Gas production device, and gas production method

Abstract

To provide a gas production device efficiently using sunlight energy.SOLUTION: The gas production device comprises an aqueous electrolyte solution and a pair of electrodes immersed in the aqueous electrolyte solution, with the pair of electrodes being constituted of a p-type semiconductor electrode consisting of a p-type semiconductor photocatalyst and a n-type semiconductor electrode consisting of a n-type semiconductor photocatalyst, which are mutually short-circuited, the p-type semiconductor electrode and n-type semiconductor electrode being arranged in a manner of being separated from each other to enable the sunlight to enter thereon, the maximum absorption wavelength of both of the p-type semiconductor photocatalyst and n-type semiconductor photocatalyst being 560 nm, the p-type semiconductor electrode generating oxygen gas, and the n-type semiconductor electrode generating hydrogen gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas production apparatus and a gas production method, and more particularly to a gas production apparatus and a gas production method for producing hydrogen gas and oxygen gas from water using visible light as an energy source. [Background technology]

[0002] A hydrogen gas production device described in Patent Document 1 is known as a technology for producing hydrogen gas and oxygen gas by decomposing water. This conventional technology includes a container part containing water, a photocatalyst body having a photocatalytic substance dispersed in the water in the container, a light source for irradiating the photocatalyst body with light to cause a water decomposition reaction, and a housing equipped with the light source. The housing is placed in the water in the container part, the water is heated by exhaust heat released from the surface of the housing, and the surface of the housing that comes into contact with the water is covered with the photocatalytic substance. In this conventional technology, titanium oxide-based semiconductor photocatalysts such as strontium titanate (SrTiO3), lanthanum titanate (La2Ti), and titanium oxide (TiO2), which have the property of reacting to ultraviolet light (wavelength 380 nm or less), can be used as the photocatalytic substance. As a light source of ultraviolet light to be irradiated to these photocatalytic substances, artificial light sources using indium gallium nitride, diamond, and gallium nitride can be used. These light sources are operated by electricity obtained by solar power generation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-94488 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above hydrogen gas production device is mainly configured to generate hydrogen gas using an artificial light source that generates ultraviolet light for a titanium oxide-based semiconductor photocatalyst, and does not directly use solar energy to cause a water decomposition reaction with a photocatalytic substance. Even in recent years, the semiconductor photocatalysts that are often used are titanium oxide-based, and there is currently no effective photocatalytic substance that decomposes water using light other than ultraviolet light in the solar wavelength range. Titanium oxide has a band gap of approximately 3.0 eV or more and can absorb ultraviolet light, but can hardly absorb visible light with a wavelength of 420 nm to 780 nm. This means that the utilization efficiency of sunlight is very low when it is considered as a light source.

[0005] As described above, in order to generate hydrogen gas and oxygen gas using solar energy, conventional photocatalytic substances could only utilize the ultraviolet light wavelength band, which resulted in a very low utilization efficiency and was not practical.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a gas production device and a gas production method that can efficiently produce hydrogen gas and oxygen gas from water using visible light as an energy source. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, an aspect of the present invention is a gas production apparatus comprising an electrolyte aqueous solution and a pair of electrodes immersed in the electrolyte aqueous solution, the pair of electrodes being composed of a p-type semiconductor electrode made of a p-type semiconductor photocatalyst and an n-type semiconductor electrode made of an n-type semiconductor photocatalyst, which are short-circuited to each other, the p-type semiconductor electrode and the n-type semiconductor electrode being arranged to be spaced apart and both being set to allow sunlight to be incident thereon, the p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a maximum absorption wavelength of 560 nm, oxygen gas is generated at the n-type semiconductor electrode, and hydrogen gas is generated at the p-type semiconductor electrode.

[0008] In the above embodiment, the p-type semiconductor photocatalyst is preferably selected from cuprous oxide (Cu2O) and silicon carbide (β-SiC), and the n-type semiconductor photocatalyst is preferably ferric oxide (hematite: α-Fe2O3).

[0009] In the above aspect, it is preferable that the p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a band gap energy (Eg) of 2.2 eV.

[0010] In the above embodiment, the aqueous electrolyte solution is preferably selected from an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous sodium carbonate solution, and an aqueous potassium carbonate solution adjusted to be weakly alkaline.

[0011] In the above aspect, it is preferable that a water supply unit be provided for injecting water into the aqueous electrolyte solution.

[0012] In the above aspect, the electrolyte aqueous solution is preferably placed in a reaction vessel made of a transparent material that is transparent to visible light.

[0013] In the above aspect, the p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst are preferably thin films formed on the surfaces of the respective electrode bodies.

[0014] Another aspect of the present invention is a gas production method for producing a gas by immersing a pair of electrodes in an electrolyte aqueous solution, the pair of electrodes being composed of a p-type semiconductor electrode made of a p-type semiconductor photocatalyst and an n-type semiconductor electrode made of an n-type semiconductor photocatalyst, which are short-circuited to each other, the p-type semiconductor electrode and the n-type semiconductor electrode are arranged so as to be spaced apart and both are set so as to allow sunlight to be incident thereon, the p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a maximum absorption wavelength of 560 nm, oxygen gas is generated by the n-type semiconductor electrode, and hydrogen gas is generated by the p-type semiconductor electrode.

[0015] In the above embodiment, the p-type semiconductor photocatalyst is preferably selected from cuprous oxide (Cu2O) and silicon carbide (β-SiC), and the n-type semiconductor photocatalyst is preferably ferric oxide (hematite: α-Fe2O3).

[0016] In the above aspect, it is preferable that the p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a band gap energy (Eg) of 2.2 eV.

[0017] In the above embodiment, the aqueous electrolyte solution is preferably selected from an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous sodium carbonate solution, and an aqueous potassium carbonate solution adjusted to be weakly alkaline.

[0018] In the above aspect, it is preferable that water is injected into the aqueous electrolyte solution from a water supply unit.

[0019] In the above aspect, the electrolyte aqueous solution is preferably placed in a reaction vessel made of a transparent material that is transparent to visible light.

[0020] In the above aspect, the p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst are preferably thin films formed on the surfaces of the respective electrode bodies. Effect of the Invention

[0021] According to the present invention, it is possible to realize a gas production device and a gas production method that efficiently utilize solar energy. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is an explanatory diagram of a gas production device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the relationship between the wavelength and energy of sunlight irradiating the Earth. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The gas production apparatus and the gas production method according to the embodiment of the present invention will be described in detail below. However, it should be noted that the drawings are schematic and the dimensions, dimensional ratios, shapes, etc. of each member may differ from the actual ones.

[0024] [First embodiment] (Configuration of gas production equipment) 1 shows a gas production apparatus according to an embodiment of the present invention. The gas production apparatus 1 includes a reaction vessel 2, an electrolyte aqueous solution 3, a p-type semiconductor electrode 4, an n-type semiconductor electrode 5, a connection wiring 6, and a water supply unit (not shown). The p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 form a pair and are housed in the reaction vessel 2.

[0025] As shown in Fig. 1, the reaction vessel 2 is made of a transparent material such as glass or synthetic resin that transmits sunlight hv. The inner space of the reaction vessel 2 is set so that sunlight hv can enter the entirety. The reaction vessel 2 contains an aqueous electrolyte solution 3.

[0026] The electrolyte aqueous solution 3 is preferably selected from a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a sodium carbonate aqueous solution, and a potassium carbonate aqueous solution adjusted to a weak alkaline state. The reason for adjusting the electrolyte aqueous solution 3 to a weak alkaline state is to prevent dissolution of cuprous oxide (Cu2O), which is a p-type semiconductor photocatalyst, as described below. By using such an electrolyte aqueous solution 3, the durability of the p-type semiconductor electrode 4 containing cuprous oxide (Cu2O) can be improved, and the throughput of hydrogen production can be improved. In this embodiment, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of sodium carbonate, and an aqueous solution of potassium carbonate are used as the electrolyte aqueous solution 3, but it is also possible to apply other electrolyte aqueous solutions adjusted to a weak alkaline state. However, ammonia water cannot be used as the electrolyte aqueous solution 3 because it dissolves cuprous oxide.

[0027] The p-type semiconductor electrode 4 is made of cuprous oxide (Cu2O) which is a p-type semiconductor photocatalyst. In this embodiment, the p-type semiconductor electrode 4 is formed by forming a thin film of cuprous oxide (Cu2O) on the surface of a rod-shaped electrode body (not shown). In this embodiment, the cuprous oxide (Cu2O) is formed in a thin film shape, but this is not limited thereto, and it is possible to set it to various shapes and thickness dimensions. Cuprous oxide (Cu2O) is a p-type semiconductor photocatalyst, and its band gap energy Eg is 2.2 eV. The maximum absorption wavelength of cuprous oxide (Cu2O) is 560 nm.

[0028] The n-type semiconductor electrode 5 is made of ferric oxide (hematite: α-Fe2O3) which is an n-type semiconductor photocatalyst. In this embodiment, the n-type semiconductor electrode 5 is formed by forming a thin film of ferric oxide (hematite: α-Fe2O3) on the surface of a rod-shaped electrode body (not shown). In this embodiment, the ferric oxide (hematite: α-Fe2O3) is formed in a thin film shape, but this is not limited thereto, and it is possible to set various shapes and thickness dimensions as in the case of the p-type semiconductor electrode 4. The ferric oxide (hematite: α-Fe2O3) is an n-type semiconductor photocatalyst, and its band gap energy Eg is 2.2 eV, which is the same as the above-mentioned cuprous oxide (Cu2O). In addition, the maximum absorption wavelength of the ferric oxide (hematite: α-Fe2O3) is also 560 nm, which is the same as the above-mentioned cuprous oxide (Cu2O).

[0029] Ferric oxide (hematite: α-Fe2O3) exists inexhaustibly as red rust, is a material that has no adverse effects on the human body and is environmentally friendly.

[0030] The p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 are immersed in the electrolyte aqueous solution 3 and are arranged at a predetermined distance from each other. The upper ends of the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 are short-circuited by a connection wire 6.

[0031] Furthermore, the gas production apparatus 1 is provided with a water supply unit (not shown) above the upper opening of the reaction vessel 2, which supplies water to the reaction vessel 2, so that water can be added as needed depending on the amount of water consumed by electrolysis. The gas production apparatus 1 also includes a hydrogen gas collector (not shown) for collecting hydrogen gas, and an oxygen gas collector (not shown) for collecting oxygen gas.

[0032] (Action and Effects) In the gas production apparatus 1 of this embodiment, the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 are composed of semiconductor photocatalysts of opposite conductivity types, and the cuprous oxide (CuO) and ferric oxide (hematite: α-FeO) that compose both electrodes have equivalent band gap energy Eg and maximum absorption wavelength.

[0033] In the p-type semiconductor electrode 4, cuprous oxide (Cu2O) reduces water with light of 560 nm or less in the wavelength band of sunlight to produce hydrogen gas. FIG. 2 is a diagram showing the relationship between the wavelength and energy of sunlight irradiated on the earth, where the solid line A in the figure shows the solar radiation energy outside the atmosphere, and the dashed line B in the figure shows the solar radiation energy reaching the earth's surface. As shown in the figure, sunlight in the wavelength band of 560 nm or less in the wavelength band of visible light is light with high energy reaching the earth's surface and has a wide wavelength band. As shown in FIG. 1, in the p-type semiconductor electrode 4, electrons (e) generated by absorbing visible light and ultraviolet light in such a wide wavelength band reduce water to produce hydrogen gas (H2). Here, the energy level of the conduction band of cuprous oxide (Cu2O) is located on the negative side of the reduction potential of water.

[0034] In the p-type semiconductor electrode 4, the p-type semiconductor photocatalyst cuprous oxide (CuO) absorbs sunlight in the long wavelength (560 nm) and shorter wavelength band, and electrons (e) in the conduction band reduce hydrogen ions to generate hydrogen gas (H) as shown in the following formula (1). 2H + +2e - →H2(1)

[0035] In the n-type semiconductor electrode 5, ferric oxide (hematite: α-Fe2O3) oxidizes water with sunlight of wavelengths of 560 nm or less to generate oxygen gas (O2). As in the explanation for the p-type semiconductor electrode 4, sunlight of wavelengths of 560 nm or less in the visible light wavelength band is light of a wide wavelength band with high energy that reaches the earth's surface. As shown in FIG. 1, in the n-type semiconductor electrode 5, holes (h) generated by absorbing visible light and ultraviolet light in such a wide wavelength band oxidize water to produce oxygen gas (O2). Here, the energy level of the valence band of ferric oxide (hematite: α-Fe2O3) is located on the positive side of the oxidation potential of water.

[0036] In the n-type semiconductor electrode 5, the n-type semiconductor photocatalyst ferric oxide (hematite: α-Fe2O3) absorbs sunlight in the long wavelength (560 nm) and shorter wavelength band and generates oxygen gas (O2) as shown in the following formula (2). H2O→1 / 2O2+2H + +2e - (2)

[0037] The above describes the gas production apparatus 1 according to the first embodiment. With this gas production apparatus 1, hydrogen gas (H2) and oxygen gas (O2) can be produced with high efficiency using sunlight without using a semiconductor photocatalyst material made from rare metals.

[0038] In the gas manufacturing apparatus 1 of this embodiment, the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 are spaced a predetermined distance apart, so that hydrogen gas (H2) and oxygen gas (O2) can be collected in a separate state without being mixed together.

[0039] In this embodiment, the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 are short-circuited by the connection wiring 6, so that a current I flows from the p-type semiconductor electrode 4 to the n-type semiconductor electrode 5. Here, the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 have the same band gap energy Eg=2.2 (eV), so there is an advantage that the open circuit voltage between the two electrodes is large. According to this embodiment, both the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 are reliably excited by light in a wide band in the visible light wavelength band, and sufficient hydrogen generation potential and oxygen generation potential can be obtained. Therefore, in this embodiment, a gas production device 1 having a photovoltaic cell configuration that does not require an external bias can be realized.

[0040] In this embodiment, the semiconductor photocatalyst materials constituting the p-type semiconductor electrode 4 and the n-type semiconductor electrode 5 both have the same band gap energy Eg = 2.2 eV and a maximum absorption wavelength of 560 nm, so that light can be absorbed over a wide wavelength band of the ultraviolet wavelength band, and water decomposition can be performed with high efficiency, as shown in Figure 2.

[0041] [Second embodiment] In the gas production apparatus 1 shown in FIG. 1, the semiconductor photocatalytic material of the p-type semiconductor electrode 4 is replaced with silicon carbide (β-SiC) in the second embodiment of the present invention, and since the apparatus configuration is the same as that of the first embodiment, a description of the configuration will be omitted. Silicon carbide (SiC) includes β-SiC having a zinc blende structure and α-SiC which is a combination of zinc blende and wurtzite structures. In this embodiment, β-SiC is used. Silicon carbide (β-SiC) is mainly manufactured for sintering, and β-SiC is synthesized by synthesis methods such as solid-phase reaction and gas-phase reaction, and also by the Acheson method in the low reaction temperature range.

[0042] Silicon carbide (β-SiC) is a p-type semiconductor photocatalyst, and its band gap energy Eg is 2.2 eV and its maximum absorption wavelength is 560 nm. These physical properties are the same as those of the above-mentioned cuprous oxide (Cu2O). Therefore, in the case of silicon carbide (β-SiC), like the above-mentioned cuprous oxide (Cu2O), the p-type semiconductor electrode 4 absorbs sunlight in the long wavelength (560 nm) and shorter wavelength bands, and reliably advances the reaction of the above formula (1), thereby efficiently producing hydrogen gas (H2).

[0043] The semiconductor photocatalyst material of the n-type semiconductor electrode 5 is ferric oxide (hematite: α-Fe2O3) as in the first embodiment, so that the reaction of the above formula (2) can be reliably promoted and oxygen gas (O2) can be efficiently produced on the n-type semiconductor electrode 5 side.

[0044] The gas production apparatus 1 according to the present embodiment also provides the same functions and effects as the gas production apparatus 1 according to the first embodiment.

[0045] [Gas production method] Hereinafter, a gas production method will be described using the device configuration in the above-mentioned first embodiment. First, this method uses an electrolyte aqueous solution 3 adjusted to be weakly alkaline. Specifically, it is preferable to select from an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous sodium carbonate solution, and an aqueous potassium carbonate solution adjusted to be weakly alkaline.

[0046] First, an aqueous electrolyte solution 3 is placed in a reaction vessel 2, and a p-type semiconductor electrode 4 and an n-type semiconductor electrode 5 are immersed in the aqueous electrolyte solution 3 while being spaced apart from each other by a predetermined distance.

[0047] The pair of p-type semiconductor electrode 4 and n-type semiconductor electrode 5 are short-circuited with each other. Then, the pair of p-type semiconductor electrode 4 and n-type semiconductor electrode 5 immersed in the electrolyte aqueous solution 3 is irradiated with sunlight.

[0048] The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst are both selected to have a band gap energy Eg of 2.2 eV and a maximum absorption wavelength of 560 nm. As a result, hydrogen gas is produced at the p-type semiconductor electrode 4, and oxygen gas is produced at the n-type semiconductor electrode 5.

[0049] In this method, the p-type semiconductor photocatalyst may be either cuprous oxide (Cu2O) or silicon carbide (β-SiC), or both may be combined. The n-type semiconductor photocatalyst is ferric oxide (hematite: α-Fe2O3).

[0050] In this method, water is injected into the reaction vessel 2 as needed depending on the progress of water decomposition. In addition, the generated hydrogen gas (H2) and oxygen gas (O2) are appropriately collected in a hydrogen gas collector and an oxygen gas collector, not shown. (Other embodiments)

[0051] Although the embodiment of the present invention has been described above, the description and drawings forming a part of the disclosure of the embodiment should not be understood as limiting the present invention. From this disclosure, various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art.

[0052] In each of the above embodiments, a pair of rod-shaped p-type semiconductor electrode 4 and n-type semiconductor electrode 5 are used, but the shapes can be changed to various shapes, and multiple pairs may be used. [Explanation of symbols]

[0053] 1 Gas production equipment 2 Reaction vessel 3 Electrolyte aqueous solution 4 p-type semiconductor electrode 5. n-type semiconductor electrode 6 Connection Wiring

Claims

1. A gas producing apparatus comprising an electrolyte aqueous solution and a pair of electrodes immersed in the electrolyte aqueous solution, The pair of electrodes is composed of a p-type semiconductor electrode made of a p-type semiconductor photocatalyst and an n-type semiconductor electrode made of an n-type semiconductor photocatalyst, which are short-circuited with each other; the p-type semiconductor electrode and the n-type semiconductor electrode are disposed to be spaced apart from each other and configured to allow sunlight to enter both electrodes; The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a maximum absorption wavelength of 560 nm, Oxygen gas is generated at the n-type semiconductor electrode, and hydrogen gas is generated at the p-type semiconductor electrode. A gas producing apparatus comprising:

2. The p-type semiconductor photocatalyst is cuprous oxide (Cu ２ O), silicon carbide (β-SiC), and the n-type semiconductor photocatalyst is selected from ferric oxide (hematite: α-Fe ２ O ３ ) The gas production apparatus according to claim 1 .

3. The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a band gap energy (Eg) of 2.2 eV. The gas production apparatus according to claim 1 .

4. The electrolyte aqueous solution is selected from a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a sodium carbonate aqueous solution, and a potassium carbonate aqueous solution adjusted to a weak alkalinity. The gas production apparatus according to claim 1 .

5. A water supply unit is provided for injecting water into the electrolyte aqueous solution. The gas production apparatus according to claim 1 .

6. The electrolyte aqueous solution is contained in a reaction vessel formed of a transparent material having transparency to visible light. The gas production apparatus according to claim 1 .

7. The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst are thin films formed on the surfaces of the respective electrode bodies. The gas production apparatus according to claim 1 .

8. A gas producing method for producing a gas by immersing a pair of electrodes in an electrolyte aqueous solution, comprising the steps of: The pair of electrodes is composed of a p-type semiconductor electrode made of a p-type semiconductor photocatalyst and an n-type semiconductor electrode made of an n-type semiconductor photocatalyst, which are short-circuited with each other; The p-type semiconductor electrode and the n-type semiconductor electrode are arranged to be spaced apart from each other and are configured so that sunlight can be incident on both electrodes; The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst are both set to have a maximum absorption wavelength of 560 nm, Oxygen gas is generated at the n-type semiconductor electrode, and hydrogen gas is generated at the p-type semiconductor electrode. A method for producing a gas comprising the steps of:

9. The p-type semiconductor photocatalyst is cuprous oxide (Cu ２ O), silicon carbide (β-SiC), and the n-type semiconductor photocatalyst is selected from ferric oxide (hematite: α-Fe ２ O ３ ) The gas production method according to claim 8.

10. The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst both have a band gap energy (Eg) of 2.2 eV. The gas production method according to claim 8.

11. The electrolyte aqueous solution is selected from a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a sodium carbonate aqueous solution, and a potassium carbonate aqueous solution adjusted to a weak alkalinity. The gas production method according to claim 8.

12. Injecting water into the electrolyte aqueous solution from a water supply unit; The gas production method according to claim 8.

13. The electrolyte aqueous solution is placed in a reaction vessel made of a transparent material that is transparent to visible light. The gas production method according to claim 8.

14. The p-type semiconductor photocatalyst and the n-type semiconductor photocatalyst are thin films formed on the surfaces of the respective electrode bodies. The gas production method according to claim 8.

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