Water electrolysis system

Abstract

After stopping water electrolysis, residual gases in the water electrolysis stack are removed, and high-purity hydrogen gas is generated after restarting water electrolysis. [Solution] The water electrolysis system comprises a water electrolysis stack and a supply system. The water electrolysis stack is made up of multiple membrane electrode assemblies, each having an electrolyte membrane between an anode and a cathode. The anode of the first membrane electrode assembly and the cathode of the second membrane electrode assembly are adjacent to each other and face each other. A third channel is formed on the surface of the first membrane electrode assembly facing the anode, a first channel on the surface facing the cathode, a second channel on the surface of the second membrane electrode assembly facing the anode, and a fourth channel on the surface facing the cathode. The supply system supplies reaction solution to the second and third channels during water electrolysis, supplies a first cleaning solution to the first and fourth channels and a second cleaning solution to the second and third channels during the cleaning process after water electrolysis has stopped, and supplies gas to the first and fourth channels during the preparation process from the stop to the restart of water electrolysis.

Description

Technical Field

[0001] The present disclosure relates to technologies for water electrolysis.

Background Art

[0002] In water electrolysis using a water electrolysis stack in which a plurality of membrane electrode assemblies are stacked, after stopping the water electrolysis, a potential difference is generated due to the hydrogen gas remaining in the cathode part and the oxygen gas remaining in the anode part, and it has been found that each part of the water electrolysis stack deteriorates. Therefore, as a method for removing the gas remaining in the electrode, a method has been proposed in which a reaction solution is supplied to the cathode part and the anode part after stopping the water electrolysis to remove the remaining gas. For example, Patent Document 1 discloses a method for removing the remaining oxygen and hydrogen by continuously supplying pure water to the anode side and the cathode side after stopping energization in a water electrolysis cell having a configuration in which a large number of solid polymer electrolyte membranes are arranged in parallel in series.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the method of Patent Document 1, after removing the remaining gas, the supplied pure water remains on the cathode side. Therefore, when restarting the water electrolysis, there is a problem that the remaining pure water and the hydrogen gas generated by the water electrolysis are discharged at the same time, and the purity of the hydrogen gas decreases. In consideration of the above circumstances, one aspect of the present disclosure aims to remove the oxygen gas and hydrogen gas remaining in the water electrolysis stack after stopping the water electrolysis process, suppress the deterioration of the anode part and the cathode part, and generate high-purity hydrogen gas after restarting the water electrolysis process.

Means for Solving the Problems

[0005] To solve the above problems, a water electrolysis system according to one aspect of the present disclosure comprises a water electrolysis stack for electrolyzing a reaction solution with water, and a supply system, wherein the water electrolysis stack is made up of a plurality of membrane electrode assemblies stacked, each having an electrolyte membrane between an anode and a cathode, and the anode of a first membrane electrode assembly and the cathode of a second membrane electrode assembly are adjacent to each other so as to face each other, and a first channel is formed on the surface facing the cathode of the first membrane electrode assembly, and a second channel is formed on the surface facing the anode of the second membrane electrode assembly The supply system includes a second channel section in which a path is formed, and a third channel section in which a third channel is formed on the surface facing the anode portion of the first film electrode assembly, and a fourth channel is formed on the surface facing the cathode portion of the second film electrode assembly. The supply system supplies reaction solution to the second and third channels during the water electrolysis process, supplies a first cleaning solution to the first and fourth channels and a second cleaning solution to the second and third channels during the cleaning process after the water electrolysis process has stopped, and supplies gas to the first and fourth channels during the preparation process during the period from the stopping to the restart of the water electrolysis process. [Brief explanation of the drawing]

[0006] [Figure 1] This is a diagram showing the configuration of the water electrolysis system in the first embodiment. [Figure 2] This is a schematic diagram of the water electrolysis stack in the first embodiment. [Figure 3] This is a flowchart of the control process in the first embodiment. [Figure 4] This is a schematic diagram of the electrolyte supply in the water electrolysis process in the first embodiment. [Figure 5] This is a schematic diagram of the supply of electrolyte and pure water in the cleaning process in the first embodiment. [Figure 6] This is a schematic diagram of the hydrogen gas supply in the preparation step in the first embodiment. [Figure 7] This is a diagram showing the configuration of the water electrolysis system in the second embodiment. [Figure 8] This is a diagram showing the configuration of the water electrolysis system in the modified example 7. [Figure 9]This is a diagram showing the configuration of the water electrolysis system in the modified example 8. [Figure 10] This is a diagram showing the configuration of the water electrolysis system in modified example 9. [Modes for carrying out the invention]

[0007] The embodiments for implementing this disclosure will be described with reference to the drawings. Note that the dimensions and scale of the elements in each drawing may differ from those of the actual product. Furthermore, the embodiments described below are illustrative examples of embodiments that may be envisioned when implementing this disclosure. Therefore, the scope of this disclosure is not limited to the embodiments exemplified below.

[0008] A: First Embodiment Figure 1 is a diagram showing the configuration of the water electrolysis system 100 in the first embodiment. The water electrolysis system 100 in the first embodiment comprises a liquid storage tank 1, a power supply unit 2, a water electrolysis stack 3, a pure water tank 4, a gas tank 5, a supply system 6, a gas-liquid separator 7, and a gas-liquid separator 8.

[0009] The storage tank 1 is a tank for storing the electrolyte used in water electrolysis. The material of the storage tank 1 can be a resin material (or metal material) that has strong resistance to the corrosive action of the electrolyte. The electrolyte is an aqueous solution containing an electrolyte that facilitates water electrolysis. Examples of electrolytes that can be used include aqueous potassium hydroxide solution and aqueous sodium hydroxide solution. Note that the electrolyte is an example of a "reaction solution".

[0010] Power supply unit 2 is a DC power supply that supplies electricity used for water electrolysis to the water electrolysis stack 3.

[0011] The water electrolysis stack 3 is a mechanism that generates hydrogen gas and oxygen gas from an electrolyte solution by water electrolysis. Figure 2 is a schematic diagram of the water electrolysis stack 3 in the first embodiment. As illustrated in Figure 2, the water electrolysis stack 3 comprises a first membrane electrode assembly 30, a second membrane electrode assembly 40, and a flow channel member 50.

[0012] For example, the first membrane electrode assembly 30 is composed of a stack of an electrolyte membrane 31, a cathode portion 32, and an anode portion 33. Specifically, the electrolyte membrane 31 is disposed between the cathode portion 32 and the anode portion 33.

[0013] The electrolyte membrane 31 is an ion exchange membrane that separates the cathode portion 32 and the anode portion 33. Examples of the electrolyte membrane 31 include an anion exchange membrane that is an electrolyte membrane through which anions such as hydroxide ions (OH - , ) can selectively move.

[0014] The cathode portion 32 is a portion (and further a portion that promotes the generation) where hydrogen gas is generated by water electrolysis. In the cathode portion 32, 4H2O + 4e - → 2H2 + 4OH - hydrogen gas is generated by the first reaction. The cathode portion 32 includes a first catalyst layer 34 and a first diffusion layer 35.

[0015] The first catalyst layer 34 is located between the electrolyte membrane 31 and the first diffusion layer 35. The first catalyst layer 34 is a thin film that adheres to the electrolyte membrane 31 and promotes the first reaction. For example, the first catalyst layer 34 is formed of carbon supporting a metal material such as platinum (Pt). Note that the material of the first catalyst layer 34 is arbitrary, and materials such as nickel (Ni) may be used. <​​​​​​​​​​​​​This second reaction produces oxygen gas. And the overall reaction in water electrolysis stack 3 is as follows: 2H2O → 2H2 + O2 The following reaction occurs. The anode portion 33 includes a second catalyst layer 36 and a second diffusion layer 37.

[0018] The second catalyst layer 36 is located between the electrolyte membrane 31 and the second diffusion layer 37. The second catalyst layer 36 is a thin film that adheres closely to the electrolyte membrane 31 and promotes the second reaction described above. For example, the second catalyst layer 36 is formed from a metallic material such as iridium (Ir), iron (Fe), or nickel (Ni). The second catalyst layer 36 may also be formed from an oxide of the metallic material exemplified above. The electrolyte membrane 31 is located between the first catalyst layer 34 and the second catalyst layer 36.

[0019] The second diffusion layer 37 is an element for efficiently separating and discharging the oxygen gas generated by the second reaction. For example, a porous membrane made of nickel (Ni) foam or a carbon-based material is used as the second diffusion layer 37. The second diffusion layer 37 also functions as an element for efficiently supplying the electrolyte to the second catalyst layer 36 (and further to the electrolyte membrane 31). In addition, the second diffusion layer 37 is formed of a conductive material and also functions as a pathway for electrons exchanged by the second catalyst layer 36.

[0020] In the above explanation, we focused on the relationship between the electrolyte membrane 31, the cathode portion 32, and the anode portion 33 in the first membrane electrode assembly 30, but the relationship between the electrolyte membrane 41, the cathode portion 42, and the anode portion 43 in the second membrane electrode assembly 40 is similar. Specifically, the electrolyte membrane 41 is placed between the cathode portion 42 and the anode portion 43. The cathode portion 42 includes a first catalyst layer 44 and a first diffusion layer 45, and the anode portion 43 includes a second catalyst layer 46 and a second diffusion layer 47.

[0021] The flow channel member 50 includes a first flow channel section 51, a second flow channel section 52, and a third flow channel section 53.

[0022] The first channel section 51 is a plate-shaped structure (separator) formed of a conductive material such as metal. The cathode section 32 is located between the first channel section 51 and the electrolyte membrane 31. A first channel section 54 is formed on the surface of the first channel section 51 facing the cathode section 32.

[0023] The first channel 54 is a channel that communicates with the cathode section 32. The first channel 54 is a channel formed on the surface of the first channel section 51 that faces the cathode section 32. For example, hydrogen gas generated in the cathode section 32 by the first reaction flows through the first channel 54. The first channel 54 also functions as a channel for flowing pure water, which will be described later.

[0024] The second channel section 52 is a plate-shaped structure (separator) formed of a conductive material such as metal. The anode section 43 is located between the second channel section 52 and the electrolyte membrane 41. A second channel section 55 is formed on the surface of the second channel section 52 facing the anode section 43.

[0025] The second channel 55 is a channel that communicates with the anode 43. The second channel 55 is a channel formed on the surface of the second channel 52 that faces the anode 43. For example, oxygen gas generated in the anode 43 by the second reaction flows through the second channel 55. The second channel 55 also functions as a channel for circulating the electrolyte.

[0026] The third channel section 53 is a plate-shaped structure (separator) formed from a conductive material such as metal. The third channel section 53 is located between the anode section 33 and the cathode section 42. A third channel section 56 is formed on the surface of the third channel section 53 facing the anode section 33. A fourth channel section 57 is formed on the surface of the third channel section 53 facing the cathode section 42.

[0027] The third channel 56 is a channel that communicates with the anode 33. The third channel 56 is a channel formed on the surface of the third channel 53 that faces the anode 33. For example, oxygen gas generated in the anode 33 by the second reaction flows through the third channel 56. The third channel 56 also functions as a channel for circulating the electrolyte.

[0028] The fourth channel 57 is a channel that communicates with the cathode section 42. The fourth channel 57 is a channel formed on the surface of the third channel section 53 that faces the cathode section 42. For example, hydrogen gas generated in the cathode section 42 by the first reaction flows through the fourth channel 57. The fourth channel 57 also functions as a channel for flowing pure water, which will be described later.

[0029] As described above, the first membrane electrode assembly 30 is installed between the first channel section 51 and the third channel section 53, and the second membrane electrode assembly 40 is installed between the second channel section 52 and the third channel section 53. In other words, in the water electrolysis stack 3, the first membrane electrode assembly 30 and the second membrane electrode assembly 40 are stacked. Specifically, the anode portion 33 of the first membrane electrode assembly 30 and the cathode portion 42 of the second membrane electrode assembly 40 are adjacent to each other and face each other.

[0030] Furthermore, it can be said that the water electrolysis stack 3 is composed of multiple water electrolysis cells. A water electrolysis cell is the smallest unit of the mechanism that generates hydrogen and oxygen from an electrolyte by water electrolysis. In the water electrolysis stack 3, a first water electrolysis cell and a second water electrolysis cell are stacked. The first water electrolysis cell consists of a first channel section 51, a first membrane electrode assembly 30, and a third channel section 53. The second water electrolysis cell consists of a second channel section 52, a second membrane electrode assembly 40, and a third channel section 53.

[0031] As illustrated in Figure 1, the pure water tank 4 is a tank for storing pure water. Resin materials (or metal materials) can be used as the material for the pure water tank 4.

[0032] Gas tank 5 is a tank for storing hydrogen gas. The material used for gas tank 5 may be resin or metal.

[0033] The supply system 6 is a mechanism that supplies fluid stored in each tank to the water electrolysis stack 3. The supply system 6 includes a piping system 60 and a control system 80.

[0034] The piping system 60 supplies hydrogen gas or multiple types of liquids to the water electrolysis stack 3. The piping system 60 includes a first pipe 61, a second pipe 62, a third pipe 63, a fourth pipe 64, a fifth pipe 65, a sixth pipe 66, a seventh pipe 67, an eighth pipe 68, a first branch 71, a second branch 72, a valve device 73, an electrolyte pump 75, a pure water pump 76, and a gas pump 77.

[0035] The first pipe 61 connects the liquid storage tank 1 to the first branch section 71. The first branch section 71 is the point where the first pipe 61 branches into the second pipe 62 and the third pipe 63. The second pipe 62 supplies electrolyte to the second flow path 55. The third pipe 63 supplies electrolyte to the third flow path 56. In other words, the second pipe 62 connects the first branch section 71 and the second flow path 55. Also, the third pipe 63 connects the first branch section 71 and the third flow path 56.

[0036] The fourth pipe 64 connects the pure water tank 4 to the valve device 73. The fifth pipe 65 connects the gas tank 5 to the valve device 73. The valve device 73 is a device that supplies either pure water supplied from the fourth pipe 64 or hydrogen gas supplied from the fifth pipe 65 to the sixth pipe 66 by opening and closing a valve. In other words, the valve device 73 is connected to the fourth pipe 64, the fifth pipe 65, and the sixth pipe 66.

[0037] The sixth pipe 66 connects the valve device 73 to the second branch section 72. The second branch section 72 is the point where the sixth pipe 66 branches into the seventh pipe 67 and the eighth pipe 68. The seventh pipe 67 supplies pure water or hydrogen gas to the first flow path 54. The eighth pipe 68 supplies pure water or hydrogen gas to the fourth flow path 57. In other words, the seventh pipe 67 connects the second branch section 72 to the first flow path 54. Also, the eighth pipe 68 connects the second branch section 72 to the fourth flow path 57. Resin materials (or metal materials) can be used as the material for each pipe.

[0038] The electrolyte pump 75 is installed in the first piping 61 between the liquid storage tank 1 and the first branching section 71. The electrolyte pump 75 supplies the electrolyte drawn from the liquid storage tank 1 to the first piping 61. The electrolyte supplied to the first piping 61 branches into the second piping 62 and the third piping 63 at the first branching section 71, and is supplied to the second flow path 55 via the second piping 62 and to the third flow path 56 via the third piping 63. In other words, the electrolyte pump 75 is a pump that supplies electrolyte to the second flow path 55 and the third flow path 56.

[0039] The pure water pump 76 is installed in the fourth piping 64 between the pure water tank 4 and the valve device 73. The pure water pump 76 draws pure water from the pure water tank 4 and supplies it to the sixth piping 66 via the fourth piping 64 and the valve device 73. The pure water supplied to the sixth piping 66 branches off into the seventh piping 67 and the eighth piping 68 at the second branching section 72, and is supplied to the first flow path 54 via the seventh piping 67 and to the fourth flow path 57 via the eighth piping 68. In other words, the pure water pump 76 is a pump that supplies pure water to the first flow path 54 and the fourth flow path 57.

[0040] The gas pump 77 is installed in the fifth piping 65 between the gas tank 5 and the valve device 73. The gas pump 77 draws hydrogen gas from the gas tank 5 and supplies it to the sixth piping 66 via the fifth piping 65 and the valve device 73. The hydrogen gas supplied to the sixth piping 66 branches off into the seventh piping 67 and the eighth piping 68 at the second branching section 72, and is supplied to the first flow path 54 via the seventh piping 67 and to the fourth flow path 57 via the eighth piping 68. In other words, the gas pump 77 is a pump that supplies hydrogen gas to the first flow path 54 and the fourth flow path 57.

[0041] The control system 80 controls the supply of hydrogen gas or multiple liquids to the water electrolysis stack 3 by controlling the state of the piping system 60. The control system 80 includes a control device 81 and a storage device 82.

[0042] The control device 81 consists of one or more processors that control each element of the control system 80. Specifically, the control device 81 is composed of one or more types of processors, such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit).

[0043] The storage device 82 is one or more memories that store programs executed by the control device 81 and data used by the control device 81. The storage device 82 is composed of known recording media, such as magnetic recording media or semiconductor recording media. The storage device 82 may be composed of a combination of multiple types of recording media. A portable recording media that can be attached to and detached from the control system 80 may be used as the storage device 82.

[0044] The gas-liquid separator 7 is a device that separates and discharges oxygen gas generated by water electrolysis from the electrolyte. The gas-liquid separator 7 is connected to the second channel 55, the third channel 56, and the storage tank 1, respectively. The oxygen gas generated by the first membrane electrode assembly 30 and the excess electrolyte supplied from the storage tank 1 that is not consumed by water electrolysis are supplied to the gas-liquid separator 7 via the second channel 55. Similarly, the oxygen gas generated by the second membrane electrode assembly 40 and the excess electrolyte supplied from the storage tank 1 that is not consumed by water electrolysis are supplied to the gas-liquid separator 7 via the third channel 56. The gas-liquid separator 7 is a device that separates the oxygen gas supplied from the second channel 55 and the third channel 56 from the electrolyte. The oxygen gas separated by the gas-liquid separator 7 is recovered from the gas-liquid separator 7 via a discharge pipe. The electrolyte separated by the gas-liquid separator 7 is sent to the storage tank 1.

[0045] The gas-liquid separator 8 is connected to the first flow path 54 and the fourth flow path 57, respectively. The gas-liquid separator 8 is a device that separates hydrogen gas from the electrolyte. The separated hydrogen gas is recovered from the gas-liquid separator 8 via the discharge pipe. In the cathode sections 32 and 42, the water of the electrolyte supplied to the cathode sections 32 and 42 is consumed, so the hydrogen gas generated in the cathode sections 32 and 42 is hardly mixed with the electrolyte. Therefore, the small amount of electrolyte accumulated in the gas-liquid separator 8 is discarded without being recovered into the storage tank 1.

[0046] Figure 3 is a flowchart illustrating the specific steps of the processing performed by the supply system 6. Processing begins in response to instructions from the user to the water electrolysis system 100. As illustrated in Figure 3, the processing in Figure 3 includes a water electrolysis process, a washing process, and a preparation process, and these processes are repeated in sequence. While these processes may be started in any order, in the first embodiment, the water electrolysis process will be described first.

[0047] Figure 4 is a schematic diagram of the electrolyte supply in the water electrolysis process. As illustrated in Figure 4, the control device 81 drives the electrolyte pump 75. The electrolyte drawn in by the electrolyte pump 75 from the storage tank 1 is supplied to the first pipe 61. The electrolyte supplied to the first pipe 61 branches into the second pipe 62 and the third pipe 63 at the first branching section 71, and is supplied to the second flow path 55 via the second pipe 62 and to the third flow path 56 via the third pipe 63. In other words, the supply system 6 functions as an element (supply unit) that supplies electrolyte to the second flow path 55 and the third flow path 56 in the water electrolysis process.

[0048] The electrolyte supplied to the second channel 55 by the supply system 6 flows through the second channel 55. The electrolyte flowing through the second channel 55 passes through the anode section 43 and the electrolyte membrane 41 to reach the cathode section 42. When the power supply unit 2 is supplying power to the water electrolysis stack 3, oxygen gas is generated in the anode section 43 by the aforementioned second reaction using the electrolyte, and hydrogen gas is generated in the cathode section 42 by the aforementioned first reaction.

[0049] The electrolyte supplied to the third channel 56 by the supply system 6 flows through the third channel 56. The electrolyte flowing through the third channel 56 passes through the anode section 33 and the electrolyte membrane 31 to reach the cathode section 32. When the power supply unit 2 is supplying power to the water electrolysis stack 3, oxygen gas is generated in the anode section 33 by the aforementioned second reaction using the electrolyte, and hydrogen gas is generated in the cathode section 32 by the aforementioned first reaction.

[0050] The oxygen gas and excess electrolyte generated in the anodes 33 and 43 are sent to the gas-liquid separator 7 via the second channel 55 and the third channel 56. The oxygen gas and excess electrolyte are separated into oxygen gas and electrolyte by the gas-liquid separator 7. The separated oxygen gas is recovered from the discharge pipe. The electrolyte separated from the oxygen gas is recovered into the storage tank 1.

[0051] The hydrogen gas generated in the cathode sections 32 and 42, mixed with the electrolyte, is sent to the gas-liquid separator 8 via the first channel 54 and the fourth channel 57. The hydrogen gas and electrolyte are separated into hydrogen gas and electrolyte by the gas-liquid separator 8, and the separated hydrogen is recovered through the discharge pipe. The electrolyte accumulated in the gas-liquid separator 8 is discarded without being recovered into the storage tank 1.

[0052] The water electrolysis process is stopped when a user instructs the water electrolysis system 100 to stop, or when a problem occurs in the water electrolysis system 100. Specifically, stopping the water electrolysis process means stopping the power supply from the power supply unit 2 to the water electrolysis stack 3. When the water electrolysis process is stopped, hydrogen gas remains in the first channel 54 and the fourth channel 57, and oxygen gas remains in the second channel 55 and the third channel 56, so a potential difference is created between the third channel 56 and the fourth channel 57. Specifically, the potential of the third channel 56 decreases, and the potential of the fourth channel 57 increases. Since the third channel 56 and the fourth channel 57 are formed on opposite sides of the third channel section 53, the third channel 56 and the fourth channel 57 are electrically conductive. Therefore, as described above, when a potential difference is created between the third channel 56 and the fourth channel 57, a current flows between the third channel 56 and the fourth channel 57 in the opposite direction to the water electrolysis process.

[0053] When current flows in the opposite direction, a first reaction occurs in the anode section 33, which is the opposite of the second reaction in the water electrolysis process, resulting in deterioration of the anode section 33. Similarly, a second reaction occurs in the cathode section 42, which is the opposite of the first reaction in the water electrolysis process, resulting in deterioration of the cathode section 42. By continuing to supply electrolyte to the second channel 55 and the third channel 56 even after stopping the water electrolysis process, oxygen gas remaining in the second channel 55 and the third channel 56 is removed. However, hydrogen gas remaining in the first channel 54 and the fourth channel 57 cannot be removed. Therefore, as illustrated in Figure 3, the supply system 6 performs a cleaning process after stopping the water electrolysis process.

[0054] Figure 5 is a schematic diagram of the supply of electrolyte and pure water in the cleaning process. The cleaning process removes oxygen gas remaining in the second channel 55 and the third channel 56, and removes hydrogen gas remaining in the first channel 54 and the fourth channel 57.

[0055] As illustrated in Figure 5, in the cleaning process, the control device 81 drives the electrolyte pump 75, similar to the water electrolysis process, to supply electrolyte from the storage tank 1 to the second channel 55 and the third channel 56. The electrolyte supplied to the second channel 55 flows through the second channel 55 and removes any oxygen gas remaining in the second channel 55 when the water electrolysis process is stopped. Similarly, the electrolyte supplied to the third channel 56 flows through the third channel 56 and removes any oxygen gas remaining in the third channel 56 when the water electrolysis process is stopped. Therefore, the oxygen concentration in the second channel 55 and the third channel 56 can be reduced. Note that the electrolyte supplied from the storage tank 1 to the second channel 55 and the third channel 56 in the cleaning process is an example of the "second cleaning solution". In the above embodiment, the electrolyte used in the water electrolysis process is also used as the second cleaning solution. Therefore, the configuration of the water electrolysis system 100 can be simplified compared to a configuration in which a liquid different from the electrolyte used in the water electrolysis process is supplied as a second cleaning solution to the second channel 55 and the third channel 56.

[0056] The supply of electrolyte and pure water in the cleaning process are carried out in parallel. The control device 81 drives the pure water pump 76 and controls the opening and closing of the valve device 73. The pure water drawn in by the pure water pump 76 from the pure water tank 4 is supplied to the fourth pipe 64. The pure water supplied to the fourth pipe 64 is supplied to the sixth pipe 66 via the valve device 73. The pure water supplied to the sixth pipe 66 branches into the seventh pipe 67 and the eighth pipe 68 at the second branching section 72, and is supplied to the first flow path 54 via the seventh pipe 67, and to the fourth flow path 57 via the eighth pipe 68. The pure water supplied to the first flow path 54 flows through the first flow path 54 and removes hydrogen gas remaining in the first flow path 54 when the water electrolysis process is stopped. Similarly, the pure water supplied to the fourth flow path 57 flows through the fourth flow path 57 and removes hydrogen gas remaining in the fourth flow path 57 when the water electrolysis process is stopped. Therefore, the hydrogen concentration in the first channel 54 and the fourth channel 57 can be reduced. In other words, the supply system 6 functions as an element (cleaning unit) that supplies pure water to the first channel 54 and the fourth channel 57 and electrolyte to the second channel 55 and the third channel 56 during the cleaning process after the water electrolysis process has been stopped. The pure water supplied from the pure water tank 4 to the first channel 54 and the fourth channel 57 during the cleaning process is an example of the "first cleaning solution".

[0057] The residual oxygen gas in the second channel 55 and the third channel 56, along with the supplied electrolyte, are sent to a gas-liquid separator 7 connected to the second channel 55 and the third channel 56. The oxygen gas and the supplied electrolyte are separated into oxygen gas and electrolyte by the gas-liquid separator 7. The separated oxygen gas is recovered through the discharge pipe. The electrolyte separated from the oxygen gas is recovered into the storage tank 1.

[0058] The residual hydrogen gas in the first channel 54 and the fourth channel 57, along with the supplied pure water, are sent to the gas-liquid separator 8 via the first channel 54 and the fourth channel 57. The hydrogen gas and the supplied pure water are separated into hydrogen gas and pure water by the gas-liquid separator 8, and the separated hydrogen is recovered from the discharge pipe. The pure water accumulated in the gas-liquid separator 8 is discarded without being recovered.

[0059] As mentioned above, in the water electrolysis process, the electrolyte water supplied to the cathode sections 32 and 42 is consumed in the cathode sections 32 and 42. Therefore, the hydrogen gas generated in the cathode sections 32 and 42 is hardly mixed with the electrolyte. On the other hand, when the water electrolysis process is restarted after the cleaning process, the pure water used to discharge the hydrogen gas in the cleaning process remains in the first channel 54 and the fourth channel 57. Therefore, the remaining pure water mixes with the hydrogen gas generated in the cathode sections 32 and 42. In other words, the purity of the hydrogen gas generated in the water electrolysis process becomes low. Therefore, as illustrated in Figure 3, the supply system 6 performs a preparation process after the cleaning process.

[0060] Figure 6 is a schematic diagram of the hydrogen gas supply in the preparation process. The preparation process is a process of removing the pure water remaining in the first channel 54 and the fourth channel 57 in the washing process.

[0061] As illustrated in Figure 6, the control device 81 drives the gas pump 77 and controls the opening and closing of the valve device 73. The hydrogen gas drawn in by the gas pump 77 from the gas tank 5 is supplied to the fifth pipe 65. The hydrogen gas supplied to the fifth pipe 65 is supplied to the sixth pipe 66 via the valve device 73. The hydrogen gas supplied to the sixth pipe 66 branches into the seventh pipe 67 and the eighth pipe 68 at the second branching section 72, and is supplied to the first flow path 54 via the seventh pipe 67 and to the fourth flow path 57 via the eighth pipe 68. The hydrogen gas supplied to the first flow path 54 flows through the first flow path 54 and removes any pure water remaining in the first flow path 54 when the cleaning process is stopped. The hydrogen gas supplied to the fourth flow path 57 flows through the fourth flow path 57 and removes any pure water remaining in the fourth flow path 57 when the cleaning process is stopped. Therefore, the supply system 6 functions as an element (preparation unit) that supplies gas to the first channel 54 and the fourth channel 57 during the preparation process from the stop to the restart of the water electrolysis process.

[0062] The pure water remaining in the first channel 54 and the fourth channel 57, along with the supplied hydrogen gas, are sent to the gas-liquid separator 8 via the first channel 54 and the fourth channel 57. The gas-liquid separator 8 separates the remaining pure water and the supplied hydrogen gas into hydrogen gas and pure water, and the separated hydrogen is recovered through the discharge pipe. The pure water accumulated in the gas-liquid separator 8 is discarded without being recovered into the storage tank 1.

[0063] Once the preparation process is complete, the supply system 6 performs the water electrolysis process again. Therefore, compared to a configuration in which hydrogen gas is not supplied to the first channel 54 and the fourth channel 57 during the preparation process, it is possible to produce hydrogen gas with less contamination from pure water (i.e., higher purity).

[0064] B: Second Embodiment A second embodiment of this disclosure will now be described. For elements whose function is the same as in the first embodiment in each of the embodiments described below, the same reference numerals as in the first embodiment will be used, and detailed descriptions of each will be omitted as appropriate.

[0065] Figure 7 is a diagram showing the configuration of the water electrolysis system 100 in the second embodiment. As illustrated in Figure 7, the water electrolysis system 100 in the second embodiment further comprises hydrogen transfer piping 9.

[0066] The hydrogen transfer piping 9 connects the gas-liquid separator 8 and the gas tank 5. In other words, the hydrogen gas generated in the gas-liquid separator 8 is supplied to the gas tank 5. The hydrogen gas supplied to the gas tank 5 is not only recovered via a discharge pipe installed in the gas tank 5, but is also used as the gas supplied to the first channel 54 and the fourth channel 57 in the preparation process. Therefore, the configuration of the water electrolysis system 100 can be simplified compared to a configuration in which hydrogen gas prepared separately from the hydrogen gas generated in the water electrolysis process is used in the preparation process.

[0067] C: Variant The following are examples of specific modifications that may be added to the embodiments exemplified above. Two or more embodiments selected from the following examples may be merged as appropriate, provided they do not contradict each other.

[0068] (1) In each embodiment, the water electrolysis stack 3 is shown to include two membrane electrode assemblies, a first membrane electrode assembly 30 and a second membrane electrode assembly 40. However, the water electrolysis stack 3 may also be configured to include a stack of three or more membrane electrode assemblies. In a configuration in which the water electrolysis stack 3 includes a stack of three or more membrane electrode assemblies, one of two adjacent membrane electrode assemblies among the three or more is an example of a "first membrane electrode assembly," and the other is an example of a "second membrane electrode assembly."

[0069] (2) In each embodiment, the liquid used in the water electrolysis process is shown to be an electrolyte, but this is not limited to any liquid that can generate hydrogen gas and oxygen gas in the water electrolysis process. For example, pure water may be used in the water electrolysis process. In other words, pure water is an example of a "reaction solution".

[0070] (3) In each embodiment, the gas used in the preparation step is shown to be hydrogen gas, but the gas used in the preparation step is not limited to the above examples. For example, the gas used in the preparation step may be nitrogen gas. However, in the configuration in which nitrogen gas is used in the preparation step, nitrogen gas may remain in the first channel 54 and the fourth channel 57 at the end of the preparation step. Therefore, immediately after restarting the water electrolysis process, nitrogen gas may be mixed into the hydrogen gas sent to the gas-liquid separator 8 via the first channel 54 and the fourth channel 57. In contrast, the configuration in which hydrogen gas is used in the preparation step has the advantage that hydrogen gas with a low mixing ratio of other gases (i.e., high purity) can be produced in the water electrolysis process. Therefore, from the viewpoint of producing high-purity hydrogen gas, the configuration in which hydrogen gas is used in the preparation step is particularly preferred.

[0071] (4) In each embodiment, the electrolyte and pure water separated from the hydrogen gas by the gas-liquid separator 8 are shown to be discarded without being recovered, but the electrolyte or the pure water may be recovered into the storage tank 1.

[0072] (5) In each embodiment, the configuration is shown in which the supply of electrolyte to the second channel 55 and the third channel 56 and the supply of pure water to the first channel 54 and the fourth channel 57 are carried out in parallel during the cleaning process. However, the supply of electrolyte and the supply of pure water in the cleaning process may be carried out sequentially in different periods.

[0073] (6) In each embodiment, a configuration is shown in which the preparation step is performed after the cleaning step, but this is not limited to this. For example, in the cleaning step, the supply of pure water to the first channel 54 and the fourth channel 57 may be completed first, and the preparation step may be performed in parallel while the electrolyte is still being supplied to the second channel 55 and the third channel 56.

[0074] (7) In each embodiment, a configuration is shown in which pure water is supplied to the first channel 54 and the fourth channel 57 during the cleaning process, but an electrolyte may also be supplied. Figure 8 is a diagram of the water electrolysis system 100 in modified example 7.

[0075] As illustrated in Figure 8, the supply system 6 in modified example 7 further comprises a valve device 74, a ninth pipe 69, and a tenth pipe 70. The valve device 74 is a device that supplies the electrolyte supplied to the first pipe 61 to either only the ninth pipe 69, or to both the ninth pipe 69 and the tenth pipe 70, by opening and closing a valve. That is, the valve device 74 is connected to the first pipe 61, the ninth pipe 69, and the tenth pipe 70. The ninth pipe 69 is the pipe connecting the valve device 74 and the first branch section 71. The tenth pipe 70 is the pipe connecting the valve device 74 and the valve device 73. In modified example 7, the first pipe 61 is the pipe connecting the liquid storage tank 1 and the valve device 74. The electrolyte pump 75 is installed between the liquid storage tank 1 and the valve device 74 in the first pipe 61.

[0076] In the water electrolysis process in Modification 7, the control device 81 drives the electrolyte pump 75 and controls the opening and closing of the valve device 74. The electrolyte pump 75 draws in the electrolyte from the storage tank 1 and supplies it to the first pipe 61. The electrolyte supplied to the first pipe 61 is supplied to the ninth pipe 69 via the valve device 74. The electrolyte supplied to the ninth pipe 69 branches into the second pipe 62 and the third pipe 63 at the first branching section 71, and is supplied to the second flow path 55 via the second pipe 62 and to the third flow path 56 via the third pipe 63. In other words, the supply system 6 functions as an element (supply unit) that supplies electrolyte to the second flow path 55 and the third flow path 56 in the water electrolysis process.

[0077] In the cleaning process in Modified Example 7, the control device 81 drives the electrolyte pump 75 and controls the opening and closing of valve devices 73 and 74. The electrolyte pump 75 draws in the electrolyte from the storage tank 1 and supplies it to the first pipe 61. The electrolyte supplied to the first pipe 61 is supplied to the ninth pipe 69 and the tenth pipe 70 via valve device 74. The electrolyte supplied to the ninth pipe 69 is branched at the first branching section 71 into the second pipe 62 and the third pipe 63, similar to the water electrolysis process, and is supplied to the second flow path 55 via the second pipe 62 and to the third flow path 56 via the third pipe 63. On the other hand, the electrolyte supplied to the tenth pipe 70 is supplied to the sixth pipe 66 via valve device 73. The electrolyte supplied to the sixth pipe 66 branches off to the seventh pipe 67 and the eighth pipe 68 at the second branching section 72, is supplied to the first channel 54 via the seventh pipe 67, and is supplied to the fourth channel 57 via the eighth pipe 68. The electrolyte supplied to the first channel 54 and the fourth channel 57 in the cleaning process is an example of the "first cleaning solution".

[0078] As explained above, the supply system 6 of modified example 7 functions as an element (cleaning unit) that supplies electrolyte to the first channel 54, second channel 55, third channel 56, and fourth channel 57 during the cleaning process after the water electrolysis process has stopped. However, in the configuration where the first cleaning solution is electrolyte, the electrolyte supplied during the cleaning process and remaining in the first channel 54 and fourth channel 57 is removed by the hydrogen gas supplied during the preparation process. The hydrogen gas supplied during the preparation process causes the water in the remaining electrolyte to evaporate, and there is a possibility that components of the electrolyte will remain. The remaining high concentration of electrolyte components may lead to deterioration of the cathode section (32, 42). In contrast, in the configurations of the first and second embodiments where the first cleaning solution is pure water, there is an advantage that even if the remaining pure water evaporates, the cathode section (32, 42) is less likely to deteriorate. Therefore, from the viewpoint of preventing deterioration of the cathode section (32, 42), a configuration in which the first cleaning solution is pure water is particularly preferable.

[0079] (8) In each embodiment, a configuration for supplying electrolyte to the second channel 55 and the third channel 56 has been shown, but pure water may also be supplied. Figure 9 is a diagram of the water electrolysis system 100 in modified example 8.

[0080] As illustrated in Figure 9, the supply system 6 in modified example 8 further comprises a valve device 74, a ninth pipe 69, a tenth pipe 70, an eleventh pipe 78, and a third branch section 79. The first pipe 61 connects the liquid storage tank 1 to the valve device 74. The ninth pipe 69 connects the valve device 74 to the first branch section 71. The fourth pipe 64 connects the pure water tank 4 to the third branch section 79. The third branch section 79 is the part where the fourth pipe 64 branches into the tenth pipe 70 and the eleventh pipe 78. The tenth pipe 70 connects the third branch section 79 to the valve device 74. The eleventh pipe 78 connects the third branch section 79 to the valve device 73. In other words, the valve device 74 is connected to the first pipe 61, the ninth pipe 69, and the tenth pipe 70. The valve device 74 is a device that supplies either the electrolyte supplied to the first pipe 61 or the pure water supplied to the fourth pipe 64 to the ninth pipe 69 by opening and closing a valve.

[0081] In the water electrolysis process in modified example 8, the control device 81 drives the electrolyte pump 75 and controls the opening and closing of the valve device 74. The electrolyte pump 75 draws in the electrolyte from the storage tank 1 and supplies it to the first pipe 61. The electrolyte supplied to the first pipe 61 is supplied to the ninth pipe 69 via the valve device 74. The electrolyte supplied to the ninth pipe 69 branches into the second pipe 62 and the third pipe 63 at the first branching section 71, and is supplied to the second flow path 55 via the second pipe 62 and to the third flow path 56 via the third pipe 63. In other words, the supply system 6 functions as an element (supply unit) that supplies electrolyte to the second flow path 55 and the third flow path 56 in the water electrolysis process.

[0082] In the cleaning process in modified example 8, the control device 81 starts the pure water pump 76 and controls the opening and closing of valve devices 73 and 74. The pure water drawn in by the pure water pump 76 from the pure water tank 4 is supplied to the fourth pipe 64. The pure water supplied to the fourth pipe 64 branches off to the tenth pipe 70 and the eleventh pipe 78 at the third branching section 79, is supplied to the ninth pipe 69 via valve device 74, and is supplied to the sixth pipe 66 via valve device 73. The pure water supplied to the ninth pipe 69 branches off to the second pipe 62 and the third pipe 63 at the first branching section 71, is supplied to the second flow path 55 via the second pipe 62, and is supplied to the third flow path 56 via the third pipe 63. The pure water supplied to the sixth pipe 66 branches off at the second branching section 72 into the seventh pipe 67 and the eighth pipe 68, and is supplied to the first flow path 54 via the seventh pipe 67, and to the fourth flow path 57 via the eighth pipe 68. The pure water supplied to the second flow path 55 and the third flow path 56 in the washing process is an example of the "second washing liquid".

[0083] As described above, the supply system 6 of modified example 8 functions as an element (cleaning unit) that supplies pure water to the first channel 54, the second channel 55, the third channel 56, and the fourth channel 57 during the cleaning process after the water electrolysis process has stopped. In this embodiment, the configuration of the water electrolysis system 100 can be simplified compared to a configuration in which pure water separate from the pure water tank 4 is supplied to the second channel 55 and the third channel 56 during the cleaning process.

[0084] (9) In each embodiment, a configuration was shown in which the pure water stored in the pure water tank 4 is supplied to the first channel 54 and the fourth channel 57 in the washing process. However, the supply destination of the pure water stored in the pure water tank 4 is not limited to the washing process, as long as it can be used in the washing process. Figure 10 is a configuration diagram of the water electrolysis system 100 in modified example 9. As illustrated in Figure 10, a configuration is envisioned in which a valve device 74 is provided in the middle of the fourth pipe 64, and a pure water supply line is provided connecting the pure water tank 4 and the liquid storage tank 1. In this configuration, when pure water is supplied from the pure water tank 4 to the liquid storage tank 1, the component concentration of the electrolyte in the liquid storage tank 1 can be adjusted. Therefore, the configuration of the water electrolysis system 100 can be simplified compared to a configuration in which pure water other than that from the pure water tank 4 is supplied to the liquid storage tank 1.

[0085] (10) In each embodiment, the electrolyte membrane (31,41) is shown to be an anion exchange membrane as an example, but the type of electrolyte membrane (31,41) is not limited to the above examples as long as hydrogen and oxygen can be obtained by electrolyzing the reaction solution with water. For example, a configuration in which the electrolyte membrane (31,41) is a proton exchange membrane is also conceivable. However, in the configuration in which the electrolyte membrane (31,41) is an anion exchange membrane, a non-precious metal catalyst can be used as the catalyst compared to the configuration in which the electrolyte membrane (31,41) is a proton exchange membrane, and thus the manufacturing cost can be reduced.

[0086] In the configuration where the electrolyte membrane (31,41) is a proton exchange membrane, pure water is used as the reaction solution, for example. In the configuration where the electrolyte membrane (31,41) is a proton exchange membrane, pure water is electrolyzed in the water electrolysis step. Therefore, in the washing step as well, it is preferable that pure water is used as the first washing solution and the second washing solution. With the above configuration, there is no need to prepare the first washing solution and the second washing solution used in the washing step separately from pure water, which has the advantage of simplifying the configuration of the water electrolysis system 100.

[0087] However, electrolytes other than pure water used in the water electrolysis process may be used in the cleaning process. For example, in a configuration where the electrolyte is used as the first cleaning solution, the components of the residual electrolyte may become concentrated due to the consumption of water in the water electrolysis reaction, which may result in deterioration of the cathode section (32,42). Therefore, from the viewpoint of suppressing deterioration of the cathode section (32,42), a configuration in which pure water, which is the reaction solution, is also used as the first and second cleaning solutions in the cleaning process is preferable. That is, in a preferred configuration in which the electrolyte membrane (31,41) is a proton exchange membrane, pure water is used as the "reaction solution," "first cleaning solution," and "second cleaning solution." Therefore, in a configuration in which the electrolyte membrane (31,41) is a proton exchange membrane, deterioration of the cathode section (32,42) due to the concentration of the electrolyte is not a problem.

[0088] Furthermore, when this disclosure is applied to a configuration in which the electrolyte membrane (31,41) is a proton exchange membrane and pure water is used as the reaction solution, the overall configuration of the water electrolysis system 100 will be the same as the configuration illustrated in Figure 8.

[0089] (11) The notation "nth" (where n is a natural number) in this application is used solely as a formal and convenient label to distinguish each element in notation and has no substantive meaning whatsoever. Therefore, there is no room for restrictive interpretation of the position or manufacturing order of each element based on the notation "nth".

[0090] D: Addendum From the forms exemplified above, the following configuration can be understood, for example.

[0091] A water electrolysis system according to one aspect of the present disclosure (Aspect 1) comprises a water electrolysis stack for electrolyzing a reaction solution with water, and a supply system, wherein the water electrolysis stack is made up of a plurality of membrane electrode assemblies stacked, each having an electrolyte membrane between an anode and a cathode, and the anode of a first membrane electrode assembly and the cathode of a second membrane electrode assembly are adjacent to each other and facing each other, and a first channel is formed on the surface of the first membrane electrode assembly facing the cathode, and a second channel is formed on the surface of the second membrane electrode assembly facing the anode The supply system includes a section and a third channel section in which a third channel is formed on the surface of the first membrane electrode assembly facing the anode section and a fourth channel is formed on the surface of the second membrane electrode assembly facing the cathode section, wherein the supply system supplies reaction solution to the second channel and the third channel during the water electrolysis process, supplies a first cleaning solution to the first channel and the fourth channel and supplies a second cleaning solution to the second channel and the third channel during the cleaning process after the water electrolysis process has stopped, and supplies gas to the first channel and the fourth channel during the preparation process during the period from the stopping to the restart of the water electrolysis process. According to the above embodiment, in the cleaning process, the supply of the first cleaning solution to the first channel and the fourth channel and the supply of the second cleaning solution to the second channel and the third channel allows for the discharge of gas accumulating in each channel. That is, the hydrogen concentration in the first channel and the fourth channel and the oxygen concentration in the second channel and the third channel can be reduced. By reducing the gas concentration in each channel, deterioration of the anode section and the cathode section is suppressed. Furthermore, in the preparation step, supplying gas to the first and fourth channels discharges the first cleaning solution from the first and fourth channels. Therefore, compared to a configuration in which gas is not supplied to the first and fourth channels in the preparation step, it is possible to produce hydrogen with less mixing of the first cleaning solution (i.e., higher purity). Note that the "reaction solution," "first cleaning solution," and "second cleaning solution" are liquids such as pure water or electrolyte.

[0092] In a specific example of Embodiment 1 (Embodiment 2), the first cleaning solution is pure water. In the above embodiment, pure water is supplied to the first and fourth channels during the cleaning process. In a configuration where the first cleaning solution is an electrolyte, when gas is supplied to the first and fourth channels during the preparation process, the concentration of components due to the evaporation of the remaining first cleaning solution may cause deterioration of the channels and cathode. In contrast, in a configuration where the first cleaning solution is pure water, deterioration of the channels and cathode is less likely to occur even if the remaining first cleaning solution evaporates.

[0093] In Embodiment 1 or a specific example of Embodiment 2 (Embodiment 3), the second cleaning solution is the reaction solution. In the above embodiments, the reaction solution used for water electrolysis is also used as the second cleaning solution. Therefore, the configuration of the water electrolysis system can be simplified compared to a configuration in which a liquid different from the reaction solution used for water electrolysis is supplied to the second and third channels as the second cleaning solution. Note that the "reaction solution" is a liquid such as pure water or an electrolyte.

[0094] In any specific example of Embodiments 1 to 3 (Embodiment 4), the gas is hydrogen. In the above embodiments, hydrogen is supplied to the first and fourth channels during the preparation step. Therefore, compared to a configuration in which a gas other than hydrogen is supplied to the first and fourth channels during the preparation step, hydrogen with a lower mixing ratio of other gases (i.e., higher purity) can be produced in the water electrolysis step restarted after the preparation step.

[0095] In a specific example (Aspect 5) relating to aspects 1 to 4, the hydrogen is generated by the water electrolysis stack in the water electrolysis process. In these embodiments, the hydrogen generated in the water electrolysis process is also used as hydrogen for the preparation process. Therefore, the configuration of the water electrolysis system can be simplified compared to a configuration in which hydrogen different from the hydrogen generated in the water electrolysis process is supplied to the first and fourth channels as hydrogen for the preparation process.

[0096] In specific examples relating to embodiments 1 to 3 (embodiment 6), the gas is nitrogen. In the embodiments described above, nitrogen is supplied to the first and fourth channels during the preparation process. However, in the configuration in which nitrogen is used during the preparation process, there is a possibility that nitrogen will remain in the first and fourth channels at the end of the preparation process. Therefore, there is a high possibility that hydrogen mixed with nitrogen will be produced in the water electrolysis process that is restarted after the preparation process. In contrast, the configuration in which hydrogen is used during the preparation process has the advantage that hydrogen with a low mixing ratio of other gases (i.e., high purity) can be produced in the water electrolysis process.

[0097] In specific examples relating to embodiments 1 to 6 (embodiment 7), the electrolyte membrane is a proton exchange membrane, and the reaction solution is pure water. According to the above embodiments, in a configuration in which the electrolyte membrane is a proton exchange membrane, pure water is electrolyzed in the water electrolysis process.

[0098] In specific examples relating to embodiments 1 to 6 (embodiment 8), the electrolyte membrane is an anion exchange membrane. According to the above embodiments, compared to a configuration in which the electrolyte membrane is a proton exchange membrane, a non-precious metal catalyst can be used as the catalyst for the water electrolysis process, thereby reducing manufacturing costs. [Explanation of Symbols]

[0099] 1…Liquid storage tank, 2…Power supply unit, 3…Water electrolysis stack, 4…Pure water tank, 5…Gas tank, 6…Supply system, 7…Gas-liquid separator, 8…Gas-liquid separator, 9…Hydrogen transfer piping, 30…First membrane electrode assembly, 31…Electrolyte membrane of the first membrane electrode assembly, 32…Cathode section of the first membrane electrode assembly, 33…Anode section of the first membrane electrode assembly, 34…First catalyst layer of the first membrane electrode assembly, 35…First diffusion layer of the first membrane electrode assembly, 36…Second catalyst layer of the first membrane electrode assembly, 37…Second diffusion layer of the first membrane electrode assembly, 38…First water electrolysis cell, 40…Second membrane electrode assembly, 41…Electrolyte membrane of the second membrane electrode assembly, 42…Cathode section of the second membrane electrode assembly, 43…Anode section of the second membrane electrode assembly, 44…First catalyst layer of the second membrane electrode assembly, 45…First diffusion layer of the second membrane electrode assembly , 46...Second catalyst layer of the second membrane electrode assembly, 47...Second diffusion layer of the second membrane electrode assembly, 48...Second water electrolysis cell, 50...Flow channel member, 51...First flow channel section, 52...Second flow channel section, 53...Third flow channel section, 54...First flow channel, 55...Second flow channel, 56...Third flow channel, 57...Fourth flow channel, 60...Piping system, 61...First piping, 62...Second piping, 63...Third piping, 64...Fourth piping, 65... 5th pipe, 66...6th pipe, 67...7th pipe, 68...8th pipe, 69...9th pipe, 70...10th pipe, 71...1st branch, 72...2nd branch, 73...valve device, 74...valve device, 75...electrolyte pump, 76...pure water pump, 77...gas pump, 78...11th pipe, 79...3rd branch, 80...control system, 81...control device, 82...memory device, 100...water electrolysis system.

Claims

1. A water electrolysis stack for electrolyzing the reaction solution with water, Supply system and It is equipped with, The aforementioned water electrolysis stack is Multiple membrane electrode assemblies are stacked, with an electrolyte membrane positioned between the anode and cathode portions. Of the plurality of film electrode assemblies, the anode portion of the first film electrode assembly and the cathode portion of the second film electrode assembly are adjacent to each other so as to face each other. A first channel portion is formed on the surface of the first film electrode assembly facing the cathode portion, A second channel portion is formed on the surface of the second film electrode assembly facing the anode portion, A third channel is formed on the surface of the first film electrode assembly facing the anode portion, and a fourth channel is formed on the surface of the second film electrode assembly facing the cathode portion, Includes, The supply system is In the water electrolysis process, the reaction solution is supplied to the second channel and the third channel. In the cleaning step after stopping the water electrolysis step, a first cleaning solution is supplied to the first channel and the fourth channel, and a second cleaning solution is supplied to the second channel and the third channel. During the preparation process within the period from the cessation to the restart of the water electrolysis process, gas is supplied to the first channel and the fourth channel. Water electrolysis system.

2. The first washing solution is pure water. The water electrolysis system according to claim 1.

3. The second washing solution is the reaction solution. A water electrolysis system according to claim 1 or claim 2.

4. The aforementioned gas is hydrogen. The water electrolysis system according to claim 1.

5. The hydrogen is generated by the water electrolysis stack in the water electrolysis process. The water electrolysis system according to claim 4.

6. The gas is nitrogen. The water electrolysis system according to claim 1.

7. The electrolyte membrane is a proton exchange membrane, The reaction solution is pure water. The water electrolysis system according to claim 1.

8. The electrolyte membrane is an anion exchange membrane. The water electrolysis system according to claim 1.

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