Artificial photosynthesis device

Abstract

This artificial photosynthesis device is used by floating same on water or an aqueous solution, the device comprising: an oxidation electrode 1 brought into contact with water or an aqueous solution; a reduction electrode 2 electrically connected to the oxidation electrode 1 and brought into contact with a gas containing carbon dioxide; an electrolyte membrane 3 joined to the reduction electrode 2 and brought into contact with the water or the aqueous solution; and a float 4 for floating the reduction electrode 2 on water or an aqueous solution.

Description

artificial photosynthesis device

[0001] The present disclosure relates to an artificial photosynthesis device.

[0002] Artificial photosynthesis is a technology that uses light to irradiate an oxidation electrode made of a photocatalyst, causing the oxidation of water and the reduction of carbon dioxide. It has attracted attention as a technology that can recycle carbon dioxide into carbon monoxide, formic acid, hydrocarbons such as ethylene, or alcohols such as methanol and ethanol, and has been actively researched in recent years.

[0003] Conventionally, a reaction system has been used in which a reduction electrode is immersed in an aqueous solution and carbon dioxide dissolved in the aqueous solution is supplied to the reduction electrode for reduction, as described in Non-Patent Document 1. However, in this method of reducing carbon dioxide, there are limitations on the concentration of carbon dioxide dissolved in the aqueous solution and the diffusion coefficient of carbon dioxide in the aqueous solution, which limits the amount of carbon dioxide that can be supplied to the reduction electrode.

[0004] To address this problem, research is being conducted into supplying gaseous carbon dioxide to the reduction electrode in order to increase the amount of carbon dioxide supplied to the reduction electrode. According to Non-Patent Document 2, by using a gas-phase reduction device having a structure capable of supplying gaseous carbon dioxide to the reduction electrode, the amount of carbon dioxide supplied to the reduction electrode is increased, and the carbon dioxide reduction reaction is promoted.

[0005] Satoshi Yotsuhashi and 6 others, “CO2 Conversion with Light and Water by GaN Photoelectrode”, Japanese Journal of Applied Physics, 51, 2012, p.02BP07-1-p.02BP07-3Qingxin Jia and 2 others, “Direct Gas-phase CO2Reduction for Solar Methane Generation Using a Gas Diffusion Electrode with a BiVO4:Mo and a Cu-In-Se Photoanode”, Chemistry Letter, 47, 2018, p.436-439

[0006] The apparatus in Non-Patent Document 2 is a two-tank gas-phase reduction apparatus equipped with an oxidation tank and a reduction tank, in which the water oxidation reaction shown in formula (1) proceeds in the oxidation tank. In the reduction tank, the carbon dioxide reduction reaction shown in formulas (2) to (5) proceeds in combination with the water oxidation reaction in the oxidation tank. As a side reaction, the hydrogen production reaction shown in formula (6) proceeds.

[0007] 2H ２ O+4h ＋ →O ２ +4H ＋ ... (1) CO ２ +2H ＋ +2e － →CO+H ２ O...(2) CO ２ +2H ＋ +2e － →HCOOH...(3) CO ２ +6H ＋ +6e － →CH ３ OH+H ２ O...(4) CO ２ +8H ＋ +8e － →CH ４ +2H ２ O...(5) 2H ＋ +2e － →H ２ ...(6)

[0008] To achieve the carbon dioxide reduction reaction described above, a three-phase interface consisting of an electrolyte, a reduction electrode, and gaseous carbon dioxide is required between the oxidation and reduction cells. Protons (H + Since carbon dioxide cannot move in the gas phase in the reduction cell, the electrolyte and the reduction electrode are in contact (joined) with each other. By directly supplying gaseous carbon dioxide to the interface between the electrolyte and the reduction electrode, the reduction reaction of carbon dioxide proceeds.

[0009] In the case of such conventional two-tank gas-phase reduction devices, water is consumed in the carbon dioxide conversion, so equipment to supply water to the oxidation tank is required. Furthermore, in a closed system such as a two-tank gas-phase reduction device, carbon dioxide gas must be introduced into the reduction tank. In particularly large devices, water pressure or carbon dioxide gas pressure is applied to the reduction electrode separating the two tanks, which can cause damage to the reduction electrode. Another issue is the need for housings for the oxidation and reduction tanks, which increases the cost of the device.

[0010] The present disclosure has been made in view of the above, and aims to provide an artificial photosynthesis device that can realize a carbon dioxide reduction reaction with a simple configuration.

[0011] One aspect of the present disclosure is an artificial photosynthesis device that is used by floating it on water or an aqueous solution, and includes an oxidation electrode in contact with the water or aqueous solution, a reduction electrode electrically connected to the oxidation electrode and in contact with a gas containing carbon dioxide, an electrolyte membrane joined to the reduction electrode and in contact with the water or aqueous solution, and a flotation device for floating the reduction electrode on the water or aqueous solution.

[0012] According to the present disclosure, it is possible to provide an artificial photosynthesis device that can realize a carbon dioxide reduction reaction with a simple configuration.

[0013] FIG. 1 is a cross-sectional view showing an example of the configuration of an artificial-photosynthesis device of a first embodiment. FIG. 2 is a cross-sectional view showing an example of the configuration of an artificial-photosynthesis device of a second embodiment. FIG. 3A is a cross-sectional view of an artificial-photosynthesis device of Example 1. FIG. 3B is a top view of the artificial-photosynthesis device of Example 1. FIG. 4A is a cross-sectional view of an artificial-photosynthesis device of Example 2. FIG. 4B is a top view of the artificial-photosynthesis device of Example 2. FIG. 5 is a diagram showing an example of the configuration of a gas-phase reduction device of a comparative example.

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the embodiments described below, and modifications may be made without departing from the spirit of the present disclosure.

[0015] <First embodiment> Figure 1 shows a cross-sectional view of an artificial-photosynthesis device according to a first embodiment of the present disclosure. The illustrated artificial-photosynthesis device is a device that performs artificial photosynthesis by irradiating an oxidation electrode with light to cause a water oxidation reaction at the oxidation electrode and a carbon dioxide reduction reaction at the reduction electrode. The oxidation reaction is as shown in formula (1) above, and the reduction reaction is as shown in formulas (2) to (5) above.

[0016] The artificial photosynthesis device of this embodiment is an artificial photosynthesis device that is used by floating on water (on water or an aqueous solution), and includes an oxidation electrode 1 in contact with water or an aqueous solution, a reduction electrode 2 electrically connected to the oxidation electrode 1 and in contact with a gas containing carbon dioxide, an electrolyte membrane 3 joined to the reduction electrode 2 and in contact with the water or aqueous solution, and a flotation device 4 for floating the reduction electrode 2 on the water. In the artificial photosynthesis device, ions (protons (H ＋ )) is supplied to the reduction electrode 2 via water or an aqueous solution and the electrolyte membrane 3.

[0017] The artificial-photosynthesis device of this embodiment is an open-system device that does not require an oxidation tank or a reduction tank. That is, the artificial-photosynthesis device of this embodiment is an open-system device that can convert carbon dioxide simply by floating it on water in a location where light such as sunlight hits the oxidation electrode 1.

[0018] The illustrated artificial photosynthesis device comprises an oxidation electrode 1, a reduction electrode 2, an electrolyte membrane 3, and a flotation device 4, and floats on water or an aqueous solution. Gas containing carbon dioxide, such as the atmosphere, exists above the water or aqueous solution (above the water).

[0019] The oxidation electrode 1 includes a photocatalytic layer 11 and a base substrate 12. The photocatalytic layer 11 may be made of a compound exhibiting photoactivity or redox activity, such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex. The oxidation electrode 1 is electrically connected to the reduction electrode 2 via a conductor (metal wire) 5. The base substrate 12 may be made of, for example, sapphire. Note that if the base substrate 12 transmits light at least in the wavelength range absorbed by the photocatalytic layer, the photocatalytic layer 11 and the base substrate 12 may be reversed, with the base substrate 12 being placed on top of the photocatalytic layer 11.

[0020] The oxidation electrode 1 is in contact with water or an aqueous solution, and in the illustrated example, the oxidation electrode 1 is immersed in water or an aqueous solution. The oxidation electrode 1 is arranged so that light strikes the photocatalytic layer 11. When the oxidation electrode 1 is irradiated with light, electron-hole pairs are generated and separated at the oxidation electrode 1, and water (H ２ Oxygen (O ２ ) and protons are generated. The protons are supplied to the reduction electrode 2 through the water or aqueous solution and the electrolyte membrane. The electrons (e － ) moves to the reduction electrode 2 via the lead wire 5.

[0021] The reduction electrode 2 is electrically connected to the oxidation electrode 1 and is in contact with a gas (atmosphere) containing carbon dioxide. At the reduction electrode 2, hydrogen (H ２ ) is produced, and a reduction reaction of carbon dioxide is triggered by the protons, electrons, and atmospheric carbon dioxide. Gas products produced by this reduction reaction of carbon dioxide, such as carbon monoxide, formic acid, and methane, are released (discharged) into the atmosphere, and liquid products are discharged onto the reduction electrode 2 or into a liquid (water or an aqueous solution).

[0022] A porous body (porous material) is used for the reduction electrode 2. Because carbon dioxide needs to reach the reduction electrode / electrolyte membrane interface, the reduction electrode 2 needs to have a pore structure, and a porous body is preferable for supplying a sufficient amount of carbon dioxide. For example, the reduction electrode 2 may be a porous body containing copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, cadmium, or an alloy thereof; a porous body containing silver oxide, copper oxide, copper(II) oxide, nickel oxide, indium oxide, tin oxide, tungsten oxide, tungsten(VI) oxide, copper oxide, or the like; or a porous body containing a porous metal complex having a metal ion and an anionic ligand.

[0023] The electrolyte membrane 3 supplies protons generated at the oxidation electrode 1 to the reduction electrode 2 via water or an aqueous solution. The electrolyte membrane 3 can be made of perfluorocarbon materials with a carbon-fluorine skeleton, such as Nafion (registered trademark), Phorblue, or Aquivion. Alternatively, the electrolyte membrane 3 can be made of hydrocarbon-based materials such as Selemion or Neocepta. In the illustrated artificial photosynthesis device, the end of the electrolyte membrane 3 to which the electrolyte membrane 3 is bonded is connected to the end of the oxidation electrode 1, thereby integrating the oxidation electrode 1 and the reduction electrode 2. In the illustrated example, the oxidation electrode 1 is disposed parallel to the water surface or the electrolyte membrane 3. The water surface includes not only the surface of the water but also the surface of the aqueous solution.

[0024] The flotation device 4 is a member for floating the reduction electrode 2 on the water (on water or an aqueous solution). In the example shown in the figure, the flotation device 4 is arranged around the reduction electrode 2. The flotation device 4 may be a polyvinyl chloride flotation device, an ethylene vinyl acetate copolymer (EVA) flotation device, polystyrene foam, polyurethane foam, polyethylene foam, a plastic bag containing air, or the like.

[0025] The water or aqueous solution in which the artificial photosynthesis device is floated can be, for example, water (including pure water), tap water, seawater, industrial wastewater, potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, rubidium hydroxide aqueous solution, cesium hydroxide aqueous solution, calcium hydroxide aqueous solution, magnesium hydroxide aqueous solution, potassium chloride aqueous solution, sodium chloride aqueous solution, rubidium chloride aqueous solution, or cesium chloride aqueous solution.

[0026] The artificial photosynthesis device is not limited to the structure shown in FIG. 1 . Specifically, the length, width, and height of the artificial photosynthesis device are not limited. For example, the length and width may be several tens of centimeters, several meters, or even several tens of meters. The shapes of the oxidation electrode 1, reduction electrode 2, and electrolyte membrane 3 may be circular or polygonal, including triangular and rectangular, as long as they float in water. One artificial photosynthesis device may contain one of each of the oxidation electrode 1, reduction electrode 2, electrolyte membrane 3, and flotation device 4, or a combination of multiple of these.

[0027] Current collection by the conductor 5 connecting the oxidation electrode 1 and the reduction electrode 2 may be at a point or over an area. Alternatively, multiple conductors 5 may be used to connect the oxidation electrode 1 and the reduction electrode 2 at multiple locations. If the reduction electrode 2 is made of a material with high resistance (does not conduct electricity well), efficient operation can be achieved by contacting the oxidation electrode 1 and the reduction electrode 2 at multiple points or over an area. The artificial photosynthesis device may also include a support member (not shown) that supports or reinforces the electrolyte membrane 3. The support member will be described later.

[0028] The conditions for operating the artificial photosynthesis device are as follows: The light (light source) to be irradiated onto the photocatalytic layer 11 of the oxidation electrode 1 may be sunlight, a xenon lamp, a solar simulator, a halogen lamp, a mercury lamp, or a combination of these. A light source other than sunlight is disposed opposite the photocatalytic layer 11 so that the light is irradiated onto the photocatalytic layer 11. In other words, the light source other than sunlight is disposed so that the light is irradiated onto the oxidation electrode 1.

[0029] The gas filling the space above the water surface can be carbon dioxide, a mixed gas containing carbon dioxide, or the atmosphere. To prevent evaporation of the water or aqueous solution, it is desirable that the temperature of the environment in which the artificial photosynthesis device is installed be below 100°C.

[0030] In this embodiment, the oxidation electrode 1 and the reduction electrode 2 are integrated, and these electrodes 1 and 2 are electrically connected. The reduction electrode 2 is disposed so that it floats on the water and comes into contact with a gas containing carbon dioxide. That is, the artificial photosynthesis device of this embodiment is not a closed-system device such as a two-tank device (oxidation tank, reduction tank), but an open-system device that is floated in the presence of water or an aqueous solution. Therefore, the artificial photosynthesis device of this embodiment can perform artificial photosynthesis anywhere in an environment with sunlight, water, and air. In the case of a closed system such as a two-tank device, the device must be placed somewhere and water must be poured in from outside the device. However, an open system such as the artificial photosynthesis device of this embodiment can be floated and used, for example, on the ocean, in a dam, a reservoir, or an industrial wastewater tank.

[0031] Furthermore, the artificial photosynthesis device of this embodiment does not require the water supply equipment required for a two-tank device, and there is no risk of damage due to water pressure and / or gas pressure on the reduction tank separating the oxidation tank and reduction tank, and housings for the oxidation tank and reduction tank are not required. Therefore, this embodiment can achieve a carbon dioxide reduction reaction with a simple configuration and at low cost.

[0032] 2 shows a cross-sectional view of an artificial-photosynthesis device of a second embodiment. Similar to the first embodiment, the artificial-photosynthesis device of this embodiment is an artificial-photosynthesis device that is floated on water and includes an oxidation electrode 1, a reduction electrode 2, an electrolyte membrane 3, and a flotation device 4.

[0033] In the artificial-photosynthesis device of this embodiment, the oxidation electrode 1 is arranged so as to be tilted downward with respect to the water surface. In the example shown, the oxidation electrode 1 is connected to the electrolyte membrane 3 so as not to be parallel to the electrolyte membrane 3, but to be tilted downward (deeper in the water) with increasing distance from the electrolyte membrane 3. In this respect, the artificial-photosynthesis device of this embodiment differs from the first embodiment, but is otherwise similar to the first embodiment.

[0034] The oxidation electrode 1 is tilted downward with respect to the water surface (i.e., angled with respect to the water surface), which makes it easier for sunlight to be irradiated onto the oxidation electrode 1. That is, even when the sun is not directly overhead, sunlight is relatively easily irradiated onto the oxidation electrode 1. In addition, stability against fluctuations in the water surface is improved.

[0035] Example 1 Example 1 of the artificial-photosynthesis device of the first embodiment will be described with reference to Figures 3A and 3B. Figure 3A is a cross-sectional view of the artificial-photosynthesis device of this example, and Figure 3B is a top view of the artificial-photosynthesis device of this example.

[0036] The artificial photosynthesis device of this example includes a support member 6 placed on the underside of the electrolyte membrane 3, and the oxidation electrode 1 is adhered to the end of the support member 6. The support member 6 supports or reinforces the electrolyte membrane 3. The reduction electrode 2 and electrolyte membrane 3 are placed on the support member 6. The support member 6 has, for example, mesh-like holes (pores) through which ions can pass, in order to supply ions generated at the oxidation electrode 1 to the reduction electrode 2 via the aqueous solution and the electrolyte membrane 3.

[0037] The support member 6 can be made of, for example, PFA, PTFE, polyethylene, polyethylene terephthalate, polystyrene, polypropylene, polyvinyl chloride, acrylic resin, ABS resin, ASA resin, polycarbonate, nylon, etc. The support member 6 can be made using, for example, a 3D printer, but is not limited to this. In this example, a PFA plate with mesh-shaped holes made using a 3D printer was used. PFA is a thermoplastic resin, a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene.

[0038] The external shape of the oxidation electrode 1 shown in Figures 3A and 3B is a rectangle measuring 10 cm in length and width, with a cutout in the center where the reduction electrode 2 and electrolyte membrane 3 are located. The reduction electrode 2 joined to the electrolyte membrane 3 is a rectangle measuring 3 cm in length and width. The float 4 is disposed on the electrolyte membrane 3 around the reduction electrode 2. The electrolyte membrane 3 is larger than the reduction electrode 2. The illustrated artificial photosynthesis device is an example, and the artificial photosynthesis device of the present disclosure is not limited to Figures 3A and 3B. For example, in the illustrated artificial photosynthesis device, the oxidation electrode 1 is disposed around the electrolyte membrane 3, but the oxidation electrode 1 may be disposed adjacent to a portion (e.g., one side) of the electrolyte membrane 3. The shapes, sizes, and positional relationships of the oxidation electrode 1, reduction electrode 2, and electrolyte membrane 3 are not limited to those shown in Figures 3A and 3B.

[0039] A method for producing the artificial photosynthesis device of this example will be described below.

[0040] The photocatalytic layer 11 of the oxidation electrode 1 is made of AlGaN / n-GaN, and the base substrate 12 is made of 0.4 mm thick sapphire. The reduction electrode 2 is made of 0.5 cm thick sintered Au fiber with a porosity of 80%. The electrolyte membrane 3 is a Nafion 117 membrane, and the flotation device 4 is a PVC float ring. The support member 6 is a 1 cm thick PFA plate with multiple holes.

[0041] The oxide electrode 1 is fabricated by forming a semiconductor photocatalytic layer 11 on a base substrate 12. Specifically, a thin film of n-GaN, an n-type semiconductor, and AlGaN are epitaxially grown in this order on the sapphire substrate 12, and Ni is vacuum-deposited on the AlGaN and heat-treated to form a NiO promoter thin film, thereby fabricating the oxide electrode 1 (semiconductor photoelectrode). The fabricated oxide electrode 1 is then shaped to a predetermined size as shown in FIG. 3B.

[0042] The reduction electrode 2 is bonded to one side (top) of the electrolyte membrane 3 using thermocompression bonding (150°C, 5 MPa). A 1 cm thick support member 6 (PFA plate) is bonded to the other side (bottom) of the electrolyte membrane 3 with a resin adhesive. The outer edge of the bottom side of the support member 6, opposite the electrolyte membrane 3, is then bonded to the oxidation electrode 1 with a resin adhesive. Finally, the n-GaN layer of the semiconductor photocatalyst layer and the reduction electrode are electrically connected using four conductors 5 (metal wires), completing the artificial photosynthesis device.

[0043] The artificial photosynthesis device constructed in this way is floated on a 1 mol / L potassium hydroxide aqueous solution (KOH 1M) under sunlight, and 100% pure carbon dioxide is supplied to the space above the solution.

[0044] As a result, in the artificial photosynthesis device of this embodiment, the following water oxidation reaction occurs at the oxidation electrode 1 and the following reduction reaction occurs at the reduction electrode 2, thereby converting carbon dioxide into carbon monoxide.

[0045] 2H2O+4h + →O2+4H + CO 2 + 2H + + 2e - → CO + HO

[0046] Example 2 An example of the artificial-photosynthesis device of the second embodiment will be described with reference to Figures 4A and 4B. Figure 4A is a cross-sectional view of the artificial-photosynthesis device of this example, and Figure 4B is a top view of the artificial-photosynthesis device of this example.

[0047] In the artificial-photosynthesis device of this embodiment, the support member 6A is different from the support member 6 of Example 1. Specifically, the artificial-photosynthesis device of this embodiment includes a support member 6A that is arranged on the underside of the electrolyte membrane 3 to which the reduction electrode 2 is bonded and the oxidation electrode 1, and the portion of the support member 6A that is arranged on the underside of the oxidation electrode 1 is inclined downward at a predetermined angle with respect to the portion of the support member 6A that is arranged on the underside of the electrolyte membrane 3. In this embodiment, the predetermined angle is 30 degrees. The rest is the same as Example 1.

[0048] Of the support member 6A of this example, the portion disposed on the underside of the electrolyte membrane 3 has, similar to the support member 6 of Example 1, holes (pores), for example in a mesh shape, through which ions can pass in order to supply protons generated at the oxidation electrode 1 to the reduction electrode 2 via the aqueous solution and the electrolyte membrane 3. On the other hand, the support member 6A of the portion disposed on the underside of the oxidation electrode 1 does not need to have holes. In this example as well, a 1 cm thick PFA plate fabricated with a 3D printer is used as the support member 6A.

[0049] In this embodiment, the use of an angled support member 6 allows the oxidation electrode 1 to be fixed so as to tilt downward. Specifically, the oxidation electrode 1 can be fixed so as to tilt downward (deeper in water) as it moves away from the electrolyte membrane 3.

[0050] The method for producing the artificial-photosynthesis device of this example differs from that of Example 1 in that the oxidation electrode 1 is placed on a support member 6A and the two are bonded together with a resin adhesive, but is otherwise similar to that of Example 1.

[0051] The artificial photosynthesis device fabricated in this way is floated on a 1 mol / L potassium hydroxide aqueous solution (KOH 1M) under sunlight, and 100% pure carbon dioxide is supplied to the space above this solution. As a result, in the artificial photosynthesis device of this example, the following water oxidation reaction occurs at oxidation electrode 1 and the following reduction reaction occurs at reduction electrode 2, converting carbon dioxide to carbon monoxide.

[0052] 2H2O+4h + →O2+4H + CO 2 + 2H + + 2e - → CO + HO

[0053] <Comparative Example> Next, a gas-phase reduction device (artificial photosynthesis device) of a comparative example will be described with reference to FIG. 5 . The illustrated gas-phase reduction device is a two-tank device equipped with an oxidation tank 31 and a reduction tank 34, and utilizes artificial photosynthesis technology to reduce carbon dioxide by light irradiation. The oxidation tank 31 is filled with an aqueous solution 33, and an oxidation electrode 32 is inserted into the aqueous solution 33. The oxidation electrode 32 is electrically connected to a reduction electrode 35 by a conductor 37. A composite 40 formed by joining the reduction electrode 35 and an electrolyte membrane 36 is disposed between the oxidation tank 31 and the reduction tank 34. Carbon dioxide is supplied to the reduction tank 34 through the gas inlet 30, and the reduction tank 34 is filled with carbon dioxide or a gas containing carbon dioxide. A light source 39 is disposed opposite the oxidation electrode 32 to drive the gas-phase reduction device.

[0054] Such a two-tank gas-phase reduction apparatus (closed system) requires equipment (not shown) for supplying water to the oxidation tank 31, and also requires equipment (not shown) for introducing carbon dioxide gas into the reduction tank 34. Furthermore, in a large-scale apparatus, water pressure or carbon dioxide gas pressure is applied to the reduction electrode 35 separating the two tanks, which can cause damage to the reduction electrode 35. Furthermore, the gas-phase reduction apparatus of the comparative example requires housings for the oxidation tank 31 and the reduction tank 34, resulting in high equipment costs.

[0055] In contrast, the artificial-photosynthesis device of the first and second embodiments described above is an artificial-photosynthesis device that is used by floating on water or an aqueous solution, and includes an oxidation electrode 1 in contact with the water or aqueous solution, a reduction electrode 2 electrically connected to the oxidation electrode 1 and in contact with a gas containing carbon dioxide, an electrolyte membrane 3 joined to the reduction electrode 2 and in contact with the water or aqueous solution, and a flotation device 4 for floating the reduction electrode 2 on the water or aqueous solution.

[0056] As a result, in this embodiment, a carbon dioxide reduction reaction can be achieved with a simple configuration. Specifically, the artificial-photosynthesis device of this embodiment does not require an oxidation tank or a reduction tank, and can be produced at low cost. Furthermore, because the artificial-photosynthesis device of this embodiment is an open system, the reduction electrode 2 will not be damaged by water pressure or carbon dioxide gas pressure.

[0057] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0058] 1: Oxidation electrode 11: Photocatalytic layer 12: Base substrate 2: Reduction electrode 3: Electrolyte membrane 4: Float 5: Conductor 6, 6A: Support member 30: Gas inlet 31: Oxidation tank 32: Oxidation electrode 33: Aqueous solution 34: Reduction tank 35: Reduction electrode 36: Electrolyte membrane 37: Conductor 39: Light source 40: Composite

Claims

1. An artificial photosynthesis device that is used by floating on water or an aqueous solution, comprising: an oxidation electrode in contact with the water or aqueous solution; a reduction electrode electrically connected to the oxidation electrode and in contact with a gas containing carbon dioxide; an electrolyte membrane joined to the reduction electrode and in contact with the water or aqueous solution; and a flotation device for floating the reduction electrode on the water or aqueous solution.

2. The artificial photosynthesis device according to claim 1, wherein ions generated at the oxidation electrode by irradiation with light are supplied to the reduction electrode via the water or aqueous solution and the electrolyte membrane.

3. The artificial photosynthesis device according to claim 1, wherein the oxidation electrode is disposed tilted downward with respect to the water surface.

4. The artificial photosynthesis device according to claim 1, wherein the oxidation electrode is arranged parallel to the water surface or the reduction electrode.

5. The artificial photosynthesis device according to claim 1, further comprising a support member disposed on the lower surface of the electrolyte membrane, and the oxidation electrode is bonded to an end of the support member.

6. The artificial photosynthesis device according to claim 1, further comprising a support member disposed on the underside of the electrolyte membrane to which the reduction electrode is joined and the oxidation electrode, wherein the portion of the support member disposed on the underside of the oxidation electrode is inclined downward at a predetermined angle relative to the portion of the support member disposed on the underside of the electrolyte membrane.

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