Hydrogen production device using a photocatalyst

Abstract

The present invention provides a hydrogen production device using a photocatalyst. In the device for producing hydrogen by a water decomposition reaction using a photocatalyst, water is heated by exhaust heat from a light source in order to improve the production efficiency of hydrogen. The hydrogen production device (1) includes: a container portion for accommodating water; a photocatalyst body, which is a photocatalyst body dispersed or arranged in the water in the container portion and has a photocatalyst substance. When irradiated with light, the photocatalyst substance generates excited electrons and holes, and causes a water decomposition reaction that decomposes water into hydrogen and oxygen, thereby producing hydrogen; a light source, which emits light that irradiates the photocatalyst body to cause the water decomposition reaction; and a frame that supports the light source. The frame is arranged in the water in the container portion. The water is heated by exhaust heat from the light source emitted from the surface of the frame. In addition, the surface of the frame that contacts the water is covered with the photocatalyst substance.

Description

Technical Field

[0001] The present invention relates to a hydrogen production device, and more particularly, to a device for producing hydrogen by a water decomposition reaction using a photocatalyst. Background Art

[0002] Hydrogen is expected to be used as a clean, next-generation fuel that does not produce carbon dioxide even when burned. Since hydrogen can be produced by a water decomposition reaction generated by light energy using a photocatalyst, various hydrogen production technologies using photocatalysts have been proposed. For example, Patent Documents 1 and 2 disclose photocatalysts and their modulation methods that produce hydrogen by causing a water decomposition reaction by irradiation with ultraviolet light or visible light. Patent Document 3 discloses the structure of a hydrogen production device, which includes a water oxidation reaction unit using a photocatalyst from ultraviolet light to visible light in sunlight and a water reduction reaction unit using heat from visible light to infrared light in sunlight. Patent Document 4 proposes a structure of a hydrogen production device that circulates water with dispersed photocatalyst particles in a frame with a light-receiving window and causes a water decomposition reaction caused by light to produce hydrogen. Patent Document 5 proposes a structure of a hydrogen production system that irradiates a receiver having an electrode 21 composed of a photocatalyst placed in water with light concentrated by a sunlight concentrator, thereby exciting the valence electrons in the photocatalyst to perform electrolysis of the surrounding water and continuously produce hydrogen. In addition, although it is not a technology for producing hydrogen, the following technology is disclosed in Patent Document 6, namely, a plate-like carbon material composed of a carbon allotrope with an sp3 crystal structure is immersed in water in a solvent in which carbon dioxide is dissolved, and the temperature of the solvent is increased by a heater while irradiating the solvent with ultraviolet light, so that the C=O bond of the carbon dioxide is cut due to the excitation of the carbon material, and methane is generated together with carbon monoxide.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 9-510657

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2003-251197

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 2013-234077

[0008] Patent Document 4: Japanese Patent Application Laid-Open No. 2015-218103

[0009] Patent Document 5: Japanese Patent Application Laid-Open No. 2017-24956

[0010] Patent Document 6: Japanese Patent Application Laid-Open No. 2016-108181

[0011] Non-patent literature

[0012] Non-Patent Document 1: “Photocatalytic water splitting with a quantum efficiency of almost unity” Tsuyoshi Takata, Junzhe Jiang, Yoshihisa Sakata, Mamiko Nakabayashi, Naoya Shibata, Vikas Nandal, Kazuhiko Seki, Takashi Hisatomi & Kazunari Domen, Nature, Vol. 581, pp. 411-414 (2020) Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, further research by the inventors of the present invention has revealed that the efficiency of hydrogen production increases when the temperature of the water used as a reactant increases. Therefore, heating the water is effective in increasing the efficiency of hydrogen production. In this case, a heater that supplies energy from an external source is not used. By utilizing the exhaust heat of the light source that generates light irradiating the photocatalyst, or more specifically, by adopting a structure that not only radiates heat from the light source to the water but also transfers the exhaust heat of the light source directly to the water, the efficiency of energy utilization related to hydrogen production can be further improved. One such structure is to place the frame supporting the light source itself in water, thereby directly contacting the water with the surface of the heat-generating light source device. Regarding this point, the inventors of the present invention have conducted research and observed that when the surface of the light source frame is formed of a material such as metal to improve heat transfer efficiency, the metal material on the frame surface dissolves in the water, causing the frame surface to degrade. Therefore, in a structure where the frame supporting the light source is placed in water, it is preferable to suppress degradation of the frame surface while minimizing the reduction in heat transfer efficiency. Furthermore, it is advantageous to use a structure that increases the amount of photoreaction in the water.

[0015] Therefore, a main object of the present invention is to provide a structure for heating water using exhaust heat from a light source in order to improve hydrogen production efficiency in an apparatus for producing hydrogen by a water decomposition reaction using a photocatalyst.

[0016] Another object of the present invention is to provide a device as described above, which is a device capable of increasing the amount of photoreaction of water while suppressing deterioration of the surface of the housing in a structure where a light source and a housing supporting the light source are submerged in water.

[0017] Means for solving problems

[0018] According to one embodiment of the present invention, the above-mentioned problem is achieved by the following hydrogen production device, which includes: a container part, which contains water; a photocatalyst body, which is a photocatalyst body dispersed or arranged in the water in the container part and has a photocatalyst substance, and the photocatalyst substance generates excited electrons and holes when irradiated with light, and causes a water decomposition reaction that decomposes water into hydrogen and oxygen to produce hydrogen; a light source, which emits light that irradiates the photocatalyst body to cause the decomposition reaction of the water; a frame, which carries the light source, and the frame is arranged in the water in the container part, the water is heated by the exhaust heat of the light source emitted from the surface of the frame, and the surface of the frame in contact with the water is covered with the photocatalyst substance.

[0019] In the above structure, the "photocatalyst substance" can be a substance that can cause a decomposition reaction of water and reduce water to produce hydrogen when irradiated with light, as described above. The "photocatalyst body" can be particles composed of the photocatalyst substance and dispersed in water, or a component formed by the photocatalyst substance itself or a photocatalyst substance fixed on an arbitrary substrate or matrix and arranged at an arbitrary position in the water, or both (hereinafter, in this specification, when it is referred to as "photocatalyst", it refers to the photocatalyst substance). The "light source" can typically also be a light source of any form that receives a supply of electricity and emits light that is absorbed by the photocatalyst to cause a decomposition reaction of water, and is carried on a frame and is set to be waterproof, and is arranged in water together with the frame. The frame is preferably formed of a material with high thermal conductivity, and typically, it can also be formed of a metal material such as aluminum.

[0020] In order for the light irradiated to the photocatalyst to be effectively absorbed by the photocatalyst to generate excited electrons and holes, it is preferred that the emission wavelength of the light source be selected to fall within a wavelength band where the quantum yield of the photocatalyst exceeds a predetermined threshold value (which can be arbitrarily selected). In this regard, as illustrated in the specific embodiment section below, the quantum yield of a typical photocatalyst increases sharply when the wavelength of the irradiated light is lower than a certain wavelength. Therefore, the light source is selected in such a way that the emission wavelength of the light source is closer to the shorter wavelength side than the wavelength at which such a sharp increase in the quantum yield of the photocatalyst occurs. As photocatalysts that can be used in the present invention, for example, SrTiO3 (strontium titanate), La2Ti2O7 (lanthanum titanate), Ga2O3 (gallium oxide), GaN (gallium nitride), NaTaO3 (sodium tantalate), TiO2 (titanium oxide), etc. can be used. Such photocatalysts can also be used with the addition of a co-catalyst as appropriate. On the other hand, various light-emitting diodes (LEDs) can be used as light sources. 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, and blue) can be used.

[0021] Furthermore, in the device structure of the present invention, the surface of the frame that comes into contact with water is covered with a photocatalytic material. The photocatalytic material covering the frame surface can be the same as the photocatalyst or a different photocatalytic material. This prevents the surface of the metal material, etc., that constitutes the frame from coming into direct contact with water.

[0022] In the structure of the device of the present invention described above, in a device that irradiates light on a photocatalyst body that contacts water and causes a decomposition reaction of water to produce hydrogen, the following structure is provided, namely, the light source carried by the frame is submerged in water, thereby heating the water by the heat dissipation of the light source. According to the structure involved, the efficiency of hydrogen production is improved by heating the water as a reactant. In addition, since the heating of the water is achieved by utilizing the heat dissipation of the light source, there is no need to separately provide a heater for heating the water, thereby eliminating the need to separately supply energy for heating the water, thereby achieving high efficiency of the energy required for hydrogen production. Moreover, in the case of the present invention, the surface of the frame submerged in water is covered with a photocatalytic substance, thereby, when the frame is formed of a metal material, etc., it is possible to prevent the metal on the surface of the frame from directly contacting the water, and to prevent the metal on the surface of the frame from dissolving, thereby suppressing the degradation of the surface of the frame. In this regard, light emitted from a light source in water is subject to various scattering events (Rayleigh scattering, Raman scattering, etc.), or is reflected by the inner wall of the container or the water surface, thereby propagating in various directions within the water. Therefore, the scattered or reflected light is absorbed by the photocatalyst on the surface of the light source's housing, causing a water decomposition reaction on the housing surface. This is expected to further improve the efficiency of hydrogen production. Furthermore, according to the above-described structure, since the light source is arranged within the container portion and the structure outside the container portion is simplified, the space required for the device configuration can be made compact. On the other hand, it is also easy to increase the size of the container portion and proportionally scale up the device.

[0023] In the above-mentioned device of the present invention, a structure in which the light emitted from the light source also irradiates the photocatalyst material covering the surface of the frame can be set in an arbitrary manner. For example, the device of the present invention can also be constructed so that a plurality of light sources and a frame supporting the light sources are arranged in water in a container portion, and the light emitted from one light source also irradiates the photocatalyst material covering the surface of the frame of the other light sources. In addition, in other embodiments, the device of the present invention can be constructed so that the light emitted from the light source is enclosed in the container portion, so that, for example, the container portion can also have a light reflecting mechanism, and the light reflecting mechanism is provided with a light reflecting plate or the like on its inner side, thereby enclosing the light emitted from the light source in the container. According to these structures, as much light as possible emitted from the light source is irradiated onto the photocatalyst, thereby contributing to the production of hydrogen.

[0024] In addition, according to the research of the inventors of the present invention, as described in detail in the specific embodiment section below, it was found that if the light density irradiated to the photocatalyst is increased, the hydrogen production efficiency (the amount of hydrogen produced per the amount of incident light) will decrease. It can be considered that this is because even if the density of excited electrons and holes generated by the photocatalyst increases by increasing the light intensity, the speed of the decomposition reaction between the excited electrons and holes and water is slow, and the excited electrons and holes recombine and disappear before reacting with water respectively. Therefore, the energy is not effectively used in the production of hydrogen. Therefore, it is preferred that the density of light emitted from the light source is adjusted to an appropriate value that is balanced with the reduction in the hydrogen production efficiency. Therefore, in the above-mentioned device of the present invention, the density of light irradiated to the photocatalyst body can be adjusted to provide a photocatalytic efficiency (the ratio of the amount of hydrogen produced to the amount of photons incident on the photocatalyst substance) greater than a predetermined value or a density lower than it. Specifically, for example, it was found based on experiments that the density of light irradiated to the photocatalyst body is preferably 0.1W / cm 2 Therefore, it is preferable to set the output P of the light source / irradiation area A to be ≤ 0.1 W / cm 2 The relationship between the output P of the light source and the irradiation area A is adjusted in a suitable manner.

[0025] In the device of the present invention described above, the light source can be configured to operate using electricity generated from solar power generation, emitting light directed toward the photocatalyst, and the exhaust heat from the light source during operation can be transferred from the frame to water. Thus, hydrogen production is achieved using renewable energy. Furthermore, if the light source is operated using electricity derived from sunlight rather than irradiating the photocatalyst, it is possible to concentrate a thinner amount of solar energy per unit area and supply the light energy to the photocatalyst, thereby miniaturizing the device.

[0026] Furthermore, when operating a light source using electricity, it is preferable to maximize its luminous efficiency. Therefore, when operating a light source using electricity generated by solar power generation, the rated output of the light source can be adjusted so that the luminous efficiency is maximized when the rated current of the solar power generation is supplied to the light source. This allows for more efficient use of solar energy in hydrogen production. Furthermore, in the case of solar power generation, the output fluctuates depending on sunlight conditions, and the available current can fluctuate moment by moment. In this case, the light source is operated to maximize its luminous efficiency at that time, thereby achieving better energy efficiency in hydrogen production. In this regard, a plurality of LEDs can be used as the light source. In this case, the luminous efficiency of each LED varies depending on the current supplied. Therefore, the light source can be configured so that the number of operating LEDs is adjusted according to the output current of the solar power generation to maximize the luminous efficiency of the light source. This is expected to enable more efficient conversion of solar energy into light from the light source for use in hydrogen production.

[0027] Effects of the Invention

[0028] Therefore, according to the present invention described above, when the temperature of the water used as a reactant is raised to improve the efficiency of the photocatalyst during hydrogen production through a water decomposition reaction using a photocatalyst, the water temperature is raised by submerging the light source and the housing together in water, thereby releasing the exhaust heat of the light source from the housing into the water. Furthermore, since the surface of the housing is covered with a photocatalytic substance, degradation of the housing surface due to water is prevented. Furthermore, light emitted from the light source, which travels in various directions due to scattering or reflection in water, is irradiated onto the photocatalyst on the housing surface, thereby contributing to hydrogen production and achieving energy efficiency. Furthermore, when the metal surface of the housing directly contacts water, causing metal material to dissolve in the water, the dissolved metal ions react with excited electrons or holes generated by the photocatalytic substance in the water, potentially reducing hydrogen production efficiency. However, in the present invention, since the dissolution of the metal material on the housing surface into the water is prevented, the reduction in hydrogen production efficiency caused by metal ions in the water can be suppressed. Furthermore, by heating the water using the exhaust heat of the light source, the water temperature can be reliably raised compared to heating the water using radiant heat from the light source, thereby expected to improve the efficiency of the photocatalyst. Furthermore, by utilizing solar-derived electricity to operate the light source of the device of the present invention, hydrogen energy can be efficiently obtained without emitting carbon dioxide.

[0029] Other objects and advantages of the present invention will become more apparent from the following description of preferred embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1(A) is a schematic diagram of one form of a hydrogen production apparatus according to the present embodiment, and FIG1(B) is a schematic side view of its light source device.

[0031] Figure 2 This is a diagram showing an example of the wavelength characteristics of the absorbance and quantum yield of a typical photocatalyst (SrTiO3) used in the hydrogen production device of this embodiment (cited from non-patent document 1), and the emission wavelength characteristics of the light source (InGaN-type LED) (measured by the inventor of the present invention).

[0032] Figure 3(A) is a graph showing experimentally obtained changes in photocatalytic efficiency relative to temperature in water contacted by the photocatalyst. Figure 3(B) is a graph showing changes in photocatalytic efficiency relative to the density (light intensity) of light irradiating the photocatalyst. The data were obtained through experiments conducted by the inventors of the present invention.

[0033] Figure 4 This is a schematic diagram of another form of the hydrogen production apparatus according to this embodiment.

[0034] FIG5(A) is a schematic diagram of another embodiment of the hydrogen production device, and FIG5(B) is a schematic side view of the light source device.

[0035] Figure 6(A) is a graph showing experimentally obtained variations in luminous efficiency versus current supplied to a light source in which four LEDs are connected in parallel to a power supply. Figure 6(B) is a graph showing variations in luminous efficiency versus current supplied to a light source in which one LED is connected in parallel to a power supply. The data were obtained through experiments conducted by the inventors of the present invention.

[0036] Figure 7(A) to Figure 7(C) This diagram schematically shows a circuit configuration of a light source capable of changing the number of operating LEDs according to the amount of generated current of a solar panel.

[0037] Explanation of symbols

[0038] 1.1a…Hydrogen production device;

[0039] 2…Container;

[0040] 3…photocatalyst body;

[0041] 4…light source device;

[0042] 5...LED;

[0043] 6...Printed substrate;

[0044] 7…thermal conductive sheet;

[0045] 8…frame;

[0046] 9…transparent plate;

[0047] 10…reflector;

[0048] 11…power lines;

[0049] 12…photocatalyst coating;

[0050] 15…Solar panels;

[0051] 16…power supply line;

[0052] W…water;

[0053] L…light. DETAILED DESCRIPTION

[0054] Structure of hydrogen production equipment

[0055] 1(A), the hydrogen manufacturing device 1 of this embodiment has, in one mode: a container portion 2 of any shape, which contains water (liquid) W; a granular photocatalyst body 3, which is composed of a photocatalyst substance dispersed in the water in the container portion 2; a light source device 4, which emits light to irradiate the photocatalyst body 3; and an air supply pipe 2a, which transports the generated hydrogen and oxygen to the separator.

[0056] In the structure of the above-mentioned hydrogen manufacturing device 1, the photocatalyst body 3 is a particle composed of a photocatalyst substance, which can be dispersed in water, wherein the photocatalyst substance absorbs photons to generate excited electrons and holes when irradiated with light, and causes a decomposition reaction of water to reduce the water, thereby generating hydrogen. As the photocatalyst substance used in this embodiment, a substance used in this field that can generate hydrogen from water by irradiation with light can be used. Specifically, for example, SrTiO3 (strontium titanate), La2Ti2O7 (lanthanum titanate), Ga2O3 (gallium oxide), GaN (gallium nitride), NaTaO3 (sodium tantalate), TiO2 (titanium oxide), etc. can be used. Typically, as Figure 2As shown, the photocatalytic material exhibits wavelength characteristics in which the absorbance and quantum yield increase sharply around a certain wavelength when the wavelength of the irradiated light is changed from the long wavelength side to the short wavelength side (in the wavelength band where the absorbance and quantum yield increase, the amount of excited electrons and holes generated by the absorption of photons increases). When the granular photocatalyst body 3 is prepared using the above-mentioned photocatalyst material, the raw materials constituting the composition of the photocatalyst material are mixed and calcined to form semiconductor particles composed of the photocatalyst material. These particles can be dispersed in water as the photocatalyst body 3. In addition, the semiconductor particles composed of the above-mentioned photocatalyst material can be used as they are as the photocatalyst body 3, or a material with a catalyst promoter added to the surface of the particles to enhance the catalytic ability can be used.

[0057] The light source device 4 may be any light source that emits light of a wavelength that is absorbed by the photocatalytic material of the photocatalytic body 3 and generates excited electrons and holes. Figure 2 In that way, since the absorbance and quantum yield of the photocatalytic substance have a wavelength characteristic that increases when irradiated with light having a shorter wavelength than a certain wavelength, a light-emitting element or light-emitting body that generates light in a wavelength band in which the absorbance and quantum yield of the photocatalytic substance of the photocatalyst body 3 increase is selected in the light source device 4. Specifically, various light-emitting diodes (LEDs) using indium gallium nitride (InGaN), diamond (ultraviolet), gallium nitride (GaN) / aluminum gallium nitride (AlGaN) (ultraviolet, blue), zinc selenide (blue), zinc oxide (near ultraviolet, purple, blue), etc. can be used as the light-emitting element or light-emitting body of the light source. For example, in Figure 2 When SrTiO3 is used as a photocatalyst, the absorbance and quantum yield increase when the wavelength of the irradiated light is lower than 380nm. Therefore, an InGaN-type LED having a peak emission wavelength in the range of 360 to 370nm can be advantageously used as a light-emitting body of the light source device 4.

[0058] In the structure of the light source device 4, for example, as schematically depicted in FIG1(B), the light source 5, which may be an LED, may be placed on a printed circuit board 6, with a heat conductive sheet laid thereunder, and placed in a recessed structure of a frame 8. The frame 8 may be formed of any material such as a metal with high thermal conductivity, such as aluminum. Furthermore, the opening portion of the recessed structure of the frame 8 on which the light source 5 is placed is sealed or sealed by a transparent plate 9 made of translucent glass, quartz glass, resin, or the like, whereby, when the light source 5 is sealed from the outside, light from the light source 5 is radiated from the transparent plate 9. In addition, preferably, the inner wall of the recessed structure of the frame 8 is formed as a reflective plate 10, so that the light from the light source 5 is effectively radiated from the transparent plate 9 to the outside. The power supply to the light source 5 may also be implemented by a power line 11 passing through the frame 8 in a sealed state.

[0059] Furthermore, as shown in Figure 1(A), the aforementioned light source device 4 is placed in water W within container portion 2. Exhaust heat from the light source is transferred to the water via frame 8, thereby warming the water and improving the efficiency of hydrogen production. Regarding this point, as mentioned in the "Summary of the Invention" section, the inventors' research has shown that increasing the water temperature increases the efficiency of hydrogen production via the photocatalyst. This was experimentally demonstrated as follows.

[0060] In the experiment, a photocatalyst component formed by sintering 100 mg of SrTiO3 (strontium titanate) onto a glass plate was immersed in 200 ml of water placed in a quartz glass container. While the water temperature was adjusted to various values using a heater, 365 nm light was irradiated at various intensities using a spot-type LED (maximum output 0.691 W). This caused a water decomposition reaction and generated hydrogen. The generated hydrogen was recovered and the amount of hydrogen generated was measured. The irradiation area was set to 2 cm 2 The output of the LED (intensity of irradiated light) was measured and adjusted using a power meter (Ophir Japan 50(150)A-BB26). The amount of irradiated light (incident light amount) irradiating the photocatalyst was calculated as follows.

[0061] Incident light intensity (mmol·cm -2 ·hr -1 )=P×λ×3600 / (A·h·c)

[0062] Here, P is the LED output (W·cm -2 ), λ is the wavelength = 365 (nm), A is the Avogadro constant (mol -1 ), h is Planck's constant (J·s), c is the speed of light (m·s -1). The efficiency of hydrogen production (photocatalytic efficiency) was calculated as follows.

[0063] Photocatalytic efficiency (%) = hydrogen H2 production × 2 / incident light intensity

[0064] Here, the unit of hydrogen generation is mmol·cm -2 ·hr -1 (The amount of hydrogen ion reduction is twice that of hydrogen gas).

[0065] As shown in Figure 3(A), when the water temperature was raised to 30°C, 40°C, 50°C, and 60°C while maintaining the LED output at maximum, the photocatalytic efficiency increased along with the increase in water temperature. This is presumably because heating increases the reaction rate between electrons and water in the photocatalyst. Therefore, it was confirmed that increasing the water temperature improves the efficiency of hydrogen production in the photocatalyst.

[0066] Furthermore, the density of light emitted from the aforementioned light source device 4 is adjusted to improve the efficiency of hydrogen production. More specifically, as already mentioned, the inventors' research has revealed that increasing the density of light irradiating the photocatalyst reduces the hydrogen production efficiency (the amount of hydrogen produced per incident light amount). Referring to FIG3(B), based on experiments conducted under the same conditions as FIG3(A), when the water temperature was set to 25°C (room temperature) and the LED output was varied to 5%, 10%, 20%, 60%, and 100% of the maximum output, the photocatalyst efficiency decreased as the LED output, i.e., the intensity of the irradiated light, increased. This is presumably because, even if the density of excited electrons and holes generated in the photocatalyst increases due to an increase in light intensity, the decomposition reaction between the excited electrons and holes and water is slow, causing the excited electrons and holes to recombine and disappear before reacting with water. In other words, this demonstrates that the proportion of photon energy contributing to hydrogen production decreases as the density of light irradiating the photocatalyst increases. 3 (B), it can be understood that if the light intensity is 0.1 W / cm 2 The change in hydrogen production efficiency will be relatively stable in the range below. However, since the absolute amount of photocatalytic reaction decreases as the light intensity decreases, it is preferable to adjust the light density from the light source device 4 to 0.1 W / cm 2 For example, the light intensity to improve the photocatalytic efficiency is 0.1 W / cm 2 Hereinafter, when the light output from the light source device 4 is PL (W), the area Acm of the irradiated light from the light source device 4 can be expressed as 2Adjust to PL / 0.1. The area of irradiation can be adjusted by adjusting the direction of the reflector.

[0067] Moreover, in the above-mentioned light source device 4 submerged in water, a coating 12 of a photocatalytic substance is applied to the surface of the outer side of the frame 8. According to the research of the inventors of the present invention, when the light source device 4 is directly (without the coating 12 of the photocatalytic substance) submerged in water, the material on the surface of the outer side of the frame 8 dissolves in the water, etc., thereby observing surface degradation. In particular, when ultrapure water (resistivity ≥ 15MΩ·cm) is used as water, when the surface of the frame 8 is metal, dissolution and degradation occur significantly. In addition, as schematically depicted in Figure 1 (A), since the light L from the light source device 4 passes through the transparent plate 9 and advances into the water W, and light scattering occurs in the water and is reflected on the liquid surface and the inner surface of the container portion, as depicted by the dotted arrows in the figure, the light advances in all directions in the water, and the light that passes through the transparent plate 9 is repeatedly scattered and reflected, so that a considerable amount will also reach the surface of the frame 8. Therefore, if a photocatalytic reaction also occurs on the surface of the frame 8, it is expected that the efficiency of hydrogen production will be improved. Therefore, in this embodiment, in order to prevent the dissolution and degradation of the material on the surface of the frame 8 and to improve the efficiency of hydrogen production, as described above, the surface of the frame 8 can be covered with a photocatalytic substance 12. The photocatalytic substance covered on the surface of the frame 8 can be the same as the photocatalytic body 3 or a different photocatalytic substance. However, it is preferred that the photocatalytic substance on the surface of the frame 8 also has sufficient activity with respect to light of the wavelength of the light from the light source.

[0068] In the above-described structure, in order to allow as much light as possible from the light source device 4 to be irradiated on the photocatalytic body 3 and the photocatalytic coating 12 in the container portion 2 and absorbed, the container portion 2 may be provided with a structure that prevents light from leaking to the outside, that is, to seal the light within the container portion 2. For example, the inner wall of the container portion 2 may be covered with a reflective mirror that reflects light (light reflecting mechanism).

[0069] In the hydrogen production apparatus 1 of this embodiment, as Figure 4As schematically depicted, the photocatalyst body 3 may also be a plate-shaped member having a photocatalytic substance. In this case, as shown in the accompanying drawings, the photocatalyst body 3 is typically formed in a flat plate shape, but is not limited thereto as long as the photocatalyst substance can come into contact with the water W. For example, in one embodiment, the photocatalyst body 3 may be formed by placing a powder of the photocatalyst substance on a glass substrate or a ceramic substrate as a whole and heating and sintering the powder to fix the photocatalyst substance on the substrate. Alternatively, a substrate in which the photocatalyst substance is solidified into a plate shape may be used as the photocatalyst body 3. In addition, for example, a stirring unit 13 may be provided for generating convection of the water W in the container portion 2. Moreover, when a plate-shaped member is used as the photocatalyst body 3, a granular photocatalyst body 3 composed of the photocatalyst substance may be dispersed in water, thereby contributing to the production of hydrogen.

[0070] Furthermore, in the hydrogen production device 1 of this embodiment, as schematically illustrated in FIG5(A), a light source device 4 comprising multiple light sources emitting light L arranged in an array may be submerged in water W within a container, or multiple such light source devices 4 may be disposed within the water. In such a light source device 4, as schematically illustrated in FIG5(B), multiple light sources 5, which may be LEDs, are disposed on a housing 8 via a printed circuit board 6 and a heat conductive sheet 7. Reflective plates 10 are provided around each light source 5 to focus the light emitted from the light source 5. Furthermore, a transparent plate 9 is provided above the light source 5, allowing the light L from the multiple light sources 5 to pass through the transparent plate 9 and propagate into the water W. Furthermore, the outer surface of the housing 8 may be covered with a photocatalytic material 12. With this configuration, as shown in FIG5(A), light L emitted from one light source device 4 can be irradiated on the surface of the housing 8 of another light source device 4 covered with the photocatalytic material 12, thereby inducing a water decomposition reaction by the photocatalyst, thereby producing hydrogen.

[0071] The light source device 4 of the device 1 of the present embodiment described above operates by electricity, which is preferably provided by energy derived from sunlight or other renewable energy generated by a solar panel or the like. Therefore, as shown in FIG5(A), the light source device 4 can be configured to receive electricity via a power supply line 16 from a power source generated by renewable energy such as a solar panel 15.

[0072] Operation of hydrogen production equipment

[0073] During operation of the hydrogen manufacturing device 1 of the present embodiment, the light source device 4 receives the supply of electricity from a power generation source such as a solar panel 5 and emits light, which is irradiated on the photocatalyst body 3 in the container portion 2. In addition, the water W in the container portion 2 is heated by the exhaust heat of the light source device 4. Moreover, in the photocatalyst substance, light is absorbed to generate excited electrons and holes, and the hydrogen in the water is reduced by the excited electrons to form hydrogen, and the oxygen in the water is oxidized by the holes to form oxygen. In this way, the generated hydrogen and oxygen are sent to a separator (not shown) through the air supply pipe 2a, so that the hydrogen is separated and recovered. The separator can be, for example, any separator using a hydrogen separation membrane used in this field.

[0074] Output control of light source device

[0075] As already described, in the hydrogen production apparatus 1 of this embodiment, the power supplied to the light source device 4 may also be renewable energy such as from the solar array 15. Instead of directly utilizing sunlight, the light irradiating the photocatalyst uses light emitted from the light source device using electricity converted from solar energy. This allows the wavelength of the light to be converted to a wavelength band that is easily absorbed by the photocatalyst. Furthermore, the density of the light can be concentrated, thereby reducing the space occupied by the photocatalyst and facilitating miniaturization of the hydrogen production apparatus.

[0076] Furthermore, it was discovered that when power is supplied to the light source device 4 to cause the light-emitting element or light-emitting body to emit light, thereby obtaining irradiation light for irradiating the photocatalyst, the luminous efficiency of the light-emitting element or light-emitting body, such as an LED, changes relative to the amount of current connected. According to experiments conducted by the inventors of the present invention, as illustrated in FIG6(A), when four LEDs with a rated current of 1A and a rated voltage of 3.54V were connected in parallel, the luminous efficiency (%) was measured relative to the current connected. As shown in the figure, the luminous efficiency was maximized when the connected current was less than the value of the rated current (1.6A). In other words, this indicates that when a current exceeding the current at which the luminous efficiency is maximized is connected to the light-emitting element or light-emitting body, the proportion of energy that is not converted into light increases relatively, thereby increasing energy loss. Therefore, in this embodiment, it is preferred to adjust the current connected to the light source device 4 so as to maximize the luminous efficiency of the light-emitting element or light-emitting body. Alternatively, the amount of current in the light-emitting element or light-emitting body is adjusted so as to maximize the luminous efficiency among the currents that can be connected to the light source device 4. Specifically, when current that can be supplied to the light source device 4 is supplied, a light-emitting element or light-emitting body having a rated output that provides a current flow with maximum luminous efficiency can be selected. Therefore, for example, when the power source supplying power to the light source device 4 is a solar panel, it is preferable to select the light-emitting element or light-emitting body so that a current flow with maximum luminous efficiency is provided within the rated current value of the solar panel.

[0077] Furthermore, when a power generation source realized by renewable energy such as a solar panel is used as a power source for supplying electricity to the light source device 4, the output of the power generation source varies according to environmental conditions such as sunlight conditions, and the available current may vary from moment to moment. At this time, if the light source device is operated in a state where the luminous efficiency is maximized at that time, the efficiency of the energy utilized in the production of hydrogen is good. As one method of achieving this purpose, in the light source device 4 of this embodiment, as a light-emitting element or a light-emitting body, a device such as Figure 7(A) to Figure 7(C)As depicted, multiple LEDs are connected in parallel. In this configuration, the number of LEDs connected to the power source is adjusted according to the output of the power source, ensuring that current that maximizes luminous efficiency always flows through the connected LEDs. For example, when the power source output is at its rated output, as shown in Figure 7(A), all of the LEDs are connected to the power source PV. When the power source output is approximately half of its rated output, as shown in Figure 7(B), half of the LEDs are connected to the power source PV. When the power source output is approximately one-quarter of its rated output, as shown in Figure 7(C), one-quarter of the LEDs are connected to the power source PV. This allows the LEDs connected to the power source PV to flow with current that maximizes luminous efficiency, as shown in Figure 6(B). In other words, by adjusting the number of connected LEDs according to the output of the power source, the luminous efficiency of each LED receiving current from the power source is maximized, thereby suppressing energy loss that does not contribute to light generation.

[0078] For example, when the LED power is 5.664W (current 1.6A, 3.54V) and the luminous efficiency of the LED is 32%, the luminous output becomes 1.84W. In this case, the irradiation light density on the photocatalyst body 3 is 0.1W / cm 2 Therefore, it is preferable that the irradiation area is adjusted to 18.4 cm 2 In order to satisfy this condition, the position and orientation of the reflector in the light source device 4 and the arrangement interval of the LEDs may be set.

[0079] The above description is made in relation to the embodiments of the present invention. However, a person skilled in the art can easily implement a large number of modifications and changes. The present invention is not limited to the embodiments illustrated above, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. A hydrogen production device comprising: a container portion for containing water; a photocatalyst body dispersed or disposed in the water within the container portion and comprising a photocatalytic substance that generates excited electrons and holes when irradiated with light, thereby causing a water decomposition reaction that decomposes water into hydrogen and oxygen, thereby generating hydrogen gas; a light source that emits light that irradiates the photocatalytic body to induce the water decomposition reaction; a frame, which carries the light source, The frame is placed in water in the container portion. The water is heated by exhaust heat from the light source released from a surface of the frame. Furthermore, a surface of the frame in contact with the water is covered with a photocatalytic substance.

2. The hydrogen production device according to claim 1, wherein: The light emitted from the light source also irradiates the photocatalytic substance covering the surface of the frame.

3. The hydrogen production device according to claim 2, wherein: The plurality of light sources and frames supporting the light sources are disposed in water within the container portion, and light emitted from one of the light sources also irradiates the photocatalytic material covering the surfaces of the frames of the other light sources.

4. The hydrogen production device according to any one of claims 1 to 3, wherein: The density of the light irradiated on the photocatalytic body is adjusted to provide a photocatalytic efficiency equal to or greater than a predetermined value, or a density lower than the predetermined value. The photocatalytic efficiency is a ratio of the amount of hydrogen generated to the amount of photons incident on the photocatalytic substance.

5. The hydrogen production device according to claim 2, wherein: The light emitted from the light source is configured to be sealed in the container portion.

6. The hydrogen production device according to claim 5, wherein: The container portion includes a light reflecting mechanism for confining light emitted from the light source within the container portion.

7. The hydrogen production device according to any one of claims 1 to 3, wherein: The light source is configured such that it is operated by using electric power obtained by solar power generation to emit the light that is irradiated onto the photocatalytic body, and exhaust heat generated when the light source is operated is transferred to the water in contact with the frame.

8. The hydrogen production device according to claim 7, wherein: When the current of the rated current value of the solar power generation is supplied to the light source, the rated output of the light source is adjusted so that the luminous efficiency of the light source is maximized.

9. The hydrogen production device according to claim 7, wherein: The light source includes a plurality of LEDs, and the number of operating LEDs among the plurality of LEDs is changed according to an output current of the solar power generation so as to maximize the luminous efficiency of the light source.

10. The hydrogen production device according to any one of claims 1 to 3, wherein: The emission wavelength of the light source is selected to fall within a wavelength band where the quantum yield of the photocatalytic substance exceeds a predetermined threshold value.

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