Water electrolysis system

Abstract

To improve a certainty of descaling.SOLUTION: A water electrolysis system 100 includes an electrolysis tank 3. The electrolysis tank 3 has a first electrode 17, a second electrode 18, and a diaphragm 14 disposed between the first electrode 17 and the second electrode 18. The water electrolysis system 100 has a first electrolysis mode and a second electrolysis mode as modes of operation. The first electrolysis mode is an operation mode in which an aqueous solution in the electrolysis tank 3 is electrolyzed with the first electrode 17 as an anode and the second electrode 18 as a cathode. The second electrolysis mode is an operation mode in which the aqueous solution in the electrolysis tank 3 is electrolyzed at a current density of less than 0.015 A / cm2 with the second electrode 18 as the anode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to water electrolysis systems, and more particularly to water electrolysis systems including electrolytic cells. [Background technology]

[0002] Patent Document 1 discloses a continuous electrolytic ionized water generating device. This continuous electrolytic ionized water generating device has an electrolytic cell in which an anode electrode and a cathode electrode are disposed on either side of a semi-permeable diaphragm, and tap water or the like is passed through the cell while a voltage is applied between the electrodes to generate acidic water on the anode side and alkaline water on the cathode side.

[0003] The continuous electrolytic ionized water generating device of Patent Document 1 removes scale by switching the voltage applied to the anode and cathode electrodes to a lower voltage of opposite polarity when it detects that the inflow of the water to be electrolyzed has stopped. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-290167 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the voltage applied between the two electrodes falls below the theoretical decomposition voltage of water, there is a problem that scale removal is not possible.

[0006] The present disclosure has been made in view of the above-mentioned circumstances, and has an object to provide a water electrolysis system capable of improving the reliability of scale removal. [Means for solving the problem]

[0007] A water electrolysis system according to one embodiment of the present disclosure includes an electrolytic cell. The electrolytic cell has a first electrode, a second electrode, and a diaphragm disposed between the first electrode and the second electrode. The water electrolysis system has a first electrolysis mode and a second electrolysis mode as operation modes. The first electrolysis mode is an operation mode in which an aqueous solution in the electrolytic cell is electrolyzed using the first electrode as an anode and the second electrode as a cathode. The second electrolysis mode is an operation mode in which an aqueous solution in the electrolytic cell is electrolyzed using the second electrode as an anode and a current of 0.015 A / cm 2 This is an operation mode in which the aqueous solution in the electrolytic cell is electrolyzed at a current density of less than 100 kPa. Effect of the Invention

[0008] According to the water electrolysis system according to the above aspect of the present disclosure, it is possible to improve the reliability of scale removal. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a water electrolysis system according to an embodiment. [Diagram 2] FIG. 2 is a graph showing the relationship between the pH of an aqueous solution and the form of carbonate species in water. [Diagram 3] FIG. 3 is a graph showing the relationship between the amount of reduction in thickness of the platinum surface and the current-flow time when one of a pair of electrodes is used as an anode, and the relationship between the amount of reduction in thickness of the platinum surface and the current-flow time when one of a pair of electrodes is used as both an anode and a cathode. [Figure 4] FIG. 4 is a graph showing the relationship between the current density of the current flowing between a pair of electrodes and the rate of wear of the platinum surface. [Diagram 5] FIG. 5 is a graph showing the relationship between the amount of reduction in thickness of the platinum surface and the current flow time when an aqueous solution having a chloride ion concentration equal to or higher than a threshold is electrolyzed in the second electrolysis mode, and the relationship between the amount of reduction in thickness of the platinum surface and the current flow time when an aqueous solution having a chloride ion concentration less than the threshold is electrolyzed in the second electrolysis mode. [Figure 6] FIG. 6 is a flowchart showing the operation of the water electrolysis system according to the above embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. In addition, common elements in the embodiments described below are given the same reference numerals, and duplicated descriptions of common elements may be omitted. In addition, the following embodiments and modifications are only a part of various embodiments of the present disclosure. In addition, the following embodiments and modifications can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved. In addition, the configurations of the modifications can be appropriately combined.

[0011] Each drawing described in this disclosure is a schematic drawing, and the ratio of the size and thickness of each component in each drawing does not necessarily reflect the actual dimensional ratio.

[0012] (1) Overview First, an overview of a water electrolysis system 100 according to this embodiment will be described with reference to FIG.

[0013] As shown in FIG. 1, a water electrolysis system 100 of this embodiment includes an electrolytic cell 3.

[0014] The electrolytic cell 3 has a first electrode 17 and a second electrode 18 , and a diaphragm 14 disposed between the first electrode 17 and the second electrode 18 .

[0015] The water electrolysis system 100 has a first electrolysis mode and a second electrolysis mode as operation modes.

[0016] The first electrolysis mode is an operation mode in which the aqueous solution in the electrolytic cell 3 is electrolyzed using the first electrode 17 as an anode and the second electrode 18 as a cathode.

[0017] In the second electrolysis mode, the second electrode 18 is used as the anode, and the current is 0.015 A / cm 2 This is an operation mode in which the aqueous solution in the electrolytic cell 3 is electrolyzed at a current density of less than 100 kPa.

[0018] In this embodiment, the first electrolysis mode is a normal electrolysis mode aimed at electrolyzing an aqueous solution, and the second electrolysis mode is a polarity reversal electrolysis mode aimed at removing scale.

[0019] In a conventional water electrolysis device such as that described in Patent Document 1, the value of the voltage applied between the electrodes in the polarity reversal electrolysis mode is set to about 1 / 20 to 1 / 10 of the value of the voltage applied between the electrodes in the normal electrolysis mode, thereby preventing a decrease in the electrode life. However, the conventional method of controlling the voltage applied between the electrodes is not preferable because the voltage applied between the electrodes of the aqueous solution may fall below the theoretical decomposition voltage of water, making it impossible to remove scale.

[0020] The water electrolysis system 100 of this embodiment can improve the reliability of scale removal by controlling the current density of the current flowing between the first electrode 17 and the second electrode 18. Furthermore, in the water electrolysis system 100 of this embodiment, the current density is controlled to 0.015 A / cm 2 By controlling the temperature to less than this, it is possible to suppress a decrease in the electrode life of second electrode 18.

[0021] (2) Details The detailed configuration of the water electrolysis system 100 according to the first embodiment will be described below with reference to FIGS.

[0022] The water electrolysis system 100 of this embodiment is a system that performs electrolysis of an aqueous solution. The "aqueous solution" in the present disclosure includes tap water, groundwater, well water, seawater, saline water, and the like.

[0023] The water electrolysis system 100 of this embodiment is embodied by a water electrolysis apparatus 1. As shown in Fig. 1, the water electrolysis apparatus 1 includes a housing 5, a switch 7, a water pipe 8, a first pipeline 10, a water purification section 4, a second pipeline 13, a detection section 24, an electrolytic cell 3, a third pipeline 25, a fourth pipeline 26, a plug 21, a power supply section 22, and a control section 23.

[0024] The housing 5 is formed in a box shape. The housing 5 accommodates the first pipeline 10, the water purification unit 4, the second pipeline 13, the detection unit 24, the electrolytic cell 3, the power supply unit 22, and the control unit 23. The housing 5 of this embodiment also accommodates a part of the third pipeline 25 and a part of the fourth pipeline 26.

[0025] The plug 21 is electrically connected to an external power source such as a commercial power source by being connected to, for example, a socket. In this embodiment, the case where the external power source is a commercial power source that supplies AC voltage is illustrated as an example.

[0026] The power supply unit 22 is electrically connected to the plug 21. In this embodiment, the power supply unit 22 converts an AC voltage supplied from a commercial power source via the plug 21 into a DC voltage of a predetermined voltage value. The power supply unit 22 supplies the converted DC voltage to the control unit 23.

[0027] The switch 7 is attached to a faucet 6, which is an example of an aqueous solution supply unit. The switch 7 is connected to a water pipe 8. In this embodiment, the faucet 6 is not included in the configuration of the water electrolysis system 100. However, an aqueous solution supply unit such as the faucet 6 may be included in the configuration of the water electrolysis system 100.

[0028] The switch 7 has a lever 9. The lever 9 is displaced between a first position and a second position, for example, by being operated by an operator. When the lever 9 is in the first position, the switch 7 does not allow the aqueous solution discharged from the faucet 6 to flow into the water pipe 8. When the lever 9 is in the second position, the switch 7 allows the aqueous solution discharged from the faucet 6 to flow into the water pipe 8.

[0029] The water pipe 8 is connected to the switch 7. The water pipe 8 is also connected to the first pipeline 10. The water pipe 8 is formed in a tubular shape and is a part of the flow path of the aqueous solution. More specifically, the water pipe 8 is a flow path provided between the switch 7 and the first pipeline 10.

[0030] The first pipeline 10 is connected to the water pipe 8 and the water purification unit 4. The first pipeline 10 is formed in a tubular shape and is a part of the flow path of the aqueous solution. More specifically, the first pipeline 10 is a flow path provided between the water pipe 8 and the water purification unit 4.

[0031] The water purification unit 4 purifies the aqueous solution passing through the water purification unit 4. The water purification unit 4 is connected to a first pipeline 10 and a second pipeline 13. The water purification unit 4 is a flow path for the aqueous solution provided between the first pipeline 10 and the second pipeline 13. The water purification unit 4 has an activated carbon unit 11 and a hollow core filter unit 12.

[0032] The activated carbon section 11 is located upstream of the hollow core filter section 12 in the flow path. That is, the aqueous solution that flows into the water purification section 4 first passes through the activated carbon section 11. The activated carbon section 11 adsorbs and removes free chlorine, organic chlorine compounds such as trihalomethanes, mold odors, and the like.

[0033] The hollow core filter section 12 is located downstream of the flow path from the activated carbon section 11. The hollow core filter section 12 removes germs, solid impurities, and the like.

[0034] The second pipeline 13 is connected to the water purification unit 4 and the electrolytic cell 3. The second pipeline 13 is formed in a tubular shape and is a part of the flow path of the aqueous solution. More specifically, the second pipeline 13 is a flow path provided between the water purification unit 4 and the electrolytic cell 3.

[0035] The detection unit 24 is, for example, a flow meter. The detection unit 24 detects the flow rate of the aqueous solution passing through the flow path. More specifically, the detection unit 24 detects the flow rate of the aqueous solution flowing into the electrolytic cell 3. The detection unit 24 detects the start of the flow of the aqueous solution into the electrolytic cell 3 and the stop of the flow of the aqueous solution into the electrolytic cell 3. The detection unit 24 in this embodiment is provided in the second pipeline 13 and detects the flow rate of the aqueous solution passing through the second pipeline 13. The detection unit 24 outputs flow rate information, which is information on the detected flow rate, to the control unit 23.

[0036] The electrolytic cell 3 is connected to the second pipeline 13, the third pipeline 25, and the fourth pipeline 26. More specifically, the electrolytic cell 3 is a flow path provided between the second pipeline 13 and the third pipeline 25, and is a flow path provided between the second pipeline 13 and the fourth pipeline 26. The electrolytic cell 3 performs electrolysis of the aqueous solution passing through the electrolytic cell 3 under the control of the control unit 23. As shown in FIG. 1, the electrolytic cell 3 has a pair of electrodes 2 and a diaphragm 14.

[0037] The pair of electrodes 2 includes a first electrode 17 and a second electrode 18. The first electrode 17 and the second electrode 18 are arranged in the electrolytic cell 3 so as to face each other with the diaphragm 14 interposed therebetween. The first electrode 17 and the second electrode 18 are electrically connected to a control unit 23, and a direct current voltage is applied between the pair of electrodes 2 by the control unit 23. The first electrode 17 and the second electrode 18 are formed by using titanium (Ti) as a base material and coating the surface with a platinum (Pt) catalyst. The first electrode 17 and the second electrode 18 may be formed by coating with an iridium (Ir) catalyst.

[0038] The diaphragm 14 is disposed between the first electrode 17 and the second electrode 18 in the electrolytic cell 3. The diaphragm 14 divides the electrolytic cell 3 into an anode cell and a cathode cell. In this embodiment, the diaphragm 14 divides the electrolytic cell 3 into a first cell 15 and a second cell 16. In this embodiment, the first electrode 17 is disposed in the first cell 15, and the second electrode 18 is disposed in the second cell 16.

[0039] The following describes reactions that occur in the electrolytic cell 3 when the water electrolysis device 1 operates in the first electrolysis mode. When the water electrolysis device 1 operates in the first electrolysis mode, the first electrode 17 serves as an anode, and the second electrode 18 serves as a cathode. When a DC voltage is applied between the pair of electrodes 2, the aqueous solution in the electrolytic cell 3 is electrolyzed, as shown in the following formulas (1) and (2).

[0040] Anode: 2H2O → O2+4H + +4e - Formula (1) Cathode: 4H2O+4e - → 2H2+4OH - Formula (2)

[0041] As shown in formula (1), anolyte water that contains oxygen (O2) and is acidic is generated in the first tank 15 in which the first electrode 17, which is an anode, is disposed. In this embodiment, the anolyte water generated in the first tank 15 is discharged to the outside of the water electrolysis apparatus 1 through the third pipe 25.

[0042] As shown in formula (2), cathode water that contains hydrogen (H2) and is alkaline is generated in the second tank 16 in which the second electrode 18, which is a cathode, is disposed. In this embodiment, the cathode water generated in the second tank 16 is discharged to the outside of the water electrolysis device 1 through the fourth pipeline 26. The cathode water generated in the second tank 16 is used as drinking water, etc.

[0043] The cathode water generated in the second tank 16 contains hydroxide ions (OH - ), the second electrode 18 exhibits alkalinity. Since hydroxide ions are generated on the surface of the second electrode 18, the hydroxide ion concentration on the surface of the second electrode 18 increases, and the pH in the vicinity of the surface of the second electrode 18 increases. Here, an aqueous solution such as tap water originally contains calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ ) and other mineral components and bicarbonate ions (HCO3 - ) are dissolved. As shown in the following equation (3), in an alkaline environment, bicarbonate ions are converted into carbonate ions (CO3 2- ) Therefore, the proportion of carbonate ions increases near the surface of the second electrode 18 (see FIG. 2).

[0044] HCO3 - +OH - → CO3 2- +H2O Equation (3)

[0045] The following equation (4) shows the dissolution equilibrium between carbonate ions and calcium ions.

[0046] CaCO3 ⇔ Ca 2+ +CO3 2- Formula (4)

[0047] When the proportion of carbonate ions on the right side of equation (4) increases, the reaction proceeds to the left side of equation (4) to maintain equilibrium, and calcium carbonate (CaCO3), a salt, is produced. Since the solubility of calcium carbonate is very low at 0.013 g / L (25°C) and the pH near the surface of second electrode 18 is high, carbonate ions and calcium ions combine and precipitate as calcium carbonate (scale) on the surface of second electrode 18. Calcium carbonate precipitated on the surface of second electrode 18 may cause electrolysis to become impossible.

[0048] The following describes reactions that occur in the electrolytic cell 3 when the water electrolysis apparatus 1 operates in the second electrolysis mode. When the water electrolysis apparatus 1 of this embodiment operates in the second electrolysis mode, the second electrode 18 serves as an anode, and the first electrode 17 serves as a cathode. When a DC voltage is applied between the pair of electrodes 2, the aqueous solution in the electrolytic cell 3 is electrolyzed, as shown in formulas (1) and (2).

[0049] The second electrode 18, which functions as a cathode in the first electrolysis mode, functions as an anode in the second electrolysis mode. Therefore, calcium carbonate precipitated on the surface of the second electrode 18 during electrolysis in the first electrolysis mode converts hydrogen ions (H + ) and is exposed to the anode water, which is acidic due to the inclusion of carbonate ions. As shown in the following formula (5), carbonate ions are converted to carbon dioxide (CO2) under acidic conditions. Therefore, the proportion of carbon dioxide increases near the surface of the second electrode 18 (see FIG. 2).

[0050] CO3 2- +2H + → H2O+CO2↑ Equation (5)

[0051] In the dissolution equilibrium of calcium carbonate shown in formula (4), the reaction proceeds to the right of formula (4) so ​​as to maintain equilibrium by removing carbonate ions. As the reaction proceeds to the right of formula (4), calcium carbonate precipitated on the surface of second electrode 18 is washed (or removed).

[0052] The third pipeline 25 is connected to the first tank 15. The third pipeline 25 is formed in a tubular shape and is a part of the flow path of the aqueous solution. The aqueous solution electrolyzed in the first tank 15 is discharged to the outside of the water electrolysis apparatus 1 through the third pipeline 25.

[0053] The fourth pipeline 26 is connected to the second tank 16. The fourth pipeline 26 is formed in a tubular shape and is a part of the flow path of the aqueous solution. The aqueous solution electrolyzed in the second tank 16 is discharged to the outside of the water electrolysis apparatus 1 through the fourth pipeline 26.

[0054] The control unit 23 includes a computer system. The computer system mainly comprises a processor and a memory as hardware. The processor executes a program recorded in the memory of the computer system, thereby realizing the function of the control unit 23 in the present disclosure.

[0055] The control unit 23 controls the electrolysis of the aqueous solution performed in the electrolytic cell 3. The control unit 23 controls the electrolysis by controlling the DC voltage applied to the pair of electrodes 2 or the current flowing between the pair of electrodes 2. The control unit 23 in this embodiment has a first electrolysis mode and a second electrolysis mode as operation modes for controlling the electrolysis.

[0056] In the first electrolysis mode, the control unit 23 applies a DC voltage to the pair of electrodes 2 so that the first electrode 17 serves as an anode and the second electrode 18 serves as a cathode. In the first electrolysis mode, the control unit 23 starts passing electricity through the electrolytic cell 3 when the amount of aqueous solution flowing into the electrolytic cell 3 becomes equal to or greater than a threshold value based on flow rate information input from the detection unit 24. The threshold value is, for example, 2 liters.

[0057] In the first electrolysis mode, control unit 23 determines whether the inflow of the aqueous solution into electrolytic cell 3 has stopped, based on the flow rate information input from detection unit 24. When control unit 23 determines that the inflow of the aqueous solution into electrolytic cell 3 has stopped, it terminates the supply of electricity to electrolytic cell 3.

[0058] In the second electrolysis mode, the control unit 23 applies a DC voltage to the pair of electrodes 2 so that the second electrode 18 is an anode and the first electrode 17 is a cathode. In the second electrolysis mode, the control unit 23 controls the current density of the current flowing between the second electrode 18 and the first electrode 17 to be 0 A / cm 2 Larger than 0.015A / cm 2 The control unit 23 in the second electrolysis mode controls the value of the current flowing between the pair of electrodes 2 so that the voltage applied to the pair of electrodes 2 is 1.23 V (i.e., the theoretical decomposition voltage value of water) or more. The water electrolysis system 100 of this embodiment enables scale removal by a simple method of switching the polarities of the first electrode 17 and the second electrode 18.

[0059] The applicant has been studying the wear of the platinum surface of the electrode. More specifically, the applicant has studied the relationship between electrolysis with the polarity of a pair of electrodes reversed and the wear of the platinum surface. FIG. 3 is a graph showing the relationship between the amount of thickness reduction of the platinum surface and the current flow time when one of the pair of electrodes is used as an anode when electrolyzing an aqueous solution simulating tap water, and the relationship between the amount of thickness reduction [μm] of the platinum surface and the current flow time when one of the pair of electrodes is used as both the anode and the cathode. As shown in FIG. 3, the amount of thickness reduction when the polarity of the electrodes is reversed (polarity reversal electrolysis mode) is more than 10 times larger than the amount of thickness reduction when the polarity of the electrodes is not reversed (normal electrolysis mode). It is believed that the degree of wear of the platinum surface increases by repeating oxidation and reduction.

[0060] The applicant has also studied the relationship between the magnitude of the current flowing between a pair of electrodes and the wear rate of the platinum surface. Figure 4 is a graph showing the relationship between the current density of the current flowing between a pair of electrodes and the wear rate of the platinum surface. In Figure 4, when the current density of the current flowing between the pair of electrodes is 0.015 A / cm 2 The wear rate of the platinum surface at a current density of 0.015 A / cm is taken as the standard (1.0). In other words, the wear rate of the platinum surface at each current density is 2As shown in Figure 4, the consumption rate is normalized by the consumption rate when the current density is 0.015 A / cm 2 More than 0.05A / cm 2 Within the range below, the wear rate of the platinum surface does not change significantly even if the current density is changed. However, when the current density is 0.015 A / cm 2 When the current density is less than 0.005 A / cm, the rate of wear of the platinum surface drops sharply. 2 In the case of about 0.015A / cm 2 The rate of wear of the platinum surface is halved compared to the case of

[0061] In the water electrolysis system 100 of this embodiment, in consideration of the above-mentioned study results, the control unit 23 in the second electrolysis mode (polarity reversal electrolysis mode) controls the current density of the current flowing between the pair of electrodes 2 to be 0.015 A / cm 2 The value of the current flowing between the pair of electrodes 2 is controlled so that it is less than 1. Note that the control unit 23 of this embodiment detects the conductivity (or resistance value) of the aqueous solution, and applies a DC voltage to the pair of electrodes 2 based on the conductivity of the aqueous solution and the target current density value.

[0062] The control unit 23 in this embodiment performs electrolysis multiple times in the first electrolysis mode or the second electrolysis mode. For example, the control unit 23 performs electrolysis in the second electrolysis mode after performing electrolysis multiple times in succession in the first electrolysis mode.

[0063] Furthermore, the control unit 23 of this embodiment performs electrolysis in the second electrolysis mode when a predetermined condition is satisfied after performing electrolysis in the first electrolysis mode. The predetermined condition of this embodiment is to perform electrolysis in the first electrolysis mode a predetermined number of times in succession. The predetermined number of times of this embodiment is a plurality of times, for example, "2." That is, in the water electrolysis system 100 of this embodiment, the number of times electrolysis is performed in the second electrolysis mode is less than the number of times electrolysis is performed in the first electrolysis mode. By making the number of times electrolysis is performed in the second electrolysis mode less than the number of times electrolysis is performed in the first electrolysis mode, it is possible to further suppress a decrease in the electrode life of the second electrode 18.

[0064] (3) Operation of the water electrolysis system Next, the operation of the water electrolysis apparatus 1 (or the water electrolysis system 100) will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the operation of the water electrolysis apparatus 1 (or the water electrolysis system 100).

[0065] First, the water electrolysis apparatus 1 controls the operation mode to a first electrolysis mode (normal electrolysis mode) (step S1). Next, the water electrolysis apparatus 1 determines whether or not a start condition for the first electrolysis mode is satisfied (step S2). In this embodiment, the start condition for the first electrolysis mode is that the amount of aqueous solution flowing into the electrolytic cell 3 is equal to or greater than a threshold value. The water electrolysis apparatus 1 repeats the process of step S2 until it determines that the start condition for the first electrolysis mode is satisfied. When it determines that the start condition for the first electrolysis mode is satisfied (step S2: Yes), the water electrolysis apparatus 1 applies a DC voltage between the pair of electrodes 2 (step S3). Here, the first electrode 17 functions as an anode, and the second electrode 18 functions as a cathode.

[0066] Next, the water electrolysis device 1 determines whether or not a termination condition for the first electrolysis mode is satisfied (step S4). In this embodiment, the termination condition for the first electrolysis mode is that the inflow of aqueous solution into the electrolytic cell 3 stops. The water electrolysis device 1 repeats the process of step S4 until it determines, based on the inflow information input from the detection unit 24, that the termination condition for the first electrolysis mode is satisfied. When the water electrolysis device 1 determines, based on the inflow information input from the detection unit 24, that the termination condition for the first electrolysis mode is satisfied (step S4: Yes), it terminates the flow of current between the pair of electrodes 2 (step S5).

[0067] Next, the water electrolysis apparatus 1 determines whether a predetermined condition (i.e., a condition for starting the second electrolysis mode) is satisfied (step S6). In this embodiment, the predetermined condition is to perform electrolysis in the first electrolysis mode twice consecutively. If the water electrolysis apparatus 1 determines that the predetermined condition is not satisfied (step S6: No), it ends the series of processes shown in FIG. 6. On the other hand, if the water electrolysis apparatus 1 determines that the predetermined condition is satisfied (step S6: Yes), it controls the operation mode to the second electrolysis mode (polarity reversal electrolysis mode) (step S7). That is, the water electrolysis apparatus 1 of this embodiment switches the operation mode from the first electrolysis mode to the second electrolysis mode on the condition that it has detected the stop of the inflow of the aqueous solution into the electrolytic cell 3, and if the predetermined condition is also satisfied.

[0068] Next, the water electrolysis device 1 applies a DC voltage between the pair of electrodes 2 (step S8). Here, the first electrode 17 functions as a cathode, and the second electrode 18 functions as an anode. The water electrolysis device 1 also applies a DC voltage between the pair of electrodes 2 such that the current density of the current flowing between the first electrode 17 and the second electrode 18 is 0.015 A / cm. 2 The value of the current flowing between the pair of electrodes 2 is controlled so that the current is less than the threshold voltage.

[0069] Next, the water electrolysis device 1 determines whether or not a termination condition for the second electrolysis mode is satisfied (step S9). In this embodiment, the termination condition for the second electrolysis mode is that a predetermined time has elapsed since the start of electrolysis in the second electrolysis mode. The water electrolysis device 1 repeats the process of step S9 until it determines that the termination condition for the second electrolysis mode is satisfied. If the water electrolysis device 1 determines that the termination condition for the second electrolysis mode is satisfied (step S9: Yes), it stops the flow of current between the pair of electrodes 2 (step S10) and ends the series of processes shown in FIG. 6.

[0070] It should be noted that the flowchart shown in FIG. 6 is merely an example, and the order of the processes may be changed as appropriate, and processes may be added or deleted as appropriate.

[0071] (4) Variations Modifications of the above embodiment are listed below.

[0072] (4.1) Variation 1 In the water electrolysis device 1 of the first modification, the aqueous solution flowing into the electrolytic cell 3 contains chloride ions (Cl - The aqueous solution is, for example, seawater or an aqueous solution to which about 0.5% or more of table salt has been added.

[0073] Figure 5 is a graph showing the relationship between the amount of thickness reduction [μm] on the platinum surface and the current flow time when a NaCl aqueous solution having a chloride ion concentration equal to or higher than a threshold is electrolyzed in the second electrolysis mode, and the relationship between the amount of thickness reduction [μm] on the platinum surface and the current flow time when a Na2SO4 aqueous solution having a chloride ion concentration less than the threshold is electrolyzed in the second electrolysis mode.

[0074] As shown in FIG. 5, when the polarity reversal number is the same, the thickness reduction amount when an NaCl aqueous solution is electrolyzed is more than five times larger than the thickness reduction amount when an Na2SO4 aqueous solution is electrolyzed.

[0075] In the water electrolysis device 1 of the first modification, the aqueous solution flowing into the electrolytic cell 3 contains chloride ions (Cl - 6, for an aqueous solution having a concentration equal to or higher than a threshold value, the number of times electrolysis is performed in the second electrolysis mode is set to less than 1 / 5 of the number of times electrolysis is performed in the first electrolysis mode. In the water electrolysis device 1 of Modification 1, for example, the predetermined condition for step S6 in Fig. 6 is to perform electrolysis in the first electrolysis mode six times in succession.

[0076] According to the water electrolysis device 1 of the first modification, the number of electrolysis cycles in the second electrolysis mode can be increased or decreased depending on the chloride ion concentration of the aqueous solution, thereby making it possible to further suppress the shortening of the electrode life of the second electrode 18.

[0077] (4.2) Variation 2 In the above embodiment, a case has been exemplified in which the number of times electrolysis is performed in the second electrolysis mode is less than the number of times electrolysis is performed in the first electrolysis mode, but the number of times electrolysis is performed in the second electrolysis mode may be the same as the number of times electrolysis is performed in the first electrolysis mode. In other words, the control unit 23 may perform electrolysis in the second electrolysis mode on the condition that electrolysis in the first electrolysis mode is terminated. In other words, the control unit 23 may switch the operation mode from the first electrolysis mode to the second electrolysis mode on the condition that the detection unit 24 detects that the inflow of the aqueous solution into the electrolytic cell 3 has stopped.

[0078] The water electrolysis apparatus 1 of Modification 2 does not perform the process of step S6 in Fig. 6. That is, when the water electrolysis apparatus 1 of Modification 2 ends the passage of current between the pair of electrodes 2 (step S5), it controls the operation mode to the second electrolysis mode (polarity reversal electrolysis mode) (step S7).

[0079] According to the water electrolysis apparatus 1 of the second modification, electrolysis in the second electrolysis mode can be performed under the simple condition that the detection unit 24 detects that the inflow of the aqueous solution into the electrolytic cell 3 has stopped.

[0080] (4.3) Other Modifications Modifications of the above embodiment are listed below.

[0081] Functions equivalent to those of the water electrolysis system 100 (or water electrolysis device 1) according to the above embodiment may be embodied as a water electrolysis method, a (computer) program, or a non-transitory recording medium having a program recorded thereon. The water electrolysis method according to one embodiment is a method executed by one or more processors of the water electrolysis system 100 including an electrolytic cell 3. The electrolytic cell 3 has a first electrode 17 and a second electrode 18, and a diaphragm 14 disposed between the first electrode 17 and the second electrode 18. The water electrolysis method includes a first electrolysis step and a second electrolysis step. In the first electrolysis step, the aqueous solution in the electrolytic cell 3 is electrolyzed using the first electrode 17 as an anode and the second electrode 18 as a cathode. In the second electrolysis step, the aqueous solution in the electrolytic cell 3 is electrolyzed using the second electrode 18 as an anode at a current of 0.015 A / cm 2The aqueous solution in the electrolytic cell 3 is electrolyzed at a current density of less than 100 kPa. A program according to one embodiment is a program for causing one or more processors to execute the above-described water electrolysis method.

[0082] The execution entity of the water electrolysis system 100 or the water electrolysis method in the present disclosure includes a computer system. The computer system is mainly composed of a processor and a memory as hardware. The processor executes a program recorded in the memory of the computer system to realize the function of the execution entity of the water electrolysis system 100 or the water electrolysis method in the present disclosure. The program may be pre-recorded in the memory of the computer system, provided through an electric communication line, or provided in a non-transitory recording medium such as a memory card, an optical disk, or a hard disk drive that can be read by the computer system. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large scale integrated circuit (LSI). The integrated circuits such as IC or LSI referred to here are called by different names depending on the degree of integration, and include integrated circuits called system LSI, VLSI (Very Large Scale Integration), or ULSI (Ultra Large Scale Integration). Furthermore, a field-programmable gate array (FPGA) that is programmed after the manufacture of the LSI, or a logic device that allows reconfiguration of the connection relationship inside the LSI or reconfiguration of the circuit partition inside the LSI, can also be used as the processor. The electronic circuits may be integrated in one chip or distributed among multiple chips. The chips may be integrated in one device or distributed among multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Thus, the microcontroller is also composed of one or more electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit.

[0083] Furthermore, it is not essential for the water electrolysis system 100 that multiple functions are concentrated in one housing, and the components of the water electrolysis system 100 may be distributed across multiple housings. For example, the control unit 23 of the water electrolysis system 100 may be provided outside the water electrolysis apparatus 1.

[0084] In the above embodiment, the polarities of the first electrode 17 and the second electrode 18 are switched between the first electrolysis mode and the second electrolysis mode, but this is not limited to the above. For example, in the first electrolysis mode, the first electrode 17 may be an anode and the second electrode 18 may be a cathode, and in the second electrolysis mode, for example, a dummy electrode installed in the first tank 15 may be a cathode and the second electrode may be an anode.

[0085] (summary) As is apparent from the above-described embodiment and modified examples, the water electrolysis system (100) according to the first aspect includes an electrolytic cell (3). The electrolytic cell (3) has a first electrode (17), a second electrode (18), and a diaphragm (14) disposed between the first electrode (17) and the second electrode (18). The water electrolysis system (100) has a first electrolysis mode and a second electrolysis mode as operation modes. The first electrolysis mode is an operation mode in which the aqueous solution in the electrolytic cell (3) is electrolyzed using the first electrode (17) as an anode and the second electrode (18) as a cathode. The second electrolysis mode is an operation mode in which the aqueous solution in the electrolytic cell (3) is electrolyzed using the second electrode (18) as an anode, and a current of 0.015 A / cm is generated. 2 This is an operating mode in which the aqueous solution in the electrolytic cell (3) is electrolyzed at a current density of less than 1000 kPa.

[0086] According to this embodiment, the reliability of scale removal can be improved, and shortening of the electrode life of the second electrode (18) can be suppressed.

[0087] In the water electrolysis system (100) according to the second aspect, in the first aspect, the second electrolysis mode is set to 0.015 A / cm with the first electrode (17) as a cathode and the second electrode (18) as an anode. 2 This is an operating mode in which the aqueous solution in the electrolytic cell (3) is electrolyzed at a current density of less than 1000 kPa.

[0088] According to this embodiment, by switching the polarity of the first electrode (17) and the second electrode (18), it is possible to remove scale.

[0089] In the water electrolysis system (100) according to the third aspect, in the first or second aspect, electrolysis is performed multiple times in the first electrolysis mode or the second electrolysis mode. The number of times electrolysis is performed in the second electrolysis mode is smaller than the number of times electrolysis is performed in the first electrolysis mode.

[0090] According to this embodiment, it is possible to further prevent the electrode life of the second electrode (18) from being shortened.

[0091] In the water electrolysis system (100) according to the fourth aspect, in any one of the first to third aspects, the aqueous solution in the electrolytic cell (3) has a chloride ion concentration equal to or higher than a threshold value. The number of times electrolysis is performed in the second electrolysis mode is less than ⅕ of the number of times electrolysis is performed in the first electrolysis mode.

[0092] According to this embodiment, it is possible to further prevent the electrode life of the second electrode (18) from being shortened.

[0093] The water electrolysis system (100) according to a fifth aspect is any one of the first to fourth aspects, further comprising a detection unit (24) that detects stop of the inflow of the aqueous solution into the electrolytic cell (3). When the detection unit (24) detects stop of the inflow of the aqueous solution, the operation mode of the water electrolysis system (100) is switched from the first electrolysis mode to the second electrolysis mode.

[0094] According to this embodiment, electrolysis in the second electrolysis mode can be performed under simple conditions.

[0095] The components other than those of the first embodiment are not essential components of the water electrolysis system (100) and may be omitted as appropriate. [Explanation of symbols]

[0096] 100 Water electrolysis system 3 Electrolytic cell 14 Diaphragm 17 1st electrode 18 2nd electrode 24 Detection unit

Claims

1. A water electrolysis system including an electrolytic cell, The electrolytic cell comprises: A first electrode and a second electrode; A diaphragm disposed between the first electrode and the second electrode; having the water electrolysis system has a first electrolysis mode and a second electrolysis mode as operation modes; the first electrolysis mode is an operation mode in which the aqueous solution in the electrolytic cell is electrolyzed using the first electrode as an anode and the second electrode as a cathode; The second electrolysis mode is 0.015 A / cm ２ an operation mode for electrolyzing the aqueous solution in the electrolytic cell at a current density of less than Water electrolysis system.

2. The second electrolysis mode is a current flow rate of 0.015 A / cm, with the first electrode as a cathode and the second electrode as an anode. ２ an operation mode for electrolyzing the aqueous solution in the electrolytic cell at a current density of less than The water electrolysis system according to claim 1 .

3. Electrolysis is performed multiple times in the first electrolysis mode or the second electrolysis mode; The number of times electrolysis is performed in the second electrolysis mode is less than the number of times electrolysis is performed in the first electrolysis mode. The water electrolysis system according to claim 1 or 2.

4. The aqueous solution in the electrolytic cell has a chloride ion concentration equal to or higher than a threshold value, The number of times electrolysis is performed in the second electrolysis mode is less than 1 / 5 of the number of times electrolysis is performed in the first electrolysis mode. The water electrolysis system according to claim 3.

5. A detection unit that detects the stop of the inflow of the aqueous solution into the electrolytic cell is further provided, switching the operation mode of the water electrolysis system from the first electrolysis mode to the second electrolysis mode on a condition that the detection unit detects the stop of the inflow of the aqueous solution.

3. The electrolysis system according to claim 1 or 2.

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