Water electrolysis system

Abstract

To provide a water electrolysis system capable of suppressing further deterioration of an electrolyte membrane.SOLUTION: A water electrolysis system including a hydrogen electrode, an oxygen electrode, and an electrolyte membrane located between the hydrogen electrode and the oxygen electrode includes a deterioration detection unit that detects a deterioration state of the electrolyte membrane, and a hydrogen pressure adjustment unit that adjusts at least one of an increase rate of a pressure of hydrogen generated at the hydrogen electrode and an upper limit value of the pressure according to the detected deterioration state when the water electrolysis system is started.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a water electrolysis system. [Background technology]

[0002] Various technologies have been proposed to suppress deterioration of electrolyte membranes in water electrolysis systems that produce oxygen and hydrogen by electrolyzing water. For example, Patent Document 1 discloses a system in which hydrogen is pressurized at a slower rate when the water retention rate of the electrolyte membrane is low than when the water retention rate is high. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-062311 Summary of the Invention [Problem to be solved by the invention]

[0004] The water retention rate of the electrolyte membrane may increase as a result of deterioration of the electrolyte membrane and a decrease in its molecular weight. In such a case, if hydrogen pressure is increased as in Patent Document 1, the hydrogen pressure is increased at a relatively high rate despite the deterioration of the electrolyte membrane, which may further deteriorate the electrolyte membrane. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to one aspect of the present disclosure, there is provided a water electrolysis system including a hydrogen electrode, an oxygen electrode, and an electrolyte membrane located between the hydrogen electrode and the oxygen electrode, the water electrolysis system including a deterioration detection unit that detects a deterioration state of the electrolyte membrane, and a hydrogen pressure adjustment unit that, upon startup of the water electrolysis system, adjusts at least one of a rate of increase in pressure of hydrogen generated at the hydrogen electrode and an upper limit of the pressure, depending on the detected deterioration state. In this water electrolysis system, the hydrogen pressure adjustment unit adjusts at least one of the rate of increase in the pressure of generated hydrogen and the upper limit of the hydrogen pressure in accordance with the deterioration state of the electrolyte membrane. This allows the stress applied to the electrolyte membrane to be set within an appropriate range in accordance with the deterioration state, thereby suppressing further deterioration of the electrolyte membrane.

[0007] The present disclosure may be realized in various forms other than a water electrolysis system, such as a hydrogen pressure adjustment method, a program for executing the method, or the like. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram showing a schematic configuration of a water electrolysis system according to an embodiment of the present disclosure. FIG. [Figure 2] 4 is a flowchart showing a procedure for hydrogen pressure regulation control executed by the system. [Figure 3] 10 is a flowchart showing the procedure for hydrogen pressure regulation control in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. First embodiment: FIG. 1 is a block diagram showing a schematic configuration of a water electrolysis system 1 (hereinafter also referred to as "system 1") according to one embodiment of the present disclosure. The system 1 is used to electrolyze water to obtain hydrogen and oxygen. The water electrolysis system 1 includes a water electrolysis stack 100, a power source P, a cell monitor 150, a water supply unit 200, an oxygen discharge unit 300, a hydrogen discharge unit 400, and a control device 500.

[0010] The water electrolysis stack 100 includes multiple stacked water electrolysis cells 110. Each water electrolysis cell 110 includes an electrolyte membrane, a hydrogen electrode, and an oxygen electrode. The electrolyte membrane is made of a polymer material having ion exchange groups. The electrolyte membrane is located between the hydrogen electrode and the oxygen electrode. The hydrogen electrode catalyzes a reaction that produces hydrogen from protons and electrons. The oxygen electrode catalyzes a reaction that produces oxygen, protons, and electrons from water. Known catalysts are used for the hydrogen electrode and the oxygen electrode.

[0011] The power supply P supplies power to the water electrolysis stack 100. The current value of the power supply P is transmitted to the control device 500, which will be described later.

[0012] The cell monitor 150 monitors the voltage of one or more water electrolysis cells 110 to detect possible malfunctions in the water electrolysis cells 110 .

[0013] The water supply unit 200 supplies water to the oxygen electrode of the water electrolysis cell 110. The water supply unit 200 includes a water tank 210, an oxygen-gas-liquid separator 220, a pump 230, and an ion separator 240. The water supply unit 200 also includes a water supply flow path 205 and a first circulation flow path 225 as water flow paths. The water supply flow path 205 connects the water tank 210 and the oxygen-gas-liquid separator 220. The first circulation flow path 225 connects the oxygen-gas-liquid separator 220 and the water electrolysis stack 100.

[0014] The water tank 210 contains water to be used for electrolysis. The water in the water tank 210 is supplied to the oxygen gas-liquid separator 220 via the water supply passage 205.

[0015] The oxygen-gas-liquid separator 220 stores gas and water and separates the gas and water from each other. The oxygen-gas-liquid separator 220 separates the water supplied from the water tank 210 from the gas and supplies the water to the pump 230 via the first circulation flow path 225. The oxygen-gas-liquid separator 220 is also a part of the configuration of the oxygen discharge unit 300, which will be described later.

[0016] The pump 230 is provided in the first circulation flow path 225 and pumps the water supplied from the oxygen gas-liquid separator 220 toward the water electrolysis stack 100.

[0017] The ion separator 240 is provided downstream of the pump 230 in the first circulation flow path 225. The ion separator 240 reduces ions as impurities contained in the supplied water. The ion separator 240 supplies the water with reduced ions to the water electrolysis stack 100.

[0018] The oxygen discharge unit 300 discharges oxygen produced by a reaction at the oxygen electrode of the water electrolysis cell 110 to the outside of the system 1. The oxygen discharge unit 300 also discharges cross-leaked hydrogen to the outside of the system 1. Cross-leaking refers to the movement of some of the hydrogen produced at the hydrogen electrode side through the electrolyte membrane to the oxygen electrode side. Furthermore, the oxygen discharge unit 300 circulates at least a portion of the water not consumed at the oxygen electrode.

[0019] The oxygen discharge unit 300 includes an oxygen gas-liquid separator 220 and a hydrogen sensor 310. The oxygen discharge unit 300 also includes a second circulation flow path 305 as a flow path, and an oxygen discharge flow path 315 as a discharge path for oxygen and cross-leaked hydrogen. The second circulation flow path 305 connects the water electrolysis stack 100 and the oxygen gas-liquid separator 220. One end of the oxygen discharge flow path 315 is connected to the oxygen gas-liquid separator 220.

[0020] The oxygen gas-liquid separator 220 separates the oxygen and hydrogen from the water supplied via the second circulation flow path 305. The separated oxygen and hydrogen are supplied to the hydrogen sensor 310.

[0021] The hydrogen sensor 310 is provided in the oxygen discharge flow path 315. The hydrogen sensor 310 measures the hydrogen concentration and transmits the measured hydrogen concentration to the control device 500, which will be described later. The hydrogen sensor 310 is used to measure the amount of hydrogen that cross-leaks from the hydrogen electrode side to the oxygen electrode side. In this embodiment, the hydrogen sensor 310 measures the ratio of the volume of hydrogen to the total volume of oxygen and hydrogen. The oxygen and hydrogen supplied to the hydrogen sensor 310 are released to the outside of the system 1 via the other end of the oxygen discharge flow path 315.

[0022] The hydrogen discharge unit 400 discharges hydrogen produced at the hydrogen electrode of the water electrolysis cell 110. The hydrogen discharge unit 400 includes a pressure regulating valve 410 and a hydrogen gas-liquid separator 420. The hydrogen discharge unit 400 also includes flow paths: a hydrogen pressure adjustment flow path 405 and a hydrogen discharge flow path 415. The hydrogen pressure adjustment flow path 405 connects the water electrolysis stack 100 and the hydrogen gas-liquid separator 420. One end of the hydrogen discharge flow path 415 is connected to the hydrogen gas-liquid separator 420.

[0023] The pressure regulating valve 410 adjusts the pressure of hydrogen produced in the water electrolysis stack 100. The pressure regulating valve 410 is provided in the hydrogen pressure regulating flow path 405. The opening and closing of the pressure regulating valve 410 is controlled by the control device 500, which will be described later.

[0024] The hydrogen gas-liquid separator 420 separates the hydrogen supplied via the hydrogen pressure adjustment flow path 405 from the water contained in the hydrogen. The separated hydrogen is discharged to the outside of the system 1 via the other end of the hydrogen discharge flow path 415.

[0025] The control device 500 is configured as a computer including a CPU 510 and a memory 520. The CPU 510 executes a control program stored in the memory 520, thereby causing a deterioration detection unit 511 and a hydrogen pressure adjustment unit 512 to function.

[0026] The degradation detection unit 511 detects the degradation state of the electrolyte membrane of the water electrolysis stack 100. In this embodiment, the degradation state of the electrolyte membrane is detected by determining whether the hydrogen concentration transmitted from the hydrogen sensor 310 is equal to or greater than a predetermined threshold. This utilizes the correlation between the degradation state of the electrolyte membrane and the hydrogen concentration. Specifically, as the degradation of the electrolyte membrane progresses, the number of thinned portions of the electrolyte membrane increases, and the amount of cross-leakage of hydrogen increases. Therefore, it is considered that the higher the hydrogen concentration, the greater the degree of degradation of the electrolyte membrane. The threshold is set, for example, as the hydrogen concentration when water electrolysis is performed at a predetermined current value using an electrolyte membrane with a moderate degree of degradation. Therefore, if the hydrogen concentration is equal to or greater than the threshold, it is inferred that the degree of degradation of the electrolyte membrane is greater than moderate.

[0027] It is preferable to set multiple thresholds corresponding to the multiple current values ​​used for water electrolysis. This is because there is a correlation between the current value and the hydrogen concentration. Specifically, the larger the current value, the smaller the hydrogen concentration. This is because water electrolysis is performed at a large current value, generating more oxygen at the oxygen electrode, which causes the oxygen to react with cross-leaked hydrogen and consumes more hydrogen. Therefore, it is preferable that the deterioration detection unit 511 set a threshold using the current value transmitted from the power source P and detect the deterioration state of the electrolyte membrane by comparing the hydrogen concentration transmitted from the hydrogen sensor 310 with the threshold. The correspondence between the current value and the threshold is pre-stored in the memory 520.

[0028] The hydrogen pressure adjustment unit 512 adjusts at least one of the rate of increase in the pressure of hydrogen generated at the hydrogen electrode and the upper limit of the pressure, depending on the deterioration state detected by the deterioration detection unit 511. This adjustment is achieved by the hydrogen pressure adjustment unit 512 controlling the opening and closing of the pressure adjustment valve 410. In this embodiment, when the deterioration detection unit 511 determines that the hydrogen concentration has exceeded the threshold value, the hydrogen pressure adjustment unit 512 controls the pressure adjustment valve 410 so that at least one of the rate of increase in the hydrogen pressure and the upper limit of the pressure at the next or subsequent startup of the system 1 is smaller than that at the current operation of the system 1.

[0029] 2 is a flowchart showing the procedure for hydrogen pressure regulation control executed by the system 1. The hydrogen pressure regulation control is performed when the system 1 is started up or during its operation.

[0030] The hydrogen sensor 310 measures the hydrogen concentration (S100). The measured hydrogen concentration is transmitted to the deterioration detection unit 511 of the control device 500. The deterioration detection unit 511 determines whether the hydrogen concentration is equal to or greater than a predetermined threshold (S110). If the hydrogen concentration is equal to or greater than the predetermined threshold (S110: Yes), the hydrogen pressure adjustment unit 512 controls the pressure adjustment valve 410 so that at least one of the hydrogen pressure increase rate and the pressure upper limit value when the system 1 is started up next or thereafter is smaller than during the current operation of the system 1 (S120). If the hydrogen concentration is not equal to or greater than the predetermined threshold (S110: No), the hydrogen pressure adjustment control ends.

[0031] The hydrogen pressure regulation control may be performed repeatedly during the operation of the system 1. Alternatively, the hydrogen pressure regulation control may be performed periodically according to a predetermined schedule. For example, the hydrogen pressure regulation control may be performed once every 12 hours.

[0032] According to the system 1 of the first embodiment described above, at least one of the hydrogen pressure increase rate and the upper limit of the pressure is adjusted in accordance with the degradation state of the electrolyte membrane, so that the stress applied to the electrolyte membrane can be set within an appropriate range depending on the degradation state, thereby suppressing further degradation of the electrolyte membrane. Specifically, when the amount of hydrogen cross leakage exceeds a predetermined threshold, the hydrogen pressure adjustment unit 512 controls the pressure adjustment valve 410 so that at least one of the hydrogen pressure increase rate and the upper limit of the hydrogen pressure is reduced compared to the current operation of the system 1. Therefore, when it is predicted that the electrolyte membrane is deteriorating, the stress applied to the electrolyte membrane can be reduced, thereby suppressing further degradation of the electrolyte membrane.

[0033] The reason why the stress applied to the electrolyte membrane is reduced by reducing the rate of pressure rise is because the electrolyte membrane has viscoelasticity. Viscoelastic electrolyte membranes have the property that their deformation behavior changes depending on the rate of deformation. In other words, by reducing the rate of hydrogen pressure rise relatively, the stress applied to the electrolyte membrane can be made relatively small.

[0034] B. Second embodiment: 3 is a flowchart showing the procedure for hydrogen pressure regulation control in the second embodiment. The system of the second embodiment differs from the detection method of the first embodiment in the method for detecting the deterioration state of the electrolyte membrane by the deterioration detection unit 511. Other points in the system of the second embodiment are the same as those in the system of the first embodiment, and therefore description thereof will be omitted.

[0035] The deterioration detection unit 511 detects the deterioration state using the number of times the system 1 is started and stopped (hereinafter also referred to as the "number of operations") and the total operating time instead of the hydrogen concentration. Specifically, the deterioration detection unit 511 detects whether the sum of the ratio of the number of operations to the lifetime number of operations and the ratio of the total operating time to the lifetime operating time exceeds a predetermined life value. The lifetime number of operations and the lifetime operating time are predetermined arbitrary times and are pre-stored in the memory 520. The lifetime value is a predetermined arbitrary value and is pre-stored in the memory 520. In this embodiment, the life value is 1.8. The number of operations and the total operating time may be measured by the deterioration detection unit 511 or may be measured using another measuring device.

[0036] As shown in FIG. 3, in the hydrogen pressure regulation control of the second embodiment, the deterioration detection unit 511 acquires the number of operations (S200). The deterioration detection unit 511 also acquires the total operation time (S210). Regarding the processes of S200 and S210, S200 may be performed after S210, or S200 and S210 may be performed in parallel. The deterioration detection unit 511 determines whether the sum of the ratio of the number of operations to the lifetime operation number and the ratio of the total operation time to the lifetime operation time exceeds the lifetime value of 1.8 (S220). If the sum of the ratio of the total operation time to the lifetime operation time exceeds the lifetime value of 1.8 (S220: Yes), the hydrogen pressure regulation unit 512 controls the pressure regulation valve 410 to reduce at least one of the hydrogen pressure increase rate and the pressure upper limit value when the system 1 is started up next or thereafter (S230). If the sum of the ratio of the total operating time to the lifetime operating time does not exceed the lifetime value of 1.8 (S220: No), the hydrogen pressure regulation control is terminated.

[0037] According to the system of the second embodiment described above, the deterioration detection unit 511 detects the deterioration state using the number of times the system 1 is operated and the total operating time, so that the pressure applied to the electrolyte membrane can be reduced according to the number of times the system is operated and the total operating time, thereby suppressing further deterioration of the electrolyte membrane.

[0038] C. Other Embodiments: (C1) In the above embodiment, the hydrogen pressure regulator 512 controlled the pressure regulator valve 410 to reduce at least one of the hydrogen pressure increase rate and the pressure upper limit value when the system 1 is started up next time onwards, but the present disclosure is not limited to this. The hydrogen pressure regulator 512 may control the pressure regulator valve 410 at any timing. For example, the hydrogen pressure regulator 512 may control the pressure regulator valve 410 while the system 1 is operating.

[0039] (C2) In the first embodiment, when the deterioration detection unit 511 determines that the hydrogen concentration is equal to or greater than a threshold, a notification may be issued suggesting replacement of the water electrolysis stack 100. In the second embodiment, when the deterioration detection unit 511 determines that the sum of the ratio of the total operating time to the lifetime operating time exceeds the lifetime value, a notification may be issued suggesting replacement of the water electrolysis stack 100.

[0040] (C3) In the first embodiment, a plurality of water electrolysis stacks 100 may be used. In such a configuration, one oxygen gas-liquid separator 220 and one hydrogen sensor 310 may be used for the plurality of water electrolysis stacks 100. By applying the control device 500 described above to such a configuration, it is possible to detect the deterioration state of the electrolyte membrane in at least one of the plurality of water electrolysis stacks 100. Furthermore, by monitoring fluctuations in the voltage value of the cell monitor 150 in combination with the use of the control device 500, it is possible to identify which of the plurality of water electrolysis stacks 100 is more deteriorated.

[0041] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0042] 1...water electrolysis system, 100...water electrolysis stack, 110...water electrolysis cell, 150...cell monitor, 200...water supply unit, 205...water supply flow path, 210...water tank, 220...oxygen gas-liquid separator, 225...first circulation flow path, 230...pump, 240...ion separator, 300...oxygen discharge unit, 305...second circulation flow path, 310...hydrogen sensor, 315...oxygen discharge flow path, 400...hydrogen discharge unit, 405...hydrogen pressure adjustment flow path, 410...pressure adjustment valve, 415...hydrogen discharge flow path, 420...hydrogen gas-liquid separator, 500...control device, 510...CPU, 511...deterioration detection unit, 512...hydrogen pressure adjustment unit, 520...memory, P...power supply

Claims

[Claim 1] A water electrolysis system having a hydrogen electrode, an oxygen electrode, and an electrolyte membrane located between the hydrogen electrode and the oxygen electrode, a deterioration detection unit that detects a deterioration state of the electrolyte membrane; a hydrogen pressure adjusting unit that adjusts at least one of a rate of increase in the pressure of hydrogen generated at the hydrogen electrode and an upper limit of the pressure, in accordance with the detected deterioration state, at the time of startup of the water electrolysis system; A water electrolysis system comprising:

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