Hydrogen gas production device using photocatalysis

Abstract

To provide a structure that heats water with exhaust heat of a light source to improve a production efficiency of a hydrogen gas production in an apparatus for producing a hydrogen gas according to a decomposition reaction of water using a photocatalyst.SOLUTION: A hydrogen gas production apparatus 1 includes: a container for receiving water; a photocatalyst that is dispersed or arranged in the water in the container, and has a photocatalyst substance that generates excitation electrons and holles when irradiated with light, causes a decomposition reaction of water that decomposes water into oxygen and hydrogen to generate a hydrogen gas; a light source that emits light that irradiates the photocatalyst and causes the water decomposition reaction; and a housing that supports the light source. The housing is placed in the water in the container, the water is heated by the exhaust heat of the light source emitted from the surface of the housing, and a surface of the housing that is in contact with the water is coated with a photocatalytic substance.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Hydrogen gas is expected to be used as a clean next-generation fuel that does not produce carbon dioxide even when burned. Hydrogen gas can be produced by a water decomposition reaction caused by light energy using a photocatalyst, and various hydrogen gas production technologies using a photocatalyst have been proposed. For example, Patent Documents 1 and 2 disclose a photocatalyst that generates hydrogen gas by causing a water decomposition reaction by irradiation with ultraviolet light or visible light and a method for preparing the same. Patent Document 3 discloses a configuration of a hydrogen production device including a water oxidation reaction means that uses a photocatalyst caused by ultraviolet light to visible light in sunlight and a water reduction reaction means that uses heat from visible light to infrared light in sunlight. Patent Document 4 proposes a structure of a hydrogen generation device that circulates water in which photocatalyst particles are dispersed in a housing having a light receiving window, causes a water decomposition reaction caused by light, and generates hydrogen gas. Patent Document 5 proposes a configuration of a hydrogen generation system that irradiates a receiver with an electrode 21 made of a photocatalyst placed in water with light accumulated using a solar collector, excites valence electrons in the photocatalyst, electrolyzes the surrounding water, and continuously produces hydrogen gas. Incidentally, although not a technology for producing hydrogen gas, Patent Document 6 discloses that a plate-shaped carbon material made of a carbon allotrope with an sp3 crystal structure is immersed in a solvent in which carbon dioxide has been dissolved, and while the temperature of the solvent is being increased by a heater, the solvent is irradiated with ultraviolet light, exciting the carbon material and breaking the C=O bond of the carbon dioxide, generating carbon monoxide and methane. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special table 9-510657 [Patent Document 2] Patent Publication No. 2003-251197 [Patent Document 3] Patent Publication No. 2013-234077 [Patent Document 4] Patent Publication 2015-218103 [Patent Document 5] Patent Publication No. 2017-24956 [Patent Document 6] Patent Publication No. 2016-108181 [Non-patent literature]

[0004] [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 volume 581, pages411-414 (2020) Summary of the Invention [Problem to be solved by the invention]

[0005] Meanwhile, in the research of the inventors of the present invention, it has been found that the production efficiency of hydrogen gas increases as the temperature of the water, which is the reactant, increases. Therefore, in order to increase the production efficiency of hydrogen gas, it is effective to heat the water. In this case, if it is possible to use the exhaust heat of the light source that generates the light to be irradiated to the photocatalyst, rather than using a heater that supplies energy from the outside, more specifically, if a configuration is adopted in which not only the radiant heat from the light source to the water but also the exhaust heat of the light source can be directly transferred to the water, it is possible to further increase the utilization efficiency of the energy involved in hydrogen production. As one such configuration, a configuration in which the housing that supports the light source itself is placed in water and the water is directly contacted with the surface of the light source device that generates heat is considered. In relation to this point, the inventors of the present invention conducted research and observed a phenomenon in which, when the surface of the housing of the light source is formed of a material such as metal to improve the heat transfer efficiency, the metal material of the housing surface dissolves in the water, causing the housing surface to deteriorate. Therefore, in a configuration in which a housing carrying a light source is placed underwater, it is preferable to suppress deterioration of the housing surface without reducing heat transfer efficiency as much as possible, and in this case, it is advantageous to have a configuration that improves the amount of light reaction of the water.

[0006] Thus, the main object of the present invention is to provide a configuration in an apparatus for producing hydrogen gas by a water decomposition reaction using a photocatalyst, in which water is heated using exhaust heat from a light source in order to improve the efficiency of hydrogen gas production.

[0007] Another object of the present invention is to provide an apparatus as described above, in which the light source together with the housing supporting it is submerged in water, which can increase the amount of light reaction of the water while suppressing deterioration of the surface of the housing. [Means for solving the problem]

[0008] According to one aspect of the present invention, the above problem is solved by a hydrogen gas production apparatus, A container portion for receiving water; a photocatalyst dispersed or disposed in the water in the container, 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 into hydrogen and oxygen and generates hydrogen gas; a light source that emits light that is irradiated onto the photocatalyst to induce the water decomposition reaction; A housing that carries the light source; Including, The housing is placed in the water in the container, the water is heated by the exhaust heat of the light source emitted from the surface of the housing, and the surface of the housing that comes into contact with the water is coated with a photocatalytic material. This is achieved by:

[0009] In the above configuration, the "photocatalytic substance" may be a substance that, when irradiated with light, can cause a water decomposition reaction and reduce water to generate hydrogen gas. The "photocatalytic body" may be a particle made of such a photocatalytic substance and dispersed in water, or a member made of the photocatalytic substance itself, or a substrate or base on which the photocatalytic substance is fixed, and placed at an arbitrary position in the water, or both (hereinafter, in this specification, when the term "photocatalyst" is used simply, it refers to the photocatalytic substance). The "light source" may typically be any type of light that receives a supply of electric power and emits light that is absorbed by the photocatalytic substance to cause a water decomposition reaction, and is supported by a housing and placed in water in a waterproof state. The housing is preferably made of a material with high thermal conductivity, and typically may be made of a metal material such as aluminum.

[0010] The emission wavelength of the light source is preferably selected to be within a wavelength band in which the quantum yield of the photocatalyst exceeds a predetermined threshold (which may be selected arbitrarily) so that the light irradiated to the photocatalyst is efficiently absorbed by the photocatalyst to generate excited electrons and holes. In this regard, as exemplified in the following embodiment section, 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 the emission wavelength of the light source is shorter than the wavelength at which the quantum yield of the photocatalyst increases rapidly. 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), TiO2 (titanium oxide), and the like. Note that these photocatalysts may be used with the addition of a co-catalyst as appropriate. On the other hand, various light emitting diodes (LEDs) may be used as the light source. 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.

[0011] In the configuration of the device of the present invention, the surface of the housing that comes into contact with water is coated with a photocatalytic material. Here, the photocatalytic material that coats the surface of the housing may be the same material as the photocatalyst, or a different photocatalytic material. This prevents the surface of the metal material that constitutes the housing from coming into direct contact with water.

[0012] In the above-mentioned configuration of the device of the present invention, in an apparatus for producing hydrogen gas by irradiating a photocatalyst in contact with water with light to induce a decomposition reaction of water, a configuration is provided in which a light source supported on a housing is submerged in water, and the water is heated by the exhaust heat of the light source. According to such a configuration, the efficiency of hydrogen gas production is improved by heating the water, which is a reactant. In addition, since the heating of water is achieved by utilizing the exhaust heat of the light source, there is no need to separately install a heater or the like for heating the water, and therefore there is no need to separately supply energy for heating the water, so that the efficiency of the energy required for producing hydrogen gas is improved. In the case of the present invention, the surface of the housing to be submerged in water is covered with a photocatalytic substance, and thus, when the housing is formed of a metal material or the like, the metal on the surface of the housing is prevented from directly contacting water, preventing dissolution of the metal on the surface of the housing and suppressing deterioration of the surface of the housing. In this regard, the light emitted from the light source in the water is scattered in various ways (Rayleigh scattering, Raman scattering, etc.) and is reflected by the inner wall of the container and the water surface, and propagates in various directions in the water. Therefore, the scattered or reflected light is absorbed by the photocatalyst on the surface of the housing of the light source, and a water decomposition reaction occurs on the surface of the housing, which is expected to further improve the efficiency of hydrogen gas production. Furthermore, according to the above configuration, the light source is arranged inside the container, and the structure of the outside of the container is simplified, so that the space required for arranging the device can be made compact, while it is also easy to increase the dimensions of the container and scale up the device.

[0013] In the above-mentioned device of the present invention, in any embodiment, a configuration may be provided in which the light emitted from the light source is also irradiated to the photocatalytic material covering the surface of the housing. For example, the device of the present invention may be configured such that a plurality of light sources and a housing supporting the light sources are placed in water in the container, and the light emitted from one of the light sources is also irradiated to the photocatalytic material covering the surface of the housing of the other light sources. In another embodiment, the device of the present invention may be configured such that the light emitted from the light source is confined in the container, and for this purpose, for example, the container may have a light reflecting mechanism for confining the light emitted from the light source within the container, such as by providing a light reflecting plate on the inside. According to these configurations, as much light as possible emitted from the light source is irradiated to the photocatalyst, which can contribute to the generation of hydrogen gas.

[0014] However, according to the research of the inventors of the present invention, as will be described in detail in the following embodiment section, it has been found that the hydrogen gas production efficiency (amount of hydrogen gas produced per amount of incident light) decreases when the density of light irradiated to the photocatalyst is increased. This is thought to be because, even if the density of excited electrons and holes generated in the photocatalyst increases due to an increase in light intensity, the rate of the decomposition reaction between the excited electrons and holes and water is slow, and the excited electrons and holes are annihilated by recombination before reacting with water, respectively, so that the energy is not effectively used for the production of hydrogen gas. Therefore, it is preferable that the density of light emitted from the light source is adjusted to an appropriate value that balances with the decrease in the hydrogen gas production efficiency. Therefore, in the above-mentioned device of the present invention, the density of light irradiated to the photocatalyst may be adjusted to a density that gives a photocatalytic efficiency (the ratio of the amount of hydrogen gas generated per amount of photons incident on the photocatalyst material) of a predetermined value or more, or lower. Specifically, for example, according to an experiment, the density of light irradiated to the photocatalyst is 0.1 W / cm 2 It has been found that it is preferable to set the light source output P / irradiation area A to ≦0.1 W / cm 2 It is preferable to adjust the relationship between the output P of the light source and the irradiation area A so that the following holds true.

[0015] In the above-mentioned device of the present invention, the light source may be configured to be operated by power obtained by solar power generation, emit light to be irradiated to the photocatalyst, and transmit the exhaust heat during operation from the housing to the water. This allows hydrogen gas to be produced using renewable energy. In addition, by operating the light source with power obtained from sunlight, rather than irradiating the photocatalyst with sunlight itself, it becomes possible to concentrate thin solar energy per unit area and supply the light energy to the photocatalyst, thereby making it possible to miniaturize the device.

[0016] Incidentally, when the light source is operated by electric power, it is preferable that the light emission efficiency of the light source is maximized. Therefore, when the light source is operated by electric power obtained by solar power generation, the rated output of the light source may be adjusted so that the light emission efficiency of the light source is maximized when a current of the rated current value of the solar power generation is supplied to the light source. This allows the solar energy to be used more effectively for the production of hydrogen gas. In addition, in the case of solar power generation, the output varies depending on the sunshine conditions, and the available current may vary from moment to moment. In such a case, the energy used for the production of hydrogen gas is more efficient if the light source is operated so that the light emission efficiency is maximized at each moment. In this regard, a plurality of LEDs may be adopted as the light source, and in this case, since the light emission efficiency of each LED changes depending on the input current, the light source may be configured so that the number of LEDs that are operated among the plurality of LEDs is changed depending on the output current of the solar power generation so that the light emission efficiency of the light source is maximized. This is expected to allow the solar energy to be converted more effectively into light from the light source and used for the production of hydrogen gas. Effect of the Invention

[0017] Thus, according to the present invention, when the temperature of the reactant water is increased to improve the photocatalytic efficiency during the production of hydrogen gas by the decomposition reaction of water using a photocatalyst, the light source is submerged in water together with the housing, and the exhaust heat of the light source is released from the housing into the water, thereby increasing the water temperature, and the surface of the housing is covered with a photocatalytic material, which prevents the surface of the housing from being deteriorated by water, and the light emitted from the light source that is scattered or reflected in the water and travels in various directions can be made to contribute to the production of hydrogen gas by hitting the photocatalyst on the surface of the housing, thereby improving energy efficiency. In addition, when the metal surface of the housing directly contacts water and the metal material dissolves in the water, the metal ions dissolved in the water may react with excited electrons or holes generated by the photocatalytic material in the water, thereby reducing the production efficiency of hydrogen gas. However, in the present invention, the metal material on the surface of the housing is prevented from dissolving in water, so that the reduction in the production efficiency of hydrogen gas due to the metal ions in the water can be suppressed. Furthermore, by using the exhaust heat of the light source to heat the water, the water temperature can be increased more reliably than when the water is heated by the radiant heat of the light source, and it is expected that the photocatalytic efficiency will be improved. In addition, when the light source of the device of the present invention is operated by electricity derived from solar energy, it becomes possible to efficiently obtain hydrogen energy without emitting carbon dioxide.

[0018] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1(A) is a schematic diagram of a hydrogen gas production device according to the present embodiment, and FIG. 1(B) is a schematic side view of a light source device thereof. [Diagram 2] FIG. 2 is a diagram showing an example of the wavelength characteristics (cited from Non-Patent Document 1) of the absorptivity and quantum yield of a typical photocatalyst (SrTiO3) used in the hydrogen gas production device according to this embodiment, and the emission wavelength characteristics (measured by the inventors of the present invention, etc.) of a light source (InGaN-based LED). [Diagram 3] Fig. 3(A) is a graph showing the change in photocatalytic efficiency with respect to the temperature of water in contact with the photocatalyst obtained by an experiment. Fig. 3(B) is a graph showing the change in photocatalytic efficiency with respect to the density (light intensity) of light irradiated to the photocatalyst. The data was obtained by an experiment conducted by the inventors of the present invention. [Figure 4] FIG. 4 is a schematic diagram of another aspect of the hydrogen gas production device according to the present embodiment. [Diagram 5] FIG. 5(A) is a schematic diagram of still another aspect of the hydrogen gas production device according to the present embodiment, and FIG. 5(B) is a schematic side view of the light source device thereof. [Figure 6] Fig. 6(A) is a graph showing the change in luminous efficiency with respect to the current input to a light source obtained by an experiment in a light source in which four LEDs are connected in parallel to a power source. Fig. 6(B) is a graph showing the change in luminous efficiency with respect to the current input to a light source in which one LED is connected in parallel to a power source. The data was obtained by an experiment conducted by the inventors of the present invention. [Figure 7] 7(A) to 7(C) are diagrams that show schematic diagrams of circuit configurations of light sources in which the number of operating LEDs can be changed according to the amount of current generated by a solar panel. [Explanation of symbols]

[0020] 1, 1a...Hydrogen gas production device 2...Container part 3...Photocatalyst 4...Light source device 5...LED 6...Printed circuit board 7…Heat conductive sheet 8…Housing 9…Transparent plate 10...Reflector 11…Power line 12...Photocatalytic coating 15…Solar panel 16...Power line W…Water L…Light ray BEST MODE FOR CARRYING OUT THEINVENTION

[0021] Hydrogen gas production equipment configuration Referring to FIG. 1(A), in one aspect, the hydrogen gas production device 1 of this embodiment has a container portion 2 of any shape for receiving water (liquid) W, a particulate photocatalyst 3 made of a photocatalytic material dispersed in the water in the container portion 2, a light source device 4 for emitting light to be irradiated to the photocatalyst 3, and an air supply pipe 2a for sending the generated hydrogen gas and oxygen gas to a separator.

[0022] In the configuration of the hydrogen gas production device 1, the photocatalyst 3 is a particle made of a photocatalyst material that can absorb photons to generate excited electrons and holes when irradiated with light, cause a water decomposition reaction, reduce water, and generate hydrogen gas, and may be dispersed in water. As the photocatalyst material used in this embodiment, a material that can generate hydrogen gas from water by irradiation with light that is used in this field may be used, and 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 shown in FIG. 2, a photocatalyst exhibits wavelength characteristics in which the absorptivity and quantum yield increase rapidly near a certain wavelength when the wavelength of the irradiated light is changed from the long wavelength side to the short wavelength side (the amount of excited electrons and holes generated by photon absorption increases in the wavelength band where the absorptivity and quantum yield increase). When preparing a particulate photocatalyst 3 from such a photocatalyst, raw materials having the composition constituting the photocatalyst are mixed and fired to form semiconductor particles made of the photocatalyst, and the particles may be dispersed in water as the photocatalyst 3. Note that the semiconductor particles made of the above-mentioned photocatalyst may be used as the photocatalyst 3 as it is, but a photocatalyst having an appropriately selected co-catalyst added to the particle surface to enhance catalytic activity may also be used.

[0023] The light source device 4 may be any light source that emits light of a wavelength that is absorbed by the photocatalytic substance of the photocatalyst 3 and generates excited electrons and holes. In more detail, as shown in FIG. 2, the photocatalytic substance has a wavelength characteristic in which the absorptivity and quantum yield increase when light of a wavelength shorter than a certain wavelength is irradiated, so that in the light source device 4, a light emitting element or light emitter that emits light of a wavelength band in which the absorptivity and quantum yield of the photocatalytic substance of the photocatalyst 3 increase is selected. 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. may be adopted as the light emitting element or light emitter of the light source. For example, in the case of FIG. 2 where SrTiO3 is used as the photocatalytic substance, when the wavelength of the irradiated light is below 380 nm, the absorptivity and quantum yield increase, so that an InGaN-based LED having a peak emission wavelength at 360 to 370 nm can be advantageously used as the light emitter of the light source device 4.

[0024] In the configuration of the light source device 4, for example, as shown in FIG. 1(B), a light source 5, which may be an LED, is placed on a printed circuit board 6, a heat conductive sheet is laid underneath, and the light source 5 is placed in a recessed structure of a housing 8. The housing 8 may be made of any material, such as a metal with high thermal conductivity, such as aluminum. The opening of the recessed structure of the housing 8 in which the light source 5 is placed is sealed by a transparent plate 9 made of translucent glass, quartz glass, resin, or the like, so that light from the light source 5 is radiated from the transparent plate 9 while the light source 5 is sealed from the outside. In addition, it is preferable that the inner wall of the recessed structure of the housing 8 is formed into a reflector 10 so that light from the light source 5 is efficiently radiated from the transparent plate 9 to the outside. Power may be supplied to the light source 5 by a power line 11 that penetrates the housing 8 while being sealed.

[0025] 1(A), the light source device 4 is placed in the water W in the container 2, and the exhaust heat of the light source is transferred to the water via the housing 8, heating the water and improving the efficiency of hydrogen gas production. In this regard, as mentioned in the "Summary of the Invention" section, according to research by the inventors of the present invention, it has been found through the following experiments that increasing the temperature of the water increases the efficiency of hydrogen gas production by photocatalysis.

[0026] In the experiment, a photocatalytic member made by spreading and sintering 100 mg of SrTiO3 (strontium titanate) on a glass plate was immersed in 200 ml of water contained in a quartz glass container, and while the water temperature was adjusted to various values ​​using a heater, 365 nm light was irradiated at various light intensities from a spot-type LED (maximum output 0.691 W), inducing a water decomposition reaction, and the hydrogen gas generated was collected and the amount of hydrogen gas generated was measured. The light irradiation area was 2 cm 2 The LED output (irradiated light intensity) was adjusted while measuring it using a power meter (Offol Japan 50(150)A-BB26). The amount of light irradiated to the photocatalyst (incident light amount) was calculated as follows. Incident light amount (mmol cm -2 ·hr -1 )=P×λ×3600 / (A h c) where P is the LED power (W cm -2 ), λ is the wavelength = 365 (nm), and A is Avogadro's number (mol -1 ), h is Planck's constant (J s), and c is the speed of light (m s -1 The efficiency of hydrogen gas production (photocatalytic efficiency) was calculated as follows: Photocatalytic efficiency (%) = amount of hydrogen gas (H2) generated x 2 / amount of incident light The unit of hydrogen gas generation is mmol cm -2 ·hr -1 (The reduction rate of hydrogen ions is twice that of hydrogen gas.)

[0027] As a result, referring to Fig. 3(A), when the water temperature was raised to 30℃, 40℃, 50℃, and 60℃ while maintaining the LED output at maximum output, the photocatalytic efficiency increased with the increase in water temperature. This is considered to be because heating increases the reaction rate between electrons and water by the photocatalyst. Thus, it was confirmed that the efficiency of hydrogen gas production by the photocatalyst increases with the increase in water temperature.

[0028] In addition, the density of the light emitted from the light source device 4 may be adjusted so as to improve the efficiency of hydrogen gas production. More specifically, according to the research of the inventors of the present invention, as already mentioned, it has been found that the hydrogen gas production efficiency (amount of hydrogen gas produced per amount of incident light) decreases when the density of light irradiated to the photocatalyst is increased. Referring to FIG. 3(B), according to an experiment under the same conditions as FIG. 3(A), when the water temperature was set to 25° C. (room temperature) and the LED output was changed to 5%, 10%, 20%, 60%, and 100% of the maximum output, the photocatalyst efficiency decreased with an increase in the LED output, i.e., the density of the irradiated light. This is considered to be because, even if the density of excited electrons and holes generated in the photocatalyst increases due to an increase in light intensity, the rate of the decomposition reaction between the excited electrons and holes and water is slow, and the excited electrons and holes disappear due to recombination before they react with water. In other words, it has been shown that the proportion of photon energy contributing to the generation of hydrogen gas decreases when the density of light irradiated to the photocatalyst is increased. Specifically, referring to FIG. 3B, the efficiency of hydrogen gas production is 2 It can be seen that the change is gradual within the following range. However, the lower the light intensity, the lower the absolute amount of the photocatalytic reaction. Therefore, in order to obtain a larger amount of hydrogen gas, the density of the light from the light source device 4 should be 0.1 W / cm 2 For example, the area of ​​the light irradiated from the light source device 4 is adjusted to about A cm 2 The light intensity at which the photocatalytic efficiency is high is 0.1 W / cm 2 The light output from the light source device 4 is P L (W) P L / 0.1 The area of ​​the irradiated light may be adjusted by adjusting the orientation of the reflector.

[0029] Furthermore, in the above light source device 4 that is submerged in water, a photocatalytic coating 12 is applied to the outer surface of the housing 8. According to research by the inventors of the present invention, when the light source device 4 is submerged in water as it is (without the photocatalytic coating 12), deterioration of the surface was observed, such as the material of the outer surface of the housing 8 dissolving in the water. In particular, when ultrapure water (electrical resistivity ≧15 MΩ·cm) is used as the water, dissolution and deterioration occurred significantly when the surface of the housing 8 was made of metal. Meanwhile, as shown in FIG. 1(A), light L from the light source device 4 passes through a transparent plate 9 and travels into the water W, but in the water, light scattering occurs and reflection occurs at the liquid surface and the inner surface of the container, so the light travels in various directions in the water, as shown by the dotted arrows in the figure, and the light that has passed through the transparent plate 9 is repeatedly scattered and reflected, and reaches the surface of the housing 8 in a significant amount. Therefore, if a photocatalytic reaction were to occur on the surface of the housing 8 as well, it is expected that the efficiency of hydrogen gas production would improve. Therefore, in this embodiment, the surface of the housing 8 may be coated with a photocatalytic material 12 as described above in order to prevent dissolution and deterioration of the material on the surface of the housing 8 and to improve the efficiency of hydrogen gas production. The photocatalytic material coated on the surface of the housing 8 may be the same material as the photocatalyst 3, or may be a different photocatalytic material. However, it is preferable that the photocatalytic material on the surface of the housing 8 also has sufficient activity against light of the wavelength of light from the light source.

[0030] In the above configuration, in order to allow as much light as possible from the light source device 4 to be irradiated to and absorbed by the photocatalyst 3 and the photocatalytic coating 12 in the container part 2, the container part 2 may be provided with a configuration for preventing the light from leaking to the outside, that is, for confining the light within the container part 2. For example, the inner wall of the container part 2 may be covered with a reflective mirror that reflects light (light reflection mechanism).

[0031] In the hydrogen gas production device 1 of this embodiment, the photocatalyst 3 may be a plate-like member having a photocatalytic substance, as shown in FIG. 4. In that case, the photocatalyst 3 may be typically formed in a flat plate shape as shown in the figure, but is not limited thereto as long as the photocatalytic substance can come into contact with the water W. For example, in one embodiment, the photocatalyst 3 may be formed by placing a powder of the photocatalytic substance entirely on a glass substrate or a ceramic substrate, and then heating and sintering the powder to fix the photocatalytic substance on the substrate, or a substrate on which the photocatalytic substance is solidified in a plate shape may be used as the photocatalyst 3. In addition, for example, a stirring means 13 for generating convection of the water W in the container 2 may be provided. Furthermore, when a plate-like member is used as the photocatalyst 3, a particulate photocatalyst 3 made of a photocatalytic substance may be dispersed in water to contribute to the production of hydrogen gas.

[0032] In the hydrogen gas production device 1 of this embodiment, as shown in FIG. 5(A), a light source device 4 in which a plurality of light sources emitting light L are aligned may be submerged in the water W of the container, or a plurality of such light source devices 4 may be arranged in the water. In such a light source device 4, as shown in FIG. 5(B), a plurality of light sources 5, which may be LEDs, are arranged on a housing 8 via a printed circuit board 6 and a heat conductive sheet 7, and a reflector 10 that collects light emitted from the light source 5 is provided around each light source 5, and a transparent plate 9 is installed on the upper part of the light source 5, so that the light L from the plurality of light sources 5 may propagate through the transparent plate 9 into the water W. The outer surface of the housing 8 may be covered with a photocatalytic material 12. According to this configuration, as shown in FIG. 5(A), light L emitted from one light source device 4 can be irradiated onto a surface covered with a photocatalytic material 12 of the housing 8 of another light source device 4, whereby a water decomposition reaction is caused by the photocatalyst, thereby producing hydrogen gas.

[0033] The light source device 4 of the device 1 of the present embodiment is operated by electricity, and the electricity may be preferably provided by solar energy generated by a solar panel or other renewable energy. For this reason, as shown in Fig. 5(A), the light source device 4 may be configured to receive power from a renewable energy generating source such as a solar panel 15 through a power transmission line 16.

[0034] Operation of hydrogen gas production equipment In the operation of the hydrogen gas production device 1 of this embodiment, the light source device 4 receives power from a power generation source such as a solar panel 5 and emits light, and the light is irradiated onto the photocatalyst 3 in the container 2. The water W in the container 2 is heated by the exhaust heat of the light source device 4. Then, in the photocatalyst material, light is absorbed, excited electrons and holes are generated, the excited electrons reduce the hydrogen in the water to form hydrogen gas, and the holes oxidize the oxygen in the water to form oxygen gas. Thus, the generated hydrogen gas and oxygen gas pass through the air supply pipe 2a and are sent to a separator (not shown), where the hydrogen gas is separated and collected. The separator may be, for example, any separator using a hydrogen separation membrane used in this field.

[0035] Light source output control As already mentioned, in the hydrogen gas production device 1 of this embodiment, the power supplied to the light source device 4 may be derived from renewable energy such as the solar panel 15. By using light emitted from the light source device using power converted from solar energy instead of using sunlight as the light to irradiate the photocatalyst, the wavelength of the light can be converted to a wavelength band that is easily absorbed by the photocatalyst and the density of the light can be concentrated, thereby making it possible to reduce the space occupied by the photocatalyst and to facilitate miniaturization of the hydrogen gas production device.

[0036] Incidentally, when power is supplied to the light source device 4 to make the light emitting element or light emitter emit light to obtain light to be irradiated to the photocatalyst, it has been found that the light emitting efficiency of the light emitting element or light emitter, such as an LED, changes with the amount of current input. According to an experiment conducted by the inventors of the present invention, as illustrated in FIG. 6(A), when four LEDs with a rated current of 1 A and a rated voltage of 3.54 V are connected in parallel, the light emitting efficiency (%) is measured with respect to the input current. As shown in the figure, the light emitting efficiency is maximized when the input current is less than the rated current (1.6 A). That is, this indicates that when a current equal to or greater than the current at which the light emitting efficiency is maximized is input to the light emitting element or light emitter, the proportion of energy that is not converted into light increases relatively, and the energy loss increases. Therefore, in this embodiment, it is preferable that the current input to the light source device 4 is adjusted so that the light emitting efficiency of the light emitting element or light emitter is maximized. Alternatively, the amount of current in the light emitting element or light emitter may be adjusted so that the light emitting efficiency is maximized with respect to the current that can be input to the light source device 4. Specifically, a light emitting element or light emitter may be selected that has a rated output through which a current that provides the maximum light emitting efficiency flows when a current that can be input to the light source device 4 is input. Therefore, for example, when the power source that supplies power to the light source device 4 is a solar panel, a light emitting element or light emitter is preferably selected so that a current that provides the maximum light emitting efficiency flows at the rated current value of the solar panel.

[0037] In addition, when a power generating source using renewable energy such as a solar panel is used as a power source that supplies power to the light source device 4, the output of the power generating source may vary depending on environmental conditions such as sunlight conditions, and the available current may vary from moment to moment. In this case, if the light source device is operated in a state where the light emission efficiency is maximized at each time, the energy used to produce hydrogen gas will be efficient. As one method for achieving this, in the light source device 4 of this embodiment, a configuration in which multiple LEDs are connected in parallel as the light emitting element or light emitter, as shown in Figures 7(A) to 7(C), may be adopted. In such a configuration, the number of LEDs connected to the power generating source is adjusted according to the output of the power generating source, and thus the connected LEDs are configured to always flow with a current that maximizes the light emission efficiency as much as possible. For example, when the output of the power generating source is at its rated output, all of the LEDs are connected to the power generating source PV as shown in Fig. 7(A), when the output of the power generating source is about half of its rated output, half of the LEDs are connected to the power generating source PV as shown in Fig. 7(B), and when the output of the power generating source is about 1 / 4 of its rated output, 1 / 4 of the LEDs may be connected to the power generating source PV as shown in Fig. 7(C). This makes it possible to achieve a state in which a current that gives the maximum light-emitting efficiency flows in the LEDs connected to the power generating source PV as shown in Fig. 6(B). In other words, by adjusting the number of LEDs to be connected according to the output of the power generating source, the light-emitting efficiency of each of the LEDs that receives a current from the power generating source becomes as close to the maximum as possible, and it is possible to suppress the loss of energy that does not contribute to the generation of light.

[0038] For example, when the input power of the LED is 5.664 W (current 1.6 A, 3.54 V), if the luminous efficiency of the LED is 32%, the luminous output will be 1.84 W. In that case, the irradiated light density on the photocatalyst 3 is 0.1 W / cm, which is the highest photocatalytic efficiency. 2 Therefore, the irradiation area is 18.4 cm 2 The position and orientation of the reflector and the arrangement interval of the LEDs in the light source device 4 may be set so as to satisfy this condition.

[0039] The above description has been given in relation to the embodiment of the present invention, but it will be apparent to those skilled in the art that many modifications and changes can be easily made thereto, and that the present invention is not limited to the embodiment exemplified above, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. A hydrogen gas production apparatus, comprising: A container portion for receiving water; a photocatalyst dispersed or disposed in the water in the container, 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 into hydrogen and oxygen and generates hydrogen gas; a light source that emits light that is irradiated onto the photocatalyst to induce the water decomposition reaction; A housing that carries the light source; Including, The device has a housing placed under water in the container, the water is heated by the 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 is coated with a photocatalytic material.

2. 2. The apparatus of claim 1, wherein the light emitted from the light source is also irradiated onto the photocatalytic material covering the surface of the housing.

3. 3. The device of claim 2, wherein a plurality of said light sources and a housing carrying said light sources are disposed underwater within said container portion, and light emitted from one of said light sources is also irradiated onto the photocatalytic material covering the surface of the housing of the other of said light sources.

4. 4. An apparatus according to any one of claims 1 to 3, wherein the density of the light irradiated to the photocatalyst is adjusted to a density that gives a photocatalytic efficiency, which is the ratio of the amount of hydrogen gas generated per amount of photons incident on the photocatalytic material, of a predetermined value or more, or lower.

5. 3. The apparatus of claim 2, wherein light emitted from said light source is configured to be confined to said enclosure.

6. 6. The apparatus of claim 5, wherein said container portion includes a light reflecting mechanism for confining light emitted from said light source within said container.

7. 7. A device according to any one of claims 1 to 6, comprising a solar panel, the light source being operated by electricity obtained by solar power generation from the solar panel to emit the light which is irradiated onto the photocatalyst, and the exhaust heat generated during operation being transferred to the water in contact with the housing.

8. 8. The device according to claim 7, wherein the rated output of the light source is adjusted so that the light emitting efficiency of the light source is maximized when a current of a rated current value of the solar power generation is supplied to the light source.

9. 8. The device of claim 7, wherein the light source includes a plurality of LEDs, and the number of LEDs that are activated among the plurality of LEDs is changed in response to an output current of the solar power generation so that the light emitting efficiency of the light source is maximized.

10. 10. The apparatus of claim 1, wherein the emission wavelength of the light source is selected to be within a wavelength band in which the quantum yield of the photocatalytic material exceeds a predetermined threshold.

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