from the photocatalytic substance itself, or a photocatalytic substance fixed onto any substrate or base and placed at any position in the water, or both.

[0021] 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 induces a water decomposition reaction in the photocatalyst 3a used. The current supplied to the light-emitting element 5 of the light source device 4 is supplied from a power source 6 via a current controller 7 while its magnitude is controlled, thereby adjusting the amount of light irradiated onto the photocatalyst 3a in the water in the water tank section 2, and therefore the amount of hydrogen generated.

[0022] Furthermore, in the case of the hydrogen gas production device 1 of this embodiment, as shown in the figure, a water storage tank 10 for storing water is provided separately from the water tank section 2, and the water w stored in the water storage tank 10 is supplied into the water tank section 2 by a pump 12 through a water supply pipe 11, and the water 3 in the water tank section 2 can be sent to the water storage tank 10 through a water circulation pipe 13. A water circulation controller (valve) 15 for controlling the flow rate may be provided in the water circulation pipe 13. Photocatalysts (photocatalyst particles) may also be dispersed in the water w stored in the water storage tank 10, and the water may be circulated appropriately between the water tank section 2 and the water storage tank 10 together with the water.

[0023] Furthermore, the water storage tank 10 may be provided with a tank water level gauge 17 that detects the water level in the tank 10, a delivery pipe 18 that delivers photocatalyst PC to the water storage tank 10, a photocatalyst supply controller 18a that adjusts the amount of photocatalyst PC flowing therethrough, a pure water supply pipe 19 that supplies pure water to the water storage tank 10, a pure water supply controller 19a that controls the amount of water replenished flowing therethrough, a tank drain pipe 20 that drains water from the water storage tank 10, and a tank drain controller 21 that controls the amount of water drained from the tank drain pipe 20. The supply of the photocatalyst PC may be achieved by delivering photocatalyst particles dispersed in water to the delivery pipe 18. A filter 20a that does not allow the photocatalyst to pass through may be provided at the end of the tank drain pipe 20 on the tank 10 side, so that the water in the tank 10 can be drained through the tank drain pipe 20 as needed. These make it possible to adjust the water level (amount of water) in the water storage tank 10, the absolute amount of photocatalyst, and the amount of photocatalyst per amount of water.

[0024] A heater 23 for heating water may be provided at any location in the water passage that circulates between the water tank 2 and the water storage tank 10.

[0025] In the hydrogen gas production apparatus 1 to which the present embodiment is applied, the pump 12, water circulation controller (valve) 15, current controller 7, photocatalyst supply controller 18a, pure water replenishment controller 19a, tank drain controller 21, and heater 23 are controlled in accordance with control commands from a hydrogen generation amount controller 50. The hydrogen generation amount controller 50 may be a computer device that operates in accordance with a program, and is configured to control the amount of hydrogen generated by issuing control commands to the above-mentioned devices 12, 15, 7, 18a, 19a, 21, and 23 in any of the modes described below based on the value detected by the pressure gauge 16, which is an index value of the amount of hydrogen generated, or the amount of hydrogen generated estimated therefrom.

[0026] Operation of hydrogen gas production equipment As described in the Summary of the Invention section, in the hydrogen gas production device 1 of this embodiment, the amount of hydrogen generated in the water tank is controlled to a desired or appropriate value by controlling one or a combination of 1) the amount of light irradiated, 2) the amount of water circulating, 3) the amount of photocatalyst in the water, or 4) the water temperature, using a control command from the hydrogen generation amount controller 50 based on the index value of the current amount of hydrogen generated.

[0027] Specifically, 1) the intensity of the irradiated light, 2) the amount of water circulation, and 4) the water temperature are adjusted by controlling the current supplied to the light source device 4, the pump 12, and the heater 23, respectively, using the current controller 7. In each case, the amount of hydrogen generated increases as the supply current increases. Referring to FIG. 2 , in operation, a detection value P of the pressure gauge 16, which corresponds to the amount of hydrogen generated, is first acquired (step 1). If the detection value P exceeds an upper threshold value Po corresponding to the upper limit of the desired or appropriate amount of hydrogen generated (step 2), the supply current is reduced by an appropriately set value ΔI (step 3). On the other hand, if the detection value P is below the upper threshold value Po (step 2) and also below a lower threshold value Ps corresponding to the lower limit of the desired or appropriate amount of hydrogen generated (step 5), the supply current is increased by an appropriately set value ΔI (step 6). By adjusting the supply current in this way, the amount of hydrogen generated can be controlled within the desired or appropriate range. Then, when the amount A of produced hydrogen gas reaches the planned amount Ao, the production of hydrogen gas may be stopped (Step 4: the supply of current to the light source device 4 is stopped).

[0028] In the operation of controlling the amount of photocatalyst in water, referring to FIG. 3, when the value P detected by the pressure gauge 16 (step 1) exceeds the upper threshold value Po (step 2), the pure water supply controller 19a controls the supply of a suitable amount of water ΔW to the water storage tank 10 through the pure water supply pipe 19 (step 3a), thereby reducing the amount of photocatalyst per unit of water and the amount of hydrogen generated. On the other hand, when the detected value P is below the upper threshold value Po (step 2) and also below the lower threshold value Ps corresponding to the lower limit of the desired or appropriate amount of hydrogen generated (step 5), the photocatalyst supply controller 18a controls the supply of a suitable amount of photocatalyst ΔM to the water storage tank 10 through the photocatalyst delivery pipe 18 (step 6a), thereby increasing the amount of photocatalyst per unit of water and increasing the amount of hydrogen generated. By adjusting the amount of photocatalyst per unit of water, the amount of hydrogen generated can be controlled within the desired or appropriate range. Furthermore, when the water level Hw in the tank 10 detected by the tank water level gauge 17 exceeds an appropriately set predetermined value Ho due to the above-mentioned replenishment of pure water (step 7), the water in the tank 10 may be drained from the tank drain pipe 20 at an appropriately set amount ΔV under the control of the tank drainage controller 21 (step 9: in this case, the photocatalyst in the water may also be discharged).

[0029] Thus, with the above configuration, the amount of hydrogen generation can be adjusted by adjusting the irradiated light, the amount of circulating water, the amount of photocatalyst, or the water temperature. The adjustment of each of the above parameters may be performed simultaneously or in any order that may be determined. For example, if the adjustment of the amount of hydrogen generation is not sufficient after adjusting one parameter, another parameter may be adjusted. The order of adjustment may be, for example, in the order of ease of adjustment: adjusting the irradiated light, adjusting the amount of circulating water, adjusting the amount of photocatalyst, and adjusting the water temperature.

[0030] 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-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 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; a hydrogen generation amount detection means for detecting the amount of hydrogen gas generated; a hydrogen generation amount adjusting means for adjusting the amount of hydrogen gas generated based on the amount of hydrogen gas generated detected by the hydrogen generation amount detecting means; An apparatus comprising:

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