Water electrolysis system and water electrolysis method

Abstract

To suppress deterioration of a pH sensor caused by contact of the pH sensor with an electrolytic solution.SOLUTION: The water electrolysis system 100 includes a water electrolysis cell 20 that electrolyzes an electrolytic solution, a liquid storage tank 10 that stores the electrolytic solution, a first supply line 41 that supplies the electrolytic solution from the liquid storage tank 10 to the water electrolysis cell 20, a pH sensor 54 that measures the pH of the electrolytic solution, and a second supply line 51 that is a line different from the first supply line 41 and supplies the electrolytic solution from the liquid storage tank 10 to the pH sensor 54.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to techniques for water electrolysis. [Background technology]

[0002] In a hydrogen production method in which hydrogen is produced by electrolyzing an electrolyte solution, the component concentrations of the electrolyte solution change as the water electrolysis progresses. Therefore, a method for measuring the component concentrations of the electrolyte solution using a pH sensor has been proposed. For example, Patent Document 1 discloses that in a hydrogen production method in which hydrogen is produced by electrolyzing an alkaline aqueous solution, the alkaline component concentration of the alkaline aqueous solution is measured using a well-known pH meter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-178356 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional hydrogen production methods have a problem in that the sensor deteriorates due to contact with the electrolyte. For example, contact of a pH sensor with an electrolyte heated to approximately 80°C due to reaction heat generated by water electrolysis or heating of the electrolyte using a heater to improve energy efficiency accelerates deterioration of the pH sensor. Note that while we have focused on deterioration due to contact with a high-temperature electrolyte for convenience, causes of pH sensor deterioration are not limited to this. For example, contact with a highly alkaline electrolyte can also cause deterioration of a pH sensor. In consideration of the above circumstances, one aspect of the present disclosure aims to suppress deterioration of a pH sensor due to contact of the pH sensor with the electrolyte. [Means for solving the problem]

[0005] In order to solve the above problems, a water electrolysis system according to one embodiment of the present disclosure includes a water electrolysis cell that electrolyzes an electrolyte solution, a storage tank that stores the electrolyte solution, a first supply line that supplies the electrolyte solution from the storage tank to the water electrolysis cell, a pH sensor that measures the pH of the electrolyte solution, and a second supply line that is separate from the first supply line and supplies the electrolyte solution from the storage tank to the pH sensor.

[0006] A water electrolysis method according to one embodiment of the present disclosure uses a water electrolysis system including a water electrolysis cell that electrolyzes an electrolyte solution, a storage tank that stores the electrolyte solution, and a pH sensor that measures the pH of the electrolyte solution, in which the electrolyte solution is supplied from the storage tank to the water electrolysis cell via a first supply line, and the electrolyte solution is supplied from the storage tank to the pH sensor via a second supply line that is different from the first supply line. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a configuration diagram of a water electrolysis system according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram of the installation position of a pH sensor according to the first embodiment. [Figure 3] FIG. 2 is an explanatory diagram of the installation position of a pH sensor according to the first embodiment. [Figure 4] FIG. 2 is a block diagram illustrating an example of the functional configuration of the control system. [Figure 5] 4 is a flowchart of a control process in the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The embodiments for carrying out the present disclosure will be described with reference to the drawings. Note that the dimensions and scale of each element in each drawing may differ from those of the actual product. Furthermore, the embodiment described below is an exemplary embodiment that may be envisioned when carrying out the present disclosure. Therefore, the scope of the present disclosure is not limited to the embodiment exemplified below.

[0009] A: First embodiment 1 is a configuration diagram of a water electrolysis system 100 according to the first embodiment. The water electrolysis system 100 of the first embodiment includes a liquid storage tank 10, a water electrolysis cell 20, a power supply unit 30, gas-liquid separators 31 and 32, a circulation unit 40, a measurement unit 50, a pure water supply unit 60, and a control system 70.

[0010] The storage tank 10 is a tank that stores the electrolyte used in water electrolysis. The storage tank 10 can be made of a resin material (or a metal material) that is highly resistant to the corrosive action of the electrolyte. The electrolyte is an aqueous solution in which an electrolyte is dissolved, which facilitates water electrolysis. Examples of the electrolyte include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution. However, the type of electrolyte is not limited to the above examples and may be any type.

[0011] The water electrolysis cell 20 is a device that generates hydrogen and oxygen by electrolyzing water from an electrolytic solution, and includes an electrolyte membrane 21, an anode portion 22, and a cathode portion .

[0012] The electrolyte membrane 21 is an ion exchange membrane that separates the anode section 22 and the cathode section 23. An example of the electrolyte membrane 21 is a membrane that exchanges hydroxide ions (OH - However, the type of the electrolyte membrane 21 is not limited to the above examples and may be any type.

[0013] The anode section 22 is an electrode that generates oxygen through water electrolysis. 2OH - →H2O+1 / 2·O2+2e - This reaction produces oxygen gas.

[0014] The cathode section 23 is an electrode that generates hydrogen by water electrolysis. 2H2O+2e - →H2+2OH - The overall reaction in the water electrolysis cell 20 is as follows: H2O → H2 + 1 / 2 O2 The following reaction occurs.

[0015] The power supply device 30 is a device that supplies the water electrolysis cell 20 with electricity used in water electrolysis.

[0016] Gas-liquid separator 31 is a device that separates and discharges oxygen gas generated by water electrolysis from the electrolytic solution. Gas-liquid separator 32 is a device that separates and discharges hydrogen gas generated by water electrolysis from the electrolytic solution.

[0017] The gas-liquid separator 31 is connected to the anode unit 22 and the liquid storage tank 10. The gas-liquid separator 31 is a device that separates oxygen gas from the electrolyte. The separated oxygen gas is discharged from the gas-liquid separator 31 to the outside via a discharge pipe. The separated electrolyte is sent to the liquid storage tank 10.

[0018] The gas-liquid separator 32 is connected to the cathode section 23. The gas-liquid separator 32 is a device that separates hydrogen gas and electrolytic solution. The separated hydrogen gas is discharged from the gas-liquid separator 32 to the outside via an exhaust pipe. In the cathode section 23, the water in the electrolytic solution supplied to the cathode section 23 is consumed, so that the hydrogen gas generated in the cathode section 23 is hardly mixed with the electrolytic solution. Therefore, the small amount of electrolytic solution that accumulates in the gas-liquid separator 32 is discarded without being recovered in the storage tank 10.

[0019] 1, the electrolytic solution sent from the cathode unit 23 to the gas-liquid separator 32 is discarded without being recovered. However, the electrolytic solution sent from the cathode unit 23 to the gas-liquid separator 32 may be recovered. For example, it is conceivable to recover the electrolytic solution sent from the cathode unit 23 to the gas-liquid separator 32 in the liquid storage tank 10, or to recover the electrolytic solution sent from the cathode unit 23 to the gas-liquid separator 32 in the cathode unit 23.

[0020] The circulation unit 40 is a unit that supplies the electrolyte from the storage tank 10 to the water electrolysis cell 20. The circulation unit 40 includes a first supply line 41, a first supply pump 42, and a heater 43.

[0021] The first supply line 41 is a pipe connecting the storage tank 10 and the water electrolysis cell 20. That is, the first supply line 41 supplies the electrolyte from the storage tank 10 to the water electrolysis cell 20. The first supply line 41 can be made of a resin material (or a metal material) that is highly resistant to the corrosive action of the electrolyte.

[0022] The first supply pump 42 is provided midway along the first supply line 41. The first supply pump 42 is a pump that supplies the electrolyte solution drawn from the storage tank 10 to the water electrolysis cell 20 via the first supply line 41.

[0023] The heater 43 is provided along or along the entire first supply line 41. The heater 43 is a device that raises the temperature of the electrolyte solution supplied to the circulation unit 40. When the temperature of the electrolyte solution decreases, the conductivity of the electrolyte solution decreases. When the conductivity of the electrolyte solution decreases, the electrical resistance of the electrolyte solution increases, and the energy efficiency of water electrolysis decreases. To prevent a decrease in energy efficiency, the temperature of the electrolyte solution needs to be adjusted by the heater 43. Examples of types of the heater 43 include a resistance heater, an infrared heater, a plate-type heat exchanger, and a heating jacket. However, the type of the heater 43 is arbitrary and is not limited to the above examples.

[0024] Here, the water electrolysis performed in this embodiment will be described.

[0025] The electrolyte is supplied from the storage tank 10 to the water electrolysis cell 20 via the circulation unit 40. The electrolyte supplied to the circulation unit 40 is heated to approximately 80°C by a heater 43. The heated electrolyte is supplied to the anode section 22 or the cathode section 23, where water electrolysis generates oxygen gas or hydrogen gas, respectively.

[0026] The hydrogen gas generated in the cathode section 23 is sent to a gas-liquid separator 32 connected to the cathode section 23. The gas-liquid separator 32 separates the hydrogen gas from the electrolyte, and the separated hydrogen is discharged from an exhaust pipe. Because the amount of electrolyte separated from the hydrogen gas is small, it is discarded without being collected in the storage tank 10.

[0027] The electrolyte solution containing oxygen gas produced in the anode section 22 is sent to a gas-liquid separator 31 connected to the anode section 22. The electrolyte solution sent to the gas-liquid separator 31 is separated into oxygen gas and electrolyte solution. The separated oxygen gas is discharged from an exhaust pipe. The electrolyte solution separated from the oxygen gas is collected in the storage tank 10.

[0028] Because the recovered electrolyte consumes water, the component concentrations of the electrolyte increase over time as water electrolysis progresses. There is a relationship between the component concentrations of the electrolyte and the electrical conductivity, whereby the electrical conductivity is maximized at a certain concentration. Therefore, the electrical conductivity decreases whether the electrical conductivity is higher or lower than the maximum concentration. Therefore, it is necessary to measure the component concentrations of the electrolyte and supply water to the storage tank 10 so that the component concentrations of the electrolyte are maintained within a predetermined range. Therefore, in this embodiment, a measurement unit 50 for measuring the component concentrations of the electrolyte and a pure water supply device 60 for supplying pure water to the storage tank 10 are provided.

[0029] The measurement unit 50 is a unit that measures the pH of the electrolyte solution supplied from the storage tank 10. The measurement unit 50 includes a second supply line 51, a valve device 53, a pH sensor 54, and a second supply pump 52.

[0030] The second supply line 51 is a pipe that supplies the electrolyte from the storage tank 10 to the pH sensor 54. A resin material (or a metal material) that is highly resistant to the corrosive action of the electrolyte can be used as the material for the second supply line 51. Both ends of the second supply line 51 are connected to the storage tank 10, so the electrolyte supplied to the pH sensor 54 is collected in the storage tank 10.

[0031] The second supply line 51 is separate from the first supply line 41. Specifically, the first supply line 41 and the second supply line 51 may start from different positions in the liquid storage tank 10, or a single supply line starting from the liquid storage tank 10 may branch into the first supply line 41 and the second supply line 51 midway.

[0032] The electrolytic solution supplied to the pH sensor 54 via the second supply line 51 transfers and dissipates heat to the piping or the like in contact with it. Therefore, the second temperature of the electrolytic solution supplied to the pH sensor 54 via the second supply line 51 is lower than the first temperature of the electrolytic solution supplied to the water electrolysis cell 20 via the first supply line 41.

[0033] The valve devices 53 are installed in sections of the second supply line 51 upstream and downstream of the pH sensor 54. The valve devices 53 are devices that switch between supplying and stopping the supply of the electrolyte to the pH sensor 54 via the second supply line 51 by opening and closing a valve.

[0034] Water electrolysis using the water electrolysis cell 20 and the circulation unit 40 continues throughout the entire operation period of the water electrolysis system 100, whereas the supply of electrolyte to the pH sensor 54 via the second supply line 51 is limited to a part of the operation period during which the valve device 53 is open. In other words, a first length of time during which water electrolysis is performed using the electrolyte supplied to the water electrolysis cell 20 via the first supply line 41 exceeds a second length of time during which the electrolyte is supplied to the pH sensor 54 via the second supply line 51. The type of the valve device 53 may be an automatic valve that can be opened and closed in response to an external command. However, the type of the valve device 53 is arbitrary and is not limited to the above examples.

[0035] The pH sensor 54 is a device that measures the pH of the electrolyte solution supplied to the measurement unit 50. The pH sensor 54 is provided midway along the second supply line 51. The pH sensor 54 is provided so that its vertical position is higher than the liquid level in the storage tank 10. For example, the pH sensor 54 may be provided in a straight portion of the second supply line 51, as shown in FIG. 2, or in a bent portion of the second supply line 51, as shown in FIG. 3, so that its vertical position is higher than the liquid level in the storage tank 10. The bent portion is a portion where a horizontally extending portion and a vertically extending portion toward the storage tank 10 are connected. Therefore, when the supply of electrolyte solution to the measurement unit 50 is stopped, the electrolyte solution does not come into contact with the pH sensor 54.

[0036] 2, the liquid level of the electrolyte in the second supply line 51 is lower than the pH sensor 54, so the pH sensor 54 does not come into contact with the electrolyte. In the example shown in FIG. 3, the electrolyte in the second supply line 51 naturally falls along the bend in the bent portion into the storage tank 10, so the pH sensor 54 does not come into contact with the electrolyte. However, the configuration for installing the pH sensor 54 is not limited to the above example, as long as the pH sensor 54 is installed midway along the second supply line 51 so that its vertical position is higher than the liquid level in the storage tank 10.

[0037] The second supply pump 52 is provided midway along the second supply line 51. The second supply pump 52 is a device that draws in the electrolyte from the liquid storage tank 10 and supplies the electrolyte to the pH sensor 54 via the second supply line 51.

[0038] The pure water supply device 60 includes a pure water supply line 61 , a pure water tank 63 , and a pure water pump 62 .

[0039] The pure water supply line 61 is a pipe that connects the pure water tank 63 and the liquid storage tank 10 .

[0040] The pure water tank 63 is connected to the liquid storage tank 10 via a pure water supply line 61. The pure water tank 63 is a tank for storing pure water to be supplied to the liquid storage tank 10 in order to adjust the component concentrations of the electrolyte solution.

[0041] The pure water pump 62 is provided midway along the pure water supply line 61. The pure water pump 62 is a pump that sucks pure water from a pure water tank 63 and supplies it to the liquid storage tank 10 via the pure water supply line 61.

[0042] The control system 70 is a system for measuring the component concentrations of the electrolyte solution during water electrolysis and controlling the adjustment of the component concentrations. The control system 70 includes a control device 80 and a storage device 90.

[0043] The control device 80 is composed of one or more processors that control each element of the control system 70. Specifically, the control device 80 is composed of one or more types of processors, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit).

[0044] The storage device 90 is one or more memories that store programs executed by the control device 80 and data used by the control device 80. The storage device 90 is configured with a known storage medium such as a magnetic storage medium or a semiconductor storage medium. The storage device 90 may also be configured with a combination of multiple types of storage medium. A portable storage medium that can be attached to and detached from the control system 70 may also be used as the storage device 90.

[0045] 4 is a block diagram illustrating an example of the functional configuration of the control system 70. The control device 80 executes a program stored in the storage device 90 to realize multiple functions (an acquisition unit 81, a calculation unit 82, a water replenishment unit 83, a supply unit 84, and a correction unit 85) for controlling the control system 70. The control system 70 may be realized as a single device, or may be realized as a collection of multiple devices configured separately from each other.

[0046] The acquisition unit 81 acquires the value of the current flowing from the power source to the water electrolysis cell 20 for water electrolysis for each unit period of a predetermined length. Specifically, the acquisition unit 81 calculates the average of multiple current values ​​within each unit period on the time axis.

[0047] The calculation unit 82 calculates the component concentrations of the electrolyte solution from the current value acquired by the acquisition unit 81. The following methods can be considered as a method for calculating the component concentrations of the electrolyte solution.

[0048] The calculation unit 82 calculates the amount of electricity by multiplying the acquired current value by the length of the unit period, as shown in the following calculation formula:

[0049] Amount of electricity (C) = current value (A) x unit time (sec) Furthermore, the calculation unit 82 calculates the amount of water decomposition in the electrolyte from the quantity of electricity using the following calculation formula:

[0050] Amount of water split (g) = Amount of electricity (C) / Faraday's constant (96485C) x Molecular weight of water (18) / Apparent number of electron reactions (2) Since the amount of hydrogen ions in the electrolyte does not change, the calculation unit 82 calculates the component concentrations of the electrolyte using the amount of water decomposition. As described above, the calculation unit 82 calculates the component concentrations of the electrolyte from the current value.

[0051] The water replenishment unit 83 performs water replenishment control by controlling the pure water pump 62 according to the calculated component concentration of the electrolyte. The water replenishment control is a control that supplies pure water sucked by the pure water pump 62 from the pure water tank 63 to the liquid storage tank 10 via the pure water supply line 61. Specifically, the water replenishment unit 83 compares the component concentration with a predetermined threshold, and performs water replenishment control when the component concentration exceeds the threshold. The supply of pure water to the liquid storage tank 10 reduces the component concentration of the electrolyte.

[0052] The supply unit 84 controls the supply of the electrolyte from the storage tank 10 to the measurement unit 50. Specifically, the supply unit 84 controls the operation of the second supply pump 52 and the valve device 53 to supply the electrolyte sucked from the storage tank 10 to the pH sensor 54 via the second supply line 51.

[0053] Since the current value acquired by the acquisition unit 81 is subject to measurement errors due to the measuring instrument, errors may occur in the component concentrations of the electrolyte solution calculated by the calculation unit 82. Therefore, the correction unit 85 corrects the component concentrations calculated by the calculation unit 82 in accordance with the pH measured by the pH sensor 54. Correction in accordance with pH means changing the component concentrations calculated by the calculation unit 82 using correction values ​​calculated by the correction unit 85 from the measured pH.

[0054] 5 is a flowchart illustrating a specific procedure for processing in parallel with water electrolysis performed by the control system 70. The processing begins when water electrolysis begins.

[0055] When water electrolysis starts, the control device 80 (calculation unit 82) determines whether a unit period has elapsed since the start of water electrolysis (Sc1). If the unit period has not elapsed since the start of water electrolysis (Sc1: No), the control process proceeds to step Sc1. On the other hand, if the unit period has elapsed since the start of water electrolysis (Sc1: Yes), the control device 80 (acquisition unit 81) acquires the value of the current flowing from the power source to the water electrolysis cell 20 (Sc2). That is, the control device 80 (acquisition unit 81) acquires the current value for the unit period. Specifically, the control device 80 (acquisition unit 81) calculates the average of multiple current values ​​within the unit period. Once the current value has been acquired, the control device 80 (calculation unit 82) calculates the component concentrations of the electrolyte solution from the current value acquired by the control device 80 (acquisition unit 81) (Sc3).

[0056] Once the component concentrations are calculated, the control device 80 (correction unit 85) corrects the component concentrations using the correction values ​​(Sc4). Once the component concentrations are corrected, the control device 80 (water replenishment unit 83) determines whether or not to perform water replenishment control in accordance with the component concentrations (Sc5). Specifically, the control device 80 (water replenishment unit 83) determines whether or not the component concentrations exceed a threshold value.

[0057] If it is determined that water replenishment control will not be performed (Sc5: No), the control process proceeds to step Sc7, which will be described later. On the other hand, if it is determined that water replenishment control will be performed (Sc5: Yes), the control device 80 (water replenishment unit 83) performs water replenishment control by controlling the pure water pump 62 (Sc6). That is, the amount of pure water supplied is set so that the component concentration, which has increased to a level exceeding the threshold, decreases to a target value suitable for water electrolysis. The water replenishment unit 83 controls the operation of the pure water pump 62 to supply a predetermined amount of pure water from the pure water tank 63 to the liquid storage tank 10. When the water replenishment control is completed, the control process proceeds to step Sc7.

[0058] The control device 80 (correction unit 85) determines whether a predetermined time has elapsed since the start of water electrolysis (Sc7). If the predetermined time has not elapsed since the start of water electrolysis (Sc7: No), the control process proceeds to Sc1. On the other hand, if the predetermined time has elapsed since the start of water electrolysis (Sc7: Yes), the control device 80 (supply unit 84) controls the operation of the second supply pump 52 and the valve device 53 of the measurement unit 50 (Sc8). That is, the electrolyte is supplied from the storage tank 10 to the pH sensor 54. The pH sensor 54 measures the pH of the electrolyte supplied from the storage tank 10.

[0059] The control device 80 (correction unit 85) acquires the pH measurement value from the pH sensor 54 (Sc9). The control device 80 (correction unit 85) calculates a correction value based on the acquired pH measurement value (Sc10). Once the control device 80 (correction unit 85) calculates the correction value, the control process proceeds to step Sc4. Therefore, the component concentrations calculated from the current value are corrected using the most recently corrected correction value. As described above, the control system 70 can measure and adjust the component concentrations of the electrolyte solution in parallel with water electrolysis.

[0060] B: Modified example Specific modified embodiments that can be added to the embodiments exemplified above are shown below. Two or more embodiments arbitrarily selected from the following examples may be combined as appropriate within a range that does not contradict each other.

[0061] (1) In the first embodiment, the electrolyte supplied to the pH sensor 54 via the second supply line 51 is collected in the storage tank 10. However, a configuration in which all or part of the electrolyte supplied to the pH sensor 54 via the second supply line 51 is discharged to the outside is also conceivable. For example, a configuration in which the end of the second supply line 51 downstream of the pH sensor 54 is not connected to the storage tank 10 and the electrolyte is discharged to the outside, or a configuration in which the piping of the second supply line 51 downstream of the pH sensor 54 branches into an end connected to the storage tank 10 and an end that discharges the electrolyte to the outside are conceivable.

[0062] (2) In the first embodiment, the pure water supply line 61 connects the pure water tank 63 and the storage tank 10. However, the supply destination of the pure water stored in the pure water tank 63 is not limited to this as long as the pure water can be supplied to the electrolyte. For example, a configuration is envisioned in which the pure water supply line 61 connects the upstream side of the pH sensor 54 in the second supply line 51. When pure water is supplied in this configuration, the second supply line 51 and the pH sensor 54 can be cleaned.

[0063] (3) In the first embodiment, the pH sensor 54 is positioned vertically above the liquid level in the storage tank 10. However, this is not limited to a configuration in which the pH sensor 54 does not come into contact with the electrolyte as long as the pH sensor 54 does not come into contact with the electrolyte when the supply of the electrolyte to the pH sensor 54 via the second supply line 51 is stopped. For example, a configuration in which the second supply line 51 is filled with compressed air, nitrogen gas, or other gas to recover the electrolyte in the storage tank 10, or a configuration in which the electrolyte in the second supply line 51 is sucked by a pump and recovered in the storage tank 10, etc. are conceivable.

[0064] (4) In the first embodiment, the electrolytic solution supplied to the pH sensor 54 via the second supply line 51 transfers and dissipates heat to the piping or the like with which it is in contact. Therefore, the second temperature of the electrolytic solution supplied to the pH sensor 54 via the second supply line 51 is lower than the first temperature of the electrolytic solution supplied to the water electrolysis cell 20 via the first supply line 41. However, the amount of heat dissipated by the electrolytic solution in the second supply line 51 is affected by the environment in which the second supply line 51 is installed, the length or material of the second supply line 51, and the like. Therefore, there is a possibility that the second temperature and the first temperature will be almost the same.

[0065] To ensure that the second temperature is lower than the first temperature, a cooling device may be installed, for example, in a section of the second supply line 51 upstream of the pH sensor 54 or in the storage tank 10. The cooling device can control the second temperature to a temperature suitable for suppressing deterioration of the pH sensor 54. That is, the second temperature can be reliably kept lower than the first temperature. Therefore, compared to the first embodiment, the effect of suppressing deterioration of the pH sensor 54 due to contact with the high-temperature electrolyte is more pronounced. Examples of types of cooling devices include an air-cooled heat exchanger and a plate-type heat exchanger. However, the type of cooling device is arbitrary and is not limited to the above examples.

[0066] (5) In the first embodiment, the calculation unit 82 calculates the component concentration. However, the index (hereinafter referred to as the "concentration index") calculated by the calculation unit 82 is not limited to the component concentration itself. The concentration index includes, for example, the component concentration itself as well as an index that changes in conjunction with the component concentration. The index that changes in conjunction with the component concentration is, for example, an index that changes stepwise, linearly, or logarithmically with respect to the component concentration.

[0067] (6) In the first embodiment, the correction unit 85 calculated the component concentration according to the pH measured by the pH sensor 54 and corrected the component concentration calculated by the calculation unit 82. However, correction according to pH is not limited to correction by the correction unit 85 using the component concentration calculated from the measured pH to change the component concentration calculated by the calculation unit 82. For example, it is possible to calculate the corrected concentration index using an arithmetic expression that includes, as variables, the measured pH value and the pre-correction concentration index calculated by the calculation unit 82, or to correct the pH corresponding to the pre-correction concentration index according to the measured pH value and calculate the corrected concentration index according to the corrected pH.

[0068] (7) In the first embodiment, the control device 80 (calculation unit 82) calculates the component concentrations from the current values, and then the control device 80 (calculation unit 82) calculates the correction values ​​from the measured pH values. However, the order in which the correction value calculation process and the component concentration calculation process are performed may be changed. Specifically, the correction value calculation process and the component concentration calculation process may be performed in parallel, or the correction value calculation process may be performed before the component concentration calculation process.

[0069] (8) In the first embodiment, Configuration A: A configuration in which a first supply line 41 for supplying the electrolyte from the storage tank 10 to the water electrolysis cell 20 and a second supply line 51 for supplying the electrolyte from the storage tank 10 to the pH sensor 54 are separately provided. Configuration B: A configuration in which a concentration index (e.g., a component concentration) of the electrolyte is calculated from the current value flowing through the water electrolysis cell 20. The following example shows that Feature A and Feature B can exist independently. Therefore, Feature A and Feature B do not require the other.

[0070] For example, in configuration A, the component concentrations of the electrolyte solution can be calculated from the pH measured by a pH sensor 54 provided midway through the second supply line 51. That is, configuration B is not essential to the first embodiment, and a configuration in which the control system 70 (calculation unit 82) is omitted is also conceivable. For example, a configuration in which water replenishment is controlled in accordance with the measured pH value of the electrolyte solution supplied to the pH sensor 54 via the second supply line 51 is conceivable.

[0071] Furthermore, in configuration B, the component concentrations of the electrolyte solution can be measured without using the pH sensor 54. In configuration B, the component concentrations of the electrolyte solution are measured from the current value, so the pH sensor 54 that measures the pH of the electrolyte solution is not essential. However, the current value is subject to measurement errors depending on the measuring instrument. Therefore, by measuring the pH of the electrolyte solution using the pH sensor 54, calculating a correction value using the measured pH, and then correcting the component concentrations calculated from the current value using the correction value, it is possible to more accurately control rehydration.

[0072] (9) The term "nth" (n is a natural number) in this application is used only as a formal and convenient label to distinguish each element in the description and does not have any substantive meaning. Therefore, there is no room for restrictive interpretation of the position of each element or the order of manufacture, etc., based on the term "nth."

[0073] C: Notes From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0074] A water electrolysis system according to one aspect (Aspect 1) of the present disclosure includes a water electrolysis cell that electrolyzes an electrolyte solution, a storage tank that stores the electrolyte solution, a first supply line that supplies the electrolyte solution from the storage tank to the water electrolysis cell, a pH sensor that measures the pH of the electrolyte solution, and a second supply line that is separate from the first supply line and supplies the electrolyte solution from the storage tank to the pH sensor. In this aspect, water electrolysis is achieved by supplying the electrolyte solution to the water electrolysis cell via the first supply line. Meanwhile, the pH of the electrolyte solution can be measured by supplying the electrolyte solution to the pH sensor via the second supply line. In other words, because the electrolyte solution is supplied to the pH sensor via the second supply line that is separate from the first supply line for water electrolysis, it is not necessary to bring the electrolyte solution into contact with the pH sensor during the process of supplying the electrolyte solution for water electrolysis from the storage tank to the water electrolysis cell. This eliminates deterioration of the pH sensor due to contact with the electrolyte solution.

[0075] In a specific example (Aspect 2) of Aspect 1, the pH sensor is provided above the storage tank, and when the supply of electrolyte from the storage tank to the pH sensor is stopped, the electrolyte does not come into contact with the pH sensor. In this aspect, since the pH sensor is provided above the storage tank, it is easy to maintain the liquid level of the electrolyte in the second supply line at a position lower than the pH sensor. Therefore, contact of the electrolyte with the pH sensor can be easily prevented.

[0076] A specific example (Aspect 3) of Aspect 1 or Aspect 2 further includes a valve device installed in the second supply line and configured to switch on and off supply of the electrolyte to the pH sensor via the second supply line, wherein a first duration of water electrolysis using the electrolyte supplied to the water electrolysis cell via the first supply line exceeds a second duration of supply of the electrolyte to the pH sensor via the second supply line. In this aspect, switching on and off supply of the electrolyte using the valve device limits the duration of supply of the electrolyte to the pH sensor via the second supply line. Therefore, the duration of contact of the electrolyte with the pH sensor is reduced compared to a configuration in which the pH sensor is installed in the first supply line (i.e., a configuration in which the electrolyte is also supplied to the pH sensor throughout the entire duration in which the electrolyte is supplied to the water electrolysis cell via the first supply line). This significantly reduces the aforementioned effect of suppressing deterioration of the pH sensor due to contact with the electrolyte.

[0077] In a specific example (Aspect 4) of any of Aspects 1 to 3, the second temperature of the electrolyte solution supplied to the pH sensor via the second supply line is lower than the first temperature of the electrolyte solution supplied to the water electrolysis cell via the first supply line. In the above aspects, the second temperature of the electrolyte solution in contact with the pH sensor is lower than the first temperature of the electrolyte solution supplied to the water electrolysis sensor. Therefore, the temperature of the electrolyte solution in contact with the pH sensor is lower, thereby suppressing deterioration of the pH sensor.

[0078] A specific example (Aspect 5) according to Aspect 4 further includes an acquisition unit that acquires a value of a current flowing through the water electrolysis cell for water electrolysis, and a calculation unit that calculates, from the current value, a concentration index corresponding to the component concentration of the electrolyte solution. In this aspect, the concentration index corresponding to the component concentration of the electrolyte solution is calculated using the value of the current flowing during water electrolysis. In this configuration, the component concentration of the electrolyte solution is not measured using a pH sensor. In other words, there is no need to bring the pH sensor into contact with the electrolyte solution during the water electrolysis process. This prevents deterioration of the pH sensor.

[0079] In a specific example (Aspect 6) according to Aspect 5, a water replenishment unit is further provided that controls the replenishing of water into the storage tank in accordance with the concentration index. In the above aspect, the electrolyte concentration index is used for the control of the replenishing of water into the storage tank. Therefore, the storage tank can be replenished with water in accordance with the concentration index without a user's instruction.

[0080] In a specific example (Aspect 7) according to Aspect 5 or Aspect 6, the device further includes a correction unit that corrects the concentration index calculated by the calculation unit in accordance with the pH measured by the pH sensor. In the above aspects, the concentration index calculated by the calculation unit can be corrected in accordance with the pH measured by the pH sensor. Therefore, the concentration index calculated from the current value can be corrected to the actually measured component concentration.

[0081] A water electrolysis method according to one embodiment (embodiment 8) of the present disclosure uses a water electrolysis system including a water electrolysis cell that electrolyzes an electrolyte solution, a storage tank that stores the electrolyte solution, and a pH sensor that measures the pH of the electrolyte solution. The electrolyte solution is supplied from the storage tank to the water electrolysis cell via a first supply line, and from the storage tank to the pH sensor via a second supply line separate from the first supply line. In this embodiment, water electrolysis is achieved by supplying the electrolyte solution to the water electrolysis cell via the first supply line. Meanwhile, the pH of the electrolyte solution can be measured by supplying the electrolyte solution to the pH sensor via the second supply line. In other words, because the electrolyte solution is supplied to the pH sensor via the second supply line separate from the first supply line for water electrolysis, it is not necessary to bring the electrolyte solution into contact with the pH sensor during the process of supplying the electrolyte solution for water electrolysis from the storage tank to the water electrolysis cell. This eliminates deterioration of the pH sensor due to contact with the electrolyte solution.

[0082] However, a water electrolysis system has a problem in that a pH sensor is required to measure a concentration index (e.g., a component concentration). The pH sensor deteriorates when exposed to an electrolyte solution with a high component concentration for a long period of time. In consideration of the above, one aspect of the present disclosure aims to calculate a concentration index without using a pH sensor.

[0083] In order to solve the above problems, a water electrolysis system according to one aspect of the present disclosure includes a water electrolysis cell that electrolyzes an electrolytic solution, an acquisition unit that acquires a value of a current flowing through the water electrolysis cell for water electrolysis, and a calculation unit that calculates, from the current value, concentration indexes corresponding to concentrations of components in the electrolytic solution. [Explanation of symbols]

[0084] 10...storage tank, 20...water electrolysis cell, 21...electrolyte membrane, 22...anode section, 23...cathode section, 30...power supply, 31...gas-liquid separator, 32...gas-liquid separator, 40...circulation unit, 41...first supply line, 42...first supply pump, 43...heater, 50...measuring unit, 51...second supply line, 52...second supply pump, 53...valve device, 54...pH sensor, 60...pure water supply device, 61...pure water supply line, 62...pure water pump, 63...pure water tank, 70...control system, 80...control device, 81...acquisition section, 82...calculation section, 83...water replenishment section, 84...supply section, 85...correction section, 90...storage device, 100...water electrolysis system.

Claims

1. a water electrolysis cell for electrolyzing an electrolyte; a storage tank for storing an electrolyte; a first supply line for supplying the electrolyte from the storage tank to the water electrolysis cell; a pH sensor for measuring the pH of the electrolyte; a second supply line that is separate from the first supply line and supplies the electrolyte from the storage tank to the pH sensor; A water electrolysis system equipped with

2. The pH sensor is provided above the storage tank, When the supply of the electrolyte from the storage tank to the pH sensor is stopped, the electrolyte does not come into contact with the pH sensor. The water electrolysis system according to claim 1.

3. The pH sensor further includes a valve device that is installed in the second supply line and that switches between supplying and stopping the electrolyte solution to the pH sensor via the second supply line. a first time length during which water electrolysis is performed using the electrolyte solution supplied to the water electrolysis cell via the first supply line exceeds a second time length during which the electrolyte solution is supplied to the pH sensor via the second supply line; The water electrolysis system according to claim 1 or 2.

4. A second temperature of the electrolyte solution supplied to the pH sensor via the second supply line is lower than a first temperature of the electrolyte solution supplied to the water electrolysis cell via the first supply line. The water electrolysis system according to claim 1.

5. an acquisition unit that acquires a value of a current flowing through the water electrolysis cell for water electrolysis; a calculation unit that calculates a concentration index corresponding to the component concentration of the electrolyte solution from the current value; The water electrolysis system of claim 1 further comprising:

6. The water electrolysis system according to claim 5 , further comprising a water replenishment unit that controls the replenishment of water into the storage tank in accordance with the concentration index.

7. The water electrolysis system of claim 5 or 6, further comprising a correction unit that corrects the concentration index calculated by the calculation unit in accordance with the pH measured by the pH sensor.

8. a water electrolysis cell for electrolyzing an electrolyte; a storage tank for storing an electrolyte; A pH sensor that measures the pH of the electrolyte A water electrolysis method using a water electrolysis system comprising: supplying an electrolyte from the storage tank to the water electrolysis cell via a first supply line; The electrolyte is supplied from the storage tank to the pH sensor via a second supply line separate from the first supply line. Water electrolysis method.

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