Water electrolysis system

Abstract

Provided is a water electrolysis system capable of suppressing further deterioration of an electrolyte membrane. The water electrolysis system has a hydrogen electrode, an oxygen electrode, and an electrolyte membrane positioned between the hydrogen electrode and the oxygen electrode, and is further provided with: a deterioration detection unit for detecting the deterioration state of the electrolyte membrane; and a hydrogen pressure regulating unit that, when the water electrolysis system is started, regulates at least one of the rate of increase in the pressure of hydrogen generated in the hydrogen electrode and the upper limit value of the pressure on the basis of the detected deterioration condition.

Description

Technical Field

[0001] This disclosure relates to a water electrolysis system. Background Technology

[0002] In water electrolysis systems that electrolyze water to produce oxygen and hydrogen, various techniques for suppressing the degradation of the electrolyte membrane have been proposed. For example, Patent Document 1 discloses a system that pressurizes hydrogen at a slower rate than when the water retention rate of the electrolyte membrane is high, even when the water retention rate is low.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2014-062311

[0004] Electrolyte membrane deterioration leads to a decrease in its molecular weight, resulting in an increase in its water retention capacity. In such cases, if hydrogen pressure control is implemented as in Patent Document 1, hydrogen pressure will still increase at a relatively high rate despite the deterioration of the electrolyte membrane, potentially causing further deterioration. Summary of the Invention

[0005] This disclosure can be implemented in the following ways.

[0006] According to one aspect of this disclosure, a water electrolysis system is provided, comprising a hydrogen electrode, an oxygen electrode, and an electrolyte membrane located between the hydrogen electrode and the oxygen electrode. The water electrolysis system further comprises: a degradation detection unit for detecting the degradation status of the electrolyte membrane; and a hydrogen pressure regulating unit, which, upon startup of the water electrolysis system, adjusts at least one of the rate of increase of the hydrogen pressure generated in the hydrogen electrode and an upper limit value of the pressure based on the detected degradation status.

[0007] According to this water electrolysis system, the hydrogen pressure regulating unit adjusts at least one of the rising rate of the generated hydrogen pressure and the upper limit of the hydrogen pressure based on the deterioration condition of the electrolyte membrane. Therefore, the stress applied to the electrolyte membrane can be set to an appropriate range corresponding to the deterioration condition, thereby suppressing further deterioration of the electrolyte membrane.

[0008] This disclosure can be implemented in various ways other than water electrolysis systems. For example, it can be implemented by methods of hydrogen pressure regulation, programs for performing such methods, etc. Attached Figure Description

[0009] Figure 1 This is a block diagram illustrating the general structure of a water electrolysis system according to one aspect of this disclosure.

[0010] Figure 2 This is a flowchart illustrating the steps of hydrogen pressure regulation control performed by the system.

[0011] Figure 3This is a flowchart illustrating the steps of hydrogen pressure regulation control in the second embodiment.

[0012] Explanation of reference numerals in the attached figures

[0013] 1: Water electrolysis system; 100: Water electrolysis reactor; 110: Water electrolysis chamber; 150: Chamber monitor; 200: Water supply unit; 205: Water supply path; 210: Water tank; 220: Oxygen-liquid separator; 225: First circulation path; 230: Pump; 240: Ion separator; 300: Oxygen discharge unit; 305: Second circulation path; 310: Hydrogen sensor; 315: Oxygen discharge path; 400: Hydrogen discharge unit; 405: Hydrogen pressure regulating path; 410: Pressure regulating valve; 415: Hydrogen discharge path; 420: Hydrogen-liquid separator; 500: Control device; 510: CPU; 511: Deterioration detection unit; 512: Hydrogen pressure regulating unit; 520: Memory; P: Power supply. Detailed Implementation

[0014] A. First implementation method:

[0015] Figure 1 This is a block diagram of the schematic structure of a water electrolysis system 1 (hereinafter also referred to as "System 1") according to one embodiment of the present disclosure. System 1 is used to electrolyze water to obtain hydrogen and oxygen. The water electrolysis system 1 includes a water electrolysis reactor 100, a power supply P, a chamber monitor 150, a water supply unit 200, an oxygen discharge unit 300, a hydrogen discharge unit 400, and a control device 500.

[0016] The water electrolysis reactor 100 includes multiple stacked water electrolysis chambers 110. Each water electrolysis chamber 110 has an electrolyte membrane, a hydrogen electrode, and an oxygen electrode. The electrolyte membrane is made of a polymer material with ion-exchange groups. The electrolyte membrane is located between the hydrogen electrode and the oxygen electrode. The hydrogen electrode catalyzes the reaction from protons and electrons to produce hydrogen. The oxygen electrode catalyzes the reaction from water to produce oxygen, protons, and electrons. Known catalysts are used at both the hydrogen and oxygen electrodes.

[0017] Power source P supplies electricity to the water electrolysis reactor 100. The current value in the power supply from power source P is transmitted to the control device 500, which will be described later.

[0018] The cell monitor 150 detects potential adverse conditions in the water electrolysis cell 110 by monitoring the voltage of one or more water electrolysis cells 110.

[0019] The water supply unit 200 supplies water to the oxygen electrode of the water electrolysis chamber 110. The water supply unit 200 includes a water tank 210, an oxygen-liquid separator 220, a pump 230, and an ion separator 240. Furthermore, the water supply unit 200 includes a water supply path 205 and a first circulation path 225 as water flow paths. The water supply path 205 connects the water tank 210 to the oxygen-liquid separator 220. The first circulation path 225 connects the oxygen-liquid separator 220 to the water electrolysis reactor 100.

[0020] Water tank 210 contains water for electrolysis. Water in water tank 210 is supplied to oxygen-liquid separator 220 via water supply path 205.

[0021] The oxygen-liquid separator 220 collects gas and water and separates them from each other. The oxygen-liquid separator 220 separates the water supplied from the water tank 210 from the gas and supplies it to the pump 230 via the first circulation path 225. The oxygen-liquid separator 220 is also part of the structure of the oxygen discharge section 300, described later.

[0022] Pump 230 is located in the first circulation path 225 and sends water supplied from oxygen liquid separator 220 to water electrolysis reactor 100.

[0023] Ion separator 240 is located downstream of pump 230 in the first circulation path 225. Ion separator 240 reduces the number of ions that are impurities in the supplied water. Ion separator 240 supplies the ion-reduced water to water electrolysis reactor 100.

[0024] The oxygen discharge unit 300 discharges oxygen generated by the reaction at the oxygen electrode of the water electrolysis chamber 110 to the outside of system 1. Additionally, the oxygen discharge unit 300 discharges cross-leaked hydrogen to the outside of system 1. Cross-leaking refers to the situation where a portion of the hydrogen generated on the hydrogen electrode side moves 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.

[0025] The oxygen discharge section 300 includes an oxygen-liquid separator 220 and a hydrogen sensor 310. Additionally, the oxygen discharge section 300 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 electrolyzer 100 to the oxygen-liquid separator 220. One end of the oxygen discharge flow path 315 is connected to the oxygen-liquid separator 220.

[0026] The oxygen-liquid separator 220 separates oxygen and hydrogen from water supplied via the second circulation path 305. The separated oxygen and hydrogen are then supplied to the hydrogen sensor 310.

[0027] A hydrogen sensor 310 is disposed in the oxygen discharge path 315. The hydrogen sensor 310 measures the hydrogen concentration and transmits the measured hydrogen concentration to the control device 500 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 determines 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 path 315.

[0028] The hydrogen discharge section 400 discharges hydrogen generated at the hydrogen electrode of the water electrolysis chamber 110. The hydrogen discharge section 400 includes a pressure regulating valve 410 and a hydrogen-liquid separator 420. Additionally, the hydrogen discharge section 400 includes a hydrogen pressure regulating flow path 405 and a hydrogen discharge flow path 415 as flow paths. The hydrogen pressure regulating flow path 405 connects the water electrolysis stack 100 to the hydrogen-liquid separator 420. One end of the hydrogen discharge flow path 415 is connected to the hydrogen-liquid separator 420.

[0029] Pressure regulating valve 410 adjusts the pressure of hydrogen generated by water electrolysis reactor 100. Pressure regulating valve 410 is located in hydrogen pressure regulating flow path 405. The opening and closing of pressure regulating valve 410 is controlled by control device 500 described later.

[0030] The hydrogen-liquid separator 420 separates the hydrogen supplied via the hydrogen pressure regulating flow path 405 from the water contained in the hydrogen. The separated hydrogen is released to the outside of system 1 via the other end of the hydrogen discharge flow path 415.

[0031] The control device 500 is configured as a computer with a CPU 510 and a memory 520. The CPU 510 enables the degradation detection unit 511 and the hydrogen pressure regulating unit 512 to function by executing the control program stored in the memory 520.

[0032] The degradation detection unit 511 detects the degradation status of the electrolyte membrane in the water electrolysis reactor 100. In this embodiment, the degradation status of the electrolyte membrane is detected by determining whether the hydrogen concentration transmitted from the hydrogen sensor 310 is above a predetermined threshold. This utilizes the correlation between the degradation status of the electrolyte membrane and the hydrogen concentration. Specifically, as the degradation of the electrolyte membrane progresses, the area of ​​thinning of the electrolyte membrane increases, thus increasing the amount of hydrogen cross-leaking. Therefore, it is assumed that the higher the hydrogen concentration, the greater the degree of degradation of the electrolyte membrane. The threshold is, for example, set as the hydrogen concentration when water electrolysis is performed using an electrolyte membrane with a moderate degree of degradation at a specified current value. Therefore, it is presumed that when the hydrogen concentration is above the threshold, the degree of degradation of the electrolyte membrane is greater than that of a moderate degree.

[0033] Furthermore, multiple threshold values ​​are preferably set corresponding to multiple current values ​​used in water electrolysis. This is because there is a correlation between the current value and the hydrogen concentration. Specifically, a higher current value results in a lower hydrogen concentration. This is because water electrolysis with a higher current value generates more oxygen on the oxygen electrode side, thus increasing the amount of hydrogen consumed due to the reaction of oxygen with cross-leaked hydrogen. Therefore, the degradation detection unit 511 preferably uses the current value transmitted from the power supply P to set the threshold value, and detects the degradation status of the electrolyte membrane by comparing the hydrogen concentration transmitted from the hydrogen sensor 310 with this threshold value. The correspondence between the current value and the threshold value is pre-stored in the memory 520.

[0034] The hydrogen pressure regulating unit 512 adjusts at least one of the hydrogen pressure rise rate and the upper limit of pressure generated in the hydrogen electrode based on the degradation condition detected by the degradation detection unit 511. This adjustment is achieved by the hydrogen pressure regulating unit 512 controlling the opening and closing of the pressure regulating valve 410. In this embodiment, if the degradation detection unit 511 determines that the hydrogen concentration exceeds a threshold, the hydrogen pressure regulating unit 512 controls the pressure regulating valve 410 such that at least one of the hydrogen pressure rise rate and the upper limit of pressure at the next subsequent startup of system 1 is lower than the current operation of system 1.

[0035] Figure 2 This is a flowchart illustrating the steps of hydrogen pressure regulation control performed by System 1. Hydrogen pressure regulation control is performed during or after the startup of System 1.

[0036] Hydrogen sensor 310 detects hydrogen concentration (S100). The detected hydrogen concentration is transmitted to the degradation detection unit 511 of control device 500. Degradation detection unit 511 determines whether the hydrogen concentration is above a predetermined threshold (S110). If the hydrogen concentration is above the predetermined threshold (S110: Yes), hydrogen pressure regulating unit 512 controls pressure regulating valve 410 so that at least one of the hydrogen pressure rise rate and the upper pressure limit value at the next subsequent startup of system 1 is smaller than the current operation of system 1 (S120). If the hydrogen concentration is not above the predetermined threshold (S110: No), hydrogen pressure regulation control ends.

[0037] Hydrogen pressure regulation can also be performed repeatedly during the startup of System 1. Alternatively, hydrogen pressure regulation can be performed periodically according to a predetermined schedule. For example, hydrogen pressure regulation can be performed according to a 12-hour schedule.

[0038] According to the first embodiment of system 1 described above, at least one of the hydrogen pressure rise rate and the upper limit of the pressure is adjusted based on the degradation condition of the electrolyte membrane. Therefore, the stress applied to the electrolyte membrane can be set to an appropriate range corresponding to the degradation condition, and further degradation of the electrolyte membrane can be suppressed. Specifically, when the hydrogen cross-leakage exceeds a predetermined threshold, the hydrogen pressure regulating unit 512 controls the pressure regulating valve 410 in a manner that at least one of the hydrogen pressure rise rate and the upper limit of the hydrogen pressure is lower than the current operation of system 1. Therefore, in the event that the degradation of the electrolyte membrane is expected to worsen, the stress applied to the electrolyte membrane can be reduced, and further degradation of the electrolyte membrane can be suppressed.

[0039] Furthermore, the reason for reducing the stress applied to the electrolyte membrane by decreasing the rate of pressure rise is that the electrolyte membrane is viscoelastic. A viscoelastic electrolyte membrane has the property that its deformation behavior changes with the rate of deformation. That is, by reducing the rate of hydrogen pressure rise, the stress applied to the electrolyte membrane can be reduced.

[0040] B. Second implementation method:

[0041] Figure 3 This is a flowchart illustrating the sequence of hydrogen pressure regulation control in the second embodiment. The degradation detection unit 511 of the second embodiment uses a different method to detect the degradation status of the electrolyte membrane than the method in the first embodiment. Other aspects of the system in the second embodiment are the same as those in the first embodiment, and therefore their description is omitted.

[0042] The degradation detection unit 511 uses the number of starts and stops of system 1 (hereinafter also referred to as "operation count") and total operating time instead of hydrogen concentration to detect degradation. Specifically, the degradation detection unit 511 detects whether the sum of the ratio of operation count to lifetime operation count and the ratio of total operating time to lifetime operating time exceeds a predetermined lifetime value. The lifetime operation count and lifetime operating time are arbitrary predetermined times and are stored in the memory 520. The lifetime value is an arbitrary predetermined value and is stored in the memory 520. In this embodiment, the lifetime value is 1.8. In addition, the operation count and total operating time can be measured by the degradation detection unit 511 or by other measuring devices.

[0043] like Figure 3As shown, in the hydrogen pressure regulation control of the second embodiment, the degradation detection unit 511 obtains the number of operations (S200). Additionally, the degradation detection unit 511 obtains the total operating time (S210). The processing of S200 and S210 can be performed after S210, or S200 and S210 can be performed in parallel. The degradation detection unit 511 determines 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 1.8 of the lifetime value (S220). If the sum of the ratio of the total operating time to the lifetime operating time exceeds 1.8 of the lifetime value (S220: Yes), the hydrogen pressure regulation unit 512 controls the pressure regulating valve 410 to reduce at least one of the hydrogen pressure rise rate and the upper pressure limit value at the next subsequent startup of system 1 (S230). If the sum of the ratio of the total operating time to the lifetime operating time does not exceed 1.8 of the lifetime value (S220: No), the hydrogen pressure regulation control ends.

[0044] According to the system of the second embodiment described above, the degradation detection unit 511 uses the number of times the system 1 operates and the total operating time to detect the degradation status. Therefore, it can reduce the pressure applied to the electrolyte membrane based on the number of times the system operates and the total operating time, thereby suppressing further degradation of the electrolyte membrane.

[0045] C. Other implementation methods:

[0046] (C1) In the above embodiment, the hydrogen pressure regulating unit 512 controls the pressure regulating valve 410 in a manner that reduces at least one of the rate of increase in hydrogen pressure and the upper limit of pressure at the next subsequent startup of system 1, but this disclosure is not limited thereto. The hydrogen pressure regulating unit 512 may also control the pressure regulating valve 410 at any time. For example, the hydrogen pressure regulating unit 512 may also control the pressure regulating valve 410 during operation of system 1.

[0047] (C2) In the first embodiment described above, if the deterioration detection unit 511 determines that the hydrogen concentration is above a threshold, a recommendation to replace the water electrolyzer 100 may be made. Furthermore, in the second embodiment described above, if the deterioration detection unit 511 determines that the sum of the ratios of the total operating time to the lifetime operating time exceeds the lifetime value, a recommendation to replace the water electrolyzer 100 may be made.

[0048] (C3) In the first embodiment described above, multiple water electrolyzers 100 may be used. In such a configuration, one oxygen-liquid separator 220 and one hydrogen sensor 310 may be used for each of the multiple water electrolyzers 100. By applying the control device 500 described above to such a configuration, the degradation status of the electrolyte membrane in at least one of the multiple water electrolyzers 100 can be detected. Furthermore, by combining the use of the control device 500 with monitoring the voltage fluctuations of the chamber monitor 150, it is possible to determine which of the multiple water electrolyzers 100 has experienced degradation.

[0049] This disclosure is not limited to the embodiments described above, and can be implemented in various structures without departing from its spirit. For example, technical features in embodiments corresponding to the technical features in the various methods 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 to achieve some or all of the above-described effects. In addition, if a technical feature is not required to be described in this specification, it can be appropriately deleted.

Claims

1. A water electrolysis system, comprising: Hydrogen electrode; Oxygen pole; and An electrolyte membrane is located between the hydrogen electrode and the oxygen electrode, wherein, The water electrolysis system further comprises: A degradation detection unit detects the degradation status of the electrolyte membrane; and The hydrogen pressure regulating unit, when the water electrolysis system is started, adjusts at least one of the rate of increase of the hydrogen pressure generated in the hydrogen electrode and the upper limit of the pressure based on the detected deterioration condition.

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