WO2021117164A1

WO2021117164A1 - Gas-phase carbon dioxide reduction apparatus, and gas-phase carbon dioxide reduction method

Info

Publication number: WO2021117164A1
Application number: PCT/JP2019/048510
Authority: WO
Inventors: 紗弓里; 裕也渦巻; 陽子小野; 武志小松
Original assignee: 日本電信電話株式会社
Priority date: 2019-12-11
Filing date: 2019-12-11
Publication date: 2021-06-17
Also published as: JP7273346B2; JPWO2021117164A1; US20230002919A1

Abstract

The gas-phase carbon dioxide reduction apparatus comprises an oxidation compartment 2 that contains an oxidation electrode 1; a reduction compartment 3 to which carbon dioxide is fed; an intermediate compartment 4 that is disposed between the oxidation compartment 2 and the reduction compartment 3 and is capable of the introduction and discharge of an electrolyte solution; an ion-exchange membrane 5 disposed between the oxidation compartment 2 and the intermediate compartment 4; a gas reduction sheet 100 provided by the lamination of an ion-exchange membrane 6 with a reduction electrode 7 and disposed between the reduction compartment 3 and the intermediate compartment 4 with the ion-exchange membrane 6 facing the intermediate compartment 4 and with the reduction electrode 7 facing the reduction compartment 3; and a conductive wire 8 that connects the oxidation electrode 1 and the reduction electrode 7.

Description

Carbon dioxide gas phase reduction device and carbon dioxide gas phase reduction method

The present invention relates to a carbon dioxide gas phase reducing device and a carbon dioxide gas phase reducing method.

Conventionally, a carbon dioxide gas phase reduction device has been researched and developed. In the carbon dioxide gas phase reducing device disclosed in Non-Patent Document 1, an ion exchange membrane (Nafion (registered trademark)) and a reducing electrode (Cu) are combined between an oxidation tank on the left side and a reduction tank on the right side. It is constructed by arranging a gas reduction sheet. The ion exchange membrane is arranged toward the oxidation tank side, and the reduction electrode is arranged toward the reduction tank side. The oxide tank is filled with an aqueous solution of potassium hydroxide (KOH) as an electrolytic solution, and the oxide electrode of aluminum gallium nitride (AlGaN) in which a catalyst of nickel oxide (NiO) is laminated is immersed in the aqueous solution. The oxide electrode is connected to the reduction electrode of the gas reduction sheet by a conducting wire.

In such a carbon dioxide gas phase reduction device, helium (He) is put into the potassium hydroxide aqueous solution in the oxidation tank and carbon dioxide (CO ₂ ) is put into the reduction tank, and light (hv) is directed to the oxidation electrode. When irradiated with, the carbon dioxide reduction reaction proceeds at the three-phase interface consisting of the ion exchange film (Nafion) of the gas reduction sheet, the reduction electrode (Cu), and the carbon dioxide (CO _{2) in the reduction tank.} Specifically, in the oxidation tank, oxygen is generated by the oxidation reaction of water. In the reduction tank, hydrogen is generated by the reduction reaction of protons in the ion exchange membrane, and carbon monoxide and formic acid are generated by the reduction reaction of carbon dioxide.

However, since the potassium hydroxide aqueous solution, which is an electrolytic solution, is always in contact with the reducing electrode via the ion exchange membrane, the reducing electrode deteriorates, the reaction field of the carbon dioxide reduction reaction is lost, and the carbon dioxide reduction reaction. Life will be reduced. In this regard, the potassium hydroxide aqueous solution is injected into the oxide tank when the operation of the gas phase reducing device is started, and the water is discharged from the oxide tank when the operation is stopped, so that the contact between the potassium hydroxide aqueous solution and the reducing electrode is in the gas phase. A method of limiting only when the reduction device is operated is also conceivable. However, in the case of this method, oxygen generated in the oxide tank is released from the oxide tank when the valve is opened and closed, which makes recovery difficult.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of suppressing deterioration of a reducing electrode and improving the life of a carbon dioxide reduction reaction on the reducing electrode. Is.

The carbon dioxide gas phase reducing device according to one aspect of the present invention is arranged between an oxide tank including an oxide electrode, a reduction tank to which carbon dioxide is supplied, and the oxide tank and the reduction tank, and is used to prepare an electrolytic solution. It is a gas reduction sheet in which an intermediate tank capable of injecting and discharging water, an ion exchange film arranged between the oxidation tank and the intermediate tank, and an ion exchange film and a reduction electrode are laminated. A gas reduction sheet arranged between the reduction tank and the intermediate tank, a lead wire connecting the oxidation electrode and the reduction electrode, and a lead wire for connecting the reduction electrode to the intermediate tank and the reduction electrode toward the reduction tank. To be equipped.

The carbon dioxide gas-phase reduction method according to one aspect of the present invention is the carbon dioxide gas-phase reduction method performed by the carbon dioxide gas-phase reduction device, wherein the carbon dioxide gas-phase reduction device includes an oxide tank including an oxidation electrode. , Arranged between the reducing tank to which carbon dioxide is supplied, the intermediate tank which is arranged between the oxidizing tank and the reducing tank and capable of injecting and discharging the electrolytic solution, and between the oxidizing tank and the intermediate tank. It is a gas reduction sheet in which the ion exchange film, the ion exchange film, and the reduction electrode are laminated, and the ion exchange film is directed toward the intermediate tank, the reduction electrode is directed at the reduction tank, and the reduction tank and the reduction tank are described. A gas reduction sheet arranged between the intermediate tank and a lead wire connecting the oxidation electrode and the reduction electrode are provided, and an electrolytic solution is injected into the oxidation tank and carbon dioxide is supplied to the reduction tank. The first step of injecting the electrolytic solution into the intermediate tank only when the oxidizing electrode is irradiated with light is performed.

The carbon dioxide gas-phase reduction method according to one aspect of the present invention is the carbon dioxide gas-phase reduction method performed by the carbon dioxide gas-phase reduction device, wherein the carbon dioxide gas-phase reduction device includes an oxide tank including an oxidation electrode. , Arranged between the reducing tank to which carbon dioxide is supplied, the intermediate tank which is arranged between the oxidizing tank and the reducing tank and capable of injecting and discharging the electrolytic solution, and between the oxidizing tank and the intermediate tank. It is a gas reduction sheet in which the ion exchange film, the ion exchange film, and the reduction electrode are laminated, and the ion exchange film is directed toward the intermediate tank, the reduction electrode is directed at the reduction tank, and the reduction tank and the reduction tank are described. A gas reduction sheet arranged between the intermediate tank and a lead wire connecting the oxidation electrode and the reduction electrode are provided, and an electrolytic solution is injected into the oxidation tank and carbon dioxide is supplied to the reduction tank. The first step of injecting the electrolytic solution into the intermediate tank only when a voltage is applied between the oxidizing electrode and the reducing electrode is performed.

According to the present invention, it is possible to provide a technique capable of suppressing deterioration of the reducing electrode and improving the life of the carbon dioxide reduction reaction on the reducing electrode.

FIG. 1 is a configuration diagram showing a configuration of a carbon dioxide gas phase reducing device according to Examples 1 to 4. FIG. 2 is a diagram showing a method for producing a gas reduction sheet using an electroless plating method. FIG. 3 is a diagram showing a light irradiation time and a voltage application time used in Examples 1 and 5. FIG. 4 is a diagram showing a light irradiation time and a voltage application time used in Examples 2 and 6. FIG. 5 is a diagram showing a light irradiation time and a voltage application time used in Examples 3 and 7. FIG. 6 is a diagram showing a light irradiation time and a voltage application time used in Examples 4 and 8. FIG. 7 is a configuration diagram showing a configuration of a carbon dioxide gas phase reducing device according to Examples 5 to 8. FIG. 8 is a configuration diagram showing the configuration of a conventional carbon dioxide gas phase reducing device.

Hereinafter, embodiments of the present invention 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.

[Outline of Invention]
The present invention relates to a carbon dioxide gas-phase reducing device that induces a carbon dioxide reduction reaction by light irradiation or causes an electrolytic reduction reaction of carbon dioxide to improve the life of the reduction reaction, and is an invention of a fuel generation technique or the like. It belongs to the technical field of solar energy conversion technology.

The present invention uses a gas reduction sheet in which a reducing electrode is directly formed on an ion exchange membrane, and the gas phase of carbon dioxide that reduces carbon dioxide by directly supplying the carbon dioxide of the gas phase to the surface of the reducing electrode. In the reduction apparatus, an intermediate tank capable of injecting and discharging the electrolytic solution is arranged between the oxidation tank and the reduction tank. Further, only when the oxide electrode in the oxide tank is irradiated with light, or when a voltage is applied between the oxidation electrode and the reduction electrode, the electrolytic solution is injected into the intermediate tank to the reducing electrode. When they are brought into contact with each other, a carbon dioxide reduction reaction is caused at the reduction electrode of the gas reduction sheet.

As a result, deterioration of the reducing electrode can be suppressed, and the life of the carbon dioxide reduction reaction on the reducing electrode can be improved. Since the electrolytic solution in the oxidation tank is not released, it does not interfere with the recovery of oxygen generated by the oxidation electrode in the oxidation tank.

[Example 1]
[Carbon dioxide gas phase reduction device]
FIG. 1 is a configuration diagram showing a configuration of a carbon dioxide gas phase reducing device according to the first embodiment.

The carbon dioxide gas phase reducing device is arranged between the oxide tank 2 including the oxidation electrode 1, the _{reduction tank 3 to which carbon dioxide (CO 2} ) is supplied, and the oxide tank 2 and the reduction tank 3, and is an electrolytic solution. It is a gas reduction sheet in which an intermediate tank 4 capable of injecting and discharging water, an ion exchange film 5 arranged between the oxidation tank 2 and the intermediate tank 4, an ion exchange film 6 and a reduction electrode 7 are laminated. The gas reduction sheet 100 arranged between the reduction tank 3 and the intermediate tank 4, the oxidation electrode 1 and the reduction electrode 7 with the ion exchange film 6 directed toward the intermediate tank 4 and the reducing electrode 7 directed toward the reducing tank 3. A lead wire 8 for connecting the two, and a light source 9 for irradiating the oxide electrode 1 with light are provided. The details will be described below.

In the oxide electrode 1, a thin film of n-type gallium nitride (n-GaN) and aluminum gallium nitride (AlGaN), which are n-type semiconductors, are epitaxially grown on a sapphire substrate in the order of n-GaN and AlGaN, and the oxide electrode 1 is formed on the n-GaN. It is composed by forming a co-catalyst thin film of nickel oxide (NiO) by vacuum-depositing nickel (Ni) and performing heat treatment. As a result, the oxide electrode 1 of NiO / AlGaN / n-GaN / sapphire becomes. NiO is a catalyst layer. AlGaN is a light absorption layer. The oxidation electrode 1 is installed so as to be immersed in the aqueous solution 10 which is the electrolytic solution injected into the oxidation tank 2. The aqueous solution 10 in the oxidation tank 2 is a 1 mol / L potassium hydroxide (KOH) aqueous solution.

The oxidation tank 2 and the intermediate tank 4 are separated by an ion exchange membrane 5. The aqueous solution 11 as the electrolytic solution to be injected into the intermediate tank 4 is also a 1 mol / L potassium hydroxide aqueous solution. The intermediate tank 4 and the reduction tank 3 are separated by a gas reduction sheet 100 in which a reduction electrode 7 is directly formed on the ion exchange membrane 6. The ion exchange membrane 6 is arranged on the intermediate tank 4 side, and the reducing electrode 7 is arranged on the reducing tank 3 side. The ion exchange membrane 5 arranged between the oxidation tank 2 and the intermediate tank 4 and the ion exchange membrane 6 of the gas reduction sheet 100 arranged between the intermediate tank 4 and the reduction tank 3 are both Nafion. (Registered trademark) is used. Copper (Cu) is used for the reducing electrode 7.

The oxidation electrode 1 immersed in the aqueous solution 10 in the oxidation tank 2 and the reduction electrode 7 of the gas reduction sheet 100 arranged toward the reduction tank 3 are connected by a conducting wire 8.

A 300 W high-pressure xenon lamp is used as the light source 9. The light output from the light source 9 cuts wavelengths of 450 nm or more.

FIG. 2 is a diagram showing a reaction system of an electroless plating method used as a method for producing a gas reduction sheet 100. One side of the ion exchange membrane 6 is polished. Further, in order to improve the proton mobility of the ion exchange membrane 6, the ion exchange membrane 6 is immersed in nitric acid and boiling pure water, respectively. The two

tanks

21 and 22 on the left and right are filled with the plating solution 31 and the reducing agent 32 shown in Table 1, respectively.

The tank 21 and the tank 22 are separated by an ion exchange membrane 6. The ion exchange membrane 6 is arranged with the polishing surface facing the plating solution 31 side. _{Since NaBH 4,} which is the main component of the reducing agent 32, is a polar compound, it permeates the ion exchange membrane 6. A gas reduction sheet 100 in which a reduction electrode is formed on the ion exchange membrane 6 by the following redox reaction occurring at the interface between the plating solution 31 and the polished surface of the ion exchange membrane 6 to precipitate copper (Cu). Is obtained.

_{^{^{_{BH 4 - + 4OH - → BO}}}} 2 - + 2H 2 O + 2H 2 + 4e -
Cu ²⁺ + 2e ^- → Cu

[Carbon dioxide gas phase reduction method]
Next, a carbon dioxide gas phase reduction method performed by the carbon dioxide gas phase reduction device will be described.

First, the NiO-forming surface of the oxide electrode 1 is fixed toward the light source 9 so that the NiO-forming surface of the oxide electrode 1 serves as a light receiving surface (first step). The light receiving area of the oxide electrode 1 was 3.8 cm ² .

Next, a 1 mol / L potassium hydroxide aqueous solution 10 is poured into the oxide tank 2 (second step).

Next, the tube 12 is put into the aqueous solution 10 in the oxidation tank 2 and helium (He) is poured into the aqueous solution 10 at a flow rate of 5 ml / min, and carbon dioxide (CO ₂ ) is supplied to the reduction tank 3 from the gas input port 13. Pour in at the same flow rate (third step).

Next, after sufficiently replacing the oxidation tank 2 and the reduction tank 3 with helium and carbon dioxide, respectively, a 1 mol / L potassium hydroxide aqueous solution 11 is poured into the intermediate tank 4 from the aqueous solution input port 14, and the light source is used. The oxide electrode 1 is uniformly irradiated with light using No. 9 (fourth step).

At this time, the carbon dioxide reduction reaction proceeds at the three-phase interface composed of the ion exchange membrane (Nafion) 6 in the gas reduction sheet 100, the reduction electrode (Cu) 7, and the carbon dioxide (CO _{2) in the gas phase.} The surface area of the reducing electrode 7 to which carbon dioxide is directly supplied is about 6.8 cm ² .

Finally, after the light irradiation of the oxide electrode 1 is completed, the aqueous solution 11 is discharged from the aqueous solution output port 15 of the intermediate tank 4 (fifth step).

The "first step" described in the "claims" corresponds to the second step and the third step. The second step and the third step may be carried out at the same timing. The step of pouring carbon dioxide into the reduction tank 3 may be carried out at a timing prior to the step of injecting the aqueous solution 10 into the oxidation tank 2. Further, the "second step" described in the "claims" corresponds to the fourth step and the fifth step.

In Example 1, the oxide electrode 1 was irradiated with light having a profile-set illuminance as shown in FIG. The net light irradiation time is repeated by repeating "Irradiating the oxide electrode 1 with light having an illuminance of 2.2 mW / cm ^{2 having a wavelength region of 365 nm or more for 1 hour and then waiting for 1 hour without irradiating the light".} Allow the reaction to proceed until 3 hours are reached. Further, when the light irradiation is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the light irradiation is started again, the aqueous solution 11 is injected into the intermediate tank 4.

Concentration analysis of gas products in each reaction vessel was performed using a gas chromatograph at any time during light irradiation. In particular, the liquid product in the reduction tank 3 was subjected to concentration analysis by a liquid chromatograph. As a result, it was confirmed that oxygen was generated in the oxidation tank 2 by the oxidation reaction of water using the holes. In the reduction tank 3, it was confirmed that hydrogen was produced by the reduction reaction of protons using electrons, and carbon monoxide, formic acid, formaldehyde, methane, ethylene, methanol, and ethanol were produced by the reduction reaction of carbon dioxide.

[Example 2]
Example 2 also uses the same carbon dioxide gas phase reducing device as in Example 1 shown in FIG. In Example 2, the oxide electrode 1 was irradiated with light having a profile-set illuminance as shown in FIG. The net light irradiation time is repeated by repeating "Irradiating the oxide electrode 1 with light having an illuminance of 2.2 mW / cm ^{2 having a wavelength region of 365 nm or more for 1 hour and then waiting for 3 hours without irradiating the light".} Allow the reaction to proceed until 3 hours are reached. Further, when the light irradiation is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the light irradiation is started again, the aqueous solution 11 is injected into the intermediate tank 4. In other respects, it is the same as in Example 1.

[Example 3]
Example 3 also uses the same carbon dioxide gas phase reducing device as in Example 1 shown in FIG. In Example 3, the oxide electrode 1 was irradiated with light having a profile-set illuminance as shown in FIG. The net light irradiation time is repeated by repeating "Irradiating the oxide electrode 1 with light having an illuminance of 2.2 mW / cm ^{2 having a wavelength region of 365 nm or more for 1 hour and then waiting for 5 hours without irradiating the light".} Allow the reaction to proceed until 3 hours are reached. Further, when the light irradiation is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the light irradiation is started again, the aqueous solution 11 is injected into the intermediate tank 4. In other respects, it is the same as in Example 1.

[Example 4]
Example 4 also uses the same carbon dioxide gas phase reducing device as in Example 1 shown in FIG. In Example 4, the oxide electrode 1 was irradiated with light having a profile-set illuminance as shown in FIG. The net light irradiation time is repeated by repeating "Irradiating the oxide electrode 1 with light having an illuminance of 2.2 mW / cm ^{2 having a wavelength region of 365 nm or more for 1 hour and then waiting for 10 hours without irradiating the light".} Allow the reaction to proceed until 3 hours are reached. Further, when the light irradiation is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the light irradiation is started again, the aqueous solution 11 is injected into the intermediate tank 4. In other respects, it is the same as in Example 1.

[Example 5]
FIG. 7 is a block diagram showing the configuration of the carbon dioxide gas phase reducing device according to the fifth embodiment.

In the fifth embodiment, the power supply 16 is used instead of the light source 9. The power supply 16 is inserted on the path of the conductor 8. Further, since the oxide electrode 1 does not need to receive light, the oxide electrode 1 of Example 5 is made of platinum (manufactured by Niraco). The surface area of the oxide electrode 1 was set to about 0.55 cm ² . Other configurations are the same as in the first embodiment.

After sufficiently replacing the oxidation tank 2 and the reduction tank 3 with helium and carbon dioxide, respectively, the power supply 16 is connected between the oxidation electrode 1 and the reduction electrode 7 with a lead wire 8, and a voltage of 1.5 V is applied to apply a current. Shed. Other procedures are the same as in Example 1.

That is, in Example 5, a profile-set voltage was applied to the conductor 8 as shown in FIG. "After applying a voltage of 1.5V between the oxide electrode 1 and the reduction electrode 7 for 1 hour, wait for 1 hour without applying a voltage" is repeated, and the net voltage application time becomes 3 hours. Proceed with the reaction until it is reached. Further, when the application of the voltage is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the voltage is applied again, the aqueous solution 11 is injected into the intermediate tank 4.

Concentration analysis of gas products in each reaction vessel was performed using a gas chromatograph at an arbitrary time while voltage was applied. In particular, the liquid product in the reduction tank 3 was subjected to concentration analysis by a liquid chromatograph. As a result, it was confirmed that oxygen was generated in the oxide tank 2. It was confirmed that hydrogen, carbon monoxide, formic acid, formaldehyde, methane, ethylene, methanol and ethanol were produced in the reduction tank 3.

[Example 6]
Example 6 also uses the same carbon dioxide gas phase reducing device as in Example 5 shown in FIG. In Example 6, a profile-set voltage was applied to the conductor 8 as shown in FIG. "After applying a voltage of 1.5V between the oxide electrode 1 and the reduction electrode 7 for 1 hour, wait for 3 hours without applying a voltage" is repeated, and the net voltage application time becomes 3 hours. Proceed with the reaction until it is reached. Further, when the application of the voltage is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the voltage is applied again, the aqueous solution 11 is injected into the intermediate tank 4. In other respects, it is the same as in Example 5.

[Example 7]
Example 1 also uses the same carbon dioxide gas phase reducing device as in Example 5 shown in FIG. In Example 7, a profiled voltage was applied to the conductor 8 as shown in FIG. "After applying a voltage of 1.5V between the oxide electrode 1 and the reduction electrode 7 for 1 hour, wait for 5 hours without applying a voltage" is repeated, and the net voltage application time becomes 3 hours. Proceed with the reaction until it is reached. Further, when the application of the voltage is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the voltage is applied again, the aqueous solution 11 is injected into the intermediate tank 4. In other respects, it is the same as in Example 5.

[Example 8]
Example 8 also uses the same carbon dioxide gas phase reducing device as in Example 5 shown in FIG. In Example 8, a profile-set voltage was applied to the conductor 8 as shown in FIG. "After applying a voltage of 1.5V between the oxide electrode 1 and the reduction electrode 7 for 1 hour, wait for 10 hours without applying a voltage" is repeated, and the net voltage application time becomes 3 hours. Proceed with the reaction until it is reached. Further, when the application of the voltage is stopped, the aqueous solution 11 is discharged from the intermediate tank 4, and when the voltage is applied again, the aqueous solution 11 is injected into the intermediate tank 4. In other respects, it is the same as in Example 5.

[Comparison target example 1]
In the comparative example 1, the carbon dioxide gas phase reducing device shown in FIG. 1 is used as in the first embodiment. Compared with Example 1, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. This configuration is the same as the conventional carbon dioxide gas phase reducing device shown in FIG. In other respects, it is the same as in Example 1.

[Comparison target example 2]
Also in Comparative Example 2, the carbon dioxide gas phase reducing device shown in FIG. 1 is used. Compared with Example 2, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 2.

[Comparison target example 3]
Also in Comparative Example 3, the carbon dioxide gas phase reducing device shown in FIG. 1 is used. Compared with Example 3, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 3.

[Comparison target example 4]
Also in Comparative Example 4, the carbon dioxide gas phase reducing device shown in FIG. 1 is used. Compared with Example 4, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 4.

[Comparison target example 5]
In Comparative Example 5, the carbon dioxide gas phase reducing device shown in FIG. 7 is used as in Example 5. Compared with Example 5, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 5.

[Comparison target example 6]
Also in Comparative Example 6, the carbon dioxide gas phase reducing device shown in FIG. 7 is used. Compared with Example 6, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 6.

[Comparison target example 7]
Also in Comparative Example 7, the carbon dioxide gas phase reducing device shown in FIG. 7 is used. Compared with Example 7, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 7.

[Comparison target example 8]
Also in Comparative Example 8, the carbon dioxide gas phase reducing device shown in FIG. 7 is used. Compared with Example 8, the intermediate tank 4 is always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. In other respects, it is the same as in Example 8.

[effect]
Table 2 shows the current retention rate of carbon dioxide reduction when the net light irradiation time reaches 3 hours for Examples 1 to 8 and Comparative Cases 1 to 8.

The current maintenance rate of carbon dioxide reduction is calculated using equation (1). It is considered that the larger the value of the current retention rate (%) of carbon dioxide reduction, the longer the life of the carbon dioxide reduction reaction.

Current retention rate of carbon dioxide reduction (%) = (current value of carbon dioxide reduction 3 hours after light irradiation or voltage application) / (current value of carbon dioxide reduction 10 minutes after light irradiation or voltage application).・・ (1)

The "current value of carbon dioxide reduction", which is the right-hand variable of the formula (1), is required for the reduction reaction with the concentration of the reduction reaction product being A [ppm] and the flow rate of the carrier gas being B [L / sec]. It was calculated using the equation (2) when the number of electrons was Z [mol], the Faraday constant was F [C / mol], and the molar gas was V _{m [L / mol].}

Carbon dioxide reduction current value [A] = (A x B x Z x F x ^10-6 ) / V _m ... (2)

Comparing Examples 1 to 4 and Comparative Examples 1 to 4 in each case of waiting time of 1 hour, 3 hours, 5 hours, and 10 hours at the time of light irradiation, each comparative example in each example It can be understood that the current maintenance rate of carbon dioxide reduction has improved. Further, when the standby time is 1 hour, 3 hours, 5 hours, and 10 hours when the voltage is applied, when the Examples 5 to 8 and the comparison target Examples 5 to 8 are compared, the same as in the case of light irradiation. In each example, it can be grasped that the current maintenance rate of carbon dioxide reduction was improved as compared with each comparative example.

From this result, it can be seen that the life of the carbon dioxide reduction reaction was improved by filling the intermediate tank 4 with the aqueous solution 11 only for the reaction progress time, which is the light irradiation time or the voltage application time. This is because, in Examples 1 to 8, the reduction electrode was prevented from coming into contact with the reduction electrode 7 via the ion exchange membrane 6 during the reaction stop time, which is the non-light irradiation time or the non-voltage application time. It is considered that the deterioration of 7 could be suppressed.

As described above, according to Examples 1 to 8, in the carbon dioxide gas phase reducing device that directly reduces the gas phase carbon dioxide on the gas reduction sheet 100 in which the reducing electrode 7 is directly formed on the ion exchange film 6. An intermediate tank 4 capable of injecting and discharging the aqueous solution 11 which is an electrolytic solution is arranged between the oxidation tank 2 and the reduction tank 3, and only when the oxidation electrode is irradiated with light, or between the oxidation electrode and the reduction electrode. Since the reducing electrode 7 and the aqueous solution 11 are brought into contact with each other only when a voltage is applied between the two, the reduction electrode 7 can be suppressed from being deteriorated without interfering with the recovery of oxygen generated by the oxidizing electrode 1. The life of the carbon dioxide reduction reaction above can be improved.

[Other]
The present invention is not limited to the above Examples 1 to 8, and many modifications can be made within the scope of the gist thereof. The nitride semiconductors shown as the oxide electrodes 1 of Examples 1 to 4 may have different laminated structures, or may have different compositions such as containing indium and aluminum. Further, for the oxide electrodes 1 of Examples 1 to 4, instead of the nitride semiconductor, compounds exhibiting photoactivity such as titanium oxide and amorphous silicon may be used. The oxide electrode 1 of Examples 5 to 8 may be a metal such as gold, silver, copper, indium, or nickel instead of platinum. Instead of copper, the reducing electrode 7 may be gold, platinum, silver, palladium, gallium, indium, nickel, tin, cadmium, an alloy thereof, or a mixture of these metals or metal oxides and carbon. .. As the

aqueous solutions

10 and 11, instead of the potassium hydroxide aqueous solution, a sodium hydroxide aqueous solution, a potassium chloride aqueous solution, or a sodium chloride aqueous solution may be used. The ion exchange membrane 6 is, for example, a cation exchange membrane called naphthion, which is a perfluorocarbon material composed of a hydrophobic Teflon skeleton composed of carbon-fluorine and a perfluoro side chain having a sulfonic acid group. The method for producing the gas reduction sheet may be an electroplating method, a physical vapor deposition method, or a chemical vapor deposition method, in addition to the electroless plating method.

1: Oxidation electrode 2: Oxidation tank 3: Reduction tank 4: Intermediate tank 5: Ion exchange membrane 6: Ion exchange membrane 7: Reduction electrode 8: Conductor 9: Light source 10: Aqueous solution 11: Aqueous solution 12: Tube 13: Gas input port 14: Aqueous solution input port 15: Aqueous solution output port 16: Power supply 100: Gas reduction sheet

Claims

An oxide tank containing an oxidation electrode and
A reduction tank to which carbon dioxide is supplied and
An intermediate tank, which is arranged between the oxidation tank and the reduction tank and is capable of injecting and discharging the electrolytic solution,
An ion exchange membrane arranged between the oxidation tank and the intermediate tank,
It is a gas reduction sheet in which an ion exchange membrane and a reduction electrode are laminated, and the ion exchange membrane is directed toward the intermediate tank, the reduction electrode is directed toward the reduction tank, and the reduction electrode is arranged between the reduction tank and the intermediate tank. Gas reduction sheet and
A conducting wire connecting the oxidizing electrode and the reducing electrode,
A carbon dioxide gas phase reducing device equipped with.
The carbon dioxide gas phase reducing device according to claim 1, further comprising a light source for irradiating the oxide electrode with light.
The carbon dioxide gas phase reducing device according to claim 1, further comprising a power source connected to the conducting wire.
The oxide electrode is
The carbon dioxide gas phase reducing device according to any one of claims 1 to 3, which is an n-type semiconductor.
In the carbon dioxide gas phase reduction method performed by the carbon dioxide gas phase reduction device,
The carbon dioxide gas phase reducing device is
An oxide tank containing an oxidation electrode and
A reduction tank to which carbon dioxide is supplied and
An intermediate tank, which is arranged between the oxidation tank and the reduction tank and is capable of injecting and discharging the electrolytic solution,
An ion exchange membrane arranged between the oxidation tank and the intermediate tank,
It is a gas reduction sheet in which an ion exchange membrane and a reduction electrode are laminated, and the ion exchange membrane is directed toward the intermediate tank, the reduction electrode is directed toward the reduction tank, and the reduction electrode is arranged between the reduction tank and the intermediate tank. Gas reduction sheet and
A conducting wire connecting the oxidizing electrode and the reducing electrode is provided.
The first step of injecting the electrolytic solution into the oxidation tank and supplying carbon dioxide to the reduction tank, and
The second step of injecting the electrolytic solution into the intermediate tank only when the oxide electrode is irradiated with light, and
Carbon dioxide gas phase reduction method.
In the carbon dioxide gas phase reduction method performed by the carbon dioxide gas phase reduction device,
The carbon dioxide gas phase reducing device is
An oxide tank containing an oxidation electrode and
A reduction tank to which carbon dioxide is supplied and
An intermediate tank, which is arranged between the oxidation tank and the reduction tank and is capable of injecting and discharging the electrolytic solution,
An ion exchange membrane arranged between the oxidation tank and the intermediate tank,
It is a gas reduction sheet in which an ion exchange membrane and a reduction electrode are laminated, and the ion exchange membrane is directed toward the intermediate tank, the reduction electrode is directed toward the reduction tank, and the reduction electrode is arranged between the reduction tank and the intermediate tank. Gas reduction sheet and
A conducting wire connecting the oxidizing electrode and the reducing electrode is provided.
The first step of injecting the electrolytic solution into the oxidation tank and supplying carbon dioxide to the reduction tank, and
The second step of injecting the electrolytic solution into the intermediate tank only when a voltage is applied between the oxidizing electrode and the reducing electrode.
Carbon dioxide gas phase reduction method.