Water electrolysis system

Abstract

This suppresses oxidation of the components that make up the oxygen channel in a water electrolysis cell. [Solution] A water electrolysis system comprising: a membrane electrode assembly; a first separator in contact with the hydrogen electrode of the membrane electrode assembly; a hydrogen channel provided between the first separator and the hydrogen electrode; a second separator in contact with the oxygen electrode of the membrane electrode assembly; an oxygen channel provided between the second separator and the oxygen electrode; and a cooling device for cooling the hydrogen electrode so that its temperature is lower than that of the oxygen electrode.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a water electrolysis system.

[0002] Patent Document 1 discloses a water electrolysis cell. This water electrolysis cell has a structure in which a membrane electrode assembly is sandwiched between two separators. A hydrogen flow path is provided between one separator and the hydrogen electrode, and an oxygen flow path is provided between the other separator and the oxygen electrode. When the water electrolysis cell operates, hydrogen is generated in the hydrogen flow path and oxygen is generated in the oxygen flow path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During water electrolysis, the members constituting the oxygen flow path are oxidized by the oxygen in the oxygen flow path, and the members deteriorate. In this specification, a technique for suppressing the oxidation of the members constituting the oxygen flow path in a water electrolysis cell is proposed.

Means for Solving the Problems

[0005] The water electrolysis system disclosed in this specification includes a membrane electrode assembly, a first separator in contact with the hydrogen electrode of the membrane electrode assembly, a hydrogen flow path provided between the first separator and the hydrogen electrode, a second separator in contact with the oxygen electrode of the membrane electrode assembly, an oxygen flow path provided between the second separator and the oxygen electrode, and a cooling device for cooling the hydrogen electrode so that the temperature of the hydrogen electrode is lower than the temperature of the oxygen electrode.

[0006] In this water electrolysis system, a cooling device cools the hydrogen electrode so that its temperature is lower than that of the oxygen electrode. Cooling the hydrogen electrode cools the components of the oxygen channel, thereby suppressing oxidation of the components of the oxygen channel. In addition, since the temperature of the oxygen electrode is higher than that of the hydrogen electrode, the decrease in the efficiency of water electrolysis can be suppressed. [Brief explanation of the drawing]

[0007] [Figure 1] This is an exploded perspective view of water electrolysis cell 1. [Figure 2] This is a partial cross-sectional view along line II-II in Figure 1. [Figure 3] This is a diagram showing the configuration of the water electrolysis system 70. [Modes for carrying out the invention]

[0008] The water electrolysis system may further include a water supply device that supplies water to the oxygen channel. The cooling device may supply a coolant to the hydrogen channel that is cooler than the water in the oxygen channel.

[0009] With this configuration, the hydrogen electrode can be cooled so that its temperature is lower than that of the oxygen electrode.

[0010] The water electrolysis system may further include a resin frame sandwiched between the first separator and the second separator, and provided along the periphery of the membrane electrode assembly. The cooling device may cool the joint between the membrane electrode assembly and the frame.

[0011] This configuration makes it possible to suppress oxidation at the junction between the membrane electrode assembly and the frame. [Examples]

[0012] (Outline configuration of water electrolysis cell 1) Figure 1 shows an exploded perspective view of the water electrolysis cell 1. The water electrolysis cell 1 mainly comprises a first separator 10, a second separator 20, a membrane electrode assembly 40, and a frame 50. The membrane electrode assembly 40 electrolyzes water to produce hydrogen and oxygen. The structure of the membrane electrode assembly 40 will be described later.

[0013] The frame 50 is made of an insulating resin. As shown in Figure 1, a housing hole 54 is provided in the center of the frame 50, penetrating the frame 50. The membrane electrode assembly 40 is placed inside the housing hole 54. In other words, the frame 50 surrounds the membrane electrode assembly 40.

[0014] The first separator 10 and the second separator 20 are made of a gas-impermeable conductive material. Examples of separator materials include metallic materials such as stainless steel and carbon materials. The first separator 10 and the second separator 20 face each other via a film electrode assembly 40 and a frame 50.

[0015] The frame 50 is provided with multiple through holes 56 around the receiving hole 54. The first separator 10 is provided with multiple through holes 16. The second separator 20 is provided with multiple through holes 26. Each of the through holes 16 and 26 is located in a position that overlaps with the through hole 56. The connection of the through holes 16, 56, and 26 forms the first supply passage 61, the first discharge passage 62, the second supply passage 63, the second discharge passage 64, the third supply passage 65, and the drainage passage 66, respectively. These passages penetrate the water electrolysis cell 1 in the thickness direction.

[0016] (Specific configuration of water electrolysis cell 1) Figure 2 shows a partial cross-sectional view along line II-II in Figure 1. The membrane electrode assembly 40 comprises a hydrogen electrode 41, an oxygen electrode 42, and an electrolyte membrane 43. The electrolyte membrane 43 is a proton-conducting ion-exchange membrane formed from a solid polymer material. The hydrogen electrode 41 comprises a first catalyst layer 44 and a first gas diffusion layer 45. The oxygen electrode 42 comprises a second catalyst layer 46 and a second gas diffusion layer 47. The first catalyst layer 44 and the second catalyst layer 46 are porous layers in which carbon particles or metal oxide particles supporting a catalyst are linked together with resin. As catalysts, for example, iridium (Ir), ruthenium (Ru), platinum (Pt), and alloys consisting of Pt and other metals (for example, a Pt alloy mixed with cobalt and nickel, etc.) can be used. The first gas diffusion layer 45 and the second gas diffusion layer 47 are conductive members that have water permeability and gas permeability.

[0017] The electrolyte membrane 43, hydrogen electrode 41, and oxygen electrode 42 have a rectangular shape. The hydrogen electrode 41 is the same size as the electrolyte membrane 43, and the oxygen electrode 42 is smaller than the electrolyte membrane 43. An outer peripheral region PA is formed on the outer periphery of the upper surface 43u of the electrolyte membrane 43, where the second catalyst layer 46 is not present. An adhesive layer 49 is placed on the upper surface 43u within the outer peripheral region PA. The adhesive layer 49 is a layer formed by an applied adhesive. An example of an adhesive is an ultraviolet-curable adhesive containing an organic solvent.

[0018] The frame 50 has a three-layer structure in which a first resin layer 51, a core layer 53, and a second resin layer 52 are laminated in the thickness direction. The core layer 53 is a structural member that has gas sealing and insulating properties. The first resin layer 51 is a layer that adheres to the first separator 10. The second resin layer 52 is a layer that adheres to the second separator 20. The lower surface of the first resin layer 51 constitutes the lower surface 51b of the frame 50. The upper surface of the second resin layer 52 constitutes the upper surface 52u of the frame 50.

[0019] The first resin layer 51 and the second resin layer 52 may have properties of lower viscosity and melting point than the core layer 53. Specifically, the first resin layer 51 and the second resin layer 52 may be thermoplastic resins such as acid-modified olefin-based and polyester-based resins. The frame body 50 with a multilayer structure can be formed by various methods. For example, it may be formed by coextrusion molding.

[0020] When viewed from the direction (z direction) perpendicular to the membrane electrode assembly 40, the outer periphery of the membrane electrode assembly 40 and the inner periphery of the frame body 50 overlap. The overlapping region between the membrane electrode assembly 40 and the frame body 50 is the joint portion OA where the membrane electrode assembly 40 is joined to the frame body 50. Inside the joint portion OA, the lower surface 51b of the frame body 50 is adhered to the upper surface 43u of the electrolyte membrane 43 via the adhesive layer 49. Thereby, the outer peripheral portion 40e of the membrane electrode assembly 40 has a structure extending between the lower surface 51b of the frame body 50 and the first separator 10.

[0021] The first separator 10 is provided with ribs 10r. The first separator 10 contacts the hydrogen electrode 41 at portions other than the ribs 10r, and a space is provided between the ribs 10r and the hydrogen electrode 41. The hydrogen flow path 14 is formed by the space between the ribs 10r and the hydrogen electrode 41. A part of the hydrogen flow path 14 is provided at a position overlapping the joint portion OA when viewed along the z direction. The second separator 20 is provided with ribs 20r. The second separator 20 contacts the oxygen electrode 42 at portions other than the ribs 20r, and a space is provided between the ribs 20r and the oxygen electrode 42. The oxygen flow path 24 is formed by the space between the ribs 20r and the oxygen electrode 42. A part of the oxygen flow path 24 is provided at a position overlapping the joint portion OA when viewed along the z direction. A part of the surfaces of the adhesive layer 49 and the first resin layer 51 constituting the joint portion OA is exposed inside the oxygen flow path 24.

[0022] (Configuration of the water electrolysis system) The water electrolysis system 70 shown in FIG. 3 has a water electrolysis stack 72. The water electrolysis stack 72 is composed of a stack body formed by laminating a plurality of water electrolysis cells 1. The water electrolysis system 70 has a pure water supply system 80 for supplying pure water to the water electrolysis stack 72 and a coolant supply system 90 for supplying a coolant to the water electrolysis stack 72.

[0023] The pure water supply system 80 has a pure water supply passage 82, a pure water discharge passage 84, a pure water pump 86, and a pure water temperature sensor 88. The pure water supply passage 82 is connected to the oxygen flow passage 24 of each water electrolysis cell 1 via a second supply passage 63 (see FIG. 1). The oxygen flow passage 24 of each water electrolysis cell 1 is connected to the pure water discharge passage 84 via a second discharge passage 64 (see FIG. 1). The pure water pump 86 supplies pure water from the pure water supply passage 82 to the water electrolysis stack 72. When the pure water pump 86 operates, pure water flows from the pure water supply passage 82 into the oxygen flow passage 24 of each water electrolysis cell 1. The pure water that has passed through the oxygen flow passage 24 of each water electrolysis cell 1 is discharged to the pure water discharge passage 84. The pure water temperature sensor 88 detects the temperature of the pure water discharged from the water electrolysis stack 72 to the pure water discharge passage 84.

[0024] The coolant supply system 90 has a coolant supply passage 92, a coolant discharge passage 94, a coolant pump 96, a coolant temperature sensor 98, and a radiator 99. The coolant supply passage 92 is connected to the hydrogen flow passage 14 of each water electrolysis cell 1 via a first supply passage 61 (see FIG. 1). The hydrogen flow passage 14 of each water electrolysis cell 1 is connected to the coolant discharge passage 94 via a first discharge passage 62 (see FIG. 1). The coolant pump 96 supplies a coolant from the coolant supply passage 92 to the water electrolysis stack 72. The supply pressure of the coolant pump 96 is not less than the pressure of hydrogen in each water electrolysis cell 1. When the coolant pump 96 operates, the coolant flows from the coolant supply passage 92 into the hydrogen flow passage 14 of each water electrolysis cell 1. The coolant that has passed through the hydrogen flow passage 14 of each water electrolysis cell 1 is discharged to the coolant discharge passage 94. The coolant temperature sensor 98 detects the temperature of the coolant discharged from the water electrolysis stack 72 to the coolant discharge passage 94. The radiator 99 cools the coolant in the coolant supply passage 92 by heat exchange with the outside air.

[0025] The water electrolysis system 70 has a control device 100. The control device 100 is electrically connected to a pure water pump 86, a pure water temperature sensor 88, a coolant pump 96, a coolant temperature sensor 98, and a radiator 99. The control device 100 controls the coolant pump 96 and the radiator 99 according to the values ​​detected by the pure water temperature sensor 88 and the coolant temperature sensor 98.

[0026] (Operation of the water electrolysis system) When the water electrolysis system 70 is in operation, the control device 100 supplies pure water to the oxygen channel 24 of each water electrolysis cell 1 by operating the pure water pump 86. The control device 100 also supplies coolant to the hydrogen channel 14 of each water electrolysis cell 1 by operating the coolant pump 96. The control device 100 also applies a voltage to each water electrolysis cell 1 using a power supply (not shown). The voltage is applied in such a way that the second separator 20 in each water electrolysis cell 1 has a higher potential than the first separator 10. When a voltage is applied, the pure water in the oxygen channel 24 is electrolyzed in the membrane electrode assembly 40. As a result, oxygen is generated in the oxygen channel 24 and hydrogen is generated in the hydrogen channel 14. The oxygen generated in the oxygen channel 24 is discharged along with the pure water to the pure water discharge channel 84. The oxygen discharged to the pure water discharge channel 84 is separated from the pure water by a gas-liquid separator (not shown) and used. The hydrogen generated in the hydrogen channel 14 is discharged along with the coolant to the coolant discharge channel 94. The hydrogen discharged into the coolant discharge passage 94 is separated from the coolant by a gas-liquid separator (not shown) and used.

[0027] As described above, oxygen is generated in the oxygen channel 24 during water electrolysis. In addition, the water electrolysis cell 1 generates heat during water electrolysis. As a result, the components constituting the oxygen channel 24 may undergo oxidative degradation, potentially reducing the durability of the water electrolysis cell 1. In particular, if the adhesive layer 49 and the first resin layer 51 at the joint OA undergo oxidative degradation, the sealing performance between the frame 50 and the membrane electrode assembly 40 cannot be maintained, reducing the durability of the water electrolysis cell 1.

[0028] In the technology of this embodiment, as described above, coolant is supplied into the hydrogen channel 14 while the water electrolysis system 70 is in operation. The control device 100 controls the coolant pump 96 so that the flow rate of the coolant increases as the current load of the water electrolysis cell 1 increases, thereby suppressing the temperature rise of the water electrolysis cell 1. The control device 100 also controls the coolant pump 96 and the radiator 99 so that the temperature of the coolant detected by the coolant temperature sensor 98 is lower than the temperature of the pure water detected by the pure water temperature sensor 88. Therefore, in each water electrolysis cell 1, the hydrogen electrode 41 is cooled so that its temperature is lower than the temperature of the oxygen electrode 42. As the hydrogen electrode 41 is cooled, each component constituting the oxygen channel 24 is cooled, and oxidative degradation of each component constituting the oxygen channel 24 is suppressed. In particular, since the hydrogen channel 14 is positioned to overlap with the joint OA, the adhesive layer 49 and the first resin layer 51 constituting the joint OA are cooled by the coolant in the hydrogen channel 14. This suppresses oxidative degradation of the adhesive layer 49 and the first resin layer 51 that constitute the joint OA, and maintains sealing performance.

[0029] Furthermore, if the oxygen electrode 42 is excessively cooled, water electrolysis becomes difficult to occur at the oxygen electrode 42, and the efficiency of oxygen and hydrogen production decreases. In contrast, in the technology of this embodiment, the cooling liquid is flowed through the hydrogen channel 14 located on the opposite side of the oxygen electrode 42, so excessive cooling of the oxygen electrode 42 is prevented, and the temperature of the oxygen electrode 42 becomes higher than the temperature of the hydrogen electrode 41. Therefore, water electrolysis can be efficiently generated at the oxygen electrode 42. For example, by making the temperature of the pure water 5 to 10°C higher than the temperature of the cooling liquid, it is possible to suppress oxidative degradation of the junction OA while maintaining high water electrolysis efficiency.

[0030] The technology described herein is applicable to a variety of structures. For example, the frame 50 is not limited to a three-layer structure. The technology described herein is also applicable to frames with single-layer, two-layer, or four-layer or more structures.

[0031] The coolant supply system 90 in this embodiment is an example of a cooling device that cools the hydrogen electrode so that the temperature of the hydrogen electrode is lower than the temperature of the oxygen electrode.

[0032] Although embodiments have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0033] 1: Water electrolysis cell 10: First separator 20: Second separator 40: Membrane electrode assembly 50: Frame

Claims

1. A membrane electrode assembly and A first separator in contact with the hydrogen electrode of the aforementioned membrane electrode assembly, A hydrogen channel is provided between the first separator and the hydrogen electrode, A second separator in contact with the oxygen electrode of the aforementioned membrane electrode assembly, An oxygen channel is provided between the second separator and the oxygen electrode, A cooling device for cooling the hydrogen electrode such that the temperature of the hydrogen electrode becomes lower than the temperature of the oxygen electrode. A water electrolysis system having the following features.

2. The system further includes a water supply device that supplies water to the oxygen channel, The cooling device supplies a cooling liquid to the hydrogen channel that is colder than the water in the oxygen channel. The water electrolysis system according to claim 1.

3. It further comprises a resin frame sandwiched between the first separator and the second separator, and provided along the periphery of the membrane electrode assembly, The cooling device cools the joint between the membrane electrode assembly and the frame. The water electrolysis system according to claim 1 or 2.

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