JP7273346B2 - Gas phase reduction method of carbon dioxide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas phase reduction apparatus for carbon dioxide and a gas phase reduction method for carbon dioxide.

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

In such a gas-phase reduction apparatus for carbon dioxide, helium (He) is put into an aqueous solution of potassium hydroxide in the oxidation tank, carbon dioxide (CO ₂ ) is put into the reduction tank, and light (hv) is applied to the oxidation electrode. , the reduction reaction of carbon dioxide progresses at the three-phase interface consisting of the ion exchange membrane (Nafion) of the gas reduction sheet, the reduction electrode (Cu), and carbon dioxide (CO ₂ ) in the reduction tank. Specifically, in the oxidation tank, oxygen is produced 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.

Sato, et al., “Photoelectrochemical properties of CO2 reduction reaction using proton exchange membrane with Cu electrode”, Electrochemistry Autumn Meeting, Oral Presentation, 2019, 1B05

However, since the potassium hydroxide aqueous solution, which is the electrolytic solution, is always in contact with the reduction electrode via the ion exchange membrane, the reduction electrode deteriorates, the reaction site for the carbon dioxide reduction reaction is lost, and the carbon dioxide reduction reaction lifespan is reduced. In this respect, the aqueous potassium hydroxide solution is injected into the oxidation tank when the operation of the gas-phase reduction apparatus is started, and is discharged from the oxidation tank when the operation is stopped, so that the contact between the aqueous potassium hydroxide solution and the reduction electrode is maintained in the gas phase. It is also conceivable to limit it only when the reducing apparatus is in operation. However, in this method, the oxygen generated in the oxidation tank is released from the oxidation tank when the valve is opened and closed, making 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 the reduction electrode and improving the life of the carbon dioxide reduction reaction on the reduction electrode. is.

A method for gas phase reduction of carbon dioxide according to one aspect of the present invention is a method for gas phase reduction of carbon dioxide performed in a gas phase reduction apparatus for carbon dioxide, wherein the gas phase reduction apparatus for carbon dioxide includes an oxidation tank including an oxidation electrode. , a reduction tank to which carbon dioxide is supplied, an intermediate tank arranged between the oxidation tank and the reduction tank and capable of pouring and discharging the electrolytic solution, and arranged between the oxidation tank and the intermediate tank. a gas reduction sheet in which an ion exchange membrane, an ion exchange membrane, and a reduction electrode are laminated, and the ion exchange membrane is oriented toward the intermediate tank, the reduction electrode is oriented toward the reduction tank, and the reduction tank and the reduction electrode are laminated. A gas reduction sheet disposed between an intermediate tank and a lead wire connecting the oxidation electrode and the reduction electrode, and supplying an electrolytic solution to the oxidation tank and supplying carbon dioxide to the reduction tank. and a second step of pouring the electrolytic solution into the intermediate tank only when the oxidation electrode is irradiated with light.

A method for gas phase reduction of carbon dioxide according to one aspect of the present invention is a method for gas phase reduction of carbon dioxide performed in a gas phase reduction apparatus for carbon dioxide, wherein the gas phase reduction apparatus for carbon dioxide includes an oxidation tank including an oxidation electrode. , a reduction tank to which carbon dioxide is supplied, an intermediate tank arranged between the oxidation tank and the reduction tank and capable of pouring and discharging the electrolytic solution, and arranged between the oxidation tank and the intermediate tank. a gas reduction sheet in which an ion exchange membrane, an ion exchange membrane, and a reduction electrode are laminated, and the ion exchange membrane is oriented toward the intermediate tank, the reduction electrode is oriented toward the reduction tank, and the reduction tank and the reduction electrode are laminated. A gas reduction sheet disposed between an intermediate tank and a lead wire connecting the oxidation electrode and the reduction electrode, and supplying an electrolytic solution to the oxidation tank and supplying carbon dioxide to the reduction tank. and a second step of pouring the electrolytic solution into the intermediate tank only when a voltage is applied between the oxidation electrode and the reduction electrode.

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

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

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same parts are denoted by the same reference numerals, and the description thereof is omitted.

[Summary of Invention]
The present invention relates to a gas-phase reduction apparatus for carbon dioxide that causes a reduction reaction of carbon dioxide by light irradiation or causes an electrolytic reduction reaction of carbon dioxide to improve the life of the reduction reaction. Belongs to the technical field of solar energy conversion technology.

The present invention uses a gas reduction sheet in which a reduction electrode is directly formed on an ion exchange membrane, and supplies gaseous carbon dioxide directly to the surface of the reduction electrode to reduce carbon dioxide. In the reduction apparatus, an intermediate tank is arranged between the oxidation tank and the reduction tank, into which the electrolytic solution can be injected and discharged. Only when the oxidation electrode in the oxidation tank is irradiated with light or when a voltage is applied between the oxidation electrode and the reduction electrode, the electrolytic solution is poured into the intermediate tank and applied to the reduction electrode. are brought into contact with each other to cause a reduction reaction of carbon dioxide at the reduction electrode of the gas reduction sheet.

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

[Example 1]
[Gas-phase reduction apparatus for carbon dioxide]
FIG. 1 is a configuration diagram showing the configuration of a gas-phase reduction apparatus for carbon dioxide according to Example 1. As shown in FIG.

The gas phase reduction apparatus for carbon dioxide is arranged between an oxidation tank 2 including an oxidation electrode 1, a reduction tank 3 supplied with carbon dioxide (CO ₂ ), and between the oxidation tank 2 and the reduction tank 3, and an electrolytic solution A gas reduction sheet in which an intermediate tank 4 capable of injecting and discharging water, an ion-exchange membrane 5 disposed between the oxidation tank 2 and the intermediate tank 4, and an ion-exchange membrane 6 and a reduction electrode 7 are laminated, A gas reduction sheet 100 disposed between the reduction tank 3 and the intermediate tank 4 with the ion exchange membrane 6 facing the intermediate tank 4 and the reduction electrode 7 facing the reduction tank 3, the oxidation electrode 1 and the reduction electrode 7 and a light source 9 for irradiating the oxidation electrode 1 with light. Details will be described below.

The oxidation electrode 1 is formed by epitaxially growing a thin film of n-type gallium nitride (n-GaN), which is an n-type semiconductor, and aluminum gallium nitride (AlGaN) in this order on a sapphire substrate. Nickel (Ni) is vacuum deposited and heat-treated to form a promoter thin film of nickel oxide (NiO). As a result, an oxidized electrode 1 of NiO/AlGaN/n-GaN/sapphire is obtained. NiO is the catalyst layer. AlGaN is the light absorbing layer. This oxidation electrode 1 is installed so as to be submerged in an aqueous solution 10 which is an electrolytic solution poured into the oxidation bath 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 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 having a reduction electrode 7 directly formed on an ion exchange membrane 6 . The ion exchange membrane 6 is placed on the intermediate tank 4 side, and the reduction electrode 7 is placed on the reduction tank 3 side. Both 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 Nafion (registered trademark) is used. Copper (Cu) is used for the reduction electrode 7 .

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

A 300 W high pressure xenon lamp is used as the light source 9 . The light emitted from the light source 9 has a wavelength of 450 nm or more cut.

FIG. 2 is a diagram showing the reaction system of the electroless plating method used as a method of producing the gas reduction sheet 100. As shown in FIG. One side of the ion exchange membrane 6 is polished. In order to improve the proton mobility of the ion exchange membrane 6, the ion exchange membrane 6 is immersed in boiling nitric acid and boiling pure water. The two tanks 21 and 22 on the left and right sides are filled with the plating solution 31 and the reducing agent 32 shown in Table 1, respectively.

The tanks 21 and 22 are separated by an ion exchange membrane 6 . The ion exchange membrane 6 is arranged with the polished 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 . At the interface between the plating solution 31 and the polished surface of the ion-exchange membrane 6, the oxidation-reduction reaction described below occurs and copper (Cu) is deposited, thereby forming a gas reduction sheet 100 in which a reduction electrode is formed on the ion-exchange membrane 6. is obtained.

BH ₄ ⁻ +4OH ⁻ →BO ₂ ⁻ +2H ₂ O+2H ₂ +4e ⁻
Cu ²⁺ +2e ⁻ →Cu

[Gas phase reduction method of carbon dioxide]
Next, a gas phase reduction method of carbon dioxide carried out in the gas phase reduction apparatus for carbon dioxide will be described.

First, the NiO formation surface of the oxidation electrode 1 is fixed facing the light source 9 so that the NiO formation surface of the oxidation electrode 1 serves as a light receiving surface (first step). The light receiving area of the oxidation electrode 1 was set to 3.8 cm ² .

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

Next, a tube 12 is inserted into the aqueous solution 10 in the oxidation tank 2, and helium (He) is introduced into the aqueous solution ₁₀ at a flow rate of 5 ml/min. 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 9 is used to uniformly irradiate the oxidation electrode 1 with light (fourth step).

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

Finally, after the light irradiation to the oxidation 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 "Claims" corresponds to the second step and the third step. The second step and the third step may be performed at the same timing. The step of pouring carbon dioxide into the reduction tank 3 may be performed before the step of pouring the aqueous solution 10 into the oxidation tank 2 . Also, the "second step" described in "Claims" corresponds to the fourth step and the fifth step.

In Example 1, the oxidation electrode 1 was irradiated with light having an illuminance whose profile was set as shown in FIG. "After irradiating the oxidation electrode 1 with light having an illuminance of 2.2 mW/cm ² in the wavelength region of 365 nm or more for one hour, and then waiting for one hour without irradiating light", the net light irradiation time is The reaction is allowed to proceed until 3 hours is reached. Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the light irradiation is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the light irradiation is started again.

Gas products in each reaction vessel were analyzed for concentration using a gas chromatograph at an arbitrary time during light irradiation. In particular, liquid products in the reduction tank 3 were subjected to concentration analysis using a liquid chromatograph. As a result, it was confirmed that in the oxidation tank 2, oxygen was generated 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]
In Example 2, the same vapor-phase reduction apparatus for carbon dioxide as in Example 1 shown in FIG. 1 is used. In Example 2, the oxidation electrode 1 was irradiated with light having an illuminance whose profile was set as shown in FIG. ``After irradiating the oxidation electrode 1 with light having an illuminance of 2.2 mW/ ^cm2 in the wavelength region of 365 nm or more for one hour, and then waiting for three hours without irradiating light'', the net light irradiation time was The reaction is allowed to proceed until 3 hours is reached. Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the light irradiation is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the light irradiation is started again. Other points are the same as the first embodiment.

[Example 3]
In Example 3, the same vapor-phase reduction apparatus for carbon dioxide as in Example 1 shown in FIG. 1 is used. In Example 3, the oxidation electrode 1 was irradiated with light having an illuminance whose profile was set as shown in FIG. ``After irradiating the oxidation electrode 1 with light having an illuminance of 2.2 mW/ ^cm2 in the wavelength region of 365 nm or more for one hour, and then waiting for five hours without irradiating light'', the net light irradiation time was The reaction is allowed to proceed until 3 hours is reached. Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the light irradiation is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the light irradiation is started again. Other points are the same as the first embodiment.

[Example 4]
In Example 4, the same vapor phase reduction apparatus for carbon dioxide as in Example 1 shown in FIG. 1 is used. In Example 4, the oxidation electrode 1 was irradiated with light having an illuminance whose profile was set as shown in FIG. "After irradiating the oxidation electrode 1 with light having an illuminance of 2.2 mW/ ^cm2 in the wavelength region of 365 nm or more for 1 hour, and then waiting for 10 hours without irradiating light", the net light irradiation time is The reaction is allowed to proceed until 3 hours is reached. Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the light irradiation is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the light irradiation is started again. Other points are the same as the first embodiment.

[Example 5]
FIG. 7 is a configuration diagram showing the configuration of a gas-phase reduction apparatus for carbon dioxide according to the fifth embodiment.

In Example 5, instead of the light source 9, a power source 16 is used. A power supply 16 is inserted onto the path of the conductor 8 . Further, since the oxidation electrode 1 does not need to receive light, the oxidation electrode 1 of Example 5 was constructed using platinum (manufactured by The Nilaco Corporation). The surface area of the oxidation electrode 1 was about 0.55 cm ² . Other configurations are the same as those of the first embodiment.

After sufficiently replacing the oxidation tank 2 and the reduction tank 3 with helium and carbon dioxide, respectively, a 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 generate a current. flushed. Other procedures are the same as in Example 1.

That is, in Example 5, a voltage having a profile set as shown in FIG. "After applying a voltage of 1.5 V between the oxidation electrode 1 and the reduction electrode 7 for one hour, wait without applying voltage for one hour" was repeated, and the net voltage application time was reduced to 3 hours. Allow the reaction to proceed until Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the voltage application is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the voltage is applied again.

Gas products in each reaction vessel were analyzed for concentration using a gas chromatograph at an arbitrary time during voltage application. In particular, liquid products in the reduction tank 3 were subjected to concentration analysis using a liquid chromatograph. As a result, it was confirmed that oxygen was generated in the oxidation 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]
In Example 6, the same vapor phase reduction apparatus for carbon dioxide as in Example 5 shown in FIG. 7 is used. In Example 6, a voltage profiled as shown in FIG. "After applying a voltage of 1.5 V between the oxidation electrode 1 and the reduction electrode 7 for 1 hour, wait for 3 hours without applying voltage" was repeated, and the net voltage application time was reduced to 3 hours. Allow the reaction to proceed until Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the voltage application is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the voltage is applied again. Other points are the same as the fifth embodiment.

[Example 7]
Example 1 also uses the same vapor phase reduction apparatus for carbon dioxide as Example 5 shown in FIG. In Example 7, a voltage profiled as shown in FIG. "After applying a voltage of 1.5 V between the oxidation electrode 1 and the reduction electrode 7 for 1 hour, wait without applying voltage for 5 hours" was repeated, and the net voltage application time was reduced to 3 hours. Allow the reaction to proceed until Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the voltage application is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the voltage is applied again. Other points are the same as the fifth embodiment.

[Example 8]
Example 8 also uses the same vapor-phase reduction apparatus for carbon dioxide as Example 5 shown in FIG. In Example 8, a voltage profiled as shown in FIG. "After applying a voltage of 1.5 V between the oxidation electrode 1 and the reduction electrode 7 for 1 hour, wait without applying voltage for 10 hours" was repeated, and the net voltage application time was reduced to 3 hours. Allow the reaction to proceed until Further, the aqueous solution 11 is discharged from the intermediate tank 4 when the voltage application is stopped, and the aqueous solution 11 is poured into the intermediate tank 4 when the voltage is applied again. Other points are the same as the fifth embodiment.

[Example 1 for comparison]
In Comparative Example 1, as in Example 1, the gas phase reduction apparatus for carbon dioxide shown in FIG. 1 is used. 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 that of the conventional gas phase reduction apparatus for carbon dioxide shown in FIG. Other points are the same as the first embodiment.

[Comparison example 2]
Comparative Example 2 also uses the gas-phase reduction apparatus for carbon dioxide shown in FIG. 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. Other points are the same as the second embodiment.

[Example 3 for comparison]
Comparative Example 3 also uses the vapor-phase reduction apparatus for carbon dioxide shown in FIG. 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. Other points are the same as those of the third embodiment.

[Example 4 for comparison]
Comparative Example 4 also uses the gas-phase reduction apparatus for carbon dioxide shown in FIG. 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. Other points are the same as the fourth embodiment.

[Comparative example 5]
In Comparative Example 5, as in Example 5, the vapor-phase reduction apparatus for carbon dioxide shown in FIG. 7 is used. Compared with Example 5, the intermediate tank 4 was always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. Other points are the same as the fifth embodiment.

[Example 6 for comparison]
Comparative Example 6 also uses the gas-phase reduction apparatus for carbon dioxide shown in FIG. Compared with Example 6, the intermediate tank 4 was always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. Other points are the same as the sixth embodiment.

[Example 7 for comparison]
Comparative Example 7 also uses the gas-phase reduction apparatus for carbon dioxide shown in FIG. Compared with Example 7, the intermediate tank 4 was always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. Other points are the same as the seventh embodiment.

[Comparative example 8]
Comparative Example 8 also uses the gas-phase reduction apparatus for carbon dioxide shown in FIG. Compared with Example 8, the intermediate tank 4 was always filled with the aqueous solution 11 regardless of the light irradiation time and the light stop time. Other points are the same as the eighth embodiment.

[effect]
Table 2 shows the current maintenance rate of carbon dioxide reduction when the net light irradiation time reaches 3 hours for Examples 1 to 8 and Comparative Examples 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 maintenance rate (%) of carbon dioxide reduction, the longer the life of the carbon dioxide reduction reaction.

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

In addition, the "current value for carbon dioxide reduction", which is the variable on the right side of the equation (1), is the concentration of the reduction reaction product A [ppm], the flow rate of the carrier gas B [L / sec], and the amount required for the reduction reaction. When Z [mol] is the number of electrons, F [C/mol] is the Faraday constant, and V _m [L/mol] is the molar body of the gas, it was calculated using Equation (2).

Current value for carbon dioxide reduction [A]=(A×B×Z×F×10 ⁻⁶ )/V _m (2)

When comparing Examples 1 to 4 with Comparative Examples 1 to 4 for each of the standby times 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 was improved more. Further, when comparing Examples 5 to 8 with Comparative Examples 5 to 8 for each of the standby times of 1 hour, 3 hours, 5 hours, and 10 hours at the time of voltage application, the results are similar to those at the time of light irradiation. , it can be understood that the current maintenance rate for carbon dioxide reduction is improved in each example as compared to each comparative example.

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

As described above, according to Examples 1 to 8, in the gas phase reduction apparatus for carbon dioxide in which gas phase carbon dioxide is directly reduced on the gas reduction sheet 100 in which the reduction electrode 7 is directly formed on the ion exchange membrane 6, Between the oxidation tank 2 and the reduction tank 3, an intermediate tank 4 capable of pouring and discharging an aqueous solution 11, which is an electrolytic solution, is arranged, and only when the oxidation electrode is irradiated with light, or when the oxidation electrode and the reduction electrode are in contact with each other. Since the reduction electrode 7 and the aqueous solution 11 are brought into contact only when a voltage is applied between The lifetime of the carbon dioxide reduction reaction can be improved.

[others]
The present invention is not limited to the above Examples 1 to 8, and various modifications are possible within the scope of the gist of the present invention. The nitride semiconductor shown as the oxidation electrode 1 of Examples 1 to 4 may have a different layered structure or a different composition such as containing indium or aluminum. Further, for the oxidation electrode 1 of Examples 1 to 4, a compound exhibiting photoactivity such as titanium oxide or amorphous silicon may be used instead of the nitride semiconductor. The oxidation electrode 1 of Examples 5 to 8 may be made of metal such as gold, silver, copper, indium, nickel, etc. instead of platinum. Instead of copper, the reduction electrode 7 may be gold, platinum, silver, palladium, gallium, indium, nickel, tin, cadmium, alloys thereof, or a mixture of these metals or metal oxides and carbon. . The aqueous solutions 10 and 11 may be sodium hydroxide aqueous solution, potassium chloride aqueous solution, or sodium chloride aqueous solution instead of potassium hydroxide aqueous solution. The ion exchange membrane 6 is, for example, a cation exchange membrane called Nafion, which is a perfluorocarbon material composed of a hydrophobic Teflon skeleton made of carbon-fluorine and a perfluoro side chain having a sulfonic acid group. The method for producing the gas reduction sheet may be electroplating, physical vapor deposition, or chemical vapor deposition, 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: conducting wire 9: light source 10: aqueous solution 11: aqueous solution 12: tube 13: gas inlet 14: Aqueous solution input port 15: Aqueous solution output port 16: Power supply 100: Gas reduction sheet

Claims (2)

In the gas phase reduction method of carbon dioxide performed in the gas phase reduction apparatus for carbon dioxide,
The gas-phase reduction device for carbon dioxide includes:
an oxidation bath comprising an oxidation electrode;
a reduction tank to which carbon dioxide is supplied;
an intermediate tank disposed between the oxidation tank and the reduction tank and capable of injecting and discharging an electrolytic solution;
an ion exchange membrane disposed between the oxidation tank and the intermediate tank;
A gas reduction sheet in which an ion exchange membrane and a reduction electrode are laminated, and is arranged between the reduction tank and the intermediate tank with the ion exchange membrane facing the intermediate tank and the reduction electrode facing the reduction tank. a gas reduction sheet that has been
a conducting wire connecting the oxidation electrode and the reduction electrode,
a first step of injecting an electrolytic solution into the oxidation tank and supplying carbon dioxide to the reduction tank;
a second step of pouring the electrolytic solution into the intermediate tank only when the oxidation electrode is irradiated with light;
gas phase reduction method of carbon dioxide. In the gas phase reduction method of carbon dioxide performed in the gas phase reduction apparatus for carbon dioxide,
The gas-phase reduction device for carbon dioxide includes:
an oxidation bath comprising an oxidation electrode;
a reduction tank to which carbon dioxide is supplied;
an intermediate tank disposed between the oxidation tank and the reduction tank and capable of injecting and discharging an electrolytic solution;
an ion exchange membrane disposed between the oxidation tank and the intermediate tank;
A gas reduction sheet in which an ion exchange membrane and a reduction electrode are laminated, and is arranged between the reduction tank and the intermediate tank with the ion exchange membrane facing the intermediate tank and the reduction electrode facing the reduction tank. a gas reduction sheet that has been
a conducting wire connecting the oxidation electrode and the reduction electrode,
a first step of injecting an electrolytic solution into the oxidation tank and supplying carbon dioxide to the reduction tank;
a second step of pouring an electrolytic solution into the intermediate tank only when a voltage is applied between the oxidation electrode and the reduction electrode;
gas phase reduction method of carbon dioxide.

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