Carbon dioxide electrolysis device and carbon dioxide electrolysis method

Abstract

A carbon dioxide electrolysis device according to an embodiment is provided with: an electrolysis unit 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 the current density. The control unit controls the current supply unit such that the current density is from 10 mA / cm < 2 > to 1000 mA / cm < 2 >.

Description

TECHNICAL FIELD

[0001] Embodiments relate to a carbon dioxide electrolysis device and a carbon dioxide electrolysis method. BACKGROUND

[0002] In recent years, there is an increased expectation for renewable energy that can be used continuously, in light of concerns about depletion of fossil fuels such as petroleum and coal. For example, solar cells that generate electricity using solar energy, wind power generation that generates electricity using wind energy, and the like are known. The amount of electricity generated by these depends on the weather and natural conditions, and thus there is a technical problem in that it is difficult to stably supply electricity. Therefore, attempts have been made to store electricity generated by renewable energy in a storage battery to stabilize the electricity. However, there are problems in that the storage battery requires cost, or that there is a loss when discharging and charging the storage battery.

[0003] In view of this, a technique is known in which hydrogen (H2) is produced from water by water electrolysis using electricity generated by renewable energy. Alternatively, a technique is also known in which carbon dioxide (CO2) is electrochemically reduced into a chemical substance (chemical energy) such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH3OH), methane (CH4), acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), or ethylene (C2H4) using electricity generated by renewable energy. Compared to the case where electricity (electrical energy) is stored in a storage battery, storage of these chemical substances in a gas cylinder, a tank, or the like has the advantages that the storage cost of energy can be reduced, and that there is less storage loss.

[0004] A carbon dioxide electrolysis device that electrochemically reduces carbon dioxide has a stacked structure in which a plurality of electrolysis cells are stacked. By supplying carbon dioxide gas to a cathode electrode of the electrolysis cell and supplying an electric current to the electrolysis cell, the carbon dioxide is electrolyzed and reduced to generate carbon monoxide. The cathode electrode is adjacent to a cathode flow path that is a flow path of the carbon dioxide gas, and the carbon dioxide gas is mixed with an electrolyte and flows in the cathode flow path while contacting the cathode electrode. The anode electrode is adjacent to an anode flow path that is a flow path of the electrolyte, and the electrolyte flows in the anode flow path while contacting the anode electrode.

[0005] Here, the electrolysis reaction formula in the cathode electrode is represented by the following formula (1) and (2).

[0006] 2CO2+ 2e - → CO + CO3 2- (1)

[0007] 2H2O + 2e - → H2 + 2OH - (2)

[0008] Consider a case where the cathode fluid is operated at a current density at which the theoretical carbon dioxide gas concentration described later becomes 100%. In this case, the electrolysis reaction represented by the above-described formula (1) can proceed. As a result, the amount of carbonate ions (CO3 2- ) generated increases, and salt can be deposited on the inlet side of the cathode flow path. It is thought that the cathode flow path can be clogged by the deposited salt.

[0009] On the other hand, in a case where the concentration of carbon dioxide gas in the cathode fluid is low, the operation mode of the carbon dioxide electrolysis device becomes a water electrolysis mode. In this case, the electrolysis reaction represented by the above-described formula (2) can proceed. Furthermore, in a case where hydrogen gas generated according to formula (2) leaks to the anode electrode, active oxygen species including OH radicals (·OH) and the like are generated. This active oxygen species, for example, in the case of OH radicals, is generated on the outlet side of the cathode electrode as represented by the following formula (3), and becomes a main cause of degradation of the electrolyte membrane.

[0010] H2O→·OH + H + + e - (3) SUMMARY

[0011] The carbon dioxide electrolysis device of the embodiment is a device that performs electrolysis of carbon dioxide gas. The carbon dioxide electrolysis device includes an electrolysis unit 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 portion that supplies a current to the electrolysis unit; and a control portion. A value obtained by dividing the current supplied to the electrolysis unit by a planar effective area of the electrolysis unit is defined as a current density. The control portion controls the current supply portion so that the current density becomes 10 mA / cm 2 ~ 1000 mA / cm 2 .

[0012] The carbon dioxide electrolysis device of the embodiment is a device that performs electrolysis of carbon dioxide gas. The carbon dioxide electrolysis device includes an electrolysis unit 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 portion that adjusts a supply flow rate of carbon dioxide gas to the cathode electrode; and a control portion. A value obtained by dividing a current supplied to the electrolysis unit by a planar effective area of the electrolysis unit is defined as a current density. A minimum flow rate of carbon dioxide gas at which a total amount of electric quantity per unit time at a prescribed current density is used in an electrolysis 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 carbon dioxide gas to the theoretical carbon dioxide gas flow rate is defined as a flow rate ratio. The control portion controls the carbon dioxide gas flow rate adjustment portion so that the flow rate ratio becomes 50% to 500%.

[0013] The carbon dioxide electrolysis method of the embodiment is a method using a carbon dioxide electrolysis device that performs electrolysis of carbon dioxide gas, the carbon dioxide electrolysis device including an electrolysis unit including a cathode electrode to which the carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode. The carbon dioxide electrolysis method includes a step of supplying the carbon dioxide gas to the cathode electrode, a step of supplying a current to the electrolysis unit, and a step of increasing an output of the carbon dioxide electrolysis device. A value obtained by dividing the current supplied to the electrolysis unit by a planar effective area of the electrolysis unit is defined as a current density. In the step of increasing the output, the current value of the current is adjusted in such a manner that the current density becomes 10 mA / cm 2 ~ 1000 mA / cm 2 .

[0014] The carbon dioxide electrolysis method of the embodiment is a method using a carbon dioxide electrolysis device that performs electrolysis of carbon dioxide gas, the carbon dioxide electrolysis device including an electrolysis unit including a cathode electrode to which the carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode. The carbon dioxide electrolysis method includes a step of supplying the carbon dioxide gas to the cathode electrode, a step of supplying a current to the electrolysis unit, and a step of increasing an output of the carbon dioxide electrolysis device. A value obtained by dividing the current supplied to the electrolysis unit by a planar effective area of the electrolysis unit is defined as a current density. A total amount of electric quantity per unit time at a prescribed current density is defined as a theoretical carbon dioxide gas flow rate in a case where the total amount of electric quantity is used for an electrolysis reaction from carbon dioxide to carbon monoxide, 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. In the step of increasing the output, the supply flow rate of the carbon dioxide gas is adjusted in such a manner that the flow rate ratio becomes 50% to 500%. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic view that shows a carbon dioxide electrolysis device of the embodiment.

[0016] Figure 2 is a schematic cross-sectional view that shows a carbon dioxide electrolysis unit shown in Figure 1 .

[0017] Figure 3 is a flowchart that shows an example of a carbon dioxide electrolysis method of the embodiment.

[0018] Figure 4 is a graph that shows a relationship between a unit voltage and a current density.

[0019] Figure 5It is a graph showing the relationship between the theoretical carbon dioxide flow rate and the Faraday efficiency.

[0020] Figure 6 It means Figure 1 A schematic diagram of a modified example of the carbon dioxide electrolysis apparatus shown.

[0021] Figure 7 It means Figure 1 A schematic diagram of another variation of the carbon dioxide electrolysis apparatus shown. Detailed Implementation

[0022] Hereinafter, the carbon dioxide electrolysis apparatus and carbon dioxide electrolysis method of this embodiment will be described with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the carbon dioxide electrolysis apparatus 1 includes a carbon dioxide electrolysis unit 2, an electrolyte 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 the cathode electrode 20 (described later).

[0024] like Figure 2 As shown, the carbon dioxide electrolysis unit 2 includes one or more electrolysis units 10. More specifically, the carbon dioxide electrolysis unit 2 includes: a pair of current collectors 11, a plurality of electrolysis units 10 stacked between the pair of current collectors 11, and a plurality of partitions 12 alternately stacked with the electrolysis units 10. The electrolysis units 10, partitions 12, and current collectors 11 are fastened and pressed by a pair of fastening plates (not shown).

[0025] The electrolysis unit 10 includes a cathode electrode 20, an anode electrode 21, and an electrolyte membrane 22 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. Cathode gas and electrolyte can also be supplied to the cathode electrode 20. A cathode flow path 23 for the flow of cathode gas and electrolyte is formed on the 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. Electrolyte is supplied to the anode electrode 21. An anode flow path 24 for the flow of electrolyte is formed on the surface of the separator 12 in contact with the anode electrode 21.

[0026] Electrolyte can also be supplied to the cathode electrode 20 and anode electrode 21 from the electrolyte supply unit 3. The electrolyte can be, for example, an aqueous solution of an electrolyte containing potassium. Examples of electrolytes include aqueous solutions of potassium hydroxide (KOH), potassium bicarbonate (KHCO3), and potassium carbonate (K2CO3). The electrolyte supplied to the cathode electrode 20 and the electrolyte supplied to the anode electrode 21 can be the same or different. Cathode gas containing carbon dioxide is supplied to the cathode electrode 20 from the carbon dioxide gas supply unit 5. That is, the carbon dioxide gas supplied to the cathode electrode 20 is mixed with the electrolyte. However, it is also possible not to supply electrolyte to the cathode electrode 20.

[0027] The electrolyte membrane 22 is formed of an electrolyte material. Examples of electrolyte membrane 22 include ion exchange membranes or porous membranes, but are arbitrary.

[0028] like Figure 1 As shown, the electrolyte supply unit 3 supplies electrolyte to the carbon dioxide electrolysis unit 2. The electrolyte supply unit 3 may include, for example, a pump (not shown). Alternatively, the electrolyte stored in a storage unit (not shown) can be supplied to the carbon dioxide electrolysis unit 2 by driving the pump.

[0029] The current supply unit 4 supplies current to the carbon dioxide electrolysis unit 2 for the electrolysis reaction. The current supply unit 4 is also called the power supply unit. The current supply unit 4 can also be controlled by the control unit 7 to adjust the current supplied to the carbon dioxide electrolysis unit 2.

[0030] 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 carbon dioxide gas storage cylinder, or it may include a tank storing carbon dioxide gas.

[0031] The carbon dioxide gas flow rate regulating unit 6 adjusts the supply flow rate of carbon dioxide gas to the cathode electrode 20 of the carbon dioxide electrolysis unit 2. The carbon dioxide gas flow rate regulating unit 6 may, for example, include a flow regulating valve (not shown). The supply flow rate of carbon dioxide gas can also be adjusted by adjusting the opening degree of the flow regulating valve. The carbon dioxide gas flow rate regulating unit 6 can also be controlled by the control unit 7 to adjust the supply flow rate of carbon dioxide gas.

[0032] The control unit 7 controls the current supply unit 4 and the carbon dioxide gas flow adjustment unit 6.

[0033] For example, the control unit 7 can also supply a current density of 10 mA / cm² to the electrolysis unit 10. 2 ~1000mA / cm 2The current supply unit 4 is controlled in a manner that allows the current to be supplied to the electrolysis unit 10 to be divided by the effective planar area of ​​the electrolysis unit 10. The effective planar area of ​​the electrolysis unit 10 is the planar area of ​​the electrolysis unit 10 in the region through which the current passes, and when the current passes through the entire region of the electrolysis unit 10, it is the total planar area of ​​the electrolysis unit 10. The control unit 7 may also supply a current density of 100 mA / cm² to the electrolysis unit 10. 2 ~1000mA / cm 2 The current supply section 4 is controlled in a manner that allows for control.

[0034] For example, control unit 7 can also control carbon dioxide gas flow adjustment unit 6 in a manner where the supplied carbon dioxide gas flow rate 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 used in the electrolysis reaction from carbon dioxide to carbon monoxide, where the total amount of electricity per unit time at a specified current density is used. The amount of electricity per unit time is current. The ratio of the supplied carbon dioxide gas flow rate to the theoretical carbon dioxide gas flow rate is defined as the flow rate ratio. The flow rate ratio is expressed as the supplied carbon dioxide gas flow rate / theoretical carbon dioxide gas flow rate. As an example, consider a current density of 1000 mA / cm². 2 The theoretical carbon dioxide gas flow rate at that time was 10 Nm³. 3 The current density is 1000 mA / cm² under the condition of / h. 2 The supply flow rate of carbon dioxide gas when the flow ratio is 100% is 10 Nm³. 3 The supply flow rate of carbon dioxide gas at a flow rate ratio of 200% is 20 Nm³ / h. 3 / h. The control unit 7 can also control the carbon dioxide gas flow rate adjustment unit 6 in a flow rate ratio of 100% to 200%.

[0035] use Figure 3 The carbon dioxide electrolysis method using the carbon dioxide electrolysis apparatus of this embodiment with such configuration will be described.

[0036] First of all, Figure 1 and Figure 2 In the case of electrolysis of carbon dioxide gas in the carbon dioxide electrolysis apparatus 1 shown, the current supply unit 4 sets the current value supplied to the electrolysis unit 10 (step S1). Specifically, the current value is set in the control unit 7 to achieve a desired current density. For example, a current density of 10 mA / cm² can be used. 2 ~1000mA / cm 2 The current value is set in this way.

[0037] Next, carbon dioxide gas is supplied from the carbon dioxide gas supply section 5 to the carbon dioxide electrolysis section 2 (step S2). At this time, the supply flow rate of the carbon dioxide gas can also be less than the supply flow rate of the carbon dioxide gas in step S4 described later.

[0038] 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 electrolyte and flows in the cathode flow path 23 formed in the separator 12 while being in contact with the cathode electrode 20. The electrolyte supplied to the anode electrode 21 flows in the anode flow path 24 formed in the separator 12 while being in contact with the anode electrode 21.

[0039] In step S2, a non-active gas can also be mixed with the carbon dioxide gas. The carbon dioxide gas mixed with the non-active gas can also be supplied to the cathode electrode 20.

[0040] In step S2, the electrolyte is supplied from the electrolyte supply section 3 to the cathode electrode 20 and the anode electrode 21 of the electrolysis cell 10. In step S2, the concentration and flow rate of the carbon dioxide gas supplied from the carbon dioxide gas supply section 5 to the electrolysis cell 10 can also be measured after the supply of the carbon dioxide gas to the electrolysis cell 10 is started. The cooling system can also be activated after a prescribed time elapses from the start of the supply of the carbon dioxide gas. The warm-up operation of continuously supplying the carbon dioxide gas to the electrolysis cell 10 can also be performed during the period from the start of the supply of the carbon dioxide gas to the activation of the cooling system.

[0041] Next, an electric current is supplied from the electric current supply section 4 to the carbon dioxide electrolysis section 2 (step S3). In the cathode electrode 20, the electrolysis reaction represented by formula (1) described above is performed. The electric current supply section 4 supplies an electric current at the current value set in step S1 described above. When the electric current is supplied to the electrolysis cell 10, electrolysis is started. After the electrolysis is started, it is confirmed that the operation is stabilized. At this time, the current value can also be less than the current value in step S4 described later.

[0042] Then, the output of the carbon dioxide electrolysis device 1 is increased (step S4). In this case, the supply flow rate of the carbon dioxide gas to the carbon dioxide electrolysis section 2 can also be increased. The carbon dioxide gas flow rate adjustment section 6 can also adjust the supply flow rate of the carbon dioxide gas to a desired flow rate by the control section 7. For example, the supply flow rate of the carbon dioxide gas can also be adjusted in such a manner that the flow rate ratio becomes 50% to 500%.

[0043] In step S4, the current value supplied to the carbon dioxide electrolysis section 2 can also be increased. In this case, the current value can also be increased to the value set in step S1 described above. For example, the current value in step S4 can also be adjusted to a current density of 10 mA / cm 2 ~ 1000 mA / cm2 .

[0044] In this step S4, the amount of carbon monoxide produced increases, and the output of the carbon dioxide electrolysis unit 1 rises.

[0045] Thus, the startup of carbon dioxide electrolysis unit 1 is completed (step S5). After startup, operation continues, and the production of carbon monoxide continues.

[0046] When the concentration of carbon dioxide gas in the cathode gas is 100% and the current density is operating at a flow rate ratio of 100%, carbonate ions (CO3) 2- Increased production of potassium carbonate (K₂CO₃) may lead to salt precipitation at the inlet side of the cathode flow path 23. In the case where the electrolyte is an aqueous solution containing potassium, potassium carbonate (K₂CO₃) is formed as a salt. The precipitated salt may clog the cathode flow path 23.

[0047] On the other hand, if the concentration of carbon dioxide gas in the cathode gas is low, the voltage between the cathode electrode 20 and the anode electrode 21 will increase, and the electrolysis reaction shown in the above formula (3) will proceed, generating reactive oxygen species including OH radicals. For example, if the reactive oxygen species is OH radical, OH radical may be generated on the outlet side of the cathode flow path 23 and react with the material of the electrolyte membrane 22, which may deteriorate the electrolyte membrane 22.

[0048] Therefore, in this embodiment, the control unit 7 controls the current supply unit 4, and the current density of the current supplied to the electrolysis unit 10 is adjusted to a predetermined range. More specifically, the current density is adjusted to 10 mA / cm². 2 ~1000mA / cm 2 Therefore, the current density can be reduced. In this case, the electrolysis reaction in the cathode electrode 20 shown in the above formula (1) can be suppressed, and the carbonate ion concentration (CO3) can be reduced. 2- Therefore, it can reduce the amount of salt produced and suppress the blockage of the cathode flow path 23.

[0049] More specifically, by setting the current density to 1000 mA / cm 2 The following method can effectively reduce the amount of salt precipitation. On the other hand, by setting the current density to 10 mA / cm²... 2 The above methods can reduce the amount of salt precipitated, and at the same time, can... Figure 4 By conducting the electrolysis reaction (electrolysis reaction formula (1)) in the cathode electrode 20 as shown, the production of carbon monoxide can be ensured. The current density is 10 mA / cm². 2 The unit voltage at which the electrolysis reaction occurs is called the theoretical voltage. The theoretical voltage is the minimum voltage required for the electrolysis reaction to proceed. The region where the unit voltage exceeds the theoretical voltage is called the overvoltage region.

[0050] In addition, such as Figure 4 As shown, increasing the voltage (unit voltage) between the cathode electrode 20 and the anode electrode 21 makes electrolysis reaction (1) the main reaction, thereby increasing the amount of carbon monoxide produced. When the current density reaches 1000 mA / cm², 2 At this point, even if the unit voltage is further increased, the amount of carbon monoxide produced will not increase. This current density is called the limiting current density.

[0051] Furthermore, as mentioned above, by adjusting the current density to 10 mA / cm 2 ~1000mA / cm 2 This reduces the amount of OH free radicals generated. Specifically, by reducing the current density, the unit voltage can be lowered, thus suppressing the increase in overvoltage. The generation of OH free radicals increases with increasing overvoltage; therefore, reducing the current density effectively reduces the amount of OH free radicals generated. Consequently, the degradation of the electrolyte membrane 22 due to OH free radicals can be suppressed. This is achieved by setting the current density to 1000 mA / cm². 2 The following methods can effectively suppress the increase of overvoltage.

[0052] In particular, by making the current density 10 mA / cm 2 ~1000mA / cm 2 Reducing the current density within a certain range can more effectively suppress the increase of overvoltage. For example, the current density can be set to 10 mA / cm². 2 ~100mA / cm 2 On the other hand, it is possible to achieve a current density of 10 mA / cm². 2 The above measures are used to suppress the increase of overvoltage while ensuring the production of carbon monoxide through electrolysis in the cathode electrode 20.

[0053] On the other hand, regarding the slope (rate of increase) of the current density, and the current density of 10 mA / cm²... 2 ~100mA / cm 2 Compared to the range of 100 mA / cm 2 ~1000mA / cm 2 The range is wider. To more effectively suppress the increase in overvoltage, the current density is preferably 100 mA / cm². 2 nearby.

[0054] Further, in the operation of the carbon dioxide electrolysis device 1, the control unit 7 controls the carbon dioxide gas flow rate adjustment unit 6, and the supply flow rate of the carbon dioxide gas supplied to the electrolysis unit 10 is adjusted to a prescribed range. More specifically, the flow rate ratio is adjusted to 50% to 500%. Thereby, 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 in the cathode flow path 23 can be ensured, and the salt eluted in the cathode flow path 23 can be blown away. Therefore, the clogging of the cathode flow path 23 can be suppressed.

[0055] More specifically, by making the flow rate ratio 50% or more, the salt eluted in the cathode flow path 23 can be effectively blown away. On the other hand, by making the flow rate ratio 500% or less, the discharge amount of the carbon dioxide gas not subjected to the electrolysis reaction from the cathode flow path 23 can be suppressed while the salt is blown away. If the Faraday efficiency is considered, the flow rate ratio is more preferably 100% to 200%. As shown in FIG. 6, by making the flow rate ratio 100% or more, the electrolysis reaction can be performed in a region where the Faraday efficiency is high. By making the flow rate ratio 200% or less, the decrease in the production efficiency of carbon monoxide can be suppressed. That is, when the flow rate ratio reaches 200%, even if the supply flow rate of the carbon dioxide gas is further increased, the Faraday efficiency does not increase, and the production amount of carbon monoxide does not increase. Therefore, it is effective to set the flow rate ratio to 200% or less. The Faraday efficiency refers to the proportion of the partial current contributing to the production of carbon monoxide with respect to the total current. Further, by making the flow rate ratio 200% or less, the supply flow rate of the carbon dioxide gas can be increased, the salt eluted in the cathode flow path 23 can be more effectively blown away, and the discharge amount of the carbon dioxide gas not subjected to the electrolysis reaction from the cathode flow path 23 can be further suppressed. Figure 5

[0056] Further, as described above, by adjusting the flow rate ratio to 50% to 500%, 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 ensured, 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 the degradation of the electrolyte membrane 22 due to OH radicals can be suppressed. By making the flow rate ratio 50% or more, the generation amount of OH radicals can be effectively reduced. On the other hand, by making the flow rate ratio 500% or less, the generation amount of OH radicals can be reduced, and the discharge amount of the carbon dioxide gas not subjected to the electrolysis reaction from the cathode flow path 23 can be suppressed. As described above, in the case where the flow rate ratio is adjusted to 100% to 200%, the supply flow rate of the carbon dioxide gas can be increased, the generation amount of OH radicals can be more effectively reduced, and the discharge amount of the carbon dioxide gas not subjected to the electrolysis reaction from the cathode flow path 23 can be further suppressed.

[0057] ​Furthermore, in this embodiment described above, the current density supplied to the control unit 7 by the current supplied to the electrolysis unit 10 is 10 mA / cm². 2 ~1000mA / cm 2 An example has been described where the current supply unit 4 is controlled in a manner that allows for control of the current supply unit 4, and the carbon dioxide gas flow rate adjustment unit 6 is controlled in a flow rate ratio of 50% to 500%. However, this embodiment is not limited to this. For example, in the control unit 7, the current density supplied to the electrolysis unit 10 is set to 10 mA / cm². 2 ~1000mA / cm 2 When the current supply unit 4 is controlled in a manner where the flow rate ratio is between 50% and 500%, the adjustment range of the flow rate ratio is not limited to 50% to 500%. On the other hand, for example, when the control unit 7 controls the carbon dioxide gas flow rate adjustment unit 6 in a manner where the flow rate ratio is between 50% and 500%, the adjustment range of the current density is not limited to 10 mA / cm². 2 ~1000mA / cm 2 .

[0058] In addition, such as Figure 1 As shown, the carbon dioxide electrolysis apparatus 1 of this embodiment may also include an input unit 8. The input unit 8 may be configured to input the concentration of carbon dioxide gas in the cathode gas supplied to the cathode electrode 20. The control unit 7 may also control the current supply unit 4 based on the concentration of carbon dioxide gas input from the input unit 8. More specifically, the control unit 7 may control the current supply unit 4 in such a way that the current density decreases as the concentration of 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, a current density corresponding to the supply flow rate of carbon dioxide gas to the cathode electrode 20 can be set, thereby improving the carbon monoxide gas production efficiency.

[0059] The concentration of carbon dioxide gas input to input unit 8 can be a pre-obtained concentration. The structure of input unit 8 is arbitrary as long as it can input the carbon dioxide gas concentration. Input unit 8 can be configured so that the operator can input the carbon dioxide gas concentration, or it can be configured so that the carbon dioxide gas concentration is transmitted as electronic information from an external device (not shown) to input unit 8. Input unit 8 can be integrated with control unit 7 or it can be separate from it.

[0060] In addition, such as Figure 6 As shown, the carbon dioxide electrolysis device 1 may include, in addition to the input unit 8, a carbon dioxide gas concentration meter 9. 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. Figure 6In the example shown, the current supply portion 4 can be controlled based on the concentration of the carbon dioxide gas actually supplied to the cathode electrode 20, and the manufacturing efficiency of the carbon monoxide can be further improved. In Figure 6 In the example shown, the carbon dioxide gas concentration meter 9 measures the concentration of the carbon dioxide gas on the downstream side of the carbon dioxide gas flow rate adjustment portion 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 can also be sent to the input portion 8.

[0061] Further, the carbon dioxide electrolysis device 1 in the above-described embodiment can also have, as shown in Figure 7 a non-active gas supply portion 30 and a non-active gas flow rate adjustment portion 31.

[0062] The non-active gas supply portion 30 supplies a non-active gas to the cathode electrode 20 of the carbon dioxide electrolysis portion 2. The non-active gas can also be supplied to the cathode electrode 20 after being mixed with the carbon dioxide gas from the carbon dioxide gas supply portion 5. The non-active gas refers to a gas that does not affect the electrolysis reaction in the cathode electrode 20. As an example of such a non-active gas, hydrogen can be cited. The hydrogen does not undergo an electrolysis reaction during the flow in the cathode flow path 23 and is discharged from the outlet of the cathode flow path 23. The non-active gas supply portion 30 can include a gas cylinder of the non-active gas, or can also include a tank in which the non-active gas is stored.

[0063] The non-active gas flow rate adjustment portion 31 adjusts the supply flow rate of the non-active gas mixed with the carbon dioxide gas. The non-active gas flow rate adjustment portion 31 can also include, for example, a flow rate adjustment valve that is not shown. The supply flow rate of the non-active gas can also be adjusted by adjusting the opening degree of the flow rate adjustment valve. The non-active gas flow rate adjustment portion 31 can also be controlled by the control portion 7, and the supply flow rate of the non-active gas is adjusted.

[0064] Figure 7The control section 7 shown can also control the non-active gas flow rate adjustment section 31 described above. More specifically, the control section 7 can also control the non-active gas flow rate adjustment section 31 to mix the non-active gas with the carbon dioxide gas. In the case where the cathode gas does not contain the non-active gas, the control section 7 can also control the non-active gas flow rate adjustment section 31 to shut off the flow of the non-active gas. In this case, the concentration of the carbon dioxide gas in the cathode gas becomes 100%. On the other hand, in the case where the cathode gas contains the non-active gas, the non-active gas flow rate adjustment section 31 can also be controlled to supply the non-active gas to the cathode electrode 20. In this case, the concentration of the carbon dioxide gas in the cathode gas is less than 100%, and the partial pressure of the carbon dioxide gas is reduced. Along with the reduction in the partial pressure of the carbon dioxide gas, the control section 7 can also control the current supply section 4 to reduce the current density. Thus, the electrolytic reaction in the cathode electrode 20 shown in the above formula (1) can be suppressed, and the amount of precipitation of the salt can be reduced. Therefore, the clogging of the cathode flow path 23 can be suppressed. The current density can be selected within a range of 10 mA / cm 2 ~ 1000 mA / cm 2 .

[0065] The supply flow rate of the non-active gas supplied to the cathode electrode 20 can be adjusted as appropriate. Thus, the partial pressure of the carbon dioxide gas in the cathode gas can be adjusted as appropriate.

[0066] According to the embodiments described above, the clogging of the cathode flow path can be suppressed and the degradation of the electrolyte membrane can be suppressed.

[0067] Several embodiments of the present application have been described above, but these embodiments are presented as examples and are not intended to limit the scope of the application. These new embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made within the scope of the gist of the application. These embodiments and modifications thereof are included in the scope or gist of the application, and are included in the scope of the application and equivalents thereof recited in the claims. In addition, of course, these embodiments can be appropriately combined in part within the scope of the gist of the application.

Claims

1. A carbon dioxide electrolysis device that performs electrolysis of carbon dioxide gas, the carbon dioxide electrolysis device comprising: an electrolysis unit that includes a cathode electrode to which the carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode; a current supply portion that supplies a current to the electrolysis unit; and a control portion that defines a value obtained by dividing the current supplied to the electrolysis unit by a planar effective area of the electrolysis unit as a current density.

2. The carbon dioxide electrolysis device according to claim 1, wherein 3. The carbon dioxide electrolysis device according to claim 1, wherein the carbon dioxide electrolysis device further comprises a carbon dioxide gas flow rate adjustment portion that adjusts a supply flow rate of the carbon dioxide gas to the cathode electrode, a minimum flow rate of the carbon dioxide gas in a case where a total amount of electric quantity per unit time at a prescribed current density is used for an electrolysis reaction from carbon dioxide to carbon monoxide is defined as a theoretical carbon dioxide gas flow rate, and a 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 control portion controls the carbon dioxide gas flow rate adjustment portion so that the flow rate ratio becomes 50% to 500%. The control section controls the current supply section in such a way that the current density becomes 10 mA / cm 2 ~ 1000 mA / cm 2 .

4. The carbon dioxide electrolysis device according to any one of claims 1 to 3, wherein The control section controls the current supply section in such a way that the current density becomes 100 mA / cm 2 ~ 1000 mA / cm 2 . the carbon dioxide electrolysis device further comprises an input portion that inputs a concentration of the carbon dioxide gas supplied to the cathode electrode, the control portion controls the current supply portion so that the current density is adjusted on the basis of the concentration of the carbon dioxide gas input to the input portion.

5. A carbon dioxide electrolysis device that performs electrolysis of carbon dioxide gas, the carbon dioxide electrolysis device comprising: an electrolysis unit that includes a cathode electrode to which the 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 portion that adjusts a supply flow rate of the carbon dioxide gas to the cathode electrode; and a control portion that defines a value obtained by dividing a current supplied to the electrolysis unit by a planar effective area of the electrolysis unit as a current density. a minimum flow rate of the carbon dioxide gas in a case where a total amount of electric quantity per unit time at a prescribed current density is used for an electrolysis reaction from carbon dioxide to carbon monoxide is defined as a theoretical carbon dioxide gas flow rate, and a 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 control portion controls the carbon dioxide gas flow rate adjustment portion so that the flow rate ratio becomes 50% to 500%.

6. The carbon dioxide electrolysis device according to claim 3 or 5, wherein the control portion controls the carbon dioxide gas flow rate adjustment portion so that the flow rate ratio becomes 100% to 200%. further comprising: an inactive gas supply portion that supplies an inactive gas mixed with the carbon dioxide gas; and an inactive gas supply portion that supplies an inactive gas mixed with the carbon dioxide gas; and ​ ​ ​ ​ ​ ​ 7. The carbon dioxide electrolysis device of claim 3 or 5, wherein, ​ ​ a non-active gas flow rate adjustment section that adjusts a supply flow rate of a non-active gas mixed with the carbon dioxide gas, the control section controls the non-active gas flow rate adjustment section so as to mix the non-active gas with the carbon dioxide gas.

8. A carbon dioxide electrolysis method that uses a carbon dioxide electrolysis device that performs electrolysis of carbon dioxide gas, the carbon dioxide electrolysis device including an electrolysis unit that includes a cathode electrode to which the carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode, the carbon dioxide electrolysis method comprising: a step of supplying the carbon dioxide gas to the cathode electrode; a step of supplying a current to the electrolysis unit; and a step of increasing an output of the carbon dioxide electrolysis device, a value obtained by dividing the current supplied to the electrolysis unit by a planar effective area of the electrolysis unit is defined as a current density, In the step of raising the output, the current value of the current is adjusted in such a manner that the current density becomes 10 mA / cm 2 ~ 1000 mA / cm 2 after the output is raised.

9. The carbon dioxide electrolysis method according to claim 8, wherein In the step of raising the output, the current value of the current is adjusted in such a manner that the current density becomes 100 mA / cm 2 ~ 1000 mA / cm 2 after the output is raised.

10. The carbon dioxide electrolysis method according to claim 8, wherein a total amount of electric quantity per unit time at a prescribed current density is defined as a minimum flow rate of carbon dioxide gas in a case where the total amount of electric quantity is used for an electrolysis reaction from carbon dioxide to carbon monoxide, a ratio of a supply flow rate of carbon dioxide gas with respect 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 so that the flow rate ratio becomes 50% to 500%.

11. The carbon dioxide electrolysis method according to any one of claims 8 to 10, wherein the carbon dioxide electrolysis method further includes a step of inputting a concentration of the carbon dioxide gas supplied to the cathode electrode, in the step of increasing the output, a current value of the current is adjusted on the basis of the concentration of the carbon dioxide gas.

12. A carbon dioxide electrolysis method that uses a carbon dioxide electrolysis device that performs electrolysis of carbon dioxide gas, the carbon dioxide electrolysis device including an electrolysis unit that includes a cathode electrode to which the carbon dioxide gas is supplied, an anode electrode, and an electrolyte membrane interposed between the cathode electrode and the anode electrode, the carbon dioxide electrolysis method comprising: a step of supplying the carbon dioxide gas to the cathode electrode; a step of supplying a current to the electrolysis unit; and a step of increasing an output of the carbon dioxide electrolysis device, a value obtained by dividing the current supplied to the electrolysis unit by a planar effective area of the electrolysis unit is defined as a current density, a total amount of electric quantity per unit time at a prescribed current density is defined as a minimum flow rate of carbon dioxide gas in a case where the total amount of electric quantity is used for an electrolysis reaction from carbon dioxide to carbon monoxide, a ratio of a supply flow rate of carbon dioxide gas with respect 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 so that the flow rate ratio becomes 50% to 500%.

13. The carbon dioxide electrolysis method according to claim 10 or 12, wherein, In the step of increasing the output, the supply flow rate of the carbon dioxide gas is adjusted so that the flow rate ratio becomes 100% to 200%.

14. The carbon dioxide electrolysis method according to claim 10 or 12, wherein, In the step of supplying the carbon dioxide gas, an inactive gas is mixed with the carbon dioxide gas.

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