JP2024010762A - Hydrogen gas production equipment using photocatalyst - Google Patents

Abstract

[Problem] A device that produces hydrogen gas through a water decomposition reaction using a photocatalyst is configured to improve hydrogen gas production efficiency and energy efficiency by arranging a light source device in water to heat the water. In the device, total reflection of light beams at the interface between the light-transmitting surface and the water layer is avoided, and the efficiency of using energy contributing to the generation of hydrogen gas is improved. SOLUTION: A hydrogen gas production device 1 includes a container portion 2 that receives water W, and a light source device 3 that is placed in the water and emits light toward the water that causes a water decomposition reaction. , the light transmitting surface 6 through which the light of the light source device passes has a refractive index higher than the refractive index of the light transmitting surface, and when irradiated with light, excited electrons and holes are generated, and water is converted into hydrogen. A photocatalytic layer 7 made of a photocatalytic material that causes a decomposition reaction of water to decompose into oxygen and generates hydrogen gas is coated, and the photocatalytic layer is in contact with water. [Selection diagram] Figure 1

Description

The present invention relates to an apparatus for producing hydrogen gas, and more particularly to an apparatus for producing hydrogen gas through a water decomposition reaction using a photocatalyst.

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 using a photocatalyst. Various manufacturing techniques have been proposed. For example, Patent Document 1 proposes a structure of a hydrogen generation device in which water in which photocatalyst particles are dispersed is circulated in a housing having a light receiving window to cause a water decomposition reaction by light to generate hydrogen gas. There is. Patent Document 2 by the applicant of the present application discloses a photocatalyst supporting a photocatalyst that generates excited electrons and holes when irradiated with light, causes a water decomposition reaction to decompose water into hydrogen and oxygen, and generates hydrogen gas. In a device in which a member is placed so as to be immersed in water in a container, and light is irradiated from a light source to the photocatalyst member, the water in the container that will be decomposed in the photocatalyst member is removed by the exhaust heat of the light source. The proposal is to improve the production efficiency of hydrogen gas by heating the water to raise its temperature.

JP2015-218103 JP2022-63186

T. Takata, 8 others Nature, volume 581, pages 411-414 2020

As described in Patent Document 2, when exhaust heat from a light source is used to heat water to increase hydrogen gas production efficiency, the energy use efficiency related to hydrogen gas production is also improved. As one such configuration, a configuration in which the light source device is placed in water and the water is brought into direct contact with the outer surface of the light source device can be considered. In the case of such a configuration, where it is intended to transmit light from the outer surface of the light source device to the water layer, the refractive index of the outer surface (light transmitting surface) of the portion of the light source device through which the light passes is equal to the refractive index of the water. When the angle of incidence is higher than the critical angle at the interface between the light-transmitting surface and the water layer, the light rays whose incident angle exceeds the critical angle will not be transmitted to the water layer due to total internal reflection and will not contribute to the generation of hydrogen gas, resulting in a loss of energy. Utilization efficiency will decrease. In this regard, in order to avoid total reflection at the interface between the light-transmitting surface and the water layer, it is sufficient to make the refractive index of the light-transmitting surface lower than that of water, but the light-transmitting surface is generally a transparent, hard, Since it is made of materials such as silicone resin, epoxy resin, and glass, its refractive index is higher than that of water. Therefore, a novel configuration is required to avoid total internal reflection at the interface between the light-transmitting surface and the water layer.

Thus, the object of the present invention is to provide a device for producing hydrogen gas through a water decomposition reaction using a photocatalyst, and to improve hydrogen gas production efficiency and energy efficiency by arranging a light source device in water to heat the water. In a device configured to do so, total reflection of light beams at the interface between the light-transmitting surface and the water layer is avoided, and the efficiency of using energy contributing to the generation of hydrogen gas is improved.

According to one aspect of the present invention, the above problem is solved by a hydrogen gas production apparatus, comprising:
a container portion that receives water;
a light source device that is disposed in the water in the container and emits light toward the water that causes a decomposition reaction of the water;
The light transmitting surface of the light source device has a refractive index higher than the refractive index of the light transmitting surface, and when irradiated with light, excited electrons and holes are generated, and water is converted into hydrogen and oxygen. This is achieved by a device coated with a photocatalytic layer made of a photocatalytic material that causes a decomposition reaction of water to generate hydrogen gas, and in which the photocatalytic layer is in contact with the water.

In the above configuration, when the "photocatalytic material" is irradiated with light (typically, light with a wavelength of 365 nm or less), it causes a water decomposition reaction and reduces water. It is a substance capable of generating hydrogen gas, and specifically may be a photocatalytic material available in this field, such as strontium titanate. The "light source device" may be of any type that receives electricity and emits light that is absorbed by a photocatalyst material and causes a water decomposition reaction.The light source may be an LED, an organic EL, or an incandescent lamp. , a xenon lamp, etc. In a light source device, the light source is supported on a substrate, the outer periphery of which is covered with a sealing material or a mantle member, and the whole device is placed in water in a waterproof state. The portion of the device through which the light rays from the light source pass, ie, the light-transmitting surface, is made of a transparent, hard material such as silicone resin, epoxy resin, or glass. Further, the substrate supporting the light source is preferably formed of a material with high thermal conductivity, and typically may be formed of a metal material such as aluminum, a glass epoxy resin, or the like. In particular, in the configuration of the present invention, the light-transmitting surface is coated with a photocatalyst layer made of the above-mentioned photocatalyst material.

As described above, according to the configuration in which the light transmitting surface of the light source device is covered with a photocatalyst layer made of a photocatalyst material, the refractive index (1.4 to 1.6 Since the refractive index of the photocatalytic material (for example, 2.4) is higher than the refractive index of the photocatalytic material (2.4), when the light rays from the light source reach the light-transmitting surface, they enter the photocatalytic layer without being totally reflected there. , the photocatalytic material is excited to generate excited electrons and holes. Since the photocatalytic layer is in contact with water, excited electrons and holes generated therein react with water, resulting in a water decomposition reaction. Here, the waste heat from the light source is conducted to the water and the water is heated, increasing the production efficiency of hydrogen gas and allowing the light that reaches the light-transmitting surface to reach the photocatalyst without being totally reflected. Since the light is irradiated, the light energy contributing to the production of hydrogen gas increases, and the efficiency of energy use is also improved.

In the above configuration, coating the light-transmitting surface with the photocatalyst layer can be achieved in any manner. For example, by applying a solution of a powdered photocatalytic material dispersed in an organic solvent to a light-transmitting surface and drying it, the photocatalytic material is adsorbed onto the light-transmitting surface, and the light-transmitting surface is coated with the powder of the photocatalytic material. The Rukoto. Alternatively, a photocatalytic layer may be formed by dispersing a powdered photocatalytic material in any transparent resin solution, applying such resin solution onto a light-transmitting surface, and curing the resin. Note that photocatalyst materials are generally used by adding a co-catalyst to semiconductor particles that generate excited electrons and holes when irradiated with light, and which receive the excited electrons and holes and react with water (for example, (See Patent Document 1). Therefore, the photocatalyst material used in the photocatalyst layer may be one in which a co-catalyst is added to semiconductor particles. Alternatively, after forming a layer of semiconductor particles on a light-transmitting surface, a layer of a cocatalyst may be formed on the layer of semiconductor particles.

Thus, in the present invention described above, in producing hydrogen gas by a water decomposition reaction using a photocatalyst, the light source device is submerged in water, and the waste heat of the light source is released into the water to raise the temperature of the water. In a configuration that aims to improve photocatalytic efficiency, the light transmitting surface of the light source device is coated with a photocatalyst layer having a higher refractive index than that of the light transmitting surface, so that the light rays from the light source are totally reflected on the light transmitting surface. This increases the amount of light irradiated onto the photocatalyst. According to such a configuration, the amount of light confined within the light source device is reduced and the light energy that contributes to the generation of hydrogen gas in the photocatalyst layer is increased, so it is expected that the efficiency of energy use will be improved. Further, in the case of an embodiment in which the light source of the device of the present invention is operated with electric power derived from solar energy, it becomes possible to efficiently obtain hydrogen energy without emitting carbon dioxide.

Other objects and advantages of the invention will become apparent from the following description of preferred embodiments of the invention.

FIG. 1(A) is a schematic diagram of a hydrogen gas production apparatus according to this embodiment, and FIGS. 1(B) and (C) are schematic side sectional views of the light source device. FIG. 2A is a diagram schematically showing the course of light rays near the light transmitting surface of the light source device according to this embodiment. FIG. 2B is a diagram schematically showing the course of light rays near the light transmitting surface of the light source device when this embodiment is not applied. FIG. 3 is a diagram showing the range of light rays emitted from a light source, and explains the range of light rays that would be totally reflected on a light-transmitting surface when this embodiment was not applied.

1...Hydrogen gas production device 2...Container part 3...Light source device 4...Light source 5...Substrate 6...Printed circuit board 7...Photocatalyst layer 7a...Photocatalyst (semiconductor particle) layer 7b...Promoter layer W...Water L...Light ray

Configuration of Hydrogen Gas Production Apparatus Referring to FIG. , has a light source device 3 that is disposed underwater in a container section 2 and emits light, and an air supply pipe 2a that sends generated hydrogen gas and oxygen gas to a separator. Referring to FIG. 1(B), in detail, the light source device 3 includes a light source 4 that emits light placed on a substrate 5, and the periphery of the light source 4 is covered with a translucent sealing material or a mantle member 6. Furthermore, the outer surface of the translucent sealing material or mantle member 6 is coated with a photocatalyst layer 7 made of a photocatalyst material.

In the above configuration, the light source 4 may be any light emitting body that emits light that is absorbed by a photocatalyst substance and causes a water decomposition reaction, which will be described in detail later. Since the light absorption rate and quantum yield of the photocatalytic material have wavelength characteristics that increase when irradiated with light on the shorter wavelength side than a certain wavelength, the light source 4 is capable of controlling the light absorption rate and quantum yield of the photocatalytic material. A light-emitting element or emitter is selected that emits light in a wavelength band in which the wavelength increases. Specifically, as a light emitting element or light emitter, indium gallium nitride (InGaN), diamond (ultraviolet), gallium nitride (GaN)/aluminum gallium nitride (AlGaN) (ultraviolet, blue), zinc selenide (blue), oxide Various light emitting diodes (LEDs) using zinc (near ultraviolet, violet, blue) or the like may be employed. Note that the light source 4 may be an organic EL, an incandescent lamp, a xenon lamp, a mercury lamp, or the like, as long as it can be placed underwater. For example, when SrTiO ₃ is used as a photocatalyst material, the absorbance and quantum yield increase when the wavelength of the irradiated light is less than 380 nm, so InGaN-based materials having an emission wavelength peak between 360 and 370 nm are used. can be advantageously used as the light emitter of the light source device 4. The substrate 5 supporting the light source 4 may be made of any material used in this field. In particular, a highly thermally conductive metal material, glass epoxy resin, ceramic, or the like may be used to facilitate the conduction of waste heat 4 from the light source to water.

The sealing material or mantle member 6 that covers the light source 4 in the light source device 3 may be any material that is used to seal a hard light source. Specifically, the material of the sealing material or the mantle member 6 may be silicone resin, epoxy resin, glass, quartz glass, or the like.

As described above, when the outer surface of the sealing material or the mantle member 6 is irradiated with light, it absorbs photons and generates excited electrons and holes, causing a water decomposition reaction. A layer of photocatalytic material (photocatalytic layer) 7 capable of reducing water and generating hydrogen gas is coated. Examples of photocatalytic substances include SrTiO ₃ (strontium titanate), La ₂ Ti ₂ O ₇ (lanthanum titanate), Ga ₂ O ₃ (gallium oxide), GaN (gallium nitride), NaTaO ₃ (sodium tantalate), TiO ₂ (titanium oxide), gallium carbide, cerium carbide, etc. can be used. Typically, these photocatalytic materials are prepared by adding a co-catalyst (Rh (rhodium), Cr (chromium), Co (cobalt), etc.) to the surface of semiconductor particles produced in powder form. (For example, see Non-Patent Document 1). Further, according to the research conducted by the inventors of the present invention, it has been found that such a photocatalytic substance has the property of being adsorbed and fixed to the surface of the above-mentioned sealing material or mantle member 6. . Therefore, the photocatalytic layer 7 is formed by dispersing a particulate photocatalytic substance in an organic solvent or the like, applying the solution to the surface of the sealing material or the mantle member 6, and drying it to remove the solvent. Is possible. Alternatively, a photocatalyst substance dispersed in any resin (preferably one with a higher refractive index than that of the encapsulant or mantle member 6) may be applied to the surface of the encapsulant or mantle member 6 and cured. Then, the photocatalyst layer 7 may be formed. As shown in FIG. 1(C), a layer 7a of semiconductor particles serving as a photocatalyst substance is formed on the surface of the sealing material or mantle member 6, and a layer 7b of a promoter is further formed thereon. You can. For adding the co-catalyst to the semiconductor particles, for example, a photoelectrodeposition method as described in Non-Patent Document 1 may be used. Further, the photocatalytic substance may be dispersed in water, so that it can be excited by light beams that have passed through the water, causing a water decomposition reaction and generating hydrogen gas.

The water stored in the container section 2 is preferably ultrapure water from which impurities have been removed as much as possible in order to prevent excited electrons and holes generated in the photocatalyst material from reacting with substances other than water molecules.

Path of light rays on a light transmitting surface Referring first to FIG. When there is no photocatalyst layer on the surface (light-transmitting surface) and the light-transmitting surface is in direct contact with the water layer, the refractive index ne (1.5 ~1.6) is larger than the refractive index of water nw (1.33), so at the interface between the light-transmitting surface and the water layer, the light ray L whose incident angle θ is greater than the critical angle is totally reflected. However, it does not enter the water layer, is confined inside the light-transmitting surface, and does not contribute to the generation of hydrogen gas. That is, in the case of the configuration shown in FIG. 2(B), a large amount of optical energy is lost without contributing to the generation of hydrogen gas.

Therefore, in this embodiment, the light transmitting surface is covered with the photocatalyst layer 7 as explained in FIG. Then, the refractive index nc of the material used for the photocatalyst layer 7 is, for example, about 2.4 (in the case of strontium titanate), which is usually higher than the refractive index ne inside the light-transmitting surface. ), the light beam L from the light source 4 is refracted toward the photocatalyst layer 7 at the interface between the light-transmitting surface and the photocatalyst layer 7, and is not totally reflected, so that the amount of light transmitted to the photocatalyst layer 7 increases. Since the photocatalytic layer 7 is in direct contact with the water layer W, the excited electrons and holes generated by the irradiation of the light beam L in the photocatalytic layer 7 react with water molecules, resulting in hydrogen gas and oxygen gas. However, since the amount of light that has entered the photocatalyst layer 7 has increased as described above, it is expected that more hydrogen gas will be generated. That is, according to the configuration of this embodiment, an increase in the proportion of energy contributing to the generation of hydrogen gas in the light energy emitted by the light source 4 is expected. Specifically, with reference to FIG. 3, for example, when the directivity angle θd of the light beam emitted from the light source 4 is 120°, when the water layer is in contact with the light transmission surface, the critical angle θc is about 55°, so the light rays in the range of θe (=θd-θc-90°) cannot enter the water layer due to total reflection, but in the case of this embodiment, the totally reflected light rays It is found that it enters the photocatalyst layer 7 and contributes to the generation of hydrogen gas, improving the energy use efficiency by about 10%.

Thus, in this embodiment, the light source device is submerged in water, and the exhaust heat of the light source is released into the water to raise the temperature of the water and improve the photocatalytic efficiency. By coating the light-transmitting surface of the light source device with a photocatalyst layer with a higher refractive index, the amount of light irradiated to the photocatalyst is increased by avoiding total reflection of the light rays from the light source on the light-transmitting surface. However, the light energy that contributes to the generation of hydrogen gas is increased.

Although the above description has been made in connection with the embodiments of the present invention, many modifications and changes are easily possible to those skilled in the art, and the present invention is limited to the embodiments illustrated above. It will be obvious that the present invention is not limiting and may be applied to a variety of devices without departing from the inventive concept.

Claims (1)

A hydrogen gas production device,
a container portion that receives water;
a light source device that is disposed in the water in the container and emits light toward the water that causes a decomposition reaction of the water;
The light transmitting surface of the light source device has a refractive index higher than the refractive index of the light transmitting surface, and when irradiated with light, excited electrons and holes are generated, and water is converted into hydrogen and oxygen. A device coated with a photocatalytic layer made of a photocatalytic material that causes a decomposition reaction of water to generate hydrogen gas, and the photocatalytic layer is in contact with the water.

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