CARBON DIOXIDE ELECTROLYSIS APPARATUS

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-185067 filed on Nov. 18, 2022, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION
Field of the Invention

This invention relates to a carbon dioxide electrolysis apparatus configured to electrolytically reduce carbon dioxide.

Description of the Related Art

In the related art, an apparatus for electrolytically reducing carbon dioxide has been known (see, for example, JP 2022-131811 A). In the apparatus described in JP 2022-131811 A, an electrolytic solution including a strong alkaline aqueous solution in which carbon dioxide is dissolved is caused to flow in a liquid flow path provided between a cathode and an anode, and carbon dioxide dissolved in the electrolytic solution is electrolytically reduced at the cathode.

By recovering exhaust gas and carbon dioxide in the atmosphere and using them as a carbon source, it is possible to reduce carbon emissions and contribute to climate change mitigation or impact mitigation.

As the diaphragm provided between the cathode and the anode of the electrolysis stack, an anion exchange type solid polymer electrolyte membrane (anion exchange membrane (AEM)) can be used, but since the AEM has poor durability, it is difficult to shorten the startup time of the electrolysis stack without deteriorating the AEM.

SUMMARY OF THE INVENTION

An aspect of the present invention is a carbon dioxide electrolysis apparatus, including: an electrolysis stack having a diaphragm including an anion exchange type solid polymer electrolyte membrane and an anode and a cathode separated by the diaphragm; a carbon dioxide supply unit configured to supply carbon dioxide to a gas flow path provided adjacent to the cathode; a power supply unit configured to supply electric power to the electrolysis stack; a voltage sensor configured to detect a voltage of the electrolysis stack; a temperature sensor configured to detect a temperature of the electrolysis stack; and a control unit including a processor and a memory coupled to the processor and configured to control the power supply unit. The control unit controls the power supply unit so that the voltage of the electrolysis stack becomes equal to or lower than an upper limit value of the voltage of the electrolysis stack predetermined corresponding to the temperature of the electrolysis stack based on the voltage of the electrolysis stack detected by the voltage sensor and the temperature of the electrolysis stack detected by the temperature sensor during a startup period until the temperature of the electrolysis stack reaches a predetermined temperature after starting supply of the electric power from the power supply unit to the electrolysis stack.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, and advantages of the present invention will become clearer from the following description of embodiments in relation to the attached drawings, in which:

FIG. 1 is a cross-sectional view schematically illustrating an example of an electrolysis stack of a carbon dioxide electrolysis apparatus according to an embodiment of the present invention;

FIG. 2 is a block diagram schematically illustrating an example of an overall configuration of the carbon dioxide electrolysis apparatus according to the embodiment of the present invention;

FIG. 3 is a block diagram schematically illustrating an example of a control configuration of the carbon dioxide electrolysis apparatus according to the embodiment of the present invention;

FIG. 4 is a diagram for explaining an appropriate range of a stack voltage;

FIG. 5 is a diagram for explaining a case where the stack voltage at the time of startup is excessive;

FIG. 6 is a diagram for describing a case where it takes time for a stack temperature to reach a rated temperature;

FIG. 7 is a diagram for explaining a case where the stack voltage is adjusted to a target value;

FIG. 8 is a diagram for describing a target value of a stack current when the stack voltage reaches the target value;

FIG. 9 is a diagram for describing a case where the stack voltage reaches a maximum value;

FIG. 10 is a flowchart illustrating an example of a stack activation process by the carbon dioxide electrolysis apparatus according to the embodiment of the present invention; and

FIG. 11 is a flowchart illustrating an example of a stack current target value calculation process by the carbon dioxide electrolysis apparatus according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below with reference to FIGS. 1 to 11. The average global temperature is maintained in a warm state suitable for organisms by greenhouse gases in the atmosphere. Specifically, some of the heat radiated from the ground surface heated by sunlight to outer space is absorbed by greenhouse gases and re-radiated to the ground surface, whereby the atmosphere is maintained in a warm state. Increasing concentrations of greenhouse gases in the atmosphere cause a rise in average global temperature (global warming).

Among the greenhouse gases, the concentration of carbon dioxide that greatly contributes to global warming in the atmosphere is determined by the balance between carbon fixed on the ground or in the ground as plants or fossil fuels and carbon present in the atmosphere as carbon dioxide. For example, carbon dioxide in the atmosphere is absorbed through photosynthesis in the growth process of plants, causing a decrease in the concentration of carbon dioxide in the atmosphere. Carbon dioxide is also released into the atmosphere through combustion of fossil fuels, causing an increase in the concentration of carbon dioxide in the atmosphere. In order to mitigate global warming, it is necessary to replace fossil fuels with renewable energy sources such as sunlight, wind power, water power, geothermal heat, or biomass to reduce carbon emissions.

By using carbon dioxide recovered from the exhaust gas or the atmosphere as a carbon source, the carbon emission amount can be reduced. In the carbon dioxide electrolysis apparatus according to the embodiment of the present invention, carbon dioxide is electrolytically reduced to produce a carbon compound, which is used as a carbon source.

FIG. 1 is a cross-sectional view schematically illustrating an example of an electrolysis stack 10 of a carbon dioxide electrolysis apparatus (hereinafter, the apparatus) 100 according to an embodiment of the present invention. As shown in FIG. 1, the electrolysis stack 10 is configured as an electrolysis cell in which an anion exchange type solid polymer electrolyte membrane (anion exchange membrane (AEM)) 12 is sandwiched as a diaphragm between an anode portion 11a and a cathode portion 11b or an electrolysis stack in which electrolysis cells are stacked (connected in series).

The anode portion 11a and the cathode portion 11b are separated from each other by the AEM 12, and each include liquid flow paths 13a and 13b, electrocatalysts 14a and 14b, and gas flow paths 15a and 15b. The liquid flow paths 13a and 13b and the gas flow paths 15a and 15b are provided adjacent to the electrocatalysts 14a and 14b, respectively.

An electrolytic solution including a strong alkaline aqueous solution such as a potassium hydroxide aqueous solution can be introduced into the liquid flow paths 13a and 13b from the outside of the electrolysis stack 10 and circulated. The electrolytic solution flowing out from the liquid flow paths 13a and 13b may be introduced into the liquid flow paths 13a and 13b again and circulated.

Carbon dioxide can be supplied to the gas flow path 15b of the cathode portion 11b from the outside of the electrolysis stack 10. In addition, the gas generated by the electrolytic reaction can be discharged to the outside of the electrolysis stack 10 through the gas flow paths 15a and 15b.

The electrocatalyst 14a (anode) of the anode portion 11a is formed of a non-noble metal such as nickel or a noble metal such as platinum, and is connected to a positive electrode of a DC power supply (hereinafter, electrolysis power supply) 20 provided outside the electrolysis stack 10. The electrocatalyst 14b (cathode) of the cathode portion 11b is made of copper or the like, and is connected to a negative electrode of the electrolysis power supply 20.

When power is supplied from the electrolysis power supply 20 to the electrolysis stack 10, a potential difference is generated between the anode and the cathode according to the magnitude of the power, and when the potential difference reaches the electrolysis voltage, the electrolytic reaction proceeds. More specifically, carbon dioxide is reduced by an electrolytic reaction at a three-phase interface among liquid flow path 13b, electrocatalyst 14b, and gas flow path 15b of the cathode portion 11b, and a carbon compound such as ethylene is produced. For example, ethylene is produced by the electrolytic reactions of the following formulae (i) and (ii). In addition, water in the electrolytic solution is reduced by the electrolytic reaction of the following formula (iii) to generate hydroxide ions. The carbon compound (gas) and hydrogen (gas) generated in the cathode portion 11b are discharged to the outside of the electrolysis stack 10 through the gas flow path 15b.

CO₂+H₂O→CO+2OH⁻ (i)

2CO+8H₂O→C₂H₄+8OH⁻+2H₂O (ii)

2H₂O→H₂+2OH⁻ (iii)

On the other hand, hydroxide ions generated in the cathode portion 11b move in the electrolytic solution in the liquid flow path 13b of the cathode portion 11b, then pass through the AEM 12, and move in the electrolytic solution in the liquid flow path 13a of the anode portion 11a to the interface with the electrocatalyst 14a of the anode portion 11a. On the surface of electrocatalyst 14a of the anode portion 11a, hydroxide ions are oxidized by the electrolytic reaction of the following formula (iv) to generate oxygen. Oxygen (gas) generated in the anode portion 11a is discharged to the outside of the electrolysis stack 10 through the gas flow path 15a, and water (liquid) circulates through the liquid flow path 13a as it is.

4OH⁻→O₂+2H₂O (iv)

FIG. 2 is a block diagram schematically illustrating an example of an overall configuration of the apparatus 100. As shown in FIG. 2, the apparatus 100 includes an electrolysis stack 10, an electrolysis power supply 20 that supplies power to the electrolysis stack 10, a carbon dioxide supply unit 30 that supplies carbon dioxide to the electrolysis stack 10, and electrolytic solution supply units 40a and 40b that supply an electrolytic solution to the electrolysis stack 10.

The electrolysis stack 10 is provided with a voltage sensor 16 which detects the potential difference created between the anode and cathode of the electrolysis stack 10 by the voltage of the electrolysis stack 10 (hereinafter, the stack voltage), more particularly the power supplied by the electrolysis power supply 20. The voltage sensor 16 is connected to the controller 90 (see FIG. 3), and the sensor value of the voltage sensor 16 is output to the controller 90.

The electrolysis stack 10 is also provided with a current sensor 17 which detects the current of the electrolysis stack 10 (hereinafter, stack current), more particularly, the current flowing from the positive electrode of the electrolysis power supply 20 through the anode and cathode of the electrolysis stack 10 to the negative electrode of the electrolysis power supply 20. The current sensor 17 is connected to the controller 90 (see FIG. 3), and the sensor value of the current sensor 17 is output to the controller 90.

The electrolysis stack 10 is also provided with a temperature sensor 18 which detects a reference temperature (hereinafter, stack temperature) of the electrolysis stack 10. The temperature sensor 18 detects, for example, a surface temperature of the AEM 12 as a reference temperature of the electrolysis stack 10. The temperature sensor 18 is connected to the controller 90 (see FIG. 3), and the sensor value of the temperature sensor 18 is output to the controller 90.

The electrolysis power supply 20 is configured as a power generation device that supplies DC power to the electrolysis stack 10. The positive electrode of the electrolysis power supply 20 is connected to the anode of the electrolysis stack 10 (the electrocatalyst 14a of the anode portion 11a), and the negative electrode of the electrolysis power supply is connected to the cathode of the electrolysis stack 10 (the electrocatalyst 14b of the cathode portion 11b).

The carbon dioxide supply unit 30 includes a pump and the like. The carbon dioxide supply unit 30 is connected to an inlet of the gas flow path 15b of the cathode portion 11b of the electrolysis stack 10 via a pipe 31, and supplies carbon dioxide (gas) to the electrolysis stack 10 by pumping air containing carbon dioxide at a predetermined concentration or more. The air containing carbon dioxide at a predetermined concentration or more may be an exhaust gas from a device or equipment that involves combustion of fossil fuel, or may be the atmosphere in which carbon dioxide is concentrated by a concentration device. The carbon dioxide supply unit 30 is controlled by the controller 90 (see FIG. 3).

The electrolytic solution supply units 40a and 40b each include a pump and the like. The electrolytic solution supply units 40a and 40b are connected to inlets of the liquid flow paths 13a and 13b of the electrolysis stack 10 via pipes 41a and 41b, respectively, and supply the electrolytic solution to the electrolysis stack 10 by pumping the electrolytic solution. The electrolytic solution is refluxed to the electrolytic solution supply units 40a and 40b from outlets of the liquid flow paths 13a and 13b of the electrolysis stack 10 through pipes (not illustrated), respectively.

FIG. 3 is a block diagram schematically illustrating an example of a control configuration of the apparatus 100. As shown in FIG. 3, the apparatus 100 further includes a controller 90 that controls the electrolysis power supply 20, the carbon dioxide supply unit 30, and the electrolytic solution supply units 40a and 40b. The voltage sensor 16, the current sensor 17, and the temperature sensor 18 are connected to the controller 90. The controller 90 includes a computer including a calculation unit 91 such as a CPU (processor), a storage unit 92 such as a ROM and a RAM (memory), and peripheral circuits thereof. The storage unit 92 of the controller 90 stores programs executed by the calculation unit 91 and information such as setting values.

The calculation unit 91 of the controller 90 controls the electrolysis power supply 20, the carbon dioxide supply unit 30, and the electrolytic solution supply units 40a and 40b based on the stack voltage, the stack current, and the stack temperature detected by the voltage sensor 16, the current sensor 17, and the temperature sensor 18. In particular, the electrolysis power supply 20 is controlled so that the stack voltage falls within an appropriate range during a startup period after power supply from the electrolysis power supply 20 to the electrolysis stack 10 is started until the stack temperature reaches a rated temperature (for example, about 60 to 70° C.) from room temperature.

FIG. 4 is a diagram for explaining an appropriate range of the stack voltage. During the startup period of the electrolysis stack 10, the temperature of the AEM 12 and the like that constitute the electrolysis stack 10 is low and an internal resistance of the electrolysis stack 10, including a resistance when hydroxide ions permeate through the AEM 12, is high. For this reason, the stack voltage becomes excessive, and the electrocatalysts 14a and 14b, the AEM 12, and the like constituting the electrolysis stack 10 may be deteriorated. On the other hand, when the stack voltage falls below the electrolysis voltage required for the electrolytic reaction (formulae (i) to (iv)), the electrolytic reaction does not proceed, so that a desired product (carbon compound such as ethylene) cannot be obtained although electric power is supplied, and the efficiency of the entire apparatus 100 is reduced. Therefore, in order not to deteriorate the components of the electrolysis stack 10 and not to reduce the efficiency of the entire apparatus 100, it is necessary to operate the electrolysis stack 10 within an appropriate range as shown in FIG. 4.

Upper and lower limit values of such a stack voltage change according to the stack temperature. The characteristics (solid lines in FIG. 4) indicating relationship between the stack temperature and the upper and lower limit values of the stack voltage are determined in advance by a test, and are stored in the storage unit 92 of the controller 90 as, for example, a characteristic map. The upper and lower limit values of such a stack voltage are determined in advance based on a theoretical electrolysis voltage value for each carbon compound to be produced. Further, it may be predetermined based on the degree of aging deterioration from the beginning of life to the end of the life of the electrolysis stack 10.

The storage unit 92 of the controller 90 also stores a current-voltage (IV) characteristic indicating a relationship between the stack voltage and the stack current determined in advance. As the stack current increases, the internal resistance of the electrolysis stack 10 increases and the stack voltage decreases. In addition, as the stack temperature increases, the internal resistance of the electrolysis stack 10 decreases, the stack current increases, and the stack voltage decreases. The IV characteristic for each stack temperature is determined in advance by performing a test while changing the stack temperature, and is stored in the storage unit 92 of the controller 90, for example, as a characteristic map for each stack temperature.

As shown in FIG. 4, with respect to the upper and lower limit values of the stack voltage, a maximum value lower than the upper limit value and a minimum value higher than the lower limit value are set in advance on the basis of a sensor error of the voltage sensor 16 or the like. In addition, a target value lower than the maximum value is set in advance on the basis of the electrolysis efficiency of the electrolysis stack 10 or the like. The characteristics (broken lines in FIG. 4) indicating the relationship between the stack temperature and the minimum value, the maximum value, and the target value of the stack voltage are also determined in advance by the test similarly to the upper and lower limit values, and are stored in the storage unit 92 of the controller 90 as, for example, a characteristic map.

FIG. 5 is a diagram for explaining a case where the stack voltage at the time of startup is excessive. As shown in FIG. 5, during the startup period of the electrolysis stack 10, particularly immediately after starting power supply from the electrolysis power supply 20 to the electrolysis stack 10, the temperature of the AEM 12 and the like constituting the electrolysis stack 10 is low, and the internal resistance of the electrolysis stack 10 is large. If power is supplied without monitoring or limiting the stack voltage during such a period, the stack voltage exceeds a target value and becomes excessive, and the AEM 12 and the like constituting the electrolysis stack 10 may be deteriorated.

FIG. 6 is a diagram for describing a case where it takes time for the stack temperature to reach the rated temperature. When electric power is supplied to the electrolysis stack 10 and the potential difference between the anode and the cathode reaches the electrolysis voltage, the electrolytic reaction (formulae (i) to (iv)) proceeds, the temperature of the AEM 12 or the like constituting the electrolysis stack 10 increases with the movement of hydroxide ions or the like, and the stack temperature increases. As the stack temperature increases, the internal resistance of the electrolysis stack 10 decreases, the stack current increases, and the stack voltage decreases. As shown in FIG. 6, in a case where power is supplied to the electrolysis stack 10 without increasing the stack voltage, although it is possible to avoid an excessive stack voltage as shown in FIG. 5, it takes a long time until the stack temperature reaches the rated temperature.

FIG. 7 is a diagram for explaining a case where the stack voltage is adjusted to a target value. As shown in FIG. 7, the calculation unit 91 of the controller 90 controls the electrolysis power supply 20 so that the stack voltage detected by the voltage sensor 16 approaches a predetermined target value (see FIG. 4) corresponding to the stack temperature detected by the temperature sensor 18. More specifically, when the stack voltage reaches the target value, the electrolysis power supply 20 is controlled so that the stack current detected by the current sensor 17 increases, and when the stack voltage falls below the target value, the electrolysis power supply 20 is controlled so that the stack current decreases. As a result, since the stack voltage is maintained around the upper limit value within the appropriate range of FIG. 4, the temperature of the AEM 12 and the like constituting the electrolysis stack 10 is early raised within a range not deteriorating the AEM 12 and the like, and the startup time of the electrolysis stack 10 until the stack temperature reaches the rated temperature can be shortened.

FIG. 8 is a diagram for describing a target value of the stack current when the stack voltage reaches the target value. As shown in FIG. 8, when the stack voltage reaches the target value, the calculation unit 91 of the controller 90 increases the target value of the stack current and controls the electrolysis power supply 20 so that the stack current increases. In addition, when the stack voltage falls below the target value, the target value of the stack current is lowered, and the electrolysis power supply 20 is controlled so that the stack current is lowered. At this time, the target value of the stack current is set within an appropriate range that does not deteriorate the AEM 12 and the like constituting the electrolysis stack 10. Such an appropriate range (upper and lower limit values) of the stack current changes according to the stack temperature. The characteristics indicating the relationship between the stack temperature and the upper and lower limit values of the stack current are determined in advance by a test, and are stored in the storage unit 92 of the controller 90 as, for example, a characteristic map.

FIG. 9 is a diagram for describing a case where the stack voltage reaches the maximum value (see FIG. 4). As shown in FIG. 9, the calculation unit 91 of the controller 90 controls the electrolysis power supply 20 to stop supplying power to the electrolysis stack 10 when the stack voltage reaches a maximum value. As a result, deterioration of the AEM 12 and the like constituting the electrolysis stack 10 can be reliably prevented.

FIG. 10 is a flowchart illustrating an example of a stack activation process by the apparatus 100, and illustrates an example of a process executed by the calculation unit 91 of the controller 90. The process illustrated in the flowchart is started when activation of the electrolysis stack 10 is commanded.

As shown in FIG. 10, first, in S1 (S: processing step), the electrolytic solution supply units 40a and 40b are controlled to supply the electrolytic solution to the electrolysis stack 10. Next, in S2, the carbon dioxide supply unit 30 is controlled to supply carbon dioxide (gas) to the electrolysis stack 10. Next, in S3, the stack temperature detected by the temperature sensor 18 is read.

Next, in S4, it is determined whether the stack temperature read in S3 is within a normal temperature range (for example, room temperature) immediately after power supply from the electrolysis power supply 20 to the electrolysis stack 10 is started. In a case where determination is negative in S4, the process returns to S3, and when the determination is positive, the process proceeds to S5. In S5, the electrolysis power supply 20 is controlled to start power supply to the electrolysis stack 10. Next, the process proceeds to S6, and a stack current target value calculation process is executed.

FIG. 11 is a flowchart illustrating an example of a stack current target value calculation process by the apparatus 100, and illustrates an example of a process executed by the calculation unit 91 of the controller 90. The processing illustrated in the flowchart is repeatedly executed at predetermined time intervals.

As shown in FIG. 11, first, in S10, the stack voltage, the stack current, and the stack temperature detected by the voltage sensor 16, the current sensor 17, and the temperature sensor 18, respectively, are read. Next, in S11, it is determined whether or not the stack temperature read in S10 is lower than the rated temperature. In a case where the determination is negative in S11, the process ends, and when the determination is positive, the process proceeds to S12. In S12, it is determined whether the stack voltage read in S10 is lower than the target value (see FIG. 4).

In a case where determination is positive in S12, the process proceeds to S13, the target value (see FIG. 8) of the stack current is decreased by subtracting a predetermined value from the previous value, and the electrolysis power supply 20 is controlled so that the stack current is decreased. Next, in S14, it is determined whether or not the target value of the stack current calculated in S13 is lower than the lower limit value. In a case where determination is positive in S14, the process proceeds to S15, and the target value of the stack current is set to the lower limit value. In a case where determination is negative in S14, the target value of the stack current is set to the value calculated in S13.

In a case where determination is negative in S12, the process proceeds to S16, and it is determined whether the stack voltage read in S10 is lower than the maximum value (see FIG. 4). In a case where determination is positive in S16, the process proceeds to S17, the target value (see FIG. 8) of the stack current is increased by adding a predetermined value to the previous value, and the electrolysis power supply 20 is controlled so that the stack current is increased. Next, in S18, it is determined whether or not the target value of the stack current calculated in S17 exceeds the upper limit value. In a case where determination is positive in S18, the process proceeds to S19, and the target value of the stack current is set to the upper limit value. In a case where determination is negative in S18, the target value of the stack current is set to the value calculated in S17. In a case where determination is negative in S16, the process proceeds to S20, and the electrolysis power supply 20 is controlled to stop the power supply to the electrolysis stack 10.

As described above, by matching the stack voltage with the target value (see FIG. 4) and maintaining the stack voltage around the upper limit value within the appropriate range (S10 to S15, S17 to S19), the temperature of the electrolysis stack 10 can be early raised within a range in which the AEM 12 and the like are not deteriorated, and the startup time can be shortened. In addition, by controlling the electrolysis power supply so as to stop the supply of electric power to the electrolysis stack 10 when the stack voltage reaches the maximum value (S16, S20), deterioration of the AEM 12 and the like constituting the electrolysis stack 10 can be reliably prevented.

According to the present embodiment, the following functions and effects can be achieved.

(1) The apparatus 100 includes: an electrolysis stack 10 having an AEM 12 and an electrocatalyst 14a of an anode portion 11a and an electrocatalyst 14b of a cathode portion 11b separated by the AEM 12; a carbon dioxide supply unit 30 that supplies carbon dioxide to a gas flow path 15b provided adjacent to the electrocatalyst 14b of the cathode portion 11b; an electrolysis power supply 20 that supplies power to the electrolysis stack 10; a voltage sensor 16 that detects a stack voltage; a temperature sensor 18 that detects a stack temperature; and a controller 90 that controls the electrolysis power supply 20 (see FIGS. 1 to 3).

The controller 90 controls the electrolysis power supply 20 so that the stack voltage becomes equal to or lower than an upper limit value of a predetermined stack voltage corresponding to the stack temperature based on the stack voltage detected by the voltage sensor 16 and the stack temperature detected by the temperature sensor 18 during a startup period until the stack temperature reaches a predetermined temperature after starting the supply of the power from the electrolysis power supply 20 to the electrolysis stack 10. As described above, by maintaining the stack voltage within the appropriate range (see FIG. 4), particularly, at equal to or lower than the upper limit value, the temperature of the AEM 12 and the like constituting the electrolysis stack 10 can be early raised without deteriorating the AEM 12 and the like, and the startup time of the electrolysis stack 10 can be shortened.

(2) The controller 90 further controls the electrolysis power supply 20 so that the stack voltage becomes equal to or higher than a lower limit value of the predetermined stack voltage corresponding to the stack temperature based on the stack voltage detected by the voltage sensor 16 and the stack temperature detected by the temperature sensor 18 during the startup period. As described above, by maintaining the stack voltage within the appropriate range (see FIG. 4), particularly at the lower limit value or higher, the electrolytic reaction (formulae (i) to (iv)) can proceed even during the startup period, and the efficiency of the entire apparatus 100 can be improved.

(3) The upper limit value is determined in advance based on the degree of aging deterioration of the electrolysis stack 10. As a result, deterioration of the AEM 12 and the like constituting the electrolysis stack 10 can be reliably prevented regardless of the degree of aging deterioration of the electrolysis stack 10.

(4) The lower limit value is predetermined based on the degree of aging deterioration of the electrolysis stack 10. As a result, the electrolytic reaction (formulae (i) to (iv)) can be reliably processed even during the startup period regardless of the degree of aging deterioration of the electrolysis stack 10.

(5) The controller 90 controls the electrolysis power supply 20 so that the stack voltage becomes equal to or lower than a target value lower than an upper limit value set in advance on the basis of a sensor error of the voltage sensor 16 and an electrolysis efficiency of the electrolysis stack 10. As a result, deterioration of the AEM 12 and the like constituting the electrolysis stack 10 can be more reliably prevented.

(6) The apparatus 100 further comprises a current sensor 17 for detecting a stack current (see FIGS. 2 and 3). The controller 90 controls the electrolysis power supply 20 so that the stack current detected by the current sensor 17 increases when the stack voltage detected by the voltage sensor 16 reaches the target value, and the stack current detected by the current sensor 17 decreases when the stack voltage detected by the voltage sensor 16 falls below the target value, during the activation period. That is, since there is a certain correlation (IV characteristic) between the stack voltage and the stack current, the stack voltage can be adjusted by adjusting the stack current. By adjusting the stack voltage via the stack current in this manner, the stack current can also be managed so as to be within an appropriate range, so that deterioration of the AEM 12 and the like constituting the electrolysis stack 10 can be more reliably prevented.

(7) The controller 90 controls the electrolysis power supply 20 to stop supplying power to the electrolysis stack 10 when the stack voltage detected by the voltage sensor 16 reaches a maximum value set according to the upper limit value. As a result, deterioration of the AEM 12 and the like constituting the electrolysis stack 10 can be still more reliably prevented.

In the above embodiment, the electrolytic reaction that proceeds on the cathode side of the electrolysis stack 10 when carbon dioxide is supplied has been described as the electrolytic reduction reaction from carbon dioxide to ethylene in FIG. 1 and the like, but ethylene is an example, and the carbon compound generated by the electrolytic reduction of carbon dioxide is not limited to ethylene. The carbon compound produced by the electrolytic reduction of carbon dioxide is not limited to a gas component, and may be a liquid component such as formic acid, acetic acid, methanol, or ethanol.

The above embodiment can be combined as desired with one or more of the aforesaid modifications. The modifications can also be combined with one another.

According to the present invention, it becomes possible to shorten the startup time of the electrolysis stack without deteriorating the AEM.

Above, while the present invention has been described with reference to the preferred embodiments thereof, it will be understood, by those skilled in the art, that various changes and modifications may be made thereto without departing from the scope of the appended claims.

CARBON DIOXIDE ELECTROLYSIS APPARATUS

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