CARBON DIOXIDE ELECTROLYSIS APPARATUS AND CARBON DIOXIDE ELECTROLYSIS METHOD

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefits of priority from the prior Japanese Patent Application No. 2024-082760 filed on May 21, 2024, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a carbon dioxide electrolysis apparatus and a carbon dioxide electrolysis method.

BACKGROUND

In recent years, depletion of fossil fuels such as oil and coal is concerned, and expectations for renewable energy that can be continuously used are increasing. For example, solar cells that generate power using solar energy, wind power generation that generates power using wind energy, and the like are known. These have a problem that it is difficult to stably supply electric power because the amount of power generation depends on the weather and natural conditions. Therefore, attempts have been made to stabilize electric power by storing electric power generated by renewable energy in a storage battery. However, there are problems that the storage battery requires cost and that loss occurs at the time of discharging and charging the storage battery.

In this regard, there is known a technique for producing hydrogen (H₂) from water by performing water electrolysis using electric power generated by renewable energy. Alternatively, a technique is also known in which carbon dioxide (CO₂) is electrochemically reduced using electric power generated by renewable energy and converted into a chemical substance (chemical energy) such as a carbon compound such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH₃OH), methane (CH₄), acetic acid (CH₃COOH), ethanol (C₂H₅OH), ethane (C₂H₆), or ethylene (C₂H₄). The storage of these chemical substances in a cylinder, a tank, or the like has an advantage that the storage cost of energy can be reduced and the storage loss is also small as compared with the case of storing electric power (electric energy) in a storage battery.

A carbon dioxide electrolysis apparatus that electrochemically reduces carbon dioxide has a stacked structure in which a plurality of electrolysis cells are stacked. When carbon dioxide gas is supplied to the cathode electrode of the electrolysis cell and a current is supplied to the electrolysis cell, carbon dioxide is electrolyzed and reduced to generate carbon monoxide. A cathode flow path serving as a flow path of carbon dioxide gas is adjacent to the cathode electrode, and the carbon dioxide gas is mixed with the electrolytic solution and flows through the cathode flow path while being in contact with the cathode electrode. An anode flow path serving as a flow path of an electrolytic solution is adjacent to the anode electrode, and the electrolytic solution flows through the anode flow path while being in contact with the anode electrode.

Among them, the electrolytic reaction formulas in the cathode electrode are represented by the following Formulas (1) and (2).

A case of operating at a current density at which a theoretical carbon dioxide gas concentration to be described later in the cathode fluid is 100% is considered. In this case, the electrolytic reaction represented by the above-described Formula (1) can proceed. As a result, the generation amount of carbonate ions (CO₃²⁻) increases, and a salt can be precipitated on the inlet side of the cathode flow path. There is a possibility that the precipitated salt could block the cathode flow path.

Meanwhile, when the concentration of the carbon dioxide gas in the cathode fluid is small, the operation mode of the carbon dioxide electrolysis apparatus is the water electrolysis mode. In this case, the electrolytic reaction represented by the above-described Formula (2) can proceed. When the hydrogen gas generated by Formula (2) cross-leaks to the anode electrode, active oxygen species containing OH radicals (·OH) and the like are generated. When the active oxygen species are, for example, OH radicals, the active oxygen species are produced on the outlet side of the cathode electrode as shown in the following Formula (3), and cause deterioration of the electrolyte membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a carbon dioxide electrolysis apparatus according to the present embodiment;

FIG. 2 is a schematic cross-sectional view showing a carbon dioxide electrolysis unit shown in FIG. 1;

FIG. 3 is a flowchart showing an example of a carbon dioxide electrolysis method according to the present embodiment;

FIG. 4 is a graph illustrating a relationship between a cell voltage and a current density;

FIG. 5 is a graph showing a relationship between a theoretical flow rate of carbon dioxide and Faraday efficiency;

FIG. 6 is a schematic view showing a modification example of the carbon dioxide electrolysis apparatus shown in FIG. 1; and

FIG. 7 is a schematic view showing another modification example of the carbon dioxide electrolysis apparatus shown in FIG. 1.

DETAILED DESCRIPTION

The carbon dioxide electrolysis apparatus according to the embodiment is an apparatus that performs electrolysis of carbon dioxide gas. A carbon dioxide electrolysis apparatus includes an electrolysis cell including a cathode electrode to which carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode, a current supply unit that supplies a current to the electrolysis cell, and a control unit. A value obtained by dividing the current supplied to the electrolysis cell by the planar effective area of the electrolysis cell is defined as a current density. The control unit controls the current supply unit such that the current density is 10 mA/cm² to 1,000 mA/cm².

The carbon dioxide electrolysis apparatus according to the embodiment is an apparatus that performs electrolysis of carbon dioxide gas. A carbon dioxide electrolysis apparatus includes: an electrolysis cell including a cathode electrode to which carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode; a carbon dioxide gas flow rate adjustment unit that adjusts a supply flow rate of the carbon dioxide gas to the cathode electrode; and a control unit. A value obtained by dividing the current supplied to the electrolysis cell by the planar effective area of the electrolysis cell is defined as a current density. The minimum flow rate of the carbon dioxide gas when the total amount of electricity per unit time at a predetermined current density is used in the electrolytic reaction from carbon dioxide to carbon monoxide is defined as a theoretical carbon dioxide gas flow rate, and a ratio of a supply flow rate of the carbon dioxide gas to the theoretical carbon dioxide gas flow rate is defined as a flow rate ratio. The control unit controls the carbon dioxide gas flow rate adjustment unit such that the flow rate ratio is 50% to 500%.

The carbon dioxide electrolysis method according to the embodiment is a method using a carbon dioxide electrolysis apparatus that performs electrolysis of carbon dioxide gas and includes an electrolysis cell including a cathode electrode to which carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode. A carbon dioxide electrolysis method includes: a step of supplying carbon dioxide gas to a cathode electrode; a step of supplying a current to an electrolysis cell; and a step of increasing an output of the carbon dioxide electrolysis apparatus. A value obtained by dividing the current supplied to the electrolysis cell by the planar effective area of the electrolysis cell is defined as a current density. In the step of increasing the output, the current value of the current is adjusted such that the current density is 10 mA/cm² to 1,000 mA/cm².

The carbon dioxide electrolysis method according to the embodiment is a method using a carbon dioxide electrolysis apparatus that performs electrolysis of carbon dioxide gas and includes an electrolysis cell including a cathode electrode to which carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode. A carbon dioxide electrolysis method includes: a step of supplying carbon dioxide gas to a cathode electrode; a step of supplying a current to an electrolysis cell; and a step of increasing an output of the carbon dioxide electrolysis apparatus. A value obtained by dividing the current supplied to the electrolysis cell by the planar effective area of the electrolysis cell is defined as a current density. The minimum flow rate of the carbon dioxide gas when the total amount of electricity per unit time at a predetermined current density is used in the electrolytic reaction from carbon dioxide to carbon monoxide is defined as a theoretical carbon dioxide gas flow rate, and the ratio of the supply flow rate of the carbon dioxide gas to the theoretical carbon dioxide gas flow rate is defined as a flow rate ratio. In the step of increasing the output, the supply flow rate of the carbon dioxide gas is adjusted such that the flow rate ratio is 50% to 500%.

Hereinafter, a carbon dioxide electrolysis apparatus and a carbon dioxide electrolysis method according to the present embodiment will be described with reference to the drawings.

As shown in FIG. 1, a carbon dioxide electrolysis apparatus 1 includes a carbon dioxide electrolysis unit 2, an electrolytic solution supply unit 3, a current supply unit 4, a carbon dioxide gas supply unit 5, a carbon dioxide gas flow rate adjustment unit 6, and a control unit 7. The carbon dioxide electrolysis apparatus 1 performs electrolysis of carbon dioxide gas supplied to a cathode electrode 20 to be described later.

As shown in FIG. 2, the carbon dioxide electrolysis unit 2 includes one or more electrolysis cells 10. More specifically, carbon dioxide electrolysis unit 2 includes a pair of current collector plates 11, a plurality of electrolysis cells 10 stacked between the pair of current collector plates 11, and a plurality of separators 12 alternately stacked with the electrolysis cells 10. The electrolysis cell 10, the separator 12, and the current collector plate 11 are fastened and pressed by a pair of fastening plates (not shown).

The electrolysis cell 10 includes the cathode electrode 20, an anode electrode 21, and an electrolyte membrane 22 interposed between the cathode electrode 20 and the anode electrode 21. The cathode electrode 20 is in contact with the electrolyte membrane 22 and the separator 12. A cathode gas and an electrolytic solution may be supplied to the cathode electrode 20. A cathode flow path 23 through which a cathode gas and an electrolytic solution flow is formed on a surface of the separator 12 in contact with the cathode electrode 20. The anode electrode 21 is in contact with the electrolyte membrane 22 and the separator 12. An electrolytic solution is supplied to the anode electrode 21. An anode flow path 24 through which an electrolytic solution flows is formed on a surface of the separator 12 in contact with the anode electrode 21.

The cathode electrode 20 and the anode electrode 21 may be supplied with an electrolytic solution from the electrolytic solution supply unit 3. The electrolytic solution may be, for example, an aqueous solution of an electrolyte containing potassium element in the composition. Examples of the electrolytic solution include a potassium hydroxide (KOH) aqueous solution, a potassium hydrogen carbonate (KHCO₃) aqueous solution, and a potassium carbonate (K₂CO₃) aqueous solution. The electrolytic solution supplied to the cathode electrode 20 and the electrolytic solution supplied to the anode electrode 21 may be the same or different. A cathode gas containing carbon dioxide gas is supplied from the carbon dioxide gas supply unit 5 to the cathode electrode 20. That is, the carbon dioxide gas supplied to the cathode electrode 20 is mixed with the electrolytic solution. However, the electrolytic solution may not be supplied to the cathode electrode 20.

The electrolyte membrane 22 is formed of an electrolyte material. Examples of the electrolyte membrane 22 include, but are not limited to, an ion exchange membrane or a porous membrane.

As shown in FIG. 1, electrolytic solution supply unit 3 supplies an electrolytic solution to carbon dioxide electrolysis unit 2. The electrolytic solution supply unit 3 may include, for example, a pump (not shown). The electrolytic solution stored in the storage unit (not shown) may be supplied to the carbon dioxide electrolysis unit 2 by driving the pump.

The current supply unit 4 supplies a current for performing an electrolytic reaction to the carbon dioxide electrolysis unit 2. The current supply unit 4 is also referred to as a power supply unit. The current supply unit 4 may be controlled by the control unit 7 to adjust the current supplied to the carbon dioxide electrolysis unit 2.

The carbon dioxide gas supply unit 5 supplies carbon dioxide gas to the cathode electrode 20 of the carbon dioxide electrolysis unit 2. The carbon dioxide gas supply unit 5 may include a cylinder of carbon dioxide gas, or may include a tank storing carbon dioxide gas.

The carbon dioxide gas flow rate adjustment unit 6 adjusts the supply flow rate of the carbon dioxide gas to the cathode electrode 20 of the carbon dioxide electrolysis unit 2. The carbon dioxide gas flow rate adjustment unit 6 may include, for example, a flow rate adjusting valve (not shown). The supply flow rate of the carbon dioxide gas may be adjusted by adjusting the opening degree of the flow rate adjusting valve. The carbon dioxide gas flow rate adjustment unit 6 may be controlled by the control unit 7 to adjust the supply flow rate of the carbon dioxide gas.

The control unit 7 controls the current supply unit 4 and the carbon dioxide gas flow rate adjustment unit 6 described above.

For example, the control unit 7 may control the current supply unit 4 such that the current density of the current supplied to the electrolysis cell 10 becomes 10 mA/cm² to 1,000 mA/cm². The current density is a value obtained by dividing the current supplied to the electrolysis cell 10 by the planar effective area of the electrolysis cell 10. The planar effective area of the electrolysis cell 10 is the planar area of the electrolysis cell 10 in the region through which the current passes in the electrolysis cell 10, and is the entire planar area of the electrolysis cell 10 when the current passes through the entire region of the electrolysis cell 10. The control unit 7 may control the current supply unit 4 such that the current density supplied to the electrolysis cell 10 becomes 100 mA/cm² to 1,000 mA/cm².

For example, the control unit 7 may control the carbon dioxide gas flow rate adjustment unit 6 such that the supply flow rate of the carbon dioxide gas is 50% to 500% of the theoretical carbon dioxide gas flow rate. The theoretical carbon dioxide gas flow rate is defined as the minimum flow rate of carbon dioxide gas when the total amount of electricity per unit time at a predetermined current density is used in the electrolytic reaction from carbon dioxide to carbon monoxide. The amount of electricity per unit time is the current. The ratio of the supply flow rate of the carbon dioxide gas to the theoretical carbon dioxide gas flow rate is defined as a flow rate ratio. The flow rate ratio is expressed by supply flow rate of carbon dioxide gas/theoretical carbon dioxide gas flow rate. As an example, a case where the theoretical carbon dioxide gas flow rate when the current density is 1,000 mA/cm² is 10 Nm³/h is considered. In this case, the supply flow rate of the carbon dioxide gas when the flow rate ratio at the current density of 1,000 mA/cm² is 100% is 10 Nm³/h, and the supply flow rate of the carbon dioxide gas when the flow rate ratio is 200% is 20 Nm³/h. The control unit 7 may control the carbon dioxide gas flow rate adjustment unit 6 such that the flow rate ratio is 100% to 200%.

A carbon dioxide electrolysis method using the carbon dioxide electrolysis apparatus according to the present embodiment configured as described above will be described with reference to FIG. 3.

First, when carbon dioxide gas electrolysis is performed in the carbon dioxide electrolysis apparatus 1 shown in FIGS. 1 and 2, a current value to be supplied to the electrolysis cell 10 by the current supply unit 4 is set (step S1). Specifically, the current value is set in the control unit 7 to obtain a desired current density. For example, the current value may be set such that the current density is 10 mA/cm² to 1,000 mA/cm².

Subsequently, carbon dioxide gas is supplied from the carbon dioxide gas supply unit 5 to the carbon dioxide electrolysis unit 2 (step S2). At this time, the supply flow rate of the carbon dioxide gas may be smaller than the supply flow rate of the carbon dioxide gas in step S4 to be described later.

The carbon dioxide gas is supplied to the cathode electrode 20 of the electrolysis cell 10 as cathode gas. The cathode gas is mixed with the electrolytic solution, and flows through the cathode flow path 23 formed in the separator 12 while being in contact with the cathode electrode 20. The electrolytic solution supplied to the anode electrode 21 flows through the anode flow path 24 formed in the separator 12 while being in contact with the anode electrode 21.

In step S2, an inert gas may be mixed with the carbon dioxide gas. Carbon dioxide gas mixed with an inert gas may be supplied to the cathode electrode 20.

In step S2, the electrolytic solution is supplied from electrolytic solution supply unit 3 to the cathode electrode 20 and the anode electrode 21 of the electrolysis cell 10. In step S2, after the supply of the carbon dioxide gas to the electrolysis cell 10 is started, the concentration and the flow rate of the carbon dioxide gas supplied from the carbon dioxide gas supply unit 5 to the electrolysis cell 10 may be measured. The cooling system may be activated after a lapse of a predetermined time from the start of the supply of the carbon dioxide gas. During a period from the start of the supply of the carbon dioxide gas to the activation of the cooling system, a warm-up operation of continuously supplying the carbon dioxide gas to the electrolysis cell 10 may be performed.

Next, a current is supplied from the current supply unit 4 to the carbon dioxide electrolysis unit 2 (step S3). In the cathode electrode 20, the electrolytic reaction represented by the above-described Formula (1) is performed. The current supply unit 4 supplies a current at the current value set in the above-described step S1. When the current is supplied to the electrolysis cell 10, electrolysis starts. After the electrolysis starts, it is confirmed that the operation is stabilized. At this time, the current value may be smaller than the current value in step S4 to be described later.

Thereafter, the output of the carbon dioxide electrolysis apparatus 1 is increased (step S4). In this case, the supply flow rate of the carbon dioxide gas to the carbon dioxide electrolysis unit 2 may be increased.

The carbon dioxide gas flow rate adjustment unit 6 may adjust the supply flow rate of the carbon dioxide gas to a desired flow rate by the control unit 7. For example, the supply flow rate of the carbon dioxide gas may be adjusted such that the flow rate ratio is 50% to 500%.

In step S4, the current value supplied to the carbon dioxide electrolysis unit 2 may be increased. In this case, the current value may be increased to the value set in the above-described step S1. For example, the current value in step S4 may be adjusted such that the current density is 10 mA/cm² to 1,000 mA/cm².

In such step S4, the production amount of carbon monoxide increases, and the output of the carbon dioxide electrolysis apparatus 1 increases.

Thus, the activation of the carbon dioxide electrolysis apparatus 1 is completed (step S5). After activation, operation continues and the production of carbon monoxide continues.

When the operation is performed at a current density at which the concentration of the carbon dioxide gas in the cathode gas is 100% and the flow rate ratio is 100%, the generation amount of carbonate ions (CO₃²⁻) increases, and a salt may precipitate on the inlet side of the cathode flow path 23. When the electrolytic solution is an aqueous solution of an electrolyte containing potassium element in the composition, potassium carbonate (K₂CO₃) is generated as a salt. The precipitated salt may block the cathode flow path 23.

Meanwhile, when the concentration of the carbon dioxide gas in the cathode gas is small and the voltage between the cathode electrode 20 and the anode electrode 21 increases, the electrolytic reaction represented by the above-described Formula (3) proceeds, and active oxygen species including OH radicals and the like can be generated. For example, when the active oxygen species are OH radicals, the OH radicals may be produced on the outlet side of the cathode flow path 23, but may react with the material of the electrolyte membrane 22 to degrade the electrolyte membrane 22.

Therefore, in the present embodiment, the control unit 7 controls the current supply unit 4, and the current density of the current supplied to the electrolysis cell 10 is adjusted to a predetermined range. More specifically, the current density is adjusted to 10 mA/cm² to 1,000 mA/cm². As a result, the current density can be reduced. In this case, the electrolytic reaction in the cathode electrode 20 shown in the above-described Formula (1) can be suppressed, and the generation amount of carbonate ions (CO₃²⁻) can be reduced. Therefore, the precipitation amount of salt can be reduced, and blockage of the cathode flow path 23 can be suppressed.

More specifically, by setting the current density to 1,000 mA/cm² or less, the precipitation amount of salt can be effectively reduced. Meanwhile, by setting the current density to 10 mA/cm² or more, the electrolytic reaction (electrolytic reaction Formula (1)) in the cathode electrode 20 can proceed as shown in FIG. 4 while reducing the precipitation amount of salt, and the production amount of carbon monoxide can be secured. The cell voltage at a current density of 10 mA/cm² is referred to as a theoretical voltage. The theoretical voltage is the minimum voltage for allowing the electrolytic reaction to proceed. A region where the cell voltage is larger than the theoretical voltage is referred to as an overvoltage region.

As shown in FIG. 4, by increasing the voltage (cell voltage) between the cathode electrode 20 and the anode electrode 21, the electrolytic reaction Formula (1) becomes the main reaction, and the production amount of carbon monoxide can be increased. When the current density reaches 1,000 mA/cm², the production amount of carbon monoxide does not increase even when the cell voltage is further increased. This current density is referred to as a limit current density.

In addition, as described above, by adjusting the current density to 10 mA/cm² to 1,000 mA/cm², the generation amount of OH radicals can be reduced. That is, by reducing the current density, the cell voltage can be reduced, and an increase in overvoltage can be suppressed. Since the generation amount of OH radicals increases as the overvoltage increases, the generation amount of OH radicals can be effectively reduced by decreasing the current density. Therefore, deterioration of the electrolyte membrane 22 due to OH radicals can be suppressed. By setting the current density to 1,000 mA/cm² or less, an increase in overvoltage can be effectively suppressed.

In particular, by decreasing the current density in the range of 10 mA/cm² to 1,000 mA/cm², an increase in overvoltage can be more effectively suppressed. For example, the current density may be set to 10 mA/cm² to 100 mA/cm². Meanwhile, by setting the current density to 10 mA/cm² or more, an electrolytic reaction in the cathode electrode 20 can be performed while suppressing an increase in overvoltage, and a production amount of carbon monoxide can be secured.

Meanwhile, the slope (increase rate) of the current density is larger in the range of 100 mA/cm² to 1,000 mA/cm² than in the range of 10 mA/cm² to 100 mA/cm². In consideration of more effectively suppressing an increase in overvoltage, the current density is desirably around 100 mA/cm².

During the operation of the carbon dioxide electrolysis apparatus 1, the control unit 7 controls the carbon dioxide gas flow rate adjustment unit 6 to adjust the supply flow rate of the carbon dioxide gas supplied to the electrolysis cell 10 to a predetermined range. More specifically, the flow rate ratio is adjusted to be 50% to 500%. As a result, the supply flow rate of the carbon dioxide gas can be appropriately adjusted. In this case, the supply flow rate of the carbon dioxide gas flowing through the cathode flow path 23 can be secured, and the salt precipitated in the cathode flow path 23 can be blown off. Therefore, it is possible to suppress blockage of the cathode flow path 23.

More specifically, by setting the flow rate ratio to 50% or more, the salt precipitated in the cathode flow path 23 can be effectively blown off. Meanwhile, by setting the flow rate ratio to 500% or less, it is possible to suppress the discharge amount of the carbon dioxide gas, which is not subjected to the electrolytic reaction, from the cathode flow path 23 while blowing off the salt. The flow rate ratio is more desirably 100% to 200% in consideration of Faraday efficiency. As shown in FIG. 5, by setting the flow rate ratio to 100% or more, the electrolytic reaction can be performed in a region where the Faraday efficiency is high. By setting the flow rate ratio to 200% or less, it is possible to suppress a decrease in the production efficiency of carbon monoxide. That is, when the flow rate ratio reaches 200%, the Faraday efficiency does not increase and the production amount of carbon monoxide does not increase even when the supply flow rate of the carbon dioxide gas is further increased. Therefore, it is effective to set the flow rate ratio to 200% or less. Faraday efficiency refers to the percentage of partial current that contributed to the production of carbon monoxide relative to the total current. By setting the flow rate ratio to 200% or less, the supply flow rate of the carbon dioxide gas can be increased to more effectively blow off the salt precipitated in the cathode flow path 23, and the discharge amount of the carbon dioxide gas which is not subjected to the electrolytic reaction from the cathode flow path 23 can be further suppressed.

In addition, as described above, the flow rate ratio is adjusted to 50% to 500%, and accordingly, the generation amount of OH radicals can be reduced. That is, by appropriately adjusting the supply flow rate of the carbon dioxide gas, the supply flow rate of the carbon dioxide gas to the cathode electrode 20 can be secured, and the shortage of the carbon dioxide gas in the cathode electrode 20 can be suppressed. Therefore, the generation amount of OH radicals can be reduced, and deterioration of the electrolyte membrane 22 due to the OH radicals can be suppressed. By setting the flow rate ratio to 50% or more, the generation amount of OH radicals can be effectively reduced. Meanwhile, by setting the flow rate ratio to 500% or less, it is possible to suppress the discharge amount of the carbon dioxide gas, which is not subjected to the electrolytic reaction, from the cathode flow path 23 while reducing the generation amount of OH radicals. As described above, when the flow rate ratio is adjusted to be 100% to 200%, the supply flow rate of the carbon dioxide gas is increased, and accordingly, the generation amount of OH radicals can be more effectively reduced, and the discharge amount of the carbon dioxide gas, which is not subjected to the electrolytic reaction, from the cathode flow path 23 can be further suppressed.

In the above-described present embodiment, an example has been described in which the control unit 7 controls the current supply unit 4 such that the current density of the current supplied to the electrolysis cell 10 becomes 10 mA/cm² to 1,000 mA/cm², and controls the carbon dioxide gas flow rate adjustment unit 6 such that the flow rate ratio becomes 50% to 500%. However, the present embodiment is not limited to this. For example, when the control unit 7 controls the current supply unit 4 such that the current density of the current supplied to the electrolysis cell 10 becomes 10 mA/cm² to 1,000 mA/cm², the adjustment range of the flow rate ratio is not limited to 50% to 500%. Meanwhile, for example, when the control unit 7 controls the carbon dioxide gas flow rate adjustment unit 6 such that the flow rate ratio is 50% to 500%, the adjustment range of the current density is not limited to 10 mA/cm² to 1,000 mA/cm².

As shown in FIG. 1, the carbon dioxide electrolysis apparatus 1 according to the present embodiment may further include an input unit 8. The input unit 8 may be configured to input the concentration of the carbon dioxide gas in the cathode gas supplied to the cathode electrode 20. The control unit 7 may control the current supply unit 4 based on the concentration of the carbon dioxide gas input from the input unit 8. More specifically, the control unit 7 may control the current supply unit 4 to decrease the current density as the concentration of the carbon dioxide gas in the cathode gas supplied to the cathode electrode 20 decreases. By controlling the current supply unit 4 based on the carbon dioxide gas concentration, the current density can be set according to the supply flow rate of the carbon dioxide gas supplied to the cathode electrode 20, and the production efficiency of the carbon monoxide gas can be improved.

The concentration of the carbon dioxide gas input to the input unit 8 may be the concentration of the carbon dioxide gas acquired in advance. The configuration of the input unit 8 is optional as long as the concentration of the carbon dioxide gas can be input. The input unit 8 may be configured such that an operator can input the concentration of carbon dioxide gas, or may be configured such that the concentration of carbon dioxide gas is transmitted as electronic information from an external device (not shown) to be input to the input unit 8. The input unit 8 may be configured integrally with the control unit 7 or may be configured separately.

As shown in FIG. 6, the carbon dioxide electrolysis apparatus 1 may further include a carbon dioxide gas concentration meter 9 in addition to the input unit 8. The carbon dioxide gas concentration meter 9 measures the concentration of carbon dioxide gas supplied from the carbon dioxide gas supply unit 5 to the cathode electrode 20. In the example shown in FIG. 6, the current supply unit 4 can be controlled based on the concentration of the carbon dioxide gas actually supplied to the cathode electrode 20, and the production efficiency of carbon monoxide can be further improved. In the example shown in FIG. 6, the carbon dioxide gas concentration meter 9 measures the concentration of carbon dioxide gas on the downstream side of the carbon dioxide gas flow rate adjustment unit 6 and on the upstream side of the cathode electrode 20. The concentration of the carbon dioxide gas measured by the carbon dioxide gas concentration meter 9 may be transmitted to the input unit 8.

As shown in FIG. 7, the carbon dioxide electrolysis apparatus 1 according to the above-described present embodiment may further include an inert gas supply unit 30 and an inert gas flow rate adjustment unit 31.

The inert gas supply unit 30 supplies an inert gas to the cathode electrode 20 of the carbon dioxide electrolysis unit 2. The inert gas may be mixed with the carbon dioxide gas from the carbon dioxide gas supply unit 5 and supplied to the cathode electrode 20. The inert gas is a gas that does not affect the electrolytic reaction in the cathode electrode 20. Examples of such an inert gas include hydrogen gas. The hydrogen gas is discharged from the outlet of the cathode flow path 23 without an electrolytic reaction while flowing through the cathode flow path 23. The inert gas supply unit 30 may include a cylinder of an inert gas, or may include a tank storing an inert gas.

The inert gas flow rate adjustment unit 31 adjusts the supply flow rate of the inert gas to be mixed with the carbon dioxide gas. The inert gas flow rate adjustment unit 31 may include, for example, a flow rate adjusting valve (not shown). The supply flow rate of the inert gas may be adjusted by adjusting the opening degree of the flow rate adjusting valve. The inert gas flow rate adjustment unit 31 may be controlled by the control unit 7 to adjust the supply flow rate of the inert gas.

The control unit 7 shown in FIG. 7 may control the above-described inert gas flow rate adjustment unit 31. More specifically, the control unit 7 may control the inert gas flow rate adjustment unit 31 to mix the inert gas with the carbon dioxide gas. When the inert gas is not contained in the cathode gas, the control unit 7 may control the inert gas flow rate adjustment unit 31 to block the flow of the inert gas. In this case, the concentration of the carbon dioxide gas in the cathode gas is 100%. Meanwhile, when an inert gas is contained in the cathode gas, the inert gas flow rate adjustment unit 31 may be controlled to supply the inert gas to the cathode electrode 20. In this case, the concentration of the carbon dioxide gas in the cathode gas becomes less than 100%, and the partial pressure of the carbon dioxide gas decreases. As the partial pressure of the carbon dioxide gas decreases, the control unit 7 may control the current supply unit 4 to decrease the current density. This makes it possible to suppress the electrolytic reaction in the cathode electrode 20 represented by the above-described Formula (1) and to reduce the precipitation amount of salt. Therefore, it is possible to suppress blockage of the cathode flow path 23. The current density may be selected within a range of 10 mA/cm² to 1,000 mA/cm².

The supply flow rate of the inert gas supplied to the cathode electrode 20 may be appropriately adjusted. As a result, the partial pressure of the carbon dioxide gas in the cathode gas is appropriately adjusted.

According to the above-described embodiment, it is possible to suppress blockage of the cathode flow path and to suppress deterioration of the electrolyte membrane.

Although several embodiments have been described above, these embodiments have been presented only as examples, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and modification examples thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof. As a matter of course, it is also possible to appropriately combine these embodiments partially within the scope of the gist of the present invention.