Humidifier, carbon dioxide reduction device, and carbon dioxide reduction method

Abstract

This carbon dioxide reduction device comprises: an oxidation tank 1 in which an aqueous solution 3 is stored; an empty reduction tank 2; a photocatalytic oxidation electrode 4 inserted into the aqueous solution 3; an electrolyte membrane 7 arranged between the oxidation tank 1 and the reduction tank 2; a reduction electrode 8 joined to the surface of the electrolyte membrane 7 in the reduction tank 2; a lead wire 9 connected between the oxidation electrode 4 and the reduction electrode 8; and a light source 15 that irradiates the oxidation electrode 4 with light. A humidifier 14 supplies humidified carbon dioxide to the reduction tank 2 and controls the supply amount of the humidified carbon dioxide.

Description

Humidification device, carbon dioxide reduction device, and carbon dioxide reduction method

[0001] The present disclosure relates to a humidifier, a carbon dioxide reduction device, and a carbon dioxide reduction method.

[0002] There are carbon dioxide reduction devices that promote the oxidation reaction of water and the reduction reaction of carbon dioxide by irradiating an oxidation electrode made of a photocatalyst with light, and there are carbon dioxide reduction devices that promote the oxidation reaction of water and the reduction reaction of carbon dioxide by applying a voltage between an oxidation electrode and a reduction electrode made of metal.

[0003] Regarding the carbon dioxide reduction device, Non-Patent Documents 1 and 2 disclose a method 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. However, in this method, there is a limit to the concentration of carbon dioxide dissolved in the aqueous solution and the diffusion coefficient of carbon dioxide in the aqueous solution, and therefore the amount of carbon dioxide supplied to the reduction electrode is limited.

[0004] Therefore, Non-Patent Document 3 employs a method in which gaseous carbon dioxide is directly supplied to the reduction electrode without immersing the reduction electrode in an aqueous solution, thereby increasing the amount of carbon dioxide supplied to the reduction electrode and promoting the reduction reaction of carbon dioxide.

[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.02BP07-3Yoshio Hori and 2 others, “Formation of Hydrocarbons in the Electrochemical Reduction of Carbone Dioxide at a Copper Electrode in Aqueous Solution”, Journal of the Chemical Society, 85(8), 1989, p.2309-p.2326Qingxin Jia, et al., “Direct Gas-phase CO2 Reduction for Solar Methane Generation Using a Gas Diffusion Electrode with a BiVO4:Mo and a Cu-In-Se Photoanode”, Chemistry Letter, 47, January 13, 2018, p.436-p.439

[0006] However, at the interface between the reduction electrode and the electrolyte membrane, a salt is produced by a neutralization reaction between the aqueous solution in the oxidation chamber that has permeated the electrolyte membrane and the gaseous carbon dioxide in the reduction chamber. This salt solidifies when exposed to the gaseous carbon dioxide and precipitates on the surface of the reduction electrode, gradually inhibiting the supply of gaseous carbon dioxide to the reduction electrode and reducing the efficiency of the carbon dioxide reduction reaction.

[0007] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a technology capable of improving the carbon dioxide reduction reaction in a carbon dioxide reduction device that supplies gaseous carbon dioxide to a reduction electrode.

[0008] A humidification device according to one aspect of the present disclosure supplies humidified carbon dioxide to a carbon dioxide reduction device that includes an oxidation tank that stores an aqueous solution, an empty reduction tank, a photocatalytic oxidation electrode that is inserted into the aqueous solution, an electrolyte membrane that is disposed between the oxidation tank and the reduction tank, a reduction electrode that is bonded to the surface of the electrolyte membrane within the reduction tank, a conductor that is connected between the oxidation electrode and the reduction electrode, and a light source that irradiates the oxidation electrode with light, and controls the amount of humidified carbon dioxide that is supplied to the reduction tank.

[0009] A humidification device according to one aspect of the present disclosure supplies humidified carbon dioxide to a reduction tank and controls the amount of humidified carbon dioxide supplied to a carbon dioxide reduction device that includes an oxidation tank in which an aqueous solution is stored, an empty reduction tank, an oxidation electrode inserted into the aqueous solution, an electrolyte membrane disposed between the oxidation tank and the reduction tank, a reduction electrode joined to the surface of the electrolyte membrane within the reduction tank, a conductor connected between the oxidation electrode and the reduction electrode, and a power source that applies a voltage to the conductor.

[0010] A carbon dioxide reduction device according to one aspect of the present disclosure includes an oxidation tank that stores an aqueous solution, an empty reduction tank, a photocatalytic oxidation electrode that is inserted into the aqueous solution, an electrolyte membrane that is disposed between the oxidation tank and the reduction tank, a reduction electrode that is bonded to the surface of the electrolyte membrane within the reduction tank, a conducting wire that is connected between the oxidation electrode and the reduction electrode, a light source that irradiates the oxidation electrode with light, and a humidifier that supplies humidified carbon dioxide to the reduction tank and controls the amount of the humidified carbon dioxide supplied.

[0011] A carbon dioxide reduction device according to one aspect of the present disclosure includes an oxidation tank that stores an aqueous solution, an empty reduction tank, an oxidation electrode that is inserted into the aqueous solution, an electrolyte membrane that is disposed between the oxidation tank and the reduction tank, a reduction electrode that is bonded to the surface of the electrolyte membrane within the reduction tank, a conductor that is connected between the oxidation electrode and the reduction electrode, a power source that applies a voltage to the conductor, and a humidifier that supplies humidified carbon dioxide to the reduction tank and controls the amount of humidified carbon dioxide supplied.

[0012] A carbon dioxide reduction method according to one aspect of the present disclosure is a carbon dioxide reduction method performed using a carbon dioxide reduction device including an oxidation tank that stores an aqueous solution, an empty reduction tank, a photocatalytic oxidation electrode that is inserted into the aqueous solution, an electrolyte membrane that is arranged between the oxidation tank and the reduction tank, a reduction electrode that is joined to the surface of the electrolyte membrane within the reduction tank, a lead wire that is connected between the oxidation electrode and the reduction electrode, a light source that irradiates the oxidation electrode with light, and a humidifier, in which the humidifier supplies humidified carbon dioxide to the reduction tank while controlling the supply amount of the humidified carbon dioxide.

[0013] A carbon dioxide reduction method according to one aspect of the present disclosure is a carbon dioxide reduction method performed using a carbon dioxide reduction device including: an oxidation tank containing an aqueous solution; an empty reduction tank; an oxidation electrode inserted into the aqueous solution; an electrolyte membrane disposed between the oxidation tank and the reduction tank; a reduction electrode joined to the surface of the electrolyte membrane within the reduction tank; a conductor connected between the oxidation electrode and the reduction electrode; a power source that applies a voltage to the conductor; and a humidifier, wherein the humidifier supplies humidified carbon dioxide to the reduction tank while controlling the supply amount of the humidified carbon dioxide.

[0014] According to the present disclosure, it is possible to provide a technology that can suppress a decrease in the efficiency of the carbon dioxide reduction reaction.

[0015] Fig. 1 is a diagram showing a first configuration example of a carbon dioxide reduction device. Fig. 2 is a diagram showing a second configuration example of a carbon dioxide reduction device. Fig. 3 is a diagram showing a first configuration example of a humidifier. Fig. 4 is a diagram showing a second configuration example of a humidifier. Fig. 5 is a diagram showing an image of carbonates. Fig. 6 is a diagram showing an image of carbon dioxide supply obstruction.

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0017] "Summary of the Disclosure" The disclosure belongs to the technical fields of fuel generation technology, solar energy conversion technology, and carbon dioxide fixation technology, and relates to a carbon dioxide reduction device that induces a carbon dioxide reduction reaction by light irradiation, and a carbon dioxide reduction device that induces an electrolytic reduction reaction of carbon dioxide.

[0018] The present disclosure supplies humidified carbon dioxide to the oxidation tank of the carbon dioxide reduction device. That is, carbon dioxide containing moisture is supplied into the reduction tank. This causes salts that precipitate on the surface of the reduction electrode to dissolve and fall downward. In other words, it is possible to prevent salts that are generated as the carbon dioxide reduction reaction progresses from precipitating as a solid and adhering to the electrode surface. As a result, it is possible to suppress a decrease in the efficiency of the carbon dioxide reduction reaction, even when the carbon dioxide reduction device is operated for a long period of time.

[0019] [Configuration of Carbon Dioxide Reduction Device] The configuration of the carbon dioxide reduction device according to this embodiment will be described.

[0020] FIG. 1 is a diagram showing a first configuration example of a carbon dioxide reduction device.

[0021] Configuration Example 1, like Configuration Example 2 described below, is a carbon dioxide reduction device that directly supplies gaseous carbon dioxide to a reduction electrode. However, Configuration Example 1 is a light-driven carbon dioxide reduction device that causes a water oxidation reaction and a carbon dioxide reduction reaction to proceed by irradiating light onto an oxidation electrode made of a photocatalyst. This carbon dioxide reduction device is a carbon dioxide reduction device that utilizes an artificial photosynthesis reaction.

[0022] The carbon dioxide reduction device of Configuration Example 1 comprises an oxidation tank 1 and a reduction tank 2, which are formed by dividing the internal space of a single housing in two. The oxidation tank 1 is filled with an aqueous solution 3, into which a photocatalytic oxidation electrode 4 and a tube 5 are inserted. A gas outlet hole 6 is formed in the top of the oxidation tank 1.

[0023] A reduction electrode / electrolyte membrane composite, in which an electrolyte membrane 7 and a reduction electrode 8 are joined together, is disposed between the oxidation cell 1 and the reduction cell 2. The electrolyte membrane 7 is disposed on the oxidation cell 1 side, and the reduction electrode 8 is disposed on the reduction cell 2 side. The oxidation electrode 4 and the reduction electrode 8 are connected by a conductor 9, and an ammeter 10 is connected to the conductor 9.

[0024] The reduction tank 2 is empty and has a gas inlet 11 and a gas outlet 12. A pipe 13 is attached to the gas inlet 11, and a humidifier 14 is provided in the reduction tank 2 via the pipe 13.

[0025] The humidifier 14 supplies humidified carbon dioxide to the reduction tank 2 and controls the supply rate and / or supply amount of the humidified carbon dioxide. Any humidified carbon dioxide may be used, and a gas containing humidified carbon dioxide may also be used. In other words, the humidifier 14 controls the supply rate and / or supply amount of carbon dioxide containing water (water vapor) or a gas containing carbon dioxide containing water (water vapor) to input into the empty reduction tank 2.

[0026] In order to operate the carbon dioxide reduction device of the above-mentioned Configuration Example 1, a light source 15 is installed outside the oxidation vessel 1 .

[0027] FIG. 2 is a diagram showing a second configuration example of a carbon dioxide reduction device.

[0028] Configuration example 2 is a power-driven carbon dioxide reduction device that causes a water oxidation reaction and a carbon dioxide reduction reaction to proceed by applying a voltage between a metal oxidation electrode 4 and a reduction electrode 8. This carbon dioxide reduction device is a carbon dioxide reduction device that uses an electrolytic reduction reaction that utilizes electricity derived from renewable energy.

[0029] In Configuration Example 2, the oxidation electrode 4 is made of metal, and a power source 16 is connected to the lead wire 9 instead of the light source 15. Other than these, the configuration is the same as Configuration Example 1. However, the oxidation electrode 4 may be made of any material other than metal as long as it is a conductive material and active in the reaction of generating oxygen from water.

[0030] Here, specific examples of each component will be described.

[0031] The aqueous solution 3 is, for example, an aqueous potassium hydrogen carbonate solution, an aqueous sodium hydrogen carbonate solution, an aqueous potassium chloride solution, an aqueous sodium chloride solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous rubidium hydroxide solution, or an aqueous cesium hydroxide solution.

[0032] The oxidation electrode 4 is made of, for example, a nitride semiconductor, titanium oxide, or amorphous silicon. The oxidation electrode 4 may also be made of a compound that exhibits photoactivity or redox activity, such as a ruthenium complex or a rhenium complex.

[0033] The electrolyte membrane 7 is, for example, Nafion, Forblue, or Aquivion, which are electrolyte membranes having a carbon-fluorine skeleton. The electrolyte membrane 7 may also be Selemion or Neosepta, which are electrolyte membranes having a hydrocarbon skeleton.

[0034] The reduction electrode 8 is made of, for example, copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, or cadmium. The reduction electrode 8 may also be a porous body of an alloy thereof. The reduction electrode 8 may also be a porous body of silver oxide, copper oxide, copper(II) oxide, nickel oxide, indium oxide, tin oxide, tungsten oxide, tungsten(VI) oxide, copper oxide, or the like. The reduction electrode 8 may also be a porous metal complex having a metal ion and an anionic ligand.

[0035] The light source 15 is, for example, a xenon lamp, a pseudo-sunlight source, a halogen lamp, a mercury lamp, or sunlight, or may be a combination of these.

[0036] [Principle of Carbon Dioxide Reduction] The carbon dioxide reduction device of Configuration Example 1 will be described as an example.

[0037] Nitrogen is flowed into the aqueous solution 3 in the oxidation tank 1 through a tube 5, and carbon dioxide containing water is flowed into the reduction tank 2 through a humidifier 14. After the oxidation tank 1 and the reduction tank 2 are respectively replaced with nitrogen and carbon dioxide containing water, light is irradiated from a light source 15 toward the oxidation electrode 4.

[0038] When light is irradiated onto the oxidation electrode 4, electron-hole pairs are generated and separated at the oxidation electrode 4, and oxygen and protons are generated by a water oxidation reaction. The electrons move from the oxidation electrode 4 to the reduction electrode 8 via a lead wire 9. The protons reach the reduction electrode 8 from the oxidation vessel 1 via the electrolyte membrane 7. Oxygen is released from the gas outlet hole 6 of the oxidation vessel 1.

[0039] As a result, protons (H ＋ ) and electrons (e － ) and carbon dioxide (CO ) from the humidifier 14 ２) causes a reduction reaction of carbon dioxide, and simultaneously with this reduction reaction, hydrogen is produced as a by-product by the combination of protons and electrons. This reduction reaction of carbon dioxide produces carbon monoxide, formic acid, methane, and other substances that can be used as energy resources or chemical raw materials, and these are released from the gas outlet port 12 of the reduction tank 2.

[0040] <Oxidation tank: Water oxidation reaction> 2H ２ O+4h ＋ →O ２ +4H ＋ <Reduction tank: carbon dioxide reduction reaction (target reaction)> CO ２ +2H ＋ +2e － →CO+H ２ O CO ２ +2H ＋ +2e － →HCOOH CO ２ +6H ＋ +6e － →CH ３ OH+H ２ O CO ２ +8H ＋ +8e － →CH ４ +2H ２ O <Reduction chamber: hydrogen production reaction (side reaction)> 2H ＋ +2e － →H ２ The principle of carbon dioxide reduction is the same in the case of the carbon dioxide reduction device of Configuration Example 2. However, in Configuration Example 2, as described above, the oxidation electrode 4 is preferably made of a conductive material that is active in the reaction of generating oxygen from water. For example, in addition to metals such as platinum, gold, silver, copper, indium, and nickel, metal oxides and metal complexes may also be used.

[0041] As a result of the above, it is possible to recycle carbon dioxide into carbon monoxide, formic acid, hydrocarbons such as ethylene, and alcohols such as methanol and ethanol.

[0042] [Humidifier] As described above, the humidifier 14 supplies carbon dioxide containing water (water vapor) or gas containing carbon dioxide containing water (water vapor) to the reduction tank 2. The humidifier 14 will be described.

[0043] FIG. 3 is a diagram showing a first example of the configuration of the humidifier 14. As shown in FIG.

[0044] The humidifier 14 of configuration example 1 is a bubbling type humidifier that generates carbon dioxide containing water (water vapor) or a gas containing carbon dioxide containing water (water vapor) by bubbling carbon dioxide through water.

[0045] This humidifier 14 flows carbon dioxide through a tube 141 into water 143 in a humidifying tank 142 , and the carbon dioxide containing water (water vapor) passing through the water 143 is supplied to the reduction tank 2 through a pipe 13 .

[0046] At this time, the humidifier 14 supplies carbon dioxide containing water (water vapor) to the reduction tank 2 at a supply rate and / or supply amount necessary to prevent salt precipitation on the surface of the reduction electrode 8 in the reduction tank 2.

[0047] For example, the supply rate v of carbon dioxide containing water (water vapor) is calculated based on the current I [A] (measurement value of the ammeter 10) during operation of the carbon dioxide reduction device. （Ｈ２Ｏ） [g （Ｈ２Ｏ） / sec] is the supply rate v defined in equation (1) （Ｈ２Ｏ＿ｃａｌ） The feed rate is set to exceed [g / sec].

[0048]

[0049] θ [g / 100g （Ｈ２Ｏ） ] is a salt (e.g., carbonate KHCO ３ β [g / C] is a proportionality constant specific to the carbon dioxide reduction device, and when the amount of salt produced when the carbon dioxide reduction device is operated at a current of I [A] for Δt [sec] is m [g], β = m / (I Δt).

[0050] The supply rate and / or supply amount of carbon dioxide containing water (water vapor) may be controlled by the flow rate of carbon dioxide, by humidity, or by both.

[0051] In order to measure the flow rate of carbon dioxide, a mass flow controller 144 is attached to the tube 141. The mass flow controller 144 may be located upstream or downstream of the humidification tank 142, or downstream of the reduction tank 2.

[0052] To measure humidity, a hygrometer 145 is attached inside the humidification tank 142. The hygrometer 145 may be installed in the space between the humidification tank 142 and the reduction tank 2, or inside the reduction tank 2, as long as it can monitor the humidity of the gas after it has passed through the water in the humidification tank 142. An air conditioning system 146 is provided to adjust the humidity, temperature, and air pressure.

[0053] Humidity may be adjusted by temperature or pressure. Considering the durability of the housing of the carbon dioxide reduction device and the electrolyte membrane 7, high pressure is not possible and the humidity range is narrowed, so adjusting it by temperature is preferable because it allows for a wider humidity range. Temperature may be adjusted by air conditioning or a thermostatic bath.

[0054] FIG. 4 is a diagram showing a second configuration example of the humidifier 14. In FIG.

[0055] The humidifier 14 of Configuration Example 2 is a mixing-type humidifier that mixes carbon dioxide and water (water vapor) in a pipeline 13 and supplies the mixture to the reduction tank 2. This humidifier 14 outputs non-humidified carbon dioxide from a carbon dioxide output device 147 and simultaneously outputs a humidified gas (e.g., nitrogen or air) from a humidified gas output device 148, mixes them in the pipeline 13, and supplies them to the reduction tank 2. As in Configuration Example 1, the mixed carbon dioxide and gas are supplied at a supply rate and / or supply amount that exceeds the supply rate and / or supply amount defined by formula (1).

[0056] As described above, in this embodiment, a conventional carbon dioxide reduction apparatus is equipped with a humidifier 14. This humidifier 14 supplies carbon dioxide containing water (water vapor) or a gas containing carbon dioxide containing water (water vapor) to the reduction tank 2. Therefore, even if salts such as carbonates precipitate on the surface of the reduction electrode 8, the salts contain water and adhere to the surface of the reduction electrode 8 in a solution state, so they flow down to the bottom of the reduction tank 2.

[0057] This makes it possible to reliably prevent deposition and adhesion of solidified salt on the surface of the reduction electrode 8, even when the carbon dioxide reduction device is operated for a long period of time to continue the reduction reaction, and to suppress a decrease in the faradaic efficiency of the carbon dioxide reduction reaction.

[0058] [Examples] [Example 1] In Example 1, the humidifier 14 of Configuration Example 1 was attached to the carbon dioxide reduction device of Configuration Example 1.

[0059] In Example 1, a gold porous body was used for the reduction electrode 8, and a cation exchange membrane was used for the electrolyte membrane 7. The gold porous body and the cation exchange membrane were stacked one above the other and placed between a pair of copper plates. This sample was heated in a thermocompression bonding device, and pressure was applied vertically inward from above and below. The sample was then cooled and removed, yielding a reduction electrode / electrolyte membrane composite in which the reduction electrode 8 and the electrolyte membrane 7 were joined together.

[0060] The oxidation electrode 4 was prepared by epitaxially growing a gallium nitride thin film and an aluminum gallium nitride thin film, both n-type semiconductors, on a sapphire substrate in that order, and then vacuum-depositing nickel thereon and subjecting it to heat treatment to form a nickel oxide promoter thin film. The oxidation electrode 4 was then immersed in the aqueous solution 3 in the oxidation vessel 1. The aqueous solution 3 was a potassium hydroxide solution.

[0061] A high-pressure xenon lamp was used as the light source 15, and was fixed so that the surface of the semiconductor photoelectrode of the oxidation electrode 4 on which the oxidation promoter was formed was the irradiated surface. The light irradiated area of ​​the oxidation electrode 4 was set to an area sufficient to receive the light.

[0062] Nitrogen was flowed into the oxidation tank 1 through the tube 5. In addition, a gas containing carbon dioxide (or a gas consisting only of carbon dioxide) was flowed into the pure water 143 through the tube 141 of the humidifier 14, and the humidified carbon dioxide containing water after passing through the pure water 143 was flowed into the reduction tank 2.

[0063] At this time, the flow rate of the gas into the pure water 143 was controlled by a mass flow controller 144 installed upstream of the humidifying tank 142. The humidity of the gas was also adjusted using an air conditioning system 146. Furthermore, the humidity of the gas after passing through the pure water 143 was measured by a hygrometer 145 installed in the humidifying tank 142.

[0064] Water supply rate v to reduction tank 2 （Ｈ２Ｏ） [mg / sec] was controlled by the humidity H [mg / mL] of the gas and the flow rate Q [mL / min] of the gas as shown in equation (2), and was controlled so as to satisfy equation (1).

[0065]

[0066] After the oxidation vessel 1 and the reduction vessel 2 were each thoroughly purged with nitrogen and carbon dioxide gas containing water (water vapor), light was uniformly irradiated onto the oxidation electrode 4 from the light source 15 .

[0067] Example 2 In Example 2, the humidifier 14 of Configuration Example 1 was attached to the carbon dioxide reduction apparatus of Configuration Example 2. The supply rate and / or supply amount of the carbon dioxide-containing gas containing water (water vapor) to the reduction tank 2 was set to satisfy the supply rate and / or supply amount of formula (1), as in Example 1.

[0068] Comparative Example 1 was carried out using the carbon dioxide reduction apparatus of Configuration Example 1, which was not equipped with the humidifier 14, and carbon dioxide with a purity of 99.99% or higher was directly flowed into the reduction tank 2 from the pipe 13. In addition, water vapor was flowed into the reduction tank 2, and the supply rate and / or supply amount of the water vapor was set so as not to satisfy formula (1). The rest was the same as in Example 1.

[0069] Comparative Example 2 was carried out using the carbon dioxide reduction apparatus of Configuration Example 2, which did not include the humidifier 14, and carbon dioxide with a purity of 100% was directly flowed into the reduction tank 2 from the pipe 13. In addition, water vapor was flowed into the reduction tank 2, and the supply rate and / or supply amount of the water vapor was set so as not to satisfy formula (1). The rest was the same as in Example 2.

[0070] [Results of Examples and Comparative Examples] The results of Examples 1 and 2 and Comparative Examples 1 and 2 are as shown in the table below.

[0071]

[0072] FE stands for Faraday efficiency. The FE maintenance rate is the value obtained by dividing the final FE by the initial FE.

[0073] In Comparative Examples 1 and 2, the supply rate of water vapor was set to a value lower than that required to prevent salt deposition, resulting in salt deposition and a significant decrease in the Faraday efficiency. ３ As shown in FIG. 6, this carbonate KHCO３ It is believed that the deposition and adhesion of carbon dioxide gradually hindered the supply of gaseous carbon dioxide to the reduction electrode 8, resulting in a significant decrease in the faradaic efficiency.

[0074] On the other hand, in Examples 1 and 2, the supply rate of carbon dioxide gas containing water (water vapor) was set to a rate higher than that required to prevent salt deposition, which is thought to have prevented salt deposition and adhesion, and as a result, the Faraday efficiency was maintained.

[0075] [Calculation Method of Faraday Efficiency] The Faraday efficiency is calculated using equation (3).

[0076]

[0077] The current value [A] of each reduction reaction is determined by converting the measured value of the amount of each reduction product produced into the number of electrons required for that production reaction.

[0078] When the reduction reaction product is a gas, calculation is performed using equation (4).

[0079]

[0080] A [ppm] is the gas concentration. B [L / sec] is the flow rate of the carrier gas. Z is the number of electrons required for the reduction reaction. F [C / mol] is the Faraday constant. V ｍ [L / mol] is the molar volume of the gas.

[0081] When the reduction reaction product is a liquid, the integrated amount is generally measured rather than the change over time of the liquid, and therefore, calculation is performed using equation (5).

[0082]

[0083] A' [ppm] is the liquid concentration. G [L] is the total amount of liquid. ρ [g / L] is the density. Z is the number of electrons required for the reduction reaction. F [C / mol] is the Faraday constant. M [g / mol] is the molar mass. t [sec] is the measurement time.

[0084] [Effects of this embodiment] In this embodiment, humidified carbon dioxide is supplied to the reduction tank of the carbon dioxide reduction device, and the amount of humidified carbon dioxide supplied is controlled, so that salt precipitated on the surface of the reduction electrode becomes dissolved and falls downward. In other words, it is possible to prevent salt generated as the carbon dioxide reduction reaction progresses from precipitating as a solid on the electrode surface and adhering to it. As a result, it is possible to suppress a decrease in the efficiency of the carbon dioxide reduction reaction, even when the carbon dioxide reduction device is operated for a long period of time.

[0085] REFERENCE SIGNS LIST 1 Oxidation tank 2 Reduction tank 3 Aqueous solution 4 Oxidation electrode 5 Tube 6 Gas output hole 7 Electrolyte membrane 8 Reduction electrode 9 Conductor 10 Ammeter 11 Gas input hole 12 Gas output hole 13 Pipe 14 Humidifier 15 Light source 16 Power supply 141 Tube 142 Humidifier tank 143 Water 144 Mass flow controller 145 Hygrometer 146 Air conditioning equipment 147 Carbon dioxide output device 148 Humidified gas output device

Claims

1. A humidification device for a carbon dioxide reduction device comprising an oxidation tank storing an aqueous solution, an empty reduction tank, a photocatalytic oxidation electrode inserted into the aqueous solution, an electrolyte membrane arranged between the oxidation tank and the reduction tank, a reduction electrode joined to the surface of the electrolyte membrane within the reduction tank, a conductor connected between the oxidation electrode and the reduction electrode, and a light source that irradiates the oxidation electrode with light, the humidification device supplies humidified carbon dioxide to the reduction tank and controls the amount of humidified carbon dioxide supplied.

2. A humidification device for a carbon dioxide reduction device comprising an oxidation tank storing an aqueous solution, an empty reduction tank, an oxidation electrode inserted into the aqueous solution, an electrolyte membrane arranged between the oxidation tank and the reduction tank, a reduction electrode joined to the surface of the electrolyte membrane in the reduction tank, a conductor connected between the oxidation electrode and the reduction electrode, and a power source for applying a voltage to the conductor, the humidification device supplies humidified carbon dioxide to the reduction tank and controls the amount of humidified carbon dioxide supplied.

3. The humidifier according to claim 1 or 2, wherein the humidified carbon dioxide is produced by bubbling carbon dioxide through water.

4. A humidifier according to claim 1 or 2, wherein the humidifier controls the supply amount of the humidified carbon dioxide so that it exceeds the supply amount that satisfies the equation (100 β / θ) × I (β is m / (I Δt), m is the amount of salt produced on the surface of the reduction electrode, I is the current value on the conductor, Δt is time, and θ is the solubility of the salt).

5. A carbon dioxide reduction device comprising: an oxidation tank for storing an aqueous solution; an empty reduction tank; a photocatalytic oxidation electrode inserted into the aqueous solution; an electrolyte membrane arranged between the oxidation tank and the reduction tank; a reduction electrode joined to the surface of the electrolyte membrane in the reduction tank; a lead wire connected between the oxidation electrode and the reduction electrode; a light source for irradiating the oxidation electrode with light; and a humidifier for supplying humidified carbon dioxide to the reduction tank and controlling the amount of humidified carbon dioxide supplied.

6. A carbon dioxide reduction device comprising: an oxidation tank storing an aqueous solution; an empty reduction tank; an oxidation electrode inserted into the aqueous solution; an electrolyte membrane arranged between the oxidation tank and the reduction tank; a reduction electrode joined to the surface of the electrolyte membrane in the reduction tank; a lead wire connected between the oxidation electrode and the reduction electrode; a power source for applying a voltage to the lead wire; and a humidifier for supplying humidified carbon dioxide to the reduction tank and controlling the amount of humidified carbon dioxide supplied.

7. A carbon dioxide reduction method performed using a carbon dioxide reduction device comprising: an oxidation tank storing an aqueous solution; an empty reduction tank; a photocatalytic oxidation electrode inserted into the aqueous solution; an electrolyte membrane arranged between the oxidation tank and the reduction tank; a reduction electrode joined to the surface of the electrolyte membrane in the reduction tank; a conductor connected between the oxidation electrode and the reduction electrode; a light source that irradiates the oxidation electrode with light; and a humidifier, wherein the humidifier supplies humidified carbon dioxide to the reduction tank while controlling the supply amount of the humidified carbon dioxide.

8. A carbon dioxide reduction method performed using a carbon dioxide reduction device comprising: an oxidation tank storing an aqueous solution; an empty reduction tank; an oxidation electrode inserted into the aqueous solution; an electrolyte membrane arranged between the oxidation tank and the reduction tank; a reduction electrode joined to the surface of the electrolyte membrane in the reduction tank; a lead wire connected between the oxidation electrode and the reduction electrode; a power source for applying a voltage to the lead wire; and a humidifier, wherein the humidifier supplies humidified carbon dioxide to the reduction tank while controlling the supply amount of the humidified carbon dioxide.

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