Water electrolysis system

Abstract

This suppresses oxidation of the components that make up the internal flow path in a water electrolysis cell. [Solution] A water electrolysis system comprising: a water electrolysis stack having an internal channel through which water flows and which decomposes the water in the internal channel to generate oxygen in the internal channel; a gas-liquid separator that separates water from the oxygen discharged from the internal channel; a return channel that supplies the water discharged from the gas-liquid separator to the internal channel; and an oxygen concentration reduction device that reduces the oxygen concentration of the water in the return channel.

Description

Technical Field

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

[0002] The water electrolysis system disclosed in Patent Document 1 has a water electrolysis stack, a gas-liquid separator, and a reflux path. The water electrolysis stack has an internal flow path through which water flows. The water electrolysis stack decomposes the water in the internal flow path to generate oxygen in the internal flow path. The gas-liquid separator separates water from the oxygen discharged from the internal flow path of the water electrolysis stack. The reflux path supplies the water discharged from the gas-liquid separator to the internal flow path of the water electrolysis stack. Thus, the water discharged from the water electrolysis stack is refluxed to the water electrolysis stack via the gas-liquid separator and the reflux path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a water electrolysis system that refluxes water to a water electrolysis stack as in Patent Document 1, the oxygen concentration of the water flowing in the internal flow path of the water electrolysis stack gradually increases during the use of the water electrolysis system. When the oxygen concentration in the internal flow path becomes high, the members constituting the internal flow path are oxidized and the members deteriorate. In this specification, a technology for suppressing the oxidation of the members constituting the internal flow path in a water electrolysis cell is proposed.

Means for Solving the Problems

[0005] The water electrolysis system disclosed herein comprises a water electrolysis stack having an internal channel through which water flows and which decomposes the water in the internal channel to generate oxygen in the internal channel; a gas-liquid separator that separates water from the oxygen discharged from the internal channel; a return channel that supplies the water discharged from the gas-liquid separator to the internal channel; and an oxygen concentration reduction device that reduces the oxygen concentration of the water in the return channel.

[0006] In this water electrolysis system, the oxygen concentration reduction device reduces the oxygen concentration of the water in the reflux channel, thereby suppressing the increase in oxygen concentration of the water flowing through the internal channels of the water electrolysis stack. As a result, oxidation of the components of the internal channels is 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 100. [Modes for carrying out the invention]

[0008] In a water electrolysis system, the oxygen concentration reduction device may include an ultrasonic generator that applies ultrasonic waves to the water in the reflux channel.

[0009] This configuration allows for a suitable reduction in the oxygen concentration of water in the reflux channel.

[0010] In a water electrolysis system, the reflux channel may have a tank for storing water, and the ultrasonic generator may apply ultrasonic waves to the water in the tank.

[0011] This configuration allows for a more favorable reduction in the oxygen concentration of water in the reflux channel.

[0012] In a water electrolysis system, the oxygen concentration reduction device may include a pressure reducing device that reduces the pressure of the water in the reflux channel.

[0013] This configuration allows for a suitable reduction in the oxygen concentration of water in the reflux channel.

[0014] In a water electrolysis system, the return channel may have a tank for storing water, and the depressurizing device may reduce the pressure inside the tank.

[0015] This configuration allows for a more favorable reduction in the oxygen concentration of water in the reflux channel. [Examples]

[0016] (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.

[0017] 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.

[0018] 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.

[0019] The frame body 50 is provided with a plurality of through holes 56 around the accommodation hole 54. The first separator 10 is provided with a plurality of through holes 16. The second separator 20 is provided with a plurality of through holes 26. Each of the through holes 16 and 26 is located at a position overlapping with the through hole 56. By connecting the through holes 16, 56, and 26, each of the first supply path 61, the first discharge path 62, the second supply path 63, the second discharge path 64, the third supply path 65, and the drain path 66 is formed. These flow paths penetrate the water electrolysis cell 1 in the thickness direction.

[0020] (Specific configuration of the water electrolysis cell 1) FIG. 2 shows a partial cross-sectional view taken along line II-II of FIG. 1. The membrane electrode assembly 40 includes a hydrogen electrode 41, an oxygen electrode 42, and an electrolyte membrane 43. The electrolyte membrane 43 is a proton-conductive ion exchange membrane formed of a solid polymer material. The hydrogen electrode 41 includes a first catalyst layer 44 and a first gas diffusion layer 45. The oxygen electrode 42 includes 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 carrying a catalyst are connected by a resin. As the catalyst, for example, iridium (Ir), ruthenium (Ru), platinum (Pt), and an alloy composed of Pt and other metals (for example, a Pt alloy mixed with cobalt, nickel, etc.) can be used. The first gas diffusion layer 45 and the second gas diffusion layer 47 are conductive members having water permeability and gas permeability.

[0021] The electrolyte membrane 43, the hydrogen electrode 41, and the oxygen electrode 42 have a rectangular shape. The hydrogen electrode 41 has 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 where the second catalyst layer 46 does not exist is formed at the outer peripheral portion of the upper surface 43u of the electrolyte membrane 43. An adhesive layer 49 is disposed on the upper surface 43u within the outer peripheral region PA. The adhesive layer 49 is a layer formed by an applied adhesive. As an example of the adhesive, an ultraviolet curable adhesive containing an organic solvent can be mentioned.

[0022] The frame body 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 having gas sealing properties and insulation 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 body 50. The upper surface of the second resin layer 52 constitutes the upper surface 52u of the frame body 50.

[0023] 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.

[0024] When viewed from a 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 an adhesive layer 49. As a result, the outer peripheral portion 40e of the membrane electrode assembly 40 extends between the lower surface 51b of the frame body 50 and the first separator 10.

[0025] The first separator 10 is provided with a rib 10r. The first separator 10 is in contact with the hydrogen electrode 41 in the portion other than the rib 10r, and a space is provided between the rib 10r and the hydrogen electrode 41. The space between the rib 10r and the hydrogen electrode 41 constitutes a hydrogen channel 14. Part of the hydrogen channel 14 is located in a position that overlaps with the joint OA when viewed along the z direction. The second separator 20 is also provided with a rib 20r. The second separator 20 is in contact with the oxygen electrode 42 in the portion other than the rib 20r, and a space is provided between the rib 20r and the oxygen electrode 42. The space between the rib 20r and the oxygen electrode 42 constitutes an oxygen channel 24. Part of the oxygen channel 24 is located in a position that overlaps with the joint OA when viewed along the z direction. Parts of the surfaces of the adhesive layer 49 and the first resin layer 51 that constitute the joint OA are exposed within the oxygen channel 24.

[0026] (Configuration of the water electrolysis system) The water electrolysis system 100 shown in Figure 3 has a water electrolysis stack 2. The water electrolysis stack 2 is composed of a laminate formed by stacking multiple water electrolysis cells 1. The water electrolysis system 100 has a water system channel 70, an oxygen system channel 80, and a hydrogen system channel 90. The water system channel 70 supplies water to the water electrolysis stack 2. Oxygen produced in the water electrolysis stack 2 flows through the oxygen system channel 80. Hydrogen produced in the water electrolysis stack 2 flows through the hydrogen system channel 90. The arrows in Figure 3 indicate the flow of water, oxygen, and hydrogen. Although not shown in Figure 3, pumps and other devices are installed in each channel as needed.

[0027] The water system flow path 70 includes a pure water generator 71, a water supply pipe 72, a tank 73, and a water supply pipe 74.

[0028] The pure water generator 71 is connected to the tank 73 by a water supply pipe 72. The tank 73 is connected to the water electrolysis stack 2 by a water supply pipe 74. The pure water generator 71 produces pure water. Hereafter, pure water will simply be referred to as water. The water produced by the pure water generator 71 is supplied to the tank 73 by the water supply pipe 72. As will be described later, water is supplied to the tank 73 from the second drain pipe 85. The tank 73 temporarily stores the water flowing in from the water supply pipe 72 and the second drain pipe 85. Water is supplied from the tank 73 to the water electrolysis stack 2 via the water supply pipe 74.

[0029] The downstream end of the water supply pipe 74 is connected to the oxygen channel 24 inside each water electrolysis cell 1 via the second supply channel 63 (see Figure 1). Therefore, the water supplied from the water supply pipe 74 to the water electrolysis stack 2 flows into the oxygen channel 24 inside each water electrolysis cell 1. When the water electrolysis system 100 is operating, a voltage is applied to each water electrolysis cell 1. The voltage is applied in such a direction that the second separator 20 is at a higher potential than the first separator 10 in each water electrolysis cell 1. When a voltage is applied, the 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. In addition, associated water is generated in the hydrogen channel 14 as a result of the electrolysis of water.

[0030] The hydrogen system flow path 90 includes a hydrogen discharge pipe 91, a hydrogen gas-liquid separator 92, a hydrogen discharge pipe 93, and a drain pipe 94. The upstream end of the hydrogen discharge pipe 91 is connected to the hydrogen flow path 14 inside each water electrolysis cell 1 via a first discharge passage 62 (see Figure 1). The downstream end of the hydrogen discharge pipe 91 is connected to the hydrogen gas-liquid separator 92. The upstream end of the hydrogen discharge pipe 93 and the upstream end of the drain pipe 94 are connected to the hydrogen gas-liquid separator 92. The hydrogen and water (i.e., associated water) generated in the hydrogen flow path 14 inside each water electrolysis cell 1 flows into the hydrogen gas-liquid separator 92 via the hydrogen discharge pipe 91. The hydrogen gas-liquid separator 92 is a device that separates water from gas. The hydrogen gas-liquid separator 92 may be a gravity-type separator that separates gas and water using gravity, or a centrifugal separator that separates gas and water using centrifugal force. The hydrogen gas-liquid separator 92 separates water from hydrogen. The hydrogen separated in the hydrogen gas-liquid separator 92 is supplied to an external device via the hydrogen discharge pipe 93. The water separated in the hydrogen gas-liquid separator 92 is discharged to the outside of the water electrolysis system 100 via the drain pipe 94.

[0031] The oxygen system flow path 80 includes an oxygen discharge pipe 81, an oxygen gas-liquid separator 82, an oxygen discharge pipe 83, a first drain pipe 84, and a second drain pipe 85. The upstream end of the oxygen discharge pipe 81 is connected to the oxygen flow path 24 inside each water electrolysis cell 1 via a second discharge passage 64 (see Figure 1). The downstream end of the oxygen discharge pipe 81 is connected to the oxygen gas-liquid separator 82. The upstream ends of the oxygen discharge pipe 83, the first drain pipe 84, and the second drain pipe 85 are connected to the oxygen gas-liquid separator 82. The downstream end of the second drain pipe 85 is connected to the tank 73. The oxygen generated in the oxygen flow path 24 inside each water electrolysis cell 1 flows into the oxygen gas-liquid separator 82 via the oxygen discharge pipe 81 along with excess water. The oxygen gas-liquid separator 82 is a device that separates water from gas. The oxygen gas-liquid separator 82 may be a gravity-type separator or a centrifugal separator. The oxygen gas-liquid separator 82 separates water from oxygen. The oxygen separated in the oxygen vapor-liquid separator 82 is supplied to an external device via the oxygen discharge pipe 83. The water separated in the oxygen vapor-liquid separator 82 flows into a first drain pipe 84 and a second drain pipe 85. The water in the first drain pipe 84 is discharged to the outside of the water electrolysis system 100. The water in the second drain pipe 85 flows into the tank 73. In other words, a portion of the water separated in the oxygen vapor-liquid separator 82 is supplied back to the water electrolysis stack 2 via the second drain pipe 85, the tank 73, and the water supply pipe 74. In this way, the second drain pipe 85, the tank 73, and the water supply pipe 74 constitute a recirculation channel X that recirculates the water discharged from the oxygen vapor-liquid separator 82 back into the oxygen flow path 24 inside the water electrolysis stack 2.

[0032] The water separated by the oxygen-gas-liquid separator 82 contains dissolved oxygen. When this oxygen-rich water is returned to the water electrolysis stack 2, the oxygen concentration of the water flowing through the oxygen channel 24 gradually increases during the operation of the water electrolysis system 100. When the oxygen concentration of the water flowing through the oxygen channel 24 increases, the components constituting the oxygen channel 24 may oxidize and deteriorate, 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 oxidize and deteriorate, 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.

[0033] The water electrolysis system 100 of this embodiment includes an ultrasonic generator 73a and a pressure reducing device 73b to reduce the oxygen concentration of the water recirculating to the water electrolysis stack 2. The ultrasonic generator 73a applies ultrasonic waves to the water in the tank 73. When the ultrasonic generator 73a applies ultrasonic waves to the water in the tank 73, oxygen bubbles up in the water and escapes above the water surface. This reduces the oxygen concentration of the water in the tank 73. The pressure reducing device 73b discharges the gas present above the water surface in the tank 73 to the outside of the tank 73, thereby reducing the pressure inside the tank 73 to a pressure lower than atmospheric pressure (for example, 100 kPa or less). This makes it easier for oxygen to escape from the water in the tank 73, reducing the oxygen concentration of the water. In this way, in the water electrolysis system 100 of this embodiment, water with reduced oxygen concentration in the tank 73 is supplied to the water electrolysis stack 2. This reduces the oxygen concentration of the water flowing through the oxygen channel 24. This suppresses oxidative degradation of each component constituting the oxygen channel 24. In particular, oxidative degradation of the adhesive layer 49 and the first resin layer 51 constituting the joint OA is suppressed, and sealing performance is maintained. Furthermore, oxidative degradation of rubber sealing materials and the like provided in the piping within the water-based channel 70 and the oxygen-based channel 80 can be suppressed.

[0034] The ultrasonic generator 73a and pressure reducing device 73b in the embodiment are examples of an oxygen concentration reduction device. In this embodiment, the oxygen concentration reduction device was installed in the tank 73, but the oxygen concentration reduction device may be installed at any position on the reflux channel that recirculates water from the oxygen vapor-liquid separator 82 to the water electrolysis stack 2. Furthermore, the oxygen concentration reduction device may consist only of the ultrasonic generator 73a, or only of the pressure reducing device 73b, or may consist of devices other than the ultrasonic generator 73a and the pressure reducing device 73b.

[0035] 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]

[0036] 1: Water electrolysis cell 14: Hydrogen channel 24: Oxygen channel 82: Oxygen vapor-liquid separator 73: Tank 73a: Ultrasonic generator 73b: Vacuum reducer

Claims

1. A water electrolysis stack having an internal channel through which water flows, which decomposes the water in the internal channel to generate oxygen in the internal channel, A gas-liquid separator that separates water from oxygen discharged from the internal flow path, A return channel that supplies the water discharged from the gas-liquid separator to the internal channel, An oxygen concentration reduction device for reducing the oxygen concentration of water in the aforementioned reflux channel, A water electrolysis system having the following features.

2. The water electrolysis system according to claim 1, wherein the oxygen concentration reduction device has an ultrasonic generator that applies ultrasonic waves to the water in the reflux channel.

3. The aforementioned return channel has a tank for storing water, The water electrolysis system according to claim 2, wherein the ultrasonic generator applies ultrasonic waves to the water in the tank.

4. The water electrolysis system according to claim 1 or 2, wherein the oxygen concentration reduction device has a depressurization device for reducing the pressure of the water in the reflux channel.

5. The aforementioned return channel has a tank for storing water, The water electrolysis system according to claim 4, wherein the depressurizing device depressurizes the inside of the tank.

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