Water electrolysis system and method for starting a water electrolysis device

Abstract

Provided is a water electrolysis system and a method for starting a water electrolysis device, which can suppress mixing of oxygen and hydrogen generated by electrolysis of water. The water electrolysis system includes a water electrolysis unit, a power source, an oxygen tank, and a control device. The water electrolysis unit includes a solid polymer electrolyte membrane, and an anode and a cathode disposed on both sides of the solid polymer electrolyte membrane in the thickness direction. The water electrolysis unit electrolyzes water by applying a voltage between the anode and the cathode from the power source. The control device makes the pressure of oxygen generated at the anode by electrolysis of water by the water electrolysis unit higher than the pressure of hydrogen generated at the cathode by electrolysis of water by the water electrolysis unit. The control device makes the pressure on the anode side of the solid polymer electrolyte membrane higher than the pressure on the cathode side of the solid polymer electrolyte membrane by supplying oxygen from the oxygen tank to the anode before the start of electrolysis.

Description

TECHNICAL FIELD

[0001] The present application relates to a water electrolysis system and a starting method of a water electrolysis device. BACKGROUND

[0002] In the past, for example, a starting method of a water electrolysis system is known in which, in a case where the possibility of hydrogen remaining on the anode side is high at the start of a water electrolysis system that has a water electrolysis unit of a solid polymer type, the rising speed of an electric current is suppressed (for example, refer to Japanese Patent Application Publication No. 2017-206730). In this starting method, by suppressing the rising speed of the electric current, the increase in the concentration of hydrogen that is discharged together with oxygen generated at the anode is suppressed. SUMMARY

[0003] In a case where a water electrolysis system as described above has a water electrolysis unit of a solid polymer type, sometimes mixing of oxygen and hydrogen occurs due to crossover of oxygen generated at the anode and hydrogen generated at the cathode through an electrolyte membrane. In a case where the amount of crossover increases, the purity of each of oxygen and hydrogen decreases, and adverse situations such as degradation of the electrolyte membrane occur, and thus it is desirable to suppress mixing of oxygen and hydrogen.

[0004] The present application is achieved in consideration of such a situation, and aims to provide a water electrolysis system and a starting method of a water electrolysis device that can suppress mixing of oxygen and hydrogen generated by electrolysis of water.

[0005] In order to solve the above-mentioned problems and achieve the object, the present application adopts the following solutions.

[0006] (1) A water electrolysis system according to an aspect of the present application includes: a water electrolysis unit that has an electrolyte membrane and an anode and a cathode provided on both sides in a thickness direction of the electrolyte membrane, and that electrolyzes water by applying a voltage between the anode and the cathode; a power supply that applies the voltage between the anode and the cathode; an oxygen supply source that supplies oxygen to the anode; and a control device that makes the pressure of oxygen generated at the anode by electrolysis of water by the water electrolysis unit higher than the pressure of hydrogen generated at the cathode by electrolysis of water by the water electrolysis unit, and makes the pressure of the anode side of the electrolyte membrane higher than the pressure of the cathode side of the electrolyte membrane by supplying the oxygen from the oxygen supply source to the anode before the electrolysis is started.

[0007] (2) In the aspect of the above (1), the oxygen supply source can include an oxygen container that stores the oxygen generated at the anode by electrolysis of water by the water electrolysis unit.

[0008] (3) In the aspect of (1) above, there can also be provided a first oxygen container that stores at least a portion of oxygen generated at the anode by electrolysis of water by the water electrolysis unit, and the oxygen supply source can include a second oxygen container that is connected to a flow path branched from a flow path connecting the water electrolysis unit and the first oxygen container, and that stores a portion of the oxygen generated at the anode by electrolysis of water by the water electrolysis unit.

[0009] (4) In the aspect of (3) above, there can also be provided a pressure acquisition unit that acquires a pressure of oxygen in the second oxygen container, and the control device can perform processing to preferentially supply oxygen generated at the anode after the start of electrolysis to the second oxygen container compared to the first oxygen container, and to switch a supply destination of oxygen generated at the anode from the second oxygen container to the first oxygen container based on the pressure acquired by the pressure acquisition unit.

[0010] (5) In the aspect of (3) or (4) above, the control device can switch the oxygen supply source from the second oxygen container to the first oxygen container when a pressure on the anode side in a state where the oxygen is supplied from the second oxygen container to the anode is less than a prescribed pressure.

[0011] (6) In any of the aspects of (1) to (5) above, there can also be provided a water supply unit that supplies water to the cathode.

[0012] (7) A starting method of a water electrolysis device according to an aspect of the present application is a starting method performed by an electronic device of a water electrolysis device that includes a water electrolysis unit having an electrolyte membrane and an anode and a cathode provided on both sides in a thickness direction of the electrolyte membrane, and that electrolyzes water by applying a voltage between the anode and the cathode, a power supply that applies the voltage between the anode and the cathode, and the electronic device, wherein the starting method of the water electrolysis device includes a step in which the electronic device causes a pressure of oxygen generated at the anode by electrolysis of water by the water electrolysis unit to be higher than a pressure of hydrogen generated at the cathode by electrolysis of water by the water electrolysis unit, and a step in which the electronic device causes a pressure on the anode side of the electrolyte membrane to be higher than a pressure on the cathode side of the electrolyte membrane by supplying oxygen from an oxygen supply source to the anode before the start of electrolysis.

[0013] According to (1) above, there is provided a control device that causes a pressure on the anode side of an electrolyte membrane to be higher than a pressure on the cathode side of the electrolyte membrane before the start of electrolysis of water, whereby it is possible to suppress movement of hydrogen, which is more likely to permeate the electrolyte membrane than oxygen due to a difference in molecular weight, from the cathode side to the anode side.

[0014] In the case of (2) above, the pressure on the anode side can be increased by the oxygen stored in advance in the oxygen container before the start of electrolysis of water. For example, compared to a case where the pressure on the anode side is increased by supply of oxygen from the outside, or the like, there is no need to provide a dedicated device for increasing the pressure, and the system configuration can be inhibited from becoming complex.

[0015] In the case of (3) above, a second oxygen container is provided in addition to the first oxygen container that stores oxygen generated at the anode by electrolysis of water, and thus the pressure on the anode side can be increased by oxygen supplied from the second oxygen container regardless of the residual pressure of the first oxygen container. For example, even in a case where the residual pressure of the first oxygen container decreases before the start of electrolysis of water, the pressure on the anode side can be increased by oxygen stored in advance in the second oxygen container.

[0016] The second oxygen container is connected to a flow path branched from a flow path connecting the water electrolysis unit and the first oxygen container, and thus even in a case where the residual pressure of the second oxygen container decreases due to the increase in pressure on the anode side before the start of electrolysis of water, the second oxygen container can be filled with oxygen generated at the anode after the start of electrolysis of water. By maintaining the residual pressure of the second oxygen container to be equal to or higher than a predetermined value, the increase in pressure on the anode side at the time of the next start can be appropriately performed.

[0017] In the case of (4) above, a pressure acquisition unit that acquires the pressure of oxygen in the second oxygen container is provided, and thus the residual pressure of the second oxygen container can be appropriately maintained to be equal to or higher than a predetermined value. A control device that switches the supply destination of oxygen generated at the anode from the second oxygen container to the first oxygen container in accordance with the pressure of oxygen stored in the second oxygen container is provided, and thus the supply of excess oxygen to the second oxygen container can be inhibited, and the supply of oxygen to the first oxygen container and the second oxygen container can be performed with good efficiency.

[0018] In the case of (5) above, a control device that switches the oxygen supply source from the second oxygen container to the first oxygen container in a case where the increase in pressure on the anode side by the second oxygen container is insufficient is provided, and thus the pressure on the anode side can be increased by oxygen supplied from the first oxygen container regardless of the residual pressure of the second oxygen container. For example, even in a case where the residual pressure of the second oxygen container decreases before the start of electrolysis of water, the pressure on the anode side can be increased by oxygen stored in advance in the first oxygen container.

[0019] In the case of (6) above, a water supply unit that supplies water for electrolysis to the cathode by so-called cathode supply is provided, and thus compared to a case where water for electrolysis is supplied to the anode, for example, the anode side can be easily increased in pressure.

[0020] According to the above (7), including the step of making the pressure on the anode side of the electrolyte membrane higher than the pressure on the cathode side before starting electrolysis of water, it is possible to suppress the movement of hydrogen, which is more likely to permeate the electrolyte membrane than oxygen due to the difference in molecular weight, from the cathode side to the anode side. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a diagram schematically showing the structure of an energy system equipped with the water electrolysis system of the embodiment of the present application.

[0022] Figure 2 is a sectional view showing the structure of a water electrolysis unit of the water electrolysis device in the embodiment of the present application.

[0023] Figure 3 is a diagram showing the arrangement of a plurality of sensors and a plurality of valves in the water electrolysis system of the embodiment of the present application.

[0024] Figure 4 is a flowchart showing a start-up method of the water electrolysis device in the embodiment of the present application.

[0025] Figure 5 is a flowchart showing a stop method of the water electrolysis device in the embodiment of the present application.

[0026] Figure 6 is a diagram showing the arrangement of a plurality of sensors and a plurality of valves in the water electrolysis system in the modified example of the embodiment of the present application.

[0027] Figure 7 is a flowchart showing a start-up method of the water electrolysis device in the modified example of the embodiment of the present application. DETAILED DESCRIPTION

[0028] Hereinafter, a water electrolysis system and a start-up method of a water electrolysis device of an embodiment of the present application will be described with reference to the drawings.

[0029] Figure 1 is a diagram schematically showing the structure of an energy system 1 equipped with the water electrolysis system 10 of the embodiment.

[0030] As shown in Figure 1 , the water electrolysis system 10 of the embodiment is provided, for example, in an energy system 1 in which electric power, heat, and water are utilized in association with each other.

[0031] The energy system 1 is equipped, for example, with the water electrolysis system 10, a humidifier 11, a fuel cell 13, a heat storage mechanism 15, a storage battery 17, and a control device 19. The storage battery 17 and the control device 19 constitute a part of the water electrolysis system 10.

[0032] The humidifier 11 humidifies hydrogen and oxygen supplied from the water electrolysis system 10 with water supplied from the heat storage mechanism 15, and supplies them to the fuel cell 13. The fuel cell 13 generates electricity by catalytic reaction of hydrogen and oxygen supplied from the water electrolysis system 10. The heat storage mechanism 15 stores water (exhaust water and generated water) supplied from the hydrogen pressure increasing device 27 of the water electrolysis system 10 and the fuel cell 13 described later. The heat storage mechanism 15 supplies water for preheating at the time of startup to the water electrolysis system 10 and the fuel cell 13 described later. The heat storage mechanism 15 supplies water for humidification to the humidifier 11. The heat storage mechanism 15 supplies water for circulation to the water supply part 21 of the water electrolysis system 10 described later.

[0033] The storage battery 17 accumulates electric power generated by the fuel cell 13 and the like.

[0034] The control device 19 comprehensively controls the entire energy system 1. The control device 19 is, for example, a software function part that functions by a prescribed program being executed by a processor such as a CPU (Central Processing Unit). The software function part is an ECU (Electronic Control Unit) that is provided with a processor such as a CPU, a ROM (Read Only Memory) that stores a program, a RAM (Random Access Memory) that temporarily stores data, and an electronic circuit such as a timer. At least a part of the control device 19 can also be an integrated circuit such as an LSI (Large Scale Integration).

[0035] The water electrolysis system 10 is provided with, for example, a water supply part 21, a water supply flow path 22, a water electrolysis device 23, a hydrogen supply flow path 24a and an oxygen supply flow path 24b, a gas-liquid separator 25, a cooling water supply flow path 26, a hydrogen pressure increasing device 27, an exhaust water flow path 28, two water vapor separators 29, a hydrogen tank 31, and an oxygen tank 33.

[0036] The water supply part 21 supplies water to the water electrolysis device 23 via the water supply flow path 22 provided between the water supply part 21 and the water electrolysis device 23. The water supply part 21 is provided with, for example, a pure water generator, a circulation pump, and an ion exchanger, and the like. The pure water generator generates pure water from tap water or the like. The circulation pump transports water supplied from the pure water generator, the heat storage mechanism 15, and the like to the water electrolysis device 23. The ion exchanger removes impurities from water supplied from the heat storage mechanism 15 and the like.

[0037] The water electrolysis device 23 is, for example, a solid polymer type water electrolysis device. The water electrolysis device 23 electrolyzes water supplied from the water supply portion 21 via the water supply flow path 22. The water electrolysis device 23 supplies hydrogen generated by electrolysis of water to the hydrogen tank 31 via a hydrogen supply flow path 24a provided between the water electrolysis device 23 and the hydrogen tank 31. The water electrolysis device 23 supplies oxygen generated by electrolysis of water to the oxygen tank 33 via an oxygen supply flow path 24b provided between the water electrolysis device 23 and the oxygen tank 33.

[0038] The water electrolysis device 23 includes at least one water electrolysis stack. The water electrolysis stack includes a plurality of water electrolysis cells 41 stacked, and a pair of end plates (not shown) sandwiching the stack of the plurality of water electrolysis cells 41 from both sides in the stacking direction.

[0039] Figure 2 is a cross-sectional view showing the structure of the water electrolysis cell 41 of the water electrolysis device 23 in the embodiment.

[0040] As shown in Figure 2 , the water electrolysis cell 41 includes an electrolyte electrode structure 43, and an anode-side separator 45 and a cathode-side separator 47 sandwiching the electrolyte electrode structure 43 from both sides in the thickness direction (i.e., the stacking direction of the cell group).

[0041] The electrolyte electrode structure 43 includes a solid polymer electrolyte membrane 51, and an anode 53 and a cathode 55 sandwiching the solid polymer electrolyte membrane 51 from both sides in the thickness direction.

[0042] The solid polymer electrolyte membrane 51 includes, for example, an anion exchange membrane or a proton exchange membrane that selectively conducts anions such as hydroxide ions (OH-).

[0043] The anode 53 includes, for example, an anode catalyst 53a and a gas diffusion layer 53b as a power supply, and the like.

[0044] The cathode 55 includes, for example, a cathode catalyst 55a and a gas diffusion layer 55b as a power supply, and the like.

[0045] The gas diffusion layer 53b as the power supply of the anode 53 and the gas diffusion layer 55b as the power supply of the cathode 55 are connected to a power supply 57 constituted by the battery 17 or the like, for example.

[0046] An anode-side flow path 45a is formed between the anode-side separator 45 and the anode 53. The anode-side flow path 45a is formed by, for example, a groove formed on the surface of the anode-side separator 45 and the surface of the anode 53 covering the open end of the groove of the anode-side separator 45. The anode-side flow path 45a opens into an oxygen discharge through hole 65 described later.

[0047] A cathode-side flow path 47a is formed between the cathode-side diaphragm 47 and the cathode 55. The cathode-side flow path 47a is formed, for example, by a groove formed on the surface of the cathode-side diaphragm 47 and the surface of the cathode 55 covering the opening end of the groove of the cathode-side diaphragm 47. The cathode-side flow path 47a leads to the water supply through-hole 61 and the hydrogen discharge through-hole 63, which will be described later.

[0048] In a water electrolysis stack 23a consisting of a unit group having multiple water electrolysis units 41 and a pair of end plates, a water supply through hole 61, a hydrogen discharge through hole 63 and an oxygen discharge through hole 65 are formed that extend along the stacking direction.

[0049] The water supply through hole 61 leads to the water supply flow path 22 outside the water electrolysis device 23, and leads to the cathode side flow path 47a inside the water electrolysis device 23.

[0050] The hydrogen discharge through-hole 63 leads to the hydrogen supply flow path 24a outside the water electrolysis device 23, and to the cathode side flow path 47a inside the water electrolysis device 23.

[0051] The oxygen discharge through-hole 65 leads to the oxygen supply flow path 24b outside the water electrolysis device 23, and to the anode side flow path 45a inside the water electrolysis device 23.

[0052] The water electrolysis unit 41 supplies water to the cathode 55 through a so-called cathode feed, and the power supply 57 causes current to flow to the anode 53 and the cathode 55 to electrolyze the water.

[0053] The cathode 55 generates hydrogen and hydroxide ions by electrolyzing water supplied from the water supply through-hole 61 to the cathode-side flow path 47a. The hydrogen generated at the cathode 55, together with unreacted water, is discharged from the cathode-side flow path 47a to the hydrogen discharge through-hole 63. The hydroxide ions generated at the cathode 55 are conducted through the solid polymer electrolyte membrane 51 and move towards the anode 53.

[0054] Anode 53 utilizes hydroxide ions conducted from cathode 55 through solid polymer electrolyte membrane 51 to generate oxygen and water. The oxygen and water generated at anode 53 are discharged from anode-side flow path 45a to oxygen discharge through hole 65.

[0055] like Figure 1 As shown, a gas-liquid separator 25 is disposed between the water electrolysis unit 23 and the hydrogen booster unit 27 in the hydrogen supply flow path 24a. The gas-liquid separator 25 separates the fluid containing hydrogen and unreacted water discharged from the water electrolysis unit 23 into gaseous and liquid components. The gaseous components include, for example, hydrogen and water vapor. The liquid components include, for example, water.

[0056] The gas component hydrogen and water vapor obtained by the gas-liquid separation is discharged toward the hydrogen pressure increasing device 27 via the hydrogen supply flow path 24a as hydrogen.

[0057] The gas-liquid separator 25 discharges the liquid component water obtained by the gas-liquid separation toward the hydrogen pressure increasing device 27 and the fuel cell 13 as cooling water (cooling water) for cooling via the cooling water supply flow path 26 provided between the hydrogen pressure increasing device 27 and the fuel cell 13.

[0058] The hydrogen pressure increasing device 27 is provided between the gas-liquid separator 25 and the water vapor separator 29 in the hydrogen supply flow path 24a. The hydrogen pressure increasing device 27 is, for example, an electrochemical hydrogen pressure increasing device (EHC: Electrochemical Hydrogen Compressor) that electrochemically compresses hydrogen. The hydrogen pressure increasing device 27 increases the pressure of the hydrogen supplied from the gas-liquid separator 25 and discharges it toward the water vapor separator 29 via the hydrogen supply flow path 24a.

[0059] The hydrogen pressure increasing device 27 is cooled by the cooling water supplied from the gas-liquid separator 25 via the cooling water supply flow path 26. The hydrogen pressure increasing device 27 discharges the cooled cooling water toward the heat accumulation mechanism 15 as discharge water via the discharge water flow path 28 provided between the hydrogen pressure increasing device 27 and the heat accumulation mechanism 15.

[0060] The two water vapor separators 29 are provided between the hydrogen pressure increasing device 27 and the hydrogen tank 31 in the hydrogen supply flow path 24a and between the water electrolysis device 23 and the oxygen tank 33 in the oxygen supply flow path 24b. The water vapor separator 29 separates water vapor from a fluid containing hydrogen and oxygen each and water vapor, for example, by cooling or water adsorption.

[0061] Each water vapor separator 29 discharges hydrogen toward the hydrogen tank 31 via the hydrogen supply flow path 24a or discharges oxygen toward the oxygen tank 33 via the oxygen supply flow path 24b.

[0062] Figure 3 is a view showing the arrangement of the plurality of sensors and the plurality of valves in the water electrolysis system 10 of the embodiment.

[0063] As shown in Figure 3 , the water electrolysis system 10 is provided with a plurality of sensors and a plurality of valves.

[0064] The plurality of sensors are provided with, for example, a first pressure sensor 71a, a second pressure sensor 71b, a third pressure sensor 71c, a fourth pressure sensor 71d, and a hydrogen concentration sensor 71e.

[0065] The plurality of valves are provided with, for example, a back pressure valve 73a, a purge valve 73b, and an on-off valve 73c. The plurality of valves are, for example, solenoid valves, electric valves, or air valves, and are controlled by the control device 19 to open and close and to adjust the opening degree and the like.

[0066] The first pressure sensor 71a is disposed in the water supply flow path 22. The first pressure sensor 71a detects the pressure of the water circulating in the water supply flow path 22 (supply water pressure: first pressure P1), and outputs a signal of the detected value of the first pressure P1.

[0067] The second pressure sensor 71b is disposed in the hydrogen supply flow path 24a. The second pressure sensor 71b detects the pressure of the fluid of unreacted water and hydrogen circulating in the hydrogen supply flow path 24a (second pressure P2), and outputs a signal of the detected value of the second pressure P2.

[0068] The third pressure sensor 71c is disposed between the water electrolysis device 23 and the back pressure valve 73a described later in the oxygen supply flow path 24b. The third pressure sensor 71c detects the pressure of the fluid containing oxygen circulating in the oxygen supply flow path 24b (third pressure P3), and outputs a signal of the detected value of the third pressure P3.

[0069] The fourth pressure sensor 71d is disposed between the opening and closing valve 73c described later and the oxygen tank 33 in the oxygen supply flow path 24b. The fourth pressure sensor 71d detects the pressure of the oxygen stored in the oxygen tank 33 (fourth pressure P4), and outputs a signal of the detected value of the fourth pressure P4.

[0070] The hydrogen concentration sensor 71e is disposed between the water electrolysis device 23 and the back pressure valve 73a described later in the oxygen supply flow path 24b. The hydrogen concentration sensor 71e detects the concentration of hydrogen contained in the fluid circulating in the oxygen supply flow path 24b (hydrogen concentration C), and outputs a signal of the detected value of the hydrogen concentration C.

[0071] The back pressure valve 73a is disposed between the water electrolysis device 23 and the branch portion 75a of the discharge flow path 75 branched from the oxygen supply flow path 24b in the oxygen supply flow path 24b. The back pressure valve 73a maintains the pressure of the fluid on the water electrolysis device 23 side (i.e., the upstream side) in the oxygen supply flow path 24b at a predetermined set pressure in a state where a predetermined reference is set. The back pressure valve 73a allows the fluid containing oxygen to circulate from the oxygen tank 33 side (i.e., the downstream side) to the water electrolysis device 23 side (i.e., the upstream side) in an open state.

[0072] The discharge valve 73b is disposed in the discharge flow path 75. The discharge valve 73b switches whether or not the fluid is discharged to the outside from the oxygen supply flow path 24b via the discharge flow path 75 by switching the opening and closing of the discharge flow path 75.

[0073] The opening and closing valve 73c is disposed between the branch portion 75a of the discharge flow path 75 and the fourth pressure sensor 71d in the oxygen supply flow path 24b. The opening and closing valve 73c switches whether or not the fluid circulates to the back pressure valve 73a side or the oxygen tank 33 side in the oxygen supply flow path 24b by switching the opening and closing of the oxygen supply flow path 24b.

[0074] The following describes a control method of the water electrolysis system 10 in the embodiment, that is, a control action performed by the control device 19.

[0075] Figure 4 is a flowchart showing a start-up method of the water electrolysis device 23 in the embodiment.

[0076] As shown in Figure 4 , a series of processes from Step S01 to Step S20 are executed at the time of start-up of the water electrolysis device 23.

[0077] First, in Step S01, the control device 19 performs initial setting of the plurality of valves. For example, the discharge valve 73b and the on-off valve 73c are in a closed state. The back pressure valve 73a is in a state set to a prescribed reference, which is a state in which the pressure of the fluid on the water electrolysis device 23 side (i.e., the upstream side) is maintained at a prescribed set pressure at which oxygen can be filled into the oxygen tank 33. The prescribed set pressure is, for example, around 10 MPa or the like.

[0078] Next, in Step S02, the control device 19 starts supply of water from the water supply portion 21 to the water electrolysis device 23 via the water supply flow path 22.

[0079] Next, in Step S03, the control device 19 acquires the first pressure P1 and the fourth pressure P4 from the first pressure sensor 71a and the fourth pressure sensor 71d.

[0080] Next, in Step S04, the control device 19 determines whether the fourth pressure P4 is equal to or higher than a prescribed residual pressure. The prescribed residual pressure is, for example, a pressure required to pressurize the third pressure P3 by a prescribed pressure or more than the first pressure P1 in Step S05 described later.

[0081] In the case where the determination result thereof is "Yes", the control device 19 causes the process to proceed to Step S05. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the process to proceed to Step S11.

[0082] Next, in Step S05, the control device 19 starts supply of oxygen from the oxygen tank 33 to the water electrolysis device 23 by bringing the on-off valve 73c to an open state and bringing the back pressure valve 73a to an open state. The control device 19 causes the pressure on the anode 53 side of the solid polymer electrolyte membrane 51 in the water electrolysis cell 41 of the water electrolysis device 23 to be higher than the pressure on the cathode 55 side.

[0083] Next, in Step S06, the control device 19 acquires the third pressure P3 from the third pressure sensor 71c.

[0084] Next, in step S07, the control device 19 determines whether the third pressure P3 is greater than the first pressure Pl by a prescribed pressure or more. The prescribed pressure is, for example, 0.1 MPa or more, and more preferably 0.2 MPa to 0.5 MPa, for example, 0.2 MPa or the like.

[0085] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S08. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the processing to return to step S06.

[0086] Next, in step S08, the control device 19 stops the pressure increase on the anode 53 side by supplying oxygen from the oxygen tank 33 to the water electrolysis device 23 by returning the back pressure valve 73a to a prescribed reference set state.

[0087] Next, in step S09, the control device 19 starts the electric conduction from the power supply 57 of the water electrolysis device 23 to the anode 53 and the cathode 55.

[0088] Next, in step S10, the control device 19 executes the processing of the electrolysis of water by the water electrolysis device 23. The control device 19 causes the pressure of the oxygen generated at the anode 53 by the electrolysis of water by the water electrolysis unit 41 to be higher than the pressure of the hydrogen generated at the cathode 55. Further, the processing is caused to proceed to the end phase.

[0089] In step Sll, the control device 19 determines whether the fourth pressure P4 is greater than zero.

[0090] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S12. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the processing to proceed to step S15.

[0091] Next, in step S12, the control device 19 starts the supply of oxygen from the oxygen tank 33 to the water electrolysis device 23 by causing the on-off valve 73c to be in the open state and causing the back pressure valve 73a to be in the open state. The control device 19 causes the pressure of the anode 53 side of the solid polymer electrolyte membrane 51 in the water electrolysis unit 41 of the water electrolysis device 23 to be higher than the pressure of the cathode 55 side.

[0092] Next, in step S13, the control device 19 determines whether the pressure increase on the anode 53 side by the supply of oxygen from the oxygen tank 33 to the water electrolysis device 23 is completed.

[0093] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S14. On the other hand, in the case where the determination result thereof is "No", the control device 19 repeatedly executes the determination processing of step S13.

[0094] Next, in step S14, the control device 19 returns the back pressure valve 73a to the prescribed reference set state.

[0095] Next, in step S15, the control device 19 sets the discharge valve 73b to the open state, and sets the on-off valve 73c to the closed state.

[0096] Next, in step S16, the control device 19 starts to apply power from the power supply 57 of the water electrolysis device 23 to the anode 53 and the cathode 55.

[0097] Next, in step S17, the control device 19 executes the process of electrolysis of water by the water electrolysis device 23. The control device 19 causes the pressure of oxygen generated at the anode 53 by electrolysis of water by the water electrolysis unit 41 to be higher than the pressure of hydrogen generated at the cathode 55.

[0098] Next, in step S18, the control device 19 acquires the third pressure P3 from the third pressure sensor 71c, and acquires the hydrogen concentration C from the hydrogen concentration sensor 71e.

[0099] Next, in step S19, the control device 19 determines whether the third pressure P3 is greater than the first pressure P1 by a prescribed pressure or more, and whether the hydrogen concentration C is lower than a prescribed concentration or not. The prescribed pressure is, for example, 0.1 MPa or more, and more preferably 0.2 MPa or more in the range of 0.2 MPa to 0.5 MPa, or the like.

[0100] In the case where the determination result thereof is "Yes", the control device 19 causes the process to proceed to step S20. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the process to return to step S18.

[0101] Next, the control device 19 sets the discharge valve 73b to the closed state, and sets the on-off valve 73c to the open state. Further, the process is caused to proceed to the end phase.

[0102] Figure 5 is a flowchart showing a stop method of the water electrolysis device 23 in the embodiment.

[0103] As shown in Figure 5 , a series of processes from step S31 to step S38 are executed at the time of stop of the water electrolysis device 23.

[0104] First, in step S31, the control device 19 sets the discharge valve 73b to the open state, and sets the on-off valve 73c to the closed state.

[0105] Next, in step S32, the control device 19 gradually reduces the pressure of fluid on the water electrolysis device 23 side (i.e., the upstream side) by causing the back pressure valve 73a to change from the prescribed reference set state toward the open state.

[0106] Next, in step S33, the control device 19 acquires the third pressure P3 from the third pressure sensor 71c.

[0107] Next, in step S34, the control device 19 determines whether the third pressure P3 is below a prescribed threshold pressure.

[0108] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S35. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the processing to return to step S33.

[0109] Next, in step S35, the control device 19 gradually reduces the electric current that is passed from the power supply 57 of the water electrolysis device 23 to the anode 53 and the cathode 55.

[0110] Next, in step S36, the control device 19 determines whether the electric current that is passed from the power supply 57 to the anode 53 and the cathode 55 is zero.

[0111] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S37. On the other hand, in the case where the determination result thereof is "No", the control device 19 repeatedly executes the determination processing of step S36.

[0112] Next, in step S37, the control device 19 causes the discharge valve 73b to be in a closed state.

[0113] Next, in step S37, the control device 19 gradually reduces the amount of water (water supply amount) that is supplied from the water supply portion 21 to the water electrolysis device 23. Further, the processing is caused to proceed to an ending stage.

[0114] As described above, according to the water electrolysis system 10 and the control method of the water electrolysis device 23 of the embodiment, the control device 19 causes the pressure on the anode 53 side of the solid polymer electrolyte membrane 51 to be higher than the pressure on the cathode 55 side before starting the electrolysis of water. Thereby, it is possible to suppress the case where hydrogen that is more likely to permeate the solid polymer electrolyte membrane 51 than oxygen moves from the cathode 55 side to the anode 53 side due to the difference in the size of the molecular weight.

[0115] The control device 19 can increase the pressure on the anode 53 side before starting the electrolysis of water by the oxygen that is stored in advance in the oxygen tank 33. For example, compared to the case where the pressure on the anode 53 side is increased by the supply of oxygen from the outside, it is possible to suppress the system structure from becoming complicated without having to equip a dedicated device for increasing the pressure.

[0116] The control device 19 supplies the water for electrolysis from the water supply portion 21 to the cathode 55 by so-called cathode supply, and thereby, compared to the case where the water for electrolysis is supplied to, for example, the anode 53, it is possible to easily increase the pressure on the anode 53 side.

[0117] (Modified example)

[0118] A modified example of the embodiment will be described below. As for the same parts as those of the above-described embodiment, the same reference numerals are marked and the description will be omitted or simplified.

[0119] In the above-described embodiment, the control device 19 supplies oxygen from the oxygen tank 33 to the water electrolysis device 23 at the start of the water electrolysis device 23 (reverse flow), thereby boosting the anode 53 side, but is not limited thereto, and a tank for boosting can be provided in addition to the oxygen tank 33.

[0120] Figure 6 is a view showing the configuration of the plurality of sensors and the plurality of valves of the water electrolysis system 10A in the modified example of the embodiment.

[0121] As shown in Figure 6 , the water electrolysis system 10A of the modified example is provided with a plurality of sensors and a plurality of valves, and a buffer tank 81.

[0122] The buffer tank 81 is, for example, a tank having a smaller capacity than the oxygen tank 33. The buffer tank 81 is disposed at a buffer filling flow path 83 branched between the branch portion 75a of the discharge flow path 75 in the oxygen supply flow path 24b and the oxygen tank 33. The buffer tank 81 is connected to a boost flow path 85 that converges to the oxygen supply flow path 24b at a convergence portion 85a between the water electrolysis device 23 and the back pressure valve 73a in the oxygen supply flow path 24b.

[0123] The buffer tank 81 is filled with oxygen by the flow containing oxygen supplied from the oxygen supply flow path 24b via the buffer filling flow path 83 at the time of filling. The buffer tank 81 supplies oxygen to the convergence portion 85a on the water electrolysis device 23 side (i.e., the upstream side) of the back pressure valve 73a in the oxygen supply flow path 24b via the boost flow path 85 at the time of boosting.

[0124] The plurality of sensors are provided with, for example, a first pressure sensor 71a, a second pressure sensor 71b, a third pressure sensor 71c, a hydrogen concentration sensor 71e, and a fifth pressure sensor 87a.

[0125] The plurality of valves are provided with, for example, a back pressure valve 73a, a discharge valve 73b, an on-off valve 73c, a switching valve 89a, a first check valve 89b, a second check valve 89c, and a buffer on-off valve 89d. The plurality of valves are, for example, solenoid valves, electric valves, or air valves, and are controlled by the control device 19 in terms of opening and closing, degree of opening, and the like.

[0126] The fifth pressure sensor 87a is disposed between the buffer tank 81 and the convergence portion 85a in the boost flow path 85. The fifth pressure sensor 87a detects the pressure (fifth pressure P5) of the oxygen stored in the buffer tank 81 and outputs a signal of the detected value of the fifth pressure P5.

[0127] The switching valve 89a is provided in the branch portion of the buffer filling flow path 83 in the oxygen supply flow path 24b. The switching valve 89a switches the water electrolysis device 23 side (i.e., the upstream side) in the oxygen supply flow path 24b to be open to the oxygen tank 33 side (i.e., the downstream side) or the buffer tank 81 side of the buffer filling flow path 83.

[0128] The first check valve 89b is provided between the switching valve 89a and the oxygen tank 33 in the oxygen supply flow path 24b. The first check valve 89b allows fluid to flow from the water electrolysis device 23 side (i.e., the upstream side) to the oxygen tank 33 side (i.e., the downstream side) in the oxygen supply flow path 24b, and prohibits reverse flow.

[0129] The second check valve 89c is provided between the switching valve 89a and the buffer tank 81 in the buffer filling flow path 83. The second check valve 89c allows fluid to flow from the water electrolysis device 23 side to the buffer tank 81 side in the buffer filling flow path 83, and prohibits reverse flow.

[0130] The buffer on-off valve 89d is provided between the fifth pressure sensor 87a and the merging portion 85a in the pressure boosting flow path 85. The buffer on-off valve 89d switches whether or not fluid flows from the buffer tank 81 side to the merging portion 85a side in the pressure boosting flow path 85 by switching the opening and closing of the pressure boosting flow path 85.

[0131] Figure 7 is a flowchart showing a start-up method of the water electrolysis device 23 in the modification of the embodiment.

[0132] As shown in Figure 7 , a series of processes of steps S51 to S63 are executed at the start-up of the water electrolysis device 23.

[0133] First, in step S51, the control device 19 performs initial setting of the plurality of valves. For example, the discharge valve 73b, the on-off valve 73c, and the buffer on-off valve 89d are in the closed state. The back pressure valve 73a is in a state in which the pressure of the fluid on the water electrolysis device 23 side (i.e., the upstream side) is maintained at a prescribed set pressure at which the buffer tank 81 can be filled with oxygen. The prescribed set pressure is, for example, about 10 MPa or the like. The switching valve 89a is in a state in which the water electrolysis device 23 side (i.e., the upstream side) in the oxygen supply flow path 24b is open to the buffer tank 81 side.

[0134] Next, in step S52, the control device 19 starts to supply water from the water supply portion 21 to the water electrolysis device 23 via the water supply flow path 22.

[0135] Next, in step S53, the control device 19 causes the on-off valve 73c to be in the open state.

[0136] Next, in step S54, the control device 19 acquires the first pressure P1 from the first pressure sensor 71a.

[0137] Next, in step S55, the control device 19 starts supplying oxygen from the buffer tank 81 to the water electrolysis device 23 via the pressure-boosting flow path 85 by bringing the buffer on-off valve 89d to the open state. The control device 19 makes the pressure on the anode 53 side of the solid polymer electrolyte membrane 51 in the water electrolysis unit 41 of the water electrolysis device 23 higher than the pressure on the cathode 55 side.

[0138] Next, in step S56, the control device 19 acquires the third pressure P3 from the third pressure sensor 71c.

[0139] Next, in step S57, the control device 19 determines whether the third pressure P3 is greater than the first pressure P1 by a prescribed pressure or more. The prescribed pressure is, for example, 0.1 MPa or more, and more preferably 0.2 MPa or more in the range of 0.2 MPa to 0.5 MPa, or the like.

[0140] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S58. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the processing to return to step S56.

[0141] Next, in step S58, the control device 19 stops boosting the pressure on the anode 53 side by supplying oxygen from the buffer tank 81 to the water electrolysis device 23 by bringing the buffer on-off valve 89d to the closed state.

[0142] Next, in step S59, the control device 19 starts applying electric power from the power supply 57 of the water electrolysis device 23 to the anode 53 and the cathode 55.

[0143] Next, in step S60, the control device 19 acquires the fifth pressure P5 from the fifth pressure sensor 87a.

[0144] Next, in step S61, the control device 19 determines whether the fifth pressure P5 is a prescribed residual pressure or more. The prescribed residual pressure is, for example, about 9.8 MPa, or the like.

[0145] In the case where the determination result thereof is "Yes", the control device 19 causes the processing to proceed to step S62. On the other hand, in the case where the determination result thereof is "No", the control device 19 causes the processing to return to step S60.

[0146] Next, in step S62, the control device 19 switches the switching valve 89a to a state in which the water electrolysis device 23 side (i.e., the upstream side) in the oxygen supply flow path 24b is open to the oxygen tank 33 side.

[0147] Next, in step S63, the control device 19 executes the process of electrolysis of water by the water electrolysis device 23. The control device 19 makes the pressure of oxygen generated at the anode 53 by electrolysis of water by the water electrolysis unit 41 higher than the pressure of hydrogen generated at the cathode 55. Also, the process is made to proceed to the end phase.

[0148] According to the above-described modification example, in addition to the oxygen tank 33 that stores oxygen generated at the anode 53 by electrolysis of water, the buffer tank 81 is provided, whereby the pressure on the anode 53 side can be increased by oxygen supplied from the buffer tank 81 regardless of the residual pressure of the oxygen tank 33. For example, even in the case where the residual pressure of the oxygen tank 33 is reduced before the start of electrolysis of water, the anode 53 side can be boosted by oxygen stored in advance in the buffer tank 81.

[0149] The buffer tank 81 is connected to a buffer filling flow path 83 branched from an oxygen supply flow path 24b that connects the water electrolysis device 23 and the oxygen tank 33. Thereby, even in the case where the residual pressure of the buffer tank 81 is reduced due to the boost of the anode 53 side before the start of electrolysis of water, oxygen generated at the anode 53 can be filled to the buffer tank 81 after the start of electrolysis of water. By maintaining the residual pressure of the buffer tank 81 to be equal to or higher than a predetermined value, the boost of the anode 53 side can be appropriately performed at the next start.

[0150] By providing the fifth pressure sensor 87a, the residual pressure of the buffer tank 81 can be appropriately maintained to be equal to or higher than a predetermined value. The control device 19 switches the supply destination of oxygen generated at the anode 53 from the buffer tank 81 to the oxygen tank 33 in accordance with the pressure of oxygen stored in the buffer tank 81, whereby the supply of excess oxygen to the buffer tank 81 can be suppressed and the supply of oxygen to the oxygen tank 33 and the buffer tank 81 can be performed with high efficiency.

[0151] In the above-described modification example, the control device 19 can switch to the state where oxygen is supplied to the water electrolysis device 23 from the oxygen tank 33 as in the above-described embodiment in the case where the pressure on the anode 53 side in the state where oxygen is supplied to the water electrolysis device 23 from the buffer tank 81 before the start of electrolysis of water is lower than a predetermined pressure.

[0152] In this case, the control device 19 switches the oxygen supply source from the buffer tank 81 to the oxygen tank 33 in the case where the boost of the anode 53 side by the buffer tank 81 is insufficient. Thereby, the pressure on the anode 53 side can be increased by oxygen supplied from the oxygen tank 33 regardless of the residual pressure of the buffer tank 81. For example, even in the case where the residual pressure of the buffer tank 81 is reduced before the start of electrolysis of water, the anode 53 side can be boosted by oxygen stored in advance in the oxygen tank 33.

[0153] In the above-described embodiment, the control device 19 causes the discharge valve 73b to be in the open state to discharge the fluid from the oxygen supply flow path 24b to the outside in the case where the hydrogen concentration C obtained from the hydrogen concentration sensor 71e is greater than the prescribed concentration, but is not limited thereto.

[0154] For example, the control device 19 can also fill the oxygen tank 33 with oxygen obtained by removing hydrogen from the fluid of the oxygen supply flow path 24b by adsorption of hydrogen or the like.

[0155] The embodiments of the present application suggested as examples are not intended to limit the scope of the application. These embodiments can be implemented in other various forms, and various omissions, substitutions, and changes can be made thereto without departing from the scope of the application. These embodiments, variations thereof, are included in the scope and spirit of the application, and are also included in the scope of the application described in the application and equivalents thereof.

Claims

1. A water electrolysis system, characterized in that, The water electrolysis system comprises: A water electrolysis unit has an electrolyte membrane and an anode and a cathode disposed on both sides of the electrolyte membrane in the thickness direction, and electrolyzes water by applying a voltage between the anode and the cathode; A power source that applies the voltage between the anode and the cathode; An oxygen container that stores oxygen produced at the anode by electrolysis of water in the water electrolysis unit; An oxygen supply source that supplies oxygen to the anode; Control device, The control device performs the following processing: The oxygen pre-stored in the oxygen container is used as the oxygen supply source. The pressure on the anode side of the electrolyte membrane is made higher than the pressure on the cathode side of the electrolyte membrane by supplying the oxygen from the oxygen supply source to the anode before the electrolysis begins. After the anode is pressurized, the voltage is applied such that the pressure of oxygen produced at the anode by the electrolysis of water in the water electrolysis unit is higher than the pressure of hydrogen produced at the cathode by the electrolysis of water in the water electrolysis unit; and The water supply unit supplies water only to the cathode via a cathode supply.

2. The water electrolysis system according to claim 1, characterized in that, The system includes a first oxygen container that stores at least a portion of the oxygen generated at the anode through the electrolysis of water by the water electrolysis unit. The oxygen supply source includes a second oxygen container connected to a flow path branching from the flow path connecting the water electrolysis unit to the first oxygen container, and stores a portion of the oxygen generated at the anode through the electrolysis of water by the water electrolysis unit.

3. The water electrolysis system according to claim 2, characterized in that, The water electrolysis system includes a pressure acquisition unit that acquires the pressure of oxygen in the second oxygen container. The control device performs the following processing: Oxygen generated at the anode after the start of electrolysis is preferentially supplied to the second oxygen container compared to the first oxygen container, and the supply destination of the oxygen generated at the anode is switched from the second oxygen container to the first oxygen container based on the pressure obtained by the pressure acquisition unit.

4. The water electrolysis system according to claim 2, characterized in that, When the pressure on the anode side is less than a predetermined pressure while oxygen is being supplied from the second oxygen container to the anode, the control device switches the oxygen supply source from the second oxygen container to the first oxygen container.

5. A starting method for a water electrolysis device, wherein the starting method is executed by the electronic equipment of the water electrolysis device. The water electrolysis device includes: A water electrolysis unit has an electrolyte membrane and an anode and a cathode disposed on both sides of the electrolyte membrane in the thickness direction, and electrolyzes water by applying a voltage between the anode and the cathode; A power source that applies the voltage between the anode and the cathode; and The electronic device, Its features are, The starting method of the water electrolysis device includes the following steps: The electronic device uses oxygen pre-stored in an oxygen container that stores oxygen generated at the anode through the electrolysis of water by the water electrolysis unit as an oxygen supply source. By supplying oxygen from the oxygen supply source to the anode before the electrolysis begins, the pressure on the anode side of the electrolyte membrane is higher than the pressure on the cathode side of the electrolyte membrane. After the anode is boosted, the electronic device applies the voltage to make the pressure of oxygen generated at the anode by the electrolysis of water by the water electrolysis unit higher than the pressure of hydrogen generated at the cathode by the electrolysis of water by the water electrolysis unit. The electronic device supplies water only to the cathode via a cathode supply.

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